Small Angle X-ray Scattering Sensing Membrane Composition: The Role of Sphingolipids in Membrane-Amyloid β-Peptide Interaction

Abstract

The early impairments appearing in Alzheimer’s disease are related to neuronal membrane damage. Both aberrant Aβ species and specific membrane components play a role in promoting aggregation, deposition, and signaling dysfunction. Ganglioside GM1, present with cholesterol and sphingomyelin in lipid rafts, preferentially interacts with the Aβ peptide. GM1 at physiological conditions clusters in the membrane, the assembly also involves phospholipids, sphingomyelin, and cholesterol. The structure of large unilamellar vesicles (LUV), made of a basic POPC:POPS matrix in a proportion of 9:1, and containing different amounts of GM1 (1%, 3%, and 4% mol/mol) in the presence of 5% mol/mol sphingomyelin and 15% mol/mol cholesterol, was studied using small angle X-ray scattering (SAXS). The effect of the membrane composition on the LUVs–Aβ-peptide interaction, both for Aβ1–40 and Aβ1–42 variants, was, thus, monitored. The presence of GM1 leads to a significant shift of the main peak, towards lower scattering angles, up to 6% of the initial value with SM and 8% without, accompanied by an opposite shift of the first minimum, up to 21% and 24% of the initial value, respectively. The analysis of the SAXS spectra, using a multi-Gaussian model for the electronic density profile, indicated differences in the bilayer of the various compositions. An increase in the membrane thickness, by 16% and 12% when 2% and 3% mol/mol GM1 was present, without and with SM, respectively, was obtained. Furthermore, in these cases, in the presence of Aβ40, a very small decrease of the bilayer thickness, less than 4% and 1%, respectively, was derived, suggesting the inhibiting effect that the presence of sphingomyelin has on the GM1–Aβ interaction.

Cholesterol as a key player in amyloid β-mediated toxicity in Alzheimer’s disease

“…It appears that cholesterol can promote or inhibit Aβ aggregation at the membrane, affect the secondary structure of amyloid and its ability to penetrate the bilayer (Williams and Serpell, 2011 ; Yu and Zheng, 2012 ). Many factors influence the outcome of the interaction: the molar ratio of lipid/cholesterol in the cell membrane, the presence of anionic lipids, SM, and gangliosides (especially GM1), lipid membrane ordering and fluidity, the amyloid species, the extent of Aβ oligomerization, the pH, the presence of other proteins or amyloid membrane receptors (Yu and Zheng, 2012 ; Meleleo et al, 2013 ; Dies et al, 2014 ; Amaro et al, 2016 ; West et al, 2017 ; Owen et al, 2018 ; Carrotta et al, 2021 ; Smeralda et al, 2021 ; Wiatrak et al, 2021 ). Moreover, physical parameters such as macromolecular crowding or vesicle size and membrane curvature play a role in Aβ–membrane interaction (Hirai et al, 2018 ; Terakawa et al, 2018 ).…”

“…It must be emphasized that Aβ40 and Aβ42 differ significantly in their interaction with membranes. Aβ42 exhibits a higher ability to bind the bilayer or form Ca 2+ -selective transmembrane pores and shows more complex behavior than Aβ40 (Yip et al, 2001 ; Williams et al, 2010 ; Phan et al, 2013 ; Bode et al, 2017 ; Carrotta et al, 2021 ).…”

“…Moreover, there is a difference in the interaction of Aβ40 and Aβ42 with membranes, as Aβ42, but not Aβ40, bound to Ld-phase liposomes formed from 1-palmitoyl-2-oleoylphosphatidylserine, POPC, and 15% cholesterol. The addition of SM led to the formation of Lo phase and increased Aβ40- but decreased Aβ42-membrane association (Carrotta et al, 2021 ). Fluorescence colocalization experiments on lipid vesicles revealed that Aβ42 was preferentially bound to and incorporated into the Ld phase.…”

αS1-Casein-Loaded Proteo-liposomes as Potential Inhibitors in Amyloid Fibrillogenesis: In Vivo Effects on a C. elegans Model of Alzheimer’s Disease

“…By modeling the electronic density with a combination of three Gaussians and using the Fourier transform of this model function to fit the data, it is possible to extract information about the structure of the bilayer. − The three Gaussians account for the electronic density distribution of the two internal and external polar lipid heads and the third one of the central hydrophobic matrix, giving relative contrast with respect to the bulk.…”

“…The Gaussian representing the hydrophobic interior was taken ϵ 1 = 0 and ρ 1 = 1, as described elsewhere. 58 The bilayer thickness is evaluated as d = ϵ 3 − ϵ 2 , i.e., the distance between the internal and external polar head peaks. MALS and SAXS data in Figure 2a are sewed according to the expression: Animal treatments with α s1 -Casein, Lip0, LipCas, and buffer as control were performed in liquido in 96-multiwell plates from Falcon (cat.…”