Multiple sclerosis (MS) is the most common neurological immune-mediated disease leading to disability in young adults. The outcome of the disease is unpredictable, and over time, neurological disabilities accumulate. Interferon beta-1b was the first drug to be approved in the 1990s for relapsing-remitting MS to modulate the course of the disease. Over the past two decades, the treatment landscape has changed tremendously. Currently, more than a dozen drugs representing 1 substances with different mechanisms of action have been approved (interferon beta preparations, glatiramer acetate, fingolimod, siponimod, mitoxantrone, teriflunomide, dimethyl fumarate, cladribine, alemtuzumab, ocrelizumab, and natalizumab). Ocrelizumab was the first medication to be approved for primary progressive MS. The objective of this review is to present the modes of action of these drugs and their effects on the immunopathogenesis of MS. Each agent's clinical development and potential side effects are discussed.

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Immunological Aspects of Approved MS Therapeutics.

NLRP3 inflammasome-mediated pyroptosis is a proinflammatory programmed cell death pathway, which plays a vital role in functional outcomes after stroke. We previously described the beneficial effects of curcumin against stroke-induced neuronal damage through modulating microglial polarization. However, the impact of curcumin on microglial pyroptosis remains unknown. Here, stroke was modeled in mice by middle cerebral artery occlusion (MCAO) for 60 minutes and treated with curcumin (150 mg/kg) intraperitoneally immediately after reperfusion, followed by daily administrations for 7 days. Curcumin ameliorated white matter (WM) lesions and brain tissue loss 21 days poststroke and improved sensorimotor function 3, 10, and 21 days after stroke. Furthermore, curcumin significantly reduced the number of gasdermin D+ (GSDMD+) Iba1+ and caspase-1+Iba1+ microglia/macrophage 21 days after stroke. In vitro, lipopolysaccharide (LPS) with ATP treatment was used to induce pyroptosis in primary microglia. Western blot revealed a decrease in pyroptosis-related proteins, e.g., GSDMD-N, cleaved caspase-1, NLRP3, IL-1β, and IL-18, following in vitro or in vivo curcumin treatment. Mechanistically, both in vivo and in vitro studies confirmed that curcumin inhibited the activation of the NF-κB pathway. NLRP3 knocked down by siRNA transfection markedly increased the inhibitory effects of curcumin on microglial pyroptosis and proinflammatory responses, both in vitro and in vivo. Furthermore, stereotaxic microinjection of AAV-based NLRP3 shRNA significantly improved sensorimotor function and reduced WM lesion following curcumin treatment in MCAO mice. Our study suggested that curcumin reduced stroke-induced WM damage, improved functional outcomes, and attenuated microglial pyroptosis, at least partially, through suppression of the NF-κB/NLRP3 signaling pathway, further supporting curcumin as a potential therapeutic drug for stroke.

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Curcumin Ameliorates White Matter Injury after Ischemic Stroke by Inhibiting Microglia/Macrophage Pyroptosis through NF-κB Suppression and NLRP3 Inflammasome Inhibition.

Die vorliegende Dissertationsarbeit befasst sich mit den Mechanismen glialer Differenzierung und der Frage, inwieweit diese im Rahmen inflammatorischer Erkrankungen des Zentralen Nerversystems (ZNS) wie der Multiplen Sklerose (MS) von Bedeutung sind. Multiple Sklerose ist eine autoimmune inflammatorische ZNS Erkrankung, die eine Zerstorung der axon-isolierenden Myelinscheiden zur Folge hat. Hierdurch kommt es zunachst zu einer Herabsetzung der elektrischen Uberleitungsgeschwindigkeit in den neuronalen Axonen und schlieslich zum direkten axonalen Schaden. Die myelinbildenden Zellen des ZNS, die Oligodendrozyten, konnen die zerstorten Myelinscheiden in der Folge nur unvollstandig erneuern, wobei dies nicht zuletzt mit der eingeschrankten Fahigkeit von residenten Oligodendrozytenvorlauferzellen zu differenzieren in Verbindung gebracht wird. In der vorgelegten Arbeit konnte nun gezeigt werden, dass eine anhaltende Reduzierung der Genexpression von p57kip2, eines Zyklin abhangigen Kinaseinhibitors, in oligodendroglialen Vorlauferzellen zu einer erleichterten und verstarkten Differenzierung dieser myelinisierenden Zellen fuhrt. Zu diesem Zweck wurden primare Rattenoligodendrozyten aus dem neugeborenen Rattenhirn mit einem Gensuppressionsvektor fur p57kip2 transfiziert und anschliesend immunzytochemisch und morphologisch analysiert. Neben diesen in vitro Studien wurde gezeigt, dass p57kip2 im Rahmen der MOG-EAE (Myelin-Oligodendrozyten- Glykoprotein induzierte experimentelle autoimmune Enzephalomyelitis), einer Modellerkrankung der MS in der Ratte, fast ausschlieslich von Oligodendrozyten und ihren Vorlauferzellen exprimiert und schubabhangig reguliert wird. Hierfur wurde Material aus dem gesunden und dem EAE-Rattenhirn mittels qRT-PCR und Immunhistochemie aufgearbeitet und miteinander verglichen. Gemeinsam legen die in dieser Arbeit vorgestellten Ergebnisse nahe, dass es sich bei p57kip2 um einen neuartigen negativen Regulator der (Re-) Myelinisierung handelt, der sich an der Schnittstelle zwischen Genexpression und Zellmorphogenese befindet. Insbesondere in Hinblick auf das immer noch begrenzte Verstandnis der zerebralen (Re-) Myelinisierungsmechanismen kann die vorgelegte Arbeit neue Wege in Richtung auf alternative Therapiestrategien, wie der Stimulierung hirneigener Regenerationsprozesse weisen. Die im Rahmen dieser Doktorarbeit generierten Daten konnten in einem Fachjournal publiziert werden (Kremer et al., PNAS 2009 106:9087-9092).

