Oligomeric and fibrillar species of amyloid-beta peptides differentially affect neuronal viability

Amyloid-β Dysregulates Oligodendroglial Lineage Cell Dynamics and Myelination via PKC in the Zebrafish Spinal Cord

Soluble forms of amyloid-β (Aβ) peptide have been proposed as candidates to induce oligodendrocyte (OL) and myelin dysfunctions in the early stages of Alzheimer's disease (AD) pathology. Nevertheless, little is known about how Aβ affects OL differentiation and myelination in vivo, and the underlying molecular mechanisms. In this study, we explored the effects of a brain intraventricular injection of Aβ on OLs and myelin in the developing spinal cord of zebrafish larvae. Using quantitative fluorescent in situ RNA hybridization assays, we demonstrated that Aβ altered myrf and mbp mRNA levels and the regional distribution of mbp during larval development, suggesting an early differentiation of OLs. Through live imaging of Tg(myrf:mScarlet) and Tg(mbpa:tagRFP) zebrafish lines, both crossed with Tg(olig2:EGFP), we found that Aβ increased the number of myrf + and mbp + OLs in the dorsal spinal cord at 72 hpf and 5 dpf, respectively, without affecting total cell numbers. Furthermore, Aβ also increased the number of Sox10+cells, myelin sheaths per OL, and the number of myelinated axons in the dorsal spinal cord at 8 dpf compared to vehicle-injected control animals. Interestingly, the treatment of Aβ-injected zebrafish with the pan-PKC inhibitor Gö6983 restored the aforementioned alterations in OLs and myelin to control levels. Altogether, not only do we demonstrate that Aβ induces a precocious oligodendroglial differentiation leading to dysregulated myelination, but we also identified PKC as a key player in Aβ-induced pathology.

Effects of Solvent Dimethyl Sulfoxide Invites a Rethink of Its Application in Amyloid Beta Cytotoxicity

Dimethyl sulfoxide (DMSO) is commonly used as a solvent for preparing amyloid-beta (Aβ) peptides implicated in Alzheimer's disease. While considered relatively non-toxic at low concentrations, DMSO itself may exert biological effects that could confound experimental outcomes, especially for weakly cytotoxic substances like Aβ. Seven brain cell types (BV-2, N2a, SH-SY5Y, U87, neurons, astrocytes, microglia) were treated with varying DMSO concentrations or Aβ1-42 oligomers/protofibrils/fibrils prepared using DMSO. Cell viability was assessed by CCK-8 and LDH assays. Matched DMSO controls were prepared alongside Aβ treatments to delineate solvent effects. Low DMSO concentrations (0.0625-0.015625%) exhibited hormetic cytoprotective and growth-promoting effects, while higher concentrations (≥2%) were cytotoxic. Importantly, these hormetic solvent effects confounded the measurement of Aβ cytotoxicity. By accounting for matched DMSO controls, the study revealed that Aβ fibril toxicity may have been underestimated due to the cytoprotective solvent effects of low DMSO concentrations used in their preparation. In conclusion, DMSO exhibits complex hormetic dose-responses that can significantly influence experimental outcomes, especially for weakly cytotoxic agents like Aβ. Rigorous solvent controls are crucial to delineate genuine substance effects from potential solvent confounds and avoid erroneous interpretations.

Fibrillar structures detected by AFM in the cerebrospinal fluid of patients affected by Alzheimer's disease and other neurological conditions

Alzheimer's disease (AD) is a progressive debilitating neurodegenerative disorder that is usually diagnosed after irreversible brain damage has occurred. The detection and morphological characterization of amyloid-β fibrils, which are predominantly implicated in the pathogenic process of the disease, in the cerebrospinal fluid (CSF), emphasized the significance of examining such biofluid. In this work the crude CSF samples collected from patients with Alzheimer's disease and with other neurological conditions were analyzed by atomic force microscopy (AFM). This approach allowed for the identification of peculiar fibrillar structures, exhibiting the regular repetition of dimeric globular units along the longitudinal axis, which share morphological similarities with fibrin protofibrils. Several studies have consistently shown that the disruption of the blood-brain barrier (BBB) and the infiltration of fibrinogen and components of the coagulation cascade are linked with a wide range of neurological diseases, including AD. Therefore, the role of the fibrillar structures we identified must be clarified, in order to ascertain if they contribute to the etiology of the disease, and their use as possible biomarkers of brain damage and disease progression should be assessed.

Investigating the combined effect of copper, zinc, and iron ions on truncated and full-length Aβ peptides: insights from molecular dynamics simulation

The truncated Aβ1 - 16 peptide containing the metal-binding domain is frequently used in in silico and experimental investigations because it is more soluble and thus more suitable for studies in solution and does not form amyloids. Several spectroscopic studies have shown that the metal binding of Aβ1 - 16 is very similar to that of the full-length Aβ1 - 42. However, since small changes can have a significant impact on aggregation, further experimental and theoretical are needed to elucidate the detailed structures of truncated and full-length Aβ. In this research, the binding of copper ion to the Aβ1 - 16 and Aβ1 - 42 has been studied by molecular dynamics simulation method. To investigate the effect of copper ion on beta-amyloid peptide structure, the simulations were repeated in the copper and zinc ions, copper and iron binary system, and the copper, zinc and iron ions ternary system. The conformation factor was calculated to calculate the binding affinity of copper ion to beta-amyloid peptide residues. The results showed that the initial 16 residues of the beta-amyloid peptide have high binding affinity for copper ions, and histidine 13 and histidine 14 have significantly higher binding affinity for copper ions in all studied systems. Zinc and iron ions were found to reduce the conformational factor of peptide residues in binding to copper ions, and the aggregation tendency was lower in the truncated structure. The SASA results suggest that the side chains of peptide residues are more affected by shortening and the presence of ions.

Quantitative Analysis of the Influence of Trehalose on Amyloid-β Binding to Membranes by Localized Surface Plasmon Resonance Spectroscopy

The damaging effect of amyloid-β (Aβ) on cellular membranes is an essential factor that contributes to Aβ's neurotoxicity in Alzheimer's disease. In this work, we explore the role of trehalose sugar in protecting model lipid membranes composed of DPPC-POPC-Cholesterol against Aβ toxicity. We used localized surface plasmon resonance (LSPR) spectroscopy and conducted a quantitative analysis to study the influence of trehalose on Aβ-membrane interactions. The LSPR data indicate that trehalose can effectively reduce the level of binding of Aβ to the lipid membrane, indicating its protective role against amyloid toxicity. Additionally, atomic force microscopy (AFM) was used to visualize the lipid membranes supported on the LSPR sensors and to elucidate the effect of trehalose on membrane morphology. The ability of trehalose to alter the physical properties of model membranes is discussed in relation to its protective role against Aβ during dehydration.

