In the absence of endogenous mouse apolipoprotein E, apolipoprotein E*2(Arg-158 --> Cys) transgenic mice develop more severe hyperlipoproteinemia than apolipoprotein E*3-Leiden transgenic mice.
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.
van Vlijmen
B J
BJ
TNO Prevention and Health, Gaubius Laboratory, 2301 CE Leiden, The Netherlands. lm.havekes@pg.tno.nl
van Dijk
K W
KW
van't Hof
H B
HB
van Gorp
P J
PJ
van der Zee
A
A
van der Boom
H
H
Breuer
M L
ML
Hofker
M H
MH
Havekes
L M
LM
D000818:Animals; D001057:Apolipoproteins E / Q000502:physiology*; D001120:Arginine / Q000737:chemistry; D002478:Cells, Cultured; D003545:Cysteine / Q000737:chemistry; D005799:Genes, Dominant; D026541:Heymann Nephritis Antigenic Complex; D006951:Hyperlipoproteinemias / Q000235:genetics*; D008077:Lipoproteins, LDL / Q000378:metabolism; D008079:Lipoproteins, VLDL / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D011973:Receptors, LDL / Q000378:metabolism
D001057:Apolipoproteins E; D026541:Heymann Nephritis Antigenic Complex; D008077:Lipoproteins, LDL; D008079:Lipoproteins, VLDL; D008562:Membrane Glycoproteins; D011973:Receptors, LDL; D001120:Arginine; D003545:Cysteine