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Fibronectin regulates calvarial osteoblast differentiationThe secretion of fibronectin by differentiating osteoblasts and its accumulation at sites of osteogenesis suggest that fibronectin participates in bone formation. To test this directly, we determined whether fibronectin-cell interactions regulate progressive differentiation of cultured fetal rat calvarial osteoblasts. Spatial distributions of alpha 5 integrin subunit, fibronectin, osteopontin (bone sialoprotein I) and osteocalcin (bone Gla-protein) were similar in fetal rat calvaria and mineralized, bone-like nodules formed by cultured osteoblasts. Addition of anti-fibronectin antibodies to cultures at confluence reduced subsequent formation of nodules to less than 10% of control values, showing that fibronectin is required for normal nodule morphogenesis. Anti-fibronectin antibodies selectively inhibited steady-state expression of mRNA for genes associated with osteoblast differentiation; mRNA levels for alkaline phosphatase and osteocalcin were suppressed, whereas fibronectin, type I collagen and osteopontin were unaffected. To identify functionally relevant domains of fibronectin, we treated cells with soluble fibronectin fragments and peptides. Cell-binding fibronectin fragments (type III repeats 6-10) containing the Arg-Gly-Asp (RGD) sequence blocked both nodule initiation and maturation, whether or not they contained a functional synergy site. In contrast, addition of the RGD-containing peptide GRGDSPK alone did not inhibit nodule initiation, although it did block nodule maturation. Thus, in addition to the RGD sequence, other features of the large cell-binding fragments contribute to the full osteogenic effects of fibronectin. Nodule formation and osteoblast differentiation resumed after anti-fibronectin antibodies or GRGDSPK peptides were omitted from the media, showing that the inhibition was reversible and the treatments were not cytotoxic. Outside the central cell-binding domain, peptides from the IIICS region and antibodies to the N terminus did not inhibit nodule formation. We conclude that osteoblasts interact with the central cell-binding domain of endogenously produced fibronectin during early stages of differentiation, and that these interactions regulate both normal morphogenesis and gene expression.
Document ID
20040173205
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Moursi, A. M.
(University of California San Francisco 94143-0512, United States)
Damsky, C. H.
Lull, J.
Zimmerman, D.
Doty, S. B.
Aota, S.
Globus, R. K.
Date Acquired
August 22, 2013
Publication Date
June 1, 1996
Publication Information
Publication: Journal of cell science
Volume: 109 ( Pt 6)
ISSN: 0021-9533
Subject Category
Aerospace Medicine
Funding Number(s)
CONTRACT_GRANT: P50-DE10306
CONTRACT_GRANT: T32 DE07204
Distribution Limits
Public
Copyright
Other
Keywords
NASA Program Space Physiology and Countermeasures
NASA Discipline Number 26-10
NASA Center ARC
NASA Discipline Musculoskeletal

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