Aβ40 Fibril Assembly on Human Cerebral Smooth Muscle Cells Impairs Cell Viability

Cerebral vascular deposition of the amyloid-β (Aβ) peptide, a condition known as cerebral amyloid angiopathy (CAA), is associated with intracerebral hemorrhaging and contributes to disease progression in Alzheimer's disease (AD) and vascular cognitive impairment and dementia (VCID). Familial mutations at positions 22 and 23 within the Aβ peptide lead to early onset and severe CAA pathology. Here, we evaluate the effects of fibrillar Aβ peptides on the viability of primary-cultured human cerebral smooth muscle (HCSM) cells, which are the major site of amyloid deposition in cerebral blood vessel walls. Comparisons are made of the familial E22Q (Dutch) mutant of Aβ40 with wild-type Aβ40 and Aβ42. In agreement with previous studies, we find that there is a significant reduction in cell viability when Aβ40-Dutch or Aβ42-WT peptides are added to HCSM cell cultures as monomeric Aβ, whereas Aβ40-WT is relatively nontoxic. The binding of Aβ fibrils derived from sporadic CAA or familial Dutch-type CAA brain tissue to the membrane surface of HCSM cells does not result in a significant loss of cell viability. In contrast, when Aβ40-WT monomers and sporadic CAA fibrils are coincubated in HCSM cell cultures, there is a significant reduction in HCSM cell viability that is accompanied by an increase in cell surface fibril formation. Lastly, intrathecal administration of Aβ40-Dutch fibrillar seeds promotes fibrillar amyloid accumulation in the smooth muscle of meningeal vessels in the rTg-D transgenic rat model of CAA. Together, the present findings suggest that fibrillar Aβ seeds propagate the expansion of new amyloid fibrils on cerebral vascular smooth muscle, leading to membrane disruption and cell death.

Astrocyte-secreted factors modulate synaptic protein synthesis as revealed by puromycin labeling of isolated synaptosomes

The synaptic proteome can be shaped by proteins transported from the neuronal soma and/or by mRNAs that are delivered to synapses where proteins are locally synthesized. This last mechanism is known as local translation. Local translation has been extensively studied in neurons in physiological conditions and, more recently, in neurological disorders, in which local transcriptomes and translatomes become dysregulated. It is widely believed that in neurons, the main source of localized transcripts is the neuronal soma and that localized translation is primarily regulated by the neuron itself. However, we wondered whether glial cells, especially astrocytes, could contribute to the modulation of synaptic local protein synthesis. To address this question, we compared levels of proteins produced in synaptic compartments in neuronal and neuron-astrocyte co-cultures using modified Boyden chambers or astrocyte-conditioned medium. We developed a methodology to measure local protein synthesis by puromycin labeling of isolated synaptosomes devoid of somatic input. Our results show that synaptic local translation is enhanced or retained when neurons are cultured in the presence of astrocytes and in response to astrocyte-conditioned medium. Puromycin labeling coupled with proximity ligation identified Rpl26 as one of the proteins whose local synthesis is regulated by astrocyte-secreted factors. Our results thus unravel the contribution of glia to synaptic protein synthesis and point to a previously unexplored extra layer of complexity in the regulation of local translation in neurons.

An Expanded Narrative Review of Neurotransmitters on Alzheimer's Disease: The Role of Therapeutic Interventions on Neurotransmission

Alzheimer's disease (AD) is a progressive neurodegenerative disease. The accumulation of amyloid-β (Aβ) plaques and tau neurofibrillary tangles are the key players responsible for the pathogenesis of the disease. The accumulation of Aβ plaques and tau affect the balance in chemical neurotransmitters in the brain. Thus, the current review examined the role of neurotransmitters in the pathogenesis of Alzheimer's disease and discusses the alterations in the neurochemical activity and cross talk with their receptors and transporters. In the presence of Aβ plaques and neurofibrillary tangles, changes may occur in the expression of neuronal receptors which in turn triggers excessive release of glutamate into the synaptic cleft contributing to cell death and neuronal damage. The GABAergic system may also be affected by AD pathology in a similar way. In addition, decreased receptors in the cholinergic system and dysfunction in the dopamine neurotransmission of AD pathology may also contribute to the damage to cognitive function. Moreover, the presence of deficiencies in noradrenergic neurons within the locus coeruleus in AD suggests that noradrenergic stimulation could be useful in addressing its pathophysiology. The regulation of melatonin, known for its effectiveness in enhancing cognitive function and preventing Aβ accumulation, along with the involvement of the serotonergic system and histaminergic system in cognition and memory, becomes remarkable for promoting neurotransmission in AD. Additionally, nitric oxide and adenosine-based therapeutic approaches play a protective role in AD by preventing neuroinflammation. Overall, neurotransmitter-based therapeutic strategies emerge as pivotal for addressing neurotransmitter homeostasis and neurotransmission in the context of AD. This review discussed the potential for neurotransmitter-based drugs to be effective in slowing and correcting the neurodegenerative processes in AD by targeting the neurochemical imbalance in the brain. Therefore, neurotransmitter-based drugs could serve as a future therapeutic strategy to tackle AD.

Dynamic protein hydration water mediates the aggregation kinetics of amyloid β peptides at interfaces

Protein hydration water is essential for protein misfolding and amyloid formation, but how it directs the course of amyloid formation has yet to be elucidated. Here, we experimentally demonstrated that femtosecond sum frequency generation vibrational spectroscopy (SFG-VS) and the femtosecond IR pump-SFG probe technique can serve as powerful tools for addressing this issue. Using amyloid β(1-42) peptide as a model, we determined the transient misfolding intermediates by probing the amide band spectral features and the local hydration water changes by measuring the ultrafast vibrational dynamics of the amide I band. For the first time, we established a correlation between the dynamic change in protein hydration water and aggregation propensity. The aggregation propensity depends on the dynamic change in the hydration water, rather than the static hydration water content of the initial protein state. Water expulsion enhances the aggregation propensity and promotes amyloid formation, while protein hydration attenuates the aggregation propensity and inhibits amyloid formation. The suppression of water expulsion and protein hydration can prevent protein aggregation and stabilize proteins. These findings contribute to a better understanding of the underlying effect of hydration water on amyloid formation and protein structural stability and provide a strategy for maintaining long-term stabilization of biomolecules.

Aromatic polyketides isolated from the marine-derived fungus Didymella aeria and their neuroprotective activity

Two novel aromatic polyketides, penicanesins J and K (1, 2), were isolated from the marine-derived fungus Didymella aeria, along with the known compound integrastatin B (3). The structures of the new compounds were determined by NMR spectroscopy and synthetic methods. The isolated compounds were tested for monoamine oxidase (MAO) B inhibition, anti-amyloid beta (Aβ) aggregation, and protective activity against H2O2-induced cell death in human neuroblastoma SH-SY5Y cells. Integrastatin B (3) showed potential activity for inhibition of Aβ aggregation and protection against H2O2-induced cell death.

