Inhibition of reactive astrocytosis in established experimental autoimmune encephalomyelitis favors infiltration by myeloid cells over T cells and enhances severity of disease

BATF2 is a regulator of interferon-γ signaling in astrocytes during neuroinflammation

Astrocytic interferon (IFN)γ signaling is associated with a reduction in neuroinflammation. We have previously shown that the benefits of astrocytic IFNγ arise from a variety of mechanisms; however, downstream effectors responsible for regulating this protection are unknown. We address this by identifying a specific transcription factor that may play a key role in modulating the consequences of IFNγ signaling. RNA-sequencing of primary human astrocytes treated with IFNγ revealed basic leucine zipper ATF-like transcription factor ( BATF )2 as a highly expressed interferon-specific gene. Primarily studied in the periphery, BATF2 has been shown to exert both inflammatory and protective functions; however, its function in the central nervous system (CNS) is unknown. Here, we demonstrate that human spinal cord astrocytes upregulate BATF2 transcript and protein in an IFNγ-specific manner. Additionally, we found that BATF2 prevents overexpression of interferon regulatory factor (IRF)1 and IRF1 targets such as Caspase-1, which are known downstream pro-inflammatory mediators. We also show that Batf2 -/- mice exhibit exacerbated clinical disease severity in a murine model of CNS autoimmunity, characterized by an increase in both CNS immune cell infiltration and demyelination. Batf2 -/- mice also exhibit increased astrocyte-specific expression of IRF1 and Caspase-1, suggesting an amplified interferon response in vivo . Further, we demonstrate that BATF2 is expressed primarily in astrocytes in MS lesions and that this expression is co-localized with IRF1. Collectively, our results further support a protective role for IFNγ and implicate BATF2 as a key suppressor of overactive immune signaling in astrocytes during neuroinflammation.

Basic Science of Neuroinflammation and Involvement of the Inflammatory Response in Disorders of the Nervous System

Neuroinflammation is a key immune response observed in many neurologic diseases. Although an appropriate immune response can be beneficial, aberrant activation of this response recruits excessive proinflammatory cells to cause damage. Because the central nervous system is separated from the periphery by the blood-brain barrier (BBB) that creates an immune-privileged site, it has its own unique immune cells and immune response. Moreover, neuroinflammation can compromise the BBB causing an influx of peripheral immune cells and factors. Recent advances have brought a deeper understanding of neuroinflammation that can be leveraged to develop more potent therapies and improve patient selection.

Deletion of voltage-gated calcium channels in astrocytes decreases neuroinflammation and demyelination in a murine model of multiple sclerosis

The experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis was used in combination with a Cav1.2 conditional knock-out mouse (Cav1.2KO) to study the role of astrocytic voltage-gated Ca++ channels in autoimmune CNS inflammation and demyelination. Cav1.2 channels were specifically ablated in Glast-1-positive astrocytes by means of the Cre-lox system before EAE induction. After immunization, motor activity was assessed daily, and a clinical score was given based on the severity of EAE symptoms. Cav1.2 deletion in astrocytes significantly reduced the severity of the disease. While no changes were found in the day of onset and peak disease severity, EAE mean clinical score was lower in Cav1.2KO animals during the chronic phase of the disease. This corresponded to better performance on the rotarod and increased motor activity in Cav1.2KO mice. Furthermore, decreased numbers of reactive astrocytes, activated microglia, and infiltrating lymphocytes were found in the lumbar section of the spinal cord of Cav1.2KO mice 40 days after immunization. The degree of myelin protein loss and size of demyelinated lesions were also attenuated in Cav1.2KO spinal cords. Similar results were found in EAE animals treated with nimodipine, a Cav1.2 Ca++ channel inhibitor with high affinity to the CNS. Mice injected with nimodipine during the acute and chronic phases of the disease exhibited lower numbers of reactive astrocytes, activated microglial, and infiltrating immune cells, as well as fewer demyelinated lesions in the spinal cord. These changes were correlated with improved clinical scores and motor performance. In summary, these data suggest that antagonizing Cav1.2 channels in astrocytes during EAE alleviates neuroinflammation and protects the spinal cord from autoimmune demyelination.

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.

Chemogenetic manipulation of astrocyte activity at the synapse- a gateway to manage brain disease

Astrocytes are the major glial cell type in the central nervous system (CNS). Initially regarded as supportive cells, it is now recognized that this highly heterogeneous cell population is an indispensable modulator of brain development and function. Astrocytes secrete neuroactive molecules that regulate synapse formation and maturation. They also express hundreds of G protein-coupled receptors (GPCRs) that, once activated by neurotransmitters, trigger intracellular signalling pathways that can trigger the release of gliotransmitters which, in turn, modulate synaptic transmission and neuroplasticity. Considering this, it is not surprising that astrocytic dysfunction, leading to synaptic impairment, is consistently described as a factor in brain diseases, whether they emerge early or late in life due to genetic or environmental factors. Here, we provide an overview of the literature showing that activation of genetically engineered GPCRs, known as Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), to specifically modulate astrocyte activity partially mimics endogenous signalling pathways in astrocytes and improves neuronal function and behavior in normal animals and disease models. Therefore, we propose that expressing these genetically engineered GPCRs in astrocytes could be a promising strategy to explore (new) signalling pathways which can be used to manage brain disorders. The precise molecular, functional and behavioral effects of this type of manipulation, however, differ depending on the DREADD receptor used, targeted brain region and timing of the intervention, between healthy and disease conditions. This is likely a reflection of regional and disease/disease progression-associated astrocyte heterogeneity. Therefore, a thorough investigation of the effects of such astrocyte manipulation(s) must be conducted considering the specific cellular and molecular environment characteristic of each disease and disease stage before this has therapeutic applicability.

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.

