Astrocytes In Multiple Sclerosis Research Articles

Astrocytic TIMP-1 regulates production of Anastellin, an inhibitor of oligodendrocyte differentiation and FTY720 responses

Astrocyte activation is associated with neuropathology and the production of tissue inhibitor of metalloproteinase-1 (TIMP1). TIMP1 is a pleiotropic extracellular protein that functions both as a protease inhibitor and as a growth factor. Astrocytes that lack expression of Timp1 do not support rat oligodendrocyte progenitor cell (rOPC) differentiation, and adult global Timp1 knockout (Timp1KO) mice do not efficiently remyelinate following a demyelinating injury. Here, we performed an unbiased proteomic analysis and identified a fibronectin-derived peptide called Anastellin (Ana) that was unique to the Timp1KO astrocyte secretome. Ana was found to block rOPC differentiation in vitro and enhanced the inhibitory influence of fibronectin on rOPC differentiation. Ana is known to act upon the sphingosine-1-phosphate receptor 1, and we determined that Ana also blocked the pro-myelinating effect of FTY720 (or fingolimod) on rOPC differentiation in vitro. Administration of FTY720 to wild-type C57BL/6 mice during MOG35-55-experimental autoimmune encephalomyelitis ameliorated clinical disability while FTY720 administered to mice lacking expression of Timp1 (Timp1KO) had no effect. Analysis of Timp1 and fibronectin (FN1) transcripts from primary human astrocytes from healthy and multiple sclerosis (MS) donors revealed lower TIMP1 expression was coincident with elevated FN1 in MS astrocytes. Last, analyses of proteomic databases of MS samples identified Ana peptides to be more abundant in the cerebrospinal fluid (CSF) of human MS patients with high disease activity. A role for Ana in MS as a consequence of a lack of astrocytic TIMP-1 production could influence both the efficacy of fingolimod responses and innate remyelination potential in the MS brain.

Synaptic pathology in multiple sclerosis: a role for Nogo-A signaling in astrocytes?

Synaptic pathology in multiple sclerosis: a role for Nogo-A signaling in astrocytes?

The Role of the Proinflammatory and Anti-inflammatory Cytokines in Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disease affecting 2.5 million individuals globally. MS majorly affects younger adults, especially women, than males having an incidence ratio of 3:1. MS conditions are characterized by demyelination, axonal deterioration, gliosis, heterogeneous lesions, and lymphocytes entrance infiltrates into the CNS by breaching the blood brain barrier and leading to concurrent relapse remitting episodes. Environmental Factors have an essential role in the etiopathogenesis of the disease. The leukocytes infiltrate secrete the immune mediator's cytokines responsible for the inflammation milieu in the CNS and the disease progression through immune-mediated neurodegeneration. The Cytokines are the small protein molecules secreted for facilitating communication among other cells conducting a complex multicellular behavior. This review aims to discuss the role of the proinflammatory cytokines such as GM-CSF, IL-17, Il-6, IL-1β, IL-22, INF-γ accountable for the initiating and the MS progression. Even though the objective behind these inflammatory mediators' production is to protect the CNS tissue from further impairment, on the contrary sometimes they may severely damage the neurons, myelin sheath, and the other glial cells oligodendrocytes, microglia, and astrocytes in MS due to their pleiotropic nature whereas, the anti inflammatory cytokines such as IL-4 and IL-10 may possess protective role against MS which could potentially be a novel drug target and could lead us towards a new promising treatment for MS in the future.

MS-Driven Metabolic Alterations Are Recapitulated in iPSC-Derived Astrocytes.

ObjectiveAstrocytes play a significant role in the pathology of multiple sclerosis (MS). Nevertheless, for ethical reasons, most studies in these cells were performed using the Experimental Autoimmune Encephalomyelitis model. As there are significant differences between human and mouse cells, we aimed here to better characterize astrocytes from patients with MS (PwMS), focusing mainly on mitochondrial function and cell metabolism.MethodsWe obtained and characterized induced pluripotent stem cell (iPSC)‐derived astrocytes from three PwMS and three unaffected controls, and performed electron microscopy, flow cytometry, cytokine and glutamate measurements, gene expression, in situ respiration, and metabolomics. We validated our findings using a single‐nuclei RNA sequencing dataset.ResultsWe detected several differences in MS astrocytes including: (i) enrichment of genes associated with neurodegeneration, (ii) increased mitochondrial fission, (iii) increased production of superoxide and MS‐related proinflammatory chemokines, (iv) impaired uptake and enhanced release of glutamate, (v) increased electron transport capacity and proton leak, in line with the increased oxidative stress, and (vi) a distinct metabolic profile, with a deficiency in amino acid catabolism and increased sphingolipid metabolism, which have already been linked to MS.InterpretationHere we describe the metabolic profile of iPSC‐derived astrocytes from PwMS and validate this model as a very powerful tool to study disease mechanisms and to perform non‐invasive drug targeting assays in vitro. Our findings recapitulate several disease features described in patients and provide new mechanistic insights into the metabolic rewiring of astrocytes in MS, which could be targeted in future therapeutic studies. ANN NEUROL 2022;91:652–669

Astrocyte-Derived Pleiotrophin Mitigates Late-Stage Autoimmune CNS Inflammation.

