Toxic Soluble Oligomers Research Articles

Selective targeting and protection against toxic amyloid‐beta oligomers by PMN310, a monoclonal antibody rationally designed for greater therapeutic potency in Alzheimer’s disease

AbstractBackgroundA large body of evidence indicates that the most pathogenic species of amyloid‐beta (Aß) in Alzheimer’s disease (AD) consists of soluble toxic oligomers (AßO) as opposed to insoluble fibrils and monomers. Clinical results to date indicate that non‐selective antibodies that bind Aß monomers, oligomers and plaque fail to provide a therapeutic benefit. Partially selective antibodies that bind AßO and plaque have shown improved success but are associated with dose‐limiting adverse events (amyloid‐related imaging abnormalities; ARIA). These findings suggest that antibodies capable of selectively neutralizing toxic AßO may achieve improved efficacy and safety. Monoclonal antibody PMN310 was raised against a conformational epitope predicted by computational modeling to be exposed on toxic AßO but not monomers or fibrils. A summary of the selectivity and protective activity of PMN310 against toxic AßO in vitro and in vivo is presented.MethodThe binding selectivity of PMN310 was characterized and compared to that of other Aß‐directed antibodies by surface plasmon resonance (SPR) and immunohistochemistry (IHC). Its ability to neutralize the propagation and toxicity of AßO was assessed in vitro in a thioflavin‐T propagation assay and in cultures of primary rodent neurons, respectively. In vivo protective activity was tested in wild‐type mice injected intracerebroventricularly (ICV) with AßO and in the APP/L transgenic mouse model of AD.ResultIn SPR analysis, PMN310 showed selective binding to AßO over monomers and, compared to otherAß‐directed antibodies, was minimally impacted by monomer competition in binding to toxic oligomers from AD brain extract. In addition, PMN310 did not bind to Aß plaque or vascular deposits as determined by IHC suggesting a potentially reduced risk of ARIA compared to other Aß‐directed antibodies. In vitro, PMN310 inhibited AßO propagation and neuronal toxicity. In vivo, PMN310 prevented AßO‐induced loss of memory formation after ICV injection. Systemic administration to APP/L transgenic mice preserved memory and learning in the water maze task.ConclusionThe antibody PMN310 was shown to selectively bind toxic AßO and protect against their pathogenic activity in vitro. In two rodent models of AD, PMN310 protected memory function, suggesting that PMN310 may offer a new therapeutic option for the treatment or prevention of AD.

Renin-angiotensin system in the central nervous system: focus on Huntington's disease.

Renin-angiotensin system in the central nervous system: focus on Huntington's disease.

Distinguishing between amyloid‐beta‐directed antibodies: Ability of PMN310 to target toxic oligomers despite competing species

AbstractBackgroundA large body of evidence indicates that the most pathogenic species of Abeta in Alzheimer’s disease (AD) consist of soluble toxic oligomers as opposed to insoluble fibrils and monomers. The ability of a therapeutic antibody to target toxic Abeta oligomers without being diverted by binding to competing non‐toxic species is expected to result in greater efficacy. This is supported by clinical results to date showing poor efficacy of non‐selective antibodies but improved success with partially selective antibodies that bind oligomers and plaque. As a next generation antibody, PMN310 is a therapeutic candidate designed to more selectively target toxic oligomers. Avoiding interaction with plaque and vascular deposits has the additional advantage of potentially decreasing the incidence of amyloid‐related imaging abnormalities (ARIA). In this study, PMN310 was compared to other Abeta antibodies for selectivity and ability to maintain interaction with toxic oligomers in the presence of competing monomers.MethodsThe binding of multiple Abeta‐directed antibodies (PMN310 and biosimilars donanemab, aducanumab, lecanemab, crenezumab, solanezumab) to synthetic oligomers, with and without pre‐exposure to competing monomers, was evaluated by surface plasmon resonance (SPR). Binding of the antibodies to a toxic oligomer‐enriched low molecular fraction of brain extract from AD patients was similarly evaluated by SPR, with and without monomer competition. Binding to insoluble Abeta deposits was examined by immunohistochemistry (IHC) of AD brain sections.ResultsPMN310 showed little or no interaction with monomers and was among the least impacted by excess monomer competition in binding to synthetic oligomers or naturally occurring toxic oligomers in AD brain extract. This characteristic was shared by other Abeta antibodies that have shown positive clinical outcomes. Non‐selective antibodies that failed in the clinic were strongly inhibited by monomer competition. In contrast to other Abeta antibodies, PMN310 additionally avoided interaction with plaque and vascular deposits as determined by IHC.ConclusionsPMN310 distinguishes itself from other Abeta antibodies by its enhanced selectivity for toxic oligomers (negligible binding to monomers and plaque) along with its ability to withstand competition by abundant monomers. Additionally, the avoidance of interaction with plaque and vascular deposits by PMN310 could potentially reduce the risk of ARIA.

