Interaction between phpspholipid bilayers and Alzheimer’s Aß(25-35)

There is mounting evidence that the lipid matrix of neuronal cell membranes plays an important role in the accumulation of β-amyloid peptides into senile plaques, one of the hallmarks of Alzheimer’s disease (AD). With the aim to clarify the molecular basis of the interaction between amyloid peptides and cellular membranes, we investigated the interaction between a cytotoxic fragment of Aβ(1-42), i.e., Aβ (25-35), and phospholipid bilayer membranes. These systems were studied by Electron Paramagnetic Resonance (EPR) spectroscopy, using either phospholipids spin-labeled on the acyl chain or spin-labeled cholesterol. The effect of inclusion of charged phospholipids or/and cholesterol in the bilayer composition was considered in relation to the peptide/membrane interaction. The results show that Aβ(25-35) inserts in bilayers formed by the zwitterionic phospholipid dilauroyl phosphatidylcholine (DLPC), positioning between the outer part of the hydrophobic core and the external hydrophilic layer. This process is not significantly influenced by the inclusion of the anionic phospholipid phosphatidylglycerol (DLPG) in the bilayer, indicating the peptide insertion to be driven by hydrophobic rather than electrostatic interactions. Cholesterol plays a fundamental role in regulating the peptide/membrane association, inducing a membrane transition from a fluid-disordered to a fluid-ordered phase. At low cholesterol content, in the fluid-disordered phase, the insertion of the peptide in the membrane causes a displacement of cholesterol towards the more external part of the membrane, probably because of a direct cholesterol-peptide association. The crowding of cholesterol enhances its rigidifying effect on this region of the bilayer. Finally, the cholesterol-rich fluid-ordered membrane looses the ability to include Aβ(25-35).