Abeta Oligomers Research Articles

Impaired adult neurogenesis is an early event in Alzheimer\u2019s disease neurodegeneration, mediated by intracellular A\u03b2 oligomers

Alterations of adult neurogenesis have been reported in several Alzheimer's disease (AD) animal models and human brains, while defects in this process at presymptomatic/early stages of AD have not been explored yet. To address this, we investigated potential neurogenesis defects in Tg2576 transgenic mice at 1.5 months of age, a prodromal asymptomatic age in terms of Aβ accumulation and neurodegeneration. We observe that Tg2576 resident and SVZ-derived adult neural stem cells (aNSCs) proliferate significantly less. Further, they fail to terminally differentiate into mature neurons due to pathological, tau-mediated, and microtubule hyperstabilization. Olfactory bulb neurogenesis is also strongly reduced, confirming the neurogenic defect in vivo. We find that this phenotype depends on the formation and accumulation of intracellular A-beta oligomers (AβOs) in aNSCs. Indeed, impaired neurogenesis of Tg2576 progenitors is remarkably rescued both in vitro and in vivo by the expression of a conformation-specific anti-AβOs intrabody (scFvA13-KDEL), which selectively interferes with the intracellular generation of AβOs in the endoplasmic reticulum (ER). Altogether, our results demonstrate that SVZ neurogenesis is impaired already at a presymptomatic stage of AD and is caused by endogenously generated intracellular AβOs in the ER of aNSCs. From a translational point of view, impaired SVZ neurogenesis may represent a novel biomarker for AD early diagnosis, in association to other biomarkers. Further, this study validates intracellular Aβ oligomers as a promising therapeutic target and prospects anti-AβOs scFvA13-KDEL intrabody as an effective tool for AD treatment.

Abeta oligomers mediate proteasome inhibition especially at synapse

Abeta oligomers mediate proteasome inhibition especially at synapse

High-Speed AFM to Characterize Nanoscale Dynamics of Cross-Linked ABETA42 Oligomers

High-Speed AFM to Characterize Nanoscale Dynamics of Cross-Linked ABETA42 Oligomers

Synapse formation in the brain can be enhanced by co-administering three specific nutrients

The memory impairments of early Alzheimer's disease [AD] are thought to result from a deficiency in synapses within the hippocampus and related brain regions. This deficiency could result from an acceleration in synapse turnover – perhaps caused by an endogenous neurotoxin like A-beta oligomers – or from a decrease in the production of the synaptic membrane needed to form new synapses. An AD-associated decrease in synaptogenesis almost certainly does occur, inasmuch as major decreases are also observed in the numbers of hippocampal dendritic spines, the immediate cytologic precursor of glutamatergic synapses. The syntheses of new dendritic spines and synapses can, however, be increased by concurrently raising brain levels of three circulating nutrients – uridine, omega-3 fatty acids docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA), and choline. This could provide an additional strategy for restoring synapses and thereby memory. The three nutrients are rate-limiting precursors in the Kennedy Cycle, the pathway which forms the phosphatides that are the major component of synaptic membranes. Uridine also increases the production of synaptic proteins, the other major membrane constituent, and the outgrowth of neurites. Hence administering the three nutrients accelerates synapse formation.These actions of uridine are largely mediated by uridine triphosphate (UTP), which can be released as a neurotransmitter from presynaptic terminals and can then activate P2Y2 receptors. The UTP in neurons can also be converted to cytidylyl triphosphate, CTP, the intermediate utilized in the Kennedy Cycle.

