心肌胰岛素抵抗促发缺血性心力衰竭的机制：FoxO1激活致线粒体融合-分裂失衡

Accumulating evidence from clinical and experimental studies has documented a strong association between systemic insulin resistance and heart failure. We previously found that myocardial insulin resistance, independent of systemic insulin resistance, occurred at the early stage of ischemic heart failure. Moreover, myocardial insulin resistance promoted the development of post-ischemic heart failure, while its underlying mechanisms remained largely elusive. Dynamic balance of mitochondrial fusion and fission is particularly important to maintain normal mitochondrial function. Insulin regulates mitochondrial metabolism and improves mitochondrial function. Our further experiments showed that blunted myocardial insulin signaling post ischemia impaired mitochondrial fusion associated with activation of transcription factor FoxO1. In addition, overexpression of FoxO1 reduced the expressions of Opa-1 and Mfn2 and induced mitochondrial fission, suggesting that impaired balance of mitochondrial fission and fusion induced by activation of FoxO1 may play an important role in the mechanisms that myocardial insulin resistance aggravates cardiac dysfunction. The present study was designed to determine the exact mechanisms of how myocardial insulin resistance promoted the development of heart failure and the role of FoxO1-induced mitochondrial fission and dysfunction therein. This research is hoped to further understand the pathogenesis of ischemic heart failure and provide novel possible targets for the treatment of heart failure.

胰岛素抵抗与心衰之间存在密切的关系，我们前期发现，缺血性心衰早期即存在独立于全身胰岛素抵抗的心肌胰岛素抵抗，且后者参与心衰的发生发展，但其具体机制尚不清楚。线粒体融合-分裂的动态平衡对线粒体功能的正常维持具有重要作用，胰岛素可增强线粒体功能并调控其代谢水平。我们预实验发现，心肌缺血后胰岛素信号通路受损可阻碍线粒体融合，同时伴有转录因子FoxO1的激活，而FoxO1过表达可直接下调线粒体融合蛋白Opa-1与Mfn2的表达，诱导线粒体分裂，提示FoxO1激活介导的线粒体融合-分裂失衡可能是心肌胰岛素抵抗加重心脏功能障碍的重要机制。本课题拟在前期工作基础上，探讨心肌缺血发生胰岛素抵抗后，FoxO1激活通过下调Opa-1与Mfn2，诱导线粒体融合-分裂失衡，引起线粒体功能障碍，从而促进缺血性心衰发生发展的机制，期望为深入认识缺血性心衰的发病机理并探索早期治疗策略提供新思路和新靶点。

心肌胰岛素信号受损促进心力衰竭的发生发展，但其具体机制尚不清楚。线粒体融合-分裂的动力学平衡在心脏功能的调节中发挥重要作用，本项目旨在探讨心肌胰岛素信号受损促进心衰发生发展的线粒体动力学机制。主要研究内容和结果如下：（1）选用以胰岛素抵抗为主要特征的2型糖尿病db/db小鼠以及其对照小鼠db/+，使用超声心动图监测小鼠心功能变化；透射电镜观察心肌线粒体形态变化；Western Blotting检测融合-分裂相关蛋白的表达，发现糖尿病心肌线粒体分裂增加，融合蛋白Mfn2表达下调，恢复Mfn2的表达可抑制心肌线粒体分裂，抑制线粒体凋亡途径，减轻氧化应激，改善线粒体氧化呼吸功能，改善心脏功能，延缓心衰发生。Mfn2表达下调的主要原因与转录因子PPARα表达下调有关，PPARα可直接结合至Mfn2启动子区域促进其转录；（2）给予胰岛素缺失的1型糖尿病动物线粒体融合剂M1处理，观察其对心衰发生发展的影响，发现融合促进剂M1可通过上调融合蛋白Opa1表达促进糖尿病心肌的线粒体融合，抑制线粒体来源的氧化应激，改善线粒体功能和心脏功能，延缓心衰发生；（3）发现胰岛素信号受损的糖尿病心肌FoxO1激活，应用FoxO1过表达的腺病毒转染原代心肌细胞，发现过表达FoxO1的心肌细胞线粒体分裂增加，其机制为FoxO1结合在融合蛋白Mfn2的启动子区域，诱导其表达下调，引起线粒体分裂增加。本研究首次阐明了线粒体动力学在心肌胰岛素信号受损促发心衰中的重要作用和调节机制，从线粒体动力学角度阐述了糖尿病心肌病的病理生理机制并提出治疗策略，为临床治疗糖尿病相关的心肌疾病提供了新策略和新靶点。