Early diagnosis and treatment of Alzheimer’s disease by targeting toxic soluble Aβ oligomers

Transient soluble oligomers of amyloid-β (Aβ) are toxic and accumulate early prior to insoluble plaque formation and cognitive impairment in Alzheimer's disease (AD). Synthetic cyclic D,L-α-peptides (e.g., 1) self-assemble into cross β-sheet nanotubes, react with early Aβ species (1-3 mers), and inhibit Aβ aggregation and toxicity in stoichiometric concentrations, in vitro. Employing a semicarbazide as an aza-glycine residue with an extra hydrogen-bond donor to tune nanotube assembly and amyloid engagement, [azaGly6]-1 inhibited Aβ aggregation and toxicity at substoichiometric concentrations. High-resolution NMR studies revealed dynamic interactions between [azaGly6]-1 and Aβ42 residues F19 and F20, which are pivotal for early dimerization and aggregation. In an AD mouse model, brain positron emission tomography (PET) imaging using stable 64Cu-labeled (aza)peptide tracers gave unprecedented early amyloid detection in 44-d presymptomatic animals. No tracer accumulation was detected in the cortex and hippocampus of 44-d-old 5xFAD mice; instead, intense PET signal was observed in the thalamus, from where Aβ oligomers may spread to other brain parts with disease progression. Compared with standard 11C-labeled Pittsburgh compound-B (11C-PIB), which binds specifically fibrillar Aβ plaques, 64Cu-labeled (aza)peptide gave superior contrast and uptake in young mouse brain correlating with Aβ oligomer levels. Effectively crossing the blood-brain barrier (BBB), peptide 1 and [azaGly6]-1 reduced Aβ oligomer levels, prolonged lifespan of AD transgenic Caenorhabditis elegans, and abated memory and behavioral deficits in nematode and murine AD models. Cyclic (aza)peptides offer novel promise for early AD diagnosis and therapy.

The role of α-sheet structure in amyloidogenesis: characterization and implications.

Amyloid diseases are linked to protein misfolding whereby the amyloidogenic protein undergoes a conformational change, aggregates and eventually forms amyloid fibrils. While the amyloid fibrils and plaques are hallmarks of these diseases, they typically form late in the disease process and do not correlate with disease. Instead, there is growing evidence that smaller, soluble toxic oligomers form prior and appear to be early triggers of the molecular pathology underlying these diseases. Nearly 20 years ago, we proposed the α-sheet hypothesis after discovering that the early conformational changes observed during atomistic molecular dynamics simulations involve the formation of a non-standard protein structure, α-sheet. Furthermore, we proposed that toxic oligomers contain α-sheet structure and that preferentially targeting this structure could neutralize the toxicity, prevent further aggregation and serve as the basis for early detection of disease. Here, we present the origin of the α-sheet hypothesis and describe α-sheet structure and the corresponding mechanisms of conversion. We discuss experimental studies demonstrating that both mammalian and bacterial amyloid systems form α-sheet oligomers before converting to conventional β-sheet fibrils. Furthermore, we show that the process can be inhibited with de novo designed α-sheet peptides complementary to the structure in the toxic oligomers.

Influence of force field choice on the conformational landscape of rat and human islet amyloid polypeptide.

