Local expression of acute phase serum amyloid A mRNA in rheumatoid arthritis synovial tissue and cells

Objective, Serum amyloid A (SAA) protein, a bioactive protein produced duri ng inflammation, is present in synovial fluid (SF) of patients with rheumat oid arthritis (RA). Based on our recent finding that SF SAA concentration e xceeded the serum counterpart in some patients with RA, we examined the loc al steady state concentration of SAA mRNA isoforms in synovia and in synovi al cells cultured from patients with RA and osteoarthritis (OA). Methods. Total cellular RNA from synovial membranes of patients with RA or OA and from cultured synovial cells of patients with RA was analyzed by rev erse transcription polymerase chain reaction and Northern blot. Results. Acute phase SAA (A-SAA) mRNA isoforms were detected only in RA syn ovia, but not in OA synovia; however, the constitutive SAA (C-SAA) mRNA iso form was detected in similar abundance in both OA and RA synovia. There was evidence of C-SAA, but not A-SAA mRNA in cultured synovial cells at quiesc ence. After stimulation with both 1 mM dexamethasone and 10 ng/ml interleuk in 1 beta (IL-1 beta), the quantity of steady state A-SAA mu RNA in culture d synovial cells was markedly increased. Conclusion. Both A-SAA and C-SAA mRNA are detectable in RA synovia, while o nly C-SAA mRNA is detectable in OA and in quiescent cultured synovial cells . The steady state A-SAA mRNA isoform in cultured synovial cells was marked ly increased in the presence of dexamethasone plus IL-1 beta. The local syn thesis of A-SAA may contribute, at least in part, to the concentration of A -SAA protein in SF and may contribute to the altered molecular and cellular physiology in RA joints.