Blockade of Wnt-5A/Frizzled 5 signaling inhibits rheumatoid synoviocyte activation

Objective. It is not understood why cultured fibroblast-like synoviocytes ( FLS) from patients with rheumatoid arthritis (RA) often display a persisten tly activated phenotype, despite removal from an inflammatory environment. Previously, we found that these FLS expressed high levels of both Wnt-5A an d Frizzled 5 (Fz5), a receptor-ligand pair implicated in both limb bud and bone marrow stem cell development. The objective of the present experiments was to determine whether Wnt-5A/Fz5 signaling contributes to FLS activatio n. Methods. Wnt-5A expression in FLS was inhibited by transfection with both a ntisense and dominant negative (dn) vectors. Fz:5 signaling was blocked wit h an antibody to the extracellular domain of the receptor. The effects of t hese treatments on the expression of the proinflammatory cytokines interleu kin-6 (IL-6) and IL-15 and on the expression of receptor activator of nucle ar factor kappaB ligand (RANKL) were assessed by reverse transcriptase-poly merase chain reaction and immunoblotting. Results. Both antisense Wnt-5A and dnWnt-5A vectors, but not empty vector, diminished IL-6 and IL-15 expression in RA FLS. Anti-Fz:5 antibody exerted similar effects and also reduced RANKL expression. Conclusion. Wnt-5A/Fz5 signaling may contribute to the activated state of F LS in RA. Receptor antagonists of Fz5 should be considered for the treatmen t of refractory synovitis.