Aβ Dimers Research Articles

Molecular insights into the primary nucleation of polymorphic amyloid β dimers in DOPC lipid bilayer membrane.

Alzheimer's disease (AD) pathology is characterized by loss of memory cognitive and behavioral deterioration. One of the hallmarks of AD is amyloid β (Aβ) plaques in the brain that consists of Aβ oligomers and fibrils. It is accepted that oligomers, particularly dimers, are toxic species that are produced extracellularly and intracellularly in membranes. It is believed that the disruption of membranes by polymorphic Aβ oligomers is the key for the pathology of AD. This is a first study that investigate the effect of polymorphic “α‐helix/random coil” and “fibril‐like” Aβ dimers on 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC) membrane. It has been found that the DOPC membrane promotes Aβ1–42 “fibril‐like” dimers and impedes Aβ1–42 “α‐helix/random coil” dimers. The N‐termini domains within Aβ1–42 dimers play a role in Aβ aggregation in membrane milieus. In addition, the aromatic π–π interactions (involving residues F19 and F20 in Aβ1–42) are the driving forces for the hydrophobic interactions that initiate the primary nucleation of polymorphic Aβ1–42 dimers within DOPC membrane. Finally, the DOPC bilayer membrane thickness is locally decreased, and it is disrupted by an embedded distinct Aβ1–42 dimer, due to relatively large contacts between Aβ1–42 monomers and the DOPC membrane. This study reveals insights into the molecular mechanisms by which polymorphic early‐stage Aβ1–42 dimers have distinct impacts on DOPC membrane.

Molecular docking and molecular dynamics simulations studies on the protective and pathogenic roles of the amyloid-β peptide between herpesvirus infection and Alzheimer's disease

The protective innate immune response of β-amyloid peptide (Aβ) has been indicated as a risk factor for Alzheimer's disease (AD) due to the rapid amyloidosis. In order to obtain molecular-level insights into the protective and pathogenic roles of Aβ, the binding modes between Aβ1-42 and the envelop glycoprotein D (gD) of Herpes simplex virus-1 (HSV-1)/Aβ1-42 were theoretically investigated by using molecular docking, molecular dynamics (MD) simulations and binding free energy decomposition methods in the present study. The Aβ1-42 stably binds to the envelop gD via intermolecular hydrogen bonds and van der Waals (vdW) interactions. The Aβ1-42 acquires its equilibrium with higher fluctuation amplitude and a better structured C-terminal in the HSV-1 gD–Aβ1-42 complex comparing to that in the Aβ1-42–Aβ1-42 complex. The amino acid residues of Aβ1-42 involved in the formation of the Aβ1-42 dimer are fully free and accessible in the HSV-1 gD–Aβ1-42 complex. It is favorable for the Aβ1-42 monomer to interact with the HSV-1 gD–Aβ1-42 complex. It may be responsible for the rapid amyloidosis which entraps the herpesvirus as well as causing AD.

A Disulfide-Stabilized Aβ that Forms Dimers but Does Not Form Fibrils.

Aβ dimers are a basic building block of many larger Aβ oligomers and are among the most neurotoxic and pathologically relevant species in Alzheimer's disease. Homogeneous Aβ dimers are difficult to prepare, characterize, and study because Aβ forms heterogeneous mixtures of oligomers that vary in size and can rapidly aggregate into more stable fibrils. This paper introduces AβC18C33 as a disulfide-stabilized analogue of Aβ42 that forms stable homogeneous dimers in lipid environments but does not aggregate to form insoluble fibrils. The AβC18C33 peptide is readily expressed in Escherichia coli and purified by reverse-phase HPLC to give ca. 8 mg of pure peptide per liter of bacterial culture. SDS-PAGE establishes that AβC18C33 forms homogeneous dimers in the membrane-like environment of SDS and that conformational stabilization of the peptide with a disulfide bond prevents the formation of heterogeneous mixtures of oligomers. Mass spectrometric (MS) studies in the presence of dodecyl maltoside (DDM) further confirm the formation of stable noncovalent dimers. Circular dichroism (CD) spectroscopy establishes that AβC18C33 adopts a β-sheet conformation in detergent solutions and supports a model in which the intramolecular disulfide bond induces β-hairpin folding and dimer formation in lipid environments. Thioflavin T (ThT) fluorescence assays and transmission electron microscopy (TEM) studies indicate that AβC18C33 does not undergo fibril formation in aqueous buffer solutions and demonstrate that the intramolecular disulfide bond prevents fibril formation. The recently published NMR structure of an Aβ42 tetramer (PDB: 6RHY) provides a working model for the AβC18C33 dimer, in which two β-hairpins assemble through hydrogen bonding to form a four-stranded antiparallel β-sheet. It is anticipated that AβC18C33 will serve as a stable, nonfibrilizing, and noncovalent Aβ dimer model for amyloid and Alzheimer's disease research.

