Journal of Lipid Research, Vol 27, 892-900, Copyright © 1986 by Lipid Research, Inc.
Recognition of vesicular lipoproteins by the apolipoprotein B,E receptor of cultured fibroblasts
KJ Williams, AR Tall, I Tabas and C Blum
Vesicular lipoproteins (e.g., lipoprotein-X) are found in plasma in
cholestasis or following infusion of Intralipid or phospholipid. To
investigate the metabolism of vesicular lipoproteins, we isolated them from
the plasma of subjects with cholestasis or following chronic or single
Intralipid infusion. Cholestasis and chronic Intralipid therapy were found
to be associated with elevated plasma concentrations of apoE, as determined
by radioimmunoassay. Vesicular lipoproteins purified from each of the three
types of plasma contained apoE, as well as other proteins. In cholestasis,
in which levels of apoE were up to five times normal, a major portion of
the plasma apoE was on vesicular lipoproteins. Normalized for apoE content,
all preparations of vesicular lipoproteins displaced 125I-labeled LDL from
apoB,E receptors of cultured fibroblasts identically. This displacement was
inhibited by monoclonal antibodies that block receptor binding of apoE.
Vesicular lipoproteins containing 125I-labeled apoE were internalized and
degraded by fibroblasts. Different preparations caused small losses or
gains of cellular cholesterol, with appropriate stimulation or suppression
of apoB,E receptors. Thus, vesicular lipoproteins contain apoE, and apoE
mediates their interaction with the apoB,E receptor. Our results suggest
that the catabolism of cholesterol-rich vesicular lipoproteins, formed
during cholestasis or following infusions of Intralipid or phospholipid,
may be receptor-mediated.
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