Lack of appropriate stoichiometry: Strong evidence against an energetically important astrocyte-neuron lactate shuttle in brain.

Science.gov (United States)

Dienel, Gerald A

2017-11-01

Glutamate-stimulated aerobic glycolysis in astrocytes coupled with lactate shuttling to neurons where it can be oxidized was proposed as a mechanism to couple excitatory neuronal activity with glucose utilization (CMR glc ) during brain activation. From the outset, this model was not viable because it did not fulfill critical stoichiometric requirements: (i) Calculated glycolytic rates and measured lactate release rates were discordant in cultured astrocytes. (ii) Lactate oxidation requires oxygen consumption, but the oxygen-glucose index (OGI, calculated as CMR O2 /CMR glc ) fell during activation in human brain, and the small rise in CMR O2 could not fully support oxidation of lactate produced by disproportionate increases in CMR glc . (iii) Labeled products of glucose metabolism are not retained in activated rat brain, indicating rapid release of a highly labeled, diffusible metabolite identified as lactate, thereby explaining the CMR glc -CMR O2 mismatch. Additional independent lines of evidence against lactate shuttling include the following: astrocytic oxidation of glutamate after its uptake can help "pay" for its uptake without stimulating glycolysis; blockade of glutamate receptors during activation in vivo prevents upregulation of metabolism and lactate release without impairing glutamate uptake; blockade of β-adrenergic receptors prevents the fall in OGI in activated human and rat brain while allowing glutamate uptake; and neurons upregulate glucose utilization in vivo and in vitro under many stimulatory conditions. Studies in immature cultured cells are not appropriate models for lactate shuttling in adult brain because of their incomplete development of metabolic capability and astrocyte-neuron interactions. Astrocyte-neuron lactate shuttling does not make large, metabolically significant contributions to energetics of brain activation. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

A porcine astrocyte/endothelial cell co-culture model of the blood-brain barrier.

Science.gov (United States)

Jeliazkova-Mecheva, Valentina V; Bobilya, Dennis J

2003-10-01

A method for the isolation of porcine atrocytes as a simple extension of a previously described procedure for isolation of brain capillary endothelial cells from adolescent pigs [Methods Cell Sci. 17 (1995) 2] is described. The obtained astroglial culture purified through two passages and by the method of the selective detachment was validated by a phase contrast microscopy and through an immunofluorescent assay for the glial fibrillary acidic protein (GFAP). Porcine astrocytes were co-cultivated with porcine brain capillary endothelial cells (PBCEC) for the development of an in vitro blood-brain barrier (BBB) model. The model was visualized by an electron microscopy and showed elevated transendothellial electrical resistance and reduced inulin permeability. To our knowledge, this is the first report for the establishment of a porcine astrocyte/endothelial cell co-culture BBB model, which avoids interspecies and age differences between the two cell types, usually encountered in the other reported co-culture BBB models. Considering the availability of the porcine brain tissue and the close physiological and anatomical relation between the human and pig brain, the porcine astrocyte/endothelial cell co-culture system can serve as a reliable and easily reproducible model for different in vitro BBB studies.

Accumulation of silver nanoparticles by cultured primary brain astrocytes

Energy Technology Data Exchange (ETDEWEB)

Luther, Eva M; Koehler, Yvonne; Dringen, Ralf [Center for Biomolecular Interactions Bremen, University of Bremen, PO Box 330440, D-28334 Bremen (Germany); Diendorf, Joerg; Epple, Matthias, E-mail: ralf.dringen@uni-bremen.de [Inorganic Chemistry and Center for Nanointegration Duisburg-Essen, University of Duisburg-Essen, Universitaetsstrasse 5-7, D-45117 Essen (Germany)

2011-09-16

Silver nanoparticles (AgNP) are components of various food industry products and are frequently used for medical equipment and materials. Although such particles enter the vertebrate brain, little is known on their biocompatibility for brain cells. To study the consequences of an AgNP exposure of brain cells we have treated astrocyte-rich primary cultures with polyvinylpyrrolidone (PVP)-coated AgNP. The incubation of cultured astrocytes with micromolar concentrations of AgNP for up to 24 h resulted in a time- and concentration-dependent accumulation of silver, but did not compromise the cell viability nor lower the cellular glutathione content. In contrast, the incubation of astrocytes for 4 h with identical amounts of silver as AgNO{sub 3} already severely compromised the cell viability and completely deprived the cells of glutathione. The accumulation of AgNP by astrocytes was proportional to the concentration of AgNP applied and significantly lowered by about 30% in the presence of the endocytosis inhibitors chloroquine or amiloride. Incubation at 4 {sup 0}C reduced the accumulation of AgNP by 80% compared to the values obtained for cells that had been exposed to AgNP at 37 {sup 0}C. These data demonstrate that viable cultured brain astrocytes efficiently accumulate PVP-coated AgNP in a temperature-dependent process that most likely involves endocytotic pathways.

Functional organization of the transcriptome in human brain

Science.gov (United States)

Oldham, Michael C; Konopka, Genevieve; Iwamoto, Kazuya; Langfelder, Peter; Kato, Tadafumi; Horvath, Steve; Geschwind, Daniel H

2009-01-01

The enormous complexity of the human brain ultimately derives from a finite set of molecular instructions encoded in the human genome. These instructions can be directly studied by exploring the organization of the brain’s transcriptome through systematic analysis of gene coexpression relationships. We analyzed gene coexpression relationships in microarray data generated from specific human brain regions and identified modules of coexpressed genes that correspond to neurons, oligodendrocytes, astrocytes and microglia. These modules provide an initial description of the transcriptional programs that distinguish the major cell classes of the human brain and indicate that cell type–specific information can be obtained from whole brain tissue without isolating homogeneous populations of cells. Other modules corresponded to additional cell types, organelles, synaptic function, gender differences and the subventricular neurogenic niche. We found that subventricular zone astrocytes, which are thought to function as neural stem cells in adults, have a distinct gene expression pattern relative to protoplasmic astrocytes. Our findings provide a new foundation for neurogenetic inquiries by revealing a robust and previously unrecognized organization to the human brain transcriptome. PMID:18849986

Immunocytochemical detection of astrocytes in brain slices in combination with Nissl staining.

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Korzhevskii, D E; Otellin, V A

2005-07-01

The present study was performed to develop a simple and reliable method for the combined staining of specimens to allow the advantages of immunocytochemical detection of astrocytes and assessment of the functional state of neurons by the Nissl method to be assessed simultaneously. The protocol suggested for processing paraffin sections allows preservation of tissue structure at high quality and allows the selective identification of astrocytes with counterstaining of neurons by the Nissl method. The protocol can be used without modification for processing brain specimens from humans and various mammals--except mice and rabbits.

STAT3 labels a subpopulation of reactive astrocytes required for brain metastasis.

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Priego, Neibla; Zhu, Lucía; Monteiro, Cátia; Mulders, Manon; Wasilewski, David; Bindeman, Wendy; Doglio, Laura; Martínez, Liliana; Martínez-Saez, Elena; Cajal, Santiago Ramón Y; Megías, Diego; Hernández-Encinas, Elena; Blanco-Aparicio, Carmen; Martínez, Lola; Zarzuela, Eduardo; Muñoz, Javier; Fustero-Torres, Coral; Pineiro, Elena; Hernández-Laín, Aurelio; Bertero, Luca; Poli, Valeria; Sánchez-Martínez, Melchor; Menendez, Javier A; Soffietti, Riccardo; Bosch-Barrera, Joaquim; Valiente, Manuel

2018-06-11

The brain microenvironment imposes a particularly intense selective pressure on metastasis-initiating cells, but successful metastases bypass this control through mechanisms that are poorly understood. Reactive astrocytes are key components of this microenvironment that confine brain metastasis without infiltrating the lesion. Here, we describe that brain metastatic cells induce and maintain the co-option of a pro-metastatic program driven by signal transducer and activator of transcription 3 (STAT3) in a subpopulation of reactive astrocytes surrounding metastatic lesions. These reactive astrocytes benefit metastatic cells by their modulatory effect on the innate and acquired immune system. In patients, active STAT3 in reactive astrocytes correlates with reduced survival from diagnosis of intracranial metastases. Blocking STAT3 signaling in reactive astrocytes reduces experimental brain metastasis from different primary tumor sources, even at advanced stages of colonization. We also show that a safe and orally bioavailable treatment that inhibits STAT3 exhibits significant antitumor effects in patients with advanced systemic disease that included brain metastasis. Responses to this therapy were notable in the central nervous system, where several complete responses were achieved. Given that brain metastasis causes substantial morbidity and mortality, our results identify a novel treatment for increasing survival in patients with secondary brain tumors.

A critical role for astrocytes in hypercapnic vasodilation in brain

DEFF Research Database (Denmark)

Howarth, C; Sutherland, B A; Choi, H B

2017-01-01

increases in astrocyte calcium signaling which in turn stimulates COX-1 activity and generates downstream PgE2 production. We demonstrate that astrocyte calcium-evoked production of the vasodilator, PgE2, is critically dependent on brain levels of the antioxidant, glutathione. These data suggest a novel......Cerebral blood flow (CBF) is controlled by arterial blood pressure, arterial CO2, arterial O2, and brain activity and is largely constant in the awake state. Although small changes in arterial CO2 are particularly potent to change CBF (1 mmHg variation in arterial CO2 changes CBF by 3...... in brain slices with in vivo work in rats and C57Bl/6J mice to examine the hemodynamic responses to CO2 and somatosensory stimulation before and after inhibition of astrocytic glutathione and PgE2 synthesis. We demonstrate that hypercapnia (increased CO2) evokes an increase in astrocyte [Ca(2+)]i...

Glucose metabolism and astrocyte-neuron interactions in the neonatal brain.

Science.gov (United States)

Brekke, Eva; Morken, Tora Sund; Sonnewald, Ursula

2015-03-01

Glucose is essentially the sole fuel for the adult brain and the mapping of its metabolism has been extensive in the adult but not in the neonatal brain, which is believed to rely mainly on ketone bodies for energy supply. However, glucose is absolutely indispensable for normal development and recent studies have shed light on glycolysis, the pentose phosphate pathway and metabolic interactions between astrocytes and neurons in the 7-day-old rat brain. Appropriately (13)C labeled glucose was used to distinguish between glycolysis and the pentose phosphate pathway during development. Experiments using (13)C labeled acetate provided insight into the GABA-glutamate-glutamine cycle between astrocytes and neurons. It could be shown that in the neonatal brain the part of this cycle that transfers glutamine from astrocytes to neurons is operating efficiently while, in contrast, little glutamate is shuttled from neurons to astrocytes. This lack of glutamate for glutamine synthesis is compensated for by anaplerosis via increased pyruvate carboxylation relative to that in the adult brain. Furthermore, compared to adults, relatively more glucose is prioritized to the pentose phosphate pathway than glycolysis and pyruvate dehydrogenase activity. The reported developmental differences in glucose metabolism and neurotransmitter synthesis may determine the ability of the brain at various ages to resist excitotoxic insults such as hypoxia-ischemia. Copyright © 2015 Elsevier Ltd. All rights reserved.

Globular adiponectin induces a pro-inflammatory response in human astrocytic cells

International Nuclear Information System (INIS)

Wan, Zhongxiao; Mah, Dorrian; Simtchouk, Svetlana; Klegeris, Andis; Little, Jonathan P.

2014-01-01

Highlights: • Adiponectin receptors are expressed in human astrocytes. • Globular adiponectin induces secretion of IL-6 and MCP-1 from cultured astrocytes. • Adiponectin may play a pro-inflammatory role in astrocytes. - Abstract: Neuroinflammation, mediated in part by activated brain astrocytes, plays a critical role in the development of neurodegenerative disorders, including Alzheimer’s disease (AD). Adiponectin is the most abundant adipokine secreted from adipose tissue and has been reported to exert both anti- and pro-inflammatory effects in peripheral tissues; however, the effects of adiponectin on astrocytes remain unknown. Shifts in peripheral concentrations of adipokines, including adiponectin, could contribute to the observed link between midlife adiposity and increased AD risk. The aim of the present study was to characterize the effects of globular adiponectin (gAd) on pro-inflammatory cytokine mRNA expression and secretion in human U373 MG astrocytic cells and to explore the potential involvement of nuclear factor (NF)-κB, p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK)1/2, c-Jun N-terminal kinase (JNK) and phosphatidylinositide 3-kinases (PI3 K) signaling pathways in these processes. We demonstrated expression of adiponectin receptor 1 (adipoR1) and adipoR2 in U373 MG cells and primary human astrocytes. gAd induced secretion of interleukin (IL)-6 and monocyte chemoattractant protein (MCP)-1, and gene expression of IL-6, MCP-1, IL-1β and IL-8 in U373 MG cells. Using specific inhibitors, we found that NF-κB, p38MAPK and ERK1/2 pathways are involved in gAd-induced induction of cytokines with ERK1/2 contributing the most. These findings provide evidence that gAd may induce a pro-inflammatory phenotype in human astrocytes

Globular adiponectin induces a pro-inflammatory response in human astrocytic cells

Energy Technology Data Exchange (ETDEWEB)

Wan, Zhongxiao; Mah, Dorrian; Simtchouk, Svetlana [School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC (Canada); Klegeris, Andis [Department of Biology, University of British Columbia Okanagan, Kelowna, BC (Canada); Little, Jonathan P., E-mail: jonathan.little@ubc.ca [School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC (Canada)

2014-03-28

Highlights: • Adiponectin receptors are expressed in human astrocytes. • Globular adiponectin induces secretion of IL-6 and MCP-1 from cultured astrocytes. • Adiponectin may play a pro-inflammatory role in astrocytes. - Abstract: Neuroinflammation, mediated in part by activated brain astrocytes, plays a critical role in the development of neurodegenerative disorders, including Alzheimer’s disease (AD). Adiponectin is the most abundant adipokine secreted from adipose tissue and has been reported to exert both anti- and pro-inflammatory effects in peripheral tissues; however, the effects of adiponectin on astrocytes remain unknown. Shifts in peripheral concentrations of adipokines, including adiponectin, could contribute to the observed link between midlife adiposity and increased AD risk. The aim of the present study was to characterize the effects of globular adiponectin (gAd) on pro-inflammatory cytokine mRNA expression and secretion in human U373 MG astrocytic cells and to explore the potential involvement of nuclear factor (NF)-κB, p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK)1/2, c-Jun N-terminal kinase (JNK) and phosphatidylinositide 3-kinases (PI3 K) signaling pathways in these processes. We demonstrated expression of adiponectin receptor 1 (adipoR1) and adipoR2 in U373 MG cells and primary human astrocytes. gAd induced secretion of interleukin (IL)-6 and monocyte chemoattractant protein (MCP)-1, and gene expression of IL-6, MCP-1, IL-1β and IL-8 in U373 MG cells. Using specific inhibitors, we found that NF-κB, p38MAPK and ERK1/2 pathways are involved in gAd-induced induction of cytokines with ERK1/2 contributing the most. These findings provide evidence that gAd may induce a pro-inflammatory phenotype in human astrocytes.

[Immunocytochemical demonstration of astrocytes in brain sections combined with Nissl staining].

Science.gov (United States)

Korzhevskiĭ, D E; Otellin, V A

2004-01-01

The aim of the present study was to develop an easy and reliable protocol of combined preparation staining, which would unite the advantages of immunocytochemical demonstration of astrocytes with the availability to evaluate functional state of neurons provided by Nissl technique. The presented protocol of paraffin sections processing allows to retain high quality of tissue structure and provides for selective demonstration of astrocytes using the monoclonal antibodies against glial fibrillary acidic protein and contrast Nissl staining of cells. The protocol can be used without any changes for processing of brain sections obtained from the humans and other mammals with the exception of mice and rabbits.

Endothelial-astrocytic interactions in acute liver failure.

Science.gov (United States)

Jayakumar, A R; Norenberg, M D

2013-06-01

Brain edema and the subsequent increase in intracranial pressure are major neurological complications of acute liver failure (ALF), and swelling of astrocytes (cytotoxic brain edema) is the most prominent neuropathological abnormality in ALF. Recent studies, however, have suggested the co-existence of cytotoxic and vasogenic mechanisms in the brain edema associated with ALF. This review 1) summarizes the nature of the brain edema in humans and experimental animals with ALF; 2) reviews in vitro studies supporting the presence of cytotoxic brain edema (cell swelling in cultured astrocytes); and 3) documents the role of brain endothelial cells in the development of astrocyte swelling/brain edema in ALF.

Nonproductive human immunodeficiency virus type 1 infection of human fetal astrocytes: independence from CD4 and major chemokine receptors.

Science.gov (United States)

Sabri, F; Tresoldi, E; Di Stefano, M; Polo, S; Monaco, M C; Verani, A; Fiore, J R; Lusso, P; Major, E; Chiodi, F; Scarlatti, G

1999-11-25

Human immunodeficiency virus type 1 (HIV-1) infection of the brain is associated with neurological manifestations both in adults and in children. The primary target for HIV-1 infection in the brain is the microglia, but astrocytes can also be infected. We tested 26 primary HIV-1 isolates for their capacity to infect human fetal astrocytes in culture. Eight of these isolates, independent of their biological phenotype and chemokine receptor usage, were able to infect astrocytes. Although no sustained viral replication could be demonstrated, the virus was recovered by coculture with receptive cells such as macrophages or on stimulation with interleukin-1beta. To gain knowledge into the molecular events that regulate attachment and penetration of HIV-1 in astrocytes, we investigated the expression of several chemokine receptors. Fluorocytometry and calcium-mobilization assay did not provide evidence of expression of any of the major HIV-1 coreceptors, including CXCR4, CCR5, CCR3, and CCR2b, as well as the CD4 molecule on the cell surface of human fetal astrocytes. However, mRNA transcripts for CXCR4, CCR5, Bonzo/STRL33/TYMSTR, and APJ were detected by RT-PCR. Furthermore, infection of astrocytes by HIV-1 isolates with different chemokine receptor usage was not inhibited by the chemokines SDF-1beta, RANTES, MIP-1beta, or MCP-1 or by antibodies directed against the third variable region or the CD4 binding site of gp120. These data show that astrocytes can be infected by primary HIV-1 isolates via a mechanism independent of CD4 or major chemokine receptors. Furthermore, astrocytes are potential carriers of latent HIV-1 and on activation may be implicated in spreading the infection to other neighbouring cells, such as microglia or macrophages. Copyright 1999 Academic Press.

GABAergic interneuron to astrocyte signalling: a neglected form of cell communication in the brain.

Science.gov (United States)

Losi, Gabriele; Mariotti, Letizia; Carmignoto, Giorgio

2014-10-19

GABAergic interneurons represent a minority of all cortical neurons and yet they efficiently control neural network activities in all brain areas. In parallel, glial cell astrocytes exert a broad control of brain tissue homeostasis and metabolism, modulate synaptic transmission and contribute to brain information processing in a dynamic interaction with neurons that is finely regulated in time and space. As most studies have focused on glutamatergic neurons and excitatory transmission, our knowledge of functional interactions between GABAergic interneurons and astrocytes is largely defective. Here, we critically discuss the currently available literature that hints at a potential relevance of this specific signalling in brain function. Astrocytes can respond to GABA through different mechanisms that include GABA receptors and transporters. GABA-activated astrocytes can, in turn, modulate local neuronal activity by releasing gliotransmitters including glutamate and ATP. In addition, astrocyte activation by different signals can modulate GABAergic neurotransmission. Full clarification of the reciprocal signalling between different GABAergic interneurons and astrocytes will improve our understanding of brain network complexity and has the potential to unveil novel therapeutic strategies for brain disorders. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Does Global Astrocytic Calcium Signaling Participate in Awake Brain State Transitions and Neuronal Circuit Function?

DEFF Research Database (Denmark)

Kjaerby, Celia; Rasmussen, Rune; Andersen, Mie

2017-01-01

of the neuromodulators, noradrenaline and acetylcholine. Astrocytes have emerged as a new player participating in the regulation of brain activity, and have recently been implicated in brain state shifts. Astrocytes display global Ca(2+) signaling in response to activation of the noradrenergic system, but whether...... astrocytic Ca(2+) signaling is causative or correlative for shifts in brain state and neural activity patterns is not known. Here we review the current available literature on astrocytic Ca(2+) signaling in awake animals in order to explore the role of astrocytic signaling in brain state shifts. Furthermore......We continuously need to adapt to changing conditions within our surrounding environment, and our brain needs to quickly shift between resting and working activity states in order to allow appropriate behaviors. These global state shifts are intimately linked to the brain-wide release...

Impairments of astrocytes are involved in the D-galactose-induced brain aging

International Nuclear Information System (INIS)

Lei Ming; Hua Xiangdong; Xiao Ming; Ding Jiong; Han Qunying; Hu Gang

2008-01-01

Astrocyte dysfunction is implicated in course of various age-related neurodegenerative diseases. Chronic injection of D-galactose can cause a progressive deterioration in learning and memory capacity and serve as an animal model of aging. To investigate the involvement of astrocytes in this model, oxidative stress biomarkers, biochemical and pathological changes of astrocytes were examined in the hippocampus of the rats with six weeks of D-galactose injection. D-galactose-injected rats displayed impaired antioxidant systems, an increase in nitric oxide levels, and a decrease in reduced glutathione levels. Consistently, western blotting and immunostaining of glial fibrillary acidic protein showed extensive activation of astrocytes. Double-immunofluorescent staining further showed activated astrocytes highly expressed inducible nitric oxide synthase. Electron microscopy demonstrated the degeneration of astrocytes, especially in the aggregated area of synapse and brain microvessels. These findings indicate that impairments of astrocytes are involved in oxidative stress-induced brain aging by chronic injection of D-galactose

Synergistic induction of astrocytic differentiation by factors secreted from meninges in the mouse developing brain.

Science.gov (United States)

Kawamura, Yoichiro; Katada, Sayako; Noguchi, Hirofumi; Yamamoto, Hiroyuki; Sanosaka, Tsukasa; Iihara, Koji; Nakashima, Kinichi

2017-11-01

Astrocytes, which support diverse neuronal functions, are generated from multipotent neural stem/precursor cells (NS/PCs) during brain development. Although many astrocyte-inducing factors have been identified and studied in vitro, the regions and/or cells that produce these factors in the developing brain remain elusive. Here, we show that meninges-produced factors induce astrocytic differentiation of NS/PCs. Consistent with the timing when astrocytic differentiation of NS/PCs increases, expression of astrocyte-inducing factors is upregulated. Meningeal secretion-mimicking combinatorial treatment of NS/PCs with bone morphogenetic protein 4, retinoic acid and leukemia inhibitory factor synergistically activate the promoter of a typical astrocytic marker, glial fibrillary acidic protein. Taken together, our data suggest that meninges play an important role in astrocytic differentiation of NS/PCs in the developing brain. © 2017 Federation of European Biochemical Societies.

Identification of gene products suppressed by human immunodeficiency virus type 1 infection or gp120 exposure of primary human astrocytes by rapid subtraction hybridization.

Science.gov (United States)

Su, Zao-Zhong; Kang, Dong-Chul; Chen, Yinming; Pekarskaya, Olga; Chao, Wei; Volsky, David J; Fisher, Paul B

2003-06-01

Neurodegeneration and human immunodeficiency virus type 1 (HIV-1)-associated dementia (HAD) are the major disease manifestations of HIV-1 colonization of the central nervous system (CNS). In the brain, HIV-1 replicates in microglial cells and infiltrating macrophages and it persists in a low-productive, noncytolytic state in astrocytes. Astrocytes play critical roles in the maintenance of the brain microenvironment, responses to injury, and in neuronal signal transmission, and disruption of these functions by HIV-1 could contribute to HAD. To better understand the potential effects of HIV-1 on astrocyte biology, the authors investigated changes in gene expression using an efficient and sensitive rapid subtraction hybridization approach, RaSH. Primary human astrocytes were isolated from abortus brain tissue, low-passage cells were infected with HIV-1 or mock infected, and total cellular RNAs were isolated at multiple time points over a period of 1 week. This approach is designed to identify gene products modulated early and late after HIV-1 infection and limits the cloning of genes displaying normal cell-cycle fluctuations in astrocytes. By subtracting temporal cDNAs derived from HIV-1-infected astrocytes from temporal cDNAs made from uninfected cells, 10 genes displaying reduced expression in infected cells, termed astrocyte suppressed genes (ASGs), were identified and their suppression was confirmed by Northern blot hybridization. Both known and novel ASGs, not reported in current DNA databases, that are down-regulated by HIV-1 infection are described. Northern blotting confirms suppression of the same panel of ASGs by treatment of astrocytes with recombinant HIV-1 envelope glycoprotein, gp120. These results extend our previous analysis of astrocyte genes induced or enhanced by HIV-1 infection and together they suggest that HIV-1 and viral proteins have profound effects on astrocyte physiology, which may influence their function in the CNS.

Astrocytic modulation of Blood Brain Barrier: Perspectives on Parkinson´s Disease

Directory of Open Access Journals (Sweden)

Ricardo eCabezas

2014-08-01

Full Text Available TThe blood–brain barrier (BBB is a tightly regulated interface in the Central Nervous System that regulates the exchange of molecules in and out from the brain thus maintaining the CNS homeostasis. It is mainly composed of endothelial cells, pericytes and astrocytes that create a neurovascular unit with the adjacent neurons. Astrocytes are essential for the formation and maintenance of the BBB by providing secreted factors that lead to the adequate association between the cells of the BBB and the formation of strong tight junctions. Under neurological disorders, such as chronic cerebral ischemia, brain trauma, Epilepsy, Alzheimer and Parkinson´s Diseases, a disruption of the BBB takes place, involving a lost in the permeability of the barrier and phenotypical changes in both the endothelial cells and astrocytes. In this aspect, it has been established that the process of reactive gliosis is a common feature of astrocytes during BBB disruption, which has a detrimental effect on the barrier function and a subsequent damage in neuronal survival. In this review we discuss the implications of astrocyte functions in the protection of the BBB, and in the development of Parkinson´s disease and related disorders. Additionally, we highlight the current and future strategies in astrocyte protection aimed at the development of restorative therapies for the BBB in pathological conditions.

Synthetic AAV/CRISPR vectors for blocking HIV-1 expression in persistently infected astrocytes.

Science.gov (United States)

Kunze, Christine; Börner, Kathleen; Kienle, Eike; Orschmann, Tanja; Rusha, Ejona; Schneider, Martha; Radivojkov-Blagojevic, Milena; Drukker, Micha; Desbordes, Sabrina; Grimm, Dirk; Brack-Werner, Ruth

2018-02-01

Astrocytes, the most abundant cells in the mammalian brain, perform key functions and are involved in several neurodegenerative diseases. The human immunodeficiency virus (HIV) can persist in astrocytes, contributing to the HIV burden and neurological dysfunctions in infected individuals. While a comprehensive approach to HIV cure must include the targeting of HIV-1 in astrocytes, dedicated tools for this purpose are still lacking. Here we report a novel Adeno-associated virus-based vector (AAV9P1) with a synthetic surface peptide for transduction of astrocytes. Analysis of AAV9P1 transduction efficiencies with single brain cell populations, including primary human brain cells, as well as human brain organoids demonstrated that AAV9P1 targeted terminally differentiated human astrocytes much more efficiently than neurons. We then investigated whether AAV9P1 can be used to deliver HIV-inhibitory genes to astrocytes. To this end we generated AAV9P1 vectors containing genes for HIV-1 proviral editing by CRISPR/Cas9. Latently HIV-1 infected astrocytes transduced with these vectors showed significantly diminished reactivation of proviruses, compared with untransduced cultures. Sequence analysis identified mutations/deletions in key HIV-1 transcriptional control regions. We conclude that AAV9P1 is a promising tool for gene delivery to astrocytes and may facilitate inactivation/destruction of persisting HIV-1 proviruses in astrocyte reservoirs. © 2017 Wiley Periodicals, Inc.

Detection of mouse endogenous type B astrocytes migrating towards brain lesions

Directory of Open Access Journals (Sweden)

Gema Elvira

2015-01-01

Full Text Available Neuroblasts represent the predominant migrating cell type in the adult mouse brain. There are, however, increasing evidences of migration of other neural precursors. This work aims at identifying in vivo endogenous early neural precursors, different from neuroblasts, able to migrate in response to brain injuries. The monoclonal antibody Nilo1, which unequivocally identifies type B astrocytes and embryonic radial glia, was coupled to magnetic glyconanoparticles (mGNPs. Here we show that Nilo1–mGNPs in combination with magnetic resonance imaging in living mice allowed the in vivo identification of endogenous type B astrocytes at their niche, as well as their migration to the lesion site in response to glioblastoma, demyelination, cryolesion or mechanical injuries. In addition, Nilo1+ adult radial glia-like structures were identified at the lesion site a few hours after damage. For all damage models used, type B astrocyte migration was fast and orderly. Identification of Nilo1+ cells surrounding an induced glioblastoma was also possible after intraperitoneal injection of the antibody. This opens up the possibility of an early identification of the initial damage site(s after brain insults, by the migration of type B astrocytes.

The indispensable roles of microglia and astrocytes during brain development

NARCIS (Netherlands)

Reemst, Kitty; Noctor, Stephen C.; Lucassen, Paul J.; Hol, Elly M.

2016-01-01

Glia are essential for brain functioning during development and in the adult brain. Here, we discuss the various roles of both microglia and astrocytes, and their interactions during brain development. Although both cells are fundamentally different in origin and function, they often affect the same

The Indispensable Roles of Microglia and Astrocytes during Brain Development

NARCIS (Netherlands)

Reemst, K.; Noctor, S.C.; Lucassen, P.J.; Hol, E.M.

2016-01-01

Glia are essential for brain functioning during development and in the adult brain. Here, we discuss the various roles of both microglia and astrocytes, and their interactions during brain development. Although both cells are fundamentally different in origin and function, they often affect the same

Cholesterol efflux is differentially regulated in neurons and astrocytes: implications for brain cholesterol homeostasis

Science.gov (United States)

Chen, Jing; Zhang, Xiaolu; Kusumo, Handojo; Costa, Lucio G.; Guizzetti, Marina

2012-01-01

Disruption of cholesterol homeostasis in the central nervous system (CNS) has been associated with neurological, neurodegenerative, and neurodevelopmental disorders. The CNS is a closed system with regard to cholesterol homeostasis, as cholesterol-delivering lipoproteins from the periphery cannot pass the blood-brain-barrier and enter the brain. Different cell types in the brain have different functions in the regulation of cholesterol homeostasis, with astrocytes producing and releasing apolipoprotein E and lipoproteins, and neurons metabolizing cholesterol to 24(S)-hydroxycholesterol. We present evidence that astrocytes and neurons adopt different mechanisms also in regulating cholesterol efflux. We found that in astrocytes cholesterol efflux is induced by both lipid-free apolipoproteins and lipoproteins, while cholesterol removal from neurons is triggered only by lipoproteins. The main pathway by which apolipoproteins induce cholesterol efflux is through ABCA1. By upregulating ABCA1 levels and by inhibiting its activity and silencing its expression, we show that ABCA1 is involved in cholesterol efflux from astrocytes but not from neurons. Furthermore, our results suggest that ABCG1 is involved in cholesterol efflux to apolipoproteins and lipoproteins from astrocytes but not from neurons, while ABCG4, whose expression is much higher in neurons than astrocytes, is involved in cholesterol efflux from neurons but not astrocytes. These results indicate that different mechanisms regulate cholesterol efflux from neurons and astrocytes, reflecting the different roles that these cell types play in brain cholesterol homeostasis. These results are important in understanding cellular targets of therapeutic drugs under development for the treatments of conditions associated with altered cholesterol homeostasis in the CNS. PMID:23010475

Direct Signaling from Astrocytes to Neurons in Cultures of Mammalian Brain Cells

Science.gov (United States)

Nedergaard, Maiken

1994-03-01

Although astrocytes have been considered to be supportive, rather than transmissive, in the adult nervous system, recent studies have challenged this assumption by demonstrating that astrocytes possess functional neurotransmitter receptors. Astrocytes are now shown to directly modulate the free cytosolic calcium, and hence transmission characteristics, of neighboring neurons. When a focal electric field potential was applied to single astrocytes in mixed cultures of rat forebrain astrocytes and neurons, a prompt elevation of calcium occurred in the target cell. This in turn triggered a wave of calcium increase, which propagated from astrocyte to astrocyte. Neurons resting on these astrocytes responded with large increases in their concentration of cytosolic calcium. The gap junction blocker octanol attenuated the neuronal response, which suggests that the astrocytic-neuronal signaling is mediated through intercellular connections rather than synaptically. This neuronal response to local astrocytic stimulation may mediate local intercellular communication within the brain.

Astrocytic Insulin Signaling Couples Brain Glucose Uptake with Nutrient Availability.

Science.gov (United States)

García-Cáceres, Cristina; Quarta, Carmelo; Varela, Luis; Gao, Yuanqing; Gruber, Tim; Legutko, Beata; Jastroch, Martin; Johansson, Pia; Ninkovic, Jovica; Yi, Chun-Xia; Le Thuc, Ophelia; Szigeti-Buck, Klara; Cai, Weikang; Meyer, Carola W; Pfluger, Paul T; Fernandez, Ana M; Luquet, Serge; Woods, Stephen C; Torres-Alemán, Ignacio; Kahn, C Ronald; Götz, Magdalena; Horvath, Tamas L; Tschöp, Matthias H

2016-08-11

We report that astrocytic insulin signaling co-regulates hypothalamic glucose sensing and systemic glucose metabolism. Postnatal ablation of insulin receptors (IRs) in glial fibrillary acidic protein (GFAP)-expressing cells affects hypothalamic astrocyte morphology, mitochondrial function, and circuit connectivity. Accordingly, astrocytic IR ablation reduces glucose-induced activation of hypothalamic pro-opio-melanocortin (POMC) neurons and impairs physiological responses to changes in glucose availability. Hypothalamus-specific knockout of astrocytic IRs, as well as postnatal ablation by targeting glutamate aspartate transporter (GLAST)-expressing cells, replicates such alterations. A normal response to altering directly CNS glucose levels in mice lacking astrocytic IRs indicates a role in glucose transport across the blood-brain barrier (BBB). This was confirmed in vivo in GFAP-IR KO mice by using positron emission tomography and glucose monitoring in cerebral spinal fluid. We conclude that insulin signaling in hypothalamic astrocytes co-controls CNS glucose sensing and systemic glucose metabolism via regulation of glucose uptake across the BBB. Copyright © 2016 Elsevier Inc. All rights reserved.

Molecular and Functional Properties of Regional Astrocytes in the Adult Brain.

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Morel, Lydie; Chiang, Ming Sum R; Higashimori, Haruki; Shoneye, Temitope; Iyer, Lakshmanan K; Yelick, Julia; Tai, Albert; Yang, Yongjie

2017-09-06

The molecular signature and functional properties of astroglial subtypes in the adult CNS remain largely undefined. By using translational ribosome affinity purification followed by RNA-Seq, we profiled astroglial ribosome-associated (presumably translating) mRNAs in major cortical and subcortical brain regions (cortex, hippocampus, caudate-putamen, nucleus accumbens, thalamus, and hypothalamus) of BAC aldh1l1 -translational ribosome affinity purification (TRAP) mice (both sexes). We found that the expression of astroglial translating mRNAs closely follows the dorsoventral axis, especially from cortex/hippocampus to thalamus/hypothalamus posteriorly. This region-specific expression pattern of genes, such as synaptogenic modulator sparc and transcriptional factors ( emx2 , lhx2 , and hopx ), was validated by qRT-PCR and immunostaining in brain sections. Interestingly, cortical or subcortical astrocytes selectively promote neurite growth and synaptic activity of neurons only from the same region in mismatched cocultures, exhibiting region-matched astrocyte to neuron communication. Overall, these results generated new molecular signature of astrocyte types in the adult CNS, providing insights into their origin and functional diversity. SIGNIFICANCE STATEMENT We investigated the in vivo molecular and functional heterogeneity of astrocytes inter-regionally from adult brain. Our results showed that the expression pattern of ribosome-associated mRNA profiles in astrocytes closely follows the dorsoventral axis, especially posteriorly from cortex/hippocampus to thalamus/hypothalamus. In line with this, our functional results further demonstrated region-selective roles of cortical and subcortical astrocytes in regulating cortical or subcortical neuronal synaptogenesis and maturation. These in vivo studies provide a previously uncharacterized and important molecular atlas for exploring region-specific astroglial functions. Copyright © 2017 the authors 0270-6474/17/378706-12$15.00/0.

Astrocytes in Alzheimer’s disease

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Verkhratsky, Alexei; Olabarria, Markel; Noristani, Harun N.; Yeh, Chia-Yu; Rodriguez, Jose Julio

2010-01-01

The circuitry of the human brain is formed by neuronal networks embedded into astroglial syncytia. The astrocytes perform numerous functions, providing for the overall brain homeostasis, assisting in neurogenesis, determining the micro-architecture of the grey matter, and defending the brain through evolutionary conserved astrogliosis programs.

Upregulation of adenosine kinase in astrocytes in experimental and human temporal lobe epilepsy.

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Aronica, Eleonora; Zurolo, Emanuele; Iyer, Anand; de Groot, Marjolein; Anink, Jasper; Carbonell, Caterina; van Vliet, Erwin A; Baayen, Johannes C; Boison, Detlev; Gorter, Jan A

2011-09-01

Adenosine kinase (ADK) represents the key metabolic enzyme for the regulation of extracellular adenosine levels in the brain. In adult brain, ADK is primarily present in astrocytes. Several lines of experimental evidence support a critical role of ADK in different types of brain injury associated with astrogliosis, which is also a prominent morphologic feature of temporal lobe epilepsy (TLE). We hypothesized that dysregulation of ADK is an ubiquitous pathologic hallmark of TLE. Using immunocytochemistry and Western blot analysis, we investigated ADK protein expression in a rat model of TLE during epileptogenesis and the chronic epileptic phase and compared those findings with tissue resected from TLE patients with mesial temporal sclerosis (MTS). In rat control hippocampus and cortex, a low baseline expression of ADK was found with mainly nuclear localization. One week after the electrical induction of status epilepticus (SE), prominent up-regulation of ADK became evident in astrocytes with a characteristic cytoplasmic localization. This increase in ADK persisted at least for 3-4 months after SE in rats developing a progressive form of epilepsy. In line with the findings from the rat model, expression of astrocytic ADK was also found to be increased in the hippocampus and temporal cortex of patients with TLE. In addition, in vitro experiments in human astrocyte cultures showed that ADK expression was increased by several proinflammatory molecules (interleukin-1β and lipopolysaccharide). These results suggest that dysregulation of ADK in astrocytes is a common pathologic hallmark of TLE. Moreover, in vitro data suggest the existence of an additional layer of modulatory crosstalk between the astrocyte-based adenosine cycle and inflammation. Whether this interaction also can play a role in vivo needs to be further investigated. Wiley Periodicals, Inc. © 2011 International League Against Epilepsy.

An improved in vitro blood-brain barrier model: rat brain endothelial cells co-cultured with astrocytes.

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Abbott, N Joan; Dolman, Diana E M; Drndarski, Svetlana; Fredriksson, Sarah M

2012-01-01

In vitro blood-brain barrier (BBB) models using primary cultured brain endothelial cells are important for establishing cellular and molecular mechanisms of BBB function. Co-culturing with BBB-associated cells especially astrocytes to mimic more closely the in vivo condition leads to upregulation of the BBB phenotype in the brain endothelial cells. Rat brain endothelial cells (RBECs) are a valuable tool allowing ready comparison with in vivo studies in rodents; however, it has been difficult to obtain pure brain endothelial cells, and few models achieve a transendothelial electrical resistance (TEER, measure of tight junction efficacy) of >200 Ω cm(2), i.e. the models are still relatively leaky. Here, we describe methods for preparing high purity RBECs and neonatal rat astrocytes, and a co-culture method that generates a robust, stable BBB model that can achieve TEER >600 Ω cm(2). The method is based on >20 years experience with RBEC culture, together with recent improvements to kill contaminating cells and encourage BBB differentiation.Astrocytes are isolated by mechanical dissection and cell straining and are frozen for later co-culture. RBECs are isolated from 3-month-old rat cortices. The brains are cleaned of meninges and white matter and enzymatically and mechanically dissociated. Thereafter, the tissue homogenate is centrifuged in bovine serum albumin to separate vessel fragments from other cells that stick to the myelin plug. The vessel fragments undergo a second enzyme digestion to separate pericytes from vessels and break down vessels into shorter segments, after which a Percoll gradient is used to separate capillaries from venules, arterioles, and single cells. To kill remaining contaminating cells such as pericytes, the capillary fragments are plated in puromycin-containing medium and RBECs grown to 50-60% confluence. They are then passaged onto filters for co-culture with astrocytes grown in the bottom of the wells. The whole procedure takes ∼2

Astrocytes and energy metabolism.

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Prebil, Mateja; Jensen, Jørgen; Zorec, Robert; Kreft, Marko

2011-05-01

Astrocytes are glial cells, which play a significant role in a number of processes, including the brain energy metabolism. Their anatomical position between blood vessels and neurons make them an interface for effective glucose uptake from blood. After entering astrocytes, glucose can be involved in different metabolic pathways, e.g. in glycogen production. Glycogen in the brain is localized mainly in astrocytes and is an important energy source in hypoxic conditions and normal brain functioning. The portion of glucose metabolized into glycogen molecules in astrocytes is as high as 40%. It is thought that the release of gliotransmitters (such as glutamate, neuroactive peptides and ATP) into the extracellular space by regulated exocytosis supports a significant part of communication between astrocytes and neurons. On the other hand, neurotransmitter action on astrocytes has a significant role in brain energy metabolism. Therefore, understanding the astrocytes energy metabolism may help understanding neuron-astrocyte interactions.

Regional Susceptibility to Domoic Acid in Primary Astrocyte Cells Cultured from the Brain Stem and Hippocampus

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Olga M. Pulido

2008-02-01

Full Text Available Domoic acid is a marine biotoxin associated with harmful algal blooms and is the causative agent of amnesic shellfish poisoning in marine animals and humans. It is also an excitatory amino acid analog to glutamate and kainic acid which acts through glutamate receptors eliciting a very rapid and potent neurotoxic response. The hippocampus, among other brain regions, has been identified as a specific target site having high sensitivity to DOM toxicity. Histopathology evidence indicates that in addition to neurons, the astrocytes were also injured. Electron microscopy data reported in this study further supports the light microscopy findings. Furthermore, the effect of DOM was confirmed by culturing primary astrocytes from the hippocampus and the brain stem and subsequently exposing them to domoic acid. The RNA was extracted and used for biomarker analysis. The biomarker analysis was done for the early response genes including c-fos, c-jun, c-myc, Hsp-72; specific marker for the astrocytes- GFAP and the glutamate receptors including GluR 2, NMDAR 1, NMDAR 2A and B. Although, the astrocyte-GFAP and c-fos were not affected, c-jun and GluR 2 were down-regulated. The microarray analysis revealed that the chemokines / cytokines, tyrosine kinases (Trk, and apoptotic genes were altered. The chemokines that were up-regulated included - IL1-a, IL-1B, IL-6, the small inducible cytokine, interferon protein IP-10, CXC chemokine LIX, and IGF binding proteins. The Bax, Bcl-2, Trk A and Trk B were all downregulated. Interestingly, only the hippocampal astrocytes were affected. Our findings suggest that astrocytes may present a possible target for pharmacological interventions for the prevention and treatment of amnesic shellfish poisoning and for other brain pathologies involving excitotoxicity

Glutamate metabolism in the brain focusing on astrocytes

DEFF Research Database (Denmark)

Schousboe, Arne; Scafidi, Susanna; Bak, Lasse Kristoffer

2014-01-01

, as well as in nitrogen trafficking and ammonia homeostasis in brain. The anatomical specialization of astrocytic endfeet enables these cells to rapidly and efficiently remove neurotransmitters from the synaptic cleft to maintain homeostasis, and to provide glutamine to replenish neurotransmitter pools...

Significance of MDR1 and multiple drug resistance in refractory human epileptic brain

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Dini Gabriele

2004-10-01

Full Text Available Abstract Background The multiple drug resistance protein (MDR1/P-glycoprotein is overexpressed in glia and blood-brain barrier (BBB endothelium in drug refractory human epileptic tissue. Since various antiepileptic drugs (AEDs can act as substrates for MDR1, the enhanced expression/function of this protein may increase their active extrusion from the brain, resulting in decreased responsiveness to AEDs. Methods Human drug resistant epileptic brain tissues were collected after surgical resection. Astrocyte cell cultures were established from these tissues, and commercially available normal human astrocytes were used as controls. Uptake of fluorescent doxorubicin and radioactive-labeled Phenytoin was measured in the two cell populations, and the effect of MDR1 blockers was evaluated. Frozen human epileptic brain tissue slices were double immunostained to locate MDR1 in neurons and glia. Other slices were exposed to toxic concentrations of Phenytoin to study cell viability in the presence or absence of a specific MDR1 blocker. Results MDR1 was overexpressed in blood vessels, astrocytes and neurons in human epileptic drug-resistant brain. In addition, MDR1-mediated cellular drug extrusion was increased in human 'epileptic' astrocytes compared to 'normal' ones. Concomitantly, cell viability in the presence of cytotoxic compounds was increased. Conclusions Overexpression of MDR1 in different cell types in drug-resistant epileptic human brain leads to functional alterations, not all of which are linked to drug pharmacokinetics. In particular, the modulation of glioneuronal MDR1 function in epileptic brain in the presence of toxic concentrations of xenobiotics may constitute a novel cytoprotective mechanism.

The HSPB8-BAG3 chaperone complex is upregulated in astrocytes in the human brain affected by protein aggregation diseases.

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Seidel, K; Vinet, J; Dunnen, W F A den; Brunt, E R; Meister, M; Boncoraglio, A; Zijlstra, M P; Boddeke, H W G M; Rüb, U; Kampinga, H H; Carra, S

2012-02-01

HSPB8 is a small heat shock protein that forms a complex with the co-chaperone BAG3. Overexpression of the HSPB8-BAG3 complex in cells stimulates autophagy and facilitates the clearance of mutated aggregation-prone proteins, whose accumulation is a hallmark of many neurodegenerative disorders. HSPB8-BAG3 could thus play a protective role in protein aggregation diseases and might be specifically upregulated in response to aggregate-prone protein-mediated toxicity. Here we analysed HSPB8-BAG3 expression levels in post-mortem human brain tissue from patients suffering of the following protein conformation disorders: Alzheimer's disease, Parkinson's disease, Huntington's disease and spinocerebellar ataxia type 3 (SCA3). Western blotting and immunohistochemistry techniques were used to analyse HSPB8 and BAG3 expression levels in fibroblasts from SCA3 patients and post-mortem brain tissues, respectively. In all diseases investigated, we observed a strong upregulation of HSPB8 and a moderate upregulation of BAG3 specifically in astrocytes in the cerebral areas affected by neuronal damage and degeneration. Intriguingly, no significant change in the HSPB8-BAG3 expression levels was observed within neurones, irrespective of their localization or of the presence of proteinaceous aggregates. We propose that the upregulation of HSPB8 and BAG3 may enhance the ability of astrocytes to clear aggregated proteins released from neurones and cellular debris, maintain the local tissue homeostasis and/or participate in the cytoskeletal remodelling that astrocytes undergo during astrogliosis. © 2011 The Authors. Neuropathology and Applied Neurobiology © 2011 British Neuropathological Society.

Astrocyte Sodium Signalling and Panglial Spread of Sodium Signals in Brain White Matter.

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Moshrefi-Ravasdjani, Behrouz; Hammel, Evelyn L; Kafitz, Karl W; Rose, Christine R

2017-09-01

In brain grey matter, excitatory synaptic transmission activates glutamate uptake into astrocytes, inducing sodium signals which propagate into neighboring astrocytes through gap junctions. These sodium signals have been suggested to serve an important role in neuro-metabolic coupling. So far, it is unknown if astrocytes in white matter-that is in brain regions devoid of synapses-are also able to undergo such intra- and intercellular sodium signalling. In the present study, we have addressed this question by performing quantitative sodium imaging in acute tissue slices of mouse corpus callosum. Focal application of glutamate induced sodium transients in SR101-positive astrocytes. These were largely unaltered in the presence of ionotropic glutamate receptors blockers, but strongly dampened upon pharmacological inhibition of glutamate uptake. Sodium signals induced in individual astrocytes readily spread into neighboring SR101-positive cells with peak amplitudes decaying monoexponentially with distance from the stimulated cell. In addition, spread of sodium was largely unaltered during pharmacological inhibition of purinergic and glutamate receptors, indicating gap junction-mediated, passive diffusion of sodium between astrocytes. Using cell-type-specific, transgenic reporter mice, we found that sodium signals also propagated, albeit less effectively, from astrocytes to neighboring oligodendrocytes and NG2 cells. Again, panglial spread was unaltered with purinergic and glutamate receptors blocked. Taken together, our results demonstrate that activation of sodium-dependent glutamate transporters induces sodium signals in white matter astrocytes, which spread within the astrocyte syncytium. In addition, we found a panglial passage of sodium signals from astrocytes to NG2 cells and oligodendrocytes, indicating functional coupling between these macroglial cells in white matter.

Conceptual Network Model From Sensory Neurons to Astrocytes of the Human Nervous System.

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Yang, Yiqun; Yeo, Chai Kiat

2015-07-01

From a single-cell animal like paramecium to vertebrates like ape, the nervous system plays an important role in responding to the variations of the environment. Compared to animals, the nervous system in the human body possesses more intricate organization and utility. The nervous system anatomy has been understood progressively, yet the explanation at the cell level regarding complete information transmission is still lacking. Along the signal pathway toward the brain, an external stimulus first activates action potentials in the sensing neuron and these electric pulses transmit along the spinal nerve or cranial nerve to the neurons in the brain. Second, calcium elevation is triggered in the branch of astrocyte at the tripartite synapse. Third, the local calcium wave expands to the entire territory of the astrocyte. Finally, the calcium wave propagates to the neighboring astrocyte via gap junction channel. In our study, we integrate the existing mathematical model and biological experiments in each step of the signal transduction to establish a conceptual network model for the human nervous system. The network is composed of four layers and the communication protocols of each layer could be adapted to entities with different characterizations. We verify our simulation results against the available biological experiments and mathematical models and provide a test case of the integrated network. As the production of conscious episode in the human nervous system is still under intense research, our model serves as a useful tool to facilitate, complement and verify current and future study in human cognition.

Deciphering the Astrocyte Reaction in Alzheimer’s Disease

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Beatriz G. Perez-Nievas

2018-04-01

Full Text Available Reactive astrocytes were identified as a component of senile amyloid plaques in the cortex of Alzheimer’s disease (AD patients several decades ago. However, their role in AD pathophysiology has remained elusive ever since, in part owing to the extrapolation of the literature from primary astrocyte cultures and acute brain injury models to a chronic neurodegenerative scenario. Recent accumulating evidence supports the idea that reactive astrocytes in AD acquire neurotoxic properties, likely due to both a gain of toxic function and a loss of their neurotrophic effects. However, the diversity and complexity of this glial cell is only beginning to be unveiled, anticipating that astrocyte reaction might be heterogeneous as well. Herein we review the evidence from mouse models of AD and human neuropathological studies and attempt to decipher the main conundrums that astrocytes pose to our understanding of AD development and progression. We discuss the morphological features that characterize astrocyte reaction in the AD brain, the consequences of astrocyte reaction for both astrocyte biology and AD pathological hallmarks, and the molecular pathways that have been implicated in this reaction.

Acetazolamide Mitigates Astrocyte Cellular Edema Following Mild Traumatic Brain Injury

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Sturdivant, Nasya M.; Smith, Sean G.; Ali, Syed F.; Wolchok, Jeffrey C.; Balachandran, Kartik

2016-09-01

Non-penetrating or mild traumatic brain injury (mTBI) is commonly experienced in accidents, the battlefield and in full-contact sports. Astrocyte cellular edema is one of the major factors that leads to high morbidity post-mTBI. Various studies have reported an upregulation of aquaporin-4 (AQP4), a water channel protein, following brain injury. AZA is an antiepileptic drug that has been shown to inhibit AQP4 expression and in this study we investigate the drug as a therapeutic to mitigate the extent of mTBI induced cellular edema. We hypothesized that mTBI-mediated astrocyte dysfunction, initiated by increased intracellular volume, could be reduced when treated with AZA. We tested our hypothesis in a three-dimensional in vitro astrocyte model of mTBI. Samples were subject to no stretch (control) or one high-speed stretch (mTBI) injury. AQP4 expression was significantly increased 24 hours after mTBI. mTBI resulted in a significant increase in the cell swelling within 30 min of mTBI, which was significantly reduced in the presence of AZA. Cell death and expression of S100B was significantly reduced when AZA was added shortly before mTBI stretch. Overall, our data point to occurrence of astrocyte swelling immediately following mTBI, and AZA as a promising treatment to mitigate downstream cellular mortality.

Transplantation of specific human astrocytes promotes functional recovery after spinal cord injury.

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Stephen J A Davies

2011-03-01

Full Text Available Repairing trauma to the central nervous system by replacement of glial support cells is an increasingly attractive therapeutic strategy. We have focused on the less-studied replacement of astrocytes, the major support cell in the central nervous system, by generating astrocytes from embryonic human glial precursor cells using two different astrocyte differentiation inducing factors. The resulting astrocytes differed in expression of multiple proteins thought to either promote or inhibit central nervous system homeostasis and regeneration. When transplanted into acute transection injuries of the adult rat spinal cord, astrocytes generated by exposing human glial precursor cells to bone morphogenetic protein promoted significant recovery of volitional foot placement, axonal growth and notably robust increases in neuronal survival in multiple spinal cord laminae. In marked contrast, human glial precursor cells and astrocytes generated from these cells by exposure to ciliary neurotrophic factor both failed to promote significant behavioral recovery or similarly robust neuronal survival and support of axon growth at sites of injury. Our studies thus demonstrate functional differences between human astrocyte populations and suggest that pre-differentiation of precursor cells into a specific astrocyte subtype is required to optimize astrocyte replacement therapies. To our knowledge, this study is the first to show functional differences in ability to promote repair of the injured adult central nervous system between two distinct subtypes of human astrocytes derived from a common fetal glial precursor population. These findings are consistent with our previous studies of transplanting specific subtypes of rodent glial precursor derived astrocytes into sites of spinal cord injury, and indicate a remarkable conservation from rat to human of functional differences between astrocyte subtypes. In addition, our studies provide a specific population of human

Astrocyte oxidative metabolism and metabolite trafficking after fluid percussion brain injury in adult rats.

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Bartnik-Olson, Brenda L; Oyoyo, Udochukwu; Hovda, David A; Sutton, Richard L

2010-12-01

Despite various lines of evidence pointing to the compartmentation of metabolism within the brain, few studies have reported the effect of a traumatic brain injury (TBI) on neuronal and astrocyte compartments and/or metabolic trafficking between these cells. In this study we used ex vivo ¹³C NMR spectroscopy following an infusion of [1-¹³C] glucose and [1,2-¹³C₂] acetate to study oxidative metabolism in neurons and astrocytes of sham-operated and fluid percussion brain injured (FPI) rats at 1, 5, and 14 days post-surgery. FPI resulted in a decrease in the ¹³C glucose enrichment of glutamate in neurons in the injured hemisphere at day 1. In contrast, enrichment of glutamine in astrocytes from acetate was not significantly decreased at day 1. At day 5 the ¹³C enrichment of glutamate and glutamine from glucose in the injured hemisphere of FPI rats did not differ from sham levels, but glutamine derived from acetate metabolism in astrocytes was significantly increased. The ¹³C glucose enrichment of the C3 position of glutamate (C3) in neurons was significantly decreased ipsilateral to FPI at day 14, whereas the enrichment of glutamine in astrocytes had returned to sham levels at this time point. These findings indicate that the oxidative metabolism of glucose is reduced to a greater extent in neurons compared to astrocytes following a FPI. The increased utilization of acetate to synthesize glutamine, and the acetate enrichment of glutamate via the glutamate-glutamine cycle, suggests an integral protective role for astrocytes in maintaining metabolic function following TBI-induced impairments in glucose metabolism.

Analysis of p53- immunoreactivity in astrocytic brain tumors

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Shinkarenko T.V.

2016-12-01

Full Text Available P53 is an antioncogene with the frequently occured mutations in human tumor cells, leading to corresponding protein overexpression which can be detected by immunohistochemistry. Researches dedicated to the investigation of possibilities of using this technique gave controversial results. The authors investigated features of p53 protein expression in astrocytic brain tumors with different degrees of malignancy. Analyzed the relationship of the expression level of p53 by tumor cells with clinical parameters and Ki-67 proliferation index (PI as well. Tissues were collected from 52 cases with diagnosed astrocytic brain tumors. The sections were immunohistochemically stained with p53 and Ki-67. For each marker, 1000 tumor cells were counted and the ratio of positive tumor cells was calculated using software package ImageJ 1,47v. In normal brain tissue p53- expression was not identified. p53-immunoreactive tumor cells were detected in 25% (1/4 pilocytic astrocytomas, 33.3% (2/6 of diffuse astrocytomas, 53.8% (7/13 anaplastic astrocytomas, 58.6% (17/29 glioblastomas. A high proportion of p53-immunoreactive cells (> 30% was observed only in glioblastomas. The level of p53-imunoreactivity was not related to the age, gender and Grade WHO (p> 0,05. Spearman correlation coefficient between the relative quantity of ki-67- and p53-immunoreactive nuclei showed weak direct correlation (0.023, but the one was not statistically significant (p> 0,05. The level of p53-imunoreactivity is not dependent from age and sex of patients, Grade (WHO and proliferative activity (p>0,05 but the high level of p53-immunoreactive cells (>30% is found in glioblastoma specimens only, that may be due to the accumulation of mutations in DNA of tumor cells. There is insignificant weak relationship between relative quantities of ki-67- and p53-immunoreactive tumor cells (p>0,05.

Astrocyte uncoupling as a cause of human temporal lobe epilepsy.

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Bedner, Peter; Dupper, Alexander; Hüttmann, Kerstin; Müller, Julia; Herde, Michel K; Dublin, Pavel; Deshpande, Tushar; Schramm, Johannes; Häussler, Ute; Haas, Carola A; Henneberger, Christian; Theis, Martin; Steinhäuser, Christian

2015-05-01

Glial cells are now recognized as active communication partners in the central nervous system, and this new perspective has rekindled the question of their role in pathology. In the present study we analysed functional properties of astrocytes in hippocampal specimens from patients with mesial temporal lobe epilepsy without (n = 44) and with sclerosis (n = 75) combining patch clamp recording, K(+) concentration analysis, electroencephalography/video-monitoring, and fate mapping analysis. We found that the hippocampus of patients with mesial temporal lobe epilepsy with sclerosis is completely devoid of bona fide astrocytes and gap junction coupling, whereas coupled astrocytes were abundantly present in non-sclerotic specimens. To decide whether these glial changes represent cause or effect of mesial temporal lobe epilepsy with sclerosis, we developed a mouse model that reproduced key features of human mesial temporal lobe epilepsy with sclerosis. In this model, uncoupling impaired K(+) buffering and temporally preceded apoptotic neuronal death and the generation of spontaneous seizures. Uncoupling was induced through intraperitoneal injection of lipopolysaccharide, prevented in Toll-like receptor4 knockout mice and reproduced in situ through acute cytokine or lipopolysaccharide incubation. Fate mapping confirmed that in the course of mesial temporal lobe epilepsy with sclerosis, astrocytes acquire an atypical functional phenotype and lose coupling. These data suggest that astrocyte dysfunction might be a prime cause of mesial temporal lobe epilepsy with sclerosis and identify novel targets for anti-epileptogenic therapeutic intervention. © The Author (2015). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Aerobic glycolysis during brain activation: adrenergic regulation and influence of norepinephrine on astrocytic metabolism.

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Dienel, Gerald A; Cruz, Nancy F

2016-07-01

Aerobic glycolysis occurs during brain activation and is characterized by preferential up-regulation of glucose utilization compared with oxygen consumption even though oxygen level and delivery are adequate. Aerobic glycolysis is a widespread phenomenon that underlies energetics of diverse brain activities, such as alerting, sensory processing, cognition, memory, and pathophysiological conditions, but specific cellular functions fulfilled by aerobic glycolysis are poorly understood. Evaluation of evidence derived from different disciplines reveals that aerobic glycolysis is a complex, regulated phenomenon that is prevented by propranolol, a non-specific β-adrenoceptor antagonist. The metabolic pathways that contribute to excess utilization of glucose compared with oxygen include glycolysis, the pentose phosphate shunt pathway, the malate-aspartate shuttle, and astrocytic glycogen turnover. Increased lactate production by unidentified cells, and lactate dispersal from activated cells and lactate release from the brain, both facilitated by astrocytes, are major factors underlying aerobic glycolysis in subjects with low blood lactate levels. Astrocyte-neuron lactate shuttling with local oxidation is minor. Blockade of aerobic glycolysis by propranolol implicates adrenergic regulatory processes including adrenal release of epinephrine, signaling to brain via the vagus nerve, and increased norepinephrine release from the locus coeruleus. Norepinephrine has a powerful influence on astrocytic metabolism and glycogen turnover that can stimulate carbohydrate utilization more than oxygen consumption, whereas β-receptor blockade 're-balances' the stoichiometry of oxygen-glucose or -carbohydrate metabolism by suppressing glucose and glycogen utilization more than oxygen consumption. This conceptual framework may be helpful for design of future studies to elucidate functional roles of preferential non-oxidative glucose utilization and glycogen turnover during brain

Impact of commercial cigarette smoke condensate on brain tissue co-cultured with astrocytes and blood-brain barrier endothelial cells.

