Native and acetylated low density lipoprotein metabolism in proliferating and quiescent XXXX endothelial cells in culture.

@entity17638 @entity291 @entity941 @entity9717
Lipoprotein binding and metabolism in actively dividing (sparse) and quiescent (confluent) @entity291 aortic endothelial cells (EC) were compared quantitatively using 125I-labelled lipoproteins. The amounts of receptor-bound low density lipoproteins (LDL) decreased five- to ten-fold as the cultures progressed from sparse to confluent morphology. High affinity receptor-bound LDL levels were extremely low in confluent EC and accounted for the inability of confluent EC to internalize and degrade significant amounts of LDL. Conversely, the amounts of acetylated LDL (acLDL) bound and degraded via distinct sites increased at least five-fold during EC growth to confluence. LDL binding and metabolism in individual cells was assessed by fluorescence microscopy using @entity9717 -labelled lipoproteins or @entity941 -conjugated antibodies. LDL and acLDL bound to the surfaces of sparse EC, at either 4 degrees or 37 degrees C, in a random distribution of fine punctate foci, contrary to a previous report. EC therefore appear to resemble fibroblasts in their distribution of surface LDL receptors. No binding or uptake of LDL was seen in confluent EC. Patterns of acLDL binding and uptake in confluent EC resembled those of LDL in sparse EC. Intracellular LDL and acLDL occurred as perinuclear accumulations of large fluorescent foci in sparse EC. Regeneration experiments were carried out in artificially wounded confluent cultures and renewed @entity17638 activity was shown in actively-dividing cells which had migrated into the "wounded" areas. We conclude that quiescent endothelial cells metabolize little LDL via the @entity17638 pathway due to a drastically reduced number of receptors in confluent cells. This contrasts with the ability of confluent cells to metabolize relatively large amounts of acLDL via a receptor-mediated mechanism.
