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Amyloid-? oligomers are sequestered by both intracellular and extracellular chaperones.

ABSTRACT: The aberrant aggregation of the amyloid-? peptide into ?-sheet rich, fibrillar structures proceeds via a heterogeneous ensemble of oligomeric intermediates that have been associated with neurotoxicity in Alzheimer's disease (AD). Of particular interest in this context are the mechanisms by which molecular chaperones, part of the primary biological defenses against protein misfolding, influence A? aggregation. We have used single-molecule fluorescence techniques to compare the interactions between distinct aggregation states (monomers, oligomers, and amyloid fibrils) of the AD-associated amyloid-?(1-40) peptide, and two molecular chaperones, both of which are upregulated in the brains of patients with AD and have been found colocalized with A? in senile plaques. One of the chaperones, ?B-crystallin, is primarily found inside cells, while the other, clusterin, is predominantly located in the extracellular environment. We find that both chaperones bind to misfolded oligomeric species and form long-lived complexes, thereby preventing both their further growth into fibrils and their dissociation. From these studies, we conclude that these chaperones have a common mechanism of action based on sequestering A? oligomers. This conclusion suggests that these chaperones, both of which are ATP-independent, are able to inhibit potentially pathogenic A? oligomer-associated processes whether they occur in the extracellular or intracellular environment.

SUBMITTER: Narayan P

PROVIDER: S-EPMC4981287 | biostudies-literature | 2012 Nov

REPOSITORIES: biostudies-literature

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Amyloid-β oligomers are sequestered by both intracellular and extracellular chaperones.

Narayan Priyanka P Meehan Sarah S Carver John A JA Wilson Mark R MR Dobson Christopher M CM Klenerman David D

Biochemistry 20121108 46

The aberrant aggregation of the amyloid-β peptide into β-sheet rich, fibrillar structures proceeds via a heterogeneous ensemble of oligomeric intermediates that have been associated with neurotoxicity in Alzheimer's disease (AD). Of particular interest in this context are the mechanisms by which molecular chaperones, part of the primary biological defenses against protein misfolding, influence Aβ aggregation. We have used single-molecule fluorescence techniques to compare the interactions betwee ...[more]

PMID: 23106396

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Project description:Introduction: β-Amyloid protein (Aβ) putatively plays a seminal role in synaptic loss in Alzheimer's disease (AD). While there is no consensus regarding the synaptic-relevant species of Aβ, it is known that Aβ oligomers (AβOs) are noticeably increased in the early stages of AD, localizing at or within the synapse. In cell and animal models, AβOs have been shown to attach to synapses and instigate synapse dysfunction and deterioration. To establish the pathological mechanism of synaptic loss in AD, it will be important to identify the synaptic targets to which AβOs attach. Methods: An unbiased approach using far western ligand blots has identified three synaptic proteins to which AβOs specifically attach. These proteins (p100, p140, and p260) were subsequently enriched by detergent extraction, ultracentrifugation, and CHT-HPLC column separation, and sequenced by LC-MS/MS. P100, p140, and p260 were identified. These levels of AβOs targets in human AD and aging frontal cortexes were analyzed by quantitative proteomics and western-blot. The polyclonal antibody to AβOs was developed and used to block the toxicity of AβOs. The data were analyzed with one-way analysis of variance. Results: AβOs binding proteins p100, p140, and p260 were identified as Na/K-ATPase, synGap, and Shank3, respectively. α3-Na/K-ATPase, synGap, and Shank3 proteins showed loss in the postsynaptic density (PSD) of human AD frontal cortex. In short term experiments, oligomers of Aβ inhibited Na/K-ATPase at the synapse. Na/K-ATPase activity was restored by an antibody specific for soluble forms of Aβ. α3-Na/K-ATPase protein and synaptic β-amyloid peptides were pulled down from human AD synapses by co-immunoprecipitation. Results suggest synaptic dysfunction in early stages of AD may stem from inhibition of Na/K-ATPase activity by Aβ oligomers, while later stages could hypothetically result from disrupted synapse structure involving the PSD proteins synGap and Shank3. Conclusion: We identified three AβO binding proteins as α3-Na/K-ATPase, synGap, and Shank3. Soluble Aβ oligomers appear capable of attacking neurons via specific extracellular as well as intracellular synaptic proteins. Impact on these proteins hypothetically could lead to synaptic dysfunction and loss, and could serve as novel therapeutic targets for AD treatment by antibodies or other agents.

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Amyloid-? oligomers are sequestered by both intracellular and extracellular chaperones.

Publications

Amyloid-β oligomers are sequestered by both intracellular and extracellular chaperones.

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