It is not understood why cultured fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA) often display a persistently activated phenotype, despite removal from an inflammatory environment. Previously, we found that these FLS expressed high levels of both Wnt-5A and 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/FzS signaling contributes to FLS activation.
Wnt-5A expression in FLS was inhibited by transfection with both antisense and dominant negative (dn) vectors. Fz5 signaling was blocked with an antibody to the extracellular domain of the receptor. The effects of these treatments on the expression of the proinflammatory cytokines interleukin-6 (IL-6) and IL-15 and on the expression of receptor activator of nuclear factor kappaB ligand (RANKL) were assessed by reverse transcriptase-polymerase chain reaction and immunoblotting.
Both antisense Wnt-5A and dnWnt-5A vectors, but not empty vector, diminished IL-6 and IL-15 expression in RA FLS. Anti-Fz5 antibody exerted similar effects and also reduced RANKL expression.
Wnt-5A/Fz5 signaling may contribute to the activated state of FLS in RA. Receptor antagonists of Fz5 should be considered for the treatment of refractory synovitis.