Vaccination with soluble Abeta oligomers generates toxicity-neutralizing antibodies

Magnetic stirring with iron oxide nanospinners accretes neurotoxic Aβ42 oligomers into phagocytic clearable plaques for Alzheimer's disease treatment

An increasing number of medications have been explored to treat the progressive and irreversible Alzheimer's disease (AD) that stands as the predominant form of dementia among neurodegenerative ailments. However, assertions about toxic side effects of these drugs are a significant hurdle to overcome, calling for drug-free nanotherapeutics. Herein, a new therapeutic strategy devoid of conventional drugs or other cytotoxic species was developed. The constructed superparamagnetic iron oxide nanoparticles (SPIONs) nanospinners can accrete neurotoxic β-amyloid 42 oligomers (oAβ42) into aggregated magnetic plaques (mpAβ) by mechanical rotating force via remote interaction between nanoparticles and the applied magnetic field. While the cellular uptake of mpAβ attained from the magnetic stirring treatment by neuronal cells is severely limited, the facile phagocytic uptake of mpAβ by microglial cells leads to the polarization of the brain macrophages to M2 phenotype and thus the increased anti-inflammatory responses to the treatment. The SPION stirring treatment protects the AD mice from memory deterioration and maintain cognitive ability as evidenced from both nesting and Barnes maze tests. The examination of the oAβ42 injected brain tissues with the stirring treatment showed significant amelioration of functional impairment of neurons, microglia, astrocytes and oligodendrocytes alongside no obvious tissue damage caused by stirring meanwhile complete degradation of SPION was observed at day 7 after the treatment. The in vitro and animal data of this work strongly corroborate that this new modality of undruggable stirring treatment with SPIONs provides a new feasible strategy for developing novel AD treatments.

Targeting soluble amyloid-beta oligomers with a novel nanobody

The classical amyloid cascade hypothesis postulates that the aggregation of amyloid plaques and the accumulation of intracellular hyperphosphorylated Tau tangles, together, lead to profound neuronal death. However, emerging research has demonstrated that soluble amyloid-β oligomers (SAβOs) accumulate early, prior to amyloid plaque formation. SAβOs induce memory impairment and disrupt cognitive function independent of amyloid-β plaques, and even in the absence of plaque formation. This work describes the development and characterization of a novel anti-SAβO (E3) nanobody generated from an alpaca immunized with SAβO. In-vitro assays and in-vivo studies using 5XFAD mice indicate that the fluorescein (FAM)-labeled E3 nanobody recognizes both SAβOs and amyloid-β plaques. The E3 nanobody traverses across the blood-brain barrier and binds to amyloid species in the brain of 5XFAD mice. Imaging of mouse brains reveals that SAβO and amyloid-β plaques are not only different in size, shape, and morphology, but also have a distinct spatial distribution in the brain. SAβOs are associated with neurons, while amyloid plaques reside in the extracellular matrix. The results of this study demonstrate that the SAβO nanobody can serve as a diagnostic agent with potential theragnostic applications in Alzheimer's disease.

Molecular basis of selective amyloid-β degrading enzymes in Alzheimer's disease

The accumulation of the small 42-residue long peptide amyloid-β (Aβ) has been proposed as a major trigger for the development of Alzheimer's disease (AD). Within the brain, the concentration of Aβ peptide is tightly controlled through production and clearance mechanisms. Substantial experimental evidence now shows that reduced levels of Aβ clearance are present in individuals living with AD. This accumulation of Aβ can lead to the formation of large aggregated amyloid plaques-one of two detectable hallmarks of the disease. Aβ-degrading enzymes (ADEs) are major players in the clearance of Aβ. Stimulating ADE activity or expression, in order to compensate for the decreased clearance in the AD phenotype, provides a promising therapeutic target. It has been reported in mice that upregulation of ADEs can reduce the levels of Aβ peptide and amyloid plaques-in some cases, this led to improved cognitive function. Among several known ADEs, neprilysin (NEP), endothelin-converting enzyme-1 (ECE-1), insulin degrading enzyme (IDE) and angiotensin-1 converting enzyme (ACE) from the zinc metalloprotease family have been identified as important. These ADEs have the capacity to digest soluble Aβ which, in turn, cannot form the toxic oligomeric species. While they are known for their amyloid degradation, they exhibit complexity through promiscuous nature and a broad range of substrates that they can degrade. This review highlights current structural and functional understanding of these key ADEs, giving some insight into the molecular interactions that leads to the hydrolysis of peptide substrates, the crucial tasks performed by them and the potential for therapeutic use in the future.

EPR Studies of Aβ42 Oligomers Indicate a Parallel In-Register β-Sheet Structure

Aβ aggregation leads to the formation of both insoluble amyloid fibrils and soluble oligomers. Understanding the structures of Aβ oligomers is important for delineating the mechanism of Aβ aggregation and developing effective therapeutics. Here, we use site-directed spin labeling and electron paramagnetic resonance (EPR) spectroscopy to study Aβ42 oligomers prepared by using the protocol of Aβ-derived diffusible ligands. We obtained the EPR spectra of 37 Aβ42 oligomer samples, each spin-labeled at a unique residue position of the Aβ42 sequence. Analysis of the disordered EPR components shows that the N-terminal region has a lower local structural stability. Spin label mobility analysis reveals three structured segments at residues 9-11, 15-22, and 30-40. Intermolecular spin-spin interactions indicate a parallel in-register β-sheet structure, with residues 34-38 forming the structural core. Residues 16-21 also adopt the parallel in-register β-structure, albeit with weaker intermolecular packing. Our results suggest that there is a structural class of Aβ oligomers that adopt fibril-like conformations.

The 3-(3-oxoisoindolin-1-yl)pentane-2,4-dione (ISOAC1) as a new molecule able to inhibit Amyloid β aggregation and neurotoxicity

Amyloid β 1-42 (Aβ1-42) protein aggregation is considered one of the main triggers of Alzheimer's disease (AD). In this study, we examined the in vitro anti-amyloidogenic activity of the isoindolinone derivative 3-(3-oxoisoindolin-1-yl)pentane-2,4-dione (ISOAC1) and its neuroprotective potential against the Aβ1-42 toxicity. By performing the Thioflavin T fluorescence assay, Western blotting analyses, and Circular Dichroism experiments, we found that ISOAC1 was able to reduce the Aβ1-42 aggregation and conformational transition towards β-sheet structures. Interestingly, in silico studies revealed that ISOAC1 was able to bind to both the monomer and a pentameric protofibril of Aβ1-42, establishing a hydrophobic interaction with the PHE19 residue of the Aβ1-42 KLVFF motif. In vitro analyses on primary cortical neurons showed that ISOAC1 counteracted the increase of intracellular Ca2+ levels and decreased the Aβ1-42-induced toxicity, in terms of mitochondrial activity reduction and increase of reactive oxygen species production. In addition, confocal microscopy analyses showed that ISOAC1 was able to reduce the Aβ1-42 intraneuronal accumulation. Collectively, our results clearly show that ISOAC1 exerts a neuroprotective effect by reducing the Aβ1-42 aggregation and toxicity, hence emerging as a promising compound for the development of new Aβ-targeting therapeutic strategies for AD treatment.

Beta Amyloid Oligomers with Higher Cytotoxicity have Higher Sidechain Dynamics

The underlying biophysical principle governing the cytotoxicity of the oligomeric aggregates of β-amyloid (Aβ) peptides has long been an enigma. Here we show that the size of Aβ40 oligomers can be actively controlled by incubating the peptides in reverse micelles. Our approach allowed for the first time a detailed comparison of the structures and dynamics of two Aβ40 oligomers of different sizes, viz., 10 and 23 nm, by solid-state NMR. From the chemical shift data, we infer that the conformation and/or the chemical environments of the residues from K16 to K28 are different between the 10-nm and 23-nm oligomers. We find that the 10-nm oligomers are more cytotoxic, and the molecular motion of the sidechain of its charged residue K16 is more dynamic. Interestingly, the residue A21 exhibits unusually high structural rigidity. Our data raise an interesting possibility that the cytotoxicity of Aβ40 oligomers could also be correlated to the motional dynamics of the sidechains.

