Remyelination in multiple sclerosis: from concept to clinical trials

Vitamin C and MEK Inhibitor PD0325901 Synergistically Promote Oligodendrocytes Generation by Promoting DNA Demethylation

DNA methylation and demethylation are key epigenetic events that regulate gene expression and cell fate. DNA demethylation via oxidation of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) is typically mediated by TET (ten-eleven translocation) enzymes. The 5hmC modification is considered an intermediate state of DNA demethylation; it is particularly prevalent in the brain and is believed to play a role in the development of many cell types in the brain. Our previous studies have identified that vitamin C (Vc) and MEK inhibitor PD0325901 could significantly promote OPC (oligodendrocyte progenitor cell)-to-OL (oligodendrocyte) differentiation. Here we discovered that Vc and PD0325901 may promote OPC-to-OL differentiation by inducing DNA demethylation via hydroxymethylation. Blocking 5hmC formation almost totally blocked Vc- and PD0325901-stimulated OPC-to-OL differentiation. In addition, TET1 is not involved in Vc,- and PD0325901-promoted OL generation. We also found a synergistic effect between the two compounds in inducing OL generation, suggesting the possibility of a combination therapy for demyelination diseases in the future.

Trametinib, an anti-tumor drug, promotes oligodendrocytes generation and myelin formation

Oligodendrocytes (OLs) are differentiated from oligodendrocyte precursor cells (OPCs) in the central nervous system (CNS). Demyelination is a common feature of many neurological diseases such as multiple sclerosis (MS) and leukodystrophies. Although spontaneous remyelination can happen after myelin injury, nevertheless, it is often insufficient and may lead to aggravated neurodegeneration and neurological disabilities. Our previous study has discovered that MEK/ERK pathway negatively regulates OPC-to-OL differentiation and remyelination in mouse models. To facilitate possible clinical evaluation, here we investigate several MEK inhibitors which have been approved by FDA for cancer therapies in both mouse and human OPC-to-OL differentiation systems. Trametinib, the first FDA approved MEK inhibitor, displays the best effect in stimulating OL generation in vitro among the four MEK inhibitors examined. Trametinib also significantly enhances remyelination in both MOG-induced EAE model and LPC-induced focal demyelination model. More exciting, trametinib facilitates the generation of MBP+ OLs from human embryonic stem cells (ESCs)-derived OPCs. Mechanism study indicates that trametinib promotes OL generation by reducing E2F1 nuclear translocation and subsequent transcriptional activity. In summary, our studies indicate a similar inhibitory role of MEK/ERK in human and mouse OL generation. Targeting the MEK/ERK pathway might help to develop new therapies or repurpose existing drugs for demyelinating diseases.

Alterations of Oligodendrocyte and Myelin Energy Metabolism in Multiple Sclerosis

Multiple sclerosis (MS) is a complex autoimmune disease of the central nervous system (CNS), characterized by demyelination and neurodegeneration. Oligodendrocytes play a vital role in maintaining the integrity of myelin, the protective sheath around nerve fibres essential for efficient signal transmission. However, in MS, oligodendrocytes become dysfunctional, leading to myelin damage and axonal degeneration. Emerging evidence suggests that metabolic changes, including mitochondrial dysfunction and alterations in glucose and lipid metabolism, contribute significantly to the pathogenesis of MS. Mitochondrial dysfunction is observed in both immune cells and oligodendrocytes within the CNS of MS patients. Impaired mitochondrial function leads to energy deficits, affecting crucial processes such as impulse transmission and axonal transport, ultimately contributing to neurodegeneration. Moreover, mitochondrial dysfunction is linked to the generation of reactive oxygen species (ROS), exacerbating myelin damage and inflammation. Altered glucose metabolism affects the energy supply required for oligodendrocyte function and myelin synthesis. Dysregulated lipid metabolism results in changes to the composition of myelin, affecting its stability and integrity. Importantly, low levels of polyunsaturated fatty acids in MS are associated with upregulated lipid metabolism and enhanced glucose catabolism. Understanding the intricate relationship between these mechanisms is crucial for developing targeted therapies to preserve myelin and promote neurological recovery in individuals with MS. Addressing these metabolic aspects may offer new insights into potential therapeutic strategies to halt disease progression and improve the quality of life for MS patients.