Central nervous system demyelinating diseases: glial cells at the hub of pathology

Inflammatory demyelinating diseases (IDDs) are among the main causes of inflammatory and neurodegenerative injury of the central nervous system (CNS) in young adult patients. Of these, multiple sclerosis (MS) is the most frequent and studied, as it affects about a million people in the USA alone. The understanding of the mechanisms underlying their pathology has been advancing, although there are still no highly effective disease-modifying treatments for the progressive symptoms and disability in the late stages of disease. Among these mechanisms, the action of glial cells upon lesion and regeneration has become a prominent research topic, helped not only by the discovery of glia as targets of autoantibodies, but also by their role on CNS homeostasis and neuroinflammation. In the present article, we discuss the participation of glial cells in IDDs, as well as their association with demyelination and synaptic dysfunction throughout the course of the disease and in experimental models, with a focus on MS phenotypes. Further, we discuss the involvement of microglia and astrocytes in lesion formation and organization, remyelination, synaptic induction and pruning through different signaling pathways. We argue that evidence of the several glia-mediated mechanisms in the course of CNS demyelinating diseases supports glial cells as viable targets for therapy development.

Glia Connect Inflammation and Neurodegeneration in Multiple Sclerosis

Multiple sclerosis (MS) is regarded as a chronic inflammatory disease that leads to demyelination and eventually to neurodegeneration. Activation of innate immune cells and other inflammatory cells in the brain and spinal cord of people with MS has been well described. However, with the innovation of technology in glial cell research, we have a deep understanding of the mechanisms of glial cells connecting inflammation and neurodegeneration in MS. In this review, we focus on the role of glial cells, including microglia, astrocytes, and oligodendrocytes, in the pathogenesis of MS. We mainly focus on the connection between glial cells and immune cells in the process of axonal damage and demyelinating neuron loss.

Glia Connect Inflammation and Neurodegeneration in Multiple Sclerosis

Multiple sclerosis (MS) is regarded as a chronic inflammatory disease that leads to demyelination and eventually to neurodegeneration. Activation of innate immune cells and other inflammatory cells in the brain and spinal cord of people with MS has been well described. However, with the innovation of technology in glial cell research, we have a deep understanding of the mechanisms of glial cells connecting inflammation and neurodegeneration in MS. In this review, we focus on the role of glial cells, including microglia, astrocytes, and oligodendrocytes, in the pathogenesis of MS. We mainly focus on the connection between glial cells and immune cells in the process of axonal damage and demyelinating neuron loss.

Potential biological contributers to the sex difference in multiple sclerosis progression

Multiple sclerosis (MS) is an immune-mediated disease that targets the myelin sheath of central nervous system (CNS) neurons leading to axon injury, neuronal death, and neurological progression. Though women are more highly susceptible to developing MS, men that develop this disease exhibit greater cognitive impairment and accumulate disability more rapidly than women. Magnetic resonance imaging and pathology studies have revealed that the greater neurological progression seen in males correlates with chronic immune activation and increased iron accumulation at the rims of chronic white matter lesions as well as more intensive whole brain and grey matter atrophy and axon loss. Studies in humans and in animal models of MS suggest that male aged microglia do not have a higher propensity for inflammation, but may become more re-active at the rim of white matter lesions as a result of the presence of pro-inflammatory T cells, greater astrocyte activation or iron release from oligodendrocytes in the males. There is also evidence that remyelination is more efficient in aged female than aged male rodents and that male neurons are more susceptible to oxidative and nitrosative stress. Both sex chromosome complement and sex hormones contribute to these sex differences in biology.

Oral Administration of Myelin Oligodendrocyte Glycoprotein Attenuates Experimental Autoimmune Encephalomyelitis through Induction of Th2/Treg Cells and Suppression of Th1/Th17 Immune Responses

Multiple Sclerosis (MS) is a demyelinating autoimmune disorder of the central nervous system (CNS). Experimental autoimmune encephalomyelitis (EAE) has been widely used to determine the pathogenesis of the disease and evaluate new treatment strategies for MS. Therefore, we investigated the efficacy of oral administration of a Myelin Oligodendrocyte Glycoprotein (MOG) in the treatment of EAE. Female C57BL/6 mice were utilized in three groups (Control group, received PBS orally; prevention group, oral administration of MOG35–55 two weeks before EAE induction; treatment group, oral administration of MOG35–55 after EAE induction). MOG administration, both as prevention and treatment, significantly controlled clinical score, weight loss, CNS inflammation, and demyelination, mainly through the modulation of T cell proliferation, and reduction in pro-inflammatory cytokines and transcription factors, including TNF-α, IFN-γ, IL-17, T-bet, and ROR-γt. MOG administration, both as prevention and treatment, also induced anti-inflammatory cytokines and transcription factors, including IL-4, TGF-β, GATA-3, and Foxp3. The results showed that oral administration of MOG, both as prevention and treatment, could efficiently control EAE development. Immunomodulatory mechanisms include the induction of Th2 and Treg cells and the suppression of pro-inflammatory Th1 and Th17 cells.

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.

Tumor necrosis factor (TNF) induces astrogliosis, microgliosis and promotes survival of cortical neurons

Objectives

Neuro-inflammation occurs as a sequence of brain injury and is associated with production of cytokines. Cytokines can modulate the function and survival of neurons, microglia and astrocytes. The objective of this study is to examine the effect of TNF on the neurons, microglia and astrocytes in normal brain and stab wound brain injury.

Methods

Normal BALB/c male mice (N) without any injury were subdivided into NA and NB groups. Another set mouse was subjected to stab wound brain injury (I) and were subdivided into IA and IB. NA and IA groups received intraperitoneal injections of TNF (1 µg/kg body weight/day) for nine days, whereas NB and IB groups received intraperitoneal injections of PBS. Animals were killed on 1^st, 2^nd, 3^rd, 7^th, and 9^th day. Frozen brain sections through the injury site in IA and IB or corresponding region in NA and NB groups were stained for neurodegeneration, immunostained for astrocytes, microglia and neurons. Western blotting for GFAP and ELISA for BDNF were done from the tissues collected from all groups.

