ApoE (apolipoprotein E) is an essential component of lipoprotein particles. Three human APOE isoforms exist: E2, E3, and E4. Compared to E3, E2 is protective with regard to susceptibility to develop Alzheimer's disease (AD), is more prevalent among centenarians, and is associated with improved episodic memory performance, larger hippocampal volume, and reduced hippocampal atrophy rate. Little is known, however, about the mechanisms involved in the neuroprotection of E2 in aging, including slowing AD progression. In this proposal, we will use targeted replacement mice and an unbiased epigenomics approach to identify pathway changes that underlie the protective role of E2. The mouse strains to be used include human ApoE and AD genotypes. We have mouse strains expressing human E2 E3, and E4 under the mouse apoE promoter (apoE TR mice). These strains will be crossed with human APP knock in mice developed by Dr. Takaomi Saido (Riken Research Brain Institute) that contain the Swedish and Iberian mutations (APP NL-F) or contain these mutations in combination with the Artic mutation (APP NL-G-F). APP NL-G-F mice accumulate neuropathology and show cognitive impairments one year earlier than the APP NL-F mice (6 versus 18 months). This difference in disease onset will allow us to examine the interaction between neuropathological and aging processes and the E2 isoform. We hypothesize that E2 slows the development of cognitive injury and AD pathology because it enhances neuroprotective and aging protective pathways. To test this hypothesis, three Specific Aims are proposed.
The first Aim will examine the protective effect of the E2 isoform, relative to E3 and E4, with regard to early onset histopathological and behavioral and cognitive changes in the NL-G-F mouse strain. We expect to observe less change in the E2 background.
Aim 2 will resemble Aim 1, with the exception of crossing the ApoE mice with the slower acting APP NL-F gene. Again, we expect protection from the AD phenotype in the E2 background, which may be relatively greater than in Aim 1 if aging processes are also slowed in the E2 background. Because the association of E2 with reduced AD risk is seen in men but not women, we will examine male and female mice in Aims 1 and 2.
For Aim 3, we will use omics approaches to examine DNA methylation (both methylcytosine and hydroxymethylcytosine) and RNA expression profiles in the different strain backgrounds to identify neuroprotective and aging protective pathways that are enhanced in the E2 mice and help explain the protective effect that is conferred by this isoform. Overall, we expect that the work and analyses proposed in this application to identify disease-related pathways that change more slowly and neuroprotective pathways that will be more pronounced in the E2 background, facilitating the identification of diagnostic markers and the development of novel therapeutic targets for AD and other age-related cognitive disorders.
This proposal is submitted with the goal of testing the hypothesis that E2 slows the development of cognitive injury and AD pathology because it enhances neuroprotective pathways that are associated with epigenetic changes and slows aging processes. We expect to identify disease-related pathways that change more slowly and neuroprotective pathways that will be more pronounced in the E2 background, facilitating the identification of diagnostic markers and the development of novel therapeutic targets for AD and other age-related cognitive disorders.
