Coexpression of two mesenchymal cadherins, cadherin 11 and N-cadherin, on murine fibroblast-like synoviocytes

Objective. Cadherin 11 has recently been identified on fibroblast-like synoviocytes (FLS), and studies in mice have demonstrated its importance in synovial lining architecture and inflammation. However, many tissues express more than 1 cadherin. Given the newly appreciated functional significance of cadherins in the synovium, this study was undertaken to determine whether mouse FLS express other cadherins in addition to cadherin 11. Methods. The characterization of cadherin expression was determined in FLS derived from wild-type and cadherin 11-null mice using immunofluorescence (IF), biochemical, and immunohistologic techniques. Results. Cadherin 11 expression was observed at points of cell-cell contact in cultured wild-type mouse FLS. However, despite the lack of cell surface cadherin 11, cadherin 11-null mouse FLS cells still formed intimate cell-cell contacts that contained beta-catenin. Immunoprecipitation of cell surface biotinylated FLS with anti-beta-catenin antibody demonstrated the presence of 2 cell surface catenin-associated proteins in FLS from wild-type mice and 1 in FLS sample from cadherin 11-null mice. Using biochemical approaches and reverse transcriptase-polymerase chain reaction, these proteins were determined to be N-cadherin and cadherin 11. Expression of both N-cadherin and cadherin 11 in the synovial lining was demonstrated by immunohistochemical analysis of mouse synovium. IF analyses demonstrated colocalization of N-cadherin and cadherin 11 to the same points of cell-cell contact. However, the inability to coimmunoprecipitate both cadherins using either anti-N-cadherin or anti-cadherin 11 antibodies suggests that these cadherins are not contained within the same molecular complexes. Conclusion. These findings demonstrate that FLS express both N-cadherin and cadherin 11, and suggest that these cadherins are not contained within the same molecular complex. Given their importance in modulating cellular behavior, understanding how these cadherins regulate FLS behavior individually and in concert will be critical to understanding synovial architecture and inflammation.