GPR52调控变异HTT蛋白水平的验证与机制研究

亨廷顿病是一种具代表性的神经退行性及多聚谷氨酰胺疾病，由基因HTT的CAG重复区域的变异引起。直接降低变异HTT蛋白水平理论上可以抑制其下游各种机制产生的毒性，并在各种疾病模型中被证实可以显著抑制疾病相关表型。寻找影响变异HTT蛋白水平的基因或信号通路，对选择适合小分子作用的潜在靶位点，开发针对此类疾病新药有着重要意义。我们前期工作通过高通量筛选发现敲低GPR52这个G蛋白偶联受体可以降低变异HTT蛋白水平，在细胞及动物模型中初步验证其对变异HTT蛋白水平的调控。本项目将利用基因操控、信号通路的小分子调控、细胞及动物疾病表型分析等方法，在神经元及动物模型中对GPR52对变异HTT蛋白水平的调控机理深入研究，进一步确认GPR52的作用并揭示其降低变异HTT的机制，特别是与G蛋白的信号通路的关联。本项目的成功实施将对基于调控GPR52的抗亨廷顿病药物提供细胞生物学层面的理论支持。

Huntington's disease (HD) is the third most prevalent neurodegenerative disorder with no cure. HD is an autosomal dominant monogenetic disorder caused by an expanded CAG repeat in exon 1 of the HTT gene, resulting in the expression of an mHTT protein with a polyglutamine repeat containing greater than ~36Q. Although it is reported that wild-type HTT (wtHTT) has neuroprotective functions; the gain of toxic function of mHTT, rather than loss of activity of wtHTT, is the major cause of the disease. Research groups have reported that expression of mHTT protein causes neuronal death, dementia, and motor dysfunction via a variety of cellular processes such as transcriptional dysregulation, imbalances in axonal transport, endocytosis/exocytosis, and calcium homeostasis. While each of these processes is critical to survival, it is unclear which one(s) underlie the etiology from mHTT expression to neuronal toxicity. Given the complex nature of HTT biology following its synthesis, we postulated that targeting HTT protein level at a point upstream of the pathological phenotypes would be the best way to mitigate any possible toxic phenotypes. There is evidence that, by lowering mHTT, the associated toxic phenotypes may be inhibited or reversed.Therefore, lowering mHTT level may provide an effective approach to treat HD by ameliorating all the downstream toxic effects, and identifying genes and pathways that regulate mHTT level is of great interest. To achieve this goal, we have performed genome-wide RNAi screenings and identified GPR52 as a promising target in suppressing mHTT protein level. Preliminary validation showed that knock-down of GPR52 decreased mHTT protein level and rescued relavant disease phenotypes.In this project, we will further validate the potential role of GPR52 in HD and mHTT clearance, and reveal its mechanism, especially the potential involvement of G protein relavant pathways.