FRI0416 Xiap as novel integrator of tgf Βeta signalling and canonical wnt signalling in tissue fibrosis

Background Aberrant activation of profibrotic pathways is a key feature of systemic sclerosis (SSc). Extensive evidence characterises TGFβ- and canonical WNT-signalling as key drivers of fibroblast activation. The crosstalk between those pathways, however, remains largely unknown. A better understanding of the interplay of different profibrotic pathways may be the key to the development of effective targeted therapies. XIAP (X-linked inhibitor of apoptosis protein) is an ubiquitously expressed member of the IAP protein family with important functions in tissue turnover. XIAP was recently described to be implicated in canonical Wnt signalling and TGFβ signalling. Objectives The aim of this study is to characterise the role of XIAP in fibrotic disease. Methods XIAP-expression was analysed by qPCR, IF and Western blot. XIAP was targeted pharmacologically with Embelin. The activation of the canonical Wnt pathway was assessed by analyses of Wnt target genes and by TOPflash/FOPflash luciferase reporter assay. In vivo, XIAP inhibition was analysed in two different models of fibrosis. Results The expression of XIAP is increased in the skin of SSc patients compared to matched healthy individuals with a particularly prominent expression in fibroblasts. The overexpression of XIAP is more pronounced in SSc patients with diffuse and active skin fibrosis compared to SSc patients with limited and inactive disease. The overexpression of XIAP is also reflected in several experimental fibrosis models: the model of sclerodermatous graft versus host disease, the model of bleomycin induced skin fibrosis and in Wnt10b transgenic mice. Stimulation with either recombinant Wnt1 or TGFβ cytokine induces the expression of XIAP in cultured fibroblasts. Inhibition of XIAP reduced the Wnt1- and TGFβ induced activation of fibroblasts with reduced collagen release and expression of myofibroblast markers. In addition, XIAP inhibition reverted the activated fibroblast phenotype in SSc fibroblasts with reduced expression of stress fibres and αSMA. The antifibrotic effects of XIAP inhibition occurred in non-toxic doses. Mechanistically, XIAP inhibition reduced the activation of canonical Wnt signalling as demonstrated by TOPflash reporter assays and by the analysis of canonical Wnt target genes. XIAP inhibition also reduced the expression of canonical Wnt target genes in Wnt10b transgenic mice. To analyse the effects of XIAP inhibition in vivo, two mouse models were used: the model of bleomycin-induced dermal fibrosis and Wnt10b-transgenic mice. In both models, the pharmacological inhibition of XIAP exerted anti-fibrotic effects with reduced dermal thickening, reduced myofibroblast counts and reduced hydroxyproline contents. Conclusions XIAP is upregulated in SSc fibroblasts in a TGFβ-dependent manner and promotes fibroblast activation by fostering canonical WNT signalling. Our data suggest that XIAP mediates an amplification loop between TGF-β and canonical Wnt signalling. Inhibition of XIAP may thus be a novel approach to target aberrant canonical WNT signalling in fibrotic diseases. Disclosure of Interest None declared