Lauric acid engages an O-GlcNAc-sensitive BCKDH regulatory node to modulate branched-chain amino acid oxidation in...

Branched-chain amino acid (BCAA) catabolism is controlled by the phosphorylation state of the branched-chain α-ketoacid dehydrogenase (BCKDH) complex, which is regulated by the opposing actions of BCKDH kinase and the phosphatase PPM1K. Although fatty acids and amino acids both contribute to skeletal muscle energy metabolism, how fatty acid availability influences BCAA catabolic regulation remains incompletely understood. Here, we examined the effects of lauric acid (C12), a medium-chain fatty acid abundant in dietary lipids, on BCAA metabolism in differentiated skeletal myotubes. Lauric acid increased phosphorylation of the BCKDH E1α subunit at Ser293 during nutrient perturbation in both mouse and human skeletal myotubes. Stable isotope tracing with U-[¹³C₆]-leucine revealed that C12 reduced incorporation of leucine-derived carbon into downstream tricarboxylic acid (TCA) cycle-associated metabolites, indicating suppression of BCAA oxidative flux, whereas incorporation of labeled leucine into protein was not significantly altered. Mechanistically, genetic and pharmacological perturbation experiments indicated that the C12 effect requires PPM1K and is sensitive to O-linked β-N-acetylglucosamine (O-GlcNAc) cycling. Knockdown of O-GlcNAc transferase attenuated the C12-induced increase in BCKDH phosphorylation and reversed suppression of leucine-derived carbon flux. Dual-tracer experiments further showed that carbon derived from lauric acid and leucine converges in shared tricarboxylic acid cycle-associated metabolite pools, including glutamate and glutamine. Together, these findings identify a nutrient-sensitive regulatory node linking fatty acid availability, O-GlcNAc signaling, and BCKDH phosphorylation that modulates BCAA oxidation in skeletal myotubes.