Quantitative assessment of oligomeric amyloid β peptide binding to α7 nicotinic receptor

Abstract

Background and Purpose Progressive dysfunction of cholinergic transmission is a well‐known characteristic of Alzheimer's disease (AD). Amyloid β (Aβ) peptide oligomers are known to play a central role in AD and are suggested to impair the function of the cholinergic nicotinic ACh receptor α7 (α7nAChR). However, the mechanism underlying the effect of Aβ on α7nAChR function is not fully understood, limiting the therapeutic exploration of this observation in AD. Here, we aimed to detect and characterize Aβ binding to α7nAChR, including the possibility of interfering with this interaction for therapeutic purposes. Experimental Approach We developed a specific and quantitative time‐resolved FRET (TR‐FRET)‐based binding assay for Aβ to α7nAChR and pharmacologically characterized this interaction. Key Results We demonstrated specific and high‐affinity (low nanomolar) binding of Aβ to the orthosteric binding site of α7nAChR. Aβ binding was prevented and reversed by the well‐characterized orthosteric ligands of α7nAChR (epibatidine, α‐bungarotoxin, methylylcaconitine, PNU‐282987, S24795, and EVP6124) and by the type II positive allosteric modulator (PAM) PNU‐120596 but not by the type I PAM NS1738. Conclusions and Implications Our TR‐FRET Aβ binding assay demonstrates for the first time the specific binding of Aβ to α7nAChR, which will be a crucial tool for the development, testing, and selection of a novel generation of AD drug candidates targeting Aβ/α7nAChR complexes with high specificity and fewer side effects compared to currently approved α7nAChR drugs. Linked Articles This article is part of a themed section on Therapeutics for Dementia and Alzheimer's Disease: New Directions for Precision Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.18/issuetoc

The Toxicity and Polymorphism of β-Amyloid Oligomers

“…Aβos have high affinity with α7nAChR [ 50 ], and lead to the internalization of the Aβ–α7nAChR complex, which induces plaque formation and promotes neurotoxicity [ 51 , 52 ]. However, some studies have found that α7nAChR had a neuroprotective effect.…”

Single-molecule studies of amyloid proteins: from biophysical properties to diagnostic perspectives

“…Recently, FRET has been used to identify the binding of A β oligomers to the cholinergic nicotinic ACh receptor α 7 ( α 7nAChR) (Cecon et al ., 2019). Loss of activity of α 7nAChR is believed to impair cognitive performance in AD (Bertrand et al ., 2015).…”

“…The result showed that the A β binding site on α 7nAChR overlaps with the orthosteric ligand binding sites comprising loop C with a high-binding affinity (p K D 10.3 ± 0.2). FRET was also used to evaluate different α 7nAChR-related compounds of interfering with the binding abilities of A β to α 7nAChR (Cecon et al ., 2019). In addition, FRET was applied for the screening of various compounds against Zn 2+ –A β interaction (Lee et al ., 2019).…”

Therapeutics for dementia and Alzheimer's disease: New directions for precision medicine

“…Even though strategies to elevate expression or activity of these mechanisms still heavily rely on the amyloid cascade hypothesis, they do provide alternative therapeutic opportunities in dementia and relate to the overall increased interest in proteostatic clearance pathways that are further mentioned below. Better preclinically characterized tool compounds that modulate cellular Aβ and APP levels may also assist researchers such as Lopez Sanchez, van Wijngaarden, and Trounce () and Cecon et al (), providing insights into whether it is the loss of protective non‐amyloidogenic APP fragments or a gain of Aβ toxic function that is more detrimental in AD. Cellular location also appears to be an important factor in pathogenesis—the link between APP or APP‐derived peptides and mitochondrial metabolism remains unclear, despite the mitochondria being a location for APP and Aβ, and energy deficiency a recognized early event in AD progression (Lopez Sanchez et al, ).…”

“…Continued identification and characterization of binding partners for APP and Aβ also increase the appreciation of the complexity in the pathways related to APP metabolism and their involvement in disease. There are various species of Aβ that are known to act as ligands to neurotransmitter receptors in the brain, and Cecon et al () highlight the α7 nicotinic receptor (α7nAChR) as one of these binding partners. As a receptor involved in learning and memory processes, the function of α7nAChR is altered in the course of AD pathology (Bertrand, Lee, Flood, Marger, & Donnelly‐Roberts, ) and provides the basis of a sensitive Aβ screening assay for identifying inhibitors that will specifically target a detrimental effect of oligomeric Aβ accumulation (Cecon et al, ).…”