Inhibition of IGF-1 receptor kinase blocks the differentiation into cardiomyocyte-like cells of BMSCs induced by IGF-1

Bone marrow mesenchymal stem cells (BMSCs) have the potential to transdifferentiate into cardiomyocyte-like cells (CLCs) if an appropriate cardiac environment is provided. Insulin-like growth factor-1 (IGF-1) plays an important role in the cell migration, survival and differentiation of BMSCs. However, the effect of IGF-1 on the cellular differentiation remains unclear. In the present study, BMSCs were isolated from rat femurs and tibias and the cells were purified at passage 6 (P6). IGF-1 and IGF-1 receptor (IGF-1R) kinase inhibitor I-OMe AG538 were added to detect if IGF-1 could induce BMSCs to transdifferentiate into CLCs and if I-OMe AG538 could inhibit IGF-1-mediated receptor activation and downstream signaling. Immunostaining demonstrated that all P6 BMSCs express CD29 and CD44 but not CD45. BMSCs induced by 15 ng/ml IGF-1 revealed positivity for cardiac troponin-T and cardiac troponin-I. The optimal induction time was 14 days but the expression of these proteins were incompletely inhibited by 300 nmol/l I-OMe AG538 and completely inhibited by 10 µmol/l I-OMe AG538. Western blotting showed that the level of IGF-1R autophosphorylation and the expression of cTnT and cTnI were higher when BMSCs were induced for 14 days. I-OMe AG538 selectively inhibited IGF-1-mediated growth and signal transduction and the inhibitory effect of I-OMe AG538 were not reverted in the presence of exogenous IGF-1. In addition, when a time course analysis of the effects of I-OMe AG538 on mitogen-activated protein kinase kinase and phosphatidylinositol 3-kinase signaling were done, we observed a transient inhibitory effect on Erk1/2 and Akt phosphorylation, in keeping with the inhibitory effects on cell growth. Taken together, these data indicate that I-OMe AG538 could inhibit IGF-1-induced CLCs in BMSCs and this effect is time- and concentration-dependent.