Hypercholesterolemia in Low Density Lipoprotein Receptor Knockout Mice and Its Reversal by Adenovirus-mediated Gene Delivery

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We employed homologous recombination in embryonic stem cells to produce mice lacking functional LDL receptor genes.Homozygous male and female mice lacking LDL receptors (LDLR-/- mice) were viable and fertile. Total plasma cholesterol levels were twofold higher than those of wild-type littermates, owing to a seven- to ninefold increase in intermediate density lipoproteins (IDL) and LDL without a significant change in HDL. Plasma triglyceride levels were normal. The half-lives for intravenously administered Iodine-125-VLDL and Iodine-125-LDL were prolonged by 30-fold and 2.5-fold, respectively, but the clearance of Iodine-125-HDL was normal in the LDLR-/- mice. Unlike wild-type mice, LDLR-/- mice responded to moderate amounts of dietary cholesterol (0.2% cholesterol/10% coconut oil) with a major increase in the cholesterol content of IDL and LDL particles. The elevated IDL/LDL level of LDLR-/- mice was reduced to normal 4 d after the intravenous injection of a recombinant replication-defective adenovirus encoding the human LDL receptor driven by the cytomegalovirus promoter. The virus restored expression of LDL receptor protein in the liver and increased the clearance of Iodine-125-VLDL. We conclude that the LDL receptor is responsible in part for the low levels of VLDL, IDL, and LDL in wild-type mice and that adenovirus-encoded LDL receptors can acutely reverse the hypercholesterolemic effects of LDL receptor deficiency. (J. Clin. Invest. 1993. 92:883-893.) Key words: homologous recombination. lipoprotein metabolism. very low density lipoprotein. gene therapy. liver receptors

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