High-concentration of BMP2 reduces cell proliferation and increases apoptosis via DKK1 and SOST in human primary periosteal cells.

BMP2, a well-known osteoinductive agent approved by FDA, is currently being used for various off-label orthopedic applications. Recently, concerns about its efficacy for off-label use, concentration, and complications have emerged. Interestingly, there is an extremely large discrepancy in BMP2 concentration between clinical use (i.e. 1.5mg/ml) and in vitro studies (50-300 ng/ml). The purpose of this study was to determine the effects of a relatively high-concentration of BMP2 on cell proliferation and apoptosis using human primary periosteal cells as BMP2 is generally applied around the periosteum in orthopedic surgeries. We isolated periosteal cells from three independent patients. The cell proliferation assessed by MTT activity was significantly reduced by a high-concentration of BMP2 (2000 ng/ml), while such a reduction was not observed by using a low-concentration of BMP2 (200 ng/ml). The cell apoptosis assessed by caspase activity was significantly increased by high-concentration BMP2, while such an increase was not observed by low-concentration BMP2. We found that Wnt signaling activity was significantly reduced by high-concentration BMP2 along with a dramatic increase in DKK1 and SOST, key inhibitors of Wnt signaling in bone. The addition of DKK1 or SOST protein to the primary periosteal cells reduced MTT activity and significantly increased caspase activity. Silencing the DKK1 or SOST expression using the siRNA technique normalized cell proliferation and apoptosis in the periosteum-derived cells when exposed to a high-concentration BMP2. Taken together, these results suggest that a high-concentration BMP2 decreases human periosteal cell proliferation and induces apoptosis via the activation of Wnt inhibitors DKK1 and SOST. This study provides new insights to the effects of high BMP2 concentration on human periosteal cells and brings out the possibility of multiple effects of current BMP2 therapy on various skeletal tissues.