Background It is known that IL-1 has played an important role in the progression of rheumatoid arthritis. IPAF [the IL1B converting enzyme (ICE)-protease activating factor] and NALP [NOD and the NTPases implicated in apoptosis and multihistocompatability complex transcription (NACHT) leucine-rich repeat protein] 1 are important components of inflammasome, which can promote the synthesis of certain cytokines such as IL-1beta. We supposed that IPAF and NALP1 might have some relationship with RA inflammation, because of their role in inflammatory reaction.

Objectives To investigate the expression of IPAF and NALP1, and study the influence of TNF-α, LPS and Z-VAD-FMK on NALP1 and IPAF in rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS).

Methods All of the synovial tissues were obtained during joint replacement surgery and arthroscopic operation from 6 patients with RA, 4 with OA and 3 with joint trauma. The NALP1 and IPAF protein expression was tested by immunohistochemical in synovial tissue. FLS were cultured in vitro. The mRNA and protein expression of NALP1 and IPAF was detected by Real-time PCR and western blotting respectively. RA-FLS were treated with LPS, LPS+Z-VAD-FMK, TNF-α and TNF-α+Z-VAD-FMK. Then the mRNA and protein expression of NALP1 and IPAF was tested by Real-time PCR and western blotting.

Results Immunohistochemistry revealed that the expression of IPAF in synovial lining cells of RA samples was significantly higher than that of OA or Trauma (p<0.05). NALP1 was expressed in RA samples only, but not expressed in OA and Trauma samples (P<0.05). Western blotting and Real-time PCR showed that IPAF expression in OA-FLS > that in RA-FLS > that in Trauma-FLS (p<0.05). NALP1 expression at the mRNA level in OA-FLS was greater than that in RA-FLS, which is more than that in Trauma-FLS (p<0.05). But no difference of NALP1 expression was found at the protein level in the three groups above. The mRNA and protein expression of IPAF in RA-FLS which was treated with TNF-α was 4.08 times more than that in control (both p<0.05), and was also more than that treated with TNF-α+ Z-VAD-FMK (both p<0.05). The mRNA expression of NALP1 in the RA-FLS treated with TNF-α was 1.19 times of that in control. But there was no difference between the NALP1 expression in RA-FLS treated with different drugs (p>0.05).

Conclusions Theses results suggest that IPAF and NALP1 may be involved in RA chronic synovial inflammation process. TNF-α can promote the expression of IPAF in RA-FLS, and this effect can be inhibited by Z-VAD-FMK—the inhibitor of caspase which is located in the downstream of inflammasome, reconfirming the effect dependents on inflammatory.

References

1. Sidiropoulos PI, Goulielmos G, Voloudaskis GK, et al. Inflammasomes and rheumatic diseases: evolving concept [J]. Ann Rheum Dis, 2008,67(10):1382-1389.

Disclosure of Interest None Declared