Background/Purpose:

Mutiple organ fibrosis, a hallmark of systemic sclerosis (SSc), remains poorly understood. Recent GWAS have uncovered consistent genetic linkage between TNFAIP3, encoding the ubiquitin-editing enzyme A20, and fibrotic SSc phenotypes. A20 has been previously implicated in negative regulation of innate immune cell activity, and hypomorphic variants are linked with autoimmunity in SLE, RA, IBD and Behcet syndrome. In view of its potential importance in SSc, we sought to characterize the regulation and role of A20 in the context of fibrosis and SSc pathogenesis.

Methods:

We evaluated A20 expression in skin and lung biopsies from patients with SSc, and examined the effect of A20 gain- and loss-of-function in explanted human and mouse fibroblasts. Moreover, we generated transgenic mice with partial or fibroblast-specific deletion of A20, and analysed the effect on experimentally-induced fibrosis and associated transcriptome changes by RNA seq.

Results: Unbiased transcriptome analysis of SSc skin and lung biopsies revealed significantly decreased A20 levels and robust anti-correlation with fibrotic TGF-ß signaling (r=-0.84, p<0.005). Lesional skin myofibroblasts in SSc showed a notable absence of A20 expression. In vitro, A20 expression was markedly reduced in fibroblasts treated with TGF-ß. Moreover, TGF-ß abrogated the stimulation of A20 elicited by TLR4. Remarkably, ectopic A20 in skin and lung fibroblasts abrogated profibrotic responses and disrupted Smad signalling, and prevented myofibroblast differentiation in mesenchymal progenitor cells. Conversely, reduced A20 activity was associated with enhanced magnitude of fibrotic responses. A20 haploinsufficient mice, which show a partial reduction of A20 levels comparable to individuals harbouring A20 risk alleles, showed augmented bleomycin-induced skin and lung fibrosis, increased tissue levels of F4/80, procollagen I and ASMA, and transcriptome signatures with altered fibrotic and inflammatory gene expression.

Conclusion:

We uncover a novel role for the SSc risk gene A20 as a fundamental checkpoint in modulating fibroblast activity and differentiation. Reduced A20 renders fibroblasts and transgenic mice susceptible to fibrosis. These observations suggest that reduced A20 in SSc patients carrying TNFAIP3 risk variants may underlie unchecked fibroblast activation and contribute to the pathogenesis of multiple organ fibrosis.

« Back to 2018 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/hypomorphic-a20-expression-modulates-fibrosis-susceptibility-implications-for-systemic-sclerosis/