title: Harmful effects of increased LDLR expression in mice with human APOE*4 but not APOE*3.
abstract: OBJECTIVE
  Increased expression of the low-density lipoprotein receptor (LDLR) is generally considered beneficial for reducing plasma cholesterol and atherosclerosis, and its downregulation has been thought to explain the association between apolipoprotein (apo) E4 and increased risk of coronary heart disease in humans.
  
  
  RESULTS
  Contrary to this hypothesis, doubling Ldlr expression caused severe atherosclerosis with marked accumulation of cholesterol-rich, apoE-poor remnants in mice with human apoE4, but not apoE3, when the animals were fed a Western-type diet. The increased Ldlr expression enhanced in vivo clearance of exogenously introduced remnants in mice with apoE4 only when the remnants were already enriched with apoE4. The rates of nascent lipoprotein production were the same. The adverse effects of increased LDLR suggest a possibility that the receptor can trap apoE4, reducing its availability for the transfer to nascent lipoproteins needed for their rapid clearance, thereby increasing the production of apoE-poor remnants that are slowly cleared. The lower affinity for the LDLR of apoE3 compared with apoE4 could then explain why increased receptor expression had no adverse effects with apoE3.
  
  
  CONCLUSIONS
  Our results emphasize the occurrence of important and unexpected interactions between APOE genotype, LDLR expression, and diet.
authors.affiliation: Curriculum in Genetics and Molecular Biology, University of North Carolina, Chapel Hill 27599, USA.
authors.forename: Sudi I
authors.initials: SI
authors.lastname: Malloy
authors.forename: Michael K
authors.initials: MK
authors.lastname: Altenburg
authors.forename: Christopher
authors.initials: C
authors.lastname: Knouff
authors.forename: Lorraine
authors.initials: L
authors.lastname: Lanningham-Foster
authors.forename: John S
authors.initials: JS
authors.lastname: Parks
authors.forename: Nobuyo
authors.initials: N
authors.lastname: Maeda
mesh_terms: D000818:Animals; D053318:Apolipoprotein E3; D053327:Apolipoprotein E4; D001057:Apolipoproteins E / Q000235:genetics / Q000502:physiology*; D001161:Arteriosclerosis / Q000097:blood / Q000235:genetics*; D003433:Crosses, Genetic; D004036:Diet, Atherogenic; D004041:Dietary Fats / Q000009:adverse effects; D005260:Female; D015870:Gene Expression; D018390:Gene Targeting; D006801:Humans; D006937:Hypercholesterolemia / Q000097:blood / Q000235:genetics*; D008079:Lipoproteins, VLDL / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D011973:Receptors, LDL / Q000235:genetics / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000502:physiology; D013045:Species Specificity; D014162:Transfection
chemical_list: D053318:Apolipoprotein E3; D053327:Apolipoprotein E4; D001057:Apolipoproteins E; D004041:Dietary Fats; D008079:Lipoproteins, VLDL; D011973:Receptors, LDL; D011993:Recombinant Fusion Proteins