Amyloid-β peptide dimers undergo a random coil to β-sheet transition in the aqueous phase but not at the neuronal membrane

Mounting evidence suggests that the neuronal cell membrane is the main site of oligomer-mediated neuronal toxicity of amyloid-β peptides in Alzheimer's disease. To gain a detailed understanding of the mutual interference of amyloid-β oligomers and the neuronal membrane, we carried out microseconds of all-atom molecular dynamics (MD) simulations on the dimerization of amyloid-β (Aβ)42 in the aqueous phase and in the presence of a lipid bilayer mimicking the in vivo composition of neuronal membranes. The dimerization in solution is characterized by a random coil to β-sheet transition that seems on pathway to amyloid aggregation, while the interactions with the neuronal membrane decrease the order of the Aβ42 dimer by attenuating its propensity to form a β-sheet structure. The main lipid interaction partners of Aβ42 are the surface-exposed sugar groups of the gangliosides GM1. As the neurotoxic activity of amyloid oligomers increases with oligomer order, these results suggest that GM1 is neuroprotective against Aβ-mediated toxicity.

Formaldehyde-Crosslinked Nontoxic Aβ Monomers to Form Toxic Aβ Dimers and Aggregates: Pathogenicity and Therapeutic Perspectives.

Alzheimer's disease (AD) is characterized by the presence of senile plaques in the brain. However, medicines targeting amyloid-beta (Aβ) have not achieved the expected clinical effects. This review focuses on the formation mechanism of the Aβ dimer (the basic unit of oligomers and fibrils) and its tremendous potential as a drug target. Recently, age-associated formaldehyde and Aβ-derived formaldehyde have been found to crosslink the nontoxic Aβ monomer to form the toxic dimers, oligomers and fibrils. Particularly, Aβ-induced formaldehyde accumulation and formaldehyde-promoted Aβ aggregation form a vicious cycle. Subsequently, formaldehyde initiates Aβ toxicity in both the early-and late-onset AD. These facts also explain why AD drugs targeting only Aβ do not have the desired therapeutic effects. Development of the nanoparticle-based medicines targeting both formaldehyde and Aβ dimer is a promising strategy for improving the drug efficacy by penetrating blood-brain barrier and extracellular space into the cortical neurons in AD patients.

A Comprehensive Insight into the Mechanisms of Dopamine in Disrupting Aβ Protofibrils and Inhibiting Aβ Aggregation.

Fibrillary aggregates of amyloid-β (Aβ) are the pathological hallmark of Alzheimer's disease (AD). Clearing Aβ deposition or inhibiting Aβ aggregation is a promising approach to treat AD. Experimental studies reported that dopamine (DA), an important neurotransmitter, can inhibit Aβ aggregation and disrupt Aβ fibrils in a dose-dependent manner. However, the underlying molecular mechanisms still remain mostly elusive. Herein, we investigated the effect of DA on Aβ42 protofibrils at three different DA-to-Aβ molar ratios (1:1, 2:1, and 10:1) using all-atom molecular dynamics simulations. Our simulations demonstrate that protonated DA at a DA-to-Aβ ratio of 2:1 exhibits stronger Aβ protofibril disruptive capacity than that at a molar-ratio of 1:1 by mostly disrupting the F4-L34-V36 hydrophobic core. When the ratio of DA-to-Aβ increases to 10:1, DA has a high probability to bind to the outer surface of protofibril and has negligible effect on the protofibril structure. Interestingly, at the same DA-to-Aβ ratio (10:1), a mixture of protonated (DA+) and deprotonated (DA0) DA molecules significantly disrupts Aβ protofibrils by the binding of DA0 to the F4-L34-V36 hydrophobic core. Replica-exchange molecular dynamics simulations of Aβ42 dimer show that DA+ inhibits the formation of β-sheets, K28-A42/K28-D23 salt-bridges, and interpeptide hydrophobic interactions and results in disordered coil-rich Aβ dimers, which would inhibit the subsequent fibrillization of Aβ. Further analyses reveal that DA disrupts Aβ protofibril and prevents Aβ dimerization mostly through π-π stacking interactions with residues F4, H6, and H13, hydrogen bonding interactions with negatively charged residues D7, E11, E22 and D23, and cation-π interactions with residues R5. This study provides a complete picture of the molecular mechanisms of DA in disrupting Aβ protofibril and inhibiting Aβ aggregation, which could be helpful for the design of potent drug candidates for the treatment/intervention of AD.