GABAB receptor agonist baclofen promotes central nervous system remyelination

Promoting remyelination is considered as a potential neurorepair strategy to prevent/limit the development of permanent neurological disability in patients with multiple sclerosis (MS). To this end, a number of clinical trials are investigating the potential of existing drugs to enhance oligodendrocyte progenitor cell (OPC) differentiation, a process that fails in chronic MS lesions. We previously reported that oligodendroglia express GABA_B receptors (GABA_B Rs) both in vitro and in vivo, and that GABA_B R-mediated signaling enhances OPC differentiation and myelin protein expression in vitro. Our goal here was to evaluate the pro-remyelinating potential of GABA_B R agonist baclofen (Bac), a clinically approved drug to treat spasticity in patients with MS. We first demonstrated that Bac increases myelin protein production in lysolecithin (LPC)-treated cerebellar slices. Importantly, Bac administration to adult mice following induction of demyelination by LPC injection in the spinal cord resulted in enhanced OPC differentiation and remyelination. Thus, our results suggest that Bac repurposing should be considered as a potential therapeutic strategy to stimulate remyelination in patients with MS.

Total astragalosides promote oligodendrocyte precursor cell differentiation and enhance remyelination in cuprizone-induced mice through suppression of Wnt/β-catenin signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Radix Astragali is a traditional Chinese medicine with various pharmacological effects. Total astragalosides (TA), the main effective ingredients in Radix Astragali, exert properties including anti-oxidative stress, anti-neuroinflammation, and neuroprotection. We previously found that TA alleviated experimental autoimmune encephalomyelitis (EAE) progression, a widely used animal model of multiple sclerosis (MS). As a chronic demyelination disease, MS generally manifests myelin loss and fails to myelin regeneration. Regulation of oligodendrocyte progenitor cells (OPCs) differentiation and remyelination is the fundamental strategy for MS treatment. However, whether TA could directly promote OPCs differentiation and remyelination is still unknown.

AIMS OF THE STUDY

This study was aimed to investigate pro-differentiation and myelin regeneration effects of TA on OPCs and Cuprizone (CPZ)-induced demyelination mice, an animal model of MS, and to explore mechanism underlying from regulation of OPCs differentiation and maturation.

MATERIALS AND METHODS

Mice were orally given CPZ (400 mg/kg) daily for 4 weeks to induce myelin loss, and then treated with TA (25 and 50 mg/kg) daily for 1 week. Cell proliferation assay, Western blot, RT-PCR, immunocytochemistry and immunohistochemistry were performed to explore the mechanisms. The role of TA in oligodendrocyte differentiation and maturation was evaluated using MO3.13, a human oligodendrocytic hybrid cell line.

RESULTS

TA was shown to mitigate behavioral impairment in CPZ-induced mice. It markedly ameliorated myelin loss and enhanced remyelination in the corpus callosum of mice, evidenced by increased expression of myelin basic protein (MBP) and the number of CC1⁺ newly generated oligodendrocytes (OLs). TA also enhanced the expression of MBP at both mRNA and protein levels in MO3.13 cells. In CPZ-induced mice and MO3.13 cells, TA remarkably promoted the activation of GSK3β, repressed the phosphorylation of β-catenin, reduced the expression of transcription factor 4 and inhibitor of DNA binding 2. The agonist of β-catenin, SKL2001, partially abolished the pro-differentiation effect of TA in MO3.13 cells.

CONCLUSIONS

Taken together, we clarified that TA could effectively enhance the differentiation and maturation of OPCs and accelerate remyelination in CPZ-induced mice through inhibition of Wnt/β-catenin signaling pathway. This study provides new insight into the beneficial effect of TA in the treatment of MS.

From pathology to MRI and back: Clinically relevant biomarkers of multiple sclerosis lesions

Focal lesions in both white and gray matter are characteristic of multiple sclerosis (MS). Histopathological studies have helped define the main underlying pathological processes involved in lesion formation and evolution, serving as a gold standard for many years. However, histopathology suffers from an intrinsic bias resulting from over-reliance on tissue samples from late stages of the disease or atypical cases and is inadequate for routine patient assessment. Pathological-radiological correlative studies have established advanced MRI's sensitivity to several relevant MS-pathological substrates and its practicality for assessing dynamic changes and following lesions over time. This review focuses on novel imaging techniques that serve as biomarkers of critical pathological substrates of MS lesions: the central vein, chronic inflammation, remyelination and repair, and cortical lesions. For each pathological process, we address the correlative value of MRI to MS pathology, its contribution in elucidating MS pathology in vivo, and the clinical utility of the imaging biomarker.

