Obese Skeletal Muscle-Expressed Interferon Regulatory Factor 4 Transcriptionally Regulates Mitochondrial Branched-Chain Aminotransferase Reprogramming Metabolome.

In addition to the significant role in physical activity, skeletal muscle also contributes to health through the storage and use of macronutrients associated with energy homeostasis. However, the mechanisms of regulating integrated metabolism in skeletal muscle are not well-defined. Here, we compared the skeletal muscle transcriptome from obese and lean control subjects in different species (human and mouse) and found that interferon regulatory factor 4 (IRF4), an inflammation-immune transcription factor, conservatively increased in obese subjects. Thus, we investigated whether IRF4 gain of function in the skeletal muscle predisposed to obesity and insulin resistance. Conversely, mice with specific IRF4 loss in skeletal muscle showed protection against the metabolic effects of high-fat diet, increased branched-chain amino acids (BCAA) level of serum and muscle, and reprogrammed metabolome in serum. Mechanistically, IRF4 could transcriptionally upregulate mitochondrial branched-chain aminotransferase (BCATm) expression; subsequently, the enhanced BCATm could counteract the effects caused by IRF4 deletion. Furthermore, we demonstrated that IRF4 ablation in skeletal muscle enhanced mitochondrial activity, BCAA, and fatty acid oxidation in a BCATm-dependent manner. Taken together, these studies, for the first time, established IRF4 as a novel metabolic driver of macronutrients via BCATm in skeletal muscle in terms of diet-induced obesity.