In vitro response of primary human bone marrow stromal cells to recombinant human bone morphogenic protein-2 in the early and late stages of osteoblast differentiation

A number of factors must be added to human bone marrow stromal cells (hBMSCs) in vitro to induce osteogenesis, including ascorbic acid (AA), beta-glycerophosphate (GP), and dexamethasone (Dex). Bone morphogenic protein (BMP)-2 is an osteoinductive factor that can commit stromal cells to differentiate into osteoblasts. However, it is still not clear whether the addition of BMP-2 alone in vitro can induce hBMSCs to complete osteoblast differentiation, resulting in matrix mineralization. This study compares the effects of BMP-2 and Dex, alone and combined, on the early and late stages of hBMSC differentiation. We found that BMP-2 causes a significant induction of alkaline phosphatase (ALP) activity in hBMSCs, with a transcriptional upregulation of known BMP-2-responsive genes, and the stable expression of cbfa1 in the nucleus and the regions surrounding the nucleus in the early phase of osteoblast differentiation. However, continuous treatment with BMP-2 alone at doses ranging from 100 to 300 ng/mL results in a less efficient enhancement of in vitro matrix mineralization, despite a significant induction of ALP activity at a concentration of 100 ng/mL. Our results reflect how the effects of BMP-2 on hBMSCs can vary depending on the stage of osteoblast differentiation, and highlight the need to understand the role of BMP-2 in primary hBMSCs derived from diverse sources in order to increase the efficiency of using BMP-2 in osteoinductive therapies.