Current status of neuroprotective and neuroregenerative strategies in multiple sclerosis: A systematic review

BACKGROUND

Immune-mediated demyelination and consequent degeneration of oligodendrocytes and axons are hallmark features of multiple sclerosis (MS). Remyelination declines in progressive MS, causing permanent axonal loss and irreversible disabilities. Strategies aimed at enhancing remyelination are critical to attenuate disease progression.

OBJECTIVE

We systematically reviewed recent advances in neuroprotective and regenerative therapies for MS, covering preclinical and clinical studies.

METHODS

We searched three biomedical databases using defined keywords. Two authors independently reviewed articles for inclusion based on pre-specified criteria. The data were extracted from each study and assessed for risk of bias.

RESULTS

Our search identified 7351 studies from 2014 to 2020, of which 221 met the defined criteria. These studies reported 262 interventions, wherein 92% were evaluated in animal models. These interventions comprised protein, RNA, lipid and cellular biologics, small molecules, inorganic compounds, and dietary and physiological interventions. Small molecules were the most highly represented strategy, followed by antibody therapies and stem cell transplantation.

CONCLUSION

While significant strides have been made to develop regenerative treatments for MS, the current evidence illustrates a skewed representation of the types of strategies that advance to clinical trials. Further examination is thus required to address current barriers to implementing experimental treatments in clinical settings.

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

Myelin repair in the adult central nervous system (CNS) is driven by successful differentiation of resident oligodendroglial precursor cells (OPCs) and thus constitutes a neurodegenerative 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 an MS-specific pathogenic entity, and its envelope (ENV) protein was previously identified as a negative regulator of OPC maturation—hence, it is 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 improved remyelination. ENV-mediated activation of toll like receptor 4 (TLR4) increases inducible nitric oxide synthase (iNOS) expression, prompts nitrosative stress, and results in myelin-associated deficits, such as decreased levels of oligodendroglial maturation marker expression and morphological alterations. The 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, was 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.

Small molecule screening as an approach to encounter inefficient myelin repair

While current multiple sclerosis therapies are focused on immunomodulation, thereby slowing down disease progression, scientific interest has nowadays been shifted toward regenerative therapies aiming at reversing already existing deficits. The application of chemical compounds was proven to be valuable for the understanding of oligodendrogenesis and for exposing mechanisms that can boost remyelination. However, sufficient myelin repair has not been achieved yet, thus underscoring the need for more studies toward this unmet clinical goal. In this regard, many research groups have significantly contributed to the field via developing compound screening approaches or using single substances. We, here, present an overview of recent studies addressing the identification of myelin repair drugs and provide insights into technical aspects and identified substances.

Changing Paradigms and Unmet Needs in Multiple Sclerosis: The Role of Clinical Neurophysiology

SUMMARY

Our increasing understanding of the immunopathogenesis of multiple sclerosis has led to the development of many disease-modifying therapies that have revolutionized the care of patients with relapsing forms of the disease. Our understanding of the pathophysiologic basis of progressive forms of the disease is much more limited but has dramatically changed over the past several decades. We are now on the verge of developing therapies that promote remyelination, reduce axonal loss, and restore axonal function. This progress is challenged by inadequate animal models of progressive disease and incomplete biomarkers of progression. In measuring central nervous system function, evoked potentials may have an advantage over biomarkers, which measure only pathologic change. Monitoring multifocal visual evoked potential amplitude may be one possible means of monitoring disease progression in multiple sclerosis. Additional clinical studies are required to document whether evoked potentials can adequately serve as effective biomarkers of progression.

