Cyclooxygenase-2 regulates mesenchymal cell differentiation into the osteoblast lineage and is critically involved in bone repair
Xinping Zhang, … , Randy N. Rosier, Regis J. O’Keefe
Xinping Zhang, … , Randy N. Rosier, Regis J. O’Keefe
Published June 1, 2002
Citation Information: J Clin Invest. 2002;109(11):1405-1415. https://doi.org/10.1172/JCI15681.
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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 (PGE2) 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 PGE2 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 PGE2 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

Xinping Zhang, Edward M. Schwarz, Donald A. Young, J. Edward Puzas, Randy N. Rosier, Regis J. O’Keefe

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Defective intramembranous bone formation in COX-2–/– calvaria in respons...
Defective intramembranous bone formation in COX-2–/– calvaria in response to FGF-1. FGF-1 was injected subcutaneously (1 μg/d for 3 days) on the calvaria of wild-type, COX-1–/–, and COX-2–/– mice, and osteogenesis was analyzed by histomorphometry 14 days later as described in Methods. The photographs of representative H&E-stained sections from wild-type (a), COX-1–/– (b), and COX-2–/– mice (c) are shown at ×20 magnification. New bone width was measured at ×20 magnification, and the data from five animals in each group are presented as the mean ± SEM (d). Statistical significance compared with wild-type is indicated (*P < 0.01). Histology sections were examined by in situ hybridization using a riboprobe specific for osteocalcin as described in Methods. Dark-field photographs (e–h) were taken at ×4 magnification. The signal for osteocalcin mRNA was markedly reduced in COX-2–/– mice (f and h) compared with wild-type (e and g) at both the sagittal suture (e and f) and the lateral region (g and h) of the calvaria.