Phenotype-dependent differences in apolipoprotein E metabolism and in cholesterol homeostasis in human monocyte-derived macrophages.
In this study, we investigated the impact of the common apoE polymorphism on apoE metabolism and cholesterol homeostasis in monocyte-derived macrophages isolated from E2/2, E3/3, and E4/4 subjects. Unloaded cells of all genotypes contained similar amounts of free cholesterol, cholesteryl ester, and apoE mRNA. E3/3 cells secreted 77 and 30% more apoE than E2/2 or E4/4 cells, respectively. Pulse-chase studies confirmed that the apoE secretion rate was greatest in E3/3 and least in E2/2 cells and showed that a portion of apoE2, but not apoE3 or apoE4, was degraded intracellularly. Surface binding of apoE was greatest in E4/4 cells, as revealed by heparinase treatment. On cholesterol loading with acetylated LDL, apoE mRNA levels and protein secretion rose most in E4/4 and least in E2/2 cells. Cholesterol and cholesteryl ester content, however, rose most in E2/2 and least in E3/3 cells. Incubations with 3H-cholesterol-labeled acetylated LDL revealed that E2/2 cells were most efficient at secreting cholesterol. The greatest reuptake of 3H-cholesterol-rich particles was from E4/4 macrophage- conditioned media. Thus, E2/2 macrophages, despite a low apoE secretion rate, are protected from cholesterol storage by apoE-mediated cholesterol efflux. In E3/3 macrophages, cholesterol accumulation is lessened by a high basal apoE secretion rate. E4/4 macrophages secrete the most apoE but lack effective net cholesterol efflux due to enhanced surface binding and reuptake of cholesterol-rich particles.
Cullen
P
P
Institut für Arterioskleroseforschung, Westfälische Wilhelms-Universität, 48149 Münster, Germany. cullen@uni-muenster.de
Cignarella
A
A
Brennhausen
B
B
Mohr
S
S
Assmann
G
G
von Eckardstein
A
A
D000328:Adult; D000544:Alzheimer Disease / Q000209:etiology / Q000235:genetics / Q000378:metabolism; D001057:Apolipoproteins E / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D001161:Arteriosclerosis / Q000209:etiology / Q000235:genetics / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism*; D002788:Cholesterol Esters / Q000378:metabolism; D005260:Female; D005487:Foam Cells / Q000378:metabolism; D015870:Gene Expression; D019763:Heparin Lyase / Q000494:pharmacology; D006706:Homeostasis; D006801:Humans; D066298:In Vitro Techniques; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009000:Monocytes / Q000378:metabolism; D010641:Phenotype; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013498:Suramin / Q000494:pharmacology
D001057:Apolipoproteins E; D002788:Cholesterol Esters; D012333:RNA, Messenger; D013498:Suramin; D002784:Cholesterol; D019763:Heparin Lyase