Results

The number of degenerating neurons significantly decreased in TNF treated groups. There was a significant increase in the number of astrocytes and microglia in TNF treated groups compared to PBS treated groups. In addition, it was found that TNF stimulated the expression of GFAP and BDNF in NA and IA groups.

Conclusions

TNF induces astrogliosis and microgliosis in normal and injured brain and promotes the survival of cortical neurons in stab wound brain injury, may be by upregulating the BDNF level.

Stem Cell Therapies for Progressive Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system characterized by demyelination and axonal degeneration. MS patients typically present with a relapsing-remitting (RR) disease course, manifesting as sporadic attacks of neurological symptoms including ataxia, fatigue, and sensory impairment. While there are several effective disease-modifying therapies able to address the inflammatory relapses associated with RRMS, most patients will inevitably advance to a progressive disease course marked by a gradual and irreversible accrual of disabilities. Therapeutic intervention in progressive MS (PMS) suffers from a lack of well-characterized biological targets and, hence, a dearth of successful drugs. The few medications approved for the treatment of PMS are typically limited in their efficacy to active forms of the disease, have little impact on slowing degeneration, and fail to promote repair. In looking to address these unmet needs, the multifactorial therapeutic benefits of stem cell therapies are particularly compelling. Ostensibly providing neurotrophic support, immunomodulation and cell replacement, stem cell transplantation holds substantial promise in combatting the complex pathology of chronic neuroinflammation. Herein, we explore the current state of preclinical and clinical evidence supporting the use of stem cells in treating PMS and we discuss prospective hurdles impeding their translation into revolutionary regenerative medicines.

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.

Roles of astrocytes in response to aging, Alzheimer's disease and multiple sclerosis

Astrocytes are traditionally recognized for their multiple roles in support of brain function. However, additional changes in these roles are evident in response to brain diseases. In this review, we highlight positive and negative effects of astrocytes in response to aging, Alzheimer's disease and Multiple Sclerosis. We summarize data suggesting that reactive astrocytes may perform critical functions that might be relevant to the etiology of these conditions. In particular, we relate astrocytes effects to actions on synaptic transmission, cognition, and myelination. We suggest that a better understanding of astrocyte functions and how these become altered in response to aging or disease will lead to the appreciation of these cells as useful therapeutic targets.

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.

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.

Protective Functions of Reactive Astrocytes Following Central Nervous System Insult

Astrocytes play important roles in numerous central nervous system disorders including autoimmune inflammatory, hypoxic, and degenerative diseases such as Multiple Sclerosis, ischemic stroke, and Alzheimer’s disease. Depending on the spatial and temporal context, activated astrocytes may contribute to the pathogenesis, progression, and recovery of disease. Recent progress in the dissection of transcriptional responses to varying forms of central nervous system insult has shed light on the mechanisms that govern the complexity of reactive astrocyte functions. While a large body of research focuses on the pathogenic effects of reactive astrocytes, little is known about how they limit inflammation and contribute to tissue regeneration. However, these protective astrocyte pathways might be of relevance for the understanding of the underlying pathology in disease and may lead to novel targeted approaches to treat autoimmune inflammatory and degenerative disorders of the central nervous system. In this review article, we have revisited the emerging concept of protective astrocyte functions and discuss their role in the recovery from inflammatory and ischemic disease as well as their role in degenerative disorders. Focusing on soluble astrocyte derived mediators, we aggregate the existing knowledge on astrocyte functions in the maintenance of homeostasis as well as their reparative and tissue-protective function after acute lesions and in neurodegenerative disorders. Finally, we give an outlook of how these mediators may guide future therapeutic strategies to tackle yet untreatable disorders of the central nervous system.

Astrocyte Crosstalk in CNS Inflammation

Astrocytes control multiple processes in the nervous system in health and disease. It is now clear that specific astrocyte subsets or activation states are associated with specific genomic programs and functions. The advent of novel genomic technologies has enabled rapid progress in the characterization of astrocyte heterogeneity and its control by astrocyte interactions with other cells in the central nervous system (CNS). In this review, we provide an overview of the multifaceted roles of astrocytes in the context of CNS inflammation, highlighting recent discoveries on astrocyte subsets and their regulation. We explore mechanisms of crosstalk between astrocytes and other cells in the CNS in the context of neuroinflammation and neurodegeneration and discuss how these interactions shape pathological outcomes.

The Role of Astrocytes in CNS Inflammation

Astrocytes are the most abundant cell type in the central nervous system (CNS), performing complex functions in health and disease. It is now clear that multiple astrocyte subsets or activation states (plastic phenotypes driven by intrinsic and extrinsic cues) can be identified, associated to specific genomic programs and functions. The characterization of these subsets and the mechanisms that control them may provide unique insights into the pathogenesis of neurologic diseases, and identify potential targets for therapeutic intervention. In this article, we provide an overview of the role of astrocytes in CNS inflammation, highlighting recent discoveries on astrocyte subsets and the mechanisms that control them.

The Gut-CNS Axis in Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune inflammatory disease of the CNS driven by the inflammatory activity of peripheral immune cells recruited to the CNS and by CNS-resident glial cells. MS pathogenesis has been linked to both genetic and environmental factors. In addition, the commensal flora have been shown to modulate immune processes relevant to MS pathogenesis. We discuss the effects of the gut microbiota on T cells and glial cells, and their relevance for the control of inflammation and neurodegeneration in MS. A better understanding of the gut-CNS axis will shed new light on the mechanisms of disease pathogenesis, and may help to guide the development of efficacious therapies for MS.