Astrocytes are the most abundant glial cells in the central nervous system (CNS) with the capacity to sense and react to injury and inflammatory events. While it has been widely documented that astrocytes can exert tissue-degenerative functions, less is known about their protective and disease-limiting roles. Here, we report the upregulation of pleiotrophin (PTN) by mouse and human astrocytes in multiple sclerosis (MS) and its preclinical model experimental autoimmune encephalomyelitis (EAE). Using CRISPR-Cas9-based genetic perturbation systems, we demonstrate in vivo that astrocyte-derived PTN is critical for the recovery phase of EAE and limits chronic CNS inflammation. PTN reduces pro-inflammatory signaling in astrocytes and microglia and promotes neuronal survival following inflammatory challenge. Finally, we show that intranasal administration of PTN during the late phase of EAE successfully reduces disease severity, making it a potential therapeutic candidate for the treatment of progressive MS, for which existing therapies are limited.

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.

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.

MAFG-driven astrocytes promote CNS inflammation.

Multiple sclerosis is a chronic inflammatory disease of the CNS1. Astrocytes contribute to the pathogenesis of multiple sclerosis2, but little is known about the heterogeneity of astrocytes and its regulation. Here we report the analysis of astrocytes in multiple sclerosis and its preclinical model experimental autoimmune encephalomyelitis (EAE) by single-cell RNA sequencing in combination with cell-specific Ribotag RNA profiling, assay for transposase-accessible chromatin with sequencing (ATAC-seq), chromatin immunoprecipitation with sequencing (ChIP-seq), genome-wide analysis of DNA methylation and in vivo CRISPR-Cas9-based genetic perturbations. We identified astrocytes in EAE and multiple sclerosis that were characterized by decreased expression of NRF2 and increased expression of MAFG, which cooperates with MAT2α to promote DNA methylation and represses antioxidant and anti-inflammatory transcriptional programs. Granulocyte-macrophage colony-stimulating factor (GM-CSF) signalling in astrocytes drives the expression of MAFG and MAT2α and pro-inflammatory transcriptional modules, contributing to CNS pathology in EAE and, potentially, multiple sclerosis. Our results identify candidate therapeutic targets in multiple sclerosis.

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

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. 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. 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. 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.

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.

Clonal Glial Response in a Multiple Sclerosis Mouse Model.

Multiple sclerosis (MS) is an autoimmune disease causing central nervous system (CNS) demyelination and axonal injury. In the last years the importance of astrocytes in MS is rapidly increasing, recognizing astrocytes as highly active players in MS pathogenesis. Usually the role assigned to astrocytes in MS lesions has been the formation of the glial scar, but now their implication during lesion formation and the immune response increasingly recognized. Since astrocytes are a heterogeneous cell population with diverse roles in the CNS, the aim of this study was to analyze the putative clonal response of astrocytes in a demyelinating scenario. To undertake this aim, we used the induced experimental autoimmune encephalomyelitis (EAE) as a murine model for MS in previously electroporated mice with in vivo multicolor lineage tracing system, the StarTrack methodology. Our data revealed a variety of morphological changes that were different among distinct clones. In many cases, cells of the same clone responded equally to the injury, while in other cases clonally-related cells responded differently to the injury. Therefore, whereas some clones exhibited a strong morphological alteration, other clones located at similar distances to the lesion were apparently unresponsive. Thus, at present there is no compelling evidences that clonal relationship influences the position or function of astrocytes in the EAE model. Further, the coexistence of different astroglial clonal responses to the bran injury reveals the significance of development to determine the astrocyte features that respond to brain injuries.

The Role of Astrocytes in Multiple Sclerosis.

The role traditionally assigned to astrocytes in the pathogenesis of multiple sclerosis (MS) lesions has been the formation of the glial scar once inflammation has subsided. Astrocytes are now recognized to be early and highly active players during lesion formation and key for providing peripheral immune cells access to the central nervous system. Here, we review the role of astrocytes in the formation and evolution of MS lesions, including the recently described functional polarization of astrocytes, discuss prototypical pathways for astrocyte activation, and summarize mechanisms by which MS treatments affect astrocyte function.

Anti-SPAG16 antibodies in primary progressive multiple sclerosis are associated with an elevated progression index.