Probing the Structure of Toxic Amyloid-β Oligomers with Electron Spin Resonance and Molecular Modeling

Structural models of the toxic species involved in the development of Alzheimer’s disease are of utmost importance to understand the molecular mechanism and to describe early biomarkers of the disease. Among toxic species, soluble oligomers of amyloid-β (Aβ) peptides are particularly important, because they are responsible for spreading cell damages over brain regions, thus rapidly impairing brain functions. In this work we obtain structural information on a carefully prepared Aβ(1-42) sample, representing a toxic state for cell cultures, by combining electron spin resonance spectroscopy and computational models. We exploited the binding of Cu2+ to Aβ(1-42) and used copper as a probe for estimating Cu–Cu distances in the oligomers by applying double electron–electron resonance (DEER) pulse sequence. The DEER trace of this sample displays a unique feature that fits well with structural models of oligomers formed by Cu-cross-linked peptide dimers. Because Cu is bound to the Aβ(1-42) N-terminus, for the first time structural constraints that are missing in reported studies are provided at physiological conditions for the Aβ N-termini. These constraints suggest the Aβ(1-42) dimer as the building block of soluble oligomers, thus changing the scenario for any kinetic model of Aβ(1-42) aggregation.

Binding of Amyloid β(1-42)-Calmodulin Complexes to Plasma Membrane Lipid Rafts in Cerebellar Granule Neurons Alters Resting Cytosolic Calcium Homeostasis.

Lipid rafts are a primary target in studies of amyloid β (Aβ) cytotoxicity in neurons. Exogenous Aβ peptides bind to lipid rafts, which in turn play a key role in Aβ uptake, leading to the formation of neurotoxic intracellular Aβ aggregates. On the other hand, dysregulation of intracellular calcium homeostasis in neurons has been observed in Alzheimer’s disease (AD). In a previous work, we showed that Aβ(1–42), the prevalent Aβ peptide found in the amyloid plaques of AD patients, binds with high affinity to purified calmodulin (CaM), with a dissociation constant ≈1 nM. In this work, to experimentally assess the Aβ(1–42) binding capacity to intracellular CaM, we used primary cultures of mature cerebellar granule neurons (CGN) as a neuronal model. Our results showed a large complexation of submicromolar concentrations of Aβ(1–42) dimers by CaM in CGN, up to 120 ± 13 picomoles of Aβ(1–42) /2.5 × 106 cells. Using fluorescence microscopy imaging, we showed an extensive co-localization of CaM and Aβ(1–42) in lipid rafts in CGN stained with up to 100 picomoles of Aβ(1–42)-HiLyteTM-Fluor555 monomers. Intracellular Aβ(1–42) concentration in this range was achieved by 2 h incubation of CGN with 2 μM Aβ(1–42), and this treatment lowered the resting cytosolic calcium of mature CGN in partially depolarizing 25 mM potassium medium. We conclude that the primary cause of the resting cytosolic calcium decrease is the inhibition of L-type calcium channels of CGN by Aβ(1–42) dimers, whose activity is inhibited by CaM:Aβ(1–42) complexes bound to lipid rafts.

The interaction of insoluble Amyloid-β with soluble Amyloid-β dimers decreases Amyloid-β plaque numbers.

