Modulation of aggregation and structural polymorphisms of β-amyloid fibrils in cellular environments by pyroglutamate-3 variant cross-seeding
Letticia Cruceta, Yan Sun, June M. Kenyaga, Dmitry Ostrovsky, Aryana Rodgers, Liliya Vugmeyster, Lan Yao, Wei Qiang
Abstract
Amyloidogenic deposition of β-amyloid (Aβ) peptides in human brain involves not only the wild-type Aβ (wt-Aβ) sequences, but also a heterogeneous pool of post-translationally modified Aβ (PTM-Aβ) variants. Recent studies raise a hypothesis that the PTM-Aβ variants may trigger the deposition of wt-Aβ, which may underlie the pathology of sporadic Alzheimer's disease (sAD). Among all PTM-Aβ variants, the pyroglutamate-3-Aβ ( pyro E3-Aβ) has attracted much attention because of their significant abundances and broad distributions in not only senile plaques but also dispersible and soluble oligomers. pyro E3-specific antibodies are being tested as potential anti-Aβ drugs in clinical trials. However, evidence that support the triggering effect of pyro E3-Aβ on wt-Aβ in cellular environments remain lacking, which diminishes its pathological relevance. We show here that cross-seeding with pyro E3-Aβ 40 leads to accelerated extra- and intracellular amyloid deposition of wt-Aβ 40 in different neuronal cells. Cytotoxicity levels are elevated through the cross-seeded aggregation process, comparing with the self-seeded aggregation of wt-Aβ 40 or the static presence of pyro E3-Aβ 40 seeds. For the extracellular deposition that occurs predominantly in mouse neuroblastoma Neuro2a (N2a) cells, the cytotoxicity elevation correlates positively with the seeding efficiency. Besides aggregation rates, cross-seeding with pyro E3-Aβ 40 also modulates the molecular level structural polymorphisms of the resultant wt-Aβ 40 fibrils. Using solid-state nuclear magnetic resonance (ssNMR) spectroscopy, we identified key structural differences between the parent pyro E3/ΔE3 and wt-Aβ 40 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 40 fibrils, but less significant in the intracellular seeding process in human neuroblastoma SH-SY5Y cells.