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Alzheimer's disease (AD) is becoming increasingly prevalent worldwide. It represents one of the greatest medical challenges as no pharmacologic treatments are available to prevent disease progression. Astrocytes play crucial functions within neuronal circuits by providing metabolic and functional support, regulating interstitial solute composition, and modulating synaptic transmission. In addition to these physiological functions, growing evidence points to an essential role of astrocytes in neurodegenerative diseases like AD. Early-stage AD is associated with hypometabolism and oxidative stress. Contrary to neurons that are vulnerable to oxidative stress, astrocytes are particularly resistant to mitochondrial dysfunction and are therefore more resilient cells. In our study, we leveraged astrocytic mitochondrial uncoupling and examined neuronal function in the 3xTg AD mouse model. We overexpressed the mitochondrial uncoupling protein 4 (UCP4), which has been shown to improve neuronal survival in vitro. We found that this treatment efficiently prevented alterations of hippocampal metabolite levels observed in AD mice, along with hippocampal atrophy and reduction of basal dendrite arborization of subicular neurons. This approach also averted aberrant neuronal excitability observed in AD subicular neurons and preserved episodic-like memory in AD mice assessed in a spatial recognition task. These findings show that targeting astrocytes and their mitochondria is an effective strategy to prevent the decline of neurons facing AD-related stress at the early stages of the disease.

Background Astrocytes play a crucial, yet not fully elucidated role in the selective motor neuron pathology in amyotrophic lateral sclerosis (ALS). Among other responsibilities, astrocytes provide important neuronal homeostatic support, however this function is highly compromised in ALS. The establishment of fully human coculture systems can be used to further study the underlying mechanisms of the dysfunctional intercellular interplay, and has the potential to provide a platform for revealing novel therapeutic entry points. Methods In this study, we characterised human induced pluripotent stem cell (hiPSC)-derived astrocytes from FUS-ALS patients, and incorporated these cells into a human motor unit microfluidics model to investigate the astrocytic effect on hiPSC-derived motor neuron network and functional neuromuscular junctions (NMJs) using immunocytochemistry and live-cell recordings. FUS-ALS cocultures were systematically compared to their CRISPR-Cas9 gene-edited isogenic control systems. Results We observed a dysregulation of astrocyte homeostasis, which resulted in a FUS-ALS-mediated increase in reactivity and secretion of inflammatory cytokines. Upon coculture with motor neurons and myotubes, we detected a cytotoxic effect on motor neuron-neurite outgrowth, NMJ formation and functionality, which was improved or fully rescued by isogenic control astrocytes. We demonstrate that ALS astrocytes have both a gain-of-toxicity and loss-of-support function involving the WNT/β-catenin pathway, ultimately contributing to the disruption of motor neuron homeostasis, intercellular networks and NMJs. Conclusions Our findings shine light on a complex, yet highly important role of astrocytes in ALS, and provides further insight in to their pathological mechanisms. Graphical Abstract

Tauopathies are neurodegenerative disorders involving the accumulation of tau isoforms in cell subpopulations such as astrocytes. The origins of the 3R and 4R isoforms of tau that accumulate in astrocytes remain unclear. Extracellular vesicles (EVs) were isolated from primary neurons overexpressing 1N3R or 1N4R tau or from human brain extracts (progressive supranuclear palsy or Pick disease patients or controls) and characterized (electron microscopy, nanoparticle tracking analysis (NTA), proteomics). After the isolated EVs were added to primary astrocytes or human iPSC-derived astrocytes, tau transfer and mitochondrial system function were evaluated (ELISA, immunofluorescence, MitoTracker staining). We demonstrated that neurons in which 3R or 4R tau accumulated had the capacity to transfer tau to astrocytes and that EVs were essential for the propagation of both isoforms of tau. Treatment with tau-containing EVs disrupted the astrocytic mitochondrial system, altering mitochondrial morphology, dynamics, and redox state. Although similar levels of 3R and 4R tau were transferred, 3R tau-containing EVs were significantly more damaging to astrocytes than 4R tau-containing EVs. Moreover, EVs isolated from the brain fluid of patients with different tauopathies affected mitochondrial function in astrocytes derived from human iPSCs. Our data indicate that tau pathology spreads to surrounding astrocytes via EVs-mediated transfer and modifies their function.

