Soluble Aβ Species Research Articles

APP Osaka Mutation in Familial Alzheimer's Disease-Its Discovery, Phenotypes, and Mechanism of Recessive Inheritance.

Alzheimer’s disease is believed to begin with synaptic dysfunction caused by soluble Aβ oligomers. When this oligomer hypothesis was proposed in 2002, there was no direct evidence that Aβ oligomers actually disrupt synaptic function to cause cognitive impairment in humans. In patient brains, both soluble and insoluble Aβ species always coexist, and therefore it is difficult to determine which pathologies are caused by Aβ oligomers and which are caused by amyloid fibrils. Thus, no validity of the oligomer hypothesis was available until the Osaka mutation was discovered. This mutation, which was found in a Japanese pedigree of familial Alzheimer’s disease, is the deletion of codon 693 of APP gene, resulting in mutant Aβ lacking the 22nd glutamate. Only homozygous carriers suffer from dementia. In vitro studies revealed that this mutation has a very unique character that accelerates Aβ oligomerization but does not form amyloid fibrils. Model mice expressing this mutation demonstrated that all pathologies of Alzheimer’s disease can be induced by Aβ oligomers alone. In this review, we describe the story behind the discovery of the Osaka mutation, summarize the mutant’s phenotypes, and propose a mechanism of its recessive inheritance.

Interactions between Soluble Species of β-Amyloid and α-Synuclein Promote Oligomerization while Inhibiting Fibrillization.

Aggregations of β-amyloid (Aβ) and α-synuclein (αS) into oligomeric and fibrillar assemblies are the pathological hallmarks of Alzheimer's and Parkinson's diseases, respectively. Although Aβ and αS affect different regions of the brain and are separated at the cellular level, there is evidence of their eventual interaction in the pathology of both disorders. Characterization of interactions of Aβ and αS at various stages of their aggregation pathways could reveal mechanisms and therapeutic targets for the prevention and cure of these neurodegenerative diseases. In this study, we comprehensively examined the interactions and their molecular manifestations using an array of characterization tools. We show for the first time that αS monomers and oligomers, but not αS fibrils, inhibit Aβ fibrillization while promoting oligomerization of Aβ monomers and stabilizing preformed Aβ oligomers via coassembly, as judged by Thioflavin T fluorescence, transmission electron microscopy, and SDS- and native-PAGE with fluorescently labeled peptides/proteins. In contrast, soluble Aβ species, such as monomers and oligomers, aggregate into fibrils, when incubated alone under the otherwise same condition. Our study provides evidence that the interactions with αS soluble species, responsible for the effects, are mediated primarily by the C-terminus of Aβ, when judged by competitive immunoassays using antibodies recognizing various fragments of Aβ. We also show that the C-terminus of Aβ is a primary site for its interaction with αS fibrils. Collectively, these data demonstrate aggregation state-specific interactions between αS and Aβ and offer insight into a molecular basis of synergistic biological effects between the two polypeptides.

A simple approach to quantitative determination of soluble amyloid-β peptides using a ratiometric fluorescence probe

Alzheimer's disease (AD) is a progressive neurodegenerative illness that affects the elderly population worldwide. The definite diagnosis of AD still depends on post-mortem pathological examination of amyloid plaques consisting of amyliod-β peptides (Aβ) fibrils in the brain so far. However, these fibrils are not closely linked to the development of the disease. Alternatively, soluble Aβ are believed to be more reliable biomarkers for early diagnosis of AD. Here, we report a simple approach to quantitative detection of soluble Aβ species using N-(6-(benzothiazol-2-yl)pyridin-3-yl)-5-(dimethylamino)naphthalene-1-sulfonamide (BPNS) as a ratiometric fluorescence Zn2+ probe. This ratiometric fluorescence assay is based on the competition of soluble Aβ with BPNS for Zn2+, that is, soluble Aβ species with higher chelation affinity can capture Zn2+ from BPNS‒Zn2+ adduct, thereby reactivating the ratiometric fluorescence response of BPNS. BPNS exhibited perfect linear relationship (R2 = 0.998) in accordance with the concentration of soluble Aβ in the presence of Zn2+. The assay possesses strong anti-interference capacity against exogenous agent or the other proteins, thanks to the high selectivity for soluble Aβ species. Importantly, this assay can quantitatively detect soluble Aβ species from different types of biological fluids, such as artificial cerebrospinal fluid (ACSF), serum, and plasma in half an hour. This assay provides a low-cost, fast, sensitive, and simple approach for quantitative detection of soluble Aβ species and may serve as a potential tool for early-stage AD diagnosis.

