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Extensive activation of glial cells during a latent period has been well documented in various animal models of epilepsy. However, it remains unclear whether activated glial cells contribute to epileptogenesis, i.e., the chronically persistent process leading to epilepsy. Particularly, it is not clear whether interglial communication between different types of glial cells contributes to epileptogenesis, because past literature has mainly focused on one type of glial cell. Here, we show that temporally distinct activation profiles of microglia and astrocytes collaboratively contributed to epileptogenesis in a drug-induced status epilepticus model. We found that reactive microglia appeared first, followed by reactive astrocytes and increased susceptibility to seizures. Reactive astrocytes exhibited larger Ca2+ signals mediated by IP3R2, whereas deletion of this type of Ca2+ signaling reduced seizure susceptibility after status epilepticus. Immediate, but not late, pharmacological inhibition of microglial activation prevented subsequent reactive astrocytes, aberrant astrocyte Ca2+ signaling, and the enhanced seizure susceptibility. These findings indicate that the sequential activation of glial cells constituted a cause of epileptogenesis after status epilepticus. Thus, our findings suggest that the therapeutic target to prevent epilepsy after status epilepticus should be shifted from microglia (early phase) to astrocytes (late phase).

Peripheral nerve injury causes maladaptive plasticity in the central nervous system and induces chronic pain. In addition to the injured limb, abnormal pain sensation can appear in the limb contralateral to the injury, called mirror image pain. Because synaptic remodeling in the primary somatosensory cortex (S1) has critical roles in the induction of chronic pain, cortical reorganization in the S1 ipsilateral to the injured limb may also accompany mirror image pain. To elucidate this, we conducted in vivo 2-photon calcium imaging of neuron and astrocyte activity in the ipsilateral S1 after a peripheral nerve injury. We found that cross-callosal inputs enhanced the activity of both S1 astrocytes and inhibitory neurons, whereas activity of excitatory neurons decreased. When local inhibitory circuits were blocked, astrocyte-dependent spine plasticity and allodynia were revealed. Thus, we propose that cortical astrocytes prime the induction of spine plasticity and mirror image pain after peripheral nerve injury. Moreover, this result suggests that cortical synaptic rewiring could be sufficient to cause allodynia on the uninjured periphery.

The blood-brain barrier (BBB) is composed of capillary endothelial cells, pericytes, and perivascular astrocytes, which regulate central nervous system homeostasis. Sonic hedgehog (SHH) released from astrocytes plays an important role in the maintenance of BBB integrity. BBB disruption and microglial activation are common pathological features of various neurologic diseases such as multiple sclerosis, Parkinson's disease, amyotrophic lateral sclerosis, and Alzheimer's disease. Interleukin-1β (IL-1β), a major pro-inflammatory cytokine released from activated microglia, increases BBB permeability. Here we show that IL-1β abolishes the protective effect of astrocytes on BBB integrity by suppressing astrocytic SHH production. Astrocyte conditioned media, SHH, or SHH signal agonist strengthened BBB integrity by upregulating tight junction proteins, whereas SHH signal inhibitor abrogated these effects. Moreover, IL-1β increased astrocytic production of pro-inflammatory chemokines such as CCL2, CCL20, and CXCL2, which induce immune cell migration and exacerbate BBB disruption and neuroinflammation. Our findings suggest that astrocytic SHH is a potential therapeutic target that could be used to restore disrupted BBB in patients with neurologic diseases.

