Background/Purpose:

Aberrant activation of profibrotic pathways is a key feature of systemic sclerosis (SSc). Extensive evidence characterizes TGFβ- and canonical WNT-signaling as key drivers of fibroblast activation. The crosstalk between those pathways, however, remains largely enigmatic. A better understanding of the interplay of different profibrotic pathways may be 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 and cell motility. XIAP was recently described as positive regulator of canonical Wnt signaling in embryogenesis. The aim of this study is to characterize the role of XIAP in fibrotic disease in SSc and to analyze the effects XIAP inhibition in vitro and in vivo.

Methods:

XIAP-expression was analyzed 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. The interaction of XIAP with TLE3 was analyzed by co-immunoprecipitation. In vivo, XIAP inhibition was analyzed in three 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 staining in fibroblasts. In addition, XIAP-expression is increased in experimental fibrosis models. The induction of XIAP in SSc in experimental fibrosis was mimicked by TGFβ in cultured fibroblasts. Moreover, targeted inhibition of TGFβ signaling prevented the induction of XIAP in experimental fibrosis. The upregulation of XIAP augmented the stimulatory effects of recombinant WNT proteins on fibroblasts. Inhibition of XIAP reduced the Wnt1-induced activation of normal dermal fibroblasts with reduced expression of myofibroblast markers and decreased collagen release. In addition, XIAP inhibition reverted the activated fibroblast phenotype in SSc fibroblasts. Inhibition of XIAP also demonstrated potent antifibrotic effects in experimental fibrosis in bleomycin-induced dermal fibrosis, in Topoisomerase-I-induced (TopoI) dermal and pulmonary fibrosis and in Wnt10b-transgenic mice. The inhibitory effects of Embelin on fibroblast activation were associated with impaired canonical WNT signaling with reduced TCF-dependent transcription in reporter assays and reduced levels of WNT target genes such as Axin2 in cultured fibroblasts and in fibrotic tissues. Mechanistically, we demonstrate that XIAP interacts with the endogenous antagonist TLE3 to regulate canonical WNT signaling.

Conclusion:

XIAP is upregulated in SSc fibroblasts in a TGFβ-dependent manner and promotes fibroblast activation by fostering canonical WNT signaling. XIAP thus serves to integrate TGFβ- and WNT signaling as two core pathways in SSc. XIAP-inhibition demonstrated antifibrotic effects in vitro and in vivo in non-toxic concentrations. Inhibition of XIAP may thus be a novel approach to target aberrant canonical WNT signaling in fibrotic diseases.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/tgf%ce%b2-dependent-upregulation-of-xiap-fosters-fibroblast-activation-and-tissue-fibrosis-by-promoting-canonical-wnt-signaling/