0102: Iron Metabolism Dysregulation and Inflammation in Ankylosing Spondylitis: Role of SLC39A14 in Extracellular Matrix Remodeling

Background/Purpose: Iron metabolism dysregulation has been increasingly recognized as a key factor in the pathogenesis of inflammatory arthritis, with evidence linking altered iron homeostasis to disease progression. However, the mechanisms through which iron dysregulation contributes to inflammation and tissue remodeling in inflammatory arthritis, particularly in ankylosing spondylitis, remain poorly understood. This study aims to investigate the role of iron metabolism dysregulation, particularly the inflammatory mediator SLC39A14, in driving extracellular matrix (ECM) remodeling and ectopic ossification in inflammatory arthritis, using ankylosing spondylitis as a model.

Methods: Primary fibroblasts were isolated from spinal ligament tissues of AS patients, and THP-1 cells were differentiated into macrophages for in vitro studies. The CAIA and SKG mouse models were used, with ferric ammonium citrate (FAC) injected locally in the SKG model to induce iron overload. SLC39A14 conditional knockout (CKO) mice were generated by crossing SLC39A14-flox mice with SCX-cre mice. Ferritin levels and plasma iron concentrations were measured using a colorimetric assay. Immunohistochemistry and immunofluorescence were performed to assess co-localization of Ferritin in fibroblasts and macrophages. CRISPR-Cas9 was used to knock out SLC39A14 in the TTD6 fibroblast cell line, and gene editing efficiency was confirmed by PCR and western blotting. FerroOrange, combined with flow cytometry, assessed iron uptake in treated cells. In vivo, the effects of iron overload were evaluated in the CAIA and SKG models, with western blotting to analyze SLC39A14, Ferritin, and ECM-related proteins.

Results: Our research demonstrated that inflammation-induced iron overload in spinal ligaments led to ECM remodeling and ectopic ossification. Increased Ferritin levels and decreased plasma iron were observed in AS patients, with serum iron negatively correlated with ASDAS-CRP scores, linking iron metabolism to disease severity. TNFα stimulation upregulated SLC39A14 in fibroblasts, promoting excessive ECM deposition. SLC39A14 knockout in fibroblasts inhibited ECM-related gene expression, such as TNC, FN1, and collagen types I and III, highlighting its role in ECM remodeling. Immunohistochemistry showed co-localization of SLC39A14 and Ferritin in activated fibroblasts and macrophages. Single-cell RNA sequencing identified fibroblast subpopulations sensitive to iron accumulation, with elevated ECM gene expression. In vivo, FAC injections in the SKG mouse model induced ectopic ossification in the Achilles tendon, further supporting the role of iron overload in ECM remodeling.

Conclusion: In an inflammatory state, upregulation of SLC39A14 in fibroblasts leads to iron overload, driving ECM remodeling and ectopic ossification in inflammatory arthritis, such as ankylosing spondylitis. Targeting SLC39A14 and modulating iron metabolism may offer potential therapeutic strategies to prevent these pathological changes.