A global downregulation of microRNAs occurs in human quiescent satellite cells during myogenesis.

During myogenesis, human satellite cells differentiate and form multinucleated myotubes, while a fraction of the human satellite cells enter quiescence. These quiescent satellite cells are able to activate, proliferate and contribute to muscle regeneration. Post-transcriptional regulation of myogenesis occurs through specific myogenic microRNAs, also known as myomiRs. Although many microRNAs are involved in myotube formation, little is known on the involvement of microRNAs in satellite cells entering quiescence. This current study aims to investigate microRNA involvement during differentiation of human satellite cells, specifically proliferating satellite cells entering quiescence. For this, clonally expanded human satellite cells were differentiated for 5 days, after which myotubes and quiescent satellite cells were separated through FACS sorting. Next, a microRNA microarray comparison of proliferating satellite cells, myotubes and quiescent satellite cells was performed and verified through qRT-PCR. We show that during human satellite cell differentiation, microRNAs are globally downregulated in quiescent satellite cells compared to proliferating satellite cells, in particular microRNA-106b, microRNA-25, microRNA-29c and microRNA-320c. Furthermore, we show that during myogenesis microRNA-1, microRNA-133, microRNA-206 and microRNA-486 are involved in myotube formation rather than satellite cells entering quiescence. Finally, we show an overall decrease in total mRNA in quiescent satellite cells, and an indication that RNaseL regulation plays a role in promoting and maintaining quiescence. Given the importance of quiescent satellite cells in skeletal muscle development and regenerative medicine, it is imperative to distinguish between myotubes and quiescent satellite cells when investigating skeletal muscle development, especially in microRNA studies, since we show that microRNAs are globally downregulated in quiescent human satellite cells.