Induction of phosphorylated tau and fyn-NMDA receptor transduction pathway by abeta oligomers in synapse

Induction of phosphorylated tau and fyn-NMDA receptor transduction pathway by abeta oligomers in synapse

A HUMAN 3D NEURAL CULTURE MODEL UTILISING INDUCED PLURIPOTENT STEM CELLS FROM AN ALZHEIMER’S PATIENT TO STUDY MECHANISMS OF ALZHEIMER DISEASE PATHOLOGY

Alzheimer's Disease (AD) is the leading cause of dementia and with a population of increasing longevity is set to become a major burden on health services. Currently human tissue from AD cases is only available for research from post mortem brain but we can now utilise iPSC technology to obtain neural stem cells from AD patients with the aim to produce mature neurons with the same genetic signature of AD patients. Using induced Pluripotent Stem Cells (iPSCs) from early onset AD patients containing Presenilin 1 mutations we have created a 3D human neural culture system for the study of some early onset Alzheimer's disease mechanisms. Using immunofluorescence, western blotting and electrophysiology we have characterised neuronal morphology and maturity, synaptic function and disease-protein profiles. Neural progenitors derived from AD iPSCs (Axol Biosciences) were plated in matrigel and self-organised into 3D structures by week 3. These cultures contained a heterogeneous cell population expressing differentiation markers for neurons and astrocytes and importantly AD-associated proteins, amyloid precursor protein/Abeta and tau. These 3D cultures were maintained in vitrofor 18+ weeks. They expressed the mature 4R tau isoform and Abeta oligomers by week 6 and exhibited repetitive firing by week 12. Together these results suggest the presence of mature neurons within these cultures and the expression of pathology-associated proteins. We have created 3D mature neural cultures derived from AD patients to study mechanisms of the disease pathology in a human cell model. This is a viable new in vitro 3D neural model for the study of neuropathology, which can serve as a powerful new translational tool in this area of research.

SYNAPTIC RESILIENCE TO TAU AND AMYLOID BETA OLIGOMERS INDUCED BY NEURAL STEM CELL-DERIVED EXOSOMES

Certain individuals remain cognitively intact despite the presence of Alzheimer's Disease (AD) neuropathology, suggesting that there is a way for the brain to evade AD-dementia. Understanding the involved mechanism(s) would reveal a novel therapeutic concept for AD based on inducing cognitive resilience. We previously found that these resilient individuals have synapses resistant to the binding of toxic oligomers of both tau and amyloid beta (which have been shown to synergistically converge onto synapses and disrupt their function) along with displaying higher numbers of neural stem cells (NSC) in the hippocampus. Our objective was to investigate a possible link between the two phenomena testing the hypothesis that NSC-derived exosomes render synapse resistant to toxic tau and Abeta oligomers, thus preventing oligomer-driven synaptic dysfunction and memory deficits. Exosomes from the culture medium of undifferentiated and differentiated (MN) NSC were administered ex vivo and in vivo to test their effect on oligomer synaptic binding, oligomer-induced synaptic dysfunction and memory deficits using wt and tg mice with modifiable levels of NSC. Exosome miRNA's were analyzed by deep sequencing. NSC exosomes, not MN exosomes, decreased oligomer synaptic binding, prevented oligomer-induced LTP deficit and opposed oligomer-driven memory impairment. Abolishing NSC in vivo increased oligomer synaptic binding (a phenomenon reversed by NSC exosomes but not MN exosomes). Specific miRNA present only in NSC exosomes, possibly mediating such effects, were also identified. These results suggest a novel mechanism involving NSC-derived exosomes reducing synaptic vulnerability to both Tau and Ab oigomers, thus allowing individuals with increased neurogenesis to resist AD cognitive decline. They also illustrate a previously unappreciated target for the development of a new treatment concept for AD centered on inducing brain resilience by delivery of NSC-derived exosome or their cargo miRNAs. Supported by NIA/NIH 5R01AG042890 and the Kleberg Foundation.

A-beta oligomers and brain pathology: a difficult marriage

A-beta oligomers and brain pathology: a difficult marriage

Liraglutide protects the brains of macaques against synapse loss caused by abeta oligomers

Liraglutide protects the brains of macaques against synapse loss caused by abeta oligomers

Abeta oligomers as a pharmacodynamic biomarker of secretase therapy in Alzheimer's disease?

Abeta oligomers as a pharmacodynamic biomarker of secretase therapy in Alzheimer's disease?

