AD constitutes a critical health problem, with millions of individuals worldwide suffering from AD-associated loss of cognition and dementia. There are two types of peptide aggregates: amyloid beta, found in extracellular plaques, and the intracellular microtubule associated tau protein which forms neurofibrillary tangles. Emerging evidence indicates that these aggregates interact and damage the neuronal membrane, but the mechanism remains elusive.
Visualisation of the interaction of amyloid peptides with the neuronal membrane
The AMNEsIA project, undertaken with the support of the Marie Skłodowska-Curie programme, aimed to shed light on the underlying mechanism of toxicity of amyloid peptide aggregates. “Our goal was to visualise at the nanoscale the interaction of amyloid peptides with membranes over time,” explains the MSCA fellow Cécile Feuillie. In collaboration with the Institute of Chemistry and Biology of Membranes and Nano-objects (CBMN) in Bordeaux, Feuillie employed atomic force microscopy (AFM) to study the association of amyloid beta aggregates with lipid bilayers that mimicked in nature the neuronal membrane. At the same time, the scientific team developed a method for generating amyloid peptides of homogeneous structure and tested their impact on target membranes. This approach overcame two major challenges: the inherent complexity of biological membranes in terms of lipid composition and the heterogeneous aggregation state of amyloid peptides. Researchers assessed the influence of composition, charge and packing density of membrane lipids on the amyloid peptide interaction with biomimetic membranes. AFM offered a high spatial and temporal resolution that enabled scientists to image rapid phenomena of membrane degradation induced by amyloid oligomers. “We observed in real time a rapid detergent-like effect on membranes upon interaction with amyloid peptides,” emphasises Feuillie. Both amyloid beta peptide and tau interacted with specific membrane lipids, such as ganglioside GM1 and cholesterol in the case of amyloid beta, to induce membrane degradation. These findings clearly underscored the importance of lipids in the amyloid peptide toxicity encountered in AD. At the same time, they highlighted the need for further investigation under more biologically relevant conditions where a combination of lipids is present in the target membranes.
Future prospects of AFM in AD research
AMNEsIA has successfully developed a robust AFM-based methodology for studying dynamic processes such as peptide-membrane interactions. By labelling lipids and amyloid peptides, it is possible to combine AFM with fluorescence microscopy and enhance the imaging of the interaction. Collectively, this work has important ramifications for understanding the pathogenic events that lead to AD-associated neurodegeneration and paves the way for the identification of novel targets for treatment. Future plans include the development of an AFM-based spectroscopy approach to study the mechanism of amyloid fibre formation at the chemical level. Moreover, functionalised AFM probes carrying a covalently attached amyloid peptide can be used to study the interaction with the membrane at the molecular level. “AMNEsIA has had a great impact on the AFM team of CBMN which is now called ‘Nanobiotechnology and methodological developments in AFM’,” concludes Feuillie.
AMNEsIA, AFM, AD, neuronal membrane, amyloid beta, tau, Alzheimer’s disease, atomic force microscopy