Involvement of NEK7 in the activation of NLRP3 inflammasome in macrophages of rheumatoid arthritis and the intervention of Er Miao San

Abstract

Introduction: Er Miao San (EMS) has a historical usage in Traditional Chinese Medicine (TCM). The aim of this study is to explore whether EMS can target NEK7 for inhibiting activation of NEK7/NLRP3 inflammasome pathway to protect rheumatoid arthritis (RA). Methods The EMS ethyl acetate part was concentrated to the required experimental doses and EMS-containing serum was prepared. DBA/1 mice were used to establish the collagen-induced arthritis (CIA) model, and the general indicators of the mice were evaluated. The extent of inflammation in mice ankle joint tissues were detected using HE staining, radiography. Anti-tartrate-resistant acid phosphatase (Trap) staining was used to observe osteoclasts in the ankle joint of mice. Changes in the immune system of the mice were determined via thymus/spleen index and the ability of T/B cell proliferation. NEK7 small interfering RNA (NEK7 siRNA) and Mus NEK7 were transfected into RAW264.7 cells, respectively. The formation of NEK7-NLRP3 complex in RAW264.7 cells was detected by immunoprecipitation. The protein expressions of NLRP3, NEK7 and caspase-1 in peritoneal macrophages (PMs), ankle joint tissues of CIA mice and RAW264.7 cells were examined using Western blot and immunohistochemistry. The immunofluorescence was used to investigate the formation of ASC spots in PMs and RAW264.7 cells. Elisa was employed to quantify the amounts of IL-1β and IL-18 in the serum of CIA mice, PMs and RAW264.7 cells supernatants. Results The results indicated that EMS decreased arthritis index, joint swelling score and pathological changes of the ankle joint in CIA mice. EMS decreased the expression levels of NEK7, Caspase-1 and NLRP3 in the ankle joint tissues and PMs of CIA mice and reduced the formation of ASC spots in PMs. Additionally, EMS also decreased the levels of IL-1β and IL-18 in the serum and supernatants of PMs in CIA mice. Finally, it was discovered that EMS-containing serum decreased the expression proteins of NEK7, Caspase-1, NLRP3, and ASC in RAW264.7 cells. It also decreased the formation of ASC spots and reduced the IL-1β and IL-18 levels in the cell supernatants of RAW264.7. Conclusion EMS protects CIA mice by inhibiting the NEK7/NLRP3 inflammasome pathway, which suggests a potential application of EMS in the treatment of RA.