Distinct HIF1α and HIF2α functions control skeletal muscle metabolism and erythropoiesis.

Skeletal muscle frequently encounters hypoxic stress, particularly during exercise, but the specific functions of the hypoxia-inducible factors HIF1α and HIF2α within myofibers remain unclear due to the lack of appropriate in vivo models. Here, we generated 3 complementary mouse models, myofiber-specific triple-PHD knockout (PHD mTKO) and inducible myofiber-specific overexpression of stabilized HIF1α or HIF2α, to delineate isoform-specific roles of HIFα signaling in skeletal muscle. HIF1α stabilization increased the proportion of oxidative fibers yet paradoxically impaired exercise capacity and mitochondrial function. In contrast, HIF2α activation protected against diet-induced obesity, improved glucose tolerance, and maintained mitochondrial function without altering fiber-type composition. Notably, HIF2α stabilization markedly elevated erythropoietin (EPO) expression in skeletal muscle and serum. Myofiber-specific deletion of EPO in the PHD mTKO background abolished polycythemia, demonstrating that this phenotype is driven specifically by muscle-derived EPO. Together, these findings uncover distinct roles of HIF1α and HIF2α in regulating muscle metabolism and mitochondrial function and establish the PHD-HIF2α axis as a myofiber-derived driver of systemic EPO production.