Modulation of aggregation and structural polymorphisms of β-amyloid fibrils in cellular environments by pyroglutamate-3 variant cross-seeding.

Amyloidogenic deposition of β-amyloid (Aβ) peptides in human brain involves not only the wild-type Aβ (wt-Aβ) sequences, but also posttranslationally modified Aβ (PTM-Aβ) variants. Recent studies hypothesizes that the PTM-Aβ variants may trigger the deposition of wt-Aβ, which underlies the pathology of Sporadic Alzheimer's disease. Among PTM-Aβ variants, the pyroglutamate-3-Aβ (E3-Aβ) has attracted much attention because of their significant abundances and broad distributions in senile plaques and dispersible and soluble oligomers. E3-specific antibodies are being tested as potential anti-Aβ drugs in clinical trials. However, evidence that support the triggering effect of E3-Aβ on wt-Aβ in cells remain lacking, which diminishes its pathological relevance. We show here that cross-seeding with E3-Aβ leads to accelerated extracellular and intracellular aggregation of wt-Aβ in different neuronal cells. Cytotoxicity levels are elevated through the cross-seeded aggregation, comparing with the self-seeded aggregation of wt-Aβ or the static presence of E3-Aβ seeds. For the extracellular deposition in mouse neuroblastoma Neuro2a (N2a) cells, the cytotoxicity elevation correlates positively with the seeding efficiency. Besides aggregation rates, cross-seeding with E3-Aβ also modulates the molecular level structural polymorphisms of the resultant wt-Aβ fibrils. Using solid-state nuclear magnetic resonance (ssNMR) spectroscopy, we identified key structural differences between the parent E3/ΔE3 and wt-Aβ fibrils within their fibrillar cores. Structural propagation from seeds to daughter fibrils is demonstrated to be more pronounced in the extracellular seeding in N2a cells by comparing the ssNMR spectra from different seeded wt-Aβ fibrils, but less significant in the intracellular seeding process in human neuroblastoma SH-SY5Y cells.