FOXO3a-dependent PARKIN Negatively Regulates Cardiac Hypertrophy By Mediating Mitophagy

Objective:Persistent cardiac hypertrophy often progresses to maladaptive myocardial remodeling and eventually to heart failure and sudden death.Therefore,maladaptive cardiac hypertrophy is considered an important therapeutic target for many heart diseases.Mitophagy,a crucial mechanism in mitochondria quality control and cellular homeostasis,has been implicated in diverse cardiac disorders such as myocardial infarction,diabetic cardiomyopathy,cardiac hypertrophy and heart failure.However,what role mitophagy plays in heart diseases remains an enigma.PARKIN functions as an E3 ubiquitin protein ligase and mediates mitophagy cascades.It is still unclear whether PARKIN participates in the regulation of cardiac hypertrophy.In this study,we investigated whether PARKIN is involved in Angiotensin Ⅱ(Ang Ⅱ)-induced cardiac hypertrophy and its mechanism,and whether mitophagy plays an important role in it.Methods:Cardiac-specific Parkin transgenic mice were used to investigate the role of PARKIN in Ang Ⅱ-induced myocardial hypertrophy in mice.The expression levels of ANP(atrial natriuretic peptide)and BNP(brain natriuretic peptide),the ratio of heart weight to body weight,the cross-sectional area of cardiomyocytes,histopathological analysis and echocardiography were used to evaluate the response of myocardial hypertrophy.Primary cardiomyocytes and H9c2 cells were used to investigate the role of PARKIN in Ang Ⅱ-induced cardiomyocyte hypertrophy in vitro.The hypertrophic response of cardiomyocytes was evaluated by measuring the cell surface area and the expression levels of cardiac hypertrophy markers ANP and BNP.The level of mitophagy was evaluated by measuring the ratio of microtubule-associated protein light chain 3Ⅱ/ microtubule-associated protein light chain 3Ⅰ(LC3Ⅱ/LC3Ⅰ),detecting LC3 co-localized with mitochondria,observing the quantitation of autophagic vacuoles under transmission electron microscope and detecting mitophagy flux.Results:PARKIN was downregulated in cardiomyocytes and hearts under hypertrophic stress.Compared to wide-type mice with Ang Ⅱ-induced cardiac hypertrophy,Parkin transgenic mice subjected to Ang Ⅱ administration showed attenuated cardiac hypertrophy and improved cardiac function.Enforced expression of PARKIN also inhibited Ang Ⅱ-induced cardiomyocyte hypertrophy.In addition,mitophagy machinery was impaired in response to Ang Ⅱ,which was rescued by overexpression of PARKIN.PARKIN exerted the anti-hypertrophy effect through restoring mitophagy.In further exploring the underlying mechanisms,we found that Parkin was transcriptionally activated by FOXO3 a.FOXO3a promoted mitophagy and suppressed cardiac hypertrophy by targeting PARKIN.Conclusion:The present study reveals a novel cardiac hypertrophy regulating model composed of FOXO3 a,PARKIN and mitophagy program.Modulation of their levels may provide a new approach for preventing cardiac hypertrophy and heart failure.