Glioblastoma (GBM) ranks among the most lethal cancers, with current therapies offering only palliation. Inter- and intrapatient heterogeneity is a hallmark of GBM, with epigenetically distinct cancer stem-like cells (CSCs) at the apex. Targeting GSCs remains a challenging task because of their unique biology, resemblance to normal neural stem/progenitor cells, and resistance to standard cytotoxic therapy. Here, we find that the chromatin regulator, JmjC domain histone H3K36me2/me1 demethylase KDM2B, is highly expressed in glioblastoma surgical specimens compared to normal brain. Targeting KDM2B function genetically or pharmacologically impaired the survival of patient-derived primary glioblastoma cells through the induction of DNA damage and apoptosis, sensitizing them to chemotherapy. KDM2B loss decreased the GSC pool, which was potentiated by coadministration of chemotherapy. Collectively, our results demonstrate KDM2B is crucial for glioblastoma maintenance, with inhibition causing loss of GSC survival, genomic stability, and chemoresistance.

© 2015 Elsevier Inc. All rights reserved. The occurrence of cognitive disturbances upon CNS inflammation or infection has been correlated with increased levels of the cytokine tumor necrosis factor a (TNFa). To date however no specific mechanism via which this cytokine could alter cognitive circuits has been demonstrated. Here we show that local increase of TNFa in the hippocampal dentate gyrus activates astrocyte TNF receptor type 1 (TNFR1) which in turn triggers an astrocyte neuron signaling cascade that results in persistent functional modification of hippocampal excitatory synapses. Astrocytic TNFR1 signaling is necessary for the hippocampal synaptic alteration and contextual learning memory impairment observed in experimental autoimmune encephalitis (EAE) an animal model of multiple sclerosis (MS). This process may contribute to the pathogenesis of cognitive disturbances in MS as well as in other CNS conditions accompanied by inflammatory states or infections.

Mitochondria vary in morphology and function in different tissues; however, little is known about their molecular diversity among cell types. Here we engineered MitoTag mice, which express a Cre recombinase-dependent green fluorescent protein targeted to the outer mitochondrial membrane, and developed an isolation approach to profile tagged mitochondria from defined cell types. We determined the mitochondrial proteome of the three major cerebellar cell types (Purkinje cells, granule cells and astrocytes) and identified hundreds of mitochondrial proteins that are differentially regulated. Thus, we provide markers of cell-type-specific mitochondria for the healthy and diseased mouse and human central nervous systems, including in amyotrophic lateral sclerosis and Alzheimer's disease. Based on proteomic predictions, we demonstrate that astrocytic mitochondria metabolize long-chain fatty acids more efficiently than neuronal mitochondria. We also characterize cell-type differences in mitochondrial calcium buffering via the mitochondrial calcium uniporter (Mcu) and identify regulator of microtubule dynamics protein 3 (Rmdn3) as a determinant of endoplasmic reticulum-mitochondria proximity in Purkinje cells. Our approach enables exploring mitochondrial diversity in many in vivo contexts.

International audience; Astrocytes, microglia, and tanycytes play active roles in the regulation of hypothalamic feeding circuits. These non-neuronal cells are crucial in determining the functional interactions of specific neuronal subpopulations involved in the control of metabolism. Recent advances in biology, optics, genetics, and pharmacology have resulted in the emergence of novel and highly sophisticated approaches for studying hypothalamic neuronal-glial networks. Here we summarize the progress in the field and argue that glial-neuronal interactions provide a core hub integrating food-related cues, interoceptive signals, and internal states to adapt a complex set of physiological responses operating on different timescales to finely tune behavior and metabolism according to metabolic status. This expanding knowledge helps to redefine our understanding of the physiology of food intake and energy metabolism.

The communication between the immune and central nervous system (CNS) is affected in many neurological disorders. Peripheral injections of the endotoxin lipopolysaccharide (LPS) are widely used to study this communication: an LPS challenge leads to a biphasic syndrome that starts with acute sickness and is followed by persistent brain inflammation and chronic behavioral alterations such as depressive-like symptoms. In vitro, the response to LPS treatment has been shown to involve enhanced expression of system x c - . This cystine-glutamate antiporter, with xCT as specific subunit, represents the main glial provider of extracellular glutamate in mouse hippocampus. Here we injected male xCT knockout and wildtype mice with a single intraperitoneal dose of 5 mg/kg LPS. LPS-injection increased hippocampal xCT expression but did not alter the mainly astroglial localization of the xCT protein. Peripheral and central inflammation (as defined by cytokine levels and morphological activation of microglia) as well as LPS-induced sickness and depressive-like behavior were significantly attenuated in xCT-deficient mice compared with wildtype mice. Our study is the first to demonstrate the involvement of system x c - in peripheral and central inflammation in vivo and the potential therapeutic relevance of its inhibition in brain disorders characterized by peripheral and central inflammation, such as depression.