Differential Effects of Cell-derived Amyloid-beta Monomers and Dimers on Spontaneous Neuronal Network Activity

Introduction Growing evidence suggests that soluble amyloid-beta (Abeta) peptides play a pivotal role in Alzheimer’s disease(AD) pathogenesis by mediating synaptotoxic effects particularly at early disease stages. Objectives/ Aims We quantified the effects of different order Abeta assemblies on spontaneous firing dynamics ofneuronal networks cultured on multielectrode arrays ('neurochips”) as a read-out. We used naturally secreted, stable and conformationally highly homogenous Abeta monomers, dimers, and a mixture of different low-noligomers, derived from permanently transfected cell lines. Results Abeta dimers promoted a dose-dependent suppression of overall activity and network synchrony and altered the burst structure already in the low picomolar dose range. By contrast, Abeta monomers exhibited no effect on overall activity, but only a slight effect on burst structure and a moderate effect on network synchrony. A yet different response pattern was seen for a mixture of various low-n Abeta oligomers. Thus, multiparametric assessment of electrical activity changes on neurochips revealed characteristic signatures of the network response for the different Abeta assemblies. Since alterations of Network function likely occur in initial disease stages, these results confirm the pivotal role of Abeta dimers in early AD pathogenesis. Conclusions Neurochip recordings of toxic dimeric Abeta species may serve as a valuable diagnostic read-out in early AD and may also be applicable for future testing of drugs, antibodies, or small molecules aiming at Abeta dimers.

Abstract T P243: Death Receptors and Mitochondria as Crucial Targets for Drug Discovery in Cerebral Amyloid Angiopathy

The vascular deposition of amyloid, known as Cerebral Amyloid Angiopathy (CAA) is an age-associated condition featured in about 90% of Alzheimer’s disease cases and in the aging brain. Amyloid beta (Abeta) deposition in CAA compromises cerebral blood flow and can cause cerebral hemorrhage and cognitive impairment, by mechanisms that are still poorly understood. Our goal was to identify the molecular events underlying the apoptotic cascade generated by Abeta in cerebrovascular cells and to pinpoint new targets for drug discovery. Human brain microvascular endothelial cells were challenged with vasculotropic Abeta variants associated with cerebrovascular deposition and hemorrhagic outcome, and the resulting signaling pathways were analysed. The in vitro findings were validated in vivo in mice subjected to intrahippocampal Abeta injections and confirmed in human CAA cases. Our findings highlighted an activation of caspase-8 and -9, together with mitochondrial dysfunction and release of cytochrome C, suggesting death receptor mediated apoptosis, which was confirmed by an overexpression of the TRAIL (TNF-related apoptosis inducing ligand) death receptors DR4 and DR5. Signaling cascades typical of TRAIL death receptor-mediated pathways were activated. The same receptors colocalized with Abeta on the cell membrane after amyloid challenge, and immunoprecipitated in vitro with Abeta oligomers. SiRNAs against DR4 and DR5 and the prevention of mitochondrial dysfunction through Carbonic Anhydrase Inhibitors, significantly diminished Abeta mediated apoptosis in endothelial cells. In vivo experiments in mice injected with vasculotropic Abeta peptide and in human CAA cases confirmed the upregulation of the receptors, their colocalization with Abeta on the cerebral vasculature, and the activation of caspases, which could be prevented by carbonic anhydrase inhibitors. Our data strongly suggests that TRAIL death-receptors and mitochondrial functioning are key cellular targets for therapeutic intervention against Abeta-induced vascular cell death in CAA.

Alzheimer's therapeutics targeting amyloid beta 1-42 oligomers II: Sigma-2/PGRMC1 receptors mediate Abeta 42 oligomer binding and synaptotoxicity.

