miR-487b-3p Suppresses the Proliferation and Differentiation of Myoblasts by Targeting IRS1 in Skeletal Muscle Myogenesis

MicroRNAs are endogenous, small non-coding RNAs that can play critical gene-regulatory roles during skeletal muscle development and are highly conserved. miR-487b-3p is expressed in muscle, and the detailed mechanism by which it regulates myoblast proliferation and differentiation has not been explored. Here, we found that miR-487b-3p expression was significantly higher in goat muscle tissues than in other tissues and was higher in fetal goat muscle tissues than in mature goat tissues, suggesting that miR-487b-3p has an important effect on skeletal muscle myogenesis. Functional studies showed that miR-487b-3p overexpression significantly suppressed C2C12 myoblast proliferation and differentiation, which was accompanied by the down-regulation of functional genes related to proliferation (MyoD, Pax7 and PCNA) and differentiation (Myf5, MyoG and Mef2c), whereas the inhibition of miR-487b-3p accelerated C2C12 myoblast proliferation and differentiation and was accompanied by the up-regulation of functional genes. Using Target-Scan and David, we found that miR-487b-3p targeted the 3'-UTR of IRS1, an essential regulator in the PI3K/Akt and MAPK/Erk pathways. We then confirmed the targeting of IRS1 by miR-487b-3p using dual-luciferase assays, RT-qPCR and western blotting. Furthermore, IRS1 silencing markedly inhibited proliferation and differentiation in cultured C2C12 myoblasts, confirming the important role of IRS1 in myogenesis. These results reveal an IRS1-mediated regulatory link between miR-487b-3p and the PI3K/Akt and MAPK/Erk pathways during skeletal muscle myogenesis.