In the Absence of Endogenous Mouse Apolipoprotein E, Apolipoprotein E2(Arg-158 → Cys) Transgenic Mice Develop More Severe Hyperlipoproteinemia than Apolipoprotein E3-Leiden Transgenic Mice

• Published in: The Journal of biological chemistry Vol. 271; no. 48; pp. 30595 - 30602
• Main Authors: van Vlijmen, Bart J.M., van Dijk, Ko Willems, van't Hof, H. Belinda, van Gorp, Patrick J.J., van der Zee, André, van der Boom, Hans, Breuer, Marco L., Hofker, Marten H., Havekes, Louis M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 29-11-1996; American Society for Biochemistry and Molecular Biology
• Subjects: adenovirus; animal transgenique; animales transgenicos; Animals; Apolipoproteins E - physiology; Arginine - chemistry; blood lipids; catabolism; catabolisme; catabolismo; Cells, Cultured; chemoreceptors; chimiorecepteur; cholesterol; colesterol; consommation alimentaire; consumo de alimentos; corps gras; Cysteine - chemistry; diet; dieta; fats; food consumption; genero humano; Genes, Dominant; genre humain; grasas; hemolipidos; Heymann Nephritis Antigenic Complex; hiperlipidemia; hyperlipidaemia; hyperlipidemie; Hyperlipoproteinemias - genetics; lipide sanguin; lipoproteinas; lipoproteine; lipoproteins; Lipoproteins, LDL - metabolism; Lipoproteins, VLDL - metabolism; mankind; Membrane Glycoproteins - metabolism; Mice; Mice, Knockout; Mice, Transgenic; mutant; mutantes; mutants; quimioreceptores; raton; Receptors, LDL - metabolism; regime alimentaire; souris; transgenic animals; trigliceridos; triglyceride; triglycerides
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.271.48.30595

Apolipoprotein E*2(Arg-158 → Cys) (APOE*2) transgenic mice were generated and compared to the previously generated apolipoprotein E*3-Leiden (APOE*3-Leiden) transgenic mice to study the variable expression of hyperlipoproteinemia associated with these two APOE variants. In the presence of the endogenous mouse Apoe gene, the expression of the APOE*3-Leiden gene resulted in slightly elevated levels of serum cholesterol as compared with control mice (2.7 ± 0.5 versus 2.1 ± 0.2 mmol/liter, respectively), whereas the expression of the APOE*2(Arg-158 → Cys) gene did not affect serum cholesterol levels, even after high/fat cholesterol feeding. The extreme cholesterol level usually found in apoE-deficient mice (Apoe−/− mice; 23.6 ± 5.0 mmol/liter) could be rescued by introducing the APOE*3-Leiden gene (APOE*3-Leiden·;Apoe−/−; 3.6 ± 1.5 mmol/liter), whereas the expression of the APOE*2(Arg-158 → Cys) gene in Apoe−/− mice minimally reduced serum cholesterol levels (APOE*2·;Apoe−/−; 16.6 ± 2.9 mmol/liter). In vivo very low density lipoprotein (VLDL) turnover studies revealed that APOE*2·;Apoe−/− VLDL and APOE*3-Leiden·;Apoe−/− VLDL display strongly reduced fractional catabolic rates as compared with control mouse VLDL (4.0 and 6.1 versus 22.1 pools/h). In vitro low density lipoprotein (LDL) receptor binding studies using HepG2 and J774 cells showed that APOE*2·; Apoe−/− VLDL is completely defective in binding to the LDL receptor, whereas APOE*3-Leiden·;Apoe−/− VLDL still displayed a considerable binding activity to the LDL receptor. After transfection of APOE*2·;Apoe−/− and APOE*3-Leiden·;Apoe−/− mice with adenovirus carrying the gene for the receptor-associated protein (AdCMV-RAP), serum lipid levels strongly increased (15.3 to 42.8 and 1.4 to 15.3 mmol/liter for cholesterol and 5.0 to 35.7 and 0.3 to 20.7 mmol/liter for triglycerides, respectively). This indicates that RAP-sensitive receptors, possibly the LDL receptor-related protein (LRP), mediate the plasma clearance of both APOE*2·;Apoe−/− and APOE*3-Leiden·; Apoe−/− VLDL.
We conclude that in vivo the APOE*2 variant is completely defective in LDL receptor binding but not in binding to LRP, whereas for the APOE*3-Leiden mutant both LRP and LDL receptor binding activity are only mildly affected. As a consequence of this difference, APOE*2·;Apoe−/− develop more severe hypercholesterolemia than APOE*3-Leiden·;Apoe−/− mice.