Doxycycline for Alzheimer's Disease: Fighting β-Amyloid Oligomers and Neuroinflammation.

Alzheimer’s disease (AD) is the most widespread form of dementia, affecting about 45 million people worldwide. Although the β-amyloid peptide (Aβ) remains the most acknowledged culprit of AD, the multiple failures of Aβ-centric therapies call for alternative therapeutic approaches. Conceivably, the complexity of the AD neuropathological scenario cannot be solved with single-target therapies, so multiple-target approaches are needed. Core targets of AD to date are soluble oligomeric Aβ species and neuroinflammation, in an intimate detrimental dialogue. Aβ oligomers, the most neurotoxic species, appear to induce synaptic and cognitive dysfunction through the activation of glial cells. Anti-inflammatory drugs can prevent the action of Aβ oligomers. Neuroinflammation is a chronic event whose perpetuation leads to the continuous release of pro-inflammatory cytokines, promoting neuronal cell death and gross brain atrophy. Among the possible multi-target therapeutic alternatives, this review highlights the antibiotic tetracyclines, which besides antimicrobial activity also have pleiotropic action against amyloidosis, neuroinflammation, and oxidative stress. A particular focus will be on doxycycline (Doxy), a second-generation tetracycline that crosses the blood–brain barrier more easily and has a safer clinical profile. Doxy emerged as a promising preventive strategy in prion diseases and gave compelling pre-clinical results in mouse models of AD against Aβ oligomers and neuroinflammation. This strongly supports its therapeutic potential and calls for deciphering its exact mechanisms of action so as to maximize its effects in the clinic.

Monoaminergic System Modulation in Depression and Alzheimer's Disease: A New Standpoint?

The prevalence of depression has dramatically increased, and it has been estimated that over 300 million people suffer from depression all over the world. Depression is highly comorbid with many central and peripheral disorders. In this regard, depressive states have been associated with the development of neurological disorders such as Alzheimer’s disease (AD). Accordingly, depression is a risk factor for AD and depressive symptomatology is common in pre-clinical AD, representing an early manifestation of this disease. Neuropsychiatric symptoms may represent prodromal symptoms of dementia deriving from neurobiological changes in specific cerebral regions; thus, the search for common biological substrates is becoming an imperative and intriguing field of research. Soluble forms of beta amyloid peptide (Aβ) have been implicated both in the development of early memory deficits and neuropsychiatric symptoms. Indeed, soluble Aβ species have been shown to induce a depressive-like phenotype in AD animal models. Alterations in monoamine content are a common feature of these neuropathologies. Interestingly, serotonergic system modulation has been implicated in alteration of Aβ production. In addition, noradrenaline is considered crucially involved in compensatory mechanisms, leading to increased Aβ degradation via several mechanisms, including microglia modulation. In further agreement, antidepressant drugs have also been shown to potentially modulate cognitive symptoms in AD and depression. Thus, the present review summarizes the main knowledge about biological and pathological substrates, such as monoamine and related molecules, commonly involved in AD and depression pathology, thus shading light on new therapeutic approaches.

