Soluble Aβ Oligomers Research Articles

Tau phosphorylation and tau mislocalization mediate soluble Aβ oligomer‐induced AMPA glutamate receptor signaling deficits

In our previous studies, phosphorylation-dependent tau mislocalization to dendritic spines resulted in early cognitive and synaptic deficits. It is well known that amyloid beta (Aβ) oligomers cause synaptic dysfunction by inducing calcineurin-dependent AMPA receptor (AMPAR) internalization. However, it is unknown whether Aβ-induced synaptic deficits depend upon tau phosphorylation. It is also unknown whether changes in tau can cause calcineurin-dependent loss of AMPARs in synapses. Here, we show that tau mislocalizes to dendritic spines in cultured hippocampal neurons from APPSwe Alzheimer's disease (AD)-transgenic mice and in cultured rat hippocampal neurons treated with soluble Aβ oligomers. Interestingly, Aβ treatment also impairs synaptic function by decreasing the amplitude of miniature excitatory postsynaptic currents (mEPSCs). The above tau mislocalization and Aβ-induced synaptic impairment are both diminished by the expression of AP tau, indicating that these events require tau phosphorylation. The phosphatase activity of calcineurin is important for AMPAR internalization via dephosphorylation of GluA1 residue S845. The effects of Aβ oligomers on mEPSCs are blocked by the calcineurin inhibitor FK506. Aβ-induced loss of AMPARs is diminished in neurons from knock-in mice expressing S845A mutant GluA1 AMPA glutamate receptor subunits. This finding suggests that changes in phosphorylation state at S845 are involved in this pathogenic cascade. Furthermore, FK506 rescues deficits in surface AMPAR clustering on dendritic spines in neurons cultured from transgenic mice expressing P301L tau proteins. Together, our results support the role of tau and calcineurin as two intermediate signaling molecules between Aβ initiation and eventual synaptic dysfunction early in AD pathogenesis.

Interactions of APOE genotype and RXR agonists on soluble Aβ and oAβ levels (LB624)

Interactions of APOE genotype and RXR agonists on soluble Aβ and oAβ levels Kevin Koster1, Jia Luo2, Sue Lee2, Varsha Shete2, Gregory RJ Thatcher2, Mary Jo LaDu1, Leon M Tai1 There is a critical need to develop novel Alzheimer’s disease (AD) therapeutics that lower amyloid beta (Aβ) levels, as current therapeutics are failing in clinical trials. APOE4 (encodes apolipoprotein E; apoE) is the greatest AD genetic risk factor compared to APOE3. ApoE represents a promising target for modulating A levels, as it has been shown to have genotype‐specific effects on Aβ pathology in humans and mice. Recently, bexarotene (Bex), a retinoid X receptor (RXR) agonist, was shown to reduce soluble and insoluble levels of Aβ via increasing mouse apoE levels. However, subsequent data have raised concerns over the activity and mechanism of action of Bex. A major issue is that the effect of modulating human apoE on Aβ levels is unclear. Further, the levels of Aβ pathology at time of treatment may determine RXR agonist activity i.e. treatment vs prevention paradigms. Therefore, novel EFAD mice (overexpress Aβ42 and express human apoE3 or apoE4) were treated with Bex and LG268, a more selective RXR agonist. RXR agonist treatment of E3FAD and E4FAD mice with intermediate Aβ levels resulted in increased soluble Aβ42 and oligomeric Aβ levels (oAβ), with a trend to increase insoluble Aβ levels. RXR agonist treatment of E4FAD mice with high Aβ levels decreased soluble Aβ42 and oAβ levels, with no effect on insoluble Aβ. Further, our data indicate that the beneficial effects of RXR agonists are mediated through: increased ABCA1 and ABCG1 expression, increased lipidation of apoE‐containing lipoproteins, and thus increased apoE/A complex levels. Collectively these data suggest that RXR agonists may increase neurotoxic Aβ levels in prevention paradigms. However, RXR agonists may be effective for AD patients expressing APOE4 at a more advanced stage of the disease via a novel mechanism of action: enhanced apoE4 lipidation.Grant Funding Source: Supported by Alzheimer's Disease Drug Discovery Foundation

TLR4‐p38 pathway as a mechanism of APOE‐modulated neuroinflammation in Alzheimer disease (1056.6)

