The role of astrocytes response triggered by hyperglycaemia during spinal cord injury

OBJECTIVE

This manuscript aimed to provide a comprehensive overview of the physiological, molecular, and cellular mechanisms triggered by reactive astrocytes (RA) in the context of spinal cord injury (SCI), with a particular focus on cases involving hyperglycaemia.

METHODS

The compilation of articles related to astrocyte responses in neuropathological conditions, with a specific emphasis on those related to SCI and hyperglycaemia, was conducted by searching through databases including Science Direct, Web of Science, and PubMed.

RESULTS AND CONCLUSIONS

This article explores the dual role of astrocytes in both neurophysiological and neurodegenerative conditions within the central nervous system (CNS). In the aftermath of SCI and hyperglycaemia, astrocytes undergo a transformation into RA, adopting a distinct phenotype. While there are currently no approved therapies for SCI, various therapeutic strategies have been proposed to alleviate the detrimental effects of RAs following SCI and hyperglycemia. These strategies show promising potential in the treatment of SCI and its likely comorbidities.

Epigenetic modifications of inflammation in spinal cord injury

Spinal cord injury (SCI) is a central nervous system injury that leads to neurological dysfunction or paralysis, which seriously affects patients' quality of life and causes a heavy social and economic burden. The pathological mechanism of SCI has not been fully revealed, resulting in unsatisfactory clinical treatment. Therefore, more research is urgently needed to reveal its precise pathological mechanism. Numerous studies have shown that inflammation is closely related to various pathological processes in SCI. Inflammatory response is an important pathological process leading to secondary injury, and sustained inflammatory response can exacerbate the injury and hinder the recovery of neurological function after injury. Epigenetic modification is considered to be an important regulatory mechanism in the pathological process of many diseases. Epigenetic modification mainly affects the function and characteristics of genes through the reversibility of mechanisms such as DNA methylation, histone modification, and regulation of non-coding RNA, thus having a significant impact on the pathological process of diseases and the survival state of the body. Recently, the role of epigenetic modification in the inflammatory response of SCI has gradually entered the field of view of researchers, and epigenetic modification may be a potential means to treat SCI. In this paper, we review the effects and mechanisms of different types of epigenetic modifications (including histone modifications, DNA methylation, and non-coding RNAs) on post-SCI inflammation and their potential therapeutic effects on inflammation to improve our understanding of the secondary SCI stage. This review aims to help identify new markers, signaling pathways and targeted drugs, and provide theoretical basis and new strategies for the diagnosis and treatment of SCI.

Reactive Astrocytes and Emerging Roles in Central Nervous System (CNS) Disorders

In addition to their many functions in the healthy central nervous system (CNS), astrocytes respond to CNS damage and disease through a process called "reactivity." Recent evidence reveals that astrocyte reactivity is a heterogeneous spectrum of potential changes that occur in a context-specific manner. These changes are determined by diverse signaling events and vary not only with the nature and severity of different CNS insults but also with location in the CNS, genetic predispositions, age, and potentially also with "molecular memory" of previous reactivity events. Astrocyte reactivity can be associated with both essential beneficial functions as well as with harmful effects. The available information is rapidly expanding and much has been learned about molecular diversity of astrocyte reactivity. Emerging functional associations point toward central roles for astrocyte reactivity in determining the outcome in CNS disorders.

Immunopathogenesis of multiple sclerosis: molecular and cellular mechanisms and new immunotherapeutic approaches

BACKGROUND

Multiple sclerosis (MS) is a central nervous system (CNS) demyelinating autoimmune disease with increasing global prevalence. It predominantly affects females, especially those of European descent. The interplay between environmental factors and genetic predisposition plays a crucial role in MS etiopathogenesis.

METHODS

We searched recent relevant literature on reputable databases, which include, PubMed, Embase, Web of Science, Scopus, and ScienceDirect using the following keywords: multiple sclerosis, pathogenesis, autoimmunity, demyelination, therapy, and immunotherapy.

RESULTS

Various animal models have been employed to investigate the MS etiopathogenesis and therapeutics. Autoreactive T cells within the CNS recruit myeloid cells through chemokine expression, leading to the secretion of inflammatory cytokines driving the MS pathogenesis, resulting in demyelination, gliosis, and axonal loss. Key players include T cell lymphocytes (CD4+ and CD8+), B cells, and neutrophils. Signaling dysregulation in inflammatory pathways and the immunogenetic basis of MS are essential considerations for any successful therapy to MS. Data indicates that B cells and neutrophils also have significant roles in MS, despite the common belief that T cells are essential. High neutrophil-to-lymphocyte ratios correlate with MS severity, indicating their contribution to disease progression. Dysregulated signaling pathways further exacerbate MS progression.

CONCLUSION

MS remains incurable, but disease-modifying therapies, monoclonal antibodies, and immunomodulatory drugs offer hope for patients. Research on the immunogenetics and immunoregulatory functions of gut microbiota is continuing to provide light on possible treatment avenues. Understanding the complex interplay between genetic predisposition, environmental factors, and immune dysregulation is critical for developing effective treatments for MS.

Astrocytes in human central nervous system diseases: a frontier for new therapies

Astroglia are a broad class of neural parenchymal cells primarily dedicated to homoeostasis and defence of the central nervous system (CNS). Astroglia contribute to the pathophysiology of all neurological and neuropsychiatric disorders in ways that can be either beneficial or detrimental to disorder outcome. Pathophysiological changes in astroglia can be primary or secondary and can result in gain or loss of functions. Astroglia respond to external, non-cell autonomous signals associated with any form of CNS pathology by undergoing complex and variable changes in their structure, molecular expression, and function. In addition, internally driven, cell autonomous changes of astroglial innate properties can lead to CNS pathologies. Astroglial pathophysiology is complex, with different pathophysiological cell states and cell phenotypes that are context-specific and vary with disorder, disorder-stage, comorbidities, age, and sex. Here, we classify astroglial pathophysiology into (i) reactive astrogliosis, (ii) astroglial atrophy with loss of function, (iii) astroglial degeneration and death, and (iv) astrocytopathies characterised by aberrant forms that drive disease. We review astroglial pathophysiology across the spectrum of human CNS diseases and disorders, including neurotrauma, stroke, neuroinfection, autoimmune attack and epilepsy, as well as neurodevelopmental, neurodegenerative, metabolic and neuropsychiatric disorders. Characterising cellular and molecular mechanisms of astroglial pathophysiology represents a new frontier to identify novel therapeutic strategies.

The miRNA transcriptome of cerebrospinal fluid in preterm infants reveals the signaling pathways that promote reactive gliosis following cerebral hemorrhage

Introduction

Germinal Matrix-Intraventricular Haemorrhage (GM-IVH) is one of the most common neurological complications in preterm infants, which can lead to accumulation of cerebrospinal fluid (CSF) and is a major cause of severe neurodevelopmental impairment in preterm infants. However, the pathophysiological mechanisms triggered by GM-IVH are poorly understood. Analyzing the CSF that accumulates following IVH may allow the molecular signaling and intracellular communication that contributes to pathogenesis to be elucidated. Growing evidence suggests that miRs, due to their key role in gene expression, have a significant utility as new therapeutics and biomarkers.

Methods

The levels of 2,083 microRNAs (miRs) in 15 CSF samples from 10 infants with IVH were measured using miRNA whole transcriptome sequencing. Gene ontology (GO) and miR family analysis were used to uncover dysregulated signalling which were then validated in vitro in human foetal neural progenitor cells treated with IVH-CSF.

