Brain-derived gangliosides suppress the chronic relapsing-remitting experimental autoimmune encephalomyelitis in NOD mice induced with myelin oligodendrocyte glycoprotein peptide

Sphingolipid Players in Multiple Sclerosis: Their Influence on the Initiation and Course of the Disease

Sphingolipids (SLs) play a significant role in the nervous system, as major components of the myelin sheath, contributors to lipid raft formation that organize intracellular processes, as well as active mediators of transport, signaling and the survival of neurons and glial cells. Alterations in SL metabolism and content are observed in the course of central nervous system diseases, including multiple sclerosis (MS). In this review, we summarize the current evidence from studies on SLs (particularly gangliosides), which may shed new light upon processes underlying the MS background. The relevant aspects of these studies include alterations of the SL profile in MS, the role of antibodies against SLs and complexes of SL-ligand-invariant NKT cells in the autoimmune response as the core pathomechanism in MS. The contribution of lipid-raft-associated SLs and SL-laden extracellular vesicles to the disease etiology is also discussed. These findings may have diagnostic implications, with SLs and anti-SL antibodies as potential markers of MS activity and progression. Intriguing prospects of novel therapeutic options in MS are associated with SL potential for myelin repair and neuroprotective effects, which have not been yet addressed by the available treatment strategies. Overall, all these concepts are promising and encourage the further development of SL-based studies in the field of MS.

Ganglioside GD3 May Suppress the Functional Activities of Benign Skin T Cells in Cutaneous T-Cell Lymphoma

In cutaneous T-cell lymphoma (CTCL), which arises from skin-tropic memory T cells, malignant T cells and benign T cells are confined in the same skin lesions. It is thus difficult to evaluate the phenotypic characteristics and functional activities of benign T cells in CTCL. Disialoganglioside with three glycosyl groups (GD3) is increasingly expressed on the surface of solid malignant tumor cells and takes part in tumor progression and suppression of tumor immunity. However, the role of GD3 in CTCL is not well-understood. In this study, the malignant and benign T cells in CTCL skin lesions were distinguished by flow cytometry and their phenotypic characteristics were compared with those of T cells from control skin specimens. In CTCL skin lesions, the benign T cells included limited resident memory T cells (T_RM), which are sessile in skin and known to exert strong antitumor function. The benign T cells showed diminished Th17 property, and the expression of GD3 was high in the malignant T cells. The expression of GD3 in the malignant T cells inversely correlated with IL-17A production from the benign CD4 T cells. GD3 from the malignant T cells was implied to be involved in suppressing the Th17 activity of the benign T cells independent of the regulation of T_RM differentiation in CTCL. Revealing the role of GD3 in inhibiting the production of IL-17A in CTCL would aid the understanding of the suppressive mechanism of the antitumor activity by malignant tumor cells.

Gangliosides in the Brain: Physiology, Pathophysiology and Therapeutic Applications

Gangliosides are glycosphingolipids highly abundant in the nervous system, and carry most of the sialic acid residues in the brain. Gangliosides are enriched in cell membrane microdomains ("lipid rafts") and play important roles in the modulation of membrane proteins and ion channels, in cell signaling and in the communication among cells. The importance of gangliosides in the brain is highlighted by the fact that loss of function mutations in ganglioside biosynthetic enzymes result in severe neurodegenerative disorders, often characterized by very early or childhood onset. In addition, changes in the ganglioside profile (i.e., in the relative abundance of specific gangliosides) were reported in healthy aging and in common neurological conditions, including Huntington's disease (HD), Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), stroke, multiple sclerosis and epilepsy. At least in HD, PD and in some forms of epilepsy, experimental evidence strongly suggests a potential role of gangliosides in disease pathogenesis and potential treatment. In this review, we will summarize ganglioside functions that are crucial to maintain brain health, we will review changes in ganglioside levels that occur in major neurological conditions and we will discuss their contribution to cellular dysfunctions and disease pathogenesis. Finally, we will review evidence of the beneficial roles exerted by gangliosides, GM1 in particular, in disease models and in clinical trials.

