IN THE ABSENCE OF ENDOGENOUS MOUSE APOLIPOPROTEIN-E, APOLIPOPROTEIN E-ASTERISK-2(ARG-158-]CYS) TRANSGENIC MICE DEVELOP MORE SEVERE HYPERLIPOPROTEINEMIA THAN APOLIPOPROTEIN E-ASTERISK-3-LEIDEN TRANSGENIC MICE

Apolipoprotein E2(Arg-158 --> Cys) (APOE*2) transgenic mice were gene rated and compared to the previously generated apolipoprotein E3-Leid en (APOE3-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 cholester ol as compared with control mice (2.7 +/- 0.5 versus 2.1 +/- 0.2 mmol/ liter, respectively), whereas the expression of the APOE2 (Arg-158 -- > Cys) gene did not affect serum cholesterol levels, even after high/f at cholesterol-feeding, The extreme cholesterol level usually found in apoE-deficient mice (Apoe(-/-) mice; 23.6 +/- 5.0 mmol/liter) could b e rescued by introducing the APOE3-Leiden gene (APOE*3-Leiden . Apoe( -/-); 3.6 +/- 1.5 mmol/liter), whereas the expression of the APOE2(Ar g-158 --> Cys) gene in Apoe(-/-) mice minimally reduced serum choleste rol levels (APOE2 . Apoe(-/-); 16.6 +/- 2.9 mmol/liter), In vivo very low density lipoprotein (VLDL) turnover studies revealed that APOE2 . Apoe(-/-) VLDL and APOE3-Leiden . Apoe(-/-) VLDL display strongly r educed fractional catabolic rates as compared with control mouse VLDL (4.0 and 6.1 versus 22.1 pools/h), In vitro low density lipoprotein (L DL) receptor binding studies using HepG2 and J774 cells showed that AP OE2 . Apoe(-/-) VLDL is completely defective in binding to the LDL re ceptor, whereas APOE3-Leiden . Apoe(-/-) VLDL still displayed a consi derable binding activity to the LDL receptor, After transfection of AP OE(2) . Apoe(-/-) and APOE*3-Leiden . Apoe(-/-) mice with adenovirus carrying the gene for the receptor-associated protein (AdCMV-RAP), ser um 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 t riglycerides, respectively), This indicates that RAP-sensitive recepto rs, possibly the LDL receptor-related protein (LRP), mediate the plasm a clearance of both APOE2 . Apoe(-/-) and APOE*3-Leiden . Apoe(-/-) V LDL. We conclude that in vivo the APOE2 variant is completely defecti ve in LDL receptor binding but not in binding to LRP, whereas for the APOE3-Leiden mutant both LRP and LDL receptor binding activity are on ly mildly affected. As a consequence of this difference, APOE2 . Apoe (-/-) develop more severe hypercholesterolemia than APOE3-Leiden . Ap oe(-/-) mice.