Retention of oxidized LDL by extracellular matrix proteoglycans leads to its uptake by macrophages: an alternative approach to study lipoproteins cellular uptake.
Interaction between arterial macrophages and oxidized LDL (Ox-LDL) leads to foam cell formation, a critical step during early atherogenesis. Until now, cellular uptake of lipoproteins was studied through incubation of the media-soluble lipoprotein with cultured macrophages. However, as lipoproteins in the arterial wall are bound to subendothelial matrix, we questioned whether the retention (binding) of Ox-LDL to a macrophage-derived extracellular matrix (ECM) could lead to enhanced uptake by macrophages. The uptake of ECM-bound Ox-LDL by activated macrophages (by phorbol myristate acetate) was lipoprotein dose dependent, time dependent and higher (by 1.5-fold) than the uptake of ECM-bound native LDL. Preincubation of the ECM with lipoprotein lipase before the addition of Ox-LDL was essential for the uptake of ECM-bound Ox-LDL by the macrophages. After radiolabeling of the ECM glycosaminoglycans (GAGs), we found that ECM-bound Ox-LDL is taken up by the macrophages together with the ECM-GAG. Finally, these results were further confirmed through the use of ECM obtained from mouse peritoneal macrophages (MPMs), derived from atherosclerotic, apoE-deficient mice. In 24-week-old mice with developed atherosclerosis, the GAG content of their MPM-derived ECM increased by 52%, the ability of their MPM-derived ECM to bind Ox-LDL increased by 57%, and macrophage uptake of Ox-LDL that was retained by the MPM-derived ECM increased by 86%. In conclusion, the present study demonstrated that ECM-bound Ox-LDL is taken up by activated macrophages. This may represent a physiopathological phenomenon that leads to cholesterol and oxysterol accumulation in arterial macrophages, the hallmark of early atherosclerosis.
Kaplan
M
M
Lipid Research Laboratory, Bruce Rappaport Faculty of Medicine, Technion, The Rappaport Family Institute for Research in the Medical Sciences and Rambam Medical Center, Haifa, Israel.
Aviram
M
M
D000375:Aging; D000818:Animals; D001057:Apolipoproteins E / Q000172:deficiency / Q000235:genetics; D002460:Cell Line; D005109:Extracellular Matrix / Q000378:metabolism*; D006025:Glycosaminoglycans / Q000378:metabolism / Q000493:pharmacokinetics; D008070:Lipopolysaccharides / Q000494:pharmacology; D008071:Lipoprotein Lipase / Q000378:metabolism; D008074:Lipoproteins / Q000378:metabolism / Q000493:pharmacokinetics; D008077:Lipoproteins, LDL / Q000378:metabolism* / Q000493:pharmacokinetics; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D010084:Oxidation-Reduction; D011485:Protein Binding; D011509:Proteoglycans / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D001057:Apolipoproteins E; D006025:Glycosaminoglycans; D008070:Lipopolysaccharides; D008074:Lipoproteins; D008077:Lipoproteins, LDL; D011509:Proteoglycans; C099252:oxidized low density lipoprotein; D008071:Lipoprotein Lipase; D013755:Tetradecanoylphorbol Acetate