Human islet amyloid polypeptide (hIAPP) is a naturally occurring, intrinsically disordered protein (IDP) whose abnormal aggregation into toxic soluble oligomers and insoluble amyloid fibrils is a pathological feature in type-2 diabetes. Rat IAPP (rIAPP) differs from hIAPP by only six amino acids yet has a reduced tendency to aggregate or form fibrils. The structures of the monomeric forms of IAPP are difficult to characterize due to their intrinsically disordered nature. Molecular dynamics simulations can provide a detailed characterization of the monomeric forms of rIAPP and hIAPP in near-physiological conditions. In this work, the conformational landscapes of rIAPP and hIAPP as a function of secondary structure content were predicted using well-tempered bias exchange metadynamics simulations. Several combinations of commonly used biomolecular force fields and water models were tested. The predicted conformational preferences of both rIAPP and hIAPP are typical of IDPs, exhibiting dominant random coil structures but showing a low propensity for transient α-helical conformations. Predicted nuclear magnetic resonance Cα chemical shifts reveal different preferences with each force field towards certain conformations, with AMBERff99SBnmr2/TIP4Pd showing the best agreement with the experiment. Comparisons of secondary structure content demonstrate residue-specific differences between hIAPP and rIAPP that may reflect their different aggregation propensities.

Deducing the affinity between apolipoprotein E and soluble amyloid-beta oligomers using fluorescence correlation spectroscopy

Human apolipoprotein E (apoE), which plays a central role in lipid and cholesterol metabolism, exists in three major isoforms: E2, E3, and E4. The E4 allele is a major genetic factor for late-onset Alzheimer's disease (AD), while the E2 allele is thought to be protective. ApoE was shown to be connected to the aggregation, degradation, and clearance of toxic soluble oligomers of disordered amyloid-beta (Aβ) peptides, which are central to AD pathogenesis. However, previously reported interactions between apoE and Aβ are ambiguous since they rarely account for the dynamic and transient nature of Aβ oligomers or the aggregation and lipidation of apoE.

The amyloid concentric β-barrel hypothesis: Models of amyloid beta 42 oligomers and annular protofibrils.

Amyloid beta (Aβ) peptides are a major contributor to Alzheimer's disease. They occur in differing lengths, each of which forms a multitude of assembly types. The most toxic soluble oligomers are formed by Aβ42; some of which have antiparallel β-sheets. Previously, our group proposed molecular models of Aβ42 hexamers in which the C-terminus third of the peptide (S3) forms an antiparallel 6-stranded β-barrel that is surrounded by an antiparallel barrel formed by the more polar N-terminus (S1) and middle (S2) portions. These hexamers were proposed to act as seeds from which dodecamers, octadecamers, both smooth annular protofibrils (sAPFs) and beaded annular protofibrils (bAPFs), and transmembrane channels form. Since then, numerous aspects of our models have been supported by experimental findings. Recently, NMR-based structures have been proposed for Aβ42 tetramers and octamers, and NMR studies have been reported for oligomers composed of ~32 monomers. Here we propose a range of concentric β-barrel models and compare their dimensions to image-averaged electron micrographs of both bAPFs and sAPFs of Aβ42. The smaller oligomers have 6, 8, 12, 16, and 18 monomers. These beads string together to form necklace-like bAPFs. These bAPRs gradually morph into sAPFs in which a S3 β-barrel is shielded on one or both sides by β-barrels formed from S1 and S2 segments.

Abstract MP59: Soluble Protein Oligomers Induce Endoplasmic Reticulum Stress In Mesenteric Resistance Arteries From Male And Female Mice

