SUN-LB006 Skeletal Muscle Krüppel-Like Factor 15 and PPARd Cooperate to Regulate Skeletal Muscle Lipid Metabolism

Abstract

Skeletal muscle lipid metabolism significantly modulates systemic metabolic status; unsurprisingly, aberrant skeletal muscle nutrient handling is closely associated with metabolic diseases. The mechanisms underlying skeletal muscle regulation of lipid metabolism remain to be fully elucidated. Previous studies have shown that mice deficient in nuclear receptor PPARδ suffer from deranged skeletal muscle lipid handling; a similar phenotype is observed in mice deficient in the transcription factor Krüppel-like factor 15 (KLF15). Preliminary data support the existence of KLF15-PPARδ cooperativity in regulating skeletal muscle lipid metabolism, and thus we sought to 1) define the metabolic role of skeletal muscle specific KLF15; and 2) elucidate the molecular basis of KLF15-PPARδ interaction and impact on skeletal muscle lipid metabolism. We generated a skeletal muscle specific KLF15 knockout (K15-SKO) mouse and characterized the metabolic phenotype of this animal. K15-SKO mice have increased body weight and fat mass, elevated circulating free-fatty acids and triglyceride, insulin insensitivity, and glucose intolerance compared to controls. Importantly, K15-SKO mice demonstrated decreased skeletal muscle expression of a number of lipid flux genes, many of which are targets of PPARδ. To determine the necessity of KLF15 for PPARδ-mediated gene expression, we depleted KLF15 in C2C12 cells and looked at a number of PPARδ targets. The expression levels of Fatp1, Cpt1b, and Scl25a20 were attenuated - this response was unchanged in the presence or absence of GW501516 (GW), a PPARδ agonist. We used Seahorse cell metabolism analyzer to assess fatty acid oxidation and observed that knockdown of KLF15 reduces GW induction of palmitate oxygen consumption rates. We conducted co-transfection studies and determined that KLF15 and PPARδ act synergistically on the Fatp1 promoter. Co-immunoprecipitation studies confirmed physical interaction between KLF15 and PPARδ. Finally, control and K15-SKO mice were gavaged with GW for 10 days, and K15-SKO animals demonstrated attenuated induction of a number of PPARδ targets in skeletal muscle. Taken together, these data suggest that skeletal muscle specific KLF15 is critical in the regulation of lipid handling and necessary for optimal PPARδ-mediated regulation of skeletal muscle lipid metabolism.