Background/Purpose: A recent global gene expression profile study in a large early SSc patient samples revealed a type I interferon (IFN) signature. Type I IFN and associated genes might serve as biomarkers of more severe disease. Interferon regulatory factors (IRFs) are transcriptional regulators of type I IFN and IFN-inducible genes. Furthermore, IRF7 gene polymorphisms are associated with SSc susceptibility. In our most recent global gene expression study, IRF7 was the most prominent transcription factor in SSc skin (manuscript in press). However, the specific role of IRF7 in SSc pathogenesis has not been identified.

Methods: Early passage SSc fibroblasts (n=20) and age-, gender-, and ethnicity- matched control fibroblasts (n=20) were investigated. SSc and healthy control skin biopsies (14 SSc patients and 14 healthy controls) were used to quantify IRF7 expression by qPCR and protein expression by immunohistochemistry (IHC) analyses. IRF7 expression and activation were also determined in bleomycin induced SSc mouse model. Lesional murine skin tissues were examined by IHC analysis. To better understand the role of IRF7 in SSc pathogenesis, we utilized the bleomycin animal model with a loss-of-function approach. IRF7 KO (n=10) and wild-type mice (n=10) received daily subcutaneous bleomycin injection for 7 or 28 days. The lesional skin was harvested and processed for analysis. For in vitro experiments, we used IRF7 KO and wild-type fibroblasts to further investigate the role of IRF7 in fibroblast biology.

Results: IRF7 mRNA and protein levels were significantly up-regulated in SSc skin biopsies compared to control subjects. Furthermore, compared to control subjects, IRF7 activation was prominent in fibroblasts and macrophages in SSc skin.  Explanted skin fibroblast results further confirmed IRF7 mRNA up-regulation (SSc vs control; fold change = 2.37; p=0.024) and protein activation (IRF7 phosphorylation) in SSc. Interestingly, IRF7 showed complex dimerization with SMAD3 in vitro which is a major transcription factor of the TGF-b driven fibrosis signaling. In the bleomycin animal model studies, IRF7 KO mice demonstrated attenuated dermal thickness (IRF7 KO vs wild-type: 162.8 ± 13.6 µm vs 251.3 ± 24.5 µm; p=0.004 ) as well as  inflammatory response and other fibrosis features compared to C57BL/6 wild-type mice after receiving bleomycin for 7 or 28 days. TGF-β1 (IRF7 KO vs wild-type: 1.98 ± 0.76 vs 3.09 ± 0.14 fold changes; p=0.025) and IL6 mRNA expression were significantly abrogated in IRF7 KO mice skin tissue compared to wild-type mice exposed to bleomycin for 7 days. Interestingly, Col1a2 (IRF7 KO vs wild-type: 1.23 ± 0.13 vs 2.36 ± 0.68 fold changes; p=0.008), α-SMA (p=0.035) and CTGF (p=0.046) mRNA expression were also significantly abrogated in IRF7 KO mice skin tissue compared to wild-type mice of 28 days bleomycin injection. Furthermore, IRF7 KO dermal fibroblasts showed reduced collagen and a-SMA protein levels compared to wild-type mice fibroblasts.

Conclusion: Up-regulation and activation of IRF7 in SSc might play a pivotal role in the IFN driven inflammatory response as well as the TGF-ß-driven fibrotic process. IRF7 may therefore represent as a promising novel therapeutic target in SSc.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/interferon-regulatory-factor-7-irf7-the-possible-link-between-inflammation-and-fibrosis-in-ssc-pathogenesis/