Bosentan reverses the pro-fibrotic phenotype of systemic sclerosis dermal fibroblasts via increasing DNA binding ability of transcription factor Fli1.
BACKGROUND
Although the pathogenesis of systemic sclerosis (SSc) still remains unknown, recent studies have demonstrated that endothelins are deeply involved in the developmental process of fibrosis and vasculopathy associated with SSc, and a dual endothelin receptor antagonist, bosentan, has a potential to serve as a disease modifying drug for this disorder. Importantly, endothelin-1 (ET-1) exerts a pro-fibrotic effect on normal dermal fibroblasts and bosentan reverses the pro-fibrotic phenotype of SSc dermal fibroblasts. The purpose of this study was to clarify the details of molecular mechanisms underlying the effects of ET-1 and bosentan on dermal fibroblasts, which have not been well studied.


METHODS
The mRNA levels of target genes and the expression and phosphorylation levels of target proteins were determined by reverse transcription real-time PCR and immunoblotting, respectively. Promoter assays were performed using a sequential deletion of human α2 (I) collagen (COL1A2) promoter. DNA affinity precipitation and chromatin immunoprecipitation were employed to evaluate the DNA binding ability of Fli1. Fli1 protein levels in murine skin were evaluated by immunostaining.


RESULTS
In normal fibroblasts, ET-1 activated c-Abl and protein kinase C (PKC)-δ and induced Fli1 phosphorylation at threonine 312, leading to the decreased DNA binding of Fli1, a potent repressor of the COL1A2 gene, and the increase in type I collagen expression. On the other hand, bosentan reduced the expression of c-Abl and PKC-δ, the nuclear localization of PKC-δ, and Fli1 phosphorylation, resulting in the increased DNA binding of Fli1 and the suppression of type I collagen expression in SSc fibroblasts. In bleomycin-treated mice, bosentan prevented dermal fibrosis and increased Fli1 expression in lesional dermal fibroblasts.


CONCLUSIONS
ET-1 exerts a potent pro-fibrotic effect on normal fibroblasts by activating "c-Abl - PKC-δ - Fli1" pathway. Bosentan reverses the pro-fibrotic phenotype of SSc fibroblasts and prevents the development of dermal fibrosis in bleomycin-treated mice by blocking this signaling pathway. Although the efficacy of bosentan for dermal and pulmonary fibrosis is limited in SSc, the present observation definitely provides us with a useful clue to further explore the potential of the upcoming new dual endothelin receptor antagonists as disease modifying drugs for SSc.
Kaname
K
Akamata
Yoshihide
Y
Asano
Naohiko
N
Aozasa
Shinji
S
Noda
Takashi
T
Taniguchi
Takehiro
T
Takahashi
Yohei
Y
Ichimura
Tetsuo
T
Toyama
Shinichi
S
Sato
D000818:Animals; D000077300:Bosentan; D047369:Chromatin Immunoprecipitation; D024042:Collagen Type I / Q000187:drug effects / Q000378:metabolism; D004195:Disease Models, Animal; D065128:Endothelin Receptor Antagonists / Q000494:pharmacology*; D019332:Endothelin-1 / Q000378:metabolism* / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D005355:Fibrosis; D006801:Humans; D015151:Immunoblotting; D051379:Mice; D010641:Phenotype; D051789:Proto-Oncogene Protein c-fli-1 / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012595:Scleroderma, Systemic / Q000378:metabolism* / Q000473:pathology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D012867:Skin / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D013449:Sulfonamides / Q000494:pharmacology*
D024042:Collagen Type I; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1; D051789:Proto-Oncogene Protein c-fli-1; D013449:Sulfonamides; D000077300:Bosentan