Abstract
BACKGROUND: Type 2 diabetes mellitus (T2DM) markedly increases susceptibility to myocardial ischemia/reperfusion (I/R) injury, contributing to elevated mortality. Sirtuin 3 (Sirt3), a mitochondrial NAD(+)-dependent deacetylase, is downregulated in T2DM and is closely associated with mitochondrial protein hyperacetylation, possibly as a mediator of this effect. This study aimed to elucidate the molecular mechanisms underlying increased susceptibility to myocardial I/R injury in T2DM, with a particular focus on Sirt3 deficiency-mediated mitochondrial protein hyperacetylation. METHODS: Wild-type (WT) and Sirt3-knockout (KO) mice were fed a high-fat diet (HFD) for 8 weeks and received intraperitoneal injections of streptozotocin (STZ, 50 mg/kg for three consecutive days) beginning at week 5 to establish a T2DM model. Both in vitro and in vivo models were used to examine the effects of Sirt3 deficiency-induced hyperacetylation on mitochondrial function, reactive oxygen species (ROS) production, and myocardial I/R injury. Mitochondrial supercomplex (SC) assembly and the activities of respiratory chain complexes I, II, III and IV were assessed by blue-native PAGE or a microplate assay kit. Protein-protein interactions were analyzed using proximity ligation assay, and Western blot and functional experiments were performed to explore the underlying molecular mechanisms. RESULTS: In T2DM, the Sirt3 deficiency-induced mitochondrial protein hyperacetylation significantly increased myocardial susceptibility to I/R injury. Mitochondrial hyperacetylation impaired mitochondrial respiratory function and increased mitochondrial ROS production. Mechanistically, Sirt3 deficiency-induced hyperacetylation of SC-associated mitochondrial proteins disrupted mitochondrial SC assembly, thereby compromising mitochondrial integrity and function. CONCLUSIONS: These findings demonstrate that the increased myocardial susceptibility to I/R injury in T2DM is driven, at least in part, by Sirt3 deficiency-mediated hyperacetylation of mitochondrial SC-associated proteins. Disruption of SC assembly leads to mitochondrial dysfunction and ROS accumulation, providing a mechanistic link between metabolic dysregulation and heightened cardiac I/R injury in T2DM.