Rab21 对γ-分泌酶的调控机制以及其作为治疗阿尔兹海默症潜在靶点的研究

One of the pathological hallmarks of Alzheimer’s disease (AD) is the abnormal accumulation of β-Amyloid peptides (Aβ) in senile plaques. Aβ is a cleavage product derived from the amyloid precursor protein (APP) that is sequentially cleaved by β- and γ-secretases. Countless studies have indicated protein-trafficking associated Rab proteins play crucial roles in Aβ production. Our pre-experiments revealed that Rab21 protein can interact with Presenilin 1 (PS1), the catalytic subunit of γ-secretase, and also regulate the activity of γ-secretase. This project aims at studying the regulatory role of Rab21 protein on γ-secretase and the possibility of Rab21 as a potential therapeutic target of AD. Firstly, the interaction between Rab21 and PS1 will be further determined in mouse brain. Secondly, the role of Rab21 on the enzymatic activity and trafficking of γ-secretase, as well as whether Rab21 affect APP processing through γ-secretase, will be examined in cell line. Finally, the function of Rab21 on the cognitive ability, and the molecular mechanisms of Rab21 on the pathology of AD will be studied in AD-model mouse. These will provide experimental clues of Rab21 protein-trafficking on AD pathology, which raises the possibility of it being a potential target for AD therapeutics.

阿尔兹海默症(AD)最主要的一个病理特征是淀粉样蛋白(Aβ)异常聚集形成的老年斑块。Aβ是由β-和γ-分泌酶依次切割淀粉样前体蛋白(APP)所得的产物。诸多研究显示许多与蛋白转运相关的Rab蛋白在Aβ产生过程中发挥重要作用。本课题前期研究发现Rab21与γ-分泌酶催化亚基-早老素(PS1)存在相互作用，并影响γ-分泌酶的活性。本项目旨在研究Rab21对γ-分泌酶活性的调控机制及其作为AD治疗潜在靶点的可能性。首先在鼠脑中进一步确认Rab21和PS1相互作用；其次在细胞水平探讨Rab21对γ-分泌酶蛋白水平、活性和细胞内转运的影响，以及Rab21是否通过调控γ-分泌酶对APP水解过程产生作用；最后在AD模型鼠中，研究Rab21对AD模型鼠认知能力及Aβ相关病理改变的影响，进一步阐明Rab21在AD发病病程中的作用，为细胞内转运过程对AD病理的调控机制提供实验依据，为AD治疗提供潜在作用靶点。

γ-分泌酶是水解切割淀粉样前体蛋白（APP）产生淀粉样蛋白(Aβ)的关键酶。最近研究显示，γ-分泌酶的相互作用蛋白显示出良好的调控APP水解但不影响Notch通路的效果，但具体的作用机制不详。在细胞水平，免疫共沉淀实验证明Rab21蛋白与γ-分泌酶的活性亚基Presenilin1（PS1）之间存在相互作用。通过分子生物学手段发现，Rab21介导了APP的水解过程以及Aβ的生成。过表达Rab21能够促进Aβ的生成，而敲低Rab21则降低了Aβ的生成。Rab21并不影响α-或者β-分泌酶的蛋白水平和活性。这与Rab21调控γ-分泌酶的活性有直接关系。进一步的研究发现，Rab21能够促进PS1从早期内含体向晚期内含体/溶酶体迁移且调控PS1在亚细胞的分布。在动物水平，Rab21表达水平在AD患者和AD模型鼠脑中有明显上升，通过在AD模型鼠中敲低Rab21能够一定程度上改善AD模型书的认知功能并减少了老年斑块。总而言之，我们发现Rab21， 作为PS1相互作用蛋白，通过调控PS1在亚细胞分布和内吞来影响其活性，进而影响APP的水解过程和Aβ的生成。这些研究使得Rab21成为非常有潜力的AD治疗靶点。