Alzheimer’s disease (AD) is a chronic neurodegenerative disease, characterized by loss of neurons and synapses in the cerebral cortex, whose molecular basis are still not clear. According to the amyloid hypothesis, AD is considered a protein misfolding disease because characterized by the formation of the amyloid plaques in the neuropil due to the accumulation of insoluble amyloid fibrils1. These amyloid fibrils are composed of amyloid-β peptide (Aβ), a 39-43 amino acid residue peptide produced by cleavage from the amyloid precursor protein (APP). The peptide is involved in a conformational switch that leads it to the formation of ordered aggregates with a fibrillar structure rich in β-sheet with a high level of kinetic and thermodynamic stability2. The polymerization pathway gives rise to oligomeric intermediates, transiently formed during fibril assembly, that could be involved in the pathogenic process3. The interaction of the Aβ oligomers and fibrils with neuron membranes is a crucial step in the neurodegenerative process of the AD. It is believed that they can form ion channels in the neuron membranes that are responsible for the disruption of the cellular calcium ion homeostasis, which leads it to apoptosis4. The understanding of the molecular mechanisms at the basis of AD is a crucial step for the developing of drugs and treatments. The amyloid state was identified in the context of many diseases5, but it is also possible to convert a wide range of non pathological peptides into fibrils, with the same features, under appropriate laboratory conditions6.
Aiming to understand the mechanisms through which the amyloid fibrils interact with the phospholipid bilayer causing neuronal membrane damage, we report a study on the interaction of hen egg white lysozyme (HEWL) at different stages of fibrillation7 and large unilamellar vesicles (LUVs) as membrane model system. The LUVs were prepared by extrusion and Carboxyfluorescein was used as a fluorescence probe able to detect the interaction between LUVs and lysozyme aggregates in solution. LUVs size and stability was monitored by dynamic light scattering and small angle X-ray scattering (SAXS). The kinetic of aggregation of HEWL was investigated by Thioflavin T (ThT) fluorescence and SAXS. The interactions between intermediate and final amyloid aggregates and LUVs were studied by a Carboxyfluorescein fluorescence assay, suggesting different responses of the model cellular membrane in respect to different lysozyme aggregates.
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4T.L. Williams, et al., Langmuir, 26(22):17260-8 (2010);
5 C.A. Ross, M.A. Poirier, Nat Med, 10:S10-S17 (2004);
6C.M. Dobson, Nature, 426:884-890 (2003);
7S. Poniková, et al., J Biol Inorg Chem, 20(6):921-33 (2015).