2439-P: Activation of FOXO1 Impairs Muscle Mitochondrial Respiration and Strength prior to Decreased Mass

Introduction and Objective: Insulin-deficient diabetes is characterized by decreased muscle mass, mitochondrial dysfunction, and defective oxidative metabolism. FOXO1/3/4 transcription factors have emerged as major regulators of diabetes-induced muscle atrophy and mitochondrial dysfunction. However, the specific contribution of each FOXO to mitochondrial metabolism remains unclear. Methods: To elucidate the role of FoxO1 in skeletal muscle, we generated C2C12 cell lines overexpressing either a dominant negative FOXO1 (DNFOXO1, lacking the transactivation domain) or a constitutively active FoxO1 (CAFOXO1, with 3 mutated Akt phosphorylation sites). Results: DN-FOXO1 overexpression blocked the induction of FOXO-dependent atrophy genes, including Gadd45a, Gabarapl1, and MuRF1 during serum starvation, but did not affect mitochondrial function. By contrast, CA-FOXO1 reduced mitochondrial respiration, and downregulated OXPHOS subunits Ndufv2 and Sdhb by 12 and 24%, respectively. To evaluate effects in vivo, we overexpressed CA-FOXO1 in mouse tibialis anterior (TA) muscle via electroporation, achieving a five-fold overexpression of protein levels. CA-FOXO1 reduced mitochondrial genes Ndusf1 by 22%, and Ndufv2 by 33%, and induced FOXO1 targets Gadd45a, Gabarapl1, and MuRF1. Mitochondrial functional measurements showed a 45% decrease in mitochondrial respiration and 23% reduction in ATP production using pyruvate/malate substrates 2 weeks after electroporation. Despite unchanged muscle size, tetanic force decreased by 29%, showing impaired muscle strength associated with mitochondrial decline. Conclusion: These data demonstrate that FOXO1 activation represses mitochondrial genes and impairs mitochondrial function in skeletal muscle after just 2 weeks of expression, prior to measurable atrophy, and could affect muscle strength in uncontrolled diabetes. Disclosure C. Penniman: None. J. Jena: None. V. Lira: None. G. Bhardwaj: None. B.T. O'Neill: Stock/Shareholder; Current; Johnson & Johnson, Bristol-Myers Squibb Company, Pfizer Inc. Funding VA Merit I01BX004468 Fraternal Order of Eagles Diabetes Research Center Catalyst Award 2023