Amyloid beta (Abeta) 1–42 oligomers accumulate in brains of patients with Mild Cognitive Impairment (MCI) and disrupt synaptic plasticity processes that underlie memory formation. Synaptic binding of Abeta oligomers to several putative receptor proteins is reported to inhibit long-term potentiation, affect membrane trafficking and induce reversible spine loss in neurons, leading to impaired cognitive performance and ultimately to anterograde amnesia in the early stages of Alzheimer's disease (AD). We have identified a receptor not previously associated with AD that mediates the binding of Abeta oligomers to neurons, and describe novel therapeutic antagonists of this receptor capable of blocking Abeta toxic effects on synapses in vitro and cognitive deficits in vivo. Knockdown of sigma-2/PGRMC1 (progesterone receptor membrane component 1) protein expression in vitro using siRNA results in a highly correlated reduction in binding of exogenous Abeta oligomers to neurons of more than 90%. Expression of sigma-2/PGRMC1 is upregulated in vitro by treatment with Abeta oligomers, and is dysregulated in Alzheimer's disease patients' brain compared to age-matched, normal individuals. Specific, high affinity small molecule receptor antagonists and antibodies raised against specific regions on this receptor can displace synthetic Abeta oligomer binding to synaptic puncta in vitro and displace endogenous human AD patient oligomers from brain tissue sections in a dose-dependent manner. These receptor antagonists prevent and reverse the effects of Abeta oligomers on membrane trafficking and synapse loss in vitro and cognitive deficits in AD mouse models. These findings suggest sigma-2/PGRMC1 receptors mediate saturable oligomer binding to synaptic puncta on neurons and that brain penetrant, small molecules can displace endogenous and synthetic oligomers and improve cognitive deficits in AD models. We propose that sigma-2/PGRMC1 is a key mediator of the pathological effects of Abeta oligomers in AD and is a tractable target for small molecule disease-modifying therapeutics.

Alzheimer's therapeutics targeting amyloid beta 1-42 oligomers I: Abeta 42 oligomer binding to specific neuronal receptors is displaced by drug candidates that improve cognitive deficits.

Synaptic dysfunction and loss caused by age-dependent accumulation of synaptotoxic beta amyloid (Abeta) 1–42 oligomers is proposed to underlie cognitive decline in Alzheimer's disease (AD). Alterations in membrane trafficking induced by Abeta oligomers mediates reduction in neuronal surface receptor expression that is the basis for inhibition of electrophysiological measures of synaptic plasticity and thus learning and memory. We have utilized phenotypic screens in mature, in vitro cultures of rat brain cells to identify small molecules which block or prevent the binding and effects of Abeta oligomers. Synthetic Abeta oligomers bind saturably to a single site on neuronal synapses and induce deficits in membrane trafficking in neuronal cultures with an EC50 that corresponds to its binding affinity. The therapeutic lead compounds we have found are pharmacological antagonists of Abeta oligomers, reducing the binding of Abeta oligomers to neurons in vitro, preventing spine loss in neurons and preventing and treating oligomer-induced deficits in membrane trafficking. These molecules are highly brain penetrant and prevent and restore cognitive deficits in mouse models of Alzheimer's disease. Counter-screening these compounds against a broad panel of potential CNS targets revealed they are highly potent and specific ligands of the sigma-2/PGRMC1 receptor. Brain concentrations of the compounds corresponding to greater than 80% receptor occupancy at the sigma-2/PGRMC1 receptor restore cognitive function in transgenic hAPP Swe/Ldn mice. These studies demonstrate that synthetic and human-derived Abeta oligomers act as pharmacologically-behaved ligands at neuronal receptors - i.e. they exhibit saturable binding to a target, they exert a functional effect related to their binding and their displacement by small molecule antagonists blocks their functional effect. The first-in-class small molecule receptor antagonists described here restore memory to normal in multiple AD models and sustain improvement long-term, representing a novel mechanism of action for disease-modifying Alzheimer's therapeutics.

Homotaurine induces measurable changes of short latency afferent inhibition in a group of mild cognitive impairment individuals.

