213-LB: Mechanisms of Metabolic Cross Talk between Mitochondrial Pyruvate Carrier Inhibition and Branched-Chain Amino Acid Catabolism in Hepatocytes

Abstract

The mitochondrial pyruvate carrier (MPC) has emerged as a therapeutic target for treating insulin resistance, type 2 diabetes, and nonalcoholic steatohepatitis (NASH). However, the molecular mechanisms by which MPC inhibition leads to metabolic improvements are incompletely understood. We evaluated whether MPC inhibitors might correct impairments in branched chain amino acid (BCAA) catabolism, which are predictive of developing diabetes and NASH. BCAA concentrations were assessed in plasma collected in EMMINENCE (NCT02784444), a randomized, placebo-controlled trial of the MPC inhibitor MSDC-0602K in people with NASH. MSDC-0602K treatment, which led to marked improvements in insulin sensitivity and diabetes endpoints, decreased plasma concentrations of BCAAs compared to baseline while placebo had no effect. The rate-limiting enzyme in BCAA catabolism is the mitochondrial branched chain ketoacid dehydrogenase (BCKDH). BCKDH activity is suppressed by phosphorylation mediated by a kinase (BDK) and activated by the phosphatase (PPM1K). In Huh7 or HepG2 cells, MPC inhibitors markedly reduced BCKDH phosphorylation, suggesting increased BCKDH activity. Chemical inhibition or siRNA-mediated silencing of BDK had no effect on suppression of BCKDH phosphorylation by MPC inhibitors. In contrast, PPM1K knockdown prevented the effects of MPC inhibition on phospho-BCKDH. Lastly, we quantified BCKDH phosphorylation in liver of wild-type and hepatocyte-specific MPC2 knockout (LS-Mpc2-/-) mice after 20 weeks of high fat diet. LS-Mpc2-/- mice exhibited reduced phosphorylation of BCKDH compared to wild-type mice. Lean LS-Mpc2-/- mice also exhibited reduced plasma BCAA concentrations after an overnight fast. These data demonstrate novel cross talk between mitochondrial pyruvate and BCAA metabolism and suggest that MPC inhibition leads to lower plasma BCAA concentrations and BCKDH phosphorylation via the phosphatase PPM1K. Disclosure D. Ferguson: None. N. K. H. Yiew: None. K. S. Mccommis: None. J. R. Colca: Board Member; Self; Metabolic Solutions Development Company, LLC, Employee; Self; Cirius Therapeutics. B. N. Finck: Advisory Panel; Self; Cirius Therapeutics, Stock/Shareholder; Self; Cirius Therapeutics. Funding National Institutes of Health (R01DK104735, T32DK007120)