Soluble oligomeric Aβ (oAβ) is a neurotoxic aggregate thought to be a proximal cause of Alzheimer disease (AD). Chronic inflammation of glial cells induced by oAβ‐induced likely results in both direct neurotoxicity and decreased phagocytic clearance of Aβ and cellular debris. The strongest genetic risk factor for AD is the ε4 allele of the APOE gene. As APOE4 is associated with a proinflammatory response compared to APOE3, we determined the APOE‐specific neuroinflammatory phenotype in novel EFAD transgenic mice, which overexpress human Aβ42 and apolipoprotein E (apoE). Overall, our data are consistent with an increased pro‐inflammatory, anti‐phagocytic (M1) and reduced anti‐inflammatory, repair, (M2) response in E4FAD compared to E3FAD mice. To determine the mechanism underlying these effects and test our hypothesis that TLR4 signaling mediates Aβ‐induced APOE‐modulated neuroinflammation, a primary glial screen was developed. LPS‐ and oAβ‐induced secretion of TNF‐α is concentration dependent and higher with apoE4 than apoE3 in vitro. Importantly, TLR4 antagonists (LPS‐RS, IAXO series), and an inhibitor of p38α (a down‐stream target of TLR4) prevented oAβ42‐induced TNF‐α secretion. Thus, TLR4 signaling represents a novel pathway for APOE4‐specific neuroinflammation.

Soluble Aβ Oligomers Are Rapidly Sequestered from Brain ISF In Vivo and Bind GM1 Ganglioside on Cellular Membranes

Soluble Aβ oligomers contribute importantly to synaptotoxicity in Alzheimer's disease, but their dynamics in vivo remain unclear. Here, we found that soluble Aβ oligomers were sequestered from brain interstitial fluid onto brain membranes much more rapidly than nontoxic monomers and were recovered in part as bound to GM1 ganglioside on membranes. Aβ oligomers bound strongly to GM1 ganglioside, and blocking the sialic acid residue on GM1 decreased oligomer-mediated LTP impairment in mouse hippocampal slices. In a hAPP transgenic mouse model, substantial levels of GM1-bound Aβ₄₂ were recovered from brain membrane fractions. We also detected GM1-bound Aβ in human CSF, and its levels correlated with Aβ₄₂, suggesting its potential as a biomarker of Aβ-related membrane dysfunction. Together, these findings highlight a mechanism whereby hydrophobic Aβ oligomers become sequestered onto GM1 ganglioside and presumably other lipids on neuronal membranes, where they may induce progressive functional and structural changes.

Rutin improves spatial memory in Alzheimer's disease transgenic mice by reducing Aβ oligomer level and attenuating oxidative stress and neuroinflammation

Alzheimer's disease (AD) is a progressive, neurodegenerative disease characterized by extracellular β-amyloid (Aβ) plaques and intracellular neurofibrillary tangles in the brain. Aβ aggregation is closely associated with neurotoxicity, oxidative stress, and neuronal inflammation. The soluble Aβ oligomers are believed to be the most neurotoxic form among all forms of Aβ aggregates. We have previously reported a polyphenol compound rutin that could inhibit Aβ aggregation and cytotoxicity, attenuate oxidative stress, and decrease the production of nitric oxide and proinflammatory cytokines in vitro. In the current study, we investigated the effect of rutin on APPswe/PS1dE9 transgenic mice. Results demonstrated that orally administered rutin significantly attenuated memory deficits in AD transgenic mice, decreased oligomeric Aβ level, increased super oxide dismutase (SOD) activity and glutathione (GSH)/glutathione disulfide (GSSG) ratio, reduced GSSG and malondialdehyde (MDA) levels, downregulated microgliosis and astrocytosis, and decreased interleukin (IL)-1β and IL-6 levels in the brain. These results indicated that rutin is a promising agent for AD treatment because of its antioxidant, anti-inflammatory, and reducing Aβ oligomer activities.

ApoE and Aβ in Alzheimer’s Disease: Accidental Encounters or Partners?

Among the three human apolipoprotein E (apoE) isoforms, apoE4 increases the risk of Alzheimer's disease (AD). While transporting cholesterol is a primary function, apoE also regulates amyloid-β (Aβ) metabolism, aggregation, and deposition. Although earlier work suggests that different affinities of apoE isoforms to Aβ might account for their effects on Aβ clearance, recent studies indicate that apoE also competes with Aβ for cellular uptake through apoE receptors. Thus, several factors probably determine the variable effects apoE has on Aβ. In this Review, we examine biochemical, structural, and functional studies and propose testable models that address the complex mechanisms underlying apoE-Aβ interaction and how apoE4 may increase AD risk and also serve as a target pathway for therapy.