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Lee, Seon-Bong; Kim, Ju-Hyeong; Cho, Myung-Haing; Choe, Eun-Sang; Kim, Kwang-Sik; Shim, Soon-Mi

2017-01-01

The purpose of the current study was to investigate the effect of two commercial cigarette smoke condensates (CCSC) on oxidative stress and cell cytotoxicity in human brain (T98G) or astrocytes (U-373 MG) in the presence of human brain microvascular endothelial cells (HBMEC). Cell viability of mono-culture of T98G or U-373 MG was markedly decreased in a concentration-dependent manner, and T98G was more susceptible than U-373 MG to CCSC exposure. Cytotoxicity was less prominent when T98G was co-cultured with HBMEC than when T98G was co-cultured with U-373 MG. Significant reduction in trans-epithelial electric resistance (TEER), a biomarker of cellular integrity was noted in HBMEC co-cultured with T98G (HBMEC-T98G co-culture) and U-373 MG co-cultured with T98G (U-373 MG-T98G co-culture) after 24 or 48 hr CCSC exposure, respectively. TEER value of U-373 MG co-cultured with T98G (79-84%) was higher than HBMEC co-cultured with T98G (62-63%) within 120-hr incubation with CCSC. Reactive oxygen species (ROS) generated by CCSC in mono-culture of T98G and U-373 MG reached highest levels at 4 and 16 mg/ml, respectively. ROS production by T98G fell when co-cultured with HBMEC or U-373MG. These findings suggest that adverse consequences of CCSC treatment on brain cells may be protected by blood-brain barrier or astrocytes, but with chronic exposure toxicity may be worsened due to destruction of cellular integrity.

Platelet-derived growth factor (PDGF-BB-mediated induction of monocyte chemoattractant protein 1 in human astrocytes: implications for HIV-associated neuroinflammation

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Bethel-Brown Crystal

2012-12-01

Full Text Available Abstract Chemokine (C-C motif ligand 2, also known as monocyte chemoattractant protein 1 (MCP-1 is an important factor for the pathogenesis of HIV-associated neurocognitive disorders (HAND. The mechanisms of MCP-1-mediated neuropathogenesis, in part, revolve around its neuroinflammatory role and the recruitment of monocytes into the central nervous system (CNS via the disrupted blood-brain barrier (BBB. We have previously demonstrated that HIV-1/HIV-1 Tat upregulate platelet-derived growth factor (PDGF-BB, a known cerebrovascular permeant; subsequently, the present study was aimed at exploring the regulation of MCP-1 by PDGF-BB in astrocytes with implications in HAND. Specifically, the data herein demonstrate that exposure of human astrocytes to HIV-1 LAI elevated PDGF-B and MCP-1 levels. Furthermore, treating astrocytes with the human recombinant PDGF-BB protein significantly increased the production and release of MCP-1 at both the RNA and protein levels. MCP-1 induction was regulated by activation of extracellular-signal-regulated kinase (ERK1/2, c-Jun N-terminal kinase (JNK and p38 mitogen-activated protein (MAP kinases and phosphatidylinositol 3-kinase (PI3K/Akt pathways and the downstream transcription factor, nuclear factor κB (NFκB. Chromatin immunoprecipitation (ChIP assays demonstrated increased binding of NFκB to the human MCP-1 promoter following PDGF-BB exposure. Conditioned media from PDGF-BB-treated astrocytes increased monocyte transmigration through human brain microvascular endothelial cells (HBMECs, an effect that was blocked by STI-571, a tyrosine kinase inhibitor (PDGF receptor (PDGF-R blocker. PDGF-BB-mediated release of MCP-1 was critical for increased permeability in an in vitro BBB model as evidenced by blocking antibody assays. Since MCP-1 is linked to disease severity, understanding its modulation by PDGF-BB could aid in understanding the proinflammatory responses in HAND. These results suggest that astrocyte

Genome-Scale Reconstruction of the Human Astrocyte Metabolic Network

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Mart?n-Jim?nez, Cynthia A.; Salazar-Barreto, Diego; Barreto, George E.; Gonz?lez, Janneth

2017-01-01

Astrocytes are the most abundant cells of the central nervous system; they have a predominant role in maintaining brain metabolism. In this sense, abnormal metabolic states have been found in different neuropathological diseases. Determination of metabolic states of astrocytes is difficult to model using current experimental approaches given the high number of reactions and metabolites present. Thus, genome-scale metabolic networks derived from transcriptomic data can be used as a framework t...

Astrocytic glycogen-derived lactate fuels the brain during exhaustive exercise to maintain endurance capacity.

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Matsui, Takashi; Omuro, Hideki; Liu, Yu-Fan; Soya, Mariko; Shima, Takeru; McEwen, Bruce S; Soya, Hideaki

2017-06-13

Brain glycogen stored in astrocytes provides lactate as an energy source to neurons through monocarboxylate transporters (MCTs) to maintain neuronal functions such as hippocampus-regulated memory formation. Although prolonged exhaustive exercise decreases brain glycogen, the role of this decrease and lactate transport in the exercising brain remains less clear. Because muscle glycogen fuels exercising muscles, we hypothesized that astrocytic glycogen plays an energetic role in the prolonged-exercising brain to maintain endurance capacity through lactate transport. To test this hypothesis, we used a rat model of exhaustive exercise and capillary electrophoresis-mass spectrometry-based metabolomics to observe comprehensive energetics of the brain (cortex and hippocampus) and muscle (plantaris). At exhaustion, muscle glycogen was depleted but brain glycogen was only decreased. The levels of MCT2, which takes up lactate in neurons, increased in the brain, as did muscle MCTs. Metabolomics revealed that brain, but not muscle, ATP was maintained with lactate and other glycogenolytic/glycolytic sources. Intracerebroventricular injection of the glycogen phosphorylase inhibitor 1,4-dideoxy-1,4-imino-d-arabinitol did not affect peripheral glycemic conditions but suppressed brain lactate production and decreased hippocampal ATP levels at exhaustion. An MCT2 inhibitor, α-cyano-4-hydroxy-cinnamate, triggered a similar response that resulted in lower endurance capacity. These findings provide direct evidence for the energetic role of astrocytic glycogen-derived lactate in the exhaustive-exercising brain, implicating the significance of brain glycogen level in endurance capacity. Glycogen-maintained ATP in the brain is a possible defense mechanism for neurons in the exhausted brain.

Neuron-astrocyte interactions, pyruvate carboxylation and the pentose phosphate pathway in the neonatal rat brain.

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Morken, Tora Sund; Brekke, Eva; Håberg, Asta; Widerøe, Marius; Brubakk, Ann-Mari; Sonnewald, Ursula

2014-01-01

Glucose and acetate metabolism and the synthesis of amino acid neurotransmitters, anaplerosis, glutamate-glutamine cycling and the pentose phosphate pathway (PPP) have been extensively investigated in the adult, but not the neonatal rat brain. To do this, 7 day postnatal (P7) rats were injected with [1-(13)C]glucose and [1,2-(13)C]acetate and sacrificed 5, 10, 15, 30 and 45 min later. Adult rats were injected and sacrificed after 15 min. To analyse pyruvate carboxylation and PPP activity during development, P7 rats received [1,2-(13)C]glucose and were sacrificed 30 min later. Brain extracts were analysed using (1)H- and (13)C-NMR spectroscopy. Numerous differences in metabolism were found between the neonatal and adult brain. The neonatal brain contained lower levels of glutamate, aspartate and N-acetylaspartate but similar levels of GABA and glutamine per mg tissue. Metabolism of [1-(13)C]glucose at the acetyl CoA stage was reduced much more than that of [1,2-(13)C]acetate. The transfer of glutamate from neurons to astrocytes was much lower while transfer of glutamine from astrocytes to glutamatergic neurons was relatively higher. However, transport of glutamine from astrocytes to GABAergic neurons was lower. Using [1,2-(13)C]glucose it could be shown that despite much lower pyruvate carboxylation, relatively more pyruvate from glycolysis was directed towards anaplerosis than pyruvate dehydrogenation in astrocytes. Moreover, the ratio of PPP/glucose-metabolism was higher. These findings indicate that only the part of the glutamate-glutamine cycle that transfers glutamine from astrocytes to neurons is operating in the neonatal brain and that compared to adults, relatively more glucose is prioritised to PPP and pyruvate carboxylation. Our results may have implications for the capacity to protect the neonatal brain against excitotoxicity and oxidative stress.

Astrocytes in physiological aging and Alzheimer's disease.

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Rodríguez-Arellano, J J; Parpura, V; Zorec, R; Verkhratsky, A

2016-05-26

Astrocytes are fundamental for homoeostasis, defence and regeneration of the central nervous system. Loss of astroglial function and astroglial reactivity contributes to the aging of the brain and to neurodegenerative diseases. Changes in astroglia in aging and neurodegeneration are highly heterogeneous and region-specific. In animal models of Alzheimer's disease (AD) astrocytes undergo degeneration and atrophy at the early stages of pathological progression, which possibly may alter the homeostatic reserve of the brain and contribute to early cognitive deficits. At later stages of AD reactive astrocytes are associated with neurite plaques, the feature commonly found in animal models and in human diseased tissue. In animal models of the AD reactive astrogliosis develops in some (e.g. in the hippocampus) but not in all regions of the brain. For instance, in entorhinal and prefrontal cortices astrocytes do not mount gliotic response to emerging β-amyloid deposits. These deficits in reactivity coincide with higher vulnerability of these regions to AD-type pathology. Astroglial morphology and function can be regulated through environmental stimulation and/or medication suggesting that astrocytes can be regarded as a target for therapies aimed at the prevention and cure of neurodegenerative disorders. Copyright © 2015 IBRO. Published by Elsevier Ltd. All rights reserved.

In Vitro Modeling of Blood-Brain Barrier with Human iPSC-Derived Endothelial Cells, Pericytes, Neurons, and Astrocytes via Notch Signaling

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Kohei Yamamizu

2017-03-01

Full Text Available The blood-brain barrier (BBB is composed of four cell populations, brain endothelial cells (BECs, pericytes, neurons, and astrocytes. Its role is to precisely regulate the microenvironment of the brain through selective substance crossing. Here we generated an in vitro model of the BBB by differentiating human induced pluripotent stem cells (hiPSCs into all four populations. When the four hiPSC-derived populations were co-cultured, endothelial cells (ECs were endowed with features consistent with BECs, including a high expression of nutrient transporters (CAT3, MFSD2A and efflux transporters (ABCA1, BCRP, PGP, MRP5, and strong barrier function based on tight junctions. Neuron-derived Dll1, which activates Notch signaling in ECs, was essential for the BEC specification. We performed in vitro BBB permeability tests and assessed ten clinical drugs by nanoLC-MS/MS, finding a good correlation with the BBB permeability reported in previous cases. This technology should be useful for research on human BBB physiology, pathology, and drug development.

Characterisation of the expression of NMDA receptors in human astrocytes.

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Ming-Chak Lee

Full Text Available Astrocytes have long been perceived only as structural and supporting cells within the central nervous system (CNS. However, the discovery that these glial cells may potentially express receptors capable of responding to endogenous neurotransmitters has resulted in the need to reassess astrocytic physiology. The aim of the current study was to characterise the expression of NMDA receptors (NMDARs in primary human astrocytes, and investigate their response to physiological and excitotoxic concentrations of the known endogenous NMDAR agonists, glutamate and quinolinic acid (QUIN. Primary cultures of human astrocytes were used to examine expression of these receptors at the mRNA level using RT-PCR and qPCR, and at the protein level using immunocytochemistry. The functionality role of the receptors was assessed using intracellular calcium influx experiments and measuring extracellular lactate dehydrogenase (LDH activity in primary cultures of human astrocytes treated with glutamate and QUIN. We found that all seven currently known NMDAR subunits (NR1, NR2A, NR2B, NR2C, NR2D, NR3A and NR3B are expressed in astrocytes, but at different levels. Calcium influx studies revealed that both glutamate and QUIN could activate astrocytic NMDARs, which stimulates Ca2+ influx into the cell and can result in dysfunction and death of astrocytes. Our data also show that the NMDAR ion channel blockers, MK801, and memantine can attenuate glutamate and QUIN mediated cell excitotoxicity. This suggests that the mechanism of glutamate and QUIN gliotoxicity is at least partially mediated by excessive stimulation of NMDARs. The present study is the first to provide definitive evidence for the existence of functional NMDAR expression in human primary astrocytes. This discovery has significant implications for redefining the cellular interaction between glia and neurons in both physiological processes and pathological conditions.

Expression of the human isoform of glutamate dehydrogenase, hGDH2, augments TCA cycle capacity and oxidative metabolism of glutamate during glucose deprivation in astrocytes

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Nissen, Jakob D; Lykke, Kasper; Bryk, Jaroslaw

2017-01-01

A key enzyme in brain glutamate homeostasis is glutamate dehydrogenase (GDH) which links carbohydrate and amino acid metabolism mediating glutamate degradation to CO2 and expanding tricarboxylic acid (TCA) cycle capacity with intermediates, i.e. anaplerosis. Humans express two GDH isoforms, GDH1...... and 2, whereas most other mammals express only GDH1. hGDH1 is widely expressed in human brain while hGDH2 is confined to astrocytes. The two isoforms display different enzymatic properties and the nature of these supports that hGDH2 expression in astrocytes potentially increases glutamate oxidation...

Acute and chronic glucocorticoid treatments regulate astrocyte-enriched mRNAs in multiple brain regions in vivo

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Bradley S. Carter

2013-08-01

Full Text Available Previous studies have primarily interpreted gene expression regulation by glucocorticoids in the brain in terms of impact on neurons; however, less is known about the corresponding impact of glucocorticoids on glia and specifically astrocytes in vivo. Recent microarray experiments have identified glucocorticoid-sensitive mRNAs in primary astrocyte cell culture, including a number of mRNAs that have reported astrocyte-enriched expression patterns relative to other brain cell types. Here, we have tested whether elevations of glucocorticoids regulate a subset of these mRNAs in vivo following acute and chronic corticosterone exposure in adult mice. Acute corticosterone exposure was achieved by a single injection of 10 mg/kg corticosterone, and tissue samples were harvested two hours post-injection. Chronic corticosterone exposure was achieved by administering 10 mg/mL corticosterone via drinking water for two weeks. Gene expression was then assessed in two brain regions associated with glucocorticoid action (prefrontal cortex and hippocampus by qPCR and by in situ hybridization. The majority of measured mRNAs regulated by glucocorticoids in astrocytes in vitro were similarly regulated by acute and/or chronic glucocorticoid exposure in vivo. In addition, the expression levels for mRNAs regulated in at least one corticosterone exposure condition (acute/chronic demonstrated moderate positive correlation between the two conditions by brain region. In situ hybridization analyses suggest that select mRNAs are regulated by chronic corticosterone exposure specifically in astroctyes based on (1 similar general expression patterns between corticosterone-treated and vehicle-treated animals and (2 similar expression patterns to the pan-astrocyte marker Aldh1l1. Our findings demonstrate that glucocorticoids regulate astrocyte-enriched mRNAs in vivo and suggest that glucocorticoids regulate gene expression in the brain in a cell type-dependent fashion.

Identification of diverse astrocyte populations and their malignant analogs.

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John Lin, Chia-Ching; Yu, Kwanha; Hatcher, Asante; Huang, Teng-Wei; Lee, Hyun Kyoung; Carlson, Jeffrey; Weston, Matthew C; Chen, Fengju; Zhang, Yiqun; Zhu, Wenyi; Mohila, Carrie A; Ahmed, Nabil; Patel, Akash J; Arenkiel, Benjamin R; Noebels, Jeffrey L; Creighton, Chad J; Deneen, Benjamin

2017-03-01

Astrocytes are the most abundant cell type in the brain, where they perform a wide array of functions, yet the nature of their cellular heterogeneity and how it oversees these diverse roles remains shrouded in mystery. Using an intersectional fluorescence-activated cell sorting-based strategy, we identified five distinct astrocyte subpopulations present across three brain regions that show extensive molecular diversity. Application of this molecular insight toward function revealed that these populations differentially support synaptogenesis between neurons. We identified correlative populations in mouse and human glioma and found that the emergence of specific subpopulations during tumor progression corresponded with the onset of seizures and tumor invasion. In sum, we have identified subpopulations of astrocytes in the adult brain and their correlates in glioma that are endowed with diverse cellular, molecular and functional properties. These populations selectively contribute to synaptogenesis and tumor pathophysiology, providing a blueprint for understanding diverse astrocyte contributions to neurological disease.

Cell-penetrating anti-GFAP VHH and corresponding fluorescent fusion protein VHH-GFP spontaneously cross the blood-brain barrier and specifically recognize astrocytes: application to brain imaging.

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Li, Tengfei; Bourgeois, Jean-Pierre; Celli, Susanna; Glacial, Fabienne; Le Sourd, Anne-Marie; Mecheri, Salah; Weksler, Babette; Romero, Ignacio; Couraud, Pierre-Olivier; Rougeon, François; Lafaye, Pierre

2012-10-01

Antibodies normally do not cross the blood-brain barrier (BBB) and cannot bind an intracellular cerebral antigen. We demonstrate here for the first time that a new class of antibodies can cross the BBB without treatment. Camelids produce native homodimeric heavy-chain antibodies, the paratope being composed of a single-variable domain called VHH. Here, we used recombinant VHH directed against human glial fibrillary acidic protein (GFAP), a specific marker of astrocytes. Only basic VHHs (e.g., pI=9.4) were able to cross the BBB in vitro (7.8 vs. 0% for VHH with pI=7.7). By intracarotid and intravenous injections into live mice, we showed that these basic VHHs are able to cross the BBB in vivo, diffuse into the brain tissue, penetrate into astrocytes, and specifically label GFAP. To analyze their ability to be used as a specific transporter, we then expressed a recombinant fusion protein VHH-green fluorescent protein (GFP). These "fluobodies" specifically labeled GFAP on murine brain sections, and a basic variant (pI=9.3) of the fusion protein VHH-GFP was able to cross the BBB and to label astrocytes in vivo. The potential of VHHs as diagnostic or therapeutic agents in the central nervous system now deserves attention.

An Efficient Platform for Astrocyte Differentiation from Human Induced Pluripotent Stem Cells

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Julia TCW

2017-08-01

Full Text Available Growing evidence implicates the importance of glia, particularly astrocytes, in neurological and psychiatric diseases. Here, we describe a rapid and robust method for the differentiation of highly pure populations of replicative astrocytes from human induced pluripotent stem cells (hiPSCs, via a neural progenitor cell (NPC intermediate. We evaluated this protocol across 42 NPC lines (derived from 30 individuals. Transcriptomic analysis demonstrated that hiPSC-astrocytes from four individuals are highly similar to primary human fetal astrocytes and characteristic of a non-reactive state. hiPSC-astrocytes respond to inflammatory stimulants, display phagocytic capacity, and enhance microglial phagocytosis. hiPSC-astrocytes also possess spontaneous calcium transient activity. Our protocol is a reproducible, straightforward (single medium, and rapid (<30 days method to generate populations of hiPSC-astrocytes that can be used for neuron-astrocyte and microglia-astrocyte co-cultures for the study of neuropsychiatric disorders.

From the Cover: AstrocytesAre Protective Against Chlorpyrifos Developmental Neurotoxicity in Human Pluripotent Stem Cell-Derived Astrocyte-Neuron Cocultures.

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Wu, Xian; Yang, Xiangkun; Majumder, Anirban; Swetenburg, Raymond; Goodfellow, Forrest T; Bartlett, Michael G; Stice, Steven L

2017-06-01

Human neural progenitor cells are capable of independent, directed differentiation into astrocytes, oligodendrocytes and neurons and thus offer a potential cell source for developmental neurotoxicity (DNT) systems. Human neural progenitor-derived astrocyte-neuron cocultured at defined ratios mimic cellular heterogeneity and interaction in the central nervous system. Cytochrome P450 enzymes are expressed at a relatively high level in astrocytes and may play a critical role in the biotransformation of endogenous or exogenous compounds, including chlorpyrifos, an organophosphate insecticide that affects the central nervous system. P450 enzymes metabolize chlorpyrifos to chlorpyrifos-oxon, which is then metabolized primarily to 3, 5, 6-trichloropyridinol in addition to diethylphosphate and diethylthiophosphate. These end metabolites are less neurotoxic than chlorpyrifos and chlorpyrifos-oxon. Our objective was to identify the interactive role of astrocytes and neurons in chlorpyrifos-induced human DNT. In neuron-only cultures, chlorpyrifos inhibited neurite length, neurite number and branch points per neuron in a dose-dependent manner during a 48 h exposure, starting at 10 μM. However, in astrocyte-neuron cocultures, astrocytes protected neurons from the effects of chlorpyrifos at higher concentrations, up to and including 30 μM chlorpyrifos and endogenous astrocyte P450 enzymes effectively metabolized chlorpyrifos. The P450 inhibitor SKF525A partly negated the protective effect of astrocytes, allowing reduction in branch points with chlorpyrifos (10 μM). Thus, the scalable and defined astrocyte-neuron cocultures model that we established here has potentially identified a role for P450 enzymes in astrocytic neuroprotection against chlorpyrifos and provides a novel model for addressing DNT in a more accurate multicellular environment. © The Author 2017. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For

Acute treatment with 17beta-estradiol attenuates astrocyte-astrocyte and astrocyte-neuron communication.

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Rao, Shilpa P; Sikdar, Sujit Kumar

2007-12-01

Astrocytes are now recognized as dynamic signaling elements in the brain. Bidirectional communication between neurons and astrocytes involves integration of neuronal inputs by astrocytes and release of gliotransmitters that modulate neuronal excitability and synaptic transmission. The ovarian steroid hormone, 17beta-estradiol, in addition to its rapid actions on neuronal electrical activity can rapidly alter astrocyte intracellular calcium concentration ([Ca2+]i) through a membrane-associated estrogen receptor. Using calcium imaging and electrophysiological techniques, we investigated the functional consequences of acute treatment with estradiol on astrocyte-astrocyte and astrocyte-neuron communication in mixed hippocampal cultures. Mechanical stimulation of an astrocyte evoked a [Ca2+]i rise in the stimulated astrocyte, which propagated to the surrounding astrocytes as a [Ca2+]i wave. Following acute treatment with estradiol, the amplitude of the [Ca2+]i elevation in astrocytes around the stimulated astrocyte was attenuated. Further, estradiol inhibited the [Ca2+]i rise in individual astrocytes in response to the metabotropic glutamate receptor agonist, trans-(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid. Mechanical stimulation of astrocytes induced [Ca2+]i elevations and electrophysiological responses in adjacent neurons. Estradiol rapidly attenuated the astrocyte-evoked glutamate-mediated [Ca2+]i rise and slow inward current in neurons. Also, the incidence of astrocyte-induced increase in spontaneous postsynaptic current frequency was reduced in the presence of estradiol. The effects of estradiol were stereo-specific and reversible following washout. These findings may indicate that the regulation of neuronal excitability and synaptic transmission by astrocytes is sensitive to rapid estradiol-mediated hormonal control. (c) 2007 Wiley-Liss, Inc.

Implications of astrocytes in mediating the protective effects of Selective Estrogen Receptor Modulators upon brain damage

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George E. Barreto

2015-04-01

Full Text Available Selective Estrogen Receptor Modulators (SERMs are steroidal or non-steroidal compounds that are already used in clinical practice for the treatment of breast cancer, osteoporosis and menopausal symptoms. While SERMs actions in the breast, bone, and uterus have been well characterized, their actions in the brain are less well understood. Previous works have demonstrated the beneficial effects of SERMs in different chronic neurodegenerative diseases like Alzheimer, Parkinson’s disease and Multiple sclerosis, as well as acute degeneration as stroke and traumatic brain injury. Moreover, these compounds exhibit similar protective actions as those of estradiol in the Central Nervous System, overt any secondary effect. For these reasons, in the past few years, there has been a growing interest in the neuroprotective effects exerted directly or indirectly by SERMs in the SNC. In this context, astrocytes play an important role in the maintenance of brain metabolism, and antioxidant support to neurons, thus indicating that better protection of astrocytes are an important asset targeting neuronal protection. Moreover, various clinical and experimental studies have reported that astrocytes are essential for the neuroprotective effects of SERMs during neuronal injuries, as these cells express different estrogen receptors in cell membrane, demonstrating that part of SERMs effects upon injury may be mediated by astrocytes. The present work highlights the current evidence on the protective mechanisms of SERMs, such as tamoxifen and raloxifene, in the SNC, and their modulation of astrocytic properties as promising therapeutic targets during brain damage.

Hyperglycaemia and diabetes impair gap junctional communication among astrocytes.

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Gandhi, Gautam K; Ball, Kelly K; Cruz, Nancy F; Dienel, Gerald A

2010-03-15

Sensory and cognitive impairments have been documented in diabetic humans and animals, but the pathophysiology of diabetes in the central nervous system is poorly understood. Because a high glucose level disrupts gap junctional communication in various cell types and astrocytes are extensively coupled by gap junctions to form large syncytia, the influence of experimental diabetes on gap junction channel-mediated dye transfer was assessed in astrocytes in tissue culture and in brain slices from diabetic rats. Astrocytes grown in 15-25 mmol/l glucose had a slow-onset, poorly reversible decrement in gap junctional communication compared with those grown in 5.5 mmol/l glucose. Astrocytes in brain slices from adult STZ (streptozotocin)-treated rats at 20-24 weeks after the onset of diabetes also exhibited reduced dye transfer. In cultured astrocytes grown in high glucose, increased oxidative stress preceded the decrement in dye transfer by several days, and gap junctional impairment was prevented, but not rescued, after its manifestation by compounds that can block or reduce oxidative stress. In sharp contrast with these findings, chaperone molecules known to facilitate protein folding could prevent and rescue gap junctional impairment, even in the presence of elevated glucose level and oxidative stress. Immunostaining of Cx (connexin) 43 and 30, but not Cx26, was altered by growth in high glucose. Disruption of astrocytic trafficking of metabolites and signalling molecules may alter interactions among astrocytes, neurons and endothelial cells and contribute to changes in brain function in diabetes. Involvement of the microvasculature may contribute to diabetic complications in the brain, the cardiovascular system and other organs.

An Efficient Platform for Astrocyte Differentiation from Human Induced Pluripotent Stem Cells.

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Tcw, Julia; Wang, Minghui; Pimenova, Anna A; Bowles, Kathryn R; Hartley, Brigham J; Lacin, Emre; Machlovi, Saima I; Abdelaal, Rawan; Karch, Celeste M; Phatnani, Hemali; Slesinger, Paul A; Zhang, Bin; Goate, Alison M; Brennand, Kristen J

2017-08-08

Growing evidence implicates the importance of glia, particularly astrocytes, in neurological and psychiatric diseases. Here, we describe a rapid and robust method for the differentiation of highly pure populations of replicative astrocytes from human induced pluripotent stem cells (hiPSCs), via a neural progenitor cell (NPC) intermediate. We evaluated this protocol across 42 NPC lines (derived from 30 individuals). Transcriptomic analysis demonstrated that hiPSC-astrocytes from four individuals are highly similar to primary human fetal astrocytes and characteristic of a non-reactive state. hiPSC-astrocytes respond to inflammatory stimulants, display phagocytic capacity, and enhance microglial phagocytosis. hiPSC-astrocytes also possess spontaneous calcium transient activity. Our protocol is a reproducible, straightforward (single medium), and rapid (method to generate populations of hiPSC-astrocytes that can be used for neuron-astrocyte and microglia-astrocyte co-cultures for the study of neuropsychiatric disorders. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

Transferrin receptor-1 and ferritin heavy and light chains in astrocytic brain tumors

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Rosager, Ann Mari; Sørensen, Mia D; Dahlrot, Rikke H

2017-01-01

Astrocytic brain tumors are the most frequent primary brain tumors. Treatment with radio- and chemotherapy has increased survival making prognostic biomarkers increasingly important. The aim of the present study was to investigate the expression and prognostic value of transferrin receptor-1 (TfR...

Endocannabinoids mediate neuron-astrocyte communication.

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Navarrete, Marta; Araque, Alfonso

2008-03-27

Cannabinoid receptors play key roles in brain function, and cannabinoid effects in brain physiology and drug-related behavior are thought to be mediated by receptors present in neurons. Neuron-astrocyte communication relies on the expression by astrocytes of neurotransmitter receptors. Yet, the expression of cannabinoid receptors by astrocytes in situ and their involvement in the neuron-astrocyte communication remain largely unknown. We show that hippocampal astrocytes express CB1 receptors that upon activation lead to phospholipase C-dependent Ca2+ mobilization from internal stores. These receptors are activated by endocannabinoids released by neurons, increasing astrocyte Ca2+ levels, which stimulate glutamate release that activates NMDA receptors in pyramidal neurons. These results demonstrate the existence of endocannabinoid-mediated neuron-astrocyte communication, revealing that astrocytes are targets of cannabinoids and might therefore participate in the physiology of cannabinoid-related addiction. They also reveal the existence of an endocannabinoid-glutamate signaling pathway where astrocytes serve as a bridge for nonsynaptic interneuronal communication.

The long-term risk of malignant astrocytic tumors after structural brain injury--a nationwide cohort study

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Munch, Tina Noergaard; Gørtz, Sanne; Wohlfahrt, Jan

2015-01-01

% CI: 0.49-0.90) compared with no injury. The specific long-term risks by type of injury were: traumatic brain injury RR = 0.32 (95% CI: 0.10-0.75); cerebral ischemic infarction RR = 0.69 (95% CI: 0.47-0.96); and intracerebral hemorrhage RR = 1.39 (95% CI: 0.64-2.60). CONCLUSION: We found no evidence......BACKGROUND: Neoplastic transformation of damaged astrocytes has been proposed as a possible pathological mechanism behind malignant astrocytic tumors. This study investigated the association between structural brain injuries causing reactive astrogliosis and long-term risk for malignant astrocytic...... tumors. METHODS: The cohort consisted of all individuals living in Denmark between 1978 and 2011. The personal identification number assigned to all individuals allowed retrieval of diagnoses of traumatic brain injury, cerebral ischemic infarction, and intracerebral hemorrhage from the National Patient...

Phenotypic and gene expression modification with normal brain aging in GFAP-positive astrocytes and neural stem cells.

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Bernal, Giovanna M; Peterson, Daniel A

2011-06-01

Astrocytes secrete growth factors that are both neuroprotective and supportive for the local environment. Identified by glial fibrillary acidic protein (GFAP) expression, astrocytes exhibit heterogeneity in morphology and in the expression of phenotypic markers and growth factors throughout different adult brain regions. In adult neurogenic niches, astrocytes secrete vascular endothelial growth factor (VEGF) and fibroblast growth factor-2 (FGF-2) within the neurogenic niche and are also a source of special GFAP-positive multipotent neural stem cells (NSCs). Normal aging is accompanied by a decline in CNS function and reduced neurogenesis. We asked whether a decreased availability of astrocyte-derived factors may contribute to the age-related decline in neurogenesis. Determining alterations of astrocytic activity in the aging brain is crucial for understanding CNS homeostasis in aging and for assessing appropriate therapeutic targets for an aging population. We found region-specific alterations in the gene expression of GFAP, VEGF, and FGF-2 and their receptors in the aged brain corresponding to changes in astrocytic reactivity, supporting astrocytic heterogeneity and demonstrating a differential aging effect. We found that GFAP-positive NSCs uniquely coexpress both VEGF and its key mitotic receptor Flk-1 in both young and aged hippocampus, indicating a possible autocrine/paracrine signaling mechanism. VEGF expression is lost once NSCs commit to a neuronal fate, but Flk-1-mediated sensitivity to VEGF signaling is maintained. We propose that age-related astrocytic changes result in reduced VEGF and FGF-2 signaling, which in turn limits NSC and progenitor cell maintenance and contributes to decreased neurogenesis. © 2011 The Authors. Aging Cell © 2011 Blackwell Publishing Ltd/Anatomical Society of Great Britain and Ireland.

The Anti-Inflammatory Effects of Lipoxygenase and Cyclo-Oxygenase Inhibitors in Inflammation-Induced Human Fetal Glia Cells and the Aβ Degradation Capacity of Human Fetal Astrocytes in an Ex vivo Assay

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Rea Pihlaja

2017-05-01

Full Text Available Chronic inflammation is a common phenomenon present in the background of multiple neurodegenerative diseases, including Alzheimer's disease (AD. The arachidonic acid pathway overproduces proinflammatory eicosanoids during these states and glial cells in the brain gradually lose their vital functions of protecting and supporting neurons. In this study, the role of different key enzymes of the eicosanoid pathway mediating inflammatory responses was examined in vitro and ex vivo using human fetal glial cells. Astrocytes and microglia were exposed to proinflammatory agents i.e., cytokines interleukin 1-β (IL-1β and tumor necrosis factor (TNF-α. ELISA assays were used to examine the effects of inhibitors of key enzymes in the eicosanoid pathway. Inhibitors for 5-lipoxygenase (5-LOX and cyclo-oxygenase 2 (COX-2 in both cell types and 5-, 12-, and 15-LOX-inhibitor in astrocytes reduced significantly IL-6 secretion, compared to exposed glial cells without inhibitors. The cytokine antibody array showed that especially treatments with 5, -12, and -15 LOX inhibitor in astrocytes, 5-LOX inhibitor in microglia and COX-2 inhibitor in both glial cell types significantly reduced the expression of multiple proinflammatory cytokines. Furthermore, human fetal astrocytes and microglia were cultured on top of AD-affected and control human brain sections for 30 h. According to the immunochemical evaluation of the level of total Aβ, astrocytes were very efficient at degrading Aβ from AD-affected brain sections ex vivo; simultaneously added enzyme inhibitors did not increase their Aβ degradation capabilities. Microglia were not able to reduce the level of total Aβ during the 30 h incubation time.

Three-dimensional culture conditions differentially affect astrocyte modulation of brain endothelial barrier function in response to transforming growth factor β1.

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Hawkins, Brian T; Grego, Sonia; Sellgren, Katelyn L

2015-05-22

Blood-brain barrier (BBB) function is regulated by dynamic interactions among cell types within the neurovascular unit, including astrocytes and endothelial cells. Co-culture models of the BBB typically involve astrocytes seeded on two-dimensional (2D) surfaces, which recent studies indicate cause astrocytes to express a phenotype similar to that of reactive astrocytes in situ. We hypothesized that the culture conditions of astrocytes would differentially affect their ability to modulate BBB function in vitro. Brain endothelial cells were grown alone or in co-culture with astrocytes. Astrocytes were grown either as conventional (2D) monolayers, or in a collagen-based gel which allows them to grow in a three-dimensional (3D) construct. Astrocytes were viable in 3D conditions, and displayed a marked reduction in their expression of glial fibrillary acidic protein (GFAP), suggesting reduced activation. Stimulation of astrocytes with transforming growth factor (TGF)β1 decreased transendothelial electrical resistance (TEER) and reduced expression of claudin-5 in co-cultures, whereas treatment of endothelial cells in the absence of astrocytes was without effect. The effect of TGFβ1 on TEER was significantly more pronounced in endothelial cells cultured with 3D astrocytes compared to 2D astrocytes. These results demonstrate that astrocyte culture conditions differentially affect their ability to modulate brain endothelial barrier function, and suggest a direct relationship between reactive gliosis and BBB permeability. Moreover, these studies demonstrate the potential importance of physiologically relevant culture conditions to in vitro modeling of disease processes that affect the neurovascular unit. Copyright © 2015 Elsevier B.V. All rights reserved.

Characterization of the L-glutamate clearance pathways across the blood-brain barrier and the effect of astrocytes in an in vitro blood-brain barrier model

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Helms, Hans CC; Aldana, Blanca I; Groth, Simon

2017-01-01

The aim was to characterize the clearance pathways for L-glutamate from the brain interstitial fluid across the blood-brain barrier using a primary in vitro bovine endothelial/rat astrocyte co-culture. Transporter profiling was performed using uptake studies of radiolabeled L-glutamate with co...... brain to blood via the concerted action of abluminal and luminal transport proteins, but the total brain clearance is highly dependent on metabolism in astrocytes and endothelial cells followed by transport of metabolites....

Astrocyte-targeted expression of IL-6 protects the CNS against a focal brain injury

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Penkowa, Milena; Giralt, Mercedes; Lago, Natalia

2003-01-01

significantly increased up to but not including 20 dpl in the GFAP-IL6 mice. Oxidative stress as well as apoptotic cell death was significantly decreased throughout the time period studied in the GFAP-IL6 mice compared to controls. This could be linked to the altered inflammatory response as well......The effect of CNS-targeted IL-6 gene expression has been thoroughly investigated in the otherwise nonperturbed brain but not following brain injury. Here we examined the impact of astrocyte-targeted IL-6 production in a traumatic brain injury (cryolesion) model using GFAP-IL6 transgenic mice...... as to the transgenic IL-6-induced increase of the antioxidant, neuroprotective proteins metallothionein-I + II. These results indicate that although in the brain the chronic astrocyte-targeted expression of IL-6 spontaneously induces an inflammatory response causing significant damage, during an acute...

T cells' immunological synapses induce polarization of brain astrocytes in vivo and in vitro: a novel astrocyte response mechanism to cellular injury.

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Barcia, Carlos; Sanderson, Nicholas S R; Barrett, Robert J; Wawrowsky, Kolja; Kroeger, Kurt M; Puntel, Mariana; Liu, Chunyan; Castro, Maria G; Lowenstein, Pedro R

2008-08-20

Astrocytes usually respond to trauma, stroke, or neurodegeneration by undergoing cellular hypertrophy, yet, their response to a specific immune attack by T cells is poorly understood. Effector T cells establish specific contacts with target cells, known as immunological synapses, during clearance of virally infected cells from the brain. Immunological synapses mediate intercellular communication between T cells and target cells, both in vitro and in vivo. How target virally infected astrocytes respond to the formation of immunological synapses established by effector T cells is unknown. Herein we demonstrate that, as a consequence of T cell attack, infected astrocytes undergo dramatic morphological changes. From normally multipolar cells, they become unipolar, extending a major protrusion towards the immunological synapse formed by the effector T cells, and withdrawing most of their finer processes. Thus, target astrocytes become polarized towards the contacting T cells. The MTOC, the organizer of cell polarity, is localized to the base of the protrusion, and Golgi stacks are distributed throughout the protrusion, reaching distally towards the immunological synapse. Thus, rather than causing astrocyte hypertrophy, antiviral T cells cause a major structural reorganization of target virally infected astrocytes. Astrocyte polarization, as opposed to hypertrophy, in response to T cell attack may be due to T cells providing a very focused attack, and thus, astrocytes responding in a polarized manner. A similar polarization of Golgi stacks towards contacting T cells was also detected using an in vitro allogeneic model. Thus, different T cells are able to induce polarization of target astrocytes. Polarization of target astrocytes in response to immunological synapses may play an important role in regulating the outcome of the response of astrocytes to attacking effector T cells, whether during antiviral (e.g. infected during HIV, HTLV-1, HSV-1 or LCMV infection), anti

T cells' immunological synapses induce polarization of brain astrocytes in vivo and in vitro: a novel astrocyte response mechanism to cellular injury.

Directory of Open Access Journals (Sweden)

Carlos Barcia

2008-08-01

Full Text Available Astrocytes usually respond to trauma, stroke, or neurodegeneration by undergoing cellular hypertrophy, yet, their response to a specific immune attack by T cells is poorly understood. Effector T cells establish specific contacts with target cells, known as immunological synapses, during clearance of virally infected cells from the brain. Immunological synapses mediate intercellular communication between T cells and target cells, both in vitro and in vivo. How target virally infected astrocytes respond to the formation of immunological synapses established by effector T cells is unknown.Herein we demonstrate that, as a consequence of T cell attack, infected astrocytes undergo dramatic morphological changes. From normally multipolar cells, they become unipolar, extending a major protrusion towards the immunological synapse formed by the effector T cells, and withdrawing most of their finer processes. Thus, target astrocytes become polarized towards the contacting T cells. The MTOC, the organizer of cell polarity, is localized to the base of the protrusion, and Golgi stacks are distributed throughout the protrusion, reaching distally towards the immunological synapse. Thus, rather than causing astrocyte hypertrophy, antiviral T cells cause a major structural reorganization of target virally infected astrocytes.Astrocyte polarization, as opposed to hypertrophy, in response to T cell attack may be due to T cells providing a very focused attack, and thus, astrocytes responding in a polarized manner. A similar polarization of Golgi stacks towards contacting T cells was also detected using an in vitro allogeneic model. Thus, different T cells are able to induce polarization of target astrocytes. Polarization of target astrocytes in response to immunological synapses may play an important role in regulating the outcome of the response of astrocytes to attacking effector T cells, whether during antiviral (e.g. infected during HIV, HTLV-1, HSV-1 or LCMV

Glycogen distribution in the microwave-fixed mouse brain reveals heterogeneous astrocytic patterns.

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Oe, Yuki; Baba, Otto; Ashida, Hitoshi; Nakamura, Kouichi C; Hirase, Hajime

2016-09-01

In the brain, glycogen metabolism has been implied in synaptic plasticity and learning, yet the distribution of this molecule has not been fully described. We investigated cerebral glycogen of the mouse by immunohistochemistry (IHC) using two monoclonal antibodies that have different affinities depending on the glycogen size. The use of focused microwave irradiation yielded well-defined glycogen immunoreactive signals compared with the conventional periodic acid-Schiff method. The IHC signals displayed a punctate distribution localized predominantly in astrocytic processes. Glycogen immunoreactivity (IR) was high in the hippocampus, striatum, cortex, and cerebellar molecular layer, whereas it was low in the white matter and most of the subcortical structures. Additionally, glycogen distribution in the hippocampal CA3-CA1 and striatum had a 'patchy' appearance with glycogen-rich and glycogen-poor astrocytes appearing in alternation. The glycogen patches were more evident with large-molecule glycogen in young adult mice but they were hardly observable in aged mice (1-2 years old). Our results reveal brain region-dependent glycogen accumulation and possibly metabolic heterogeneity of astrocytes. GLIA 2016;64:1532-1545. © 2016 The Authors. Glia Published by Wiley Periodicals, Inc.

Glycogen distribution in the microwave‐fixed mouse brain reveals heterogeneous astrocytic patterns

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Baba, Otto; Ashida, Hitoshi; Nakamura, Kouichi C.

2016-01-01

In the brain, glycogen metabolism has been implied in synaptic plasticity and learning, yet the distribution of this molecule has not been fully described. We investigated cerebral glycogen of the mouse by immunohistochemistry (IHC) using two monoclonal antibodies that have different affinities depending on the glycogen size. The use of focused microwave irradiation yielded well‐defined glycogen immunoreactive signals compared with the conventional periodic acid‐Schiff method. The IHC signals displayed a punctate distribution localized predominantly in astrocytic processes. Glycogen immunoreactivity (IR) was high in the hippocampus, striatum, cortex, and cerebellar molecular layer, whereas it was low in the white matter and most of the subcortical structures. Additionally, glycogen distribution in the hippocampal CA3‐CA1 and striatum had a ‘patchy’ appearance with glycogen‐rich and glycogen‐poor astrocytes appearing in alternation. The glycogen patches were more evident with large‐molecule glycogen in young adult mice but they were hardly observable in aged mice (1–2 years old). Our results reveal brain region‐dependent glycogen accumulation and possibly metabolic heterogeneity of astrocytes. GLIA 2016;64:1532–1545 PMID:27353480

The metabolic trinity, glucose-glycogen-lactate, links astrocytes and neurons in brain energetics, signaling, memory, and gene expression.

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Dienel, Gerald A

2017-01-10

Glucose, glycogen, and lactate are traditionally identified with brain energetics, ATP turnover, and pathophysiology. However, recent studies extend their roles to include involvement in astrocytic signaling, memory consolidation, and gene expression. Emerging roles for these brain fuels and a readily-diffusible by-product are linked to differential fluxes in glycolytic and oxidative pathways, astrocytic glycogen dynamics, redox shifts, neuron-astrocyte interactions, and regulation of astrocytic activities by noradrenaline released from the locus coeruleus. Disproportionate utilization of carbohydrate compared with oxygen during brain activation is influenced by catecholamines, but its physiological basis is not understood and its magnitude may be affected by technical aspects of metabolite assays. Memory consolidation and gene expression are impaired by glycogenolysis blockade, and prevention of these deficits by injection of abnormally-high concentrations of lactate was interpreted as a requirement for astrocyte-to-neuron lactate shuttling in memory and gene expression. However, lactate transport was not measured and evidence for presumed shuttling is not compelling. In fact, high levels of lactate used to preserve memory consolidation and induce gene expression are sufficient to shut down neuronal firing via the HCAR1 receptor. In contrast, low lactate levels activate a receptor in locus coeruleus that stimulates noradrenaline release that may activate astrocytes throughout brain. Physiological relevance of exogenous concentrations of lactate used to mimic and evaluate metabolic, molecular, and behavioral effects of lactate requires close correspondence with the normal lactate levels, the biochemical and cellular sources and sinks, and specificity of lactate delivery to target cells. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

The beta1 subunit of the Na,K-ATPase pump interacts with megalencephalic leucoencephalopathy with subcortical cysts protein 1 (MLC1) in brain astrocytes: new insights into MLC pathogenesis.

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Brignone, Maria S; Lanciotti, Angela; Macioce, Pompeo; Macchia, Gianfranco; Gaetani, Matteo; Aloisi, Francesca; Petrucci, Tamara C; Ambrosini, Elena

2011-01-01

Megalencephalic leucoencephalopathy with subcortical cysts (MLC) is a rare congenital leucodystrophy caused by mutations in MLC1, a membrane protein of unknown function. MLC1 expression in astrocyte end-feet contacting blood vessels and meninges, along with brain swelling, fluid cysts and myelin vacuolation observed in MLC patients, suggests a possible role for MLC1 in the regulation of fluid and ion homeostasis and cellular volume changes. To identify MLC1 direct interactors and dissect the molecular pathways in which MLC1 is involved, we used NH2-MLC1 domain as a bait to screen a human brain library in a yeast two-hybrid assay. We identified the β1 subunit of the Na,K-ATPase pump as one of the interacting clones and confirmed it by pull-downs, co-fractionation assays and immunofluorescence stainings in human and rat astrocytes in vitro and in brain tissue. By performing ouabain-affinity chromatography on astrocyte and brain extracts, we isolated MLC1 and the whole Na,K-ATPase enzyme in a multiprotein complex that included Kir4.1, syntrophin and dystrobrevin. Because Na,K-ATPase is involved in intracellular osmotic control and volume regulation, we investigated the effect of hypo-osmotic stress on MLC1/Na,K-ATPase relationship in astrocytes. We found that hypo-osmotic conditions increased MLC1 membrane expression and favoured MLC1/Na,K-ATPase-β1 association. Moreover, hypo-osmosis induced astrocyte swelling and the reversible formation of endosome-derived vacuoles, where the two proteins co-localized. These data suggest that through its interaction with Na,K-ATPase, MLC1 is involved in the control of intracellular osmotic conditions and volume regulation in astrocytes, opening new perspectives for understanding the pathological mechanisms of MLC disease.

Increased toll-like receptor 4 in cerebral endothelial cells contributes to the astrocyte swelling and brain edema in acute hepatic encephalopathy.

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Jayakumar, Arumugam R; Tong, Xiao Y; Curtis, Kevin M; Ruiz-Cordero, Roberto; Abreu, Maria T; Norenberg, Michael D

2014-03-01

Astrocyte swelling and the subsequent increase in intracranial pressure and brain herniation are major clinical consequences in patients with acute hepatic encephalopathy. We recently reported that conditioned media from brain endothelial cells (ECs) exposed to ammonia, a mixture of cytokines (CKs) or lipopolysaccharide (LPS), when added to astrocytes caused cell swelling. In this study, we investigated the possibility that ammonia and inflammatory agents activate the toll-like receptor 4 (TLR4) in ECs, resulting in the release of factors that ultimately cause astrocyte swelling. We found a significant increase in TLR4 protein expression when ECs were exposed to ammonia, CKs or LPS alone, while exposure of ECs to a combination of these agents potentiate such effects. In addition, astrocytes exposed to conditioned media from TLR4-silenced ECs that were treated with ammonia, CKs or LPS, resulted in a significant reduction in astrocyte swelling. TLR4 protein up-regulation was also detected in rat brain ECs after treatment with the liver toxin thioacetamide, and that thioacetamide-treated TLR4 knock-out mice exhibited a reduction in brain edema. These studies strongly suggest that ECs significantly contribute to the astrocyte swelling/brain edema in acute hepatic encephalopathy, likely as a consequence of increased TLR4 protein expression by blood-borne noxious agents. © 2013 International Society for Neurochemistry.

Glycogen metabolism in brain and neurons - astrocytes metabolic cooperation can be altered by pre- and neonatal lead (Pb) exposure.

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Baranowska-Bosiacka, Irena; Falkowska, Anna; Gutowska, Izabela; Gąssowska, Magdalena; Kolasa-Wołosiuk, Agnieszka; Tarnowski, Maciej; Chibowska, Karina; Goschorska, Marta; Lubkowska, Anna; Chlubek, Dariusz

2017-09-01

Lead (Pb) is an environmental neurotoxin which particularly affects the developing brain but the molecular mechanism of its neurotoxicity still needs clarification. The aim of this paper was to examine whether pre- and neonatal exposure to Pb (concentration of Pb in rat offspring blood below the "threshold level") may affect the brain's energy metabolism in neurons and astrocytes via the amount of available glycogen. We investigated the glycogen concentration in the brain, as well as the expression of the key enzymes involved in glycogen metabolism in brain: glycogen synthase 1 (Gys1), glycogen phosphorylase (PYGM, an isoform active in astrocytes; and PYGB, an isoform active in neurons) and phosphorylase kinase β (PHKB). Moreover, the expression of connexin 43 (Cx43) was evaluated to analyze whether Pb poisoning during the early phase of life may affect the neuron-astrocytes' metabolic cooperation. This work shows for the first time that exposure to Pb in early life can impair brain energy metabolism by reducing the amount of glycogen and decreasing the rate of its metabolism. This reduction in brain glycogen level was accompanied by a decrease in Gys1 expression. We noted a reduction in the immunoreactivity and the gene expression of both PYGB and PYGM isoform, as well as an increase in the expression of PHKB in Pb-treated rats. Moreover, exposure to Pb induced decrease in connexin 43 immunoexpression in all the brain structures analyzed, both in astrocytes as well as in neurons. Our data suggests that exposure to Pb in the pre- and neonatal periods results in a decrease in the level of brain glycogen and a reduction in the rate of its metabolism, thereby reducing glucose availability, which as a further consequence may lead to the impairment of brain energy metabolism and the metabolic cooperation between neurons and astrocytes. Copyright © 2017 Elsevier B.V. All rights reserved.

The computational power of astrocyte mediated synaptic plasticity

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Rogier eMin

2012-11-01

Full Text Available Research in the last two decades has made clear that astrocytes play a crucial role in the brain beyond their functions in energy metabolism and homeostasis. Many studies have shown that astrocytes can dynamically modulate neuronal excitability and synaptic plasticity, and might participate in higher brain functions like learning and memory. With the plethora of astrocyte-mediated signaling processes described in the literature today, the current challenge is to identify which of these processes happen under what physiological condition, and how this shapes information processing and, ultimately, behavior. To answer these questions will require a combination of advanced physiological, genetical and behavioral experiments. Additionally, mathematical modeling will prove crucial for testing predictions on the possible functions of astrocytes in neuronal networks, and to generate novel ideas as to how astrocytes can contribute to the complexity of the brain. Here, we aim to provide an outline of how astrocytes can interact with neurons. We do this by reviewing recent experimental literature on astrocyte-neuron interactions, discussing the dynamic effects of astrocytes on neuronal excitability and short- and long-term synaptic plasticity. Finally, we will outline the potential computational functions that astrocyte-neuron interactions can serve in the brain. We will discuss how astrocytes could govern metaplasticity in the brain, how they might organize the clustering of synaptic inputs, and how they could function as memory elements for neuronal activity. We conclude that astrocytes can enhance the computational power of neuronal networks in previously unexpected ways.

Medium-chain fatty acids inhibit mitochondrial metabolism in astrocytes promoting astrocyte-neuron lactate and ketone body shuttle systems.

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Thevenet, Jonathan; De Marchi, Umberto; Domingo, Jaime Santo; Christinat, Nicolas; Bultot, Laurent; Lefebvre, Gregory; Sakamoto, Kei; Descombes, Patrick; Masoodi, Mojgan; Wiederkehr, Andreas

2016-05-01

Medium-chain triglycerides have been used as part of a ketogenic diet effective in reducing epileptic episodes. The health benefits of the derived medium-chain fatty acids (MCFAs) are thought to result from the stimulation of liver ketogenesis providing fuel for the brain. We tested whether MCFAs have direct effects on energy metabolism in induced pluripotent stem cell-derived human astrocytes and neurons. Using single-cell imaging, we observed an acute pronounced reduction of the mitochondrial electrical potential and a concomitant drop of the NAD(P)H signal in astrocytes, but not in neurons. Despite the observed effects on mitochondrial function, MCFAs did not lower intracellular ATP levels or activate the energy sensor AMP-activated protein kinase. ATP concentrations in astrocytes were unaltered, even when blocking the respiratory chain, suggesting compensation through accelerated glycolysis. The MCFA decanoic acid (300 μM) promoted glycolysis and augmented lactate formation by 49.6%. The shorter fatty acid octanoic acid (300 μM) did not affect glycolysis but increased the rates of astrocyte ketogenesis 2.17-fold compared with that of control cells. MCFAs may have brain health benefits through the modulation of astrocyte metabolism leading to activation of shuttle systems that provide fuel to neighboring neurons in the form of lactate and ketone bodies.-Thevenet, J., De Marchi, U., Santo Domingo, J., Christinat, N., Bultot, L., Lefebvre, G., Sakamoto, K., Descombes, P., Masoodi, M., Wiederkehr, A. Medium-chain fatty acids inhibit mitochondrial metabolism in astrocytes promoting astrocyte-neuron lactate and ketone body shuttle systems. © FASEB.

Spatial organization of astrocytes in ferret visual cortex

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López‐Hidalgo, Mónica; Hoover, Walter B.

2016-01-01

ABSTRACT Astrocytes form an intricate partnership with neural circuits to influence numerous cellular and synaptic processes. One prominent organizational feature of astrocytes is the “tiling” of the brain with non‐overlapping territories. There are some documented species and brain region–specific astrocyte specializations, but the extent of astrocyte diversity and circuit specificity are still unknown. We quantitatively defined the rules that govern the spatial arrangement of astrocyte somata and territory overlap in ferret visual cortex using a combination of in vivo two‐photon imaging, morphological reconstruction, immunostaining, and model simulations. We found that ferret astrocytes share, on average, half of their territory with other astrocytes. However, a specific class of astrocytes, abundant in thalamo‐recipient cortical layers (“kissing” astrocytes), overlap markedly less. Together, these results demonstrate novel features of astrocyte organization indicating that different classes of astrocytes are arranged in a circuit‐specific manner and that tiling does not apply universally across brain regions and species. J. Comp. Neurol. 524:3561–3576, 2016. © 2016 The Authors The Journal of Comparative Neurology Published by Wiley Periodicals, Inc. PMID:27072916

Cell Biology of Astrocyte-Synapse Interactions.

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Allen, Nicola J; Eroglu, Cagla

2017-11-01

Astrocytes, the most abundant glial cells in the mammalian brain, are critical regulators of brain development and physiology through dynamic and often bidirectional interactions with neuronal synapses. Despite the clear importance of astrocytes for the establishment and maintenance of proper synaptic connectivity, our understanding of their role in brain function is still in its infancy. We propose that this is at least in part due to large gaps in our knowledge of the cell biology of astrocytes and the mechanisms they use to interact with synapses. In this review, we summarize some of the seminal findings that yield important insight into the cellular and molecular basis of astrocyte-neuron communication, focusing on the role of astrocytes in the development and remodeling of synapses. Furthermore, we pose some pressing questions that need to be addressed to advance our mechanistic understanding of the role of astrocytes in regulating synaptic development. Copyright © 2017 Elsevier Inc. All rights reserved.

The Endo-Lysosomal System of Brain Endothelial Cells Is Influenced by Astrocytes In Vitro.

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Toth, Andrea E; Siupka, Piotr; P Augustine, Thomas J; Venø, Susanne T; Thomsen, Louiza B; Moos, Torben; Lohi, Hannes T; Madsen, Peder; Lykke-Hartmann, Karin; Nielsen, Morten S

2018-03-20

Receptor- and adsorptive-mediated transport through brain endothelial cells (BEC) of the blood-brain barrier (BBB) involves a complex array of subcellular vesicular structures, the endo-lysosomal system. It consists of several types of vesicles, such as early, recycling, and late endosomes, retromer-positive structures, and lysosomes. Since this system is important for receptor-mediated transcytosis of drugs across brain capillaries, our aim was to characterise the endo-lysosomal system in BEC with emphasis on their interactions with astrocytes. We used primary porcine BEC in monoculture and in co-culture with primary rat astrocytes. The presence of astrocytes changed the intraendothelial vesicular network and significantly impacted vesicular number, morphology, and distribution. Additionally, gene set enrichment analysis revealed that 60 genes associated with vesicular trafficking showed altered expression in co-cultured BEC. Cytosolic proteins involved in subcellular trafficking were investigated to mark transport routes, such as RAB25 for transcytosis. Strikingly, the adaptor protein called AP1-μ1B, important for basolateral sorting in epithelial cells, was not expressed in BEC. Altogether, our data pin-point unique features of BEC trafficking network, essentially mapping the endo-lysosomal system of in vitro BBB models. Consequently, our findings constitute a valuable basis for planning the optimal route across the BBB when advancing drug delivery to the brain.

HIV and drug abuse mediate astrocyte senescence in a β-catenin-dependent manner leading to neuronal toxicity.

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Yu, Chunjiang; Narasipura, Srinivas D; Richards, Maureen H; Hu, Xiu-Ti; Yamamoto, Bryan; Al-Harthi, Lena

2017-10-01

Emerging evidence suggests that cell senescence plays an important role in aging-associated diseases including neurodegenerative diseases. HIV leads to a spectrum of neurologic diseases collectively termed HIV-associated neurocognitive disorders (HAND). Drug abuse, particularly methamphetamine (meth), is a frequently abused psychostimulant among HIV+ individuals and its abuse exacerbates HAND. The mechanism by which HIV and meth lead to brain cell dysregulation is not entirely clear. In this study, we evaluated the impact of HIV and meth on astrocyte senescence using in vitro and several animal models. Astrocytes constitute up to 50% of brain cells and play a pivotal role in marinating brain homeostasis. We show here that HIV and meth induce significant senescence of primary human fetal astrocytes, as evaluated by induction of senescence markers (β-galactosidase and p16 INK 4A ), senescence-associated morphologic changes, and cell cycle arrest. HIV- and meth-mediated astrocyte senescence was also demonstrated in three small animal models (humanized mouse model of HIV/NSG-huPBMCs, HIV-transgenic rats, and in a meth administration rat model). Senescent astrocytes in turn mediated neuronal toxicity. Further, we show that β-catenin, a pro-survival/proliferation transcriptional co-activator, is downregulated by HIV and meth in human astrocytes and this downregulation promotes astrocyte senescence while induction of β-catenin blocks HIV- and meth-mediated astrocyte senescence. These studies, for the first time, demonstrate that HIV and meth induce astrocyte senescence and implicate the β-catenin pathway as potential therapeutic target to overcome astrocyte senescence. © 2017 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.

Sulfocerebrosides upregulate liposome uptake in human astrocytes without inducing a proinflammatory response.

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Suesca, Elizabeth; Alejo, Jose Luis; Bolaños, Natalia I; Ocampo, Jackson; Leidy, Chad; González, John M

2013-07-01

Astrocytes are involved in the pathogenesis of demyelinating diseases, where they actively regulate the secretion of proinflammatory factors, and trigger the recruitment of immune cells in the central nervous system (CNS). Antigen presentation of myelin-derived proteins has been shown to trigger astrocyte response, suggesting that astrocytes can directly sense demyelination. However, the direct response of astrocytes to lipid-debris generated during demyelination has not been investigated. The lipid composition of the myelin sheath is distinct, presenting significant amounts of cerebrosides, sulfocerebrosides (SCB), and ceramides. Studies have shown that microglia are activated in the presence of myelin-derived lipids, pointing to the possibility of lipid-induced astrocyte activation. In this study, a human astrocyte cell line was exposed to liposomes enriched in each myelin lipid component. Although liposome uptake was observed for all compositions, astrocytes had augmented uptake for liposomes containing sulfocerebroside (SCB). This enhanced uptake did not modify their expression of human leukocyte antigen (HLA) molecules or secretion of chemokines. This was in contrast to changes observed in astrocyte cells stimulated with IFNγ. Contrary to human monocytes, astrocytes did not internalize beads in the size-range of liposomes, indicating that liposome uptake is lipid specific. Epifluorescence microscopy corroborated that liposome uptake takes place through endocytosis. Soluble SCB were found to partially block uptake of liposomes containing this same lipid. Endocytosis was not decreased when cells were treated with cytochalasin D, but it was decreased by cold temperature incubation. The specific uptake of SCB in the absence of a proinflammatory response indicates that astrocytes may participate in the trafficking and regulation of sulfocerebroside metabolism and homeostasis in the CNS. Copyright © 2013 International Society for Advancement of Cytometry.

Generation of primary cultures of bovine brain endothelial cells and setup of cocultures with rat astrocytes

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Helms, Hans C; Brodin, Birger

2014-01-01

-brain barrier. The present protocol describes the setup of an in vitro coculture model based on primary cultures of endothelial cells from bovine brain microvessels and primary cultures of rat astrocytes. The model displays a high electrical tightness and expresses blood-brain barrier marker proteins....

Astrocyte, the star avatar: redefined

Indian Academy of Sciences (India)

This review summarizes the past and present knowledge of glial cell functions that has evolved over the years, and has resulted in a new appreciation of astrocytes and their value in studying the neurobiology of human brain cells and their functions. In this review, we highlight recent advances in the role of glial cells in ...

