Two-Step Mechanism of Membrane Disruption by Aβ through Membrane Fragmentation and Pore Formation

Abstract

Disruption of cell membranes by Aβ is believed to be one of the key components of Aβ toxicity. However, the mechanism by which this occurs is not fully understood. Here, we demonstrate that membrane disruption by Aβ occurs by a two-step process, with the initial formation of ion-selective pores followed by nonspecific fragmentation of the lipid membrane during amyloid fiber formation. Immediately after the addition of freshly dissolved Aβ(1-40), defects form on the membrane that share many of the properties of Aβ channels originally reported from single-channel electrical recording, such as cation selectivity and the ability to be blockaded by zinc. By contrast, subsequent amyloid fiber formation on the surface of the membrane fragments the membrane in a way that is not cation selective and cannot be stopped by zinc ions. Moreover, we observed that the presence of ganglioside enhances both the initial pore formation and the fiber-dependent membrane fragmentation process. Whereas pore formation by freshly dissolved Aβ(1-40) is weakly observed in the absence of gangliosides, fiber-dependent membrane fragmentation can only be observed in their presence. These results provide insights into the toxicity of Aβ and may aid in the design of specific compounds to alleviate the neurodegeneration of Alzheimer's disease.

Distinct Membrane Disruption Pathways Are Induced by 40-Residue β-Amyloid Peptides

“…Chemical cross-linking may help stabilize the ionic channel structures (19). Similar temporary cation-selected membrane pore formation for the membrane-associated 40-residue A␤ has been reported in a previous article where the monomeric peptide was added to preformed liposomes (40). The peptide concentration (ϳ10 M) utilized in that work was approximately five times lower than our A␤ concentration, and the P:L ratio (1:500ϳ1:1000) was also much lower.…”

“…Peptides were pretreated using an approach reported in the literature to ensure the monomeric state (40). For the external addition protocol, we have shown that the thioflavin T (ThT) fluorescence emission was detected immediately after the addition of A␤ to liposomes for P:L values of 1:30, 1:60, and 1:90 but not for the P:L ratio of 1:120 (23).…”

Reduced Lipid Bilayer Thickness Regulates the Aggregation and Cytotoxicity of Amyloid-β

“…Pore formation has been suggested to facilitate disruption of the ionic gradient across neuronal membranes (6,7). Alternatively, elongation of the amyloid species on the bilayer may remove lipids from the membrane and create holes that allow for the uncontrolled transit of biomacromolecules across the membrane (8,9). These two modes of membrane disruption are proposed to coexist; it is thought that porelike oligomers form first, whereas the fibril-induced perturbations occur later (8).…”

“…Alternatively, elongation of the amyloid species on the bilayer may remove lipids from the membrane and create holes that allow for the uncontrolled transit of biomacromolecules across the membrane (8,9). These two modes of membrane disruption are proposed to coexist; it is thought that porelike oligomers form first, whereas the fibril-induced perturbations occur later (8). Extensive work by Matsuzaki (5) has revealed that incorporating glycolipids, such as the ganglioside GM1, can promote the formation of toxic, membrane-associated A␤ aggregates linked to membrane disruption.…”

Ultrasensitive Measurement of Ca2+ Influx into Lipid Vesicles Induced by Protein Aggregates

“…Methods to detect membrane disruption in bulk solution, based on measuring dye leakage, are valuable for high μ m concentrations of toxic species,20 but we utilize nanosized vesicles filled with a dye whose fluorescence increases on binding Ca 2+ ions. The entry of a small number of Ca 2+ ions into such small volumes leads to a significant change in concentration, enabling high resolution measurements to be made.…”