Soluble Aβ Oligomers Formed Channels Leading to Calcium Dysregulation
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PROVIDER: S-EPMC10423025 | biostudies-literature | 2023 Jan
REPOSITORIES: biostudies-literature
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Project description:Aggregation of α-synuclein is a hallmark of Parkinson's disease and dementia with Lewy bodies. We here investigate the relationship between cytosolic Ca2+ and α-synuclein aggregation. Analyses of cell lines and primary culture models of α-synuclein cytopathology reveal an early phase with reduced cytosolic Ca2+ levels followed by a later Ca2+ increase. Aggregated but not monomeric α-synuclein binds to and activates SERCA in vitro, and proximity ligation assays confirm this interaction in cells. The SERCA inhibitor cyclopiazonic acid (CPA) normalises both the initial reduction and the later increase in cytosolic Ca2+ CPA protects the cells against α-synuclein-aggregate stress and improves viability in cell models and in Caenorhabditis elegans in vivo Proximity ligation assays also reveal an increased interaction between α-synuclein aggregates and SERCA in human brains affected by dementia with Lewy bodies. We conclude that α-synuclein aggregates bind SERCA and stimulate its activity. Reducing SERCA activity is neuroprotective, indicating that SERCA and down-stream processes may be therapeutic targets for treating α-synucleinopathies.
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Project description:IntroductionEvidence strongly suggests that soluble oligomers of amyloid beta protein (oAβ) help initiate the pathogenic cascade of Alzheimer's disease (AD). To date, there have been no validated assays specific for detecting and quantifying oAβ in human blood.MethodsWe developed an ultrasensitive oAβ immunoassay using a novel capture antibody (71A1) with N-terminal antibody 3D6 for detection that specifically quantifies soluble oAβ in the human brain, cerebrospinal fluid (CSF), and plasma.ResultsTwo new antibodies (71A1; 1G5) are oAβ-selective, label Aβ plaques in non-fixed AD brain sections, and potently neutralize the synaptotoxicity of AD brain-derived oAβ. The 71A1/3D6 assay showed excellent dilution linearity in CSF and plasma without matrix effects, good spike recovery, and specific immunodepletion.DiscussionWe have created a sensitive, high throughput, and inexpensive method to quantify synaptotoxic oAβ in human plasma for analyzing large cohorts of aged and AD subjects to assess the dynamics of this key pathogenic species and response to therapy.
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Project description:Transient soluble oligomers of amyloid-β (Aβ) are toxic and accumulate early prior to insoluble plaque formation and cognitive impairment in Alzheimer's disease (AD). Synthetic cyclic D,L-α-peptides (e.g., 1) self-assemble into cross β-sheet nanotubes, react with early Aβ species (1-3 mers), and inhibit Aβ aggregation and toxicity in stoichiometric concentrations, in vitro. Employing a semicarbazide as an aza-glycine residue with an extra hydrogen-bond donor to tune nanotube assembly and amyloid engagement, [azaGly6]-1 inhibited Aβ aggregation and toxicity at substoichiometric concentrations. High-resolution NMR studies revealed dynamic interactions between [azaGly6]-1 and Aβ42 residues F19 and F20, which are pivotal for early dimerization and aggregation. In an AD mouse model, brain positron emission tomography (PET) imaging using stable 64Cu-labeled (aza)peptide tracers gave unprecedented early amyloid detection in 44-d presymptomatic animals. No tracer accumulation was detected in the cortex and hippocampus of 44-d-old 5xFAD mice; instead, intense PET signal was observed in the thalamus, from where Aβ oligomers may spread to other brain parts with disease progression. Compared with standard 11C-labeled Pittsburgh compound-B (11C-PIB), which binds specifically fibrillar Aβ plaques, 64Cu-labeled (aza)peptide gave superior contrast and uptake in young mouse brain correlating with Aβ oligomer levels. Effectively crossing the blood-brain barrier (BBB), peptide 1 and [azaGly6]-1 reduced Aβ oligomer levels, prolonged lifespan of AD transgenic Caenorhabditis elegans, and abated memory and behavioral deficits in nematode and murine AD models. Cyclic (aza)peptides offer novel promise for early AD diagnosis and therapy.
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Project description:Alzheimer's disease, which is the most common form of dementia, is characterized by the aggregation of the amyloid β peptide (Aβ) and by an impairment of calcium homeostasis caused by excessive activation of glutamatergic receptors (excitotoxicity). Here, we studied the effects on calcium homeostasis caused by the formation of Aβ oligomeric assemblies. We found that Aβ oligomers cause a rapid influx of calcium ions (Ca2+) across the cell membrane by rapidly activating extrasynaptic N-methyl-d-aspartate (NMDA) receptors and, to a lower extent, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. We also observed, however, that misfolded oligomers do not interact directly with these receptors. Further experiments with lysophosphatidylcholine and arachidonic acid, which cause membrane compression and stretch, respectively, indicated that these receptors are activated through a change in membrane tension induced by the oligomers and transmitted mechanically to the receptors via the lipid bilayer. Indeed, lysophosphatidylcholine is able to neutralize the oligomer-induced activation of the NMDA receptors, whereas arachidonic acid activates the receptors similarly to the oligomers with no additive effects. An increased rotational freedom observed for a fluorescent probe embedded within the membrane in the presence of the oligomers also indicates a membrane stretch. These results reveal a mechanism of toxicity of Aβ oligomers in Alzheimer's disease through the perturbation of the mechanical properties of lipid membranes sensed by NMDA and AMPA receptors.