Quantitative magnetic resonance imaging towards clinical application in multiple sclerosis

Quantitative MRI provides biophysical measures of the microstructural integrity of the CNS, which can be compared across CNS regions, patients, and centres. In patients with multiple sclerosis, quantitative MRI techniques such as relaxometry, myelin imaging, magnetization transfer, diffusion MRI, quantitative susceptibility mapping, and perfusion MRI, complement conventional MRI techniques by providing insight into disease mechanisms. These include: (i) presence and extent of diffuse damage in CNS tissue outside lesions (normal-appearing tissue); (ii) heterogeneity of damage and repair in focal lesions; and (iii) specific damage to CNS tissue components. This review summarizes recent technical advances in quantitative MRI, existing pathological validation of quantitative MRI techniques, and emerging applications of quantitative MRI to patients with multiple sclerosis in both research and clinical settings. The current level of clinical maturity of each quantitative MRI technique, especially regarding its integration into clinical routine, is discussed. We aim to provide a better understanding of how quantitative MRI may help clinical practice by improving stratification of patients with multiple sclerosis, and assessment of disease progression, and evaluation of treatment response.

Identification of novel myelin repair drugs by modulation of oligodendroglial differentiation competence

BACKGROUND

In multiple sclerosis loss of myelin and oligodendrocytes impairs saltatory signal transduction and leads to neuronal loss and functional deficits. Limited capacity of oligodendroglial precursor cells to differentiate into mature cells is the main reason for inefficient myelin repair in the central nervous system. Drug repurposing constitutes a powerful approach for identification of pharmacological compounds promoting this process.

METHODS

A phenotypic compound screening using the subcellular distribution of a potent inhibitor of oligodendroglial cell differentiation, namely p57kip2, as differentiation competence marker was conducted. Hit compounds were validated in terms of their impact on developmental cell differentiation and myelination using both rat and human primary cell cultures and organotypic cerebellar slice cultures, respectively. Their effect on spontaneous remyelination was then investigated following cuprizone-mediated demyelination of the corpus callosum.

FINDINGS

A number of novel small molecules able to promote oligodendroglial cell differentiation were identified and a subset was found to foster human oligodendrogenesis as well as myelination ex vivo. Among them the steroid danazol and the anthelminthic parbendazole were found to increase myelin repair.

INTERPRETATION

We provide evidence that early cellular processes involved in differentiation decisions are applicable for the identification of regeneration promoting drugs and we suggest danazol and parbendazole as potent therapeutic candidates for demyelinating diseases.

FUNDING

This work was supported by the Jürgen Manchot Foundation, Düsseldorf; Research Commission of the Medical Faculty of Heinrich-Heine-University Düsseldorf; Christiane and Claudia Hempel Foundation; Stifterverband/Novartisstiftung; James and Elisabeth Cloppenburg, Peek and Cloppenburg Düsseldorf Stiftung and International Progressive MS Alliance (BRAVEinMS).

Relapsing and progressive MS: the sex-specific perspective

Background:

Multiple sclerosis (MS) is an inflammatory and neurodegenerative disease whose aetiology is not fully understood. The female sex is clearly predominant, with a sex ratio between 2 and 3. In primary progressive MS the sex ratio almost balances out. Since the age at onset is higher for patients with progressive onset (POMS) than for relapsing onset (ROMS), it can be hypothesized that the age at onset is a decisive factor for the sex ratio.

Methods:

To address this aspect, we compare clinical and demographic data between females and males for the different disease courses within the population of the German MS Register by the German MS Society. Only patients with complete details in mandatory data items and a follow-up visit since 01. Jan 2018 were included.

Results:

A total of 18,728 patients were included in our analyses, revealing a female-to-male ratio of 2.6 (2.7 for patients with ROMS and 1.3 for POMS). The age at diagnosis is higher in patients with POMS (43.3 and 42.3 years for females and males versus 32.1 and 33.2 years, respectively). Females irrespective of disease course are statistically significantly more often affected by cognitive impairment (POMS: p = 0.013, ROMS: p = 0.001) and depression (POMS: p = 0.002, ROMS: 0.001) and suffer more often from pain (POMS and ROMS: p < 0.001). Fatigue is significantly more often seen in females with ROMS (p < 0.001) but not in POMS. Females with ROMS retire significantly (p < 0.001) earlier (42.8 versus 44.2 years) and to a greater extent than males (28 versus 24%). Disease progression was similar for women and men.