Astrocytic expression of the Alzheimer's disease beta-secretase (BACE1) is stimulus-dependent

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Hartlage-Rübsamen, Maike; Zeitschel, Ulrike; Apelt, Jenny

2003-01-01

The beta-site APP-cleaving enzyme (BACE1) is a prerequisite for the generation of beta-amyloid peptides, which give rise to cerebrovascular and parenchymal beta-amyloid deposits in the brain of Alzheimer's disease patients. BACE1 is neuronally expressed in the brains of humans and experimental...... paradigms studied. In contrast, BACE1 expression by reactive astrocytes was evident in chronic but not in acute models of gliosis. Additionally, we observed BACE1-immunoreactive astrocytes in proximity to beta-amyloid plaques in the brains of aged Tg2576 mice and Alzheimer's disease patients....

Hippocampal Astrocyte Cultures from Adult and Aged Rats Reproduce Changes in Glial Functionality Observed in the Aging Brain.

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Bellaver, Bruna; Souza, Débora Guerini; Souza, Diogo Onofre; Quincozes-Santos, André

2017-05-01

Astrocytes are dynamic cells that maintain brain homeostasis, regulate neurotransmitter systems, and process synaptic information, energy metabolism, antioxidant defenses, and inflammatory response. Aging is a biological process that is closely associated with hippocampal astrocyte dysfunction. In this sense, we demonstrated that hippocampal astrocytes from adult and aged Wistar rats reproduce the glial functionality alterations observed in aging by evaluating several senescence, glutamatergic, oxidative and inflammatory parameters commonly associated with the aging process. Here, we show that the p21 senescence-associated gene and classical astrocyte markers, such as glial fibrillary acidic protein (GFAP), vimentin, and actin, changed their expressions in adult and aged astrocytes. Age-dependent changes were also observed in glutamate transporters (glutamate aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1)) and glutamine synthetase immunolabeling and activity. Additionally, according to in vivo aging, astrocytes from adult and aged rats showed an increase in oxidative/nitrosative stress with mitochondrial dysfunction, an increase in RNA oxidation, NADPH oxidase (NOX) activity, superoxide levels, and inducible nitric oxide synthase (iNOS) expression levels. Changes in antioxidant defenses were also observed. Hippocampal astrocytes also displayed age-dependent inflammatory response with augmentation of proinflammatory cytokine levels, such as TNF-α, IL-1β, IL-6, IL-18, and messenger RNA (mRNA) levels of cyclo-oxygenase 2 (COX-2). Furthermore, these cells secrete neurotrophic factors, including glia-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), S100 calcium-binding protein B (S100B) protein, and transforming growth factor-β (TGF-β), which changed in an age-dependent manner. Classical signaling pathways associated with aging, such as nuclear factor erythroid-derived 2-like 2 (Nrf2), nuclear factor kappa B (NFκ

Systematic Three-Dimensional Coculture Rapidly Recapitulates Interactions between Human Neurons and Astrocytes

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Robert Krencik

2017-12-01

Full Text Available Summary: Human astrocytes network with neurons in dynamic ways that are still poorly defined. Our ability to model this relationship is hampered by the lack of relevant and convenient tools to recapitulate this complex interaction. To address this barrier, we have devised efficient coculture systems utilizing 3D organoid-like spheres, termed asteroids, containing pre-differentiated human pluripotent stem cell (hPSC-derived astrocytes (hAstros combined with neurons generated from hPSC-derived neural stem cells (hNeurons or directly induced via Neurogenin 2 overexpression (iNeurons. Our systematic methods rapidly produce structurally complex hAstros and synapses in high-density coculture with iNeurons in precise numbers, allowing for improved studies of neural circuit function, disease modeling, and drug screening. We conclude that these bioengineered neural circuit model systems are reliable and scalable tools to accurately study aspects of human astrocyte-neuron functional properties while being easily accessible for cell-type-specific manipulations and observations. : In this article, Krencik and colleagues show that high-density cocultures of pre-differentiated human astrocytes with induced neurons, from pluripotent stem cells, elicit mature characteristics by 3–5 weeks. This provides a faster and more defined alternative method to organoid cultures for investigating human neural circuit function. Keywords: human pluripotent stem cells, neurons, astrocytes, synapses, coculture, three-dimensional spheres, organoids, disease modeling

Recent molecular approaches to understanding astrocyte function in vivo

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David eDavila

2013-12-01

Full Text Available Astrocytes are a predominant glial cell type in the nervous systems, and are becoming recognized as important mediators of normal brain function as well as neurodevelopmental, neurological, and neurodegenerative brain diseases. Although numerous potential mechanisms have been proposed to explain the role of astrocytes in the normal and diseased brain, research into the physiological relevance of these mechanisms in vivo is just beginning. In this review, we will summarize recent developments in innovative and powerful molecular approaches, including knockout mouse models, transgenic mouse models, and astrocyte-targeted gene transfer/expression, which have led to advances in understanding astrocyte biology in vivo that were heretofore inaccessible to experimentation. We will examine the recently improved understanding of the roles of astrocytes - with an emphasis on astrocyte signaling - in the context of both the healthy and diseased brain, discuss areas where the role of astrocytes remains debated, and suggest new research directions.

Human glial chimeric mice reveal astrocytic dependence of JC virus infection

DEFF Research Database (Denmark)

Kondo, Yoichi; Windrem, Martha S; Zou, Lisa

2014-01-01

with humanized white matter by engrafting human glial progenitor cells (GPCs) into neonatal immunodeficient and myelin-deficient mice. Intracerebral delivery of JCV resulted in infection and subsequent demyelination of these chimeric mice. Human GPCs and astrocytes were infected more readily than...... that was chimeric for human astrocytes and GPCs. JCV effectively propagated in these mice, which indicates that astroglial infection is sufficient for JCV spread. Sequencing revealed progressive mutation of the JCV capsid protein VP1 after infection, suggesting that PML may evolve with active infection...

Protective and Antioxidant Effects of a Chalconoid from Pulicaria incisa on Brain Astrocytes

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Anat Elmann

2013-01-01

Full Text Available Oxidative stress is involved in the pathogenesis of neurodegenerative diseases such as Parkinson's and Alzheimer's diseases. Astrocytes, the most abundant glial cells in the brain, protect neurons from reactive oxygen species (ROS and provide them with trophic support, such as glial-derived neurotrophic factor (GDNF. Thus, any damage to astrocytes will affect neuronal survival. In the present study, by activity-guided fractionation, we have purified from the desert plant Pulicaria incisa two protective compounds and determined their structures by spectroscopic methods. The compounds were found to be new chalcones—pulichalconoid B and pulichalconoid C. This is the first study to characterize the antioxidant and protective effects of these compounds in any biological system. Using primary cultures of astrocytes, we have found that pulichalconoid B attenuated the accumulation of ROS following treatment of these cells with hydrogen peroxide by 89% and prevented 89% of the H2O2-induced death of astrocytes. Pulichalconoid B exhibited an antioxidant effect both in vitro and in the cellular antioxidant assay in astrocytes and microglial cells. Pulichalconoid B also caused a fourfold increase in GDNF transcription in these cells. Thus, this chalcone deserves further studies in order to evaluate if beneficial therapeutic effect exists.

Development of antibody-modified chitosan nanoparticles for the targeted delivery of siRNA across the blood-brain barrier as a strategy for inhibiting HIV replication in astrocytes.

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Gu, Jijin; Al-Bayati, Karam; Ho, Emmanuel A

2017-08-01

RNA interference (RNAi)-mediated gene silencing offers a novel treatment and prevention strategy for human immunodeficiency virus (HIV) infection. HIV was found to infect and replicate in human brain cells and can cause neuroinfections and neurological deterioration. We designed dual-antibody-modified chitosan/small interfering RNA (siRNA) nanoparticles to deliver siRNA across the blood-brain barrier (BBB) targeting HIV-infected brain astrocytes as a strategy for inhibiting HIV replication. We hypothesized that transferrin antibody and bradykinin B2 antibody could specifically bind to the transferrin receptor (TfR) and bradykinin B2 receptor (B2R), respectively, and deliver siRNA across the BBB into astrocytes as potential targeting ligands. In this study, chitosan nanoparticles (CS-NPs) were prepared by a complex coacervation method in the presence of siRNA, and antibody was chemically conjugated to the nanoparticles. The antibody-modified chitosan nanoparticles (Ab-CS-NPs) were spherical in shape, with an average particle size of 235.7 ± 10.2 nm and a zeta potential of 22.88 ± 1.78 mV. The therapeutic potential of the nanoparticles was evaluated based on their cellular uptake and gene silencing efficiency. Cellular accumulation and gene silencing efficiency of Ab-CS-NPs in astrocytes were significantly improved compared to non-modified CS-NPs and single-antibody-modified CS-NPs. These results suggest that the combination of anti-Tf antibody and anti-B2 antibody significantly increased the knockdown effect of siRNA-loaded nanoparticles. Thus, antibody-mediated dual-targeting nanoparticles are an efficient and promising delivery strategy for inhibiting HIV replication in astrocytes. Graphical abstract Graphic representation of dual-antibody-conjugated chitosan nanoparticles for the targeted delivery of siRNA across the blood-brain barrier (BBB) for inhibiting HIV replication in astrocytes. a Nanoparticle delivery to the BBB and penetration. b Tf

Astrocyte-neuron communication: functional consequences.

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Ben Achour, Sarrah; Pascual, Olivier

2012-11-01

Astrocyte-neuron communication has recently been proposed as a potential mechanism participating to synaptic transmission. With the development of this concept and accumulating evidences in favor of a modulation of synaptic transmission by astrocytes, has emerged the term gliotransmission. It refers to the capacity of astrocytes to release various transmitters, such as ATP, glutamate, D-serine, and GABA in the vicinity of synapses. While the cellular mechanisms involved in gliotransmission still need to be better described and, for some, identified, the aim of more and more studies is to determine the role of astrocytes from a functional point of view. This review will summarize the principal studies that have investigated a potential role of astrocytes in the various functions regulated by the brain (sleep, breathing, perception, learning and memory…). This will allow us to highlight the similarities and discrepancies in the signaling pathways involved in the different areas of the brain related to these functions.

Alteration of astrocytes and Wnt/β-catenin signaling in the frontal cortex of autistic subjects

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Cao Fujiang

2012-09-01

Full Text Available Abstract Background Autism is a neurodevelopmental disorder characterized by impairments in social interaction, verbal communication and repetitive behaviors. To date the etiology of this disorder is poorly understood. Studies suggest that astrocytes play critical roles in neural plasticity by detecting neuronal activity and modulating neuronal networks. Recently, a number of studies suggested that an abnormal function of glia/astrocytes may be involved in the development of autism. However, there is yet no direct evidence showing how astrocytes develop in the brain of autistic individuals. Methods Study subjects include brain tissue from autistic subjects, BTBR T + tfJ (BTBR and Neuroligin (NL-3 knock-down mice. Western blot analysis, Immunohistochemistry and confocal microscopy studies have be used to examine the density and morphology of astrocytes, as well as Wnt and β-catenin protein expression. Results In this study, we demonstrate that the astrocytes in autisitcsubjects exhibit significantly reduced branching processes, total branching length and cell body sizes. We also detected an astrocytosis in the frontal cortex of autistic subjects. In addition, we found that the astrocytes in the brain of an NL3 knockdown mouse exhibited similar alterations to what we found in the autistic brain. Furthermore, we detected that both Wnt and β-catenin proteins are decreased in the frontal cortex of autistic subjects. Wnt/β-catenin pathway has been suggested to be involved in the regulation of astrocyte development. Conclusions Our findings imply that defects in astrocytes could impair neuronal plasticity and partially contribute to the development of autistic-like behaviors in both humans and mice. The alteration of Wnt/β-catenin pathway in the brain of autistic subjects may contribute to the changes of astrocytes.

The presence of serum alters the properties of iron oxide nanoparticles and lowers their accumulation by cultured brain astrocytes

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Geppert, Mark; Petters, Charlotte; Thiel, Karsten; Dringen, Ralf

2013-01-01

Iron oxide nanoparticles (IONPs) are considered for various diagnostic and therapeutic applications. Such particles are able to cross the blood–brain barrier and are taken up into brain cells. To test whether serum components affect the properties of IONPs and/or their uptake into brain cells, we have incubated dimercaptosuccinate-coated magnetic IONPs without and with fetal calf serum (FCS) and have exposed cultured brain astrocytes with IONPs in the absence or presence of FCS. Incubation with FCS caused a concentration-dependent increase in the average hydrodynamic diameter of the particles and of their zeta-potential. In the presence of 10 % FCS, the diameter of the IONPs increased from 57 ± 2 to 107 ± 6 nm and the zeta-potential of the particles from −22 ± 5 to −9 ± 1 mV. FCS affected also strongly the uptake of IONPs by cultured astrocytes. The efficient time- and temperature-dependent cellular accumulation of IONPs was lowered with increasing concentration of FCS by up to 90 %. In addition, in the absence of serum, endocytosis inhibitors did not alter the IONP accumulation by astrocytes, while chlorpromazine or wortmannin lowered significantly the accumulation of IONPs in the presence of FCS, suggesting that clathrin-mediated endocytosis and macropinocytosis are involved in astrocytic IONP uptake from serum-containing medium. These data demonstrate that the presence of FCS strongly affects the properties of IONPs as well as their accumulation by cultured brain cells.

A role for thrombospondin-1 deficits in astrocyte-mediated spine and synaptic pathology in Down's syndrome.

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Octavio Garcia

2010-12-01

Full Text Available Down's syndrome (DS is the most common genetic cause of mental retardation. Reduced number and aberrant architecture of dendritic spines are common features of DS neuropathology. However, the mechanisms involved in DS spine alterations are not known. In addition to a relevant role in synapse formation and maintenance, astrocytes can regulate spine dynamics by releasing soluble factors or by physical contact with neurons. We have previously shown impaired mitochondrial function in DS astrocytes leading to metabolic alterations in protein processing and secretion. In this study, we investigated whether deficits in astrocyte function contribute to DS spine pathology.Using a human astrocyte/rat hippocampal neuron coculture, we found that DS astrocytes are directly involved in the development of spine malformations and reduced synaptic density. We also show that thrombospondin 1 (TSP-1, an astrocyte-secreted protein, possesses a potent modulatory effect on spine number and morphology, and that both DS brains and DS astrocytes exhibit marked deficits in TSP-1 protein expression. Depletion of TSP-1 from normal astrocytes resulted in dramatic changes in spine morphology, while restoration of TSP-1 levels prevented DS astrocyte-mediated spine and synaptic alterations. Astrocyte cultures derived from TSP-1 KO mice exhibited similar deficits to support spine formation and structure than DS astrocytes.These results indicate that human astrocytes promote spine and synapse formation, identify astrocyte dysfunction as a significant factor of spine and synaptic pathology in the DS brain, and provide a mechanistic rationale for the exploration of TSP-1-based therapies to treat spine and synaptic pathology in DS and other neurological conditions.

Multifunctional role of astrocytes as gatekeepers of neuronal energy supply

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Jillian L Stobart

2013-04-01

Full Text Available Dynamic adjustments to neuronal energy supply in response to synaptic activity are critical for neuronal function. Glial cells known as astrocytes have processes that ensheath most central synapses and express G-protein-coupled neurotransmitter receptors and transporters that respond to neuronal activity. Astrocytes also release substrates for neuronal oxidative phosphorylation and have processes that terminate on the surface of brain arterioles and can influence vascular smooth muscle tone and local blood flow. Membrane receptor or transporter-mediated effects of glutamate represent a convergence point of astrocyte influence on neuronal bioenergetics. Astrocytic glutamate uptake drives glycolysis and subsequent shuttling of lactate from astrocytes to neurons for oxidative metabolism. Astrocytes also convert synaptically reclaimed glutamate to glutamine, which is returned to neurons for glutamate salvage or oxidation. Finally, astrocytes store brain energy currency in the form of glycogen, which can be mobilized to produce lactate for neuronal oxidative phosphorylation in response to glutamatergic neurotransmission. These mechanisms couple synaptically-driven astrocytic responses to glutamate with release of energy substrates back to neurons to match demand with supply. In addition, astrocytes directly influence the tone of penetrating brain arterioles in response to glutamatergic neurotransmission, coordinating dynamic regulation of local blood flow. We will describe the role of astrocytes in neurometabolic and neurovascular coupling in detail and discuss, in turn, how astrocyte dysfunction may contribute to neuronal bioenergetic deficit and neurodegeneration. Understanding the role of astrocytes as a hub for neurometabolic and neurovascular coupling mechanisms is a critical underpinning for therapeutic development in a broad range of neurodegenerative disorders characterized by chronic generalized brain ischemia and brain microvascular

The RNA helicase DDX1 is involved in restricted HIV-1 Rev function in human astrocytes

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Fang Jianhua; Acheampong, Edward; Dave, Rajnish; Wang Fengxiang; Mukhtar, Muhammad; Pomerantz, Roger J.

2005-01-01

Productive infection by human immunodeficiency virus type I (HIV-1) in the central nervous system (CNS) involves mainly macrophages and microglial cells. A frequency of less than 10% of human astrocytes is estimated to be infectable with HIV-1. Nonetheless, this relatively low percentage of infected astrocytes, but associated with a large total number of astrocytic cells in the CNS, makes human astrocytes a critical part in the analyses of potential HIV-1 reservoirs in vivo. Investigations in astrocytic cell lines and primary human fetal astrocytes revealed that limited HIV-1 replication in these cells resulted from low-level viral entry, transcription, viral protein processing, and virion maturation. Of note, a low ratio of unspliced versus spliced HIV-1-specific RNA was also investigated, as Rev appeared to act aberrantly in astrocytes, via loss of nuclear and/or nucleolar localization and diminished Rev-mediated function. Host cellular machinery enabling Rev function has become critical for elucidation of diminished Rev activity, especially for those factors leading to RNA metabolism. We have recently identified a DEAD-box protein, DDX1, as a Rev cellular co-factor and now have explored its potential importance in astrocytes. Cells were infected with HIV-1 pseudotyped with envelope glycoproteins of amphotropic murine leukemia viruses (MLV). Semi-quantitative reverse transcriptase-polymerase chain reactions (RT-PCR) for unspliced, singly-spliced, and multiply-spliced RNA clearly showed a lower ratio of unspliced/singly-spliced over multiply-spliced HIV-1-specific RNA in human astrocytes as compared to Rev-permissive, non-glial control cells. As well, the cellular localization of Rev in astrocytes was cytoplasmically dominant as compared to that of Rev-permissive, non-glial controls. This endogenous level of DDX1 expression in astrocytes was demonstrated directly to lead to a shift of Rev sub-cellular distribution dominance from nuclear and/or nucleolar to

Differentiation of Inflammation-Responsive Astrocytes from Glial Progenitors Generated from Human Induced Pluripotent Stem Cells

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Renata Santos

2017-06-01

Full Text Available Astrocyte dysfunction and neuroinflammation are detrimental features in multiple pathologies of the CNS. Therefore, the development of methods that produce functional human astrocytes represents an advance in the study of neurological diseases. Here we report an efficient method for inflammation-responsive astrocyte generation from induced pluripotent stem cells (iPSCs and embryonic stem cells. This protocol uses an intermediate glial progenitor stage and generates functional astrocytes that show levels of glutamate uptake and calcium activation comparable with those observed in human primary astrocytes. Stimulation of stem cell-derived astrocytes with interleukin-1β or tumor necrosis factor α elicits a strong and rapid pro-inflammatory response. RNA-sequencing transcriptome profiling confirmed that similar gene expression changes occurred in iPSC-derived and primary astrocytes upon stimulation with interleukin-1β. This protocol represents an important tool for modeling in-a-dish neurological diseases with an inflammatory component, allowing for the investigation of the role of diseased astrocytes in neuronal degeneration.

Nanosecond UV lasers stimulate transient Ca2+ elevations in human hNT astrocytes.

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Raos, B J; Graham, E S; Unsworth, C P

2017-06-01

Astrocytes respond to various stimuli resulting in intracellular Ca 2+ signals that can propagate through organized functional networks. Recent literature calls for the development of techniques that can stimulate astrocytes in a fast and highly localized manner to emulate more closely the characteristics of astrocytic Ca 2+ signals in vivo. In this article we demonstrate, for the first time, how nanosecond UV lasers are capable of reproducibly stimulating Ca 2+ transients in human hNT astrocytes. We report that laser pulses with a beam energy of 4-29 µJ generate transient increases in cytosolic Ca 2+ . These Ca 2+ transients then propagate to adjacent astrocytes as intercellular Ca 2+ waves. We propose that nanosecond laser stimulation provides a valuable tool for enabling the study of Ca 2+ dynamics in human astrocytes at both a single cell and network level. Compared to previously developed techniques nanosecond laser stimulation has the advantage of not requiring loading of photo-caged or -sensitising agents, is non-contact, enables stimulation with a high spatiotemporal resolution and is comparatively cost effective.

On the nature of the Cu-rich aggregates in brain astrocytes

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Sullivan, Brendan; Robison, Gregory; Osborn, Jenna; Kay, Martin; Thompson, Peter; Davis, Katherine; Zakharova, Taisiya; Antipova, Olga; Pushkar, Yulia

2017-04-01

Fulfilling a bevy of biological roles, copper is an essential metal for healthy brain function. Cu dyshomeostasis has been demonstrated to be involved in some neurological conditions including Menkes and Alzheimer’s diseases. We have previously reported localized Cu-rich aggregates in astrocytes of the subventricular zone (SVZ) in rodent brains with Cu concentrations in the hundreds of millimolar. Metallothionein, a cysteine-rich protein critical to metal homeostasis and known to participate in a variety of neuroprotective and neuroregenerative processes, was proposed as a binding protein. Here, we present an analysis of metallothionein(1,2) knockout (MTKO) mice and age-matched controls using X-ray fluorescence microscopy. In large structures such as the corpus callosum, cortex, and striatum, there is no significant difference in Cu, Fe, or Zn concentrations in MTKO mice compared to age-matched controls. In the astrocyte-rich subventricular zone where Cu-rich aggregates reside, approximately 1/3 as many Cu-rich aggregates persist in MTKO mice resulting in a decrease in periventricular Cu concentration. Aggregates in both wild-type and MTKO mice show XANES spectra characteristic of CuxSy multimetallic clusters and have similar [S]/[Cu] ratios. Consistent with assignment as a CuxSy multimetallic cluster, the astrocyte-rich SVZ of both MTKO and wild-type mice exhibit autofluorescent bodies, though MTKO mice exhibit fewer. Furthermore, XRF imaging of Au-labeled lysosomes and ubiquitin demonstrates a lack of co-localization with Cu-rich aggregates suggesting they are not involved in a degradation pathway. Overall, these data suggest that Cu in aggregates is bound by either metallothionein-3 or a yet unknown protein similar to metallothionein.

Molecular Neuropathology of Astrocytes and Oligodendrocytes in Alcohol Use Disorders

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José J. Miguel-Hidalgo

2018-03-01

Full Text Available Postmortem studies reveal structural and molecular alterations of astrocytes and oligodendrocytes in both the gray and white matter (GM and WM of the prefrontal cortex (PFC in human subjects with chronic alcohol abuse or dependence. These glial cellular changes appear to parallel and may largely explain structural and functional alterations detected using neuroimaging techniques in subjects with alcohol use disorders (AUDs. Moreover, due to the crucial roles of astrocytes and oligodendrocytes in neurotransmission and signal conduction, these cells are very likely major players in the molecular mechanisms underpinning alcoholism-related connectivity disturbances between the PFC and relevant interconnecting brain regions. The glia-mediated etiology of alcohol-related brain damage is likely multifactorial since metabolic, hormonal, hepatic and hemodynamic factors as well as direct actions of ethanol or its metabolites have the potential to disrupt distinct aspects of glial neurobiology. Studies in animal models of alcoholism and postmortem human brains have identified astrocyte markers altered in response to significant exposures to ethanol or during alcohol withdrawal, such as gap-junction proteins, glutamate transporters or enzymes related to glutamate and gamma-aminobutyric acid (GABA metabolism. Changes in these proteins and their regulatory pathways would not only cause GM neuronal dysfunction, but also disturbances in the ability of WM axons to convey impulses. In addition, alcoholism alters the expression of astrocyte and myelin proteins and of oligodendrocyte transcription factors important for the maintenance and plasticity of myelin sheaths in WM and GM. These changes are concomitant with epigenetic DNA and histone modifications as well as alterations in regulatory microRNAs (miRNAs that likely cause profound disturbances of gene expression and protein translation. Knowledge is also available about interactions between astrocytes and

Differentiation of Inflammation-Responsive Astrocytes from Glial Progenitors Generated from Human Induced Pluripotent Stem Cells.

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Santos, Renata; Vadodaria, Krishna C; Jaeger, Baptiste N; Mei, Arianna; Lefcochilos-Fogelquist, Sabrina; Mendes, Ana P D; Erikson, Galina; Shokhirev, Maxim; Randolph-Moore, Lynne; Fredlender, Callie; Dave, Sonia; Oefner, Ruth; Fitzpatrick, Conor; Pena, Monique; Barron, Jerika J; Ku, Manching; Denli, Ahmet M; Kerman, Bilal E; Charnay, Patrick; Kelsoe, John R; Marchetto, Maria C; Gage, Fred H

2017-06-06

Astrocyte dysfunction and neuroinflammation are detrimental features in multiple pathologies of the CNS. Therefore, the development of methods that produce functional human astrocytes represents an advance in the study of neurological diseases. Here we report an efficient method for inflammation-responsive astrocyte generation from induced pluripotent stem cells (iPSCs) and embryonic stem cells. This protocol uses an intermediate glial progenitor stage and generates functional astrocytes that show levels of glutamate uptake and calcium activation comparable with those observed in human primary astrocytes. Stimulation of stem cell-derived astrocytes with interleukin-1β or tumor necrosis factor α elicits a strong and rapid pro-inflammatory response. RNA-sequencing transcriptome profiling confirmed that similar gene expression changes occurred in iPSC-derived and primary astrocytes upon stimulation with interleukin-1β. This protocol represents an important tool for modeling in-a-dish neurological diseases with an inflammatory component, allowing for the investigation of the role of diseased astrocytes in neuronal degeneration. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

Human microglia and astrocytes express cGAS-STING viral sensing components.

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Jeffries, Austin M; Marriott, Ian

2017-09-29

While microglia and astrocytes are known to produce key inflammatory and anti-viral mediators following infection with replicative DNA viruses, the mechanisms by which these cell types perceive such threats are poorly understood. Recently, cyclic GMP-AMP synthase (cGAS) has been identified as an important cytosolic sensor for DNA viruses and retroviruses in peripheral leukocytes. Here we confirm the ability of human microglial and astrocytic cell lines and primary human glia to respond to foreign intracellular double stranded DNA. Importantly, we provide the first demonstration that human microglia and astrocytes show robust levels of cGAS protein expression at rest and following activation. Furthermore, we show these cell types also constitutively express the critical downstream cGAS adaptor protein, stimulator of interferon genes (STING). The present finding that human glia express the principle components of the cGAS-STING pathway provides a foundation for future studies to investigate the relative importance of these molecules in clinically relevant viral CNS infections. Copyright © 2017 Elsevier B.V. All rights reserved.

Simultaneous neuron- and astrocyte-specific fluorescent marking

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Schulze, Wiebke [Laboratory of Molecular Neuropharmacology, Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871 (Japan); Hayata-Takano, Atsuko [Molecular Research Center for Children' s Mental Development, United Graduate School of Child Development, Osaka University, Kanazawa University, Hamamatsu University School of Medicine, Chiba University and University of Fukui, 2-2 Yamadaoka, Suita, Osaka 565-0871 (Japan); Kamo, Toshihiko [Laboratory of Molecular Neuropharmacology, Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871 (Japan); Nakazawa, Takanobu, E-mail: takanobunakazawa-tky@umin.ac.jp [iPS Cell-based Research Project on Brain Neuropharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871 (Japan); Nagayasu, Kazuki [iPS Cell-based Research Project on Brain Neuropharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871 (Japan); Kasai, Atsushi; Seiriki, Kaoru [Laboratory of Molecular Neuropharmacology, Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871 (Japan); Interdisciplinary Program for Biomedical Sciences, Institute for Academic Initiatives, Osaka University, 1-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Shintani, Norihito [Laboratory of Molecular Neuropharmacology, Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871 (Japan); Ago, Yukio [Laboratory of Medicinal Pharmacology, Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871 (Japan); Farfan, Camille [Laboratory of Molecular Neuropharmacology, Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871 (Japan); and others

2015-03-27

Systematic and simultaneous analysis of multiple cell types in the brain is becoming important, but such tools have not yet been adequately developed. Here, we aimed to generate a method for the specific fluorescent labeling of neurons and astrocytes, two major cell types in the brain, and we have developed lentiviral vectors to express the red fluorescent protein tdTomato in neurons and the enhanced green fluorescent protein (EGFP) in astrocytes. Importantly, both fluorescent proteins are fused to histone 2B protein (H2B) to confer nuclear localization to distinguish between single cells. We also constructed several expression constructs, including a tandem alignment of the neuron- and astrocyte-expression cassettes for simultaneous labeling. Introducing these vectors and constructs in vitro and in vivo resulted in cell type-specific and nuclear-localized fluorescence signals enabling easy detection and distinguishability of neurons and astrocytes. This tool is expected to be utilized for the simultaneous analysis of changes in neurons and astrocytes in healthy and diseased brains. - Highlights: • We develop a method for the specific fluorescent labeling of neurons and astrocytes. • Neuron-specific labeling is achieved using Scg10 and synapsin promoters. • Astrocyte-specific labeling is generated using the minimal GFAP promoter. • Nuclear localization of fluorescent proteins is achieved with histone 2B protein.

Simultaneous neuron- and astrocyte-specific fluorescent marking

International Nuclear Information System (INIS)

Schulze, Wiebke; Hayata-Takano, Atsuko; Kamo, Toshihiko; Nakazawa, Takanobu; Nagayasu, Kazuki; Kasai, Atsushi; Seiriki, Kaoru; Shintani, Norihito; Ago, Yukio; Farfan, Camille

2015-01-01

Systematic and simultaneous analysis of multiple cell types in the brain is becoming important, but such tools have not yet been adequately developed. Here, we aimed to generate a method for the specific fluorescent labeling of neurons and astrocytes, two major cell types in the brain, and we have developed lentiviral vectors to express the red fluorescent protein tdTomato in neurons and the enhanced green fluorescent protein (EGFP) in astrocytes. Importantly, both fluorescent proteins are fused to histone 2B protein (H2B) to confer nuclear localization to distinguish between single cells. We also constructed several expression constructs, including a tandem alignment of the neuron- and astrocyte-expression cassettes for simultaneous labeling. Introducing these vectors and constructs in vitro and in vivo resulted in cell type-specific and nuclear-localized fluorescence signals enabling easy detection and distinguishability of neurons and astrocytes. This tool is expected to be utilized for the simultaneous analysis of changes in neurons and astrocytes in healthy and diseased brains. - Highlights: • We develop a method for the specific fluorescent labeling of neurons and astrocytes. • Neuron-specific labeling is achieved using Scg10 and synapsin promoters. • Astrocyte-specific labeling is generated using the minimal GFAP promoter. • Nuclear localization of fluorescent proteins is achieved with histone 2B protein

Silver nanoparticles induce tight junction disruption and astrocyte neurotoxicity in a rat blood–brain barrier primary triple coculture model

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Xu L

2015-09-01

Full Text Available Liming Xu,1,2,* Mo Dan,1,* Anliang Shao,1 Xiang Cheng,1,3 Cuiping Zhang,4 Robert A Yokel,5 Taro Takemura,6 Nobutaka Hanagata,6 Masami Niwa,7,8 Daisuke Watanabe7,81National Institutes for Food and Drug Control, No 2, Temple of Heaven, Beijing, 2School of Information and Engineering, Wenzhou Medical University, Wenzhou, 3School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu, 4Beijing Neurosurgical Institute, Capital Medical University, Beijing, People’s Republic of China; 5College of Pharmacy, University of Kentucky, Lexington, KY, USA; 6Nanotechnology Innovation Station for Nanoscale Science and Technology, National Institute for Materials Science, Tsukuba, Ibaraki, 7Department of Pharmacology, Nagasaki University, 8BBB Laboratory, PharmaCo-Cell Company, Ltd., Nagasaki, Japan*These authors contributed equally to this workBackground: Silver nanoparticles (Ag-NPs can enter the brain and induce neurotoxicity. However, the toxicity of Ag-NPs on the blood–brain barrier (BBB and the underlying mechanism(s of action on the BBB and the brain are not well understood.Method: To investigate Ag-NP suspension (Ag-NPS-induced toxicity, a triple coculture BBB model of rat brain microvascular endothelial cells, pericytes, and astrocytes was established. The BBB permeability and tight junction protein expression in response to Ag-NPS, NP-released Ag ions, and polystyrene-NP exposure were investigated. Ultrastructural changes of the microvascular endothelial cells, pericytes, and astrocytes were observed using transmission electron microscopy (TEM. Global gene expression of astrocytes was measured using a DNA microarray.Results: A triple coculture BBB model of primary rat brain microvascular endothelial cells, pericytes, and astrocytes was established, with the transendothelial electrical resistance values >200 Ω·cm2. After Ag-NPS exposure for 24 hours, the BBB permeability was significantly increased and expression of the

Astrocytic glutamate transport regulates a Drosophila CNS synapse that lacks astrocyte ensheathment.

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MacNamee, Sarah E; Liu, Kendra E; Gerhard, Stephan; Tran, Cathy T; Fetter, Richard D; Cardona, Albert; Tolbert, Leslie P; Oland, Lynne A

2016-07-01

Anatomical, molecular, and physiological interactions between astrocytes and neuronal synapses regulate information processing in the brain. The fruit fly Drosophila melanogaster has become a valuable experimental system for genetic manipulation of the nervous system and has enormous potential for elucidating mechanisms that mediate neuron-glia interactions. Here, we show the first electrophysiological recordings from Drosophila astrocytes and characterize their spatial and physiological relationship with particular synapses. Astrocyte intrinsic properties were found to be strongly analogous to those of vertebrate astrocytes, including a passive current-voltage relationship, low membrane resistance, high capacitance, and dye-coupling to local astrocytes. Responses to optogenetic stimulation of glutamatergic premotor neurons were correlated directly with anatomy using serial electron microscopy reconstructions of homologous identified neurons and surrounding astrocytic processes. Robust bidirectional communication was present: neuronal activation triggered astrocytic glutamate transport via excitatory amino acid transporter 1 (Eaat1), and blocking Eaat1 extended glutamatergic interneuron-evoked inhibitory postsynaptic currents in motor neurons. The neuronal synapses were always located within 1 μm of an astrocytic process, but none were ensheathed by those processes. Thus, fly astrocytes can modulate fast synaptic transmission via neurotransmitter transport within these anatomical parameters. J. Comp. Neurol. 524:1979-1998, 2016. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

NT2 derived neuronal and astrocytic network signalling.

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Eric J Hill

Full Text Available A major focus of stem cell research is the generation of neurons that may then be implanted to treat neurodegenerative diseases. However, a picture is emerging where astrocytes are partners to neurons in sustaining and modulating brain function. We therefore investigated the functional properties of NT2 derived astrocytes and neurons using electrophysiological and calcium imaging approaches. NT2 neurons (NT2Ns expressed sodium dependent action potentials, as well as responses to depolarisation and the neurotransmitter glutamate. NT2Ns exhibited spontaneous and coordinated calcium elevations in clusters and in extended processes, indicating local and long distance signalling. Tetrodotoxin sensitive network activity could also be evoked by electrical stimulation. Similarly, NT2 astrocytes (NT2As exhibited morphology and functional properties consistent with this glial cell type. NT2As responded to neuronal activity and to exogenously applied neurotransmitters with calcium elevations, and in contrast to neurons, also exhibited spontaneous rhythmic calcium oscillations. NT2As also generated propagating calcium waves that were gap junction and purinergic signalling dependent. Our results show that NT2 derived astrocytes exhibit appropriate functionality and that NT2N networks interact with NT2A networks in co-culture. These findings underline the utility of such cultures to investigate human brain cell type signalling under controlled conditions. Furthermore, since stem cell derived neuron function and survival is of great importance therapeutically, our findings suggest that the presence of complementary astrocytes may be valuable in supporting stem cell derived neuronal networks. Indeed, this also supports the intriguing possibility of selective therapeutic replacement of astrocytes in diseases where these cells are either lost or lose functionality.

Astrocyte mega-domain hypothesis of the autistic savantism.

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Mitterauer, Bernhard J

2013-01-01

Individuals with autism who show high abilities are called savants. Whereas in their brains a disconnection in and between neural networks has been identified, savantism is yet poorly understood. Focusing on astrocyte domain organization, it is hypothesized that local astrocyte mega-organizations may be responsible for exerting high capabilities in brains of autistic savants. Astrocytes, the dominant glial cell type, modulate synaptic information transmission. Each astrocyte is organized in non-overlapping domains. Formally, each astrocyte contacting n-neurons with m-synapses via its processes generates dynamic domains of synaptic interactions based on qualitative computation criteria, and hereby it structures neuronal information processing. If the number of processes is genetically significantly increased, these astrocytes operate in a mega-domain with a higher complexitiy of computation. From this model savant abilities are deduced. Copyright © 2012 Elsevier Ltd. All rights reserved.

Transcriptomic analyses of primary astrocytes under TNFα treatment

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Cindy Birck

2016-03-01

Full Text Available Astrocytes, the most abundant glial cell population in the central nervous system, have important functional roles in the brain as blood brain barrier maintenance, synaptic transmission or intercellular communications [1,2]. Numerous studies suggested that astrocytes exhibit a functional and morphological high degree of plasticity. For example, following any brain injury, astrocytes become reactive and hypertrophic. This phenomenon, also called reactive gliosis, is characterized by a set of progressive gene expression and cellular changes [3]. Interestingly, in this context, astrocytes can re-acquire neurogenic properties. It has been shown that astrocytes can undergo dedifferentiation upon injury and inflammation, and may re-acquire the potentiality of neural progenitors [4,5,6,7].To assess the effect of inflammation on astrocytes, primary mouse astrocytes were treated with tumor necrosis factor α (TNFα, one of the main pro-inflammatory cytokines. The strength of this study is that pure primary astrocytes were used. As microglia are highly reactive immune cells, we used a magnetic cell sorting separation (MACS method to further obtain highly pure astrocyte cultures devoid of microglia.Here, we provide details of the microarray data, which have been deposited in the Gene Expression Omnibus (GEO under the series accession number GSE73022. The analysis and interpretation of these data are included in Gabel et al. (2015. Analysis of gene expression indicated that the NFκB pathway-associated genes were induced after a TNFα treatment. We have shown that primary astrocytes devoid of microglia can respond to a TNFα treatment with the re-expression of genes implicated in the glial cell development. Keywords: Primary astrocytes, Inflammation, Microarrays, Gene expression

Expression of the human isoform of glutamate dehydrogenase, hGDH2, augments TCA cycle capacity and oxidative metabolism of glutamate during glucose deprivation in astrocytes.

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Nissen, Jakob D; Lykke, Kasper; Bryk, Jaroslaw; Stridh, Malin H; Zaganas, Ioannis; Skytt, Dorte M; Schousboe, Arne; Bak, Lasse K; Enard, Wolfgang; Pääbo, Svante; Waagepetersen, Helle S

2017-03-01

A key enzyme in brain glutamate homeostasis is glutamate dehydrogenase (GDH) which links carbohydrate and amino acid metabolism mediating glutamate degradation to CO 2 and expanding tricarboxylic acid (TCA) cycle capacity with intermediates, i.e. anaplerosis. Humans express two GDH isoforms, GDH1 and 2, whereas most other mammals express only GDH1. hGDH1 is widely expressed in human brain while hGDH2 is confined to astrocytes. The two isoforms display different enzymatic properties and the nature of these supports that hGDH2 expression in astrocytes potentially increases glutamate oxidation and supports the TCA cycle during energy-demanding processes such as high intensity glutamatergic signaling. However, little is known about how expression of hGDH2 affects the handling of glutamate and TCA cycle metabolism in astrocytes. Therefore, we cultured astrocytes from cerebral cortical tissue of hGDH2-expressing transgenic mice. We measured glutamate uptake and metabolism using [ 3 H]glutamate, while the effect on metabolic pathways of glutamate and glucose was evaluated by use of 13 C and 14 C substrates and analysis by mass spectrometry and determination of radioactively labeled metabolites including CO 2 , respectively. We conclude that hGDH2 expression increases capacity for uptake and oxidative metabolism of glutamate, particularly during increased workload and aglycemia. Additionally, hGDH2 expression increased utilization of branched-chain amino acids (BCAA) during aglycemia and caused a general decrease in oxidative glucose metabolism. We speculate, that expression of hGDH2 allows astrocytes to spare glucose and utilize BCAAs during substrate shortages. These findings support the proposed role of hGDH2 in astrocytes as an important fail-safe during situations of intense glutamatergic activity. GLIA 2017;65:474-488. © 2016 Wiley Periodicals, Inc.

Computational Models for Calcium-Mediated Astrocyte Functions

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Tiina Manninen

2018-04-01

Full Text Available The computational neuroscience field has heavily concentrated on the modeling of neuronal functions, largely ignoring other brain cells, including one type of glial cell, the astrocytes. Despite the short history of modeling astrocytic functions, we were delighted about the hundreds of models developed so far to study the role of astrocytes, most often in calcium dynamics, synchronization, information transfer, and plasticity in vitro, but also in vascular events, hyperexcitability, and homeostasis. Our goal here is to present the state-of-the-art in computational modeling of astrocytes in order to facilitate better understanding of the functions and dynamics of astrocytes in the brain. Due to the large number of models, we concentrated on a hundred models that include biophysical descriptions for calcium signaling and dynamics in astrocytes. We categorized the models into four groups: single astrocyte models, astrocyte network models, neuron-astrocyte synapse models, and neuron-astrocyte network models to ease their use in future modeling projects. We characterized the models based on which earlier models were used for building the models and which type of biological entities were described in the astrocyte models. Features of the models were compared and contrasted so that similarities and differences were more readily apparent. We discovered that most of the models were basically generated from a small set of previously published models with small variations. However, neither citations to all the previous models with similar core structure nor explanations of what was built on top of the previous models were provided, which made it possible, in some cases, to have the same models published several times without an explicit intention to make new predictions about the roles of astrocytes in brain functions. Furthermore, only a few of the models are available online which makes it difficult to reproduce the simulation results and further develop

Computational Models for Calcium-Mediated Astrocyte Functions.

Science.gov (United States)

Manninen, Tiina; Havela, Riikka; Linne, Marja-Leena

2018-01-01

The computational neuroscience field has heavily concentrated on the modeling of neuronal functions, largely ignoring other brain cells, including one type of glial cell, the astrocytes. Despite the short history of modeling astrocytic functions, we were delighted about the hundreds of models developed so far to study the role of astrocytes, most often in calcium dynamics, synchronization, information transfer, and plasticity in vitro , but also in vascular events, hyperexcitability, and homeostasis. Our goal here is to present the state-of-the-art in computational modeling of astrocytes in order to facilitate better understanding of the functions and dynamics of astrocytes in the brain. Due to the large number of models, we concentrated on a hundred models that include biophysical descriptions for calcium signaling and dynamics in astrocytes. We categorized the models into four groups: single astrocyte models, astrocyte network models, neuron-astrocyte synapse models, and neuron-astrocyte network models to ease their use in future modeling projects. We characterized the models based on which earlier models were used for building the models and which type of biological entities were described in the astrocyte models. Features of the models were compared and contrasted so that similarities and differences were more readily apparent. We discovered that most of the models were basically generated from a small set of previously published models with small variations. However, neither citations to all the previous models with similar core structure nor explanations of what was built on top of the previous models were provided, which made it possible, in some cases, to have the same models published several times without an explicit intention to make new predictions about the roles of astrocytes in brain functions. Furthermore, only a few of the models are available online which makes it difficult to reproduce the simulation results and further develop the models. Thus

Reduced expression of glutamate transporter EAAT2 and impaired glutamate transport in human primary astrocytes exposed to HIV-1 or gp120

International Nuclear Information System (INIS)

Wang Zhuying; Pekarskaya, Olga; Bencheikh, Meryem; Chao Wei; Gelbard, Harris A.; Ghorpade, Anuja; Rothstein, Jeffrey D.; Volsky, David J.

2003-01-01

L-Glutamate is the major excitatory neurotransmitter in the brain. Astrocytes maintain low levels of synaptic glutamate by high-affinity uptake and defects in this function may lead to neuronal cell death by excitotoxicity. We tested the effects of HIV-1 and its envelope glycoprotein gp120 upon glutamate uptake and expression of glutamate transporters EAAT1 and EAAT2 in fetal human astrocytes in vitro. Astrocytes isolated from fetal tissues between 16 and 19 weeks of gestation expressed EAAT1 and EAAT2 RNA and proteins as detected by Northern blot analysis and immunoblotting, respectively, and the cells were capable of specific glutamate uptake. Exposure of astrocytes to HIV-1 or gp120 significantly impaired glutamate uptake by the cells, with maximum inhibition within 6 h, followed by gradual decline during 3 days of observation. HIV-1-infected cells showed a 59% reduction in V max for glutamate transport, indicating a reduction in the number of active transporter sites on the cell surface. Impaired glutamate transport after HIV-1 infection or gp120 exposure correlated with a 40-70% decline in steady-state levels of EAAT2 RNA and protein. EAAT1 RNA and protein levels were less affected. Treatment of astrocytes with tumor necrosis factor-α (TNF-α) decreased the expression of both EAAT1 and EAAT2, but neither HIV-1 nor gp120 were found to induce TNF-α production by astrocytes. These findings demonstrate that HIV-1 and gp120 induce transcriptional downmodulation of the EAAT2 transporter gene in human astrocytes and coordinately attenuate glutamate transport by the cells. Reduction of the ability of HIV-1-infected astrocytes to take up glutamate may contribute to the development of neurological disease

Major Shifts in Glial Regional Identity Are a Transcriptional Hallmark of Human Brain Aging

OpenAIRE

Soreq, Lilach; Rose, Jamie; Soreq, Eyal; Hardy, John; Trabzuni, Daniah; Cookson, Mark R.; Smith, Colin; Ryten, Mina; Patani, Rickie; Ule, Jernej

2017-01-01

Summary Gene expression studies suggest that aging of the human brain is determined by a complex interplay of molecular events, although both its region- and cell-type-specific consequences remain poorly understood. Here, we extensively characterized aging-altered gene expression changes across ten human brain regions from 480 individuals ranging in?age from 16 to 106 years. We show that astrocyte-?and oligodendrocyte-specific genes, but not neuron-specific genes, shift their regional express...

Brain monoamine oxidase B and A in human parkinsonian dopamine deficiency disorders.

Science.gov (United States)

Tong, Junchao; Rathitharan, Gausiha; Meyer, Jeffrey H; Furukawa, Yoshiaki; Ang, Lee-Cyn; Boileau, Isabelle; Guttman, Mark; Hornykiewicz, Oleh; Kish, Stephen J

2017-09-01

enzyme in the parkinsonian substantia nigra; instead, increased nigral levels of a MAOA fragment and 'turnover' of the enzyme were observed in the conditions. Our findings provide support that MAOB might serve as a biochemical imaging marker, albeit not entirely specific, for astrocyte activation in human brain. The observation that MAOB protein concentration is generally increased in degenerating brain areas in multiple system atrophy (especially putamen) and in progressive supranuclear palsy, but not in the nigra in Parkinson's disease, also distinguishes astrocyte behaviour in Parkinson's disease from that in the two 'Parkinson-plus' conditions. The question remains whether suppression of either MAOB in astrocytes or MAOA in dopamine neurons might influence progression of the parkinsonian disorders. © The Author (2017). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Calcium dynamics of cortical astrocytic networks in vivo.

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Hajime Hirase

2004-04-01

Full Text Available Large and long-lasting cytosolic calcium surges in astrocytes have been described in cultured cells and acute slice preparations. The mechanisms that give rise to these calcium events have been extensively studied in vitro. However, their existence and functions in the intact brain are unknown. We have topically applied Fluo-4 AM on the cerebral cortex of anesthetized rats, and imaged cytosolic calcium fluctuation in astrocyte populations of superficial cortical layers in vivo, using two-photon laser scanning microscopy. Spontaneous [Ca(2+](i events in individual astrocytes were similar to those observed in vitro. Coordination of [Ca(2+](i events among astrocytes was indicated by the broad cross-correlograms. Increased neuronal discharge was associated with increased astrocytic [Ca(2+](i activity in individual cells and a robust coordination of [Ca(2+](i signals in neighboring astrocytes. These findings indicate potential neuron-glia communication in the intact brain.

Neurosphere based differentiation of human iPSC improves astrocyte differentiation

DEFF Research Database (Denmark)

Zhou, Shuling; Szczesna, Karolina; Ochalek, Anna

2016-01-01

Neural progenitor cells (NPCs) derived from human induced pluripotent stem cells (iPSCs) are traditionally maintained and proliferated utilizing two-dimensional (2D) adherent monolayer culture systems. However, NPCs cultured using this system hardly reflect the intrinsic spatial development...... of brain tissue. In this study, we determined that culturing iPSC-derived NPCs as three-dimensional (3D) floating neurospheres resulted in increased expression of the neural progenitor cell (NPC) markers, PAX6 and NESTIN. Expansion of NPCs in 3D culture methods also resulted in a more homogenous PAX6...... expression when compared to 2D culture methods. Furthermore, the 3D propagation method for NPCs resulted in a significant higher expression of the astrocyte markers  GFAP and aquaporin 4 (AQP4) in the differentiated cells. Thus, our 3D propagation method could constitute a useful tool to promote NPC...

CCL2 binding is CCR2 independent in primary adult human astrocytes.

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Fouillet, A; Mawson, J; Suliman, O; Sharrack, B; Romero, I A; Woodroofe, M N

2012-02-09

Chemokines are low relative molecular mass proteins, which have chemoattractant actions on many cell types. The chemokine, CCL2, has been shown to play a major role in the recruitment of monocytes in central nervous system (CNS) lesions in multiple sclerosis (MS). Since resident astrocytes constitute a major source of chemokine synthesis including CCL2, we were interested to assess the regulation of CCL2 by astrocytes. We showed that CCL2 bound to the cell surface of astrocytes and binding was not modulated by inflammatory conditions. However, CCR2 protein was not detected nor was activation of the classical CCR2 downstream signaling pathways. Recent studies have shown that non-signaling decoy chemokine receptors bind and modulate the expression of chemokines at site of inflammation. Here, we show that the D6 chemokine decoy receptor is constitutively expressed by primary human adult astrocytes at both mRNA and protein level. In addition, CCL3, which binds to D6, but not CCL19, which does not bind to D6, displaced CCL2 binding to astrocytes; indicating that CCL2 may bind to this cell type via the D6 receptor. Our results suggest that CCL2 binding to primary adult human astrocytes is CCR2-independent and is likely to be mediated via the D6 decoy chemokine receptor. Therefore we propose that astrocytes are implicated in both the establishment of chemokine gradients for the migration of leukocytes into and within the CNS and in the regulation of CCL2 levels at inflammatory sites in the CNS. Copyright © 2011 Elsevier B.V. All rights reserved.

Neocortical glial cell numbers in human brains.

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Pelvig, D P; Pakkenberg, H; Stark, A K; Pakkenberg, B

2008-11-01

Stereological cell counting was applied to post-mortem neocortices of human brains from 31 normal individuals, age 18-93 years, 18 females (average age 65 years, range 18-93) and 13 males (average age 57 years, range 19-87). The cells were differentiated in astrocytes, oligodendrocytes, microglia and neurons and counting were done in each of the four lobes. The study showed that the different subpopulations of glial cells behave differently as a function of age; the number of oligodendrocytes showed a significant 27% decrease over adult life and a strong correlation to the total number of neurons while the total astrocyte number is constant through life; finally males have a 28% higher number of neocortical glial cells and a 19% higher neocortical neuron number than females. The overall total number of neocortical neurons and glial cells was 49.3 billion in females and 65.2 billion in males, a difference of 24% with a high biological variance. These numbers can serve as reference values in quantitative studies of the human neocortex.

Taurine Biosynthesis by Neurons and Astrocytes*

Science.gov (United States)

Vitvitsky, Victor; Garg, Sanjay K.; Banerjee, Ruma

2011-01-01

The physiological roles of taurine, a product of cysteine degradation and one of the most abundant amino acids in the body, remain elusive. Taurine deficiency leads to heart dysfunction, brain development abnormalities, retinal degradation, and other pathologies. The taurine synthetic pathway is proposed to be incomplete in astrocytes and neurons, and metabolic cooperation between these cell types is reportedly needed to complete the pathway. In this study, we analyzed taurine synthesis capability as reported by incorporation of radioactivity from [35S]cysteine into taurine, in primary murine astrocytes and neurons, and in several transformed cell lines (human (SH-SY5Y) and murine (N1E-115) neuroblastoma, human astrocytoma (U-87MG and 1321 N1), and rat glioma (C6)). Extensive incorporation of radioactivity from [35S]cysteine into taurine was observed in rat glioma cells as well as in primary mouse astrocytes and neurons, establishing the presence of an intact taurine synthesis pathway in these cells. Interestingly, exposure of cells to cysteine or cysteamine resulted in elevated intracellular hypotaurine without a corresponding increase in taurine levels, suggesting that oxidation of hypotaurine limits taurine synthesis in cells. Consistent with its role as an organic osmolyte, taurine synthesis was stimulated under hypertonic conditions in neurons. PMID:21778230

Astrocytes mediated the nootropic and neurotrophic effects of Sarsasapogenin-AA13 via upregulating brain-derived neurotrophic factor.

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Dong, Dong; Mao, Yu; Huang, Cui; Jiao, Qian; Pan, Hui; Ma, Lei; Wang, Rui

2017-01-01

Rhizoma Anemarrhena , a widely used traditional Chinese medicine, has previously been shown to have neuroprotective effect. Sarsasapogenin-AA13 (AA13) is a novel synthetic derivative of Sarsasapogenin, which is extracted from Rhizoma Anemarrhena . The aim of this study is to investigate the nootropic and neurotrophic effects of AA13 and underlying mechanisms. In vitro , cell viability of rat primary astrocytes treated with AA13 and neurons cultured with conditioned medium of AA13-treated rat primary astrocytes was tested by MTT assays. In vivo , a pharmacological model of cognitive impairment induced by scopolamine was employed and spatial memory of the mice was assessed by Morris water maze. This study found that AA13 increased cell viability of primary astrocytes and AA13-treated astrocyte-conditioned medium enhanced the survival rate of primary neurons. Interestingly, AA13 markedly enhanced the level of BDNF in astrocytes. Furthermore, AA13 (6 mg/kg) improved the cognitive deficits in animal models (p<0.05) and BDNF and PSD95 levels were increased in brain. Therefore, we hypothesize that AA13 exerts nootropic and neurotrophic activities through astrocytes mediated upregulation of BDNF secretion. The results suggest that AA13 could be a potential compound for cognitive impairment after further research.

Deep brain stimulation results in local glutamate and adenosine release: investigation into the role of astrocytes.

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Tawfik, Vivianne L; Chang, Su-Youne; Hitti, Frederick L; Roberts, David W; Leiter, James C; Jovanovic, Svetlana; Lee, Kendall H

2010-08-01

Several neurological disorders are treated with deep brain stimulation; however, the mechanism underlying its ability to abolish oscillatory phenomena associated with diseases as diverse as Parkinson's disease and epilepsy remain largely unknown. To investigate the role of specific neurotransmitters in deep brain stimulation and determine the role of non-neuronal cells in its mechanism of action. We used the ferret thalamic slice preparation in vitro, which exhibits spontaneous spindle oscillations, to determine the effect of high-frequency stimulation on neurotransmitter release. We then performed experiments using an in vitro astrocyte culture to investigate the role of glial transmitter release in high-frequency stimulation-mediated abolishment of spindle oscillations. In this series of experiments, we demonstrated that glutamate and adenosine release in ferret slices was able to abolish spontaneous spindle oscillations. The glutamate release was still evoked in the presence of the Na channel blocker tetrodotoxin, but was eliminated with the vesicular H-ATPase inhibitor bafilomycin and the calcium chelator 2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid tetrakis acetoxymethyl ester. Furthermore, electrical stimulation of purified primary astrocytic cultures was able to evoke intracellular calcium transients and glutamate release, and bath application of 2-bis (2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid tetrakis acetoxymethyl ester inhibited glutamate release in this setting. Vesicular astrocytic neurotransmitter release may be an important mechanism by which deep brain stimulation is able to achieve clinical benefits.

Immune and inflammatory responses in the CNS : Modulation by astrocytes

DEFF Research Database (Denmark)

Penkowa, Milena; aschner, michael; hidalgo, juan

2008-01-01

Beyond their long-recognized support functions, astrocytes are active partners of neurons in processing information, synaptic integration, and production of trophic factors, just to name a few. Both microglia and astrocytes produce and secrete a number of cytokines, modulating and integrating...... the communication between hematogenous cells and resident cells of the central nervous system (CNS). This review will address (1) the functions of astrocytes in the normal brain and (2) their role in surveying noxious stimuli within the brain, with particular emphasis on astrocytic responses to damage or disease...

A neuron-astrocyte transistor-like model for neuromorphic dressed neurons.

Science.gov (United States)

Valenza, G; Pioggia, G; Armato, A; Ferro, M; Scilingo, E P; De Rossi, D

2011-09-01

Experimental evidences on the role of the synaptic glia as an active partner together with the bold synapse in neuronal signaling and dynamics of neural tissue strongly suggest to investigate on a more realistic neuron-glia model for better understanding human brain processing. Among the glial cells, the astrocytes play a crucial role in the tripartite synapsis, i.e. the dressed neuron. A well-known two-way astrocyte-neuron interaction can be found in the literature, completely revising the purely supportive role for the glia. The aim of this study is to provide a computationally efficient model for neuron-glia interaction. The neuron-glia interactions were simulated by implementing the Li-Rinzel model for an astrocyte and the Izhikevich model for a neuron. Assuming the dressed neuron dynamics similar to the nonlinear input-output characteristics of a bipolar junction transistor, we derived our computationally efficient model. This model may represent the fundamental computational unit for the development of real-time artificial neuron-glia networks opening new perspectives in pattern recognition systems and in brain neurophysiology. Copyright © 2011 Elsevier Ltd. All rights reserved.

Oxidative metabolism of astrocytes is not reduced in hepatic encephalopathy

DEFF Research Database (Denmark)

Iversen, Peter; Mouridsen, Kim; Hansen, Mikkel B

2014-01-01

In patients with impaired liver function and hepatic encephalopathy (HE), consistent elevations of blood ammonia concentration suggest a crucial role in the pathogenesis of HE. Ammonia and acetate are metabolized in brain both primarily in astrocytes. Here, we used dynamic [(11)C]acetate PET...... of the brain to measure the contribution of astrocytes to the previously observed reduction of brain oxidative metabolism in patients with liver cirrhosis and HE, compared to patients with cirrhosis without HE, and to healthy subjects. We used a new kinetic model to estimate uptake from blood to astrocytes...

Effect of long-term (2 years) exposure of mouse brains to global system for mobile communication (GSM) radiofrequency fields on astrocytic immunoreactivity.

Science.gov (United States)

Court-Kowalski, Stefan; Finnie, John W; Manavis, Jim; Blumbergs, Peter C; Helps, Stephen C; Vink, Robert

2015-04-01

This study was designed to determine whether long-term (2 years) brain exposure to mobile telephone radiofrequency (RF) fields produces any astrocytic activation as these glia react to a wide range of neural perturbations by astrogliosis. Using a purpose-designed exposure system at 900 MHz, mice were given a single, far-field whole body exposure at a specific absorption rate of 4 W/kg on five successive days per week for 104 weeks. Control mice were sham-exposed or freely mobile in a cage to control any stress caused by immobilization in the exposure module. Brains were perfusion-fixed with 4% paraformaldehyde and three coronal levels immunostained for glial fibrillary acidic protein (GFAP). These brain slices were then examined by light microscopy and the amount of this immunomarker quantified using a color deconvolution method. There was no change in astrocytic GFAP immunostaining in brains after long-term exposure to mobile telephony microwaves compared to control (sham-exposed or freely moving caged mice). It was concluded that long-term (2 years) exposure of murine brains to mobile telephone RF fields did not produce any astrocytic reaction (astrogliosis) detectable by GFAP immunostaining. © 2015 Wiley Periodicals, Inc.

ASTROCYTES IN THE NEUROPROTECTION AFTER BRAIN STROKE

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Gloria Patricia Cardona Gomez

2015-03-01

Full Text Available Astrocytes are specialized glial cells of the nervous system, which have multiple homeostatic functions for the survival and maintenance of the neurovascular unit. It has been shown that astrocytes have critical role in the dynamics pro survival conferring neuroprotective, angiogenic, immunomodulatory, neurogenic, antioxidants and regulatory synapse functions (Shen et al 2012; Gimsa et al 2013; Proschel et al 2014; making them excellent candidates as the source of neuroprotection and neurorestauration of tissue affected by events ischemia and / or reperfusion. However, these cells also may be involved in negative responses such as reactive astrocytes and glial scar under chronic excitotoxic responses generated by these events. To know what are the key points in the pro and anti-survival responses of astrocytes, would allow use them as targets in cellular therapies. This review has aim to study the mechanisms for neuroprotection in these cells (Posada-Duque et al submitted, which would make them targets of cell therapy, through of inducing regeneration, such as vehicle for corrective molecular systems and trigger endogenous cellular events that can recover the tissue homeostasis, which is lost after progressive damage.

Astrocytes at the Hub of the Stress Response: Potential Modulation of Neurogenesis by miRNAs in Astrocyte-Derived Exosomes.

