MicroRNA-664-5p Promotes Myoblast Proliferation and Inhibits Myoblast Differentiation by Targeting Serum Response Factor and

MicroRNAs (miRNAs) are noncoding RNAs that regulate gene expression at the post-transcriptional level and are involved in the regulation of the formation, maintenance, and function of skeletal muscle. Using miRNA sequencing and bioinformatics analysis, we previously found that the miRNA miR-664-5p is significantly differentially expressed in longissimus dorsi muscles of Rongchang pigs. However, the molecular mechanism by which miR-664-5p regulates myogenesis remains unclear. In this study, using flow cytometry, 5-ethynyl-2'-deoxyuridine staining, and cell count and immunofluorescent assays, we found that cell-transfected miR-664-5p mimics greatly promoted proliferation of C2C12 mouse myoblasts by increasing the proportion of cells in the S- and G-phases and up-regulating the expression of cell cycle genes. Moreover, miR-664-5p inhibited myoblast differentiation by down-regulating myogenic gene expression. In contrast, miR-664-5p inhibitor repressed myoblast proliferation and promoted myoblast differentiation. Mechanistically, using dual-luciferase reporter gene experiments, we demonstrated that miR-664-5p directly targets the 3'-UTR of serum response factor () and mRNAs. We also observed that miR-664-5p inhibits both mRNA and protein levels of and during myoblast proliferation and myogenic differentiation, respectively. Furthermore, the activating effect of miR-664-5p on myoblast proliferation was attenuated by overexpression, and miR-664-5p repressed myogenic differentiation by diminishing the accumulation of nuclear β-catenin. Of note, miR-664-5p's inhibitory effect on myogenic differentiation was abrogated by treatment with Wnt1 protein, the key activator of the Wnt/β-catenin signaling pathway. Collectively, our findings suggest that miR-664-5p controls and canonical Wnt/β-catenin signaling pathways in myogenesis.