Pathological Increases in Neuronal Hyperactivity in Selective Cholinergic and Noradrenergic Pathways May Limit the Efficacy of Amyloid-β-Based Interventions in Mild Cognitive Impairment and Alzheimer’s Disease

In spite of compelling evidence linking amyloid-β (Aβ) disturbances to the pathophysiology of Alzheimer’s disease (AD), Aβ-based treatments have consistently failed to produce any beneficial effects both in mild cognitive impairment (MCI) and AD, even with successful reductions of toxic aggregated and soluble Aβ species. Before abandoning both the hypothesis and approach, there is a need to examine some overlooked factors that may have contributed to the lack of efficacy, such as the potential drug-induced increases in neuronal hyperactivity leading to adverse cognitive effects. In particular, we posit that selective cholinergic and noradrenergic pathways will be especially vulnerable to this adverse effect. If confirmed, this idea could help identify a potentially preventable and treatable obstacle for enhancing the efficacy of therapeutic agents in MCI and AD.

Fluorescent Imaging of β-Amyloid Using BODIPY Based Near-Infrared Off-On Fluorescent Probe.

Fluorescent imaging of β-amyloid (Aβ) is one of the most promising methods for Alzheimer's disease diagnosis. Several fluorescent probes have been reported to detect Aβ both in vitro and in vivo. However, highly sensitive and highly selective probes with low background signals are still greatly needed. Herein, we rationally designed and synthesized a PIET quenched near-infrared probe QAD-1 to detect Aβ. This probe contains BODIPY as fluorophore and tetrahydroquinoxaline as the quenching group. QAD-1 exhibited significant fluorescent switch-on after binding to soluble and insoluble Aβ species, and the probe had the benefit of low background signal to stain Aβ plaques without the need of wash-out procedures in vitro, which was specially found by the fluorescence off-on probe. QAD-1 could identify the overproduced Aβ in transgenic (APPSWE/PSEN 1dE9) AD mice as early as 6 months old in vivo, which indicated that QAD-1 may be a potential probe for monitoring Aβ species at an early stage of AD.

Distinctive temporal profiles of detergent-soluble and -insoluble tau and Aβ species in human Alzheimer’s disease

Alzheimer’s disease (AD) pathology relevant proteins tau and beta-amyloid (Aβ) exist as an array of post-translationally modified and conformationally altered species with varying abundance, solubility and toxicity. Insoluble neurofibrillary tau tangles and Aβ plaques are end-stage AD hallmarks, yet may carry less disease significance compared to soluble species. At present, it is unclear how soluble and insoluble tau and Aβ relate to each other as well as to disease progression. Here, detergent soluble and insoluble fractions generated from post-mortem human temporal lobe samples (Brodmann area 21) were probed for tau and Aβ markers in immuno-dot assays. Measures were quantified according to diagnosis (AD cf. Non-AD), neuropathological severity, and correlated with disease progression (Braak stages). All markers were elevated within AD cases cf. non-AD controls (p < 0.05) independent of solubility. However, when considered according to neuropathological severity, phospho-tau (detected via CP13 and AT8 antibodies) was elevated early within the soluble fraction (p < 0.05 intermediate cf. low severity) and emerged only later within the insoluble fraction (p < 0.05 high cf. low severity). In contrast, PHF1 phospho-tau, TOC1 reactive tau oligomers and amyloid markers rose within the two fractions simultaneously. Independent of solubility, cognitive correlations were observed for tau makers and for fibrillary amyloid (OC), however only soluble total Aβ was significantly correlated with intellectual impairment. Following the exclusion of end-stage cases, only soluble total Aβ remained correlated with cognition. The data indicate differential rates of protein aggregation during AD progression and confirm the disease relevance of early emerging soluble Aβ species.

Soluble amyloid-beta buffering by plaques in Alzheimer disease dementia versus high-pathology controls.

