Single-Molecule Microscopy Studies of Interactions between Alzheimer's Amyloid-(1-40) and Amyloid-(1-42) on the Membrane.

[摘要] Two amyloid-β peptides (Aβ40 and Aβ42) feature prominently in the extracellular brain deposits associated with Alzheimer’s disease. While Aβ40 is the prevalent form in the cerebrospinal fluid, the fraction of Aβ42 increases in the amyloid deposits over the course of disease development. The low in vivo concentration (pM-nM) and metastable nature of Aβ oligomers have made identification of their size, composition, cellular binding sites and mechanism of action challenging and elusive. Furthermore, recent studies have suggested that synergistic effects between Aβ40 and Aβ42 alter both the formation and stability of various peptide oligomers and as well as their cytotoxicity. These studies often utilized Aβ oligomers that were prepared in solution and at μM peptide concentrations. Here we utilized various single-molecule microscopies to follow peptide binding and association on the model membrane as well as the primary cultured neurons under physiological Aβ concentrations. At these concentrations monomers constitute the dominant Aβ species in solution. These monomers tightly associate with the model membrane and are highly mobile, whereas trimers and higher-order oligomers are largely immobilized. The Aβ dimer appears to exist in a metastable state that can be either mobile or immobile. Additionally, oligomer growth on the model membrane occurs more rapidly for Aβ40 than for Aβ42 while oligomer growth is largely inhibited for a 1:1 Aβ40:Aβ42 mixture. Interestingly, when the neuronal cells were exposed to a 1:1 mixture of nM Aβ40:Aβ42, significantly larger membrane-bound oligomers developed compared to those formed from either peptide alone. Fluorescence resonance energy transfer experiments at the single molecule level reveal that these larger oligomers contained both Aβ40 and Aβ42, but that the growth of these oligomers was predominantly by addition of Aβ42. Both pure peptides form very few oligomers larger than dimers, but either cell membrane bound Aβ40/42 complex, or Aβ40, bind Aβ42 to form increasingly larger oligomers. These findings provide a hypothesis for the structural differences between Aβ42, Aβ40 and different oligomers, which may explain how Aβ42-dominant oligomers, suspected of being more cytotoxic, develop on the neuronal membrane under physiological conditions.

[发布机构] University of Michigan

[效力级别] s

[关键词] Alzheimer"s;Amyloid-beta;Single Molecule Microscopy;In Vivo Imaging;Protein Membrane Interactions Aggregation;Biological Chemistry;Physics;Science;Biophysics