Reduction of type I interferon biomarkers by cGAS inhibition in scleroderma and GvHD skin

Summary: Abstract Body: Systemic sclerosis/scleroderma (SSc) and the sclerotic form of chronic graft-versus-host-disease (SclGvHD) both feature elevated type I interferon gene expression and skin fibrosis. However, direct evidence of cGAS-STING activation as source of type I interferon in SSc and SclGvHD has remained unclear. To assess interferon stimulated gene (ISG) expression in each disease, we generated an integrated scRNA-Seq atlas of skin from patients with SSc (n=17), SclGvHD (n=3) and healthy controls (n=16). ISG were highly expressed in both SSc and SclGvHD, including myeloid APCs and pericytes in both diseases, fibroblasts in SSc, and endothelial cells in SclGvHD. High ISG RNA levels corresponded with high STING protein staining by immunohistochemistry. Compared to lupus as a positive control, STING was elevated in diffuse SSc, morphea and SclGvHD, but unchanged in limited SSc like healthy controls. To validate cGAS inhibition as a potential therapeutic strategy in fibrotic skin, we used two skin explants assays. The first was an inducible model of cGAS activation via mitochondrial DNA leakage. In the second, we tested cGAS inhibition on active SclGvHD (n=3) and SSc (n=1) patient skin explants. We observed in both models reduction in biomarkers associated with type I interferon. In the inducible model of cGAS activation, cGAS inhibition decreased MX1(p=0.0008) and IFI27(p=0.0004) RNA levels and CXCL10(p=0.048) protein secretion. In the patient skin explants, cGAS inhibition decreased secreted fibrotic and inflammatory proteins IL6(p=0.042), pro-collagen1 N-terminal peptide (PINP) (p=0.037), and TNC(p=0.0046). In sum, our results indicate differential cGAS-STING activity among SSc disease subsets and SclGvHD and that cGAS inhibition can reduce interferon associated disease biomarkers in skin. Nathan M. Newton³, Anahi V. Odell^{1, 2}, Ian D. Odell^{1, 2, 3} 1. Dermatology, Yale University School of Medicine, New Haven, CT, United States. 2. Immunobiology, Yale University School of Medicine, New Haven, CT, United States. 3. Program in Translational Biomedicine, Yale University School of Medicine, New Haven, CT, United States. Translational Studies: Preclinical