Neuroprotective Effect of NO-Delivery Dinitrosyl Iron Complexes (DNICs) on Amyloid Pathology in the Alzheimer's Disease Cell Model

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive impairment, memory loss, and behavioral deficits. β-amyloid1-42 (Aβ1-42) aggregation is a significant cause of the pathogenesis in AD. Despite the numerous types of research, the current treatment efficacy remains insufficient. Hence, a novel therapeutic strategy is required. Nitric oxide (NO) is a multifunctional gaseous molecule. NO displays a neuroprotective role in the central nervous system by inhibiting the Aβ aggregation and rescuing memory and learning deficit through the NO signaling pathway. Targeting the NO pathway might be a therapeutic option; however, NO has a limited half-life under the biological system. To address this issue, a biomimetic dinitrosyl iron complex [(NO)2Fe(μ-SCH2CH2COOH)2Fe(NO)2] (DNIC-COOH) that could stably deliver NO was explored in the current study. To determine whether DNIC-COOH exerts anti-AD efficacy, DNIC-COOH was added to neuron-like cells and primary cortical neurons along with Aβ1-42. This study found that DNIC-COOH protected neuronal cells from Aβ-induced cytotoxicity, potentiated neuronal functions, and facilitated Aβ1-42 degradation through the NO-sGC-cGMP-AKT-GSK3β-CREB/MMP-9 pathway.

Quantitative Attribution of the Protective Effects of Aminosterols against Protein Aggregates to Their Chemical Structures and Ability to Modulate Biological Membranes

Natural aminosterols are promising drug candidates against neurodegenerative diseases, like Alzheimer and Parkinson, and one relevant protective mechanism occurs via their binding to biological membranes and displacement or binding inhibition of amyloidogenic proteins and their cytotoxic oligomers. We compared three chemically different aminosterols, finding that they exhibited different (i) binding affinities, (ii) charge neutralizations, (iii) mechanical reinforcements, and (iv) key lipid redistributions within membranes of reconstituted liposomes. They also had different potencies (EC₅₀) in protecting cultured cell membranes against amyloid-β oligomers. A global fitting analysis led to an analytical equation describing quantitatively the protective effects of aminosterols as a function of their concentration and relevant membrane effects. The analysis correlates aminosterol-mediated protection with well-defined chemical moieties, including the polyamine group inducing a partial membrane-neutralizing effect (79 ± 7%) and the cholestane-like tail causing lipid redistribution and bilayer mechanical resistance (21 ± 7%), linking quantitatively their chemistry to their protective effects on biological membranes.

Flow cytometric isolation of drug-like conformational antibodies specific for amyloid fibrils

Antibodies that recognize specific protein conformational states are broadly important for research, diagnostic and therapeutic applications, yet they are difficult to generate in a predictable and systematic manner using either immunization or in vitro antibody display methods. This problem is particularly severe for conformational antibodies that recognize insoluble antigens such as amyloid fibrils associated with many neurodegenerative disorders. Here we report a quantitative fluorescence-activated cell sorting (FACS) method for directly selecting high-quality conformational antibodies against different types of insoluble (amyloid fibril) antigens using a single, off-the-shelf human library. Our approach uses quantum dots functionalized with antibodies to capture insoluble antigens, and the resulting quantum dot conjugates are used in a similar manner as conventional soluble antigens for multi-parameter FACS selections. Notably, we find that this approach is robust for isolating high-quality conformational antibodies against tau and α-synuclein fibrils from the same human library with combinations of high affinity, high conformational specificity and, in some cases, low off-target binding that rival or exceed those of clinical-stage antibodies specific for tau (zagotenemab) and α-synuclein (cinpanemab). This approach is expected to enable conformational antibody selection and engineering against diverse types of protein aggregates and other insoluble antigens (e.g., membrane proteins) that are compatible with presentation on the surface of antibody-functionalized quantum dots.

A new class of monoclonal Aβ antibodies selectively targets and triggers deposition of Aβ protofibrils

Aggregation and accumulation of amyloid-β peptide (Aβ) are a critical trigger for the onset of Alzheimer's disease (AD). While the plaques are the most outstanding Aβ pathological feature, much of the recent research emphasis has been on soluble Aβ species because of their diffusible, proinflammatory, and toxic properties. The focus on soluble aggregated Aβ species has also increased the interest in antibodies that are selective for different Aβ conformations. In the current study, we developed and characterized a new class of monoclonal antibodies (referred to as mAbSL) that are selective for Aβ protofibrils. Cloning and sequencing of the heavy and light chain variable regions for multiple antibodies identified sequence characteristics that may impart the conformational selectivity by the antibodies. Transfection of FreeStyle 293F cells with the plasmids permitted in-house expression and purification of mAbSL antibodies along with non-conformation-selective Aβ monoclonal antibodies (Aβ mAbs). Several of the purified mAbSL antibodies demonstrated significant affinity and selectivity for Aβ42 protofibrils compared with Aβ42 monomers and Aβ42 fibrils. Competition ELISA assays assessing the best overall antibody, mAbSL 113, yielded affinity constants of 7 nM for the antibody-Aβ42 protofibril interaction, while the affinity for either Aβ42 monomers or Aβ42 fibrils was roughly 80 times higher. mAbSL 113 significantly inhibited Aβ42 monomer aggregation by a unique mechanism compared with the inhibition displayed by Aβ mAb 513. Aβ42 protofibril dynamics were also markedly altered in the presence of mAbSL 113, whereby insoluble complex formation and protofibril deposition were stimulated by the antibody at low substoichiometric molar ratios. As the field contemplates the therapeutic effectiveness of Aβ conformation-selective antibodies, the findings presented here demonstrate new information on a monoclonal antibody that selectively targets Aβ protofibrils and impacts Aβ dynamics.

The Amyloid-Beta Clearance: From Molecular Targets to Glial and Neural Cells

The deposition of amyloid-beta (Aβ) plaques in the brain is one of the primary pathological characteristics of Alzheimer's disease (AD). It can take place 20-30 years before the onset of clinical symptoms. The imbalance between the production and the clearance of Aβ is one of the major causes of AD. Enhancing Aβ clearance at an early stage is an attractive preventive and therapeutic strategy of AD. Direct inhibition of Aβ production and aggregation using small molecules, peptides, and monoclonal antibody drugs has not yielded satisfactory efficacy in clinical trials for decades. Novel approaches are required to understand and combat Aβ deposition. Neurological dysfunction is a complex process that integrates the functions of different types of cells in the brain. The role of non-neurons in AD has not been fully elucidated. An in-depth understanding of the interactions between neurons and non-neurons can contribute to the elucidation of Aβ formation and the identification of effective drug targets. AD patient-derived pluripotent stem cells (PSCs) contain complete disease background information and have the potential to differentiate into various types of neurons and non-neurons in vitro, which may bring new insight into the treatment of AD. Here, we systematically review the latest studies on Aβ clearance and clarify the roles of cell interactions among microglia, astroglia and neurons in response to Aβ plaques, which will be beneficial to explore methods for reconstructing AD disease models using inducible PSCs (iPSCs) through cell differentiation techniques and validating the applications of models in understanding the formation of Aβ plaques. This review may provide the most promising directions of finding the clues for preventing and delaying the development of AD.

Combinations of Vitamin A and Vitamin E Metabolites Confer Resilience against Amyloid-β Aggregation

Alzheimer's disease is characterized by the presence in the brain of amyloid plaques formed by the aberrant deposition of the amyloid-β peptide (Aβ). Since many vitamins are dysregulated in this disease, we explored whether these molecules contribute to the protein homeostasis system by modulating Aβ aggregation. By screening 18 fat-soluble and water-soluble vitamin metabolites, we found that retinoic acid and α-tocopherol, two metabolites of vitamin A and vitamin E, respectively, affect Aβ aggregation both in vitro and in a Caenorhabditis elegans model of Aβ toxicity. We then show that the effects of these two vitamin metabolites in specific combinations cancel each other out, consistent with the "resilience in complexity" hypothesis, according to which the complex composition of the cellular environment could have an overall protective role against protein aggregation through the simultaneous presence of aggregation promoters and inhibitors. Taken together, these results indicate that vitamins can be added to the list of components of the protein homeostasis system that regulate protein aggregation.

Identification of amyloid antibodies for Alzheimer disease - immunotherapy

The current study identified the specific antibodies that recognise amyloid protein for Alzheimer disease - immunotherapy. The immune-selection of random sequences from a phage display library and sequencing to obtain the random 12 amino acids peptide library for each antibody, and then we analysed these peptides for unique and common sequences, relation to Aβ42 sequence and shape and pattern of the amino acid reaction to the antibody to predict the epitopes. Data obtained for 4G8 showed that, the sequence segment related to the putative epitope of 4G8 was LVFFAED. Nine of the ten top sequences contain the sequence RHD corresponding to the Aβ sequence from residues 5-7. Peptide 7 has the sequence IRYDTGSYHIH, which has a RYD. It was concluded that, 4G8 and 6E10 can tolerate the binding the sequences that explain it is able to recognise amyloid aggregates.

