Fibroblast growth factor 2 inhibits bone morphogenetic protein 9-induced osteogenic differentiation of mesenchymal stem cells by repressing Smads signaling and subsequently reducing Smads dependent up-regulation of ALK1 and ALK2

Understanding the interactions between growth factors and bone morphogenic proteins (BMPs) signaling remains a crucial issue to optimize the use of mesenchymal stem cells (MSCs) and BMPs in bone tissue engineering. BMP9 is highly capable of promoting osteogenic differentiation of MSCs. Fibroblast growth factor 2 (FGF2) is abundantly secreted during the healing process of fractures or in surgery bone sites. Herein, we explore the detail effect of FGF2 on BMP9-induced osteogenic differentiation of MSCs. It was found that FGF2 inhibited BMP9-induced osteogenic differentiation by blocking BMP9-induced Smads signaling and subsequently reducing Smads dependent up-regulation of ALK1 and ALK2 in MSCs. This effect was rescued by exogenous expression of ALK1 and ALK2, which are proved to be receptors for BMP9. Our results discovered a clue to explain the mechanism involved in the inhibitory effect of FGF2 on BMP9-induced osteogenic differentiation of MSCs. This crosstalk between FGF2 and BMP9 should be emphasized in the future use of BMP9 in therapeutic purpose of fracture repair.