The heterogeneity of Amyloid-beta (Aβ) plaque load in patients with Alzheimer's disease (AD) has puzzled neuropathology. Since brain Aβ plaque load does not correlate with cognitive decline, neurotoxic soluble Aβ oligomers have been championed as disease-causing agents in early AD. So far, investigating molecular interactions between soluble oligomeric Aβ and insoluble Aβ in vivo has been difficult because of the abundance of Aβ oligomer species and the kinetic equilibrium in which they coexist. Here, we investigated whether Aβ plaque heterogeneity relates to interactions of different Aβ conformers. We took advantage of transgenic mice that generate exclusively Aβ dimers (tgDimer mice) but do not develop Aβ plaques or neuroinflammation during their lifetime, crossed them to the transgenic CRND8 mice that develop plaques after 90days and measured Aβ plaque load using immunohistochemical and biochemical assays. Furthermore, we performed in vitro thioflavin T (ThT) aggregation assays titrating synthetic Aβ42 -S8C dimers into fibril-forming synthetic Aβ42 . We observed a lower number of Aβ plaques in the brain of double transgenic mice compared to tgCRND8 mice alone while the average plaque size remained unaltered. Corroborating these in vivo findings, synthetic Aβ-S8C dimers inhibited fibril formation of wild-type Aβ also in vitro, seen by an increased half-time in the ThT assay. Our study indicates that Aβ dimers directly interfere with Aβ fibril formation in vivo and in vitro. The variable interaction of Aβ dimers with insoluble Aβ seeds could thus contribute to the heterogeneity of Aβ plaque load in AD patients.

Fluorescent indolizine derivative YI-13 detects amyloid-β monomers, dimers, and plaques in the brain of 5XFAD Alzheimer transgenic mouse model.

Alzheimer disease (AD) is a neurodegenerative disorder characterized by the aberrant production and accumulation of amyloid-β (Aβ) peptides in the brain. Accumulated Aβ in soluble oligomer and insoluble plaque forms are considered to be a pathological culprit and biomarker of the disorder. Here, we report a fluorescent universal Aβ-indicator YI-13, 5-(4-fluorobenzoyl)-7,8-dihydropyrrolo[1,2-b]isoquinolin-9(6H)-one, which detects Aβ monomers, dimers, and plaques. We synthesized a library of 26 fluorescence chemicals with the indolizine core and screen them through a series of in vitro tests utilizing Aβ as a target and YI-13 was selected as the final imaging candidate. YI-13 was found to stain and visualize insoluble Aβ plaques in the brain tissue, of a transgenic mouse model with five familial AD mutations (5XFAD), by a histochemical approach and to label soluble Aβ oligomers within brain lysates of the mouse model under a fluorescence plate reader. Among oligomers aggregated from monomers and synthetic dimers from chemically conjugated monomers, YI-13 preferred the dimeric Aβ.

Degradation of FA reduces Aβ neurotoxicity and Alzheimer-related phenotypes.

Dysregulation of formaldehyde (FA) has been implicated in the development of Alzheimer's Disease (AD). Elevated FA levels in Alzheimer's patients and animal models are associated with impaired cognitive functions. However, the exact role of FA in AD remains unknown. We now identified that oxidative demethylation at serine8/26 of amyloid-beta protein (Aβ) induced FA generation and FA cross-linked with the lysine28 residue in the β-turn of Aβ monomer to form Aβ dimers, and then accelerated Aβ oligomerization and fibrillogenesis in vitro. However, Aβ42 mutation in serine8/26, lysine28 abolished Aβ self-aggregation. Furthermore, Aβ inhibited the activity of formaldehyde dehydrogenase (FDH), the enzyme for FA degradation, resulting in FA accumulation. In turn, excess of FA stimulated Aβ aggregation both in vitro and in vivo by increasing the formation of Aβ oligomers and fibrils. We found that degradation of FA by formaldehyde scavenger-NaHSO3 or coenzyme Q10 reduced Aβ aggregation and ameliorated the neurotoxicity, and improved the cognitive performance in APP/PS1 mice. Our study provides evidence that endogenous FA is essential for Aβ self-aggregation and scavenging FA could be an effective strategy for treating AD.

