Metabolism and acetylation contribute to leucine-mediated inhibition of cardiac glucose uptake.

High plasma leucine levels strongly correlate with type 2 diabetes. Studies of muscle cells suggest that leucine alters the insulin response for glucose transport by activating an insulin-negative feedback loop driven by the mammalian target of rapamycin/p70 ribosomal S6 kinase (mTOR/p70S6K) pathway. Here, we examined the molecular mechanism involved in leucine's action on cardiac glucose uptake. Leucine was indeed able to curb glucose uptake after insulin stimulation in both cultured cardiomyocytes and perfused hearts. Although leucine activated mTOR/p70S6K, the mTOR inhibitor rapamycin did not prevent leucine's inhibitory action on glucose uptake, ruling out the contribution of the insulin-negative feedback loop. α-Ketoisocaproate, the first metabolite of leucine catabolism, mimicked leucine's effect on glucose uptake. Incubation of cardiomyocytes with (13)C-labeled leucine ascertained its metabolism to ketone bodies (KBs), which had similar negative impact on insulin-stimulated glucose transport. Both leucine and KBs reduced glucose uptake by affecting translocation of the glucose transporter 4 (GLUT4) to the plasma membrane. Finally, we found that leucine elevated global protein acetylation level. Pharmacological inhibition of lysine acetyltransferases counteracted this increase in protein acetylation and prevented leucine's inhibitory action on both glucose uptake and GLUT4 translocation. Taken together, these results indicate that leucine metabolism into KBs contributes to inhibition of cardiac glucose uptake by hampering the translocation of GLUT4-containing vesicles via acetylation. They offer new insight into the establishment of insulin resistance in the heart