Background/Purpose: In light of heterogeneous clinical manifestations in systemic sclerosis (SSc), transcriptional analysis of fibrotic tissue and circulating leukocytes may illuminate conserved processes driving inflammation and fibrosis. Prior studies of sorted circulating monocytes and lymphocytes from patients with SSc revealed an interferon gene expression signature. We hypothesized that classical monocytes play an important role in SSc pathogenesis and are responsible for the observed interferon signature in SSc.

Methods: Whole blood was obtained from patients enrolled in the Prospective Registry of Early Systemic Sclerosis (PRESS) study, and from age-, sex-, and race-matched healthy controls. The PRESS cohort includes patients with early (< 2 years’ duration since first non-Raynaud symptom attributed to SSc) diffuse cutaneous SSc (swollen hands or sclerodactyly PLUS ≥1 of the following: anti-topoisomerase I or anti-RNA polymerase III serum autoantibodies; proximal skin involvement; tendon friction rubs) who are recruited at participating US scleroderma centers. RNA was isolated from classical monocytes obtained by fluorescence-activated cell sorting and subjected to RNA-seq using Illumina NextSeq 500.

Results: We identified approximately 6500 genes that were differentially expressed in two or more patients (Z score > 2) compared to healthy controls –this ensured inclusion of genes that are dysregulated only in a subset of the patient population. Hierarchal clustering of patients based on expression of these 6500 genes revealed three prospective disease subtypes, each with a distinct profile of disease-regulated genes. No significant clinical variables were attributable to any subtype, although there is a trend toward increased mRSS in the third subtype (S3). Subtypes one (S1) and two (S2) were both enriched for genes involved in chemotaxis/motility and regulated cell death; however, S1 was also associated with inflammation and cytokine production while S2 linked to TGFb signaling and extracellular matrix remodeling. Genes upregulated in S3 were involved in myeloid activation. Furthermore, 19 previously reported interferon-related genes were significantly (p<0.05) upregulated in the patient cohort compared to controls. By examining interferon-related gene expression in the three subtypes, we observe subtype-specific upregulation in S1 (e.g. TIMP2), S1 and S2 (TIMP1 and OASL), S2 and S3 (IRF7), or S3 (OAS1).

Conclusion: We observed that transcriptional profiling of classical monocytes reveals patient subtypes with distinct disease-regulated genes. Interferon-related genes, which are upregulated globally in monocytes from SSc patients, are also upregulated in specific disease subtypes. These insights provide us with a framework through which to interrogate the transcriptional profile of sorted macrophages from skin biopsies and other fibrotic tissues, which will ultimately improve our understanding of systemic inflammation and end-organ fibrosis in SSc.

« Back to 2017 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/classical-monocytes-in-the-pathogenesis-of-early-diffuse-cutaneous-systemic-sclerosis/