Insulin‐like growth factor‐1 (IGF‐1) promotes myoblast proliferation and skeletal muscle growth of embryonic chickens via the PI3K/Akt signalling pathway

Abstract During embryonic development, IGF‐1 fulfils crucial roles in skeletal myogenesis. However, the involvement of IGF‐1‐induced myoblast proliferation in muscle growth is still unclear. In the present study, we have characterised the role of IGF‐1 in myoblast proliferation both in vitro and in vivo and have revealed novel details of how exogenous IGF‐1 influences myogenic genes in chicken embryos. The results show that IGF‐1 significantly induces the proliferation of cultured myoblasts in a dose‐dependent manner. Additionally, the IGF‐1 treatment significantly promoted myoblasts entering a new cell cycle and increasing the mRNA expression levels of cell cycle‐dependent genes. However, these effects were inhibited by the PI3K inhibitor LY294002 and the Akt inhibitor KP372‐1. These data indicated that the pro‐proliferative effect of IGF‐1 was mediated in response to the PI3K/Akt signalling pathway. Moreover, we also showed that exogenous IGF‐1 stimulated myoblast proliferation in vivo. IGF‐1 administration obviously promoted the incorporation of BrdU and remarkably increased the number of PAX7‐positive cells in the skeletal muscle of chicken embryos. Administration of IGF‐1 also significantly induced the upregulation of myogenic factors gene, the enhancement of c‐Myc and the inhibition of myostatin (Mstn) expression. These findings demonstrate that IGF‐1 has strong activity as a promoter of myoblast expansion and muscle fiber formation during early myogenesis. Therefore, this study offers insight into the mechanisms responsible for IGF‐1‐mediated stimulation of embryonic skeletal muscle development, which could have important implications for the improvement of chicken meat production.