Synaptic Targeting by Alzheimer's-Related Amyloid β Oligomers

Abstract

The cognitive hallmark of early Alzheimer's disease (AD) is an extraordinary inability to form new memories. For many years, this dementia was attributed to nerve-cell death induced by deposits of fibrillar amyloid ␤ (A␤). A newer hypothesis has emerged, however, in which early memory loss is considered a synapse failure caused by soluble A␤ oligomers. Such oligomers rapidly block long-term potentiation, a classic experimental paradigm for synaptic plasticity, and they are strikingly elevated in AD brain tissue and transgenicmouse AD models. The current work characterizes the manner in which A␤ oligomers attack neurons. Antibodies raised against synthetic oligomers applied to AD brain sections were found to give diffuse stain around neuronal cell bodies, suggestive of a dendritic pattern, whereas soluble brain extracts showed robust AD-dependent reactivity in dot immunoblots. Antigens in unfractionated AD extracts attached with specificity to cultured rat hippocampal neurons, binding within dendritic arbors at discrete puncta. Crude fractionation showed ligand size to be between 10 and 100 kDa. Synthetic A␤ oligomers of the same size gave identical punctate binding, which was highly selective for particular neurons. Image analysis by confocal double-label immunofluorescence established that Ͼ90% of the punctate oligomer binding sites colocalized with the synaptic marker PSD-95 (postsynaptic density protein 95). Synaptic binding was accompanied by ectopic induction of Arc, a synaptic immediate-early gene, the overexpression of which has been linked to dysfunctional learning. Results suggest the hypothesis that targeting and functional disruption of particular synapses by A␤ oligomers may provide a molecular basis for the specific loss of memory function in early AD.

Synapse-Binding Subpopulations of Aβ Oligomers Sensitive to Peptide Assembly Blockers and scFv Antibodies

“…3,27−31 Additionally, previous studies from our laboratory have shown that Aβ1−42 oligomeric species between 50 and 100 kDa, either synthetically prepared or derived from human AD brain extracts, carried synapse binding capacities. 4,12 Retentate and filtrate fractions were analyzed by SDS-PAGE for protein profile (silver stain; Figure 1a) and Western blot staining by oligomer-selective NU1 (Figure 1b). Some blots were heat-treated and immunostained with the anti-Aβ antibody 6E10, which resulted in sensitive detection of monomers (Figure 1c).…”

Structure-Selective Anisotropy Assay for Amyloid Beta Oligomers

“…When the bis-pyrenyl peptide PP is incubated with a preparation of Abeta oligomers, it exhibits a reduced proportion of the broad excimer emission (460−500 nm) and enhanced emission from the pyrene monomer with its characteristic narrow peaks at 380−400 nm. Figure 1 shows the fluorescence emission spectral profile of peptide PP alone (curve 1) and PP incubated with synthetic Abeta oligomer (2). PP in aqueous solution exhibits a profile characteristic of pyrene excimer, which has been shown to be associated with amyloid beta beta-sheet conformation (1 on Figure.1) with a maximum from 460 to 500 nm (broad peak with maximum about 470 nm on Figure.1).…”

Prophylactic treatment with paroxetine ameliorates behavioral deficits and retards the development of amyloid and tau pathologies in 3xTgAD mice

“…The improved functional outcome was correlated with reduced levels of Aβ1−40 in paroxetine-treated 3xTgAD mice suggesting that paroxetine intervenes in the pathogenic process upstream of Aβ production. It is thought that small oligomers of Aβ are particularly damaging to synapses (Lambert et al, 1998;Lacor et al, 2004), possibly by causing membrane-associated oxidative stress which perturbs calcium homeostasis and impairs energy metabolism (Mattson et al, 1992;Keller et al, 1997).…”