Misfolded protein oligomers induce an increase of intracellular Ca2+ causing an escalation of reactive oxidative species

Alzheimer's disease is characterized by the accumulation in the brain of the amyloid β (Aβ) peptide in the form of senile plaques. According to the amyloid hypothesis, the aggregation process of Aβ also generates smaller soluble misfolded oligomers that contribute to disease progression. One of the mechanisms of Aβ oligomer cytotoxicity is the aberrant interaction of these species with the phospholipid bilayer of cell membranes, with a consequent increase in cytosolic Ca²⁺ levels, flowing from the extracellular space, and production of reactive oxygen species (ROS). Here we investigated the relationship between the increase in Ca²⁺ and ROS levels immediately after the exposure to misfolded protein oligomers, asking whether they are simultaneous or instead one precedes the other. Using Aβ₄₂-derived diffusible ligands (ADDLs) and type A HypF-N model oligomers (OAs), we followed the kinetics of ROS production and Ca²⁺ influx in human neuroblastoma SH-SY5Y cells and rat primary cortical neurons in a variety of conditions. In all cases we found a faster increase of intracellular Ca²⁺ than ROS levels, and a lag phase in the latter process. A Ca²⁺-deprived cell medium prevented the increase of intracellular Ca²⁺ ions and abolished ROS production. By contrast, treatment with antioxidant agents prevented ROS formation, did not prevent the initial Ca²⁺ flux, but allowed the cells to react to the initial calcium dyshomeostasis, restoring later the normal levels of the ions. These results reveal a mechanism in which the entry of Ca²⁺ causes the production of ROS in cells challenged by aberrant protein oligomers.

Monosialotetrahexosylganglioside Promotes Early Aβ42 Oligomer Formation and Maintenance

The aggregation of the amyloid beta (Aβ) peptide is associated with Alzheimer's disease (AD) pathogenesis. Cell membrane composition, especially monosialotetrahexosylganglioside (GM1), is known to promote the formation of Aβ fibrils, yet little is known about the roles of GM1 in the early steps of Aβ oligomer formation. Here, by using GM1-contained liposomes as a mimic of the neuronal cell membrane, we demonstrate that GM1 is a critical trigger of Aβ oligomerization and aggregation. We find that GM1 not only promotes the formation of Aβ fibrils but also facilitates the maintenance of Aβ42 oligomers on liposome membranes. We structurally characterize the Aβ42 oligomers formed on the membrane and find that GM1 captures Aβ by binding to its arginine-5 residue. To interrogate the mechanism of Aβ42 oligomer toxicity, we design a new liposome-based Ca²⁺-encapsulation assay and provide new evidence for the Aβ42 ion channel hypothesis. Finally, we determine the toxicity of Aβ42 oligomers formed on membranes. Overall, by uncovering the roles of GM1 in mediating early Aβ oligomer formation and maintenance, our work provides a novel direction for pharmaceutical research for AD.

Amyloid-β Oligomers: Multiple Moving Targets

Alzheimer’s Disease (AD) is a neurodegenerative disorder that is characterized clinically by progressive cognitive decline and pathologically by the β-sheet rich fibril plaque deposition of the amyloid-β (Aβ) peptide in the brain. While plaques are a hallmark of AD, plaque burden is not correlated with cognitive impairment. Instead, Aβ oligomers formed during the aggregation process represent the main agents of neurotoxicity, which occurs 10–20 years before patients begin to show symptoms. These oligomers are dynamic in nature and represented by a heterogeneous distribution of aggregates ranging from low- to high-molecular weight, some of which are toxic while others are not. A major difficulty in determining the pathological mechanism(s) of Aβ, developing reliable diagnostic markers for early-stage detection, as well as effective therapeutics for AD are the differentiation and characterization of oligomers formed throughout disease propagation based on their molecular features, effects on biological function, and relevance to disease propagation and pathology. Thus, it is critical to methodically identify the mechanisms of Aβ aggregation and toxicity, as well as describe the roles of different oligomers and aggregates in disease progression and molecular pathology. Here, we describe a variety of biophysical techniques used to isolate and characterize a range of Aβ oligomer populations, as well as discuss proposed mechanisms of toxicity and therapeutic interventions aimed at specific assemblies formed during the aggregation process. The approaches being used to map the misfolding and aggregation of Aβ are like what was done during the fundamental early studies, mapping protein folding pathways using combinations of biophysical techniques in concert with protein engineering. Such information is critical to the design and molecular engineering of future diagnostics and therapeutics for AD.

ACU193: An Immunotherapeutic Poised to Test the Amyloid β Oligomer Hypothesis of Alzheimer’s Disease

Alzheimer’s disease (AD) is an age-related neurodegenerative disease that affects 50 million people worldwide, with 10 million new cases occurring each year. The emotional and economic impacts of AD on patients and families are devastating. Approved treatments confer modest improvement in symptoms, and recently one treatment obtained accelerated approval from the United States Food and Drug Administration (FDA) and may have modest disease modifying benefit. Research over the past three decades has established a clear causal linkage between AD and elevated brain levels of amyloid β (Aβ) peptide, and substantial evidence now implicates soluble, non-fibrillar Aβ oligomers (AβOs) as the molecular assemblies directly responsible for AD-associated memory and cognitive failure and accompanying progressive neurodegeneration. The widely recognized linkage of elevated Aβ and AD spawned a comprehensive 20-year therapeutic campaign that focused primarily on two strategies – inhibition of the secretase enzymes responsible for Aβ production and clearance of Aβ peptide or amyloid plaques with Aβ-directed immunotherapeutics. Unfortunately, all clinical trials of secretase inhibitors were unsuccessful. Of the completed phase 3 immunotherapy programs, bapineuzumab (targeting amyloid plaque) and solanezumab (targeting Aβ monomers) were negative, and the crenezumab program (targeting Aβ monomers and to a small extent oligomers) was stopped for futility. Aducanumab (targeting amyloid plaques), which recently received FDA accelerated approval, had one positive and one negative phase 3 trial. More than 25 negative randomized clinical trials (RCTs) have evaluated Aβ-targeting therapeutics, yet none has directly evaluated whether selective blockage of disease-relevant AβOs can stop or reverse AD-associated cognitive decline. Here, we briefly summarize studies that establish the AD therapeutic rationale to target AβOs selectively, and we describe ACU193, the first AβO-selective immunotherapeutic to enter human clinical trials and the first positioned to test the AβO hypothesis of AD.

α-synuclein-assisted oligomerization of β-amyloid (1-42)

Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most common neurodegenerative disorders, characterized by aggregation of amyloid polypeptides, β-amyloid (Aβ) and α-synuclein (αS), respectively. Aβ and αS follow similar aggregation pathways, starting from monomers, to soluble toxic oligomeric assemblies, and to insoluble fibrils. Various studies have suggested overlaps in the pathologies of AD and PD, and have shown Aβ-αS interactions. Unfortunately, whether these protein-protein interactions lead to self- and co-assembly of Aβ and αS into oligomers - a potentially toxic synergistic mechanism - is poorly understood. Among the various Aβ isoforms, interactions of Aβ containing 42 amino acids (Aβ (1-42), referred to as Aβ42) with αS are of most direct relevance due to the high aggregation propensity and the strong toxic effect of this Aβ isoform. In this study, we carefully determined molecular consequences of interactions between Aβ42 and αS in their respective monomeric, oligomeric, and fibrillar forms using a comprehensive set of experimental tools. We show that the three αS conformers, namely, monomers, oligomers and fibrils interfered with fibrillization of Aβ42. Specifically, αS monomers and oligomers promoted oligomerization and stabilization of soluble Aβ42, possibly via direct binding or co-assembly, while αS fibrils hindered soluble Aβ42 species from converting into insoluble aggregates by the formation of large oligomers. We also provide evidence that the interactions with αS were mediated by various parts of Aβ42, depending on Aβ42 and αS conformers. Furthermore, we compared similarities and dissimilarities between Aβ42-αS and Aβ40-αS interactions. Overall, the present study provides a comprehensive depiction of the molecular interplay between Aβ42 and αS, providing insight into its synergistic toxic mechanism.