Modelling MS: Chronic-Relapsing EAE in the NOD/Lt Mouse Strain

Modelling complex disorders presents considerable challenges, and multiple sclerosis (MS) is no exception to this rule. The aetiology of MS is unknown, and its pathophysiology is poorly understood. Moreover, the last two decades have witnessed a dramatic revision of the long-held view of MS as an inflammatory demyelinating white matter disease. Instead, it is now regarded as a global central nervous system (CNS) disorder with a neurodegenerative component. Currently, there is no animal model recapitulating MS immunopathogenesis. Available models are based on autoimmune-mediated demyelination, denoted experimental autoimmune encephalomyelitis (EAE) or virally or chemically induced demyelination. Of these, the EAE model has been the most commonly used. It has been extensively improved since its first description and now exists as a number of variants, including genetically modified and humanized versions. Nonetheless, EAE is a distinct disease, and each variant models only certain facets of MS. Whilst the search for more refined MS models must continue, it is important to further explore where mechanisms underlying EAE provide proof-of-principle for those driving MS pathogenesis. EAE variants generated with the myelin component myelin oligodendrocyte glycoprotein (MOG) have emerged as the preferred ones, because in this particular variant disease is associated with both T- and B-cell effector mechanisms, together with demyelination. MOG-induced EAE in the non-obese diabetic (NOD) mouse strain exhibits a chronic-relapsing EAE clinical profile and high disease incidence. We describe the generation of this variant, its contribution to the understanding of MS immune and pathogenetic mechanisms and potential for evaluation of candidate therapies.

Cross-linking of GM1 ganglioside by galectin-1 mediates regulatory T cell activity involving TRPC5 channel activation: possible role in suppressing experimental autoimmune encephalomyelitis

Several animal autoimmune disorders are suppressed by treatment with the GM1 cross-linking units of certain toxins such as B subunit of cholera toxin (CtxB). Due to the recent observation of GM1 being a binding partner for the endogenous lectin galectin-1 (Gal-1), which is known to ameliorate symptoms in certain animal models of autoimmune disorders, we tested the hypothesis that an operative Gal-1/GM1 interplay induces immunosuppression in a manner evidenced by both in vivo and in vitro systems. Our study of murine experimental autoimmune encephalomyelitis (EAE) indicated suppressive effects by both CtxB and Gal-1 and further highlighted the role of GM1 in demonstrating enhanced susceptibility to EAE in mice lacking this ganglioside. At the in vitro level, polyclonal activation of murine regulatory T (Treg) cells caused up-regulation of Gal-1 that was both cell bound and released to the medium. Similar activation of murine CD4(+) and CD8(+) effector T (Teff) cells resulted in significant elevation of GM1 and GD1a, the neuraminidase-reactive precursor to GM1. Activation of Teff cells also up-regulated TRPC5 channels which mediated Ca(2+) influx upon GM1 cross-linking by Gal-1 or CtxB. This involved co-cross-linking of heterodimeric integrin due to close association of these alpha(4)beta(1) and alpha(5)beta(1) glycoproteins with GM1. Short hairpin RNA (shRNA) knockdown of TRPC5 in Teff cells blocked contact-dependent proliferation inhibition by Treg cells as well as Gal-1/CtxB-triggered Ca(2+) influx. Our results thus indicate GM1 in Teff cells to be the primary target of Gal-1 expressed by Treg cells, the resulting co-cross-linking and TRPC5 channel activation contributing importantly to the mechanism of autoimmune suppression.

Antibodies to myelin oligodendrocyte glycoprotein are not involved in the severity of chronic non-remitting experimental autoimmune encephalomyelitis

To elucidate the role of antibodies in development of chronic non-remitting experimental autoimmune encephalomyelitis (EAE) in C57BL/6 mice, which is a well-established Th1-mediated autoimmune disease, and the involvement of activation-induced cytidine deaminase (AID) in Th1-mediated function, we have investigated the myelin oligodendrocyte glycoprotein (MOG)-induced EAE in mice deficient of AID, which is absolutely required for class switching and somatic hypermutation. Following immunization with MOG, AID(-/-) had completely same levels of clinical and pathological severity of EAE when compared with AID(+/-) and AID(+/+), although AID(-/-) did not produce IgG and anti-MOG IgG. Similar levels of T cell proliferation and a modest increase of anti-MOG IgM synthesis were found in spleen cells of AID(-/-) stimulated with MOG. These results indicate that antibodies are not involved in development of EAE in C57BL/6 mice.