IKKε aggravates inflammatory response via activation of NF-κB in rheumatoid arthritis

Rheumatoid Arthritis (RA) is a chronic systemic autoimmune disease, whereas its cause still remains elusive. Typical pathological manifestations of RA include persistent synovitis and bone degeneration in the surrounding joints. Although the incidence of RA is high in population, currently there have been no effective cures for it. The purpose of this study is to investigate the therapeutic effects and main mechanism of IKKε (inhibitor of nuclear factor kappa-B kinase ε) in collagen II induced- Rheumatoid Arthritis (CIA) mice model.

IKKε-/- and wild-type (WT) littermate control mice were intraperitoneally injected with 5 mg/kg collagen II monoclonal antibody cocktail (Cab) for 5 days. After that, the nociception threshold and clinical rheumatoid arthritis articular damage score of mice were evaluated. After 5 days-CAb treatment, serum levels of a series of inflammatory cytokines including interleukin-6 (IL-6), IL-1β, tumor necrosis factor-α (TNF-α) and interferon (IFN) were detected with enzyme-linked immunosorbent assay (ELISA) in both groups. Besides, Real-time reverse transcription polymerase chain reaction (Real-time RT-PCR) was used to evaluate the expression of these inflammatory cytokines in plantar tissues. In addition, Western blot was performed to investigate the protein levels of NF-κB (nuclear factor kappa-light-chain-enhancer of activated B) signaling pathway. Moreover, WT mice receiving CAb were further applied with or without IKK inhibitor amlexanox (25 mg/kg) to investigate the expression of the above-mentioned inflammatory cytokines.

Our work showed that IKKε-/- mice with CIA displayed less nociception and suppressed inflammatory response than WT mice. Meanwhile, the clinical rheumatoid arthritis articular damage scores were significantly decreased in IKKε-/- mice. The levels of TNF-α, IL-1β, IL-6 in serum and plantar tissues in IKKε-/- mice were significantly lower than those in WT mice. Besides, NF-κB expression in IKKε-/- mice was significantly decreased. Similarly, the same phenotype was observed in WT mice administrated with IKKε inhibitor amlexanox as that of IKKε-/- mice, indicating that inflammatory and nociception responses were remarkably decreased than those of the negative controls.

IKKε plays an important role in promoting nociception and inflammatory response in CIA. Our research demonstrated that knockout of IKKε may serve as a new direction for clinical prevention and treatment of rheumatoid arthritis. IKKε inhibitor amlexanox may become a new drug for the treatment of rheumatoid arthritis.