Temporal microRNA expression during in vitro myogenic progenitor cell proliferation and differentiation: Regulation of proliferation by miR-682

MicroRNAs (miRNAs) regulate gene expression by repressing target genes at the posttranscriptional level. Since miRNAs have unique expression profiles in different tissues, they provide pivotal regulation of many biological processes. The present study defined miRNA expression during murine myogenic progenitor cell (MPC) proliferation and differentiation to identify miRNAs involved in muscle regeneration. Muscle-related gene expression analyses revealed that the time course and expression of myosin heavy chain (MHC) and transcription factors (Myf5, MyoD, myogenin, and Pax7) were similar during in vitro MPC proliferation/differentiation and in vivo muscle regeneration. Comprehensive profiling revealed that 139 or 16 miRNAs were significantly changed more than twofold [false discovery rate (FDR) < 0.05] during MPC differentiation or proliferation, respectively; cluster analyses revealed five distinct patterns of miRNA expression during the time course of MPC differentiation. Not unexpectedly, the largest miRNA changes occurred in muscle-specific miRNAs (miR-1, -133a, and -499), which were upregulated > 10-fold during MPC differentiation (FDR < 0.01). However, several previously unreported miRNAs were differentially expressed, including miR-10b, -335-3p, and -682. Interestingly, the temporal patterns of miR-1, -499, and -682 expression during in vitro MPC proliferation/ differentiation were remarkably similar to those observed during in vivo muscle regeneration. Moreover, in vitro inhibition of miR-682, the only miRNA upregulated in proliferating compared with quiescent MPC, led to decreased MPC proliferation, further validating our in vitro assay system for the identification of miRNAs involved in muscle regeneration. Thus the differentially expressed miRNAs identified in the present study could represent new regulatory elements in MPC proliferation and differentiation.