Science.gov (United States)

Luarte, Alejandro; Cisternas, Pablo; Caviedes, Ariel; Batiz, Luis Federico; Lafourcade, Carlos; Wyneken, Ursula; Henzi, Roberto

2017-01-01

Repetitive stress negatively affects several brain functions and neuronal networks. Moreover, adult neurogenesis is consistently impaired in chronic stress models and in associated human diseases such as unipolar depression and bipolar disorder, while it is restored by effective antidepressant treatments. The adult neurogenic niche contains neural progenitor cells in addition to amplifying progenitors, neuroblasts, immature and mature neurons, pericytes, astrocytes, and microglial cells. Because of their particular and crucial position, with their end feet enwrapping endothelial cells and their close communication with the cells of the niche, astrocytes might constitute a nodal point to bridge or transduce systemic stress signals from peripheral blood, such as glucocorticoids, to the cells involved in the neurogenic process. It has been proposed that communication between astrocytes and niche cells depends on direct cell-cell contacts and soluble mediators. In addition, new evidence suggests that this communication might be mediated by extracellular vesicles such as exosomes, and in particular, by their miRNA cargo. Here, we address some of the latest findings regarding the impact of stress in the biology of the neurogenic niche, and postulate how astrocytic exosomes (and miRNAs) may play a fundamental role in such phenomenon.

Astrocytes at the Hub of the Stress Response: Potential Modulation of Neurogenesis by miRNAs in Astrocyte-Derived Exosomes

Directory of Open Access Journals (Sweden)

Alejandro Luarte

2017-01-01

Full Text Available Repetitive stress negatively affects several brain functions and neuronal networks. Moreover, adult neurogenesis is consistently impaired in chronic stress models and in associated human diseases such as unipolar depression and bipolar disorder, while it is restored by effective antidepressant treatments. The adult neurogenic niche contains neural progenitor cells in addition to amplifying progenitors, neuroblasts, immature and mature neurons, pericytes, astrocytes, and microglial cells. Because of their particular and crucial position, with their end feet enwrapping endothelial cells and their close communication with the cells of the niche, astrocytes might constitute a nodal point to bridge or transduce systemic stress signals from peripheral blood, such as glucocorticoids, to the cells involved in the neurogenic process. It has been proposed that communication between astrocytes and niche cells depends on direct cell-cell contacts and soluble mediators. In addition, new evidence suggests that this communication might be mediated by extracellular vesicles such as exosomes, and in particular, by their miRNA cargo. Here, we address some of the latest findings regarding the impact of stress in the biology of the neurogenic niche, and postulate how astrocytic exosomes (and miRNAs may play a fundamental role in such phenomenon.

Memory in astrocytes: a hypothesis

Directory of Open Access Journals (Sweden)

Caudle Robert M

2006-01-01

Full Text Available Abstract Background Recent work has indicated an increasingly complex role for astrocytes in the central nervous system. Astrocytes are now known to exchange information with neurons at synaptic junctions and to alter the information processing capabilities of the neurons. As an extension of this trend a hypothesis was proposed that astrocytes function to store information. To explore this idea the ion channels in biological membranes were compared to models known as cellular automata. These comparisons were made to test the hypothesis that ion channels in the membranes of astrocytes form a dynamic information storage device. Results Two dimensional cellular automata were found to behave similarly to ion channels in a membrane when they function at the boundary between order and chaos. The length of time information is stored in this class of cellular automata is exponentially related to the number of units. Therefore the length of time biological ion channels store information was plotted versus the estimated number of ion channels in the tissue. This analysis indicates that there is an exponential relationship between memory and the number of ion channels. Extrapolation of this relationship to the estimated number of ion channels in the astrocytes of a human brain indicates that memory can be stored in this system for an entire life span. Interestingly, this information is not affixed to any physical structure, but is stored as an organization of the activity of the ion channels. Further analysis of two dimensional cellular automata also demonstrates that these systems have both associative and temporal memory capabilities. Conclusion It is concluded that astrocytes may serve as a dynamic information sink for neurons. The memory in the astrocytes is stored by organizing the activity of ion channels and is not associated with a physical location such as a synapse. In order for this form of memory to be of significant duration it is necessary

In vitro evidence for the brain glutamate efflux hypothesis: brain endothelial cells cocultured with astrocytes display a polarized brain-to-blood transport of glutamate.

Science.gov (United States)

Helms, Hans Christian; Madelung, Rasmus; Waagepetersen, Helle Sønderby; Nielsen, Carsten Uhd; Brodin, Birger

2012-05-01

The concentration of the excitotoxic amino acid, L-glutamate, in brain interstitial fluid is tightly regulated by uptake transporters and metabolism in astrocytes and neurons. The aim of this study was to investigate the possible role of the blood-brain barrier endothelium in brain L-glutamate homeostasis. Transendothelial transport- and accumulation studies of (3) H-L-glutamate, (3) H-L-aspartate, and (3) H-D-aspartate in an electrically tight bovine endothelial/rat astrocyte blood-brain barrier coculture model were performed. After 6 days in culture, the endothelium displayed transendothelial resistance values of 1014 ± 70 Ω cm(2) , and (14) C-D-mannitol permeability values of 0.88 ± 0.13 × 10(-6) cm s(-1) . Unidirectional flux studies showed that L-aspartate and L-glutamate, but not D-aspartate, displayed polarized transport in the brain-to-blood direction, however, all three amino acids accumulated in the cocultures when applied from the abluminal side. The transcellular transport kinetics were characterized with a K(m) of 69 ± 15 μM and a J(max) of 44 ± 3.1 pmol min(-1) cm(-2) for L-aspartate and a K(m) of 138 ± 49 μM and J(max) of 28 ± 3.1 pmol min(-1) cm(-2) for L-glutamate. The EAAT inhibitor, DL-threo-ß-Benzyloxyaspartate, inhibited transendothelial brain-to-blood fluxes of L-glutamate and L-aspartate. Expression of EAAT-1 (Slc1a3), -2 (Slc1a2), and -3 (Slc1a1) mRNA in the endothelial cells was confirmed by conventional PCR and localization of EAAT-1 and -3 in endothelial cells was shown with immunofluorescence. Overall, the findings suggest that the blood-brain barrier itself may participate in regulating brain L-glutamate concentrations. Copyright © 2012 Wiley Periodicals, Inc.

Astrocyte Ca2+ signalling: an unexpected complexity

OpenAIRE

Volterra, Andrea; Liaudet, Nicolas; Savtchouk, Iaroslav

2014-01-01

Astrocyte Ca(2+) signalling has been proposed to link neuronal information in different spatial-temporal dimensions to achieve a higher level of brain integration. However, some discrepancies in the results of recent studies challenge this view and highlight key insufficiencies in our current understanding. In parallel, new experimental approaches that enable the study of astrocyte physiology at higher spatial-temporal resolution in intact brain preparations are beginning to reveal an unexpec...

Neocortical glial cell numbers in human brains

DEFF Research Database (Denmark)

Pelvig, D.P.; Pakkenberg, H.; Stark, A.K.

2008-01-01

Stereological cell counting was applied to post-mortem neocortices of human brains from 31 normal individuals, age 18-93 years, 18 females (average age 65 years, range 18-93) and 13 males (average age 57 years, range 19-87). The cells were differentiated in astrocytes, oligodendrocytes, microglia...... while the total astrocyte number is constant through life; finally males have a 28% higher number of neocortical glial cells and a 19% higher neocortical neuron number than females. The overall total number of neocortical neurons and glial cells was 49.3 billion in females and 65.2 billion in males...... and neurons and counting were done in each of the four lobes. The study showed that the different subpopulations of glial cells behave differently as a function of age; the number of oligodendrocytes showed a significant 27% decrease over adult life and a strong correlation to the total number of neurons...

Energy Metabolism of the Brain, Including the Cooperation between Astrocytes and Neurons, Especially in the Context of Glycogen Metabolism.

Science.gov (United States)

Falkowska, Anna; Gutowska, Izabela; Goschorska, Marta; Nowacki, Przemysław; Chlubek, Dariusz; Baranowska-Bosiacka, Irena

2015-10-29

Glycogen metabolism has important implications for the functioning of the brain, especially the cooperation between astrocytes and neurons. According to various research data, in a glycogen deficiency (for example during hypoglycemia) glycogen supplies are used to generate lactate, which is then transported to neighboring neurons. Likewise, during periods of intense activity of the nervous system, when the energy demand exceeds supply, astrocyte glycogen is immediately converted to lactate, some of which is transported to the neurons. Thus, glycogen from astrocytes functions as a kind of protection against hypoglycemia, ensuring preservation of neuronal function. The neuroprotective effect of lactate during hypoglycemia or cerebral ischemia has been reported in literature. This review goes on to emphasize that while neurons and astrocytes differ in metabolic profile, they interact to form a common metabolic cooperation.

Energy Metabolism of the Brain, Including the Cooperation between Astrocytes and Neurons, Especially in the Context of Glycogen Metabolism

OpenAIRE

Falkowska, Anna; Gutowska, Izabela; Goschorska, Marta; Nowacki, Przemys?aw; Chlubek, Dariusz; Baranowska-Bosiacka, Irena

2015-01-01

Glycogen metabolism has important implications for the functioning of the brain, especially the cooperation between astrocytes and neurons. According to various research data, in a glycogen deficiency (for example during hypoglycemia) glycogen supplies are used to generate lactate, which is then transported to neighboring neurons. Likewise, during periods of intense activity of the nervous system, when the energy demand exceeds supply, astrocyte glycogen is immediately converted to lactate, s...

Artificial Astrocytes Improve Neural Network Performance

Science.gov (United States)

Porto-Pazos, Ana B.; Veiguela, Noha; Mesejo, Pablo; Navarrete, Marta; Alvarellos, Alberto; Ibáñez, Oscar; Pazos, Alejandro; Araque, Alfonso

2011-01-01

Compelling evidence indicates the existence of bidirectional communication between astrocytes and neurons. Astrocytes, a type of glial cells classically considered to be passive supportive cells, have been recently demonstrated to be actively involved in the processing and regulation of synaptic information, suggesting that brain function arises from the activity of neuron-glia networks. However, the actual impact of astrocytes in neural network function is largely unknown and its application in artificial intelligence remains untested. We have investigated the consequences of including artificial astrocytes, which present the biologically defined properties involved in astrocyte-neuron communication, on artificial neural network performance. Using connectionist systems and evolutionary algorithms, we have compared the performance of artificial neural networks (NN) and artificial neuron-glia networks (NGN) to solve classification problems. We show that the degree of success of NGN is superior to NN. Analysis of performances of NN with different number of neurons or different architectures indicate that the effects of NGN cannot be accounted for an increased number of network elements, but rather they are specifically due to astrocytes. Furthermore, the relative efficacy of NGN vs. NN increases as the complexity of the network increases. These results indicate that artificial astrocytes improve neural network performance, and established the concept of Artificial Neuron-Glia Networks, which represents a novel concept in Artificial Intelligence with implications in computational science as well as in the understanding of brain function. PMID:21526157

Artificial astrocytes improve neural network performance.

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Ana B Porto-Pazos

Full Text Available Compelling evidence indicates the existence of bidirectional communication between astrocytes and neurons. Astrocytes, a type of glial cells classically considered to be passive supportive cells, have been recently demonstrated to be actively involved in the processing and regulation of synaptic information, suggesting that brain function arises from the activity of neuron-glia networks. However, the actual impact of astrocytes in neural network function is largely unknown and its application in artificial intelligence remains untested. We have investigated the consequences of including artificial astrocytes, which present the biologically defined properties involved in astrocyte-neuron communication, on artificial neural network performance. Using connectionist systems and evolutionary algorithms, we have compared the performance of artificial neural networks (NN and artificial neuron-glia networks (NGN to solve classification problems. We show that the degree of success of NGN is superior to NN. Analysis of performances of NN with different number of neurons or different architectures indicate that the effects of NGN cannot be accounted for an increased number of network elements, but rather they are specifically due to astrocytes. Furthermore, the relative efficacy of NGN vs. NN increases as the complexity of the network increases. These results indicate that artificial astrocytes improve neural network performance, and established the concept of Artificial Neuron-Glia Networks, which represents a novel concept in Artificial Intelligence with implications in computational science as well as in the understanding of brain function.

Artificial astrocytes improve neural network performance.

Science.gov (United States)

Porto-Pazos, Ana B; Veiguela, Noha; Mesejo, Pablo; Navarrete, Marta; Alvarellos, Alberto; Ibáñez, Oscar; Pazos, Alejandro; Araque, Alfonso

2011-04-19

Compelling evidence indicates the existence of bidirectional communication between astrocytes and neurons. Astrocytes, a type of glial cells classically considered to be passive supportive cells, have been recently demonstrated to be actively involved in the processing and regulation of synaptic information, suggesting that brain function arises from the activity of neuron-glia networks. However, the actual impact of astrocytes in neural network function is largely unknown and its application in artificial intelligence remains untested. We have investigated the consequences of including artificial astrocytes, which present the biologically defined properties involved in astrocyte-neuron communication, on artificial neural network performance. Using connectionist systems and evolutionary algorithms, we have compared the performance of artificial neural networks (NN) and artificial neuron-glia networks (NGN) to solve classification problems. We show that the degree of success of NGN is superior to NN. Analysis of performances of NN with different number of neurons or different architectures indicate that the effects of NGN cannot be accounted for an increased number of network elements, but rather they are specifically due to astrocytes. Furthermore, the relative efficacy of NGN vs. NN increases as the complexity of the network increases. These results indicate that artificial astrocytes improve neural network performance, and established the concept of Artificial Neuron-Glia Networks, which represents a novel concept in Artificial Intelligence with implications in computational science as well as in the understanding of brain function.

Subcellular location of astrocytic calcium stores favors extrasynaptic neuron-astrocyte communication.

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Patrushev, Ilya; Gavrilov, Nikolay; Turlapov, Vadim; Semyanov, Alexey

2013-11-01

Neuron-astrocyte interactions are important for brain computations and synaptic plasticity. Perisynaptic astrocytic processes (PAPs) contain a high density of transporters that are responsible for neurotransmitter clearance. Metabotropic glutamate receptors are thought to trigger Ca(2+) release from Ca(2+) stores in PAPs in response to synaptic activity. Our ultrastructural study revealed that PAPs are actually devoid of Ca(2+) stores and have a high surface-to-volume ratio favorable for uptake. Astrocytic processes containing Ca(2+) stores were located further away from the synapses and could therefore respond to changes in ambient glutamate. Thus, the anatomic data do not support communication involving Ca(2+) stores in tripartite synapses, but rather point to extrasynaptic communication. Copyright © 2013 Elsevier Ltd. All rights reserved.

Astrocyte morphology, heterogeneity and density in the developing African Giant Rat (Cricetomys gambianus

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James Olukayode Olopade

2015-05-01

Full Text Available Astrocyte morphologies and heterogeneity were described in male African giant rats (AGR (Cricetomys gambianus, Waterhouse across three age groups (5 neonates, 5 juveniles and 5 adults using Silver impregnation method and immunohistochemistry against glia fibrillary acidic protein (GFAP. Immunopositive cell signaling, cell size and population were least in neonates, followed by adults and juveniles respectively. In neonates, astrocyte processes were mostly detected within the glia limitans of the mid and hind brain; their cell bodies measuring 32±4.8 µm in diameter against 91±5.4µm and 75± 1.9µm in juveniles and adults respectively. Astrocyte heterogeneity in juvenile and adult groups revealed eight subtypes to include fibrous astrocytes chiefly in the corpus callosum and brain stem, protoplasmic astrocytes in the cortex and dentate gyrus (DG; radial glia were found along the olfactory bulb (OB and subventricular zone (SVZ; velate astrocytes were mainly found in the cerebellum and hippocampus; marginal astrocytes close to the pia mater; Bergmann glia in the molecular layer of the cerebellum; perivascular and periventricular astrocytes in the cortex and third ventricle respectively. Cell counts from twelve anatomical regions of the brain were significantly higher in juveniles than in adults (p≤0.01 using unpaired student t-test in the cerebral cortex, pia, corpus callosum, rostral migratory stream (RMS, DG and cerebellum. Highest astrocyte count was found in the DG, while the least count was in the brain stem and sub cortex. Astrocytes along the periventricular layer of the OB are believed to be part of the radial glia system that transport newly formed cells towards the hippocampus and play roles in neurogenesis migration and homeostasis in the AGR. Therefore, astrocyte heterogeneity was examined across age groups in the AGR to determine whether age influences astrocytes population in different regions of the AGR brain and discuss

RNA Localization in Astrocytes

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Thomsen, Rune

2012-01-01

, regulation of the blood brain barrier and glial scar tissue formation. Despite the involvement in various CNS functions only a limited number of studies have addressed mRNA localization in astrocytes. This PhD project was initially focused on developing and implementing methods that could be used to asses mRNA......Messenger RNA (mRNA) localization is a mechanism by which polarized cells can regulate protein synthesis to specific subcellular compartments in a spatial and temporal manner, and plays a pivotal role in multiple physiological processes from embryonic development to cell differentiation...... localization in astrocyte protrusions, and following look into the subcellular localization pattern of specific mRNA species of both primary astrocytes isolated from cortical hemispheres of newborn mice, and the mouse astrocyte cell line, C8S. The Boyden chamber cell fractionation assay was optimized, in a way...

Control of HIV replication in astrocytes by a family of highly conserved host proteins with a common Rev-interacting domain (Risp).

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Vincendeau, Michelle; Kramer, Susanne; Hadian, Kamyar; Rothenaigner, Ina; Bell, Jeanne; Hauck, Stefanie M; Bickel, Christian; Nagel, Daniel; Kremmer, Elisabeth; Werner, Thomas; Leib-Mösch, Christine; Brack-Werner, Ruth

2010-10-23

In human astrocytes, restriction of HIV replication involves inhibition of HIV Rev activity. We previously identified a Rev-interacting human protein fragment (16.4.1) that can reduce Rev activity. The 16.4.1 sequence is contained in a group of highly similar host cell proteins, which we call the Risp family. Here we investigate whether the Risp family is connected to HIV replication in astrocytes. Cell/tissue lysates were analyzed for Risp expression by western blot with various anti-Risp antibodies. The interaction of astrocytic Risp members with Rev was investigated by affinity chromatography. Astrocytes were transfected with expression plasmids containing cDNAs encoding full-length Risp or the isolated 16.4.1 region for Risp overexpression or with siRNAs designed for Risp knock-down. Rev activity was investigated with a Rev-reporter assay. RNA levels were quantified by real-time RT-PCR, HIV Gag levels by p24ELISA. Expression of the Risp family was demonstrated in human brain tissues and astrocytes. Astrocytes were shown to produce Risp family members that interact with Rev. Production of HIV Gag proteins and Rev-dependent RNAs in persistently infected astrocytes increased upon Risp knock-down and decreased upon Risp overexpression. Risp knock-down increased Rev activity and raised proportions of Rev proteins in the nucleus of astrocytes. Our results link the Risp family to restriction of HIV production and inhibition of Rev activity in astrocytes. We conclude that the Risp family represents a novel family of host factors that can control HIV replication and may be important for the containment of HIV infection in brain reservoirs.

Large-scale recording of astrocyte activity

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Nimmerjahn, Axel; Bergles, Dwight E.

2015-01-01

Astrocytes are highly ramified glial cells found throughout the central nervous system (CNS). They express a variety of neurotransmitter receptors that can induce widespread chemical excitation, placing these cells in an optimal position to exert global effects on brain physiology. However, the activity patterns of only a small fraction of astrocytes have been examined and techniques to manipulate their behavior are limited. As a result, little is known about how astrocytes modulate CNS function on synaptic, microcircuit, or systems levels. Here, we review current and emerging approaches for visualizing and manipulating astrocyte activity in vivo. Deciphering how astrocyte network activity is controlled in different physiological and pathological contexts is critical for defining their roles in the healthy and diseased CNS. PMID:25665733

Transcriptional profiling of human brain endothelial cells reveals key properties crucial for predictive in vitro blood-brain barrier models.

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Eduard Urich

Full Text Available Brain microvascular endothelial cells (BEC constitute the blood-brain barrier (BBB which forms a dynamic interface between the blood and the central nervous system (CNS. This highly specialized interface restricts paracellular diffusion of fluids and solutes including chemicals, toxins and drugs from entering the brain. In this study we compared the transcriptome profiles of the human immortalized brain endothelial cell line hCMEC/D3 and human primary BEC. We identified transcriptional differences in immune response genes which are directly related to the immortalization procedure of the hCMEC/D3 cells. Interestingly, astrocytic co-culturing reduced cell adhesion and migration molecules in both BECs, which possibly could be related to regulation of immune surveillance of the CNS controlled by astrocytic cells within the neurovascular unit. By matching the transcriptome data from these two cell lines with published transcriptional data from freshly isolated mouse BECs, we discovered striking differences that could explain some of the limitations of using cultured BECs to study BBB properties. Key protein classes such as tight junction proteins, transporters and cell surface receptors show differing expression profiles. For example, the claudin-5, occludin and JAM2 expression is dramatically reduced in the two human BEC lines, which likely explains their low transcellular electric resistance and paracellular leakiness. In addition, the human BEC lines express low levels of unique brain endothelial transporters such as Glut1 and Pgp. Cell surface receptors such as LRP1, RAGE and the insulin receptor that are involved in receptor-mediated transport are also expressed at very low levels. Taken together, these data illustrate that BECs lose their unique protein expression pattern outside of their native environment and display a more generic endothelial cell phenotype. A collection of key genes that seems to be highly regulated by the local

Astrocytic Gap Junctional Communication is Reduced in Amyloid-β-Treated Cultured Astrocytes, but not in Alzheimer's Disease Transgenic Mice

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Nancy F Cruz

2010-07-01

Full Text Available Alzheimer's disease is characterized by accumulation of amyloid deposits in brain, progressive cognitive deficits and reduced glucose utilization. Many consequences of the disease are attributed to neuronal dysfunction, but roles of astrocytes in its pathogenesis are not well understood. Astrocytes are extensively coupled via gap junctions, and abnormal trafficking of metabolites and signalling molecules within astrocytic syncytia could alter functional interactions among cells comprising the neurovascular unit. To evaluate the influence of amyloid-β on astrocyte gap junctional communication, cultured astrocytes were treated with monomerized amyloid-β1-40 (1 μmol/l for intervals ranging from 2 h to 5 days, and the areas labelled by test compounds were determined by impaling a single astrocyte with a micropipette and diffusion of material into coupled cells. Amyloid-β-treated astrocytes had rapid, sustained 50-70% reductions in the area labelled by Lucifer Yellow, anionic Alexa Fluor® dyes and energy-related compounds, 6-NBDG (a fluorescent glucose analogue, NADH and NADPH. Amyloid-β treatment also caused a transient increase in oxidative stress. In striking contrast with these results, spreading of Lucifer Yellow within astrocytic networks in brain slices from three regions of 8.5-14-month-old control and transgenic Alzheimer's model mice was variable, labelling 10-2000 cells; there were no statistically significant differences in the number of dye-labelled cells among the groups or with age. Thus amyloid-induced dysfunction of gap junctional communication in cultured astrocytes does not reflect the maintenance of dye transfer through astrocytic syncytial networks in transgenic mice; the pathophysiology of Alzheimer's disease is not appropriately represented by the cell culture system.

Astrocytic gap junctional communication is reduced in amyloid-β-treated cultured astrocytes, but not in Alzheimer's disease transgenic mice.

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Cruz, Nancy F; Ball, Kelly K; Dienel, Gerald A

2010-08-17

Alzheimer's disease is characterized by accumulation of amyloid deposits in brain, progressive cognitive deficits and reduced glucose utilization. Many consequences of the disease are attributed to neuronal dysfunction, but roles of astrocytes in its pathogenesis are not well understood. Astrocytes are extensively coupled via gap junctions, and abnormal trafficking of metabolites and signalling molecules within astrocytic syncytia could alter functional interactions among cells comprising the neurovascular unit. To evaluate the influence of amyloid-beta on astrocyte gap junctional communication, cultured astrocytes were treated with monomerized amyloid-β(1-40) (1 μmol/l) for intervals ranging from 2 h to 5 days, and the areas labelled by test compounds were determined by impaling a single astrocyte with a micropipette and diffusion of material into coupled cells. Amyloid-β-treated astrocytes had rapid, sustained 50-70% reductions in the area labelled by Lucifer Yellow, anionic Alexa Fluor® dyes and energy-related compounds, 6-NBDG (a fluorescent glucose analogue), NADH and NADPH. Amyloid-β treatment also caused a transient increase in oxidative stress. In striking contrast with these results, spreading of Lucifer Yellow within astrocytic networks in brain slices from three regions of 8.5-14-month-old control and transgenic Alzheimer's model mice was variable, labelling 10-2000 cells; there were no statistically significant differences in the number of dye-labelled cells among the groups or with age. Thus amyloid-induced dysfunction of gap junctional communication in cultured astrocytes does not reflect the maintenance of dye transfer through astrocytic syncytial networks in transgenic mice; the pathophysiology of Alzheimer's disease is not appropriately represented by the cell culture system.

Differences in distribution and regulation of astrocytic aquaporin-4 in human and rat hydrocephalic brain

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Skjolding, Anders Daehli; Holst, Anders Vedel; Broholm, Helle

2013-01-01

findings to human pathophysiology. This study compares expression of aquaporin-4 in hydrocephalic human brain with human controls and hydrocephalic rat brain. Methods:  Cortical biopsies from patients with chronic hydrocephalus (n=29) were sampled secondary to planned surgical intervention. Aquaporin-4...

Class I HDAC inhibition is a novel pathway for regulating astrocytic apoE secretion.

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Dresselhaus, Erica; Duerr, James M; Vincent, Fabien; Sylvain, Emily K; Beyna, Mercedes; Lanyon, Lorraine F; LaChapelle, Erik; Pettersson, Martin; Bales, Kelly R; Ramaswamy, Gayathri

2018-01-01

Despite the important role of apolipoprotein E (apoE) secretion from astrocytes in brain lipid metabolism and the strong association of apoE4, one of the human apoE isoforms, with sporadic and late onset forms of Alzheimer's disease (AD) little is known about the regulation of astrocytic apoE. Utilizing annotated chemical libraries and a phenotypic screening strategy that measured apoE secretion from a human astrocytoma cell line, inhibition of pan class I histone deacetylases (HDACs) was identified as a mechanism to increase apoE secretion. Knocking down select HDAC family members alone or in combination revealed that inhibition of the class I HDAC family was responsible for enhancing apoE secretion. Knocking down LXRα and LXRβ genes revealed that the increase in astrocytic apoE in response to HDAC inhibition occurred via an LXR-independent pathway. Collectively, these data suggest that pan class I HDAC inhibition is a novel pathway for regulating astrocytic apoE secretion.

Proteomics Analyses of Human Optic Nerve Head Astrocytes Following Biomechanical Strain*

OpenAIRE

Rogers, Ronan S.; Dharsee, Moyez; Ackloo, Suzanne; Sivak, Jeremy M.; Flanagan, John G.

2011-01-01

We investigate the role of glial cell activation in the human optic nerve caused by raised intraocular pressure, and their potential role in the development of glaucomatous optic neuropathy. To do this we present a proteomics study of the response of cultured, optic nerve head astrocytes to biomechanical strain, the magnitude and mode of strain based on previously published quantitative models. In this case, astrocytes were subjected to 3 and 12% stretches for either 2 h or 24 h. Proteomic me...

Kynurenine Pathway Metabolism is Involved in the Maintenance of the Intracellular NAD Concentration in Human Primary Astrocytes

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Ross Grant

2010-01-01

Full Text Available Efficient synthesis of NAD + is critical to maintaining cell viability in all organs of the body. However, little is known of the pathway(s by which cells of the central nervous system produce NAD + . The aim of this study was to investigate the relationship, between tryptophan degradation via the kynurenine pathway (KP and de novo NAD + synthesis in human astrocytes, a major cell type within the brain. In this study we observed that inhibition of single enzymes of the KP resulted in significant decreases in NAD + levels in astroglial cells after a 24 hr period. We also observed that astrocytes cultured in media deficient in tryptophan, nicotinic acid and nicotinamide resulted in a 50% decrease in NAD + levels after 24 hrs. This decrease in NAD + was partially restored by supplementation of the culture media with either tryptophan or kynurenine, or nicotinic acid or with supply of the salvage pathway precursor nicotinamide.

Kynurenine Pathway Metabolism is Involved in the Maintenance of the Intracellular NAD+ Concentration in Human Primary Astrocytes

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Grant, Ross; Nguyen, Susan; Guillemin, Gilles

2010-01-01

Efficient synthesis of NAD+ is critical to maintaining cell viability in all organs of the body. However, little is known of the pathway(s) by which cells of the central nervous system produce NAD+. The aim of this study was to investigate the relationship, between tryptophan degradation via the kynurenine pathway (KP) and de novo NAD+ synthesis in human astrocytes, a major cell type within the brain. In this study we observed that inhibition of single enzymes of the KP resulted in significant decreases in NAD+ levels in astroglial cells after a 24 hr period. We also observed that astrocytes cultured in media deficient in tryptophan, nicotinic acid and nicotinamide resulted in a 50% decrease in NAD+ levels after 24 hrs. This decrease in NAD+ was partially restored by supplementation of the culture media with either tryptophan or kynurenine, or nicotinic acid or with supply of the salvage pathway precursor nicotinamide. PMID:22084595

Hypoxia Epigenetically Confers Astrocytic Differentiation Potential on Human Pluripotent Cell-Derived Neural Precursor Cells

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Tetsuro Yasui

2017-06-01

Full Text Available Human neural precursor cells (hNPCs derived from pluripotent stem cells display a high propensity for neuronal differentiation, but they require long-term culturing to differentiate efficiently into astrocytes. The mechanisms underlying this biased fate specification of hNPCs remain elusive. Here, we show that hypoxia confers astrocytic differentiation potential on hNPCs through epigenetic gene regulation, and that this was achieved by cooperation between hypoxia-inducible factor 1α and Notch signaling, accompanied by a reduction of DNA methylation level in the promoter region of a typical astrocyte-specific gene, Glial fibrillary acidic protein. Furthermore, we found that this hypoxic culture condition could be applied to rapid generation of astrocytes from Rett syndrome patient-derived hNPCs, and that these astrocytes impaired neuronal development. Thus, our findings shed further light on the molecular mechanisms regulating hNPC differentiation and provide attractive tools for the development of therapeutic strategies for treating astrocyte-mediated neurological disorders.

Astrocytic actions on extrasynaptic neuronal currents

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Balazs ePal

2015-12-01

Full Text Available In the last few decades, knowledge about astrocytic functions has significantly increased. It was demonstrated that astrocytes are not passive elements of the central nervous system, but active partners of neurons. There is a growing body of knowledge about the calcium excitability of astrocytes, the actions of different gliotransmitters and their release mechanisms, as well as the participation of astrocytes in the regulation of synaptic functions and their contribution to synaptic plasticity. However, astrocytic functions are even more complex than being a partner of the 'tripartite synapse', as they can influence extrasynaptic neuronal currents either by releasing substances or regulating ambient neurotransmitter levels. Several types of currents or changes of membrane potential with different kinetics and via different mechanisms can be elicited by astrocytic activity. Astrocyte-dependent phasic or tonic, inward or outward currents were described in several brain areas. Such currents, together with the synaptic actions of astrocytes, can contribute to neuromodulatory mechanisms, neurosensory and –secretory processes, cortical oscillatory activity, memory and learning or overall neuronal excitability. This mini-review is an attempt to give a brief summary of astrocyte-dependent extrasynaptic neuronal currents and their possible functional significance.

Astrocytes in endocannabinoid signalling.

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Navarrete, Marta; Díez, Adolfo; Araque, Alfonso

2014-10-19

Astrocytes are emerging as integral functional components of synapses, responding to synaptically released neurotransmitters and regulating synaptic transmission and plasticity. Thus, they functionally interact with neurons establishing tripartite synapses: a functional concept that refers to the existence of communication between astrocytes and neurons and its crucial role in synaptic function. Here, we discuss recent evidence showing that astrocytes are involved in the endocannabinoid (ECB) system, responding to exogenous cannabinoids as well as ECBs through activation of type 1 cannabinoid receptors, which increase intracellular calcium and stimulate the release of glutamate that modulates synaptic transmission and plasticity. We also discuss the consequences of ECB signalling in tripartite synapses on the astrocyte-mediated regulation of synaptic function, which reveal novel properties of synaptic regulation by ECBs, such as the spatially controlled dual effect on synaptic strength and the lateral potentiation of synaptic efficacy. Finally, we discuss the potential implications of ECB signalling for astrocytes in brain pathology and animal behaviour. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Three-dimensional Ca2+ imaging advances understanding of astrocyte biology.

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Bindocci, Erika; Savtchouk, Iaroslav; Liaudet, Nicolas; Becker, Denise; Carriero, Giovanni; Volterra, Andrea

2017-05-19

Astrocyte communication is typically studied by two-dimensional calcium ion (Ca 2+ ) imaging, but this method has not yielded conclusive data on the role of astrocytes in synaptic and vascular function. We developed a three-dimensional two-photon imaging approach and studied Ca 2+ dynamics in entire astrocyte volumes, including during axon-astrocyte interactions. In both awake mice and brain slices, we found that Ca 2+ activity in an individual astrocyte is scattered throughout the cell, largely compartmented between regions, preponderantly local within regions, and heterogeneously distributed regionally and locally. Processes and endfeet displayed frequent fast activity, whereas the soma was infrequently active. In awake mice, activity was higher than in brain slices, particularly in endfeet and processes, and displayed occasional multifocal cellwide events. Astrocytes responded locally to minimal axonal firing with time-correlated Ca 2+ spots. Copyright © 2017, American Association for the Advancement of Science.

Expression of iron-related genes in human brain and brain tumors

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Britton Robert S

2009-04-01

Full Text Available Abstract Background Defective iron homeostasis may be involved in the development of some diseases within the central nervous system. Although the expression of genes involved in normal iron balance has been intensively studied in other tissues, little is known about their expression in the brain. We investigated the mRNA levels of hepcidin (HAMP, HFE, neogenin (NEO1, transferrin receptor 1 (TFRC, transferrin receptor 2 (TFR2, and hemojuvelin (HFE2 in normal human brain, brain tumors, and astrocytoma cell lines. The specimens included 5 normal brain tissue samples, 4 meningiomas, one medulloblastoma, 3 oligodendrocytic gliomas, 2 oligoastrocytic gliomas, 8 astrocytic gliomas, and 3 astrocytoma cell lines. Results Except for hemojuvelin, all genes studied had detectable levels of mRNA. In most tumor types, the pattern of gene expression was diverse. Notable findings include high expression of transferrin receptor 1 in the hippocampus and medulla oblongata compared to other brain regions, low expression of HFE in normal brain with elevated HFE expression in meningiomas, and absence of hepcidin mRNA in astrocytoma cell lines despite expression in normal brain and tumor specimens. Conclusion These results indicate that several iron-related genes are expressed in normal brain, and that their expression may be dysregulated in brain tumors.

α-Synuclein transfer between neurons and astrocytes indicates that astrocytes play a role in degradation rather than in spreading.

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Loria, Frida; Vargas, Jessica Y; Bousset, Luc; Syan, Sylvie; Salles, Audrey; Melki, Ronald; Zurzolo, Chiara

2017-11-01

Recent evidence suggests that disease progression in Parkinson's disease (PD) could occur by the spreading of α-synuclein (α-syn) aggregates between neurons. Here we studied the role of astrocytes in the intercellular transfer and fate of α-syn fibrils, using in vitro and ex vivo models. α-Syn fibrils can be transferred to neighboring cells; however, the transfer efficiency changes depending on the cell types. We found that α-syn is efficiently transferred from astrocytes to astrocytes and from neurons to astrocytes, but less efficiently from astrocytes to neurons. Interestingly, α-syn puncta are mainly found inside the lysosomal compartments of the recipient cells. However, differently from neurons, astrocytes are able to efficiently degrade fibrillar α-syn, suggesting an active role for these cells in clearing α-syn deposits. Astrocytes co-cultured with organotypic brain slices are able to take up α-syn fibrils from the slices. Altogether our data support a role for astrocytes in trapping and clearing α-syn pathological deposits in PD.

Adrenoceptors in Brain: Cellular Gene Expression and Effects on Astrocytic Metabolism and [Ca2+]i

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Hertz, Leif; Lovatt, Ditte; Goldman, Steven A.; Nedergaard, Maiken

2010-01-01

Recent in vivo studies have established astrocytes as a major target for locus coeruleus activation (Bekar et al., Cereb. Cortex 18, 2789–2795), renewing interest in cell culture studies on noradrenergic effects on astrocytes in primary cultures and calling for additional information about the expression of adrenoceptor subtypes on different types of brain cells. In the present communication, mRNA expression of α1-, α2- and β-adrenergic receptors and their subtypes was determined in freshly-isolated, cell marker-defined populations of astrocytes, NG2-positive cells, microglia, endothelial cells, and Thy1-positive neurons (mainly glutamatergic projection neurons) in murine cerebral cortex. Immediately after dissection of frontal, parietal and occipital cortex of 10–12-week-old transgenic mice, which combined each cell-type marker with a specific fluorescent signal, the tissue was digested, triturated and centrifuged, yielding a solution of dissociated cells of all types, which were separated by fluorescence-activated cell sorting (FACS). mRNA expression in each cell fraction was determined by microarray analysis. α1A-Receptors were unequivocally expressed in astrocytes and NG2-positive cells, but absent in other cell types, and α1B-receptors were not expressed in any cell population. Among α2-receptors only α2A-receptors were expressed, unequivocally in astrocytes and NG-positive cells, tentatively in microglia and questionably in Thy1-positive neurons and endothelial cells. β1-Receptors were unequivocally expressed in astrocytes, tentatively in microglia, and questionably in neurons and endothelial cells, whereas β2-adrenergic receptors showed tentative expression in neurons and astrocytes and unequivocal expression in other cell types. This distribution was supported by immunochemical data and its relevance established by previous studies in well-differentiated primary cultures of mouse astrocytes, showing that stimulation of α2-adrenoceptors

Complete Neuron-Astrocyte Interaction Model: Digital Multiplierless Design and Networking Mechanism.

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Haghiri, Saeed; Ahmadi, Arash; Saif, Mehrdad

2017-02-01

Glial cells, also known as neuroglia or glia, are non-neuronal cells providing support and protection for neurons in the central nervous system (CNS). They also act as supportive cells in the brain. Among a variety of glial cells, the star-shaped glial cells, i.e., astrocytes, are the largest cell population in the brain. The important role of astrocyte such as neuronal synchronization, synaptic information regulation, feedback to neural activity and extracellular regulation make the astrocytes play a vital role in brain disease. This paper presents a modified complete neuron-astrocyte interaction model that is more suitable for efficient and large scale biological neural network realization on digital platforms. Simulation results show that the modified complete interaction model can reproduce biological-like behavior of the original neuron-astrocyte mechanism. The modified interaction model is investigated in terms of digital realization feasibility and cost targeting a low cost hardware implementation. Networking behavior of this interaction is investigated and compared between two cases: i) the neuron spiking mechanism without astrocyte effects, and ii) the effect of astrocyte in regulating the neurons behavior and synaptic transmission via controlling the LTP and LTD processes. Hardware implementation on FPGA shows that the modified model mimics the main mechanism of neuron-astrocyte communication with higher performance and considerably lower hardware overhead cost compared with the original interaction model.

The endo-lysosomal system of brain endothelial cells is influenced by astrocytes in vitro

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Toth, Andrea E; Siupka, Piotr; P Augustine, Thomas J

2018-01-01

Receptor- and adsorptive-mediated transport through brain endothelial cells (BEC) of the blood-brain barrier (BBB) involves a complex array of subcellular vesicular structures, the endo-lysosomal system. It consists of several types of vesicles, such as early, recycling, and late endosomes......, retromer-positive structures, and lysosomes. Since this system is important for receptor-mediated transcytosis of drugs across brain capillaries, our aim was to characterise the endo-lysosomal system in BEC with emphasis on their interactions with astrocytes. We used primary porcine BEC in monoculture....... Altogether, our data pin-point unique features of BEC trafficking network, essentially mapping the endo-lysosomal system of in vitro BBB models. Consequently, our findings constitute a valuable basis for planning the optimal route across the BBB when advancing drug delivery to the brain....

Computational model of neuron-astrocyte interactions during focal seizure generation

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Davide eReato

2012-10-01

Full Text Available Empirical research in the last decade revealed that astrocytes can respond to neurotransmitters with Ca2+ elevations and generate feedback signals to neurons which modulate synaptic transmission and neuronal excitability. This discovery changed our basic understanding of brain function and provided new perspectives for how astrocytes can participate not only to information processing, but also to the genesis of brain disorders, such as epilepsy. Epilepsy is a neurological disorder characterized by recurrent seizures that can arise focally at restricted areas and propagate throughout the brain. Studies in brain slice models suggest that astrocytes contribute to epileptiform activity by increasing neuronal excitability through a Ca2+-dependent release of glutamate. The underlying mechanism remains, however, unclear. In this study, we implemented a parsimonious network model of neurons and astrocytes. The model consists of excitatory and inhibitory neurons described by Izhikevich's neuron dynamics. The experimentally observed Ca2+ change in astrocytes in response to neuronal activity was modeled with linear equations. We considered that glutamate is released from astrocytes above certain intracellular Ca2+ concentrations thus providing a non-linear positive feedback signal to neurons. Propagating seizure-like ictal discharges (IDs were reliably evoked in our computational model by repeatedly exciting a small area of the network, which replicates experimental results in a slice model of focal ID in entorhinal cortex. We found that the threshold of focal ID generation was lowered when an excitatory feedback-loop between astrocytes and neurons was included. Simulations show that astrocytes can contribute to ID generation by directly affecting the excitatory/inhibitory balance of the neuronal network. Our model can be used to obtain mechanistic insights into the distinct contributions of the different signaling pathways to the generation and

Unravelling and Exploiting Astrocyte Dysfunction in Huntington's Disease

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Khakh, Baljit S.; Beaumont, Vahri; Cachope, Roger

2017-01-01

Astrocytes are abundant within mature neural circuits and are involved in brain disorders. Here, we summarize our current understanding of astrocytes and Huntington's disease (HD), with a focus on correlative and causative dysfunctions of ion homeostasis, calcium signaling, and neurotransmitter...

Decreased STAT3 Phosphorylation Mediates Cell Swelling in Ammonia-Treated Astrocyte Cultures

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Arumugam R. Jayakumar

2016-12-01

Full Text Available Brain edema, due largely to astrocyte swelling, and the subsequent increase in intracranial pressure and brain herniation, are major complications of acute liver failure (ALF. Elevated level of brain ammonia has been strongly implicated in the development of astrocyte swelling associated with ALF. The means by which ammonia brings about astrocyte swelling, however, is incompletely understood. Recently, oxidative/nitrosative stress and associated signaling events, including activation of mitogen-activated protein kinases (MAPKs, as well as activation of the transcription factor, nuclear factor-kappaB (NF-κB, have been implicated in the mechanism of ammonia-induced astrocyte swelling. Since these signaling events are known to be regulated by the transcription factor, signal transducer and activator of transcription 3 (STAT3, we examined the state of STAT3 activation in ammonia-treated cultured astrocytes, and determined whether altered STAT3 activation and/or protein expression contribute to the ammonia-induced astrocyte swelling. STAT3 was found to be dephosphorylated (inactivated at Tyrosine705 in ammonia-treated cultured astrocytes. Total STAT3 protein level was also reduced in ammonia-treated astrocytes. We also found a significant increase in protein tyrosine phosphatase receptor type-1 (PTPRT-1 protein expression in ammonia-treated cultured astrocytes, and that inhibition of PTPRT-1 enhanced the phosphorylation of STAT3 after ammonia treatment. Additionally, exposure of cultured astrocytes to inhibitors of protein tyrosine phosphatases diminished the ammonia-induced cell swelling, while cultured astrocytes over-expressing STAT3 showed a reduction in the astrocyte swelling induced by ammonia. Collectively, these studies strongly suggest that inactivation of STAT3 represents a critical event in the mechanism of the astrocyte swelling associated with acute liver failure.

Involvement of astrocytes in neurovascular communication.

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Nuriya, M; Hirase, H

2016-01-01

The vascular interface of the brain is distinct from that of the peripheral tissue in that astrocytes, the most numerous glial cell type in the gray matter, cover the vasculature with their endfeet. This morphological feature of the gliovascular junction has prompted neuroscientists to suggest possible functional roles of astrocytes including astrocytic modulation of the vasculature. Additionally, astrocytes develop an intricate morphology that intimately apposes neuronal synapses, making them an ideal cellular mediator of neurovascular coupling. In this article, we first introduce the classical anatomical and physiological findings that led to the proposal of various gliovascular interaction models. Next, we touch on the technological advances in the past few decades that enabled investigations and evaluations of neuro-glio-vascular interactions in situ. We then review recent experimental findings on the roles of astrocytes in neurovascular coupling from the viewpoints of intra- and intercellular signalings in astrocytes. © 2016 Elsevier B.V. All rights reserved.

Immune and Inflammatory Responses in the Central Nervous System: Modulation by Astrocytes

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Penkowa, Milena; hidalgo, juan; aschner, michael

2008-01-01

Beyond their long-recognized support functions, astrocytes are active partners of neurons in processing information, synaptic integration, and production of trophic factors, just to name a few. Both microglia and astrocytes produce and secrete a number of cytokines, modulating and integrating...... the communication between hematogenous cells and resident cells of the central nervous system (CNS). This review will address (1) the functions of astrocytes in the normal brain and (2) their role in surveying noxious stimuli within the brain, with particular emphasis on astrocytic responses to damage or disease...

Glucose and Intermediary Metabolism and Astrocyte-Neuron Interactions Following Neonatal Hypoxia-Ischemia in Rat.

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Brekke, Eva; Berger, Hester Rijkje; Widerøe, Marius; Sonnewald, Ursula; Morken, Tora Sund

2017-01-01

Neonatal hypoxia-ischemia (HI) and the delayed injury cascade that follows involve excitotoxicity, oxidative stress and mitochondrial failure. The susceptibility to excitotoxicity of the neonatal brain may be related to the capacity of astrocytes for glutamate uptake. Furthermore, the neonatal brain is vulnerable to oxidative stress, and the pentose phosphate pathway (PPP) may be of particular importance for limiting this kind of injury. Also, in the neonatal brain, neurons depend upon de novo synthesis of neurotransmitters via pyruvate carboxylase in astrocytes to increase neurotransmitter pools during normal brain development. Several recent publications describing intermediary brain metabolism following neonatal HI have yielded interesting results: (1) Following HI there is a prolonged depression of mitochondrial metabolism in agreement with emerging evidence of mitochondria as vulnerable targets in the delayed injury cascade. (2) Astrocytes, like neurons, are metabolically impaired following HI, and the degree of astrocytic malfunction may be an indicator of the outcome following hypoxic and hypoxic-ischemic brain injury. (3) Glutamate transfer from neurons to astrocytes is not increased following neonatal HI, which may imply that astrocytes fail to upregulate glutamate uptake in response to the massive glutamate release during HI, thus contributing to excitotoxicity. (4) In the neonatal brain, the activity of the PPP is reduced following HI, which may add to the susceptibility of the neonatal brain to oxidative stress. The present review aims to discuss the metabolic temporal alterations observed in the neonatal brain following HI.

Characterisation of an in vitro blood-brain barrier model based on primary porcine capillary endothelial cells in monoculture or co-culture with primary rat or porcine astrocytes and pericytes

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Thomsen, Louiza Bohn; Larsen, Annette Burkhart; Moos, Torben

to in vivo such as efflux transporters, tight junction proteins, and high transendothelial electric resistance (TEER). Primary BCECs are isolated from a variety of mammals such as rats, mice, cattle and pigs. Often bovine and porcine BCECs are cultured in monoculture or in co-culture with rat astrocytes......In vitro blood-brain barrier (BBB) models based on primary brain capillary endothelial cells (BCECs) in monoculture or in co-culture with primary astrocytes and pericytes are often applied for studying physiology of the BBB. Primary BCECs retain many morphological and biochemical properties similar...... obtained from neonatal rats which have been shown to strengthen the barrier properties of the BCECs. In this study, brain endothelial cells (PBECs), astrocytes and pericytes are isolated from pig brains donated by the local abattoir. The brains are from 6 month old domestic pigs. The availability and high...

Human T-cell lymphotropic virus type 1-infected T lymphocytes impair catabolism and uptake of glutamate by astrocytes via Tax-1 and tumor necrosis factor alpha.

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Szymocha, R; Akaoka, H; Dutuit, M; Malcus, C; Didier-Bazes, M; Belin, M F; Giraudon, P

2000-07-01

Human T-cell lymphotropic virus type 1 (HTLV-1) is the causative agent of a chronic progressive myelopathy called tropical spastic paraparesis/HTLV-1-associated myelopathy (TSP/HAM). In this disease, lesions of the central nervous system (CNS) are associated with perivascular infiltration by lymphocytes. We and others have hypothesized that these T lymphocytes infiltrating the CNS may play a prominent role in TSP/HAM. Here, we show that transient contact of human or rat astrocytes with T lymphocytes chronically infected by HTLV-1 impairs some of the major functions of brain astrocytes. Uptake of extracellular glutamate by astrocytes was significantly decreased after transient contact with infected T cells, while the expression of the glial transporters GLAST and GLT-1 was decreased. In two-compartment cultures avoiding direct cell-to-cell contact, similar results were obtained, suggesting possible involvement of soluble factors, such as cytokines and the viral protein Tax-1. Recombinant Tax-1 and tumor necrosis factor alpha (TNF-alpha) decreased glutamate uptake by astrocytes. Tax-1 probably acts by inducing TNF-alpha, as the effect of Tax-1 was abolished by anti-TNF-alpha antibody. The expression of glutamate-catabolizing enzymes in astrocytes was increased for glutamine synthetase and decreased for glutamate dehydrogenase, the magnitudes of these effects being correlated with the level of Tax-1 transcripts. In conclusion, Tax-1 and cytokines produced by HTLV-1-infected T cells impair the ability of astrocytes to manage the steady-state level of glutamate, which in turn may affect neuronal and oligodendrocytic functions and survival.

Brain alanine formation as an ammonia-scavenging pathway during hyperammonemia: effects of glutamine synthetase inhibition in rats and astrocyte-neuron co-cultures.

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Dadsetan, Sherry; Kukolj, Eva; Bak, Lasse K; Sørensen, Michael; Ott, Peter; Vilstrup, Hendrik; Schousboe, Arne; Keiding, Susanne; Waagepetersen, Helle S

2013-08-01

Hyperammonemia is a major etiological toxic factor in the development of hepatic encephalopathy. Brain ammonia detoxification occurs primarily in astrocytes by glutamine synthetase (GS), and it has been proposed that elevated glutamine levels during hyperammonemia lead to astrocyte swelling and cerebral edema. However, ammonia may also be detoxified by the concerted action of glutamate dehydrogenase (GDH) and alanine aminotransferase (ALAT) leading to trapping of ammonia in alanine, which in vivo likely leaves the brain. Our aim was to investigate whether the GS inhibitor methionine sulfoximine (MSO) enhances incorporation of (15)NH4(+) in alanine during acute hyperammonemia. We observed a fourfold increased amount of (15)NH4 incorporation in brain alanine in rats treated with MSO. Furthermore, co-cultures of neurons and astrocytes exposed to (15)NH4Cl in the absence or presence of MSO demonstrated a dose-dependent incorporation of (15)NH4 into alanine together with increased (15)N incorporation in glutamate. These findings provide evidence that ammonia is detoxified by the concerted action of GDH and ALAT both in vivo and in vitro, a mechanism that is accelerated in the presence of MSO thereby reducing the glutamine level in brain. Thus, GS could be a potential drug target in the treatment of hyperammonemia in patients with hepatic encephalopathy.

Disruption of astrocyte-neuron cholesterol cross talk affects neuronal function in Huntington's disease.

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Valenza, M; Marullo, M; Di Paolo, E; Cesana, E; Zuccato, C; Biella, G; Cattaneo, E

2015-04-01

In the adult brain, neurons require local cholesterol production, which is supplied by astrocytes through apoE-containing lipoproteins. In Huntington's disease (HD), such cholesterol biosynthesis in the brain is severely reduced. Here we show that this defect, occurring in astrocytes, is detrimental for HD neurons. Astrocytes bearing the huntingtin protein containing increasing CAG repeats secreted less apoE-lipoprotein-bound cholesterol in the medium. Conditioned media from HD astrocytes and lipoprotein-depleted conditioned media from wild-type (wt) astrocytes were equally detrimental in a neurite outgrowth assay and did not support synaptic activity in HD neurons, compared with conditions of cholesterol supplementation or conditioned media from wt astrocytes. Molecular perturbation of cholesterol biosynthesis and efflux in astrocytes caused similarly altered astrocyte-neuron cross talk, whereas enhancement of glial SREBP2 and ABCA1 function reversed the aspects of neuronal dysfunction in HD. These findings indicate that astrocyte-mediated cholesterol homeostasis could be a potential therapeutic target to ameliorate neuronal dysfunction in HD.

Glutamate mediated astrocytic filtering of neuronal activity.

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Gilad Wallach

2014-12-01

Full Text Available Neuron-astrocyte communication is an important regulatory mechanism in various brain functions but its complexity and role are yet to be fully understood. In particular, the temporal pattern of astrocyte response to neuronal firing has not been fully characterized. Here, we used neuron-astrocyte cultures on multi-electrode arrays coupled to Ca2+ imaging and explored the range of neuronal stimulation frequencies while keeping constant the amount of stimulation. Our results reveal that astrocytes specifically respond to the frequency of neuronal stimulation by intracellular Ca2+ transients, with a clear onset of astrocytic activation at neuron firing rates around 3-5 Hz. The cell-to-cell heterogeneity of the astrocyte Ca2+ response was however large and increasing with stimulation frequency. Astrocytic activation by neurons was abolished with antagonists of type I metabotropic glutamate receptor, validating the glutamate-dependence of this neuron-to-astrocyte pathway. Using a realistic biophysical model of glutamate-based intracellular calcium signaling in astrocytes, we suggest that the stepwise response is due to the supralinear dynamics of intracellular IP3 and that the heterogeneity of the responses may be due to the heterogeneity of the astrocyte-to-astrocyte couplings via gap junction channels. Therefore our results present astrocyte intracellular Ca2+ activity as a nonlinear integrator of glutamate-dependent neuronal activity.

Glutamate Mediated Astrocytic Filtering of Neuronal Activity

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Herzog, Nitzan; De Pittà, Maurizio; Jacob, Eshel Ben; Berry, Hugues; Hanein, Yael

2014-01-01

Neuron-astrocyte communication is an important regulatory mechanism in various brain functions but its complexity and role are yet to be fully understood. In particular, the temporal pattern of astrocyte response to neuronal firing has not been fully characterized. Here, we used neuron-astrocyte cultures on multi-electrode arrays coupled to Ca2+ imaging and explored the range of neuronal stimulation frequencies while keeping constant the amount of stimulation. Our results reveal that astrocytes specifically respond to the frequency of neuronal stimulation by intracellular Ca2+ transients, with a clear onset of astrocytic activation at neuron firing rates around 3-5 Hz. The cell-to-cell heterogeneity of the astrocyte Ca2+ response was however large and increasing with stimulation frequency. Astrocytic activation by neurons was abolished with antagonists of type I metabotropic glutamate receptor, validating the glutamate-dependence of this neuron-to-astrocyte pathway. Using a realistic biophysical model of glutamate-based intracellular calcium signaling in astrocytes, we suggest that the stepwise response is due to the supralinear dynamics of intracellular IP3 and that the heterogeneity of the responses may be due to the heterogeneity of the astrocyte-to-astrocyte couplings via gap junction channels. Therefore our results present astrocyte intracellular Ca2+ activity as a nonlinear integrator of glutamate-dependent neuronal activity. PMID:25521344

Astrocytes, therapeutic targets for neuroprotection and neurorestoration in ischemic stroke

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Liu, Zhongwu; Chopp, Michael

2015-01-01

Astrocytes are the most abundant cell type within the central nervous system. They play essential roles in maintaining normal brain function, as they are a critical structural and functional part of the tripartite synapses and the neurovascular unit, and communicate with neurons, oligodendrocytes and endothelial cells. After an ischemic stroke, astrocytes perform multiple functions both detrimental and beneficial, for neuronal survival during the acute phase. Aspects of the astrocytic inflammatory response to stroke may aggravate the ischemic lesion, but astrocytes also provide benefit for neuroprotection, by limiting lesion extension via anti-excitotoxicity effects and releasing neurotrophins. Similarly, during the late recovery phase after stroke, the glial scar may obstruct axonal regeneration and subsequently reduce the functional outcome; however, astrocytes also contribute to angiogenesis, neurogenesis, synaptogenesis, and axonal remodeling, and thereby promote neurological recovery. Thus, the pivotal involvement of astrocytes in normal brain function and responses to an ischemic lesion designates them as excellent therapeutic targets to improve functional outcome following stroke. In this review, we will focus on functions of astrocytes and astrocyte-mediated events during stroke and recovery. We will provide an overview of approaches on how to reduce the detrimental effects and amplify the beneficial effects of astrocytes on neuroprotection and on neurorestoration post stroke, which may lead to novel and clinically relevant therapies for stroke. PMID:26455456

Astrocyte regulation of sleep circuits: experimental and modeling perspectives

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Tommaso eFellin

2012-08-01

Full Text Available Integrated within neural circuits, astrocytes have recently been shown to modulate brain rhythms thought to mediate sleep function. Experimental evidence suggests that local impact of astrocytes on single synapses translates into global modulation of neuronal networks and behavior. We discuss these findings in the context of current conceptual models of sleep generation and function, each of which have historically focused on neural mechanisms. We highlight the implications and the challenges introduced by these results from a conceptual and computational perspective. We further provide modeling directions on how these data might extend our knowledge of astrocytic properties and sleep function. Given our evolving understanding of how local cellular activities during sleep lead to functional outcomes for the brain, further mechanistic and theoretical understanding of astrocytic contribution to these dynamics will undoubtedly be of great basic and translational benefit.

[Mechanism of potassium channel in hypoxia-ischemic brain edema: experiment with neonatal rat astrocyte].

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Fu, Xue-mei; Xiang, Long; Liao, Da-qing; Feng, Zhi-chun; Mu, De-zhi

2008-11-04

To investigate the mechanism of potassium channel in brain edema caused by hypoxia-ischemia (HI). Astrocytes were obtained from 3-day-old SD rats, cultured, and randomly divided into 2 groups: normoxia group, cultured under normoxic condition, and hypoxic-ischemic group, cultured under hypoxic-ischemic condition. The cell volume was measured by radiologic method. Patch-clamp technique was used to observe the electric physiological properties of the voltage-gated potassium channels (Kv) in a whole cell configuration, and the change of voltage-gated potassium channel current (IKv) was recorded in cultured neonatal rat astrocyte during HI. Aquaporin 4 (AQP4) expression vector was constructed from pSUPER vector and transfected into the astrocytes (AQP4 RNAi) to construct AQP4 knockdown (AQP4-/-) cells. cellular volume was determined using [3H]-3-O-methyl-D-glucose uptake in both AQP4-/- and AQP4+/+ cells under the condition of HI. Real time PCR and Western blotting were used to detect the mRNA and protein expression of AQP4. The percentages of the AQP4+/+ and AQP4-/- astrocyte volumes in the condition of HI for 0.5, 1, 2, and 4 h were 104+/-7, 109+/-6, 126+/-12, and 152+/-9 times, and 97+/-7, 105+/-9, 109+/-7, and 132+/-6 times as those of their corresponding control groups (all Pastrocytes significantly increased during HI and the degrees of edema mediated by AQP4 knockdown at different time points were all significantly milder (all Pastrocytes via aquaporin-4 and then cell swelling.

Electrical coupling between hippocampal astrocytes in rat brain slices.

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Meme, William; Vandecasteele, Marie; Giaume, Christian; Venance, Laurent

2009-04-01

Gap junctions in astrocytes play a crucial role in intercellular communication by supporting both biochemical and electrical coupling between adjacent cells. Despite the critical role of electrical coupling in the network organization of these glial cells, the electrophysiological properties of gap junctions have been characterized in cultures while no direct evidence has been sought in situ. In the present study, gap-junctional currents were investigated using simultaneous dual whole-cell patch-clamp recordings between astrocytes from rat hippocampal slices. Bidirectional electrotonic coupling was observed in 82% of the cell pairs with an average coupling coefficient of 5.1%. Double patch-clamp analysis indicated that junctional currents were independent of the transjunctional voltage over a range from -100 to +110 mV. Interestingly, astrocytic electrical coupling displayed weak low-pass filtering properties compared to neuronal electrical synapses. Finally, during uncoupling processes triggered by either the gap-junction inhibitor carbenoxolone or endothelin-1, an increase in the input resistance in the injected cell paralleled the decrease in the coupling coefficient. Altogether, these results demonstrate that hippocampal astrocytes are electrically coupled through gap-junction channels characterized by properties that are distinct from those of electrical synapses between neurons. In addition, gap-junctional communication is efficiently regulated by endogenous compounds. This is taken to represent a mode of communication that may have important implications for the functional role of astrocyte networks in situ.