A VEGF Fragment Encompassing Residues 10-30 Inhibits Aβ1-42 Amyloid Aggregation and Exhibits Neuroprotective Properties Matching the Full-Length Protein

The intricate relationship between brain vascular diseases and neurodegeneration has garnered increased attention in the scientific community. With an aging population, the incidence of these two conditions is likely to increase, making it imperative to understand the underlying common molecular mechanisms and unveiling novel avenues for therapy. Prompted by the observation that Aβ peptide aggregation has been implicated in the development of cerebral amyloid angiopathy (CAA) and that elevated concentrations of vascular endothelial growth factor (VEGF) in the cerebrospinal fluid (CSF) have been correlated with less cognitive decline in Alzheimer's disease (AD), we demonstrate that a small peptide (Pep9) encompassing the 10-30 sequence of VEGF exhibits significant ability to inhibit the aggregation of the Aβ1-42 peptide, as well as the formation of toxic oligomers. AFM studies confirmed this inhibitory capacity, which is also paralleled by a significant reduction of the random coil to a beta-sheet conformational transition. Further studies have shown that Pep9 protects differentiated neuroblastoma SH-SY5Y cells from Aβ toxicity, being even more effective than full-length protein in preventing amyloid-induced neuronal death. The use of a control peptide wherein two histidines are substituted with glycines (H11G and H12G) suggests a close relationship between the peptide amino acid sequence and its antiaggregating/neuroprotective activity. Overall, this study provides insight into the role of VEGF in AD and suggests that specific VEGF fragments could be beneficial in the treatment of this condition.

Oligomeric Amyloid-β and Tau Alter Cell Adhesion Properties and Induce Inflammatory Responses in Cerebral Endothelial Cells Through the RhoA/ROCK Pathway

Dysfunction of cerebral endothelial cells (CECs) has been implicated in the pathology of Alzheimer's disease (AD). Despite evidence showing cytotoxic effects of oligomeric amyloid-β (oAβ) and Tau (oTau) in the central nervous system, their direct effects on CECs have not been fully investigated. In this study, we examined the direct effects of oAβ, oTau, and their combination on cell adhesion properties and inflammatory responses in CECs. We found that both oAβ and oTau increased cell stiffness, as well as the p-selectin/Sialyl-LewisX (sLeX) bonding-mediated membrane tether force and probability of adhesion in CECs. Consistent with these biomechanical alterations, treatments with oAβ or oTau also increased actin polymerization and the expression of p-selectin at the cell surface. These toxic oligomeric peptides also triggered inflammatory responses, including upregulations of p-NF-kB p65, IL-1β, and TNF-α. In addition, they rapidly activated the RhoA/ROCK pathway. These biochemical and biomechanical changes were further enhanced by the treatment with the combination of oAβ and oTau, which were significantly suppressed by Fasudil, a specific inhibitor for the RhoA/ROCK pathway. In conclusion, our data suggest that oAβ, oTau, and their combination triggered subcellular mechanical alterations and inflammatory responses in CECs through the RhoA/ROCK pathway.

Akt-activated GSK3β inhibitory peptide effectively blocks tau hyperphosphorylation

Tau hyperphosphorylation and accumulation in neurofibrillary tangles are closely associated with cognitive deficits in Alzheimer's disease (AD). Glycogen synthase kinase 3β (GSK3β) overexpression has been implicated in tau hyperphosphorylation, and many GSK3β inhibitors have been developed as potential therapeutic candidates for AD. However, the potent GSK3β inhibitors produced are prone to side effects because they can interfere with the basic functions of GSK3β. We previously found that when the phosphorylated PPPSPxS motifs in Wnt coreceptor LRP6 can directly inhibit GSK3β, and thus, we produced a novel GSK3β inhibitory peptide (GIP), specifically activated by Akt, by combining the PPPSPxS motif of LRP6 and the Akt targeted sequence (RxRxxS) of GSK3β. GIP effectively blocked GSK3β-induced tau phosphorylation in hippocampal homogenates and, when fused with a cell-permeable sequence, attenuated Aβ-induced tau phosphorylation in human neuroblastoma cells and inhibited cell death. An in vivo study using a 3 × Tg-AD mouse model revealed that intravenous GIP significantly reduced tau phosphorylation in the hippocampus without affecting Aβ plaque levels or neuroinflammation and ameliorated memory defects. The study provides a novel neuroprotective drug development strategy targeting tau hyperphosphorylation in AD.

The Dual Role of Amyloid Beta-Peptide in Oxidative Stress and Inflammation: Unveiling Their Connections in Alzheimer's Disease Etiopathology

Alzheimer's disease (AD) is a progressive neurodegenerative disease, and it is currently the seventh leading cause of death worldwide. It is characterized by the extracellular aggregation of the amyloid β-peptide (Aβ) into oligomers and fibrils that cause synaptotoxicity and neuronal death. Aβ exhibits a dual role in promoting oxidative stress and inflammation. This review aims to unravel the intricate connection between these processes and their contribution to AD progression. The review delves into oxidative stress in AD, focusing on the involvement of metals, mitochondrial dysfunction, and biomolecule oxidation. The distinct yet overlapping concept of nitro-oxidative stress is also discussed, detailing the roles of nitric oxide, mitochondrial perturbations, and their cumulative impact on Aβ production and neurotoxicity. Inflammation is examined through astroglia and microglia function, elucidating their response to Aβ and their contribution to oxidative stress within the AD brain. The blood-brain barrier and oligodendrocytes are also considered in the context of AD pathophysiology. We also review current diagnostic methodologies and emerging therapeutic strategies aimed at mitigating oxidative stress and inflammation, thereby offering potential treatments for halting or slowing AD progression. This comprehensive synthesis underscores the pivotal role of Aβ in bridging oxidative stress and inflammation, advancing our understanding of AD and informing future research and treatment paradigms.

A small TAT-TrkB peptide prevents BDNF receptor cleavage and restores synaptic physiology in Alzheimer's disease

In Alzheimer's disease (AD), amyloid β (Aβ)-triggered cleavage of TrkB-FL impairs brain-derived neurotrophic factor (BDNF) signaling, thereby compromising neuronal survival, differentiation, and synaptic transmission and plasticity. Using cerebrospinal fluid and postmortem human brain samples, we show that TrkB-FL cleavage occurs from the early stages of the disease and increases as a function of pathology severity. To explore the therapeutic potential of this disease mechanism, we designed small TAT-fused peptides and screened their ability to prevent TrkB-FL receptor cleavage. Among these, a TAT-TrkB peptide with a lysine-lysine linker prevented TrkB-FL cleavage both in vitro and in vivo and rescued synaptic deficits induced by oligomeric Aβ in hippocampal slices. Furthermore, this TAT-TrkB peptide improved the cognitive performance, ameliorated synaptic plasticity deficits and prevented Tau pathology progression in vivo in the 5XFAD mouse model of AD. No evidence of liver or kidney toxicity was found. We provide proof-of-concept evidence for the efficacy and safety of this therapeutic strategy and anticipate that this TAT-TrkB peptide has the potential to be a disease-modifying drug that can prevent and/or reverse cognitive deficits in patients with AD.

