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Fetal cutaneous wounds that occur in early gestation heal without scar formation. Although much work has been done to characterize the role of transforming growth factor-beta (TGF-beta) isoforms in the adult wound repair process, their function in fetal scarless wound repair is not well understood. The authors hypothesized that the pattern of expression for TGF-beta isoforms and their receptors may influence the phenotypic transition from scarless to scar-forming repair observed during fetal gestation. Using time-dated fetal Sprague-Dawley rat fibroblasts and unwounded skin at gestational ages 14, 16, 18, and 21 days postcoitum of the scarless (or =16 days) and scar-forming (16 days) periods of gestation (term = 21.5 days), the authors analyzed the endogenous messenger RNA (mRNA) levels of TGF-beta 1 and TGF-beta 3 and their signaling receptors TGF-beta-RI and TGF-beta-RII. Northern blot analyses in both fibroblasts and unwounded skin revealed that levels of TGF-beta 1 were not differentially expressed, whereas more TGF-beta 3 mRNA transcript was found in early than in late gestation. Fibroblast expression of TGF-beta-RI showed no substantial differences, whereas expression of TGF-beta-RII increased during gestation. In contrast, expression of both TGF-beta-RI and TGF-beta-RII in unwounded skin showed decreasing levels as a function of gestational age. The differential levels of TGF-beta 1 and TGF-beta 3 suggest that the ratio of these cytokines may provide a predominantly antiscarring or profibrotic signal upon wounding during the scar-free or scar-forming periods of gestation, respectively. Furthermore, lower amounts of the ligand-binding TGF-beta-RII seen in early gestation fibroblasts suggest a decreased ability to perceive ligand during the period of scarless repair.

Introduction: Early mammalian fetal wounds heal skin wounds scarlessly, by regeneration rather than repair, through unknown mechanisms. During normal wound healing, plasmin plays a vital role in matrix remodeling, a critical determinant of scar formation. Its activity depends on the ratio of plasminogen activator inhibitor-1 (PAI-1, a marker of fibrosis) and urokinase-type plasminogen activator (uPA), which we have found to increase during fetal development. TGF-beta is essential in tissue injury repair. Of the three mammalian isoforms, TGF-beta 3 appears to be anti-scarring. Whilst TGF-beta 1 is a potent inducer of PAI-1, TGF-beta 3 may have the opposite effect. We hypothesize that the ratio of TGF-beta isoforms influences cutaneous scarring by altering the PAI-1:uPA activity ratio. Methods: The PAI-1/uPA activity in E14 TGF-beta 3 KO mice skins, skin fibroblasts and whole embryo lysates was studied using fibrin and reverse fibrin overlay. Additionally, an in vitro 3-D collagen gel model for wound contraction was employed to compare E14 TGF-beta 3 KO and wild-type (WT) fibroblasts. Results: E14 TGF-beta 3 KO skin, skin fibroblasts and embryo lysates had more PAI-1 and less uPA activity, compared to WT. Additionally, fibroblasts from E14 TGF-beta 3 KO mice contracted collagen gels less compared to WT, but could be rescued by adding TGF-beta 3. These fibroblasts also had a distinct morphology from WT. Conclusions: E14 TGF-beta 3 KO mice have a higher PAI-1:uPA ratio than WT. Furthermore, fibroblasts from this KO mouse are altered in matrix remodeling, which may provide a mechanism for the anti-scarring effects of TGF-beta 3.