Sirtuin 1 (SIRT1) exerts a neuroprotective effect on various neurologic diseases. Here we investigated the protective functions of SIRT1 in astrocytes, which are the most abundant cells in the central nervous system. Upregulation of SIRT1 suppressed the expression levels of pro-inflammatory cytokines and increased the expression levels of superoxide dismutase 2 and catalase. Inversely, inhibition of SIRT1 significantly increased the acetylation of forkhead box protein O4, decreased the expression levels of superoxide dismutase 2 and catalase, and increased the production of reactive oxygen species. Our data suggest that astrocytic SIRT1 may elicit neuroprotective effects through its anti-oxidative and anti-inflammatory functions., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Alexander disease (AxD) is an intractable neurodegenerative disorder caused by GFAP mutations. It is a primary astrocyte disease with a pathological hallmark of Rosenthal fibres within astrocytes. AxD astrocytes show several abnormal phenotypes. Our previous study showed that AxD astrocytes in model mice exhibit aberrant Ca2+ signals that induce AxD aetiology. Here, we show that microglia have unique phenotypes with morphological and functional alterations, which are related to the pathogenesis of AxD. Immunohistochemical studies of 60TM mice (AxD model) showed that AxD microglia exhibited highly ramified morphology. Functional changes in microglia were assessed by Ca2+ imaging using hippocampal brain slices from Iba1-GCaMP6-60TM mice and two-photon microscopy. We found that AxD microglia showed aberrant Ca2+ signals, with high frequency Ca2+ signals in both the processes and cell bodies. These microglial Ca2+ signals were inhibited by pharmacological blockade or genetic knockdown of P2Y12 receptors but not by tetrodotoxin, indicating that these signals are independent of neuronal activity but dependent on extracellular ATP from non-neuronal cells. Our single-cell RNA sequencing data showed that the expression level of Entpd2 , an astrocyte-specific gene encoding the ATP-degrading enzyme NTPDase2, was lower in AxD astrocytes than in wild-type astrocytes. In situ ATP imaging using the adeno-associated virus vector GfaABC1D ATP1.0 showed that exogenously applied ATP was present longer in 60TM mice than in wild-type mice. Thus, the increased ATP level caused by the decrease in its metabolizing enzyme in astrocytes could be responsible for the enhancement of microglial Ca2+ signals. To determine whether these P2Y12 receptor-mediated Ca2+ signals in AxD microglia play a significant role in the pathological mechanism, a P2Y12 receptor antagonist, clopidogrel, was administered. Clopidogrel significantly exacerbated pathological markers in AxD model mice and attenuated the morphological features of microglia, suggesting that microglia play a protective role against AxD pathology via P2Y12 receptors. Taken together, we demonstrated that microglia sense AxD astrocyte dysfunction via P2Y12 receptors as an increase in extracellular ATP and alter their morphology and Ca2+ signalling, thereby protecting against AxD pathology. Although AxD is a primary astrocyte disease, our study may facilitate understanding of the role of microglia as a disease modifier, which may contribute to the clinical diversity of AxD. [ABSTRACT FROM AUTHOR]

Objective: A pathological excitatory action of the major inhibitory neurotransmitter γ‐aminobutyric acid (GABA) has been observed in epilepsy. Blocking the Cl− importer NKCC1 with bumetanide is expected to reduce the neuronal intracellular Cl− concentration ([Cl−]i) and thereby attenuate the excitatory GABA response. Accordingly, several clinical trials of bumetanide for epilepsy were conducted. Although NKCC1 is expressed in both neurons and glial cells, an involvement of glial NKCC1 in seizures has not yet been reported. Astrocytes maintain high [Cl−]i with NKCC1, and this gradient promotes Cl− efflux via the astrocytic GABAA receptor (GABAAR). This Cl− efflux buffers the synaptic cleft Cl− concentration to maintain the postsynaptic Cl− gradient during intense firing of GABAergic neurons, thereby sustaining its inhibitory action during seizure. In this study, we investigated the function of astrocytic NKCC1 in modulating the postsynaptic action of GABA in acute seizure models. Methods: We used the astrocyte‐specific conditional NKCC1 knockout (AstroNKCC1KO) mice. The seizurelike events (SLEs) in CA1 pyramidal neurons were triggered by tetanic stimulation of stratum radiatum in acute hippocampus slices. The SLE underlying GABAAR‐mediated depolarization was evaluated by applying the GABAAR antagonist bicuculline. The pilocarpine‐induced seizure in vivo was monitored in adult mice by the Racine scale. The SLE duration and tetanus stimulation intensity threshold and seizure behavior in AstroNKCC1KO mice and wild‐type (WT) mice were compared. Results: The AstroNKCC1KO mice were prone to seizures with lower threshold and longer duration of SLEs and larger GABAAR‐mediated depolarization underlying the SLEs, accompanied by higher Racine‐scored seizures. Bumetanide reduced these indicators of seizure in AstroNKCC1KO mice (which still express neuronal NKCC1), but not in the WT, both in vitro and in vivo. Significance: Astrocytic NKCC1 inhibits GABA‐mediated excitatory action during seizures, whereas neuronal NKCC1 has the converse effect, suggesting opposing actions of bumetanide on these cells. [ABSTRACT FROM AUTHOR]

