Reversal of Hypercholesterolemia in Apolipoprotein E2 and Apolipoprotein E3-Leiden Transgenic Mice by Adenovirus-Mediated Gene Transfer of the VLDL Receptor

From the Department of Human Genetics, Leiden University (K.W.van D., A.van der Z., M.H.H.); TNO Prevention and Health, Gaubius Laboratory (B.J.M. van V., B.van't H., H.van der B., L.M.H.), Leiden, The Netherlands; and Departments of Cell Biology and Medicine, Baylor College of Medicine, Houston (K.K., L.C.), Tex.

Correspondence to Dr. K. Willems van Dijk, Department of Human Genetics, Leiden University, PO Box 9503, 2300 RA Leiden, Netherlands. E-mail ko{at}ruly46.medfac.leidenuniv.nl

Abstract—We have investigated the interaction of apolipoprotein E2(Arg₁₅₈-Cys) (apoE2) and apolipoprotein E3Leiden (apoE3-Leiden) with the very low density lipoprotein (VLDL) receptor in vivo and in vitro to define the possible role of this receptor in lipoprotein metabolism and atherosclerosis. The in vivo binding specificity of the VLDL receptor for apoE2 and apoE3-Leiden was investigated by adenovirus-mediated gene transfer of the VLDL receptor in apoE2 and apoE3-Leiden transgenic mice lacking endogenous mouse apoE (Apoe-/-). Ectopic overexpression of the VLDL receptor gene in the liver resulted in a >50% decrease of plasma cholesterol levels in both apoE2 and apoE3-Leiden transgenic mice compared with liver expression of the ß-galactosidase gene. This reduction in plasma cholesterol was mainly due to a reduction in the VLDL level. Overexpression of the VLDL receptor did not affect the hepatic VLDL triglyceride production, indicating that the hypocholesterolemic effect is due to an increased level of plasma clearance mediated by the VLDL receptor. In vitro binding analysis showed that both apoE2 and apoE3-Leiden VLDL compete efficiently with rabbit ß-VLDL for binding to the VLDL receptor expressed on LDL receptor–deficient Chinese hamster ovary cells. We conclude from these data that both apoE2 and apoE3-Leiden function as proper ligands for the VLDL receptor in vitro and in vivo. This finding substantiates a possible role for the VLDL receptor in atherosclerosis in hyperlipidemic subjects homozygous for apoE2 or carrying apoE3-Leiden and indicates that the VLDL receptor expressed on the liver has therapeutic potential as an alternative route for clearance of binding-defective lipoproteins.

Key Words: VLDL receptor • apoE variants • atherosclerosis • gene therapy

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