Conclusion:

Our analysis shows that clinical and demographic data differ more between disease courses than between men and women. For pain, depression and cognitive impairment the female sex is the decisive factor. Whether these factors are responsible for the earlier retirement of females with ROMS is not clear. Appropriate measures for optimization of symptomatic treatment as well as to promote employment should be taken.

Associations Between Findings From Myelin Water Imaging and Cognitive Performance Among Individuals With Multiple Sclerosis

IMPORTANCE

Cognitive impairment is a debilitating symptom of multiple sclerosis (MS) that affects up to 70% of patients. An improved understanding of the underlying pathology of MS-related cognitive impairment would provide considerable benefit to patients and clinicians.

OBJECTIVE

To determine whether there is an association between myelin damage in tissue that appears completely normal on standard clinical imaging, but can be detected by myelin water imaging (MWI), with cognitive performance in MS.

DESIGN, SETTING, AND PARTICIPANTS

In this cross-sectional study, participants with MS and controls underwent cognitive testing and magnetic resonance imaging (MRI) from August 23, 2017, to February 20, 2019. Participants were recruited through the University of British Columbia Hospital MS clinic and via online recruitment advertisements on local health authority websites. Cognitive testing was performed in the MS clinic, and MRI was performed at the adjacent academic research neuroimaging center. Seventy-three participants with clinically definite MS fulfilling the 2017 revised McDonald criteria for diagnosis and 22 age-, sex-, and education-matched healthy volunteers without neurological disease were included in the study. Data analysis was performed from March to November 2019.

EXPOSURES

MWI was performed at 3 T with a 48-echo, 3-dimensional, gradient and spin-echo (GRASE) sequence. Cognitive testing was performed with assessments drawn from cognitive batteries validated for use in MS.

MAIN OUTCOMES AND MEASURES

The association between myelin water measures, a measurement of the T2 relaxation signal from water in the myelin bilayers providing a specific marker for myelin, and cognitive test scores was assessed using Pearson correlation. Three white matter regions of interest-the cingulum, superior longitudinal fasciculus (SLF), and corpus callosum-were selected a priori according to their known involvement in MS-related cognitive impairment.

RESULTS

For the 95 total participants, the mean (SD) age was 49.33 (11.44) years. The mean (SD) age was 50.2 (10.7) years for the 73 participants with MS and 46.4 (13.5) for the 22 controls. Forty-eight participants with MS (66%) and 14 controls (64%) were women. The mean (SD) years of education were 14.7 (2.2) for patients and 15.8 (2.5) years for controls. In MS, significant associations were observed between myelin water measures and scores on the Symbol Digit Modalities Test (SLF, r = -0.490; 95% CI, -0.697 to -0.284; P < .001; corpus callosum, r = -0.471; 95% CI, -0.680 to -0.262; P < .001; and cingulum, r = -0.419; 95% CI, -0.634 to -0.205; P < .001), Selective Reminding Test (SLF, r = -0.444; 95% CI, -0.660 to -0.217; P < .001; corpus callosum, r = -0.411; 95% CI, -0.630 to -0.181; P = .001; and cingulum, r = -0.361; 95% CI, -0.602 to -0.130; P = .003), and Controlled Oral Word Association Test (SLF, r = -0.317; 95% CI, -0.549 to -0.078; P = .01; and cingulum, r = -0.335; 95% CI, -0.658 to -0.113; P = .006). No significant associations were found in controls.

CONCLUSIONS AND RELEVANCE

This study used MWI to demonstrate that otherwise normal-appearing brain tissue is diffusely damaged in MS, and the findings suggest that myelin water measures are associated with cognitive performance. MWI offers an in vivo biomarker feasible for use in clinical trials investigating cognition, providing a means for monitoring changes in myelination and its association with symptom worsening or improvement.

