Objectives The hallmark of systemic sclerosis (SSc) is the accumulation of extracellular matrix proteins by pathologically activated fibroblasts. This study analysed the antifibrotic effects of the selective c-Jun N-terminal kinase (JNK) inhibitor, CC-930, which recently entered first clinical trials as a novel antifibrotic approach.

Methods Phosphorylated c-Jun was detected by western blot and immunohistochemistry. The model of bleomycin-induced dermal fibrosis and the tight skin 1 (TSK1) mouse model were used to investigate the effects of CC-930 on the prevention of experimental fibrosis. The potential of CC-930 to induce regression of fibrosis was assessed in a modified model of established fibrosis.

Results Transforming growth factor beta (TGFβ) and platelet-derived growth factor (PDGF) activate JNK and stimulate the phosphorylation of its downstream target c-Jun. Incubation with CC-930 prevented the phosphorylation of c-Jun and reduced the stimulatory levels of these cytokines on the release of collagen. Inhibition of JNK prevented dermal thickening, myofibroblast differentiation and the accumulation of collagen in a dose-dependent manner in mice challenged with bleomycin and in TSK1 mice. In addition to the prevention of fibrosis, treatment with pharmacologically relevant doses of CC-930 also induced regression of established experimental fibrosis.

Conclusions These data identify JNK as a downstream mediator of the pro-fibrotic effects of of TGFβ and PDGF in SSc fibroblasts. Selective inhibition of JNK by CC-930 exerted potent antifibrotic effects in vitro and in different models in vivo. JNK might thus be a novel molecular target for the treatment of fibrosis in SSc.