Age-Dependent Shift of AMPA Receptors From Synapses to Intracellular Compartments in Alzheimer's Disease: Immunocytochemical Analysis of the CA1 Hippocampal Region in APP/PS1 Transgenic Mouse Model.

Alejandro Martín-Belmonte,Yugo Fukazawa,Ana Esther Moreno-Martínez,Rocío Alfaro-Ruíz,Carolina Aguado,Makoto Itakura,Elek Molnár,Luis de la Ossa,Rafael Luján

doi:10.3389/fnagi.2020.577996

Abstract

Synapse loss occurs early in Alzheimer’s disease (AD) patients and animal models. Alterations at synaptic level are a major morphological correlate of the memory deficits and related symptoms of AD. Given the predominant roles of synaptic AMPA receptors (AMPARs) in excitatory synaptic transmission in the brain, changes in their dynamic regulation are also implicated in the pathophysiology of AD. Here, we used immunolocalization techniques to analyze the expression and subcellular distribution of AMPARs in the hippocampal region of APP/PS1 mouse model of AD. Immunoblots and histoblots revealed that the total amount of AMPARs and their regional expression pattern in the hippocampus was similar in APP/PS1 mice and in age-matched wild type mice. At the ultrastructural level, two synapse populations were examined using SDS-digested freeze-fracture replica labeling in the stratum radiatum in mice: (i) on spines of CA1 pyramidal cells; and (ii) on randomly found dendritic shafts of CA1 interneurons. While 1- and 6-months-old APP/PS1 mice exhibited no change, we observed a significant reduction at 12 months in AMPAR density at synapses in both pyramidal cells and interneurons, compared to wild-type. This reduction of AMPARs in dendritic spines was accompanied by a significant increase in AMPAR subunit proteins identified in intracellular compartments. Our data demonstrate an age-dependent reduction of synaptic AMPARs in APP/PS1 mice, which may contribute to impaired learning and memory at later stages of AD.

Highlights

Alzheimer’s disease (AD) is a devastating neurodegenerative disorder characterized by progressive cognitive deficit and memory loss
Using the guinea pig anti-GluA1–4 antibody in conventional histoblots (Aguado and Luján, 2019), we determined in first place whether the expression of AMPA receptors (AMPARs) was altered in the brain of APP/PS1 mice at different ages: 1 month (Figures 1A–C), 6 months (Figures 1D–F), and 12 months (Figures 1G–I)
In AD, hippocampal dysfunction is produced by synaptic failure (Li and Selkoe, 2020), which leads to memory deficits

Summary

Introduction

Alzheimer’s disease (AD) is a devastating neurodegenerative disorder characterized by progressive cognitive deficit and memory loss. Immunoelectron microscopy using post-embedding immunogold labeling has been used to investigate AMPARs at excitatory synapses in the hippocampus in normal brains (Nusser et al, 1998; Petralia et al, 1999; Takumi et al, 1999; Racca et al, 2000). Until now, these high-resolution techniques have not been applied for the identification of AD-related pathological changes in AMPAR numbers and densities

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Conclusion