DIFFERENT RESPONSE TO OSTEO-INDUCTIVE AGENTS IN BONE-MARROW- DERIVED AND PERIOSTEUM-DERIVED CELL PREPARATIONS

Rabbit bone marrow- and periosteum-derived cells were cultured in medi um containing dexamethasone, bone morphogenetic protein-2 (BMP2) or bo th. The response of bone marrow-derived cells, measured as alkaline ph osphatase expression, depended on the stage of growth. In subconfluent cultures, BMP2 had a greater effect than dexamethasone and treatment with both further increased enzyme activity. In confluent cultures, th e effect of dexamethasone was greater than that of BMP2 and, when used together, they had an additive effect. The mineral deposition observe d in these cultures did not have the typical structure of bone nodules . For periosteum-derived cells, dexamethasone did not increase the exp ression of alkaline phosphatase, while BMP2 did; treatment with both w as less effective than treatment with BMP2 alone. Typical bone nodules were observed in cultures of periosteum-derived cells treated with de xamethasone and BMP2. These findings indicate that either osteoprogeni tor cells from these two sources are intrinsically different or else n on-progenitor cells in the preparations directly or indirectly affect the responsiveness to osteo-inductive agents.