肝脏MED1表观调控PPARγ-LRP6信号在高胆固醇血症中的作用及机制研究

高胆固醇血症是动脉粥样硬化发生的主要危险因素，其发病是由多个遗传和环境因素相互作用所致。申请人前期发现转录辅激活子MED1在肝脏特异敲除后小鼠出现高胆固醇血症和动脉粥样硬化表型，且PPARγ和LRP6表达下降，其中机制不清。推测MED1可能通过表观调控PPARγ-LRP6信号介导高胆固醇血症发生。本项目拟通过构建肝脏MED1敲除/LRP6突变小鼠研究MED1在LRP6介导高胆固醇血症中的调控作用；细胞水平过表达或敲减PPARγ阐明MED1参与胆固醇代谢的转录机制；运用CRISPR/Cas9、ChIP和ATAC-qPCR等技术揭示MED1通过PPARγ结合影响LRP6启动子区PolII招募、组蛋白修饰和染色质可及性等表观遗传学改变及机制；通过人群病例对照分析MED1-PPARγ-LRP6和高胆固醇血症罹患的相关关系。本研究有助于揭示胆固醇代谢调控的新机制，为治疗高胆固醇血症提供潜在新靶点。

Hypercholesterolemia is a major risk factor for atherosclerosis. There are genetic and acquired causes of hypercholesterolemia. Our previous study found that transcriptional co-activator MED1 is required for PPARγ-regulated lipid metabolism. Liver-specific MED1 knockout mice when fed a Western diet developed hypercholesterolemia and atherosclerosis. Furthermore, the expression of PPARγ and LRP6 in liver was decreased, which molecular mechanism is unknown. In this project, we will investigate the contribution of hepatic MED1 expression on hypercholesterolemia via LRP6 using liver MED1 null/LRP6 mutant mice. To reveal the molecular mechanism of how MED1 regulates PPARγ-LRP6, we will measure the LRP6 expression, trans-activation, and promoter binding under overexpression or knockdown of PPARγ through qPCR, luciferase reporter assays and ChIP. Furthermore, we will analyze the regulation of MED1 on PolII recruitment, histone modification and chromatin accessibility in the promoter and enhance regions of LRP6 gene using CRISPR/Cas9, ChIP and ATAC-qPCR. Finally, we will measure the expression of MED1, PPARγ and LRP6, and analyze their association in hypercholesterolemic patients by population case-control study. This project will be greatly helpful for revealing new mechanisms of cholesterol metabolism and provide potential targets for the treatment of hypercholesterolemia.