Autoimmune versus oligodendrogliopathy: the pathogenesis of multiple sclerosis

Cathepsin-B inhibitor CA-074 attenuates retinopathy and optic neuritis in experimental autoimmune encephalomyelitis induced in SJL/J mice

The complicated multiple sclerosis (MS) can exhibit subacute sight deterioration and can lead to total deprivation of vision. In the current work, we explored the therapeutic outcome of Cathepsin B inhibitor (CA-074) against retinopathy and optic neuritis (ON) caused by experimental autoimmune encephalomyelitis (EAE) induced by proteolipid protein peptide (PLP) in female SJL/J mice. A daily dose of 10 mg/kg CA-074 was administered to the EAE mice intraperitoneally for 14 days from day 14 post-immunization until day 28. The Western blot and immunofluorescence analyses show inflammation in the optic nerve through the elevation of iNOS and NFkB markers in EAE mice. Optic neuritis was reported which is a consequence of demyelination and axon injury, estimated with the reduction in myelin basic protein (MBP). The glial fibrillary acidic protein (GFAP) expression level was found to be elevated in the retina of EAE mice which confirmed the retinopathy. The administration of CA-074 ameliorated optic neuritis and retinopathy by reducing inflammation. The treatment with CA-074 also reduced the demyelination and axonal injuries in the EAE mice. The findings of this study have shown the protective effect of CA-074 in the case of retinopathy and ON inflicted by EAE in SJL/J mice.

Full spectrum of vitamin D immunomodulation in multiple sclerosis: mechanisms and therapeutic implications

Vitamin D deficiency has been associated with the risk of multiple sclerosis, disease activity and progression. Results from in vitro experiments, animal models and analysis of human samples from randomized controlled trials provide comprehensive data illustrating the pleiotropic actions of Vitamin D on the immune system. They globally result in immunomodulation by decreasing differentiation of effector T and B cells while promoting regulatory subsets. Vitamin D also modulates innate immune cells such as macrophages, monocytes and dendritic cells, and acts at the level of the blood–brain barrier reducing immune cell trafficking. Vitamin D exerts additional activity within the central nervous system reducing microglial and astrocytic activation. The immunomodulatory role of Vitamin D detected in animal models of multiple sclerosis has suggested its potential therapeutic use for treating multiple sclerosis. In this review, we focus on recent published data describing the biological effects of Vitamin D in animal models of multiple sclerosis on immune cells, blood–brain barrier function, activation of glial cells and its potential neuroprotective effects. Based on the current knowledge, we also discuss optimization of therapeutic interventions with Vitamin D in patients with multiple sclerosis, as well as new technologies allowing in-depth analysis of immune cell regulations by vitamin D.

Cathepsin B Gene Knockout Improves Behavioral Deficits and Reduces Pathology in Models of Neurologic Disorders

Cathepsin B (CTSB) is a powerful lysosomal protease. This review evaluated CTSB gene knockout (KO) outcomes for amelioration of brain dysfunctions in neurologic diseases and aging animal models. Deletion of the CTSB gene resulted in significant improvements in behavioral deficits, neuropathology, and/or biomarkers in traumatic brain injury, ischemia, inflammatory pain, opiate tolerance, epilepsy, aging, transgenic Alzheimer's disease (AD), and periodontitis AD models as shown in 12 studies. One study found beneficial effects for double CTSB and cathepsin S KO mice in a multiple sclerosis model. Transgenic AD models using amyloid precursor protein (APP) mimicking common sporadic AD in three studies showed that CTSB KO improved memory, neuropathology, and biomarkers; two studies used APP representing rare familial AD and found no CTSB KO effect, and two studies used highly engineered APP constructs and reported slight increases in a biomarker. In clinical studies, all reports found that CTSB enzyme was upregulated in diverse neurologic disorders, including AD in which elevated CTSB was positively correlated with cognitive dysfunction. In a wide range of neurologic animal models, CTSB was also upregulated and not downregulated. Further, human genetic mutation data provided precedence for CTSB upregulation causing disease. Thus, the consilience of data is that CTSB gene KO results in improved brain dysfunction and reduced pathology through blockade of CTSB enzyme upregulation that causes human neurologic disease phenotypes. The overall findings provide strong support for CTSB as a rational drug target and for CTSB inhibitors as therapeutic candidates for a wide range of neurologic disorders. SIGNIFICANCE STATEMENT: This review provides a comprehensive compilation of the extensive data on the effects of deleting the cathepsin B (CTSB) gene in neurological and aging mouse models of brain disorders. Mice lacking the CTSB gene display improved neurobehavioral deficits, reduced neuropathology, and amelioration of neuronal cell death and inflammatory biomarkers. The significance of the compelling CTSB evidence is that the data consilience validates CTSB as a drug target for discovery of CTSB inhibitors as potential therapeutics for treating numerous neurological diseases.

