ORF49-01 - RARRES1 Is Highly Expressed in Thyroid Eye Disease Orbital Fibroblasts and Regulates IL-17 -Dependent MCP-1 Production

Autoimmune thyroid diseases, including Graves’ disease, affect ~2-5% of the global population. Close to half of these patients develop thyroid eye disease (TED), a debilitating condition that causes ocular irritation, proptosis, eyelid retraction, optic neuropathy, and, in severe cases, vision loss. Orbital fibroblasts (OFs) are key cellular drivers of TED as they produce high levels of pro-inflammatory cytokines, chemokines, and extracellular matrix (ECM). Interestingly, orbital fat contains higher levels of retinoids than eyelid fat and subcutaneous fat. Retinoic acid (RA) induces monocyte chemoattractant protein-1 (MCP-1), a chemokine that causes increased monocyte recruitment and activation in inflamed tissue; however, the molecular mechanisms remain unclear. RA receptors are ligand-activated nuclear receptors that play a crucial role in cell growth, differentiation, and the immune system. Here, we investigated the role of RA signaling in TED OFs using qPCR for RARs and RAR-dependent genes, and ELISA for chemokine/cytokine levels. Our new data reveal that OFs from TED patients express significantly higher levels of RAR beta (RARβ) and RAR responder 1 (RARRES1) than non-TED OFs. MCP-1 and RARRES1 are also induced by treatment with all-trans retinoic acid (atRA), and a pan-RAR antagonist mitigated this effect. In comparison to non-TED OFs, TED-derived OFs display higher sensitivity to atRA-mediated MCP-1 production. IL-17, a pro-fibrotic and pro-inflammatory cytokine implicated in autoimmune diseases, is elevated in TED orbital tissue compared to non-TED tissue. We show that IL-17 and atRA work in concert to further increase MCP-1 and interleukin-8 (IL-8) production, while interleukin-6 (IL-6) was not affected. RARRES1, an RA-dependent gene known to be involved in inflammation, has not yet been implicated in TED pathology. We hypothesize that pro-inflammatory responses in TED are driven by RA-induced RARRES1 expression. To support this hypothesis, we discovered that siRNA-mediated depletion of RARRES1 reduces IL-17/atRA-induced MCP-1 production. These studies support the concept that RA signaling promotes the inflammatory microenvironment in TED orbits and may be a target for future therapeutic interventions.