The Aβ1–42M35C mutated amyloid peptide Aβ1–42 and the 25–35 fragment fail to mimic the subtype-specificity of actions on recombinant human nicotinic acetylcholine receptors (α7, α4β2, α3β4)

Abstract

Alzheimer's disease (AD) is a neurodegenerative condition involving accumulation of the beta-amyloid peptide, Abeta1-42. Previously we have shown that amyloid peptides (Abeta1-42, Abeta1-40) have different actions on the three major brain nicotinic acetylcholine receptor (nAChR) subtypes (alpha7, alpha4beta2 and alpha3beta4). The methionine in position 35 of Abeta (M35) has been shown to be important in the toxicity of Abeta and the 25-35 fragment can mimic some of the actions of the Abeta1-42 peptide. However, the extent to which this mutant and the fragment mimic subtype selectivity is unknown. Two-electrode voltage-clamp electrophysiology has been used to study the actions on alpha7, alpha4beta2 and alpha3beta4 recombinant nAChRs expressed in Xenopus laevis oocytes of full length Abeta1-42, and Abeta peptide fragments, scrambled peptides, and the Abeta1-42 peptide containing mutations of the methionine in position 35. The Abeta25-35 fragment did not display subunit specificity. Abeta1-42 with an M35C mutation showed similar subtype-specificity to wild-type Abeta1-42. However, Abeta1-42 with an M35V substitution reduced the peak amplitude of ACh-induced currents recorded from alpha4beta2 nAChRs, but did not affect those recorded from alpha7 or alpha3beta4. These results indicate that the amino acid in position 35 of Abeta1-42 is an important determinant of the subtype-specificity of this peptide on human recombinant alpha7, alpha4beta2 and alpha3beta4 nAChRs and that the 25-35 fragment fails to mimic all of the actions of the full-length peptide.