Results

Five hundred eighty-seven miRs were differentially expressed in the CSF extracted at least 2 months after injury, compared to CSF extracted within the first month of injury. GO uncovered key pathways targeted by differentially expressed miRs including the MAPK cascade and the JAK/STAT pathway. Astrogliosis is known to occur in preterm infants, and we hypothesized that this could be due to abnormal CSF-miR signaling resulting in dysregulation of the JAK/STAT pathway - a key controller of astrocyte differentiation. We then confirmed that treatment with IVH-CSF promotes astrocyte differentiation from human fetal NPCs and that this effect could be prevented by JAK/STAT inhibition. Taken together, our results provide novel insights into the CSF/NPCs crosstalk following perinatal brain injury and reveal novel targets to improve neurodevelopmental outcomes in preterm infants.

The NF-κB Pathway: a Focus on Inflammatory Responses in Spinal Cord Injury

Spinal cord injury (SCI) is a type of central nervous system trauma that can lead to severe nerve injury. Inflammatory reaction after injury is an important pathological process leading to secondary injury. Long-term stimulation of inflammation can further deteriorate the microenvironment of the injured site, leading to the deterioration of neural function. Understanding the signaling pathways that regulate responses after SCI, especially inflammatory responses, is critical for the development of new therapeutic targets and approaches. Nuclear transfer factor-κB (NF-κB) has long been recognized as a key factor in regulating inflammatory responses. The NF-κB pathway is closely related to the pathological process of SCI. Inhibition of this pathway can improve the inflammatory microenvironment and promote the recovery of neural function after SCI. Therefore, the NF-κB pathway may be a potential therapeutic target for SCI. This article reviews the mechanism of inflammatory response after SCI and the characteristics of NF-κB pathway, emphasizing the effect of inhibiting NF-κB on the inflammatory response of SCI to provide a theoretical basis for the biological treatment of SCI.

MicroRNA-124-3p Attenuated Retinal Neovascularization in Oxygen-Induced Retinopathy Mice by Inhibiting the Dysfunction of Retinal Neuroglial Cells through STAT3 Pathway

MicroRNA (miRNA) is a non-coding RNA that can regulate the expression of many target genes, and it is widely involved in various important physiological activities. MiR-124-3p was found to associate with the normal development of retinal vessels in our previous study, but the mechanism of its anti-angiogenic effect on pathological retinal neovascularization still needed to be explored. Therefore, this study aimed to investigate the effect and mechanism of miR-124-3p on retinal neovascularization in mice with oxygen-induced retinopathy (OIR). Here, we found that intravitreal injection of miR-124-3p agomir attenuated pathological retinal neovascularization in OIR mice. Moreover, miR-124-3p preserved the astrocytic template, inhibited reactive gliosis, and reduced the inflammatory response as well as necroptosis. Furthermore, miR-124-3p inhibited the signal transducer and activator of transcription 3 (STAT3) pathway and decreased the expression of hypoxia-inducible factor-1α and vascular endothelial growth factor. Taken together, our results revealed that miR-124-3p inhibited retinal neovascularization and neuroglial dysfunction by targeting STAT3 in OIR mice.

Revisiting the critical roles of reactive astrocytes in neurodegeneration

Astrocytes, an integral component of the central nervous system (CNS), contribute to the maintenance of physiological homeostasis through their roles in synaptic function, K+ buffering, blood-brain barrier (BBB) maintenance, and neuronal metabolism. Reactive astrocytes refer to astrocytes undergoing morphological, molecular and functional remodelling in response to pathological stimuli. The activation and differentiation of astrocytes are implicated in the pathogenesis of multiple neurodegenerative diseases. However, there are still controversies regarding their subset identification, function and nomenclature in neurodegeneration. In this review, we revisit the multidimensional roles of reactive astrocytes in Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS). Furthermore, we propose a precise linkage between astrocyte subsets and their functions based on single-cell sequencing analyses.

Non-Coding RNAs Regulate Spinal Cord Injury-Related Neuropathic Pain via Neuroinflammation

Secondary chronic neuropathic pain (NP) in addition to sensory, motor, or autonomic dysfunction can significantly reduce quality of life after spinal cord injury (SCI). The mechanisms of SCI-related NP have been studied in clinical trials and with the use of experimental models. However, in developing new treatment strategies for SCI patients, NP poses new challenges. The inflammatory response following SCI promotes the development of NP. Previous studies suggest that reducing neuroinflammation following SCI can improve NP-related behaviors. Intensive studies of the roles of non-coding RNAs in SCI have discovered that ncRNAs bind target mRNA, act between activated glia, neuronal cells, or other immunocytes, regulate gene expression, inhibit inflammation, and influence the prognosis of NP.

Intracellular DAMPs in Neurodegeneration and Their Role in Clinical Therapeutics

Neuroinflammation is the major implication of neurodegeneration. This is a complex process which initiates from the cellular injury triggering the innate immune system which gives rise to damage-associated molecular patterns (DAMPs) which are also recognized as endogenous danger indicators. These originate from various compartments of the cell under pathological stimulus. These are very popular candidates having their origin in the intracellular compartments and organelles of the cell and may have their site of action itself in the intracellular or at the extracellular spaces. Under the influence of the pathological stimuli, they interact with the pattern-recognition receptor to initiate their pro-inflammatory cascade followed by the cytokine release. This provides a good opportunity for diagnostic and therapeutic interventions creating better conditions for repair and reversal. Since the major contributors arise from the intracellular compartment, in this review, we have attempted to focus on the DAMP molecules arising from the intracellular compartments and their specific roles in the neurodegenerative events explaining their downstream mediators and signaling. Moreover, we have tried to cover the latest interventions in terms of DAMPs as clinical biomarkers which can assist in detecting the disease and also target it to reduce the innate-immune activation response which can help in reducing the sterile neuroinflammation having an integral role in the neurodegenerative processes.

A Panax quinquefolius-Based Preparation Prevents the Impact of 5-FU on Activity/Exploration Behaviors and Not on Cognitive Functions Mitigating Gut Microbiota and Inflammation in Mice

Simple Summary

Chemotherapy-related cognitive impairment (CRCI) and fatigue worsen the quality of life (QoL) of cancer patients. Multicenter studies have shown that Panax quinquefolius and vitamin C, respectively, were effective in reducing the symptoms of fatigue in treated cancer patients. We developed a behavioral C57Bl/6j mouse model to study the impact of 5-Fluorouracil (5-FU) chemotherapy on activity/fatigue, emotional reactivity and cognitive functions. We used this model to evaluate the potentially beneficial role of a Panax quinquefolius-based solution containing vitamin C (Qiseng^®) or vitamin C alone in these chemotherapy side effects. We established that Qiseng^® prevents the reduction in activity/exploration and symptoms of fatigue induced by 5-FU and dampens chemotherapy-induced intestinal dysbiosis and systemic inflammation. We further showed that Qiseng^® decreases macrophage infiltration in the intestinal compartment, thus preventing, at least in part, the systemic elevation of IL-6 and MCP-1 and further reducing the neuroinflammation likely responsible for the fatigue induced by chemotherapy, a major advance toward improving the QoL of patients.