Assessments of the Effect of Neurokinin B on Toxic Aβ Aggregates in Alzheimer's Disease with the Molecular Mechanisms' Action.

Clinical trials of past and current treatments for Alzheimer's disease (AD) patients on the market suffer from the dual drawbacks of a lack of efficacy and side effects. Neuropeptides have been highlighted by their potential to protect cells against AD and can reverse the toxic effect induced by Aβ in cultured neurons. One of the neuropeptides that has insufficient attention in the literature as a potential treatment for prevention of the progression of AD is neurokinin B (NKB). There are critical and unresolved questions concerning the activation, and the molecular mechanisms underlying NKB effect on prevention of Aβ aggregation remain unknown. The current work identifies for the first time the specific interactions that contribute to the inhibition and prevention of initial seeding of polymorphic early-stage dimers. Three main conclusions are observed in this work. First, NKB inhibits formation of polymorphic early-stage fibrillar Aβ dimers. The efficiency of the inhibition depends on the concentration of NKB (i.e., NKB:Aβ ratio). Second, NKB has an excellent effect of preventing the formation of initial seeding of early-stage nonfibrillar Aβ dimers. Third, NKB peptides may self-assemble to form cross-α fibril-like structure during the inhibition activity of the polymorphic early-stage fibrillar Aβ dimers but not during the prevention activity of early-stage nonfibrillar Aβ dimers. The work provides crucial information for future experimental studies to approve the functional effect of NKB on inhibition and prevention of Aβ polymorphic early-stage oligomers.

The Pathogenesis Mechanism, Structure Properties, Potential Drugs and Therapeutic Nanoparticles against the Small Oligomers of Amyloid-β.

Alzheimer's Disease (AD) is a devastating neurodegenerative disease that affects millions of people in the world. The abnormal aggregation of amyloid β protein (Aβ) is regarded as the key event in AD onset. Meanwhile, the Aβ oligomers are believed to be the most toxic species of Aβ. Recent studies show that the Aβ dimers, which are the smallest form of Aβ oligomers, also have the neurotoxicity in the absence of other oligomers in physiological conditions. In this review, we focus on the pathogenesis, structure and potential therapeutic molecules against small Aβ oligomers, as well as the nanoparticles (NPs) in the treatment of AD. In this review, we firstly focus on the pathogenic mechanism of Aβ oligomers, especially the Aβ dimers. The toxicity of Aβ dimer or oligomers, which attributes to the interactions with various receptors and the disruption of membrane or intracellular environments, were introduced. Then the structure properties of Aβ dimers and oligomers are summarized. Although some structural information such as the secondary structure content is characterized by experimental technologies, detailed structures are still absent. Following that, the small molecules targeting Aβ dimers or oligomers are collected; nevertheless, all of these ligands have failed to come into the market due to the rising controversy of the Aβ-related "amyloid cascade hypothesis". At last, the recent progress about the nanoparticles as the potential drugs or the drug delivery for the Aβ oligomers are present.

Detection of Amyloid β Oligomers with RNA Aptamers in AppNL-G-F/NL-G-F Mice: A Model of Arctic Alzheimer's Disease.

RNA aptamers have garnered attention for diagnostic applications due to their ability to recognize diverse targets. Oligomers of 42-mer amyloid β-protein (Aβ42), whose accumulation is relevant to the pathology of Alzheimer’s disease (AD), are among the most difficult molecules for aptamer recognition because they are prone to aggregate in heterogeneous forms. In addition to designing haptens for in vitro selection of aptamers, the difficulties involved in determining their effect on Aβ42 oligomerization impede aptamer research. We previously developed three RNA aptamers (E22P-AbD4, -AbD31, and -AbD43) with high affinity for protofibrils (PFs) derived from a toxic Aβ42 dimer. Notably, these aptamers recognized diffuse staining, which likely originated from PFs or higher-order oligomers with curvilinear structures in a knock-in AppNL-G-F/NL-G-F mouse, carrying the Arctic mutation that preferentially induced the formation of PFs, in addition to a PS2Tg2576 mouse. To determine which oligomeric sizes were mainly altered by the aptamer, ion mobility–mass spectrometry (IM–MS) was carried out. One aptamer, E22P-AbD43, formed adducts with the Aβ42 monomer and dimer, leading to suppression of further oligomerization. These findings support the utility of these aptamers as diagnostics for AD.