Current treatment options for patients with Alzheimer’s disease (AD) are limited at providing symptomatic relief, with no effects on the underlying pathophysiology. Recently, advances in the understanding of the AD pathogenesis highlighted the role of ABeta (Aβ) oligomers particularly interfering with mechanisms of cortical plasticity such as long-term potentiation (LTP) and long-term depression (LTD). These findings led to the development of potential anti-amyloid therapies, and among them homotaurine, a glycosaminoglycan mimetic designed to interfere with the actions of Aβ early in the cascade of amyloidogenic events, and by its γ-aminobutyric acid type (GABA) A receptor affinity. Recently, we showed that AD patients have impaired LTP-like cortical plasticity, as measured by standard theta burst stimulation protocols applied over the primary motor cortex (M1). Furthermore, AD patients have a weakened short latency afferent inhibition (SLAI), a neurophysiological measure of central cholinergic transmission, which changes reflect the cholinergic dysfunction occurring in the pathology. Here, we aimed at investigating whether homotaurine administration could modulate in vivo measured mechanisms of synaptic plasticity, namely LTP and LTD, and also SLAI in a group of mild cognitive impaired patients. We observed that homotaurine administration did not induce relevant changes of both LTP and LTD recordings, while induced changes of SLAI in our group of patients. We suggest that homotaurine effects are dependent on changes of cortical GABA transmission suggesting a potential role for this compound in ameliorating the cholinergic transmission by modulating the inhibitory cortical activity.

Early Failure of the Default‐Mode Network and the Pathogenesis of Alzheimer's Disease

The default-mode network (DMN) is a major resting-state network that supports most of the baseline brain activity. Recent studies revealed that DMN cortical hub regions, including the medial prefrontal cortex, parietal cortex, posterior cingulum, and precuneus, are all affected early during Alzheimer’s disease (AD) and exhibit high amounts of A-beta deposits. The cells generating A-beta are chiefly cortical and some brainstem projection neurons. Because processing of the amyloid precursor protein is activity-dependent, it can be speculated that due to their constant activity, DMN neurons produce and release more A- beta than occur elsewhere in the neocortex, thus leading to an increase in production, oligomerization, and aggregation of Ab as well as tau hyperphosphorylation, which presumably is caused by the released A-beta oligomers. DMN cortical regions are richly innervated by long projection fibers from the noradrenergic locus coeruleus (LC), the serotonergic dorsal raphe nucleus (DRN), as well as the cholinergic basal forebrain (nucleus basalis complex, NB), which all may release high amounts of A-beta in the vicinity of glutamatergic projection neurons in the DMN cortical regions that are vulnerable to tau pathology and neurofibrillary degeneration. Recent findings provide converging evidence that the amyloid accumulation and DMN functional alterations are closely linked with the changes of sleep–wake cycle (particularly in regard to lesser amount of shortwave deep sleep when metabolic demands are about 50% lower in comparison with awake state and when presumably less amyloid is produced) and pretangle changes of LC, thus opening new promising area for future research.

Injection of specific amyloid-beta oligomers (beta1-40:beta1-42 = 10:1) into rat medial septum impairs memory retention without inducing hippocampal apoptosis

Objectives: Because of the well-known neurochemical interactions between the septum and hippocampus during memory processes, we investigated the effect of amyloid-beta (A-beta) injection into the medial septum (MS) on the behavior in Wistar rats. We also assessed whether the observed effects were functional or due to apoptosis.Methods: Specific A-beta oligomers (beta1-40:beta1-42 = 10:1) were injected into MS for seven consecutive days. Behavior was assessed with the Morris water maze task.Results: Compared with the control group, rats that received A-beta oligomers exhibited significant memory retention impairment (P < 0·05) without apoptosis in the cornu ammonis (CA)1 and CA3 regions of the dorsal hippocampus.Discussion: These data indicate that septal injection of A-beta impairs memory retention, even in the absence of hippocampal apoptosis. This result might bring new insight to spatial memory-related disorders like Alzheimer’s disease (AD).

