Different cellular traffic of LDL-cholesterol and acetylated LDL-cholesterol leads to distinct reverse cholesterol transport pathways.
Endocytosis of LDL and modified LDL represents regulated and unregulated cholesterol delivery to macrophages. To elucidate the mechanisms of cellular cholesterol transport and egress under both conditions, various primary macrophages were labeled and loaded with cholesterol or cholesteryl ester from LDL or acetylated low density lipoprotein (AcLDL), and the cellular cholesterol traffic pathways were examined. Confocal microscopy using fluorescently labeled 3,3'-dioctyldecyloxacarbocyanine perchlorate-labeled LDL and 1,1'-dioctyldecyl-3,3,3',3'-tetramethylindodicarbocyanine perchlorate-labeled AcLDL demonstrated their discrete traffic pathways and accumulation in distinct endosomes. ABCA1-mediated cholesterol efflux to apolipoprotein A-I (apoA-I) was much greater for AcLDL-loaded macrophages compared with LDL. Treatment with the liver X receptor ligand 22-OH increased efflux to apoA-I in AcLDL-loaded but not LDL-loaded cells. In contrast, at a level equivalent to AcLDL, LDL-derived cholesterol was preferentially effluxed to HDL, in keeping with increased ABCG1. In vivo studies of reverse cholesterol transport (RCT) from cholesterol-labeled macrophages injected intraperitoneally demonstrated that LDL-derived cholesterol was more efficiently transported to the liver and secreted into bile than AcLDL-derived cholesterol. This indicates a greater efficiency of HDL than lipid-poor apoA-I in interstitial fluid in controlling in vivo RCT. These assays, taken together, emphasize the importance of mediators of diffusional cholesterol efflux in RCT.
Wang
Ming-Dong
MD
Lipoprotein and Atherosclerosis Research Group, University of Ottawa Heart Institute, and Department of Biochemistry, University of Ottawa, Ottawa, Ontario, Canada.
Kiss
Robert S
RS
Franklin
Vivian
V
McBride
Heidi M
HM
Whitman
Stewart C
SC
Marcel
Yves L
YL
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D001692:Biological Transport; D015153:Blotting, Western; D051242:Caveolin 1 / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism*; D008078:Cholesterol, LDL / Q000378:metabolism*; D005260:Female; D047908:Intracellular Signaling Peptides and Proteins; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D000077296:Niemann-Pick C1 Protein; D011506:Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D011973:Receptors, LDL / Q000235:genetics / Q000378:metabolism / Q000502:physiology
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D051242:Caveolin 1; D008078:Cholesterol, LDL; D047908:Intracellular Signaling Peptides and Proteins; D008077:Lipoproteins, LDL; D000077296:Niemann-Pick C1 Protein; C106831:Npc1 protein, mouse; D011506:Proteins; D011973:Receptors, LDL; C032629:acetyl-LDL; D002784:Cholesterol