GSK-3alpha-BNIP3 axis promotes mitophagy in human cardiomyocytes under hypoxia

Dysregulated autophagy/mitophagy is one of the major causes of cardiac injury in ischemic conditions. Glycogen synthase kinase-3alpha (GSK-3) has been shown to play a crucial role in the pathophysiology of cardiac diseases. However, the precise role of GSK-3 in cardiac mitophagy remains unknown. Herein, we investigated the role of GSK-3 in cardiac mitophagy by employing AC16 human cardiomyocytes under the condition of acute hypoxia. We observed that the gain-of-GSK-3 function profoundly induced mitophagy in the AC16 cardiomyocytes post-hypoxia. Moreover, GSK-3 overexpression led to increased ROS generation and mitochondrial dysfunction in cardiomyocytes, accompanied by enhanced mitophagy displayed by increased mt-mKeima intensity under hypoxia. Mechanistically, we identified that GSK-3 promotes mitophagy through upregulation of BNIP3, caused by GSK-3-mediated increase in expression of HIF-1 and FOXO3a in cardiomyocytes post-hypoxia. Moreover, GSK-3 displayed a physical interaction with BNIP3 and, inhibited PINK1 and Parkin recruitment to mitochondria was observed specifically under hypoxia. Taken together, we identified a novel mechanism of mitophagy in human cardiomyocytes. GSK-3 promotes mitochondrial dysfunction and regulates FOXO3a -mediated BNIP3 overexpression in cardiomyocytes to facilitate mitophagy following hypoxia. An interaction between GSK-3 and BNIP3 suggests a role of GSK-3 in BNIP3 recruitment to the mitochondrial membrane where it enhances mitophagy in stressed cardiomyocytes independent of the PINK1/Parkin.