X-ray Crystallography Reveals Parallel and Antiparallel β-Sheet Dimers of a β-Hairpin Derived from Aβ16-36 that Assemble to Form Different Tetramers.

High-resolution structures of oligomers formed by the β-amyloid peptide, Aβ, are important for understanding the molecular basis of Alzheimer's disease. Dimers of Aβ are linked to the pathogenesis and progression of Alzheimer's disease, and tetramers of Aβ are neurotoxic. This paper reports the X-ray crystallographic structures of dimers and tetramers, as well as an octamer, formed by a peptide derived from the central and C-terminal regions of Aβ. In the crystal lattice, the peptide assembles to form two different dimers-an antiparallel β-sheet dimer and a parallel β-sheet dimer-that each further self-assemble to form two different tetramers-a sandwich-like tetramer and a twisted β-sheet tetramer. The structures of these dimers and tetramers derived from Aβ serve as potential models for dimers and tetramers of full-length Aβ that form in vitro and in Alzheimer's disease-afflicted brains.

Redox-Dependent Copper Ion Modulation of Amyloid-β (1-42) Aggregation In Vitro.

Plaque deposits composed of amyloid-β (Aβ) fibrils are pathological hallmarks of Alzheimer’s disease (AD). Although copper ion dyshomeostasis is apparent in AD brains and copper ions are found co-deposited with Aβ peptides in patients’ plaques, the molecular effects of copper ion interactions and redox-state dependence on Aβ aggregation remain elusive. By combining biophysical and theoretical approaches, we here show that Cu2+ (oxidized) and Cu+ (reduced) ions have opposite effects on the assembly kinetics of recombinant Aβ(1-42) into amyloid fibrils in vitro. Cu2+ inhibits both the unseeded and seeded aggregation of Aβ(1-42) at pH 8.0. Using mathematical models to fit the kinetic data, we find that Cu2+ prevents fibril elongation. The Cu2+-mediated inhibition of Aβ aggregation shows the largest effect around pH 6.0 but is lost at pH 5.0, which corresponds to the pH in lysosomes. In contrast to Cu2+, Cu+ ion binding mildly catalyzes the Aβ(1-42) aggregation via a mechanism that accelerates primary nucleation, possibly via the formation of Cu+-bridged Aβ(1-42) dimers. Taken together, our study emphasizes redox-dependent copper ion effects on Aβ(1-42) aggregation and thereby provides further knowledge of putative copper-dependent mechanisms resulting in AD.

Amyloid-β (Aβ42) Peptide Aggregation Rate and Mechanism on Surfaces with Widely Varied Properties: Insights from Brownian Dynamics Simulations.

Amyloid-β (Aβ) plaques, which form by aggregation of harmless Aβ peptide monomers into larger fibrils, are characteristic of neurodegenerative disorders such as Alzheimer's disease. Efforts to treat Alzheimer's disease focus on stopping or reversing the aggregation process that leads to fibril formation. However, effective treatments are elusive due to certain unknown aspects of the process. Many hypotheses point to disruption of cell membranes by adsorbed Aβ monomers or oligomers, but how Aβ behaves and aggregates on surfaces of widely varying properties, such as those present in a cell, is unclear. Elucidating the effects of various surfaces on the dynamics of Aβ and the kinetics of the aggregation process from bulk solution to a surface-adsorbed multimer can help identify what drives aggregation, leading to new methods of intervention by inhibitory drugs or other means. In this work, we used all-atom Brownian dynamics simulations to study the association of two distinct Aβ42 monomer conformations with a surface-adsorbed or free-floating Aβ42 dimer. We calculated the association time, surface interaction energy, surface diffusion coefficient, surface residence time, and the mechanism of association on four different surfaces and two different bulk solution scenarios. In the presence of a surface, the majority of monomers underwent a two-dimensional surface-mediated association that depended primarily on an Aβ42 electrostatic interaction with the self-assembled monolayer (SAM) surfaces. Moreover, aggregation could be inhibited greatly by surfaces with high affinity for Aβ42 and heterogeneous charge distribution. Our results can be used to identify new opportunities for disrupting or reversing the Aβ42 aggregation process.