Glycine Receptor Activation Impairs ATP-Induced Calcium Transients in Cultured Cortical Astrocytes

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Tatiana P. Morais

2018-01-01

Full Text Available In central nervous system, glycine receptor (GlyR is mostly expressed in the spinal cord and brainstem, but glycinergic transmission related elements have also been identified in the brain. Astrocytes are active elements at the tripartite synapse, being responsible for the maintenance of brain homeostasis and for the fine-tuning of synaptic activity. These cells communicate, spontaneously or in response to a stimulus, by elevations in their cytosolic calcium (calcium transients, Ca2+T that can be propagated to other cells. How these Ca2+T are negatively modulated is yet poorly understood. In this work, we evaluated GlyR expression and its role on calcium signaling modulation in rat brain astrocytes. We first proved that GlyR, predominantly subunits α2 and β, was expressed in brain astrocytes and its localization was confirmed in the cytoplasm and astrocytic processes by immunohistochemistry assays. Calcium imaging experiments in cultured astrocytes showed that glycine (500 μM, a GlyR agonist, caused a concentration-dependent reduction in ATP-induced Ca2+T, an effect abolished by the GlyR antagonist, strychnine (0.8 μM, as well as by nocodazole (1 μM, known to impair GlyR anchorage to the plasma membrane. This effect was mimicked by activation of GABAAR, another Cl--permeable channel. In summary, we demonstrated that GlyR activation in astrocytes mediates an inhibitory effect upon ATP induced Ca2+T, which most probably involves changes in membrane permeability to Cl- and requires GlyR anchorage at the plasma membrane. GlyR in astrocytes may thus be part of a mechanism to modulate astrocyte-to-neuron communication.

Functional alterations of astrocytes in mental disorders: pharmacological significance as a drug target

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Yutaka eKoyama

2015-07-01

Full Text Available Astrocytes play an essential role in supporting brain functions in physiological and pathological states. Modulation of their pathophysiological responses have beneficial actions on nerve tissue injured by brain insults and neurodegenerative diseases, therefore astrocytes are recognized as promising targets for neuroprotective drugs. Recent investigations have identified several astrocytic mechanisms for modulating synaptic transmission and neural plasticity. These include altered expression of transporters for neurotransmitters, release of gliotransmitters and neurotrophic factors, and intercellular communication through gap junctions. Investigation of patients with mental disorders shows morphological and functional alterations in astrocytes. According to these observations, manipulation of astrocytic function by gene mutation and pharmacological tools reproduce mental disorder-like behavior in experimental animals. Some drugs clinically used for mental disorders affect astrocyte function. As experimental evidence shows their role in the pathogenesis of mental disorders, astrocytes have gained much attention as drug targets for mental disorders. In this article, I review functional alterations of astrocytes in several mental disorders including schizophrenia, mood disorder, drug dependence, and neurodevelopmental disorders. The pharmacological significance of astrocytes in mental disorders is also discussed.

The Preferential Infection of Astrocytes by Enterovirus 71 Plays a Key Role in the Viral Neurogenic Pathogenesis.

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Feng, Min; Guo, Sujie; Fan, Shengtao; Zeng, Xiaofeng; Zhang, Ying; Liao, Yun; Wang, Jianbin; Zhao, Ting; Wang, Lichun; Che, Yanchun; Wang, Jingjing; Ma, Na; Liu, Longding; Yue, Lei; Li, Qihan

2016-01-01

The pathological manifestations of fatal cases of human hand, foot, and mouth disease (HFMD) caused by enterovirus 71 (EV71) are characterized by inflammatory damage to the central nervous system (CNS). Here, the dynamic distribution of EV71 in the CNS and the subsequent pathological characteristics within different regions of neonatal rhesus macaque brain tissue were studied using a chimeric EV71 expressing green fluorescence protein. The results were compared with brain tissue obtained from the autopsies of deceased EV71-infected HFMD patients. These observations suggested that the virus was prevalent in areas around the blood vessels and nerve nuclei in the brain stem and showed a preference for astrocytes in the CNS. Interestingly, infected astrocytes within the in vivo and in vitro human and macaque systems exhibited increased expression of excitatory neurotransmitters and cytokines that also stimulated the neuronal secretion of the excitatory neurotransmitters noradrenalin and adrenalin, and this process most likely plays a role in the pathophysiological events that occur during EV71 infection.

Peptide gH625 enters into neuron and astrocyte cell lines and crosses the blood–brain barrier in rats

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Valiante S

2015-03-01

Full Text Available Salvatore Valiante,1,* Annarita Falanga,2,3,* Luisa Cigliano,1 Giuseppina Iachetta,1 Rosa Anna Busiello,1 Valeria La Marca,1 Massimiliano Galdiero,4 Assunta Lombardi,1 Stefania Galdiero1,2 1Department of Biology, 2Department of Pharmacy, 3DFM Scarl, University of Naples Federico II, 4Department of Experimental Medicine, II University of Naples, Naples, Italy *These authors contributed equally to this paper and are considered joint first authors Abstract: Peptide gH625, derived from glycoprotein H of herpes simplex virus type 1, can enter cells efficiently and deliver a cargo. Nanoparticles armed with gH625 are able to cross an in vitro model of the blood–brain barrier (BBB. In the present study, in vitro experiments were performed to investigate whether gH625 can enter and accumulate in neuron and astrocyte cell lines. The ability of gH625 to cross the BBB in vivo was also evaluated. gH625 was administered in vivo to rats and its presence in the liver and in the brain was detected. Within 3.5 hours of intravenous administration, gH625 can be found beyond the BBB in proximity to cell neurites. gH625 has no toxic effects in vivo, since it does not affect the maximal oxidative capacity of the brain or the mitochondrial respiration rate. Our data suggest that gH625, with its ability to cross the BBB, represents a novel nanocarrier system for drug delivery to the central nervous system. These results open up new possibilities for direct delivery of drugs into patients in the field of theranostics and might address the treatment of several human diseases. Keywords: drug delivery, neurons, astrocytes, blood–brain barrier, peptide

Altered astrocytic swelling in the cortex of α-syntrophin-negative GFAP/EGFP mice.

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Miroslava Anderova

Full Text Available Brain edema accompanying ischemic or traumatic brain injuries, originates from a disruption of ionic/neurotransmitter homeostasis that leads to accumulation of K(+ and glutamate in the extracellular space. Their increased uptake, predominantly provided by astrocytes, is associated with water influx via aquaporin-4 (AQP4. As the removal of perivascular AQP4 via the deletion of α-syntrophin was shown to delay edema formation and K(+ clearance, we aimed to elucidate the impact of α-syntrophin knockout on volume changes in individual astrocytes in situ evoked by pathological stimuli using three dimensional confocal morphometry and changes in the extracellular space volume fraction (α in situ and in vivo in the mouse cortex employing the real-time iontophoretic method. RT-qPCR profiling was used to reveal possible differences in the expression of ion channels/transporters that participate in maintaining ionic/neurotransmitter homeostasis. To visualize individual astrocytes in mice lacking α-syntrophin we crossbred GFAP/EGFP mice, in which the astrocytes are labeled by the enhanced green fluorescent protein under the human glial fibrillary acidic protein promoter, with α-syntrophin knockout mice. Three-dimensional confocal morphometry revealed that α-syntrophin deletion results in significantly smaller astrocyte swelling when induced by severe hypoosmotic stress, oxygen glucose deprivation (OGD or 50 mM K(+. As for the mild stimuli, such as mild hypoosmotic or hyperosmotic stress or 10 mM K(+, α-syntrophin deletion had no effect on astrocyte swelling. Similarly, evaluation of relative α changes showed a significantly smaller decrease in α-syntrophin knockout mice only during severe pathological conditions, but not during mild stimuli. In summary, the deletion of α-syntrophin markedly alters astrocyte swelling during severe hypoosmotic stress, OGD or high K(+.

The role of astrocytes in multiple sclerosis pathogenesis.

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Guerrero-García, J J

2017-09-25

Multiple sclerosis (MS) is a demyelinating autoimmune disease of the central nervous system (CNS), in which astrocytes play an important role as CNS immune cells. However, the activity of astrocytes as antigen-presenting cells (APC) continues to be subject to debate. This review analyses the existing evidence on the participation of astrocytes in CNS inflammation in MS and on several mechanisms that modify astrocyte activity in the disease. Astrocytes play a crucial role in the pathogenesis of MS because they express toll-like receptors (TLR) and major histocompatibility complex (MHC) classI andII. In addition, astrocytes participate in regulating the blood-brain barrier (BBB) and in modulating T cell activity through the production of cytokines. Future studies should focus on the role of astrocytes in order to find new therapeutic targets for the treatment of MS. Copyright © 2017 Sociedad Española de Neurología. Publicado por Elsevier España, S.L.U. All rights reserved.

Astrocytic Insulin Signaling Couples Brain Glucose Uptake with Nutrient Availability

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García-Cáceres, Cristina; Quarta, Carmelo; Varela, Luis; Gao, Yuanqing; Gruber, Tim; Legutko, Beata; Jastroch, Martin; Johansson, Pia; Ninkovic, Jovica; Yi, Chun-Xia; Le Thuc, Ophelia; Szigeti-Buck, Klara; Cai, Weikang; Meyer, Carola W.; Pfluger, Paul T.; Fernandez, Ana M.; Luquet, Serge; Woods, Stephen C.; Torres-Alemán, Ignacio; Kahn, C. Ronald; Götz, Magdalena; Horvath, Tamas L.; Tschöp, Matthias H.

2016-01-01

We report that astrocytic insulin signaling co-regulates hypothalamic glucose sensing and systemic glucose metabolism. Postnatal ablation of insulin receptors (IRs) in glial fibrillary acidic protein (GFAP)-expressing cells affects hypothalamic astrocyte morphology, mitochondrial function, and

Astrocyte truncated-TrkB mediates BDNF antiapoptotic effect leading to neuroprotection.

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Saba, Julieta; Turati, Juan; Ramírez, Delia; Carniglia, Lila; Durand, Daniela; Lasaga, Mercedes; Caruso, Carla

2018-05-31

Astrocytes are glial cells that help maintain brain homeostasis and become reactive in neurodegenerative processes releasing both harmful and beneficial factors. We have demonstrated that brain-derived neurotrophic factor (BDNF) expression is induced by melanocortins in astrocytes but BDNF actions in astrocytes are largely unknown. We hypothesize that BDNF may prevent astrocyte death resulting in neuroprotection. We found that BDNF increased astrocyte viability, preventing apoptosis induced by serum deprivation by decreasing active caspase-3 and p53 expression. The antiapoptotic action of BDNF was abolished by ANA-12 (a specific TrkB antagonist) and by K252a (a general Trk antagonist). Astrocytes only express the BDNF receptor TrkB truncated isoform 1, TrkB-T1. BDNF induced ERK, Akt and Src (a non-receptor tyrosine kinase) activation in astrocytes. Blocking ERK and Akt pathways abolished BDNF protection in serum deprivation-induced cell death. Moreover, BDNF protected astrocytes from death by 3-nitropropionic acid (3-NP), an effect also blocked by ANA-12, K252a, and inhibitors of ERK, calcium and Src. BDNF reduced reactive oxygen species (ROS) levels induced in astrocytes by 3-NP and increased xCT expression and glutathione levels. Astrocyte conditioned media (ACM) from untreated astrocytes partially protected PC12 neurons whereas ACM from BDNF-treated astrocytes completely protected PC12 neurons from 3-NP-induced apoptosis. Both ACM from control and BDNF-treated astrocytes markedly reduced ROS levels induced by 3-NP in PC12 cells. Our results demonstrate that BDNF protects astrocytes from cell death through TrkB-T1 signaling, exerts an antioxidant action, and induces release of neuroprotective factors from astrocytes. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

In vivo CHI3L1 (YKL-40 expression in astrocytes in acute and chronic neurological diseases

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Hamilton Ronald L

2010-06-01

Full Text Available Abstract Background CHI3L1 (YKL-40 is up-regulated in a variety of inflammatory conditions and cancers. We have previously reported elevated CHI3L1 concentration in the cerebrospinal fluid (CSF of human and non-human primates with lentiviral encephalitis and using immunohistochemistry showed that CHI3L1 was associated with astrocytes. Methods In the current study CHI3L1 transcription and expression were evaluated in a variety of acute and chronic human neurological diseases. Results ELISA revealed significant elevation of CHI3L1 in the CSF of multiple sclerosis (MS patients as well as mild elevation with aging. In situ hybridization (ISH showed CHI3L1 transcription mostly associated with reactive astrocytes, that was more pronounced in inflammatory conditions like lentiviral encephalitis and MS. Comparison of CHI3L1 expression in different stages of brain infarction showed that YKL40 was abundantly expressed in astrocytes during acute phases and diminished to low levels in chronic infarcts. Conclusions Taken together, these findings demonstrate that CHI3L1 is induced in astrocytes in a variety of neurological diseases but that it is most abundantly associated with astrocytes in regions of inflammatory cells.

Stretch-induced Ca2+ independent ATP release in hippocampal astrocytes.

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Xiong, Yingfei; Teng, Sasa; Zheng, Lianghong; Sun, Suhua; Li, Jie; Guo, Ning; Li, Mingli; Wang, Li; Zhu, Feipeng; Wang, Changhe; Rao, Zhiren; Zhou, Zhuan

2018-02-28

Similar to neurons, astrocytes actively participate in synaptic transmission via releasing gliotransmitters. The Ca 2+ -dependent release of gliotransmitters includes glutamate and ATP. Following an 'on-cell-like' mechanical stimulus to a single astrocyte, Ca 2+ independent single, large, non-quantal, ATP release occurs. Astrocytic ATP release is inhibited by either selective antagonist treatment or genetic knockdown of P2X7 receptor channels. Our work suggests that ATP can be released from astrocytes via two independent pathways in hippocampal astrocytes; in addition to the known Ca 2+ -dependent vesicular release, larger non-quantal ATP release depends on P2X7 channels following mechanical stretch. Astrocytic ATP release is essential for brain functions such as synaptic long-term potentiation for learning and memory. However, whether and how ATP is released via exocytosis remains hotly debated. All previous studies of non-vesicular ATP release have used indirect assays. By contrast, two recent studies report vesicular ATP release using more direct assays. In the present study, using patch clamped 'ATP-sniffer cells', we re-investigated astrocytic ATP release at single-vesicle resolution in hippocampal astrocytes. Following an 'on-cell-like' mechanical stimulus of a single astrocyte, a Ca 2+ independent single large non-quantal ATP release occurred, in contrast to the Ca 2+ -dependent multiple small quantal ATP release in a chromaffin cell. The mechanical stimulation-induced ATP release from an astrocyte was inhibited by either exposure to a selective antagonist or genetic knockdown of P2X7 receptor channels. Functional P2X7 channels were expressed in astrocytes in hippocampal brain slices. Thus, in addition to small quantal ATP release, larger non-quantal ATP release depends on P2X7 channels in astrocytes. © 2018 The Authors. The Journal of Physiology © 2018 The Physiological Society.

Dynamic volume changes in astrocytes are an intrinsic phenomenon mediated by bicarbonate ion flux.

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Clare M Florence

Full Text Available Astrocytes, the major type of non-neuronal cells in the brain, play an important functional role in extracellular potassium ([K(+](o and pH homeostasis. Pathological brain states that result in [K(+](o and pH dysregulation have been shown to cause astrocyte swelling. However, whether astrocyte volume changes occur under physiological conditions is not known. In this study we used two-photon imaging to visualize real-time astrocyte volume changes in the stratum radiatum of the hippocampus CA1 region. Astrocytes were observed to swell by 19.0±0.9% in response to a small physiological increase in the concentration of [K(+](o (3 mM. Astrocyte swelling was mediated by the influx of bicarbonate (HCO(3- ions as swelling was significantly decreased when the influx of HCO(3- was reduced. We found: 1 in HCO(3- free extracellular solution astrocytes swelled by 5.4±0.7%, 2 when the activity of the sodium-bicarbonate cotransporter (NBC was blocked the astrocytes swelled by 8.3±0.7%, and 3 in the presence of an extracellular carbonic anhydrase (CA inhibitor astrocytes swelled by 11.4±0.6%. Because a significant HCO(3- efflux is known to occur through the γ-amino-butyric acid (GABA channel, we performed a series of experiments to determine if astrocytes were capable of HCO(3- mediated volume shrinkage with GABA channel activation. Astrocytes were found to shrink -7.7±0.5% of control in response to the GABA(A channel agonist muscimol. Astrocyte shrinkage from GABA(A channel activation was significantly decreased to -5.0±0.6% of control in the presence of the membrane-permeant CA inhibitor acetazolamide (ACTZ. These dynamic astrocyte volume changes may represent a previously unappreciated yet fundamental mechanism by which astrocytes regulate physiological brain functioning.

Characteristics of calcium signaling in astrocytes induced by photostimulation with femtosecond laser

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Zhao, Yuan; Zhang, Yuan; Zhou, Wei; Liu, Xiuli; Zeng, Shaoqun; Luo, Qingming

2010-05-01

Astrocytes have been identified to actively contribute to brain functions through Ca2+ signaling, serving as a bridge to communicate with neurons and other brain cells. However, conventional stimulation techniques are hard to apply to delicate investigations on astrocytes. Our group previously reported photostimulation with a femtosecond laser to evoke astrocytic calcium (Ca2+) waves, providing a noninvasive and efficient approach with highly precise targeting. In this work, detailed characteristics of astrocytic Ca2+ signaling induced by photostimulation are presented. In a purified astrocytic culture, after the illumination of a femtosecond laser onto one cell, a Ca2+ wave throughout the network with reduced speed is induced, and intracellular Ca2+ oscillations are observed. The intercellular propagation is pharmacologically confirmed to be mainly mediated by ATP through P2Y receptors. Different patterns of Ca2+ elevations with increased amplitude in the stimulated astrocyte are discovered by varying the femtosecond laser power, which is correspondingly followed by broader intercellular waves. These indicate that the strength of photogenerated Ca2+ signaling in astrocytes has a positive relationship with the stimulating laser power. Therefore, distinct Ca2+ signaling is feasibly available for specific studies on astrocytes by employing precisely controlled photostimulation.

A phase plane analysis of neuron-astrocyte interactions.

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Amiri, Mahmood; Montaseri, Ghazal; Bahrami, Fariba

2013-08-01

Intensive experimental studies have shown that astrocytes are active partners in modulation of synaptic transmission. In the present research, we study neuron-astrocyte signaling using a biologically inspired model of one neuron synapsing one astrocyte. In this model, the firing dynamics of the neuron is described by the Morris-Lecar model and the Ca(2+) dynamics of a single astrocyte explained by a functional model introduced by Postnov and colleagues. Using the coupled neuron-astrocyte model and based on the results of the phase plane analyses, it is demonstrated that the astrocyte is able to activate the silent neuron or change the neuron spiking frequency through bidirectional communication. This suggests that astrocyte feedback signaling is capable of modulating spike transmission frequency by changing neuron spiking frequency. This effect is described by a saddle-node on invariant circle bifurcation in the coupled neuron-astrocyte model. In this way, our results suggest that the neuron-astrocyte crosstalk has a fundamental role in producing diverse neuronal activities and therefore enhances the information processing capabilities of the brain. Crown Copyright © 2013. Published by Elsevier Ltd. All rights reserved.

Astrocytes in neurodegenerative diseases (I): function and molecular description.

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Guillamón-Vivancos, T; Gómez-Pinedo, U; Matías-Guiu, J

2015-03-01

Astrocytes have been considered mere supporting cells in the CNS. However, we now know that astrocytes are actively involved in many of the functions of the CNS and may play an important role in neurodegenerative diseases. This article reviews the roles astrocytes play in CNS development and plasticity; control of synaptic transmission; regulation of blood flow, energy, and metabolism; formation of the blood-brain barrier; regulation of the circadian rhythms, lipid metabolism and secretion of lipoproteins; and in neurogenesis. Astrocyte markers and the functions of astrogliosis are also described. Astrocytes play an active role in the CNS. A good knowledge of astrocytes is essential to understanding the mechanisms of neurodegenerative diseases. Copyright © 2012 Sociedad Española de Neurología. Published by Elsevier Espana. All rights reserved.

Distribution of the branched-chain α-ketoacid dehydrogenase complex E1α subunit and glutamate dehydrogenase in the human brain and their role in neuro-metabolism.

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Hull, Jonathon; Usmari Moraes, Marcela; Brookes, Emma; Love, Seth; Conway, Myra E

2018-01-01

Glutamate is the major excitatory neurotransmitter of the central nervous system, with the branched-chain amino acids (BCAAs) acting as key nitrogen donors for de novo glutamate synthesis. Despite the importance of these major metabolites, their metabolic pathway in the human brain is still not well characterised. The metabolic pathways that influence the metabolism of BCAAs have been well characterised in rat models. However, the expression of key proteins such as the branched-chain α-ketoacid dehydrogenase (BCKD) complex and glutamate dehydrogenase isozymes (GDH) in the human brain is still not well characterised. We have used specific antibodies to these proteins to analyse their distribution within the human brain and report, for the first time, that the E1α subunit of the BCKD is located in both neurons and vascular endothelial cells. We also demonstrate that GDH is localised to astrocytes, although vascular immunolabelling does occur. The labelling of GDH was most intense in astrocytes adjacent to the hippocampus, in keeping with glutamatergic neurotransmission in this region. GDH was also present in astrocyte processes abutting vascular endothelial cells. Previously, we demonstrated that the branched-chain aminotransferase (hBCAT) proteins were most abundant in vascular cells (hBCATm) and neurons (hBCATc). Present findings are further evidence that BCAAs are metabolised within both the vasculature and neurons in the human brain. We suggest that GDH, hBCAT and the BCKD proteins operate in conjunction with astrocytic glutamate transporters and glutamine synthetase to regulate the availability of glutamate. This has important implications given that the dysregulation of glutamate metabolism, leading to glutamate excitotoxicity, is an important contributor to the pathogenesis of several neurodegenerative conditions such as Alzheimer's disease. Crown Copyright © 2017. Published by Elsevier Ltd. All rights reserved.

Is there an astrocyte-neuron ketone body shuttle?

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Guzmán, M; Blázquez, C

2001-01-01

Ketone bodies can replace glucose as the major source of brain energy when glucose becomes scarce. Although it is generally assumed that the liver supplies extrahepatic tissues with ketone bodies, recent evidence shows that astrocytes are also ketogenic cells. Moreover, the partitioning of fatty acids between ketogenesis and ceramide synthesis de novo might control the survival/death decision of neural cells. These findings support the notion that astrocytes might supply neurons with ketone bodies in situ, and raise the possibility that astrocyte ketogenesis is a cytoprotective pathway.

Astrocytic Vesicle Mobility in Health and Disease

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Robert Zorec

2013-05-01

Full Text Available Astrocytes are no longer considered subservient to neurons, and are, instead, now understood to play an active role in brain signaling. The intercellular communication of astrocytes with neurons and other non-neuronal cells involves the exchange of molecules by exocytotic and endocytotic processes through the trafficking of intracellular vesicles. Recent studies of single vesicle mobility in astrocytes have prompted new views of how astrocytes contribute to information processing in nervous tissue. Here, we review the trafficking of several types of membrane-bound vesicles that are specifically involved in the processes of (i intercellular communication by gliotransmitters (glutamate, adenosine 5'-triphosphate, atrial natriuretic peptide, (ii plasma membrane exchange of transporters and receptors (EAAT2, MHC-II, and (iii the involvement of vesicle mobility carrying aquaporins (AQP4 in water homeostasis. The properties of vesicle traffic in astrocytes are discussed in respect to networking with neighboring cells in physiologic and pathologic conditions, such as amyotrophic lateral sclerosis, multiple sclerosis, and states in which astrocytes contribute to neuroinflammatory conditions.

Bi-directionally protective communication between neurons and astrocytes under ischemia.

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Wu, Xiao-Mei; Qian, Christopher; Zhou, Yu-Fu; Yan, Yick-Chun; Luo, Qian-Qian; Yung, Wing-Ho; Zhang, Fa-Li; Jiang, Li-Rong; Qian, Zhong Ming; Ke, Ya

2017-10-01

The extensive existing knowledge on bi-directional communication between astrocytes and neurons led us to hypothesize that not only ischemia-preconditioned (IP) astrocytes can protect neurons but also IP neurons protect astrocytes from lethal ischemic injury. Here, we demonstrated for the first time that neurons have a significant role in protecting astrocytes from ischemic injury. The cultured medium from IP neurons (IPcNCM) induced a remarkable reduction in LDH and an increase in cell viability in ischemic astrocytes in vitro. Selective neuronal loss by kainic acid injection induced a significant increase in apoptotic astrocyte numbers in the brain of ischemic rats in vivo. Furthermore, TUNEL analysis, DNA ladder assay, and the measurements of ROS, GSH, pro- and anti-apoptotic factors, anti-oxidant enzymes and signal molecules in vitro and/or in vivo demonstrated that IP neurons protect astrocytes by an EPO-mediated inhibition of pro-apoptotic signals, activation of anti-apoptotic proteins via the P13K/ERK/STAT5 pathways and activation of anti-oxidant proteins via up-regulation of anti-oxidant enzymes. We demonstrated the existence of astro-protection by IP neurons under ischemia and proposed that the bi-directionally protective communications between cells might be a common activity in the brain or peripheral organs under most if not all pathological conditions. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

Bi-directionally protective communication between neurons and astrocytes under ischemia

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Xiao-Mei Wu

2017-10-01

Full Text Available The extensive existing knowledge on bi-directional communication between astrocytes and neurons led us to hypothesize that not only ischemia-preconditioned (IP astrocytes can protect neurons but also IP neurons protect astrocytes from lethal ischemic injury. Here, we demonstrated for the first time that neurons have a significant role in protecting astrocytes from ischemic injury. The cultured medium from IP neurons (IPcNCM induced a remarkable reduction in LDH and an increase in cell viability in ischemic astrocytes in vitro. Selective neuronal loss by kainic acid injection induced a significant increase in apoptotic astrocyte numbers in the brain of ischemic rats in vivo. Furthermore, TUNEL analysis, DNA ladder assay, and the measurements of ROS, GSH, pro- and anti-apoptotic factors, anti-oxidant enzymes and signal molecules in vitro and/or in vivo demonstrated that IP neurons protect astrocytes by an EPO-mediated inhibition of pro-apoptotic signals, activation of anti-apoptotic proteins via the P13K/ERK/STAT5 pathways and activation of anti-oxidant proteins via up-regulation of anti-oxidant enzymes. We demonstrated the existence of astro-protection by IP neurons under ischemia and proposed that the bi-directionally protective communications between cells might be a common activity in the brain or peripheral organs under most if not all pathological conditions.

Bicarbonate sensing in mouse cortical astrocytes during extracellular acid/base disturbances

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Naoshin, Zinnia; Defren, Sabrina; Schmaelzle, Jana; Weber, Tobias; Schneider, Hans‐Peter

2017-01-01

Key points The present study suggests that the electrogenic sodium–bicarbonate cotransporter, NBCe1, supported by carbonic anhydrase II, CAII, provides an efficient mechanism of bicarbonate sensing in cortical astrocytes. This mechanism is proposed to play a major role in setting the pHi responses to extracellular acid/base challenges in astrocytes.A decrease in extracellular [HCO3 −] during isocapnic acidosis and isohydric hypocapnia, or an increase in intracellular [HCO3 −] during hypercapnic acidosis, was effectively sensed by NBCe1, which carried bicarbonate out of the cells under these conditions, and caused an acidification and sodium fall in WT astrocytes, but not in NBCe1‐knockout astrocytes.Isocapnic acidosis, hypercapnic acidosis and isohydric hypocapnia evoked inward currents in NBCe1‐ and CAII‐expressing Xenopus laevis oocytes, but not in native oocytes, suggesting that NBCe1 operates in the outwardly directed mode under these conditions consistent with our findings in astrocytes.We propose that bicarbonate sensing of astrocytes may have functional significance during extracellular acid/base disturbances in the brain, as it not only alters intracellular pH/[HCO3 −]‐dependent functions of astrocytes, but also modulates the extracellular pH/[HCO3 −] in brain tissue. Abstract Extracellular acid/base status of the mammalian brain undergoes dynamic changes during many physiological and pathological events. Although intracellular pH (pHi) of astrocytes responds to extracellular acid/base changes, the mechanisms mediating these changes have remained unresolved. We have previously shown that the electrogenic sodium–bicarbonate cotransporter, NBCe1, is a high‐affinity bicarbonate carrier in cortical astrocytes. In the present study, we investigated whether NBCe1 plays a role in bicarbonate sensing in astrocytes, and in determining the pHi responses to extracellular acid/base challenges. We measured changes in intracellular H+ and Na+ in

Palmitoylethanolamide Blunts Amyloid-β42-Induced Astrocyte Activation and Improves Neuronal Survival in Primary Mouse Cortical Astrocyte-Neuron Co-Cultures.

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Beggiato, Sarah; Borelli, Andrea Celeste; Ferraro, Luca; Tanganelli, Sergio; Antonelli, Tiziana; Tomasini, Maria Cristina

2018-01-01

Based on the pivotal role of astrocytes in brain homeostasis and the strong metabolic cooperation existing between neurons and astrocytes, it has been suggested that astrocytic dysfunctions might cause and/or contribute to neuroinflammation and neurodegenerative processes. Therapeutic approaches aimed at both neuroprotection and neuroinflammation reduction may prove particularly effective in slowing the progression of these diseases. The endogenous lipid mediator palmitoylethanolamide (PEA) displayed neuroprotective and anti(neuro)inflammatory properties, and demonstrated interesting potential as a novel treatment for Alzheimer's disease. We firstly evaluated whether astrocytes could participate in regulating the Aβ42-induced neuronal damage, by using primary mouse astrocytes cell cultures and mixed astrocytes-neurons cultures. Furthermore, the possible protective effects of PEA against Aβ42-induced neuronal toxicity have also been investigated by evaluating neuronal viability, apoptosis, and morphometric parameters. The presence of astrocytes pre-exposed to Aβ42 (0.5μM; 24 h) induced a reduction of neuronal viability in primary mouse astrocytes-neurons co-cultures. Furthermore, under these experimental conditions, an increase in the number of neuronal apoptotic nuclei and a decrease in the number of MAP-2 positive neurons were observed. Finally, astrocytic Aβ42 pre-exposure induced an increase in the number of neurite aggregations/100μm as compared to control (i.e., untreated) astrocytes-neurons co-cultures. These effects were not observed in neurons cultured in the presence of astrocytes pre-exposed to PEA (0.1μM), applied 1 h before and maintained during Aβ42 treatment. Astrocytes contribute to Aβ42-induced neurotoxicity and PEA, by blunting Aβ42-induced astrocyte activation, improved neuronal survival in mouse astrocyte-neuron co-cultures.

TGFβ signaling in the brain increases with aging and signals to astrocytes and innate immune cells in the weeks after stroke

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Buckwalter Marion S

2010-10-01

Full Text Available Abstract Background TGFβ is both neuroprotective and a key immune system modulator and is likely to be an important target for future stroke therapy. The precise function of increased TGF-β1 after stroke is unknown and its pleiotropic nature means that it may convey a neuroprotective signal, orchestrate glial scarring or function as an important immune system regulator. We therefore investigated the time course and cell-specificity of TGFβ signaling after stroke, and whether its signaling pattern is altered by gender and aging. Methods We performed distal middle cerebral artery occlusion strokes on 5 and 18 month old TGFβ reporter mice to get a readout of TGFβ responses after stroke in real time. To determine which cell type is the source of increased TGFβ production after stroke, brain sections were stained with an anti-TGFβ antibody, colocalized with markers for reactive astrocytes, neurons, and activated microglia. To determine which cells are responding to TGFβ after stroke, brain sections were double-labelled with anti-pSmad2, a marker of TGFβ signaling, and markers of neurons, oligodendrocytes, endothelial cells, astrocytes and microglia. Results TGFβ signaling increased 2 fold after stroke, beginning on day 1 and peaking on day 7. This pattern of increase was preserved in old animals and absolute TGFβ signaling in the brain increased with age. Activated microglia and macrophages were the predominant source of increased TGFβ after stroke and astrocytes and activated microglia and macrophages demonstrated dramatic upregulation of TGFβ signaling after stroke. TGFβ signaling in neurons and oligodendrocytes did not undergo marked changes. Conclusions We found that TGFβ signaling increases with age and that astrocytes and activated microglia and macrophages are the main cell types that undergo increased TGFβ signaling in response to post-stroke increases in TGFβ. Therefore increased TGFβ after stroke likely regulates glial

TGFβ signaling in the brain increases with aging and signals to astrocytes and innate immune cells in the weeks after stroke.

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Doyle, Kristian P; Cekanaviciute, Egle; Mamer, Lauren E; Buckwalter, Marion S

2010-10-11

TGFβ is both neuroprotective and a key immune system modulator and is likely to be an important target for future stroke therapy. The precise function of increased TGF-β1 after stroke is unknown and its pleiotropic nature means that it may convey a neuroprotective signal, orchestrate glial scarring or function as an important immune system regulator. We therefore investigated the time course and cell-specificity of TGFβ signaling after stroke, and whether its signaling pattern is altered by gender and aging. We performed distal middle cerebral artery occlusion strokes on 5 and 18 month old TGFβ reporter mice to get a readout of TGFβ responses after stroke in real time. To determine which cell type is the source of increased TGFβ production after stroke, brain sections were stained with an anti-TGFβ antibody, colocalized with markers for reactive astrocytes, neurons, and activated microglia. To determine which cells are responding to TGFβ after stroke, brain sections were double-labelled with anti-pSmad2, a marker of TGFβ signaling, and markers of neurons, oligodendrocytes, endothelial cells, astrocytes and microglia. TGFβ signaling increased 2 fold after stroke, beginning on day 1 and peaking on day 7. This pattern of increase was preserved in old animals and absolute TGFβ signaling in the brain increased with age. Activated microglia and macrophages were the predominant source of increased TGFβ after stroke and astrocytes and activated microglia and macrophages demonstrated dramatic upregulation of TGFβ signaling after stroke. TGFβ signaling in neurons and oligodendrocytes did not undergo marked changes. We found that TGFβ signaling increases with age and that astrocytes and activated microglia and macrophages are the main cell types that undergo increased TGFβ signaling in response to post-stroke increases in TGFβ. Therefore increased TGFβ after stroke likely regulates glial scar formation and the immune response to stroke.

Notch Signaling and Brain Tumors

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Stockhausen, Marie; Kristoffersen, Karina; Poulsen, Hans Skovgaard

2011-01-01

Human brain tumors are a heterogenous group of neoplasms occurring inside the cranium and the central spinal cord. In adults and children, astrocytic glioma and medulloblastoma are the most common subtypes of primary brain tumors. These tumor types are thought to arise from cells in which Notch...

RNase H2 Loss in Murine Astrocytes Results in Cellular Defects Reminiscent of Nucleic Acid-Mediated Autoinflammation

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Kareen Bartsch

2018-03-01

Full Text Available Aicardi–Goutières syndrome (AGS is a rare early onset childhood encephalopathy caused by persistent neuroinflammation of autoimmune origin. AGS is a genetic disorder and >50% of affected individuals bear hypomorphic mutations in ribonuclease H2 (RNase H2. All available RNase H2 mouse models so far fail to mimic the prominent CNS involvement seen in AGS. To establish a mouse model recapitulating the human disease, we deleted RNase H2 specifically in the brain, the most severely affected organ in AGS. Although RNase H2ΔGFAP mice lacked the nuclease in astrocytes and a majority of neurons, no disease signs were apparent in these animals. We additionally confirmed these results in a second, neuron-specific RNase H2 knockout mouse line. However, when astrocytes were isolated from brains of RNase H2ΔGFAP mice and cultured under mitogenic conditions, they showed signs of DNA damage and premature senescence. Enhanced expression of interferon-stimulated genes (ISGs represents the most reliable AGS biomarker. Importantly, primary RNase H2ΔGFAP astrocytes displayed significantly increased ISG transcript levels, which we failed to detect in in vivo in brains of RNase H2ΔGFAP mice. Isolated astrocytes primed by DNA damage, including RNase H2-deficiency, exhibited a heightened innate immune response when exposed to bacterial or viral antigens. Taken together, we established a valid cellular AGS model that utilizes the very cell type responsible for disease pathology, the astrocyte, and phenocopies major molecular defects observed in AGS patient cells.

The multi-dimensional roles of astrocytes in ALS.

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Yamanaka, Koji; Komine, Okiru

2018-01-01

Despite significant progress in understanding the molecular and genetic aspects of amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease characterized by the progressive loss of motor neurons, the precise and comprehensive pathomechanisms remain largely unknown. In addition to motor neuron involvement, recent studies using cellular and animal models of ALS indicate that there is a complex interplay between motor neurons and neighboring non-neuronal cells, such as astrocytes, in non-cell autonomous neurodegeneration. Astrocytes are key homeostatic cells that play numerous supportive roles in maintaining the brain environment. In neurodegenerative diseases such as ALS, astrocytes change their shape and molecular expression patterns and are referred to as reactive or activated astrocytes. Reactive astrocytes in ALS lose their beneficial functions and gain detrimental roles. In addition, interactions between motor neurons and astrocytes are impaired in ALS. In this review, we summarize growing evidence that astrocytes are critically involved in the survival and demise of motor neurons through several key molecules and cascades in astrocytes in both sporadic and inherited ALS. These observations strongly suggest that astrocytes have multi-dimensional roles in disease and are a viable therapeutic target for ALS. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

Dephosphorylation of 2-deoxyglucose 6-phosphate and 2-deoxyglucose export from cultured astrocytes.

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Forsyth, R J; Bartlett, K; Eyre, J

1996-03-01

Neurotransmitter-stimulated mobilization of astrocyte glycogen has been proposed as a basis for local energy homeostasis in brain. However, uncertainty remains over the fate of astrocyte glycogen. Upon transfer of cultured astrocytes pre-loaded with [2-3H]2-deoxyglucose 6-phosphate at non-tracer concentrations to a glucose-free, 2-deoxyglucose-free medium, rapid dephosphorylation of a proportion of the intracellular 2-deoxyglucose 6-phosphate pool and export of 2-deoxyglucose to the extracellular fluid occurs. Astrocytes show very low, basal rates of gluconeogenesis from pyruvate (approx. 1 nmol mg protein-1 h-1). Astrocytes in vivo may be capable of physiologically significant glucose export from glucose-6-phosphate. The low gluconeogenic activity in astrocytes suggests that the most likely source of glucose-6-phosphate may be glycogen. These findings support the hypothesis that export, as glucose, to adjacent neurons may be one of the possible fate(s) of astrocytic glycogen. Such export of glycogen as glucose occurring in response to increases in neuronal activity could contribute to energy homeostasis on a paracrine scale within brain.

Astrocytes and endoplasmic reticulum stress: A bridge between obesity and neurodegenerative diseases.

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Martin-Jiménez, Cynthia A; García-Vega, Ángela; Cabezas, Ricardo; Aliev, Gjumrakch; Echeverria, Valentina; González, Janneth; Barreto, George E

2017-11-01

Endoplasmic reticulum (ER) is a subcellular organelle involved in protein folding and processing. ER stress constitutes a cellular process characterized by accumulation of misfolded proteins, impaired lipid metabolism and induction of inflammatory responses. ER stress has been suggested to be involved in several human pathologies, including neurodegenerative diseases and obesity. Different studies have shown that both neurodegenerative diseases and obesity trigger similar cellular responses to ER stress. Moreover, both diseases are assessed in astrocytes as evidences suggest these cells as key regulators of brain homeostasis. However, the exact contributions to the effects of ER stress in astrocytes in the various neurodegenerative diseases and its relation with obesity are not well known. Here, we discuss recent advances in the understanding of molecular mechanisms that regulate ER stress-related disorders in astrocytes such as obesity and neurodegeneration. Moreover, we outline the correlation between the activated proteins of the unfolded protein response (UPR) in these pathological conditions in order to identify possible therapeutic targets for ER stress in astrocytes. We show that ER stress in astrocytes shares UPR activation pathways during both obesity and neurodegenerative diseases, demonstrating that UPR related proteins like ER chaperone GRP 78/Bip, PERK pathway and other exogenous molecules ameliorate UPR response and promote neuroprotection. Copyright © 2017 Elsevier Ltd. All rights reserved.

Thyroid hormone action: Astrocyte-neuron communication.

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Beatriz eMorte

2014-05-01

Full Text Available Thyroid hormone action is exerted mainly through regulation of gene expression by binding of T3 to the nuclear receptors. T4 plays an important role as a source of intracellular T3 in the central nervous system via the action of the type 2 deiodinase, expressed in the astrocytes. A model of T3 availability to neural cells has been proposed and validated. The model contemplates that brain T3 has a double origin: a fraction is available directly from the circulation, and another is produced locally from T4 in the astrocytes by type 2 deiodinase. The fetal brain depends almost entirely on the T3 generated locally. The contribution of systemic T3 increases subsequently during development to account for approximately 50% of total brain T3 in the late postnatal and adult stages. In this article we review the experimental data in support of this model, and how the factors affecting T3 availability in the brain, such as deiodinases and transporters, play a decisive role in modulating local thyroid hormone action during development.

Cultured human astrocytes secrete large cholesteryl ester- andtriglyceride-rich lipoproteins along with endothelial lipase

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Yang, Lin; Liu, Yanzhu; Forte, Trudy M.; Chisholm, Jeffrey W.; Parks, John S.; Shachter, Neil S.

2003-12-01

We cultured normal human astrocytes and characterized their secreted lipoproteins. Human astrocytes secreted lipoproteins in the size range of plasma VLDL (Peak 1), LDL (Peak 2), HDL (Peak 3) and a smaller peak (Peak 4), as determined by gel filtration chromatography, nondenaturing gradient gel electrophoresis and transmission electron microscopy. Cholesterol enrichment of astrocytes led to a particular increase in Peak 1. Almost all Peak 2, 3 and 4 cholesterol and most Peak 1 cholesterol was esterified (unlike mouse astrocyte lipoproteins, which exhibited similar peaks but where cholesterol was predominantly non-esterified). Triglycerides were present at about 2/3 the level of cholesterol. LCAT was detected along with two of its activators, apolipoprotein (apo) A-IV and apoC-I. ApoA-I and apoA-II mRNA and protein were absent. ApoJ was present equally in all peaks but apoE was present predominantly in peaks 3 and 4. ApoB was not detected. The electron microscopic appearance of Peak 1 lipoproteins suggested partial lipolysis leading to the detection of a heparin-releasable triglyceride lipase consistent with endothelial lipase. The increased neuronal delivery of lipids from large lipoprotein particles, for which apoE4 has greater affinity than does apoE3, may be a mechanism whereby the apoE {var_epsilon}4 allele contributes to neurodegenerative risk.

Exocytosis of gliotransmitters from cortical astrocytes: implications for synaptic plasticity and aging.

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Lalo, Ulyana; Rasooli-Nejad, Seyed; Pankratov, Yuriy

2014-10-01

Maintaining brain function during aging is very important for mental and physical health. Recent studies showed a crucial importance of communication between two major types of brain cells: neurons transmitting electrical signals, and glial cells, which maintain the well-being and function of neurons. Still, the study of age-related changes in neuron-glia signalling is far from complete. We have shown previously that cortical astrocytes are capable of releasing ATP by a quantal soluble N-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE) complex-dependent mechanism. Release of ATP from cortical astrocytes can be activated via various pathways, including direct UV-uncaging of intracellular Ca²⁺ or G-protein-coupled receptors. Importantly, release of both ATP and glutamate from neocortical astrocytes was not observed in brain slices of dominant-negative SNARE (dnSNARE) mice, expressing dnSNARE domain selectively in astrocytes. We also discovered that astrocyte-driven ATP can cause significant attenuation of synaptic inhibition in the pyramidal neurons via Ca²⁺-interaction between the neuronal ATP and γ-aminobutyric acid (GABA) receptors. Furthermore, we showed that astrocyte-derived ATP can facilitate the induction of long-term potentiation of synaptic plasticity in the neocortex. Our recent data have shown that an age-related decrease in the astroglial Ca²⁺ signalling can cause a substantial decrease in the exocytosis of gliotransmitters, in particular ATP. Age-related impairment of ATP release from cortical astrocytes can cause a decrease in the extent of astroglial modulation of synaptic transmission in the neocortex and can therefore contribute to the age-related impairment of synaptic plasticity and cognitive decline. Combined, our results strongly support the physiological relevance of glial exocytosis for glia-neuron communications and brain function.

Trafficking of astrocytic vesicles in hippocampal slices

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Potokar, Maja; Kreft, Marko; Lee, So-Young; Takano, Hajime; Haydon, Philip G.; Zorec, Robert

2009-01-01

The increasingly appreciated role of astrocytes in neurophysiology dictates a thorough understanding of the mechanisms underlying the communication between astrocytes and neurons. In particular, the uptake and release of signaling substances into/from astrocytes is considered as crucial. The release of different gliotransmitters involves regulated exocytosis, consisting of the fusion between the vesicle and the plasma membranes. After fusion with the plasma membrane vesicles may be retrieved into the cytoplasm and may continue to recycle. To study the mobility implicated in the retrieval of secretory vesicles, these structures have been previously efficiently and specifically labeled in cultured astrocytes, by exposing live cells to primary and secondary antibodies. Since the vesicle labeling and the vesicle mobility properties may be an artifact of cell culture conditions, we here asked whether the retrieving exocytotic vesicles can be labeled in brain tissue slices and whether their mobility differs to that observed in cell cultures. We labeled astrocytic vesicles and recorded their mobility with two-photon microscopy in hippocampal slices from transgenic mice with fluorescently tagged astrocytes (GFP mice) and in wild-type mice with astrocytes labeled by Fluo4 fluorescence indicator. Glutamatergic vesicles and peptidergic granules were labeled by the anti-vesicular glutamate transporter 1 (vGlut1) and anti-atrial natriuretic peptide (ANP) antibodies, respectively. We report that the vesicle mobility parameters (velocity, maximal displacement and track length) recorded in astrocytes from tissue slices are similar to those reported previously in cultured astrocytes.

THE CAJAL SCHOOL AND THE PHYSIOLOGICAL ROLE OF ASTROCYTES: A WAY OF THINKING

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Marta eNavarrete

2014-05-01

Full Text Available Cajal is widely recognized by the scientific community for his important contributions to our knowledge of the neuronal organization of the nervous system. His studies on neuroglial cells are less recognized, yet they are no less relevant to our current understanding of the cellular bases of brain structure. Two pioneering studies published a century ago ⎯Something about the physiological significance of neuroglia (Cajal, 1897 and A contribution to the understanding of neuroglia in the human brain (Cajal, 1913⎯ focused on glial cells and their role in brain physiology. Novel findings obtained using state-of-the-art and sophisticated technologies largely confirm many of the groundbreaking hypotheses proposed by Cajal related to the structural-functional properties of neuroglia. Here we propose to the reader a journey guided by the ideas of Cajal through the recent findings on the functional significance of astrocytes, the most abundant neuroglial cell type in the nervous system. Astrocyte-neuron interaction, which represents an emerging field in current neuroscience with important implications for our understanding of the cellular processes underlying brain function, has its roots in many of the original concepts proposed by Cajal.

Gliovascular and cytokine interactions modulate brain endothelial barrier in vitro.

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Chaitanya, Ganta V; Cromer, Walter E; Wells, Shannon R; Jennings, Merilyn H; Couraud, P Olivier; Romero, Ignacio A; Weksler, Babette; Erdreich-Epstein, Anat; Mathis, J Michael; Minagar, Alireza; Alexander, J Steven

2011-11-23

The glio-vascular unit (G-unit) plays a prominent role in maintaining homeostasis of the blood-brain barrier (BBB) and disturbances in cells forming this unit may seriously dysregulate BBB. The direct and indirect effects of cytokines on cellular components of the BBB are not yet unclear. The present study compares the effects of cytokines and cytokine-treated astrocytes on brain endothelial barrier. 3-dimensional transwell co-cultures of brain endothelium and related-barrier forming cells with astrocytes were used to investigate gliovascular barrier responses to cytokines during pathological stresses. Gliovascular barrier was measured using trans-endothelial electrical resistance (TEER), a sensitive index of in vitro barrier integrity. We found that neither TNF-α, IL-1β or IFN-γ directly reduced barrier in human or mouse brain endothelial cells or ECV-304 barrier (independent of cell viability/metabolism), but found that astrocyte exposure to cytokines in co-culture significantly reduced endothelial (and ECV-304) barrier. These results indicate that the barrier established by human and mouse brain endothelial cells (and other cells) may respond positively to cytokines alone, but that during pathological conditions, cytokines dysregulate the barrier forming cells indirectly through astrocyte activation involving reorganization of junctions, matrix, focal adhesion or release of barrier modulating factors (e.g. oxidants, MMPs). © 2011 Chaitanya et al; licensee BioMed Central Ltd.

Astrocytes mediate synapse elimination through MEGF10 and MERTK pathways

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Chung, Won-Suk; Clarke, Laura E.; Wang, Gordon X.; Stafford, Benjamin K.; Sher, Alexander; Chakraborty, Chandrani; Joung, Julia; Foo, Lynette C.; Thompson, Andrew; Chen, Chinfei; Smith, Stephen J.; Barres, Ben A.

2013-12-01

To achieve its precise neural connectivity, the developing mammalian nervous system undergoes extensive activity-dependent synapse remodelling. Recently, microglial cells have been shown to be responsible for a portion of synaptic pruning, but the remaining mechanisms remain unknown. Here we report a new role for astrocytes in actively engulfing central nervous system synapses. This process helps to mediate synapse elimination, requires the MEGF10 and MERTK phagocytic pathways, and is strongly dependent on neuronal activity. Developing mice deficient in both astrocyte pathways fail to refine their retinogeniculate connections normally and retain excess functional synapses. Finally, we show that in the adult mouse brain, astrocytes continuously engulf both excitatory and inhibitory synapses. These studies reveal a novel role for astrocytes in mediating synapse elimination in the developing and adult brain, identify MEGF10 and MERTK as critical proteins in the synapse remodelling underlying neural circuit refinement, and have important implications for understanding learning and memory as well as neurological disease processes.

Fluoxetine requires the endfeet protein aquaporin-4 to enhance plasticity of astrocyte processes

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Barbara eDi Benedetto

2016-02-01

Full Text Available Morphological alterations in astrocytes are characteristic for post mortem brains of patients affected by major depressive disorder (MDD. Recently, a significant reduction in the coverage of blood vessels (BVs by aquaporin-4 (AQP-4-positive astrocyte endfeet has been shown in the prefrontal cortex (PFC of MDD patients, suggesting that either alterations in the morphology of endfeet or in AQP-4 distribution might be responsible for the disease phenotype or constitute a consequence of its progress. Antidepressant drugs (ADs regulate the expression of several proteins, including astrocyte-specific ones. Thus, they may target AQP-4 to induce morphological changes in astrocytes and restore their proper shape or relocate AQP-4 to endfeet. Using an animal model of depression, rats selectively bred for high anxiety-like behavior (HAB, we confirmed a reduced coverage of BVs in the adult PFC by AQP-4-immunoreactive (AQP-4-IR astrocyte processes with respect to nonselected Wistar rats (NAB, thereby validating it for our study. A further evaluation of the morphology of astrocyte in brain slices (ex vivo and in vitro using an antibody against the astrocyte-specific cytoskeletal protein glial fibrillary acidic protein (GFAP revealed that HAB astrocytes extended less processes than NAB cells. Furthermore, short-term drug treatment in vitro with the AD fluoxetine (FLX was sufficient to increase the plasticity of astrocyte processes, enhancing their number in NAB-derived cells and recovering their basal number in HAB-derived cells. This enhanced FLX-dependent plasticity occurred, however, only in the presence of intact AQP-4, as demonstrated by the lack of effect after the downregulation of AQP-4 with RNAi in both NAB and HAB cells. Nonetheless, a similar short-term treatment did neither modulate the coverage of BVs with AQP-4-positive astrocyte endfeet in NAB nor in HAB rats, although dosage and time of treatment were sufficient to fully recover GFAP expression

DJ-1 KNOCK-DOWN IMPAIRS ASTROCYTE MITOCHONDRIAL FUNCTION

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LARSEN, N. J.; AMBROSI, G.; MULLETT, S. J.; BERMAN, S. B.; HINKLE, D. A.

2012-01-01

Mitochondrial dysfunction has long been implicated in the pathogenesis of Parkinson’s disease (PD). PD brain tissues show evidence for mitochondrial respiratory chain Complex I deficiency. Pharmacological inhibitors of Complex I, such as rotenone, cause experimental parkinsonism. The cytoprotective protein DJ-1, whose deletion is sufficient to cause genetic PD, is also known to have mitochondria-stabilizing properties. We have previously shown that DJ-1 is over-expressed in PD astrocytes, and that DJ-1 deficiency impairs the capacity of astrocytes to protect co-cultured neurons against rotenone. Since DJ-1 modulated, astrocyte-mediated neuroprotection against rotenone may depend upon proper astrocytic mitochondrial functioning, we hypothesized that DJ-1 deficiency would impair astrocyte mitochondrial motility, fission/fusion dynamics, membrane potential maintenance, and respiration, both at baseline and as an enhancement of rotenone-induced mitochondrial dysfunction. In astrocyte-enriched cultures, we observed that DJ-1 knock-down reduced mitochondrial motility primarily in the cellular processes of both untreated and rotenone treated cells. In these same cultures, DJ-1 knock-down did not appreciably affect mitochondrial fission, fusion, or respiration, but did enhance rotenone-induced reductions in the mitochondrial membrane potential. In neuron–astrocyte co-cultures, astrocytic DJ-1 knock-down reduced astrocyte process mitochondrial motility in untreated cells, but this effect was not maintained in the presence of rotenone. In the same co-cultures, astrocytic DJ-1 knock-down significantly reduced mitochondrial fusion in the astrocyte cell bodies, but not the processes, under the same conditions of rotenone treatment in which DJ-1 deficiency is known to impair astrocyte-mediated neuroprotection. Our studies therefore demonstrated the following new findings: (i) DJ-1 deficiency can impair astrocyte mitochondrial physiology at multiple levels, (ii) astrocyte

Mitochondrial dysfunction and loss of glutamate uptake in primary astrocytes exposed to titanium dioxide nanoparticles

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Wilson, Christina L.; Natarajan, Vaishaali; Hayward, Stephen L.; Khalimonchuk, Oleh; Kidambi, Srivatsan

2015-11-01

Titanium dioxide (TiO2) nanoparticles are currently the second most produced engineered nanomaterial in the world with vast usage in consumer products leading to recurrent human exposure. Animal studies indicate significant nanoparticle accumulation in the brain while cellular toxicity studies demonstrate negative effects on neuronal cell viability and function. However, the toxicological effects of nanoparticles on astrocytes, the most abundant cells in the brain, have not been extensively investigated. Therefore, we determined the sub-toxic effect of three different TiO2 nanoparticles (rutile, anatase and commercially available P25 TiO2 nanoparticles) on primary rat cortical astrocytes. We evaluated some events related to astrocyte functions and mitochondrial dysregulation: (1) glutamate uptake; (2) redox signaling mechanisms by measuring ROS production; (3) the expression patterns of dynamin-related proteins (DRPs) and mitofusins 1 and 2, whose expression is central to mitochondrial dynamics; and (4) mitochondrial morphology by MitoTracker® Red CMXRos staining. Anatase, rutile and P25 were found to have LC50 values of 88.22 +/- 10.56 ppm, 136.0 +/- 31.73 ppm and 62.37 +/- 9.06 ppm respectively indicating nanoparticle specific toxicity. All three TiO2 nanoparticles induced a significant loss in glutamate uptake indicative of a loss in vital astrocyte function. TiO2 nanoparticles also induced an increase in reactive oxygen species generation, and a decrease in mitochondrial membrane potential, suggesting mitochondrial damage. TiO2 nanoparticle exposure altered expression patterns of DRPs at low concentrations (25 ppm) and apoptotic fission at high concentrations (100 ppm). TiO2 nanoparticle exposure also resulted in changes to mitochondrial morphology confirmed by mitochondrial staining. Collectively, our data provide compelling evidence that TiO2 nanoparticle exposure has potential implications in astrocyte-mediated neurological dysfunction.Titanium dioxide (Ti

Glucocorticoid regulation of astrocytic fate and function.

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Shuang Yu

Full Text Available Glial loss in the hippocampus has been suggested as a factor in the pathogenesis of stress-related brain disorders that are characterized by dysregulated glucocorticoid (GC secretion. However, little is known about the regulation of astrocytic fate by GC. Here, we show that astrocytes derived from the rat hippocampus undergo growth inhibition and display moderate activation of caspase 3 after exposure to GC. Importantly, the latter event, observed both in situ and in primary astrocytic cultures is not followed by either early- or late-stage apoptosis, as monitored by stage I or stage II DNA fragmentation. Thus, unlike hippocampal granule neurons, astrocytes are resistant to GC-induced apoptosis; this resistance is due to lower production of reactive oxygen species (ROS and a greater buffering capacity against the cytotoxic actions of ROS. We also show that GC influence hippocampal cell fate by inducing the expression of astrocyte-derived growth factors implicated in the control of neural precursor cell proliferation. Together, our results suggest that GC instigate a hitherto unknown dialog between astrocytes and neural progenitors, adding a new facet to understanding how GC influence the cytoarchitecture of the hippocampus.

Inhibition of Inwardly Rectifying Potassium (Kir 4.1 Channels Facilitates Brain-Derived Neurotrophic Factor (BDNF Expression in Astrocytes

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Masato Kinboshi

2017-12-01

Full Text Available Inwardly rectifying potassium (Kir 4.1 channels in astrocytes regulate neuronal excitability by mediating spatial potassium buffering. Although dysfunction of astrocytic Kir4.1 channels is implicated in the development of epileptic seizures, the functional mechanisms of Kir4.1 channels in modulating epileptogenesis remain unknown. We herein evaluated the effects of Kir4.1 inhibition (blockade and knockdown on expression of brain-derived neurotrophic factor (BDNF, a key modulator of epileptogenesis, in the primary cultures of mouse astrocytes. For blockade of Kir4.1 channels, we tested several antidepressant agents which reportedly bound to and blocked Kir4.1 channels in a subunit-specific manner. Treatment of astrocytes with fluoxetine enhanced BDNF mRNA expression in a concentration-dependent manner and increased the BDNF protein level. Other antidepressants (e.g., sertraline and imipramine also increased the expression of BDNF mRNA with relative potencies similar to those for inhibition of Kir4.1 channels. In addition, suppression of Kir4.1 expression by the transfection of small interfering RNA (siRNA targeting Kir4.1 significantly increased the mRNA and protein levels of BDNF. The BDNF induction by Kir4.1 siRNA transfection was suppressed by the MEK1/2 inhibitor U0126, but not by the p38 MAPK inhibitor SB202190 or the JNK inhibitor SP600125. The present results demonstrated that inhibition of Kir4.1 channels facilitates BDNF expression in astrocytes primarily by activating the Ras/Raf/MEK/ERK pathway, which may be linked to the development of epilepsy and other neuropsychiatric disorders.

Evidence for aberrant astrocyte hemichannel activity in Juvenile Neuronal Ceroid Lipofuscinosis (JNCL).

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Burkovetskaya, Maria; Karpuk, Nikolay; Xiong, Juan; Bosch, Megan; Boska, Michael D; Takeuchi, Hideyuki; Suzumura, Akio; Kielian, Tammy

2014-01-01

Juvenile Neuronal Ceroid Lipofuscinosis (JNCL) is a lysosomal storage disease caused by an autosomal recessive mutation in CLN3 that leads to vision loss, progressive cognitive and motor decline, and premature death. Morphological evidence of astrocyte activation occurs early in the disease process and coincides with regions where neuronal loss eventually ensues. However, the consequences of CLN3 mutation on astrocyte function remain relatively ill-defined. Astrocytes play a critical role in CNS homeostasis, in part, by their ability to regulate the extracellular milieu via the formation of extensive syncytial networks coupled by gap junction (GJ) channels. In contrast, unopposed hemichannels (HCs) have been implicated in CNS pathology by allowing the non-discriminant passage of molecules between the intracellular and extracellular milieus. Here we examined acute brain slices from CLN3 mutant mice (CLN3Δex7/8) to determine whether CLN3 loss alters the balance of GJ and HC activity. CLN3Δex7/8 mice displayed transient increases in astrocyte HC opening at postnatal day 30 in numerous brain regions, compared to wild type (WT) animals; however, HC activity steadily decreased at postnatal days 60 and 90 in CLN3Δex7/8 astrocytes to reach levels lower than WT cells. This suggested a progressive decline in astrocyte function, which was supported by significant reductions in glutamine synthetase, GLAST, and connexin expression in CLN3Δex7/8 mice compared to WT animals. Based on the early increase in astrocyte HC activity, CLN3Δex7/8 mice were treated with the novel carbenoxolone derivative INI-0602 to inhibit HCs. Administration of INI-0602 for a one month period significantly reduced lysosomal ceroid inclusions in the brains of CLN3Δex7/8 mice compared to WT animals, which coincided with significant increases in astrocyte GJ communication and normalization of astrocyte resting membrane potential to WT levels. Collectively, these findings suggest that alterations in

Evidence for aberrant astrocyte hemichannel activity in Juvenile Neuronal Ceroid Lipofuscinosis (JNCL.

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Maria Burkovetskaya

Full Text Available Juvenile Neuronal Ceroid Lipofuscinosis (JNCL is a lysosomal storage disease caused by an autosomal recessive mutation in CLN3 that leads to vision loss, progressive cognitive and motor decline, and premature death. Morphological evidence of astrocyte activation occurs early in the disease process and coincides with regions where neuronal loss eventually ensues. However, the consequences of CLN3 mutation on astrocyte function remain relatively ill-defined. Astrocytes play a critical role in CNS homeostasis, in part, by their ability to regulate the extracellular milieu via the formation of extensive syncytial networks coupled by gap junction (GJ channels. In contrast, unopposed hemichannels (HCs have been implicated in CNS pathology by allowing the non-discriminant passage of molecules between the intracellular and extracellular milieus. Here we examined acute brain slices from CLN3 mutant mice (CLN3Δex7/8 to determine whether CLN3 loss alters the balance of GJ and HC activity. CLN3Δex7/8 mice displayed transient increases in astrocyte HC opening at postnatal day 30 in numerous brain regions, compared to wild type (WT animals; however, HC activity steadily decreased at postnatal days 60 and 90 in CLN3Δex7/8 astrocytes to reach levels lower than WT cells. This suggested a progressive decline in astrocyte function, which was supported by significant reductions in glutamine synthetase, GLAST, and connexin expression in CLN3Δex7/8 mice compared to WT animals. Based on the early increase in astrocyte HC activity, CLN3Δex7/8 mice were treated with the novel carbenoxolone derivative INI-0602 to inhibit HCs. Administration of INI-0602 for a one month period significantly reduced lysosomal ceroid inclusions in the brains of CLN3Δex7/8 mice compared to WT animals, which coincided with significant increases in astrocyte GJ communication and normalization of astrocyte resting membrane potential to WT levels. Collectively, these findings suggest that

Active sulforhodamine 101 uptake into hippocampal astrocytes.

