Abstract
Objective
The rheumatoid synovium displays characteristics of Toll‐like receptor (TLR) activation and antiviral gene expression, including production of RANTES and interferon‐β (IFNβ). The mechanism of this activation in rheumatoid synovial tissue is unknown. This study was designed to investigate the role of the IKK‐related kinase IKKϵ and IFN regulatory factor 3 (IRF‐3) in the activation of antiviral genes in rheumatoid arthritis (RA).
Methods
Kinase assay and immunostaining were performed on synovial tissue. Dominant‐negative (DN) IKKϵ adenoviral infection of human fibroblast‐like synoviocytes (FLS) was followed by poly(I‐C) stimulation and Western blotting. Quantitative polymerase chain reaction was performed on DN IKKϵ–infected FLS and IKKϵ^−/−^ and IKKϵ^+/+^ mouse FLS.
Results
Western blotting showed that IKKϵ phosphorylation was significantly greater in RA synovium compared with osteoarthritis synovium. Kinase assay confirmed that IKKϵ was activated in RA synovium, and immunostaining showed localization of pIKKϵ to the intimal lining. Western blot analysis demonstrated that activation of IRF‐3 was also increased in RA synovium. Poly(I‐C), lipopolysaccharide, and tumor necrosis factor α (TNFα) activated phosphorylation of IKKϵ and IRF‐3 in FLS. DN IKKϵ inhibited IRF‐3 phosphorylation as well as RANTES and IFNβ protein production in synoviocytes. Antiviral gene expression was also reduced in FLS from IKKϵ^−/−^ mice compared with IKKϵ^+/+^ mice.
Conclusion
Antiviral gene expression in RA, especially due to TLR ligands and TNFα, is dependent on IKKϵ and IRF‐3, and this pathway plays a key role in the production of type I IFNs and chemokines such as RANTES. These findings indicate that the IKKϵ pathway may have potential as a therapeutic target in RA.