Syndapin-2 mediated transcytosis of amyloid-ß across the blood-brain barrier

A deficient transport of amyloid-β across the blood–brain barrier, and its diminished clearance from the brain, contribute to neurodegenerative and vascular pathologies, such as Alzheimer’s disease and cerebral amyloid angiopathy, respectively. At the blood–brain barrier, amyloid-β efflux transport is associated with the low-density lipoprotein receptor-related protein 1. However, the precise mechanisms governing amyloid-β transport across the blood–brain barrier, in health and disease, remain to be fully understood. Recent evidence indicates that the low-density lipoprotein receptor-related protein 1 transcytosis occurs through a tubulation-mediated mechanism stabilized by syndapin-2. Here, we show that syndapin-2 is associated with amyloid-β clearance via low-density lipoprotein receptor-related protein 1 across the blood–brain barrier. We further demonstrate that risk factors for Alzheimer’s disease, amyloid-β expression and ageing, are associated with a decline in the native expression of syndapin-2 within the brain endothelium. Our data reveals that syndapin-2-mediated pathway, and its balance with the endosomal sorting, are important for amyloid-β clearance proposing a measure to evaluate Alzheimer’s disease and ageing, as well as a target for counteracting amyloid-β build-up. Moreover, we provide evidence for the impact of the avidity of amyloid-β assemblies in their trafficking across the brain endothelium and in low-density lipoprotein receptor-related protein 1 expression levels, which may affect the overall clearance of amyloid-β across the blood–brain barrier.

Amyloid beta acts synergistically as a pro-inflammatory cytokine

The amyloid beta (Aβ) peptide is believed to play a central role in Alzheimer's disease (AD), the most common age-related neurodegenerative disorder. However, the natural, evolutionarily selected functions of Aβ are incompletely understood. Here, we report that nanomolar concentrations of Aβ act synergistically with known cytokines to promote pro-inflammatory activation in primary human astrocytes (a cell type increasingly implicated in brain aging and AD). Using transcriptomics (RNA-seq), we show that Aβ can directly substitute for the complement component C1q in a cytokine cocktail previously shown to induce astrocyte immune activation. Furthermore, we show that astrocytes synergistically activated by Aβ have a transcriptional signature similar to neurotoxic "A1" astrocytes known to accumulate with age and in AD. Interestingly, we find that this biological action of Aβ at low concentrations is distinct from the transcriptome changes induced by the high/supraphysiological doses of Aβ often used in in vitro studies. Collectively, our results suggest an important, cytokine-like function for Aβ and a novel mechanism by which it may directly contribute to the neuroinflammation associated with brain aging and AD.

An ultra-sensitive immunoassay detects and quantifies soluble Aβ oligomers in human plasma

INTRODUCTION

Evidence strongly suggests that soluble oligomers of amyloid beta protein (oAβ) help initiate the pathogenic cascade of Alzheimer's disease (AD). To date, there have been no validated assays specific for detecting and quantifying oAβ in human blood.

METHODS

We developed an ultrasensitive oAβ immunoassay using a novel capture antibody (71A1) with N-terminal antibody 3D6 for detection that specifically quantifies soluble oAβ in the human brain, cerebrospinal fluid (CSF), and plasma.

RESULTS

Two new antibodies (71A1; 1G5) are oAβ-selective, label Aβ plaques in non-fixed AD brain sections, and potently neutralize the synaptotoxicity of AD brain-derived oAβ. The 71A1/3D6 assay showed excellent dilution linearity in CSF and plasma without matrix effects, good spike recovery, and specific immunodepletion.

DISCUSSION

We have created a sensitive, high throughput, and inexpensive method to quantify synaptotoxic oAβ in human plasma for analyzing large cohorts of aged and AD subjects to assess the dynamics of this key pathogenic species and response to therapy.

Squalamine and Its Derivatives Modulate the Aggregation of Amyloid-β and α-Synuclein and Suppress the Toxicity of Their Oligomers

The aberrant aggregation of proteins is a key molecular event in the development and progression of a wide range of neurodegenerative disorders. We have shown previously that squalamine and trodusquemine, two natural products in the aminosterol class, can modulate the aggregation of the amyloid-β peptide (Aβ) and of α-synuclein (αS), which are associated with Alzheimer's and Parkinson's diseases. In this work, we expand our previous analyses to two squalamine derivatives, des-squalamine and α-squalamine, obtaining further insights into the mechanism by which aminosterols modulate Aβ and αS aggregation. We then characterize the ability of these small molecules to alter the physicochemical properties of stabilized oligomeric species in vitro and to suppress the toxicity of these aggregates to varying degrees toward human neuroblastoma cells. We found that, despite the fact that these aminosterols exert opposing effects on Aβ and αS aggregation under the conditions that we tested, the modifications that they induced to the toxicity of oligomers were similar. Our results indicate that the suppression of toxicity is mediated by the displacement of toxic oligomeric species from cellular membranes by the aminosterols. This study, thus, provides evidence that aminosterols could be rationally optimized in drug discovery programs to target oligomer toxicity in Alzheimer's and Parkinson's diseases.

Alzheimer's protection effect of A673T mutation may be driven by lower Aβ oligomer binding affinity

Several mutations conferring protection against Alzheimer's disease (AD) have been described, none as profound as the A673T mutation, where carriers are four times less likely to get AD compared to noncarriers. This mutation results in reduced amyloid beta (Aβ) protein production in vitro and lower lifetime Aβ concentration in carriers. Better understanding of the protective mechanisms of the mutation may provide important insights into AD pathophysiology and identify productive therapeutic intervention strategies for disease modification. Aβ(1-42) protein forms oligomers that bind saturably to a single receptor site on neuronal synapses, initiating the downstream toxicities observed in AD. Decreased formation, toxicity, or stability of soluble Aβ oligomers, or reduction of synaptic binding of these oligomers, may combine with overall lower Aβ concentration to underlie A673T's disease protecting mechanism. To investigate these possibilities, we compared the formation rate of soluble oligomers made from Icelandic A673T mutant and wild type (wt) Aβ(1-42) synthetic protein, the amount and intensity of oligomer bound to mature primary rat hippocampal/cortical neuronal synapses, and the potency of bound oligomers to impact trafficking rate in neurons in vitro using a physiologically relevant oligomer preparation method. At equal protein concentrations, mutant protein forms approximately 50% or fewer oligomers of high molecular weight (>50 kDa) compared to wt protein. Mutant oligomers are twice as potent at altering the cellular vesicle trafficking rate as wt at equivalent concentrations, however, mutant oligomers have a >4-fold lower binding affinity to synaptic receptors (Kd  = 1,950 vs. 442 nM). The net effect of these differences is a lower overall toxicity at a given concentration. This study demonstrates for the first time that mutant A673T Aβ oligomers prepared with this method have fundamentally different assembly characteristics and biological impact from wt protein and indicates that its disease protecting mechanism may result primarily from the mutant protein's much lower binding affinity to synaptic receptors. This suggests that therapeutics that effectively reduce oligomer binding to synapses in the brain may be beneficial in AD.

Nucleoside reverse transcriptase inhibitors and Kamuvudines inhibit amyloid-β induced retinal pigmented epithelium degeneration

Nonfibrillar amyloid-β oligomers (AβOs) are a major component of drusen, the sub-retinal pigmented epithelium (RPE) extracellular deposits characteristic of age-related macular degeneration (AMD), a common cause of global blindness. We report that AβOs induce RPE degeneration, a clinical hallmark of geographic atrophy (GA), a vision-threatening late stage of AMD that is currently untreatable. We demonstrate that AβOs induce activation of the NLRP3 inflammasome in the mouse RPE in vivo and that RPE expression of the purinergic ATP receptor P2RX7, an upstream mediator of NLRP3 inflammasome activation, is required for AβO-induced RPE degeneration. Two classes of small molecule inflammasome inhibitors—nucleoside reverse transcriptase inhibitors (NRTIs) and their antiretrovirally inert modified analog Kamuvudines—both inhibit AβOs-induced RPE degeneration. These findings crystallize the importance of P2RX7 and NLRP3 in a disease-relevant model of AMD and identify inflammasome inhibitors as potential treatments for GA.

Rational affinity maturation of anti-amyloid antibodies with high conformational and sequence specificity

The aggregation of amyloidogenic polypeptides is strongly linked to several neurodegenerative disorders, including Alzheimer's and Parkinson's diseases. Conformational antibodies that selectively recognize protein aggregates are leading therapeutic agents for selectively neutralizing toxic aggregates, diagnostic and imaging agents for detecting disease, and biomedical reagents for elucidating disease mechanisms. Despite their importance, it is challenging to generate high-quality conformational antibodies in a systematic and site-specific manner due to the properties of protein aggregates (hydrophobic, multivalent, and heterogeneous) and limitations of immunization (uncontrolled antigen presentation and immunodominant epitopes). Toward addressing these challenges, we have developed a systematic directed evolution procedure for affinity maturing antibodies against Alzheimer's Aβ fibrils and selecting variants with strict conformational and sequence specificity. We first designed a library based on a lead conformational antibody by sampling combinations of amino acids in the antigen-binding site predicted to mediate high antibody specificity. Next, we displayed this library on the surface of yeast, sorted it against Aβ42 aggregates, and identified promising clones using deep sequencing. The resulting antibodies displayed similar or higher affinities than clinical-stage Aβ antibodies (aducanumab and crenezumab). Moreover, the affinity-matured antibodies retained high conformational specificity for Aβ aggregates, as observed for aducanumab and unlike crenezumab. Notably, the affinity-maturated antibodies displayed extremely low levels of nonspecific interactions, as observed for crenezumab and unlike aducanumab. We expect that our systematic methods for generating antibodies with unique combinations of desirable properties will improve the generation of high-quality conformational antibodies specific for diverse types of aggregated conformers.

