Keratinocyte regulation of TGF-β and connective tissue growth factor expression:: A role in suppression of scar tissue formation

Allogeneic keratinocytes applied to large full-thickness wounds promote healing while suppressing scar tissue formation. This effect may be mediated in part by their effect on the levels of transforming growth factor-beta s (TGF-beta s) and connective tissue growth factor (CTGF) in the wound and subsequent modulation of fibroblast activity. We have examined the levels of TGF-beta and CTGF produced by keratinocytes and fibroblasts, and the effect of keratinocyte-conditioned medium using monolayer and living skin-equivalent cultures. Keratinocyte monolayers did not release any detectable TGF-beta 1, but released moderate levels of TGF-beta 2 into culture medium, and stained strongly for TGF-beta 1, but only weakly for TGF-beta 2. Fibroblasts released large amounts of TGF-beta 1, no TGF-beta 2, and stained strongly for TGF-beta 1. Neither cell type released TGF-beta 3, but both stained strongly for TGF-beta 3. Keratinocyte-conditioned medium suppressed the levels of TGF-beta s and CTGF associated with the fibroblasts compared with fibroblasts incubated in Dulbecco's minimal essential medium and fibroblast-conditioned medium. In living skin equivalents, keratinocytes stained very strongly for TGF-beta 1 and CTGF, moderately strongly for TGF-beta 3, and only weakly for TGF-beta 2. Fibroblasts stained strongly for TGF-beta 1 and 3 and CTGF. These observations suggest that keratinocytes may affect the TGF-beta profile in such a way as to suppress the formation of scar tissue.