Macrophage scavenger receptor CD36 is the major receptor for LDL modified by monocyte-generated reactive nitrogen species
Eugene A. Podrez, Maria Febbraio, Nader Sheibani, David Schmitt, Roy L. Silverstein, David P. Hajjar, Peter A. Cohen, William A. Frazier, Henry F. Hoff, Stanley L. Hazen
Eugene A. Podrez, Maria Febbraio, Nader Sheibani, David Schmitt, Roy L. Silverstein, David P. Hajjar, Peter A. Cohen, William A. Frazier, Henry F. Hoff, Stanley L. Hazen
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Article

Macrophage scavenger receptor CD36 is the major receptor for LDL modified by monocyte-generated reactive nitrogen species

Abstract

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-H2O2-NO2–) system as a novel mechanism for converting LDL into a high-uptake form (NO2-LDL) for macrophages. We now identify the scavenger receptor CD36 as the major receptor responsible for high-affinity and saturable cellular recognition of NO2-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 NO2-LDL. Modification of LDL by the MPO-H2O2-NO2– 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 Cu2+-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 NO2-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.

Authors

Eugene A. Podrez, Maria Febbraio, Nader Sheibani, David Schmitt, Roy L. Silverstein, David P. Hajjar, Peter A. Cohen, William A. Frazier, Henry F. Hoff, Stanley L. Hazen

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Figure 10

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Effect of lipid competitors on the binding of NO2-LDL to CD36-transfecte...
Effect of lipid competitors on the binding of NO2-LDL to CD36-transfected cells. [125I]LDL was modified as described for the complete system in Figure 2a. [125I]-NO2LDL (5 μg/mL) was then incubated with CD36-expressing 293 cells for 3 hours at 4°C in the presence of (a) 20 μg lipid/mL or (b) the indicated concentrations (μg lipid/mL) of competitors. PAPC, PAPC(SnCl2), PLPC, and POPC unilamellar vesicles were oxidized for 8 hours at 37°C as described for the complete system in Figure 2 in the presence (+NO2–, filled symbols) or absence (–NO2–, open symbols) of NO2–. Where indicated, BSA (0.2 mg protein/mL final concentration) was also included during liposome preparation as described in Methods (hatched bars). PAPC (SnCl2), hydroperoxide-free PAPC generated by reduction of PAPC with SnCl2, and then reisolation of PAPC under argon atmosphere before use were used as described in Methods. Data represent the mean ± SD of triplicate determinations (a) or means of triplicate determinations (b) of a representative experiment performed 3 times. AP < 0.001 for comparison versus control (no competitor).