Abstract 220: Emerging Roles of Altered NAD Metabolism in Diabetic Cardiomyopathy

Abstract

Diabetes is linked to altered NAD metabolism whose causal roles in cardiac dysfunction are poorly understood. Synthesis, consumption and redox balance of NAD dictate NAD metabolism and its homeostasis, and we here explored their roles in diabetic cardiomyopathy. 16 week of Type 1 diabetes (T1D) to C57BL6N mice was associated with lowered cardiac NAD/NADH, mild systolic and more severe diastolic dysfunction. We next used mouse models with altered NAD metabolism to determine how NAD redox balance impacts diabetic cardiomyopathy. Using cardiac-specific Ndufs4-KO mice (cKO) as a model of latent decrease in cardiac NAD/NADH, we observed accelerated systolic and diastolic dysfunction (lowered fractional shortening, E’/A’ ratio, and increased e/E’ ratio) in male cKO mice stressed with chronic T1D. Cardiac hypertrophy (heart weight/tibia length), insulin depletion and hyperglycemia levels were similar in these mice. Serum metabolomic analyses (~240 metabolites) also showed unchanged aqueous and lipid metabolite levels, suggesting that the diabetic stresses on these hearts were similar. The accelerated dysfunction of T1D cKO hearts was also observed in another female cohort. Importantly, elevation of cardiac NAD levels to attenuate NAD redox imbalance mitigated the accelerated dysfunction of T1D cKO hearts. In another cohort, control and cKO mice were stressed by 16-week high fat diet feeding. Accelerated systolic and diastolic dysfunction, and increased hypertrophy were observed in T2D cKO mice with similar glycemic levels to control mice. The data suggested that NAD redox imbalance is a positive regulator of cardiac dysfunction induced by T1D or T2D. However, NAD-dependent pathogenic mechanism induced by T1D or T2D (e.g. hypertrophy) can be different, and is under further investigation. Tissue fibrosis and mRNA levels of pro-fibrotic genes, including Adamts proteinases, integrins, laminins, matrix metalloproteinases and collagens were unchanged in T1D cKO hearts. Therefore, the accelerated dysfunction of T1D cKO hearts is due to cardiomyocyte dysfunction. We examined how NAD metabolism, other than the redox balance, may alter cardiomyocyte function. Levels of metabolite and mRNA regulating NAD synthesis and consumption pathways were measured. Of 32 transcripts assayed, Nmrk2 levels were uniquely up-regulated in T1D cKO hearts, and lowered by elevation of cardiac NAD levels. NMRK product levels were concomitantly decreased in T1D cKO hearts. NAD-dependent global acetylation and inhibitory superoxide dismutase 2 acetylation were increased in T1D cKO hearts. Protein oxidation levels were concomitantly raised. Hyperacetylation in proteins like CaM kinase was associated with increased phosphorylation in troponin I, not in MyBPC or PLN in T1D cKO hearts. These data support the emerging, multifaceted roles of altered NAD metabolism in the progression of diabetic cardiomyopathy.