Background: Grafting of cultured epithelium has become a useful technique for the treatment of epithelial defects, since grafted epithelial cells secrete factors promoting wound healing. We identified one such factor produced by cultured oral epithelial cells as thrombospondin-1 (TSP-1). Recently, TSP-1 was reported to act as an activator of transforming growth factor-β1 (TGF-β1). Objective: The role of TSP-1 in wound healing and its mechanism were investigated in vitro and in vivo. Methods: The cultured oral epithelial cell-conditioned medium was harvested and applied to Heparin–Sepharose affinity chromatography. Proteins were analyzed by N-Terminal sequencer. TSP-1 and the other factors were applied to fibroblasts-mediated collagen gel contraction assay. The amount of TGF-β1 (latent TGF-β1 (LTGF) and active TGF-β1) in collagen gels was quantified by ELISA and Western blotting analysis. Collagen sponges were soaked with TSP-1 and implanted subcutaneously into rats. Results: A 38 kDa protein secreted from cultured oral epithelial cells was found to be human TSP-1. TSP-1 promoted collagen gel contraction activity, and anti-human TSP-1 and TGF-β1 antibody inhibited the activity. The diameters of the gels treated with LTGF and TSP-1 were reduced to a greater extent than those of gels treated with either factor alone. Although there were no significant differences in the amounts of total TGF-β1, which include LTGF, the amount of 25 kDa TGF-β1 was 3.30-fold greater in TSP-1-treated samples than controls. In vivo, 7 days after implantation, increased numbers of fibroblasts were observed in the sponges treated with TSP-1. Conclusion: These findings suggested that TSP-1 causes collagen gel contraction by activation of LTGF. TSP-1 is expected to be especially suitable for regulating wound healing.