p57kip2 is dynamically regulated in experimental autoimmune encephalomyelitis

Current multiple sclerosis (MS) therapies are effective in reducing relapse rate, short-term measures of disability, and magnetic resonance imaging (MRI) measures of inflammation in relapsing remitting MS (RRMS), whereas in progressive/degenerative disease phases these medications are of little or no benefit. Therefore, the development of new therapies aimed at reversing neurodegeneration is of great interest. Remyelination, which is usually a spontaneous endogenous process, is achieved when myelin-producing oligodendrocytes are generated from oligodendrocyte precursor cells (OPCs). Even though these precursor cells are abundant in MS brains, their regeneration capacity is limited. Enhancing the generation of myelin-producing cells is therefore a major focus of MS research. Here we present an overview of the different advancements in the field of remyelination, including suitable animal models for testing remyelination therapies, approved medications with a proposed role in regeneration, myelin repair treatments under investigation in clinical trials, as well as future therapeutics aimed at facilitating myelin repair.

https://journals.sagepub.com/doi/pdf/10.1177/1352458518800827

Current advancements in promoting remyelination in multiple sclerosis.

In contrast to the multiple disease-modifying therapies that are available for relapsing–remitting multiple sclerosis (MS), the therapeutic options for progressive MS (PMS) are limited. Recent advances in our understanding of the neuroimmunology of PMS, including the mechanisms that drive slowly expanding lesions, have fuelled optimism for improved treatment of this condition. In this Review, we highlight the commonly observed neuropathology of PMS and discuss the associated mechanisms of CNS injury. We then apply this knowledge to formulate criteria for therapeutic efficacy in PMS, beginning with the need for early treatment owing to the substantial neuropathology that is already present at the initial clinical presentation. Other requirements include: antagonism of neuroaxonal injury mediators such as pro-inflammatory microglia and lymphocytes; remediation of oxidative stress resulting from iron deposition and mitochondrial dysfunction; and promotion of neuroprotection through remyelination. We consider whether current disease-modifying therapies for relapsing–remitting MS meet the criteria for successful therapeutics in PMS and suggest that the evidence favours the early introduction of sphingosine 1-phosphate receptor modulators. Finally, we weigh up emerging medications, including repurposed generic medications and Bruton’s tyrosine kinase inhibitors, against these fundamental criteria. In this new therapeutic era in PMS, success depends collectively on understanding disease mechanisms, drug characteristics (including brain penetration) and rational use. Despite substantial progress in the development of disease-modifying therapies for multiple sclerosis (MS), the therapeutic options for progressive MS (PMS) remain limited. The authors present criteria for therapeutic success in PMS and consider the extent to which current drugs meet these criteria.

Mechanism-based criteria to improve therapeutic outcomes in progressive multiple sclerosis.

http://www.thelancet.com/article/S2352396422003863/pdf

Myelin repair is fostered by the corticosteroid medrysone specifically acting on astroglial subpopulations

