Direct Observation of Single Amyloid-[beta]

• Published in: PloS one Vol. 6; no. 8; p. e23970
• Main Authors: Johnson, Robin D, Schauerte, Joseph A, Wisser, Kathleen C, Gafni, Ari, Steel, Duncan G
• Format: Journal Article
• Language: English
• Published: Public Library of Science 25.08.2011
• Subjects: Oligomers; Peptides; Physiological aspects
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0023970

Understanding how amyloid-[beta] peptide interacts with living cells on a molecular level is critical to development of targeted treatments for Alzheimer's disease. Evidence that oligomeric A[beta] interacts with neuronal cell membranes has been provided, but the mechanism by which membrane binding occurs and the exact stoichiometry of the neurotoxic aggregates remain elusive. Physiologically relevant experimentation is hindered by the high A[beta] concentrations required for most biochemical analyses, the metastable nature of A[beta] aggregates, and the complex variety of A[beta] species present under physiological conditions. Here we use single molecule microscopy to overcome these challenges, presenting direct optical evidence that small A[beta](1-40) oligomers bind to living neuroblastoma cells at physiological A[beta] concentrations. Single particle fluorescence intensity measurements indicate that cell-bound A[beta] species range in size from monomers to hexamers and greater, with the majority of bound oligomers falling in the dimer-to-tetramer range. Furthermore, while low-molecular weight oligomeric species do form in solution, the membrane-bound oligomer size distribution is shifted towards larger aggregates, indicating either that bound A[beta] oligomers can rapidly increase in size or that these oligomers cluster at specific sites on the membrane. Calcium indicator studies demonstrate that small oligomer binding at physiological concentrations induces only mild, sporadic calcium leakage. These findings support the hypothesis that small oligomers are the primary A[beta] species that interact with neurons at physiological concentrations.