ABSTRACT
The formation of Aß amyloid fibrils is a neuropathological hallmark of Alzheimer's disease and cerebral amyloid angiopathy. However, the structure of Aß amyloid fibrils from brain tissue is poorly understood. Here we report the purification of Aß amyloid fibrils from meningeal Alzheimer's brain tissue and their structural analysis with cryo-electron microscopy. We show that these fibrils are polymorphic but consist of similarly structured protofilaments. Brain derived Aß amyloid fibrils are right-hand twisted and their peptide fold differs sharply from previously analyzed Aß fibrils that were formed in vitro. These data underscore the importance to use patient-derived amyloid fibrils when investigating the structural basis of the disease.
Subject(s)
Alzheimer Disease/metabolism , Alzheimer Disease/pathology , Amyloid/metabolism , Brain/metabolism , Brain/pathology , Cryoelectron Microscopy/methods , Amyloid beta-Peptides/metabolism , Humans , NeuropathologyABSTRACT
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 Aß 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 Aß fibrils within a cell culture model of Alzheimer's disease. STEM images taken from the formed Aß 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.
Subject(s)
Amyloid/metabolism , Amyloid/ultrastructure , Cell Membrane/metabolism , Plaque, Amyloid/metabolism , Plaque, Amyloid/ultrastructure , Alzheimer Disease/metabolism , Amyloid beta-Peptides/metabolism , Cell Membrane/ultrastructure , Cell Survival , Cells, Cultured , Electron Microscope Tomography , Humans , Lipids , Plaque, Amyloid/pathology , Protein Aggregates , Protein Aggregation, PathologicalABSTRACT
Electron tomography is an increasingly powerful method to study the detailed architecture of macromolecular complexes or cellular structures. Applied to amyloid deposits formed in a cell culture model of systemic amyloid A amyloidosis, we could determine the structural morphology of the fibrils directly in the deposit. The deposited fibrils are arranged in different networks, and depending on the relative fibril orientation, we can distinguish between fibril meshworks, fibril bundles, and amyloid stars. These networks are frequently infiltrated by vesicular lipid inclusions that may originate from the death of the amyloid-forming cells. Our data support the role of nonfibril components for constructing fibril deposits and provide structural views of different types of lipid-fibril interactions.