Impact of Astrocyte Depletion upon Inflammation and Demyelination in a Murine Animal Model of Multiple Sclerosis

Astrocytes play a key role in demyelinating diseases, like multiple sclerosis (MS), although many of their functions remain unknown. The aim of this study was to investigate the impact of astrocyte depletion upon de- and remyelination, inflammation, axonal damage, and virus distribution in Theiler`s murine encephalomyelitis (TME). Groups of two to six glial fibrillary acidic protein (GFAP)-thymidine-kinase transgenic SJL mice and SJL wildtype mice were infected with TME virus (TMEV) or mock (vehicle only). Astrocyte depletion was induced by the intraperitoneal administration of ganciclovir during the early and late phase of TME. The animals were clinically investigated while using a scoring system and a rotarod performance test. Necropsies were performed at 46 and 77 days post infection. Cervical and thoracic spinal cord segments were investigated using hematoxylin and eosin (H&E), luxol fast blue-cresyl violet (LFB), immunohistochemistry targeting Amigo2, aquaporin 4, CD3, CD34, GFAP, ionized calcium-binding adapter molecule 1 (Iba1), myelin basic protein (MBP), non-phosphorylated neurofilaments (np-NF), periaxin, S100A10, TMEV, and immunoelectron microscopy. The astrocyte depleted mice showed a deterioration of clinical signs, a downregulation and disorganization of aquaporin 4 in perivascular astrocytes accompanied by vascular leakage. Furthermore, astrocyte depleted mice showed reduced inflammation and lower numbers of TMEV positive cells in the spinal cord. The present study indicates that astrocyte depletion in virus triggered CNS diseases contributes to a deterioration of clinical signs that are mediated by a dysfunction of perivascular astrocytes.

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.

The contribution of astrocytes to the neuroinflammatory response in multiple sclerosis and experimental autoimmune encephalomyelitis

Neuroinflammation is the coordinated response of the central nervous system (CNS) to threats to its integrity posed by a variety of conditions, including autoimmunity, pathogens and trauma. Activated astrocytes, in concert with other cellular elements of the CNS and immune system, are important players in the modulation of the neuroinflammatory response. During neurological disease, they produce and respond to cellular signals that often lead to dichotomous processes, which can promote further damage or contribute to repair. This occurs also in multiple sclerosis (MS), where astrocytes are now recognized as key components of its immunopathology. Evidence supporting this role has emerged not only from studies in MS patients, but also from animal models, among which the experimental autoimmune encephalomyelitis (EAE) model has proved especially instrumental. Based on this premise, the purpose of the present review is to summarize the current knowledge of astrocyte behavior in MS and EAE. Following a brief description of the pathological characteristics of the two diseases and the main functional roles of astrocytes in CNS physiology, we will delve into the specific responses of this cell population, analyzing MS and EAE in parallel. We will define the temporal and anatomical profile of astroglial activation, then focus on key processes they participate in. These include: (1) production and response to soluble mediators (e.g., cytokines and chemokines), (2) regulation of oxidative stress, and (3) maintenance of BBB integrity and function. Finally, we will review the state of the art on the available methods to measure astroglial activation in vivo in MS patients, and how this could be exploited to optimize diagnosis, prognosis and treatment decisions. Ultimately, we believe that integrating the knowledge obtained from studies in MS and EAE may help not only better understand the pathophysiology of MS, but also uncover new signals to be targeted for therapeutic intervention.

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.

A proliferation-inducing ligand-mediated anti-inflammatory response of astrocytes in multiple sclerosis

OBJECTIVE

The two related tumor necrosis factor members a proliferation-inducing ligand (APRIL) and B-cell activation factor (BAFF) are currently targeted in autoimmune diseases as B-cell regulators. In multiple sclerosis (MS), combined APRIL/BAFF blockade led to unexpected exacerbated inflammation in the central nervous system (CNS) of patients. Here, we investigate the role of the APRIL/BAFF axis in the CNS.

METHODS

APRIL expression was analyzed in MS lesions by immunohistochemistry. The in vivo role of APRIL was assessed in the murine MS model, experimental autoimmune encephalitis (EAE). Functional in vitro studies were performed with human and mouse astrocytes.

RESULTS

APRIL was expressed in lesions from EAE. In its absence, the disease was worst. Lesions from MS patients also showed APRIL expression upon infiltration of macrophages. Notably, all the APRIL secreted by these macrophages specifically targeted astrocytes. The upregulation of chondroitin sulfate proteoglycan, sometimes bearing chondroitin sulfate of type E sugar moieties, binding APRIL, in reactive astrocytes explained the latter selectivity. Astrocytes responded to APRIL by producing a sufficient amount of IL-10 to dampen antigen-specific T-cell proliferation and pathogenic cytokine secretion. Finally, an intraspinal delivery of recombinant APRIL before disease onset, shortly reduced EAE symptoms. Repeated intravenous injections of recombinant APRIL before and even at disease onset also had an effect.

INTERPRETATION

Our data show that APRIL mediates an anti-inflammatory response from astrocytes in MS lesions. This protective activity is not shared with BAFF. ANN NEUROL 2019;85:406-420.

Regulation of Astrocyte Functions in Multiple Sclerosis

Astrocytes play complex roles in health and disease. Here, we review recent findings on molecular pathways that control astrocyte function in multiple sclerosis (MS) as well as new tools for their investigation. In particular, we describe positive and negative regulators of astrocyte-mediated pathogenesis in MS, such as sphingolipid metabolism and aryl hydrocarbon receptor signaling, respectively. In addition, we also discuss the issue of astrocyte heterogeneity and its relevance for the contribution of astrocytes to MS pathogenesis. Finally, we discuss how new genomic tools could transform the study of astrocyte biology in MS.

