SR-BI-mediated high density lipoprotein (HDL) endocytosis leads to HDL resecretion facilitating cholesterol efflux.
The high density lipoprotein (HDL) receptor, scavenger receptor class B, type I (SR-BI), mediates selective cholesteryl ester uptake from lipoproteins into liver and steroidogenic tissues but also cholesterol efflux from macrophages to HDL. Recently, we demonstrated the uptake of HDL particles in SR-BI overexpressing Chinese hamster ovarian cells (ldlA7-SRBI) using ultrasensitive microscopy. In this study we show that this uptake of entire HDL particles is followed by resecretion. After uptake, HDL is localized in endocytic vesicles and organelles en route to the perinuclear area; many HDL-positive compartments were classified as multivesiculated and multilamellated organelles by electron microscopy. By using 125I-labeled HDL, we found that approximately 0.8% of the HDL added to the media is taken up by the ldlA7-SRBI cells within 1 h, and almost all HDL is finally resecreted. 125I-Labeled low density lipoprotein showed a very similar association, uptake, and resecretion pattern in ldlA7-SRBI cells that do not express any low density lipoprotein receptor. Moreover, we demonstrate that the process of HDL cell association, uptake, and resecretion occurs in three physiologically relevant cell systems, the liver cell line HepG2, the adrenal cell line Y1BS1, and phorbol myristate acetate-differentiated THP-1 cells as a model for macrophages. Finally, we present evidence that HDL retroendocytosis represents one of the pathways for cholesterol efflux.
Center for Physiology and Pathophysiology, Department of Medical Chemistry, Medical University of Vienna, Währingerstrasse 10, A-1090 Vienna, Austria.
Tamara A
TA
Pagler
Sebastian
S
Rhode
Angelika
A
Neuhofer
Hildegard
H
Laggner
Wolfgang
W
Strobl
Claudia
C
Hinterndorfer
Ivo
I
Volf
Margit
M
Pavelka
Erik R M
ER
Eckhardt
Deneys R
DR
van der Westhuyzen
Gerhard J
GJ
Schütz
Herbert
H
Stangl
D000818:Animals; D018955:CD36 Antigens / Q000378:metabolism / Q000502:physiology*; D016466:CHO Cells; D002460:Cell Line; D002738:Chloroquine / Q000494:pharmacology; D002784:Cholesterol / Q000737:chemistry / Q000378:metabolism; D002788:Cholesterol Esters / Q000378:metabolism; D003102:Colloids / Q000737:chemistry; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism; D005089:Exocytosis; D005434:Flow Cytometry; D006801:Humans; D008074:Lipoproteins / Q000378:metabolism; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D011485:Protein Binding; D013997:Time Factors
D018955:CD36 Antigens; D002788:Cholesterol Esters; D003102:Colloids; D008074:Lipoproteins; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D002738:Chloroquine; D002784:Cholesterol