Role of Huntingtin in Vesicle Transport

描述（由申请人提供）：亨廷顿蛋白（N-hn） n端多谷氨酰胺扩增导致亨廷顿病（HD）。目前还没有有效的治疗HD的方法。虽然已知突变的N-Fin片段在HD神经元中积累并在体外引起细胞功能障碍，但解释纹状体和皮质投射神经元选择性丧失的机制仍然难以捉摸。野生型和突变型htt在内吞和分泌途径中与膜相关。我们的总体假设是突变的N-htt与神经元膜的关联有助于HD细胞质的早期细胞功能障碍。其中一个膜室包括自噬体/溶酶体系统，它积累突变体htt的全长或大N-htt片段。虽然htt表面上缺乏跨膜结构域，但它与膜紧密结合。我们推测，参与蛋白-蛋白相互作用的n端候选结构域促进了膜结合。我们对体内形成N-htt片段的降解途径知之甚少。确定htt的n端蛋白酶裂解位点对于理解该蛋白是如何被调控的非常重要。Calpain是一种钙依赖性蛋白酶，它调节许多参与膜/细胞骨架组织的蛋白质的功能，在其n端附近切割htt并产生长寿命的N-htt片段，这些片段在脑膜组分中富集。我们推测，钙蛋白酶裂解的N-htt突变产物在神经元中经历了与wt片段不同的加工过程，从而导致HD的细胞功能障碍。HD小鼠纹状体NMDA受体功能也出现异常。突变的Fin可能导致NMDA受体功能障碍的一种方式是通过破坏NMDA受体亚型在细胞表面的组装。具体目的是：1：了解突变体htt诱导的自噬在细胞功能障碍中的作用；2：确定calpain对htt蛋白的水解是否参与了HD的发病机制；3：确定突变体htt对分泌途径中蛋白质转运的影响。这些研究结果将为HD的细胞功能障碍机制提供新的见解，并提出新的治疗靶点，可以减少突变N-htt片段的潜在有害影响。

DESCRIPTION (provided by applicant): A polygutamine expansion in the N-terminus of huntingtin (N-hn) causes Huntington's disease (HD). There is no effective treatment for HD. Although mutant N-Fin fragments are known to accumulate in HD neurons and cause cell dysfunction in vitro, a mechanism (or mechanisms) that explains the selective loss of striatal and cortical projection neurons remains elusive. Wild type and mutant htt associate with membranes in the endocytic and secretory pathway. Our overall hypothesis is that mutant N-htt 's association with neuronal membranes contributes to early cellular dysfunction in the cytoplasm in HD. One of these membrane compartments includes the autophagosome/lysosomal system, which accumulates full-length or large N-htt fragments of mutant htt. Although htt ostensibly lacks transmembrane domains, it associates tightly with membranes. We speculate that candidate domains in the N-terminus involved in protein-protein interactions promote membrane binding. Little is known about the degradative pathways that form N-htt fragments in vivo. Identifying the sites of protease cleavage in the N-terminus of htt is important for understanding how the protein is regulated. Calpain, a calcium dependent protease, which regulates the function of many proteins involved in membrane/cytoskeleton organization, cleaves htt near its N-terminus and produces long-lived N-htt fragments that are enriched in membrane fractions in brain. We speculate that mutant N-htt products of calpain cleavage undergo a different processing from the wt fragments in neurons that leads to cellular dysfunction in HD. HD mice also show abnormal function of striatal NMDA receptors. One way that mutant Fin might cause the dysfunction of NMDA receptors is by disrupting the assembly of NMDA receptor subtypes at the cell surface. The specific aims are: 1: To understand the role of mutant htt induced autophagy in cell dysfunction, 2: To determine whether htt proteolysis by calpain contributes to HD pathogenesis and 3: To determine the effects of mutant htt on protein transport within the secretory pathway. The results of these studies will provide new insights about the mechanisms of cellular dysfunction in HD and suggest novel therapeutic targets that can reduce the potentially harmful effects of mutant N-htt fragments.