Antigen-presenting cell diversity for T cell reactivation in central nervous system autoimmunity

Autoreactive T cells are considered the major culprits in the pathogenesis of many autoimmune diseases like multiple sclerosis (MS). Upon activation in the lymphoid organs, autoreactive T cells migrate towards the central nervous system (CNS) and target the myelin sheath-forming oligodendrocytes, resulting in detrimental neurological symptoms. Despite the availability of extensively studied systems like the experimental autoimmune encephalomyelitis (EAE) model, our understanding of this disease and the underlying pathogenesis is still elusive. One vividly discussed subject represents the T cell reactivation in the CNS. In order to exert their effector functions in the CNS, autoreactive T cells must encounter antigen-presenting cells (APCs). This interaction provides an antigen-restricted stimulus in the context of major histocompatibility complex class II (MHC-II) and other co-stimulatory molecules. Peripherally derived dendritic cells (DCs), B cells, border-associated macrophages (BAM), CNS-resident microglia, and astrocytes have the capacity to express molecules required for antigen presentation under inflammatory conditions. Also, endothelial cells can fulfill these prerequisites in certain situations. Which of these cells in fact act as APCs for T cell reactivation and to which extent they can exert this function has been studied intensively, but unfortunately with no firm conclusion. In this review, we will summarize the findings that support or question the antigen presenting capacities of the mentioned cell types of CNS-localized T cell reactivation.

IFN-γ Producing Th1 Cells Induce Different Transcriptional Profiles in Microglia and Astrocytes

Autoreactive T cells that infiltrate into the central nervous system (CNS) are believed to have a significant role in mediating the pathology of neuroinflammatory diseases like multiple sclerosis. Their interaction with microglia and astrocytes in the CNS is crucial for the regulation of neuroinflammatory processes. Our previous work demonstrated that effectors secreted by Th1 and Th17 cells have different capacities to influence the phenotype and function of glial cells. We have shown that Th1-derived effectors altered the phenotype and function of both microglia and astrocytes whereas Th17-derived effectors induced direct effects only on astrocytes but not on microglia. Here we investigated if effector molecules associated with IFN-γ producing Th1 cells induced different gene expression profiles in microglia and astrocytes. We performed a microarray analysis of RNA isolated from microglia and astrocytes treated with medium and Th-derived culture supernatants and compared the gene expression data. By using the criteria of 2-fold change and a false discovery rate of 0.01 (corrected p < 0.01), we demonstrated that a total of 2,106 and 1,594 genes were differentially regulated in microglia and astrocytes, respectively, in response to Th1-derived factors. We observed that Th1-derived effectors induce distinct transcriptional changes in microglia and astrocytes in addition to commonly regulated transcripts. These distinct transcriptional changes regulate peculiar physiological functions, and this knowledge can help to better understand T cell mediated neuropathologies.

Mechanisms underlying dental-derived stem cell-mediated neurorestoration in neurodegenerative disorders

BACKGROUND

Neurodegenerative disorders have a complex pathology and are characterized by a progressive loss of neuronal architecture in the brain or spinal cord. Neuroprotective agents have demonstrated promising results at the preclinical stage, but this has not been confirmed at the clinical stage. Thus far, no neuroprotective drug that can prevent neuronal degeneration in patients with neurodegenerative disorders is available.

MAIN BODY

Recent studies have focused on neurorestorative measures, such as cell-based therapy, rather than neuroprotective treatment. The utility of cell-based approaches for the treatment of neurodegenerative disorders has been explored extensively, and the results have been somewhat promising with regard to reversing the outcome. Because of their neural crest origin, ease of harvest, accessibility, ethical suitability, and potential to differentiate into the neurogenic lineage, dental-derived stem cells (DSCs) have become an attractive source for cell-based neurorestoration therapies. In the present review, we summarize the possible use of DSC-based neurorestoration therapy as an alternative treatment for neurodegenerative disorders, with a particular emphasis on the mechanism underlying recovery in neurodegenerative disorders.

CONCLUSION

Transplantation research in neurodegenerative diseases should aim to understand the mechanism providing benefits both at the molecular and functional level. Due to their ease of accessibility, plasticity, and ethical suitability, DSCs hold promise to overcome the existing challenges in the field of neurodegeneration through multiple mechanisms, such as cell replacement, bystander effect, vasculogenesis, synaptogenesis, immunomodulation, and by inhibiting apoptosis.

Nav1.5 in astrocytes plays a sex-specific role in clinical outcomes in a mouse model of multiple sclerosis

Astrogliosis is a hallmark of neuroinflammatory disorders such as multiple sclerosis (MS). A detailed understanding of the underlying molecular mechanisms governing astrogliosis might facilitate the development of therapeutic targets. We investigated whether Nav1.5 expression in astrocytes plays a role in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), a murine model of MS. We created a conditional knockout of Nav1.5 in astrocytes and determined whether this affects the clinical course of EAE, focal macrophage and T cell infiltration, and diffuse activation of astrocytes. We show that deletion of Nav1.5 from astrocytes leads to significantly worsened clinical outcomes in EAE, with increased inflammatory infiltrate in both early and late stages of disease, unexpectedly, in a sex-specific manner. Removal of Nav1.5 in astrocytes leads to increased inflammation in female mice with EAE, including increased astroglial response and infiltration of T cells and phagocytic monocytes. These cellular changes are consistent with more severe EAE clinical scores. Additionally, we found evidence suggesting possible dysregulation of the immune response-particularly with regard to infiltrating macrophages and activated microglia-in female Nav1.5 KO mice compared with WT littermate controls. Together, our results show that deletion of Nav1.5 from astrocytes leads to significantly worsened clinical outcomes in EAE, with increased inflammatory infiltrate in both early and late stages of disease, in a sex-specific manner.

