Binding, internalization and transport of apolipoprotein A-I by vascular endothelial cells.
High density lipoproteins (HDL) and their main protein constituent, apolipoprotein A-I (apoA-I), exert potentially anti-atherogenic properties within the arterial wall. However, it is unknown how they are transported from the blood stream into the vascular wall. Here we investigated the interaction of apoA-I with endothelial cells. At 4 degrees C endothelial cells bound 125I-apoA-I with high affinity, Kd = 2.1 microg/ml and in a saturable manner (Bmax of 35 ng/mg cell protein). At 37 degrees C, the cell association of apoA-I revealed similar affinity as at 4 degrees C (Kd = 2.2 microg/ml) but the maximum specific cell association was much enhanced (Bmax = 360 ng/mg cell protein). Binding and cell association was competed by excess unlabeled apoA-I and HDL but not by albumin. Biotinylation experiments and electron microscopy studies showed that endothelial cells internalize labeled apoA-I. Only minor amounts of the internalized apoA-I were degraded. Cultivated in a Transwell system, the cells transported a fraction of 125I-apoA-I from the apical to the basolateral compartment in a competable and temperature-sensitive manner. Furthermore, after specific transport the originally prebeta-mobile and lipid-free apoA-I was recovered as particles which have electrophoretic alpha-mobility. We conclude that endothelial cells transcytose and lipidate lipid-free apoA-I.
Institute of Clinical Chemistry, University Hospital Zurich and Center for Integrative Human Physiology, University Zurich, Raemistrasse 100, CH-8091 Zürich, Switzerland.
Lucia
L
Rohrer
Clara
C
Cavelier
Séverine
S
Fuchs
Marc Alexander
MA
Schlüter
Wolfgang
W
Völker
Arnold
A
von Eckardstein
D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism*; D001693:Biological Transport, Active; D002417:Cattle; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D008075:Lipoproteins, HDL / Q000378:metabolism; D008854:Microscopy, Electron
D016632:Apolipoprotein A-I; D008075:Lipoproteins, HDL