Carbon dots fluorescence can be used to distinguish isobaric peptide and to monitor protein oligomerization dynamics

Carbon dots (CD) are widely investigated particles with interesting fluorescent properties which are reported to be used for various purposes, as they are biocompatible, resistant to photobleaching and with tuneable properties depending on the specific CD surface chemistry. In this work, we report on the possibility to use opportunely designed CD to distinguish among isobaric peptides almost undistinguishable by mass spectrometry, as well as to monitor protein aggregation phenomena. Particularly, cell-penetrating peptides containing the carnosine moiety at different positions in the peptide chain produce sequence specific fluorescent signals. Analogously, different insulin oligomerization states can also be distinguished by the newly proposed experimental approach. The latter is here described in details and can be potentially applied to any kind of peptide or protein.

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.

An 11-mer Synthetic Peptide Suppressing Aggregation of Aβ25-35 and Resolving Its Aggregated Form Improves Test Performance in an Aβ25-35-Induced Alzheimer's Mouse Model

There is a high demand for the development of drugs against Alzheimer's disease (AD), which is related to the misfolding and aggregation of Amyloid-β (Aβ), due to the increasing number of patients with AD. In our present study, we aimed to assess the aggregation inhibitory effect of various synthetic YS-peptides on Aβ25-35 to identify an applicable peptide for clinical use for AD treatment and prevention. Suppression and aggregate resolution activities of YS-peptides against Aβ25-35 were evaluated using a Thioflavin T assay and scanning electron microscopy (SEM). Structure-activity relationship studies revealed that YS-RD11 (RETLVYLTHLD) and YS-RE16 (RETLVYLTHLDYDDTE) showed suppression and aggregate-resolution activities. The effect of YS-peptides on phagocytosis in microglial cells (BV-2 cells) demonstrated that YS-RD11 and YS-RE16 activated the phagocytic ability of microglia. In the Aβ25-35-induced AD mouse model, YS-RD11 prevented and improved the deficits in short-term memory. In conclusion, YS-RD11 is a suitable candidate therapeutic drug against AD and uses a strategy similar to that used for antibodies.

Elevated concentrations of amyloid-β oligomers and their proapoptotic effects on age-related cataract

Recently, amyloid-β oligomers (AβOs) have been studied as the primary pathogenic substances in Alzheimer's disease (AD). Our previous study revealed that the Aβ expression level is closely related to ARC progression. Here, we demonstrated that the accumulation of AβOs in the lens epithelium of age-related cataract (ARC) patients increased during ARC progression and that this alteration was consistent with the changes in mitochondrial function, oxidative stress, and cellular apoptosis. In vitro, human lens epithelial cells (HLECs) treated with AβOs exhibited Ca2+ dyshomeostasis, impaired mitochondrial function, elevated oxidative stress levels, and increased apoptosis. Moreover, the proapoptotic effect of AβOs was alleviated after the uptake of mitochondrial Ca2+ was inhibited. These results establish that AβOs may promote HLEC apoptosis by inducing mitochondrial Ca2+ overload, thus preliminarily revealing the possible association between the accumulation of AβOs and other pathological processes in ARC.

Protein aggregation: A detrimental symptom or an adaptation mechanism?

Protein quality control mechanisms oversee numerous aspects of protein lifetime. From the point of protein synthesis, protein homeostasis machineries take part in folding, solubilization, and/or degradation of impaired proteins. Some proteins follow an alternative path upon loss of their solubility, thus are secluded from the cytosol and form protein aggregates. Protein aggregates differ in their function and composition, rendering protein aggregation a complex phenomenon that continues to receive plenty of attention in the scientific and medical communities. Traditionally, protein aggregates have been associated with aging and a large spectrum of protein folding diseases, such as neurodegenerative diseases, type 2 diabetes, or cataract. However, a body of evidence suggests that they may act as an adaptive mechanism to overcome transient stressful conditions, serving as a sink for the removal of misfolded proteins from the cytosol or storage compartments for machineries required upon stress release. In this review, we present examples and evidence elaborating different possible roles of protein aggregation and discuss their potential roles in stress survival, aging, and disease, as well as possible anti-aggregation interventions.

Truncated GPNMB, a microglial transmembrane protein, serves as a scavenger receptor for oligomeric β-amyloid peptide1-42 in primary type 1 microglia

Glycoprotein non-metastatic melanoma protein B (GPNMB) is up-regulated in one subtype of microglia (MG) surrounding senile plaque depositions of amyloid-beta (Aβ) peptides. However, whether the microglial GPNMB can recognize the fibrous Aβ peptides as ligands remains unknown. In this study, we report that the truncated form of GPNMB, the antigen for 9F5, serves as a scavenger receptor for oligomeric Aβ1-42 (o-Aβ1-42) in rat primary type 1 MG. 125I-labeled o-Aβ1-42 exhibited specific and saturable endosomal/lysosomal degradation in primary-cultured type 1 MG from GPNMB-expressing wild-type mice, whereas the degradation activity was markedly reduced in cells from Gpnmb-knockout mice. The Gpnmb-siRNA significantly inhibits the degradation of 125I-o-Aβ1-42 by murine microglial MG5 cells. Therefore, GPNMB contributes to mouse MG's o-Aβ1-42 clearance. In rat primary type 1 MG, the cell surface expression of truncated GPNMB was confirmed by a flow cytometric analysis using a previously established 9F5 antibody. 125I-labeled o-Aβ1-42 underwent endosomal/lysosomal degradation by rat primary type 1 MG in a dose-dependent fashion, while the 9F5 antibody inhibited the degradation. The binding of 125I-o-Aβ1-42 to the rat primary type 1 MG was inhibited by 42% by excess unlabeled o-Aβ1-42, and by 52% by the 9F5 antibody. Interestingly, the 125I-o-Aβ1-42 degradations by MG-like cells from human-induced pluripotent stem cells was inhibited by the 9F5 antibody, suggesting that truncated GPNMB also serve as a scavenger receptor for o-Aβ1-42 in human MG. Our study demonstrates that the truncated GPNMB (the antigen for 9F5) binds to oligomeric form of Aβ1-42 and functions as a scavenger receptor on MG, and 9F5 antibody can act as a blocking antibody for the truncated GPNMB.

Mass spectrometry imaging highlights dynamic patterns of lipid co-expression with Aβ plaques in mouse and human brains

Lipids play crucial roles in the susceptibility and brain cellular responses to Alzheimer's disease (AD) and are increasingly considered potential soluble biomarkers in cerebrospinal fluid (CSF) and plasma. To delineate the pathological correlations of distinct lipid species, we conducted a comprehensive characterization of both spatially localized and global differences in brain lipid composition in AppNL-G-F mice with spatial and bulk mass spectrometry lipidomic profiling, using human amyloid-expressing (h-Aβ) and WT mouse brains controls. We observed age-dependent increases in lysophospholipids, bis(monoacylglycerol) phosphates, and phosphatidylglycerols around Aβ plaques in AppNL-G-F mice. Immunohistology-based co-localization identified associations between focal pro-inflammatory lipids, glial activation, and autophagic flux disruption. Likewise, in human donors with varying Braak stages, similar studies of cortical sections revealed co-expression of lysophospholipids and ceramides around Aβ plaques in AD (Braak stage V/VI) but not in earlier Braak stage controls. Our findings in mice provide evidence of temporally and spatially heterogeneous differences in lipid composition as local and global Aβ-related pathologies evolve. Observing similar lipidomic changes associated with pathological Aβ plaques in human AD tissue provides a foundation for understanding differences in CSF lipids with reported clinical stage or disease severity.