An unanswered question regarding Alzheimer disease dementia (ADD) is whether amyloid-beta (Aβ) plaques sequester toxic soluble Aβ species early during pathological progression. We previously reported that the concentration of soluble Aβ aggregates from patients with mild dementia was higher than soluble Aβ aggregates from patients with modest Aβ plaque burden but no dementia. The ratio of soluble Aβ aggregate concentration to Aβ plaque area fully distinguished these groups of patients. We hypothesized that initially plaques may serve as a reservoir or sink for toxic soluble Aβ aggregates, sequestering them from other targets in the extracellular space and thereby preventing their toxicity. To initially test a generalized version of this hypothesis, we have performed binding assessments using biotinylated synthetic Aβ1–42 peptide. Aβ1-42-biotin peptide was incubated on unfixed frozen sections from non-demented high plaque pathology controls and patients with ADD. The bound peptide was measured using ELISA and confocal microscopy. We observed no quantitative difference in Aβ binding between the groups using either method. Further testing of the buffering hypothesis using various forms of synthetic and human derived soluble Aβ aggregates will be required to definitively address the role of plaque buffering as it relates to ADD.

Contribution of early Alzheimer's disease-related pathophysiology to the development of acquired epilepsy.

Aberrant epileptic activity is detectable at early disease stages in Alzheimer's disease (AD) patients and in AD mouse models. Here, we investigated in young ArcticAβ mice whether AD-like pathology renders neuronal networks more susceptible to the development of acquired epilepsy induced by unilateral intrahippocampal injection of kainic acid (IHK). In this temporal lobe epilepsy model, IHK induces a status epilepticus followed after two weeks by spontaneous recurrent seizures (SRS). ArcticAβ mice exhibited more severe status epilepticus and early onset of SRS. This hyperexcitable phenotype was characterized in CA1 neurons by decreased synaptic strength, increased kainic acid-induced LTP and reduced frequency of spontaneous inhibitory currents. However, no difference in neurodegeneration, neuroinflammation, axonal reorganization or adult neurogenesis was observed in ArcticAβ mice compared to wild-type littermates following IHK-induced epileptogenesis. Neuropeptide Y (NPY) expression was reduced at baseline and its IHK-induced elevation in mossy fibres and granule cells was attenuated. However, although this alteration might underlie premature seizure onset, neutralization of soluble Aβ species by intracerebroventricular Aβ-specific antibody application mitigated the hyperexcitable phenotype of ArcticAβ mice and prevented early SRS onset. Therefore, the development of seizures at early stages of AD is mediated primarily by Aβ species causing widespread changes in synaptic function.

Anti-IL17 treatment ameliorates Down syndrome phenotypes in mice

Down syndrome (DS) is characterized by structural and functional anomalies that are present prenatally and that lead to intellectual disabilities. Later in life, the cognitive abilities of DS individuals progressively deteriorate due to the development of Alzheimer’s disease (AD)-associated neuropathology (i.e., β-amyloid (Aβ) plaques, neurofibrillary tangles (NFTs), neurodegeneration, synaptic pathology, neuroinflammation and increased oxidative stress). Increasing evidence has shown that among these pathological processes, neuroinflammation plays a predominant role in AD etiopathology. In AD mouse models, increased neuroinflammation appears earlier than Aβ plaques and NFTs, and in DS and AD models, neuroinflammation exacerbates the levels of soluble and insoluble Aβ species, favoring neurodegeneration. The Ts65Dn (TS) mouse, the most commonly used murine model of DS, recapitulates many alterations present in both DS and AD individuals, including enhanced neuroinflammation. In this study, we observed an altered neuroinflammatory milieu in the hippocampus of the TS mouse model. Pro-inflammatory mediators that were elevated in the hippocampus of this model included pro-inflammatory cytokine IL17A, which has a fundamental role in mediating brain damage in neuroinflammatory processes. Here, we analyzed the ability of an anti-IL17A antibody to reduce the neuropathological alterations that are present in TS mice during early neurodevelopmental stages (i.e., hippocampal neurogenesis and hypocellularity) or that are aggravated in later-life stages (i.e., cognitive abilities, cholinergic neuronal loss and increased cellular senescence, APP expression, Aβ peptide expression and neuroinflammation). Administration of anti-IL17 for 5 months, starting at the age of 7 months, partially improved the cognitive abilities of the TS mice, reduced the expression of several pro-inflammatory cytokines and the density of activated microglia and normalized the APP and Aβ1–42 levels in the hippocampi of the TS mice. These results suggest that IL17-mediated neuroinflammation is involved in several AD phenotypes in TS mice and provide a new therapeutic target to reduce these pathological characteristics.