Amyloid β proteins, including toxic soluble oligomers (SPOs) are not only found in the brain duringAlzheimer’s, but also in the peripheral vascular system. The precise mechanism linking increasedcirculating levels of SPOs and vascular dysfunction remains unknown. We hypothesized that SPOslead to endoplasmic reticulum (ER) stress, further release of SPOs and vascular injury. Mesentericresistance arteries (MRAs) from 14 weeks old, male and female C57BL/6 mice were used forvascular function. Agonists were acetylcholine and phenylephrine (1nM-10mM). In acuteconditions, SPOs (0.1μM) caused pathologically exacerbated endothelium-dependent vasodilationcompared to vehicle (F12 media) [Male: EC50: SPOs: -7.0 ± 0.1 (n=4), vs. Vehicle -6.6 ± 0.1 (n=7)p=0.03; Female: EC50: SPOs: -7.3 ± 0.06 (n=5) vs. Vehicle -6.7 ± 0.1 (n=6), p=0.001]. Thisphenotype was similar to the positive control tunicamycin (5mg/ml) [Male: EC50: Tunicamycin: -7.3(n=4), vs. Vehicle -6.6 (n=7) p=0.2; Female: EC50: Tunicamycin: -7.7 (n=4) vs. Vehicle -6.8 (n=5)p=0.04]. To determine whether SPO’s cause ER stress, arteries were treated with ER stressinhibitor 4-Phenylbutyric acid (2mM). The ER stress inhibitor prevented the exacerbatedvasodilation induced by SPOs showing SPOs trigger ER stress in acute conditions independent ofsex. To determine whether SPOs are a consequence of ER stress, arteries were incubated withtunicamycin in the presence of the SPO inhibitor K01-162 (10mM). Interestingly, K01-162 did notprevent the tunicamycin-induced exacerbated vasodilation in arteries from male mice. However,this response was decreased in arteries from female mice showing that inducing ER stress leadsto the release of SPOs, escalating a feed-forward mechanism of further SPO release. There wereno changes in vascular contraction with tunicamycin or SPOs irrespective of sex. ER stress wasconfirmed with anti-KDEL antibody staining, specific for ER resident chaperones Grp78/94 andvisualized with multiphoton fluorescent confocal microscopy. These results demonstrate that SPO’sexacerbate endothelium-dependent vasodilation acutely and may contribute to brain and peripheralvascular edema and loss of autoregulation observed during cardiovascular and Alzheimer’sdisease.

Soluble Protein Oligomers induce Endoplasmic Reticulum Stress in Acute Conditions in Mesenteric Resistance Arteries from Male and Female Mice

Background While amyloid β proteins, including toxic soluble oligomers, are a well established pathogenic mechanism of alzheimer's disease, SPOs are also found in the peripheral vascular system where their accumulation is considered to be a fundamental mechanism that underlies vascular dysfunction and cell death. However, the precise mechanism linking increased circulating levels of SPOs and vascular dysfunction remains unknown. We therefore hypothesized that SPOs are recognized by the vasculature leading to endoplasmic reticulum (ER) stress which further induces the release of SPOs and vascular injury. Methods & results Mesenteric resistance arteries (MRAs) from male and female wild type C57BL/6 mice (14-20 weeks old) were isolated to measure vascular function via a wire myograph. Concentration response curves to acetylcholine (10-9-10-5mol/L) and phenylephrine (10-9-10-5 mol/L) were performed. We observed that in acute conditions, and in arteries from both male and female mice, incubation with SPOs (0.1mM) caused exacerbated endothelium-dependent vasodilation compared to vehicle (F12 media, 5mL) [Male: EC50: Vehicle -6.6 ± 0.1 (n=7) vs. SPOs: -7.0 ± 0.1 (n=4), p=0.03; Female: EC50: Vehicle -6.7 ± 0.1 (n=6) vs. SPOs: -7.3 ± 0.06 (n=5), p=0.001]. A similar phenotype was observed in arteries treated with ER stress inducer tunicamycin (5mg/ml, positive control). This suggests that SPOs and ER stress exacerbate endothelium-dependent vasodilation, independent of sex. To determine whether SPO's are a cause of ER stress, arteries were treated with SPOs or vehicle for 15 min prior to incubation with an ER stress inhibitor 4-Phenylbutyric acid (4-PBA) (2mM) for 30 min. We observed that incubation with 4-PBA prevented the exacerbated vasodilation induced by SPOs in both male and female arteries, indicating that SPOs trigger ER stress in acute conditions and this is also independent of sex (Fig 1). On the other hand, to determine whether SPOs are a consequence of ER stress, arteries were incubated with ER stress inducer tunicamycin (5mg/ml) or vehicle for 15 min prior to incubation with the oligomer inhibitor K01-162 (10mM) for 30 min. Interestingly, the SPO inhibitor K01-162 did not prevent the exacerbated vasodilation induced by tunicamycin in arteries from male mice. However, this response was restored in arteries from female mice suggesting that ER stress induces the release of SPOs in arteries from female but not from male mice in acute conditions. Phenylephrine-induced vascular contraction did not change in the presence of tunicamycin or SPOs irrespective of sex. Conclusion We concluded that SPOs induce ER stress and subsequently exacerbate endothelium-dependent vasodilation in acute conditions irrespective of sex. However, ER stress induction in arteries from females also leads to the release of SPOs, escalating a feed-forward mechanism of further SPO release. Collectively, these results demonstrate that SPO's exacerbate endothelium-dependent vasodilation acutely and may contribute to vascular damage.

