Sequential induction of marrow stromal cells by FGF2 and BMP2 improves their growth and differentiation potential in vivo

Abstract Background Repairing bone loss by autologous grafting requires that a patient's marrow stromal cells (MSCs) be collected and cultured until the number of cells is adequate for implantation. Currently used techniques allow a slow proliferation rate and produce a culture that contains only small amounts of pluripotent stem cells that will become osteoblasts in culture. Objective To develop culture conditions that permit a rapid increase in the number of MSCs while retaining or improving their potential for complete differentiation in vivo. Results Sequential applications of low doses of basic fibroblast growth factor 2 (FGF2) and bone morphogenetic protein 2 (BMP2) improved the growth and differentiation potential of MSCs. FGF2 also elevated sensitivity of the cells to BMP2. BMP2 increased the syntheses of alkaline phosphatase (ALP), collagen type I and bone sialoprotein, while FGF2 increased the expression of osteocalcin (OC). Full induction as determined by the formation of mineralised nodules in vitro was observed within 7 days. Seeding the induced cells onto scaffolds and then implanting them into nude mice resulted in newly formed bone 4 weeks later. The results of real-time polymerase chain reaction (PCR) and Western blotting suggested that FGF2 increased the pool of committed osteoblasts by up-regulating the Cbfa1/Runx2 gene. The later stages of bone formation seemed to be induced by Cbfa1/Runx2-downstream factors such as BMP2, ALP, collagen type I, bone sialoprotein and OC. Conclusion The culture system that was developed increased both the proliferation of MSC and the proportion that developed into pre-osteoblasts.