Differential effect of amyloid beta peptides on mitochondrial axonal trafficking depends on their state of aggregation and binding to the plasma membrane

Inhibition of mitochondrial axonal trafficking by amyloid beta (Aβ) peptides has been implicated in early pathophysiology of Alzheimer's Disease (AD). Yet, it remains unclear whether the loss of motility inevitably induces the loss of mitochondrial function, and whether restoration of axonal trafficking represents a valid therapeutic target. Moreover, while some investigations identify Aβ oligomers as the culprit of trafficking inhibition, others propose that fibrils play the detrimental role. We have examined the effect of a panel of Aβ peptides with different mutations found in familial AD on mitochondrial motility in primary cortical mouse neurons. Peptides with higher propensity to aggregate inhibit mitochondrial trafficking to a greater extent with fibrils inducing the strongest inhibition. Binding of Aβ peptides to the plasma membrane was sufficient to induce trafficking inhibition where peptides with reduced plasma membrane binding and internalization had lesser effect on mitochondrial motility. We also found that Aβ peptide with Icelandic mutation A673T affects axonal trafficking of mitochondria but has very low rates of plasma membrane binding and internalization in neurons, which could explain its relatively low toxicity. Inhibition of mitochondrial dynamics caused by Aβ peptides or fibrils did not instantly affect mitochondrial bioenergetic and function. Our results support a mechanism where inhibition of axonal trafficking is initiated at the plasma membrane by soluble low molecular weight Aβ species and is exacerbated by fibrils. Since trafficking inhibition does not coincide with the loss of mitochondrial function, restoration of axonal transport could be beneficial at early stages of AD progression. However, strategies designed to block Aβ aggregation or fibril formation alone without ensuring the efficient clearance of soluble Aβ may not be sufficient to alleviate the trafficking phenotype.

Wnt signaling loss accelerates the appearance of neuropathological hallmarks of Alzheimer's disease in J20-APP transgenic and wild-type mice.

Alzheimer's disease (AD) is a neurodegenerative pathology characterized by aggregates of amyloid-β (Aβ) and phosphorylated tau protein, synaptic dysfunction, and spatial memory impairment. The Wnt signaling pathway has several key functions in the adult brain and has been associated with AD, mainly as a neuroprotective factor against Aβ toxicity and tau phosphorylation. However, dysfunction of Wnt/β-catenin signaling might also play a role in the onset and development of the disease. J20 APPswInd transgenic (Tg) mouse model of AD was treated i.p. with various Wnt signaling inhibitors for 10weeks during pre-symptomatic stages. Then, cognitive, biochemical and histochemical analyses were performed. Wnt signaling inhibitors induced severe changes in the hippocampus, including alterations in Wnt pathway components and loss of Wnt signaling function, severe cognitive deficits, increased tau phosphorylation and Aβ1-42 peptide levels, decreased Aβ42/Aβ40 ratio and Aβ1-42 concentration in the cerebral spinal fluid, and high levels of soluble Aβ species and synaptotoxic oligomers in the hippocampus, together with changes in the amount and size of senile plaques. More important, we also observed severe alterations in treated wild-type (WT) mice, including behavioral impairment, tau phosphorylation, increased Aβ1-42 in the hippocampus, decreased Aβ1-42 in the cerebral spinal fluid, and hippocampal dysfunction. Wnt inhibition accelerated the development of the pathology in a Tg AD mouse model and contributed to the development of Alzheimer's-like changes in WT mice. These results indicate that Wnt signaling plays important roles in the structure and function of the adult hippocampus and suggest that inhibition of the Wnt signaling pathway is an important factor in the pathogenesis of AD. Read the Editorial Highlight for this article on page 356.