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Christian Schnell

Full Text Available Sulforhodamine 101 (SR101 is widely used as a marker of astrocytes. In this study we investigated labeling of astrocytes by SR101 in acute slices from the ventrolateral medulla and the hippocampus of transgenic mice expressing EGFP under the control of the astrocyte-specific human GFAP promoter. While SR101 efficiently and specifically labeled EGFP-expressing astrocytes in hippocampus, we found that the same staining procedure failed to label astrocytes efficiently in the ventrolateral medulla. Although carbenoxolone is able to decrease the SR101-labeling of astrocytes in the hippocampus, it is unlikely that SR101 is taken up via gap-junction hemichannels because mefloquine, a blocker for pannexin and connexin hemichannels, was unable to prevent SR101-labeling of hippocampal astrocytes. However, SR101-labeling of the hippocampal astrocytes was significantly reduced by substrates of organic anion transport polypeptides, including estron-3-sulfate and dehydroepiandrosterone sulfate, suggesting that SR101 is actively transported into hippocampal astrocytes.

Apolipoproteins E and J interfere with amyloid-beta uptake by primary human astrocytes and microglia in vitro

NARCIS (Netherlands)

Mulder, S.D.; Nielsen, H.M.; Blankenstein, M.A.; Eikelenboom, P.; Veerhuis, R.

2014-01-01

Defective clearance of the amyloid-β peptide (Aβ) from the brain is considered a strong promoter in Alzheimer's disease (AD) pathogenesis. Astrocytes and microglia are important mediators of Aβ clearance and Aβ aggregation state and the presence of amyloid associated proteins (AAPs), such as

Proteomics analyses of human optic nerve head astrocytes following biomechanical strain.

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Rogers, Ronan S; Dharsee, Moyez; Ackloo, Suzanne; Sivak, Jeremy M; Flanagan, John G

2012-02-01

We investigate the role of glial cell activation in the human optic nerve caused by raised intraocular pressure, and their potential role in the development of glaucomatous optic neuropathy. To do this we present a proteomics study of the response of cultured, optic nerve head astrocytes to biomechanical strain, the magnitude and mode of strain based on previously published quantitative models. In this case, astrocytes were subjected to 3 and 12% stretches for either 2 h or 24 h. Proteomic methods included nano-liquid chromatography, tandem mass spectrometry, and iTRAQ labeling. Using controls for both stretch and time, a six-plex iTRAQ liquid chromatography- tandem MS (LC/MS/MS) experiment yielded 573 proteins discovered at a 95% confidence limit. The pathways included transforming growth factor β1, tumor necrosis factor, caspase 3, and tumor protein p53, which have all been implicated in the activation of astrocytes and are believed to play a role in the development of glaucomatous optic neuropathy. Confirmation of the iTRAQ analysis was performed by Western blotting of various proteins of interest including ANXA 4, GOLGA2, and αB-Crystallin.

Proteomics Analyses of Human Optic Nerve Head Astrocytes Following Biomechanical Strain*

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Rogers, Ronan S.; Dharsee, Moyez; Ackloo, Suzanne; Sivak, Jeremy M.; Flanagan, John G.

2012-01-01

We investigate the role of glial cell activation in the human optic nerve caused by raised intraocular pressure, and their potential role in the development of glaucomatous optic neuropathy. To do this we present a proteomics study of the response of cultured, optic nerve head astrocytes to biomechanical strain, the magnitude and mode of strain based on previously published quantitative models. In this case, astrocytes were subjected to 3 and 12% stretches for either 2 h or 24 h. Proteomic methods included nano-liquid chromatography, tandem mass spectrometry, and iTRAQ labeling. Using controls for both stretch and time, a six-plex iTRAQ liquid chromatography- tandem MS (LC/MS/MS) experiment yielded 573 proteins discovered at a 95% confidence limit. The pathways included transforming growth factor β1, tumor necrosis factor, caspase 3, and tumor protein p53, which have all been implicated in the activation of astrocytes and are believed to play a role in the development of glaucomatous optic neuropathy. Confirmation of the iTRAQ analysis was performed by Western blotting of various proteins of interest including ANXA 4, GOLGA2, and αB-Crystallin. PMID:22126795

Targeting of astrocytic glucose metabolism by beta-hydroxybutyrate.

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Valdebenito, Rocío; Ruminot, Iván; Garrido-Gerter, Pamela; Fernández-Moncada, Ignacio; Forero-Quintero, Linda; Alegría, Karin; Becker, Holger M; Deitmer, Joachim W; Barros, L Felipe

2016-10-01

The effectiveness of ketogenic diets and intermittent fasting against neurological disorders has brought interest to the effects of ketone bodies on brain cells. These compounds are known to modify the metabolism of neurons, but little is known about their effect on astrocytes, cells that control the supply of glucose to neurons and also modulate neuronal excitability through the glycolytic production of lactate. Here we have used genetically-encoded Förster Resonance Energy Transfer nanosensors for glucose, pyruvate and ATP to characterize astrocytic energy metabolism at cellular resolution. Our results show that the ketone body beta-hydroxybutyrate strongly inhibited astrocytic glucose consumption in mouse astrocytes in mixed cultures, in organotypic hippocampal slices and in acute hippocampal slices prepared from ketotic mice, while blunting the stimulation of glycolysis by physiological and pathophysiological stimuli. The inhibition of glycolysis was paralleled by an increased ability of astrocytic mitochondria to metabolize pyruvate. These results support the emerging notion that astrocytes contribute to the neuroprotective effect of ketone bodies. © The Author(s) 2015.

CPEB1 modulates lipopolysaccharide-mediated iNOS induction in rat primary astrocytes

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Kim, Ki Chan; Hyun Joo, So; Shin, Chan Young

2011-01-01

Highlights: → Expression and phosphorylation of CPEB1 is increased by LPS stimulation in rat primary astrocytes. → JNK regulates expression and phosphorylation of CPEB1 in reactive astrocytes. → Down-regulation of CPEB1 using siRNA inhibits oxidative stress and iNOS induction by LPS stimulation. → CPEB1 may play an important role in regulating inflammatory responses in reactive astrocytes induced by LPS. -- Abstract: Upon CNS damage, astrocytes undergo a series of biological changes including increased proliferation, production of inflammatory mediators and morphological changes, in a response collectively called reactive gliosis. This process is an essential part of the brains response to injury, yet much is unknown about the molecular mechanism(s) that induce these changes. In this study, we investigated the role of cytoplasmic polyadenylation element binding protein 1 (CPEB1) in the regulation of inflammatory responses in a model of reactive gliosis, lipopolysaccharide-stimulated astrocytes. CPEB1 is an mRNA-binding protein recently shown to be expressed in astrocytes that may play a role in astrocytes migration. After LPS stimulation, the expression and phosphorylation of CPEB1 was increased in rat primary astrocytes in a JNK-dependent process. siRNA-induced knockdown of CPEB1 expression inhibited the LPS-induced up-regulation of iNOS as well as NO and ROS production, a hallmark of immunological activation of astrocytes. The results from the study suggest that CPEB1 is actively involved in the regulation of inflammatory responses in astrocytes, which might provide new insights into the regulatory mechanism after brain injury.

Patterning of functional human astrocytes onto parylene-C/SiO2 substrates for the study of Ca2+ dynamics in astrocytic networks

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Raos, B. J.; Simpson, M. C.; Doyle, C. S.; Murray, A. F.; Graham, E. S.; Unsworth, C. P.

2018-06-01

Objective. Recent literature suggests that astrocytes form organized functional networks and communicate through transient changes in cytosolic Ca2+. Traditional techniques to investigate network activity, such as pharmacological blocking or genetic knockout, are difficult to restrict to individual cells. The objective of this work is to develop cell-patterning techniques to physically manipulate astrocytic interactions to enable the study of Ca2+ in astrocytic networks. Approach. We investigate how an in vitro cell-patterning platform that utilizes geometric patterns of parylene-C on SiO2 can be used to physically isolate single astrocytes and small astrocytic networks. Main results. We report that single astrocytes are effectively isolated on 75  ×  75 µm square parylene nodes, whereas multi-cellular astrocytic networks are isolated on larger nodes, with the mean number of astrocytes per cluster increasing as a function of node size. Additionally, we report that astrocytes in small multi-cellular clusters exhibit spatio-temporal clustering of Ca2+ transients. Finally, we report that the frequency and regularity of Ca2+ transients was positively correlated with astrocyte connectivity. Significance. The significance of this work is to demonstrate how patterning hNT astrocytes replicates spatio-temporal clustering of Ca2+ signalling that is observed in vivo but not in dissociated in vitro cultures. We therefore highlight the importance of the structure of astrocytic networks in determining ensemble Ca2+ behaviour.

Electrospun fiber surface nanotopography influences astrocyte-mediated neurite outgrowth.

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Johnson, Christopher D; D'Amato, Anthony R; Puhl, Devan L; Wich, Douglas M; Vespermann, Amanda; Gilbert, Ryan J

2018-05-15

Aligned, electrospun fiber scaffolds provide topographical guidance for regenerating neurons and glia after central nervous system injury. To date, no study has explored how fiber surface nanotopography affects astrocyte response to fibrous scaffolds. Astrocytes play important roles in the glial scar, the blood brain barrier, and in maintaining homeostasis in the central nervous system. In this study, electrospun poly L-lactic acid fibers were engineered with smooth, pitted, or divoted surface nanotopography. Cortical or spinal cord primary rat astrocytes were cultured on the surfaces for either 1 or 3 days to examine the astrocyte response over time. The results showed that cortical astrocytes were significantly shorter and broader on the pitted and divoted fibers compared to those on smooth fibers. However, spinal cord astrocyte morphology was not significantly altered by the surface features. These findings indicate that astrocytes from unique anatomical locations respond differently to the presence of nanotopography. Western Blot results show that the differences in morphology were not associated with significant changes in GFAP or vinculin in either astrocyte population, suggesting that surface pits and divots do not induce a reactive phenotype in either cortical or spinal cord astrocytes. Finally, astrocytes were co-cultured with dorsal root ganglia to determine how the surfaces affected astrocyte-mediated neurite outgrowth. Astrocytes cultured on the fibers for shorter periods of time (1 day) generally supported longer neurite outgrowth. Pitted and divoted fibers restricted spinal cord astrocyte-mediated neurite outgrowth, while smooth fibers increased 3 day spinal cord astrocyte-mediated neurite outgrowth. In total, fiber surface nanotopography can influence astrocyte elongation and influence the capability of astrocytes to direct neurites. Therefore, fiber surface characteristics should be carefully controlled to optimize astrocyte-mediated axonal

Astrocytes mediate in vivo cholinergic-induced synaptic plasticity.

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Marta Navarrete

2012-02-01

Full Text Available Long-term potentiation (LTP of synaptic transmission represents the cellular basis of learning and memory. Astrocytes have been shown to regulate synaptic transmission and plasticity. However, their involvement in specific physiological processes that induce LTP in vivo remains unknown. Here we show that in vivo cholinergic activity evoked by sensory stimulation or electrical stimulation of the septal nucleus increases Ca²⁺ in hippocampal astrocytes and induces LTP of CA3-CA1 synapses, which requires cholinergic muscarinic (mAChR and metabotropic glutamate receptor (mGluR activation. Stimulation of cholinergic pathways in hippocampal slices evokes astrocyte Ca²⁺ elevations, postsynaptic depolarizations of CA1 pyramidal neurons, and LTP of transmitter release at single CA3-CA1 synapses. Like in vivo, these effects are mediated by mAChRs, and this cholinergic-induced LTP (c-LTP also involves mGluR activation. Astrocyte Ca²⁺ elevations and LTP are absent in IP₃R2 knock-out mice. Downregulating astrocyte Ca²⁺ signal by loading astrocytes with BAPTA or GDPβS also prevents LTP, which is restored by simultaneous astrocyte Ca²⁺ uncaging and postsynaptic depolarization. Therefore, cholinergic-induced LTP requires astrocyte Ca²⁺ elevations, which stimulate astrocyte glutamate release that activates mGluRs. The cholinergic-induced LTP results from the temporal coincidence of the postsynaptic activity and the astrocyte Ca²⁺ signal simultaneously evoked by cholinergic activity. Therefore, the astrocyte Ca²⁺ signal is necessary for cholinergic-induced synaptic plasticity, indicating that astrocytes are directly involved in brain storage information.

Glutamate-induced glutamate release: A proposed mechanism for calcium bursting in astrocytes

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Larter, Raima; Craig, Melissa Glendening

2005-12-01

Here we present a new model for the generation of complex calcium-bursting patterns in astrocytes, a type of brain cell recently implicated in a variety of neural functions including memory formation. The model involves two positive feedback processes, in which the key feedback species are calcium ion and glutamate. The latter is the most abundant excitatory neurotransmitter in the brain and has been shown to be involved in bidirectional communication between astrocytes and nearby neurons. The glutamate feedback process considered here is shown to be critical for the generation of complex bursting oscillations in the astrocytes and to, perhaps, code for information which may be passed from neuron to neuron via the astrocyte. These processes may be involved in memory storage and formation as well as in mechanisms which lead to dynamical diseases such as epilepsy.

Astrocyte-neuronal interactions in epileptogenesis.

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Hadera, Mussie Ghezu; Eloqayli, Haytham; Jaradat, Saied; Nehlig, Astrid; Sonnewald, Ursula

2015-07-01

Pentylenetetrazol, kainic acid, or pilocarpine can be used to induce seizures in animal models of epilepsy. The present Review describes disturbances in astrocyte-neuron interactions in the acute, latent, and chronic phases analyzed by magnetic resonance spectroscopy of brain tissue extracts from rats injected with [1-(13)C]glucose and [1,2-(13)C]acetate. The most consistent change after onset of seizures was the decrease in (13)C labeling of glutamate (GLU) from [1-(13) C]glucose regardless of brain area, severity, or duration of the period with seizures and toxin used. In most cases this decrease was accompanied by a reduction in glutamine (GLN) labeling from [1-(13)C]glucose, presumably as a direct consequence of the reduction in labeling of GLU and the GLU-GLN cycle. Amounts of GLN were never changed. Reduction in the content of N-acetyl aspartate (NAA) was first detectable some time after status epilepticus but before the occurrence of spontaneous seizures. This decrease can be an indication of neuronal death and/or mitochondrial impairment and might indicate beginning gliosis. It is known that gliosis occurs in the chronic phase of temporal lobe epilepsy in hippocampus, but astrocyte metabolism appears normal in this phase, indicating that the gliotic astrocytes have a somewhat reduced metabolism per volume. A decrease in (13)C labeling of GLU from [1-(13)C]glucose is a very sensitive measure for the onset of epileptogenesis, whereas reduction of NAA is first detectable later. In the chronic phases of the hippocampal formation, astrocyte metabolism is upregulated given that the number of neurons is reduced. © 2015 Wiley Periodicals, Inc.

Major Shifts in Glial Regional Identity Are a Transcriptional Hallmark of Human Brain Aging

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Lilach Soreq

2017-01-01

Full Text Available Gene expression studies suggest that aging of the human brain is determined by a complex interplay of molecular events, although both its region- and cell-type-specific consequences remain poorly understood. Here, we extensively characterized aging-altered gene expression changes across ten human brain regions from 480 individuals ranging in age from 16 to 106 years. We show that astrocyte- and oligodendrocyte-specific genes, but not neuron-specific genes, shift their regional expression patterns upon aging, particularly in the hippocampus and substantia nigra, while the expression of microglia- and endothelial-specific genes increase in all brain regions. In line with these changes, high-resolution immunohistochemistry demonstrated decreased numbers of oligodendrocytes and of neuronal subpopulations in the aging brain cortex. Finally, glial-specific genes predict age with greater precision than neuron-specific genes, thus highlighting the need for greater mechanistic understanding of neuron-glia interactions in aging and late-life diseases.

Major Shifts in Glial Regional Identity Are a Transcriptional Hallmark of Human Brain Aging.

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Soreq, Lilach; Rose, Jamie; Soreq, Eyal; Hardy, John; Trabzuni, Daniah; Cookson, Mark R; Smith, Colin; Ryten, Mina; Patani, Rickie; Ule, Jernej

2017-01-10

Gene expression studies suggest that aging of the human brain is determined by a complex interplay of molecular events, although both its region- and cell-type-specific consequences remain poorly understood. Here, we extensively characterized aging-altered gene expression changes across ten human brain regions from 480 individuals ranging in age from 16 to 106 years. We show that astrocyte- and oligodendrocyte-specific genes, but not neuron-specific genes, shift their regional expression patterns upon aging, particularly in the hippocampus and substantia nigra, while the expression of microglia- and endothelial-specific genes increase in all brain regions. In line with these changes, high-resolution immunohistochemistry demonstrated decreased numbers of oligodendrocytes and of neuronal subpopulations in the aging brain cortex. Finally, glial-specific genes predict age with greater precision than neuron-specific genes, thus highlighting the need for greater mechanistic understanding of neuron-glia interactions in aging and late-life diseases. Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.

Hemin inhibits NO production by IL-1β-stimulated human astrocytes through induction of heme oxygenase-1 and reduction of p38 MAPK activation

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Sheng Wen S

2010-09-01

Full Text Available Abstract Background Heme oxygenase (HO-1 has been shown to attenuate oxidative injury and reduce apoptosis. HO-1 can be induced by various stimuli released during cellular injury, such as heme. Deleterious free heme is degraded by HO-1 to carbon monoxide, iron and biliverdin, which have potent anti-oxidant and anti-inflammatory properties. In this study, we tested the hypothesis that upregulation of HO-1 would inhibit production of the free radical (NO by interlukin (IL-1β-activated human astrocytes. Methods To measure NO production, inducible NO synthase (iNOS, HO-1 expression and mitogen-activated protein (MAP kinase activation we used hemin as an HO-1 inducer and tin protoporphyrin (SnPP IX as an inhibitor of HO-1 activity in human astrocyte cultures prior to IL-1β exposure. Transfection of astrocyte cultures was performed using a pLEX expression vector carrying the human HO-1 sequence prior to IL-1β treatment. Supernatants of astrocyte cultures pretreated with inhibitors of p38 MAPK or MEK1/2 prior to IL-1β exposure were collected for NO assay. Results IL-1β treatment of astrocytes alone induced undetectable amounts of HO-1 protein by western blot. However, HO-1 mRNA expression was modestly up-regulated in response to IL-1β stimulation. Pretreatment with hemin alone substantially induced both HO-1 mRNA and protein expression, and HO-1 mRNA expression was further enhanced when hemin was combined with IL-1β treatment. In contrast, IL-1β-induced iNOS mRNA expression and NO production were markedly inhibited by hemin treatment. When pretreated with SnPP, the inhibitory effect of hemin on IL-1β-induced NO production and iNOS expression was reversed, suggesting the involvement of HO-1. IL-1β-induced p38 MAPK activation, which is known to be required for NO production, was also down-regulated by hemin. Conclusion These findings support the hypothesis that up-regulation of HO-1 in astrocytes is associated with down-regulation of i

GFAP promoter driven transgenic expression of PDGFB in the mouse brain leads to glioblastoma in a Trp53 null background

NARCIS (Netherlands)

Hede, Sanna-Maria; Hansson, Inga; Afink, Gijs B.; Eriksson, Anna; Nazarenko, Inga; Andrae, Johanna; Genove, Guillem; Westermark, Bengt; Nistér, Monica

2009-01-01

Glioblastomas are the most common and malignant astrocytic brain tumors in human adults. The tumor suppressor gene TP53 is commonly mutated and/or lost in astrocytic brain tumors and the TP53 alterations are often found in combination with excessive growth factor signaling via PDGF/PDGFRalpha. Here,

Astrocytes take the stage in a tale of signaling-metabolism coupling

DEFF Research Database (Denmark)

Bak, Lasse K

2017-01-01

Astrocytes are crucial cells in the brain that are intimately coupled with neuronal metabolism. A new paper from San Martín et al. provides evidence that physiological levels of the gaseous signal molecule NO can rapidly and reversibly increase astrocyte metabolism of glucose and production...... of lactate. A proposed neurological coupling-from the potential source of NO, endothelial cells, to the potential beneficiary from the lactate, neurons-prompts new questions regarding the controversial role of lactate in the brain....

Metabolic Communication between Astrocytes and Neurons via Bicarbonate-Responsive Soluble Adenylyl Cyclase

OpenAIRE

Choi, Hyun B.; Gordon, Grant R.J.; Zhou, Ning; Tai, Chao; Rungta, Ravi L.; Martinez, Jennifer; Milner, Teresa A.; Ryu, Jae K.; McLarnon, James G.; Tresguerres, Martin; Levin, Lonny R.; Buck, Jochen; MacVicar, Brian A.

2012-01-01

Astrocytes are proposed to participate in brain energy metabolism by supplying substrates to neurons from their glycogen stores and from glycolysis. However, the molecules involved in metabolic sensing and the molecular pathways responsible for metabolic coupling between different cell types in the brain are not fully understood. Here we show that a recently cloned bicarbonate (HCO3−) sensor, soluble adenylyl cyclase (sAC), is highly expressed in astrocytes and becomes activated in response t...

Neuroinflammation alters voltage-dependent conductance in striatal astrocytes.

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Karpuk, Nikolay; Burkovetskaya, Maria; Kielian, Tammy

2012-07-01

Neuroinflammation has the capacity to alter normal central nervous system (CNS) homeostasis and function. The objective of the present study was to examine the effects of an inflammatory milieu on the electrophysiological properties of striatal astrocyte subpopulations with a mouse bacterial brain abscess model. Whole cell patch-clamp recordings were performed in striatal glial fibrillary acidic protein (GFAP)-green fluorescent protein (GFP)(+) astrocytes neighboring abscesses at postinfection days 3 or 7 in adult mice. Cell input conductance (G(i)) measurements spanning a membrane potential (V(m)) surrounding resting membrane potential (RMP) revealed two prevalent astrocyte subsets. A1 and A2 astrocytes were identified by negative and positive G(i) increments vs. V(m), respectively. A1 and A2 astrocytes displayed significantly different RMP, G(i), and cell membrane capacitance that were influenced by both time after bacterial exposure and astrocyte proximity to the inflammatory site. Specifically, the percentage of A1 astrocytes was decreased immediately surrounding the inflammatory lesion, whereas A2 cells were increased. These changes were particularly evident at postinfection day 7, revealing increased cell numbers with an outward current component. Furthermore, RMP was inversely modified in A1 and A2 astrocytes during neuroinflammation, and resting G(i) was increased from 21 to 30 nS in the latter. In contrast, gap junction communication was significantly decreased in all astrocyte populations associated with inflamed tissues. Collectively, these findings demonstrate the heterogeneity of striatal astrocyte populations, which experience distinct electrophysiological modifications in response to CNS inflammation.

Glutamate metabolism is down-regulated in astrocytes during experimental allergic encephalomyelitis

DEFF Research Database (Denmark)

Hardin-Pouzet, H; Krakowski, M; Bourbonnière, L

1997-01-01

dehydrogenase (GDH) expression were dramatically reduced. These two astrocytic enzymes are responsible for degradation of glutamate, the most abundant excitatory neurotransmitter in the brain. Since elevated levels of glutamate may be neurotoxic, we propose that the decreased capacity of astrocytes...... to metabolize glutamate may contribute to EAE pathology....

(13)C heteronuclear NMR studies of the interaction of cultured neurons and astrocytes and aluminum blockade of the preferential release of citrate from astrocytes.

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Meshitsuka, Shunsuke; Aremu, David A

2008-02-01

Citrate has been identified as a major tricarboxylic acid (TCA) cycle constituent preferentially released by astrocytes. We undertook the present study to examine further the nature of metabolic compartmentation in central nervous system tissues using (13)C-labeled glucose and to provide new information on the influence of aluminum on the metabolic interaction between neurons and astrocytes. Metabolites released into the culture medium from astrocytes and neuron-astrocyte coculture, as well as the perchloric acid extracts of the cells were analyzed using 2D (1)H and (13)C NMR spectroscopy. Astrocytes released citrate into the culture medium and the released citrate was consumed by neurons in coculture. Citrate release by astrocytes was blocked in the presence of aluminum, with progressive accumulation of citrate within the cells. We propose citrate supply is a more efficient energy source than lactate for neurons to produce ATP, especially in the hypoglycemic state on account of it being a direct component of the TCA cycle. Astrocytes may be the cellular compartment for aluminum accumulation as a citrate complex in the brain.

Sodium signaling and astrocyte energy metabolism

KAUST Repository

Chatton, Jean-Yves; Magistretti, Pierre J.; Barros, L. Felipe

2016-01-01

The Na+ gradient across the plasma membrane is constantly exploited by astrocytes as a secondary energy source to regulate the intracellular and extracellular milieu, and discard waste products. One of the most prominent roles of astrocytes in the brain is the Na+-dependent clearance of glutamate released by neurons during synaptic transmission. The intracellular Na+ load collectively generated by these processes converges at the Na,K-ATPase pump, responsible for Na+ extrusion from the cell, which is achieved at the expense of cellular ATP. These processes represent pivotal mechanisms enabling astrocytes to increase the local availability of metabolic substrates in response to neuronal activity. This review presents basic principles linking the intracellular handling of Na+ following activity-related transmembrane fluxes in astrocytes and the energy metabolic pathways involved. We propose a role of Na+ as an energy currency and as a mediator of metabolic signals in the context of neuron-glia interactions. We further discuss the possible impact of the astrocytic syncytium for the distribution and coordination of the metabolic response, and the compartmentation of these processes in cellular microdomains and subcellular organelles. Finally, we illustrate future avenues of investigation into signaling mechanisms aimed at bridging the gap between Na+ and the metabolic machinery. © 2016 Wiley Periodicals, Inc.

Sodium signaling and astrocyte energy metabolism

KAUST Repository

Chatton, Jean-Yves

2016-03-31

The Na+ gradient across the plasma membrane is constantly exploited by astrocytes as a secondary energy source to regulate the intracellular and extracellular milieu, and discard waste products. One of the most prominent roles of astrocytes in the brain is the Na+-dependent clearance of glutamate released by neurons during synaptic transmission. The intracellular Na+ load collectively generated by these processes converges at the Na,K-ATPase pump, responsible for Na+ extrusion from the cell, which is achieved at the expense of cellular ATP. These processes represent pivotal mechanisms enabling astrocytes to increase the local availability of metabolic substrates in response to neuronal activity. This review presents basic principles linking the intracellular handling of Na+ following activity-related transmembrane fluxes in astrocytes and the energy metabolic pathways involved. We propose a role of Na+ as an energy currency and as a mediator of metabolic signals in the context of neuron-glia interactions. We further discuss the possible impact of the astrocytic syncytium for the distribution and coordination of the metabolic response, and the compartmentation of these processes in cellular microdomains and subcellular organelles. Finally, we illustrate future avenues of investigation into signaling mechanisms aimed at bridging the gap between Na+ and the metabolic machinery. © 2016 Wiley Periodicals, Inc.

Involvement of astrocyte metabolic coupling in Tourette syndrome pathogenesis.

Science.gov (United States)

de Leeuw, Christiaan; Goudriaan, Andrea; Smit, August B; Yu, Dongmei; Mathews, Carol A; Scharf, Jeremiah M; Verheijen, Mark H G; Posthuma, Danielle

2015-11-01

Tourette syndrome is a heritable neurodevelopmental disorder whose pathophysiology remains unknown. Recent genome-wide association studies suggest that it is a polygenic disorder influenced by many genes of small effect. We tested whether these genes cluster in cellular function by applying gene-set analysis using expert curated sets of brain-expressed genes in the current largest available Tourette syndrome genome-wide association data set, involving 1285 cases and 4964 controls. The gene sets included specific synaptic, astrocytic, oligodendrocyte and microglial functions. We report association of Tourette syndrome with a set of genes involved in astrocyte function, specifically in astrocyte carbohydrate metabolism. This association is driven primarily by a subset of 33 genes involved in glycolysis and glutamate metabolism through which astrocytes support synaptic function. Our results indicate for the first time that the process of astrocyte-neuron metabolic coupling may be an important contributor to Tourette syndrome pathogenesis.

Astrocytic gap junctional networks suppress cellular damage in an in vitro model of ischemia

International Nuclear Information System (INIS)

Shinotsuka, Takanori; Yasui, Masato; Nuriya, Mutsuo

2014-01-01

Highlights: • Astrocytes exhibit characteristic changes in [Ca 2+ ] i under OGD. • Astrocytic [Ca 2+ ] i increase is synchronized with a neuronal anoxic depolarization. • Gap junctional couplings protect neurons as well as astrocytes during OGD. - Abstract: Astrocytes play pivotal roles in both the physiology and the pathophysiology of the brain. They communicate with each other via extracellular messengers as well as through gap junctions, which may exacerbate or protect against pathological processes in the brain. However, their roles during the acute phase of ischemia and the underlying cellular mechanisms remain largely unknown. To address this issue, we imaged changes in the intracellular calcium concentration ([Ca 2+ ] i ) in astrocytes in mouse cortical slices under oxygen/glucose deprivation (OGD) condition using two-photon microscopy. Under OGD, astrocytes showed [Ca 2+ ] i oscillations followed by larger and sustained [Ca 2+ ] i increases. While the pharmacological blockades of astrocytic receptors for glutamate and ATP had no effect, the inhibitions of gap junctional intercellular coupling between astrocytes significantly advanced the onset of the sustained [Ca 2+ ] i increase after OGD exposure. Interestingly, the simultaneous recording of the neuronal membrane potential revealed that the onset of the sustained [Ca 2+ ] i increase in astrocytes was synchronized with the appearance of neuronal anoxic depolarization. Furthermore, the blockade of gap junctional coupling resulted in a concurrent faster appearance of neuronal depolarizations, which remain synchronized with the sustained [Ca 2+ ] i increase in astrocytes. These results indicate that astrocytes delay the appearance of the pathological responses of astrocytes and neurons through their gap junction-mediated intercellular network under OGD. Thus, astrocytic gap junctional networks provide protection against tissue damage during the acute phase of ischemia

Subthalamic nucleus electrical stimulation modulates calcium activity of nigral astrocytes.

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Elodie Barat

Full Text Available The substantia nigra pars reticulata (SNr is a major output nucleus of the basal ganglia, delivering inhibitory efferents to the relay nuclei of the thalamus. Pathological hyperactivity of SNr neurons is known to be responsible for some motor disorders e.g. in Parkinson's disease. One way to restore this pathological activity is to electrically stimulate one of the SNr input, the excitatory subthalamic nucleus (STN, which has emerged as an effective treatment for parkinsonian patients. The neuronal network and signal processing of the basal ganglia are well known but, paradoxically, the role of astrocytes in the regulation of SNr activity has never been studied.In this work, we developed a rat brain slice model to study the influence of spontaneous and induced excitability of afferent nuclei on SNr astrocytes calcium activity. Astrocytes represent the main cellular population in the SNr and display spontaneous calcium activities in basal conditions. Half of this activity is autonomous (i.e. independent of synaptic activity while the other half is dependent on spontaneous glutamate and GABA release, probably controlled by the pace-maker activity of the pallido-nigral and subthalamo-nigral loops. Modification of the activity of the loops by STN electrical stimulation disrupted this astrocytic calcium excitability through an increase of glutamate and GABA releases. Astrocytic AMPA, mGlu and GABA(A receptors were involved in this effect.Astrocytes are now viewed as active components of neural networks but their role depends on the brain structure concerned. In the SNr, evoked activity prevails and autonomous calcium activity is lower than in the cortex or hippocampus. Our data therefore reflect a specific role of SNr astrocytes in sensing the STN-GPe-SNr loops activity and suggest that SNr astrocytes could potentially feedback on SNr neuronal activity. These findings have major implications given the position of SNr in the basal ganglia network.

Subthalamic nucleus electrical stimulation modulates calcium activity of nigral astrocytes.

Science.gov (United States)

Barat, Elodie; Boisseau, Sylvie; Bouyssières, Céline; Appaix, Florence; Savasta, Marc; Albrieux, Mireille

2012-01-01

The substantia nigra pars reticulata (SNr) is a major output nucleus of the basal ganglia, delivering inhibitory efferents to the relay nuclei of the thalamus. Pathological hyperactivity of SNr neurons is known to be responsible for some motor disorders e.g. in Parkinson's disease. One way to restore this pathological activity is to electrically stimulate one of the SNr input, the excitatory subthalamic nucleus (STN), which has emerged as an effective treatment for parkinsonian patients. The neuronal network and signal processing of the basal ganglia are well known but, paradoxically, the role of astrocytes in the regulation of SNr activity has never been studied. In this work, we developed a rat brain slice model to study the influence of spontaneous and induced excitability of afferent nuclei on SNr astrocytes calcium activity. Astrocytes represent the main cellular population in the SNr and display spontaneous calcium activities in basal conditions. Half of this activity is autonomous (i.e. independent of synaptic activity) while the other half is dependent on spontaneous glutamate and GABA release, probably controlled by the pace-maker activity of the pallido-nigral and subthalamo-nigral loops. Modification of the activity of the loops by STN electrical stimulation disrupted this astrocytic calcium excitability through an increase of glutamate and GABA releases. Astrocytic AMPA, mGlu and GABA(A) receptors were involved in this effect. Astrocytes are now viewed as active components of neural networks but their role depends on the brain structure concerned. In the SNr, evoked activity prevails and autonomous calcium activity is lower than in the cortex or hippocampus. Our data therefore reflect a specific role of SNr astrocytes in sensing the STN-GPe-SNr loops activity and suggest that SNr astrocytes could potentially feedback on SNr neuronal activity. These findings have major implications given the position of SNr in the basal ganglia network.

A population of human brain cells expressing phenotypic markers of more than one lineage can be induced in vitro to differentiate into mesenchymal cells

International Nuclear Information System (INIS)

Rieske, Piotr; Augelli, Brian J.; Stawski, Robert; Gaughan, John; Azizi, S. Ausim; Krynska, Barbara

2009-01-01

Proliferating astrocytic cells from germinal, as well as mature areas of brain parenchyma, have the characteristics of neural stem/progenitor cells and are capable of generating both neurons and glia. We previously reported that primary fetal human brain cells, designated as Normal Human Astrocytes (NHA), expressed, in addition to GFAP, Vimentin and Nestin, low levels of βIII-Tubulin, an early neuronal marker, and differentiated into neurons and astrocytes in vitro. Here, we showed that primary NHA cells co-express low levels of mesenchymal markers Fibronectin and Collagen-1 in culture. These cells transitioned into mesenchymal-like cells when cultured in adherent conditions in serum containing media. The mesenchymal-like derivatives of these cells were characterized based on their morphological changes, high expression of Vimentin and extracellular matrix (ECM) proteins, Collagen-1 and Fibronectin, and decline of neural markers. When incubated in osteogenic and adipogenic induction media, the mesenchymal-like cells differentiated into osteoblasts and adipocytes. Furthermore, NHA cells express markers of neural crest cells, SOX-10 and p75. These data support the idea of ectoderm-derived mesenchymal lineages. These findings suggest that a population of primitive fetal brain cells with neural/neural crest/mesenchymal phenotype, resembles the remarkable phenotypic plasticity of neural crest cells, and differentiates into adipocytes and osteocytes under the influence of environmental factors

Preferential lentiviral targeting of astrocytes in the central nervous system.

Directory of Open Access Journals (Sweden)

Michael Fassler

Full Text Available The ability to visualize and genetically manipulate specific cell populations of the central nervous system (CNS is fundamental to a better understanding of brain functions at the cellular and molecular levels. Tools to selectively target cells of the CNS include molecular genetics, imaging, and use of transgenic animals. However, these approaches are technically challenging, time consuming, and difficult to control. Viral-mediated targeting of cells in the CNS can be highly beneficial for studying and treating neurodegenerative diseases. Yet, despite specific marking of numerous cell types in the CNS, in vivo selective targeting of astrocytes has not been optimized. In this study, preferential targeting of astrocytes in the CNS was demonstrated using engineered lentiviruses that were pseudotyped with a modified Sindbis envelope and displayed anti-GLAST IgG on their surfaces as an attachment moiety. Viral tropism for astrocytes was initially verified in vitro in primary mixed glia cultures. When injected into the brains of mice, lentiviruses that displayed GLAST IgG on their surface, exhibited preferential astrocyte targeting, compared to pseudotyped lentiviruses that did not incorporate any IgG or that expressed a control isotype IgG. Overall, this approach is highly flexible and can be exploited to selectively target astrocytes or other cell types of the CNS. As such, it can open a window to visualize and genetically manipulate astrocytes or other cells of the CNS as means of research and treatment.

Regulation of neurotrophic factors and energy metabolism by antidepressants in astrocytes

KAUST Repository

Martin, Jean Luc; Magistretti, Pierre J.; Allaman, Igor

2013-01-01

There is growing evidence that astrocytes are involved in the neuropathology of major depression. In particular, decreases in glial cell density observed in the cerebral cortex of individuals with major depressive disorder are accompanied by a reduction of several astrocytic markers suggesting that astrocyte dysfunction may contribute to the pathophysiology of major depression. In rodents, glial loss in the prefrontal cortex is sufficient to induce depressive-like behaviors and antidepressant treatment prevents the stress-induced reduction of astrocyte number in the hippocampus. Collectively, these data support the existence of a link between astrocyte loss or dysfunction, depressive-like behavior and antidepressant treatment. Astrocytes are increasingly recognized to play important roles in neuronal development, neurotransmission, synaptic plasticity and maintenance of brain homeostasis. It is also well established that astrocytes provide trophic, structural, and metabolic support to neurons. In this article, we review evidence that antidepressants regulate energy metabolism and neurotrophic factor expression with particular emphasis on studies in astrocytes. These observations support a role for astrocytes as new targets for antidepressants. The contribution of changes in astrocyte glucose metabolism and neurotrophic factor expression to the therapeutic effects of antidepressants remains to be established. © 2013 Bentham Science Publishers.

Regulation of neurotrophic factors and energy metabolism by antidepressants in astrocytes

KAUST Repository

Martin, Jean Luc

2013-09-01

There is growing evidence that astrocytes are involved in the neuropathology of major depression. In particular, decreases in glial cell density observed in the cerebral cortex of individuals with major depressive disorder are accompanied by a reduction of several astrocytic markers suggesting that astrocyte dysfunction may contribute to the pathophysiology of major depression. In rodents, glial loss in the prefrontal cortex is sufficient to induce depressive-like behaviors and antidepressant treatment prevents the stress-induced reduction of astrocyte number in the hippocampus. Collectively, these data support the existence of a link between astrocyte loss or dysfunction, depressive-like behavior and antidepressant treatment. Astrocytes are increasingly recognized to play important roles in neuronal development, neurotransmission, synaptic plasticity and maintenance of brain homeostasis. It is also well established that astrocytes provide trophic, structural, and metabolic support to neurons. In this article, we review evidence that antidepressants regulate energy metabolism and neurotrophic factor expression with particular emphasis on studies in astrocytes. These observations support a role for astrocytes as new targets for antidepressants. The contribution of changes in astrocyte glucose metabolism and neurotrophic factor expression to the therapeutic effects of antidepressants remains to be established. © 2013 Bentham Science Publishers.

Effects of aspartame metabolites on astrocytes and neurons.

Science.gov (United States)

Rycerz, Karol; Jaworska-Adamu, Jadwiga Elżbieta

2013-01-01

Aspartame, a widespread sweetener used in many food products, is considered as a highly hazardous compound. Aspartame was discovered in 1965 and raises a lot of controversy up to date. Astrocytes are glial cells, the presence and functions of which are closely connected with the central nervous system (CNS). The aim of this article is to demonstrate the direct and indirect role of astrocytes participating in the harmful effects of aspartame metabolites on neurons. The artificial sweetener is broken down into phenylalanine (50%), aspartic acid (40%) and methanol (10%) during metabolism in the body. The excess of phenylalanine blocks the transport of important amino acids to the brain contributing to reduced levels of dopamine and serotonin. Astrocytes directly affect the transport of this amino acid and also indirectly by modulation of carriers in the endothelium. Aspartic acid at high concentrations is a toxin that causes hyperexcitability of neurons and is also a precursor of other excitatory amino acid - glutamates. Their excess in quantity and lack of astrocytic uptake induces excitotoxicity and leads to the degeneration of astrocytes and neurons. The methanol metabolites cause CNS depression, vision disorders and other symptoms leading ultimately to metabolic acidosis and coma. Astrocytes do not play a significant role in methanol poisoning due to a permanent consumption of large amounts of aspartame. Despite intense speculations about the carcinogenicity of aspartame, the latest studies show that its metabolite - diketopiperazine - is cancirogenic in the CNS. It contributes to the formation of tumors in the CNS such as gliomas, medulloblastomas and meningiomas. Glial cells are the main source of tumors, which can be caused inter alia by the sweetener in the brain. On the one hand the action of astrocytes during aspartame poisoning may be advantageous for neuro-protection while on the other it may intensify the destruction of neurons. The role of the glia in

Eph receptors and ephrins in neuron-astrocyte communication at synapses.

Science.gov (United States)

Murai, Keith K; Pasquale, Elena B

2011-11-01

Neuron-glia communication is essential for regulating the properties of synaptic connections in the brain. Astrocytes, in particular, play a critical and complex role in synapse development, maintenance, and plasticity. Likewise, neurons reciprocally influence astrocyte physiology. However, the molecular signaling events that enable astrocytes and neurons to effectively communicate with each other are only partially defined. Recent findings have revealed that Eph receptor tyrosine kinases and ephrins play an important role in contact-dependent neuron-glia communication at synapses. Upon binding, these two families of cell surface-associated proteins trigger bidirectional signaling events that regulate the structural and physiological properties of both neurons and astrocytes. This review will focus on the emerging role of Eph receptors and ephrins in neuron-astrocyte interaction at synapses and discuss implications for synaptic plasticity, behavior, and disease. Copyright © 2011 Wiley-Liss, Inc.

In Vivo Evidence for a Lactate Gradient from Astrocytes to Neurons

KAUST Repository

Mä chler, Philipp; Wyss, Matthias  T.; Elsayed, Maha; Stobart, Jillian; Gutierrez, Robin; von  Faber-Castell, Alexandra; Kaelin, Vincens; Zuend, Marc; San  Martí n, Alejandro; Romero-Gó mez, Ignacio; Baeza-Lehnert, Felipe; Lengacher, Sylvain; Schneider, Bernard  L.; Aebischer, Patrick; Magistretti, Pierre J.; Barros, L.  Felipe; Weber, Bruno

2015-01-01

Investigating lactate dynamics in brain tissue is challenging, partly because in vivo data at cellular resolution are not available. We monitored lactate in cortical astrocytes and neurons of mice using the genetically encoded FRET sensor Laconic in combination with two-photon microscopy. An intravenous lactate injection rapidly increased the Laconic signal in both astrocytes and neurons, demonstrating high lactate permeability across tissue. The signal increase was significantly smaller in astrocytes, pointing to higher basal lactate levels in these cells, confirmed by a one-point calibration protocol. Trans-acceleration of the monocarboxylate transporter with pyruvate was able to reduce intracellular lactate in astrocytes but not in neurons. Collectively, these data provide in vivo evidence for a lactate gradient from astrocytes to neurons. This gradient is a prerequisite for a carrier-mediated lactate flux from astrocytes to neurons and thus supports the astrocyte-neuron lactate shuttle model, in which astrocyte-derived lactate acts as an energy substrate for neurons. © 2016 Elsevier Inc.

In Vivo Evidence for a Lactate Gradient from Astrocytes to Neurons

KAUST Repository

Mächler, Philipp

2015-11-19

Investigating lactate dynamics in brain tissue is challenging, partly because in vivo data at cellular resolution are not available. We monitored lactate in cortical astrocytes and neurons of mice using the genetically encoded FRET sensor Laconic in combination with two-photon microscopy. An intravenous lactate injection rapidly increased the Laconic signal in both astrocytes and neurons, demonstrating high lactate permeability across tissue. The signal increase was significantly smaller in astrocytes, pointing to higher basal lactate levels in these cells, confirmed by a one-point calibration protocol. Trans-acceleration of the monocarboxylate transporter with pyruvate was able to reduce intracellular lactate in astrocytes but not in neurons. Collectively, these data provide in vivo evidence for a lactate gradient from astrocytes to neurons. This gradient is a prerequisite for a carrier-mediated lactate flux from astrocytes to neurons and thus supports the astrocyte-neuron lactate shuttle model, in which astrocyte-derived lactate acts as an energy substrate for neurons. © 2016 Elsevier Inc.

Astrocytes protect neurons against methylmercury via ATP/P2Y(1) receptor-mediated pathways in astrocytes.

Science.gov (United States)

Noguchi, Yusuke; Shinozaki, Youichi; Fujishita, Kayoko; Shibata, Keisuke; Imura, Yoshio; Morizawa, Yosuke; Gachet, Christian; Koizumi, Schuichi

2013-01-01

Methylmercury (MeHg) is a well known environmental pollutant that induces serious neuronal damage. Although MeHg readily crosses the blood-brain barrier, and should affect both neurons and glial cells, how it affects glia or neuron-to-glia interactions has received only limited attention. Here, we report that MeHg triggers ATP/P2Y1 receptor signals in astrocytes, thereby protecting neurons against MeHg via interleukin-6 (IL-6)-mediated pathways. MeHg increased several mRNAs in astrocytes, among which IL-6 was the highest. For this, ATP/P2Y1 receptor-mediated mechanisms were required because the IL-6 production was (i) inhibited by a P2Y1 receptor antagonist, MRS2179, (ii) abolished in astrocytes obtained from P2Y1 receptor-knockout mice, and (iii) mimicked by exogenously applied ATP. In addition, (iv) MeHg released ATP by exocytosis from astrocytes. As for the intracellular mechanisms responsible for IL-6 production, p38 MAP kinase was involved. MeHg-treated astrocyte-conditioned medium (ACM) showed neuro-protective effects against MeHg, which was blocked by anti-IL-6 antibody and was mimicked by the application of recombinant IL-6. As for the mechanism of neuro-protection by IL-6, an adenosine A1 receptor-mediated pathway in neurons seems to be involved. Taken together, when astrocytes sense MeHg, they release ATP that autostimulates P2Y1 receptors to upregulate IL-6, thereby leading to A1 receptor-mediated neuro-protection against MeHg.

Astrocytic gap junctional networks suppress cellular damage in an in vitro model of ischemia

Energy Technology Data Exchange (ETDEWEB)

Shinotsuka, Takanori; Yasui, Masato; Nuriya, Mutsuo, E-mail: mnuriya@z2.keio.jp

2014-02-07

Highlights: • Astrocytes exhibit characteristic changes in [Ca{sup 2+}]{sub i} under OGD. • Astrocytic [Ca{sup 2+}]{sub i} increase is synchronized with a neuronal anoxic depolarization. • Gap junctional couplings protect neurons as well as astrocytes during OGD. - Abstract: Astrocytes play pivotal roles in both the physiology and the pathophysiology of the brain. They communicate with each other via extracellular messengers as well as through gap junctions, which may exacerbate or protect against pathological processes in the brain. However, their roles during the acute phase of ischemia and the underlying cellular mechanisms remain largely unknown. To address this issue, we imaged changes in the intracellular calcium concentration ([Ca{sup 2+}]{sub i}) in astrocytes in mouse cortical slices under oxygen/glucose deprivation (OGD) condition using two-photon microscopy. Under OGD, astrocytes showed [Ca{sup 2+}]{sub i} oscillations followed by larger and sustained [Ca{sup 2+}]{sub i} increases. While the pharmacological blockades of astrocytic receptors for glutamate and ATP had no effect, the inhibitions of gap junctional intercellular coupling between astrocytes significantly advanced the onset of the sustained [Ca{sup 2+}]{sub i} increase after OGD exposure. Interestingly, the simultaneous recording of the neuronal membrane potential revealed that the onset of the sustained [Ca{sup 2+}]{sub i} increase in astrocytes was synchronized with the appearance of neuronal anoxic depolarization. Furthermore, the blockade of gap junctional coupling resulted in a concurrent faster appearance of neuronal depolarizations, which remain synchronized with the sustained [Ca{sup 2+}]{sub i} increase in astrocytes. These results indicate that astrocytes delay the appearance of the pathological responses of astrocytes and neurons through their gap junction-mediated intercellular network under OGD. Thus, astrocytic gap junctional networks provide protection against tissue damage

Astrocyte-derived proinflammatory cytokines induce hypomyelination in the periventricular white matter in the hypoxic neonatal brain.

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Yiyu Deng

Full Text Available Hypoxic exposure in the perinatal period causes periventricular white matter damage (PWMD, a condition associated with myelination abnormalities. Under hypoxic conditions, glial cells were activated and released a large number of inflammatory mediators in the PWM in neonatal brain, which may result in oligodendrocyte (OL loss and axonal injury. This study aims to determine if astrocytes are activated and generate proinflammatory cytokines that may be coupled with the oligodendroglial loss and hypomyelination observed in hypoxic PWMD. Twenty-four 1-day-old Wistar rats were exposed to hypoxia for 2 h. The rats were then allowed to recover under normoxic conditions for 7 or 28 days before being killed. Another group of 24 rats kept outside the chamber was used as age-matched controls. Upregulated expression of TNF-α and IL-1β was observed in astrocytes in the PWM of P7 hypoxic rats by double immunofluorescence, western blotting and real time RT-PCR. This was linked to apoptosis and enhanced expression of TNF-R1 and IL-1R1 in APC(+ OLs. PLP expression was decreased significantly in the PWM of P28d hypoxic rats. The proportion of myelinated axons was markedly reduced by electron microscopy (EM and the average g-ratios were higher in P28d hypoxic rats. Upregulated expression of TNF-α and IL-1β in primary cultured astrocytes as well as their corresponding receptors in primary culture APC(+ oligodendrocytes were detected under hypoxic conditions. Our results suggest that following a hypoxic insult, astrocytes in the PWM of neonatal rats produce inflammatory cytokines such as TNF-α and IL-1β, which induce apoptosis of OLs via their corresponding receptors associated with them. This results in hypomyelination in the PWM of hypoxic rats.

Characterization of Amino Acid Profile and Enzymatic Activity in Adult Rat Astrocyte Cultures.

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Souza, Débora Guerini; Bellaver, Bruna; Hansel, Gisele; Arús, Bernardo Assein; Bellaver, Gabriela; Longoni, Aline; Kolling, Janaina; Wyse, Angela T S; Souza, Diogo Onofre; Quincozes-Santos, André

2016-07-01

Astrocytes are multitasking players in brain complexity, possessing several receptors and mechanisms to detect, participate and modulate neuronal communication. The functionality of astrocytes has been mainly unraveled through the study of primary astrocyte cultures, and recently our research group characterized a model of astrocyte cultures derived from adult Wistar rats. We, herein, aim to characterize other basal functions of these cells to explore the potential of this model for studying the adult brain. To characterize the astrocytic phenotype, we determined the presence of GFAP, GLAST and GLT 1 proteins in cells by immunofluorescence. Next, we determined the concentrations of thirteen amino acids, ATP, ADP, adenosine and calcium in astrocyte cultures, as well as the activities of Na(+)/K(+)-ATPase and acetylcholine esterase. Furthermore, we assessed the presence of the GABA transporter 1 (GAT 1) and cannabinoid receptor 1 (CB 1) in the astrocytes. Cells demonstrated the presence of glutamine, consistent with their role in the glutamate-glutamine cycle, as well as glutamate and D-serine, amino acids classically known to act as gliotransmitters. ATP was produced and released by the cells and ADP was consumed. Calcium levels were in agreement with those reported in the literature, as were the enzymatic activities measured. The presence of GAT 1 was detected, but the presence of CB 1 was not, suggesting a decreased neuroprotective capacity in adult astrocytes under in vitro conditions. Taken together, our results show cellular functionality regarding the astrocytic role in gliotransmission and neurotransmitter management since they are able to produce and release gliotransmitters and to modulate the cholinergic and GABAergic systems.

HIV-1, Methamphetamine and Astrocytes at Neuroinflammatory crossroads

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Kathleen eBorgmann

2015-10-01

Full Text Available As a popular psychostimulant, methamphetamine (METH use leads to long-lasting, strong euphoric effects. While METH abuse is common in the general population, between 10-15% of human immunodeficiency virus-1 (HIV-1 patients report having abused METH. METH exacerbates the severity and onset of HIV-1-associated neurocognitive disorders (HAND through direct and indirect mechanisms. Repetitive METH use decreases adherence to antiretroviral drug regimens, increasing the likelihood of HIV-1 disease progression towards AIDS. METH exposure also directly affects both innate and adaptive immunity, altering lymphocyte number and activity, cytokine signaling, phagocytic function, and CNS infiltration through the blood brain barrier. Further, METH triggers the neuronal dopamine reward pathway and leads to altered neuronal activity and direct toxicity. Concurrently, METH and HIV-1 alter the neuroimmune balance and induce neuroinflammation. Neuroinflammation modulates a wide range of brain functions including neuronal signaling and activity, glial activation, viral infection, oxidative stress and excitotoxicity. Pathologically, glial activation is a hallmark of both HIV-1 and METH-associated neuroinflammation. Significant commonality exists in the neurotoxic mechanisms for both METH and HAND; however, the pathways dysregulated in astroglia during METH exposure are less clear. Thus alterations in astrocyte intracellular signaling pathways, gene expression and function during METH and HIV-1 comorbidity, neuroinflammation and HAND are carefully reviewed. Interventions targeting astrocytes in HAND and METH are presented as potential novel therapeutic approaches.

Endogenous IL-6 of mesenchymal stem cell improves behavioral outcome of hypoxic-ischemic brain damage neonatal rats by supressing apoptosis in astrocyte.

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Gu, Yan; He, Mulan; Zhou, Xiaoqin; Liu, Jinngjing; Hou, Nali; Bin, Tan; Zhang, Yun; Li, Tingyu; Chen, Jie

2016-01-14

Mesenchymal stem cell (MSC) transplantation reduces the neurological impairment caused by hypoxic-ischemic brain damage (HIBD) via immunomodulation. In the current study, we found that MSC transplantation improved learning and memory function and enhanced long-term potentiation in neonatal rats subjected to HIBD and the amount of IL-6 released from MSCs was far greater than that of other cytokines. However, the neuroprotective effect of MSCs infected with siIL-6-transduced recombinant lentivirus (siIL-6 MSCs) was significantly weakened in the behavioural tests and electrophysiological analysis. Meanwhile, the hippocampal IL-6 levels were decreased following siIL-6 MSC transplantation. In vitro, the levels of IL-6 release and the levels of IL-6R and STAT3 expression were increased in both primary neurons and astrocytes subjected to oxygen and glucose deprivation (OGD) following MSCs co-culture. The anti-apoptotic protein Bcl-2 was upregulated and the pro-apoptotic protein Bax was downregulated in OGD-injured astrocytes co-cultured with MSCs. However, the siIL-6 MSCs suppressed ratio of Bcl-2/Bax in the injured astrocytes and induced apoptosis number of the injured astrocytes. Taken together, these data suggest that the neuroprotective effect of MSC transplantation in neonatal HIBD rats is partly mediated by IL-6 to enhance anti-apoptosis of injured astrocytes via the IL-6/STAT3 signaling pathway.

Metabolic communication between astrocytes and neurons via bicarbonate-responsive soluble adenylyl cyclase.

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Choi, Hyun B; Gordon, Grant R J; Zhou, Ning; Tai, Chao; Rungta, Ravi L; Martinez, Jennifer; Milner, Teresa A; Ryu, Jae K; McLarnon, James G; Tresguerres, Martin; Levin, Lonny R; Buck, Jochen; MacVicar, Brian A

2012-09-20

Astrocytes are proposed to participate in brain energy metabolism by supplying substrates to neurons from their glycogen stores and from glycolysis. However, the molecules involved in metabolic sensing and the molecular pathways responsible for metabolic coupling between different cell types in the brain are not fully understood. Here we show that a recently cloned bicarbonate (HCO₃⁻) sensor, soluble adenylyl cyclase (sAC), is highly expressed in astrocytes and becomes activated in response to HCO₃⁻ entry via the electrogenic NaHCO₃ cotransporter (NBC). Activated sAC increases intracellular cAMP levels, causing glycogen breakdown, enhanced glycolysis, and the release of lactate into the extracellular space, which is subsequently taken up by neurons for use as an energy substrate. This process is recruited over a broad physiological range of [K⁺](ext) and also during aglycemic episodes, helping to maintain synaptic function. These data reveal a molecular pathway in astrocytes that is responsible for brain metabolic coupling to neurons. Copyright © 2012 Elsevier Inc. All rights reserved.

Fluxes of lactate into, from, and among gap junction-coupled astrocytes and their interaction with noradrenaline

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Leif eHertz

2014-09-01

Full Text Available Lactate is a versatile metabolite with important roles in modulation of brain glucose utilization rate (CMRglc, diagnosis of brain-injured patients, redox- and receptor-mediated signaling, memory, and alteration of gene transcription. Neurons and astrocytes release and accumulate lactate using equilibrative monocarboxylate transporters that carry out net transmembrane transport of lactate only until intra- and extracellular levels reach equilibrium. Astrocytes have much faster lactate uptake than neurons and shuttle more lactate among gap junction-coupled astrocytes than to nearby neurons. Lactate diffusion within syncytia can provide precursors for oxidative metabolism and glutamate synthesis and facilitate its release from endfeet to perivascular space to stimulate blood flow. Lactate efflux from brain during activation underlies the large underestimation of CMRglc with labeled glucose and fall in CMRO2/CMRglc ratio. Receptor-mediated effects of lactate on locus coeruleus neurons include noradrenaline release in cerebral cortex and c-AMP-mediated stimulation of astrocytic gap junctional coupling, thereby enhancing its dispersal and release from brain. Lactate transport is essential for its multifunctional roles.

Neuroinflammation leads to region-dependent alterations in astrocyte gap junction communication and hemichannel activity.

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Karpuk, Nikolay; Burkovetskaya, Maria; Fritz, Teresa; Angle, Amanda; Kielian, Tammy

2011-01-12

Inflammation attenuates gap junction (GJ) communication in cultured astrocytes. Here we used a well-characterized model of experimental brain abscess as a tool to query effects of the CNS inflammatory milieu on astrocyte GJ communication and electrophysiological properties. Whole-cell patch-clamp recordings were performed on green fluorescent protein (GFP)-positive astrocytes in acute brain slices from glial fibrillary acidic protein-GFP mice at 3 or 7 d after Staphylococcus aureus infection in the striatum. Astrocyte GJ communication was significantly attenuated in regions immediately surrounding the abscess margins and progressively increased to levels typical of uninfected brain with increasing distance from the abscess proper. Conversely, astrocytes bordering the abscess demonstrated hemichannel activity as evident by enhanced ethidium bromide (EtBr) uptake that could be blocked by several pharmacological inhibitors, including the connexin 43 (Cx43) mimetic peptide Gap26, carbenoxolone, the pannexin1 (Panx1) mimetic peptide (10)Panx1, and probenecid. However, hemichannel opening was transient with astrocytic EtBr uptake observed near the abscess at day 3 but not day 7 after infection. The region-dependent pattern of hemichannel activity at day 3 directly correlated with increases in Cx43, Cx30, Panx1, and glutamate transporter expression (glial L-glutamate transporter and L-glutamate/L-aspartate transporter) along the abscess margins. Changes in astrocyte resting membrane potential and input conductance correlated with the observed changes in GJ communication and hemichannel activity. Collectively, these findings indicate that astrocyte coupling and electrical properties are most dramatically affected near the primary inflammatory site and reveal an opposing relationship between the open states of GJ channels versus hemichannels during acute infection. This relationship may extend to other CNS diseases typified with an inflammatory component.

Translation of the prion protein mRNA is robust in astrocytes but does not amplify during reactive astrocytosis in the mouse brain.

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Walker S Jackson

Full Text Available Prion diseases induce neurodegeneration in specific brain areas for undetermined reasons. A thorough understanding of the localization of the disease-causing molecule, the prion protein (PrP, could inform on this issue but previous studies have generated conflicting conclusions. One of the more intriguing disagreements is whether PrP is synthesized by astrocytes. We developed a knock-in reporter mouse line in which the coding sequence of the PrP expressing gene (Prnp, was replaced with that for green fluorescent protein (GFP. Native GFP fluorescence intensity varied between and within brain regions. GFP was present in astrocytes but did not increase during reactive gliosis induced by scrapie prion infection. Therefore, reactive gliosis associated with prion diseases does not cause an acceleration of local PrP production. In addition to aiding in Prnp gene activity studies, this reporter mouse line will likely prove useful for analysis of chimeric animals produced by stem cell and tissue transplantation experiments.

Circadian control of p75 neurotrophin receptor leads to alternate activation of Nrf2 and c-Rel to reset energy metabolism in astrocytes via brain-derived neurotrophic factor.