3,3',4',5'-Tetrahydroxyflavone induces formation of large aggregates of amyloid β protein.

Amyloid β protein (Aβ) self-assembles into insoluble fibrils, and forms the senile plaques associated with Alzheimer's disease. 3,3',4',5'-Tetrahydroxyflavone, a synthetic analogue of the natural flavonoid fisetin, has been found to potently inhibit Aβ fibril formation. In the present study, we investigated how inhibition of Aβ fibril formation by this flavonoid affects Aβ conformation and neurotoxicity. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of Aβ1-42 (20 µM) incubated with or without 3,3',4',5'-tetrahydroxyflavone demonstrated that 3,3',4',5'-tetrahydroxyflavone (100 µM) rapidly caused formation of atypical Aβ conformers, which appeared as a very broad, smear-like band in the high molecular weight region and were distinguishable from soluble Aβ oligomers or mature Aβ fibrils. Transmission electron microscopy (TEM) revealed that large spherical Aβ aggregates were preferentially formed in the presence of 3,3',4',5'-tetrahydroxyflavone. The SDS-resistant, smear-like band on SDS-PAGE and the large spherical aggregates in TEM both disappeared after heat treatment (100°C, 10 min). Furthermore, a neurotoxicity assay with cultured rat hippocampal neurons demonstrated that Aβ incubated with 3,3',4',5'-tetrahydroxyflavone was significantly less toxic than Aβ incubated without the flavonoid. These results suggest that the newly synthesized fisetin analogue 3,3',4',5'-tetrahydroxyflavone directly produces atypical, large Aβ aggregates and reduces Aβ toxicity.

Simulation Study of Soluble Toxic Oligomeric Structures of Amyloid-Beta

Although early attention has focused on toxicity of amyloid plaques as the cause of Alzheimer's disease (AD), there is stronger evidence that soluble Aβ oligomers, and more recently pre-fibrillar oligomers, show better correlation with AD symptoms than do the insoluble fibrillar states exhibited at the completion of the amyloid cascade. In recent work a new oligomeric Aβ form known as the was found to inhibit calcium uptake by neuronal cells and to contribute to memory loss in lab animals. At present we have no knowledge of the globulomer structure, nor a smaller species known as the pre-globulomer, which is usually a necessary first step in the design of small molecule drug therapeutics. We will present our hypothesis about the structural ensembles of these two oligomeric forms based on molecular dynamics simulations and calculation of NMR observables and amide exchange data.

Environmental enrichment strengthens corticocortical interactions and reduces amyloid-β oligomers in aged mice

Brain aging is characterized by global changes which are thought to underlie age-related cognitive decline. These include variations in brain activity and the progressive increase in the concentration of soluble amyloid-β (Aβ) oligomers, directly impairing synaptic function and plasticity even in the absence of any neurodegenerative disorder. Considering the high social impact of the decline in brain performance associated to aging, there is an urgent need to better understand how it can be prevented or contrasted. Lifestyle components, such as social interaction, motor exercise and cognitive activity, are thought to modulate brain physiology and its susceptibility to age-related pathologies. However, the precise functional and molecular factors that respond to environmental stimuli and might mediate their protective action again pathological aging still need to be clearly identified. To address this issue, we exploited environmental enrichment (EE), a reliable model for studying the effect of experience on the brain based on the enhancement of cognitive, social and motor experience, in aged wild-type mice. We analyzed the functional consequences of EE on aged brain physiology by performing in vivo local field potential (LFP) recordings with chronic implants. In addition, we also investigated changes induced by EE on molecular markers of neural plasticity and on the levels of soluble Aβ oligomers. We report that EE induced profound changes in the activity of the primary visual and auditory cortices and in their functional interaction. At the molecular level, EE enhanced plasticity by an upward shift of the cortical excitation/inhibition balance. In addition, EE reduced brain Aβ oligomers and increased synthesis of the Aβ-degrading enzyme neprilysin. Our findings strengthen the potential of EE procedures as a non-invasive paradigm for counteracting brain aging processes.

