Abstract
Myocyte differentiation involves complex interactions between signal transduction pathways and transcription factors. The estrogen-related receptors (ERRs) regulate energy substrate uptake, mitochondrial respiration, and biogenesis and may target structural gene programs in striated muscle. However, ERRα's role in regulating myocyte differentiation is not known. ERRα and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) are coordinately upregulated with metabolic and skeletal muscle-specific genes early in myogenesis. We analyzed effects of ERRα overexpression and loss of function in myogenic models. In C2C12 myocytes ERRα overexpression accelerated differentiation, whereas XCT790 treatment delayed myogenesis and resulted in myotubes with fewer mitochondria and disorganized sarcomeres. ERRα-/- primary myocytes showed delayed myogenesis, resulting in structurally immature myotubes with reduced sarcomeric assembly and mitochondrial function. However, sarcomeric and metabolic gene expression was unaffected or upregulated in ERRα-/- cells. Instead, ERRα-/- myocytes exhibited aberrant ERK activation early in myogenesis, consistent with delayed myotube formation. XCT790 treatment also increased ERK phosphorylation in C2C12, whereas ERRα overexpression decreased early ERK activation, consistent with the opposing effects of these treatments on differentiation. The transient induction of MAP kinase phosphatase-1 (MKP-1), which mediates ERK dephosphorylation at the onset of myogenesis, was lost in ERRα-/- myocytes and in XCT790-treated C2C12. The ERRα-PGC-1α complex activates the Dusp1 gene, which encodes MKP-1, and ERRα occupies the proximal 5' regulatory region during early differentiation in C2C12 myocytes. Finally, treatment of ERRα-/- myocytes with MEK inhibitors rescued normal ERK signaling and myogenesis. Collectively, these data demonstrate that ERRα is required for normal skeletal myocyte differentiation via modulation of MAP kinase signaling.