Abstract

Chemotherapy-related cognitive impairment (CRCI) and fatigue constitute common complaints among cancer patient survivors. Panax quinquefolius has been shown to be effective against fatigue in treated cancer patients. We developed a behavioral C57Bl/6j mouse model to study the role of a Panax quinquefolius-based solution containing vitamin C (Qiseng^®) or vitamin C alone in activity/fatigue, emotional reactivity and cognitive functions impacted by 5-Fluorouracil (5-FU) chemotherapy. 5-FU significantly reduces the locomotor/exploration activity potentially associated with fatigue, evokes spatial cognitive impairments and leads to a decreased neurogenesis within the hippocampus (Hp). Qiseng^® fully prevents the impact of chemotherapy on activity/fatigue and on neurogenesis, specifically in the ventral Hp. We observed that the chemotherapy treatment induces intestinal damage and inflammation associated with increased levels of Lactobacilli in mouse gut microbiota and increased expression of plasma pro-inflammatory cytokines, notably IL-6 and MCP-1. We demonstrated that Qiseng^® prevents the 5-FU-induced increase in Lactobacilli levels and further compensates the 5-FU-induced cytokine release. Concomitantly, in the brains of 5-FU-treated mice, Qiseng^® partially attenuates the IL-6 receptor gp130 expression associated with a decreased proliferation of neural stem cells in the Hp. In conclusion, Qiseng^® prevents the symptoms of fatigue, reduced chemotherapy-induced neuroinflammation and altered neurogenesis, while regulating the mouse gut microbiota composition, thus protecting against intestinal and systemic inflammation.

Mechanisms of ginsenosides exert neuroprotective effects on spinal cord injury: A promising traditional Chinese medicine

Spinal cord injury (SCI) is a devastating disorder of the central nervous system (CNS). It is mainly caused by trauma and reduces the quality of life of the affected individual. Ginsenosides are safe and effective traditional Chinese medicines (TCMs), and their efficacy against SCI is being increasingly researched in many countries, especially in China and Korea. This systematic review evaluated the neuroprotective effects of ginsenosides in SCI and elucidated their properties.

Oncostatin M triggers brain inflammation by compromising blood-brain barrier integrity

Oncostatin M (OSM) is an IL-6 family member which exerts neuroprotective and remyelination-promoting effects after damage to the central nervous system (CNS). However, the role of OSM in neuro-inflammation is poorly understood. Here, we investigated OSM's role in pathological events important for the neuro-inflammatory disorder multiple sclerosis (MS). We show that OSM receptor (OSMRβ) expression is increased on circulating lymphocytes of MS patients, indicating their elevated responsiveness to OSM signalling. In addition, OSM production by activated myeloid cells and astrocytes is increased in MS brain lesions. In experimental autoimmune encephalomyelitis (EAE), a preclinical model of MS, OSMRβ-deficient mice exhibit milder clinical symptoms, accompanied by diminished T helper 17 (Th17) cell infiltration into the CNS and reduced BBB leakage. In vitro, OSM reduces BBB integrity by downregulating the junctional molecules claudin-5 and VE-cadherin, while promoting secretion of the Th17-attracting chemokine CCL20 by inflamed BBB-endothelial cells and reactive astrocytes. Using flow cytometric fluorescence resonance energy transfer (FRET) quantification, we found that OSM-induced endothelial CCL20 promotes activation of lymphocyte function-associated antigen 1 (LFA-1) on Th17 cells. Moreover, CCL20 enhances Th17 cell adhesion to OSM-treated inflamed endothelial cells, which is at least in part ICAM-1 mediated. Together, these data identify an OSM-CCL20 axis, in which OSM contributes significantly to BBB impairment during neuro-inflammation by inducing permeability while recruiting Th17 cells via enhanced endothelial CCL20 secretion and integrin activation. Therefore, care should be taken when considering OSM as a therapeutic agent for treatment of neuro-inflammatory diseases such as MS.

Divergent transcriptional regulation of astrocyte reactivity across disorders

Astrocytes respond to injury and disease in the central nervous system with reactive changes that influence the outcome of the disorder1-4. These changes include differentially expressed genes (DEGs) whose contextual diversity and regulation are poorly understood. Here we combined biological and informatic analyses, including RNA sequencing, protein detection, assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) and conditional gene deletion, to predict transcriptional regulators that differentially control more than 12,000 DEGs that are potentially associated with astrocyte reactivity across diverse central nervous system disorders in mice and humans. DEGs associated with astrocyte reactivity exhibited pronounced heterogeneity across disorders. Transcriptional regulators also exhibited disorder-specific differences, but a core group of 61 transcriptional regulators was identified as common across multiple disorders in both species. We show experimentally that DEG diversity is determined by combinatorial, context-specific interactions between transcriptional regulators. Notably, the same reactivity transcriptional regulators can regulate markedly different DEG cohorts in different disorders; changes in the access of transcriptional regulators to DNA-binding motifs differ markedly across disorders; and DEG changes can crucially require multiple reactivity transcriptional regulators. We show that, by modulating reactivity, transcriptional regulators can substantially alter disorder outcome, implicating them as therapeutic targets. We provide searchable resources of disorder-related reactive astrocyte DEGs and their predicted transcriptional regulators. Our findings show that transcriptional changes associated with astrocyte reactivity are highly heterogeneous and are customized from vast numbers of potential DEGs through context-specific combinatorial transcriptional-regulator interactions.

Function and therapeutic value of astrocytes in neurological diseases

Astrocytes are abundant glial cells in the central nervous system (CNS) that perform diverse functions in health and disease. Astrocyte dysfunction is found in numerous diseases, including multiple sclerosis, Alzheimer disease, Parkinson disease, Huntington disease and neuropsychiatric disorders. Astrocytes regulate glutamate and ion homeostasis, cholesterol and sphingolipid metabolism and respond to environmental factors, all of which have been implicated in neurological diseases. Astrocytes also exhibit significant heterogeneity, driven by developmental programmes and stimulus-specific cellular responses controlled by CNS location, cell-cell interactions and other mechanisms. In this Review, we highlight general mechanisms of astrocyte regulation and their potential as therapeutic targets, including drugs that alter astrocyte metabolism, and therapies that target transporters and receptors on astrocytes. Emerging ideas, such as engineered probiotics and glia-to-neuron conversion therapies, are also discussed. We further propose a concise nomenclature for astrocyte subsets that we use to highlight the roles of astrocytes and specific subsets in neurological diseases.

The AIM2 inflammasome is activated in astrocytes during the late phase of EAE

Inflammasomes are a class of innate immune signaling platforms that activate in response to an array of cellular damage and pathogens. Inflammasomes promote inflammation under many circumstances to enhance immunity against pathogens and inflammatory responses through their effector cytokines, IL-1β and IL-18. Multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE), are autoimmune conditions influenced by inflammasomes. Despite work investigating inflammasomes during EAE, little remains known concerning the role of inflammasomes in the central nervous system (CNS) during the disease. Here, we used multiple genetically modified mouse models to monitor activated inflammasomes in situ based on oligomerization of apoptosis-associated speck-like protein containing a CARD (ASC) in the spinal cord. Using inflammasome reporter mice, we found heightened inflammasome activation in astrocytes after the disease peak. In contrast, microglia and CNS-infiltrated myeloid cells had few activated inflammasomes in the CNS during EAE. Astrocyte inflammasome activation during EAE was dependent on absent in melanoma 2 (AIM2), but low IL-1β release and no significant signs of cell death were found. Thus, the AIM2 inflammasome activation in astrocytes may have a distinct role from traditional inflammasome-mediated inflammation.

