MGAT5 alters the severity of multiple sclerosis

N-acetylglucosamine inhibits T-helper 1 (Th1)/T-helper 17 (Th17) cell responses and treats experimental autoimmune encephalomyelitis

Current treatments and emerging oral therapies for multiple sclerosis (MS) are limited by effectiveness, cost, and/or toxicity. Genetic and environmental factors that alter the branching of Asn (N)-linked glycans result in T cell hyperactivity, promote spontaneous inflammatory demyelination and neurodegeneration in mice, and converge to regulate the risk of MS. The sugar N-acetylglucosamine (GlcNAc) enhances N-glycan branching and inhibits T cell activity and adoptive transfer experimental autoimmune encephalomyelitis (EAE). Here, we report that oral GlcNAc inhibits T-helper 1 (Th1) and T-helper 17 (Th17) responses and attenuates the clinical severity of myelin oligodendrocyte glycoprotein (MOG)-induced EAE when administered after disease onset. Oral GlcNAc increased expression of branched N-glycans in T cells in vivo as shown by high pH anion exchange chromatography, MALDI-TOF mass spectroscopy and FACS analysis with the plant lectin l-phytohemagglutinin. Initiating oral GlcNAc treatment on the second day of clinical disease inhibited MOG-induced EAE as well as secretion of interferon-γ, tumor necrosis factor-α, interleukin-17, and interleukin-22. In the more severe 2D2 T cell receptor transgenic EAE model, oral GlcNAc initiated after disease onset also inhibits clinical disease, except for those with rapid lethal progression. These data suggest that oral GlcNAc may provide an inexpensive and nontoxic oral therapeutic agent for MS that directly targets an underlying molecular mechanism causal of disease.

Genetics and the environment converge to dysregulate N-glycosylation in multiple sclerosis

How environmental factors combine with genetic risk at the molecular level to promote complex trait diseases such as multiple sclerosis (MS) is largely unknown. In mice, N-glycan branching by the Golgi enzymes Mgat1 and/or Mgat5 prevents T cell hyperactivity, cytotoxic T-lymphocyte antigen 4 (CTLA-4) endocytosis, spontaneous inflammatory demyelination and neurodegeneration, the latter pathologies characteristic of MS. Here we show that MS risk modulators converge to alter N-glycosylation and/or CTLA-4 surface retention conditional on metabolism and vitamin D₃, including genetic variants in interleukin-7 receptor-α (IL7RA*C), interleukin-2 receptor-α (IL2RA*T), MGAT1 (IV_AV_T−T) and CTLA-4 (Thr17Ala). Downregulation of Mgat1 by IL7RA*C and IL2RA*T is opposed by MGAT1 (IV_AV_T−T) and vitamin D₃, optimizing branching and mitigating MS risk when combined with enhanced CTLA-4 N-glycosylation by CTLA-4 Thr17. Our data suggest a molecular mechanism in MS whereby multiple environmental and genetic inputs lead to dysregulation of a final common pathway, namely N-glycosylation.

Complex diseases such as multiple sclerosis have both genetic and environmental components. This study demonstrates that variants of genes implicated in multiple sclerosis, and alterations in cellular metabolism and vitamin D3 levels, alter N-glycosylation, a post-translational modification causal of the disease in mice.

Mgat5 deficiency in T cells and experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an inflammatory demyelinating and neurodegenerative disease initiated by autoreactive T cells. Mgat5, a gene in the Asn (N-) linked protein glycosylation pathway, associates with MS severity and negatively regulates experimental autoimmune encephalomyelitis (EAE) and spontaneous inflammatory demyelination in mice. N-glycan branching by Mgat5 regulates interaction of surface glycoproteins with galectins, forming a molecular lattice that differentially controls the concentration of surface glycoproteins. T-cell receptor signaling, T-cell proliferation, T_H1 differentiation, and CTLA-4 endocytosis are inhibited by Mgat5 branching. Non-T cells also contribute to MS pathogenesis and express abundant Mgat5 branched N-glycans. Here we explore whether Mgat5 deficiency in myelin-reactive T cells is sufficient to promote demyelinating disease. Adoptive transfer of myelin-reactive Mgat5^−/− T cells into Mgat5^+/+ versus Mgat5^−/− recipients revealed more severe EAE in the latter, suggesting that Mgat5 branching deficiency in recipient naive T cells and/or non-T cells contribute to disease pathogenesis.

Entering a new phase of multiple sclerosis genetic epidemiology

Multiple sclerosis (MS) is a complex disease, where multiple genetic variants have been found to influence the risk of development. The evidence for environmental-attributable risk is also strong, indicating an interaction of risk factors leading to the development of disease in the individual. An importance of genetic variation within the human leukocyte antigen (HLA) region has been known for almost 40 years, but the search for additional variants connected to susceptibility has been long and largely fruitless. Joint efforts of the MS research community in collecting and sharing results from genetic case control cohorts, together with the technical development, eventually lead to the identification of multiple risk factors for MS as in other complex diseases. The list of identified genetic variants associated with disease is increasingly growing and some leads for functional mechanisms are emerging. Many of the identified regions also harbor associations with other immune-mediated diseases, suggesting common etiology across these various diseases. The great challenge in front of us now is to translate these point-wise indications of genetic effects to functional understanding of how disease develops.

Multiple sclerosis etiology: beyond genes and environment

Multiple sclerosis (MS) is a disorder of the CNS with inflammatory and neurodegenerative components. The etiology is unknown, but there is evidence for a role of both genetic and environmental factors. Among the heritable factors, MHC class II genes are strongly involved, as well as genes coding for others molecules of immunological relevance, genes controlling neurobiological pathways and genes of unknown function. Among nonheritable factors, many infectious agents (mainly viruses) and environmental factors (e.g., smoke, sun exposition and diet) seem to be of etiologic importance. Here, we report and discuss recent findings in MS on largely unexplored fields: the alternative splicing of mRNAs and regulatory noncoding RNAs, the major sources of transcriptome diversity; and epigenetic changes with special attention paid to DNA methylation and histone acetylation, the main regulators of gene expression.