Molecular etiology of a dominant form of type III hyperlipoproteinemia caused by R142C substitution in apoE4

Abstract

clearance of lipoprotein remnants from the circulation and is essential for atheroprotection ( 1-3 ).Lipoprotein-bound apoE is the ligand for the LDL receptor as well as other receptors in vitro ( 4-6 ). In vivo and in vitro studies have shown that mutations in apoE that diminish binding of apoE-containing lipoproteins to the LDL receptor are associated with high plasma cholesterol levels and cause premature atherosclerosis in humans and experimental animals ( 1-3, 7, 8 ). Most recently we have shown that apoE is involved in the biogenesis of distinct apoE-containing HDL species with the participation of the ABCA1 lipid transporter and lecithin cholesterol acyltransferase (LCAT) ( 9 ).Certain apoE phenotypes and genotypes are associated with recessive or dominant forms of type III hyperlipoproteinemia (HLP). The recessive form of type III HLP is encountered in subjects with the E2/2 phenotype which results from the substitution of Cys for . This mutation combined with other genetic or environmental factors affects the catabolism of apoE-containing lipoproteins and results in the accumulation in plasma of remnants of lipopro tein catabolism ( 7, 11 ). A variety of rare mutations in the 136-147 region of apoE are associated with a dominant mode of inheritance of type III HLP that is expressed at an early age ( 7,8,12,13 ). The degree of penetrance of the disease varies depending on the mutation ( 7 ).In the present study we investigated the molecular etiology of a dominant form of type III HLP caused by the R142C substitution in apoE4. Using adenovirusmediated gene transfer in apoE

apoE3[K146N/R147W] acts as a dominant negative apoE form that prevents remnant clearance and inhibits the biogenesis of HDL

“…The low levels of triglycerides when the truncated apoE3[K146N/R147W]202 form is overexpressed (Fig. 1B) supports the concept that induction of hypertriglyceridemia requires the C-terminal domain of apoE, as shown previously ( 34,35 ). The decrease in plasma apoE of the truncated relative to the fulllength apoE mutant on day 4 (Fig.…”

“…Hypertriglyceridemia was prevented but hypercholesterolemia persisted when the C-terminal 203-299 residues of the apoE3[K146N/R147W] mutant were deleted. The inability of the truncated apoE3[K146N/R147W]202 mutant to clear plasma cholesterol is unique to this mutant and was not observed in previous studies using apoE-202 truncations of other normal apoE isoforms, as well as apoE4 [R142C] that is associated with a dominant form of type III HLP ( 34,35 ). The fi ndings suggest that the apoE3 [K146N/R147W] mutant acts as a dominant negative ligand that blocks clearance of the lipoprotein remnants and inhibits the maturation of apoA-I-containing HDL particles.…”

“…1A-C ). The inability of this truncated apoE3[K146N/ R147W]202 form to clear plasma cholesterol in apoE Ϫ / Ϫ mice, differentiates this mutant from all the apoE truncated forms studied previously, which cleared plasma cholesterol but did not induce hypertriglyceridemia ( 34,35,44 ). In contrast to the inability of the truncated forms to induce hypertriglyceridemia, even when they are expressed at high levels, previous studies showed that overexpression of full-length apoE forms induced severe hypertriglyceridemia and did not clear the plasma cholesterol in apoE ( 35,44 ).…”

“…The combined data established that the amino terminal 1-202 or 1-184 domains of apoE are effi cient ligands for the LDL receptor ( 34,48,61 ).…”

Alteration of negatively charged residues in the 89 to 99 domain of apoA-I affects lipid homeostasis and maturation of HDL

“…The recombinant adenoviruses were packaged in 911 cells, amplifi ed in human embryonic kidney 293 (HEK 293) cells, purifi ed, and titrated as described ( 10 ). The adenovirus expressing human lipoprotein lipase (hLPL) was a gift of Dr. Alex Vezeridis ( 17 ).…”