Emerging as an important correlate of neurological dysfunction in Multiple Sclerosis (MS), extended focal and diffuse gray matter abnormalities have been found and linked to clinical manifestations such as seizures, fatigue and cognitive dysfunction. To investigate possible underlying mechanisms we analyzed the molecular alterations in histopathological normal appearing cortical gray matter (NAGM) in MS. By performing a differential gene expression analysis of NAGM of control and MS cases we identified reduced transcription of astrocyte specific genes involved in the astrocyte–neuron lactate shuttle (ANLS) and the glutamate–glutamine cycle (GGC). Additional quantitative immunohistochemical analysis demonstrating a CX43 loss in MS NAGM confirmed a crucial involvement of astrocytes and emphasizes their importance in MS pathogenesis. Concurrently, a Toll-like/IL-1β signaling expression signature was detected in MS NAGM, indicating that immune-related signaling might be responsible for the downregulation of ANLS and GGC gene expression in MS NAGM. Indeed, challenging astrocytes with immune stimuli such as IL-1β and LPS reduced their ANLS and GGC gene expression in vitro. The detected upregulation of IL1B in MS NAGM suggests inflammasome priming. For this reason, astrocyte cultures were treated with ATP and ATP/LPS as for inflammasome activation. This treatment led to a reduction of ANLS and GGC gene expression in a comparable manner. To investigate potential sources for ANLS and GGC downregulation in MS NAGM, we first performed an adjuvant-driven stimulation of the peripheral immune system in C57Bl/6 mice in vivo. This led to similar gene expression changes in spinal cord demonstrating that peripheral immune signals might be one source for astrocytic gene expression changes in the brain. IL1B upregulation in MS NAGM itself points to a possible endogenous signaling process leading to ANLS and GGC downregulation. This is supported by our findings that, among others, MS NAGM astrocytes express inflammasome components and that astrocytes are capable to release Il-1β in-vitro. Altogether, our data suggests that immune signaling of immune- and/or central nervous system origin drives alterations in astrocytic ANLS and GGC gene regulation in the MS NAGM. Such a mechanism might underlie cortical brain dysfunctions frequently encountered in MS patients.

Traumatic brain injury (TBI) is one of the major causes of death and disability in pediatrics, and results in a complex cascade of events including the disruption of the blood-brain barrier (BBB). A controlled-cortical impact on post-natal 17-day-old rats induced BBB disruption by IgG extravasation from 1 to 3 days after injury and returned to normal at day 7. In parallel, we characterized the expression of three caveolin isoforms, caveolin 1 (cav-1), caveolin 2 (cav-2) and caveolin 3 (cav-3). While cav-1 and cav-2 are expressed on endothelial cells, both cav-1 and cav-3 were found to be present on reactive astrocytes, in vivo and in vitro. Following TBI, cav-1 expression was increased in blood vessels at 1 and 7 days in the perilesional cortex. An increase of vascular cav-2 expression was observed 7 days after TBI. In contrast, astrocytic cav-3 expression decreased 3 and 7 days after TBI. Activation of endothelial nitric oxide synthase (eNOS) (via its phosphorylation) was detected 1 day after TBI and phospho-eNOS was detected both in association with blood vessels and with astrocytes. The molecular changes involving caveolins occurring in endothelial cells following juvenile-TBI might participate, independently of eNOS activation, to a mechanism of BBB repair while, they might subserve other undefined roles in astrocytes.

Neurodegenerative disorders are a major public health problem because of the high frequency of these diseases. Genome editing with the CRISPR/Cas9 system is making it possible to modify the sequence of genes linked to these disorders. We designed the KamiCas9 self-inactivating editing system to achieve transient expression of the Cas9 protein and high editing efficiency. In the first application, the gene responsible for Huntington’s disease (HD) was targeted in adult mouse neuronal and glial cells. Mutant huntingtin (HTT) was efficiently inactivated in mouse models of HD, leading to an improvement in key markers of the disease. Sequencing of potential off-targets with the constitutive Cas9 system in differentiated human iPSC revealed a very low incidence with only one site above background level. This off-target frequency was significantly reduced with the KamiCas9 system. These results demonstrate the potential of the self-inactivating CRISPR/Cas9 editing for applications in the context of neurodegenerative diseases.

