Involvement of the Apoer2 and Lrp1 Receptors in Mediating the Pathological Effects of ApoE4 in Vivo

Curr Alzheimer Res. 2014;11(6):549-57. doi: 10.2174/1567205010666131119232444.

Abstract

This study investigated the possible role of the ApoE receptors Lrp1 and Apoer2 in mediating the pathological effects of ApoE4 in ApoE-targeted-replacement mice expressing either the human ApoE3 or ApoE4 allele. In this study we show that activation of the amyloid cascade by inhibition of the Aβ-degrading enzyme neprilysin results in upregulation of the ApoE receptor Lrp1 in the CA1 hippocampal neurons of 4-month-old ApoE4 mice, but not in the corresponding ApoE3 or ApoE-deficient (KO) mice. These results are in accordance with the previous findings that activation of the amyloid cascade induces Aβ accumulation in the CA1 neurons of ApoE4 mice, but not in ApoE3 or ApoE-KO mice. This suggests that the apoE4-driven elevation of Lrp1 is mediated via a gain of function mechanism and may play a role in mediating the effects of ApoE4 on Aβ. In contrast, no changes were observed in the levels of the corresponding Apoer2 receptor following the neprilysin inhibition. The ApoE receptors of naive ApoE4 mice were also affected differentially and isoform specifically by ApoE4. However, under these conditions, the effect was an ApoE4-driven reduction in the levels of Apoer2 in CA1 and CA3 pyramidal neurons, whereas the levels of Lrp1 were not affected. RT-PCR measurements revealed that the levels of Apoer2 and Lrp1 mRNA in the hippocampus of naïve and neprilysin-inhibited mice were not affected by ApoE4, suggesting that the observed effects of ApoE4 on the levels of these receptors is posttranscriptional. In conclusion, this study shows that the levels of hippocampal ApoE receptors Lrp1 and Apoer2 in vivo are affected isoform specifically by ApoE4 and that the type of receptor affected is context dependent.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amyloid beta-Peptides / metabolism
  • Animals
  • Apolipoprotein E3 / metabolism
  • Apolipoprotein E4 / metabolism*
  • Hippocampus / drug effects
  • Hippocampus / metabolism*
  • Humans
  • LDL-Receptor Related Proteins / metabolism*
  • Lysosomes / metabolism
  • Male
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Neprilysin / antagonists & inhibitors
  • Neprilysin / metabolism
  • Protease Inhibitors / pharmacology
  • Pyramidal Cells / drug effects
  • Pyramidal Cells / metabolism*
  • RNA, Messenger / metabolism
  • Receptors, LDL / metabolism*
  • Signal Transduction / drug effects
  • Thiorphan / pharmacology
  • Tumor Suppressor Proteins / metabolism*

Substances

  • Amyloid beta-Peptides
  • Apolipoprotein E3
  • Apolipoprotein E4
  • LDL-Receptor Related Proteins
  • Lrp1 protein, mouse
  • Protease Inhibitors
  • RNA, Messenger
  • Receptors, LDL
  • Tumor Suppressor Proteins
  • low density lipoprotein receptor-related protein 8
  • Thiorphan
  • Neprilysin