Oxidized LDL Binds to CD36 on Human Monocyte-Derived Macrophages and Transfected Cell Lines

Abstract

Accumulating evidence strongly implicates oxidized LDL (Ox-LDL) in the pathogenesis of atherosclerosis. Several receptors have been identified that bind and internalize Ox-LDL, but their relative importance in vivo is unclear. CD36 is an 88-kD transmembrane glycoprotein expressed on monocytes/macrophages, platelets, and microvascular endothelium that has been implicated as a putative receptor for Ox-LDL. We demonstrate that an anti-CD36 monoclonal antibody inhibited 50% of the specific binding and 26% of the specific degradation of Ox-LDL by human monocyte–derived macrophages. To characterize more completely this binding we evaluated interactions between CD36 and Ox-LDL in murine NIH-3T3 cells stably transfected with human CD36 cDNA. Ox-LDL bound to CD36-transfected 3T3 cells in a saturable manner. Specific binding, internalization, and degradation of Ox-LDL were increased fourfold in CD36-transfected cell lines compared with 3T3 cells transfected with vector alone. Binding of Ox-LDL to CD36-transfected 3T3 cells was inhibited by a panel of anti-CD36 antibodies and by soluble CD36 but not by thrombospondin. Specificity of binding was demonstrated by the equivalent binding of LDL and acetylated LDL to control and CD36-transfected 3T3 cells. The epitope or epitopes on Ox-LDL recognized by CD36 are undefined. Two observations suggest that CD36 recognizes a lipid moiety or that the lipid portion of the lipoprotein is essential for apoprotein recognition. The first is that the increased binding of Ox-LDL to CD36-transfected 3T3 cells is abrogated by delipidation of the lipoprotein, and the second is that oleic acid competes for the binding of Ox-LDL to CD36-transfected 3T3 cells. These data demonstrate that CD36 functions as an Ox-LDL receptor and suggest that CD36 may play a functional role in lipid accumulation by human macrophages and subsequent foam cell development during atherosclerosis.