Myeloid hypoxia-inducible factor-1α is essential for skeletal muscle regeneration in mice.

The outstanding regeneration ability of skeletal muscle is based on stem cells that become activated and develop to myoblasts after myotrauma. Proliferation and growth of myoblasts result in self-renewal of skeletal muscle. In this article, we show that myotrauma causes a hypoxic microenvironment leading to accumulation of the transcription factor hypoxia-inducible factor-1 (HIF-1) in skeletal muscle cells, as well as invading myeloid cells. To evaluate the impact of HIF-1 in skeletal muscle injury and repair, we examined mice with a conditional HIF-1α knockout targeted to skeletal muscle or myeloid cells in a model of soft tissue trauma. No differences in acute trauma size were detected between control and HIF-1α knockout mice. However, muscles of myeloid HIF-1α knockout mice showed a significant delay in myoblast proliferation and growth of regenerating myofibers, in association with decreased expression of cyclooxygenase-2 in HIF-1α-deficient myeloid cells. Moreover, the removal of necrotic cell debris and the regeneration of endothelial cell structure were impaired in myeloid HIF-1α knockout mice that showed delayed invasion of macrophages to the injury site. Our findings for the first time, to our knowledge, demonstrate that myeloid HIF-1α is required for adequate skeletal muscle regeneration.