Sperm-associated antigen 16 (SPAG16), a sperm protein which is upregulated in reactive astrocytes in multiple sclerosis (MS) lesions, has recently been identified as a novel autoantibody target in MS. The aim of this study was to investigate whether anti-SPAG16 antibody levels differ between MS subtypes (relapsing-remitting, RR; primary or secondary progressive, PP, SP) and whether antibody positivity is associated with clinical characteristics. Plasma anti-SPAG16 antibody levels were determined by recombinant protein enzyme-linked immunosorbent assay (ELISA) in 374 MS patients (274 RRMS, 39 SPMS and 61 PPMS) and 106 healthy controls. Significantly elevated anti-SPAG16 antibodies were found in 22% of MS patients with 93% specificity. Anti-SPAG16 seropositivity was associated with an increased Expanded Disability Status Scale (EDSS) in overall MS. A higher proportion of PPMS patients showed anti-SPAG16 antibody reactivity (34%) compared to RRMS (19%) and SPMS (26%), and presented with higher anti-SPAG16 antibody levels. Seropositive PPMS patients had a significantly increased progression index compared to seronegative patients. Anti-SPAG16 antibodies are associated with an increased EDSS in overall MS, indicating that they are linked to a worse MS disease outcome. Moreover, the presence of anti-SPAG16 antibodies may be a biomarker for a more severe disease in PPMS patients, as indicated by an increased progression index.

Endothelin-B Receptor Activation in Astrocytes Regulates the Rate of Oligodendrocyte Regeneration during Remyelination

Reactive astrogliosis is an essential and ubiquitous response to CNS injury, but in some cases, aberrant activation of astrocytes and their release of inhibitory signaling molecules can impair endogenous neural repair processes. Our lab previously identified a secreted intercellular signaling molecule, called endothelin-1 (ET-1), which is expressed at high levels by reactive astrocytes in multiple sclerosis (MS) lesions and limits repair by delaying oligodendrocyte progenitor cell (OPC) maturation. However, as ET receptors are widely expressed on neural cells, the cell- and receptor-specific mechanisms of OPC inhibition by ET-1 action remain undefined. Using pharmacological approaches and cell-specific endothelin receptor (EDNR) ablation, we show that ET-1 acts selectively through EDNRB on astrocytes--and not OPCs--to indirectly inhibit remyelination. These results demonstrate that targeting specific pathways in reactive astrocytes represents a promising therapeutic target in diseases with extensive reactive astrogliosis, including MS.

White-Matter Astrocytes, Axonal Energy Metabolism, and Axonal Degeneration in Multiple Sclerosis

In patients with multiple sclerosis (MS), a diffuse axonal degeneration occurring throughout the white matter of the central nervous system causes progressive neurologic disability. The underlying mechanism is unclear. This review describes a number of pathways by which dysfunctional astrocytes in MS might lead to axonal degeneration. White-matter astrocytes in MS show a reduced metabolism of adenosine triphosphate-generating phosphocreatine, which may impair the astrocytic sodium potassium pump and lead to a reduced sodium-dependent glutamate uptake. Astrocytes in MS white matter appear to be deficient in β(2) adrenergic receptors, which are involved in stimulating glycogenolysis and suppressing inducible nitric oxide synthase (NOS2). Glutamate toxicity, reduced astrocytic glycogenolysis leading to reduced lactate and glutamine production, and enhanced nitric oxide (NO) levels may all impair axonal mitochondrial metabolism, leading to axonal degeneration. In addition, glutamate-mediated oligodendrocyte damage and impaired myelination caused by a decreased production of N-acetylaspartate by axonal mitochondria might also contribute to axonal loss. White-matter astrocytes may be considered as a potential target for neuroprotective MS therapies.

Astrocytes in multiple sclerosis: a product of their environment.

It has long been thought that astrocytes, like other glial cells, simply provide a support mechanism for neuronal function in the healthy and inflamed central nervous system (CNS). However, recent evidence suggests that astrocytes play an active and dual role in CNS inflammatory diseases such as multiple sclerosis (MS). Astrocytes not only have the ability to enhance immune responses and inhibit myelin repair, but they can also be protective and limit CNS inflammation while supporting oligodendrocyte and axonal regeneration. The particular impact of these cells on the pathogenesis and repair of an inflammatory demyelinating process is dependent upon a number of factors, including the stage of the disease, the type and microenvironment of the lesion, and the interactions with other cell types and factors that influence their activation. In this review, we summarize recent data supporting the idea that astrocytes play a complex role in the regulation of CNS autoimmunity.