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Ishii, Tetsuro; Warabi, Eiji; Mann, Giovanni E

2018-05-01

Circadian clock genes regulate energy metabolism partly through neurotrophins in the body. The low affinity neurotrophin receptor p75 NTR is a clock component directly regulated by the transcriptional factor Clock:Bmal1 complex. Brain-derived neurotrophic factor (BDNF) is expressed in the brain and plays a key role in coordinating metabolic interactions between neurons and astrocytes. BDNF transduces signals through TrkB and p75 NTR receptors. This review highlights a novel molecular mechanism by which BDNF via circadian control of p75 NTR leads to daily resetting of glucose and glycogen metabolism in brain astrocytes to accommodate their functional interaction with neurons. Astrocytes store glycogen as an energy reservoir to provide active neurons with the glycolytic metabolite lactate. Astrocytes predominantly express the truncated receptor TrkB.T1 which lacks an intracellular receptor tyrosine kinase domain. TrkB.T1 retains the capacity to regulate cell morphology through regulation of Rho GTPases. In contrast, p75 NTR mediates generation of the bioactive lipid ceramide upon stimulation with BDNF and inhibits PKA activation. As ceramide directly activates PKCζ, we discuss the importance of the TrkB.T1-p75 NTR -ceramide-PKCζ signaling axis in the stimulation of glycogen and lipid synthesis and activation of RhoA. Ceramide-PKCζ-casein kinase 2 signaling activates Nrf2 to support oxidative phosphorylation via upregulation of antioxidant enzymes. In the absence of p75 NTR , TrkB.T1 functionally interacts with adenosine A 2A R and dopamine D1R receptors to enhance cAMP-PKA signaling and activate Rac1 and NF-κB c-Rel, favoring glycogen hydrolysis, gluconeogenesis and aerobic glycolysis. Thus, diurnal changes in p75 NTR levels in astrocytes resets energy metabolism via BDNF to accommodate their metabolic interaction with neurons. Copyright © 2018 Elsevier Inc. All rights reserved.

A digital implementation of neuron-astrocyte interaction for neuromorphic applications.

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Nazari, Soheila; Faez, Karim; Amiri, Mahmood; Karami, Ehsan

2015-06-01

Recent neurophysiologic findings have shown that astrocytes play important roles in information processing and modulation of neuronal activity. Motivated by these findings, in the present research, a digital neuromorphic circuit to study neuron-astrocyte interaction is proposed. In this digital circuit, the firing dynamics of the neuron is described by Izhikevich model and the calcium dynamics of a single astrocyte is explained by a functional model introduced by Postnov and colleagues. For digital implementation of the neuron-astrocyte signaling, Single Constant Multiply (SCM) technique and several linear approximations are used for efficient low-cost hardware implementation on digital platforms. Using the proposed neuron-astrocyte circuit and based on the results of MATLAB simulations, hardware synthesis and FPGA implementation, it is demonstrated that the proposed digital astrocyte is able to change the firing patterns of the neuron through bidirectional communication. Utilizing the proposed digital circuit, it will be illustrated that information processing in synaptic clefts is strongly regulated by astrocyte. Moreover, our results suggest that the digital circuit of neuron-astrocyte crosstalk produces diverse neural responses and therefore enhances the information processing capabilities of the neuromorphic circuits. This is suitable for applications in reconfigurable neuromorphic devices which implement biologically brain circuits. Copyright © 2015 Elsevier Ltd. All rights reserved.

Sex differences in the inflammatory response of primary astrocytes to lipopolysaccharide

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Santos-Galindo María

2011-07-01

Full Text Available Abstract Background Numerous neurological and psychiatric disorders show sex differences in incidence, age of onset, symptomatology or outcome. Astrocytes, one of the glial cell types of the brain, show sex differences in number, differentiation and function. Since astrocytes are involved in the response of neural tissue to injury and inflammation, these cells may participate in the generation of sex differences in the response of the brain to pathological insults. To explore this hypothesis, we have examined whether male and female astrocytes show a different response to an inflammatory challenge and whether perinatal testosterone influences this response. Methods Cortical astrocyte cultures were prepared from postnatal day 1 (one day after birth male or female CD1 mice pups. In addition, cortical astrocyte cultures were also prepared from female pups that were injected at birth with 100 μg of testosterone propionate or vehicle. Cultures were treated for 5 hours with medium containing lipopolysaccharide (LPS or with control medium. The mRNA levels of IL6, interferon-inducible protein 10 (IP10, TNFα, IL1β, Toll-like receptor 4 (TLR4, steroidogenic acute regulatory protein and translocator protein were assessed by quantitative real-time polymerase chain reaction. Statistical significance was assessed by unpaired t-test or by one-way analysis of variance followed by the Tukey post hoc test. Results The mRNA levels of IL6, TNFα and IL1β after LPS treatment were significantly higher in astrocytes derived from male or androgenized females compared to astrocytes derived from control or vehicle-injected females. In contrast, IP10 mRNA levels after LPS treatment were higher in astrocytes derived from control or vehicle-injected females than in those obtained from males or androgenized females. The different response of male and female astrocytes to LPS was due neither to differences in the basal expression of the inflammatory molecules nor to

Two classes of astrocytes in the adult human and pig retina in terms of their expression of high affinity NGF receptor (TrkA).

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Ruiz-Ederra, Javier; Hitchcock, Peter F; Vecino, Elena

2003-02-13

Astrocytes have been implicated in axon guidance and synaptic regeneration in the retina and these processes involve activation of the high affinity nerve growth factor receptor, known as the tyrosine kinase A (TrkA) receptor. The purpose of the present study was to characterize the expression of TrkA in astrocytes of the adult pig and human retina. To this end, sections of human and pig retinas were immunolabeled with a combination of antibodies to glial fibrillary acidic protein (GFAP) and TrkA. Our study revealed that most of the GFAP-positive cells express TrkA, whereas a rare, novel subpopulation of astrocytes was found to be devoid of TrkA. Our results support the idea that astrocytes play an important neurotrophic role in the retina.

Cellular Origin of [18F]FDG-PET Imaging Signals During Ceftriaxone-Stimulated Glutamate Uptake: Astrocytes and Neurons.

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Dienel, Gerald A; Behar, Kevin L; Rothman, Douglas L

2017-12-01

Ceftriaxone stimulates astrocytic uptake of the excitatory neurotransmitter glutamate, and it is used to treat glutamatergic excitotoxicity that becomes manifest during many brain diseases. Ceftriaxone-stimulated glutamate transport was reported to drive signals underlying [ 18 F]fluorodeoxyglucose-positron emission tomographic ([ 18 F]FDG-PET) metabolic images of brain glucose utilization and interpreted as supportive of the notion of lactate shuttling from astrocytes to neurons. This study draws attention to critical roles of astrocytes in the energetics and imaging of brain activity, but the results are provocative because (1) the method does not have cellular resolution or provide information about downstream pathways of glucose metabolism, (2) neuronal and astrocytic [ 18 F]FDG uptake were not separately measured, and (3) strong evidence against lactate shuttling was not discussed. Evaluation of potential metabolic responses to ceftriaxone suggests lack of astrocytic specificity and significant contributions by pre- and postsynaptic neuronal compartments. Indeed, astrocytic glycolysis may not make a strong contribution to the [ 18 F]FDG-PET signal because partial or complete oxidation of one glutamate molecule on its uptake generates enough ATP to fuel uptake of 3 to 10 more glutamate molecules, diminishing reliance on glycolysis. The influence of ceftriaxone on energetics of glutamate-glutamine cycling must be determined in astrocytes and neurons to elucidate its roles in excitotoxicity treatment.

Imaging activity in astrocytes and neurons with genetically encoded calcium indicators following in utero electroporation

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J. Michael eGee

2015-04-01

Full Text Available Complex interactions between networks of astrocytes and neurons are beginning to be appreciated, but remain poorly understood. Transgenic mice expressing fluorescent protein reporters of cellular activity, such as the GCaMP family of genetically encoded calcium indicators, have been used to explore network behavior. However, in some cases, it may be desirable to use long-established rat models that closely mimic particular aspects of human conditions such as Parkinson’s disease and the development of epilepsy following status epilepticus. Methods for expressing reporter proteins in the rat brain are relatively limited. Transgenic rat technologies exist but are fairly immature. Viral-mediated expression is robust but unstable, requires invasive injections, and only works well for fairly small genes (< 5 kb. In utero electroporation offers a valuable alternative. IUE is a proven method for transfecting populations of astrocytes and neurons in the rat brain without the strict limitations on transgene size. We built a toolset of IUE plasmids carrying GCaMP variants 3, 6s or 6f driven by CAG and targeted to the cytosol or the plasma membrane. Because low baseline fluorescence of GCaMP can hinder identification of transfected cells, we included the option of co-expressing a cytosolic tdTomato protein. A binary system consisting of a plasmid carrying a piggyBac inverted terminal repeat-flanked CAG-GCaMP-IRES-tdTomato cassette and a separate plasmid encoding for expression of piggyBac transposase was employed to stably express GCaMP and tdTomato. The plasmids were co-electroporated on embryonic days 13.5-14.5 and astrocytic and neuronal activity was subsequently imaged in acute or cultured brain slices prepared from the cortex or hippocampus. Large spontaneous transients were detected in slices obtained from rats of varying ages up to 127 days. In this report, we demonstrate the utility of this toolset for interrogating astrocytic and neuronal

Amitriptyline induces brain-derived neurotrophic factor (BDNF) mRNA expression through ERK-dependent modulation of multiple BDNF mRNA variants in primary cultured rat cortical astrocytes and microglia.

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Hisaoka-Nakashima, Kazue; Kajitani, Naoto; Kaneko, Masahiro; Shigetou, Takahiro; Kasai, Miho; Matsumoto, Chie; Yokoe, Toshiki; Azuma, Honami; Takebayashi, Minoru; Morioka, Norimitsu; Nakata, Yoshihiro

2016-03-01

A significant role of brain-derived neurotrophic factor (BDNF) has been previously implicated in the therapeutic effect of antidepressants. To ascertain the contribution of specific cell types in the brain that produce BDNF following antidepressant treatment, the effects of the tricyclic antidepressant amitriptyline on rat primary neuronal, astrocytic and microglial cortical cultures were examined. Amitriptyline increased the expression of BDNF mRNA in astrocytic and microglial cultures but not neuronal cultures. Antidepressants with distinct mechanisms of action, such as clomipramine, duloxetine and fluvoxamine, also increased BDNF mRNA expression in astrocytic and microglial cultures. There are multiple BDNF mRNA variants (exon I, IIA, IV and VI) expressed in astrocytes and microglia and the variant induced by antidepressants has yet to be elaborated. Treatment with antidepressants increased the expression of exon I, IV and VI in astrocyte and microglia. Clomipramine alone significantly upregulated expression of exon IIA. The amitriptyline-induced expression of both total and individual BDNF mRNA variants (exon I, IV and VI) were blocked by MEK inhibitor U0126, indicating MEK/ERK signaling is required in the expression of BDNF. These findings indicate that non-neural cells are a significant target of antidepressants and further support the contention that glial production of BDNF is crucial role in the therapeutic effect of antidepressants. The current data suggest that targeting of glial function could lead to the development of antidepressants with a truly novel mechanism of action. Copyright © 2016 Elsevier B.V. All rights reserved.

Single-Cell Detection of Secreted Aβ and sAPPα from Human IPSC-Derived Neurons and Astrocytes.

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Liao, Mei-Chen; Muratore, Christina R; Gierahn, Todd M; Sullivan, Sarah E; Srikanth, Priya; De Jager, Philip L; Love, J Christopher; Young-Pearse, Tracy L

2016-02-03

Secreted factors play a central role in normal and pathological processes in every tissue in the body. The brain is composed of a highly complex milieu of different cell types and few methods exist that can identify which individual cells in a complex mixture are secreting specific analytes. By identifying which cells are responsible, we can better understand neural physiology and pathophysiology, more readily identify the underlying pathways responsible for analyte production, and ultimately use this information to guide the development of novel therapeutic strategies that target the cell types of relevance. We present here a method for detecting analytes secreted from single human induced pluripotent stem cell (iPSC)-derived neural cells and have applied the method to measure amyloid β (Aβ) and soluble amyloid precursor protein-alpha (sAPPα), analytes central to Alzheimer's disease pathogenesis. Through these studies, we have uncovered the dynamic range of secretion profiles of these analytes from single iPSC-derived neuronal and glial cells and have molecularly characterized subpopulations of these cells through immunostaining and gene expression analyses. In examining Aβ and sAPPα secretion from single cells, we were able to identify previously unappreciated complexities in the biology of APP cleavage that could not otherwise have been found by studying averaged responses over pools of cells. This technique can be readily adapted to the detection of other analytes secreted by neural cells, which would have the potential to open new perspectives into human CNS development and dysfunction. We have established a technology that, for the first time, detects secreted analytes from single human neurons and astrocytes. We examine secretion of the Alzheimer's disease-relevant factors amyloid β (Aβ) and soluble amyloid precursor protein-alpha (sAPPα) and present novel findings that could not have been observed without a single-cell analytical platform. First, we

Phosphorylation status of pyruvate dehydrogenase distinguishes metabolic phenotypes of cultured rat brain astrocytes and neurons.

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Halim, Nader D; Mcfate, Thomas; Mohyeldin, Ahmed; Okagaki, Peter; Korotchkina, Lioubov G; Patel, Mulchand S; Jeoung, Nam Ho; Harris, Robert A; Schell, Michael J; Verma, Ajay

2010-08-01

Glucose metabolism in nervous tissue has been proposed to occur in a compartmentalized manner with astrocytes contributing largely to glycolysis and neurons being the primary site of glucose oxidation. However, mammalian astrocytes and neurons both contain mitochondria, and it remains unclear why in culture neurons oxidize glucose, lactate, and pyruvate to a much larger extent than astrocytes. The objective of this study was to determine whether pyruvate metabolism is differentially regulated in cultured neurons versus astrocytes. Expression of all components of the pyruvate dehydrogenase complex (PDC), the rate-limiting step for pyruvate entry into the Krebs cycle, was determined in cultured astrocytes and neurons. In addition, regulation of PDC enzymatic activity in the two cell types via protein phosphorylation was examined. We show that all components of the PDC are expressed in both cell types in culture, but that PDC activity is kept strongly inhibited in astrocytes through phosphorylation of the pyruvate dehydrogenase alpha subunit (PDH alpha). In contrast, neuronal PDC operates close to maximal levels with much lower levels of phosphorylated PDH alpha. Dephosphorylation of astrocytic PDH alpha restores PDC activity and lowers lactate production. Our findings suggest that the glucose metabolism of astrocytes and neurons may be far more flexible than previously believed. (c) 2010 Wiley-Liss, Inc.

Disentangling the role of astrocytes in alcohol use disorder

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Adermark, Louise; Bowers, M. Scott

2016-01-01

Several laboratories recently identified that astrocytes are critical regulators of addiction machinery. It is now known that astrocyte pathology is a common feature of ethanol exposure in both humans and animal models, as even brief ethanol exposure is sufficient to elicit long-lasting perturbations in astrocyte gene expression, activity, and proliferation. Astrocytes were also recently shown to modulate the motivational properties of ethanol and other strongly reinforcing stimuli. Given the role of astrocytes in regulating glutamate homeostasis, a crucial component of alcohol use disorder, astrocytes might be an important target for the development of next generation alcoholism treatments. This review will outline some of the more prominent features displayed by astrocytes, how these properties are influenced by acute and long term ethanol exposure, and future directions that may help to disentangle astrocytic from neuronal functions in the etiology of alcohol use disorder. PMID:27476876

Infection and upregulation of proinflammatory cytokines in human brain vascular pericytes by human cytomegalovirus

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Alcendor Donald J

2012-05-01

Full Text Available Abstract Background Congenital human cytomegalovirus (HCMV infections can result in CNS abnormalities in newborn babies including vision loss, mental retardation, motor deficits, seizures, and hearing loss. Brain pericytes play an essential role in the development and function of the blood–brain barrier yet their unique role in HCMV dissemination and neuropathlogy has not been reported. Methods Primary human brain vascular pericytes were exposed to a primary clinical isolate of HCMV designated ‘SBCMV’. Infectivity was analyzed by microscopy, immunofluorescence, Western blot, and qRT-PCR. Microarrays were performed to identify proinflammatory cytokines upregulated after SBCMV exposure, and the results validated by real-time quantitative polymerase chain reaction (qPCR methodology. In situ cytokine expression of pericytes after exposure to HCMV was examined by ELISA and in vivo evidence of HCMV infection of brain pericytes was shown by dual-labeled immunohistochemistry. Results HCMV-infected human brain vascular pericytes as evidenced by several markers. Using a clinical isolate of HCMV (SBCMV, microscopy of infected pericytes showed virion production and typical cytomegalic cytopathology. This finding was confirmed by the expression of major immediate early and late virion proteins and by the presence of HCMV mRNA. Brain pericytes were fully permissive for CMV lytic replication after 72 to 96 hours in culture compared to human astrocytes or human brain microvascular endothelial cells (BMVEC. However, temporal transcriptional expression of pp65 virion protein after SBCMV infection was lower than that seen with the HCMV Towne laboratory strain. Using RT-PCR and dual-labeled immunofluorescence, proinflammatory cytokines CXCL8/IL-8, CXCL11/ITAC, and CCL5/Rantes were upregulated in SBCMV-infected cells, as were tumor necrosis factor-alpha (TNF-alpha, interleukin-1 beta (IL-1beta, and interleukin-6 (IL-6. Pericytes exposed to SBCMV elicited

Albumin induces upregulation of matrix metalloproteinase-9 in astrocytes via MAPK and reactive oxygen species-dependent pathways

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Ranaivo Hantamalala

2012-04-01

Full Text Available Abstract Background Astrocytes are an integral component of the blood–brain barrier (BBB which may be compromised by ischemic or traumatic brain injury. In response to trauma, astrocytes increase expression of the endopeptidase matrix metalloproteinase (MMP-9. Compromise of the BBB leads to the infiltration of fluid and blood-derived proteins including albumin into the brain parenchyma. Albumin has been previously shown to activate astrocytes and induce the production of inflammatory mediators. The effect of albumin on MMP-9 activation in astrocytes is not known. We investigated the molecular mechanisms underlying the production of MMP-9 by albumin in astrocytes. Methods Primary enriched astrocyte cultures were used to investigate the effects of exposure to albumin on the release of MMP-9. MMP-9 expression was analyzed by zymography. The involvement of mitogen-activated protein kinase (MAPK, reactive oxygen species (ROS and the TGF-β receptor-dependent pathways were investigated using pharmacological inhibitors. The production of ROS was observed by dichlorodihydrofluorescein diacetate fluorescence. The level of the MMP-9 inhibitor tissue inhibitor of metalloproteinase (TIMP-1 produced by astrocytes was measured by ELISA. Results We found that albumin induces a time-dependent release of MMP-9 via the activation of p38 MAPK and extracellular signal regulated kinase, but not Jun kinase. Albumin-induced MMP-9 production also involves ROS production upstream of the MAPK pathways. However, albumin-induced increase in MMP-9 is independent of the TGF-β receptor, previously described as a receptor for albumin. Albumin also induces an increase in TIMP-1 via an undetermined mechanism. Conclusions These results link albumin (acting through ROS and the p38 MAPK to the activation of MMP-9 in astrocytes. Numerous studies identify a role for MMP-9 in the mechanisms of compromise of the BBB, epileptogenesis, or synaptic remodeling after ischemia or

Differentiation of a medulloblastoma cell line towards an astrocytic lineage using the human T lymphotropic retrovirus-1.

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Giraudon, P; Dufay, N; Hardin, H; Reboul, A; Tardy, M; Belin, M F

1993-02-01

Constituent cells of medulloblastoma, the most common brain tumor occurring in childhood, resemble the primitive neuroepithelial cells normally found in the developing nervous system. However, mutational events prevent their further differentiation. We used the human T cell lymphotrophic virus type 1 to activate these deregulated immature cells by means of its transactivating protein Tax. Concomitant with viral infection was a decrease in cell proliferation characterized by inhibition of [3H]thymidine incorporation and in the number of cells in the G2/M phase of the cell cycle. Morphological changes suggested that medulloblastoma cells differentiated along the astrocytic lineage. The glial phenotype was confirmed by the induction of the glial fibrillary acidic protein and the glial enzyme glutamine synthetase. A direct viral effect and/or secondary effects to viral infection via paracrine/autocrine pathways could counterbalance the maturational defect in these medulloblastoma cells.

Astrocytes play a key role in activation of microglia by persistent Borna disease virus infection

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Sauder Christian

2008-11-01

Full Text Available Abstract Neonatal Borna disease virus (BDV infection of the rat brain is associated with microglial activation and damage to certain neuronal populations. Since persistent BDV infection of neurons is nonlytic in vitro, activated microglia have been suggested to be responsible for neuronal cell death in vivo. However, the mechanisms of activation of microglia in neonatally BDV-infected rat brains remain unclear. Our previous studies have shown that activation of microglia by BDV in culture requires the presence of astrocytes as neither the virus nor BDV-infected neurons alone activate microglia. Here, we evaluated the mechanisms whereby astrocytes can contribute to activation of microglia in neuron-glia-microglia mixed cultures. We found that persistent infection of neuronal cells leads to activation of uninfected astrocytes as measured by elevated expression of RANTES. Activation of astrocytes then produces activation of microglia as evidenced by increased formation of round-shaped, MHCI-, MHCII- and IL-6-positive microglia cells. Our analysis of possible molecular mechanisms of activation of astrocytes and/or microglia in culture indicates that the mediators of activation may be soluble heat-resistant, low molecular weight factors. The findings indicate that astrocytes may mediate activation of microglia by BDV-infected neurons. The data are consistent with the hypothesis that microglia activation in the absence of neuronal damage may represent initial steps in the gradual neurodegeneration observed in brains of neonatally BDV-infected rats.

Computational Flux Balance Analysis Predicts that Stimulation of Energy Metabolism in Astrocytes and their Metabolic Interactions with Neurons Depend on Uptake of K+ Rather than Glutamate.

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DiNuzzo, Mauro; Giove, Federico; Maraviglia, Bruno; Mangia, Silvia

2017-01-01

Brain activity involves essential functional and metabolic interactions between neurons and astrocytes. The importance of astrocytic functions to neuronal signaling is supported by many experiments reporting high rates of energy consumption and oxidative metabolism in these glial cells. In the brain, almost all energy is consumed by the Na + /K + ATPase, which hydrolyzes 1 ATP to move 3 Na + outside and 2 K + inside the cells. Astrocytes are commonly thought to be primarily involved in transmitter glutamate cycling, a mechanism that however only accounts for few % of brain energy utilization. In order to examine the participation of astrocytic energy metabolism in brain ion homeostasis, here we attempted to devise a simple stoichiometric relation linking glutamatergic neurotransmission to Na + and K + ionic currents. To this end, we took into account ion pumps and voltage/ligand-gated channels using the stoichiometry derived from available energy budget for neocortical signaling and incorporated this stoichiometric relation into a computational metabolic model of neuron-astrocyte interactions. We aimed at reproducing the experimental observations about rates of metabolic pathways obtained by 13 C-NMR spectroscopy in rodent brain. When simulated data matched experiments as well as biophysical calculations, the stoichiometry for voltage/ligand-gated Na + and K + fluxes generated by neuronal activity was close to a 1:1 relationship, and specifically 63/58 Na + /K + ions per glutamate released. We found that astrocytes are stimulated by the extracellular K + exiting neurons in excess of the 3/2 Na + /K + ratio underlying Na + /K + ATPase-catalyzed reaction. Analysis of correlations between neuronal and astrocytic processes indicated that astrocytic K + uptake, but not astrocytic Na + -coupled glutamate uptake, is instrumental for the establishment of neuron-astrocytic metabolic partnership. Our results emphasize the importance of K + in stimulating the activation of

Ictal but not interictal epileptic discharges activate astrocyte endfeet and elicit cerebral arteriole responses.

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Marta eGomez-Gonzalo

2011-06-01

Full Text Available Activation of astrocytes by neuronal signals plays a central role in the control of neuronal activity-dependent blood flow changes in the normal brain. The cellular pathways that mediate neurovascular coupling in the epileptic brain remain, however, poorly defined. In a cortical slice model of epilepsy, we found that the ictal, seizure-like discharge, and only to a minor extent the interictal discharge, evokes both a Ca2+ increase in astrocyte endfeet and a vasomotor response. We also observed that rapid ictal discharge-induced arteriole responses were regularly preceded by Ca2+ elevations in endfeet and were abolished by pharmacological inhibition of Ca2+ signals in these astrocyte processes. Under these latter conditions, arterioles exhibited after the ictal discharge only slowly developing vasodilations. The poor efficacy of interictal discharges, compared with ictal discharges, to activate endfeet was confirmed also in the intact in vitro isolated guinea pig brain. Although the possibility of a direct contribution of neurons, in particular in the late response of cerebral blood vessels to epileptic discharges, should be taken into account, our study supports the view that astrocytes are central for neurovascular coupling also in the epileptic brain. The massive endfeet Ca2+ elevations evoked by ictal discharges and the poor response to interictal events represent new information potentially relevant to interpret data from diagnostic brain imaging techniques, such as functional magnetic resonance, utilized in the clinic to localize neural activity and to optimize neurosurgery of untreatable epilepsies.

Does rapid and physiological astrocyte-neuron signalling amplify epileptic activity?

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Henneberger, Christian

2017-03-15

The hippocampus is a key brain region in the pathophysiology of mesial temporal lobe epilepsy. Long-term changes of its architecture and function on the network and cellular level are well documented in epilepsy. Astrocytes can control many aspects of neuronal function and their long-term alterations over weeks, months and years play an important role in epilepsy. However, a pathophysiological transformation of astrocytes does not seem to be required for astrocytes to contribute to epileptic activity. Some of the properties of physiological astrocyte-neuron communication could allow these cells to exacerbate or synchronize neuronal firing on shorter time scales of milliseconds to minutes. Therefore, these astrocyte-neuron interactions are increasingly recognized as potential contributors to epileptic activity. Fast and reciprocal communication between astrocytes and neurons is enabled by a diverse set of mechanisms that could both amplify and counteract epileptic activity. They may thus promote or cause development of epileptic activity or inhibit it. Mechanisms of astrocyte-neuron interactions that can quickly increase network excitability involve, for example, astrocyte Ca 2+ and Na + signalling, K + buffering, gap junction coupling and metabolism. However, rapid changes of astrocyte neurotransmitter uptake and morphology may also underlie or support development of network hyperexcitability. The temporal characteristics of these interactions, their ability to synchronize neuronal activity and their net effect on network activity will determine their contribution to the emergence or maintenance of epileptic activity. © 2016 The Authors. The Journal of Physiology © 2016 The Physiological Society.

Enhancing NAD+ Salvage Pathway Reverts the Toxicity of Primary Astrocytes Expressing Amyotrophic Lateral Sclerosis-linked Mutant Superoxide Dismutase 1 (SOD1)*

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Harlan, Benjamin A.; Pehar, Mariana; Sharma, Deep R.; Beeson, Gyda; Beeson, Craig C.; Vargas, Marcelo R.

2016-01-01

Nicotinamide adenine dinucleotide (NAD+) participates in redox reactions and NAD+-dependent signaling pathways. Although the redox reactions are critical for efficient mitochondrial metabolism, they are not accompanied by any net consumption of the nucleotide. On the contrary, NAD+-dependent signaling processes lead to its degradation. Three distinct families of enzymes consume NAD+ as substrate: poly(ADP-ribose) polymerases, ADP-ribosyl cyclases (CD38 and CD157), and sirtuins (SIRT1–7). Because all of the above enzymes generate nicotinamide as a byproduct, mammalian cells have evolved an NAD+ salvage pathway capable of resynthesizing NAD+ from nicotinamide. Overexpression of the rate-limiting enzyme in this pathway, nicotinamide phosphoribosyltransferase, increases total and mitochondrial NAD+ levels in astrocytes. Moreover, targeting nicotinamide phosphoribosyltransferase to the mitochondria also enhances NAD+ salvage pathway in astrocytes. Supplementation with the NAD+ precursors nicotinamide mononucleotide and nicotinamide riboside also increases NAD+ levels in astrocytes. Amyotrophic lateral sclerosis (ALS) is caused by the progressive degeneration of motor neurons in the spinal cord, brain stem, and motor cortex. Superoxide dismutase 1 (SOD1) mutations account for up to 20% of familial ALS and 1–2% of apparently sporadic ALS cases. Primary astrocytes isolated from mutant human superoxide dismutase 1-overexpressing mice as well as human post-mortem ALS spinal cord-derived astrocytes induce motor neuron death in co-culture. Increasing total and mitochondrial NAD+ content in ALS astrocytes increases oxidative stress resistance and reverts their toxicity toward co-cultured motor neurons. Taken together, our results suggest that enhancing the NAD+ salvage pathway in astrocytes could be a potential therapeutic target to prevent astrocyte-mediated motor neuron death in ALS. PMID:27002158

Glycogenolysis in astrocytes supports blood-borne glucose channeling not glycogen-derived lactate shuttling to neurons: evidence from mathematical modeling.

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DiNuzzo, Mauro; Mangia, Silvia; Maraviglia, Bruno; Giove, Federico

2010-12-01

In this article, we examined theoretically the role of human cerebral glycogen in buffering the metabolic requirement of a 360-second brain stimulation, expanding our previous modeling study of neurometabolic coupling. We found that glycogen synthesis and degradation affects the relative amount of glucose taken up by neurons versus astrocytes. Under conditions of 175:115 mmol/L (∼1.5:1) neuronal versus astrocytic activation-induced Na(+) influx ratio, ∼12% of astrocytic glycogen is mobilized. This results in the rapid increase of intracellular glucose-6-phosphate level on stimulation and nearly 40% mean decrease of glucose flow through hexokinase (HK) in astrocytes via product inhibition. The suppression of astrocytic glucose phosphorylation, in turn, favors the channeling of glucose from interstitium to nearby activated neurons, without a critical effect on the concurrent intercellular lactate trafficking. Under conditions of increased neuronal versus astrocytic activation-induced Na(+) influx ratio to 190:65 mmol/L (∼3:1), glycogen is not significantly degraded and blood glucose is primarily taken up by neurons. These results support a role for astrocytic glycogen in preserving extracellular glucose for neuronal utilization, rather than providing lactate to neurons as is commonly accepted by the current 'thinking paradigm'. This might be critical in subcellular domains during functional conditions associated with fast energetic demands.

The glia doctrine: addressing the role of glial cells in healthy brain ageing.

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Nagelhus, Erlend A; Amiry-Moghaddam, Mahmood; Bergersen, Linda H; Bjaalie, Jan G; Eriksson, Jens; Gundersen, Vidar; Leergaard, Trygve B; Morth, J Preben; Storm-Mathisen, Jon; Torp, Reidun; Walhovd, Kristine B; Tønjum, Tone

2013-10-01

Glial cells in their plurality pervade the human brain and impact on brain structure and function. A principal component of the emerging glial doctrine is the hypothesis that astrocytes, the most abundant type of glial cells, trigger major molecular processes leading to brain ageing. Astrocyte biology has been examined using molecular, biochemical and structural methods, as well as 3D brain imaging in live animals and humans. Exosomes are extracelluar membrane vesicles that facilitate communication between glia, and have significant potential for biomarker discovery and drug delivery. Polymorphisms in DNA repair genes may indirectly influence the structure and function of membrane proteins expressed in glial cells and predispose specific cell subgroups to degeneration. Physical exercise may reduce or retard age-related brain deterioration by a mechanism involving neuro-glial processes. It is most likely that additional information about the distribution, structure and function of glial cells will yield novel insight into human brain ageing. Systematic studies of glia and their functions are expected to eventually lead to earlier detection of ageing-related brain dysfunction and to interventions that could delay, reduce or prevent brain dysfunction. Copyright © 2013 The Authors. Published by Elsevier Ireland Ltd.. All rights reserved.

Expression and activation by Epstein Barr virus of human endogenous retroviruses-W in blood cells and astrocytes: inference for multiple sclerosis.

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Giuseppe Mameli

Full Text Available BACKGROUND: Proposed co-factors triggering the pathogenesis of multiple sclerosis (MS are the Epstein Barr virus (EBV, and the potentially neuropathogenic MSRV (MS-associated retrovirus and syncytin-1, of the W family of human endogenous retroviruses. METHODOLOGY/PRINCIPAL FINDINGS: In search of links, the expression of HERV-W/MSRV/syncytin-1, with/without exposure to EBV or to EBV glycoprotein350 (EBVgp350, was studied on peripheral blood mononuclear cells (PBMC from healthy volunteers and MS patients, and on astrocytes, by discriminatory env-specific RT-PCR assays, and by flow cytometry. Basal expression of HERV-W/MSRV/syncytin-1 occurs in astrocytes and in monocytes, NK, and B, but not in T cells. This uneven expression is amplified in untreated MS patients, and dramatically reduced during therapy. In astrocytes, EBVgp350 stimulates the expression of HERV-W/MSRV/syncytin-1, with requirement of the NF-κB pathway. In EBVgp350-treated PBMC, MSRVenv and syncytin-1 transcription is activated in B cells and monocytes, but not in T cells, nor in the highly expressing NK cells. The latter cells, but not the T cells, are activated by proinflammatory cytokines. CONCLUSIONS/SIGNIFICANCE: In vitro EBV activates the potentially immunopathogenic and neuropathogenic HERV-W/MSRV/syncytin-1, in cells deriving from blood and brain. In vivo, pathogenic outcomes would depend on abnormal situations, as in late EBV primary infection, that is often symptomatic, or/and in the presence of particular host genetic backgrounds. In the blood, HERV-Wenv activation might induce immunopathogenic phenomena linked to its superantigenic properties. In the brain, toxic mechanisms against oligodendrocytes could be established, inducing inflammation, demyelination and axonal damage. Local stimulation by proinflammatory cytokines and other factors might activate further HERV-Ws, contributing to the neuropathogenity. In MS pathogenesis, a possible model could include EBV as

Hippocampal astrocytes are necessary for antidepressant treatment of learned helplessness rats.

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Iwata, Masaaki; Shirayama, Yukihiko; Ishida, Hisahito; Hazama, Gen-i; Nakagome, Kazuyuki

2011-08-01

The astrocyte is a major component of the neural network and plays a role in brain function. Previous studies demonstrated changes in the number of astrocytes in depression. In this study, we examined alterations in the number of astrocytes in the learned helplessness (LH) rat, an animal model of depression. The numbers of activated and nonactivated astrocytes in the dentate gyrus (molecular layer, subgranular zone, and hilus), and CA1 and CA3 regions of the hippocampus were significantly increased 2 and 8 days after attainment of LH. Subchronic treatment with imipramine showed a tendency (although not statistically significant) to decrease the LH-induced increment of activated astrocytes in the CA3 region and dentate gyrus. Furthermore, subchronic treatment of naïve rats with imipramine did not alter the numbers of activated and nonactivated astrocytes. However, the antidepressant-like effects of imipramine in the LH paradigm were blocked when fluorocitrate (a reversible inhibitor of astrocyte function) was injected into the dentate gyrus or CA3 region. Injection of fluorocitrate into naive rats failed to induce behavioral deficits in the conditioned avoidance test. These results indicate that astrocytes are responsive to the antidepressant-like effect of imipramine in the dentate gyrus and CA3 region of the hippocampus. Copyright © 2010 Wiley-Liss, Inc.

Connexin-based intercellular communication and astrocyte heterogeneity.

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Theis, Martin; Giaume, Christian

2012-12-03

This review gives an overview of the current knowledge on connexin-mediated communication in astrocytes, covering gap junction and hemichannel functions mediated by connexins. Astroglia is the main brain cell type that expresses the largest amount of connexin and exhibits high level of gap junctional communication compared to neurons and oligodendrocytes. However, in certain developmental and regional situations, astrocytes are also coupled with oligodendrocytes and neurons. This heterotypic coupling is infrequent and minor in terms of extent of the coupling area, which does not mean that it is not important in terms of cell interaction. Here, we present an update on heterogeneity of connexin expression and function at the molecular, subcellular, cellular and networking levels. Interestingly, while astrocytes were initially considered as a homogenous population, there is now increasing evidence for morphological, developmental, molecular and physiological heterogeneity of astrocytes. Consequently, the specificity of gap junction channel- and hemichannel-mediated communication, which tends to synchronize cell populations, is also a parameter to take into account when neuroglial interactions are investigated. This article is part of a Special Issue entitled Electrical Synapses. Copyright © 2012 Elsevier B.V. All rights reserved.

Automated Functional Analysis of Astrocytes from Chronic Time-Lapse Calcium Imaging Data.

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Wang, Yinxue; Shi, Guilai; Miller, David J; Wang, Yizhi; Wang, Congchao; Broussard, Gerard; Wang, Yue; Tian, Lin; Yu, Guoqiang

2017-01-01

Recent discoveries that astrocytes exert proactive regulatory effects on neural information processing and that they are deeply involved in normal brain development and disease pathology have stimulated broad interest in understanding astrocyte functional roles in brain circuit. Measuring astrocyte functional status is now technically feasible, due to recent advances in modern microscopy and ultrasensitive cell-type specific genetically encoded Ca 2+ indicators for chronic imaging. However, there is a big gap between the capability of generating large dataset via calcium imaging and the availability of sophisticated analytical tools for decoding the astrocyte function. Current practice is essentially manual, which not only limits analysis throughput but also risks introducing bias and missing important information latent in complex, dynamic big data. Here, we report a suite of computational tools, called Functional AStrocyte Phenotyping (FASP), for automatically quantifying the functional status of astrocytes. Considering the complex nature of Ca 2+ signaling in astrocytes and low signal to noise ratio, FASP is designed with data-driven and probabilistic principles, to flexibly account for various patterns and to perform robustly with noisy data. In particular, FASP explicitly models signal propagation, which rules out the applicability of tools designed for other types of data. We demonstrate the effectiveness of FASP using extensive synthetic and real data sets. The findings by FASP were verified by manual inspection. FASP also detected signals that were missed by purely manual analysis but could be confirmed by more careful manual examination under the guidance of automatic analysis. All algorithms and the analysis pipeline are packaged into a plugin for Fiji (ImageJ), with the source code freely available online at https://github.com/VTcbil/FASP.

Activation of the sigma-1 receptor by haloperidol metabolites facilitates brain-derived neurotrophic factor secretion from human astroglia.

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Dalwadi, Dhwanil A; Kim, Seongcheol; Schetz, John A

2017-05-01

Glial cells play a critical role in neuronal support which includes the production and release of the neurotrophin brain-derived neurotrophic factor (BDNF). Activation of the sigma-1 receptor (S1R) has been shown to attenuate inflammatory stress-mediated brain injuries, and there is emerging evidence that this may involve a BDNF-dependent mechanism. In this report we studied S1R-mediated BDNF release from human astrocytic glial cells. Astrocytes express the S1R, which mediates BDNF release when stimulated with the prototypical S1R agonists 4-PPBP and (+)-SKF10047. This effect could be antagonized by a selective concentration of the S1R antagonist BD1063. Haloperidol is known to have high affinity interactions with the S1R, yet it was unable to facilitate BDNF release. Remarkably, however, two metabolites of haloperidol, haloperidol I and haloperidol II (reduced haloperidol), were discovered to facilitate BDNF secretion and this effect was antagonized by BD1063. Neither 4-PPBP, nor either of the haloperidol metabolites affected the level of BDNF mRNA as assessed by qPCR. These results demonstrate for the first time that haloperidol metabolites I and II facilitate the secretion of BDNF from astrocytes by acting as functionally selective S1R agonists. Copyright © 2017 Elsevier Ltd. All rights reserved.

[Effects of electric stimulation at the cerebellar fastigial nucleus on astrocytes in the hippocampus of neonatal rats with hypoxic-ischemic brain damage].

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Li, Xiao-Li; Jia, Tian-Ming; Luan, Bin; Liu, Tao; Yuan, Yan

2011-04-01

To study the effects of electric stimulation at the cerebellar fastigial nucleus on astrocytes in the hippocampus of neonatal rats with hypoxic-ischemic brain damage (HIBD) and the possible mechanism. One hundred and eighty 7-day-old neonatal Sprague-Dawley rats were randomly divided into three groups: sham-operation (control group) and HIBD with and without electric stimulation (n=60 each). The HIBD model of neonatal rats was prepared by the Rice-Vennucci method. Electric stimulation at the cerebellar fastigial nucleus was given 24 hrs after the operation in the electric stimulation group once daily and lasted for 30 minutes each time. The other two groups were not subjected to electric stimulation but captured to fix in corresponding periods. Rats were sacrificed 3, 7, 14 and 21 days after stimulations to observe the glial fibrillary acidic protein (GFAP) expression by immunohistochemisty and the ultrastructural changes of astrocytes in the hippocampus under an electron microscope. Immunohistochemical analysis showed the expression of GFAP in the HIBD groups with and without electric stimulation increased significantly compared with the control group on day 3, reached the peak on day 7, and the increased expression remained till to day 21. The GFAP expression in the electric stimulation group was significantly lower than that in the untreated HIBD group at all time points. Under the electron microscope, the astrocytes in the untreated HIBD group were swollen and the amount of organelles was reduced, while the swelling of astrocytes was alleviated and the organelles remained in integrity in the electric stimulation group. The electric stimulation at the cerebellar fastigial nucleus can inhibit the excessive proliferation of astrocytes and relieve the structural damage of astrocytes in neonatal rats following HIBD.

Amyloid-β and Astrocytes Interplay in Amyloid-β Related Disorders

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Yazan S. Batarseh

2016-03-01

Full Text Available Amyloid-β (Aβ pathology is known to promote chronic inflammatory responses in the brain. It was thought previously that Aβ is only associated with Alzheimer’s disease and Down syndrome. However, studies have shown its involvement in many other neurological disorders. The role of astrocytes in handling the excess levels of Aβ has been highlighted in the literature. Astrocytes have a distinctive function in both neuronal support and protection, thus its involvement in Aβ pathological process may tip the balance toward chronic inflammation and neuronal death. In this review we describe the involvement of astrocytes in Aβ related disorders including Alzheimer’s disease, Down syndrome, cerebral amyloid angiopathy, and frontotemporal dementia.

Metal ion toxins and brain aquaporin-4 expression: an overview

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Adriana eXimenes-Da-Silva

2016-06-01

Full Text Available Metal ions such as iron, zinc, and manganese are essential to metabolic functions, protein synthesis, neurotransmission, and antioxidant neuroprotective mechanisms. Conversely, non-essential metals such as mercury and lead are sources of human intoxication due to occupational activities or environmental contamination. Essential or non-essential metal accumulation in the central nervous system (CNS results in changes in blood-brain barrier (BBB permeability, as well as triggering microglia activation and astrocyte reactivity and changing water transport through the cells, which could result in brain swelling. Aquaporin-4 is the main water channel in the CNS, is expressed in astrocyte foot processes in brain capillaries and along the circumventricular epithelium in the ventricles, and has important physiological functions in maintaining brain osmotic homeostasis and supporting brain excitability through regulation of the extracellular space. Some evidence has pointed to a role of AQP4 during metal intoxication in the brain, where it may act in a dual form as a neuroprotector or a mediator of the development of oxidative stress in neurons and astrocytes, resulting in brain swelling and neuronal damage. This mini-review presents the way some metal ions affect changes in AQP4 expression in the CNS and discuss the ways in which water transport in brain cells can be involved in brain damage.

Culturing of PC12 Cells, Neuronal Cells, Astrocytes Cultures and Brain Slices in an Open Microfluidic System

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Al Atraktchi, Fatima Al-Zahraa; Bakmand, Tanya; Rømer Sørensen, Ane

The brain is the center of the nervous system, where serious neurodegenerative diseases such as Parkinson’s, Alzheimer’s and Huntington’s are products of functional loss in the neural cells (1). Typical techniques used to investigate these diseases lack precise control of the cellular surroundings......, in addition to isolating the neural tissue from nutrient delivery and to creating unwanted gradients (2). This means that typical techniques used to investigate neurodegenerative diseases cannot mimic in vivo conditions, as closely as desired. We have developed a novel microfluidic system for culturing PC12...... cells, neuronal cells, astrocytes cultures and brain slices. The microfluidic system provides efficient nutrient delivery, waste removal, access to oxygen, fine control over the neurochemical environment and access to modern microscopy. Additionally, the setup consists of an in vitro culturing...

Involvement of Astrocytes in Mediating the Central Effects of Ghrelin

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Frago, Laura M.; Chowen, Julie A.

2017-01-01

Although astrocytes are the most abundant cells in the mammalian brain, much remains to be learned about their molecular and functional features. Astrocytes express receptors for numerous hormones and metabolic factors, including the appetite-promoting hormone ghrelin. The metabolic effects of ghrelin are largely opposite to those of leptin, as it stimulates food intake and decreases energy expenditure. Ghrelin is also involved in glucose-sensing and glucose homeostasis. The widespread expression of the ghrelin receptor in the central nervous system suggests that this hormone is not only involved in metabolism, but also in other essential functions in the brain. In fact, ghrelin has been shown to promote cell survival and neuroprotection, with some studies exploring the use of ghrelin as a therapeutic agent against metabolic and neurodegenerative diseases. In this review, we highlight the possible role of glial cells as mediators of ghrelin’s actions within the brain. PMID:28257088

Influence of drugs on gap junctions in glioma cell lines and primary astrocytes in vitro

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Zahra eMoinfar

2014-05-01

Full Text Available Gap junctions (GJs are hemichannels on cell membrane. Once they are intercellulary connected to the neighboring cells, they build a functional syncytium which allows rapid transfer of ions and molecules between cells. This characteristic makes GJs a potential modulator in proliferation, migration and development of the cells. So far, several types of GJs are recognized on different brain cells as well as in glioma. Astrocytes, as one of the major cells that maintain neuronal homeostasis, express different types of GJs that let them communicate with neurons, oligodendrocytes and endothelial cells of the blood brain barrier; however, the main GJ in astrocytes is connexin 43. There are different cerebral diseases in which astrocyte GJs might play a role. Several drugs have been reported to modulate gap junctional communication in the brain which can consequently have beneficial or detrimental effects on the course of treatment in certain diseases. However, the exact cellular mechanism behind those pharmaceutical efficacies on GJs is not well-understood. Accordingly, how specific drugs would affect GJs and what some consequent specific brain diseases would be are the interests of the authors of this chapter. We would focus on pharmaceutical effects on GJs on astrocytes in specific diseases where GJs could possibly play a role including: 1 migraine and a novel therapy for migraine with aura, 2 neuroautoimmune diseases and immunomodulatory drugs in the treatment of demyelinating diseases of the central nervous system such as multiple sclerosis, 3 glioma and antineoplastic and anti-inflammatory agents that are used in treating brain tumors and 4 epilepsy and anticonvulsants that are widely used for seizures therapy. All of the above-mentioned therapeutic categories can possibly affect GJs expression of astrocytes and the role is discussed in the upcoming chapter.

Astrocytes

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Rasmussen, Rune; Samson, Andrew J.

2017-01-01

Anatomy, physiology, proteomics, and genomics reveal the prospect of distinct highly specialized astrocyte subtypes within neural circuits.......Anatomy, physiology, proteomics, and genomics reveal the prospect of distinct highly specialized astrocyte subtypes within neural circuits....

Protection by neuroglobin expression in brain pathologies

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Eliana Baez

2016-09-01

Full Text Available Astrocytes play an important role in physiological, metabolic and structural functions and, when impaired, they can be involved in various pathologies including Alzheimer, focal ischemic stroke and traumatic brain injury. These disorders involve an imbalance in the blood flow and nutrients such as glucose and lactacte, leading to biochemical and molecular changes that cause neuronal damage, which is followed by loss of cognitive and motor functions. Previous studies have shown that astrocytes are more resilient than neurons during brain insults as a consequence of their more effective antioxidant systems, transporters and enzymes, which made them less susceptible to excitotoxicity. In addition, astrocytes synthesize and release different protective molecules for neurons, including neuroglobin, a member of the globin family of proteins. After brain injury neuroglobin expression is induced in astrocytes. Since neuroglobin promotes neuronal survival, its increased expression in astrocytes after brain injury may represent an endogenous neuroprotective mechanism. Here, we review the role of neuroglobin in the CNS, its relationship with different pathologies, and the role of different factors that regulate its expression in astrocytes.

NFkappaB in the mechanism of ammonia-induced astrocyte swelling in culture.

NARCIS (Netherlands)

Sinke, A.P.; Jayakumar, A.R.; Panickar, K.S.; Moriyama, M.; Reddy, P.V.; Norenberg, M.D.

2008-01-01

Astrocyte swelling and brain edema are major neuropathological findings in the acute form of hepatic encephalopathy (fulminant hepatic failure), and substantial evidence supports the view that elevated brain ammonia level is an important etiological factor in this condition. Although the mechanism

Huperzine A, but not tacrine, stimulates S100B secretion in astrocyte cultures.

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Lunardi, Paula; Nardin, Patrícia; Guerra, Maria Cristina; Abib, Renata; Leite, Marina Concli; Gonçalves, Carlos-Alberto

2013-04-09

The loss of cholinergic function in the central nervous system contributes significantly to the cognitive decline associated with advanced age and dementias. Huperzine A (HupA) is a selective inhibitor of acetylcholinesterase (AChE) and has been shown to significantly reduce cognitive impairment in animal models of dementia. Based on the importance of astrocytes in physiological and pathological brain activities, we investigated the effect of HupA and tacrine on S100B secretion in primary astrocyte cultures. S100B is an astrocyte-derived protein that has been proposed to be a marker of brain injury. Primary astrocyte cultures were exposed to HupA, tacrine, cholinergic agonists, and S100B secretion was measured by enzyme-linked immunosorbent assay (ELISA) at 1 and 24h. HupA, but not tacrine, at 100μM significantly increased S100B secretion in astrocyte cultures. Nicotine (at 100 and 1000μM) was able to stimulate S100B secretion in astrocyte cultures. Our data reinforce the idea that AChE inhibitors, particularly HupA, do not act exclusively on the acetylcholine balance. This effect of HupA could contribute to improve the cognitive deficit observed in patients, which are attributed to cholinergic dysfunction. In addition, for the first time, to our knowledge, these data indicate that S100B secretion can be modulated by nicotinic receptors, in addition to glutamate, dopamine and serotonin receptors. Copyright © 2013 Elsevier Inc. All rights reserved.

Enhancing NAD+ Salvage Pathway Reverts the Toxicity of Primary Astrocytes Expressing Amyotrophic Lateral Sclerosis-linked Mutant Superoxide Dismutase 1 (SOD1).

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Harlan, Benjamin A; Pehar, Mariana; Sharma, Deep R; Beeson, Gyda; Beeson, Craig C; Vargas, Marcelo R

2016-05-13

Nicotinamide adenine dinucleotide (NAD(+)) participates in redox reactions and NAD(+)-dependent signaling pathways. Although the redox reactions are critical for efficient mitochondrial metabolism, they are not accompanied by any net consumption of the nucleotide. On the contrary, NAD(+)-dependent signaling processes lead to its degradation. Three distinct families of enzymes consume NAD(+) as substrate: poly(ADP-ribose) polymerases, ADP-ribosyl cyclases (CD38 and CD157), and sirtuins (SIRT1-7). Because all of the above enzymes generate nicotinamide as a byproduct, mammalian cells have evolved an NAD(+) salvage pathway capable of resynthesizing NAD(+) from nicotinamide. Overexpression of the rate-limiting enzyme in this pathway, nicotinamide phosphoribosyltransferase, increases total and mitochondrial NAD(+) levels in astrocytes. Moreover, targeting nicotinamide phosphoribosyltransferase to the mitochondria also enhances NAD(+) salvage pathway in astrocytes. Supplementation with the NAD(+) precursors nicotinamide mononucleotide and nicotinamide riboside also increases NAD(+) levels in astrocytes. Amyotrophic lateral sclerosis (ALS) is caused by the progressive degeneration of motor neurons in the spinal cord, brain stem, and motor cortex. Superoxide dismutase 1 (SOD1) mutations account for up to 20% of familial ALS and 1-2% of apparently sporadic ALS cases. Primary astrocytes isolated from mutant human superoxide dismutase 1-overexpressing mice as well as human post-mortem ALS spinal cord-derived astrocytes induce motor neuron death in co-culture. Increasing total and mitochondrial NAD(+) content in ALS astrocytes increases oxidative stress resistance and reverts their toxicity toward co-cultured motor neurons. Taken together, our results suggest that enhancing the NAD(+) salvage pathway in astrocytes could be a potential therapeutic target to prevent astrocyte-mediated motor neuron death in ALS. © 2016 by The American Society for Biochemistry and Molecular

Stretch induced endothelin-1 secretion by adult rat astrocytes involves calcium influx via stretch-activated ion channels (SACs)

International Nuclear Information System (INIS)

Ostrow, Lyle W.; Suchyna, Thomas M.; Sachs, Frederick

2011-01-01

Highlights: → Endothelin-1 expression by adult rat astrocytes correlates with cell proliferation. → Stretch-induced ET-1 is inhibited by GsMtx-4, a specific inhibitor of Ca 2+ permeant SACs. → The less specific SAC inhibitor streptomycin also inhibits ET-1 secretion. → Stretch-induced ET-1 production depends on a calcium influx. → SAC pharmacology may provide a new class of therapeutic agents for CNS pathology. -- Abstract: The expression of endothelins (ETs) and ET-receptors is often upregulated in brain pathology. ET-1, a potent vasoconstrictor, also inhibits the expression of astrocyte glutamate transporters and is mitogenic for astrocytes, glioma cells, neurons, and brain capillary endothelia. We have previously shown that mechanical stress stimulates ET-1 production by adult rat astrocytes. We now show in adult astrocytes that ET-1 production is driven by calcium influx through stretch-activated ion channels (SACs) and the ET-1 production correlates with cell proliferation. Mechanical stimulation using biaxial stretch ( 2+ threshold. This coupling of mechanical stress to the astrocyte endothelin system through SACs has treatment implications, since all pathology deforms the surrounding parenchyma.

Ketogenic diet and astrocyte/neuron metabolic interactions

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Vamecq Joseph

2007-05-01

Full Text Available The ketogenic diet is an anticonvulsant diet enriched in fat. It provides the body with a minimal protein requirement and a restricted carbohydrate supply, the vast majority of calories (more than 80-90% being given by fat. Though anticonvulsant activity of ketogenic diet has been well documented by a large number of experimental and clinical studies, underlying mechanisms still remain partially unclear. Astrocyte-neuron interactions, among which metabolic shuttles, may influence synaptic activity and hence anticonvulsant protection. The astrocyte-neuron metabolic shuttles may be themselves influenced by the availability in energetic substrates such as hydrates of carbon and fats. Historically, ketogenic diet had been designed to mimic changes such as ketosis occurring upon starvation, a physiological state already known to exhibit anticonvulsant protection and sometimes referred to as “water diet”. For this reason, a special attention should be paid to metabolic features shared in common by ketogenic diet and starvation and especially those features that might result in anticonvulsant protection. Compared to feeding by usual mixed diet, starvation and ketogenic diet are both characterised by increased fat, lowered glucose and aminoacid supplies to cells. The resulting impact of these changes in energetic substrates on astrocyte/neuron metabolic shuttles might have anticonvulsant and/or neuroprotective properties. This is the aim of this communication to review some important astrocyte/neuron metabolic interactions (astrocyte/neuron lactate shuttle, glutamateinduced astrocytic glycolysis activation, glutamate/glutamine cycle along with the neurovascular coupling and the extent to which the way of their alteration by starvation and/or ketogenic diet might result in seizure and/or brain protection.

The effect of tobacco smoke exposure on the generation of reactive oxygen species and cellular membrane damage using co-culture model of blood brain barrier with astrocytes.

Science.gov (United States)

Seo, Seung-Beom; Choe, Eun Sang; Kim, Kwang-Sik; Shim, Soon-Mi

2017-06-01

Brain tissue is known to be vulnerable to the exposure by tobacco smoke. Tobacco smoke can induce generation of reactive oxygen species (ROS), causing inflammatory activity and blood-brain barrier (BBB) impairment. The aim of the present study was to investigate the effect of tobacco smoke on cell cytotoxicity, generation of ROS, and cellular membrane damage in astrocytes and BBB using a co-culture system. Cell viability of U373MG cells was reduced in a dose-dependent manner, ranging from 96.7% to 40.3% by tobacco smoke condensate (TSC). Cell viability of U373MG co-cultured with human brain microvascular endothelial cells (HBMECs) was 104.9% at the IC 50 value of TSC. Trans-epithelial electric resistance values drastically decreased 80% following 12-h incubation. The value was maintained until 48 h and then increased at 72-h incubation (85%). It then decreased to 75% at 120 h. Generation of ROS increased in a dose-dependent manner, ranging from 102.7% to 107.9%, when various concentrations of TSC (4-16 mg/mL) were administered to the U373MG monoculture. When TSC was added into U373MG co-cultured with HBMECs, production of ROS ranged from 101.7% to 102.6%, slightly increasing over 12 h. Maximum exposure-generated ROS of 104.8% was reached at 24 h. Cell cytotoxicity and oxidative stress levels in the U373MG co-culture model system with HBMECs were lower than U373MG monoculture. HBMECs effectively acted as a barrier to protect the astrocytes (U373MG) from toxicity of TSC.

Astrocyte lipid metabolism is critical for synapse development and function in vivo.

Science.gov (United States)

van Deijk, Anne-Lieke F; Camargo, Nutabi; Timmerman, Jaap; Heistek, Tim; Brouwers, Jos F; Mogavero, Floriana; Mansvelder, Huibert D; Smit, August B; Verheijen, Mark H G

2017-04-01

The brain is considered to be autonomous in lipid synthesis with astrocytes producing lipids far more efficiently than neurons. Accordingly, it is generally assumed that astrocyte-derived lipids are taken up by neurons to support synapse formation and function. Initial confirmation of this assumption has been obtained in cell cultures, but whether astrocyte-derived lipids support synapses in vivo is not known. Here, we address this issue and determined the role of astrocyte lipid metabolism in hippocampal synapse formation and function in vivo. Hippocampal protein expression for the sterol regulatory element-binding protein (SREBP) and its target gene fatty acid synthase (Fasn) was found in astrocytes but not in neurons. Diminishing SREBP activity in astrocytes using mice in which the SREBP cleavage-activating protein (SCAP) was deleted from GFAP-expressing cells resulted in decreased cholesterol and phospholipid secretion by astrocytes. Interestingly, SCAP mutant mice showed more immature synapses, lower presynaptic protein SNAP-25 levels as well as reduced numbers of synaptic vesicles, indicating impaired development of the presynaptic terminal. Accordingly, hippocampal short-term and long-term synaptic plasticity were defective in mutant mice. These findings establish a critical role for astrocyte lipid metabolism in presynaptic terminal development and function in vivo. GLIA 2017;65:670-682. © 2017 Wiley Periodicals, Inc.

Cell-type-specific and differentiation-status-dependent variations in cytotoxicity of tributyltin in cultured rat cerebral neurons and astrocytes.

Science.gov (United States)

Oyanagi, Koshi; Tashiro, Tomoko; Negishi, Takayuki

2015-08-01

Tributyltin (TBT) is an organotin used as an anti-fouling agent for fishing nets and ships and it is a widespread environmental contaminant at present. There is an increasing concern about imperceptible but serious adverse effect(s) of exposure to chemicals existing in the environment on various organs and their physiological functions, e.g. brain and mental function. Here, so as to contribute to improvement of and/or advances in in vitro cell-based assay systems for evaluating brain-targeted adverse effect of chemicals, we tried to evaluate cell-type-specific and differentiation-status-dependent variations in the cytotoxicity of TBT towards neurons and astrocytes using the four culture systems differing in the relative abundance of these two types of cells; primary neuron culture (> 95% neurons), primary neuron-astrocyte (2 : 1) mix culture, primary astrocyte culture (> 95% astrocytes), and passaged astrocyte culture (100% proliferative astrocytes). Cell viability was measured at 48 hr after exposure to TBT in serum-free medium. IC50's of TBT were 198 nM in primary neuron culture, 288 nM in primary neuron-astrocyte mix culture, 2001 nM in primary astrocyte culture, and 1989 nM in passaged astrocyte culture. Furthermore, in primary neuron-astrocyte mix culture, vulnerability of neurons cultured along with astrocytes to TBT toxicity was lower than that of neurons cultured purely in primary neuron culture. On the other hand, astrocytes in primary neuron-astrocyte mix culture were considered to be more vulnerable to TBT than those in primary or passaged astrocyte culture. The present study demonstrated variable cytotoxicity of TBT in neural cells depending on the culture condition.

Calcium in the Mechanism of Ammonia-Induced Astrocyte Swelling

Science.gov (United States)

Jayakumar, A.R.; Rao, K.V. Rama; Tong, X.Y; Norenberg, M.D.

2016-01-01

Brain edema, due largely to astrocyte swelling, is an important clinical problem in patients with acute liver failure. While mechanisms underlying astrocyte swelling in this condition are not fully understood, ammonia and associated oxidative/nitrosative stress (ONS) appear to be involved. Mechanisms responsible for the increase in reactive oxygen/nitrogen species (RONS) and their role in ammonia-induced astrocyte swelling, however, are poorly understood. Recent studies have demonstrated a transient increase in intracellular Ca2+ in cultured astrocytes exposed to ammonia. As Ca2+ is a known inducer of RONS, we investigated potential mechanisms by which Ca2+ may be responsible for the production of RONS and cell swelling in cultured astrocytes after treatment with ammonia. Exposure of cultured astrocytes to ammonia (5 mM) increased the formation of free radicals, including nitric oxide, and such increase was significantly diminished by treatment with the Ca2+ chelator BAPTA-AM. We then examined the activity of Ca2+-dependent enzymes that are known to generate RONS and found that ammonia significantly increased the activities of NADPH oxidase (NOX), constitutive nitric oxide synthase (cNOS) and phospholipase A2 (PLA2) and such increases in activity were significantly diminished by BAPTA. Pretreatment of cultures with 7-nitroindazole, apocyanin and quinacrine, respective inhibitors of cNOS, NOX and PLA2, all significantly diminished RONS production. Additionally, treatment of cultures with BAPTA or with inhibitors of cNOS, NOX and PLA2 reduced ammonia-induced astrocyte swelling. These studies suggest that the ammonia-induced rise in intracellular Ca2+ activates free radical producing enzymes that ultimately contribute to the mechanism of astrocyte swelling. PMID:19393035

Staphylococcus epidermidis polysaccharide intercellular adhesin induces IL-8 expression in human astrocytes via a mechanism involving TLR2.

