Unraveling the Dual Role of circ‐CBLB and ETS‐1 in Rheumatoid Arthritis: Biomarkers and Therapeutic Targets

ABSTRACT Objective To investigate the effects of circ‐CBLB and ETS‐1 on the proliferation, apoptosis, and inflammatory cytokine expression in the fibroblast‐like synoviocytes (FLSs) from patients with rheumatoid arthritis (RA). Methods Peripheral blood was collected from 15 pairs of healthy controls (HCs) and patients with RA to isolate peripheral blood mononuclear cells (PBMCs). mRNA expression of circ‐CBLB and ETS‐1 was determined using qRT‐PCR. Levels of the inflammatory markers (ESR, CRP, CCP, and RF) were determined, and the 28‐joint Disease Activity Score (DAS28) was calculated. For in vitro experiments, human FLS and RA‐FLS were cultured, and constructs (pcDNA3.1/siRNA‐circ‐CBLB, pcDNA3.1/siRNA‐ETS‐1) were transfected into RA‐FLS. Cotransfection of pcDNA3.1‐circ‐CBLB and siRNA‐ETS‐1 was undertaken to explore their combined effects. Levels of the key inflammatory cytokines (interleukin [IL]‐4, IL‐23, IL‐13, and tumor necrosis factor [TNF]‐α) were evaluated using qRT‐PCR and enzyme‐linked immunosorbent assays. Functional assays (CCK‐8) were used to assess cell viability, apoptosis (flow cytometry), and migration. Western blotting was used to determine protein expression. Results In vivo analysis showed significant downregulation of circ‐CBLB and ETS‐1 in PBMCs from patients with RA compared with the HCs, as confirmed using qRT‐PCR. Correlation analysis indicated a positive association among circ‐CBLB, ETS‐1, and IL‐4, while circ‐CBLB and ETS‐1 were negatively correlated with inflammatory markers (ESR, CRP, RF, CCP, DAS28, IL‐23, and TNF‐α). Receiver operating characteristic curve analysis suggested circ‐CBLB and ETS‐1 as potential biomarkers for high disease activity in RA. In vitro, circ‐CBLB overexpression increased IL‐4 levels while decreasing IL‐23, IL‐13, and TNF‐α levels. Additionally, circ‐CBLB inhibited the apoptosis of RA‐FLS, prolonged the cell cycle, and reduced cell migration. ETS‐1 negatively regulated circ‐CBLB, indicating a feedback loop. Conclusion circ‐CBLB and ETS‐1 are downregulated in RA and correlate with inflammation and disease activity. They regulate each other bidirectionally. circ‐CBLB reduces RA‐FLS viability, promotes apoptosis, and inhibits migration by modulating cytokines. ETS‐1 has similar effects, and interfering with its expression reverses the impact of circ‐CBLB.