Aβ Oligomers Dysregulate Calcium Homeostasis by Mechanosensitive Activation of AMPA and NMDA Receptors

Alzheimer's disease, which is the most common form of dementia, is characterized by the aggregation of the amyloid β peptide (Aβ) and by an impairment of calcium homeostasis caused by excessive activation of glutamatergic receptors (excitotoxicity). Here, we studied the effects on calcium homeostasis caused by the formation of Aβ oligomeric assemblies. We found that Aβ oligomers cause a rapid influx of calcium ions (Ca2+) across the cell membrane by rapidly activating extrasynaptic N-methyl-d-aspartate (NMDA) receptors and, to a lower extent, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. We also observed, however, that misfolded oligomers do not interact directly with these receptors. Further experiments with lysophosphatidylcholine and arachidonic acid, which cause membrane compression and stretch, respectively, indicated that these receptors are activated through a change in membrane tension induced by the oligomers and transmitted mechanically to the receptors via the lipid bilayer. Indeed, lysophosphatidylcholine is able to neutralize the oligomer-induced activation of the NMDA receptors, whereas arachidonic acid activates the receptors similarly to the oligomers with no additive effects. An increased rotational freedom observed for a fluorescent probe embedded within the membrane in the presence of the oligomers also indicates a membrane stretch. These results reveal a mechanism of toxicity of Aβ oligomers in Alzheimer's disease through the perturbation of the mechanical properties of lipid membranes sensed by NMDA and AMPA receptors.

Preclinical and clinical biomarker studies of CT1812: A novel approach to Alzheimer's disease modification

INTRODUCTION

Amyloid beta (Aβ) oligomers are one of the most toxic structural forms of the Aβ protein and are hypothesized to cause synaptotoxicity and memory failure as they build up in Alzheimer's disease (AD) patients' brain tissue. We previously demonstrated that antagonists of the sigma-2 receptor complex effectively block Aβ oligomer toxicity. CT1812 is an orally bioavailable, brain penetrant small molecule antagonist of the sigma-2 receptor complex that appears safe and well tolerated in healthy elderly volunteers. We tested CT1812's effect on Aβ oligomer pathobiology in preclinical AD models and evaluated CT1812's impact on cerebrospinal fluid (CSF) protein biomarkers in mild to moderate AD patients in a clinical trial (ClinicalTrials.gov NCT02907567).

METHODS

Experiments were performed to measure the impact of CT1812 versus vehicle on Aβ oligomer binding to synapses in vitro, to human AD patient post mortem brain tissue ex vivo, and in living APP_Swe /PS1dE9 transgenic mice in vivo. Additional experiments were performed to measure the impact of CT1812 versus vehicle on Aβ oligomer-induced deficits in membrane trafficking rate, synapse number, and protein expression in mature hippocampal/cortical neurons in vitro. The impact of CT1812 on cognitive function was measured in transgenic Thy1 huAPP^Swe/Lnd+ and wild-type littermates. A multicenter, double-blind, placebo-controlled parallel group trial was performed to evaluate the safety, tolerability, and impact on protein biomarker expression of CT1812 or placebo given once daily for 28 days to AD patients (Mini-Mental State Examination 18-26). CSF protein expression was measured by liquid chromatography with tandem mass spectrometry or enzyme-linked immunosorbent assay in samples drawn prior to dosing (Day 0) and at end of dosing (Day 28) and compared within each patient and between pooled treated versus placebo-treated dosing groups.

RESULTS

CT1812 significantly and dose-dependently displaced Aβ oligomers bound to synaptic receptors in three independent preclinical models of AD, facilitated oligomer clearance into the CSF, increased synaptic number and protein expression in neurons, and improved cognitive performance in transgenic mice. CT1812 significantly increased CSF concentrations of Aβ oligomers in AD patient CSF, reduced concentrations of synaptic proteins and phosphorylated tau fragments, and reversed expression of many AD-related proteins dysregulated in CSF.

DISCUSSION

These preclinical studies demonstrate the novel disease-modifying mechanism of action of CT1812 against AD and Aβ oligomers. The clinical results are consistent with preclinical data and provide evidence of target engagement and impact on fundamental disease-related signaling pathways in AD patients, supporting further development of CT1812.

Emerging Promise of Immunotherapy for Alzheimer's Disease: A New Hope for the Development of Alzheimer's Vaccine

BACKGROUND

Alzheimer's disease (AD) is a chronic neurodegenerative disorder and the characteristics of this devastating disorder include the progressive and disabling deficits in the cognitive functions including reasoning, attention, judgment, comprehension, memory, and language.

OBJECTIVE

In this article, we have focused on the recent progress that has been achieved in the development of an effective AD vaccine.

SUMMARY

Currently, available treatment options of AD are limited to deliver short-term symptomatic relief only. A number of strategies targeting amyloid-beta (Aβ) have been developed in order to treat or prevent AD. In order to exert an effective immune response, an AD vaccine should contain adjuvants that can induce an effective anti-inflammatory T helper 2 (Th2) immune response. AD vaccines should also possess the immunogens which have the capacity to stimulate a protective immune response against various cytotoxic Aβ conformers. The induction of an effective vaccine's immune response would necessitate the parallel delivery of immunogen to dendritic cells (DCs) and their priming to stimulate a Th2-polarized response. The aforesaid immune response is likely to mediate the generation of neutralizing antibodies against the neurotoxic Aβ oligomers (AβOs) and also anti-inflammatory cytokines, thus preventing the AD-related inflammation.

CONCLUSION

Since there is an age-related decline in the immune functions, therefore vaccines are more likely to prevent AD instead of providing treatment. AD vaccines might be an effective and convenient approach to avoid the treatment-related huge expense.

Adsorption of Amyloid Beta Peptide by Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are capable of adsorbing a wide range of molecules. In addition to the more commonly investigated small molecules, researchers have demonstrated that MOFs adsorb much larger molecules, such as proteins and peptides. We have investigated whether MOFs are capable of adsorbing amyloid beta peptide. Amyloid beta plays a pivotal role in the progression of Alzheimer's disease because individual copies of the peptides can aggregate, forming neurotoxic oligomers and the amyloid plaques found in brains of Alzheimer's patients. After synthesizing a number of commonly studied MOFs, their adsorption capabilities were tested. We found that the MOFs tested readily adsorbed small amounts of amyloid beta (as determined by gel electrophoresis). It was determined that in most cases, adsorption occurs rapidly, with complete adsorption within minutes of incubation. Overall adsorption capacity was found to vary between different MOFs as well. Once adsorbed, amyloid beta peptide can subsequently be eluted from some MOFs by treatment with acetonitrile/water solutions, though retention strength varied between different MOFs. In some cases, MOFs that showed complete adsorption also saw high levels of peptide elution, but others showed little to no elution of the peptide. Together these data can help us begin to understand the interactions between amyloid beta and MOFs.

Targeting Pathological Amyloid Aggregates with Conformation-Sensitive Antibodies

BACKGROUND

The pathogenesis of Alzheimer's disease (AD) is not directly caused by the presence of senile plaques but rather by the detrimental effects exerted on neuronal cells by toxic soluble oligomers. Such species are formed early during the aggregation process of the Aβ1-42 peptide or can be released from mature fibrils. Nowadays, efficient tools for an early diagnosis, as well as pharmaceutical treatments targeting the harmful agents in samples of AD patients, are still missing.

OBJECTIVE

By integrating in vitro immunochemical assay with in vivo neuronal models of toxicity, we aim to understand and target the principles that drive toxicity in AD.

METHODS

We evaluated the specificity and sensitivity of A11 and OC conformational antibodies to target a range of pathologically relevant amyloid conformers and rescue their cytotoxic effects in neuronal culture models using a number of cellular readouts.

RESULTS

We demonstrated the peculiar ability of conformational antibodies to label pathologically relevant Aβ1-42 oligomers and fibrils and to prevent their detrimental effects on neuronal cells.

CONCLUSION

Our results substantially improve our knowledge on the role of toxic assemblies in neurodegenerative diseases, thus suggesting new and more effective diagnostic and therapeutic tools for AD.

