Different response to osteo-inductive agents in bone marrow- and periosteum-derived cell preparations

Rabbit bone marrow- and periosteum-derived cells were cultured in medium containing dexamethasone, bone morphogenetic protein-2 (BMP2) or both. The response of bone marrow-derived cells, measured as alkaline phosphatase 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, the effect of dexamethasone was greater than that of BMP2 and, when used together, they had an additive effect. The mineral deposition observed in these cultures did not have the typical structure of bone nodules. For periosteum-derived cells, dexamethasone did not increase the expression of alkaline phosphatase, while BMP2 did; treatment with both was less effective than treatment with BMP2 alone. Typical bone nodules were observed in cultures of periosteum-derived cells treated with dexamethasone and BMP2. These findings indicate that either osteoprogenitor cells from these two sources are intrinsically different or else non-progenitor cells in the preparations directly or indirectly affect the responsiveness to osteo-inductive agents.