Skeletal muscle mRNA expression in 25 mice with or without genetic defects of mitochondrial fatty acid oxidation (Acadl and Acadvl knockout) using RNA sequencing.

A mitochondrial long-chain fatty acid oxidation defect leads to dysregulation of plasma long-chain acyl carnitines, dysregulation of plasma amino acids, and an increased reliance on glucocorticoid signaling to maintain euglycemia during fasting. [muscle] Skeletal muscle tissue relies on products of fatty acid oxidation (FAO) during conditions of metabolic stress: fasting, prolonged exercise, febrile illness. Fasting-induced hypoglycemia and rhabdomyolysis are characteristic features of FAO disorders including very long chain acyl-CoA dehydrogenase (VLCAD) deficiency (VLCADD). However, the pathophysiological mechanisms that underlie the connection between FAO dysfunction and skeletal muscle dysfunction are not known. Here, we investigated the transcriptional response in skeletal muscle tissue (gastrocnemius) to the FAO defect in a model of VLCADD: the long-chain acyl-CoA dehydrogenase (LCAD) knockout (KO) mouse. We found that differentially expressed genes in the muscle were associated with molecular networks annotated for the cellular response to starvation from population-based models. To validate the association between the starvation response and FAO, we pharmacologically inhibited both glucocorticoid signaling and FAO in a model of fasting and observed that mice depleted in both pathways lost less weight during fasting and became hypoglycemic. These findings implicate glucocorticoid signaling as a candidate modifier of the cellular response to starvation in muscle tissue in the context of FAO disorders including VLCADD.