Amyloid-β oligomers have a profound detergent-like effect on lipid membrane bilayers, imaged by atomic force and electron microscopy

Abstract

The ability of amyloid-β peptide (Aβ) to disrupt membrane integrity and cellular homeostasis is believed to be central to Alzheimer's disease pathology. Aβ is reported to have various impacts on the lipid bilayer, but a clearer picture of Aβ influence on membranes is required. Here, we use atomic force and transmission electron microscopies to image the impact of different isolated Aβ assembly types on lipid bilayers. We show that only oligomeric Aβ can profoundly disrupt the bilayer, visualized as widespread lipid extraction and subsequent deposition, which can be likened to an effect expected from the action of a detergent. We further show that Aβ oligomers cause widespread curvature and discontinuities within lipid vesicle membranes. In contrast, this detergent-like effect was not observed for Aβ monomers and fibers, although Aβ fibers did laterally associate and embed into the upper leaflet of the bilayer. The marked impact of Aβ oligomers on membrane integrity identified here reveals a mechanism by which these oligomers may be cytotoxic.

Keywords: Alzheimer disease; amyloid-beta (AB); atomic force microscopy (AFM); cytotoxicity; electron microscopy (EM); large unilamellar vesicles; membrane bilayer; membrane disruption; mica surface; nanoscale imaging; neurodegeneration; oligomer.

Figure 1.

Aβ42 oligomers have a detergent-like effect on the bilayer, which is not seen for Aβ42 monomer nor Aβ42 fibers. AFM topographical images are shown for mica-supported lipid bilayers on exposure to Aβ42 monomer (a), Aβ42 heterogeneous oligomer (b), and Aβ42 fiber (c). Height scale range, 12 nm. d, height cross-sections. e, percentage of bilayer coverage at the edge of a lipid bilayer, exposed to Aβ42 monomer (green), heterogeneous oligomer (blue), and fiber (red). Each data point represents an average percentage of bilayer coverage within a 0.1 × 0.5-μm region. There were 20 measurements per data point, measured across three separate mica-supported lipid bilayer preparations. Error bars, S.E.

Figure 2.

Aβ42 oligomer causes holes within supported lipid bilayers. a (left), AFM topographical image depicting a region of supported lipid bilayer which has holes formed after incubation with Aβ42 heterogeneous oligomer. Height color scale range, 12 nm. Right, binary map of holes, generated by height threshold. b, height cross-section. Typically, both the upper and lower leaflets of bilayer are extracted. Scale bar, 0.3 μm. c, range of hole diameters with a modal value of 50 nm.

Figure 3.

Aβ fibers embed into the lipid bilayer, displacing the upper leaflet. a, AFM topographical images show Aβ42 fibers on mica (left) and on the surface of a lipid bilayer (right). Scale bar, 1 μm. Height scale range, 12 nm. Each image is accompanied by a height cross-section. b, mean Aβ42 fiber height recorded both on mica and above the bilayer surface. c, a scaled schematic showing how Aβ fibers displace the upper leaflet of the membrane as fibers laterally embed into the bilayer. Error bars, S.E.

Figure 4.

Aβ oligomer disruption of lipid vesicles. a–c, TEM negative-stain images of LUVs in the presence of Aβ42 (10 μm) monomer (a), Aβ42 (10 μm) heterogeneous oligomers (b), and Aβ42 (10 μm) fibers (c). Scale bars, 100 nm. Aβ42 oligomers cause widespread curvature and discontinuities of the membrane lipid bilayer, whereas vesicles are relatively unaffected by Aβ42 monomers and fibers.

Figure 5.

The mechanisms of β-amyloid mediated membrane disruption depends on Aβ structure. Aβ monomers, oligomers, and fibers have distinct impacts on membrane integrity. a, Aβ monomers have little impact on membrane structure. b, only oligomeric Aβ42 has the ability to form ion channel pores in cellular membranes (7). c, oligomers of both Aβ42 and Aβ40 have a widespread detergent effect causing lipid extraction, curvature, and rupture of the membrane bilayer. d, the ability of Aβ to form ion channels or have a detergent effect is lost on assembly into amyloid fibers; instead, fibers can laterally embed into the membrane and displace the upper leaflet of the bilayer. The fiber structure is taken from Protein Data Bank entry 2MXU (44).