Conformation-specific perturbation of membrane dynamics by structurally distinct oligomers of Alzheimer's amyloid-β peptide.

The accumulation of toxic soluble oligomers of the amyloid-β peptide (Aβ) is a key step in the pathogenesis of Alzheimer's disease. There are mainly two conformationally distinct oligomers, namely, prefibrillar and fibrillar oligomers, that are recognized by conformation-specific antibodies, anti-amyloid oligomer antibody (A11) and anti-amyloid fibrillar antibody (OC), respectively. Previous studies have shown that the interaction of Aβ oligomers with the lipid membrane is one of the key mechanisms of toxicity produced by Aβ oligomers. However, the mechanism by which structurally distinct Aβ oligomers interact with the lipid membrane remains elusive. In this work, we dissect the molecular mechanism underlying the interaction of structurally distinct Aβ42 oligomers with the lipid membrane derived from the brain total lipid extract. Using picosecond time-resolved fluorescence spectroscopy, we show that the A11-positive Aβ42 oligomers undergo a membrane-induced conformational change that promotes the deeper immersion of these oligomers into the lipid hydrocarbon region and results in an increase in the membrane micro-viscosity. In sharp contrast, OC-positive Aβ42 oligomers interact with the lipid membrane via electrostatic interactions between the negatively-charged lipid headgroup and positively-charged residues of Aβ42 without perturbing the membrane dynamics. We show that the two structurally distinct Aβ42 oligomers demonstrating different interaction mechanisms with the lipid membrane eventually lead to the formation of typical amyloid fibrils. Our findings provide the mechanistic underpinning of the perturbation of lipid membranes by two conformationally distinct Aβ42 oligomers and can be of prime importance in designing anti-Alzheimer's therapeutic agents targeting Aβ-membrane interactions.

Amyloid-β Peptide Impact on Synaptic Function and Neuroepigenetic Gene Control Reveal New Therapeutic Strategies for Alzheimer's Disease.

Amyloid-β (Aβ) peptides can form protease-resistant aggregates within and outside of neurons. Accumulation of these aggregates is a hallmark of Alzheimer’s disease (AD) neuropathology and contributes to devastating cognitive deficits associated with this disorder. The primary etiological factor for Aβ aggregation is either an increase in Aβ production or a decrease in its clearance. Aβ is produced by the sequential activity of β- and γ-secretase on the amyloid precursor protein (APP) and the clearance is mediated by chaperone-mediated mechanisms. The Aβ aggregates vary from soluble monomers and oligomers to insoluble senile plaques. While excess intraneuronal oligomers can transduce neurotoxic signals into neurons causing cellular defects like oxidative stress and neuroepigenetic mediated transcriptional dysregulation, extracellular senile plaques cause neurodegeneration by impairing neural membrane permeabilization and cell signaling pathways. Paradoxically, senile plaque formation is hypothesized to be an adaptive mechanism to sequester excess toxic soluble oligomers while leaving native functional Aβ levels intact. This hypothesis is strengthened by the absence of positive outcomes and side effects from immunotherapy clinical trials aimed at complete Aβ clearance, and support beneficial physiological roles for native Aβ in cellular function. Aβ has been shown to modulate synaptic transmission, consolidate memory, and protect against excitotoxicity. We discuss the current understanding of beneficial and detrimental roles for Aβ in synaptic function and epigenetic gene control and the future promising prospects of early therapeutic interventions aimed at mediating Aβ induced neuroepigenetic and synaptic dysfunctions to delay AD onset.

