Interaction of atherogenic lipoproteins with cultured cells: a confocal laser scanning microscopy study

Low density lipoprotein (LDL) and lipoprotein (a) [Lp(a)] were covalently labeled with the fluorescent dyes BODIPY succinimidyl ester (green) or Rhodamine iodoacetamide (red). The interaction of the fluorescent lipoproteins with HepG2 cells was visualized by means of a confocal laser scanning fluorescence microscope operating in the dual wavelength mode. If LDL or Lp(a) were incubated with the cells both lipoproteins bound to the cell surface at 4 degree(s)C or were internalized by the cells at 37 degree(s)C. In all cases larger amounts of LDL interacted with the cells compared with Lp(a). When mixtures of LDL and Lp(a), each labeled with a different dye, were incubated with cells again both lipoproteins bound to the cell surface (4 degree(s)C) or were internalized by the cells (37 degree(s)C). In addition, the major part of the lipoproteins colocalized either on the cell surface or inside the cells. thus, we conclude that interactions of Lp(a) with cells is mediated by LDL, probably via the LDL receptor, to a large extent.