Brain tissue Aβ42 levels are linked to shunt response in idiopathic normal pressure hydrocephalus.

The authors conducted a study to test if the cortical brain tissue levels of soluble amyloid beta (Aβ) reflect the propensity of cortical Aβ aggregate formation and may be an additional factor predicting surgical outcome following idiopathic normal pressure hydrocephalus (iNPH) treatment. Highly selective ELISAs (enzyme-linked immunosorbent assays) were used to quantify soluble Aβ40, Aβ42, and neurotoxic Aβ oligomers/protofibrils, associated with Aβ aggregation, in cortical biopsy samples obtained in patients with iNPH (n = 20), sampled during ventriculoperitoneal (VP) shunt surgery. Patients underwent pre- and postoperative (3-month) clinical assessment with a modified iNPH scale. The preoperative CSF biomarkers and the levels of soluble and insoluble Aβ species in cortical biopsy samples were analyzed for their association with a favorable outcome following the VP shunt procedure, defined as a ≥ 5-point increase in the iNPH scale. The brain tissue levels of Aβ42 were negatively correlated with CSF Aβ42 (Spearman’s r = -0.53, p < 0.05). The Aβ40, Aβ42, and Aβ oligomer/protofibril levels in cortical biopsy samples were higher in patients with insoluble cortical Aβ aggregates (p < 0.05). The preoperative CSF Aβ42 levels were similar in patients responding (n = 11) and not responding (n = 9) to VP shunt treatment at 3 months postsurgery. In contrast, the presence of cortical Aβ aggregates and high brain tissue Aβ42 levels were associated with a poor outcome following VP shunt treatment (p < 0.05). Brain tissue measurements of soluble Aβ species are feasible. Since high Aβ42 levels in cortical biopsy samples obtained in patients with iNPH indicated a poor surgical outcome, tissue levels of Aβ species may be associated with the clinical response to shunt treatment.

The conformational epitope for a new Aβ42 protofibril-selective antibody partially overlaps with the peptide N-terminal region.

Aggregation and accumulation of amyloid-β peptide (Aβ) is a key component of Alzheimer's disease (AD). While monomeric Aβ appears to be benign, oligomers adopt a biologically detrimental structure. These soluble structures can be detected in AD brain tissue by antibodies that demonstrate selectivity for aggregated Aβ. Protofibrils are a subset of soluble oligomeric Aβ species and are described as small (<100nm) curvilinear assemblies enriched in β-sheet structure. Our own invitro studies demonstrate that microglial cells are much more sensitive to soluble Aβ42 protofibrils compared to Aβ42 monomer or insoluble Aβ42 fibrils. Protofibrils interact with microglia, trigger Toll-like receptor signaling, elicit cytokine transcription and expression, and are rapidly taken up by the cells. Because of the importance of this Aβ species, we sought to develop an antibody that selectively recognizes protofibrils over other Aβ species. Immunization of rabbits with isolated Aβ42 protofibrils generated a high-titer anti serum with a strong affinity for Aβ42 protofibrils. The antiserum, termed AbSL, was selective for Aβ42 protofibrils over Aβ42 monomers and Aβ42 fibrils. AbSL did not react with amyloid precursor protein and recognized distinct pathological features in AD transgenic mouse brain slices. Competition studies with an Aβ antibody that targets residues 1-16 indicated that the conformational epitope for AbSL involved the N-terminal region of protofibrils in some manner. The newly developed antibody may have potential diagnostic and therapeutic uses in AD tissue and patients, and targeting of protofibrils in AD may have beneficial effects. Read the Editorial Highlight for this article on page 621. Cover Image for this issue: doi. 10.1111/jnc.13827.

Studies for Improving a Rat Model of Alzheimer's Disease: Icv Administration of Well-Characterized β-Amyloid 1-42 Oligomers Induce Dysfunction in Spatial Memory.