Targeting Pathological Amyloid Aggregates with Conformation-Sensitive Antibodies.

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. 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. 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. 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. 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.

The amyloid cascade hypothesis and Alzheimer’s disease: A mathematical model

The paper presents a conceptual mathematical model for Alzheimer’s disease (AD). According to the so-called amyloid cascade hypothesis, we assume that the progression of AD is associated with the presence of soluble toxic oligomers of beta-amyloid. Monomers of this protein are produced normally throughout life, but a change in the metabolism may increase their total production and, through aggregation, ultimately results in a large quantity of highly toxic polymers. The evolution from monomeric amyloid produced by the neurons to senile plaques (long and insoluble polymeric amyloid chains) is modelled by a system of ordinary differential equations (ODEs), in the spirit of the Smoluchowski equation. The basic assumptions of the model are that, at the scale of suitably small representative elementary volumes (REVs) of the brain, the production of monomers depends on the average degradation of the neurons and in turn, at a much slower timescale, the degradation is caused by the number of toxic oligomers. To mimic prion-like diffusion of the disease in the brain, we introduce an interaction among adjacent REVs that can be assumed to be isotropic or to follow given preferential patterns. We display the results of numerical simulations which are obtained under some simplifying assumptions. For instance, the amyloid cascade is modelled by just three ordinary differential equations (ODEs), and the simulations refer to abstract 2D domains, simplifications which can be easily avoided at the price of some additional computational costs. Since the model is suitably flexible to incorporate other mechanisms and geometries, we believe that it can be generalised to describe more realistic situations.

Drivers of α-Sheet Formation in Transthyretin under Amyloidogenic Conditions.

Amyloid diseases make up a set of fatal disorders in which proteins aggregate to form fibrils that deposit in tissues throughout the body. Amyloid-associated diseases are challenging to study because amyloid formation occurs on time scales that span several orders of magnitude and involve heterogeneous, interconverting protein conformations. The development of more effective technologies to diagnose and treat amyloid disease requires both a map of the conformations sampled during amyloidogenesis and an understanding of the molecular mechanisms that drive this process. In prior molecular dynamics simulations of amyloid proteins, we observed the formation of a nonstandard type of secondary structure, called α-sheet, that we proposed is associated with the pathogenic conformers in amyloid disease, the soluble oligomers. However, the detailed molecular interactions that drive the conversion to α-sheet remain elusive. Here we use molecular dynamics simulations to interrogate a critical event in transthyretin aggregation, the formation of aggregation-competent, monomeric species. We show that conformational changes in one of the two β-sheets in transthyretin enable solvent molecules and polar side chains to form electrostatic interactions with main-chain peptide groups to facilitate and modulate conversion to α-sheet secondary structure. Our results shed light on the early conformational changes that drive transthyretin toward the α-sheet structure associated with toxicity. Delineation of the molecular events that lead to aggregation at atomic resolution can aid strategies to target the early, critical toxic soluble oligomers.

Tau-Reactive Endogenous Antibodies: Origin, Functionality, and Implications for the Pathophysiology of Alzheimer's Disease.

In Alzheimer's disease (AD), tau pathology manifested by the accumulation of intraneuronal tangles and soluble toxic oligomers emerges as a promising therapeutic target. Multiple anti-tau antibodies inhibiting the formation and propagation of cytotoxic tau or promoting its clearance and degradation have been tested in clinical trials, albeit with the inconclusive outcome. Antibodies against tau protein have been documented both in the brain circulatory system and at the periphery, but their origin and role under normal conditions and in AD remain unclear. While it is tempting to assign them a protective role in regulating tau level and removal of toxic variants, the supportive evidence remains sporadic, requiring systematic analysis and critical evaluation. Herein, we review recent data showing the occurrence of tau-reactive antibodies in the brain and peripheral circulation and discuss their origin and significance in tau clearance. Based on the emerging evidence, we cautiously propose that impairments of tau clearance at the periphery by humoral immunity might aggravate the tau pathology in the central nervous system, with implication for the neurodegenerative process of AD.

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.

