Background/Purpose: Systemic Sclerosis is an autoimmune disease which is characterized by fibrosis of the skin and the internal organs with variable severity. Type I interferon signalling plays a major role in disease progression. The cytokine TGF-β has been extensively shown to be a major driver of fibrosis but its role in the context of Type 1 interferon activation is poorly understood. Here we aimed to dissect the crosstalk of TGF-β and type 1 interferon signalling pathways in keratinocytes, monocytes and dermal fibroblasts in SSc.

Methods: Conditioned media from healthy or SSc dermal fibroblasts was collected and used to stimulate the keratinocyte cell line Hacats and the monocyte cell line Thp1. Type 1 interferon responses were measured by analysing phosphorylated STAT1 levels by western blot, ISG expression (ISG15, CXCL10, CXCL11, IFIT1) by RT-qPCR and Interferon responsive luciferase reporter assay. Cells were stimulated with TGF-b (10ng/ml) and the TGFbR1 receptor was inhibited with SD208 (1μM). CLIC4 was disrupted with specific siRNA and the chloride channel inhibitors NPPB and IAA-94. Skin biopsies from wildtype and type 1 interferon receptor KO mice were stimulated with TGF-β ex-vivo.

Results: TGF-β stimulation of Hacats and Thp-1 led to a significant type I interferon activation signature in both cell lines (CXCL10 100-fold, IFIT1 3-fold, ISG15 12-fold). Accordingly TGF-β induced ISG expression in WT mouse skin biopsies ex-vivo and this was attenuated in the type I interferon receptor KO (CXCL11 90% knockdown, IFIT1 80% knockdown, ISG15 90% knockdown). Conditioned media from SSc fibroblasts induced type I interferon signalling in both Hacats and Thp-1 cells and this was nullified when the cells were co-treated with the TGFβR1 inhibitor SD208. Further analysis revealed the chloride channel CLIC4 played an important role in regulating the type 1 interferon response in the keratinocytes by enhancing the TGF-β signalling pathway in the cells. The conditioned media from SSc fibroblasts was unable to induce a type I interferon response in the keratinocytes when CLIC4 was disrupted in the keratinocytes by siRNA or small molecule inhibitors.

Conclusion: This study provides a first set of evidence indicating interplay between TGF-β and the type I interferon signalling pathways in the context of SSc. The cross-talk between the pathways supports the rationale of developing combination strategies for arresting the pathogenic process in SSc.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/ssc-fibroblasts-trigger-a-systemic-type-i-interferon-response-in-ssc-patients-through-canonical-tgf-%ce%b2-receptor-signalling/