Huntington's disease (HD) is a fatal neurodegenerative disease in which an early and selective vulnerability of striatal Spiny Projection Neurons is observed. However, several studies have highlighted the implication of glial cells, and in particular astrocytes, in the pathophysiological mechanisms of this disease. A better understanding of the respective contributions of neurons and astrocytes in HD is needed and would be important for the development of new therapeutic approaches. Today, no comparable in vivo models expressing the mutant HTT selectively in astrocytes or in neurons are available. In this study, we developed comparable cell-type specific mouse models expressing a fragment of Huntingtin specifically in neurons, astrocytes, or in both cell populations of the adult mouse basal ganglia circuit. This approach allowed us to characterize behavioral alterations occurring as soon as 4 weeks postinjection. Interestingly, less severe but significant behavioral alterations were also observed in the two cell-type specific models. We further showed that astrocytes are less affected by mHTT compared to neurons, in particular concerning mHTT aggregation. Additionally, a more indirect contribution of astrocytes compared to neurons was observed in several pathophysiological mechanisms such as astrogliosis and neuronal dysfunction. Finally, we showed that direct and indirect transcriptional alterations within the glial glutamatergic clearing system are caused by astrocytic and neuronal expression of mHTT, respectively. We anticipate that our study will help to better understand the contributions of astrocytes to HD and guide future therapeutic efforts. GLIA 2016;64:1841-1856.

During synaptic activity, the clearance of neuronally released glutamate leads to an intracellular sodium concentration increase in astrocytes that is associated with significant metabolic cost. The proximity of mitochondria at glutamate uptake sites in astrocytes raises the question of the ability of mitochondria to respond to these energy demands. We used dynamic fluorescence imaging to investigate the impact of glutamatergic transmission on mitochondria in intact astrocytes. Neuronal release of glutamate induced an intracellular acidification in astrocytes, via glutamate transporters, that spread over the mitochondrial matrix. The glutamate-induced mitochondrial matrix acidification exceeded cytosolic acidification and abrogated cytosol-to-mitochondrial matrix pH gradient. By decoupling glutamate uptake from cellular acidification, we found that glutamate induced a pH-mediated decrease in mitochondrial metabolism that surpasses the Ca2+-mediated stimulatory effects. These findings suggest a model in which excitatory neurotransmission dynamically regulates astrocyte energy metabolism by limiting the contribution of mitochondria to the metabolic response, thereby increasing the local oxygen availability and preventing excessive mitochondrial reactive oxygen species production.

Changes in intracellular Na(+) concentration underlie essential neurobiological processes, but few reliable tools exist for their measurement. Here we characterize a new synthetic Na(+)-sensitive fluorescent dye, Asante Natrium Green (ANG), with unique properties. This indicator was excitable in the visible spectrum and by two-photon illumination, suffered little photobleaching and located to the cytosol were it remained for long durations without noticeable unwanted effects on basic cell properties. When used in brain tissue, ANG yielded a bright fluorescent signal during physiological Na(+) responses both in neurons and astrocytes. Synchronous electrophysiological and fluorometric recordings showed that ANG produced accurate Na(+) measurement in situ. This new Na(+) indicator opens innovative ways of probing neuronal circuits.

The presenilin-1 gene is mutated in early-onset familial Alzheimer’s disease. The mutation Pro117Leu is implicated in a very severe form of the disease, with an onset of less than thirty years. The consequences of this mutation on neurogenesis in the hippocampus of adult transgenic mice have already been studied in situ. The survival of neural progenitor cells was impaired resulting in decreased neurogenesis in the dentate gyrus. Our intention was to verify if similar alterations could occur in vitro in progenitor cells from the murine ganglionic eminences isolated from embryos of this same transgenic mouse model. These cells were grown in culture as neurospheres and after differentiation the percentage of neurons generated as well as their morphology were analysed. The mutation results in a significant decrease in neurogenesis compared to the wild type mice and the neurons grow longer and more ramified neurites. A shift of differentiation towards gliogenesis was observed that could explain decreased neurogenesis despite increased proliferation of neural precursors in transgenic neurospheres. A diminished survival of the newly generated mutant neurons is also proposed. Our data raise the possibility that these alterations in embryonic development might contribute to increase the severity of the Alzheimer’s disease phenotype later in adulthood.