Loss-of-function manipulations to identify roles of diverse glia and stromal cells during CNS scar formation

Scar formation is the replacement of parenchymal cells by stromal cells and fibrotic extracellular matrix. Until as recently as 25 years ago, little was known about the major functional contributions of different neural and non-neural cell types in the formation of scar tissue and tissue fibrosis in the CNS. Concepts about CNS scar formation are evolving rapidly with the availability of different types of loss-of-function technologies that allow mechanistic probing of cellular and molecular functions in models of CNS disorders in vivo. Such loss-of-function studies are beginning to reveal that scar formation and tissue fibrosis in the CNS involves complex interactions amongst multiple types of CNS glia and non-neural stromal cells. For example, attenuating functions of the CNS resident glial cells, astrocytes or microglia, can disrupt the formation of limitans borders that form around stromal cell scars, which leads to increased spread of inflammation, increased loss of neural tissue, and increased fibrosis. Insights are being gained into specific neuropathological mechanisms whereby specific dysfunctions of different types of CNS glia could cause or contribute to disorder-related tissue pathology and dysfunction. CNS glia, as well as fibrosis-producing stromal cells, are emerging as potential major contributors to diverse CNS disorders either through loss- or gain-of-functions, and are thereby emerging as important potential targets for interventions. In this article, we will review and discuss the effects on CNS scar formation and tissue repair of loss-of-function studies targeted at different specific cell types in various disorder models in vivo.

Astroglial and Microglial Purinergic P2X7 Receptor as a Major Contributor to Neuroinflammation during the Course of Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune inflammatory disease of the central nervous system that leads to the progressive disability of patients. A characteristic feature of the disease is the presence of focal demyelinating lesions accompanied by an inflammatory reaction. Interactions between autoreactive immune cells and glia cells are considered as a central mechanism underlying the pathology of MS. A glia-mediated inflammatory reaction followed by overproduction of free radicals and generation of glutamate-induced excitotoxicity promotes oligodendrocyte injury, contributing to demyelination and subsequent neurodegeneration. Activation of purinergic signaling, in particular P2X7 receptor-mediated signaling, in astrocytes and microglia is an important causative factor in these pathological processes. This review discusses the role of astroglial and microglial cells, and in particular glial P2X7 receptors, in inducing MS-related neuroinflammatory events, highlighting the importance of P2X7R-mediated molecular pathways in MS pathology and identifying these receptors as a potential therapeutic target.

Diversity of Reactive Astrogliosis in CNS Pathology: Heterogeneity or Plasticity?

Astrocytes are essential for the development and homeostatic maintenance of the central nervous system (CNS). They are also critical players in the CNS injury response during which they undergo a process referred to as "reactive astrogliosis." Diversity in astrocyte morphology and gene expression, as revealed by transcriptional analysis, is well-recognized and has been reported in several CNS pathologies, including ischemic stroke, CNS demyelination, and traumatic injury. This diversity appears unique to the specific pathology, with significant variance across temporal, topographical, age, and sex-specific variables. Despite this, there is limited functional data corroborating this diversity. Furthermore, as reactive astrocytes display significant environmental-dependent plasticity and fate-mapping data on astrocyte subsets in the adult CNS is limited, it remains unclear whether this diversity represents heterogeneity or plasticity. As astrocytes are important for neuronal survival and CNS function post-injury, establishing to what extent this diversity reflects distinct established heterogeneous astrocyte subpopulations vs. environmentally dependent plasticity within established astrocyte subsets will be critical for guiding therapeutic development. To that end, we review the current state of knowledge on astrocyte diversity in the context of three representative CNS pathologies: ischemic stroke, demyelination, and traumatic injury, with the goal of identifying key limitations in our current knowledge and suggesting future areas of research needed to address them. We suggest that the majority of identified astrocyte diversity in CNS pathologies to date represents plasticity in response to dynamically changing post-injury environments as opposed to heterogeneity, an important consideration for the understanding of disease pathogenesis and the development of therapeutic interventions.

Leukemia Inhibitory Factor Is Required for Subventricular Zone Astrocyte Progenitor Proliferation and for Prokineticin-2 Production after a Closed Head Injury in Mice

Astrogliosis is one of the hallmarks of brain injury, and after a mild injury activated astrocytes subserve neuroprotective and pro-regenerative functions. We previously found that the astroglial response to closed head injury (CHI) was blunted in mice that were haplodeficient in leukemia inhibitory factor (LIF); therefore, the goal of these studies was to determine if the delayed astrogliosis was due to decreased recruitment of subventricular zone (SVZ) progenitors. CHI's were performed on post-natal day 20 on LIF heterozygous (Het) and wild-type (WT) mice. At 48 h post-CHI, astrocyte progenitor proliferation within the SVZ increased ∼250% in WT mice but was reduced by ∼200% in LIF Het mice compared with sham controls. Using neurospheres to model the SVZ, LIF increased the percentage of proliferating astrocyte progenitors by 2-fold compared with controls but had no effect on neural stem cell proliferation. To rule out the involvement of other cytokines, 105 cytokines were analyzed using a multi-plex array and with targeted validation on injured LIF Het versus WT neocortex. Of the cytokines analyzed, only prokineticin-2 (ProK2) required LIF signaling. Correspondingly, LIF-treated neurospheres expressed higher levels of ProK2, the ProK1 and ProK2 receptors (ProKR1 and ProKR2). Using in situ hybridization, ProK2 messenger RNA (mRNA) was most abundant in neocortical neurons and highly expressed within the SVZ. However, in contrast to LIF, ProK2 decreased astrocyte progenitor proliferation 2-fold. Altogether, these data demonstrate that LIF is necessary for astrocyte progenitor proliferation after injury and reveal a new role for LIF as an essential regulator of the neurotrophic factor ProK2.

Sigma 1 Receptor Modulates Optic Nerve Head Astrocyte Reactivity

Purpose

Stimulation of Sigma 1 Receptor (S1R) is neuroprotective in retina and optic nerve. S1R is expressed in both neurons and glia. The purpose of this work is to evaluate the ability of S1R to modulate reactivity responses of optic nerve head astrocytes (ONHAs) by investigating the extent to which S1R activation alters ONHA reactivity under conditions of ischemic cellular stress.

Methods

Wild type (WT) and S1R knockout (KO) ONHAs were derived and treated with vehicle or S1R agonist, (+)-pentazocine ((+)-PTZ). Cells were subjected to six hours of oxygen glucose deprivation (OGD) followed by 18 hours of re-oxygenation (OGD/R). Astrocyte reactivity responses were measured. Molecules that regulate ONHA reactivity, signal transducer and activator of transcription 3 (STAT3) and nuclear factor kappa B (NF-kB), were evaluated.

Results

Baseline glial fibrillary acidic protein (GFAP) levels were increased in nonstressed KO ONHAs compared with WT cultures. Baseline cellular migration was also increased in nonstressed KO ONHAs compared with WT. Treatment with (+)-PTZ increased cellular migration in nonstressed WT ONHAs but not in KO ONHAs. Exposure of both WT and KO ONHAs to ischemia (OGD/R), increased GFAP levels and cellular proliferation. However, (+)-PTZ treatment of OGD/R-exposed ONHAs enhanced GFAP levels, cellular proliferation, and cellular migration in WT but not KO cultures. The (+)-PTZ treatment of WT ONHAs also enhanced the OGD/R-induced increase in cellular pSTAT3 levels. However, treatment of WT ONHAs with (+)-PTZ abrogated the OGD/R-induced rise in NF-kB(p65) activation.

