Macrophage extracellular traps promote tumor-like biologic behaviors of fibroblast-like synoviocytes through cGAS-mediated PI3K/Akt signaling pathway in patients with rheumatoid arthritis.

Rheumatoid arthritis (RA) is an autoimmune disease characterized by synovium hyperplasia and bone destruction. Macrophage extracellular traps (METs) are released from macrophages under various stimulus and may generate stable autoantigen-DNA complexes, aggravate autoantibodies generation and autoimmune responses. We aimed to investigate the role of METs on the biologic behaviors of RA-FLSs. Synovial tissues and fibroblast-like synoviocytes (FLSs) were obtained from RA patients. ETs in synovium and synovial fluids were detected by immunofluorescence, immunohistochemistry and SYTOX Green staining. Cell viability, migration, invasion, and cytokines expression of RA-FLSs were assessed by CCK-8, wound healing assay, Transwell assays and quantitative real-time PCR (qPCR) respectively. RNA-sequencing analysis was performed to explore the underlying mechanism and Western blot was used to validate the active signaling pathways. We found that ETs formation was abundant in RA and positively correlated to anti-CCP. RA-FLSs stimulated with purified METs, demonstrated the obvious promotion in tumor-like biologic behaviors. The DNA sensor cGAS in RA-FLSs was activated after METs stimuli. RNA sequencing revealed that differential genes were significantly enriched in PI3K/Akt signaling pathway and cGAS inhibitor RU.521 effectively reversed the promotion of tumor-like biologic behaviors in METs treated RA-FLSs and downregulated the PI3K/Akt activation. In summary, our study demonstrates that METs promote the pathogenically biological behaviors of RA-FLSs through cGAS-mediated activation of PI3K/Akt signaling pathway. These findings provide a novel insight into the pathogenesis of RA and the mechanisms of macrophages in modulating RA-FLSs tumor-like behaviors.