Hyaluronan in immune dysregulation and autoimmune diseases

The tissue microenvironment contributes to local immunity and to the pathogenesis of autoimmune diseases - a diverse set of conditions characterized by sterile inflammation, immunity against self-antigens, and destruction of tissues. However, the specific factors within the tissue microenvironment that contribute to local immune dysregulation in autoimmunity are poorly understood. One particular tissue component implicated in multiple autoimmune diseases is hyaluronan (HA), an extracellular matrix (ECM) polymer. HA is abundant in settings of chronic inflammation and contributes to lymphocyte activation, polarization, and migration. Here, we first describe what is known about the size, amount, and distribution of HA at sites of autoimmunity and in associated lymphoid structures in type 1 diabetes, multiple sclerosis, and rheumatoid arthritis. Next, we examine the recent literature on HA and its impact on adaptive immunity, particularly in regards to the biology of lymphocytes and Foxp3+ regulatory T-cells (Treg), a T-cell subset that maintains immune tolerance in healthy individuals. We propose that HA accumulation at sites of chronic inflammation creates a permissive environment for autoimmunity, characterized by CD44-mediated inhibition of Treg expansion. Finally, we address potential tools and strategies for targeting HA and its receptor CD44 in chronic inflammation and autoimmunity.

Ndrg2 deficiency ameliorates neurodegeneration in experimental autoimmune encephalomyelitis

N-myc downstream-regulated gene 2 (NDRG2) is a differentiation- and stress-associated molecule that is predominantly expressed in astrocytes in the central nervous system. In this study, we examined the expression and role of NDRG2 in experimental autoimmune encephalomyelitis (EAE), which is an animal model of multiple sclerosis. Western blot and immunohistochemical analysis revealed that the expression of NDRG2 was observed in astrocytes of spinal cord, and was enhanced after EAE induction. A comparative analysis of wild-type and Ndrg2^-/- mice revealed that deletion of Ndrg2 ameliorated the clinical symptoms of EAE. Although Ndrg2 deficiency only slightly affected the inflammatory response, based on the results of flow cytometry, qRT-PCR, and immunohistochemistry, it significantly reduced demyelination in the chronic phase, and, more importantly, neurodegeneration both in the acute and chronic phases. Further studies revealed that the expression of astrocytic glutamate transporters, including glutamate aspartate transporter (GLAST) and glutamate transporter 1, was more maintained in the Ndrg2^-/- mice compared with wild-type mice after EAE induction. Consistent with these results, studies using cultured astrocytes revealed that Ndrg2 gene silencing increased the expression of GLAST, while NDRG2 over-expression decreased it without altering the expression of glial fibrillary acidic protein. The effect of NDRG2 on GLAST expression was associated with the activation of Akt, but not with the activation of nuclear factor-kappa B. These findings suggest that NDRG2 plays a key role in the pathology of EAE by modulating glutamate metabolism. Cover Image for this Issue: doi: 10.1111/jnc.14173.

Effectors of Th1 and Th17 cells act on astrocytes and augment their neuroinflammatory properties

Background

Autoreactive Th1 and Th17 cells are believed to mediate the pathology of multiple sclerosis in the central nervous system (CNS). Their interaction with microglia and astrocytes in the CNS is crucial for the regulation of the neuroinflammation. Previously, we have shown that only Th1 but not Th17 effectors activate microglia. However, it is not clear which cells are targets of Th17 effectors in the CNS.

Methods

To understand the effects driven by Th17 cells in the CNS, we induced experimental autoimmune encephalomyelitis in wild-type mice and CD4⁺ T cell-specific integrin α4-deficient mice where trafficking of Th1 cells into the CNS was affected. We compared microglial and astrocyte response in the brain and spinal cord of these mice. We further treated astrocytes with supernatants from highly pure Th1 and Th17 cultures and assessed the messenger RNA expression of neurotrophic factors, cytokines and chemokines, using real-time PCR. Data obtained was analyzed using the Kruskal-Wallis test.

Results

We observed in α4-deficient mice weak microglial activation but comparable astrogliosis to that of wild-type mice in the regions of the brain populated with Th17 infiltrates, suggesting that Th17 cells target astrocytes and not microglia. In vitro, in response to supernatants from Th1 and Th17 cultures, astrocytes showed altered expression of neurotrophic factors, pro-inflammatory cytokines and chemokines. Furthermore, increased expression of chemokines in Th1- and Th17-treated astrocytes enhanced recruitment of microglia and transendothelial migration of Th17 cells in vitro.

Conclusion

Our results demonstrate the delicate interaction between T cell subsets and glial cells and how they communicate to mediate their effects. Effectors of Th1 act on both microglia and astrocytes whereas Th17 effectors preferentially target astrocytes to promote neuroinflammation.

Electronic supplementary material

The online version of this article (10.1186/s12974-017-0978-3) contains supplementary material, which is available to authorized users.

Bifidobacterium animalis in combination with human origin of Lactobacillus plantarum ameliorate neuroinflammation in experimental model of multiple sclerosis by altering CD4+ T cell subset balance

BACKGROUND

Multiple Sclerosis (MS) is a chronic inflammatory autoimmune disease of the central nervous system (CNS). Recent reports have shown that probiotics can induce immunomodulatory activity with promising effects in inflammatory diseases. This study was designed to reveal the molecular and cellular mechanisms underlying the effect of Lactobacillus plantarum A7, which comprises human commensal bacteria, and Bifidobacterium animalis, a potential probiotic strain, on alleviation of experimental autoimmune encephalomyelitis (EAE), an animal model of MS.

METHODS

To evaluate the therapeutic effects of probiotic strains, female C57BL/6 mice (8-10 wks old) received Lactobacillus plantarum A7, Bifidobacterium animalis PTCC 1631or a mixture of both strains through oral administration daily for 22days beginning simultaneous with induction of EAE. The clinical parameters were recorded daily. On Day 22, each mouse was bled, and their spinal cord was removed for histology analysis. The effects of the treatments on regulatory T (Treg) cells level were evaluated using flow cytometry, and T-cell proliferation was assessed using a BrdU incorporation assay. The supernatants of spleen and lymph nodes cultured and mononuclear cells were collected for quantification of different panel of pro and anti-inflammatory cytokines by ELISA. The analysis of gene expression was performed at RNA level for transcription factors by real-time PCR.

