Objectives Transforming growth factor β (TGFβ) has been identified as a key player in fibrotic diseases. However, the molecular mechanisms by which TGFβ activates fibroblasts are incompletely understood. Here, the role of JunD, a member of the activator protein 1 (AP-1) family of transcription factors, as a downstream mediator of TGFβ signalling in systemic sclerosis (SSc), was investigated.
Methods The expression of JunD was analysed by real-time PCR, immunofluorescence, western blotting and immunohistochemistry. The canonical Smad pathway was specifically targeted by small interfering (si)RNA. The expression of extracellular matrix proteins in JunD deficient (JunD−/−) fibroblasts was analysed by real-time PCR and hydroxyproline assays. The mouse model of bleomycin-induced dermal fibrosis was used to assess the role of JunD in experimental fibrosis.
Results JunD was overexpressed in SSc skin and in cultured fibroblasts in a TGFβ dependent manner. The expression of JunD colocalised with pSmad 3 in fibrotic skin and silencing of Smad 3 or Smad 4 by siRNA prevented the induction of JunD by TGFβ. JunD−/− fibroblasts were less responsive to TGFβ and released less collagen upon stimulation with TGFβ. Moreover, JunD−/− mice were protected from bleomycin-induced fibrosis with reduced dermal thickening, decreased myofibroblast counts and lower collagen content of lesional skin.
Conclusions These data demonstrate that JunD is overexpressed in SSc and that JunD is a mediator of the profibrotic effects of TGFβ. Considering that inhibitors of AP-1 signalling have recently been developed and are available for clinical trials in SSc, these findings may have translational implications.
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KP and PZ contributed equally to this work.
Funding Grant A40 of the Interdisciplinary Center of Clinical Research (IZKF) in Erlangen, grants from the Deutsche Forschungsgesellschaft, CMH Research Projects No 00000023728 and the Career Support Award of Medicine of the Ernst Jung Foundation (to JHWD).
Competing interests None.
Ethics approval This study was conducted with the approval of the University of Erlangen-Nuremberg.
Provenance and peer review Not commissioned; externally peer reviewed.