Circ_AFF2 facilitates proliferation and inflammatory response of fibroblast-like synoviocytes in rheumatoid arthritis via the miR-375/TAB2 axis

Circular RNAs (circRNAs) have been implicated in the pathological regulation of human diseases by acting as microRNA (miRNA) sponges to affect gene expression. CircRNA Fragile Mental Retardation 2 (circ_AFF2) was dysregulated in rheumatoid arthritis (RA), but little is known about its specific function and hidden molecular mechanism in RA. Circ_AFF2, miR-375 and TAK1-binding 2 (TAB2) expression levels were determined through the quantitative real-time polymerase chain reaction (qRT-PCR). Flow cytometry was performed to analyze cell cycle and apoptosis. Cell proliferation detection was conducted by 3-(4, 5-dimethylthiazol-2-y1)-2, 5-diphenyl tetrazolium bromide (MTT) assay. The protein levels were measured using western blot. Inflammatory response was evaluated by enzyme-linked immunosorbent assay (ELISA). RNA pull-down assay was used to select the miRNA target of circ_AFF2. The interaction between miR-375 and circ_AFF2 or TAB2 was analyzed using the dual-luciferase reporter assay. Contrasted to normal samples and fibroblast-like synoviocytes (FLS), circ_AFF2 expression was upregulated in RA blood samples and FLS-RA cells. Cell cycle, proliferation and inflammatory response were blocked while apoptosis was promoted in FLS-RA after the downregulation of circ_AFF2. In addition, circ_AFF2 could interact with miR-375 and the function of circ_AFF2 was achieved by sponging miR-375 in FLS-RA cells. Moreover, TAB2 was a target of miR-375 and miR-375 repressed RA progression by decreasing TAB2 expression in FLS-RA cells. More importantly, circ_AFF2 promoted the expression of TAB2 by targeting miR-375. These findings clarified that circ_AFF2 induced cell progression, inflammatory response in FLS-RA cells via the miR-375/TAB2 axis. Circ_AFF2 could be used as a biomarker in the diagnosis and treatment of RA.