Group V Secretory Phospholipase A2-modified Low Density Lipoprotein Promotes Foam Cell Formation by a SR-A- and CD36-independent Process That Involves Cellular Proteoglycans

• Published in: The Journal of biological chemistry 2005-09, Vol.280 (38), p.32746-32752
• Main Authors: Boyanovsky, Boris B., van der Westhuyzen, Deneys R., Webb, Nancy R.
• Format: Article
• Language: English
• Subjects: Animals; Azo Compounds - pharmacology; CD36 Antigens - biosynthesis; Cholesterol Esters - metabolism; Coloring Agents - pharmacology; Crosses, Genetic; Female; Fluorescent Dyes - pharmacology; Foam Cells - metabolism; Group V Phospholipases A2; Heparin - metabolism; Humans; Hydrazines - pharmacology; Hydrolysis; Lipid Metabolism; Lipoproteins, LDL - metabolism; Macrophages - metabolism; Male; Mice; Mice, Inbred C57BL; Microscopy, Confocal; Models, Molecular; Peritoneum - metabolism; Phospholipases A - metabolism; Phospholipases A2; Protein Binding; Proteoglycans - metabolism; Transfection
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M502067200

Accumulating evidence indicates that secretory phospholipase A2 (sPLA2) enzymes promote atherogenic processes. We have previously showed the presence of Group V sPLA2 (GV sPLA2) in human and mouse atherosclerotic lesions, its hydrolysis of low density lipoprotein (LDL) particles, and the ability of GV sPLA2-modified LDL (GV-LDL) to induce macrophage foam cell formation in vitro. The goal of this study was to investigate the mechanisms involved in macrophage uptake of GV-LDL. Peritoneal macrophages from C57BL/6 mice (wild type (WT)), C57BL/6 mice deficient in LDL receptor (LDLR–/–), or SR-A and CD36 (DKO) were treated with control LDL, GV-LDL, oxidized LDL (ox-LDL) or LDL aggregated by vortexing (vx-LDL). As expected, ox-LDL induced significantly more cholesterol ester accumulation in WT and LDLR–/– compared with DKO macrophages. In contrast, there was no difference in the accumulation of GV-LDL or vx-LDL in the three cell types. 125I-ox-LDL exhibited high affinity, saturable binding to WT cells that was significantly reduced in DKO cells. Vx-LDL and GV-LDL showed low affinity, non-saturable binding that was similar for both cell types, and significantly higher compared with control LDL. GV-LDL degradation in WT and DKO cells was similar. Analyses by confocal microscopy indicated a distinct intracellular distribution of Alexa-568-labeled GV-LDL and Alexa-488-labeled ox-LDL. Uptake of GV-LDL (but not ox-LDL or vx-LDL) was significantly reduced in cells preincubated with heparin or NaClO3, suggesting a role for proteoglycans in GV-LDL uptake. Our data point to a physiological modification of LDL that has the potential to promote macrophage foam cell formation independent of scavenger receptors.