Membrane interaction and disruption by the Alzheimer's amyloid-beta peptide

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Abstract Alzheimer's disease (AD) is a neurodegenerative condition that currently affects more than 5 million Americans. AD is characterized by decreasing memory, loss of cognitive function and an eventual reduction in brain mass. The disease state can be linked to the cleavage of the amyloid precursor protein into smaller fragments - amyloidogenic peptides known as amyloid-β (Aβ). In fact, the formation of amyloid fibrils of the two most common alloforms of Aβ, Aβ1-40 and Aβ1-42, had previously been associated with disease pathology; however, mounting evidence points to misfolded intermediates being responsible for cell death in the Alzheimer's brain. There are a number of theories as to how Aβ elicits toxicity including the generation of free radicals, interaction with metal ions, activation of cell surface receptors, and the disruption of cell membrane integrity. The interaction of Aβ with the cellular membrane is especially significant given the ability of lipid- Aβ interactions to accelerate fibril formation, facilitate the formation of ion channel-like pores, and cause the fragmentation of the lipid membrane. While understanding and characterizing the formation of misfolded intermediates of Aβ in solution is very important (and ongoing), the interaction of Aβ peptides with the membrane has remained elusive and controversial. A lack of data surrounding Aβ-membrane studies is largely due to the difficulties associated with carrying out biochemical and biophysical studies in the presence of lipids, although much insight has been gained by molecular dynamics simulations which have provided a strong basis for experimental studies. In order to determine the mode of membrane-associated toxicity, there remains a need to further characterize the interactions of Aβ with the lipid membrane, determine how these interactions drive membrane disruption, and define the structures formed in the presence of the membrane. Therefore, we propose to investigate the membrane interaction of Aβ through the following aims: 1) Characterization of Aβ misfolding and aggregation in the presence of lipid membranes; 2) Atomistic resolution structure determination of Aβ in a membrane environment by solid-state NMR spectroscopy. In addition to a variety of biophysical experiments, a combination of solution and solid-state NMR techniques and molecular dynamics simulations will be used to successfully accomplish the goals of the proposed study. High-resolution insights gained from the proposed studies will guide the development of drugs to stop the neuronal death. Although the proposed study is focused on Aβ, the outcome will be of importance to other amyloid-linked diseases such as Parkinson's disease and Type II diabetes which have similar proteinopathies.