Human Autoimmunity and Genetic Defects in N-Glycosylation

描述（由申请人提供）：遗传信息从DNA流向大分子结构；-生命分子组织中的主导力量。然而，在后生动物中，几乎所有的细胞表面和分泌蛋白都通过在内质网/高尔基体分泌途径中添加复合碳水化合物而被修饰。我们发现，高尔基N-糖基化途径的代谢物可用性对细胞表面大分子复合物的组装施加自主控制，并在这种能力下，作用于信号传导和基因表达的上游，影响细胞生长、分化和疾病状态。每个蛋白质分子的分支和n -聚糖的数量协同调节与凝集素的结合，从而以可预测的方式调节表面糖蛋白的分布、聚集和内吞作用。遗传破坏n -糖基化通过增强T细胞受体聚集/信号传导和减少生长抑制剂CTLA-4的表面保留，促进小鼠T细胞过度活跃和自身免疫性疾病。在人类中，使糖蛋白中n -聚糖分支减少约20%的MGAT1单倍型与使n -聚糖数量减少约50%的CTLA-4等位基因协同作用，使多发性硬化症（MS）和类风湿性关节炎（RA）的风险增加约2倍。这两种变体预计会独立降低CTLA-4对凝集素的亲和力，事实上，它们协同作用以限制表面CTLA-4的表面水平。疾病促进仅在携带两种变体的受试者中观察到，并且似乎是由有缺陷的CTLA-4等位基因的拷贝数来滴定的。代谢补充高尔基体抑制小鼠T细胞功能和自身免疫，并修复与MS和RA相关的T细胞生长中的n -糖基化缺陷和CTLA-4表面保留。我们的数据表明，条件抑制高尔基GlcNAc分支的多态性与CTLA-4中N-X-S/T位点的使用之间在人类自身免疫的病因学中存在协同作用，并为环境和遗传相互作用提供了治疗策略和分子机制。为了在人类中推广这些结果，我们提出以下目标。特异性目标1将识别改变n -聚糖分支的遗传变异。特异性Aim 2将研究MS相关等位基因对n -聚糖分支的调控及其与Aim 1中鉴定的变异的相互作用。特异性Aim 3将研究改变n -聚糖分支的变体与CTLA-4 Ala17和相关等位基因之间的合作相互作用。Specific Aim 4将检查多发性硬化症和1型糖尿病患者中Specific Aim 1-3变异的遗传相互作用。

DESCRIPTION (provided by applicant): Genetic information flows from DNA to macromolecular structures;- the dominant force in the molecular organization of life. However, virtually all cell surface and secreted proteins in metazoans are modified by the addition of complex carbohydrates in the ER/Golgi secretory pathway. We find that metabolite availability to the Golgi N- glycosylation pathway exerts autonomous control over the assembly of macromolecular complexes on the cell surface, and in this capacity, acts upstream of signaling and gene expression to influence cell growth, differentiation and disease states. The branching and number of N-glycans per protein molecule cooperate to regulate binding to galectins and thereby the distribution, clustering and endocytosis of surface glycoproteins in a predictable manner. Genetic disruption of N-glycosylation promotes T cell hyper-activity and autoimmune disease in mice by enhancing T cell receptor clustering/signaling and reducing surface retention of the growth inhibitor CTLA-4. In humans, a haplotype of MGAT1 that reduces N-glycan branching in glycoproteins by ~20% synergistically interacts with an allele of CTLA-4 that reduces N-glycan number by ~50%, increasing the risk of Multiple Sclerosis (MS) and Rheumatoid Arthritis (RA) by ~2 fold. The two variants are expected to independently reduce CTLA-4 affinity for galectins and indeed, they act cooperatively to limit surface CTLA-4 surface levels. Disease promotion is observed only in subjects who harbor both variants, and appears to be titrated by the number of copies of the defective CTLA-4 allele. Metabolic supplementation to the Golgi inhibits T cell function and autoimmunity in mice and rescues the N-glycosylation defects in T cell growth and CTLA-4 surface retention associated with MS and RA. Our data suggests synergism in the etiology of human autoimmunity between polymorphisms that conditionally suppress Golgi GlcNAc branching and N-X-S/T site usage in CTLA-4, and provides a therapeutic strategy and molecular mechanism for environmental and genetic interactions. To extend these results in humans we propose the following aims. Specific Aim 1 will identify genetic variants that alter N-glycan branching. Specific Aim 2 will investigate the regulation of N-glycan branching by MS associated alleles and their interaction with variants identified in Aim 1. Specific Aim 3 will investigate for co- operative interactions between variants that alter N-glycan branching and CTLA-4 Ala17 and related alleles. Specific Aim 4 will examine for genetic interaction of variants from Specific Aim's 1-3 in Multiple Sclerosis and Type 1 Diabetes co-horts. PUBLIC HEALTH RELEVANCE: Multiple Sclerosis and Type 1 Diabetes are autoimmune diseases resulting from complex interactions between genetic background of the individual and his/her environment. Our combined data suggests that genetic deficiency in a pathway that controls the addition of specific sugars to proteins (i.e. protein glycosylation) leads to immune hyperactivity and promotes autoimmunity in mice and humans. Metabolically supplementing the pathway with a simple sugar suppresses immune hyperactivity and development of autoimmunity, suggesting human disease may be treated/prevented with metabolic therapy.