Dylan T. Garceau, United States of America
The Jackson Laboratory MODEL-ADAuthor Of 3 Presentations
DETERMINING THE MECHANISMS BY WHICH APOEΕ3/Ε4 MODIFIES RISK FOR AD AND RELATED DEMENTIAS
Abstract
Aims
Recent studies have determined the ways APOEε4 differs from APOEε3, however, little is known about the ways these two alleles interact to affect risk for AD. Here we describe the creation of a new set of humanized APOE alleles and test our hypothesis that APOEε3/ε4 modifies risk for AD and related dementias in ways distinct from APOEε4/ε4.
Methods
A new series of humanized APOE mice that includes APOEε4/ε4 and APOEε3/ε3 mice were generated by MODEL-AD. Female and male APOEε3/ε3, APOEε3/ε4 and APOEε4/ε4 mice were characterized at 2 months. Two voluntary running cohorts (4 months and 12 months) were included to determine whether the effects of exercise are modified by APOE genotype. A battery of assays included blood lipid profiles, novel spatial memory, metabolic assessment, immunofluorescence and cortical transcriptional profiling. Linear modeling and WGCNA were used to identify effects of sex, genotype, and running in gene expression data.
Results
Cholesterol and triglyceride composition were significantly influenced by APOE genotype at 2 months and 4 months, respectively. Linear modeling identified genes significantly different between mice carrying one or two APOEε4 alleles compared to the reference APOEε3/ε3 genotype as early as 2 months. Genotype-specific differences in cerebrovascular proteins were observed at 12 months. Preliminary analyses of 12 month data indicate genotype-, sex- and activity-specific effects.
Conclusions
Our study predicts differences between APOEε3/ε4 and APOEε4/ε4 genotypes on AD-relevant phenotypes, suggesting therapies aimed at modifying APOE biology to treat dementias may need to be targeted to specific APOE genotypes.
NOVEL APP KNOCK-IN MOUSE MODEL REVEALS PROFOUND METABOLIC PERTURBATIONS IN PHAGOCYTIC MICROGLIA
Abstract
Aims
Emerging human genetics and preclinical research revealed that microglia are likely contributing to AD pathophysiology. Microglia are responding to various pathogenic drivers of AD but the mechanisms by which microglia become dysfunctional and contribute to disease remain unclear. Here, we aimed to characterize amyloid-β related pathology and microglial responses in a novel APP knock-in mouse model. In particular, we sought to determine if pathogenic fibrillar form of Aβ causes transcriptomic and lipid dysregulation in microglia as a result of phagocytic uptake and to which extent this dysregulation perturbs immunometabolism.
Methods
We developed and characterized a new APP knock-in (KI) mouse model that circumvent limitations of transgenesis and applied multi-omics approaches in combination with cell population enrichment techniques to deeply characterize cellular perturbations of microglia in this mouse model.
Results
We validated the novel APP-KI mouse model by showing a dramatic increase of Aβ42/40 ratio in the brain, CSF and plasma at various ages, and demonstrated that it was associated with a progressive accumulation of amyloid plaques and an increase of markers of neuroinflammation and neurodegeneration. We then describe profound transcriptomic and lipidomic perturbations in brain-sorted microglia and reveal that some of those changes were exacerbated or unique in microglia showing evidence of Aβ accumulation.
Conclusions
Our in-depth analysis of this novel APP KI mouse model confirms emergence of disease-relevant biology and progressive accumulation of pathological hallmarks of AD. Additionally, we reveal profound immunometabolic perturbations in microglia supporting the notion that profound cellular alterations may lead to lysosomal dysfunction in highly phagocytic microglia.
USING GENETICALLY DIVERSE COLLABORATIVE CROSS MOUSE STRAINS TO MODEL ALZHEIMER’S DISEASE
Abstract
Aims
Mouse models of Alzheimer’s disease (AD), carrying rare variants in genes such as APP and PS1 (APP/PS1), have usually been created on the C57BL/6J (B6J) genetic background. While these strains often exhibit amyloid accumulation and neuroinflammation, many additional molecular alterations present in human AD are absent. To broaden the phenotypes of mouse models, we introduced genetic diversity by incorporating Collaborative Cross (CC) lines, a recombinant inbred mouse panel created from eight highly diverse founder strains.
Methods
Five CC strains were selected for maximal genetic and gene expression variation at twelve late-onset GWAS loci, including TREM2, BIN1, and CLU. Transgenic APPand PS1alleles with a humanized APOE4 allele on a B6J background were crossed with each CC line. Brain hemisphere transcriptomes and neuropathology were assessed at 8-months. Neuropathology focused on amyloid deposition, glial cell activation and neuronal health.
Results
The effect of humanized APOE4 demonstrated differences across CC lines and in the presence of mutant APP and PS1 transgenes. RNA-Seq data revealed allele-specific gene expression profiles associated with neuropathological differences. We mapped strain specific transcriptional signatures to Late-Onset AD subtypes identified in the study cohorts from AMP-AD consortium and observed correlations with subtypes specific to APP/PS1 and APOE4 alleles.
Conclusions
The findings provide new insights into the role of APOE4 in amyloid pathogenesis. Diverse genetic backgrounds of CC lines exhibit a unique resource to assess genome-wide allele-specific gene expression connecting AD risk variants to molecular and neuropathological profiles.This study suggests use of CC lines mouse models to better represent the genetic variation in AD.