Stimulation of the soluble guanylate cyclase (sGC) inhibits fibrosis by blocking non-canonical TGFß signalling.

OBJECTIVES: We 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 ß (TGFß) signalling that mediates the antifibrotic effects of the sGC. METHODS: Human 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 TGFß. sGC knockout fibroblasts were isolated from sGCI(fl/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-ß1 receptor. RESULTS: sGC stimulation inhibited TGFß-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 TGFß-dependent collagen release. While nuclear p-SMAD2 and 3 levels, SMAD reporter activity and transcription of classical TGFß target genes remained unchanged, sGC stimulation blocked the phosphorylation of ERK. In vivo, sGC stimulation inhibited TGFß-driven dermal fibrosis but did not change p-SMAD2 and 3 levels and TGFß target gene expression, confirming that non-canonical TGFß pathways mediate the antifibrotic sGC activity. CONCLUSIONS: We elucidated the antifibrotic mode of action of the sGC that increases cGMP levels, blocks non-canonical TGFß 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.