Oligomer Formation by Physiologically Relevant C-Terminal Isoforms of Amyloid β-Protein

Alzheimer's disease (AD) is a neurological disorder associated with amyloid β-protein (Aβ) assembly into toxic oligomers. In addition to the two predominant alloforms, Aβ1-40 and Aβ1-42, other C-terminally truncated Aβ peptides, including Aβ1-38 and Aβ1-43, are produced in the brain. Here, we use discrete molecular dynamics (DMD) and a four-bead protein model with amino acid-specific hydropathic interactions, DMD4B-HYDRA, to examine oligomer formation of Aβ1-38, Aβ1-40, Aβ1-42, and Aβ1-43. Self-assembly of 32 unstructured monomer peptides into oligomers is examined using 32 replica DMD trajectories for each of the four peptides. In a quasi-steady state, Aβ1-38 and Aβ1-40 adopt similar unimodal oligomer size distributions with a maximum at trimers, whereas Aβ1-42 and Aβ1-43 oligomer size distributions are multimodal with the dominant maximum at trimers or tetramers, and additional maxima at hexamers and unidecamers (for Aβ1-42) or octamers and pentadecamers (for Aβ1-43). The free energy landscapes reveal isoform- and oligomer-order specific structural and morphological features of oligomer ensembles. Our results show that oligomers of each of the four isoforms have unique features, with Aβ1-42 alone resulting in oligomers with disordered and solvent-exposed N-termini. Our findings help unravel the structure-function paradigm governing oligomers formed by various Aβ isoforms.

Hydrophobic C-Terminal Peptide Analog Aβ31-41 Protects the Neurons from Aβ-Induced Toxicity

Spontaneous aggregation of amyloid beta (Aβ) leads to the formation of neurotoxic senile plaque considered as the most crucial event in Alzheimer's disease (AD) progression. Inhibition or disruption of this deadly aggregate formation is one of the most efficient strategies for the development of potential therapeutics, and extensive research is in progress by various research groups. In this direction, the development of a peptide analogous to that of the native Aβ peptide is an attractive strategy. Based on this rationale, β-sheet breakers were developed from the Aβ central hydrophobic core. These peptide derivatives will bind to the full length of the parent Aβ and interfere in self-recognition, thereby preventing the folding of the Aβ peptide into cross β-sheet neurotoxic aggregates. However, this approach is effective in the inhibition of fibrillar aggregation, but this strategy is ineffective in the Aβ neurotoxic oligomer formation. Therefore, an alternative and efficient approach is to use the Aβ peptide analogous to the C-terminal region, which arbitrates fibrillation and oligomerization. Herein, we developed the Aβ C-terminal fragment (ACT-1 to ACT-7) for inhibition of oligomerization as well as fibrillar aggregation. Screening of these seven peptides resulted in an efficient anti-Aβ peptide aggregative agent (ACT-7), which was evaluated by the ThT assay peptide. The ThT assay reveals complete inhibition and showed significant neuroprotection of PC-12-derived neurons from Aβ-induced toxicity and reduced cell apoptosis. Further, analysis using CD and FTIR spectroscopy reveals that the ACT-7 peptide efficiently inhibits the formation of the β-sheet secondary structure content. HR-TEM microscopic analysis confirmed the inhibition of formation. Therefore, the inhibition of β-sheet Aβ fibrillary aggregation by the protease-stable ACT-7 peptide may provide a beneficial effect on AD treatment to control the Aβ aggregates. Finally, we anticipate that our newly designed ACT peptides may also assist as a template molecular scaffold for designing potential anti-AD therapeutics.

Protective effect of trehalose sugar on amyloid-membrane interactions using BLM electrophysiology

Alzheimer's disease (AD) is a neurodegenerative disease characterized by dementia and memory loss in the elderly population. The amyloid-β peptide (Aβ) is one of the main pathogenic factors in AD and is known to cause damage to neuronal cellular membranes. There is no cure currently available for AD, and new approaches, including preventive strategies, are highly desirable. In this work, we explore the possibility of protecting neuronal membranes from amyloid-induced damage with naturally existing sugar trehalose. Trehalose has been shown to protect plant cellular membranes in extreme conditions and modify Aβ misfolding. We hypothesize that trehalose can protect the neuronal membrane from amyloid toxicity. In this work, we studied the protective effect of trehalose against Aβ1-42-induced damage in model lipid membranes (DPPC/POPC/cholesterol) using atomic force microscopy and black lipid membrane electrophysiology. Our results demonstrate that Aβ1-42 damaged membranes and led to ionic current leakage across these membranes due to the formation of various defects and pores. The presence of trehalose reduced the ion current across membranes caused by Aβ1-42 peptide damage, thus efficiently protecting the membranes. These findings suggest that the trehalose sugar can potentially be useful in protecting neuronal membranes against amyloid toxicity in AD.

Exploring the Aβ1-42 fibrillogenesis timeline by atomic force microscopy and surface enhanced Raman spectroscopy

Introduction: Alzheimer's disease (AD) is a progressive debilitating neurological disorder representing the most common neurodegenerative disease worldwide. Although the exact pathogenic mechanisms of AD remain unresolved, the presence of extracellular amyloid-β peptide 1-42 (Aβ1-42) plaques in the parenchymal and cortical brain is considered one of the hallmarks of the disease. Methods: In this work, we investigated the Aβ1-42 fibrillogenesis timeline up to 48 h of incubation, providing morphological and chemo-structural characterization of the main assemblies formed during the aggregation process of Aβ1-42, by atomic force microscopy (AFM) and surface enhanced Raman spectroscopy (SERS), respectively. Results: AFM topography evidenced the presence of characteristic protofibrils at early-stages of aggregation, which form peculiar macromolecular networks over time. SERS allowed to track the progressive variation in the secondary structure of the aggregation species involved in the fibrillogenesis and to determine when the β-sheet starts to prevail over the random coil conformation in the aggregation process. Discussion: Our research highlights the significance of investigating the early phases of fibrillogenesis to better understand the molecular pathophysiology of AD and identify potential therapeutic targets that may prevent or slow down the aggregation process.

APOE2 protects against Aβ pathology by improving neuronal mitochondrial function through ERRα signaling

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disease and apolipoprotein E (APOE) genotypes (APOE2, APOE3, and APOE4) show different AD susceptibility. Previous studies indicated that individuals carrying the APOE2 allele reduce the risk of developing AD, which may be attributed to the potential neuroprotective role of APOE2. However, the mechanisms underlying the protective effects of APOE2 is still unclear.

