Endothelin 1 Contributes to the Effect of Transforming Growth Factor beta 1 on Wound Repair and Skin Fibrosis

Objective. To characterize the pathways induced by transforming growth factor beta 1 (TGF beta 1) that lead to the expression of endothelin 1 (ET-1) in human dermal fibroblasts, and to study the effects of TGF beta 1 and ET-1 on the acquisition of a profibrotic phenotype and assess the contribution of the TGF beta 1/ET-1 axis to skin wound healing and fibrosis in vivo. Methods. The mechanism of induction of ET-1 expression by TGF beta 1 and its effect on the expression of alpha-smooth muscle actin and type I collagen were studied in human dermal fibroblasts, in experiments involving the TGF beta 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 beta 1 and ET-1, with or without treatment with bosentan. The contributions of TGF beta 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 beta 1 induced ET-1 expression in human dermal fibroblasts through Smad-and activator protein 1/JNK-dependent signaling. The ability of TGF beta 1 to induce the expression of profibrotic genes was dependent on ET-1. Adenovirus-mediated overexpression of TGF beta 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 beta 1. In the bleomycin-induced fibrosis model, treatment with GW788388 and bosentan prevented the fibrotic response. Conclusion. Our results strongly support the notion that the TGF beta 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 fibrosis-related diseases.