Targeting the Aryl Hydrocarbon Receptor to Attenuate IGF1R Signaling in Thyroid Eye Disease

Background: Thyroid eye disease (TED) is an autoimmune disorder characterized by proptosis, inflammation, and fibrosis. Elevated insulin-like growth factor 1 receptor (IGF1R) signaling in TED orbital fibroblasts (OFs) drives the proliferation and biosynthesis of hyaluronan, which causes enlargement of orbital tissue volume. The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that regulates cellular stress responses, metabolism, and inflammation. Given its important role in regulating cellular responses, we hypothesized that activation of the AHR could limit excessive IGF1R signaling in TED OFs, offering therapeutic potential. Methods: We measured IGF1R and AHR expression levels in TED, non-TED, and non-OF controls. OF activation was analyzed using proliferation, hyaluronan accumulation, and migration assays. RNA sequencing was used to detect transcriptome-wide changes in IGF1-treated TED OFs. After gene set enrichment analysis, select gene expression changes were validated by quantitative polymerase chain reaction. OFs were treated with the AHR ligands 6-formylindolo[3,2-b]carbazole (FICZ) or tapinarof with or without IGF1. Western blotting evaluated signaling pathways impacted by AHR and IGF1R signaling. Results: TED OFs showed elevated IGF1R and AHR expression levels compared to controls. IGF1 significantly increased hyaluronan accumulation, proliferation, and migration in TED OFs compared to non-TED OFs. IGF1R signaling altered the expression of hundreds of genes controlling cell migration, proliferation, and metabolism in TED OFs. These genes included TUBA1B, TUBA1C, CRABP2 (upregulated), and IRS2 and SOD3 (downregulated). AHR activation blocked proliferation, migration, hyaluronan production, and gene expression mediated through IGF1R signaling. The AHR inhibited these pathways by reducing phosphorylation of GSK3β, an important mediator of IGF1R/β-catenin mediated signaling. Conclusions: AHR activation represents a promising therapeutic strategy for mitigating TED progression by inhibiting IGF1R signaling. Through modulation of GSK3β-mediated pathways, AHR activation may target additional pathologically relevant pathways beyond those affected by direct IGF1R inhibitors. This research provides novel insights into TED pathophysiology and offers a potential avenue for developing therapies to improve patient outcomes.