Teriflunomide Promotes Oligodendroglial 8,9-Unsaturated Sterol Accumulation and CNS Remyelination

Understanding Multiple Sclerosis Pathophysiology and Current Disease-Modifying Therapies: A Review of Unaddressed Aspects

Multiple sclerosis (MS) is a complex autoimmune disorder of the central nervous system (CNS) with an unknown etiology and pathophysiology that is not completely understood. Although great strides have been made in developing disease-modifying therapies (DMTs) that have significantly improved the quality of life for MS patients, these treatments do not entirely prevent disease progression or relapse. Identifying the unaddressed pathophysiological aspects of MS and developing targeted therapies to fill in these gaps are essential in providing long-term relief for patients. Recent research has uncovered some aspects of MS that remain outside the scope of available DMTs, and as such, yield only limited benefits. Despite most MS pathophysiology being targeted by DMTs, many patients still experience disease progression or relapse, indicating that a more detailed understanding is necessary. Thus, this literature review seeks to explore the known aspects of MS pathophysiology, identify the gaps in present DMTs, and explain why current treatments cannot entirely arrest MS progression.

Antidepressant effect of teriflunomide via oligodendrocyte protection in a mouse model

Addressing the treatment of depression is crucial; nevertheless, the etiology and pathogenesis remain unelucidated. Therefore, this study investigated the effects of teriflunomide (TF) on corticosterone (CORT)-induced depression-like behaviors in mice. Notably, TF administration resulted in a substantial amelioration of anxiety and depression-like behaviors observed in CORT-treated mice. This was evidenced by behavioral assessments conducted via the sucrose preference test (SPT), open-field test (OFT), novelty-suppressed feeding test (NSFT), forced swimming test (FST), and tail suspension test (TST). The administration of CORT inflicts damage upon oligodendrocytes and neurons within the hippocampus. Our findings indicate that TF offers significant protective effects on oligodendrocytes, mitigating apoptosis both invivo and invitro. Additionally, TF was found to counteract the CORT-induced neuronal loss and synaptic damage, as demonstrated by an increase in Nissl-positive cells across hippocampal regions CA1, CA3, and the dentate gyrus (DG) alongside elevated levels of synapse-related proteins including PSD-95 and synaptophysin. Additionally, TF treatment facilitated a reduction in the levels of apoptosis-related proteins while simultaneously augmenting the levels of Bcl2. Our findings indicate that TF administration effectively mitigates CORT-induced depression-like behaviors and reverses damage to oligodendrocytes and neurons in the hippocampus, suggesting TF as a promising candidate for depression.

Teriflunomide as a therapeutic means for myelin repair

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.

Chronic oligodendrocyte injury in central nervous system pathologies

Myelin, the membrane surrounding neuronal axons, is critical for central nervous system (CNS) function. Injury to myelin-forming oligodendrocytes (OL) in chronic neurological diseases (e.g. multiple sclerosis) ranges from sublethal to lethal, leading to OL dysfunction and myelin pathology, and consequent deleterious impacts on axonal health that drive clinical impairments. This is regulated by intrinsic factors such as heterogeneity and age, and extrinsic cellular and molecular interactions. Here, we discuss the responses of OLs to injury, and perspectives for therapeutic targeting. We put forward that targeting mature OL health in neurological disease is a promising therapeutic strategy to support CNS function.

The landscape of targets and lead molecules for remyelination

Remyelination, or the restoration of myelin sheaths around axons in the central nervous system, is a multi-stage repair process that remains a major need for millions of patients with multiple sclerosis and other diseases of myelin. Even into adulthood, rodents and humans can generate new myelin-producing oligodendrocytes, leading to the therapeutic hypothesis that enhancing remyelination could lessen disease burden in multiple sclerosis. Multiple labs have used phenotypic screening to identify dozens of drugs that enhance oligodendrocyte formation, and several hit molecules have now advanced to clinical evaluation. Target identification studies have revealed that a large majority of these hits share the ability to inhibit a narrow range of cholesterol pathway enzymes and thereby induce cellular accumulation of specific sterol precursors to cholesterol. This Perspective surveys the recent fruitful intersection of chemical biology and remyelination and suggests multiple approaches toward new targets and lead molecules to promote remyelination.