Inhibitory Regulation of FOXO1 in PPARδ Expression Drives Mitochondrial Dysfunction and Insulin Resistance.

Forkhead box O1 (FOXO1) regulates muscle growth, but the metabolic role of FOXO1 in skeletal muscle and its mechanisms remain unclear. To explore the metabolic role of FOXO1 in skeletal muscle, we generated skeletal muscle–specific Foxo1 inducible knockout (mFOXO1 iKO) mice and fed them a high-fat diet to induce obesity. We measured insulin sensitivity, fatty acid oxidation, mitochondrial function, and exercise capacity in obese mFOXO1 iKO mice and assessed the correlation between FOXO1 and mitochondria-related protein in the skeletal muscle of patients with diabetes. Obese mFOXO1 iKO mice exhibited improved mitochondrial respiratory capacity, which was followed by attenuated insulin resistance, enhanced fatty acid oxidation, and improved skeletal muscle exercise capacity. Transcriptional inhibition of FOXO1 in peroxisome proliferator–activated receptor δ (PPARδ) expression was confirmed in skeletal muscle, and deletion of PPARδ abolished the beneficial effects of FOXO1 deficiency. FOXO1 protein levels were higher in the skeletal muscle of patients with diabetes and negatively correlated with PPARδ and electron transport chain protein levels. These findings highlight FOXO1 as a new repressor in PPARδ gene expression in skeletal muscle and suggest that FOXO1 links insulin resistance and mitochondrial dysfunction in skeletal muscle via PPARδ. Article Highlights: Skeletal muscle FOXO1 is upregulated in metabolically unhealthy conditions, such as obesity and aging. We generated skeletal muscle–specific inducible Foxo1 -deficient mice to clarify the metabolic role of FOXO1 in skeletal muscle. FOXO1 deficiency improved mitochondrial dysfunction by increasing peroxisome proliferator–activated receptor δ (PPARδ) transcription, leading to improved insulin resistance and lipid metabolism in the skeletal muscle of obese mice. This study shows that FOXO1 is a new repressor in PPARδ gene expression in skeletal muscle and links insulin resistance and mitochondrial dysfunction in skeletal muscle via PPARδ. [ABSTRACT FROM AUTHOR]