Myelin repair in the adult central nervous system (CNS) is driven by successful differentiation of resident oligodendroglial precursor cells (OPCs) and thus constitutes a neuroregenerative process capable to compensate for functional deficits upon loss of oligodendrocytes and myelin sheaths as it is observed in multiple sclerosis (MS). The human endogenous retrovirus type W (HERV-W) represents a MS specific pathogenic entity and its envelope (ENV) protein was previously identified as negative regulator of OPC maturation – hence of relevance in the context of diminished myelin repair. We here focused on the activity of the ENV protein and investigated how it can be neutralized for an improved remyelination. ENV mediated activation of TLR4 increases inducible nitric oxide synthase (iNOS) expression, prompts nitrosative stress and results in myelin-associated deficits including decreased levels of oligodendroglial maturation marker expression and morphological alterations. Intervention of TLR4 surface expression represents a potential means to rescue such ENV dependent deficits. To this end, the rescue capacity of specific substances, either modulating V-ATPase activity or myeloid differentiation 2 (MD2) mediated TLR4 glycosylation status, such as compound 20 (C20), L48H437 or folimycin were analyzed, as these processes were demonstrated to be relevant for TLR4 surface expression. We found that pharmacological treatment can rescue the maturation arrest of oligodendroglial cells and their myelination capacity, and can prevent iNOS induction in the presence of the ENV protein. In addition, downregulation of TLR4 surface expression was observed. Furthermore, mitochondrial integrity crucial for oligodendroglial cell differentiation was affected in the presence of ENV and ameliorated upon pharmacological treatment. Our study therefore provides novel insights into possible means to overcome myelination deficits associated with HERV-W ENV mediated myelin deficits.

TLR4 Associated Signaling Disrupters as a New Means to Overcome HERV-W Envelope-Mediated Myelination Deficits

Abstract Background Promotion of myelin repair in the context of demyelinating diseases such as multiple sclerosis (MS) still represents a clinical unmet need, given that this disease is not only characterized by autoimmune activities but also by impaired regeneration processes. Hence, this relates to replacement of lost oligodendrocytes and myelin sheaths—the primary targets of autoimmune attacks. Endogenous remyelination is mainly mediated via activation and differentiation of resident oligodendroglial precursor cells (OPCs), whereas its efficiency remains limited and declines with disease progression and aging. Teriflunomide has been approved as a first-line treatment for relapsing remitting MS. Beyond its role in acting via inhibition of de novo pyrimidine synthesis leading to a cytostatic effect on proliferating lymphocyte subsets, this study aims to uncover its potential to foster myelin repair. Methods Within the cuprizone mediated de-/remyelination model teriflunomide dependent effects on oligodendroglial homeostasis and maturation, related to cellular processes important for myelin repair were analyzed in vivo. Teriflunomide administration was performed either as pulse or continuously and markers specific for oligodendroglial maturation and mitochondrial integrity were examined by means of gene expression and immunohistochemical analyses. In addition, axon myelination was determined using electron microscopy. Results Both pulse and constant teriflunomide treatment efficiently boosted myelin repair activities in this model, leading to accelerated generation of oligodendrocytes and restoration of myelin sheaths. Moreover, teriflunomide restored mitochondrial integrity within oligodendroglial cells. Conclusions The link between de novo pyrimidine synthesis inhibition, oligodendroglial rescue, and maintenance of mitochondrial homeostasis appears as a key for successful myelin repair and hence for protection of axons from degeneration. 

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Teriflunomide as a therapeutic means for myelin repair

Stroke is a major reason for persistent disability due to insufficient treatment strategies beyond reperfusion, leading to oligodendrocyte death and axon demyelination, persistent inflammation and astrogliosis in peri-infarct areas. After injury, oligodendroglial precursor cells (OPCs) have been shown to compensate for myelin loss and prevent axonal loss through the replacement of lost oligodendrocytes, an inefficient process leaving axons chronically demyelinated. Phenotypic screening approaches in demyelinating paradigms revealed substances that promote myelin repair. We established an ex vivo adult organotypic coronal slice culture (OCSC) system to study repair after stroke in a resource-efficient way. Post-photothrombotic OCSCs can be manipulated for 8 d by exposure to pharmacologically active substances testing remyelination activity. OCSCs were isolated from a NG2-CreERT2-td-Tomato knock-in transgenic mouse line to analyze oligodendroglial fate/differentiation and kinetics. Parbendazole boosted differentiation of NG2+ cells and stabilized oligodendroglial fate reflected by altered expression of associated markers PDGFR-α, CC1, BCAS1 and Sox10 and GFAP. In vitro scratch assay and chemical ischemia confirmed the observed effects upon parbendazole treatment. Adult OCSCs represent a fast, reproducible, and quantifiable model to study OPC differentiation competence after stroke. Pharmacological stimulation by means of parbendazole promoted OPC differentiation.

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Laura Reiche

Papers

Myelin repair is fostered by the corticosteroid medrysone specifically acting on astroglial subpopulations

TLR4 Associated Signaling Disrupters as a New Means to Overcome HERV-W Envelope-Mediated Myelination Deficits

Teriflunomide as a therapeutic means for myelin repair

A Novel Ex Vivo Model to Study Therapeutic Treatments for Myelin Repair following Ischemic Damage