Cadherin 11 is a homophilic cell-to-cell adhesion molecule expressed on joint synovial fibroblasts. Absence of cadherin 11 in a mouse rheumatoid arthritis (RA) model led to striking reductions in cartilage erosion. Matrix metalloproteinases (MMPs) are enzymes expressed by synovial fibroblasts important for cartilage erosion. The objective of this study was to determine if synovial fibroblast MMP production is regulated by cadherin 11.
To mimic cadherin 11 engagement, human RA synovial fibroblasts were stimulated with a chimeric construct consisting of the cadherin 11 extracellular domain linked to the human IgG1 Fc domain (Cad-11-Fc). Effects on MMP production were measured by enzyme-linked immunosorbent assay, quantitative reverse transcription-polymerase chain reaction analysis, and immunoblotting.
Human Cad-11-Fc up-regulated MMP-1 and MMP-3 protein production by RA synovial fibroblasts, both alone and in synergy with tumor necrosis factor α. This up-regulation required cell cadherin 11 engagement, since a mutant Cad-11-Fc with reduced binding affinity stimulated significantly less MMP production. Also, short hairpin RNA (shRNA) cadherin 11 silencing almost completely inhibited Cad-11-Fc-induced MMP expression. Cad-11-Fc stimulation increased RA synovial fibroblast MMP messenger RNA levels. It also increased the phosphorylation of the MAPKs JNK, ERK, and p38 kinase, the phosphorylation of NF-κB p65, and the nuclear translocation of activator protein 1 transcription factor. MAPK and NF-κB inhibitors partially blocked RA synovial fibroblast MMP expression.
Cadherin 11 engagement stimulates increased synthesis of several MMPs by RA synovial fibroblasts in a MAPK- and NF-κB-dependent manner. These results underscore the existence of a pathway by which cadherin 11 regulates MMP production and has important implications for joint destruction in RA.