C9orf72基因非编码区G4C2重复扩增突变能导致肌萎缩侧索硬化(ALS)和额颞叶痴呆(FTD)。G4C2重复扩增可激活应激反应，上调重复相关的非AUG(RAN)翻译，产生大量具有神经毒性的二肽重复蛋白。目前，关于G4C2重复扩增激活应激反应的机制还不完全清楚。申请人前期研究发现，G4C2重复扩增主要以生成的二肽重复蛋白来活化蛋白激酶R(PKR)，从而激活应激反应；抑制PKR磷酸化可明显降低应激颗粒的生成以及二肽重复蛋白的水平。我们推测PKR是G4C2重复扩增活化应激通路过程中的关键激酶，通过前馈环路调控RAN翻译异常活化，产生大量的二肽重复蛋白而导致神经变性。本项目采用分子细胞生物学及动物模型等研究手段深入探讨G4C2重复扩增活化PKR的分子机制，以及PKR在这种应激反应的前馈环路中的重要作用，将进一步阐明C9-ALS/FTD发病机制，为PKR作为新的药物靶点的研发提供理论指导。

G4C2 nucleotide repeat expansion in C9orf72 gene is one of the most common causes of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). G4C2 repeat could trigger stress response, enhance repeat-associated non-AUG (RAN) translation and produce a large number of neurotoxic dipeptide repeat proteins (DPRs). However, it’s still unknown how G4C2 repeats activate cellular stress. Our preliminary data suggests that it is the DPRs that activate double-stranded RNA-activated protein kinase (PKR) and trigger stress response in cells transfected with G4C2 repeat. Besides, inhibition of PKR could significantly reduce G4C2 RAN reporter associated stress granule formation and RAN translation. Thus, we predict that PKR is a key kinase for G4C2 repeats activating stress response. And PKR could regulate abnormal activation of RAN translation through the feed-forward loop, which could promote neurodegeneration. In the project, we will determine how G4C2 repeats activate PKR mediated stress response and test the role of PKR in the feed-forward loop of stress response. This project will be helpful to further clarify the pathogenesis of C9-ALS/FTD and provide new insights for therapeutic strategies.