Controlling the orientation of bone osteopontin via its specific binding with collagen I to modulate osteoblast adhesion

Authors

  • Lingyun Liu,

    1. Department of Bioengineering, University of Washington, Seattle, WA 98195
    2. Department of Chemical Engineering, University of Washington, Seattle, WA 98195
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  • Chunlin Qin,

    1. Department of Endodontics, Dental Branch, University of Texas – Houston Health Science Center, Houston, TX 77030
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  • William T. Butler,

    1. Department of Endodontics, Dental Branch, University of Texas – Houston Health Science Center, Houston, TX 77030
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  • Buddy D. Ratner,

    Corresponding author
    1. Department of Bioengineering, University of Washington, Seattle, WA 98195
    2. Department of Chemical Engineering, University of Washington, Seattle, WA 98195
    • Department of Bioengineering, University of Washington, Seattle, WA 98195
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  • Shaoyi Jiang

    Corresponding author
    1. Department of Bioengineering, University of Washington, Seattle, WA 98195
    2. Department of Chemical Engineering, University of Washington, Seattle, WA 98195
    • Department of Bioengineering, University of Washington, Seattle, WA 98195
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Abstract

Osteopontin (OPN) is an important matricellular protein that modulates cell functions. It is potentially an excellent surface-coating component for engineered biomaterials. It is believed that in its preferred orientation and conformation on a surface, the functional domains of OPN such as the arginine–glycine–aspartic acid (RGD) motif will be presented to cells to the greatest extent. Previously, the authors demonstrated that OPN orientation could be modulated by surface charge. In this work, the authors attempt to control the orientation/conformation of bone OPN via its specific interactions with type I collagen. Surface plasmon resonance was used to confirm the specific binding between bone OPN and collagen I. A radiolabeled OPN adsorption assay was used to determine the amount of adsorbed OPN on tissue culture polystyrene (TCPS) surfaces with or without collagen I as an interlayer. An in vitro cell adhesion assay using osteoblast MC3T3-E1 was performed to compare the functionality of collagen-bound OPN and adsorbed OPN on TCPS. With the same amount of OPN on the surfaces, the number of cells adhered to collagen-bound OPN is significantly higher than to OPN alone on TCPS. A cell inhibition assay using soluble GRGDSP peptides showed that a higher GRGDSP concentration was needed to completely block osteoblast adhesion to collagen-bound OPN than to OPN directly on TCPS. Enhanced cell adhesion and higher blocking peptide concentration suggest that collagen-bound bone OPN has a preferable orientation/conformation for cell adhesion compared with OPN alone on TCPS. Thus, the specific binding of OPN to collagen I may naturally orient OPN, thus influencing osteoblast adhesion. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2007

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