Preconditioning Human Mesenchymal Stem Cells with a Low Concentration of BMP2 Stimulates Proliferation and Osteogenic Differentiation In Vitro

Clinical trials using bone morphogenetic protein-2 (BMP2) for bone reconstruction have shown promising results. However, the relatively high concentration needed to be effective raises concerns for efficacy and safety. The aim of this study was to investigate the osteogenic effect of an alternative treatment strategy in which human bone marrow–derived mesenchymal stem cells (hMSCs) are preconditioned with low concentrations of BMP2 for a short time in vitro. hMSCs in suspension were stimulated for 15 min with 10 and 20 ng/mL of BMP2. After the BMP2 was removed, the cells were seeded and cultured in osteogenic medium. The effects of preconditioning were analyzed with regard to proliferation and expression of osteogenic markers at both gene and protein level. The results were compared to those from cultures with continuous BMP2 stimulation. A significant increase in proliferation was seen with both precondition and continuous stimulation with BMP2, with no difference between the treatments. Preconditioning with BMP2 significantly increased gene expression of RUNX2, COLI, ALP, and OC, and protein levels of COLI and ALP. This was not found with continuous stimulation. The role of preconditioning with BMP2 in osteogenesis was validated by findings of increased gene expression of SMAD1 and an increase in dual phosphorylation of ser 463 and ser 465 in the SMAD 1/5/8 pathway. We concluded that preconditioning hMSCs with BMP2 stimulates osteogenesis: proliferation with matrix secretion and matrix maturation of hMSCs. This implies that preconditioning with BMP2 might be more effective at inducing proliferation and osteogenic differentiation of hMSCs than continuous stimulation. Preconditioning with BMP2 could benefit the clinical application of BMP2 since side effects from high-dose treatments could be avoided.