| Summary: | 博士 === 國防醫學院 === 生命科學研究所 === 104 === Type 1 diabetes is an autoimmune disease and mainly caused by Th1-mediated the destruction of pancreatic β-cells. Regulated N-glycosylation controls T cell responses including threshold, differentiation and migration through the interaction with specific lectins. However, the role of N-linked glycosylation on T cell in the pathogenesis of NOD mice remains incompletely understood. To investigate the N-glycosylation-based modulation on the T helper cell development in the pathogenesis of autoimmune diabetes, we focus on glucosamine and β1,6-N-acetylglucosaminyltransferase V (Mgat5). Glucosamine is an amino sugar that interferes with the N-linked glycosylation. Here we demonstrate that glucosamine significantly impedes Th1, Th2 and iTreg but strikingly promotes Th17 cell differentiation in NOD mice. Our results reveal that glucosamine selectively down-regulates N-linked glycosylation of IL-2 receptor subunit (CD25) and subsequently inhibits its downstream signaling molecule Stat5 in a dosage-dependent manner. Moreover, glucosamine-modulating effects on T helper cell differentiation are similar to those by anti-IL-2 and anti-CD25 antibodies treatment, further supporting that its effects are IL-2/CD25 signaling-dependent. Interestingly, excess glucose significantly rescues this glucosamine-mediated regulation, suggesting a functional competition between glucose and glucosamine. Therefore, in this study, our finding suggested that glucosamine treatment inhibits Th1 cell differentiation in vivo and prolongs the survival of islet grafts in diabetic recipients, and exacerbated the severity of EAE. Mgat5 is a glycosyltransferase that transfers N-acetylglucosamine (GlcNAc) from UDP-GlcNAc to hydroxyl group on carbon 6 of mannose to increase N-glycan branching, and positively regulates the T cell activation thresholds and protects the incidence of EAE. Recent studies have shown that T cells of NOD mice have less N-glycan branching and are more susceptible to EAE. Based on the biological function of Mgat5, we generate transgenic NOD mice that overexpressed mgat5 on T cells, and detect the N-glycan branching level on T cells surface by L-PHA staining. Our results revealed that the enhanced N-glycan branching by Mgat5 attenuated T cells proliferation in antigen-specific manner. Unexpectedly, mgat5 transgenic mice display a significantly higher incidence of diabetic incidence and adoptive transfer of Mgat5-overexpressed CD8+ T cells reveal an earlier and higher diabetic kinetic, indicating that Mgat5-mediated N-glycan branching on CD8+ T cells positively contributes the development of autoimmune diabetes. To further dissect the molecular mechanism involved in this N-glycan branching-mediated T cell autoimmunity, we have generated Mgat5/NY8.3 doubly transgenic mice to analyze the properties of these Mgat5-overexpressed CD8+ T cells in an antigen-specific manner. The results indicated that Mgat5/NY8.3 doubly Tg mice have higher diabetic incidence than WT NY8.3 Tg mice, suggesting that enhanced N-glycan branching on CD8+ T cells contributes to the onset of diabetes. Our study demonstrated that enhanced N-glycan branching positively contribute to the diabetogenic properties of CD8 T cells in NOD mice.
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