Inhibition of Branched‐Chain Ketoacid Dehydrogenase Kinase (BDK) Attenuates BCKA Induced Suppression of Insulin‐Stimulated Glucose Uptake in Muscle Cells

Abstract

ObjectivePlasma levels of branched‐chain amino acids (BCAAs) and their metabolites, branched‐chain ketoacids (BCKAs) are increased in insulin resistance, a condition that can lead to type 2 diabetes mellitus (T2DM). BCAA catabolic enzymes are downregulated in diabetes and obesity in skeletal muscle. We previously showed that leucine and KIC suppressed insulin‐stimulated glucose uptake in L6 myotubes. We have also shown that knocking down branched‐chain ketoacid dehydrogenase (BCKD), an enzyme that decarboxylates BCKAs, suppressed insulin‐stimulated glucose uptake. The objective of this study was to analyze the effect of increasing BCAA catabolism on measures of insulin sensitivity. We hypothesized that upregulating BCAA catabolism increases insulin‐stimulated glucose transport and attenuates BCKA induced insulin resistance.MethodsL6 myotubes were starved of serum‐ and amino acids with vehicle (DMSO) or BDK inhibitor BT2 supplementation for 3 hours. Then myotubes were supplemented with or without BCKAs (200 uM) for 30 minutes. After, cells were incubated with or without insulin (100 nM) for 20 minutes. They were then harvested for immunoblotting or used for glucose transport assay.ResultsBDK inhibition had no effect on insulin‐stimulated glucose uptake. BCKAs suppressed insulin‐stimulated glucose uptake by 31% in control cells (p>0.05; n=3); this suppression was attenuated in cells in which BDK was inhibited. BDK inhibition also reduced KIC‐induced IRS‐1Ser612 and S6K1Thr389 phosphorylation by 28% and 60% respectively but had no effect on AktSer473 phosphorylation.ConclusionsBDK inhibition attenuated BCKA‐induced suppression of insulin‐stimulated glucose uptake, suggesting that BCAA metabolism may be implicated in the pathogenesis of insulin resistance, and is worth further investigation.