Abstract P3185: ATP Citrate Lyase Regulates Cardiomyocyte Function By Controlling Mitochondrial Reductive Stress

Abstract

ATP citrate lyase (ACLY) is a cytosolic enzyme that converts citrate transported from the mitochondria into oxaloacetate and acetyl-CoA. It was recently reported to support a non-canonical TCA cycle, which is particularly important in immature and proliferating cells. Cardiomyocytes are both mature and non-proliferating and the role of ACLY in such cells is unknown. Using uniformly labeled C 13 glucose, we found that inhibiting ACLY using highly specific BMS-303141 (ACLY-I) significantly elevated M2 malate/M2 citrate ratio in adult cardiomyocytes in 1 hour, indicating their engagement in a non-canonical TCA cycle. In isolated hearts (Langendorff), we found both dP/dt max and dP/dt min markedly depressed after 40 minutes of ACLY-I. Isolated adult myocytes exposed to 1 hour of ACLY-I had depressed sarcomere shortening and prolonged relaxation. Reactive oxygen species was unchanged. BMS303141 at >10 μM was cardiotoxic while concentrations up to 50μM are not toxic in cardiac fibroblasts or hepatocytes. Untargeted metabolomics from ACLY-I treated hearts found significant decreases in TCA cycle intermediates citrate and α-ketoglutarate, accompanied by reduction in ATP production despite accumulation of NADH. The NAD/NADH ratio was reduced after 1-hr ACLY-I in cardiomyocytes, supporting its induction of reductive stress. Consistent with this, lactate was increased perhaps as a mechanism to oxidize NADH and alleviate reductive stress. These results have translational importance, as we find in human heart failure biopsies that ACLY is significantly downregulated at both transcript and protein levels. This finding is inversely related to body mass index, raising the hypothesis that exposure to high fat diet may reduce ACLY levels. This was tested in adult cardiomyocytes isolated from hearts 4 weeks after transaortic constriction and then treated with palmitate and oleate. ACLY mRNA declined post fatty acid treatment and paralleled a decline in ACLY promoter activity. These results identify a critical role of ACLY in normal myocyte NAD/NADH balance and mitochondrial function. ACLY reduction in heart failure particularly with obesity (e.g. heart failure with preserved ejection fraction) suggests a potentially new metabolic therapeutic target.