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，几乎所有的细胞表面和分泌的蛋白质在后生动物中的ER/高尔基体分泌途径中的复杂的碳水化合物的添加进行修改。我们发现，高尔基体N-糖基化途径的代谢物可用性对细胞表面上大分子复合物的组装施加自主控制，并且在这种能力下，作用于信号传导和基因表达的上游以影响细胞生长、分化和疾病状态。每个蛋白质分子的N-聚糖的分支和数量协同调节与半乳糖凝集素的结合，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。N-糖基化的遗传破坏通过增强T细胞受体聚集/信号传导和减少生长抑制剂CTLA-4的表面保留来促进小鼠中的T细胞过度活跃和自身免疫性疾病。在人类中，将糖蛋白中的N-聚糖分支减少约20%的MGAT 1单倍型与将N-聚糖数量减少约50%的CTLA-4等位基因协同相互作用，使多发性硬化症（MS）和风湿性关节炎（RA）的风险增加约2倍。预期这两种变体独立地降低CTLA-4对半乳糖凝集素的亲和力，并且实际上，它们协同作用以限制表面CTLA-4表面水平。仅在携带两种变体的受试者中观察到疾病促进，并且似乎通过缺陷CTLA-4等位基因的拷贝数滴定。对高尔基体的代谢补充抑制小鼠中的T细胞功能和自身免疫，并挽救与MS和RA相关的T细胞生长和CTLA-4表面保留中的N-糖基化缺陷。我们的数据表明，在人类自身免疫的病因学之间的协同作用的多态性，有条件地抑制高尔基体GlcNAc分支和N-X-S/T位点的使用CTLA-4，并提供了一种治疗策略和分子机制的环境和遗传相互作用。为了在人类中推广这些结果，我们提出了以下目标。具体目标1将鉴定改变N-聚糖分支的遗传变体。具体目标2将研究MS相关等位基因对N-聚糖分支的调节及其与目标1中鉴定的变体的相互作用。具体目标3将研究改变N-聚糖分支的变体与CTLA-4 Ala 17和相关等位基因之间的协同相互作用。Specific Aim 4将检查多发性硬化症和1型糖尿病队列中Specific Aim 1-3的变异体的遗传相互作用。

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.