During the past 15 years, several genetically altered mouse models of human Alzheimer’s disease (AD) have been developed. These costly models have greatly facilitated the evaluation of novel therapeutic approaches. Injecting synthetic β-amyloid (Aβ) 1-42 species into different parts of the brain of non-transgenic rodents frequently provided unreliable results, owing to a lack of a genuine characterization of the administered Aβ aggregates. Previously, we have published a new rat AD-model in which protofibrillar-fibrillar Aβ1-42 was administered into rat entorhinal cortex (Sipos 2007). In order to develop a more reliable model, we have injected well-characterized toxic soluble Aβ1-42 species (oligomers, protofibrils and fibrils) intracerebroventricularly (icv) into rat brain. Studies of the distribution of fluorescent-labeled Aβ1-42 in the brain showed that soluble Aβ-species diffused into all parts of the rat brain. After seven days, the Aβ-treated animals showed a significant decrease of spatial memory in Morris water maze test and impairment of synaptic plasticity (LTP) measured in acute hippocampal slices. The results of histological studies (decreased number of viable neurons, increased tau levels and decreased number of dendritic spines) also supported that icv administration of well-characterized toxic soluble Aβ species into rat brain provides a reliable rat AD-model.

The Anti-Amyloid-β and Neuroprotective Properties of a Novel Tricyclic Pyrone Molecule.

There is an urgent unmet need for new therapeutics for Alzheimer’s disease (AD), the most common cause of dementia in the elderly. Therapeutic approaches targeting amyloid-β (Aβ) and its downstream toxicities have become major strategies in AD drug development. We have taken a rational design approach and synthesized a class of tricyclic pyrone (TP) compounds that show anti-Aβ and other neuroprotective actions. The in vivo efficacy of a lead TP named CP2 to ameliorate AD-like pathologies has been shown in mouse models. Here we report the selection and initial characterization of a new lead TP70, which exhibited an anti-Aβ therapeutic index even higher than CP2. Moreover, TP70 was able to reduce oxidative stress, inhibit acyl-coenzyme A:cholesterol acyltransferase (ACAT), and upregulate the expression of ATP-binding cassette subfamily A, member 1 (ABCA1), actions considered neuroprotective in AD. TP70 further showed excellent pharmacokinetic properties, including brain penetration and oral availability. When administered to 5xFAD mice via intraperitoneal or oral route, TP70 enhanced the overall solubility and decreased the level of cerebral Aβ, including both fibrillary and soluble Aβ species. Interestingly, TP70 enhanced N-methyl-D-aspartate (NMDA) receptor-mediated excitatory post-synaptic potential (EPSP) in the hippocampal CA1 area, increased the magnitude of NMDA-dependent hippocampal long-term potentiation (LTP), a cellular model of learning and memory, and prevented the Aβ oligomer-impaired LTP. Significantly, a single dose of TP70 administered to aged 5xFAD mice was effective in mitigating the impaired LTP induction, recorded at 24 h after administration. Our results support a potential of TP70 in clinical development for AD in view of its synergistic neuroprotective actions, ability to positively modulate NMDA receptor-mediated hippocampal plasticity, and favorable pharmacokinetic properties in rodents.

Soluble oligomeric amyloid-\u03b2 induces calcium dyshomeostasis that precedes synapse loss in the living mouse brain

