Project 2: Co-pathogenic Interactions between ApoE Isoforms and Abeta in Neural Network Dysfunction of Alzheimer's Disease

PROJECT 2 – SUMMARY Numerous lines of evidence suggest that human amyloid precursor protein/amyloid b (APP/Ab), apoE4, and the microtubule-associated protein tau contribute to Alzheimer’s disease (AD), but their pathogenic interactions are largely unknown. Reducing Ab accumulation in the brain was considered the most reasonable therapeutic strategy for AD, but multiple clinical trials of this approach have failed, suggesting that the pathophysiology of AD is much more complex than anticipated and that the pathogenic interactions of AD-relevant proteins need to be better understood. To decode the multifactorial etiology of AD at physiological levels of expression, we will study newly developed knock-in (KI) mouse models of late-onset (LOAD) and familial (FAD) AD without transgene overexpression and focus on the pathogenic interactions between Ab, apoE, and tau. To simulate LOAD, we will use KI mice that express humanized wildtype Ab without FAD mutations (ApphAβWT/hAβWT; referred to as Aβ mice), human apoE isoforms (APOEE2/E2, APOEE3/E3, and APOEE4/E4; E2, E3, and E4 mice), and human wildtype tau (MAPTWT/WT, TAUWT mice). To simulate FAD, we will use KI mice that express humanized wildtype Ab with the Swedish and Iberian FAD mutations (AppNL-F/NL-F; ↑Ab mice), human apoE isoforms (E3 and E4), and human wildtype tau (TAUWT). Thus, we propose to study the physiological and endogenous interactions of human Ab, apoE isoforms, and tau in vivo that contribute to AD-related abnormalities in neural network activity, cognitive functions, gene expression, and histopathology using state-of-the-art in vivo electrophysiological, optogenetics, and behavioral approaches. We will focus on mechanisms of altered neural network dysfunction, since they closely relate to brain and cognitive functions and are disrupted early in AD pathogenesis. In Aim 1, we will determine pathogenic interactions of Ab, apoE isoforms, and tau contributing to altered neural network activity (Aim 1a) and behavioral deficits (Aim 1b) in LOAD and FAD KI mice during disease progression using wireless long-term EEG/EMG recordings and standard and machine learning behavioral approaches. In Aim 2, we will determine pathogenic interactions of Ab and apoE4 contributing to cell and circuit function impairments in LOAD and FAD KI mice in vivo (Aim 2a, b) and if optogenetic activation of specific interneuron cell types reverses AD-related abnormalities (Aim 2c). We will use in vivo LFP and multi-unit recordings and optogenetic approaches in behaving mice to identify cell type and circuit-level mechanisms of network dysfunction. In Aim 3, we will determine pathogenic interactions of Ab, apoE isoforms, and tau contributing to AD-related pathology (Aim 3a) and scRNA-seq transcriptome changes (Aim 3b) in LOAD and FAD KI mice. We will perform AD-related pathological and scRNA-seq transcriptomics analyses in functionally characterized mice (in vivo physiology and behavior) from Aims 1 and 2 to identify pathological and transcriptome changes associated with cognitive vulnerability and resilience. We aim to identify human validated and behaviorally relevant candidate genes/pathways of AD pathogenesis and define cell-type-specific disease mechanisms.