D-Dopachrome Tautomerase Regulates Synovial Fibrosis and Macrophage Polarization via NF-κB/CCL2 Signaling Pathway in Knee Osteoarthritis.

This study aimed to investigate the regulatory function of D-dopachrome tautomerase (DDT) in the occurrence and development of Knee Osteoarthritis (KOA). Single-cell data (GSE248453) and transcriptome data (GSE283079) related to KOA were retrieved from the GEO database. Seurat, limma, and clusterProfiler packages were used for computational analyses. For in vitro experiments, mouse Synovial Fibroblasts (SFs) were transfected with si-DDT and then stimulated with Lipopolysaccharide (LPS). RAW264.7 cells were cultured with SFs-conditioned medium to assess macrophage polarization. Finally, Transwell, qRT-PCR, Western blot, and NF-κB agonist rescue assays were performed for validation. Computational analysis showed that DDT and chemokine-ligand-2 (CCL2) were primarily expressed in fibroblasts and macrophages in KOA and showed a positive correlation with each other. DDT was upregulated in LPS-induced SFs, while its knockdown inhibited the migration of SFs and the expressions of fibrosis-related genes, NF-κB pathway, and CCL2. However, these effects were reversed by the NF-κB agonist. DDT silencing suppressed the levels of M1 markers (IL-6, IL-1β) and elevated those of M2 markers (IL-4, CD206) in macrophages. DDT acted as a key regulator in KOA pathogenesis. It was observed that knockdown of DDT downregulated the expressions of genes related to fibrosis and tissue remodeling (including TGF‑β, COL1A1, and TIMP1), suppressed M1 macrophage polarization, and promoted M2 phenotype, potentially through modulation of the NF‑κB/CCL2 pathway. This study identified DDT as a potential therapeutic target for the clinical treatment of KOA, providing new insights into the pathogenic mechanism of the disease.