Acute Effects of β-Amyloid (1-42) Oligomers on Rat Pyramidal Entorhinal Neurons

Deposition of beta-amyloid peptide (Aβ) in senile plaques is the hallmark of Alzheimer disease neuropathology. Soluble Aβ oligomers block voltage-gated ion channels as P/Q type calcium channels (Nimmrich et al., 2008) as well as the transient potassium current (Liudyno et al., 2012) and calcium dependent potassium channels, BK type (Yamamoto et al., 2011). Exposure to Aβ may cause a loss of cellular calcium homeostasis, but the mechanism by which this occurs is uncertain. In this work we evaluated the acute response of rat pyramidal entorhinal neurons to oligomers formed from purified Aβ1-42 in both entorhinal cortex slice preparations and isolated pyramidal neurons in culture using current- and voltage-clamp conditions. Exposure to Aβ oligomers but not monomers increased the input resistance and enlarged the action potential in the slice preparation, whereas in culture neurons produced a reversible inhibition of the inward potassium current generated by voltage ramps from −70 to 70 mV in symmetric potassium conditions. This current is generated by inward rectifier potassium channels as well as the leak potassium channels, it was blocked by barium, arachidonic acid, bupivacaine and extracellular pH acidification, suggesting that TASK type K2P channels are targets of the toxic effects of Aβ. Blockage of potassium channels by Aβ could lead to prolonged cell depolarization, thereby increasing calcium influx.Supported by CONACyT (324341) Mexico.

Reduced Alzheimer’s Disease Pathology by St. John’s Wort Treatment is Independent of Hyperforin and Facilitated by ABCC1 and Microglia Activation in Mice

Soluble β-amyloid peptides (Aβ) and small Aβ oligomers represent the most toxic peptide moieties recognized in brains affected by Alzheimer's disease (AD). Here we provide the first evidence that specific St. John's wort (SJW) extracts both attenuate Aβ-induced histopathology and alleviate memory impairments in APP-transgenic mice. Importantly, these effects are attained independently of hyperforin. Specifically, two extracts characterized by low hyperforin content (i) significantly decrease intracerebral Aβ42 levels, (ii) decrease the number and size of amyloid plaques, (iii) rescue neocortical neurons, (iv) restore cognition to normal levels, and (iv) activate microglia in vitro and in vivo. Mechanistically, we reveal that the reduction of soluble Aβ42 species is the consequence of a highly increased export activity in the bloodbrain barrier ABCC1transporter, which was found to play a fundamental role in Aβ excretion into the bloodstream. These data (i) support the significant beneficial potential of SJW extracts on AD proteopathy, and (ii) demonstrate for the first time that hyperforin concentration does not necessarily correlate with their therapeutic effects. Hence, by activating ABC transporters, specific extracts of SJW may be used to treat AD and other diseases involving peptide accumulation and cognition impairment. We propose that the anti-depressant and anti-dementia effects of these hyperforin-reduced phytoextracts could be combined for treatment of the elderly, with a concomitant reduction in deleterious hyperforin-related side effects.

Experimental Traumatic Brain Injury Induces Rapid Aggregation and Oligomerization of Amyloid-Beta in an Alzheimer's Disease Mouse Model

Soluble amyloid-beta (Aβ) oligomers are hypothesized to be the pathogenic species in Alzheimer's disease (AD), and increased levels of oligomers in the brain subsequent to traumatic brain injury (TBI) may exacerbate secondary injury pathways and underlie increased risk of developing AD in later life. To determine whether TBI causes Aβ aggregation and oligomerization in the brain, we exposed triple transgenic AD model mice to controlled cortical impact injury and measured levels of soluble, insoluble, and oligomeric Aβ by enzyme-linked immunosorbent assay (ELISA) at 1, 3, and 7 days postinjury. TBI rapidly increased levels of both soluble and insoluble Aβ40 and Aβ42 in the injured cortex at 1 day postinjury. We confirmed previous findings that identified damaged axons as a major site of Aβ accumulation using both immunohistochemistry and biochemistry. We also report that soluble Aβ oligomers were significantly increased in the injured cortex, as demonstrated by both ELISA and Western blot. Interestingly, the mouse brain is able to rapidly clear trauma-induced Aβ, with both soluble and insoluble Aβ species returning to sham levels by 7 days postinjury. In conclusion, we demonstrate that TBI causes acute accumulation and aggregation of Aβ in the brain, including the formation of low- and high-molecular-weight Aβ oligomers. The formation and aggregation of Aβ into toxic species acutely after injury may play a role in secondary injury cascades after trauma and, chronically, may contribute to increased risk of developing AD in later life.

