Natural Oligomers of the Alzheimer Amyloid-β Protein Induce Reversible Synapse Loss by Modulating an NMDA-Type Glutamate Receptor-Dependent Signaling Pathway

TLDR

Alzheimer’s disease is marked by synapse loss in hippocampus and neocortex, the strongest correlate of clinical impairment, yet a direct link between a specific amyloid‑β species and synapse loss remains unestablished. The study aims to develop a quantitative cellular model to elucidate the molecular basis of amyloid‑β‑induced neuronal dysfunction. Aβ oligomers trigger spine loss via NMDA‑type glutamate receptor activation, initiating a cofilin‑calcineurin signaling cascade that reduces calcium influx. Physiological concentrations of Aβ dimers and trimers, but not monomers, progressively and reversibly reduce hippocampal synapse density, an effect that can be blocked by Aβ‑specific antibodies or a small‑molecule aggregation modulator and is mediated through NMDAR‑dependent pathways.

Abstract

Alzheimer's disease (AD) is characterized by decreased synapse density in hippocampus and neocortex, and synapse loss is the strongest anatomical correlate of the degree of clinical impairment. Although considerable evidence supports a causal role for the amyloid-β protein (Aβ) in AD, a direct link between a specific form of Aβ and synapse loss has not been established. We demonstrate that physiological concentrations of naturally secreted Aβ dimers and trimers, but not monomers, induce progressive loss of hippocampal synapses. Pyramidal neurons in rat organotypic slices had markedly decreased density of dendritic spines and numbers of electrophysiologically active synapses after exposure to picomolar levels of soluble oligomers. Spine loss was reversible and was prevented by Aβ-specific antibodies or a small-molecule modulator of Aβ aggregation. Mechanistically, Aβ-mediated spine loss required activity of NMDA-type glutamate receptors (NMDARs) and occurred through a pathway involving cofilin and calcineurin. Furthermore, NMDAR-mediated calcium influx into active spines was reduced by Aβ oligomers. Partial blockade of NMDARs by pharmacological antagonists was sufficient to trigger spine loss. We conclude that soluble, low- n oligomers of human Aβ trigger synapse loss that can be reversed by therapeutic agents. Our approach provides a quantitative cellular model for elucidating the molecular basis of Aβ-induced neuronal dysfunction.