The expression of signal regulatory protein-alpha in normal and osteoarthritic human articular cartilage and its involvement in chondrocyte mechano-transduction response.

BACKGROUND Signal regulatory proteins (SIRP) belong to immunoglobulin super family (IgSF) and relate to integrin signaling cascades. It has been shown that SIRPalpha is expressed in a variety of cells including myeloid cells and neurons. In the present study the expression of this IgSF member in articular chondrocytes was investigated. METHODS Using a panel of anti-SIRPalpha antibodies, immunohistochemistry, Western-blotting and electrophysiology methods, expression of SIRPalpha and its role in chondrocyte mechano-transduction were assessed. RESULTS No identifiable positive signal was obtained by using immunohistochemistry methods on frozen and paraffin sections. SIRPalpha is expressed by both normal and osteoarthritis cultured chondrocytes. The electrophysiological response of chondrocytes in the presence of SE7C2 mAb was significantly inhibited whereas; SE5A5 did not show any modification in this response. CONCLUSIONS It seems likely that SIRPalpha could be associated with other proteins such as integrins, CD47 and ion channels, which contribute to the electrophysiological response of human articular chondrocytes. In any case, this study has provided a specific functional role for SIRPalpha in chondrocyte mechano-transduction.