Cerebral Microvascular Rather than Parenchymal Amyloid-β Protein Pathology Promotes Early Cognitive Impairment in Transgenic Mice

Alzheimer's disease (AD) is an age-dependent neurodegenerative condition that causes a progressive decline in cognitive function. Accumulation of amyloid β-protein (Aβ) in the brain is a prominent feature of AD and related disorders. However, the levels of Aβ accumulation alone are not a reliable predictor of cognitive deficits. Aβ accumulates in AD brain in the form of parenchymal amyloid plaques and cerebral vascular deposits. Although both types of lesions can contribute to cognitive decline, their temporal impact remains unclear. Moreover, cerebral microvascular pathology is identified as an early driver of cognitive impairment. Here for the first time, we compared two transgenic mouse strains, Tg-5xFAD and Tg-SwDI, which exhibit similar onset and anatomical accumulation of Aβ, but with distinct parenchymal and microvascular compartmental deposition, respectively, to assess their impact on cognitive impairment. Cohorts of each line were tested at 3 and 6 months of age to assess the relationship between spatial working memory performance and quantitative pathology. At 3 months of age, Tg-SwDI mice with onset of cerebral microvascular amyloid were behaviorally impaired, while the Tg-5xFAD, which had disproportionately higher levels of total Aβ, soluble oligomeric Aβ, and parenchymal amyloid were not. However, at 6 months of age, behavioral deficits for both groups of transgenic mice were evident, as the levels of Aβ pathologies in the Tg-5xFAD accumulated to extremely high amounts. The present findings suggest early-onset cerebral microvascular amyloid deposition, that precedes high parenchymal levels of Aβ, may be an important early factor in the development of cognitive deficits.

Molecular dynamics study of Zn(aβ) and Zn(aβ)2.

The aggregation of Aβ-peptide (Aβ) is widely considered to be the critical step in the pathology of Alzheimer's disease. Small, soluble Aβ oligomers have been shown to be more neurotoxic than large, insoluble aggregates and fibrils. Recent studies suggest that biometal ions, including Zn(II), may play an important role in the aggregation process. Experimentally determining the details of the binding process is complicated by the kinetic lability of zinc. To study the dynamic nature of the zinc-bound Aβ complexes and the potential mechanisms by which Zn(II) affects Aβ oligomerization we have performed atomistic molecular dynamics (MD) simulations of Zn(Aβ) and Zn(Aβ)2. The models were based on NMR data and predicted coordination environments from previous density functional theory calculations. When modeled as 4-coordinate covalently bound Zn(Aβ)n complexes (where n = 1 or 2), zinc imposes conformational changes in the surrounding Aβ residues. Moreover, zinc reduces the helix content and increases the random coil content of the full peptide. Although zinc binds at the N-terminus of Aβ, β-sheet formation is observed exclusively at the C-terminus in the Zn(Aβ) and most of the Zn(Aβ)2 complexes. Furthermore, initial binding to zinc promotes the formation of intra-chain salt-bridges, while subsequent dissociation promotes the formation of inter-chain salt-bridges. These results suggest that Zn-binding to Aβ accelerates the aggregation of Aβ by unfolding the helical structure in Aβ peptide and stabilizing the formation of vital salt-bridges within and between Aβ peptides.

The targets in Alzheimer's disease are Aβ oligomers: Count them for diagnosis and destroy them for therapy

Alzheimer's disease (AD) is a progressive neurodegenerative disorder. Several lines of evidence suggest a central role of amyloid-β-peptide (Aβ) in the pathogenesis of AD. More than Aβ fibrils, small soluble and prion-like Aβ oligomers are suspected to be the major toxic species responsible for disease development and progression. Therefore, these oligomers should be our major target for therapy and used as the most direct biomarker for diagnosis and therapy monitoring.