RESULTS

The results showed that treatment with a mixture of the two strains caused a more significant delay in the time of disease onset and clinical score compared to when the strains were used alone. The pathological features of the disease, such as mononuclear infiltration into the CNS, were also inhibited more significantly by the combinational approach. The results also revealed that treatment with combination of both strains enhanced the population of CD4⁺CD25⁺Foxp3⁺-expressing T-cells in the lymph nodes and the spleen.

TREATMENT

with our probiotic strains markedly inhibited disease associated cytokines while increased anti-inflammatory cytokines. Additionally, L. plantarumA7 and B. animalis ameliorated EAE condition by favoring Th2 and Treg differentiation via up-regulation of Foxp3 and GATA3 in the brain and spleen as well as inhibited the differentiation of Th1 and Th17 cells.

CONCLUSIONS

The current research provided evidence that probiotic therapy with L. plantarum and B. animalis can effectively attenuate EAE progression as well as reinforce the polarization of regulatory T-cells.

Astrocytes to the rescue! Glia limitans astrocytic endfeet control CNS inflammation

The blood-brain barrier (BBB) and the glia limitans serve to prevent the migration of cells and other large molecules from the blood into the CNS. Neuroinflammatory diseases are characterized by disruption of the BBB and increased leukocyte infiltration into the CNS. In this issue of the JCI, Horng and colleagues demonstrate that astrocytes of the glia limitans induce tight junction formation in response to inflammatory cues, thereby tightening the border to limit the number of activated T cells infiltrating the CNS. Moreover, preventing the formation of this inducible barrier in mice increased disease severity in models of neuroinflammation. Together, the results of this study indicate that the inducible barrier of the glia limitans should be further explored as a therapeutic target.

A Refined Bead-Free Method to Identify Astrocytic Exosomes in Primary Glial Cultures and Blood Plasma

Astrocytes are the most abundant glial cell type in the central nervous system (CNS) and are known to fulfill critical homeostatic functions. Dysfunction of activated astrocytes is also known to participate in the development of several neurological diseases. Astrocytes can be uniquely identified by expression of the intermediate filament protein glial acidic fibrillary protein (GFAP). Herein, we report on the development of a rigorous and sensitive methodology to identify GFAP+ exosomes in primary culture using flow cytometry. We then demonstrate that activated astrocytes release increased amounts of exosomes in response to treatment with interleukin-1β. Using this methodology, we report the identification of GFAP+ exosomes in blood and then use a mouse model of inflammatory demyelination, experimental autoimmune encephalomyelitis (EAE), to examine whether the abundance of GFAP+ exosomes in blood circulation changes during clinical illness. We find a detectable increase in the presence of GFAP+ exosomes in EAE mice when compared with non-EAE, control mice. Our data provide a novel perspective on the presence of GFAP in blood as it identifies exosomes as potential astrocyte-derived signals within blood. These data are complementary to previous clinical studies that reported elevated GFAP protein in blood samples from multiple sclerosis (MS) patients during a clinical relapse. These data also reveal the existence of a potential systemic role for astrocyte-derived exosomes in CNS conditions involving inflammation such as multiple sclerosis.

Curcumin inhibits glial scar formation by suppressing astrocyte-induced inflammation and fibrosis in vitro and in vivo

Spinal cord injury (SCI) leads to glial scar formation by astrocytes, which severely hinders neural regeneration. Curcumin (cur) can inhibit glial scar formation, but the underlying mechanism is not fully understood. Using both in vivo and in vitro experiments, the current study investigated the phenotypic transformation of astrocytes following cur and siRNA intervention during the processes of inflammation and fibrosis and determined details of the relationship between cur treatment and the glial scar components GFAP and CSPG. We found that cur and NF-κb p65 siRNA could inhibit astrocyte activation through suppressing NF-κb signaling pathway, which led to down-regulate the expression of chemokines MCP-1, RANTES and CXCL10 released by astrocytes and decreased macrophage and T-cell infiltration, thus reducing the inflammation in the glial scar. In addition, silencing SOX-9 may reduce the deposition of extracellular matrix CSPG; whereas its over-expression could increase the CSPG expression. Cur suppressedSOX-9-inducedCSPG deposition, reduced α-SMA (an important symbol of fibrosis) expression in astrocytes, altered astrocyte phenotype, and inhibited glial scar formation by regulating fibrosis. This study confirmed that cur could regulate both the NF-κb and SOX9 signaling pathways and reduce the expression of intracellular and extracellular glial scar components through dual-target regulating both inflammation and fibrosis after SCI in the rat. This study provides an important hypothesis centered on the dual inhibition of intracellular and extracellular glial scar components as a treatment strategy for SCI.

Precision Medicine in Multiple Sclerosis: Future of PET Imaging of Inflammation and Reactive Astrocytes

Non-invasive molecular imaging techniques can enhance diagnosis to achieve successful treatment, as well as reveal underlying pathogenic mechanisms in disorders such as multiple sclerosis (MS). The cooperation of advanced multimodal imaging techniques and increased knowledge of the MS disease mechanism allows both monitoring of neuronal network and therapeutic outcome as well as the tools to discover novel therapeutic targets. Diverse imaging modalities provide reliable diagnostic and prognostic platforms to better achieve precision medicine. Traditionally, magnetic resonance imaging (MRI) has been considered the golden standard in MS research and diagnosis. However, positron emission tomography (PET) imaging can provide functional information of molecular biology in detail even prior to anatomic changes, allowing close follow up of disease progression and treatment response. The recent findings support three major neuroinflammation components in MS: astrogliosis, cytokine elevation, and significant changes in specific proteins, which offer a great variety of specific targets for imaging purposes. Regardless of the fact that imaging of astrocyte function is still a young field and in need for development of suitable imaging ligands, recent studies have shown that inflammation and astrocyte activation are related to progression of MS. MS is a complex disease, which requires understanding of disease mechanisms for successful treatment. PET is a precise non-invasive imaging method for biochemical functions and has potential to enhance early and accurate diagnosis for precision therapy of MS. In this review we focus on modulation of different receptor systems and inflammatory aspect of MS, especially on activation of glial cells, and summarize the recent findings of PET imaging in MS and present the most potent targets for new biomarkers with the main focus on experimental MS research.

