title: Cyclooxygenase-2 regulates mesenchymal cell differentiation into the osteoblast lineage and is critically involved in bone repair.
abstract: Preclinical and clinical studies suggest a possible role for cyclooxygenases in bone repair and create concerns about the use of nonsteroidal antiinflammatory drugs in patients with skeletal injury. We utilized wild-type, COX-1(-/-), and COX-2(-/-) mice to demonstrate that COX-2 plays an essential role in both endochondral and intramembranous bone formation during skeletal repair. The healing of stabilized tibia fractures was significantly delayed in COX-2(-/-) mice compared with COX-1(-/-) and wild-type controls. The histology was characterized by a persistence of undifferentiated mesenchyme and a marked reduction in osteoblastogenesis that resulted in a high incidence of fibrous nonunion in the COX-2(-/-) mice. Similarly, intramembranous bone formation on the calvaria was reduced 60% in COX-2(-/-) mice following in vivo injection of FGF-1 compared with either COX-1(-/-) or wild-type mice. To elucidate the mechanism involved in reduced bone formation, osteoblastogenesis was studied in bone marrow stromal cell cultures obtained from COX-2(-/-) and wild-type mice. Bone nodule formation was reduced 50% in COX-2(-/-) mice. The defect in osteogenesis was completely rescued by addition of prostaglandin E2 (PGE(2)) to the cultures. In the presence of bone morphogenetic protein (BMP-2), bone nodule formation was enhanced to a similar level above that observed with PGE(2) alone in both control and COX-2(-/-) cultures, indicating that BMPs complement COX-2 deficiency and are downstream of prostaglandins. Furthermore, we found that the defect in COX-2(-/-) cultures correlated with significantly reduced levels of cbfa1 and osterix, two genes necessary for bone formation. Addition of PGE(2) rescued this defect, while BMP-2 enhanced cbfa1 and osterix in both COX-2(-/-) and wild-type cultures. Finally, the effects of these agents were additive, indicating that COX-2 is involved in maximal induction of osteogenesis. These results provide a model whereby COX-2 regulates the induction of cbfa1 and osterix to mediate normal skeletal repair.
authors.affiliation: The Center for Musculoskeletal Research, University of Rochester Medical Center, New York 14642, USA.
authors.forename: Xinping
authors.initials: X
authors.lastname: Zhang
authors.forename: Edward M
authors.initials: EM
authors.lastname: Schwarz
authors.forename: Donald A
authors.initials: DA
authors.lastname: Young
authors.forename: J Edward
authors.initials: JE
authors.lastname: Puzas
authors.forename: Randy N
authors.initials: RN
authors.lastname: Rosier
authors.forename: Regis J
authors.initials: RJ
authors.lastname: O'Keefe
mesh_terms: D000818:Animals; D001846:Bone Development; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000378:metabolism; D001842:Bone and Bones / Q000502:physiology*; D002454:Cell Differentiation; D019070:Cell Lineage; D002478:Cells, Cultured; D051546:Cyclooxygenase 2; D015232:Dinoprostone / Q000378:metabolism; D005260:Female; D017102:Fracture Healing; D005786:Gene Expression Regulation; D007527:Isoenzymes / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008954:Models, Biological; D010006:Osteoblasts / Q000166:cytology / Q000201:enzymology*; D011451:Prostaglandin-Endoperoxide Synthases / Q000494:pharmacology*; D012737:Sex Factors; D013997:Time Factors; D016212:Transforming Growth Factor beta
chemical_list: C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D007527:Isoenzymes; D016212:Transforming Growth Factor beta; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D015232:Dinoprostone