There is increasing evidence that the RhoA signaling pathway may play a critical role in the inflammatory response. This study was undertaken to examine the effects of RhoA and its downstream effector Rho kinase (ROK) in synovial inflammation in rheumatoid arthritis (RA).

RhoA activity was assessed by pull‐down assay. Fasudil and Y27632, both specific inhibitors of ROK, were used to examine the role of ROK in inflammatory responses in vivo and in vitro. Nuclear translocation of NF‐κB was measured by confocal fluorescence microscopy, and DNA binding activity was assessed with a sensitive multiwell colorimetric assay. Enzyme‐linked immunosorbent assay was used to detect cytokine production.

Increased activation of RhoA was found in inflamed synovial membrane cells isolated from patients with RA and from rats with collagen‐induced arthritis (CIA). Intraperitoneal administration of fasudil in rats with CIA significantly reduced synovial inflammation and ROK activity. In vitro, treatment with fasudil or Y27632 decreased production of tumor necrosis factor α (TNFα), interleukin‐1β (IL‐1β), and IL‐6 by synovial membrane cells, peripheral blood mononuclear cells, and fibroblast‐like synoviocytes from patients with active RA. Inhibition of ROK by specific inhibitors or ROK small interfering RNA suppressed lipopolysaccharide‐ or TNFα‐induced NF‐κB nuclear translocation, DNA binding activity, luciferase reporter gene expression, and IκBα degradation.

The results of this study provide new evidence that blockade of ROK inhibits activation of NF‐κB and production of proinflammatory cytokines, suggesting a critical role of ROK in the synovial inflammation of RA. Specific inhibition of ROK may be a novel therapeutic approach in RA.