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Rare individual amyloid-? oligomers act on astrocytes to initiate neuronal damage.

ABSTRACT: Oligomers of the amyloid-? (A?) peptide have been implicated in the neurotoxicity associated with Alzheimer's disease. We have used single-molecule techniques to examine quantitatively the cellular effects of adding well characterized A? oligomers to primary hippocampal cells and hence determine the initial pathway of damage. We found that even picomolar concentrations of A? (1-40) and A? (1-42) oligomers can, within minutes of addition, increase the levels of intracellular calcium in astrocytes but not in neurons, and this effect is saturated at a concentration of about 10 nM of oligomers. Both A? (1-40) and A? (1-42) oligomers have comparable effects. The rise in intracellular calcium is followed by an increase in the rate of ROS production by NADPH oxidase in both neurons and astrocytes. The increase in ROS production then triggers caspase-3 activation resulting in the inhibition of long-term potentiation. Our quantitative approach also reveals that only a small fraction of the oligomers are damaging and that an individual rare oligomer binding to an astrocyte can initiate the aforementioned cascade of responses, making it unlikely to be due to any specific interaction. Preincubating the A? oligomers with an extracellular chaperone, clusterin, sequesters the oligomers in long-lived complexes and inhibits all of the physiological damage, even at a ratio of 100:1, total A? to clusterin. To explain how A? oligomers are so damaging but that it takes decades to develop Alzheimer's disease, we suggest a model for disease progression where small amounts of neuronal damage from individual unsequestered oligomers can accumulate over time leading to widespread tissue-level dysfunction.

SUBMITTER: Narayan P

PROVIDER: S-EPMC4004235 | biostudies-literature | 2014 Apr

REPOSITORIES: biostudies-literature

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Rare individual amyloid-β oligomers act on astrocytes to initiate neuronal damage.

Narayan Priyanka P Holmström Kira M KM Kim Dong-Hyun DH Whitcomb Daniel J DJ Wilson Mark R MR St George-Hyslop Peter P Wood Nicholas W NW Dobson Christopher M CM Cho Kwangwook K Abramov Andrey Y AY Klenerman David D

Biochemistry 20140409 15

Oligomers of the amyloid-β (Aβ) peptide have been implicated in the neurotoxicity associated with Alzheimer's disease. We have used single-molecule techniques to examine quantitatively the cellular effects of adding well characterized Aβ oligomers to primary hippocampal cells and hence determine the initial pathway of damage. We found that even picomolar concentrations of Aβ (1-40) and Aβ (1-42) oligomers can, within minutes of addition, increase the levels of intracellular calcium in astrocytes ...[more]

PMID: 24717093

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Project description:Introduction: ?-Amyloid protein (A?) putatively plays a seminal role in synaptic loss in Alzheimer's disease (AD). While there is no consensus regarding the synaptic-relevant species of A?, it is known that A? oligomers (A?Os) are noticeably increased in the early stages of AD, localizing at or within the synapse. In cell and animal models, A?Os 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 A?Os attach. Methods: An unbiased approach using far western ligand blots has identified three synaptic proteins to which A?Os 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 A?Os targets in human AD and aging frontal cortexes were analyzed by quantitative proteomics and western-blot. The polyclonal antibody to A?Os was developed and used to block the toxicity of A?Os. The data were analyzed with one-way analysis of variance. Results: A?Os binding proteins p100, p140, and p260 were identified as Na/K-ATPase, synGap, and Shank3, respectively. ?3-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 A? inhibited Na/K-ATPase at the synapse. Na/K-ATPase activity was restored by an antibody specific for soluble forms of A?. ?3-Na/K-ATPase protein and synaptic ?-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 A? oligomers, while later stages could hypothetically result from disrupted synapse structure involving the PSD proteins synGap and Shank3. Conclusion: We identified three A?O binding proteins as ?3-Na/K-ATPase, synGap, and Shank3. Soluble A? 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.

Project description:The purpose of our study was to determine the relationship between mutant huntingtin (Htt) and mitochondrial dynamics in the progression of Huntington's disease (HD). We measured the mRNA levels of electron transport chain genes, and mitochondrial structural genes, Drp1 (dynamin-related protein 1), Fis1 (fission 1), Mfn1 (mitofusin 1), Mfn2 (mitofusin 2), Opa1 (optric atrophy 1), Tomm40 (translocase of outermembrane 40) and CypD (cyclophilin D) in grade III and grade IV HD patients and controls. The mutant Htt oligomers and the mitochondrial structural proteins were quantified in the striatum and frontal cortex of HD patients. Changes in expressions of the electron transport chain genes were found in HD patients and may represent a compensatory response to mitochondrial damage caused by mutant Htt. Increased expression of Drp1 and Fis1 and decreased expression of Mfn1, Mfn2, Opa1 and Tomm40 were found in HD patients relative to the controls. CypD was upregulated in HD patients, and this upregulation increased as HD progressed. Significantly increased immunoreactivity of 8-hydroxy-guanosine was found in the cortical specimens from stage III and IV HD patients relative to controls, suggesting increased oxidative DNA damage in HD patients. In contrast, significantly decreased immunoreactivities of cytochrome oxidase 1 and cytochrome b were found in HD patients relative to controls, indicating a loss of mitochondrial function in HD patients. Immunoblotting analysis revealed 15, 25 and 50 kDa mutant Htt oligomers in the brain specimens of HD patients. All oligomeric forms of mutant Htt were significantly increased in the cortical tissues of HD patients, and mutant Htt oligomers were found in the nucleus and in mitochondria. The increase in Drp1, Fis1 and CypD and the decrease in Mfn1 and Mfn2 may be responsible for abnormal mitochondrial dynamics that we found in the cortex of HD patients, and may contribute to neuronal damage in HD patients. The presence of mutant Htt oligomers in the nucleus of HD neurons and in mitochondria may disrupt neuronal functions. Based on these findings, we propose that mutant Htt in association with mitochondria imbalance and mitochondrial dynamics impairs axonal transport of mitochondria, decreases mitochondrial function and damages neurons in affected brain regions of HD patients.

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Rare individual amyloid-? oligomers act on astrocytes to initiate neuronal damage.

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Rare individual amyloid-β oligomers act on astrocytes to initiate neuronal damage.

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