线粒体/肌质网互作网络调节心肌肥厚的作用及作用机制

Cardiac contractile activity is mediated by calcium from sarcoplasmic reticulum, and requires sustained energy supply provided by mitochondria. Physical and functional communication between mitochondria and sarcoplasmic reticulum has a critical role for the maintenance of calcium homeostasis and mitochondrial metabolism in cardiomyocytes. Cardiac hypertrophy is an adaptive response of the heart to diverse pathological stimuli, however, sustained hypertrophy is a risk factor of cardiac arrhythmia, heart failure, and sudden death. The role of mitochondria/sarcoplasmic reticulum communication and its regulation during cardiac hypertrophy remain unclear. Our previous work found that the calcium content of sarcoplasmic reticulum deceased in hypertrophic heart. Moreover, our preliminary data showed mitochondrial dysfunction in hypertrophic heart, suggesting a possible role of mitochondria/sarcoplasmic reticulum communication during cardiac hypertrophy. The mitochondrial Rho GTPase Miro is a mitochondrial outer membrane protein, initially identified as a mediator of mitochondrial transportation along microtubule in cells especially in neurons. However, mitochondria are strictly organized between sarcomeres and lack motility in cardiomyocytes, the functional role of Miro in the heart is not yet studied. In yeast, Miro was identified localizing on mitochondria/endoplasmic reticulum membrane. Our preliminary data showed that Miro2 was downregulated in transverse aortic constriction-mediated mouse hypertrophic hearts and PE stimulated hypertrophic cardiomyocytes. Overexpression of Miro2 increased, while knockdown of Miro2 decreased cardiac mitochondrial function. Moreover, Miro2 transgenic mouse displayed improved mitochondrial and cardiac function after TAC, indicating that Miro2 plays a role in cardiac hypertrophy. By using cardiac hypertrophic mouse model, combined with Miro2 transgenic mouse model, the present study will investigate the role of mitochondria/sarcoplasmic reticulum communication in the pathogenesis of cardiac hypertrophy, and explore the regulatory effect of Miro2 on mitochondria/sarcoplasmic reticulum communication in vivo and in vitro, thus to provide implications for the development of therapeutic strategies against cardiac hypertrophy.

心脏收缩/舒张活动既需线粒体提供能量，也受肌质网钙离子的精确调控；线粒体/肌质网在心肌细胞中存在广泛连接，线粒体/肌质网互作网络对维持心肌细胞稳态至关重要。心肌肥厚是心衰等疾病的主要危险因素，线粒体/肌质网互作网络在心肌肥厚过程中的作用及机制尚未可知。我们前期研究及预实验结果提示，心肌肥厚过程中肌质网钙含量降低，线粒体功能下降，提示线粒体/肌质网功能障碍。Miro2是线粒体蛋白，主要介导线粒体运动，但心肌线粒体活动严格受限，Miro2的心脏功能并无研究。我们发现，心肌肥厚时Miro2蛋白显著下降，敲减Miro2致心肌线粒体功能降低。有报道酵母中Miro2存在于线粒体/内质网连接区，本课题拟在心肌肥厚小鼠及Miro2转基因小鼠模型、心肌细胞水平，探讨线粒体/肌质网互作网络在心肌肥厚中的作用及病理生理意义，验证Miro2调控线粒体/肌质网互作网络的机制，为干预心肌肥厚发生发展提供新的思路。

心肌细胞结构严密，线粒体与肌质网等细胞器在其中构成互作网络，对维持心肌细胞代谢及信号稳态至关重要。心肌肥厚等心脏疾病过程中，线粒体/肌质网及线粒体与其他细胞器互作网络是否发生变化及变化机制尚未可知。我们在肥大心肌细胞及心肌肥厚小鼠模型中，发现心肌肥厚时线粒体/肌质网接触区蛋白Miro2, Mfn2, PTPIP53等水平降低、接触面积减少、接触距离增加，线粒体摄取钙离子减少，微区钙离子浓度增高，进而线粒体功能降低，提示线粒体/肌质网互作在心肌肥厚过程中发挥重要作用。此外，我们在前期发现成年心肌细胞中线粒体与线粒体间可通过吻合及纳米管道进行交互作用基础上，进一步发现线粒体囊泡作为一种更灵活的形式，不仅可介导成年心肌细胞线粒体与线粒体间的交互作用，还介导线粒体与肌质网、溶酶体、细胞核等细胞器的交互作用，从而形成线粒体信号与整个细胞互通的信号网络，在生理及病理情况下调控线粒体及心肌细胞功能。