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.
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.
Boyanovsky
Boris B
BB
Department of Internal Medicine and Veterans Affairs Medical Center, Graduate Center for Nutritional Sciences, University of Kentucky Medical Center, Lexington, Kentucky 40536-0200, USA.
van der Westhuyzen
Deneys R
DR
Webb
Nancy R
NR
D000818:Animals; D001391:Azo Compounds / Q000494:pharmacology; D018955:CD36 Antigens / Q000096:biosynthesis*; D002788:Cholesterol Esters / Q000378:metabolism; D004396:Coloring Agents / Q000494:pharmacology; D003433:Crosses, Genetic; D005260:Female; D005456:Fluorescent Dyes / Q000494:pharmacology; D005487:Foam Cells / Q000378:metabolism*; D054505:Group V Phospholipases A2; D006493:Heparin / Q000378:metabolism; D006801:Humans; D006834:Hydrazines / Q000494:pharmacology; D006868:Hydrolysis; D050356:Lipid Metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D008958:Models, Molecular; D010537:Peritoneum / Q000378:metabolism; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011485:Protein Binding; D011509:Proteoglycans / Q000378:metabolism*; D014162:Transfection
C417561:Alexa 488 hydrazide; D001391:Azo Compounds; D018955:CD36 Antigens; D002788:Cholesterol Esters; D004396:Coloring Agents; D005456:Fluorescent Dyes; D006834:Hydrazines; D008077:Lipoproteins, LDL; D011509:Proteoglycans; D006493:Heparin; D010741:Phospholipases A; D054505:Group V Phospholipases A2; C516299:PLA2G5 protein, human; D054467:Phospholipases A2; C516300:Pla2g5 protein, mouse; C011049:oil red O