FGF21 expression and release in muscle cells: involvement of MyoD and regulation by mitochondria-driven signalling.

Although the liver is generally considered the main site of production of FGF21 (fibroblast growth factor-21), high FGF21 levels have been found to be associated with neuromuscular mitochondrial genetic diseases, and there are indications that the muscle may be a relevant site of FGF21 production under conditions of muscular mitochondrial stress. In the present study, we found that expression and release of FGF21 was associated with myogenic differentiation, and we identified MyoD as a major controller of FGF21 gene transcription. Mimicking mitochondrial dysfunction using respiratory chain/oxidative phosphorylation inhibitors resulted in enhanced expression and release of FGF21 by muscle cells. The increased production of reactive oxygen species, subsequent induction of p38 MAPK (mitogen-activated protein kinase) and activation of an ATF2 (activating transcription factor 2)-binding site at the proximal promoter region of the FGF21 gene was found to be a major mechanism linking mitochondrial dysfunction with enhanced FGF21 gene transcription in myogenic cells. The myogenic factor MyoD was required for the induction of FGF21 gene transcription by mitochondrial dysfunction, thus explaining the preferential response of muscle cells to mitochondrial dysfunction-induced FGF21 expression and secretion. FGF21 release by muscle cells in response to mitochondrial alterations may represent a physiological mechanism by which the sensing of internal energetic status by muscles results in the release of FGF21 to favour systemic metabolic adaptations.