Effects of Dickkopf-1 on synovitis of rheumatoid arthritis

Abstract

As an important feature of rheumatoid arthritis (RA), an excessive amount of pro-inflammatory cytokines in RA synovial lesions induces the proliferation of synovial fibroblasts, cartilage erosion and systemic inflammatory immune response. Wnt inhibitor, Dkk-1, contributes to joint remodeling. This study was conducted to explore the role of Dkk-1 in the regulation of pro-inflammatory cytokine secretion. Rheumatoid arthritis synovial fibroblasts (RASF) were cultured from surgical synovial specimens and utilized at passages 4-8. For Dkk-1 silencing assay, Dkk-1-specific siRNA and control scrambled siRNA were transfected into RASF respectively. For Dkk-1 over-expression assay, Dkk-1 plasmid and control vector were transfected into RASFs respectively. Production of pro-inflammatory cytokines, such as interleukin-1β (IL-1β), tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) and interleukin-8 (IL-8), were measured by enzyme-linked immunosorbent assay (ELISA) and real-time polymerase chain reaction (PCR) at pre- and post-transfection respectively. Differences between various groups were evaluated by Wilcoxon signed-rank test. After a treatment of Dkk-1-specific siRNA, RASF exhibited decreased production of pro-inflammatory cytokines in association with down-regulated Dkk-1 levels while Dkk-1 over-expression could up-regulate the production of pro-inflammatory cytokines. The effects were marked when RAFS was activated by TNF-α and IL-1β after transfection. Dkk-1 promotes the production of pro-inflammatory cytokines in RASF so as to exacerbate synovitis of RA. And targeting Dkk-1 may provide a novel therapeutic strategy for RA.