Promising anti-amyloid behavior of cationic pyridylphenylene dendrimers: Role of structural features and mechanism of action

Misfolding and aggregation of amyloidogenic proteins are responsible for the onset of neurodegenerative diseases. This makes studies directed towards prevention of these processes of particular importance. In this paper we report that cationic pyridylphenylene dendrimers of the second (G2), third (G3) and fourth (G4) generations act as effective suppressors of the amyloid aggregation of the full-length ovine prion protein (PrP). The dendrimers are able to inhibit both the formation of the most toxic soluble oligomers and amyloid fibrils. Dendrimer binding prevents the structural conversion of PrP and further protein fibrillation. The effect is dependent on the dendrimer generation with G4 being the most potent. Importantly, after the treatment with the dendrimers, PrP does not induce the pathological conformational changes in native PrP, indicating the loss of amyloidogenic properties. The cell viability assay reveals the dependence on the cell line and the dendrimer generation used. The observed fundamental principles of the dendrimer interaction with PrP helped us to elucidate the protective effect of the dendrimers and to suggest the potential mechanism of the dendrimer action. Noteworthy, the dendrimers preserve their protective effect regardless of the aggregation conditions applied, indicating the important role of their structural features, e.g. rigidity and permanent charge, in anti-amyloid behavior.

Royal jelly coordinately enhances hippocampal neuronal expression of somatostatin and neprilysin genes conferring neuronal protection against toxic soluble amyloid-β oligomers implicated in Alzheimer’s disease pathogenesis

Hippocampal somatostatin (SST)-neprilysin (NEP) system functions as a defense system against neurotoxic soluble amyloid-β oligomers associated with onset of Alzheimer’s disease. However, it remains unknown whether royal jelly (RJ) could impact the defense system. In this study using primary cultures of hippocampal neurons, including SST-positive and NEP-positive neuronal subsets, we evaluated the ability of DMSO-soluble fraction of RJ (DRJ) to enhance SST and NEP genes expression. The DRJ potently facilitated CRE-mediated transcription, and raised SST-immunoreactivity in an SST-positive neuronal subset, where elevated phospho-CREB immunoreactivity was simultaneously observed. Chromatin immunoprecipitation-qPCR assays uncovered that the DRJ mechanistically facilitated CREB-binding to a CRE present at the promoter region of SST. Moreover, in a distinct NEP-positive neuronal subset, the DRJ led to elevation of NEP immunoreactivity, which was abolished by cyclosomatostatin, a non-selective SST receptors antagonist. Collectively, these findings provide the first evidence that the RJ possesses potential to activate the hippocampal SST-NEP system.

Lipid vesicles affect the aggregation of 4-hydroxy-2-nonenal-modified α-synuclein oligomers

Parkinson's disease (PD) and other synucleinopathies are characterized by accumulation of misfolded aggregates of α-synuclein (α-syn). The normal function of α-syn is still under investigation, but it has been generally linked to synaptic plasticity, neurotransmitter release and the maintenance of the synaptic pool. α-Syn localizes at synaptic terminals where it can bind to synaptic vesicles as well as to other cellular membranes. It has become clear that these interactions have an impact on both α-syn functional role and its propensity to aggregate. In this study, we investigated the aggregation process of α-syn covalently modified with 4-hydroxy-2-nonenal (HNE). HNE is a product of lipid peroxidation and has been implicated in the pathogenesis of different neurodegenerative diseases by modifying the kinetics of soluble toxic oligomers. Although HNE-modified α-syn has been reported to assemble into stable oligomers, we found that slightly acidic conditions promoted further protein aggregation. Lipid vesicles delayed the aggregation process in a concentration-dependent manner, an effect that was observed only when they were added at the beginning of the aggregation process. Co-aggregation of lipid vesicles with HNE-modified α-syn also induced cytotoxic effects on differentiated SHSY-5Y cells. Under conditions in which the aggregation process was delayed cell viability was reduced. By exploring the behavior and potential cytotoxic effects of HNE-α-syn under acidic conditions in relation to protein-lipid interactions our study gives a framework to examine a possible pathway leading from a physiological setting to the pathological outcome of PD.