Lin28/let-7轴：糖尿病合并心脏缺血再灌注损伤保护的新靶点

Sixty-five percent of deaths in patients with diabetes are caused by cardiovascular causes. Intensive glucose control is not effective to reduce the incidence of cardiovascular events in diabetic patients. Thus, new treatment should be developed to reduce the cardiac mortality caused by diabetes. RNA-binding protein Lin28 a/b and the Let-7 miRNA family have been involved in the embryonic development, stem cell differentiation and tumor growth. Most recently, Lin28/let-7 axis has been reported playing a key role in glucose metabolism through insulin-PI3K-mTOR pathway which could increase glucose uptake and moderate insulin resistence. Our previous study also demonstrated that insulin-PI3K-mTOR signaling pathway played an important role in ischemia-reperfusion (I/R) injury. We found decreased Lin28 a/b expression and increased let-7 expression in the diabetic rat heart underwent I/R injury. However, the roles of Lin28/let-7 axis in the I/R injury in diabetic rats are not well understood. Lin28 a/b, let-7 transgenic mice and knockout mice will be used to construct animal models of diabetes accompanied by cardiac I/R injury. The roles of Lin28/let-7 axis in diabetes accompanied by cardiac I/R injury will be investigated. The present project will further help reveal the new target in the treatment of diabetes accompanied by cardiac I/R injury.

糖尿病引起的死亡65％是源于心血管疾病，因此，急需寻找新的方法降低糖尿病患者的心源性死亡率。最新研究表明，Lin28/let-7轴在葡萄糖代谢中发挥关键作用，通过insulin-PI3K-mTOR通路，增加葡萄糖摄取及胰岛素敏感性。我们的研究提示，insulin-PI3K-mTOR通路在缺血再灌注损伤中发挥重要作用。糖尿病大鼠心脏缺血再灌注损伤后，心肌组织内Lin28 a/b表达降低，let-7表达升高。然而，Lin28/let-7轴激活是否能够降低糖尿病状态下的心脏缺血再灌注损伤？目前尚不清楚。本研究拟采用Lin28 a/b，let-7转基因鼠及基因敲除小鼠为研究对象，构建糖尿病合并心脏缺血再灌注损伤动物模型，揭示Lin28/let-7轴在糖尿病合并心脏缺血再灌注损伤保护中的作用及下游分子机制。本项目将有助于进一步揭示糖尿病合并心脏缺血再灌注损伤保护的新靶点，为该疾病的防治提供新的思路。

糖尿病是心血管疾病的重要危险因素。糖尿病合并冠心病引发的心肌损伤是心衰和心血管源性死亡的主要诱发因素。因此，降低糖尿病患者的心源性死亡率，对于糖尿病合并冠心病患者的预后改善至关重要。阐明糖尿病合并心肌缺血再灌注（I/R）损伤机制及保护策略是心血管领域中亟待解决的关键科学问题。Lin28a是RNA结合蛋白，可调控细胞增殖，胚胎干细胞分化和肿瘤发生等，但其在糖尿病心肌缺血性疾病中的作用研究尚属空白。我们在前期预实验中发现糖尿病小鼠心肌缺血再灌注损伤时Lin28a表达量下降。而上调Lin28a可以减轻糖尿病小鼠心肌缺血再灌注损伤。这一有趣的发现提示，Lin28a在糖尿病小鼠心肌缺血再灌注损伤中发挥重要作用。据此，本课题拟从在体动物、整体器官、体外细胞三个不同水平，研究Lin28a在抗糖尿病小鼠心肌I/R损伤的心肌保护中的意义及其机制。. 本课题主要发现如下：⑴上调Lin28a减轻糖尿病小鼠心肌缺血再灌注损伤，心功能障碍明显改善，梗死面积减小，心肌细胞凋亡明显减少。下调Lin28a加重糖尿病小鼠心肌缺血再灌注损伤，心功能障碍明显加重，梗死面积进一步扩大，心肌细胞凋亡明显增加。⑵ Lin28a表达上调减轻糖尿病小鼠缺血再灌注后心肌细胞线粒体损伤，而下调Lin28a加重糖尿病小鼠缺血再灌注后心肌细胞线粒体损伤。⑶糖尿病小鼠心肌I/R损伤时IGF1R 、p-AKT、p-mTOR、p-p70S6k的蛋白表达量下降。Lin28a可以促进这些蛋白的表达。阐明“Lin28a-IGF1R- p-AKT - p-mTOR”这一信号保护通路。⑷Lin28a表达上调减轻高糖高脂培养下心肌细胞缺氧复氧损伤，而下调Lin28a加重高糖高脂培养下心肌细胞缺氧复氧损伤。过表达Lin28a心肌细胞HG/HF+H/R损伤后心肌细胞凋亡指数下降。(5) Lin28a表达上调减轻HG/HF+H/R心肌细胞线粒体损伤，而下调Lin28a加重HG/HF+H/R心肌细胞线粒体损伤。Lin28a激活高糖高脂培养下心肌细胞缺氧复氧损伤后能量代谢AMPK/PGC-1α/Tfam这一信号通路。本研究阐明Lin28a对糖尿病合并心脏缺血性疾病的保护机制，为临床糖尿病合并心血管疾病患者的治疗提供了新的治疗靶点。