UBC9 ameliorates diabetic cardiomyopathy by modulating cardiomyocyte mitophagy through NEDD4/RUNX2/PSEN2 axis

AIM: Diabetic cardiomyopathy (DCM) is one of the most significant cardiovascular complications in patients with diabetes. Ubiquitin conjugating enzyme 9 (UBC9) is the only SUMO-E2 enzyme that plays a key role in cardiomyocytes homeostasis. This study aimed to elucidate the roles and mechanisms of UBC9 in DCM development. METHODS: We established cardiomyocyte-specific UBC9 knockout mice and UBC9-overexpressing mice in vivo. A DCM model was established by feeding a high-fat diet and administering a low-dose streptozotocin injection. Proteomics, H&E staining, Sirius Red staining, WGA staining, real-time PCR, and western blotting were performed to examine fibrosis, hypertrophy, and mitophagy in the myocardium. Neonatal mouse cardiomyocytes (NMCMs) were cultured in vitro and stimulated with palmitic acid, UBC9 overexpression adenovirus, and small interfering RNA to establish UBC9 overexpression or knockdown NMCMs. Real-time PCR, western blotting, and immunoprecipitation were employed to examine the roles and mechanisms of UBC9 in cardiomyocyte mitophagy. RESULTS: The transcription and protein levels of UBC9 were significantly decreased in the myocardium of DCM mice. Cardiomyocyte-specific UBC9 knockout aggravated cardiac dysfunction, myocardial fibrosis, hypertrophy, and impaired mitophagy. Conversely, UBC9 overexpression produced opposite effects. UBC9 protected cardiomyocyte mitophagy independently of SUMOylation. UBC9 exerted protective effects against defective cardiomyocyte mitophagy by directly binding to NEDD4, enhancing RUNX2 ubiquitination and degradation, which in turn increased PSEN2 expression. Moreover, the impact of UBC9 on cardiomyocyte mitophagy was reversed upon PSEN2 knockdown. CONCLUSIONS: UBC9 alleviated DCM development through the NEDD4/RUNX2/PSEN2 pathway. These findings offer novel insights into the potential of UBC9 as a therapeutic target for DCM.