Defining the role of HIF-1α and MMP-9 during skeletal myoblast differentiation

Although the hypoxia-inducible factor (HIF)-1α has been highlighted as a regulator of the functionality of the resident skeletal muscle stem cells namely satellite cells (SCs), its spatio-temporal expression and its role in SCs undergoing myogenic differentiation remain controversial. HIF-1α represents the oxygen-sensitive subunit of the transcriptional factor HIF, that is usually degraded in normoxia and stabilized in hypoxia to translocate to the nucleus and regulate its target gene expression. However, in SCs an oxygen level-independent regulation of HIF-1α expression and activation has been observed, thus suggesting a role of such protein in skeletal muscle physiological functions and homeostasis. Here we aimed to further investigate the role of HIF-1α in murine C2C12 myoblasts and primary SCs undergoing myogenic differentiation under normoxia conditions. Furthermore, based on the reported role of metalloproteinase (MMP)-9 in myogenesis, we evaluated MMP-9 as an HIF-1α downstream eff ector. We fi rst showed that the cells underwent metabolic reprogramming during diff erentiation: proliferating myoblasts mainly depends on glycolytic energy production whereas myotubes show a superior aerobic capacity. We found that: i) HIF-1α expression synchronized with that of MMP-9 and of the myogenic activation marker MyoD, increasing aft er 24 h of diff erentiation, ii) MMP-9 was a target of HIF-1α and iii) HIF-1α/MMP-9 axis was required for myoblast myogenic commitment, as judged by gene silencing experiments and morphological, biochemical and electrophysiological analyses. In conclusion, we showed HIF-1α/ MMP-9 axis involvement in the early phases of skeletal myoblast differentiation.