Reduced COX-2 expression in aged mice is associated with impaired fracture healing.
The cellular and molecular events responsible for reduced fracture healing with aging are unknown. Cyclooxygenase 2 (COX-2), the inducible regulator of prostaglandin E(2) (PGE(2)) synthesis, is critical for normal bone repair. A femoral fracture repair model was used in mice at either 7-9 or 52-56 wk of age, and healing was evaluated by imaging, histology, and gene expression studies. Aging was associated with a decreased rate of chondrogenesis, decreased bone formation, reduced callus vascularization, delayed remodeling, and altered expression of genes involved in repair and remodeling. COX-2 expression in young mice peaked at 5 days, coinciding with the transition of mesenchymal progenitors to cartilage and the onset of expression of early cartilage markers. In situ hybridization and immunohistochemistry showed that COX-2 is expressed primarily in early cartilage precursors that co-express col-2. COX-2 expression was reduced by 75% and 65% in fractures from aged mice compared with young mice on days 5 and 7, respectively. Local administration of an EP4 agonist to the fracture repair site in aged mice enhanced the rate of chondrogenesis and bone formation to levels observed in young mice, suggesting that the expression of COX-2 during the early inflammatory phase of repair regulates critical subsequent events including chondrogenesis, bone formation, and remodeling. The findings suggest that COX-2/EP4 agonists may compensate for deficient molecular signals that result in the reduced fracture healing associated with aging.
Naik
Amish A
AA
The Center for Musculoskeletal Research, University of Rochester, Rochester, New York 14642, USA.
Xie
Chao
C
Zuscik
Michael J
MJ
Kingsley
Paul
P
Schwarz
Edward M
EM
Awad
Hani
H
Guldberg
Robert
R
Drissi
Hicham
H
Puzas
J Edward
JE
Boyce
Brendan
B
Zhang
Xinping
X
O'Keefe
Regis J
RJ
D000375:Aging / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D000818:Animals; D016723:Bone Remodeling / Q000235:genetics; D002146:Bony Callus / Q000201:enzymology / Q000473:pathology; D020219:Chondrogenesis / Q000235:genetics; D051546:Cyclooxygenase 2 / Q000235:genetics / Q000378:metabolism*; D005260:Female; D017102:Fracture Healing; D050723:Fractures, Bone / Q000000981:diagnostic imaging / Q000235:genetics; D005786:Gene Expression Regulation; D051379:Mice; D008810:Mice, Inbred C57BL; D018919:Neovascularization, Physiologic; D010010:Osteoclasts / Q000201:enzymology; D010012:Osteogenesis / Q000235:genetics; D010641:Phenotype; D021381:Protein Transport; D053245:RANK Ligand / Q000378:metabolism; D011859:Radiography; D018078:Receptors, Prostaglandin E / Q000819:agonists; D058309:Receptors, Prostaglandin E, EP4 Subtype; D013234:Stem Cells / Q000201:enzymology / Q000473:pathology
C545651:Ptger4 protein, mouse; D053245:RANK Ligand; D018078:Receptors, Prostaglandin E; D058309:Receptors, Prostaglandin E, EP4 Subtype; C077623:Ptgs2 protein, mouse; D051546:Cyclooxygenase 2