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

Abstract

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-betas (TGF-betas) 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-beta1, but released moderate levels of TGF-beta2 into culture medium, and stained strongly for TGF-beta1, but only weakly for TGF-beta2. Fibroblasts released large amounts of TGF-beta1, no TGF-beta2, and stained strongly for TGF-beta1. Neither cell type released TGF-beta3, but both stained strongly for TGF-beta3. Keratinocyte-conditioned medium suppressed the levels of TGF-betas 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-beta1 and CTGF, moderately strongly for TGF-beta3, and only weakly for TGF-beta2. Fibroblasts stained strongly for TGF-beta1 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.