Diffusely abnormal white matter in multiple sclerosis

MRI enables detailed in vivo depiction of multiple sclerosis (MS) pathology. Localized areas of MS damage, commonly referred to as lesions, or plaques, have been a focus of clinical and research MRI studies for over four decades. A nonplaque MRI abnormality which is present in at least 25% of MS patients but has received far less attention is diffusely abnormal white matter (DAWM). DAWM has poorly defined boundaries and a signal intensity that is between normal-appearing white matter and classic lesions on proton density and T₂ -weighted images. All clinical phenotypes of MS demonstrate DAWM, including clinically isolated syndrome, where DAWM is associated with higher lesion volume, reduced brain volume, and earlier conversion to MS. Advanced MRI metric abnormalities in DAWM tend to be greater than those in NAWM, but not as severe as focal lesions, with myelin, axons, and water-related changes commonly reported. Histological studies demonstrate a primary lipid abnormality in DAWM, with some axonal damage and lesser involvement of myelin proteins. This review provides an overview of DAWM identification, summarizes in vivo and postmortem observations, and comments on potential pathophysiological mechanisms, which may underlie DAWM in MS. Given the prevalence and potential clinical impact of DAWM, the number of imaging studies focusing on DAWM is insufficient. Characterization of DAWM significance and microstructure would benefit from larger longitudinal and additional quantitative imaging efforts. Revisiting data from previous studies that included proton density and T₂ imaging would enable retrospective DAWM identification and analysis.

Brain energy metabolism and multiple sclerosis: progress and prospects

Multiple sclerosis (MS) is an autoimmune disease accompanied with nerve pain and paralysis. Although various pathogenic causes of MS have been suggested, including genetic and environmental factors, how MS occurs remains unclear. Moreover, MS should be diagnosed based on clinical experiences because of no disease-specific biomarker and currently available treatments for MS just can reduce relapsing frequency or severity with little effects on disease disability. Therefore, more efforts are required to identify pathophysiology of MS and diagnosis markers. Recent evidence indicates another aspect of MS pathogenesis, energy failure in the central nervous system (CNS). For instance, inflammation that is a characteristic MS symptom and occurs frequently in the CNS of MS patients can result into energy failure in mitochondria and cytosol. Indeed, metabolomics studies for MS have reported energy failure in oxidative phosphorylation and alteration of aerobic glycolysis. Therefore, studies on the metabolism in the CNS may provide another insight for understanding complexity of MS and pathogenesis, which would facilitate the discovery of promising strategies for developing therapeutics to treat MS. This review will provide an overview on recent progress of metabolomic studies for MS, with a focus on the fluctuation of energy metabolism in MS.

The DTA Mouse Model for Oligodendrocyte Ablation and CNS Demyelination

Genetic mouse models facilitate investigation of mechanisms underpinning human diseases and aid the development of novel therapeutic treatments. To better understand the demyelination and remyelination processes in adult-onset demyelinating diseases like multiple sclerosis (MS), we have developed the DTA mouse model system that allows for the widespread ablation of the mature oligodendrocytes, resulting in demyelination throughout the central nervous system (CNS). Induction of oligodendrocyte death in young adult DTA mice causes extensive CNS demyelination that leads to a severe neurological disease, followed by a full recovery that is associated with extensive replenishment of oligodendrocytes and remyelination. Thus, the DTA mouse enables investigation of the mechanisms that promote remyelination in MS and other adult-onset demyelinating diseases. Approximately 30 weeks later, the recovered DTA mice develop a fatal secondary demyelinating disease that is mediated by autoimmune T cells. Therefore, the DTA mouse model is also ideal for elucidating the role of oligodendrocyte death in eliciting autoimmunity in MS. In this chapter we describe the methods we used to generate the DTA mouse model and to analyze both the primary and secondary demyelinating diseases in DTA mice.

Microglia-induced activation of non-canonical Wnt signaling aggravates neurodegeneration in demyelinating disorders

Oligodendrocytes are myelinating cells of the central nervous system. Multiple sclerosis (MS) is a demyelinating disease characterized by both myelin loss and neuronal degeneration. However, the molecular mechanisms underlying neuronal degeneration in demyelinating disorders are not fully understood. In the experimental autoimmune encephalomyelitis (EAE) demyelinating mouse model of MS, inflammatory microglia produce cytokines including interleukin-1β (IL-1β). Since microglia and non-canonical Wnt signaling components in neurons, such as the co-receptor Ror2, were observed in the spinal cord of EAE mice, we postulated that the interplay between activated microglia and spinal neurons under EAE conditions is mediated through non-canonical Wnt signaling. EAE treatment up-regulated in vivo expression of non-canonical Wnt signaling components in spinal neurons through microglial activation. In accordance with the neuronal degeneration detected in the EAE spinal cord in vivo, co-culture of spinal neurons with microglia or the application of recombinant IL-1β up-regulated non-canonical Wnt signaling, and induced neuronal cell death, which was suppressed by the inhibition of the Wnt-Ror2 pathway. Ectopic non-canonical Wnt signaling aggravated the demyelinating pathology in another MS mouse model due to Wnt5a-induced neurodegeneration. The linkage between activated microglia and neuronal Wnt-Ror2 signaling may provide a possible candidate target for therapeutic approaches to demyelinating disorders.

