(623a) Control of Mitochondrial Substrate Utilization By the Mitochondrial Pyruvate Carrier

Pyruvate oxidation in the mitochondria marks the node connecting the two most well studied and arguably most important pathways in catabolic and anabolic metabolism, glycolysis and the tricarboxylic acid (TCA) cycle.  Deregulation of this process contributes to the pathogenesis of numerous diseases, including diabetes, obesity, and cancer.  Existence of a protein carrier to facilitate pyruvate transport into mitochondria has been recognized for decades; however the identity of the genes encoding this complex eluded researchers until last year. In this study we evaluated the function of the mitochondrial pyruvate carrier (MPC) in skeletal muscle cells using ¹³C metabolic flux analysis. Mpc1 or Mpc2 were knocked down with lentviral infection of hairpins coding for shRNA or pharmacologically inhibited in myoblasts and differentiated C2C12 mouse skeletal muscle cells. Proliferating myoblasts maintained growth and oxygen consumption with Mpc1/2 knocked down or the protein products inhibited; however their reliance on substrates for energy and biosynthetic metabolism completely shifted from glucose to amino acid oxidation. TCA cycle flux and fatty acid synthesis were maintained through glutamine anaplerosis, oxidation, and reductive carboxylation. Similar shifts were seen in differentiated myotubule energy metabolism in response to Mpc1/2 knockdown and pharmacological inhibition. The identification of the major shifts in metabolic substrate utilization in response to Mpc1/2 regulation provides new insights into the treatment of metabolic disease.