METHODS

We analyzed single-nucleus RNA sequencing and bulk RNA sequencing data of APOE2 and APOE3 carriers from the Religious Orders Study and Memory and Aging Project (ROSMAP) cohort. We validated the findings in SH-SY5Y cells and AD model mice by evaluating mitochondrial functions and cognitive behaviors respectively.

RESULTS

The pathway analysis of six major cell types revealed a strong association between APOE2 and cellular stress and energy metabolism, particularly in excitatory and inhibitory neurons, which was found to be more pronounced in the presence of beta-amyloid (Aβ). Moreover, APOE2 overexpression alleviates Aβ1-42-induced mitochondrial dysfunction and reduces the generation of reactive oxygen species in SH-SY5Y cells. These protective effects may be due to ApoE2 interacting with estrogen-related receptor alpha (ERRα). ERRα overexpression by plasmids or activation by agonist was also found to show similar mitochondrial protective effects in Aβ1-42-stimulated SH-SY5Y cells. Additionally, ERRα agonist treatment improve the cognitive performance of Aβ injected mice in both Y maze and novel object recognition tests. ERRα agonist treatment increased PSD95 expression in the cortex of agonist-treated-AD mice.

CONCLUSIONS

APOE2 appears to enhance neural mitochondrial function via the activation of ERRα signaling, which may be the protective effect of APOE2 to treat AD.

Crystal Violet Selectively Detects Aβ Oligomers but Not Fibrils In Vitro and in Alzheimer's Disease Brain Tissue

Deposition of extracellular Amyloid Beta (Aβ) and intracellular tau fibrils in post-mortem brains remains the only way to conclusively confirm cases of Alzheimer's Disease (AD). Substantial evidence, though, implicates small globular oligomers instead of fibrils as relevant biomarkers of, and critical contributors to, the clinical symptoms of AD. Efforts to verify and utilize amyloid oligomers as AD biomarkers in vivo have been limited by the near-exclusive dependence on conformation-selective antibodies for oligomer detection. While antibodies have yielded critical evidence for the role of both Aβ and tau oligomers in AD, they are not suitable for imaging amyloid oligomers in vivo. Therefore, it would be desirable to identify a set of oligomer-selective small molecules for subsequent development into Positron Emission Tomography (PET) probes. Using a kinetics-based screening assay, we confirm that the triarylmethane dye Crystal Violet (CV) is oligomer-selective for Aβ42 oligomers (AβOs) grown under near-physiological solution conditions in vitro. In postmortem brains of an AD mouse model and human AD patients, we demonstrate that A11 antibody-positive oligomers but not Thioflavin S (ThioS)-positive fibrils colocalize with CV staining, confirming in vitro results. Therefore, our kinetic screen represents a robust approach for identifying new classes of small molecules as candidates for oligomer-selective dyes (OSDs). Such OSDs, in turn, provide promising starting points for the development of PET probes for pre-mortem imaging of oligomer deposits in humans.

Pirh2 modulates the mitochondrial function and cytochrome c-mediated neuronal death during Alzheimer's disease

Pirh2 is an E3 ubiquitin ligase known to regulate the DNA damage responses through ubiquitylation of various participating signaling factors. DNA damage is a key pathological contributor to Alzheimer's disease (AD), therefore, the role of Pirh2 was investigated in streptozotocin and oligomer Aβ1-42 induced rodent experimental model of AD. Pirh2 protein abundance increased during AD conditions, and transient silencing of Pirh2 inhibited the disease-specific pathological markers like level of p-Tau, βamyloid, acetylcholinesterase activity, and neuronal death. Biochemically, Pirh2 silencing significantly attenuated the oxidative stress, depleted mitochondrial membrane potential, cytochrome c translocation from mitochondria to cytosol, and depleted mitochondrial complex-I activity, and ATP level. Pirh2 silencing also inhibited the altered level of VDAC1, hsp75, hexokinase1, t-Bid, caspase-9, and altered level of apoptotic proteins (Bcl-2, Bax). MALDI-TOF/TOF, co-immunoprecipitation, and UbcH13-linked ubiquitylation assay confirmed the interaction of Pirh2 with cytochrome c and the role of Pirh2 in ubiquitylation of cytochrome c, along with Pirh2-dependent altered proteasome activity. Additionally, Pirh2 silencing further inhibited the translocation of mitochondrion-specific endonuclease G and apoptosis-inducing factors to the nucleus and DNA damage. In conclusion, findings suggested the significant implication of Pirh2 in disease pathogenesis, particularly through impaired mitochondrial function, including biochemical alterations, translocation of cytochrome c, endonuclease G and apoptosis-inducing factor, DNA damage, and neuronal apoptosis.

Aging and brain free cholesterol concentration on amyloid-β peptide accumulation in guinea pigs

Alzheimer's disease is a complex multifactorial neurodegenerative disorder wherein age is a major risk factor. The appropriateness of the Hartley guinea pig (GP), which displays high sequence homologies of its amyloid-β (Aβ40 and Aβ42) peptides, Mdr1 and APP (amyloid precursor protein) and similarity in lipid handling to humans, was appraised among 9-40 weeks old guinea pigs. Protein expression levels of P-gp (Abcb1) and Cyp46a1 (24(S)-hydroxylase) for Aβ40, and Aβ42 efflux and cholesterol metabolism, respectively, were decreased with age, whereas those for Lrp1 (low-density lipoprotein receptor related protein 1), Rage (receptor for advanced glycation endproducts) for Aβ efflux and influx, respectively, and Abca1 (the ATP binding cassette subfamily A member 1) for cholesterol efflux, were unchanged among the ages examined. There was a strong, negative correlation of the brain Aβ peptide concentrations and Abca1 protein expression levels with free cholesterol. The correlation of Aβ peptide concentrations with Cyp46a1 was, however, not significant, and concentrations of the 24(S)-hydroxycholesterol metabolite revealed a decreasing trend from 20 weeks old toward 40 weeks old guinea pigs. The composite data suggest a role for free cholesterol on brain Aβ accumulation. The decreases in P-gp and Lrp1 protein levels should further exacerbate the accumulation of Aβ peptides in guinea pig brain.

