Isoform-dependent cholesterol efflux from macrophages by apolipoprotein E is modulated by cell surface proteoglycans.
OBJECTIVE
Apolipoprotein E (apoE) mediates cellular cholesterol efflux and plays a crucial role in the inhibition of atherogenesis. We investigated whether there is an isoform-specific difference in its function for cholesterol efflux from cholesterol-loaded RAW264.7 cells, a murine macrophage cell line that lacks endogenous apoE expression.


RESULTS
When human apoE was expressed in RAW264.7 cells, apoE2 reduced cellular total cholesterol (TC) and esterified cholesterol (EC) levels significantly, whereas apoE3 and apoE4 had no effect. However, treatment of cells with 4-methylumbelliferyl-7-beta-D-xyloside (beta-DX) resulted in all 3 isoforms' reducing cellular TC and EC contents significantly. We also investigated the effect of exogenously derived apoE on cholesterol efflux by utilizing the medium harvested from HeLa cells expressing apoE. ApoE2 and E3 reduced both cellular TC and EC contents significantly, whereas apoE4 did not. However, treatment of the cells with beta-DX resulted in all 3 exogenously derived apoE isoforms' reducing TC and EC contents significantly. The binding ability of apoE to heparan sulfate proteoglycans examined by heparinase I treatment revealed less binding ability of apoE2 compared with that of apoE3 or apoE4.


CONCLUSIONS
The present study clarified the differential cellular cholesterol-modulating effect of apoE isoforms in macrophages, which would be due to the difference in their binding to proteoglycans.
Hara
Masumi
M
Department of Metabolic Diseases, Graduate School of Medicine, University of Tokyo, Tokyo, Japan.
Matsushima
Teruhiko
T
Satoh
Hiroaki
H
Iso-o
Naoyuki
N
Noto
Hiroshi
H
Togo
Masako
M
Kimura
Satoshi
S
Hashimoto
Yoshiaki
Y
Tsukamoto
Kazuhisa
K
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D000954:Antigens, Surface / Q000378:metabolism; D053318:Apolipoprotein E3; D053327:Apolipoprotein E4; D001057:Apolipoproteins E / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D018014:Gene Transfer Techniques; D005822:Genetic Vectors / Q000235:genetics; D006367:HeLa Cells / Q000737:chemistry / Q000201:enzymology / Q000821:virology; D019763:Heparin Lyase / Q000378:metabolism; D006801:Humans; D008079:Lipoproteins, VLDL / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D017737:Macrophages, Peritoneal / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism* / Q000821:virology; D051379:Mice; D011509:Proteoglycans / Q000378:metabolism / Q000502:physiology*; D014162:Transfection; D014407:Tumor Cells, Cultured; D001616:beta-Galactosidase / Q000032:analysis / Q000235:genetics
D000954:Antigens, Surface; D053318:Apolipoprotein E3; D053327:Apolipoprotein E4; D001057:Apolipoproteins E; D008079:Lipoproteins, VLDL; D011509:Proteoglycans; D002784:Cholesterol; D001616:beta-Galactosidase; D019763:Heparin Lyase