674 Single-cell RNA sequencing (scRNA-seq) of sarcoidosis skin biopsies reveals key pathogenic cytokines and potential treatment targets

Abstract

Sarcoidosis is an idiopathic inflammatory disorder characterized by granuloma formation in affected tissues. Sarcoidosis commonly affects the skin and can be difficult to treat. An incomplete understanding of the molecular pathogenesis of this disease has impeded the development of targeted therapies. We performed scRNA-seq on dissociated skin biopsies from sarcoidosis patients (n=3) and healthy donors (n=3). Comprehensive receptor-ligand expression analysis among cell types was performed with CellphoneDB. Differential gene expression and pathway analyses were also used. Key receptor-ligand interactions identified with this approach were validated through analysis of bulk gene expression data from additional cases of cutaneous sarcoidosis (n=15). Single cell devolution with CIBERSORTx was also performed on the bulk expression data. A total of 24,034 cells were analyzed and 12 major cell types including T cells and macrophages were identified. We characterized a unique population of Th1-like CD4+ T cells in the sarcoidosis samples that produced high levels of IFNG, CSF2 (GM-CSF), IL21 and monocyte chemokines. Receptor expression and transcriptional patterns suggested these factors acted on macrophages, fibroblasts, and/or in an autocrine fashion. Sarcoidal macrophages showed an activated phenotype and in turn expressed IL15, IL6, TNF, as well as other novel factors (CHIT1, FBP1, CHI3L1) and both T-cell and monocyte chemokines. We also identified a distinct population of classical dendritic cells in the sarcoidosis samples that produced IL12B. In summary, we use scRNA-seq to deconvolute the sarcoidal granuloma microenvironment and to identify key cytokine drivers of inflammation in sarcoidosis. Notably, all cytokines identified (except TNF-alpha) signal via the JAK-STAT pathway. These observations are consistent with recent reports suggesting the potential efficacy of JAK inhibition in sarcoidosis. Further evaluation of JAK inhibitor treatment of sarcoidosis is supported by this molecular immunologic data.