Pathogenesis of Abeta Oligomers in Synaptic Failure

The soluble Abeta oligomers in brain are highly correlated with memory related synaptic dysfunctions in Alzheimer's disease (AD). However, more recent studies implicate the involvement of Abeta dimers and trimers in memory related AD pathology. Apparently, Abeta oligomers can bind with cellular prion protein at the membrane receptors, forming annular amyloid pores and membrane ion channels to induce aberrant spine cytoskeletal changes. Hence synapse targeting of Abeta oligomers involves activation of many receptors such as N-Methyl-D-aspartate (NMDA), alpha-amino-3- hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), nicotinic acetylcholine (nAChRs), p75 neurotrophin (p75NTR) following aberrant clustering of metabotropic glutamate receptors (mGluR5) leading to neuronal loss and LTP failure. In particular, NMDA and AMPA receptor activation by soluble amyloid oligomers involves calcium mediated mitochondrial dysfunction, decreased Ca((2+))/calmodulin-dependent protein kinase II (CaMKII) levels at the synapses accompanying dramatic loss of synaptic proteins such as postsynaptic density-95 (PSD-95), dynamin-1 and synaptophysin. This kind of receptor-Abeta oligomer interaction might eventually affect the neuronal membrane integrity by altering dielectric barrier, various synaptic proteins, spine morphology and density and P/Q calcium currents that might provoke a cascade of events leading to neuronal loss and memory failure. In this review, we try to explain in detail the various possible mechanisms that connect Abeta oligomers with synapse damage and memory failure.

Structure-Selective Anisotropy Assay for Amyloid Beta Oligomers

Amyloid β (Abeta) peptides in their oligomeric form have been proposed as major toxic species in Alzheimer's disease (AD). There are a limited number of anti-Abeta antibodies specific to oligomeric forms of Abeta compared to the monomeric form, and accurate measurement of oligomeric forms in biological samples, cerebrospinal fluid (CSF), or brain extracts remains challenging. We introduce an oligomer-specific (in preference to monomers or fibrils) fluorescence assay based on a conformationally sensitive bis-pyrene-labeled peptide that contains amino acid residues 16-35 of the human amyloid beta protein (pronucleon peptide, PP). This peptide exhibits a shift in fluorescence emission from pyrene excimer to pyrene monomer emission resulting from a conformational change. Specific binding of PP to oligomeric forms of Abeta can be monitored in solution by a change in fluorescence spectrum as well as a change in pyrene monomer fluorescence anisotropy (or polarization). The mechanism of binding and its relation to anisotropy and fluorescence lifetime changes are discussed. The development of a simple, rapid, anisotropy assay for measurement of Abeta oligomers is important for further study of the oligomers' role in AD, and specific detection of oligomers in biological samples, such as cerebrospinal fluid.

A Chemical Analog of Curcumin as an Improved Inhibitor of Amyloid Abeta Oligomerization

Amyloid-like plaques are characteristic lesions defining the neuropathology of Alzheimer's disease (AD). The size and density of these plaques are closely associated with cognitive decline. To combat this disease, the few therapies that are available rely on drugs that increase neurotransmission; however, this approach has had limited success as it has simply slowed an imminent decline and failed to target the root cause of AD. Amyloid-like deposits result from aggregation of the Aβ peptide, and thus, reducing amyloid burden by preventing Aβ aggregation represents an attractive approach to improve the therapeutic arsenal for AD. Recent studies have shown that the natural product curcumin is capable of crossing the blood-brain barrier in the CNS in sufficient quantities so as to reduce amyloid plaque burden. Based upon this bioactivity, we hypothesized that curcumin presents molecular features that make it an excellent lead compound for the development of more effective inhibitors of Aβ aggregation. To explore this hypothesis, we screened a library of curcumin analogs and identified structural features that contribute to the anti-oligomerization activity of curcumin and its analogs. First, at least one enone group in the spacer between aryl rings is necessary for measureable anti-Aβ aggregation activity. Second, an unsaturated carbon spacer between aryl rings is essential for inhibitory activity, as none of the saturated carbon spacers showed any margin of improvement over that of native curcumin. Third, methoxyl and hydroxyl substitutions in the meta- and para-positions on the aryl rings appear necessary for some measure of improved inhibitory activity. The best lead inhibitors have either their meta- and para-substituted methoxyl and hydroxyl groups reversed from that of curcumin or methoxyl or hydroxyl groups placed in both positions. The simple substitution of the para-hydroxy group on curcumin with a methoxy substitution improved inhibitor function by 6-7-fold over that measured for curcumin.