Summary. Background: Emerging data demonstrate important roles for tissue-type plasminogen activator (t-PA) in the central nervous system (CNS). In contrast to endothelial cells, little is known about the regulation of t-PA gene expression and secretion in astrocytes. Objectives: The aims of the present study were to investigate whether t-PA gene expression is regulated by retinoids and the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) in human astrocytes, and to study whether t-PA is stored and subject to regulated release from these cells, as with endothelial cells. Methods: Native human astrocytes were treated with RA and/or PMA. mRNA was quantified by real-time RT-PCR and protein secretion determined by ELISA. Intracellular t-PA immunoreactivity in astrocytes was examined by immunocyto- and histochemistry. Results: RA and/or PMA induced a time-dependent increase in t-PA mRNA and protein levels in astrocytes, reaching 10-fold after combined treatment. This was associated with increased amounts of t-PA storage in intracellular granular structures. Both forskolin and histamine induced regulated release of t-PA. The presence of t-PA in reactive astrocytes was confirmed in human brain tissue. Conclusions: These data show that RA and PKC activation induce a strong up-regulation of t-PA expression in astrocytes, and increased intracellular storage pools. Moreover, a regulated release of t-PA can be induced from these cells. This raises the possibility that astrocytes contribute to the regulation of extracellular t-PA levels in the CNS.

Objective: To study the effects of mild hypothermia on the 24 h concentration of serum astroglial of S-100 β protein in patients who survived cardiac arrest (CA). Design: A prospective, randomised, clinical study in a university teaching hospital. Patients: Sixty-one resuscitated patients were randomised into two prospective studies, known as the short study period (SSP) (n = 33 patients) and the long study period (LSP) (n = 28 patients). In the SSP study, patients older than 18 years of age and surviving asystole or pulseless electrical activity were included. In the LSP study, patients with ventricular fibrillation (VF) or non-perfusing ventricular tachycardia (VT) aged between 18 and 75 years were included. In each of the study groups, the patients were further randomised into either normothermic or hypothermic subgroups. The standard supportive therapy was similar, only the devices used to reduce the body temperature and the period of hypothermia were different. Serum samples for the measurement of astroglial S-100 β protein were collected at admission and 24 h later. Results: During the first 24 h after the cardiac arrest, the concentration of astroglial serum S-100 β protein decreased significantly in the hypothermic cohort. In the normothermic cohort, the decrease of serum astroglial S-100 β protein was less pronounced and even increased in the normothermic LSP group. Conclusion: Induced mild hypothermia reduced the 24 h astroglial serum S-100 β protein concentration and might play a neuroprotective effect after cardiac arrest.

