Background <p>Synovial inflammation is involved in all stages of osteoarthritis (OA) and is a key factor in promoting the occurrence and development of OA.</p> Aim <p>To investigate the effects of lncRNA TTN-AS1 on human synovial fibroblasts.</p> Materials and methods <p>RT-qPCR was employed to detect the expression of the long non-coding RNA TTN-AS1, miR-520d-5p, ADAMTS5, vascular endothelial growth factor (VEGF) and matrix metallopeptidase 13 (MMP13). The Enzyme-Linked Immunosorbent Assay (ELISA) method was employed to detect interleukin-6 (IL-6) and interleukin-8 (IL-8) in cell supernatants. The proliferation and apoptosis of cells were detected by the Cell Counting Kit-8 (CCK-8) method and flow cytometry, respectively. Interactions between genes were demonstrated using dual luciferase assays and Pearson correlation analysis.</p> Results <p>In the OA synovial tissue and cell model, lncRNA TTN-AS1 and ADAMTS5 were upregulated, while miR-520d-5p was downregulated. Following TNF-α and IL-1β treatment, IL-6 and IL-8 levels significantly increased in FLSs-OA. In terms of cellular function, inhibiting lncRNA TTN-AS1 could promote expression of SOD and GSH in FLSs-OA cells, while also decreasing the expression of MDA, VEGF and MMP13. Furthermore, inhibiting lncRNA TTN-AS1 could inhibit the proliferation of FLSs-OA cells and enhance their apoptosis. However, inhibiting miR-520d-5p could reverse the cellular effects produced by inhibiting lncRNA TTN-AS1 on FLSs-OA cells. In terms of mechanism, Negative regulatory relationships existed between lncRNA TTN-AS1 and miR-520d-5p, as well as between miR-520d-5p and ADAMTS5.</p> Conclusion <p>LncRNA TTN-AS1 regulated the functions of FLSs-OA cells induced by TNF-α and IL-1β, such as oxidative stress, angiogenesis, cell proliferation and apoptosis, as well as cartilage matrix degradation, through the miR-520d-5p, and ADAMTS5 may be the target gene for its functional effects.</p>