Chloride intracellular channel 4 (CLIC4) is a global regulator of type 1 interferon signaling in Systemic Sclerosis (SSc) epithelial cells

ObjectivesSystemic sclerosis (SSc) is an autoimmune disease in which an immune-related injury induces fibrosis of the skin, progressing to affect the internal organs in the most serve cases. Type 1 interferon (IFN) signaling plays a major role in SSc disease progression. We have previously shown the chloride intracellular channel 4 (CLIC4) is upregulated in SSc skin fibroblasts and plays an important role in SSc fibrosis. In this study we investigated the role of CLIC4 in SSc keratinocyte biology. Methodshealthy (HC) and SSc skin biopsies were analysed by immunohistochemistry for the expression of CLIC4. The skin keratinocyte cell line Hacats was stimulated with a range of type 1 IFN signaling agonists (POLY I:C, POLY dA:Dt, ODN 2216 and IFN-). CLIC4 was inhibited with the chloride channel inhibitors NPPB and IAA-94 or siRNA. Conditioned media from HC or SSc fibroblasts was employed for indirect co-culture of Hacats and HUVECs. ResultsSSc skin biopsies showed high levels of CLIC4 in SSc skin fibroblasts, keratinocytes and endothelial cells compared to HC. Co-culture of Hacats and Huvecs with SSc fibroblast media induced CLIC4 expression. CLIC4 played an important role in type 1 IFN signalling in keratinocytes. Inhibition of CLIC4 blocked TLR3, TLR9 and cGAS mediated activation of the type 1 IFN signaling pathway. Additionally, inhibition of CLIC4 prevented SSc fibroblast media from inducing a type 1 IFN response in keratinocytes. ConclusionsThe data presented in this study suggests CLIC4 is a global regulator of type 1 IFN signalling in SSc epithelial cells. Key MessagesO_ST_ABSWhat is already knownC_ST_ABSSSc disease progression is driven in part by a Type 1 IFN signature and CLIC4 has previously been implicated in SSc fibroblast activation. What this study addsWe show for the first time CLIC4 is a regulator of type 1 interferon signalling in epithelial cells and plays an important role in the signalling found in SSc skin. How this study might affect researchTargeting CLIC4 in the context of SSc may disrupt the fibrosis and inflammation associated with SSc.