circ-PTTG1IP/miR-671-5p/TLR4 axis regulates proliferation, migration, invasion and inflammatory response of fibroblast-like synoviocytes in rheumatoid arthritis

Circular RNAs (circRNAs) are related to rheumatoid arthritis (RA) development. However, the function and mechanism of circRNA pituitary tumor-transforming 1 interacting protein (circ- PTTG1IP) in RA are unknown. The expression of circ-PTTG1IP in synovial tissues of RA patients and fibroblast-like synoviocytes from RA patients (RA-FLSs) were detected by RT-qPCR. The results uncovered that circ-PTTG1IP was overexpressed in RA patients and RA-FLSs, and circ-PTTG1IP knockdown suppressed cell proliferation, migration, invasion and inflammatory response in RA-FLSs. Besides, we found that circ-PTTG1IP could directly bind to miR-671-5p, and toll-like receptor 4 (TLR4) was a target of miR-671-5p, which was confirmed by dual-luciferase reporter assay. miR-671-5p inhibitor attenuated the effects of circ-PTTG1IP knockdown on RA-FLSs, while the effects of miR-671-5p mimic on RA-FLSs were partly reversed by TLR4 overexpression. Furthermore, circ-PTTG1IP could upregulate TLR4 expression by miR-671-5p. Thus, circ-PTTG1IP knockdown repressed cell proliferation, migration, invasion and inflammatory response in RA-FLSs by regulating the miR-671-5p/TLR4 axis.