Retinoic acid-related orphan receptors regulate autophagy and cell survival in cardiac myocytes during hypoxic stress

Abstract

Introduction: Autophagy is a highly conserved evolutionary process that regulates cell quality control through protein degradation, organelle turnover, and recycling of cellular components by fusing with lysosomes. Defects in autophagy can lead to increased reactive oxygen species (ROS) and oxidative stress from impaired mitochondrial clearance by mitophagy. These defects are commonly associated with chronic human diseases such as cancer, myocardial infarction, neurodegenerative diseases, and aging. Aim: Herein, we show that the gene Retinoic Acid-Related Orphan Receptors α (Rora ) is cardioprotective through modulation of autophagy and clearance of damaged ROS-producing mitochondria in cardiac myocytes. Methods and results: We show that RORα is downregulated during hypoxia, leading to increased death of cardiac cells and enhanced mitochondrial perturbations. We demonstrate that the small molecule Nobiletin, a polymethoxy flavonoid, can induce RORα activation and downregulate the aging-associated marker p16, coincident with reduced ROS-producing mitochondria. We further show that Nobiletin binds directly to the Rora gene promoter, leading to activation of autophagic function and increased cell survival of cardiac myocytes during hypoxia. Interestingly, loss of RORα activity during hypoxia resulted in the failure of Nobiletin to rescue autophagy and inhibits its capacity for cardiac protection. Furthermore, the inactivation of autophagy by ATG7 knockdown abrogated the cytoprotective effects of Nobiletin on autophagic activation. Conclusion: Collectively, these results demonstrate that RORα regulates autophagic processes linked to aging upon activation with Nobiletin. Interventions that activate RORα may prove beneficial in reducing hypoxia-induced mitochondrial ROS associated with cardiac aging.