Role of Huntingtin in Vesicle Transport

描述(由申请人提供)：亨廷顿蛋白(N-HN)N-末端的聚谷氨酸胺扩张导致亨廷顿病(HD)。目前尚无治疗HD的有效方法。虽然已知突变的N-Fin片段会在体外积聚在HD神经元中并导致细胞功能障碍，但解释纹状体和皮质投射神经元选择性丢失的机制仍不清楚。野生型和突变型HTT与内吞和分泌途径中的膜相关。我们的总体假设是，突变的N-HTT‘S与神经细胞膜相关，导致HD患者早期细胞质中的细胞功能障碍。其中一个膜室包括自噬小体/溶酶体系统，该系统积累突变的HTT的全长或大的N-HTT片段。尽管HTT表面上缺乏跨膜结构域，但它与膜结合紧密。我们推测，参与蛋白质-蛋白质相互作用的N-末端的候选结构域促进了膜结合。人们对在体内形成N-HTT片段的降解途径知之甚少。确定HTT N-末端的蛋白酶裂解位置对于了解该蛋白是如何调控的很重要。钙蛋白酶是一种钙依赖的蛋白水解酶，它调节许多参与膜/细胞骨架组织的蛋白质的功能，在其N端附近裂解HTT，并产生长寿的N-HTT片段，这些片段在大脑中的膜部分中得到丰富。我们推测，Calain裂解的突变N-HTT产物在神经元中经历了不同于wt片段的处理，从而导致HD细胞功能障碍。HD小鼠也表现出纹状体NMDA受体功能异常。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。其具体目的是：1：了解突变型HTT诱导的自噬在细胞功能障碍中的作用；2：确定Calain对HTT蛋白的分解是否与HD的发病有关；3：确定突变型HTT对分泌途径中蛋白质运输的影响。这些研究的结果将为HD的细胞功能障碍的机制提供新的见解，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.