Pathological differences between white and grey matter multiple sclerosis lesions

Neurodegeneration in multiple sclerosis and neuromyelitis optica

Multiple sclerosis (MS) and neuromyelitis optica (NMO) are autoimmune demyelinating diseases of the central nervous system (CNS), having distinct immunological and pathological features. They have two pathogenic components, 'inflammation' and 'neurodegeneration', with different degrees of severity and pathogenetic mechanisms. The target antigen of autoimmunity in NMO is the water channel aquaporin-4 (AQP4), and antibodies directed against this antigen result in astrocyte damage. MS is a disease primarily affecting myelin and oligodendrocytes, but thus far, no MS-specific autoantigen has been identified. The distinct inflammatory processes in these diseases may trigger cascades of events leading to disease-specific neurodegeneration. Damage of the CNS tissue appears to be amplified by mechanisms that are in part shared by the two conditions and involve oxidative burst activation in microglia/macrophages, mitochondrial damage and axonal energy failure, Wallerian degeneration and meningeal inflammation. However, they appear to differ regarding the nature of the inflammatory response, the type and extent of cortical injury, and the type of astrocyte reaction and damage. Here, we provide a detailed comparison of the pathology between MS and NMO, which may help to define shared and disease-specific mechanisms of neurodegeneration in these diseases.

Heterogeneity in oligodendroglia: Is it relevant to mouse models and human disease?

There are many lines of evidence indicating that oligodendrocyte progenitor cells and oligodendrocyte populations in the central nervous system (CNS) are heterogeneous based on their developmental origins as well as from morphological and molecular criteria. Whether these distinctions reflect functional heterogeneity is less clear and has been the subject of considerable debate. Recent findings, particularly from knockout mouse models, have provided new evidence for regional variations in myelination phenotypes, particularly between brain and spinal cord. These data raise the possibility that oligodendrocytes in these regions have different functional capacities and/or ability to compensate for loss of a specific gene. The goal of this review is to briefly revisit the evidence for oligodendrocyte heterogeneity and then to present data from transgenic and demyelinating mouse models suggesting functional heterogeneity in myelination, demyelination, and remyelination in the CNS and, finally, to discuss the implications of these findings for human diseases. © 2016 Wiley Periodicals, Inc.

Secondary Progression in Multiple Sclerosis: Neuronal Exhaustion or Distinct Pathology?

Prevention of progression in neurological diseases, particularly in multiple sclerosis (MS) but also in neurodegenerative diseases, remains a significant challenge. MS patients switch from a relapsing-remitting to a progressive disease course, but it is not understood why and how this conversion occurs and why some patients never experience disease progression. Do aging and accumulation of neuronal damage induce progression, or do cognitive symptoms and accelerated grey matter (GM) atrophy point to distinct processes affecting networks? This review weighs accepted dogma against real data on the secondary progressive phase of the disease, highlighting current challenges in this important field and directions towards development of treatment strategies to slow or prevent progression of disability.

Small heat shock proteins are induced during multiple sclerosis lesion development in white but not grey matter

Introduction

The important protective role of small heat-shock proteins (HSPs) in regulating cellular survival and migration, counteracting protein aggregation, preventing apoptosis, and regulating inflammation in the central nervous system is now well-recognized. Yet, their role in the neuroinflammatory disorder multiple sclerosis (MS) is largely undocumented. With the exception of alpha B-crystallin (HSPB5), little is known about the roles of small HSPs in disease.

Results

Here, we examined the expression of four small HSPs during lesion development in MS, focussing on their cellular distribution, and regional differences between white matter (WM) and grey matter (GM). It is well known that MS lesions in these areas differ markedly in their pathology, with substantially more intense blood-brain barrier damage, leukocyte infiltration and microglial activation typifying WM but not GM lesions.

We analysed transcript levels and protein distribution profiles for HSPB1, HSPB6, HSPB8 and HSPB11 in MS lesions at different stages, comparing them with normal-appearing brain tissue from MS patients and non-neurological controls. During active stages of demyelination in WM, and especially the centre of chronic active MS lesions, we found significantly increased expression of HSPB1, HSPB6 and HSPB8, but not HSPB11. When induced, small HSPs were exclusively found in astrocytes but not in oligodendrocytes, microglia or neurons. Surprisingly, while the numbers of astrocytes displaying high expression of small HSPs were markedly increased in actively demyelinating lesions in WM, no such induction was observed in GM lesions. This difference was particularly obvious in leukocortical lesions covering both WM and GM areas.

Conclusions

Since induction of small HSPs in astrocytes is apparently a secondary response to damage, their differential expression between WM and GM likely reflects differences in mediators that accompany demyelination in either WM or GM during MS. Our findings also suggest that during MS, cortical structures fail to benefit from the protective actions of small HSPs.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-015-0267-2) contains supplementary material, which is available to authorized users.