The enhanced release of extracellular matrix proteins by fibroblast-like synoviocytes (FLS) from rheumatoid arthritis (RA) patients is suggestive of joint remodeling. Because Wnt proteins play a critical role in joint development, we investigated whether up-regulated Wnt signaling plays a role in the enhanced synthesis of extracellular matrix proteins. The purpose of the present experiments was to determine the role of Wnt-1-like molecules in the expression of matrix proteins by RA FLS and to ascertain the effects of Wnt antagonists on RA FLS function and survival.
Transfection with a reporter plasmid (TOPflash) was performed to assess whether Wnt signaling is active in RA FLS. Wnt signaling was up-regulated in normal FLS by transfection with a Wnt-1 expression plasmid and was down-regulated in RA FLS by transfection with dominant-negative lymphoid enhancer factor 1 (LEF-1)/T cell factor 4 (TCF-4) and secreted Frizzled receptor protein 1 (sFRP-1) expression plasmids. Recombinant sFRP-1 and anti-Wnt-1 antibody were also administered to RA FLS to block Wnt signaling.
RA FLS had constitutive activation of the canonical Wnt signaling pathway. Transfection of normal FLS with a Wnt-1 expression vector enhanced not only fibronectin, but also pro-matrix metalloproteinase 3 (proMMP-3) expression. In a complementary manner, interference with Wnt signaling using anti-Wnt-1 antibody, the Wnt antagonist sFRP-1, or dominant-negative vectors that inhibited the transcription factors TCF-4/LEF-1 blocked the expression of fibronectin by RA FLS and reduced cell survival. Anti-Wnt-1 antibody and sFRP-1 also blocked the expression of proMMP-3.
Our results indicate that the canonical Wnt pathway regulates fibronectin and metalloproteinase expression in RA FLS.