Therapeutic Strategies to Reduce the Toxicity of Misfolded Protein Oligomers

The aberrant aggregation of proteins is implicated in the onset and pathogenesis of a wide range of neurodegenerative disorders, including Alzheimer’s and Parkinson’s diseases. Mounting evidence indicates that misfolded protein oligomers produced as intermediates in the aggregation process are potent neurotoxic agents in these diseases. Because of the transient and heterogeneous nature of these elusive aggregates, however, it has proven challenging to develop therapeutics that can effectively target them. Here, we review approaches aimed at reducing oligomer toxicity, including (1) modulating the oligomer populations (e.g., by altering the kinetics of aggregation by inhibiting, enhancing, or redirecting the process), (2) modulating the oligomer properties (e.g., through the size–hydrophobicity–toxicity relationship), (3) modulating the oligomer interactions (e.g., by protecting cell membranes by displacing oligomers), and (4) reducing oligomer toxicity by potentiating the protein homeostasis system. We analyze examples of these complementary approaches, which may lead to the development of compounds capable of preventing or treating neurodegenerative disorders associated with protein aggregation.

Soluble Prion Peptide 107-120 Protects Neuroblastoma SH-SY5Y Cells against Oligomers Associated with Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent form of dementia and soluble amyloid β (Aβ) oligomers are thought to play a critical role in AD pathogenesis. Cellular prion protein (PrPC) is a high-affinity receptor for Aβ oligomers and mediates some of their toxic effects. The N-terminal region of PrPC can interact with Aβ, particularly the region encompassing residues 95-110. In this study, we identified a soluble and unstructured prion-derived peptide (PrP107-120) that is external to this region of the sequence and was found to successfully reduce the mitochondrial impairment, intracellular ROS generation and cytosolic Ca2+ uptake induced by oligomeric Aβ42 ADDLs in neuroblastoma SH-SY5Y cells. PrP107-120 was also found to rescue SH-SY5Y cells from Aβ42 ADDL internalization. The peptide did not change the structure and aggregation pathway of Aβ42 ADDLs, did not show co-localization with Aβ42 ADDLs in the cells and showed a partial colocalization with the endogenous cellular PrPC. As a sequence region that is not involved in Aβ binding but in PrP self-recognition, the peptide was suggested to protect against the toxicity of Aβ42 oligomers by interfering with cellular PrPC and/or activating a signaling that protected the cells. These results strongly suggest that PrP107-120 has therapeutic potential for AD.

Behavioral and neural network abnormalities in human APP transgenic mice resemble those of App knock-in mice and are modulated by familial Alzheimer's disease mutations but not by inhibition of BACE1

BACKGROUND

Alzheimer's disease (AD) is the most frequent and costly neurodegenerative disorder. Although diverse lines of evidence suggest that the amyloid precursor protein (APP) is involved in its causation, the precise mechanisms remain unknown and no treatments are available to prevent or halt the disease. A favorite hypothesis has been that APP contributes to AD pathogenesis through the cerebral accumulation of the amyloid-β peptide (Aβ), which is derived from APP through sequential proteolytic cleavage by BACE1 and γ-secretase. However, inhibitors of these enzymes have failed in clinical trials despite clear evidence for target engagement.

METHODS

To further elucidate the roles of APP and its metabolites in AD pathogenesis, we analyzed transgenic mice overexpressing wildtype human APP (hAPP) or hAPP carrying mutations that cause autosomal dominant familial AD (FAD), as well as App knock-in mice that do not overexpress hAPP but have two mouse App alleles with FAD mutations and a humanized Aβ sequence.

RESULTS

Although these lines of mice had marked differences in cortical and hippocampal levels of APP, APP C-terminal fragments, soluble Aβ, Aβ oligomers and age-dependent amyloid deposition, they all developed cognitive deficits as well as non-convulsive epileptiform activity, a type of network dysfunction that also occurs in a substantive proportion of humans with AD. Pharmacological inhibition of BACE1 effectively reduced levels of amyloidogenic APP C-terminal fragments (C99), soluble Aβ, Aβ oligomers, and amyloid deposits in transgenic mice expressing FAD-mutant hAPP, but did not improve their network dysfunction and behavioral abnormalities, even when initiated at early stages before amyloid deposits were detectable.

CONCLUSIONS

hAPP transgenic and App knock-in mice develop similar pathophysiological alterations. APP and its metabolites contribute to AD-related functional alterations through complex combinatorial mechanisms that may be difficult to block with BACE inhibitors and, possibly, also with other anti-Aβ treatments.

Preparation and in vitro activity of single chain antibodies against Alzheimer's disease

Disease-modifying passive immunotherapies focused on reducing amyloid-beta (Aβ) deposition are a potential therapeutic strategy for Alzheimer's disease (AD). However, the results of Aβ passive immunotherapy clinical trials were unsatisfactory, largely due to the low efficacy of whole antibodies due to their relatively large molecular weight and low blood-brain barrier transmittance. Furthermore, the constant region fragments of whole antibodies can trigger inflammatory reactions, which raises safety concerns. Single chain fragment variables (scFvs), containing only the variable region of the heavy and light chains of antibodies, show great potential for the treatment of AD. With the aim of generating a safe and effective AD passive immunotherapy, we designed and successfully prepared scFvs targeting Aβ and investigated their activity in vitro. The results showed that both the 10D5-scFv and 12B4-scFv have high affinities for Aβ monomers, oligomers, and fibers. Moreover, scFvs could prevent the formation of Aβ oligomers and fibers, and block their cellular toxicity. In addition, 10D5-scFv and 12B4-scFv could bind to Aβ plaques on the sections of mice brains in the in vitro study, indicating potential for the treatment of AD.

Capturing Amyloid-β Oligomers by Stirring with Microscaled Iron Oxide Stir Bars into Magnetic Plaques to Reduce Cytotoxicity toward Neuronal Cells

Soluble amyloid-β oligomers (oAβ₄₂)-induced neuronal death and inflammation response has been recognized as one of the major causes of Alzheimer’s disease (AD). In this work, a novel strategy adopting silica-coated iron oxide stir bar (MSB)-based AD therapy system via magnetic stirring-induced capture of oAβ₄₂ into magnetic plaques (mpAβ₄₂) and activation of microglia on cellular plaque clearance was developed. With oAβ₄₂ being effectively converted into mpAβ₄₂, the neurotoxicity toward neuronal cells was thus greatly reduced. In addition to the good preservation of neurite outgrowth through the diminished uptake of oAβ₄₂, neurons treated with oAβ₄₂ under magnetic stirring also exhibited comparable neuron-specific protein expression to those in the absence of oAβ₄₂. The phagocytic uptake of mpAβ₄₂ by microglia was enhanced significantly as compared to the counterpart of oAβ₄₂, and the M1 polarization of microglia often occurring after the uptake of oAβ₄₂ restricted to an appreciable extent. As a result, the inflammation induced by pro-inflammatory cytokines was greatly alleviated.

Amyloid-β oligomers in cellular models of Alzheimer's disease

Amyloid-β (Aβ) dysmetabolism is tightly associated with pathological processes in Alzheimer's disease (AD). Currently, it is thought that, in addition to Aβ fibrils that give rise to plaque formation, Aβ aggregates into non-fibrillar soluble oligomers (AβOs). Soluble AβOs have been extensively studied for their synaptotoxic and neurotoxic properties. In this review, we discuss physicochemical properties of AβOs and their impact on different brain cell types in AD. Additionally, we summarize three decades of studies with AβOs, providing a compelling bulk of evidence regarding cell-specific mechanisms of toxicity. Cellular models may lead us to a deeper understanding of the detrimental effects of AβOs in neurons and glial cells, putatively shedding light on the development of innovative therapies for AD.

Transthyretin Inhibits Primary and Secondary Nucleations of Amyloid-β Peptide Aggregation and Reduces the Toxicity of Its Oligomers

Alzheimer’s disease is associated with the deposition of the amyloid-β peptide (Aβ) into extracellular senile plaques in the brain. In vitro and in vivo observations have indicated that transthyretin (TTR) acts as an Aβ scavenger in the brain, but the mechanism has not been fully resolved. We have monitored the aggregation process of Aβ₄₀ by thioflavin T fluorescence, in the presence or absence of different concentrations of preformed seed aggregates of Aβ₄₀, of wild-type tetrameric TTR (WT-TTR), and of a variant engineered to be stable as a monomer (M-TTR). Both WT-TTR and M-TTR were found to inhibit specific steps of the process of Aβ₄₀ fibril formation, which are primary and secondary nucleations, without affecting the elongation of the resulting fibrils. Moreover, the analysis shows that both WT-TTR and M-TTR bind to Aβ₄₀ oligomers formed in the aggregation reaction and inhibit their conversion into the shortest fibrils able to elongate. Using biophysical methods, TTR was found to change some aspects of its overall structure following such interactions with Aβ₄₀ oligomers, as well as with oligomers of Aβ₄₂, while maintaining its overall topology. Hence, it is likely that the predominant mechanism by which TTR exerts its protective role lies in the binding of TTR to the Aβ oligomers and in inhibiting primary and secondary nucleation processes, which limits both the toxicity of Aβ oligomers and the ability of the fibrils to proliferate.

