Cyclooxygenase-2 Regulates Bone Marrow Stromal Cell Differentiation by Bone Morphogenetic Protein-2

Abstract Objective : To assess the transcriptional regulation of cyclooxygenase-2 by bone morphogenetic protein2 in isolated bone marrow stromal cells obtained from cyclooxygenase-2 wild-type and cyclooxygenase-2defrcient mice. Materials and Methods : Bone marrow stromal cells were cultured for 14 days in the presence of osteogenic medium with or without bone morphogenetic protein-2. Real-time polymerase chain reaction analysis of the relative expression of cyclooxygenase-2 and osteocalcin, a late osteogenic differentiation marker mRNA, were examined. Prostaglandin EZ accumulation in the culture media were measured by radioimmunoassay. Activity and staining of alkaline phosphatase, an early osteogenic differentiation marker, were examined. Results : Bone morphogenetic protein-2 induced cyclooxygenase-2 mRNA and prostaglandin production in cultured bone marrow stromal cells derived from cyclooxygenase-2 wild-type mice. Alkaline phosphatase activity was lower in cyclooxygenase-2-deficient control cultures than in cyclooxygenase-2 wild-type cultures, and treatment with bone morphogenetic protein-2 stimulated alkaline phosphatase activity only in cyclooxygenase-2 wild-type cultures. A similar reduction was seen in cyclooxygenase-2 wild-type cells treated with NS-398, a selective inhibitor of cyclooxygenase-2. Alkaline phosphatase staining revealed a 30% decrease in the cyclooxygenase-2-deficient control cultures, and the addition of bone morphogenetic protein-2 increased alkaline phosphatase staining only in cyclooxygenase-2 wild-type cultures. Bone morphogenetic protein-2 stimulated osteocalcin mRNA expression in bone marrow stromal cells derivedfrom cyclooxygenase2 wild-type mice but not in cyclooxygenase-2-deficient cells. Conclusions : Bone morphogenetic protein-2 induces cyclooxygenase-2 in bone marrow stromal cells transcriptionally and the induction of cyclooxygenase-2 may play a role in the effects of bone morphogenetic protein-2 on bone metabolism in vitro.