Hyperglycemia Induces Myocardial Dysfunction via Epigenetic Regulation of JunD.

RATIONALE: Hyperglycemia -induced reactive oxygen species are key mediators of cardiac dysfunction. JunD (Jund proto-oncogene subunit), a member of the AP-1 (activator protein-1) family of transcription factors, is emerging as a major gatekeeper against oxidative stress. However, its contribution to redox state and inflammation in the diabetic heart remains to be elucidated. OBJECTIVE: The present study investigates the role of JunD in hyperglycemia-induced and reactive oxygen species-driven myocardial dysfunction. METHODS AND RESULTS: JunD mRNA and protein expression were reduced in the myocardium of mice with streptozotocin-induced diabetes mellitus as compared to controls. JunD downregulation was associated with oxidative stress and left ventricular dysfunction assessed by electron spin resonance spectroscopy as well as conventional and 2-dimensional speckle-tracking echocardiography. Furthermore, myocardial expression of free radical scavenger superoxide dismutase 1 and aldehyde dehydrogenase 2 was reduced, whereas the NOX2 (NADPH [nicotinamide adenine dinucleotide phosphatase] oxidase subunit 2) and NOX4 (NADPH [nicotinamide adenine dinucleotide phosphatase] oxidase subunit 4) were upregulated. The redox changes were associated with increased NF-κB (nuclear factor kappa B) binding activity and expression of inflammatory mediators. Interestingly, mice with cardiac-specific overexpression of JunD via the α MHC (α- myosin heavy chain) promoter (α MHC JunDtg) were protected against hyperglycemia-induced cardiac dysfunction. We also showed that JunD was epigenetically regulated by promoter hypermethylation, post-translational modification of histone marks, and translational repression by miRNA (microRNA)-673/menin. Reduced JunD mRNA and protein expression were confirmed in left ventricular specimens obtained from patients with type 2 diabetes mellitus as compared to nondiabetic subjects. CONCLUSIONS: Here, we show that a complex epigenetic machinery involving DNA methylation, histone modifications, and microRNAs mediates hyperglycemia-induced JunD downregulation and myocardial dysfunction in experimental and human diabetes mellitus. Our results pave the way for tissue-specific therapeutic modulation of JunD to prevent diabetic cardiomyopathy.

Hyperglycaemia-induced epigenetic changes drive persistent cardiac dysfunction via the adaptor p66Shc.

AIMS: Hyperglycaemia-induced reactive oxygen species (ROS) are key mediators of cardiac dysfunction. Intensive glycaemic control (IGC) has failed to reduce risk of heart failure in patients with diabetes but the underlying mechanisms remain to be elucidated. The present study investigates whether epigenetic regulation of the pro-oxidant adaptor p66Shc contributes to persistent myocardial dysfunction despite IGC. METHODS AND RESULTS: p66Shc expression was increased in the heart of diabetic mice, and 3-week IGC by slow-release insulin implants did not revert this phenomenon. Sustained p66Shc upregulation was associated with oxidative stress, myocardial inflammation and left ventricular dysfunction, as assessed by conventional and 2D speckle-tracking echocardiography. In vivo gene silencing of p66Shc, performed during IGC, inhibited ROS production and restored cardiac function. Furthermore, we show that dysregulation of methyltransferase DNMT3b and deacetylase SIRT1 causes CpG demethylation and histone 3 acetylation on p66Shc promoter, leading to persistent transcription of the adaptor. Altered DNMT3b/SIRT1 axis in the diabetic heart was explained by upregulation of miR-218 and miR-34a. Indeed, in human cardiomyocytes exposed to high glucose, inhibition of these miRNAs restored the expression of DNMT3b and SIRT1 and erased the adverse epigenetic signatures on p66Shc promoter. Consistently, reprogramming miR-218 and miR-34a attenuated persistent p66Shc expression and ROS generation. CONCLUSIONS: In diabetic left ventricular dysfunction, a complex epigenetic mechanism linking miRNAs and chromatin modifying enzymes drives persistent p66Shc transcription and ROS generation. Our results set the stage for pharmacological targeting of epigenetic networks to alleviate the clinical burden of diabetic cardiomyopathy.