Macrophage scavenger receptor CD36 is the major receptor for LDL modified by monocyte-generated reactive nitrogen species
The oxidative conversion of LDL into an atherogenic form is considered a pivotal event in the development of cardiovascular disease. Recent studies have identified reactive nitrogen species generated by monocytes by way of the myeloperoxidase-hydrogen peroxide-nitrite (MPO-H(2)O(2)-NO(2)(-)) system as a novel mechanism for converting LDL into a high-uptake form (NO(2)-LDL) for macrophages. We now identify the scavenger receptor CD36 as the major receptor responsible for high-affinity and saturable cellular recognition of NO(2)-LDL by murine and human macrophages. Using cells stably transfected with CD36, CD36-specific blocking mAbs, and CD36-null macrophages, we demonstrated CD36-dependent binding, cholesterol loading, and macrophage foam cell formation after exposure to NO(2)-LDL. Modification of LDL by the MPO-H(2)O(2)-NO(2)(-) system in the presence of up to 80% lipoprotein-deficient serum (LPDS) still resulted in the conversion of the lipoprotein into a high-uptake form for macrophages, whereas addition of less than 5% LPDS totally blocked Cu(2+)-catalyzed LDL oxidation and conversion into a ligand for CD36. Competition studies demonstrated that lipid oxidation products derived from 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphocholine can serve as essential moieties on NO(2)-LDL recognized by CD36. Collectively, these results suggest that MPO-dependent conversion of LDL into a ligand for CD36 is a likely pathway for generating foam cells in vivo. MPO secreted from activated phagocytes may also tag phospholipid-containing targets for removal by CD36-positive cells.