Aβ Oligomers Dysregulate Calcium Homeostasis by Mechanosensitive Activation of AMPA and NMDA Receptors.

Giulia Fani,Christopher M Dobson,Roberta Cascella,Fabrizio Chiti,Cristina Cecchi,Giulia Vecchi,Michele Vendruscolo,Benedetta Mannini

doi:10.1021/acschemneuro.0c00811

Giulia Fani, Christopher M Dobson + Show 6 more

Open Access

https://doi.org/10.1021/acschemneuro.0c00811

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Abstract

Alzheimer’s disease, which is the most common form of dementia, is characterized by the aggregation of the amyloid β peptide (Aβ) and by an impairment of calcium homeostasis caused by excessive activation of glutamatergic receptors (excitotoxicity). Here, we studied the effects on calcium homeostasis caused by the formation of Aβ oligomeric assemblies. We found that Aβ oligomers cause a rapid influx of calcium ions (Ca2+) across the cell membrane by rapidly activating extrasynaptic N-methyl-d-aspartate (NMDA) receptors and, to a lower extent, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. We also observed, however, that misfolded oligomers do not interact directly with these receptors. Further experiments with lysophosphatidylcholine and arachidonic acid, which cause membrane compression and stretch, respectively, indicated that these receptors are activated through a change in membrane tension induced by the oligomers and transmitted mechanically to the receptors via the lipid bilayer. Indeed, lysophosphatidylcholine is able to neutralize the oligomer-induced activation of the NMDA receptors, whereas arachidonic acid activates the receptors similarly to the oligomers with no additive effects. An increased rotational freedom observed for a fluorescent probe embedded within the membrane in the presence of the oligomers also indicates a membrane stretch. These results reveal a mechanism of toxicity of Aβ oligomers in Alzheimer’s disease through the perturbation of the mechanical properties of lipid membranes sensed by NMDA and AMPA receptors.

Highlights

According to the amyloid cascade hypothesis, a central role in the etiology of the disease is played by the self-assembly of the amyloid β peptide (Aβ) into senile plaques.[2−4] In particular, many lines of evidence suggest that oligomeric forms of Aβ accumulating as intermediates in the aggregation process or released by mature fibrils have a variety of pathogenic effects as they are able to interact with a number of biological targets.[3,5,6]
An early biochemical modification in neurons is the disruption of calcium homeostasis, resulting in increased concentrations of calcium ions (Ca2+) in the intracellular space.[7−11] Many mechanisms have been described through which Aβ oligomers cause an increase of Ca2+ levels in neurons
The analysis that we report here allowed us to identify a molecular mechanism by which Aβ oligomers activate extrasynaptic NMDA and AMPA receptors, which is based on an interaction of the oligomers with lipid membranes that perturb their mechanical properties, which is sensed by the receptors through their mechanosensitivity, in the absence of any direct or protein-mediated interaction with the oligomers

Summary

■ INTRODUCTION

According to the amyloid cascade hypothesis, a central role in the etiology of the disease is played by the self-assembly of the amyloid β peptide (Aβ) into senile plaques.[2−4] In particular, many lines of evidence suggest that oligomeric forms of Aβ accumulating as intermediates in the aggregation process or released by mature fibrils have a variety of pathogenic effects as they are able to interact with a number of biological targets.[3,5,6]. The application of 1 μM Aβ42 ADDLs oligomers to SH-SY5Y cells pretreated with 10 μM arachidonic acid produced a slightly higher, but not significant, increase of Ca2+ influx with respect to cells pretreated with arachidonic acid alone, again in agreement with observations obtained with the model oligomers and arachidonic acid-enriched membranes (Figure 7C,D) All these effects are inhibited by memantine, indicating that they all result from an ionic influx involving the NMDA receptors (Figure 7C,D). Increase of the rotational freedom of the fluorophore, in the presence of the oligomers, resulting from a gain of free space between the membrane lipids and fluidity of the whole membrane bilayer

■ DISCUSSION

■ MATERIALS AND METHODS

■ REFERENCES