The hypoxia-inducible factors HIF1α and HIF2α are dispensable for embryonic muscle development but essential for postnatal muscle regeneration

Abstract

Muscle satellite cells are myogenic stem cells whose quiescence, activation, self-renewal, and differentiation are influenced by oxygen supply, an environmental regulator of stem cell activity. Accordingly, stem cell-specific oxygen signaling pathways precisely control the balance between muscle growth and regeneration in response to oxygen fluctuations, and hypoxia-inducible factors (HIFs) are central mediators of these cellular responses. However, the roles of HIFs in quiescent satellite cells and activated satellite cells (myoblasts) are poorly understood. Using transgenic mouse models for cell-specific HIF expression, we show here that HIF1α and HIF2α are preferentially expressed in pre- and post-differentiation myoblasts, respectively. Interestingly, double knockouts of HIF1α and HIF2α (HIF1α/2α dKO) generated with the MyoD system in embryonic myoblasts resulted in apparently normal muscle development and growth. However, HIF1α/2α dKO produced with the tamoxifen-inducible, satellite cell-specific Pax7 system in postnatal satellite cells delayed injury-induced muscle repair due to a reduced number of myoblasts during regeneration. Analysis of satellite cell dynamics on myofibers confirmed that HIF1α/2α dKO myoblasts exhibit reduced self-renewal but more pronounced differentiation under hypoxic conditions. Mechanistically, the HIF1α/2α dKO blunted hypoxia-induced activation of Notch signaling, a key determinant of satellite cell self-renewal. We conclude that HIF1α and HIF2α are dispensable for muscle stem cell function under normoxia but are required for maintaining satellite cell self-renewal in hypoxic environments. Our insights into a critical mechanism in satellite cell homeostasis during muscle regeneration could help inform research efforts to treat muscle diseases or improve muscle function.

Regulation and phylogeny of skeletal muscle regeneration

“…Consistently, the in vivo depletion of HIF1α and HIF2α (Hypoxia Inducible Factor), important transcription factors mediating the cellular response to low O 2 level, specifically in satellite cells (Pax7 CreERT2 ; HIF flox ) induces a delay in repair due to a self-renewal impairment and inhibition of Notch signalling (Yang et al, 2017).…”

Assessment of different strategies for scalable production and proliferation of human myoblasts

“…This necessarily means that the chemically defined hPSC-myoblasts would still be the most promising strategy. [39][40][41][42] . In this regard, several groups have recently made progress in improving existing chemically defined methods to further improve the purity and maturity of the terminally differentiated human myotubes obtained from hPSCs.…”

The Hypoxic Microenvironment of Stem Cells and their Progenies in the Heart

“…3 For instance, hypoxia does not regulate human ESC proliferation, but it has been shown to be critical for their differentiation into cardiac cells, mainly triggered under hypoxic conditions. 5 Yang et al, 6 showed that differentiation of myoblasts is favoured in a hypoxic microenvironment, with undifferentiated myoblasts presenting high levels of HIF1α, whereas differentiated myoblasts express high levels of HIF2α . The study by Kudová et al, 9 showed that HIF-1α deficiency significantly impaired the transcription of cardiac cell specific genes, and therefore the differentiation of ESCs into cardiomyocytes.…”

“…Three HIF-α factors-HIF-1α, HIF-2α and HIF-3α have been recognized. 6 HIF-1α and HIF-2α are closely related in their protein structures and both recognize common HIF responsive elements, but they differ in their tissue expression profiles. HIF-1α is expressed ubiquitously under hypoxic conditions in the heart and it regulates the anaerobic glycolytic metabolism in the cytoplasm.…”

“…3,6 HIFs are heterodimeric protein complexes consisting of an oxygen-independent β subunit and an oxygen-dependent α subunit with tightly regulated protein stability and activity. Three HIF-α factors-HIF-1α, HIF-2α and HIF-3α have been recognized.…”