INTRODUCTION Astrocytes translate incoming information and generate functional outputs via Ca 2+ signaling. Thereby, they respond to neuronal activity, producing downstream modulation of synaptic functions, and may participate in hemodynamics regulation. Deciphering the “Ca 2+ language” of astrocytes is therefore essential for defining their roles in brain physiology and pathology. However, the specifics of astrocytic Ca 2+ signaling are still poorly understood, and recent studies producing inconsistent or contradictory results have fostered debate on the actual role of astrocytes in synaptic and vascular functions. RATIONALE A neglected potential source of inconsistencies lies in the way astrocytic Ca 2+ signaling has been studied to date, mostly by conventional two-dimensional (2D) imaging, which assumes that sampling a single (~1 μm) focal plane is representative of the entire astrocytic cell. This is, however, dubious given that astrocytes are highly 3D cells, entertain heterogeneous 3D relations with neighboring structures, and display Ca 2+ signals on a local scale. Therefore, we developed a new method to three-dimensionally scan entire astrocytes and observe full-cell Ca 2+ dynamics. RESULTS With our 3D approach, we sampled astrocytes at a sufficient rate to detect events with durations of >1.5 s throughout the cell, and faster ones in selected substructures. We found that Ca 2+ activity in an individual astrocyte is heterogeneously scattered throughout the cell, largely compartmented within each region, and preponderantly local. The majority resides in the “gliapil,” the peripheral region composed of fine (optically subresolved) structures occupying ∼75% of the astrocyte volume. Within the central (resolvable) “core,” the soma is mostly inactive, whereas processes are frequently active yet show widely different activity between them. Even in individual processes, activity distributes heterogeneously, with alternating “hot” and “cold” spots. We performed 3D imaging in awake mice and in adult brain slices. Activity in vivo was faster and more frequent, particularly in endfeet, yet similar in properties and cellular distribution to slices, except for the presence of cell-wide “global” Ca 2+ events mainly associated with mouse movement. Contrary to current beliefs, global events were not sweeping waves, but rather consisted of multifocal Ca 2+ elevations that started at multiple gliapil loci and then spread to the core. At the vascular interface, astrocytic Ca 2+ activity was mostly restricted to individual endfeet, even to their fractions, and only occasionally coordinated with the endfoot process or the rest of the astrocyte. Two or more endfeet were mainly asynchronous, even when enwrapping the same vessel. Astrocytic structures and axons intersected three-dimensionally, and minimal axonal activity (individual action potentials) produced time-correlated astrocytic Ca 2+ elevations in small spots ( CONCLUSION We provide the first comprehensive 3D map of Ca 2+ activity in an individual astrocyte. Its widespread, heterogeneous, local, and mostly 3D nature confirms the appropriateness of our whole-cell imaging approach. Past 2D studies, often focusing on somatic Ca 2+ dynamics, inadequately described the emerging richness and complexity of the astrocyte activity, notably at astrocyte-synapse and astrocyte-vascular interfaces, where activity is small, fast, and frequent. In this context, we can foresee future challenges in extending studies to the gliapil, whose structures fall below current optical resolution, and in reporting the complete gamut of astrocyte Ca 2+ signals at the whole-cell scale, both requiring technical advances. Nonetheless, the technique demonstrated here promises to make 3D Ca 2+ imaging the state-of-the-art approach for Ca 2+ studies addressing the role of astrocytes in brain function.

Transmissible spongiform encephalopathies are characterized by spongiosis, astrocytosis and accumulation of PrPSc, an isoform of the normal host protein PrPC. The exact cell types responsible for agent propagation and pathogenesis are still uncertain. To determine the possible role of astrocytes, we generated mice devoid of murine PrP but expressing hamster PrP transgenes driven by the astrocyte-specific GFAP promoter. After inoculation with hamster scrapie, these mice accumulated infectivity and PrPSc to high levels, developed severe disease after 227 +/- 5 days and died 7 +/- 4 days later. Therefore, astrocytes could play an important role in scrapie pathogenesis, possibly by an indirect toxic effect on neurons. Interestingly, mice expressing the same transgenes but also endogenous murine PrP genes propagated infectivity without developing disease.

Inflammation is a highly regulated process with common but also specific characteristics in each tissue affected. Recruitment of leukocytes from the blood to the injured tissue is an important early step in the inflammatory cascade. This review highlights the role of connexins (Cxs) in the regulation of both acute and chronic inflammatory processes. Cxs form gap junction channels that provide a cytoplasmic continuity between adjacent cells allowing the intercellular exchange of ions and metabolites. Their structural halves form connexons or hemichannels. Each of them consists of 6 Cx proteins and hemichannels not taking part in gap junction formation but facilitating the release of small molecules such as ATP. Based on the differential distribution of various Cxs in different tissues such as the brain, lung capillaries and large blood vessels, our aim was to analyze the specific roles of Cxs in the inflammatory process in these tissues. Three typical sites of inflammation were chosen to shed light on similarities and differences in several types of responses: (1) atherosclerosis as a model for chronic inflammation, (2) the lung as an example of acute inflammation and (3) the ‘immune-privileged’ environment of the brain to highlight specific reactions of the vasculature to ischemic damage and inflammation at this site.