Angiotensin II Controls Occludin Function and Is Required for Blood–Brain Barrier Maintenance: Relevance to Multiple Sclerosis

The blood-brain barrier (BBB) restricts molecular and cellular trafficking between the blood and the CNS. Although astrocytes are known to control BBB permeability, the molecular determinants of this effect remain unknown. We show that angiotensinogen (AGT) produced and secreted by astrocytes is cleaved into angiotensin II (AngII) and acts on type 1 angiotensin receptors (AT1) expressed by BBB endothelial cells (ECs). Activation of AT1 restricts the passage of molecular tracers across human BBB-derived ECs through threonine-phosphorylation of the tight junction protein occludin and its mobilization to lipid raft membrane microdomains. We also show that AGT knock-out animals have disorganized occludin strands at the level of the BBB and a diffuse accumulation of the endogenous serum protein plasminogen in the CNS, compared with wild-type animals. Finally, we demonstrate a reduction in the number of AGT-immunopositive perivascular astrocytes in multiple sclerosis (MS) lesions, which correlates with a reduced expression of occludin similarly seen in the CNS of AGT knock-out animals. Such a reduction in astrocyte-expressed AGT and AngII is dependent, in vitro, on the proinflammatory cytokines tumor necrosis factor-alpha and interferon-gamma. Our study defines a novel physiological role for AngII in the CNS and suggests that inflammation-induced downregulation of AngII production by astrocytes is involved in BBB dysfunction in MS lesions.

A Proliferation‐inducing Ligand (APRIL) is Expressed by Astrocytes and is Increased in Multiple Sclerosis

A proliferation-inducing ligand (APRIL) is a newly described member of the tumour necrosis factor (TNF) superfamily that was first identified as a factor favouring tumorigenesis. APRIL is also important for several immune functions, including B-cell survival. Multiple sclerosis (MS) is an inflammatory, demyelinating disease of the central nervous system (CNS) that is commonly diagnosed in early adulthood. Several TNF superfamily members have been identified in brains of patients with MS, although their exact function within the CNS is presently unknown. To investigate whether APRIL is expressed in the CNS, we studied APRIL protein expression by immunohistochemistry in MS patients and controls. Morphologically, APRIL-positive cells appeared to be astrocytes. A two-colour immunohistochemistry revealed that APRIL expression was cytoplasmic, granular and restricted to GFAP-positive cells. Conversely, HLA class II-positive microglial cells were negative for APRIL expression. APRIL-positive cells were fewer in brains of controls compared with those with MS. We further corroborated our findings by studying APRIL protein expression in several glioblastoma cell lines, and found APRIL to be expressed by most cell lines analysed. APRIL's binding partner syndecan-1 (CD138) was detected in brains of neither MS nor control patients. Furthermore, B cells were detectable in the brain of one of five patients with MS. We conclude that APRIL is expressed by reactive astrocytes in MS and may be of relevance in gliotic scar formation.

Role for CXCR2 and CXCL1 on glia in multiple sclerosis

As part of a need to understand myelin repair mechanisms, molecular pathways underlying oligodendrocyte behavior and central nervous system (CNS) remyelination are currently key topics in multiple sclerosis (MS). In the present study, we report expression of a chemoattractant receptor of the immune system, the chemokine receptor, CXCR2, on normal and proliferating oligodendrocytes in active MS lesions. Proliferating oligodendrocytes were occasionally associated with reactive astrocytes positive for CXCL1 (GRO-alpha), the ligand for CXCR2. CXCL1 expression was not seen on astrocytes in control and normal CNS tissue, while CXCR2 expression was constitutive on oligodendrocytes. At the functional level, following stimulation with the proinflammatory cytokine, interleukin-1beta (IL-1beta), we found high-level synthesis of CXCL1 by human fetal astrocytes in vitro. In contrast, human oligodendrocytes in culture expressed the receptor, CXCR2, constitutively. We propose that the concurrence of CXCR2 on oligodendrocytes and induced CXCL1 on hypertrophic astrocytes in MS provides a novel mechanism for recruitment of oligodendrocytes to areas of damage, an essential prerequisite for lesion repair in this devastating human condition.

Are astrocytes central players in the pathophysiology of multiple sclerosis?

An interaction between antimyelin T cells and antigen-presenting glial cells is a crucial step in the cascade of immune events that lead to the inflammatory lesions in multiple sclerosis (MS). One of the most debated and controversial issues is whether microglial cells or astrocytes are the key players in initiating the (auto)immune reactions in the central nervous system in MS. Many investigators consider microglia to be the responsible intrinsic immunoeffector cells. In this review, we speculate that in MS astrocytes may serve as primary (facultative) antigen-presenting cells due to a failure of noradrenergic suppression of class II major histocompatibility complex molecules, which is caused by a loss of beta(2)-adrenergic receptors. If this hypothesis is correct, pharmacologic suppression of the antigen-presenting capacities of astrocytes may be a potential therapy for MS.