Cocoa powder triggers neuroprotective and preventive effects in a human Alzheimer's disease model by modulating BDNF signaling pathway

The molecular mechanisms linking Aβ to the onset of neurotoxicity are still largely unknown, but several lines of evidence point to reactive oxygen species, which are produced even under the effect of nanomolar concentrations of soluble Aβ-oligomers. The consequent oxidative stress is considered as the mediator of a cascade of degenerative events in many neurological disorders. Epidemiological studies indicate that dietary habits and antioxidants from diet can influence the incidence of neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. In the recent years, a number of reviews have reported on neuroprotective effects of polyphenols in cell and animal models. However, the majority of these studies have focused only on the anti-oxidant properties of these compounds and less on the mechanism/s of action at cellular level. In this work we investigated the effect of cocoa polyphenolic extract on a human AD in vitro model. The results obtained, other than confirming the anti-oxidant properties of cocoa, demonstrate that cocoa polyphenols triggers neuroprotection by activating BDNF survival pathway, both on Aβ plaque treated cells and on Aβ oligomers treated cells, resulting in the counteraction of neurite dystrophy. On the light of the results obtained the use of cocoa powder as preventive agent for neurodegeneration is further supported.

Amyloid-β may be released from non-junctional varicosities of axons generated from abnormal tau-containing brainstem nuclei in sporadic Alzheimer’s disease: a hypothesis

How can the relatively abruptly beginning formation of Aβ deposits be explained? That so little is known about this process is all the more remarkable when one considers that Aβ precipitations develop with such consistency during the course of the AD-associated pathological process that they belong to the hallmark lesions of AD [22, 33, 43]. Ear-lier findings could show that Aβ protein does not enter the extracellular space of the CNS from serum via the vascu-lature, via strongly vascularized ependymal organs, or by way of the choroid plexus, nor is it generated by astrocytes, oligodendrocytes, or microglia cells [ 32]. A β protein aggre-gates are the result of a sequential cleavage of an amyloid precursor protein, which is a physiological constituent of the cellular membranes of nerve cells [22, 33]. Neuronally generated soluble and diffusible Aβ is presumed to equili-brate within the interstitial fluid of the CNS and, from there, it may enter the cerebrospinal fluid that occupies the ventricles and subarachnoid space [3]. At seeds in the interstitial space, soluble oligomeric Aβ may aggregate and form insoluble plaque-like deposits [44].It is unlikely that all types of nerve cells are equally capable of generating Aβ, and, for instance, the nerve cells of the enteric as well as peripheral nervous systems are not known to do so. Nor do all neuronal types within the CNS produce Aβ, inasmuch as Aβ deposition is not ubiquitous there. Rather, Aβ deposition consistently occurs at spe-cific CNS sites according to a distinct developmental and distributional pattern [46, 47]. In general, Aβ deposits are rare in the white substance but they do tend to appear in the gray matter where the somatodendritic compartments of projection neurons are located. Even within the gray matter, regions with high densities of Aβ plaques, e.g., the All cases of sporadic Alzheimer’s disease (AD) are neu-ropathologically characterized by disease-related lesions that develop at specific sites in the human brain and gradu-ally disperse from there into hitherto uninvolved regions [5, 14, 24, 35–37, 44]. Central to this pathological process are abnormal alterations of the neuronal cytoskeleton that consist mainly of hyperphosphorylated and aggregated tau protein [17, 21, 25–27, 30, 31]. Involved nerve cells first can be seen in brainstem nuclei that diffusely project to the cerebral cortex. Among others, these include the noradren-ergic locus coeruleus, the serotonergic upper raphe nuclei, and the cholinergic magnocellular nuclei of the basal fore-brain [8]. Later on, in the pathological process, the intra-neuronal inclusions are accompanied by extracellular plaque-like deposits of a second abnormal protein, amy-loid β (Aβ) [10, 11, 42].In the present context, we are referring only to forms of both proteins that can be assessed by light microscopy, i.e., those which precipitate in aqueous solutions of formalde-hyde and can be detected in human autopsy material using immunoreactions and/or silver stains. Plaque-like deposits of aggregated Aβ are located outside of nerve cells, glial cells, or cells of the vascular wall in the interstitial space of the central nervous system (CNS) [46, 47]. Cerebral amyloid angiopathy is a frequently co-occurring lesion [19, 50].