Epigenetic insights into multiple sclerosis disease progression

Multiple sclerosis (MS), a chronic inflammatory demyelinating and neurodegenerative disease of the central nervous system, is today a leading cause of unpredictable lifelong disability in young adults. The treatment of patients in progressive stages remains highly challenging, alluding to our limited understanding of the underlying pathological processes. In this review, we provide insights into the mechanisms underpinning MS progression from a perspective of epigenetics, that refers to stable and mitotically heritable, yet reversible, changes in the genome activity and gene expression. We first recapitulate findings from epigenetic studies examining the brain tissue of progressive MS patients, which support a contribution of DNA and histone modifications in impaired oligodendrocyte differentiation, defective myelination/remyelination and sustained neuro-axonal vulnerability. We next explore possibilities for identifying factors affecting progression using easily accessible tissues such as blood by comparing epigenetic signatures in peripheral immune cells and brain tissue. Despite minor overlap at individual methylation sites, nearly 30% of altered genes reported in peripheral immune cells of progressive MS patients were found in brain tissue, jointly converging on alterations of neuronal functions. We further speculate about the mechanisms underlying shared epigenetic patterns between blood and brain, which likely imply the influence of internal (genetic control) and/or external (e.g. smoking and ageing) factors imprinting a common signature in both compartments. Overall, we propose that epigenetics might shed light on clinically relevant mechanisms involved in disease progression and open new avenues for the treatment of progressive MS patients in the future.

Neuroinflammation in Demyelinating Diseases: Oxidative Stress as a Modulator of Glial Cross-Talk

Myelin is a specialized membrane allowing for saltatory conduction of action potentials in neurons, an essential process to achieve the normal communication across the nervous system. Accordingly, in diseases characterized by the loss of myelin and myelin forming cells -oligodendrocytes in the CNS-, patients show severe neurological disabilities. After a demyelinated insult, microglia, astrocytes and oligodendrocyte precursor cells invade the lesioned area initiating a spontaneous process of myelin repair (i.e. remyelination). A preserved hallmark of this neuroinflammatory scenario is a local increase of oxidative stress, where several cytokines and chemokines are released by glial and other cells. This generates an environment that determines cell interaction resulting in oligodendrocyte maturity and the ability to synthesize new myelin. Herein we review the main features of the regulatory aspect of these molecules based on recent findings and propose new putative signal molecules involved in the remyelination process, focused in the etiology of Multiple Sclerosis, one of the main demyelinating diseases causing disabilities in the population.

Emerging myelin repair agents in preclinical and early clinical development for the treatment of multiple sclerosis

INTRODUCTION

Remyelination is a highly effective regenerative process that can restore axon function, prevent axonal loss, and reverse clinical deficits after demyelination. Hence, the promotion of remyelination is a logical goal in patients with multiple sclerosis (MS) in which remyelination is often insufficient. However, despite great progress regarding the development of immunomodulatory therapies for MS and an abundance of promising evidence from preclinical experiments so far, no therapy has convincingly demonstrated clinically significant remyelination properties. Therefore, enhancing myelin repair is an urgent and unmet need in MS.

AREAS COVERED

We searched clinicaltrials.gov and pubmed.ncbi.nlm.nih.gov and focused on therapeutic agents in development from the preclinical stage to clinical phase II. We selected agents for which data are available from in vitro experiments and at least one toxic demyelination animal model that reached at least phase I in clinical development in MS patients.

EXPERT OPINION

The evidence to promote remyelination is very promising for several agents, some of which possess anti-muscarinergic properties. Since remyelination is a complex process that involves various coordinated steps, a combination of different therapeutic approaches addressing different aspects of this regenerative mechanism may be reasonable. Furthermore, suitable surrogate markers of remyelination are necessary for proof-of-concept clinical trials.

Current Symptomatic and Disease-Modifying Treatments in Multiple System Atrophy

Multiple system atrophy (MSA) is a rare, severe, and rapidly progressive neurodegenerative disorder categorized as an atypical parkinsonian syndrome. With a mean life expectancy of 6-9 years after diagnosis, MSA is clinically characterized by parkinsonism, cerebellar ataxia, autonomic failure, and poor l-Dopa responsiveness. Aside from limited symptomatic treatment, there is currently no disease-modifying therapy available. Consequently, distinct pharmacological targets have been explored and investigated in clinical studies based on MSA-related symptoms and pathomechanisms. Parkinsonism, cerebellar ataxia, and autonomic failure are the most important symptoms targeted by symptomatic treatments in current clinical trials. The most prominent pathological hallmark is oligodendroglial cytoplasmic inclusions containing alpha-synuclein, thus classifying MSA as synucleinopathy. Additionally, myelin and neuronal loss accompanied by micro- and astrogliosis are further distinctive features of MSA-related neuropathology present in numerous brain regions. Besides summarizing current symptomatic treatment strategies in MSA, this review critically reflects upon potential cellular targets and disease-modifying approaches for MSA such as (I) targeting α-syn pathology, (II) intervening neuroinflammation, and (III) neuronal loss. Although these single compound trials are aiming to interfere with distinct pathogenetic steps in MSA, a combined approach may be necessary to slow down the rapid progression of the oligodendroglial associated synucleinopathy.

