Controlled Seeding of β-Amyloid Fibrillation Reveals Propagation of Structural Polymorphisms in Cellular Environments

Molecular-level structural polymorphisms of β-amyloid (Aβ) aggregates in Alzheimer's disease patients are pathologically important. However, tracking the propagation and modulation of Aβ structural polymorphisms via ex vivo approaches remains challenging. The successful application of cryogenic transmission electron microscopy (cryo-TEM) in this area relies on the availability of morphologically distinct micrographs, which then enable unambiguous three-dimensional structural reconstruction of individual fibrillar polymorphs to achieve optimal resolution. As a complementary approach, solid-state nuclear magnetic resonance (ssNMR) spectroscopy with guided isotope-labeling schemes can provide site-specific and quantitative information on the populations of individual polymorphs. Such ssNMR sample preparations require ex vivo seeding, in which key parameters─including seed concentration and seeding time─must be carefully controlled for individual Aβ-cell systems to avoid the introduction of self-nucleated fibrillar polymorphs. In this work, we show that the application of controlled ex vivo seeding combined with quantitative ssNMR spectroscopy reveals the propagation of molecular-level structural polymorphs, depending on the types of seeds and cells.