Conclusions

Under ischemic stress conditions, S1R activation enhanced ONHA reactivity characteristics. Future studies should address effects of these responses on RGC survival.

Astrocytes in Multiple Sclerosis-Essential Constituents with Diverse Multifaceted Functions

In multiple sclerosis (MS), astrocytes respond to the inflammatory stimulation with an early robust process of morphological, transcriptional, biochemical, and functional remodeling. Recent studies utilizing novel technologies in samples from MS patients, and in an animal model of MS, experimental autoimmune encephalomyelitis (EAE), exposed the detrimental and the beneficial, in part contradictory, functions of this heterogeneous cell population. In this review, we summarize the various roles of astrocytes in recruiting immune cells to lesion sites, engendering the inflammatory loop, and inflicting tissue damage. The roles of astrocytes in suppressing excessive inflammation and promoting neuroprotection and repair processes is also discussed. The pivotal roles played by astrocytes make them an attractive therapeutic target. Improved understanding of astrocyte function and diversity, and the mechanisms by which they are regulated may lead to the development of novel approaches to selectively block astrocytic detrimental responses and/or enhance their protective properties.

Prophylactic exposure to oral riluzole reduces the clinical severity and immune-related biomarkers of experimental autoimmune encephalomyelitis

Glutamate-mediated excitotoxicity and immune cell infiltration are hallmarks of multiple sclerosis. The glutamate release inhibitor, riluzole (RIL), has been shown to attenuate the clinical symptoms of experimental autoimmune encephalomyelitis (EAE) in mice, but an association between glutamate excitotoxicity and the progression of MOG35-55-induced EAE has not been well defined. This study investigated the effects of prophylactic and chronic oral RIL on the clinical severity of EAE. Prophylactic+chronic RIL reduced the presence of inflammatory infiltrates, altered GFAP and Foxp3, and attenuated disease severity. These findings indicate a need to delineate the distinct role of glutamate in EAE symptomatology.

Dectin-1 limits autoimmune neuroinflammation and promotes myeloid cell-astrocyte crosstalk via Card9-independent expression of Oncostatin M

Pathologic roles of innate immunity in neurologic disorders are well described, but their beneficial aspects are less understood. Dectin-1, a C-type lectin receptor (CLR), is largely known to induce inflammation. Here, we report that Dectin-1 limited experimental autoimmune encephalomyelitis (EAE), while its downstream signaling molecule, Card9, promoted the disease. Myeloid cells mediated the pro-resolution function of Dectin-1 in EAE with enhanced gene expression of the neuroprotective molecule, Oncostatin M (Osm), through a Card9-independent pathway, mediated by the transcription factor NFAT. Furthermore, we find that the Osm receptor (OsmR) functioned specifically in astrocytes to reduce EAE severity. Notably, Dectin-1 did not respond to heat-killed Mycobacteria, an adjuvant to induce EAE. Instead, endogenous Dectin-1 ligands, including galectin-9, in the central nervous system (CNS) were involved to limit EAE. Our study reveals a mechanism of beneficial myeloid cell-astrocyte crosstalk regulated by a Dectin-1 pathway and identifies potential therapeutic targets for autoimmune neuroinflammation.

Astrocytes lure CXCR2-expressing CD4+ T cells to gray matter via TAK1-mediated chemokine production in a mouse model of multiple sclerosis

Multiple sclerosis (MS) is a chronic neurological disease of the central nervous system driven by peripheral immune cell infiltration and glial activation. The pathological hallmark of MS is demyelination, and mounting evidence suggests neuronal damage in gray matter is a major contributor to disease irreversibility. While T cells are found in both gray and white matter of MS tissue, they are typically confined to the white matter of the most commonly used mouse model of MS, experimental autoimmune encephalomyelitis (EAE). Here, we used a modified EAE mouse model (Type-B EAE) that displays severe neuronal damage to investigate the interplay between peripheral immune cells and glial cells in the event of neuronal damage. We show that CD4+ T cells migrate to the spinal cord gray matter, preferentially to ventral horns. Compared to CD4+ T cells in white matter, gray matter-infiltrated CD4+ T cells were mostly immobilized and interacted with neurons, which are behaviors associated with detrimental effects to normal neuronal function. T cell-specific deletion of CXCR2 significantly decreased CD4+ T cell infiltration into gray matter in Type-B EAE mice. Further, astrocyte-targeted deletion of TAK1 inhibited production of CXCR2 ligands such as CXCL1 in gray matter, successfully prevented T cell migration into spinal cord gray matter, and averted neuronal damage and motor dysfunction in Type-B EAE mice. This study identifies astrocyte chemokine production as a requisite for the invasion of CD4+T cell into the gray matter to induce neuronal damage.

Altered astrocytic function in experimental neuroinflammation and multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) that affects about 2.5 million people worldwide. In MS, the patients' immune system starts to attack the myelin sheath, leading to demyelination, neurodegeneration, and, ultimately, loss of vital neurological functions such as walking. There is currently no cure for MS and the available treatments only slow the initial phases of the disease. The later-disease mechanisms are poorly understood and do not directly correlate with the activity of immune system cells, the main target of the available treatments. Instead, evidence suggests that disease progression and disability are better correlated with the maintenance of a persistent low-grade inflammation inside the CNS, driven by local glial cells, like astrocytes and microglia. Depending on the context, astrocytes can (a) exacerbate inflammation or (b) promote immunosuppression and tissue repair. In this review, we will address the present knowledge that exists regarding the role of astrocytes in MS and experimental animal models of the disease.

Neuroinflammation in neurodegenerative disorders: the roles of microglia and astrocytes

Neuroinflammation is associated with neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Microglia and astrocytes are key regulators of inflammatory responses in the central nervous system. The activation of microglia and astrocytes is heterogeneous and traditionally categorized as neurotoxic (M1-phenotype microglia and A1-phenotype astrocytes) or neuroprotective (M2-phenotype microglia and A2-phenotype astrocytes). However, this dichotomized classification may not reflect the various phenotypes of microglia and astrocytes. The relationship between these activated glial cells is also very complicated, and the phenotypic distribution can change, based on the progression of neurodegenerative diseases. A better understanding of the roles of microglia and astrocytes in neurodegenerative diseases is essential for developing effective therapies. In this review, we discuss the roles of inflammatory response in neurodegenerative diseases, focusing on the contributions of microglia and astrocytes and their relationship. In addition, we discuss biomarkers to measure neuroinflammation and studies on therapeutic drugs that can modulate neuroinflammation.

Astrocyte phenotypes: Emphasis on potential markers in neuroinflammation

Astrocytes, the most abundant glial cells in the central nervous system (CNS), have numerous integral roles in all CNS functions. They are essential for synaptic transmission and support neurons by providing metabolic substrates, secreting growth factors and regulating extracellular concentrations of ions and neurotransmitters. Astrocytes respond to CNS insults through reactive astrogliosis, in which they go through many functional and molecular changes. In neuroinflammatory conditions reactive astrocytes exert both beneficial and detrimental functions, depending on the context and heterogeneity of astrocytic populations. In this review we profile astrocytic diversity in the context of neuroinflammation; with a specific focus on multiple sclerosis (MS) and its best-described animal model experimental autoimmune encephalomyelitis (EAE). We characterize two main subtypes, protoplasmic and fibrous astrocytes and describe the role of intermediate filaments in the physiology and pathology of these cells. Additionally, we outline a variety of markers that are emerging as important in investigating astrocytic biology in both physiological conditions and neuroinflammation.