Chemical sensing platforms for detecting trace-level Alzheimer's core biomarkers

This review provides an overview of recent advances in optical and electrical detection of Alzheimer's disease biomarkers in clinically relevant fluids.

Reelin reverts biochemical, physiological and cognitive alterations in mouse models of Tauopathy

Reelin is an extracellular protein crucial for adult brain plasticity. Moreover, Reelin is protective against amyloid-β (Aβ) pathology in Alzheimer's Disease (AD), reducing plaque deposition, synaptic loss and cognitive decline. Given that Tau protein plays a key role in AD pathogenesis, and that the Reelin pathway modulates Tau phosphorylation, here we explored the involvement of Reelin in AD-related Tau pathology. We found that Reelin overexpression modulates the levels of Tau phosphorylation in AD-related epitopes in VLW mice expressing human mutant Tau. in vitro, Reelin reduced the Aβ-induced missorting of axonal Tau and neurofilament proteins to dendrites. Reelin also reverted in vivo the toxic somatodendritic localization of phosphorylated Tau. Finally, overexpression of Reelin in VLW mice improved long-term potentiation and long-term memory cognitive performance thus masking the cognitive and physiological deficits in VLW mice. These data suggest that the Reelin pathway, which is also protective against Aβ pathology, modulates fundamental traits of Tau pathology, strengthening the potential of Reelin as a therapeutic target in AD.

Intra- and extracellular β-amyloid overexpression via adeno-associated virus-mediated gene transfer impairs memory and synaptic plasticity in the hippocampus

Alzheimer's disease (AD), the most common age-related neurodegenerative disorder, is currently conceptualized as a disease of synaptic failure. Synaptic impairments are robust within the AD brain and better correlate with dementia severity when compared with other pathological features of the disease. Nevertheless, the series of events that promote synaptic failure still remain under debate, as potential triggers such as β-amyloid (Aβ) can vary in size, configuration and cellular location, challenging data interpretation in causation studies. Here we present data obtained using adeno-associated viral (AAV) constructs that drive the expression of oligomeric Aβ either intra or extracellularly. We observed that expression of Aβ in both cellular compartments affect learning and memory, reduce the number of synapses and the expression of synaptic-related proteins, and disrupt chemical long-term potentiation (cLTP). Together, these findings indicate that during the progression AD the early accumulation of Aβ inside neurons is sufficient to promote morphological and functional cellular toxicity, a phenomenon that can be exacerbated by the buildup of Aβ in the brain parenchyma. Moreover, our AAV constructs represent a valuable tool in the investigation of the pathological properties of Aβ oligomers both in vivo and in vitro.

Amyloid Beta Oligomers Target to Extracellular and Intracellular Neuronal Synaptic Proteins in Alzheimer's Disease

Introduction: β-Amyloid protein (Aβ) putatively plays a seminal role in synaptic loss in Alzheimer's disease (AD). While there is no consensus regarding the synaptic-relevant species of Aβ, it is known that Aβ oligomers (AβOs) are noticeably increased in the early stages of AD, localizing at or within the synapse. In cell and animal models, AβOs have been shown to attach to synapses and instigate synapse dysfunction and deterioration. To establish the pathological mechanism of synaptic loss in AD, it will be important to identify the synaptic targets to which AβOs attach. Methods: An unbiased approach using far western ligand blots has identified three synaptic proteins to which AβOs specifically attach. These proteins (p100, p140, and p260) were subsequently enriched by detergent extraction, ultracentrifugation, and CHT-HPLC column separation, and sequenced by LC-MS/MS. P100, p140, and p260 were identified. These levels of AβOs targets in human AD and aging frontal cortexes were analyzed by quantitative proteomics and western-blot. The polyclonal antibody to AβOs was developed and used to block the toxicity of AβOs. The data were analyzed with one-way analysis of variance. Results: AβOs binding proteins p100, p140, and p260 were identified as Na/K-ATPase, synGap, and Shank3, respectively. α3-Na/K-ATPase, synGap, and Shank3 proteins showed loss in the postsynaptic density (PSD) of human AD frontal cortex. In short term experiments, oligomers of Aβ inhibited Na/K-ATPase at the synapse. Na/K-ATPase activity was restored by an antibody specific for soluble forms of Aβ. α3-Na/K-ATPase protein and synaptic β-amyloid peptides were pulled down from human AD synapses by co-immunoprecipitation. Results suggest synaptic dysfunction in early stages of AD may stem from inhibition of Na/K-ATPase activity by Aβ oligomers, while later stages could hypothetically result from disrupted synapse structure involving the PSD proteins synGap and Shank3. Conclusion: We identified three AβO binding proteins as α3-Na/K-ATPase, synGap, and Shank3. Soluble Aβ oligomers appear capable of attacking neurons via specific extracellular as well as intracellular synaptic proteins. Impact on these proteins hypothetically could lead to synaptic dysfunction and loss, and could serve as novel therapeutic targets for AD treatment by antibodies or other agents.

The initial stage of structural transformation of Aβ42 peptides from the human and mole rat in the presence of Fe2+ and Fe3+: Related to Alzheimer's disease

The early stage of secondary structural conversion of amyloid beta (Aβ) to misfolded aggregations is a key feature of Alzheimer's disease (AD). Under normal physiological conditions, Aβ peptides can protect neurons from the toxicity of highly concentrated metals. However, they become toxic under certain conditions. Under conditions of excess iron, amyloid precursor proteins (APP) become overexpressed. This subsequently increases Aβ production. Experimental studies suggest that Aβ fibrillation (main-pathway) and amorphous (off-pathway) aggregate formations are two competitive pathways driven by factors such as metal binding, pH and temperature. In this study, we performed molecular dynamic (MD) simulations to examine the initial stage of conformational transformations of human Aβ (hAβ) and rat Aβ (rAβ) peptides in the presence of Fe²⁺ and Fe³⁺ ions. Our results demonstrated that Fe²⁺ and Fe³⁺ play key roles in Aβs folding and aggregation. Fe³⁺ had a greater effect than Fe²⁺on Aβs' folding during intermolecular interactions and subsequently, had a greater effect in decreasing structural diversity. Fe²⁺ was observed to be more likely than Fe³⁺ to interact with nitrogen atoms from the residues of imidazole rings of His. rAβ peptides are more energetically favorable than hAβ for intermolecular interactions and amorphous aggregations. We concluded that most hAβ structures were energetically unfavorable. However, hAβs with intermolecular β-sheet formations in the C-terminal were energetically favorable. It is notable that Fe²⁺ can change the surface charge of hAβ. Furthermore, Fe³⁺ can promote C-terminal folding by binding to Glu22 and Ala42, and by forming stable β-sheet formations on the C-terminal. Fe³⁺ can also pause the main-pathway by inducing random aggregations.

Homomeric and Heteromeric Aβ Species Exist in Human Brain and CSF Regardless of Alzheimer's Disease Status and Risk Genotype

Background: A fundamental question in Alzheimer’s disease (AD) is whether amyloid-β (Aβ) peptides and their deposition in the brain signify a direct pathological role or they are mere outcome of the disease pathophysiological events affecting neuronal function. It is therefore important to decipher their physiological role in the brain. So far, the overwhelming focus has been on the potential toxicity of Aβ, often studied outside the crucial AD characteristics, i.e.: (i) the slow, decades-long disease progression that precedes clinical symptoms; (ii) the link to apolipoprotein-E ε4 allele as major risk factor; (iii) the selective early degeneration of cholinergic neurons. Previous studies, in vitro and cerebrospinal fluid (CSF) only, indicated one possible native function of Aβ peptides is the allosteric modulation of acetylcholine homeostasis, via molecular interactions between Aβ, apolipoprotein-E, and the acetylcholine-degrading enzymes, cholinesterases, resulting in the formation of acetylcholine-hydrolyzing complexes (BAβACs).

Methods: Here, by combining sucrose-density gradient fractionation of post-mortem brains and in-house developed sensitive ELISA assays on the obtained fractions, we investigated the presence, levels and molecular interactions between Aβ, apolipoprotein-E and cholinesterases for the first time in brain tissues. We examined three distinct brain regions of Alzheimer and non-demented subjects, plus a large number of Alzheimer CSF samples.