Discovery of Chemicals to Either Clear or Indicate Amyloid Aggregates by Targeting Memory-Impairing Anti-Parallel Aβ Dimers.

Amyloid-β (Aβ) oligomers are implicated in Alzheimer disease (AD). However, their unstable nature and heterogeneous state disrupts elucidation of their explicit role in AD progression, impeding the development of tools targeting soluble Aβ oligomers. Herein parallel and anti-parallel variants of Aβ(1-40) dimers were designed and synthesized, and their pathogenic properties in AD models characterized. Anti-parallel dimers induced cognitive impairments with increased amyloidogenesis and cytotoxicity, and this dimer was then used in a screening platform. Through screening, two FDA-approved drugs, Oxytetracycline and Sunitinib, were identified to dissociate Aβ oligomers and plaques to monomers in 5XFAD transgenic mice. In addition, fluorescent Astrophloxine was shown to detect aggregated Aβ in brain tissue and cerebrospinal fluid samples of AD mice. This screening platform provides a stable and homogeneous environment for observing Aβ interactions with dimer-specific molecules.

Discovery of Chemicals to Either Clear or Indicate Amyloid Aggregates by Targeting Memory‐Impairing Anti‐Parallel Aβ Dimers

AbstractAmyloid‐β (Aβ) oligomers are implicated in Alzheimer disease (AD). However, their unstable nature and heterogeneous state disrupts elucidation of their explicit role in AD progression, impeding the development of tools targeting soluble Aβ oligomers. Herein parallel and anti‐parallel variants of Aβ(1–40) dimers were designed and synthesized, and their pathogenic properties in AD models characterized. Anti‐parallel dimers induced cognitive impairments with increased amyloidogenesis and cytotoxicity, and this dimer was then used in a screening platform. Through screening, two FDA‐approved drugs, Oxytetracycline and Sunitinib, were identified to dissociate Aβ oligomers and plaques to monomers in 5XFAD transgenic mice. In addition, fluorescent Astrophloxine was shown to detect aggregated Aβ in brain tissue and cerebrospinal fluid samples of AD mice. This screening platform provides a stable and homogeneous environment for observing Aβ interactions with dimer‐specific molecules.

An RNA aptamer with potent affinity for a toxic dimer of amyloid β42 has potential utility for histochemical studies of Alzheimer's disease

Oligomers of β-amyloid 42 (Aβ42), rather than fibrils, drive the pathogenesis of Alzheimer's disease (AD). In particular, toxic oligomeric species called protofibrils (PFs) have attracted significant attention. Herein, we report RNA aptamers with higher affinity toward PFs derived from a toxic Aβ42 dimer than toward fibrils produced from WT Aβ42 or from a toxic, conformationally constrained Aβ42 variant, E22P-Aβ42. We obtained these RNA aptamers by using the preincubated dimer model of E22P-Aβ42, which dimerized via a linker located at Val-40, as the target of in vitro selection. This dimer formed PFs during incubation. Several physicochemical characteristics of an identified aptamer, E22P-AbD43, suggested that preferential affinity of this aptamer toward PFs is due to its higher affinity for the toxic dimer unit (KD = 20 ± 6.0 nm) of Aβ42 than for less-toxic Aβ40 aggregates. Comparison of CD data from the full-length and random regions of E22P-AbD43 suggested that the preferential binding of E22P-AbD43 toward the dimer might be related to the formation of a G-quadruplex structure. E22P-AbD43 significantly inhibited the nucleation phase of the dimer and its associated neurotoxicity in SH-SY5Y human neuroblastoma cells. Of note, E22P-AbD43 also significantly protected against the neurotoxicity of WT Aβ42 and E22P-Aβ42. Furthermore, in an AD mouse model, E22P-AbD43 preferentially recognized diffuse aggregates, which likely originated from PFs or higher-order oligomers with curvilinear structures, compared with senile plaques formed from fibrils. We conclude that the E22P-AbD43 aptamer is a promising research and diagnostic tool for further studies of AD etiology.