Role of endothelial cell mitosis in transendothelial transport of low density lipoprotein in hypercholesterolemic and normal rabbits

Abstract

Background: Atherosclerosis is characterized by focal areas of lipid accumulation and intimal smooth muscle cell proliferation in large arteries. It has been suggested that the permeability of arterial endothelium to lipid is an important factor in the initiation and progression of atherosclerosis. The mechanism by which macromolecules such as low density lipoprotein (LDL) enter the arterial wall, however, is still not completely understood. Our previous studies have demonstrated that there is close association of endothelial cell turnover with transendothelial macromolecular transport in normal rat aorta. Because hypercholesterolemia has been well documented as one of the major risk factors for atherosclerosis, we explore the relationship between endothelial cell mitosis and transendothelial transport of LDL in hypercholesterolemic rabbits.

Methods: The present study is designed to perform on thoracic aortae from 30 male New Zealand white rabbits fed with either 1% cholesterol-enriched diet (HC group; n = 15) or normal diet (NC group; n = 15). The concentrations of serum cholesterol and triglycerides from two groups were measured by enzymatic procedures using commercial kits. The aortae of hypercholesterolemic and normocholesterolemic rabbits underwent perfusion-fixation 10 min following the intravenous injection of low density lipoprotein conjugated with Lucifer yellow (LY-LDL) for fluorescence microscopy. En face preparations of the thoracic aortae stained with hematoxylin allowed the identification of ECs in mitosis. The relationship between LY-LDL leakage and endothelial cell mitosis was determined.

Results: Although endothelial cell mitosis is infrequent (NC: 0.0022 +/- 0.0007%; HC: 0.0004 +/- 0.0001%) in the thoracic aorta of New Zealand white rabbits, 68.2 +/- 8.4% (NC) or 74.3 +/- 9.0% (HC) of dividing cells in the M phase were associated with LYLDL leakage. These dividing cells accounted for 65.0 +/- 9.2% (NC) or 64.4 +/- 11.3% (HC) of all LY-LDL leaky spots.

Conclusions: Thus, this study not only confirmed the close association of EC mitosis with macromolecular permeability in normal group, but also demonstrated that the same relationship existed in hypercholesterolemic rabbits. These observations lend support to the theory that transiently open junctions surrounding the endothelial cells undergoing cell turnover provide pathways through which LDL enters the subendothelial space, resulting in lipid accumulation and atherosclerosis.