A Luminex Assay Detects Amyloid β Oligomers in Alzheimer’s Disease Cerebrospinal Fluid

Amyloid beta (aβ) protein assembles into larger protein aggregates during the pathogenesis of Alzheimer’s disease (AD) and there is increasing evidence that soluble aβ oligomers are a critical pathologic species. Diagnostic evaluations rely on the measurement of increased tau and decreased aβ42 in the cerebrospinal fluid (CSF) from AD patients and evidence for oligomeric aβ in patient CSF is conflicting. In this study, we have adapted a monoclonal single antibody sandwich ELISA assay to a Luminex platform and found that this assay can detect oligomerized aβ42 and sAPPα fragments. We evaluated oligomeric aβ reactivity in 20 patients with AD relative to 19 age matched controls and compared these values with a commercially available Alzbio3 kit that detects tau, phosphorylated tau and aβ42 on the same diagnostic platform. We found that CSF samples of patients with AD had elevated aβ oligomers compared to control subjects (p < 0.05) and the ratio of aβ oligomers to aβ42 was also significantly elevated (p < 0.0001). Further research to develop high sensitivity analytical platforms and rigorous methods of developing stable assay standards will be needed before the analysis of oligomeric aβ becomes a routine diagnostic assay for the evaluation of late onset AD patients.

FcγRIIb mediates amyloid-β neurotoxicity and memory impairment in Alzheimer’s disease

Amyloid-β (Aβ) induces neuronal loss and cognitive deficits and is believed to be a prominent cause of Alzheimer's disease (AD); however, the cellular pathology of the disease is not fully understood. Here, we report that IgG Fcγ receptor II-b (FcγRIIb) mediates Aβ neurotoxicity and neurodegeneration. We found that FcγRIIb is significantly upregulated in the hippocampus of AD brains and neuronal cells exposed to synthetic Aβ. Neuronal FcγRIIb activated ER stress and caspase-12, and Fcgr2b KO primary neurons were resistant to synthetic Aβ-induced cell death in vitro. Fcgr2b deficiency ameliorated Aβ-induced inhibition of long-term potentiation and inhibited the reduction of synaptic density by naturally secreted Aβ. Moreover, genetic depletion of Fcgr2b rescued memory impairments in an AD mouse model. To determine the mechanism of action of FcγRIIb in Aβ neurotoxicity, we demonstrated that soluble Aβ oligomers interact with FcγRIIb in vitro and in AD brains, and that inhibition of their interaction blocks synthetic Aβ neurotoxicity. We conclude that FcγRIIb has an aberrant, but essential, role in Aβ-mediated neuronal dysfunction.

Somatostatin receptor subtype-4 agonist NNC 26-9100 mitigates the effect of soluble Aβ42 oligomers via a metalloproteinase-dependent mechanism

Soluble amyloid-β peptide (Aβ) oligomers have been hypothesized to be primary mediators of Alzheimer's disease progression. In this regard, reduction of soluble Aβ-oligomers levels within the brain may provide a viable means in which to treat the disease. Somatostatin receptor subtype-4 (SSTR4) agonists have been proposed to reduce Aβ levels in the brain via enhancement of enzymatic degradation. Herein we evaluated the effect of selective SSTR4 agonist NNC 26-9100 on the changes in learning and soluble Aβ42 oligomer brain content with and without co-administration of the M13-metalloproteinase family enzyme-inhibitor phosphoramidon, using the senescence-accelerated mouse prone-8 (SAMP8) model. NNC 26-9100 treatment (0.2µg i.c.v. in 2µL) improved learning, which was blocked by phosphoramidon (1 and 10mM, respectively). NNC 26-9100 decreased total soluble Aβ42, an effect which was blocked by phosphoramidon (10mM). Extracellular, intracellular, and membrane fractions were then isolated from cortical tissue and assessed for soluble oligomer alterations. NNC 26-9100 decreased the Aβ42 trimeric (12kDa) form within the extracellular and intracellular fractions, and produced a band-split effect of the Aβ42 hexameric (25kDa) form within the extracellular fraction. These effects were also blocked by phosphoramdon (1 and 10mM, respectively). Subsequent evaluation of NNC 26-9100 in APPswe Tg2576 transgenic mice showed a similar learning improvement and corresponding reduction in soluble Aβ42 oligomers within extracellular, intracellular, and membrane fractions. These data support the hypothesis that NNC 26-9100 reduces soluble Aβ42 oligomers and enhances learning through a phosphoramidon-sensitive metalloproteinase-dependent mechanism.