Pathways by which reconstituted high-density lipoprotein mobilizes free cholesterol from whole body and from macrophages.
OBJECTIVE
Reconstituted high-density lipoprotein (rHDL) is of interest as a potential novel therapy for atherosclerosis because of its ability to promote free cholesterol (FC) mobilization after intravenous administration. We performed studies to identify the underlying molecular mechanisms by which rHDL promote FC mobilization from whole body in vivo and macrophages in vitro.


RESULTS
Wild-type (WT), SR-BI knockout (KO), ABCA1 KO, and ABCG1 KO mice received either rHDL or phosphate-buffered saline intravenously. Blood was drawn before and at several time points after injection for apolipoprotein A-I, phosphatidylcholine, and FC measurement. In WT mice, serum FC peaked at 20 minutes and rapidly returned toward baseline levels by 24 hours. Unexpectedly, ABCA1 KO and ABCG1 KO mice did not differ from WT mice regarding the kinetics of FC mobilization. In contrast, in SR-BI KO mice the increase in FC level at 20 minutes was only 10% of that in control mice (P<0.01). Bone marrow-derived macrophages from WT, SR-BI O, ABCA1 KO, and ABCG1 KO mice were incubated in vitro with rHDL and cholesterol efflux was determined. Efflux from SR-BI KO and ABCA1 KO macrophages was not different from WT macrophages. In contrast, efflux from ABCG1 KO macrophages was approximately 50% lower as compared with WT macrophages (P<0.001).


CONCLUSIONS
The bulk mobilization of FC observed in circulation after rHDL administration is primarily mediated by SR-BI. However, cholesterol mobilization from macrophages to rHDL is primarily mediated by ABCG1.
Cuchel
Marina
M
Institute for Translational Medicine and Therapeutics, University of Pennsylvania School of Medicine, Maloney Building, Room 8039, 3600 Spruce Street, Philadelphia, PA 19104, USA. mcuchel@mail.med.upenn.edu
Lund-Katz
Sissel
S
de la Llera-Moya
Margarita
M
Millar
John S
JS
Chang
David
D
Fuki
Ilia
I
Rothblat
George H
GH
Phillips
Michael C
MC
Rader
Daniel J
DJ
D064286:ATP Binding Cassette Transporter 1; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism*; D007275:Injections, Intravenous; D008074:Lipoproteins / Q000235:genetics / Q000378:metabolism*; D008075:Lipoproteins, HDL / Q000008:administration & dosage / Q000494:pharmacology*; D008264:Macrophages / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D023421:Models, Animal; D051122:Scavenger Receptors, Class B / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
C487540:ABCG1 protein, mouse; D064286:ATP Binding Cassette Transporter 1; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters; D008074:Lipoproteins; D008075:Lipoproteins, HDL; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B; D002784:Cholesterol