Alzheimer's Disease: A Review of Pathology, Current Treatments, and the Potential Therapeutic Effect of Decreasing Oxidative Stress by Combined Vitamin D and l-Cysteine Supplementation

Significance: Excess oxidative stress and neuroinflammation are risk factors in the onset and progression of Alzheimer's disease (AD) and its association with amyloid-β plaque accumulation. Oxidative stress impairs acetylcholine (ACH) and N-methyl-d-aspartate receptor signaling in brain areas that function in memory and learning. Glutathione (GSH) antioxidant depletion positively correlates with the cognitive decline in AD subjects. Treatments that upregulate GSH and ACH levels, which simultaneously decrease oxidative stress and inflammation, may be beneficial for AD. Recent Advances: Some clinical trials have shown a benefit of monotherapy with vitamin D (VD), whose deficiency is linked to AD or with l-cysteine (LC), a precursor of GSH biosynthesis, in reducing mild cognitive impairment. Animal studies have shown a simultaneous decrease in ACH esterase (AChE) and increase in GSH; combined supplementation with VD and LC results in a greater decrease in oxidative stress and inflammation, and increase in GSH levels compared with monotherapy with VD or LC. Therefore, cosupplementation with VD and LC has the potential of increasing GSH, downregulation of oxidative stress, and decreased inflammation and AChE levels. Future Directions: Clinical trials are needed to determine whether safe low-cost dietary supplements, using combined VD+LC, have the potential to alleviate elevated AChE, oxidative stress, and inflammation levels, thereby halting the onset of AD. Goal of Review: The goal of this review is to highlight the pathological hallmarks and current Food and Drug Administration-approved treatments for AD, and discuss the potential therapeutic effect that cosupplementation with VD+LC could manifest by increasing GSH levels in patients. Antioxid. Redox Signal. 40, 663-678.

Synthesis of symmetrical and unsymmetrical tetrahydroxybiphenyls and their evaluation as amyloid-β aggregation inhibitors

Our group recently reported that the polyhydroxy aromatic compound 3,3',4,4'-biphenyltetrol (2a) is a successful inhibitor of amyloid-β peptide (Aβ) aggregation, decreasing Aβ aggregation by 50 % when present in equimolar concentrations. In the present study, several additional biphenyltetrols were prepared and examined for their in vitro activity against aggregation of Aβ, to investigate the effect of the relative positions of hydrogen-bond donors on the aggregation process. Congo red spectral shift assays have shown that, of the eight (8) additional biphenyltetrol compounds prepared, three (3) successfully inhibit association of Aβ monomers - two symmetrical isomers, 2,2',5,5'-biphenyltetrol (2c), and 2,2',3,3'-biphenyltetrol (2d), along with one unsymmetrical isomer, 2,3',4',5-biphenyltetrol (2g). These results, along with previously reported results of 2a, strongly suggest that hydroxyl group position affects the ability of the inhibitor to bind to Aβ assemblies, thus impacting inhibitory efficacy.

Impact of nanoplastics on Alzheimer 's disease: Enhanced amyloid-β peptide aggregation and augmented neurotoxicity

Nanoplastics, widely existing in the environment and organisms, have been proven to cross the blood-brain barrier, increasing the incidence of neurodegenerative diseases like Alzheimer's disease (AD). However, current studies mainly focus on the neurotoxicity of nanoplastics themselves, neglecting their synergistic effects with other biomolecules and the resulting neurotoxicity. Amyloid β peptide (Aβ), which triggers neurotoxicity through its self-aggregation, is the paramount pathogenic protein in AD. Here, employing polystyrene nanoparticles (PS) as a model for nanoplastics, we reveal that 100 pM PS nanoparticles significantly accelerate the nucleation rate of two Aβ subtypes (Aβ40 and Aβ42) at low concentrations, promoting the formation of more Aβ oligomers and leading to evident neurotoxicity. The hydrophobic surface of PS facilitates the interaction of hydrophobic fragments between Aβ monomers, responsible for the augmented neurotoxicity. This work provides consequential insights into the modulatory impact of low-dose PS on Aβ aggregation and the ensuing neurotoxicity, presenting a valuable foundation for future research on the intricate interplay between environmental toxins and brain diseases.

A Biomimic Nanobullet with Ameliorative Inflammatory Microenvironment for Alzheimer's Disease Treatments

Aβ oligomers, formed prior to diagnostic marker-amyloid β (Aβ) plaques, can damage neurons and trigger neuroinflammation, which accelerate the neuronal injury in Alzheimer's disease (AD). Herein, the combination of eliminating the Aβ oligomers and alleviating the inflammation is a promising therapeutic strategy for AD. However, the presence of the blood-brain barrier (BBB) and the intrinsic deficiencies of the drugs severely restrict their therapeutic effects. Inspired by the properties of rabies virus, a biomimic nanobullet (PBACR@NRs/SA) targeting neurons has been developed. The biomimic nanobullets possess the BBB penetrating character based on iron oxide nanorods; it can sequentially release rosmarinic acid and small interfering RNA targeting NF-κB triggered by microenvironment, which improve the microenvironment inflammation and realize the cure for AD. Compared with non-biomimic systems, the biomimic nanobullets exhibit a less caveolin-dependent internalization pathway, which reduces ROS production and mitochondrial fission in neurons. Therefore, the biomimic nanobullet is hopeful for the treatment of ADs and provides a promising platform for other brain diseases' treatments.

Molecular Insights into the Inhibition and Disaggregation Effects of EGCG on Aβ40 and Aβ42 Cofibrillation

The misfolding and aggregation of amyloid-β (Aβ) peptides play a pivotal role in the pathogenesis of Alzheimer's disease (AD). Aβ40 and Aβ42, the two primary isoforms of Aβ, can not only self-aggregate into homogeneous aggregates but also coaggregate to form mixed fibrils. Epigallocatechin-3-gallate (EGCG), a prominent tea polyphenol, has shown the capability to prevent the self-aggregation of Aβ40 and Aβ42 peptides and disaggregate their homogeneous fibrils. However, its effects on the cofibrillation of Aβ40 and Aβ42 have not yet been explored. Here, we employed molecular dynamic simulations to investigate the effects of EGCG on the coaggregation of Aβ40 and Aβ42, as well as on their mixed fibril. Our findings indicated that EGCG effectively inhibits the codimerization of Aβ40 and Aβ42 primarily by impeding the interchain interaction between the two isoforms. The key binding sites for EGCG on Aβ40 and Aβ42 are the polar residues and aromatic residues, engaging in hydrogen-bond , π-π, and cation-π interactions with EGCG. Additionally, EGCG disaggregates the Aβ40-Aβ42 mixed fibril by reducing its long-range interaction through similar binding sites and interactions as those between EGCG and Aβ40-Aβ42 heterodimers. Our research reveals the comprehensive inhibition and disaggregation effects of EGCG on the cofibrillation of Aβ isoforms, which provides further support for the development of EGCG as an effective antiaggregation agent for AD.

