The high concentration of low-density lipoprotein in the plasma is the major risk factor of atherosclerosis. On the other hand, another plasma lipoprotein—high-density lipoprotein (HDL) — is inversely correlated with atherosclerosis. Recent studies have demonstrated that HDL mediates the transport of cholesterol from peripheral tissues to the liver through “reverse cholesterol transport” pathway. However there is considerable debate about the mechanisms by which HDL removes excess cholesterol from cells. Two different pathways were suggested: (i) a docking receptor promoting cholesterol translocation, or (ii) a receptor mediated intracellular endosomal pathway termed “retroendocytosis”. In the present study, we performed fluorescence and electron microscopy to visualize the uptake of HDL using cholesterol-load rat aortic endothelial and smooth muscle cells in vitro.

Endothelial and smooth muscle cells were obtained from rat aorta and cultured in medium under 5% CO2/ 95% air atmosphere. Then confluent monolayers of endothelial and smooth muscle cells were incubated in cholesterol or fluorescence-labeled cholesterol DMEM medium for 48 hr.