Pharmacological treatment promoting remyelination enhances motor function after internal capsule demyelination in mice

Neurodegeneration and demyelination in multiple sclerosis

Progressive multiple sclerosis (PMS) is an immune-initiated neurodegenerative condition that lacks effective therapies. Although peripheral immune infiltration is a hallmark of relapsing-remitting MS (RRMS), PMS is associated with chronic, tissue-restricted inflammation and disease-associated reactive glial states. The effector functions of disease-associated microglia, astrocytes, and oligodendrocyte lineage cells are beginning to be defined, and recent studies have made significant progress in uncovering their pathologic implications. In this review, we discuss the immune-glia interactions that underlie demyelination, failed remyelination, and neurodegeneration with a focus on PMS. We highlight the common and divergent immune mechanisms by which glial cells acquire disease-associated phenotypes. Finally, we discuss recent advances that have revealed promising novel therapeutic targets for the treatment of PMS and other neurodegenerative diseases.

Myosin superfamily members during myelin formation and regeneration

Myelin is an insulator that forms around axons that enhance the conduction velocity of nerve fibers. Oligodendrocytes dramatically change cell morphology to produce myelin throughout the central nervous system (CNS). Cytoskeletal alterations are critical for the morphogenesis of oligodendrocytes, and actin is involved in cell differentiation and myelin wrapping via polymerization and depolymerization, respectively. Various protein members of the myosin superfamily are known to be major binding partners of actin filaments and have been intensively researched because of their involvement in various cellular functions, including differentiation, cell movement, membrane trafficking, organelle transport, signal transduction, and morphogenesis. Some members of the myosin superfamily have been found to play important roles in the differentiation of oligodendrocytes and in CNS myelination. Interestingly, each member of the myosin superfamily expressed in oligodendrocyte lineage cells also shows specific spatial and temporal expression patterns and different distributions. In this review, we summarize previous findings related to the myosin superfamily and discuss how these molecules contribute to myelin formation and regeneration by oligodendrocytes.

Neutral Red Labeling: A Novel Vital Staining Method for Investigating Central and Peripheral Nervous System Lesions

Multiple sclerosis, neuromyelitis optica, Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy are representative demyelinating diseases of the central and peripheral nervous system. Remyelination by myelin forming cells is important for functional recovery from the neurological deficits caused in the demyelinating diseases. Lysophosphatidylcholine-induced demyelination in mice is commonly used to identify and study the molecular pathways of demyelination and remyelination. However, detection of focally demyelinated lesions is difficult and usually requires sectioning of demyelinated lesions in tissues for microscopic analysis. In this review, we describe the development and application of a novel vital staining method for labeling demyelinated lesions using intraperitoneal injection of neutral red (NR) dye. NR labeling reduces the time and effort required to search for demyelinated lesions in tissues, and facilitates electron microscopic analysis of myelin structures. NR labeling also has the potential to contribute to the elucidation of pathologies in the central and peripheral nervous system and assist with identification of drug candidates that promote remyelination.

A preclinical mice model of multiple sclerosis based on the toxin-induced double-site demyelination of callosal and cerebellar fibers

BACKGROUND

Multiple sclerosis (MS) is an irreversible progressive CNS pathology characterized by the loss of myelin (i.e. demyelination). The lack of myelin is followed by a progressive neurodegeneration triggering symptoms as diverse as fatigue, motor, locomotor and sensory impairments and/or bladder, cardiac and respiratory dysfunction. Even though there are more than fourteen approved treatments for reducing MS progression, there are still no cure for the disease. Thus, MS research is a very active field and therefore we count with different experimental animal models for studying mechanisms of demyelination and myelin repair, however, we still lack a preclinical MS model assembling demyelination mechanisms with relevant clinical-like signs.

RESULTS

Here, by inducing the simultaneous demyelination of both callosal and cerebellar white matter fibers by the double-site injection of lysolecithin (LPC), we were able to reproduce CNS demyelination, astrocyte recruitment and increases levels of proinflammatory cytokines levels along with motor, locomotor and urinary impairment, as well as cardiac and respiratory dysfunction, in the same animal model. Single site LPC-injections either in corpus callosum or cerebellum only, fails in to reproduce such a complete range of MS-like signs.

CONCLUSION

We here report that the double-site LPC injections treatment evoke a complex MS-like mice model. We hope that this experimental approach will help to deepen our knowledge about the mechanisms of demyelinated diseases such as MS.

The Mouse Model of Internal Capsule Demyelination: A Novel Tool for Investigating Motor Functional Changes Caused by Demyelination and for Evaluating Drugs That Promote Remyelination

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system, characterized by remyelination failure and axonal dysfunction. Remyelination by oligodendrocytes is critical for improvement of neurological deficits associated with demyelination. Rodent models of demyelination are frequently used to develop and evaluate therapies for MS. However, a suitable mouse model for assessing remyelination-associated recovery of motor functions is currently unavailable. In this review, we describe the development of the mouse model of internal capsule (IC) demyelination by focal injection of lysolecithin into brain and its application in the evaluation of drugs for demyelinating diseases. This mouse model exhibits motor deficits and subsequent functional recovery accompanying IC remyelination. Notably, this model shows enhancement of functional recovery as well as tissue regeneration when treated with clemastine, a drug that promotes remyelination. The IC demyelination mouse model should contribute to the development of novel drugs that promote remyelination and ameliorate neurological deficits in demyelinating diseases.

How to Use the Cuprizone Model to Study De- and Remyelination

Multiple sclerosis (MS) is an autoimmune and inflammatory disorder affecting the central nervous system whose cause is still largely unknown. Oligodendrocyte degeneration results in demyelination of axons, which can eventually be repaired by a mechanism called remyelination. Prevention of demyelination and the pharmacological support of remyelination are two promising strategies to ameliorate disease progression in MS patients. The cuprizone model is commonly employed to investigate oligodendrocyte degeneration mechanisms or to explore remyelination pathways. During the last decades, several different protocols have been applied, and all have their pros and cons. This article intends to offer guidance for conducting pre-clinical trials using the cuprizone model in mice, focusing on discovering new treatment approaches to prevent oligodendrocyte degeneration or enhance remyelination.

Inflammation in multiple sclerosis: consequences for remyelination and disease progression

Despite the large number of immunomodulatory or immunosuppressive treatments available to treat relapsing-remitting multiple sclerosis (MS), treatment of the progressive phase of the disease has not yet been achieved. This lack of successful treatment approaches is caused by our poor understanding of the mechanisms driving disease progression. Emerging concepts suggest that a combination of persisting focal and diffuse inflammation within the CNS and a gradual failure of compensatory mechanisms, including remyelination, result in disease progression. Therefore, promotion of remyelination presents a promising intervention approach. However, despite our increasing knowledge regarding the cellular and molecular mechanisms regulating remyelination in animal models, therapeutic increases in remyelination remain an unmet need in MS, which suggests that mechanisms of remyelination and remyelination failure differ fundamentally between humans and demyelinating animal models. New and emerging technologies now allow us to investigate the cellular and molecular mechanisms underlying remyelination failure in human tissue samples in an unprecedented way. The aim of this Review is to summarize our current knowledge regarding mechanisms of remyelination and remyelination failure in MS and in animal models of the disease, identify open questions, challenge existing concepts, and discuss strategies to overcome the translational roadblock in the field of remyelination-promoting therapies.