Baicalin improves the inflammatory response of RA-FLS by targeting the circ_0000734/miR-197-5p/IKBKB axis.

Background: Rheumatoid arthritis (RA) is a chronic autoimmune and inflammatory disease, and circular RNAs (circRNAs) are widely involved in its progression. Baicalin, a naturally derived small molecule, has been shown to improve inflammatory responses in RA by regulating circRNAs; however, the underlying regulatory mechanism remains unclear. Objective: This study aimed to investigate how circ_0000734 participates in the inflammatory response of RA-FLS through the miR-197-5p/IKBKB axis and to clarify the intervention effect of baicalin. Methods: The expression level of circ_0000734 in peripheral blood mononuclear cells (PBMCs) from RA patients was detected by qRT-PCR. Correlation analysis was performed to evaluate the associations between circ_0000734 expression and clinical indicators, including rheumatoid factor (RF), anti-cyclic citrullinated peptide antibody (anti-CCP), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and DAS28 scores. The downstream targets miR-197-5p and IKBKB were predicted using bioinformatics databases. Dual-luciferase reporter assays were performed to verify the targeting relationship between circ_0000734 and miR-197-5p, as well as the binding relationship between miR-197-5p and IKBKB. Subsequently, circ_0000734 and miR-197-5p were silenced or overexpressed in a TNF-α-stimulated RA fibroblast-like synoviocyte (RA-FLS) model to validate their regulatory relationship. Flow cytometry (FCM), Cell Counting Kit-8 (CCK-8), reverse transcription quantitative polymerase chain reaction (RT-qPCR), Western blot (WB), and enzyme-linked immunosorbent assay (ELISA) were used to determine the effects of circ_0000734 and miR-197-5p silencing/overexpression, as well as baicalin treatment, on RA-FLS cell viability, cell cycle progression, the NF-κB signaling pathway, and the expression of inflammatory factors, including IL-17, IL-23, IL-4, and IL-10. Results: circ_0000734 was highly expressed in PBMCs from RA patients and was positively correlated with disease activity indicators, including RF, CCP, CRP, ESR, and DAS28 scores. In the TNF-α-stimulated RA-FLS cell model, overexpression of circ_0000734 promoted RA-FLS cell proliferation, activated the NF-κB pathway, and disrupted the balance between pro-inflammatory and anti-inflammatory factors, whereas circ_0000734 silencing exerted the opposite effects. Dual-uciferase reporter assays confirmed the targeting relationship between circ_0000734 and miR-197-5p. Overexpression of miR-197-5p reversed the effects of circ_0000734 overexpression on RA-FLS cell viability, the downstream target gene IKBKB, the NF-κB pathway, and inflammatory factors. In addition, baicalin treatment downregulated circ_0000734 expression, thereby inhibiting the activation of the NF-κB pathway, improving the inflammatory cytokine profile, and reversing the adverse phenotype induced by circ_0000734 overexpression. Conclusion: Highly expressed circ_0000734 in RA promotes NF-κB pathway activation by inhibiting miR-197-5p expression, thereby enhancing RA-FLS cell viability and promoting inflammatory cytokine secretion. Baicalin may inhibit the high expression of circ_0000734 and activation of the NF-κB signaling pathway, ultimately alleviating the inflammatory response in RA-FLS.