PTEN induced putative kinase 1 (PINK1) alleviates angiotensin II-induced cardiac injury by ameliorating mitochondrial dysfunction.

BACKGROUND: Mitochondrial quality control is crucial to the development of angiotensin II (AngII)-induced cardiac hypertrophy. PTEN induced putative kinase 1 (PINK1) is rapidly degraded in normal mitochondria but accumulates in damaged mitochondria, triggering autophagy to protect cells. PINK1 mediates mitophagy in general, but whether PINK1 mediates AngII-induced mitophagy and the effects of PINK1 on AngII-induced injury are unknown. This study was designed to investigate the function of PINK1 in an AngII stimulation model and its regulation of AngII-induced mitophagy.

METHODS: We studied the function of PINK1 in mitochondrial homeostasis in AngII-stimulated cardiomyocytes via RNA interference-mediated knockdown and adenovirus-mediated overexpression of the PINK1 protein. Mitochondrial membrane potential (MMP), reactive oxygen species (ROS) production, adenosine triphosphate (ATP) content, cell apoptosis rates and cardiomyocyte hypertrophy were measured. The expression of LC3B, Beclin1 and p62 was measured. Mitochondrial morphology was examined via electron microscopy. Mitophagy was detected by confocal microscopy based on the co-localization of lysosomes and mitochondria. Additionally, endogenous PINK1, phosphorylated PINK1, mito-PINK1, total Parkin, cyto-Parkin, mito-Parkin and phosphorylated Parkin protein levels were measured.

RESULTS: Cardiomyocytes untreated by AngII had very low levels of total and phosphorylated PINK1. However, in the AngII stimulation model, the MMP was decreased, and the levels of total and phosphorylated PINK1 were increased. After PINK1 was knocked down, Parkin translocation to the mitochondria was inhibited. Moreover, levels of phosphorylated Parkin were reduced, and autophagy markers were downregulated. MMP and ATP contents were further reduced, ROS production and the apoptotic rate were further increased, and myocardial hypertrophy was further aggravated compared with those in the AngII group. However, PINK1 overexpression promoted Parkin translocation and phosphorylation, autophagy markers were upregulated, and myocardial injury was reduced. In addition, the effects of PINK1 overexpression were reversed by autophagy inhibitors.

CONCLUSION: Decreased MMP induced by AngII maintains the stability of PINK1, causing PINK1 autophosphorylation. PINK1 activation promotes Parkin translocation and phosphorylation and increases autophagy to clear damaged mitochondria. Thus, PINK1/Parkin-mediated mitophagy has a compensatory, protective role in AngII-induced cytotoxicity.