IRTKS调控胰岛素信号通路在肝脏脂肪变性中的分子机制研究

Morbidity of fatty liver disease, especial nonalcoholic fatty liver disease (NAFLD), has increased annually, and which affects people's health seriously in China. However, the underlying cellular and molecular mechanisms by which hepatic steatosis initiation and progression remain obscure. Significantly, IRTKS (insulin receptor tyrosine kinase substrate) gene knockout mice established by our lab exhibit the typical pathological feature of hepatic steatosis with formation of lipid droplets and excess triglyceride (TG). IRTKS has interacted with SHIP2 (SH2 Domain-Containing Inositol 5'-Phosphatase 2) -- the signal molecule in insulin signaling pathway, and influence the catalytic activity of SHIP2 to regulate phosphatidylinositols, the second messenger molecules. More interestingly, we confirmed that IRTKS is obviously downregulated in the majority of peripheral blood lymphocytes specimens in patients with diabetes. Based on these collective data, we propose that IRTKS could function as an adaptor regulated insulin signal under the cytomembrane, and contribute to lipid metabolism disorders. In this project, we hope to confirm the hypothesis by utilizing the IRTKS-deficient mice, together with in vitro experiments and evaluation in clinical fatty liver patients. First, to explore the effect of IRTKS on lipid metabolism in insulin signal, to investigate the effect of IRTKS deficiency on cellular signaling pathways related with hepatic steatosis. Next, to assess the interaction between IRTKS and insulin receptor, IRTKS and SHIP2. Finally, we will attempt to treat the mice with hepatic steatosis through regulating IRTKS and altered signaling molecules due to the deficiency of IRTKS. In general, the proposal will facilitate the understanding of mechanism with hepatic steatosis, and provide the potential strategy for prevention and treatment in fatty liver disease.

脂肪肝发病率逐年升高，严重影响我国人民健康，但其发生的分子机制仍不清楚。有意义的是本课题组发现IRTKS（胰岛素受体酪氨酸激酶底物）基因敲除小鼠显示肝脏脂肪沉积，与胰岛素信号通路分子SHIP2（肌醇磷酸酶）存在相互作用，并影响其催化活性调控第二信使分子磷脂酰肌醇，在糖尿病患者外周血淋巴细胞中IRTKS基因表达水平显著下降。提示IRTKS缺乏导致脂肪肝，并可能通过影响胰岛素信号通路而导致脂质代谢紊乱。本项目拟基于IRTKS基因敲除小鼠模型，结合人肝细胞株样本研究IRTKS在肝脏脂质代谢过程中的作用、其缺乏对脂肪肝发生、发展的影响及机制；在此基础上探讨IRTKS或代谢相关分子机制作为靶向防治脂肪肝策略的可行性。本项目从IRTKS缺乏这一独特角度研究脂肪肝的发病机制，阐述胰岛素信号通路调控肝脏脂质代谢所涉及的病理过程及分子基础，将为脂肪肝发生、发展机制的理解提供新思路，也为脂肪肝防治提供新策略。

本课题是项目负责人博士、博后期间工作的延续。前期发现IRTKS（胰岛素受体酪氨酸激酶底物）基因敲除小鼠显示肝脏脂肪沉积，与胰岛素信号通路分子SHIP2（肌醇磷酸酶）存在相互作用，并影响其催化活性调控第二信使分子磷脂酰肌醇。提示IRTKS缺乏导致脂肪肝，并可能通过影响胰岛素信号通路而导致脂质代谢紊乱。本课题结合人肝细胞株样本研究IRTKS在肝脏脂质代谢过程中的作用、其缺乏对脂肪肝发生、发展的影响及机制。本研究结果显示IRTKS的SH3结构域与SHIP2的催化结构域INPP5c存在相互作用，IRTKS能够抑制SHIP2磷酸酶将磷脂酰肌醇3,4,5-三磷酸（PI(3,4,5)P3）转化为磷脂酰肌醇(3,4)二磷酸（PI(3,4)P2）。IRTKS敲除显著增加PI(3,4)P2水平，降低细胞PI(3,4,5)P3含量；同时IRTKS和SHIP2之间的相互作用是由胰岛素动态调节的，胰岛素反过来影响IRTKS的酪氨酸磷酸化。在糖尿病患者外周血PBMC中IRTKS的低表达和动物实验中观察到在IRTKS KO小鼠体内通过病毒上调IRTKS表达，能够缓解胰岛素抵抗，并促进脂肪分解而抑制脂肪合成，有望将来成为改善糖尿病患者脂代谢异常的药物指标靶点。本项目从IRTKS缺乏这一独特角度研究脂肪肝的发病机制，阐述胰岛素信号通路调控肝脏脂质代谢所涉及的病理过程及分子基础，为脂肪肝发生、发展机制的理解提供新思路，也为脂肪肝防治提供新策略。