Amyloid plaque structure and cell surface interactions of β-amyloid fibrils revealed by electron tomography

Abstract

The deposition of amyloid fibrils as plaques is a key feature of several neurodegenerative diseases including in particular Alzheimer’s. This disease is characterized, if not provoked, by amyloid aggregates formed from Aβ peptide that deposit inside the brain or are toxic to neuronal cells. We here used scanning transmission electron microscopy (STEM) to determine the fibril network structure and interactions of Aβ fibrils within a cell culture model of Alzheimer’s disease. STEM images taken from the formed Aβ amyloid deposits revealed three main types of fibril network structures, termed amorphous meshwork, fibril bundle and amyloid star. All three were infiltrated by different types of lipid inclusions from small-sized exosome-like structures (50–100 nm diameter) to large-sized extracellular vesicles (up to 300 nm). The fibrils also presented strong interactions with the surrounding cells such that fibril bundles extended into tubular invaginations of the plasma membrane. Amyloid formation in the cell model was previously found to have an intracellular origin and we show here that it functionally destroys the integrity of the intracellular membranes as it leads to lysosomal leakage. These data provide a mechanistic link to explain why intracellular fibril formation is toxic to the cell.

Label-free characterization of Amyloid-β-plaques and associated lipids in brain tissues using stimulated Raman scattering microscopy

“…Label-free SRS imaging of brain slices from a transgenic mouse model of Alzheimer's Disease reveals large numbers of Aβ aggregates, which we find are consistently surrounded by a halo of lipid-rich deposits. Similar associations of lipids with Aβ plaques have been observed in earlier studies using coherent Raman scattering 6,7 , imaging mass spectrometry 32 and electron microscopy 33 , albeit with much lower spatial resolution or with a lack of chemical specificity. Interactions of lipids with pathological Aβ structures are under active investigation for their relevance to AD disease progression, because lipids are thought to have the capacity to extract small Aβ oligomers from aggregates in a detergent-like fashion 34 , thereby facilitating their transport to the intracellular space where they become neurotoxic.…”

In situ SAXS of protein deposits in Alzheimer’s disease

“…The observation of larger, Rxc ~ 150 Å, aggregates within protein deposits in these tissues indicates the presence of material that is composed of fibrils that are tightly packed, coalescing side-to-side to form large fibrillar aggregates or bundles that likely represents abundant constituents of neuritic plaques. This coalescence, or bundling of fibrils is consistent with the long-range correlation of fibril orientations reported to extend over >10 microns in dense plaques 15 and the observation of bundles of A fibrils in vitro 18 and in a cell culture model of AD 19 . These observations suggest that very tight packing density is a common property of amyloid within dense cores of protein aggregates in human brain.…”

“…Although larger than most amyloid fibrils that have been observed in vitro, the paucity of previous reports may be due to difficulties intrinsic to the isolation and detailed analysis of large bundles or coalesced aggregates of material. Furthermore, twisted bundles of fibrils have been assembled in vitro 18 and bundles have been observed in a cell culture model of Alzheimer's disease 19 . Since all aspects of the scattering data and neuropathology are consistent with their being composed of A fibrils, our interpretation is that they represents aggregates of A fibrils that have coalesced side-to-side to create fibrillar bundles or macrofibrillar aggregates.…”

“…Fourier transform infrared micro-spectroscopy has been used to demonstrate conformational changes in A structures prior to formation of amyloid plaques in transgenic mouse models of AD 16 . Whereas most amyloid fibrils appear to be 5-20 nm in diameter, depending on the number of constituent protofilaments 17 , much larger, tightly packed bundles of fibrils have been observed after long term incubation in vitro 18 or in tomographic reconstructions of amyloid in a cell culture model of AD 19 . At still larger length scales, plaques exhibit a variety of morphologies.…”

Atividades biológicas dos alcaloides de Annona crassiflora Mart.

“…Caracteriza-se pela formação extracelular de placas amiloides formados a partir do peptídeo β-amiloide, derivando em uma hiperfosforilação das proteínas tau (proteínas que estabilizam os microtúbulos), desencadeando uma deficiência do neurotransmissor acetilcolina no cérebro (Acqua, 2013;Han et al, 2017 (Girdhar et al, 2015).…”