Objective. To characterize the pathways induced by transforming growth factor 1 (TGF 1) that lead to the expression of endothelin 1 (ET-1) in human dermal fibroblasts, and to study the effects of TGF 1 and ET-1 on the acquisition of a profibrotic phenotype and assess the contribution of the TGF 1/ET-1 axis to skin wound healing and fibrosis in vivo.

Methods. The mechanism of induction of ET-1 expression by TGF 1 and its effect on the expression of-smooth muscle actin and type I collagen were studied in human dermal fibroblasts, in experiments involving the TGF receptor inhibitor GW788388 and the ET receptor antagonist bosentan, by real-time reverse transcription–polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay, immunofluorescence, Western blotting, and promoter/reporter transient transfection analyses. Experiments assessing dermal wound healing in mice were performed with adenovirus-driven overexpression of active TGF 1 and ET-1, with or without treatment with bosentan. The contributions of TGF 1 and ET-1 to the fibrotic response were also assessed in a mouse model of bleomycin-induced skin fibrosis, by histologic, immunohistochemical, RT-PCR, and protein analyses.

Results. TGF 1 induced ET-1 expression in hu-man dermal fibroblasts through Smad-and activator protein 1/JNK–dependent signaling. The ability of TGF 1 to induce the expression of profibrotic genes was dependent on ET-1. Adenovirus-mediated overexpression of TGF 1 and ET-1 in mouse skin was associated with accelerated wound closure, increased fibrogenesis, and excessive scarring. Treatment with bosentan prevented the effects of TGF 1. In the bleomycin-induced fibrosis model, treatment with GW788388 and bosentan prevented the fibrotic response.

Conclusion. Our results strongly support the no-tion that the TGF 1/ET-1 axis has a role in wound repair and skin fibrosis. ET-1 receptor antagonists, such as bosentan, may represent a useful therapeutic tool in the treatment of excessive scarring and fibrosisrelated diseases.