PDGFRα(+)DPP4(+) Fibroblasts-Macrophage Crosstalk Induces Orbital Fibrosis in Treatment-Resistant Thyroid Eye Disease via the GAS6-AXL Pathway.

Thyroid eye disease (TED), the leading adult orbital disease, is an autoimmune disorder characterized by fibrosis. Effective anti-fibrotic treatments are scarce, except for orbital decompression surgery involving orbital adipose tissue (OAT) removal, due to high rates of drug resistance following hyperthyroidism treatment and the lack of suitable mouse models. Understanding the mechanisms behind fibrotic remodeling of OAT could aid mouse model development and identify novel therapies. In the present study, stromal vascular fraction cells of OAT from patients with inactive-stage TED, characterized by pronounced fibrosis, are analyzed at single-cell resolution. platelet-derived growth factor receptor (PDGFR)α(+)dipeptidyl peptidase (DPP)4(+) fibroblasts exhibiting progenitor characteristics and fibrotic potential at the transcriptional level are identified. PDGFRα(+)DPP4(+) fibroblasts showed the strongest interactions with macrophages, particularly M2 macrophages, which are enriched and topographically localized within the fibrotic area. Moreover, M2 macrophages promoted extracellular matrix production in PDGFRα(+)DPP4(+) cells via the Growth arrest specific (GAS)6-AXL Receptor Tyrosine Kinase (AXL) signaling pathway. Using a specific AXL inhibitor or AXL knockdown, fibrosis is substantially reduced in PDGFRα(+)DPP4(+) fibroblasts in vitro, and in patient cell-derived orthotopic xenograft models established via GAS6. By identifying pro-fibrotic intercellular networks in OAT, these findings establish a rapid and repeatable mouse model of TED fibrosis and propose the GAS6-AXL axis as a potential therapeutic target for TED.