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Inhibition of Human Scleral Fibroblast Cell Attachment to Collagen Type I by TGFBIp

From the Department of Cell Biology, University of Oklahoma Health Science Center, Oklahoma City, Oklahoma.

PURPOSE. Transforming growth factor β–induced protein (TGFBIp; 68 kDa) is a secreted extracellular matrix (ECM) protein that has been demonstrated to regulate cell attachment in a variety of cell types. The sclera synthesizes and secretes TGFBIp, which may function to facilitate scleral ECM remodeling events associated with myopia development. Here the authors report that human scleral fibroblasts (HSFs) express TGFBI and that its protein product, TGFBIp, mediates an effect on cell attachment.

METHODS. TGFBI/TGFBIp expression was evaluated by RT-PCR and immunoblot of HSF lysates and culture supernatants. The effect of rTGFBIp (50 µg/mL) on cell attachment to collagen type I was determined with the use of fluid-phase cell attachment assays in HSFs, human foreskin fibroblasts (HFFs), and human corneal stroma fibroblasts (HCFs). Binding assays using biotinylated rTGFBIp were used to assess TGFBIp binding to the HSF surface. Flow cytometry and immunocytochemistry were used to determine both vβ3 and vβ5 expression and localization to the HSF cell surface.

RESULTS. HSFs expressed TGFBI and secreted TGFBIp (833 ng/h). rTGFBIp significantly decreased (25 µg/mL; P 0.05) HSF attachment to collagen type I, whereas rTGFBIp did not significantly affect cell attachment of HFFs (P = 0.50) or HCFs (P = 0.24) to collagen compared with BSA. Integrins vβ3 and vβ5 were detected on the cell surface, and both anti-vβ3 and anti-vβ5 functionally blocked rTGFBIp binding to HSFs.

CONCLUSIONS. TGFBIp plays an inhibitory role in HSF attachment to collagen type I in vitro through interactions with vβ3 and vβ5 integrin receptors. These results suggest that TGFBIp may modulate scleral cell–matrix interactions in vivo, thereby affecting scleral viscoelasticity.