LENUS (Irish Health Repository)

Stevens, Niall T

2009-03-01

Staphylococcus epidermidis is an opportunistic biofilm-forming pathogen associated with neurosurgical device-related meningitis. Expression of the polysaccharide intercellular adhesin (PIA) on its surface promotes S. epidermidis biofilm formation. Here we investigated the pro-inflammatory properties of PIA against primary and transformed human astrocytes. PIA induced IL-8 expression in a dose- and\\/or time-dependent manner from U373 MG cells and primary normal human astrocytes. This effect was inhibited by depletion of N-acetyl-beta-d-glucosamine polymer from the PIA preparation with Lycopersicon esculentum lectin or sodium meta-periodate. Expression of dominant-negative versions of the TLR2 and TLR4 adaptor proteins MyD88 and Mal in U373 MG cells inhibited PIA-induced IL-8 production. Blocking IL-1 had no effect. PIA failed to induce IL-8 production from HEK293 cells stably expressing TLR4. However, in U373 MG cells which express TLR2, neutralization of TLR2 impaired PIA-induced IL-8 production. In addition to IL-8, PIA also induced expression of other cytokines from U373 MG cells including IL-6 and MCP-1. These data implicate PIA as an important immunogenic component of the S. epidermidis biofilm that can regulate pro-inflammatory cytokine production from human astrocytes, in part, via TLR2.

Astrocytes from adult Wistar rats aged in vitro show changes in glial functions.

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Souza, Débora Guerini; Bellaver, Bruna; Raupp, Gustavo Santos; Souza, Diogo Onofre; Quincozes-Santos, André

2015-11-01

Astrocytes, the most versatile cells of the central nervous system, play an important role in the regulation of neurotransmitter homeostasis, energy metabolism, antioxidant defenses and the anti-inflammatory response. Recently, our group characterized cortical astrocyte cultures from adult Wistar rats. In line with that work, we studied glial function using an experimental in vitro model of aging astrocytes (30 days in vitro after reaching confluence) from newborn (NB), adult (AD) and aged (AG) Wistar rats. We evaluated metabolic parameters, such as the glucose uptake, glutamine synthetase (GS) activity, and glutathione (GSH) content, as well as the GFAP, GLUT-1 and xCT expression. AD and AG astrocytes take up less glucose than NB astrocytes and had decreased GLUT1 expression levels. Furthermore, AD and AG astrocytes exhibited decreased GS activity compared to NB cells. Simultaneously, AD and AG astrocytes showed an increase in GSH levels, along with an increase in xCT expression. NB, AD and AG astrocytes presented similar morphology; however, differences in GFAP levels were observed. Taken together, these results improve the knowledge of cerebral senescence and represent an innovative tool for brain studies of aging. Copyright © 2015 Elsevier Ltd. All rights reserved.

The metabolism of malate by cultured rat brain astrocytes

Energy Technology Data Exchange (ETDEWEB)

McKenna, M.C.; Tildon, J.T.; Couto, R.; Stevenson, J.H.; Caprio, F.J. (Department of Pediatrics, University of Maryland School of Medicine, Baltimore (USA))

1990-12-01

Since malate is known to play an important role in a variety of functions in the brain including energy metabolism, the transfer of reducing equivalents and possibly metabolic trafficking between different cell types; a series of biochemical determinations were initiated to evaluate the rate of 14CO2 production from L-(U-14C)malate in rat brain astrocytes. The 14CO2 production from labeled malate was almost totally suppressed by the metabolic inhibitors rotenone and antimycin A suggesting that most of malate metabolism was coupled to the electron transport system. A double reciprocal plot of the 14CO2 production from the metabolism of labeled malate revealed biphasic kinetics with two apparent Km and Vmax values suggesting the presence of more than one mechanism of malate metabolism in these cells. Subsequent experiments were carried out using 0.01 mM and 0.5 mM malate to determine whether the addition of effectors would differentially alter the metabolism of high and low concentrations of malate. Effectors studied included compounds which could be endogenous regulators of malate metabolism and metabolic inhibitors which would provide information regarding the mechanisms regulating malate metabolism. Both lactate and aspartate decreased 14CO2 production from malate equally. However, a number of effectors were identified which selectively altered the metabolism of 0.01 mM malate including aminooxyacetate, furosemide, N-acetylaspartate, oxaloacetate, pyruvate and glucose, but had little or no effect on the metabolism of 0.5 mM malate. In addition, alpha-ketoglutarate and succinate decreased 14CO2 production from 0.01 mM malate much more than from 0.5 mM malate. In contrast, a number of effectors altered the metabolism of 0.5 mM malate more than 0.01 mM. These included methionine sulfoximine, glutamate, malonate, alpha-cyano-4-hydroxycinnamate and ouabain.

Primary cultures of astrocytes

DEFF Research Database (Denmark)

Lange, Sofie C; Bak, Lasse Kristoffer; Waagepetersen, Helle S

2012-01-01

During the past few decades of astrocyte research it has become increasingly clear that astrocytes have taken a central position in all central nervous system activities. Much of our new understanding of astrocytes has been derived from studies conducted with primary cultures of astrocytes...... subsequently found in vivo. Nevertheless, primary cultures of astrocytes are an in vitro model that does not fully mimic the complex events occurring in vivo. Here we present an overview of the numerous contributions generated by the use of primary astrocyte cultures to uncover the diverse functions...... of astrocytes. Many of these discoveries would not have been possible to achieve without the use of astrocyte cultures. Additionally, we address and discuss the concerns that have been raised regarding the use of primary cultures of astrocytes as an experimental model system....

Distribution of rSlo Ca2+-activated K+ channels in rat astrocyte perivascular endfeet.

Science.gov (United States)

Price, Diana L; Ludwig, Jeffrey W; Mi, Huaiyu; Schwarz, Thomas L; Ellisman, Mark H

2002-11-29

Evidence that Ca(2+)-activated K(+) (K(Ca)) channels play a role in cell volume changes and K(+) homeostasis led to a prediction that astrocytes would have K(Ca) channels near blood vessels in order to maintain K(+) homeostasis. Consistent with this thinking the present study demonstrates that rSlo K(Ca) channels are in glial cells of the adult rat central nervous system (CNS) and highly localized to specializations of astrocytes associated with the brain vasculature. Using confocal and thin-section electron microscopic immunolabeling methods the distribution of rSlo was examined in adult rat brain. Strong rSlo immunolabeling was present around the vasculature of most brain regions. Examination of dye-filled hippocampal astrocytes revealed rSlo immunolabeling polarized in astrocytic endfeet. Ultrastructural analysis confirmed that the rSlo staining was concentrated in astrocytic endfeet ensheathing capillaries as well as abutting the pia mater. Immunostaining within the endfeet was predominantly distributed at the plasma membrane directly adjacent to either the vascular basal lamina or the pial surface. The distribution of the aquaporin-4 (AQP-4) water channel was also examined using dye-filled hippocampal astrocytes. In confirmation of earlier reports, intense AQP-4 immunolabeling was generally observed at the perimeter of blood vessels, and coincided with perivascular endfeet and rSlo labeling. We propose that rSlo K(Ca) channels, with their sensitivity to membrane depolarization and intracellular calcium, play a role in the K(+) modulation of cerebral blood flow. Additional knowledge of the molecular and cellular machinery present at perivascular endfeet may provide insight into the structural and functional molecular elements responsible for the neuronal activity-dependent regulation of cerebral blood flow. Copyright 2002 Elsevier Science B.V.

Control of mitochondrial pH by uncoupling protein 4 in astrocytes promotes neuronal survival

KAUST Repository

Lambert, Hélène Perreten

2014-09-18

Brain activity is energetically costly and requires a steady and highly regulated flow of energy equivalents between neural cells. It is believed that a substantial share of cerebral glucose, the major source of energy of the brain, will preferentially be metabolized in astrocytes via aerobic glycolysis. The aim of this study was to evaluate whether uncoupling proteins (UCPs), located in the inner membrane of mitochondria, play a role in setting up the metabolic response pattern of astrocytes. UCPs are believed to mediate the transmembrane transfer of protons, resulting in the uncoupling of oxidative phosphorylation from ATP production. UCPs are therefore potentially important regulators of energy fluxes. The main UCP isoforms expressed in the brain are UCP2, UCP4, and UCP5. We examined in particular the role of UCP4 in neuron-astrocyte metabolic coupling and measured a range of functional metabolic parameters including mitochondrial electrical potential and pH, reactive oxygen species production, NAD/NADH ratio, ATP/ADP ratio, CO2 and lactate production, and oxygen consumption rate. In brief, we found that UCP4 regulates the intramitochondrial pH of astrocytes, which acidifies as a consequence of glutamate uptake, with the main consequence of reducing efficiency of mitochondrial ATP production. The diminished ATP production is effectively compensated by enhancement of glycolysis. This nonoxidative production of energy is not associated with deleterious H2O2 production. We show that astrocytes expressing more UCP4 produced more lactate, which is used as an energy source by neurons, and had the ability to enhance neuronal survival.

Astrocytes protect glioma cells from chemotherapy and upregulate survival genes via gap junctional communication.

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Lin, Qingtang; Liu, Zhao; Ling, Feng; Xu, Geng

2016-02-01

Gliomas are the most common type of primary brain tumor. Using current standard treatment regimens, the prognosis of patients with gliomas remains poor, which is predominantly due to the resistance of glioma cells to chemotherapy. The organ microenvironment has been implicated in the pathogenesis and survival of tumor cells. Thus, the aim of the present study was to test the hypothesis that astrocytes (the housekeeping cells of the brain microenvironment) may protect glioma cells from chemotherapy and to investigate the underlying mechanism. Immunofluorescent and scanning electron microscopy demonstrated that glioma cells were surrounded and infiltrated by activated astrocytes. In vitro co-culture of glioma cells with astrocytes significantly reduced the cytotoxic effects on glioma cells caused by various chemotherapeutic agents, as demonstrated by fluorescein isothiocyanate-propidium iodide flow cytometry. Transwell experiments indicated that this protective effect was dependent on physical contact and the gap junctional communication (GJC) between astrocytes and glioma cells. Microarray expression profiling further revealed that astrocytes upregulated the expression levels of various critical survival genes in the glioma cells via GJC. The results of the present study indicated that the organ microenvironment may affect the biological behavior of tumor cells and suggest a novel mechanism of resistance in glioma cells, which may be of therapeutic relevance clinically.

Astrocytes as gate-keepers in optic nerve regeneration--a mini-review.

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García, Dana M; Koke, Joseph R

2009-02-01

Animals that develop without extra-embryonic membranes (anamniotes--fish, amphibians) have impressive regenerative capacity, even to the extent of replacing entire limbs. In contrast, animals that develop within extra-embryonic membranes (amniotes--reptiles, birds, mammals) have limited capacity for regeneration as adults, particularly in the central nervous system (CNS). Much is known about the process of nerve development in fish and mammals and about regeneration after lesions in the CNS in fish and mammals. Because the retina of the eye and optic nerve are functionally part of the brain and are accessible in fish, frogs, and mice, optic nerve lesion and regeneration (ONR) has been extensively used as a model system for study of CNS nerve regeneration. When the optic nerve of a mouse is severed, the axons leading into the brain degenerate. Initially, the cut end of the axons on the proximal, eye-side of the injury sprout neurites which begin to grow into the lesion. Simultaneously, astrocytes of the optic nerve become activated to initiate wound repair as a first step in reestablishing the structural integrity of the optic nerve. This activation appears to initiate a cascade of molecular signals resulting in apoptotic cell death of the retinal ganglion cells axons of which make up the neural component of the optic nerve; regeneration fails and the injury is permanent. Evidence specifically implicating astrocytes comes from studies showing selective poisoning of astrocytes at the optic nerve lesion, along with activation of a gene whose product blocks apoptosis in retinal ganglion cells, creates conditions favorable to neurites sprouting from the cut proximal stump, growing through the lesion and into the distal portion of the injured nerve, eventually reaching appropriate targets in the brain. In anamniotes, astrocytes ostensibly present no such obstacle since optic nerve regeneration occurs without intervention; however, no systematic study of glial involvement

SLAM- and nectin-4-independent noncytolytic spread of canine distemper virus in astrocytes.

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Alves, Lisa; Khosravi, Mojtaba; Avila, Mislay; Ader-Ebert, Nadine; Bringolf, Fanny; Zurbriggen, Andreas; Vandevelde, Marc; Plattet, Philippe

2015-05-01

Measles and canine distemper viruses (MeV and CDV, respectively) first replicate in lymphatic and epithelial tissues by using SLAM and nectin-4 as entry receptors, respectively. The viruses may also invade the brain to establish persistent infections, triggering fatal complications, such as subacute sclerosis pan-encephalitis (SSPE) in MeV infection or chronic, multiple sclerosis-like, multifocal demyelinating lesions in the case of CDV infection. In both diseases, persistence is mediated by viral nucleocapsids that do not require packaging into particles for infectivity but are directly transmitted from cell to cell (neurons in SSPE or astrocytes in distemper encephalitis), presumably by relying on restricted microfusion events. Indeed, although morphological evidence of fusion remained undetectable, viral fusion machineries and, thus, a putative cellular receptor, were shown to contribute to persistent infections. Here, we first showed that nectin-4-dependent cell-cell fusion in Vero cells, triggered by a demyelinating CDV strain, remained extremely limited, thereby supporting a potential role of nectin-4 in mediating persistent infections in astrocytes. However, nectin-4 could not be detected in either primary cultured astrocytes or the white matter of tissue sections. In addition, a bioengineered "nectin-4-blind" recombinant CDV retained full cell-to-cell transmission efficacy in primary astrocytes. Combined with our previous report demonstrating the absence of SLAM expression in astrocytes, these findings are suggestive for the existence of a hitherto unrecognized third CDV receptor expressed by glial cells that contributes to the induction of noncytolytic cell-to-cell viral transmission in astrocytes. While persistent measles virus (MeV) infection induces SSPE in humans, persistent canine distemper virus (CDV) infection causes chronic progressive or relapsing demyelination in carnivores. Common to both central nervous system (CNS) infections is that

Initial Attempts of Development and Characterization of an In Vitro Blood Brain Barrier Model Derived from Human Pluripotent Stem Cells

DEFF Research Database (Denmark)

Goldeman, Charlotte; Saaby, Lasse; Hall, Vanessa Jane

The human blood brain barrier has yet to be successfully replicated as an in vitro model. One of the more promising approaches has been to develop an in vitro model derived from human pluripotent stem cells. However, as promising as this model may be, a successful replication of the differentiation...... method on different kinds of pluripotent stem cell lines have yet to be accomplished. We try to approach the promising method as described by Stebbins et al. (2015) to differentiate human pluripotent stem cells into brain like endothelial cells (BECs). Five different human pluripotent stem cell lines...... configurations (mono culture, non-contact co-culture and contact co-culture) with primary rat astrocytes to induce barrier-like properties. Endothelial cell media supplemented with retinoic acid were then applied to the cells to ensure selective expansion of BECs. The different culture configurations were...

GABA from reactive astrocytes impairs memory in mouse models of Alzheimer's disease.

Science.gov (United States)

Jo, Seonmi; Yarishkin, Oleg; Hwang, Yu Jin; Chun, Ye Eun; Park, Mijeong; Woo, Dong Ho; Bae, Jin Young; Kim, Taekeun; Lee, Jaekwang; Chun, Heejung; Park, Hyun Jung; Lee, Da Yong; Hong, Jinpyo; Kim, Hye Yun; Oh, Soo-Jin; Park, Seung Ju; Lee, Hyo; Yoon, Bo-Eun; Kim, YoungSoo; Jeong, Yong; Shim, Insop; Bae, Yong Chul; Cho, Jeiwon; Kowall, Neil W; Ryu, Hoon; Hwang, Eunmi; Kim, Daesoo; Lee, C Justin

2014-08-01

In Alzheimer's disease (AD), memory impairment is the most prominent feature that afflicts patients and their families. Although reactive astrocytes have been observed around amyloid plaques since the disease was first described, their role in memory impairment has been poorly understood. Here, we show that reactive astrocytes aberrantly and abundantly produce the inhibitory gliotransmitter GABA by monoamine oxidase-B (Maob) and abnormally release GABA through the bestrophin 1 channel. In the dentate gyrus of mouse models of AD, the released GABA reduces spike probability of granule cells by acting on presynaptic GABA receptors. Suppressing GABA production or release from reactive astrocytes fully restores the impaired spike probability, synaptic plasticity, and learning and memory in the mice. In the postmortem brain of individuals with AD, astrocytic GABA and MAOB are significantly upregulated. We propose that selective inhibition of astrocytic GABA synthesis or release may serve as an effective therapeutic strategy for treating memory impairment in AD.

Human induced pluripotent stem cell (hiPSC)-derived neurons respond to convulsant drugs when co-cultured with hiPSC-derived astrocytes.

Science.gov (United States)

Ishii, Misawa Niki; Yamamoto, Koji; Shoji, Masanobu; Asami, Asano; Kawamata, Yuji

2017-08-15

Accurate risk assessment for drug-induced seizure is expected to be performed before entering clinical studies because of its severity and fatal damage to drug development. Induced pluripotent stem cell (iPSC) technology has allowed the use of human neurons and glial cells in toxicology studies. Recently, several studies showed the advantage of co-culture system of human iPSC (hiPSC)-derived neurons with rodent/human primary astrocytes regarding neuronal functions. However, the application of hiPSC-derived neurons for seizure risk assessment has not yet been fully addressed, and not at all when co-cultured with hiPSC-derived astrocytes. Here, we characterized hiPSC-derived neurons co-cultured with hiPSC-derived astrocytes to discuss how hiPSC-derived neurons are useful to assess seizure risk of drugs. First, we detected the frequency of spikes and synchronized bursts hiPSC-derived neurons when co-cultured with hiPSC-derived astrocytes for 8 weeks. This synchronized burst was suppressed by the treatment with 6-cyano-7-nitroquinoxaline-2,3-dione, α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonist, and D-(-)-2-amino-5-phosphonopentanoic acid, an N-Methyl-d-aspartate (NMDA) receptor antagonist. These data suggested that co-cultured hiPSC-derived neurons formed synaptic connections mediated by AMPA and NMDA receptors. We also demonstrated that co-cultured hiPSC-derived neurons showed epileptiform activity upon treatment with gabazine or kaliotoxin. Finally, we performed single-cell transcriptome analysis in hiPSC-derived neurons and found that hiPSC-derived astrocytes activated the pathways involved in the activities of AMPA and NMDA receptor functions, neuronal polarity, and axon guidance in hiPSC-derived neurons. These data suggested that hiPSC-derived astrocytes promoted the development of action potential, synaptic functions, and neuronal networks in hiPSC-derived neurons, and then these functional alterations result in the epileptiform

Naltrexone treatment reverses astrocyte atrophy and immune dysfunction in self-harming macaques.

Science.gov (United States)

Lee, Kim M; Chiu, Kevin B; Didier, Peter J; Baker, Kate C; MacLean, Andrew G

2015-11-01

The role of glia in the development and treatment of behavioral abnormalities is understudied. Recent reports have observed glial activation in several disorders, including depression, autism spectrum disorders and self-injurious behaviors (SIB). In the current study, we examined SIB in the physiologically and anatomically relevant nonhuman primate (NHP) model. At the Tulane National Primate Research Center (TNPRC), approximately 5% of singly housed macaques develop symptoms of SIB. We have previously demonstrated that naltrexone hydrochloride can be effective in reducing SIB. We have also demonstrated that the astrocytes of animals with SIB are distinctly atrophic and display heightened innate immune activation compared with control animals. We have added a third group of animals (five macaques identified with SIB and treated with oral naltrexone at a dose of 3.2mg/kg) to the previous cohort (six macaques with a history of SIB but not treated, and nine animals with no history of SIB) for this study. Gray and white matter astrocytes from frontal cortical tissue were examined following necropsy. Innate immune activation of astrocytes, which was increased in SIB animals, was markedly decreased in animals receiving naltrexone, as was atrophy of both grey and white matter astrocytes. This was concomitant with improved behavioral correlates. Preventing astrocyte activation in select areas of the brain to reduce injurious behavior is an innovative concept with implications for mental health studies. Differences in multiple areas of primate brain would help determine how self-injurious behavior develops. These studies suggest a stronger role for astrocytes in the cellular events associated with self-injurious behaviors. Copyright © 2015 Elsevier Inc. All rights reserved.

Differential subnetwork of chemokines/cytokines in human, mouse, and rat brain cells after oxygen-glucose deprivation.

Science.gov (United States)

Du, Yang; Deng, Wenjun; Wang, Zixing; Ning, MingMing; Zhang, Wei; Zhou, Yiming; Lo, Eng H; Xing, Changhong

2017-04-01

Mice and rats are the most commonly used animals for preclinical stroke studies, but it is unclear whether targets and mechanisms are always the same across different species. Here, we mapped the baseline expression of a chemokine/cytokine subnetwork and compared responses after oxygen-glucose deprivation in primary neurons, astrocytes, and microglia from mouse, rat, and human. Baseline profiles of chemokines (CX3CL1, CXCL12, CCL2, CCL3, and CXCL10) and cytokines (IL-1α, IL-1β, IL-6, IL-10, and TNFα) showed significant differences between human and rodents. The response of chemokines/cytokines to oxygen-glucose deprivation was also significantly different between species. After 4 h oxygen-glucose deprivation and 4 h reoxygenation, human and rat neurons showed similar changes with a downregulation in many chemokines, whereas mouse neurons showed a mixed response with up- and down-regulated genes. For astrocytes, subnetwork response patterns were more similar in rats and mice compared to humans. For microglia, rat cells showed an upregulation in all chemokines/cytokines, mouse cells had many down-regulated genes, and human cells showed a mixed response with up- and down-regulated genes. This study provides proof-of-concept that species differences exist in chemokine/cytokine subnetworks in brain cells that may be relevant to stroke pathophysiology. Further investigation of differential gene pathways across species is warranted.

IFN-γ signaling to astrocytes protects from autoimmune mediated neurological disability.

Directory of Open Access Journals (Sweden)

Claudia Hindinger

Full Text Available Demyelination and axonal degeneration are determinants of progressive neurological disability in patients with multiple sclerosis (MS. Cells resident within the central nervous system (CNS are active participants in development, progression and subsequent control of autoimmune disease; however, their individual contributions are not well understood. Astrocytes, the most abundant CNS cell type, are highly sensitive to environmental cues and are implicated in both detrimental and protective outcomes during autoimmune demyelination. Experimental autoimmune encephalomyelitis (EAE was induced in transgenic mice expressing signaling defective dominant-negative interferon gamma (IFN-γ receptors on astrocytes to determine the influence of inflammation on astrocyte activity. Inhibition of IFN-γ signaling to astrocytes did not influence disease incidence, onset, initial progression of symptoms, blood brain barrier (BBB integrity or the composition of the acute CNS inflammatory response. Nevertheless, increased demyelination at peak acute disease in the absence of IFN-γ signaling to astrocytes correlated with sustained clinical symptoms. Following peak disease, diminished clinical remission, increased mortality and sustained astrocyte activation within the gray matter demonstrate a critical role of IFN-γ signaling to astrocytes in neuroprotection. Diminished disease remission was associated with escalating demyelination, axonal degeneration and sustained inflammation. The CNS infiltrating leukocyte composition was not altered; however, decreased IL-10 and IL-27 correlated with sustained disease. These data indicate that astrocytes play a critical role in limiting CNS autoimmune disease dependent upon a neuroprotective signaling pathway mediated by engagement of IFN-γ receptors.

Versatile and simple approach to determine astrocyte territories in mouse neocortex and hippocampus.

Directory of Open Access Journals (Sweden)

Antje Grosche

astrocytes in the aging brain and the methods presented in this study might be a powerful tool to do so.

Aquaporin 4 in Astrocytes is a Target for Therapy in Alzheimer's Disease.

Science.gov (United States)

Lan, Yu-Long; Chen, Jian-Jiao; Hu, Gang; Xu, Jun; Xiao, Ming; Li, Shao

2017-01-01

Current experimental evidence points to the conclusion that aquaporin 4 (AQP4), which is an important water-channel membrane protein found in the brain, could play major roles in various brain conditions pathologically including pathogenesis of Alzheimer's disease (AD). In this paper, we review how AQP4 and altered astrocyte functions interact in AD, and provide experimental evidence highlighting the importance of this topic for the future investigations. The interactions of AQP4 are as follows: (i) AQP4 could influence astrocytic calcium signaling and potassium homeostasis. (ii) AQP4 is linked with the removal of interstitial β-amyloid and glutamate transmission. (iii) Furthermore, AQP4 modulates the reactive astrogliosis and neuroinflammation mechanisms. (iv) To add to this, AQP4 could participate in the AD pathogenesis through affecting neurotrophic factor production. It is therefore possible to identify certain functional molecules that regulate astrocyte make-up and functions. However, making crucial efforts to develop specific agents or drugs that target AQP4 function and test their therapeutic efficiency will be a breakthrough for addressing AD in that AQP4 controls the various physiological as well as pathophysiological features of astrocytes. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Cerebral Mast Cells Participate In Postoperative Cognitive Dysfunction by Promoting Astrocyte Activation.

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Zhang, Xiang; Yao, Hao; Qian, Qingqing; Li, Nana; Jin, Wenjie; Qian, Yanning

2016-01-01

Astrocytes, the major glial cell type that has been increasingly recognized as contributing to neuroinflammation, are critical in the occurrence and development of postoperative cognitive dysfunction (POCD). Although emerging evidence showed that brain mast cells (MCs) are the "first responders" in neuroinflammation, little is known about the functional communication between MCs and astrocytes. In this study, we investigated the potential regulation of astrocyte activation by MCs. Rats received an intracerebroventricular injection of Cromolyn (an MC stabilizer) or sterile saline 30 min before undergoing open tibial fracture surgery, and the levels of neuroinflammation and the degree of memory dysfunction were evaluated at 1 day and 3 days after surgery. In the in vitro study, the effect of activated MCs on astrocytes were further clarified. Surgery increased the number of MCs, the astrocyte activation and the production of inflammatory factors, and resulted in cognitive deficits. Site-directed pre-injection of Cromolyn can inhibit this effect. In the vitro study, the conditioned medium from C48/80-stimulated mast cells (P815) could induce primary astrocyte activation and subsequent production of inflammatory cytokines, which could be inhibited by Cromolyn. These findings indicate that activated MCs could trigger astrocyte activation, be involved in neuroinflammation and possibly contribute to POCD. Interactions between MCs and astrocytes could provide potential therapeutic targets for POCD. © 2016 The Author(s) Published by S. Karger AG, Basel.

Cerebral Mast Cells Participate In Postoperative Cognitive Dysfunction by Promoting Astrocyte Activation

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Xiang Zhang

2016-11-01

Full Text Available Background: Astrocytes, the major glial cell type that has been increasingly recognized as contributing to neuroinflammation, are critical in the occurrence and development of postoperative cognitive dysfunction (POCD. Although emerging evidence showed that brain mast cells (MCs are the "first responders” in neuroinflammation, little is known about the functional communication between MCs and astrocytes. Methods: In this study, we investigated the potential regulation of astrocyte activation by MCs. Rats received an intracerebroventricular injection of Cromolyn (an MC stabilizer or sterile saline 30 min before undergoing open tibial fracture surgery, and the levels of neuroinflammation and the degree of memory dysfunction were evaluated at 1 day and 3 days after surgery. In the in vitro study, the effect of activated MCs on astrocytes were further clarified. Results: Surgery increased the number of MCs, the astrocyte activation and the production of inflammatory factors, and resulted in cognitive deficits. Site-directed pre-injection of Cromolyn can inhibit this effect. In the vitro study, the conditioned medium from C48/80-stimulated mast cells (P815 could induce primary astrocyte activation and subsequent production of inflammatory cytokines, which could be inhibited by Cromolyn. Conclusion: These findings indicate that activated MCs could trigger astrocyte activation, be involved in neuroinflammation and possibly contribute to POCD. Interactions between MCs and astrocytes could provide potential therapeutic targets for POCD.

Gap junction coupling confers isopotentiality on astrocyte syncytium

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Ma, Baofeng; Buckalew, Richard; Du, Yixing; Kiyoshi, Conrad M.; Alford, Catherine C.; Wang, Wei; McTigue, Dana D.; Enyeart, John J.; Terman, David; Zhou, Min

2015-01-01

Astrocytes are extensively coupled through gap junctions into a syncytium. However, the basic role of this major brain network remains largely unknown. Using electrophysiological and computational modeling methods, we demonstrate that the membrane potential (VM) of an individual astrocyte in a hippocampal syncytium, but not in a single, freshly isolated cell preparation, can be well-maintained at quasi-physiological levels when recorded with reduced or K+ free pipette solutions that alter the K+ equilibrium potential to non-physiological voltages. We show that an astrocyte’s associated syncytium provides powerful electrical coupling, together with ionic coupling at a lesser extent, that equalizes the astrocyte’s VM to levels comparable to its neighbors. Functionally, this minimizes VM depolarization attributable to elevated levels of local extracellular K+ and thereby maintains a sustained driving force for highly efficient K+ uptake. Thus, gap junction coupling functions to achieve isopotentiality in astrocytic networks, whereby a constant extracellular environment can be powerfully maintained for crucial functions of neural circuits. PMID:26435164

CNF1 improves astrocytic ability to support neuronal growth and differentiation in vitro.

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Fiorella Malchiodi-Albedi

Full Text Available Modulation of cerebral Rho GTPases activity in mice brain by intracerebral administration of Cytotoxic Necrotizing Factor 1 (CNF1 leads to enhanced neurotransmission and synaptic plasticity and improves learning and memory. To gain more insight into the interactions between CNF1 and neuronal cells, we used primary neuronal and astrocytic cultures from rat embryonic brain to study CNF1 effects on neuronal differentiation, focusing on dendritic tree growth and synapse formation, which are strictly modulated by Rho GTPases. CNF1 profoundly remodeled the cytoskeleton of hippocampal and cortical neurons, which showed philopodia-like, actin-positive projections, thickened and poorly branched dendrites, and a decrease in synapse number. CNF1 removal, however, restored dendritic tree development and synapse formation, suggesting that the toxin can reversibly block neuronal differentiation. On differentiated neurons, CNF1 had a similar effacing effect on synapses. Therefore, a direct interaction with CNF1 is apparently deleterious for neurons. Since astrocytes play a pivotal role in neuronal differentiation and synaptic regulation, we wondered if the beneficial in vivo effect could be mediated by astrocytes. Primary astrocytes from embryonic cortex were treated with CNF1 for 48 hours and used as a substrate for growing hippocampal neurons. Such neurons showed an increased development of neurites, in respect to age-matched controls, with a wider dendritic tree and a richer content in synapses. In CNF1-exposed astrocytes, the production of interleukin 1β, known to reduce dendrite development and complexity in neuronal cultures, was decreased. These results demonstrate that astrocytes, under the influence of CNF1, increase their supporting activity on neuronal growth and differentiation, possibly related to the diminished levels of interleukin 1β. These observations suggest that the enhanced synaptic plasticity and improved learning and memory described

CNF1 Improves Astrocytic Ability to Support Neuronal Growth and Differentiation In vitro

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Malchiodi-Albedi, Fiorella; Paradisi, Silvia; Di Nottia, Michela; Simone, Daiana; Travaglione, Sara; Falzano, Loredana; Guidotti, Marco; Frank, Claudio; Cutarelli, Alessandro; Fabbri, Alessia; Fiorentini, Carla

2012-01-01

Modulation of cerebral Rho GTPases activity in mice brain by intracerebral administration of Cytotoxic Necrotizing Factor 1 (CNF1) leads to enhanced neurotransmission and synaptic plasticity and improves learning and memory. To gain more insight into the interactions between CNF1 and neuronal cells, we used primary neuronal and astrocytic cultures from rat embryonic brain to study CNF1 effects on neuronal differentiation, focusing on dendritic tree growth and synapse formation, which are strictly modulated by Rho GTPases. CNF1 profoundly remodeled the cytoskeleton of hippocampal and cortical neurons, which showed philopodia-like, actin-positive projections, thickened and poorly branched dendrites, and a decrease in synapse number. CNF1 removal, however, restored dendritic tree development and synapse formation, suggesting that the toxin can reversibly block neuronal differentiation. On differentiated neurons, CNF1 had a similar effacing effect on synapses. Therefore, a direct interaction with CNF1 is apparently deleterious for neurons. Since astrocytes play a pivotal role in neuronal differentiation and synaptic regulation, we wondered if the beneficial in vivo effect could be mediated by astrocytes. Primary astrocytes from embryonic cortex were treated with CNF1 for 48 hours and used as a substrate for growing hippocampal neurons. Such neurons showed an increased development of neurites, in respect to age-matched controls, with a wider dendritic tree and a richer content in synapses. In CNF1-exposed astrocytes, the production of interleukin 1β, known to reduce dendrite development and complexity in neuronal cultures, was decreased. These results demonstrate that astrocytes, under the influence of CNF1, increase their supporting activity on neuronal growth and differentiation, possibly related to the diminished levels of interleukin 1β. These observations suggest that the enhanced synaptic plasticity and improved learning and memory described in CNF1-injected

Ca2+ Entry is Required for Mechanical Stimulation-induced ATP Release from Astrocyte

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Lee, Jaekwang; Chun, Ye-Eun; Han, Kyung-Seok; Lee, Jungmoo; Woo, Dong Ho

2015-01-01

Astrocytes and neurons are inseparable partners in the brain. Neurotransmitters released from neurons activate corresponding G protein-coupled receptors (GPCR) expressed in astrocytes, resulting in release of gliotransmitters such as glutamate, D-serine, and ATP. These gliotransmitters in turn influence neuronal excitability and synaptic activities. Among these gliotransmitters, ATP regulates the level of network excitability and is critically involved in sleep homeostasis and astrocytic Ca2+ oscillations. ATP is known to be released from astrocytes by Ca2+-dependent manner. However, the precise source of Ca2+, whether it is Ca2+ entry from outside of cell or from the intracellular store, is still not clear yet. Here, we performed sniffer patch to detect ATP release from astrocyte by using various stimulation. We found that ATP was not released from astrocyte when Ca2+ was released from intracellular stores by activation of Gαq-coupled GPCR including PAR1, P2YR, and B2R. More importantly, mechanical stimulation (MS)-induced ATP release from astrocyte was eliminated when external Ca2+ was omitted. Our results suggest that Ca2+ entry, but not release from intracellular Ca2+ store, is critical for MS-induced ATP release from astrocyte. PMID:25792866

Sex Differences and Laterality in Astrocyte Number and Complexity in the Adult Rat Medial Amygdala

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JOHNSON, RYAN T.; BREEDLOVE, S. MARC; JORDAN, CYNTHIA L.

2008-01-01

The posterodorsal portion of the medial amygdala (MePD) is sexually dimorphic in several rodent species. In several other brain nuclei, astrocytes change morphology in response to steroid hormones. We visualized MePD astrocytes using glial-fibrillary acidic protein (GFAP) immunocytochemistry. We compared the number and process complexity of MePD astrocytes in adult wildtype male and female rats and testicular feminized mutant (TFM) male rats that lack functional androgen receptors (ARs) to determine whether MePD astrocytes are sexually differentiated and whether ARs have a role. Unbiased stereological methods revealed laterality and sex differences in MePD astrocyte number and complexity. The right MePD contained more astrocytes than the left in all three genotypes, and the number of astrocytes was also sexually differentiated in the right MePD, with males having more astrocytes than females. In contrast, the left MePD contained more complex astrocytes than did the right MePD in all three genotypes, and males had more complex astrocytes than females in this hemisphere. TFM males were comparable to wildtype females, having fewer astrocytes on the right and simpler astrocytes on the left than do wildtype males. Taken together, these results demonstrate that astrocytes are sexually dimorphic in the adult MePD and that the nature of the sex difference is hemisphere-dependent: a sex difference in astrocyte number in the right MePD and a sex difference in astrocyte complexity in the left MePD. Moreover, functional ARs appear to be critical in establishing these sex differences in MePD astrocyte morphology. PMID:18853427

Aspects of astrocyte energy metabolism, amino acid neurotransmitter homoeostasis and metabolic compartmentation

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Kreft, Marko; Bak, Lasse Kristoffer; Waagepetersen, Helle S

2012-01-01

Astrocytes are key players in brain function; they are intimately involved in neuronal signalling processes and their metabolism is tightly coupled to that of neurons. In the present review, we will be concerned with a discussion of aspects of astrocyte metabolism, including energy......-generating pathways and amino acid homoeostasis. A discussion of the impact that uptake of neurotransmitter glutamate may have on these pathways is included along with a section on metabolic compartmentation....

Astrocytes sustain long-term productive HIV-1 infection without establishment of reactivable viral latency.

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Barat, Corinne; Proust, Alizé; Deshiere, Alexandre; Leboeuf, Mathieu; Drouin, Jean; Tremblay, Michel J

2018-02-21

The "shock and kill" HIV-1 cure strategy proposes eradication of stable cellular reservoirs by clinical treatment with latency-reversing agents (LRAs). Although resting CD4 + T cells latently infected with HIV-1 constitute the main reservoir that is targeted by these approaches, their consequences on other reservoirs such as the central nervous system are still unknown and should be taken into consideration. We performed experiments aimed at defining the possible role of astrocytes in HIV-1 persistence in the brain and the effect of LRA treatments on this viral sanctuary. We first demonstrate that the diminished HIV-1 production in a proliferating astrocyte culture is due to a reduced proliferative capacity of virus-infected cells compared with uninfected astrocytes. In contrast, infection of non-proliferating astrocytes led to a robust HIV-1 infection that was sustained for over 60 days. To identify astrocytes latently infected with HIV-1, we designed a new dual-color reporter virus called NL4.3 eGFP-IRES-Crimson that is fully infectious and encodes for all viral proteins. Although we detected a small fraction of astrocytes carrying silent HIV-1 proviruses, we did not observe any reactivation using various LRAs and even strong inducers such as tumor necrosis factor, thus suggesting that these proviruses were either not transcriptionally competent or in a state of deep latency. Our findings imply that astrocytes might not constitute a latent reservoir per se but that relentless virus production by this brain cell population could contribute to the neurological disorders seen in HIV-1-infected persons subjected to combination antiretroviral therapy. © 2018 Wiley Periodicals, Inc.

Glutamate oxidation in astrocytes: Roles of glutamate dehydrogenase and aminotransferases

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McKenna, Mary C; Stridh, Malin H; McNair, Laura Frendrup

2016-01-01

to the presynaptic neurons as the nonexcitatory amino acid glutamine. The cycle was initially thought to function with a 1:1 ratio between glutamate released and glutamine taken up by neurons. However, studies of glutamate metabolism in astrocytes have shown that a considerable proportion of glutamate undergoes...... the enzymes that mediate this conversion. Methods include pharmacological tools such as the transaminase inhibitor aminooxyacetic acid, studies using GDH knockout mice, and siRNA-mediated knockdown of GDH in astrocytes. Studies in brain slices incubated with [15N]glutamate demonstrated activity of GDH......The cellular distribution of transporters and enzymes related to glutamate metabolism led to the concept of the glutamate–glutamine cycle. Glutamate is released as a neurotransmitter and taken up primarily by astrocytes ensheathing the synapses. The glutamate carbon skeleton is transferred back...

Raindrops of synaptic noise on dual excitability landscape: an approach to astrocyte network modelling

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Verisokin, Andrey Yu.; Postnov, Dmitry E.; Verveyko, Darya V.; Brazhe, Alexey R.

2018-04-01

The most abundant non-neuronal cells in the brain, astrocytes, populate all parts of the central nervous system (CNS). Astrocytic calcium activity ranging from subcellular sparkles to intercellular waves is believed to be the key to a plethora of regulatory pathways in the central nervous system from synaptic plasticity to blood flow regulation. Modeling of the calcium wave initiation and transmission and their spatiotemporal dynamics is therefore an important step stone in understanding the crucial cogs of cognition. Astrocytes are active sensors of ongoing neuronal and synaptic activity, and neurotransmitters diffusing from the synaptic cleft make a strong impact on the astrocytic activity. Here we propose a model describing the patterns of calcium wave formation at a single cell level and discuss the interplay between astrocyte shape the calcium waves dynamics driven by local stochastic surges of glutamate simulating synaptic activity.

Astrocytes require insulin-like growth factor I to protect neurons against oxidative injury [v2; ref status: indexed, http://f1000r.es/38u

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Laura Genis

2014-04-01

Full Text Available Oxidative stress is a proposed mechanism in brain aging, making the study of its regulatory processes an important aspect of current neurobiological research. In this regard, the role of the aging regulator insulin-like growth factor I (IGF-I in brain responses to oxidative stress remains elusive as both beneficial and detrimental actions have been ascribed to this growth factor. Because astrocytes protect neurons against oxidative injury, we explored whether IGF-I participates in astrocyte neuroprotection and found that blockade of the IGF-I receptor in astrocytes abrogated their rescuing effect on neurons. We found that IGF-I directly protects astrocytes against oxidative stress (H2O2. Indeed, in astrocytes but not in neurons, IGF-I decreases the pro-oxidant protein thioredoxin-interacting protein 1 and normalizes the levels of reactive oxygen species. Furthermore, IGF-I cooperates with trophic signals produced by astrocytes in response to H2O2 such as stem cell factor (SCF to protect neurons against oxidative insult. After stroke, a condition associated with brain aging where oxidative injury affects peri-infarcted regions, a simultaneous increase in SCF and IGF-I expression was found in the cortex, suggesting that a similar cooperative response takes place in vivo. Cell-specific modulation by IGF-I of brain responses to oxidative stress may contribute in clarifying the role of IGF-I in brain aging.

Astrocyte glycogenolysis is triggered by store-operated calcium entry and provides metabolic energy for cellular calcium homeostasis

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Müller, Margit S; Fox, Rebecca; Schousboe, Arne

2014-01-01

Astrocytic glycogen, the only storage form of glucose in the brain, has been shown to play a fundamental role in supporting learning and memory, an effect achieved by providing metabolic support for neurons. We have examined the interplay between glycogenolysis and the bioenergetics of astrocytic...

Astrocyte - neuron lactate shuttle may boost more ATP supply to the neuron under hypoxic conditions - in silico study supported by in vitro expression data

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Genc, Seda; Kurnaz, Isil A; Ozilgen, Mustafa

2011-01-01

Abstract Background Neuro-glial interactions are important for normal functioning of the brain as well as brain energy metabolism. There are two major working models - in the classical view, both neurons and astrocytes can utilize glucose as the energy source through oxidative metabolism, whereas in the astrocyte-neuron lactate shuttle hypothesis (ANLSH) it is the astrocyte which can consume glucose through anaerobic glycolysis to pyruvate and then to lactate, and this lactate is secreted to ...

Andrographolide protects mouse astrocytes against hypoxia injury by promoting autophagy and S100B expression

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Juan Du

2018-04-01

Full Text Available Andrographolide (ANDRO has been studied for its immunomodulation, anti-inflammatory, and neuroprotection effects. Because brain hypoxia is the most common factor of secondary brain injury after traumatic brain injury, we studied the role and possible mechanism of ANDRO in this process using hypoxia-injured astrocytes. Mouse cortical astrocytes C8-D1A (astrocyte type I clone from C57/BL6 strains were subjected to 3 and 21% of O2 for various times (0–12 h to establish an astrocyte hypoxia injury model in vitro. After hypoxia and ANDRO administration, the changes in cell viability and apoptosis were assessed using CCK-8 and flow cytometry. Expression changes in apoptosis-related proteins, autophagy-related proteins, main factors of JNK pathway, ATG5, and S100B were determined by western blot. Hypoxia remarkably damaged C8-D1A cells evidenced by reduction of cell viability and induction of apoptosis. Hypoxia also induced autophagy and overproduction of S100B. ANDRO reduced cell apoptosis and promoted cell autophagy and S100B expression. After ANDRO administration, autophagy-related proteins, S-100B, JNK pathway proteins, and ATG5 were all upregulated, while autophagy-related proteins and s100b were downregulated when the jnk pathway was inhibited or ATG5 was knocked down. ANDRO conferred a survival advantage to hypoxia-injured astrocytes by reducing cell apoptosis and promoting autophagy and s100b expression. Furthermore, the promotion of autophagy and s100b expression by ANDRO was via activation of jnk pathway and regulation of ATG5.

Thyroid hormones upregulate apolipoprotein E gene expression in astrocytes

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Roman, Corina; Fuior, Elena V.; Trusca, Violeta G. [Institute of Cellular Biology and Pathology “Nicolae Simionescu”, Bucharest (Romania); Kardassis, Dimitris [University of Crete Medical School and Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology of Hellas, Heraklion, Crete (Greece); Simionescu, Maya [Institute of Cellular Biology and Pathology “Nicolae Simionescu”, Bucharest (Romania); Gafencu, Anca V., E-mail: anca.gafencu@icbp.ro [Institute of Cellular Biology and Pathology “Nicolae Simionescu”, Bucharest (Romania)

2015-12-04

Apolipoprotein E (apoE), a protein mainly involved in lipid metabolism, is associated with several neurodegenerative disorders including Alzheimer's disease. Despite numerous attempts to elucidate apoE gene regulation in the brain, the exact mechanism is still uncovered. The mechanism of apoE gene regulation in the brain involves the proximal promoter and multienhancers ME.1 and ME.2, which evolved by gene duplication. Herein we questioned whether thyroid hormones and their nuclear receptors have a role in apoE gene regulation in astrocytes. Our data showed that thyroid hormones increase apoE gene expression in HTB14 astrocytes in a dose-dependent manner. This effect can be intermediated by the thyroid receptor β (TRβ) which is expressed in these cells. In the presence of triiodothyronine (T3) and 9-cis retinoic acid, in astrocytes transfected to overexpress TRβ and retinoid X receptor α (RXRα), apoE promoter was indirectly activated through the interaction with ME.2. To determine the location of TRβ/RXRα binding site on ME.2, we performed DNA pull down assays and found that TRβ/RXRα complex bound to the region 341–488 of ME.2. This result was confirmed by transient transfection experiments in which a series of 5′- and 3′-deletion mutants of ME.2 were used. These data support the existence of a biologically active TRβ binding site starting at 409 in ME.2. In conclusion, our data revealed that ligand-activated TRβ/RXRα heterodimers bind with high efficiency on tissue-specific distal regulatory element ME.2 and thus modulate apoE gene expression in the brain. - Highlights: • T3 induce a dose-dependent increase of apoE expression in astrocytes. • Thyroid hormones activate apoE promoter in a cell specific manner. • Ligand activated TRβ/RXRα bind on the distal regulatory element ME.2 to modulate apoE. • The binding site of TRβ/RXRα heterodimer is located at 409 bp on ME.2.

Thyroid hormones upregulate apolipoprotein E gene expression in astrocytes

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Roman, Corina; Fuior, Elena V.; Trusca, Violeta G.; Kardassis, Dimitris; Simionescu, Maya; Gafencu, Anca V.

2015-01-01

Apolipoprotein E (apoE), a protein mainly involved in lipid metabolism, is associated with several neurodegenerative disorders including Alzheimer's disease. Despite numerous attempts to elucidate apoE gene regulation in the brain, the exact mechanism is still uncovered. The mechanism of apoE gene regulation in the brain involves the proximal promoter and multienhancers ME.1 and ME.2, which evolved by gene duplication. Herein we questioned whether thyroid hormones and their nuclear receptors have a role in apoE gene regulation in astrocytes. Our data showed that thyroid hormones increase apoE gene expression in HTB14 astrocytes in a dose-dependent manner. This effect can be intermediated by the thyroid receptor β (TRβ) which is expressed in these cells. In the presence of triiodothyronine (T3) and 9-cis retinoic acid, in astrocytes transfected to overexpress TRβ and retinoid X receptor α (RXRα), apoE promoter was indirectly activated through the interaction with ME.2. To determine the location of TRβ/RXRα binding site on ME.2, we performed DNA pull down assays and found that TRβ/RXRα complex bound to the region 341–488 of ME.2. This result was confirmed by transient transfection experiments in which a series of 5′- and 3′-deletion mutants of ME.2 were used. These data support the existence of a biologically active TRβ binding site starting at 409 in ME.2. In conclusion, our data revealed that ligand-activated TRβ/RXRα heterodimers bind with high efficiency on tissue-specific distal regulatory element ME.2 and thus modulate apoE gene expression in the brain. - Highlights: • T3 induce a dose-dependent increase of apoE expression in astrocytes. • Thyroid hormones activate apoE promoter in a cell specific manner. • Ligand activated TRβ/RXRα bind on the distal regulatory element ME.2 to modulate apoE. • The binding site of TRβ/RXRα heterodimer is located at 409 bp on ME.2.

Laser-scanning astrocyte mapping reveals increased glutamate-responsive domain size and disrupted maturation of glutamate uptake following neonatal cortical freeze-lesion

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Mortiz eArmbruster

2014-09-01

Full Text Available Astrocytic uptake of glutamate shapes extracellular neurotransmitter dynamics, receptor activation, and synaptogenesis. During development, glutamate transport becomes more robust. How neonatal brain insult affects the functional maturation of glutamate transport remains unanswered. Neonatal brain insult can lead to developmental delays, cognitive losses, and epilepsy; the disruption of glutamate transport is known to cause changes in synaptogenesis, receptor activation, and seizure. Using the neonatal freeze-lesion (FL model, we have investigated how insult affects the maturation of astrocytic glutamate transport. As lesioning occurs on the day of birth, a time when astrocytes are still functionally immature, this model is ideal for identifying changes in astrocyte maturation following insult. Reactive astrocytosis, astrocyte proliferation, and in vitro hyperexcitability are known to occur in this model. To probe astrocyte glutamate transport with better spatial precision we have developed a novel technique, Laser Scanning Astrocyte Mapping (LSAM, which combines glutamate transport current (TC recording from astrocytes with laser scanning glutamate photolysis. LSAM allows us to identify the area from which a single astrocyte can transport glutamate and to quantify spatial heterogeneity in the rate of glutamate clearance kinetics within that domain. Using LSAM, we report that cortical astrocytes have an increased glutamate-responsive area following FL and that TCs have faster decay times in distal, as compared to proximal processes. Furthermore, the developmental shift from GLAST- to GLT-1-dominated clearance is disrupted following FL. These findings introduce a novel method to probe astrocyte glutamate uptake and show that neonatal cortical FL disrupts the functional maturation of cortical astrocytes.

Self-repair in a Bidirectionally Coupled Astrocyte-Neuron (AN System based on Retrograde Signaling

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John eWade

2012-09-01

Full Text Available In this paper we demonstrate that retrograde signaling via astrocytes may underpin self-repair in the brain. Faults manifest themselves in silent or near silent neurons caused by low transmission probability synapses; the enhancement of the transmission probability of a healthy neighbouring synapse by retrograde signaling can enhance the transmission probability of the faulty synapse (repair. Our model of self-repair is based on recent research showing that retrograde signaling via astrocytes can increase the probability of neurotransmitter release at damaged or low transmission probability synapses. The model demonstrates that astrocytes are capable of bidirectional communication with neurons which leads to modulation of synaptic activity, and that indirect signaling through retrograde messengers such as endocannabinoids leads to modulation of synaptic transmission probability. Although our model operates at the level of cells, it provides a new research direction on brain-like self-repair which can be extended to networks of astrocytes and neurons. It also provides a biologically inspired basis for developing highly adaptive, distributed computing systems that can, at fine levels of granularity, fault detect, diagnose and self-repair autonomously, without the traditional constraint of a central fault detect/repair unit.

The role of astrocytic glycogen in supporting the energetics of neuronal activity.

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Dinuzzo, Mauro; Mangia, Silvia; Maraviglia, Bruno; Giove, Federico

2012-11-01

Energy homeostasis in the brain is maintained by oxidative metabolism of glucose, primarily to fulfil the energy demand associated with ionic movements in neurons and astrocytes. In this contribution we review the experimental evidence that grounds a specific role of glycogen metabolism in supporting the functional energetic needs of astrocytes during the removal of extracellular potassium. Based on theoretical considerations, we further discuss the hypothesis that the mobilization of glycogen in astrocytes serves the purpose to enhance the availability of glucose for neuronal glycolytic and oxidative metabolism at the onset of stimulation. Finally, we provide an evolutionary perspective for explaining the selection of glycogen as carbohydrate reserve in the energy-sensing machinery of cell metabolism.

Mechanisms of astrocytic K(+) clearance and swelling under high extracellular K(+) concentrations.

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Murakami, Shingo; Kurachi, Yoshihisa

2016-03-01

In response to the elevation of extracellular K(+) concentration ([K(+)]out), astrocytes clear excessive K(+) to maintain conditions necessary for neural activity. K(+) clearance in astrocytes occurs via two processes: K(+) uptake and K(+) spatial buffering. High [K(+)]out also induces swelling in astrocytes, leading to edema and cell death in the brain. Despite the importance of astrocytic K(+) clearance and swelling, the underlying mechanisms remain unclear. Here, we report results from a simulation analysis of astrocytic K(+) clearance and swelling. Astrocyte models were constructed by incorporating various mechanisms such as intra/extracellular ion concentrations of Na(+), K(+), and Cl(-), cell volume, and models of Na,K-ATPase, Na-K-Cl cotransporter (NKCC), K-Cl cotransporter, inwardly-rectifying K(+) (KIR) channel, passive Cl(-) current, and aquaporin channel. The simulated response of astrocyte models under the uniform distribution of high [K(+)]out revealed significant contributions of NKCC and Na,K-ATPase to increases of intracellular K(+) and Cl(-) concentrations, and swelling. Moreover, we found that, under the non-uniform distribution of high [K(+)]out, KIR channels localized at synaptic clefts absorbed excess K(+) by depolarizing the equivalent potential of K(+) (E K) above membrane potential, while K(+) released through perivascular KIR channels was enhanced by hyperpolarizing E K and depolarizing membrane potential. Further analysis of simulated drug effects revealed that astrocyte swelling was modulated by blocking each of the ion channels and transporters. Our simulation analysis revealed controversial mechanisms of astrocytic K(+) clearance and swelling resulting from complex interactions among ion channels and transporters.

Transformation of Astrocytes to a Neuroprotective Phenotype by Microglia via P2Y1 Receptor Downregulation

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Youichi Shinozaki

2017-05-01

Full Text Available Microglia and astrocytes become reactive following traumatic brain injury (TBI. However, the coordination of this reactivity and its relation to pathophysiology are unclear. Here, we show that microglia transform astrocytes into a neuroprotective phenotype via downregulation of the P2Y1 purinergic receptor. TBI initially caused microglial activation in the injury core, followed by reactive astrogliosis in the peri-injured region and formation of a neuroprotective astrocyte scar. Equivalent changes to astrocytes were observed in vitro after injury. This change in astrocyte phenotype resulted from P2Y1 receptor downregulation, mediated by microglia-derived cytokines. In mice, astrocyte-specific P2Y1 receptor overexpression (Astro-P2Y1OE counteracted scar formation, while astrocyte-specific P2Y1 receptor knockdown (Astro-P2Y1KD facilitated scar formation, suggesting critical roles of P2Y1 receptors in the transformation. Astro-P2Y1OE and Astro-P2Y1KD mice showed increased and reduced neuronal damage, respectively. Altogether, our findings indicate that microglia-astrocyte interaction, involving a purinergic signal, is essential for the formation of neuroprotective astrocytes.

Long-Term Plasticity of Astrocytic Metabotropic Neurotransmitter Receptors Driven by Changes in Neuronal Activity in Hippocampal Slices

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Xie, Xiaoqiao

2011-01-01

In addition to synaptic communication between neurons, there is now strong evidence for neuron-to-astrocyte receptor signaling in the brain. During trains of action potentials or repetitive stimulation, neurotransmitter spills out of the synapse to activate astrocytic Gq protein-coupled receptors (Gq GPCRs). To date, very little is known about the ability of astrocytic receptors to exhibit plasticity as a result of long-term changes in neuronal firing rates. Here we describe for the first tim...

Ethanol-Induced Neurodegeneration and Glial Activation in the Developing Brain

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Mariko Saito

2016-08-01

Full Text Available Ethanol induces neurodegeneration in the developing brain, which may partially explain the long-lasting adverse effects of prenatal ethanol exposure in fetal alcohol spectrum disorders (FASD. While animal models of FASD show that ethanol-induced neurodegeneration is associated with glial activation, the relationship between glial activation and neurodegeneration has not been clarified. This review focuses on the roles of activated microglia and astrocytes in neurodegeneration triggered by ethanol in rodents during the early postnatal period (equivalent to the third trimester of human pregnancy. Previous literature indicates that acute binge-like ethanol exposure in postnatal day 7 (P7 mice induces apoptotic neurodegeneration, transient activation of microglia resulting in phagocytosis of degenerating neurons, and a prolonged increase in glial fibrillary acidic protein-positive astrocytes. In our present study, systemic administration of a moderate dose of lipopolysaccharides, which causes glial activation, attenuates ethanol-induced neurodegeneration. These studies suggest that activation of microglia and astrocytes by acute ethanol in the neonatal brain may provide neuroprotection. However, repeated or chronic ethanol can induce significant proinflammatory glial reaction and neurotoxicity. Further studies are necessary to elucidate whether acute or sustained glial activation caused by ethanol exposure in the developing brain can affect long-lasting cellular and behavioral abnormalities observed in the adult brain.

Astrocytes require insulin-like growth factor I to protect neurons against oxidative injury [v1; ref status: indexed, http://f1000r.es/2lf

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Laura Genis

2014-01-01

Full Text Available Oxidative stress is a proposed mechanism in brain aging, making the study of its regulatory processes an important aspect of current neurobiological research. In this regard, the role of the aging regulator insulin-like growth factor I (IGF-I in brain responses to oxidative stress remains elusive as both beneficial and detrimental actions have been ascribed to this growth factor. Because astrocytes protect neurons against oxidative injury, we explored whether IGF-I participates in astrocyte neuroprotection and found that blockade of the IGF-I receptor in astrocytes abrogated their rescuing effect on neurons. The protection mediated by IGF-I against oxidative stress (H2O2 in astrocytes is probably needed for these cells to provide adequate neuroprotection. Indeed, in astrocytes but not in neurons, IGF-I helps decrease the pro-oxidant protein thioredoxin-interacting protein 1 and normalizes the levels of reactive oxygen species. Furthermore, IGF-I cooperates with trophic signals produced by astrocytes in response to H2O2 such as stem cell factor (SCF to protect neurons against oxidative insult. After stroke, a condition associated with brain aging where oxidative injury affects peri-infarcted regions, a simultaneous increase in SCF and IGF-I expression was found in the cortex, suggesting that a similar cooperative response takes place in vivo. Cell-specific modulation by IGF-I of brain responses to oxidative stress may contribute in clarifying the role of IGF-I in brain aging.

The CNS microvascular pericyte: pericyte-astrocyte crosstalk in the regulation of tissue survival

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Bonkowski Drew

2011-01-01

Full Text Available Abstract The French scientist Charles Benjamin Rouget identified the pericyte nearly 140 years ago. Since that time the role of the pericyte in vascular function has been difficult to elucidate. It was not until the development of techniques to isolate and culture pericytes that scientists have begun to understand the true impact of this unique cell in the maintenance of tissue homeostasis. In the brain the pericyte is an integral cellular component of the blood-brain barrier and, together with other cells of the neurovascular unit (endothelial cells, astrocytes and neurons the pericyte makes fine-tuned regulatory adjustments and adaptations to promote tissue survival. These regulatory changes involve trans-cellular communication networks between cells. In this review we consider evidence for cell-to-cell crosstalk between pericytes and astrocytes during development and in adult brain.

Protein targeting to glycogen is a master regulator of glycogen synthesis in astrocytes

OpenAIRE

E. Ruchti; P.J. Roach; A.A. DePaoli-Roach; P.J. Magistretti; I. Allaman

2016-01-01

The storage and use of glycogen, the main energy reserve in the brain, is a metabolic feature of astrocytes. Glycogen synthesis is regulated by Protein Targeting to Glycogen (PTG), a member of specific glycogen-binding subunits of protein phosphatase-1 (PPP1). It positively regulates glycogen synthesis through de-phosphorylation of both glycogen synthase (activation) and glycogen phosphorylase (inactivation). In cultured astrocytes, PTG mRNA levels were previously shown to be enhanced by the ...

Changes in the Proliferative Program Limit Astrocyte Homeostasis in the Aged Post-Traumatic Murine Cerebral Cortex.

Science.gov (United States)

Heimann, Gábor; Canhos, Luisa L; Frik, Jesica; Jäger, Gabriele; Lepko, Tjasa; Ninkovic, Jovica; Götz, Magdalena; Sirko, Swetlana

2017-08-01

Aging leads to adverse outcomes after traumatic brain injury. The mechanisms underlying these defects, however, are not yet clear. In this study, we found that astrocytes in the aged post-traumatic cerebral cortex develop a significantly reduced proliferative response, resulting in reduced astrocyte numbers in the penumbra. Moreover, experiments of reactive astrocytes in vitro reveal that their diminished proliferation is due to an age-related switch in the division mode with reduced cell-cycle re-entry rather than changes in cell-cycle length. Notably, reactive astrocytes in vivo and in vitro become refractory to stimuli increasing their proliferation during aging, such as Sonic hedgehog signaling. These data demonstrate for the first time that age-dependent, most likely intrinsic changes in the proliferative program of reactive astrocytes result in their severely hampered proliferative response to traumatic injury thereby affecting astrocyte homeostasis. © The Author 2017. Published by Oxford University Press.

Glycogen distribution in adult and geriatric mice brains

KAUST Repository

Alrabeh, Rana

2017-01-01

Astrocytes, the most abundant glial cell type in the brain, undergo a number of roles in brain physiology; among them, the energetic support of neurons is the best characterized. Contained within astrocytes is the brain’s obligate energy store