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Project description:Alzheimer's disease (AD) is the most common form of dementia in the elderly, and affects millions of people worldwide. As the number of AD cases continues to increase in both developed and developing countries, finding therapies that effectively halt or reverse disease progression constitutes a major research and public health challenge. Since the identification of the amyloid-β peptide (Aβ) as the major component of the amyloid plaques that are characteristically found in AD brains, a major effort has aimed to determine whether and how Aβ leads to memory loss and cognitive impairment. A large body of evidence accumulated in the past 15 years supports a pivotal role of soluble Aβ oligomers (AβOs) in synapse failure and neuronal dysfunction in AD. Nonetheless, a number of basic questions, including the exact molecular composition of the synaptotoxic oligomers, the identity of the receptor(s) to which they bind, and the signaling pathways that ultimately lead to synapse failure, remain to be definitively answered. Here, we discuss recent advances that have illuminated our understanding of the chemical nature of the toxic species and the deleterious impact they have on synapses, and have culminated in the proposal of an Aβ oligomer hypothesis for Alzheimer's pathogenesis. We also highlight outstanding questions and challenges in AD research that should be addressed to allow translation of research findings into effective AD therapies.
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Project description:Aggregation of amyloid-β (Aβ) that leads to the formation of plaques in Alzheimer's disease (AD) occurs through the stepwise formation of oligomers and fibrils. An earlier onset of aggregation is obtained upon intracerebral injection of Aβ-containing brain homogenate into human APP transgenic mice that follows a prion-like seeding mechanism. Immunoprecipitation of these brain extracts with anti-Aβ oligomer antibodies or passive immunization of the recipient animals abrogated the observed seeding activity, although induced Aβ deposition was still evident. Here, we establish that, together with Aβ monomers, Aβ oligomers trigger the initial phase of Aβ seeding and that the depletion of oligomeric Aβ delays the aggregation process, leading to a transient reduction of seed-induced Aβ deposits. This work extends the current knowledge about the role of Aβ oligomers beyond its cytotoxic nature by pointing to a role in the initiation of Aβ aggregation in vivo. We conclude that Aβ oligomers are important for the early initiation phase of the seeding process.
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Project description:Significant data suggest that soluble Aβ oligomers play an important role in Alzheimer's disease (AD), but there is great confusion over what exactly constitutes an Aβ oligomer and which oligomers are toxic. Most studies have utilized synthetic Aβ peptides, but the relevance of these test tube experiments to the conditions that prevail in AD is uncertain. A few groups have studied Aβ extracted from human brain, but they employed vigorous tissue homogenization which is likely to release insoluble Aβ that was sequestered in plaques during life. Several studies have found such extracts to possess disease-relevant activity and considerable efforts are being made to purify and better understand the forms of Aβ therein. Here, we compared the abundance of Aβ in AD extracts prepared by traditional homogenization versus using a far gentler extraction, and assessed their bioactivity via real-time imaging of iPSC-derived human neurons plus the sensitive functional assay of long-term potentiation. Surprisingly, the amount of Aβ retrieved by gentle extraction constituted only a small portion of that released by traditional homogenization, but this readily diffusible fraction retained all of the Aβ-dependent neurotoxic activity. Thus, the bulk of Aβ extractable from AD brain was innocuous, and only the small portion that was aqueously diffusible caused toxicity. This unexpected finding predicts that generic anti-oligomer therapies, including Aβ antibodies now in trials, may be bound up by the large pool of inactive oligomers, whereas agents that specifically target the small pool of diffusible, bioactive Aβ would be more useful. Furthermore, our results indicate that efforts to purify and target toxic Aβ must employ assays of disease-relevant activity. The approaches described here should enable these efforts, and may assist the study of other disease-associated aggregation-prone proteins.
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Project description:Alzheimer disease (AD) is characterized by cognitive impairment that starts with memory loss to end in dementia. Loss of synapses and synaptic dysfunction are closely associated with cognitive impairment in AD patients. Biochemical and pathological evidence suggests that soluble Aβ oligomers correlate with cognitive impairment. Here, we used the TgCRND8 AD mouse model to investigate the role of JNK in long term memory deficits. TgCRND8 mice were chronically treated with the cell-penetrating c-Jun N-terminal kinase inhibitor peptide (D-JNKI1). D-JNKI1, preventing JNK action, completely rescued memory impairments (behavioral studies) as well as the long term potentiation deficits of TgCRND8 mice. Moreover, D-JNKI1 inhibited APP phosphorylation in Thr-668 and reduced the amyloidogenic cleavage of APP and Aβ oligomers in brain parenchyma of treated mice. In conclusion, by regulating key pathogenic mechanisms of AD, JNK might hold promise as innovative therapeutic target.
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Project description:Soluble Aβ oligomers (oAβs) contribute importantly to synaptotoxicity in Alzheimer disease (AD), but the mechanisms related to heterogeneity of synaptic functions at local circuits remain elusive. Nearly all studies of the effects of oAβs on hippocampal synaptic plasticity have only examined homosynaptic plasticity. Here we stimulated the Schaffer collaterals and then simultaneously recorded in stratum radiatum (apical dendrites) and stratum oriens (basal dendrites) of CA1 neurons. We found that the apical dendrites are significantly more vulnerable to oAβ-mediated synaptic dysfunction: the heterosynaptic basal dendritic long-term potentiation (LTP) remained unchanged, whereas the homosynaptic apical LTP was impaired. However, the heterosynaptic basal dendritic plasticity induced by either spaced 10-Hz bursts or low-frequency (1-Hz) stimulation was disrupted by oAβs in a mGluR5-dependent manner. These results suggest that different firing patterns in the same neurons may be selectively altered by soluble oAβs in an early phase of AD, before frank neurodegeneration.
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