Results: We report that both monomeric and oligomeric (homomeric and heteromeric) forms of Aβ peptides are present in the brain of Alzheimer and non-demented individuals. Heteromeric Aβ was found in stable complexes with apolipoprotein-E and/or cholinesterases, irrespective of APOE genotype or disease status, arguing in favor of a physiological dynamic formation and function for these complexes in the brain. The patterns and molecular sizes of the detected soluble Aβ forms were closely matched between CSF and brain samples. This evinces that the detected Aβ-apolipoprotein-E complexes and BAβACs in CSF most likely originate from the interstitial fluids of the brain.

Conclusions: In conclusion, both light homomeric Aβ oligomers and heteromeric Aβ-ApoE and BAβACs are present and readily detectable in the brain, regardless of disease status and APOE4 genotype. Deeper knowledge of the physiological function of Aβ is crucial for better understanding the early pathological events that decades later lead to manifestation of AD.

Amyloid β oligomers constrict human capillaries in Alzheimer's disease via signaling to pericytes

Cerebral blood flow is reduced early in the onset of Alzheimer's disease (AD). Because most of the vascular resistance within the brain is in capillaries, this could reflect dysfunction of contractile pericytes on capillary walls. We used live and rapidly fixed biopsied human tissue to establish disease relevance, and rodent experiments to define mechanism. We found that in humans with cognitive decline, amyloid β (Aβ) constricts brain capillaries at pericyte locations. This was caused by Aβ generating reactive oxygen species, which evoked the release of endothelin-1 (ET) that activated pericyte ET_A receptors. Capillary, but not arteriole, constriction also occurred in vivo in a mouse model of AD. Thus, inhibiting the capillary constriction caused by Aβ could potentially reduce energy lack and neurodegeneration in AD.

Promising Results from Alzheimer's Disease Passive Immunotherapy Support the Development of a Preventive Vaccine

The apparently near-term effects of the monoclonal antibody BAN2401 in slowing the progression of prodromal Alzheimer's disease (AD) has created cautious optimism about the therapeutic use of antibodies that neutralize cytotoxic soluble amyloid-β aggregates, rather than removing plaque. Plaque being protective, as it immobilizes cytotoxic amyloid-β, rather than AD's causative agent. The presence of natural antibodies against cytotoxic amyloid-β implies the existence of a protective anti-AD immunity. Hence, for vaccines to induce a similar immunoresponse that prevents and/or delays the onset of AD, they must have adjuvants that stimulate a sole anti-inflammatory Th2 immunity, plus immunogens that induce a protective immunoresponse against diverse cytotoxic amyloid-β conformers. Indeed, amyloid-β pleomorphism may explain the lack of long-term protection by monoclonal antibodies that neutralize single conformers, like aducanumab. A situation that would allow new cytotoxic conformers to escape neutralization by previously effective monoclonal antibodies. Stimulation of a vaccine's effective immunoresponse would require the concurrent delivery of immunogen to dendritic cells and their priming, to induce a polarized Th2 immunity. An immunoresponse that would produce besides neutralizing antibodies against neurotoxic amyloid-β oligomers, anti-inflammatory cytokines; preventing inflammation that aggravates AD. Because of age-linked immune decline, vaccines would be significantly more effective in preventing, rather than treating AD. Considering the amyloid-β's role in tau's pathological hyperphosphorylation and their synergism in AD, the development of preventive vaccines against both amyloid-β and tau should be considered. Due to convenience and cost, vaccines may be the only option available to many countries to forestall the impending AD epidemic.

α-Sheet secondary structure in amyloid β-peptide drives aggregation and toxicity in Alzheimer's disease

Alzheimer's disease (AD) is characterized by the deposition of β-sheet-rich, insoluble amyloid β-peptide (Aβ) plaques; however, plaque burden is not correlated with cognitive impairment in AD patients; instead, it is correlated with the presence of toxic soluble oligomers. Here, we show, by a variety of different techniques, that these Aβ oligomers adopt a nonstandard secondary structure, termed "α-sheet." These oligomers form in the lag phase of aggregation, when Aβ-associated cytotoxicity peaks, en route to forming nontoxic β-sheet fibrils. De novo-designed α-sheet peptides specifically and tightly bind the toxic oligomers over monomeric and fibrillar forms of Aβ, leading to inhibition of aggregation in vitro and neurotoxicity in neuroblastoma cells. Based on this specific binding, a soluble oligomer-binding assay (SOBA) was developed as an indirect probe of α-sheet content. Combined SOBA and toxicity experiments demonstrate a strong correlation between α-sheet content and toxicity. The designed α-sheet peptides are also active in vivo where they inhibit Aβ-induced paralysis in a transgenic Aβ Caenorhabditis elegans model and specifically target and clear soluble, toxic oligomers in a transgenic APPsw mouse model. The α-sheet hypothesis has profound implications for further understanding the mechanism behind AD pathogenesis.

Kalirin-7 prevents dendritic spine dysgenesis induced by amyloid beta-derived oligomers

Synapse degeneration and dendritic spine dysgenesis are believed to be crucial early steps in Alzheimer's disease (AD), and correlate with cognitive deficits in AD patients. Soluble amyloid beta (Aβ)-derived oligomers, also termed Aβ-derived diffusible ligands (ADDLs), accumulate in the brain of AD patients and play a crucial role in AD pathogenesis. ADDLs bind to mature hippocampal neurons, induce structural changes in dendritic spines and contribute to neuronal death. However, mechanisms underlying structural and toxic effects are not fully understood. Here, we report that ADDLs bind to cultured mature cortical pyramidal neurons and induce spine dysgenesis. ADDL treatment induced the rapid depletion of kalirin-7, a brain-specific guanine-nucleotide exchange factor for the small GTPase Rac1, from spines. Kalirin-7 is a key regulator of dendritic spine morphogenesis and maintenance in forebrain pyramidal neurons and here we show that overexpression of kalirin-7 prevents ADDL-induced spine degeneration. Taken together, our results suggest that kalirin-7 may play a role in the early events leading to synapse degeneration, and its pharmacological activation may prevent or delay synapse pathology in AD.

Trodusquemine enhances Aβ42 aggregation but suppresses its toxicity by displacing oligomers from cell membranes

Transient oligomeric species formed during the aggregation process of the 42-residue form of the amyloid-β peptide (Aβ₄₂) are key pathogenic agents in Alzheimer's disease (AD). To investigate the relationship between Aβ₄₂ aggregation and its cytotoxicity and the influence of a potential drug on both phenomena, we have studied the effects of trodusquemine. This aminosterol enhances the rate of aggregation by promoting monomer-dependent secondary nucleation, but significantly reduces the toxicity of the resulting oligomers to neuroblastoma cells by inhibiting their binding to the cellular membranes. When administered to a C. elegans model of AD, we again observe an increase in aggregate formation alongside the suppression of Aβ₄₂-induced toxicity. In addition to oligomer displacement, the reduced toxicity could also point towards an increased rate of conversion of oligomers to less toxic fibrils. The ability of a small molecule to reduce the toxicity of oligomeric species represents a potential therapeutic strategy against AD.

In vivo induction of membrane damage by β-amyloid peptide oligomers

Exposure to the β-amyloid peptide (Aβ) is toxic to neurons and other cell types, but the mechanism(s) involved are still unresolved. Synthetic Aβ oligomers can induce ion-permeable pores in synthetic membranes, but whether this ability to damage membranes plays a role in the ability of Aβ oligomers to induce tau hyperphosphorylation, or other disease-relevant pathological changes, is unclear. To examine the cellular responses to Aβ exposure independent of possible receptor interactions, we have developed an in vivo C. elegans model that allows us to visualize these cellular responses in living animals. We find that feeding C. elegans E. coli expressing human Aβ induces a membrane repair response similar to that induced by exposure to the CRY5B, a known pore-forming toxin produced by B. thuringensis. This repair response does not occur when C. elegans is exposed to an Aβ Gly37Leu variant, which we have previously shown to be incapable of inducing tau phosphorylation in hippocampal neurons. The repair response is also blocked by loss of calpain function, and is altered by loss-of-function mutations in the C. elegans orthologs of BIN1 and PICALM, well-established risk genes for late onset Alzheimer's disease. To investigate the role of membrane repair on tau phosphorylation directly, we exposed hippocampal neurons to streptolysin O (SLO), a pore-forming toxin that induces a well-characterized membrane repair response. We find that SLO induces tau hyperphosphorylation, which is blocked by calpain inhibition. Finally, we use a novel biarsenical dye-tagging approach to show that the Gly37Leu substitution interferes with Aβ multimerization and thus the formation of potentially pore-forming oligomers. We propose that Aβ-induced tau hyperphosphorylation may be a downstream consequence of induction of a membrane repair process.