Dysfunctional BCAAs catabolism protests from diet-induced obesity via IRF4/BCATm pathway in skeletal muscle

It is well established that obese animals and humans show deficiencies in skeletal muscle content and metabolism. However, the mechanisms under how skeletal muscle metabolism affects systemic energy homeostasis is not well-defined. Here, we compared the skeletal muscle transcriptome from obese and lean controls in different species. We found an immune-responsive transcription factor interferon regulatory factor 4 (IRF4) was conserved to be increased in obese subjects from the three species (humans, non-human primates and mice). Thus, we demonstrated that loss of IRF4 specifically in skeletal muscle of mice showed protection against the metabolic effects of high-fat diet, with unexpected increased plasma and muscle branched-chain amino acid (BCAA) levels. Conversely, overexpression of skeletal muscle IRF4 caused obesity and insulin resistance, with decreased BCAA contents. Mechanistically, IRF4 can transcriptionally regulate branched-chain aminotransferase isozyme (BCATm) expression, and that overexpression of BCATm can reverse the effects of IRF4 depletion regarding to metabolic phenotypes. Further, we demonstrated ablation of IRF4 in skeletal muscle increased mitochondrial activity and glycogen synthesis in a BCATm- dependent manner. These studies establish IRF4 as a novel driver of BCAA metabolism via BCATm in skeletal muscle and may interpret the BCAAs paradox in obesity.