La sclérose en plaques et les médicaments immuno-modulateurs des récepteurs de la sphingosine 1-phosphate

La sclérose en plaques (SEP) est une maladie du système nerveux central à composante inflammatoire, très invalidante qui atteint généralement de jeunes adultes (20 à 40 ans). Cette maladie se caractérise par la destruction progressive, par les cellules du système immunitaire, de la gaine de myéline des axones, ce qui aboutit à une dégénérescence neuronale. Les lymphocytes T et B sont les acteurs principaux de cette maladie qui peut être rémittente ou progressive. Parmi les médicaments utilisés dans le cadre de son traitement, le fingolimod, un immunosuppresseur dont les cibles sont les récepteurs de la sphingosine 1-phosphate, administré par voie orale, agit en empêchant les lymphocytes de quitter le thymus et les ganglions lymphatiques, et de rejoindre les foyers inflammatoires cérébraux. Une recherche intense pour développer des traitements et des médicaments curatifs est actuellement en cours et d’autres immunosuppresseurs interagissant avec les récepteurs de sphingosine 1-phosphate sont en cours de développement.

Klotho Pathways, Myelination Disorders, Neurodegenerative Diseases, and Epigenetic Drugs

In this review we outline a rationale for identifying neuroprotectants aimed at inducing endogenous Klotho activity and expression, which is epigenetic action, by definition. Such an approach should promote remyelination and/or stimulate myelin repair by acting on mitochondrial function, thereby heralding a life-saving path forward for patients suffering from neuroinflammatory diseases. Disorders of myelin in the nervous system damage the transmission of signals, resulting in loss of vision, motion, sensation, and other functions depending on the affected nerves, currently with no effective treatment. Klotho genes and their single-pass transmembrane Klotho proteins are powerful governors of the threads of life and death, true to the origin of their name, Fates, in Greek mythology. Among its many important functions, Klotho is an obligatory co-receptor that binds, activates, and/or potentiates critical fibroblast growth factor activity. Since the discovery of Klotho a little over two decades ago, it has become ever more apparent that when Klotho pathways go awry, oxidative stress and mitochondrial dysfunction take over, and age-related chronic disorders are likely to follow. The physiological consequences can be wide ranging, potentially wreaking havoc on the brain, eye, kidney, muscle, and more. Central nervous system disorders, neurodegenerative in nature, and especially those affecting the myelin sheath, represent worthy targets for advancing therapies that act upon Klotho pathways. Current drugs for these diseases, even therapeutics that are disease modifying rather than treating only the symptoms, leave much room for improvement. It is thus no wonder that this topic has caught the attention of biomedical researchers around the world.

The Molecular Basis for Remyelination Failure in Multiple Sclerosis

Myelin sheaths in the central nervous system (CNS) insulate axons and thereby allow saltatory nerve conduction, which is a prerequisite for complex brain function. Multiple sclerosis (MS), the most common inflammatory autoimmune disease of the CNS, leads to the destruction of myelin sheaths and the myelin-producing oligodendrocytes, thus leaving behind demyelinated axons prone to injury and degeneration. Clinically, this process manifests itself in significant neurological symptoms and disability. Resident oligodendroglial precursor cells (OPCs) and neural stem cells (NSCs) are present in the adult brain, and can differentiate into mature oligodendrocytes which then remyelinate the demyelinated axons. However, for multiple reasons, in MS the regenerative capacity of these cell populations diminishes significantly over time, ultimately leading to neurodegeneration, which currently remains untreatable. In addition, microglial cells, the resident innate immune cells of the CNS, can contribute further to inflammatory and degenerative axonal damage. Here, we review the molecular factors contributing to remyelination failure in MS by inhibiting OPC and NSC differentiation or modulating microglial behavior.