Objectives Soluble oligomeric amyloid β ( oAβ) directly causes synaptic dysfunction and neuronal death, which are involved in the pathogenesis of Alzheimer's disease. In contrast, several lines of evidence have shown that glia-mediated excitotoxicity is also involved in the disease progression of Alzheimer's disease. However, it is still unclear how oAβ induces glia-mediated excitotoxicity. Therefore, we tried to clarify the mechanism of oAβ-induced glia-mediated excitotoxicity using mouse primary cultures. Methods Glial glutamate production was assessed using a colorimetric assay kit. Glial production of tumor necrosis factor-α ( TNF-α) was evaluated using a specific enzyme-linked immunosorbent assay kit. Microglial survival was examined using the MTS assay. mRNA and protein expression levels of excitatory amino acid transporter 2 were determined using quantitative polymerase chain reaction and western blotting, respectively. Results We showed that oAβ-stimulation induces glutamate release from astrocyte/microglia co-cultures, but not from single culture of astrocytes or microglia. oAβ increased TNF-α release from astrocytes, but not from microglia, and the astrocyte-derived TNF-α enhanced glutamate release from microglia. TNF-α elongated microglial survival and triggered sustained microglial glutamate release in a positive feedback mechanism through TNF-α receptor 1. Furthermore, treatment of oAβ decreased astrocytic expression of excitatory amino acid transporter 2, which plays a pivotal role in homeostasis of the extracellular glutamate level. Conclusions The present findings suggest that oAβ contributes to glia-mediated excitotoxicity through the two-hit mechanism by suppressing astrocytic glutamate uptake through excitatory amino acid transporter 2 and enhancing microglial glutamate release, and triggers chronic glial neuroinflammation through the TNF-α/ TNF-α receptor 1 positive feedback loop in Alzheimer's disease. [ABSTRACT FROM AUTHOR]

The article discusses development of fingolimod, oral drug for treatment of multiple sclerosis that is suggested to suppresses pro-inflammatory effects and improve neuroprotective effects in astrocytes. Topics discussed include action on lymphocytes, reverse transcription polymerase chain reactions and intercellular adhesion molecule-1. IL Interleukin, histocompatibility complex and tumor necrosis factor are mentioned.

The article discusses the role of astrocytic eotaxin (CCL11) on the production of microglial reactive oxygen species and in aging-related neuronal dysfunction. Topics discussed include CCL11's pathological role in allergic diseases, the study which identifies astrocytes as the primary source of CCL11 in the central nervous system (CNS), and the role of systemic inflammation to CCL11 production.

Peripheral nerve injury causes maladaptive plasticity in the central nervous system and induces chronic pain. In addition to the injured limb, abnormal pain sensation can appear in the limb contralateral to the injury, called mirror image pain. Because synaptic remodeling in the primary somatosensory cortex (S1) has critical roles in the induction of chronic pain, cortical reorganization in the S1 ipsilateral to the injured limb may also accompany mirror image pain. To elucidate this, we conducted in vivo 2-photon calcium imaging of neuron and astrocyte activity in the ipsilateral S1 after a peripheral nerve injury. We found that cross-callosal inputs enhanced the activity of both S1 astrocytes and inhibitory neurons, whereas activity of excitatory neurons decreased. When local inhibitory circuits were blocked, astrocyte-dependent spine plasticity and allodynia were revealed. Thus, we propose that cortical astrocytes prime the induction of spine plasticity and mirror image pain after peripheral nerve injury. Moreover, this result suggests that cortical synaptic rewiring could be sufficient to cause allodynia on the uninjured periphery. [ABSTRACT FROM AUTHOR]