Cholinergic Modulation of Glial Function During Aging and Chronic Neuroinflammation

Aging is a complex biological process that increases the risk of age-related cognitive degenerative diseases such as dementia, including Alzheimer’s disease (AD), Lewy Body Dementia (LBD), and mild cognitive impairment (MCI). Even non-pathological aging of the brain can involve chronic oxidative and inflammatory stress, which disrupts the communication and balance between the brain and the immune system. There has been an increasingly strong connection found between chronic neuroinflammation and impaired memory, especially in AD. While microglia and astrocytes, the resident immune cells of the central nervous system (CNS), exerting beneficial effects during the acute inflammatory phase, during chronic neuroinflammation they can become more detrimental. Central cholinergic circuits are involved in maintaining normal cognitive function and regulating signaling within the entire cerebral cortex. While neuronal-glial cholinergic signaling is anti-inflammatory and anti-oxidative, central cholinergic neuronal degeneration is implicated in impaired learning, memory sleep regulation, and attention. Although there is evidence of cholinergic involvement in memory, fewer studies have linked the cholinergic anti-inflammatory and anti-oxidant pathways to memory processes during development, normal aging, and disease states. This review will summarize the current knowledge of cholinergic effects on microglia and astroglia, and their role in both anti-inflammatory and anti-oxidant mechanisms, concerning normal aging and chronic neuroinflammation. We provided details on how stimulation of α7 nicotinic acetylcholine (α7nACh) receptors can be neuroprotective by increasing amyloid-β phagocytosis, decreasing inflammation and reducing oxidative stress by promoting the nuclear factor erythroid 2-related factor 2 (Nrf2) pathways and decreasing the release of pro-inflammatory cytokines. There is also evidence for astroglial α7nACh receptor stimulation mediating anti-inflammatory and antioxidant effects by inhibiting the nuclear factor-κB (NF-κB) pathway and activating the Nrf2 pathway respectively. We conclude that targeting cholinergic glial interactions between neurons and glial cells via α7nACh receptors could regulate neuroinflammation and oxidative stress, relevant to the treatment of several neurodegenerative diseases.

Spinal Cord Injury: Pathophysiology, Multimolecular Interactions, and Underlying Recovery Mechanisms

Spinal cord injury (SCI) is a destructive neurological and pathological state that causes major motor, sensory and autonomic dysfunctions. Its pathophysiology comprises acute and chronic phases and incorporates a cascade of destructive events such as ischemia, oxidative stress, inflammatory events, apoptotic pathways and locomotor dysfunctions. Many therapeutic strategies have been proposed to overcome neurodegenerative events and reduce secondary neuronal damage. Efforts have also been devoted in developing neuroprotective and neuro-regenerative therapies that promote neuronal recovery and outcome. Although varying degrees of success have been achieved, curative accomplishment is still elusive probably due to the complex healing and protective mechanisms involved. Thus, current understanding in this area must be assessed to formulate appropriate treatment modalities to improve SCI recovery. This review aims to promote the understanding of SCI pathophysiology, interrelated or interlinked multimolecular interactions and various methods of neuronal recovery i.e., neuroprotective, immunomodulatory and neuro-regenerative pathways and relevant approaches.

Astrocyte Reactivity: Subtypes, States, and Functions in CNS Innate Immunity

Astrocytes are neural parenchymal cells that ubiquitously tile the central nervous system (CNS). In addition to playing essential roles in healthy tissue, astrocytes exhibit an evolutionarily ancient response to all CNS insults, referred to as astrocyte reactivity. Long regarded as passive and homogeneous, astrocyte reactivity is being revealed as a heterogeneous and functionally powerful component of mammalian CNS innate immunity. Nevertheless, concepts about what astrocyte reactivity comprises and what it does are incomplete and sometimes controversial. This review discusses the goal of differentiating reactive astrocyte subtypes and states based on composite pictures of molecular expression, cell morphology, cellular interactions, proliferative state, normal functions, and disease-induced dysfunctions. A working model and conceptual framework is presented for characterizing the diversity of astrocyte reactivity.

Role of glia in optic nerve

Glial cells are critically important for maintenance of neuronal activity in the central nervous system (CNS), including the optic nerve (ON). However, the ON has several unique characteristics, such as an extremely high myelination level of retinal ganglion cell (RGC) axons throughout the length of the nerve (with virtually all fibers myelinated by 7 months of age in humans), lack of synapses and very narrow geometry. Moreover, the optic nerve head (ONH) - a region where the RGC axons exit the eye - represents an interesting area that is morphologically distinct in different species. In many cases of multiple sclerosis (demyelinating disease of the CNS) vision problems are the first manifestation of the disease, suggesting that RGCs and/or glia in the ON are more sensitive to pathological conditions than cells in other parts of the CNS. Here, we summarize current knowledge on glial organization and function in the ON, focusing on glial support of RGCs. We cover both well-established concepts on the important role of glial cells in ON health and new findings, including novel insights into mechanisms of remyelination, microglia/NG2 cell-cell interaction, astrocyte reactivity and the regulation of reactive astrogliosis by mitochondrial fragmentation in microglia.

Cannabis Use Is Associated With Increased Levels of Soluble gp130 in Schizophrenia but Not in Bipolar Disorder

The complex effects of plant cannabinoids on human physiology is not yet fully understood, but include a wide spectrum of effects on immune modulation. The immune system and its inflammatory effector pathways are recently emerging as possible causative factors in psychotic disorders. The present study aimed to investigate whether self-administered Cannabis use was associated with changes in circulating immune and neuroendocrine markers in schizophrenia (SCZ) and bipolar disorder (BD) patients. A screening of 13 plasma markers reflecting different inflammatory pathways was performed in SCZ (n = 401) and BD patients (n = 242) after subdividing each group into Cannabis user and non-user subgroups. We found that i) soluble gp130 (sgp130) concentrations were significantly elevated among Cannabis users in the SCZ group (p = 0.002) after multiple testing correction, but not in BD. ii) Nominally significant differences were observed in the levels of IL-1RA (p = 0.0059), YKL40 (p = 0.0069), CatS (p = 0.013), sTNFR1 (p = 0.031), and BDNF (p = 0.020), where these factors exhibited higher plasma levels in Cannabis user SCZ patients than in non-users. iii) These differences in systemic levels were not reflected by altered mRNA expression of genes encoding sgp130, IL-1RA, YKL40, CatS, sTNFR1, and BDNF in whole blood. Our results show that Cannabis self-administration is associated with markedly higher sgp130 levels in SCZ, but not in BD, and that this phenomenon is independent of the modulation of peripheral immune cells. These findings warrant further investigation into the potential IL-6 trans-signaling modulatory, anti-inflammatory, neuroimmune, and biobehavioral-cognitive effects of Cannabis use in SCZ.

An Integrated Global Analysis of Compartmentalized HRAS Signaling

Modern omics technologies allow us to obtain global information on different types of biological networks. However, integrating these different types of analyses into a coherent framework for a comprehensive biological interpretation remains challenging. Here, we present a conceptual framework that integrates protein interaction, phosphoproteomics, and transcriptomics data. Applying this method to analyze HRAS signaling from different subcellular compartments shows that spatially defined networks contribute specific functions to HRAS signaling. Changes in HRAS protein interactions at different sites lead to different kinase activation patterns that differentially regulate gene transcription. HRAS-mediated signaling is the strongest from the cell membrane, but it regulates the largest number of genes from the endoplasmic reticulum. The integrated networks provide a topologically and functionally resolved view of HRAS signaling. They reveal distinct HRAS functions including the control of cell migration from the endoplasmic reticulum and TP53-dependent cell survival when signaling from the Golgi apparatus.

