Recombinant CD36 inhibits oxLDL-induced ICAM-1-dependent monocyte adhesion

A key event in atherosclerosis is the interaction between monocytes and endothelial cells. Binding of oxidized low-density lipoprotein (oxLDL) to CD36 on endothelial cells results in activation and subsequent monocyte adhesion. In this study, a recombinant soluble CD36 molecule was expressed to delineate its ability to block the adhesion of monocytes. To construct soluble CD36, the extra-cellular domain of CD36 was fused to the Fc domain of human IgG1. The N-terminal sequence of CD36 was replaced with N-terminal signal peptide sequence of CD59, a type I membrane protein. The resulting chimeric sCD36-Ig cDNA (sCD36-Ig) was transfected into COS-7 and CHOK1 cells and supernatants were analyzed for secretion of this molecule. Sandwich ELISA and oxLDL binding analyses showed that recombinant sCD36-Ig is secreted in a functionally active form. Western blot analysis of the purified sCD36-Ig using three different anti-CD36 monoclonal antibodies and anti-human IgG showed that the chimeric sCD36-Ig is a dimer of 220kDa. Further, the sCD36-Ig inhibited the adhesion of monocytes to oxLDL. Interestingly, sCD36-Ig blocked the oxLDL-induced adhesion of monocytes to the endothelial cell specific protein, ICAM-1. Our results indicate that the chimeric sCD36-Ig protein is folded correctly and can effectively compete for the binding of oxLDL to membrane-expressed CD36. These results suggest that oxLDL-induced monocyte adhesion can be blocked using sCD36-Ig and this may be useful in blocking the cell-cell interaction leading to atherogenesis.