Neuroinflammation is the local reaction of the brain to infection, trauma, toxic molecules or protein aggregates. The brain resident macrophages, microglia, are able to trigger an appropriate response involving secretion of cytokines and chemokines, resulting in the activation of astrocytes and recruitment of peripheral immune cells. IL-1β plays an important role in this response; yet its production and mode of action in the brain are not fully understood and its precise implication in neurodegenerative diseases needs further characterization. Our results indicate that the capacity to form a functional NLRP3 inflammasome and secretion of IL-1β is limited to the microglial compartment in the mouse brain. We were not able to observe IL-1β secretion from astrocytes, nor do they express all NLRP3 inflammasome components. Microglia were able to produce IL-1β in response to different classical inflammasome activators, such as ATP, Nigericin or Alum. Similarly, microglia secreted IL-18 and IL-1α, two other inflammasome-linked pro-inflammatory factors. Cell stimulation with α-synuclein, a neurodegenerative disease-related peptide, did not result in the release of active IL-1β by microglia, despite a weak pro-inflammatory effect. Amyloid-β peptides were able to activate the NLRP3 inflammasome in microglia and IL-1β secretion occurred in a P2X7 receptor-independent manner. Thus microglia-dependent inflammasome activation can play an important role in the brain and especially in neuroinflammatory conditions.

Amyloid-β (Aβ) peptides play a key role in the pathogenesis of Alzheimer's disease and exert various toxic effects on neurons; however, relatively little is known about their influence on glial cells. Astrocytes play a pivotal role in brain homeostasis, contributing to the regulation of local energy metabolism and oxidative stress defense, two aspects of importance for neuronal viability and function. In the present study, we explored the effects of Aβ peptides on glucose metabolism in cultured astrocytes. Following Aβ25-35exposure, we observed an increase in glucose uptake and its various metabolic fates, i.e., glycolysis (coupled to lactate release), tricarboxylic acid cycle, pentose phosphate pathway, and incorporation into glycogen. Aβ increased hydrogen peroxide production as well as glutathione release into the extracellular space without affecting intracellular glutathione content. A causal link between the effects of Aβ on glucose metabolism and its aggregation and internalization into astrocytes through binding to members of the class A scavenger receptor family could be demonstrated. Using astrocyte-neuron cocultures, we observed that the overall modifications of astrocyte metabolism induced by Aβ impair neuronal viability. The effects of the Aβ25-35fragment were reproduced by Aβ1-42but not by Aβ1-40. Finally, the phosphoinositide 3-kinase (PI3-kinase) pathway appears to be crucial in these events since both the changes in glucose utilization and the decrease in neuronal viability are prevented by LY294002, a PI3-kinase inhibitor. This set of observations indicates that Aβ aggregation and internalization into astrocytes profoundly alter their metabolic phenotype with deleterious consequences for neuronal viability.

For decades, studies have been focusing on the neuronal abnormalities that accompany neurodegenerative disorders. Yet, glial cells are emerging as important players in numerous neurological diseases. Astrocytes, the main type of glia in the central nervous system , form extensive networks that physically and functionally connect neuronal synapses with cerebral blood vessels. Normal brain functioning strictly depends on highly specialized cellular cross-talk between these different partners to which Ca(2+), as a signaling ion, largely contributes. Altered intracellular Ca(2+) levels are associated with neurodegenerative disorders and play a crucial role in the glial responses to injury. Intracellular Ca(2+) increases in single astrocytes can be propagated toward neighboring cells as intercellular Ca(2+) waves, thereby recruiting a larger group of cells. Intercellular Ca(2+) wave propagation depends on two, parallel, connexin (Cx) channel-based mechanisms: i) the diffusion of inositol 1,4,5-trisphosphate through gap junction channels that directly connect the cytoplasm of neighboring cells, and ii) the release of paracrine messengers such as glutamate and ATP through hemichannels ('half of a gap junction channel'). This review gives an overview of the current knowledge on Cx-mediated Ca(2+) communication among astrocytes as well as between astrocytes and other brain cell types in physiology and pathology, with a focus on the processes of neurodegeneration and reactive gliosis. Research on Cx-mediated astroglial Ca(2+) communication may ultimately shed light on the development of targeted therapies for neurodegenerative disorders in which astrocytes participate. This article is part of a Special Issue entitled: Calcium signaling in health and disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau. publisher: Elsevier articletitle: The dual face of connexin-based astroglial Ca2+ communication: A key player in brain physiology and a prime target in pathology journaltitle: Biochimica et Biophysica Acta (BBA) - Molecular Cell Research articlelink: http://dx.doi.org/10.1016/j.bbamcr.2014.04.016 content_type: article copyright: Copyright © 2014 Elsevier B.V. All rights reserved. ispartof: Biochimica et Biophysica Acta. Molecular Cell Research vol:1843 issue:10 pages:2211-32 ispartof: location:Netherlands status: published