K63-linked ubiquitination of FoxO1 attenuates diabetic cardiomyopathy by restoring mitochondrial dynamics

The rising prevalence of diabetes has amplified the clinical burden of diabetic cardiomyopathy (DCM), for which no effective treatments are currently available. FoxO1 mediated mitochondrial dynamics dysfunction greatly contributes to DCM. However, the cause for persistent activation of FoxO1 in DCM has remained largely unknown. A high-fat diet combined with low-dose streptozotocin injection was used to induce type 2 diabetes. Neonatal mouse cardiomyocytes were exposed to low glucose (LG; 5.5 mM) or high glucose (HG; 30 mM) and palmitic acid. mRNA sequencing was used to identify differentially expressed genes. AAV9-shOTUD1 was utilized to investigate the changes in FoxO1 expression and mitochondrial function following OTUD1 knockdown. Co-immunoprecipitation was conducted to detect the interaction between OTUD1 and FoxO1. A marked upregulation of OTUD1 expression was observed via mRNA sequencing along with increased DRP1 expression and decreased expression of Mfn2, OPA1, PINK1 and Parkin in heart tissues of DCM. Knockdown of OTUD1 ameliorated cardiac dysfunction and improved mitochondrial dynamics by downregulating FoxO1. Mechanistically, OTUD1 regulates FoxO1 stability, at least in part, by selectively removing K63-linked polyubiquitin chains. OTUD1 overexpression in cardiac tissues contributes to excessive mitochondrial fission, insufficient mitochondrial fusion and impaired mitophagy. Inhibition of OTUD1 protects the diabetic heart in part by promoting FoxO1 proteasomal degradation, an effect associated with reduced K63-linked deubiquitination of FoxO1, which suppresses its aberrant activation and helps restore mitochondrial function. Thus, OTUD1 represents a promising potential therapeutic target for DCM.