Oligodendrocyte death results in immune-mediated CNS demyelination

Although multiple sclerosis is a common neurological disorder, the origin of the autoimmune response against myelin, which is the characteristic feature of the disease, remains unclear. To investigate whether oligodendrocyte death could cause this autoimmune response, we examined the oligodendrocyte ablation Plp1-CreER(T);ROSA26-eGFP-DTA (DTA) mouse model. Approximately 30 weeks after recovering from oligodendrocyte loss and demyelination, DTA mice develop a fatal secondary disease characterized by extensive myelin and axonal loss. Strikingly, late-onset disease was associated with increased numbers of T lymphocytes in the CNS and myelin oligodendrocyte glycoprotein (MOG)-specific T cells in lymphoid organs. Transfer of T cells derived from DTA mice to naive recipients resulted in neurological defects that correlated with CNS white matter inflammation. Furthermore, immune tolerization against MOG ameliorated symptoms. Overall, these data indicate that oligodendrocyte death is sufficient to trigger an adaptive autoimmune response against myelin, suggesting that a similar process can occur in the pathogenesis of multiple sclerosis.

Redundancy between Cysteine Cathepsins in Murine Experimental Autoimmune Encephalomyelitis

The cysteine cathepsins B, S, and L are functionally linked to antigen processing, and hence to autoimmune disorders such as multiple sclerosis. Stemming from several studies that demonstrate that mice can be protected from experimental autoimmune encephalomyelitis (EAE) through the pharmacologic inhibition of cysteine cathepsins, it has been suggested that targeting these enzymes in multiple sclerosis may be of therapeutic benefit. Utilizing mice deficient in cysteine cathepsins both individually and in combination, we found that the myelin-associated antigen myelin oligodendrocyte glycoprotein (MOG) was efficiently processed and presented by macrophages to CD4+ T cells in the individual absence of cathepsin B, S or L. Similarly, mice deficient in cathepsin B or S were susceptible to MOG-induced EAE and displayed clinical progression and immune infiltration into the CNS, similar to their wild-type counterparts. Owing to a previously described CD4+ T cell deficiency in mice deficient in cathepsin L, such mice were protected from EAE. When multiple cysteine cathepsins were simultaneously inhibited via genetic deletion of both cathepsins B and S, or by a cathepsin inhibitor (LHVS), MHC-II surface expression, MOG antigen presentation and EAE were attenuated or prevented. This study demonstrates the functional redundancy between cathepsin B, S and L in EAE, and suggests that the inhibition of multiple cysteine cathepsins may be needed to modulate autoimmune disorders such as multiple sclerosis.

Absence of CCL2 and CCL3 Ameliorates Central Nervous System Grey Matter But Not White Matter Demyelination in the Presence of an Intact Blood-Brain Barrier

A broad spectrum of diseases is characterized by myelin abnormalities, oligodendrocyte pathology, and concomitant glia activation, among multiple sclerosis (MS). Our knowledge regarding the factors triggering gliosis and demyelination is scanty. Chemokines are pivotal for microglia and astrocyte activation and orchestrate critical steps during the formation of central nervous system (CNS) demyelinating lesions. Redundant functions of chemokines complicate, however, the study of their functional relevance. We used the cuprizone model to study redundant functions of two chemokines, CCL2/MCP1 and CCL3/MIP1α, which are critically involved in the pathological process of cuprizone-induced demyelination. First, we generated a mutant mouse strain lacking functional genes of both chemokines and demonstrated that double-mutant animals are viable, fertile, and do not present with gross abnormalities. Astrocytes and peritoneal macrophages, cultured form tissues of these animals did neither express CCL2 nor CCL3. Exposure to cuprizone resulted in increased CCL2 and CCL3 brain levels in wild-type but not mutant animals. Cuprizone-induced demyelination, oligodendrocyte loss, and astrogliosis were significantly ameliorated in the cortex but not corpus callosum of chemokine-deficient animals. In summary, we provide a novel powerful model to study the redundant function of two important chemokines. Our study reveals that chemokine function in the CNS redounds to region-specific pathophysiological events.

MicroRNAs: novel regulators of oligodendrocyte differentiation and potential therapeutic targets in demyelination-related diseases

MicroRNAs (miRNAs or miRs) are a class of endogenous small non-coding RNAs that consist of about 22 nucleotides and play critical roles in various biological processes, including cell proliferation, differentiation, apoptosis, and tumorigenesis. In recent years, some specific miRNA, such as miR-219, miR-138, miR-9, miR-23, and miR-19b were found to participate in the regulation of oligodendrocyte (OL) differentiation and myelin maintenance, as well as in the pathogenesis of demyelination-related diseases (e.g., multiple sclerosis, ischemic stroke, and leukodystrophy). These miRNAs control their target mRNA or regulate the protein levels of some signaling pathways, and participate in OL differentiation and the pathogenesis of demyelination-related diseases. During pathologic processes, the expression levels of specific miRNAs are dynamically altered. Therefore, miRNAs act as diagnostic and prognostic indicators of defects in OL differentiation and demyelination-related diseases, and they can provide potential targets for therapeutic drug development.