title: Molecular mechanisms responsible for the differential effects of apoE3 and apoE4 on plasma lipoprotein-cholesterol levels.
abstract: OBJECTIVE
  The goal of this study was to understand the molecular basis of how the amino acid substitution C112R that distinguishes human apolipoprotein (apo) E4 from apoE3 causes the more proatherogenic plasma lipoprotein-cholesterol distribution that is known to be associated with the expression of apoE4.
  
  
  RESULTS
  Adeno-associated viruses, serotype 8 (AAV8), were used to express different levels of human apoE3, apoE4, and several C-terminal truncation and internal deletion variants in C57BL/6 apoE-null mice, which exhibit marked dysbetalipoproteinemia. Plasma obtained from these mice 2 weeks after the AAV8 treatment was analyzed for cholesterol and triglyceride levels, as well as for the distribution of cholesterol between the lipoprotein fractions. Hepatic expression of apoE3 and apoE4 induced similar dose-dependent decreases in plasma cholesterol and triglyceride to the levels seen in control C57BL/6 mice. Importantly, at the same reduction in plasma total cholesterol, expression of apoE4 gave rise to higher very low-density lipoprotein-cholesterol (VLDL-C) and lower high-density lipoprotein-cholesterol levels relative to the apoE3 situation. The C-terminal domain and residues 261 to 272 in particular play a critical role, because deleting them markedly affected the performance of both isoforms.
  
  
  CONCLUSIONS
  ApoE4 possesses enhanced lipid and VLDL-binding ability relative to apoE3, which gives rise to impaired lipolytic processing of VLDL in apoE4-expressing mice. These effects reduce VLDL remnant clearance from the plasma compartment and decrease the amount of VLDL surface components available for incorporation into the high-density lipoprotein pool, accounting for the more proatherogenic lipoprotein profile (higher VLDL-C/high-density lipoprotein-cholesterol ratio) occurring in apoE4-expressing animals compared with their apoE3 counterparts.
authors: Institute for Translational Medicine and Therapeutics, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, USA.
authors: Hui
authors: H
authors: Li
authors: Padmaja
authors: P
authors: Dhanasekaran
authors: Eric T
authors: ET
authors: Alexander
authors: Daniel J
authors: DJ
authors: Rader
authors: Michael C
authors: MC
authors: Phillips
authors: Sissel
authors: S
authors: Lund-Katz
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D053318:Apolipoprotein E3 / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D053327:Apolipoprotein E4 / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D002784:Cholesterol / Q000097:blood*; D008076:Cholesterol, HDL / Q000097:blood*; D015243:Cholesterol, VLDL / Q000097:blood*; D000229:Dependovirus / Q000235:genetics; D004195:Disease Models, Animal; D005822:Genetic Vectors; D006801:Humans; D006952:Hyperlipoproteinemia Type III / Q000097:blood* / Q000235:genetics; D008066:Lipolysis; D008099:Liver / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D017434:Protein Structure, Tertiary; D013997:Time Factors; D014280:Triglycerides / Q000097:blood
chemical_list: D053318:Apolipoprotein E3; D053327:Apolipoprotein E4; D008076:Cholesterol, HDL; D015243:Cholesterol, VLDL; D014280:Triglycerides; D002784:Cholesterol