Serum amyloid A activates nuclear factor-kappaB in rheumatoid synovial fibroblasts through binding to receptor of advanced glycation end-products.

Rheumatoid arthritis (RA) is a chronic, symmetric polyarticular joint disease and serum amyloid A (SAA) is an acute-phase protein that is upregulated during the course of RA. We investigated the role of SAA in the pathogenesis of RA. Fibroblast-like synovial cells (FLS) were established from RA joints. SAA-stimulated expression of cytokines from FLS was evaluated by ELISA. Nuclear factor-kappaB (NF-kappaB) activation by SAA was evaluated by luciferase assay. NF-kappaB activation and IkappaBalpha degradation were evaluated by Western blotting and nuclear localization of p65 subunit of NF-kappaB in FLS. Expression of receptor for advanced glycation end-products (RAGE) in synovial tissue was evaluated by immunohistochemical study. Effects of preincubation of soluble RAGE on NF-kappaB activation by SAA was evaluated by Western blotting of IkappaBalpha. SAA stimulated the transcriptional activation by NF-kappaB in a dose-dependent manner and induced expression of the proinflammatory cytokines interleukin 6 (IL-6) and IL-8. Higher expression of RAGE in synovial tissue from patients with RA was noted. SAA induced IkappaBalpha degradation, with the peak effect around 30 minutes. Preincubation of SAA with soluble recombinant RAGE protein prevented SAA-induced IkappaBalpha degradation. SAA stimulation promoted nuclear translocation of NF-kappaB, whereas preincubation of SAA with RAGE inhibited nuclear translocation. Our data suggested that the SAA-RAGE-stimulated NF-kappaB signaling pathway has an important role in the pathogenesis of RA.