Novel regulation of cardiac branched-chain amino acid metabolism through AMP deaminase: a possible therapeutic target for diabetic cardiomyopathy

Abstract

Background Dysregulation of branched-chain amino acid (BCAA) metabolism has been shown to be associated with type 2 diabetes mellitus (T2DM) and heart failure. BCAA reportedly protects cells from fatty acid-induced mitochondrial injury via sequestration of fatty acids in intracellular lipid droplets from mitochondria. We previously reported that up-regulation of AMP deaminase 3 (AMPD3) impairs cardiac energetics in T2DM hearts, and AMPD3 was recently shown to participate in regulation of amino acid metabolism in skeletal muscle. Purpose We hypothesized that AMPD3 regulates cardiac amino acid metabolism by interaction with branched-chain α-ketoacid dehydrogenase (BCKDH) complex and that cardioprotective effect of sodium glucose cotransporter 2 inhibitors is mediated by modification of BCAA metabolism in diabetic cardiomyocytes. Methods and results Proteomic analyses of immunoprecipitates with an anti-AMPD3 antibody in rat hearts revealed that AMPD3 interacted with the E1α component of BCKDH complex. Whereas BCKDH has been reported to localize in mitochondria matrix as a rate-limiting enzyme for BCAA catabolism, immunoblotting using subcellular fractions revealed that BCKDH E1α is present in cytosol and endoplasmic reticulum as well. AMPD3-BCKDH E1α interaction was decreased by 68% in T2DM rats (OLETF) compared to that in control rats (LETO), and significant accumulation of BCAAs was observed in OLETF hearts (317±30 vs. 213±16 nmol/g). Survival rate at 48 hours after myocardial infarction (MI) was significantly lower in OLETF than in LETO (40% vs 84%). Empagliflozin treatment (10 mg/kg/day, 14 days) before MI improved the survival rate in OLETF to 70%, increased BCAAs as the top of 92 detected metabolites (791±187 nmol/g) and significantly preserved tissue ATP in the non-MI remote region. Electron microscopy showed a significantly higher prevalence of myocardium lipid droplets in OLETF, which was further increased by empagliflozin. Conclusions Results of the present analyses support the hypotheses that conversion of BCAA-derived branched-chain α-ketoacid to branched-chain acyl-CoA is suppressed by reduced AMPD3-BCKDH interaction in the myocardium of T2DM and that empagliflozin induces compensation of the dysregulated cardiac BCAA metabolism by augmentation of BCAA influx and promotion of fatty acid sequestration in intracellular lipid droplets. Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): Boehringer Ingelheim