Astrocytes and Microglia as Major Players of Myelin Production in Normal and Pathological Conditions

Myelination is an essential process that consists of the ensheathment of axons by myelin. In the central nervous system (CNS), myelin is synthesized by oligodendrocytes. The proliferation, migration, and differentiation of oligodendrocyte precursor cells constitute a prerequisite before mature oligodendrocytes extend their processes around the axons and progressively generate a multilamellar lipidic sheath. Although myelination is predominately driven by oligodendrocytes, the other glial cells including astrocytes and microglia, also contribute to this process. The present review is an update of the most recent emerging mechanisms involving astrocyte and microglia in myelin production. The contribution of these cells will be first described during developmental myelination that occurs in the early postnatal period and is critical for the proper development of cognition and behavior. Then, we will report the novel findings regarding the beneficial or deleterious effects of astroglia and microglia, which respectively promote or impair the endogenous capacity of oligodendrocyte progenitor cells (OPCs) to induce spontaneous remyelination after myelin loss. Acute delineation of astrocyte and microglia activities and cross-talk should uncover the way towards novel therapeutic perspectives aimed at recovering proper myelination during development or at breaking down the barriers impeding the regeneration of the damaged myelin that occurs in CNS demyelinating diseases.

Resolution of inflammation during multiple sclerosis

Multiple sclerosis (MS) is a frequent autoimmune demyelinating disease of the central nervous system (CNS). There are three clinical forms described: relapsing-remitting multiple sclerosis (RRMS), the most common initial presentation (85%) among which, if not treated, about half will transform, into the secondary progressive multiple sclerosis (SPMS) and the primary progressive MS (PPMS) (15%) that is directly progressive without superimposed clinical relapses. Inflammation is present in all subsets of MS. The relapsing/remitting form could represent itself a particular interest for the study of inflammation resolution even though it remains incomplete in MS. Successful resolution of acute inflammation is a highly regulated process and dependent on mechanisms engaged early in the inflammatory response that are scarcely studied in MS. Moreover, recent classes of disease-modifying treatment (DMTs) that are effective against RRMS act by re-establishing the inflammatory imbalance, taking advantage of the pre-existing endogenous suppressor. In this review, we will discuss the active role of regulatory immune cells in inflammation resolution as well as the role of tissue and non-hematopoietic cells as contributors to inflammation resolution. Finally, we will explore how DMTs, more specifically induction therapies, impact the resolution of inflammation during MS.

Serum FAM19A5 in neuromyelitis optica spectrum disorders: Can it be a new biomarker representing clinical status?

Background:

Neuromyelitis optica spectrum disorder (NMOSD) targets astrocytes and elevates the levels of astrocyte-injury markers during attacks. FAM19A5, involved in reactive gliosis, is secreted by reactive astrocytes following central nervous system (CNS) damage.

Objective:

To investigate the significance of serum FAM19A5 in patients with NMOSD.

Methods:

We collected clinical data and sera of 199 patients from 11 hospitals over 21 months. FAM19A5 levels were compared among three groups: NMOSD with positive anti-aquaporin-4 antibody (NMOSD-AQP4), other CNS demyelinating disease, and healthy controls.

Results:

The median serum FAM19A5 level was higher in the NMOSD-AQP4 (4.90 ng/mL (3.95, 5.79)) than in the other CNS demyelinating (2.35 ng/mL (1.83, 4.07), p < 0.001) or healthy control (1.02 ng/mL (0.92, 1.14), p < 0.001) groups. There were significant differences in the median serum FAM19A5 levels between the attack and remission periods (5.89 ng/mL (5.18, 6.98); 4.40 ng/mL (2.72, 5.13), p < 0.001) in the NMOSD-AQP4 group. Sampling during an attack ( p < 0.001) and number of past attacks ( p = 0.010) were independently associated with increased serum FAM19A5.

Conclusion:

Serum FAM19A5 was higher in patients with NMOSD-AQP4 and correlated with clinical characteristics. Thus, serum FAM19A5 may be a novel clinical biomarker for NMOSD-AQP4.

Astrocytes in multiple sclerosis and experimental autoimmune encephalomyelitis: Star-shaped cells illuminating the darkness of CNS autoimmunity

Neuropathology in the human autoimmune disease multiple sclerosis (MS) is considered to be mediated by autoreactive leukocytes, such as T cells, B cells, and macrophages. However, the inflammation and tissue damage in MS and its animal model experimental autoimmune encephalomyelitis (EAE) is also critically regulated by astrocytes, the most abundant cell population in the central nervous system (CNS). Under physiological conditions, astrocytes are integral to the development and function of the CNS, whereas in CNS autoimmunity, astrocytes influence the pathogenesis, progression, and recovery of the diseases. In this review, we summarize recent advances in astrocytic functions in the context of MS and EAE, which are categorized into two opposite aspects, one being detrimental and the other beneficial. Inhibition of the detrimental functions and/or enhancement of the beneficial functions of astrocytes might be favorable for the treatment of MS.

Glial pathology and retinal neurotoxicity in the anterior visual pathway in experimental autoimmune encephalomyelitis

The animal model experimental autoimmune encephalomyelitis (EAE) has been used extensively in the past to test mechanisms that target peripheral immune cells for treatment of multiple sclerosis (MS). While there have been some notable successes in relapsing MS, the development of therapies for progressive multiple sclerosis (MS) has been hampered by lack of an appropriate animal model. Further, the mechanisms underlying CNS inflammation and neuronal injury remain incompletely elucidated. It is known that the MOG _35-55 EAE mouse model does not have insidious behavioral progression as occurs in people with MS, but there is significant neuronal and axonal injury in EAE, as a result of the inflammation. In the present study, we describe the time course of glial activation and retinal neurodegeneration in the EAE model, and highlight the utility of studying the anterior visual pathway for modeling mechanisms of neuronal injury that may recapitulate critical aspects of the pathology described in people with MS following optic neuritis and subclinical optic neuropathy. We show that A1 neurotoxic astrocytes are prevalent in optic nerve tissue and retina, and are associated with subsequent RGC loss in the most commonly used form of the EAE model induced by MOG _35-55 peptide in C57/B6 mice. We developed a semi-automatic method to quantify retinal ganglion cells (RGC) and show that RGCs remain intact at peak EAE (PID 16) but are significantly reduced in late EAE (PID 42). Postsynaptic proteins and neurites were also compromised in the retina of late EAE mice. The retinal pathology manifests weeks after the microglial and astrocyte activation, which were prominent in optic nerve tissues at PID 16. Microglia expressed iNOS and had increased gene expression of C1q, TNF-α, and IL-1α. Astrocytes expressed high levels of complement component 3 and other genes associated with A1 neurotoxic astrocytes. Our data suggest that EAE can be used to study the pathobiology of optic neuropathy and to examine the preclinical neuroprotective effects of drugs that target activation of neurotoxic A1 astrocytes.

