Fatty Acid Overload to Mitochondria Promotes Myocardial Insulin Resistance in Differentiated H9C2 Myocytes

Abstract

OBJECTIVE: In chronic heart failure, it is well known that an increase in serum fatty acid (FA) due to adrenergic stimulation induces myocardial insulin-resistance, which further deteriorates myocardial function. Since precise mechanisms of pathogenesis in FA-induced myocardial insulin-resistance is still elusive, we in this study investigated the relationship between FA-induced myocardial insulin-resistance and mitochondrial dysfunction, using an ex vivo insulin-resistant myocytes model.METHODS and RESULTS: The differentiated H9c2 myocytes were treated with saturated FA (palmitate; 0.2 mM) for 24 hours to produce the ex vivo insulin-resistant myocytes. The palmitate-treated myocytes exhibited an impaired insulin (100 nM)-mediated 2-deoxy-D-glucose (2DG) uptake (1.0 ± 0.1 fold increase from without insulin vs. 1.7 ± 0.1 of control, P< 0.01) and attenuated phosphorylation of insulin signaling molecules (IRS-1 and AKT), indicating insulin-resistance. When myocytes were pretreated with perhexiline (2 μM; an inhibitor of mitochondrial FA uptake) the reduced 2-DG uptakes (1.2 ± 0.1 fold increase from without insulin vs. palmitate-treated myocytes, P< 0.01) and attenuated phosphorylation of insulin-signaling were restored. The palmitate-treated myocytes revealed the intracellular ATP reduction (74 ± 6 % decrease from control, P< 0.01; luciferase assay), mitochondrial membrane potential depolarization (JC-1 ratio of 590/528 nm: 2.9 ± 0.1 vs. 5.3 ± 0.2 of control, P< 0.01), indicating mitochondrial dysfunction. When the myocytes were pretreated with perhexiline, the reduced intracellular ATP levels (32±14 % increase from palmitate-treated myocytes, P< 0.01) and depolarized mitochondrial membrane potential (JC-1 ratio: 3.5 ± 0.1 vs. palmitate-treated myocytes, P< 0.01) by palmitate were restored, indicating the improvement in mitochondrial function.CONCLUSION: Our findings indicated that mitochondrial dysfunction via mitochondrial FA overload may underlie the pathogenesis of myocardial insulin-resistance under HF.