Mesenchymal responses are an essential aspect of tissue repair. Failure to terminate this repair process correctly, however, results in fibrosis and organ dysfunction. Therapies that block fibrosis and restore tissue homeostasis are not yet available for clinical use. Here we characterize the nuclear receptor NR4A1 as an endogenous inhibitor of transforming growth factor-β (TGF-β) signaling and as a potential target for anti-fibrotic therapies. NR4A1 recruits a repressor complex comprising SP1, SIN3A, CoREST, LSD1, and HDAC1 to TGF-β target genes, thereby limiting pro-fibrotic TGF-β effects. Even though temporary upregulation of TGF-β in physiologic wound healing induces NR4A1 expression and thereby creates a negative feedback loop, the persistent activation of TGF-β signaling in fibrotic diseases uses AKT- and HDAC-dependent mechanisms to inhibit NR4A1 expression and activation. Small-molecule NR4A1 agonists can overcome this lack of active NR4A1 and inhibit experimentally-induced skin, lung, liver, and kidney fibrosis in mice. Our data demonstrate a regulatory role of NR4A1 in TGF-β signaling and fibrosis, providing the first proof of concept for targeting NR4A1 in fibrotic diseases.

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Objective. To investigate whether JAK-2 contributes to the pathologic activation of fibroblasts in patients with systemic sclerosis (SSc) and to evaluate the antifibrotic potential of JAK-2 inhibition for the treatment of SSc.Methods. Activation of JAK-2 in human skin and in experimental fibrosis was determined by immunohistochemical analysis. JAK-2 signaling was inhibited by the selective JAK-2 inhibitor TG101209 or by small interfering RNA. Bleomycin-induced dermal fibrosis in mice and TSK-1 mice were used to evaluate the antifibrotic potential of specific JAK-2 inhibition in vivo.Results. Increased activation of JAK-2 was detected in the skin of patients with SSc, particularly in fibroblasts. The activation of JAK-2 was dependent on transforming growth factor ␤ (TGF␤) and persisted in cultured SSc fibroblasts. Inhibition of JAK-2 reduced basal collagen synthesis selectively in SSc fibroblasts but not in resting healthy dermal fibroblasts. Moreover, inhibition of JAK-2 prevented the stimulatory effects of TGF␤ on fibroblasts. Treatment with TG101209 not only prevented bleomycin-induced fibrosis but also effectively reduced skin fibrosis in TSK-1 mice.Conclusion. We demonstrated that JAK-2 is activated in a TGF␤-dependent manner in SSc. Considering the potent antifibrotic effects of JAK-2 inhibition, our study might have direct translational implications, because inhibitors of JAK-2 are currently being evaluated in clinical trials for myeloproliferative disorders and would also be available for evaluation in patients with SSc.

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ObjectivesWe have previously described the antifibrotic role of the soluble guanylate cyclase (sGC). The mode of action, however, remained elusive. In the present study, we describe a novel link between sGC signalling and transforming growth factor β (TGFβ) signalling that mediates the antifibrotic effects of the sGC.MethodsHuman fibroblasts and murine sGC knockout fibroblasts were treated with the sGC stimulator BAY 41-2272 or the stable cyclic guanosine monophosphate (cGMP) analogue 8-Bromo-cGMP and stimulated with TGFβ. sGC knockout fibroblasts were isolated from sGCIfl/fl mice, and recombination was induced by Cre-adenovirus. In vivo, we studied the antifibrotic effects of BAY 41-2272 in mice overexpressing a constitutively active TGF-β1 receptor.ResultssGC stimulation inhibited TGFβ-dependent fibroblast activation and collagen release. sGC knockout fibroblasts confirmed that the sGC is essential for the antifibrotic effects of BAY 41-2272. Furthermore, 8-Bromo-cGMP reduced TGFβ-dependent collagen release. While nuclear p-SMAD2 and 3 levels, SMAD reporter activity and transcription of classical TGFβ target genes remained unchanged, sGC stimulation blocked the phosphorylation of ERK. In vivo, sGC stimulation inhibited TGFβ-driven dermal fibrosis but did not change p-SMAD2 and 3 levels and TGFβ target gene expression, confirming that non-canonical TGFβ pathways mediate the antifibrotic sGC activity.ConclusionsWe elucidated the antifibrotic mode of action of the sGC that increases cGMP levels, blocks non-canonical TGFβ signalling and inhibits experimental fibrosis. Since sGC stimulators have shown excellent efficacy and tolerability in phase 3 clinical trials for pulmonary arterial hypertension, they may be further developed for the simultaneous treatment of fibrosis and vascular disease in systemic sclerosis.

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Background and objectivesFibrosis is a major socioeconomic burden, but effective antifibrotic therapies are not available in the clinical routine. There is growing evidence for a central role of Wnt signalling in fibrotic diseases such as systemic sclerosis, and we therefore evaluated the translational potential of pharmacological Wnt inhibition in experimental dermal fibrosis.MethodsWe examined the antifibrotic effects of PKF118-310 and ICG-001, two novel inhibitors of downstream canonical Wnt signalling, in the models of prevention and treatment of bleomycin-induced dermal fibrosis as well as in experimental dermal fibrosis induced by adenoviral overexpression of a constitutively active transforming growth factor (TGF)-β receptor I.ResultsPKF118-310 and ICG-001 were well tolerated throughout all experiments. Both therapeutic approaches showed antifibrotic effects in preventing and reversing bleomycin-induced dermal fibrosis as measured by skin thickness, hydroxyproline content and myofibroblast counts. PKF118-310 and ICG-001 were effective in inhibiting TGF-β receptor I-driven fibrosis as assessed by the same outcome measures.ConclusionsBlockade of canonical Wnt signalling by PKF118-310 and ICG-001 showed antifibrotic effects in different models of skin fibrosis. Both therapies were well tolerated. Although further experimental evidence for efficacy and tolerability is necessary, inhibition of canonical Wnt signalling is a promising treatment approach for fibrosis.