"Hypothalamic Microinflammation" Paradigm in Aging and Metabolic Diseases

Under conditions leading to aging and metabolic syndrome, the hypothalamus atypically undergoes proinflammatory signaling activation leading to a chronic and stable background inflammation, referred to as "hypothalamic microinflammation." Through the past decade of research, progress has been made to causally link this hypothalamic inflammation to the mechanism of aging as well as metabolic syndrome, promoting the "hypothalamic microinflammation" theory, which helps characterize the consensus of these epidemic health problems. In general, it is consistently appreciated that hypothalamic microinflammation emerges during the early stages of aging and metabolic syndrome and evolves to be multifaceted and advanced alongside disease progression, while inhibition of key inflammatory components in the hypothalamus has a broad range of effects in counteracting these disorders. Herein, focusing on aging and metabolic syndrome, this writing aims to provide an overview of and insights into the mediators, signaling components, cellular impacts, and physiological significance of this hypothalamic microinflammation.

Traumatic Spinal Cord Injury: An Overview of Pathophysiology, Models and Acute Injury Mechanisms

Traumatic spinal cord injury (SCI) is a life changing neurological condition with substantial socioeconomic implications for patients and their care-givers. Recent advances in medical management of SCI has significantly improved diagnosis, stabilization, survival rate and well-being of SCI patients. However, there has been small progress on treatment options for improving the neurological outcomes of SCI patients. This incremental success mainly reflects the complexity of SCI pathophysiology and the diverse biochemical and physiological changes that occur in the injured spinal cord. Therefore, in the past few decades, considerable efforts have been made by SCI researchers to elucidate the pathophysiology of SCI and unravel the underlying cellular and molecular mechanisms of tissue degeneration and repair in the injured spinal cord. To this end, a number of preclinical animal and injury models have been developed to more closely recapitulate the primary and secondary injury processes of SCI. In this review, we will provide a comprehensive overview of the recent advances in our understanding of the pathophysiology of SCI. We will also discuss the neurological outcomes of human SCI and the available experimental model systems that have been employed to identify SCI mechanisms and develop therapeutic strategies for this condition.

The Astrocytic cAMP Pathway in Health and Disease

Astrocytes are major glial cells that play critical roles in brain homeostasis. Abnormalities in astrocytic functions can lead to brain disorders. Astrocytes also respond to injury and disease through gliosis and immune activation, which can be both protective and detrimental. Thus, it is essential to elucidate the function of astrocytes in order to understand the physiology of the brain to develop therapeutic strategies against brain diseases. Cyclic adenosine monophosphate (cAMP) is a major second messenger that triggers various downstream cellular machinery in a wide variety of cells. The functions of astrocytes have also been suggested as being regulated by cAMP. Here, we summarize the possible roles of cAMP signaling in regulating the functions of astrocytes. Specifically, we introduce the ways in which cAMP pathways are involved in astrocyte functions, including (1) energy supply, (2) maintenance of the extracellular environment, (3) immune response, and (4) a potential role as a provider of trophic factors, and we discuss how these cAMP-regulated processes can affect brain functions in health and disease.

Reactive astrocytes in multiple sclerosis impair neuronal outgrowth through TRPM7-mediated chondroitin sulfate proteoglycan production

Multiple sclerosis (MS) is a chronic inflammatory disorder of the central nervous system (CNS), characterized by inflammation‐mediated demyelination, axonal injury and neurodegeneration. The mechanisms underlying impaired neuronal function are not fully understood, but evidence is accumulating that the presence of the gliotic scar produced by reactive astrocytes play a critical role in these detrimental processes. Here, we identified astrocytic Transient Receptor Potential cation channel, subfamily M, member 7 (TRPM7), a Ca²⁺‐permeable nonselective cation channel, as a novel player in the formation of a gliotic scar. TRPM7 was found to be highly expressed in reactive astrocytes within well‐characterized MS lesions and upregulated in primary astrocytes under chronic inflammatory conditions. TRPM7 overexpressing astrocytes impaired neuronal outgrowth in vitro by increasing the production of chondroitin sulfate proteoglycans, a key component of the gliotic scar. These findings indicate that astrocytic TRPM7 is a critical regulator of the formation of a gliotic scar and provide a novel mechanism by which reactive astrocytes affect neuronal outgrowth.

Astrocytes: Heterogeneous and Dynamic Phenotypes in Neurodegeneration and Innate Immunity

Astrocytes are the most numerous cell type in the brain and perform several essential functions in supporting neuronal metabolism and actively participating in neural circuit and behavioral function. They also have essential roles as innate immune cells in responding to local neuropathology, and the manner in which they respond to brain injury and degeneration is the subject of increasing attention in neuroscience. Although activated astrocytes have long been thought of as a relatively homogenous population, which alter their phenotype in a relatively stereotyped way upon central nervous system injury, the last decade has revealed substantial heterogeneity in the basal state and significant heterogeneity of phenotype during reactive astrocytosis. Thus, phenotypic diversity occurs at two distinct levels: that determined by regionality and development and that determined by temporally dynamic changes to the environment of astrocytes during pathology. These inflammatory and pathological states shape the phenotype of these cells, with different consequences for destruction or recovery of the local tissue, and thus elucidating these phenotypic changes has significant therapeutic implications. In this review, we will focus on the phenotypic heterogeneity of astrocytes in health and disease and their propensity to change that phenotype upon subsequent stimuli.

Differing Outcome of Experimental Autoimmune Encephalitis in Macrophage/Neutrophil- and T Cell-Specific gp130-Deficient Mice

gp130 cytokines are differentially involved in regulating the T helper (H) 17-driven pathogenesis of experimental autoimmune encephalomyelitis (EAE), the animal model of human multiple sclerosis. Interleukin (IL)-6 directly promotes the development of TH17 cells through the gp130/IL-6R complex. By contrast, IL-27 has been shown to suppress a TH17 immune response by gp130/IL-27R-alpha (α) receptor ligation. The IL-27-dependent regulation of a TH17 development could be mediated on the level of CD4 T cells. However, because IL-27 also suppresses the secretion of the TH17-driving cytokines IL-6 and IL-12/23p40 in accessory cells, TH17 immune responses may also be controlled by IL-27 on the level of macrophages and/or neutrophils. To analyze these opposing effects of gp130 engagement on the pathogenesis of EAE, we immunized CD4⁺ T cell-specific gp130-deficient (CD4cre^posgp130^loxP/loxP) and macrophage/neutrophil-specific gp130-deficient (LysMcre^posgp130^loxP/loxP) mice with the myelin-oligodendrocyte-glycoprotein peptide MOG_35-55. Whereas inflammatory immune responses, TH17 differentiation, and pathology in CD4cre^posgp130^loxP/loxP mice were mitigated, disease progression was eventually enhanced in LysMcre^posgp130^loxP/loxP mice. Exacerbated disease in MOG_35-55-immunized LysMcre^posgp130^loxP/loxP mice was associated with an elevated development of TH17 cells and increased infiltration of the central nervous system with leukocytes indicating a suppressive role of macrophage/neutrophil-gp130. To further prove IL-6 to be responsible for the control of inflammation during EAE through gp130 on macrophages/neutrophils, we immunized LysMcre^posIL-6R^loxP/loxP mice. In contrast to LysMcre^posgp130^loxP/loxP mice, neuropathology in MOG_35-55-immunized macrophage/neutrophil-specific IL-6R-deficient mice was not enhanced indicating that the alleviation of EAE through macrophage/neutrophil-gp130 is mediated independently of IL-6. Together, this different pathology in macrophage/neutrophil- and CD4 T cell-specific gp130-deficient mice suggests that gp130 cytokines modulate TH17 inflammation differentially by targeting distinct cell types.