Hypoxia differentially regulates muscle oxidative fiber type and metabolism in a HIF-1α-dependent manner

Loss of skeletal muscle oxidative fiber types and mitochondrial capacity is a hallmark of chronic obstructive pulmonary disease and chronic heart failure. Based on in vivo human and animal studies, tissue hypoxia has been hypothesized as determinant, but the direct effect of hypoxia on muscle oxidative phenotype remains to be established. Hence, we determined the effect of hypoxia on in vitro cultured muscle cells, including gene and protein expression levels of mitochondrial components, myosin isoforms (reflecting slow-oxidative versus fast-glycolytic fibers), and the involvement of the regulatory PPAR/PGC-1alpha pathway. We found that hypoxia inhibits the PPAR/PGC-1alpha pathway and the expression of mitochondrial components through HIF-1alpha. However, in contrast to our hypothesis, hypoxia stimulated the expression of slow-oxidative type I myosin via HIF-1alpha. Collectively, this study shows that hypoxia differentially regulates contractile and metabolic components of muscle oxidative phenotype in a HIF-1alpha-dependent manner.