Targeting the thrombin receptor modulates inflammation and astrogliosis to improve recovery after spinal cord injury

The deregulation of serine protease activity is a common feature of neurological injury, but little is known regarding their mechanisms of action or whether they can be targeted to facilitate repair. In this study we demonstrate that the thrombin receptor (Protease Activated Receptor 1, (PAR1)) serves as a critical translator of the spinal cord injury (SCI) proteolytic microenvironment into a cascade of pro-inflammatory events that contribute to astrogliosis and functional decline. PAR1 knockout mice displayed improved locomotor recovery after SCI and reduced signatures of inflammation and astrogliosis, including expression of glial fibrillary acidic protein (GFAP), vimentin, and STAT3 signaling. SCI-associated elevations in pro-inflammatory cytokines such as IL-1β and IL-6 were also reduced in PAR1-/- mice and co-ordinate improvements in tissue sparing and preservation of NeuN-positive ventral horn neurons, and PKCγ corticospinal axons, were observed. PAR1 and its agonist's thrombin and neurosin were expressed by perilesional astrocytes and each agonist increased the production of IL-6 and STAT3 signaling in primary astrocyte cultures in a PAR1-dependent manner. In turn, IL-6-stimulated astrocytes increased expression of PAR1, thrombin, and neurosin, pointing to a model in which PAR1 activation contributes to increased astrogliosis by feedforward- and feedback-signaling dynamics. Collectively, these findings identify the thrombin receptor as a key mediator of inflammation and astrogliosis in the aftermath of SCI that can be targeted to reduce neurodegeneration and improve neurobehavioral recovery.

Astrocytes: Key Regulators of Neuroinflammation

Astrocytes are crucial regulators of innate and adaptive immune responses in the injured central nervous system. Depending on timing and context, astrocyte activity may exacerbate inflammatory reactions and tissue damage, or promote immunosuppression and tissue repair. Recent literature has unveiled key factors and intracellular signaling pathways that govern astrocyte behavior during neuroinflammation. Here we have re-visited in vivo studies on astrocyte signaling in neuroinflammatory models focusing on evidences obtained from the analysis of transgenic mice where distinct genes involved in ligand binding, transcriptional regulation and cell communication have been manipulated in astrocytes. The integration of in vivo observations with in vitro data clarifies precise signaling steps, highlights the crosstalk among pathways and identifies shared effector mechanisms in neuroinflammation.

Oligodendrocyte, Astrocyte, and Microglia Crosstalk in Myelin Development, Damage, and Repair

Oligodendrocytes are the myelinating glia of the central nervous system. Myelination of axons allows rapid saltatory conduction of nerve impulses and contributes to axonal integrity. Devastating neurological deficits caused by demyelinating diseases, such as multiple sclerosis, illustrate well the importance of the process. In this review, we focus on the positive and negative interactions between oligodendrocytes, astrocytes, and microglia during developmental myelination and remyelination. Even though many lines of evidence support a crucial role for glia crosstalk during these processes, the nature of such interactions is often neglected when designing therapeutics for repair of demyelinated lesions. Understanding the cellular and molecular mechanisms underlying glial cell communication and how they influence oligodendrocyte differentiation and myelination is fundamental to uncover novel therapeutic strategies for myelin repair.

Hyaluronan synthesis is necessary for autoreactive T-cell trafficking, activation, and Th1 polarization

The extracellular matrix polysaccharide hyaluronan (HA) accumulates at sites of autoimmune inflammation, including white matter lesions in multiple sclerosis (MS), but its functional importance in pathogenesis is unclear. We have evaluated the impact of 4-methylumbelliferone (4-MU), an oral inhibitor of HA synthesis, on disease progression in the experimental autoimmune encephalomyelitis (EAE) mouse model of MS. Treatment with 4-MU decreases the incidence of EAE, delays its onset, and reduces the severity of established disease. 4-MU inhibits the activation of autoreactive T cells and prevents their polarization toward a Th1 phenotype. Instead, 4-MU promotes polarization toward a Th2 phenotpye and induction of Foxp3(+) regulatory T cells. Further, 4-MU hastens trafficking of T cells through secondary lymphoid organs, impairs the infiltration of T cells into the CNS parenchyma, and limits astrogliosis. Together, these data suggest that HA synthesis is necessary for disease progression in EAE and that treatment with 4-MU may be a potential therapeutic strategy in CNS autoimmunity. Considering that 4-MU is already a therapeutic, called hymecromone, that is approved to treat biliary spasm in humans, we propose that it could be repurposed to treat MS.

Oligodendrocyte, Astrocyte, and Microglia Crosstalk in Myelin Development, Damage, and Repair

Oligodendrocytes are the myelinating glia of the central nervous system. Myelination of axons allows rapid saltatory conduction of nerve impulses and contributes to axonal integrity. Devastating neurological deficits caused by demyelinating diseases, such as multiple sclerosis, illustrate well the importance of the process. In this review, we focus on the positive and negative interactions between oligodendrocytes, astrocytes, and microglia during developmental myelination and remyelination. Even though many lines of evidence support a crucial role for glia crosstalk during these processes, the nature of such interactions is often neglected when designing therapeutics for repair of demyelinated lesions. Understanding the cellular and molecular mechanisms underlying glial cell communication and how they influence oligodendrocyte differentiation and myelination is fundamental to uncover novel therapeutic strategies for myelin repair.