miR-361-regulated prohibitin inhibits mitochondrial fission and apoptosis and protects heart from ischemia injury

Cardiovascular disease remains the leading cause of morbidity and mortality worldwide. Emerging evidences suggest that the abnormal mitochondrial fission participates in pathogenesis of cardiac diseases, including myocardial infarction (MI) and heart failure. However, the molecular components regulating mitochondrial network in the heart remain largely unidentified. Here we report that miR-361 and prohibitin 1 (PHB1) constitute an axis that regulates mitochondrial fission and apoptosis. The results show that PHB1 attenuates mitochondrial fission and apoptosis in response to hydrogen peroxide treatment in cardiomyocytes. Cardiac-specific PHB1 transgenic mice show reduced mitochondrial fission and myocardial infarction sizes after myocardial infarction surgery. MiR-361 is responsible for the dysfunction of PHB1 and suppresses the translation of PHB1. Knockdown of miR-361 reduces mitochondrial fission and apoptosis in vivo and in vitro. MiR-361 cardiac-specific transgenic mice represent elevated mitochondrial fission and myocardial infarction sizes upon myocardial ischemia injury. This study identifies a novel signaling pathway composed of miR-361 and PHB1 that regulates mitochondrial fission program and apoptosis. This discovery will shed new light on the therapy of myocardial infarction and heart failure.The heart drives the blood flow in the body and it has a large requirement of energy. Mitochondria meet the high energy demand of the heart by consistently providing large amounts of ATP through oxidative phosphorylation. Thus, mitochondrial malfunction is tightly related to cardiac diseases and contributes to cardiomyocyte injury, cardiomyopathy and heart failure. Mitochondria morphology is also associated with the function. Mitochondria constantly undergo fission and fusion. Fission leads to the formation of small round mitochondria and promotes cell apoptosis,^{1, 2, 3, 4, 5, 6, 7} whereas fusion results in mitochondria elongation and have a protective role in cardiomyocytes maintenance.⁸ The above findings strongly suggest that mitochondrial fission and fusion machinery is important for cardiac function. In addition, unveiling the mechanism of mitochondrial network regulation will provide a novel therapeutic strategy for heart failure.The mitochondrial prohibitin complex is a macromolecular structure at the inner mitochondrial membrane that is composed of prohibitin 1 (PHB1) and prohibitin 2 subunits.⁹ These two proteins comprise an evolutionary conserved and ubiquitously expressed family of membrane proteins and are implicated in several important cellular processes such as mitochondrial biogenesis and function, cell proliferation, replicative senescence, and cell death.^{10, 11} The first mammalian PHB1 was identified as a potential tumor suppressor with anti-proliferative activity.¹² Recent findings suggest that PHB1 has an important role in regulating mitochondrial morphology. Loss of PHB1 results in accumulation of fragmented mitochondria in MEFs and HeLa cells.^{13, 14} However, it is not yet clear whether PHB1 participates in the regulation of mitochondrial dynamics in cardiomyocytes.MicroRNAs (miRNAs) are a class of short single-stranded non-coding endogenous RNAs and act as negative regulators of gene expression by inhibiting mRNA translation or promoting mRNA degradation.^{15, 16} Although the function of miRNAs has been widely studied in apoptosis, development, differentiation and proliferation, few works have been focused on miRNAs in the mitochondrial network regulation. It has been reported that miR-30b targets to p53 and inhibits mitochondrial fission.¹⁷ In addition, other miRNAs also affect the function of mitochondria by targeting to mitochondrial calcium uniporter.¹⁸ The study of miRNA function in mitochondria may shed new light on the machinery that underlies mitochondrial regulation.This study unveils that PHB1 is involved in the regulation of mitochondrial network in cardiomyocytes. PHB1 inhibits mitochondrial fission and apoptosis in cardiomyocytes. In addition, PHB1 transgenic mice exhibit a reduced myocardial infarction sizes upon myocardial ischemia injury in vivo. In searching for the mechanism by which PHB1 is downregulated under pathologic condition, we identify miR-361 participates in the suppression of PHB1 translation. MiR-361 initiates mitochondrial fission, apoptosis and myocardial infarction through downregulating PHB1. Our results reveal a novel mitochondrial regulating model, which is composed of miR-361 and PHB1. Modulation of their levels may represent a novel approach for interventional treatment of myocardial infarction and heart failure.