BackgroundAmyloid-β oligomers (oAβ) are thought to mediate neurotoxicity in Alzheimer’s disease (AD), and previous studies in AD transgenic mice suggest that calcium dysregulation may contribute to these pathological effects. Even though AD mouse models remain a valuable resource to investigate amyloid neurotoxicity, the concomitant presence of soluble Aβ species, fibrillar Aβ, and fragments of amyloid precursor protein (APP) complicate the interpretation of the phenotypes.MethodTo explore the specific contribution of soluble oligomeric Aβ (oAβ) to calcium dyshomeostasis and synaptic morphological changes, we acutely exposed the healthy mouse brain, at 3 to 6 months of age, to naturally occurring soluble oligomers and investigated their effect on calcium levels using in vivo multiphoton imaging.ResultsWe observed a dramatic increase in the levels of neuronal resting calcium, which was dependent upon extracellular calcium influx and activation of NMDA receptors. Ryanodine receptors, previously implicated in AD models, did not appear to be primarily involved using this experimental setting. We used the high resolution cortical volumes acquired in-vivo to measure the effect on synaptic densities and observed that, while spine density remained stable within the first hour of oAβ exposure, a significant decrease in the number of dendritic spines was observed 24 h post treatment, despite restoration of intraneuronal calcium levels at this time point.ConclusionsThese observations demonstrate a specific effect of oAβ on NMDA-mediated calcium influx, which triggers synaptic collapse in vivo. Moreover, this work leverages a method to quantitatively measure calcium concentration at the level of neuronal processes, cell bodies and single synaptic elements repeatedly and thus can be applicable to testing putative drugs and/or other intervention methodologies.

Large Soluble Oligomers of Amyloid β-Protein from Alzheimer Brain Are Far Less Neuroactive Than the Smaller Oligomers to Which They Dissociate.

Oligomers of amyloid β-protein (oAβ) are tought to play an important role in Alzheimer's disease (AD), but there is confusion and controversy about what types and sizes of oligomers have disease-relevant activity. Using size-exclusion chromatography and three distinct measures of bioactivity, we show that the predominant forms of Aβ in aqueous extracts of AD brain are high molecular weight (HMW) and relatively inactive. Importantly, under certain conditions, the abundant HMW oAβ can dissociate into low molecular weight species, and these low molecular weight oligomers are significantly more bioactive on synapses and microglia than the HMW species from which they are derived. We conclude that conditions that destabilize HMW oAβ or retard the sequestration of smaller, more bioactive components are important drivers of Aβ toxicity.

Soluble pre-fibrillar tau and β-amyloid species emerge in early human Alzheimer's disease and track disease progression and cognitive decline.

Post-mortem investigations of human Alzheimer’s disease (AD) have largely failed to provide unequivocal evidence in support of the original amyloid cascade hypothesis, which postulated deposition of β-amyloid (Aβ) aggregates to be the cause of a demented state as well as inductive to tau neurofibrillary tangles (NFTs). Conflicting evidence suggests, however, that Aβ plaques and NFTs, albeit to a lesser extent, are present in a substantial subset of non-demented individuals. Hence, a range of soluble tau and Aβ species has more recently been implicated as the disease-relevant toxic entities. Despite the incorporation of soluble proteins into a revised amyloid cascade hypothesis, a detailed characterization of these species in the context of human AD onset, progression and cognitive decline has been lacking. Here, lateral temporal lobe samples (Brodmann area 21) of 46 human cases were profiled via tau and Aβ Western blot and native state dot blot protocols. Elevations in phospho-tau (antibodies: CP13, AT8 and PHF-1), pathological tau conformations (MC-1) and oligomeric tau (TOC1) agreed with medical diagnosis (non-AD cf. AD) and Braak stage classification (low, intermediate and high), alongside elevations in soluble Aβ species (MOAB-2 and pyro-glu Aβ) and a decline in levels of the amyloid precursor protein. Strong correlations were observed between individual Braak stages and multiple cognitive measures with all tau markers as well as total soluble Aβ. In contrast to previous reports, SDS-stable Aβ oligomers (*56) were not found to be reliable for all classifications and appeared likely to be a technical artefact. Critically, the robust predictive value of total soluble Aβ was dependent on native state quantification. Elevations in tau and Aβ within soluble fractions (Braak stage 2–3 cf. 0) were evident earlier than previously established in fibril-focused disease progression scales. Together, these data provide strong evidence that soluble forms of tau and Aβ co-localise early in AD and are closely linked to disease progression and cognitive decline.Electronic supplementary materialThe online version of this article (doi:10.1007/s00401-016-1632-3) contains supplementary material, which is available to authorized users.