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J. Biol. Chem., Vol. 278, Issue 34, 32005-32013, August 22, 2003

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Age-related Changes in the Biomolecular Mechanisms of Clvarial Osteoblast Biology Affect Fibroblast Growth Factor-2 Signaling and Osteogenesis^*

Catherine M. Cowan, Natalina Quarto, Stephen M. Warren, Ali Salim and Michael T. Longaker 

From the Department of Surgery, Stanford University School of Medicine, Stanford University, Stanford, California 94305-5148

The ability of immature animals to orchestrate successful calvarial ossification has been well described. This capacity is markedly attenuated in mature animals and humans greater than 2 years of age. Few studies have investigated biological differences between juvenile and adult osteoblasts that mediate successful osteogenesis. To identify possible mechanisms for this clinical observation, we investigated cellular and molecular differences between primary osteoblasts derived from juvenile (2-day-old) and adult (60-day-old) rat calvaria. Data demonstrated that juvenile osteoblasts contain a subpopulation of less differentiated cells as observed by spindle-like morphology and decreased osteocalcin production. Juvenile, compared with adult, osteoblasts showed increased proliferation and adhesion. Furthermore, following rhFGF-2 stimulation juvenile osteoblasts increased expression of collagen I1 (5-fold), osteopontin (13-fold), and osteocalcin (16-fold), compared with relatively unchanged adult osteoblasts. Additionally, juvenile osteoblasts organized and produced more matrix proteins and formed 41-fold more bone nodules. Alternatively, adult osteoblasts produced more FGF-2 and preferentially translated the high molecular weight (22 kDa) form. Although adult osteoblasts transcribed more FGF-R1 and juvenile osteoblasts transcribed more FGF-R2 at baseline levels, juvenile osteoblasts translated more FGF-R1 and -R2 and showed increased phosphorylation. Collectively, these findings begin to explain why juvenile, but not adult, osteoblasts successfully heal calvarial defects.

Received for publication, May 6, 2003 , and in revised form, May 30, 2003.

^* This work was supported by Grant R01DE-14526 from the National Institutes of Health (to M. T. L.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed: Dept. of Surgery, Stanford University School of Medicine, 257 Campus Dr., Stanford, CA 94305-5148. Tel.: 650-736-1707; Fax: 650-736-1705; E-mail: Longaker{at}Stanford.edu.

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