Muscle mitochondrial stress-induced metabolic adaptations do not require FGF21 action

Fibroblast growth factor 21 (FGF21) is a key metabolic regulator which was recently discovered as stress-induced myokine and common denominator of muscle mitochondrial disease. However, its precise function and pathophysiological relevance remains unknown. Here we demonstrate that white adipose tissue (WAT) is the major target of muscle mitochondrial stress-induced FGF21. Strikingly, substantial browning and metabolic remodeling of subcutaneous WAT, together with the reduction of circulating triglycerides and cholesterol are fully FGF21 dependent. Unexpectedly and in contrast to prior expectations, we found a negligible role of FGF21 in muscle stress-related improved glycemic control, obesity resistance and hepatic lipid homeostasis. Furthermore, we show that the protective muscle mitohormesis and metabolic stress adaptation does not require FGF21 action. Taken together, our data imply that although FGF21 drives WAT remodeling, this effect and FGF21 as stress hormone per se may not be essential for the adaptive response under muscle mitochondrial stress conditions