Copper(II) Can Kinetically Trap Arctic and Italian Amyloid-β40 as Toxic Oligomers, Mimicking Cu(II) Binding to Wild-Type Amyloid-β42: Implications for Familial Alzheimer's Disease

The self-association of amyloid-β (Aβ) peptide into neurotoxic oligomers is believed to be central to Alzheimer's disease (AD). Copper is known to impact Aβ assembly, while disrupted copper homeostasis impacts phenotype in Alzheimer's models. Here we show the presence of substoichiometric Cu(II) has very different impacts on the assembly of Aβ40 and Aβ42 isoforms. Globally fitting microscopic rate constants for fibril assembly indicates copper will accelerate fibril formation of Aβ40 by increasing primary nucleation, while seeding experiments confirm that elongation and secondary nucleation rates are unaffected by Cu(II). In marked contrast, Cu(II) traps Aβ42 as prefibrillar oligomers and curvilinear protofibrils. Remarkably, the Cu(II) addition to preformed Aβ42 fibrils causes the disassembly of fibrils back to protofibrils and oligomers. The very different behaviors of the two Aβ isoforms are centered around differences in their fibril structures, as highlighted by studies of C-terminally amidated Aβ42. Arctic and Italian familiar mutations also support a key role for fibril structure in the interplay of Cu(II) with Aβ40/42 isoforms. The Cu(II) dependent switch in behavior between nonpathogenic Aβ40 wild-type and Aβ40 Arctic or Italian mutants suggests heightened neurotoxicity may be linked to the impact of physiological Cu(II), which traps these familial mutants as oligomers and curvilinear protofibrils, which cause membrane permeability and Ca(II) cellular influx.

A Novel Drosophila Model of Alzheimer's Disease to Study Aβ Proteotoxicity in the Digestive Tract

Amyloid-β (Aβ) proteotoxicity is associated with Alzheimer's disease (AD) and is caused by protein aggregation, resulting in neuronal damage in the brain. In the search for novel treatments, Drosophila melanogaster has been extensively used to screen for anti-Aβ proteotoxic agents in studies where toxic Aβ peptides are expressed in the fly brain. Since drug molecules often are administered orally there is a risk that they fail to reach the brain, due to their inability to cross the brain barrier. To circumvent this problem, we have designed a novel Drosophila model that expresses the Aβ peptides in the digestive tract. In addition, a built-in apoptotic sensor provides a fluorescent signal from the green fluorescent protein as a response to caspase activity. We found that expressing different variants of Aβ1-42 resulted in proteotoxic phenotypes such as reduced longevity, aggregate deposition, and the presence of apoptotic cells. Taken together, this gut-based Aβ-expressing fly model can be used to study the mechanisms behind Aβ proteotoxicity and to identify different substances that can modify Aβ proteotoxicity.

Protein Corona Formation and Aggregation of Amyloid β 1-40-Coated Gold Nanocolloids

Amyloid fibrillogenesis is a pathogenic protein aggregation process that occurs through a highly ordered process of protein-protein interactions. To better understand the protein-protein interactions involved in amyloid fibril formation, we formed nanogold colloid aggregates by stepwise additions of ∼2 nmol of amyloid β 1-40 peptide (Aβ1-40) at pH ∼3.7 and ∼25 °C. The processes of protein corona formation and building of gold colloid [diameters (d) of 20 and 80 nm] aggregates were confirmed by a red-shift of the surface plasmon resonance (SPR) band, λpeak, as the number of Aβ1-40 peptides [N(Aβ1-40)] increased. The normalized red-shift of λpeak, Δλ, was correlated with the degree of protein aggregation, and this process was approximated as the adsorption isotherm explained by the Langmuir-Freundlich model. As the coverage fraction (θ) was analyzed as a function of ϕ, which is the N(Aβ1-40) per total surface area of nanogold colloids available for adsorption, the parameters for explaining the Langmuir-Freundlich model were in good agreement for both 20 and 80 nm gold, indicating that ϕ could define the stage of the aggregation process. Surface-enhanced Raman scattering (SERS) imaging was conducted at designated values of ϕ and suggested that a protein-gold surface interaction during the initial adsorption stage may be dependent on the nanosize. The 20 nm gold case seems to prefer a relatively smaller contacting section, such as a -C-N or C═C bond, but a plane of the benzene ring may play a significant role for 80 nm gold. Regardless of the size of the particles, the β-sheet and random coil conformations were considered to be used to form gold colloid aggregates. The methodology developed in this study allows for new insights into protein-protein interactions at distinct stages of aggregation.

A single-domain antibody detects and neutralises toxic Aβ42 oligomers in the Alzheimer's disease CSF

BACKGROUND

Amyloid-β42 (Aβ42) aggregation consists of a complex chain of nucleation events producing soluble oligomeric intermediates, which are considered the major neurotoxic agents in Alzheimer's disease (AD). Cerebral lesions in the brain of AD patients start to develop 20 years before symptom onset; however, no preventive strategies, effective treatments, or specific and sensitive diagnostic tests to identify people with early-stage AD are currently available. In addition, the isolation and characterisation of neurotoxic Aβ42 oligomers are particularly difficult because of their transient and heterogeneous nature. To overcome this challenge, a rationally designed method generated a single-domain antibody (sdAb), named DesAb-O, targeting Aβ42 oligomers.

METHODS

We investigated the ability of DesAb-O to selectively detect preformed Aβ42 oligomers both in vitro and in cultured neuronal cells, by using dot-blot, ELISA immunoassay and super-resolution STED microscopy, and to counteract the toxicity induced by the oligomers, monitoring their interaction with neuronal membrane and the resulting mitochondrial impairment. We then applied this approach to CSF samples (CSFs) from AD patients as compared to age-matched control subjects.

RESULTS

DesAb-O was found to selectively detect synthetic Aβ42 oligomers both in vitro and in cultured cells, and to neutralise their associated neuronal dysfunction. DesAb-O can also identify Aβ42 oligomers present in the CSFs of AD patients with respect to healthy individuals, and completely prevent cell dysfunction induced by the administration of CSFs to neuronal cells.

CONCLUSIONS

Taken together, our data indicate a promising method for the improvement of an early diagnosis of AD and for the generation of novel therapeutic approaches based on sdAbs for the treatment of AD and other devastating neurodegenerative conditions.

Coordination Chemistry of Sulfur-Containing Bifunctional Chelators: Toward in Vivo Stabilization of 64Cu PET Imaging Agents for Alzheimer's Disease

The broader utilization of 64Cu positron emission tomography (PET) imaging agents has been hindered by the unproductive demetalation induced by bioreductants. To advance the development of 64Cu-based PET imaging tracers for Alzheimer's Disease (AD), there is a need for novel ligand design strategies. In this study, we developed sulfur-containing dithiapyridinophane (N2S2) bifunctional chelators (BFCs) as well as all nitrogen-based diazapyridinophane (N4) BFCs to compare their abilities to chelate Cu and target Aβ aggregates. Through spectrophotometric titrations and electrochemical measurements, we have demonstrated that the N2S2-based BFCs exhibit >10 orders of magnitude higher binding affinity toward Cu(I) compared to their N4-based counterparts, while both types of BFCs exhibit high stability constants toward Cu(II). Notably, solid state structures for both Cu(II) and Cu(I) complexes supported by the two ligand frameworks were obtained, providing molecular insights into their copper chelating abilities. Aβ binding experiments were conducted to study the structure-affinity relationship, and fluorescence microscopy imaging studies confirmed the selective labeling of the BFCs and their copper complexes. Furthermore, we investigated the potential of these ligands for the 64Cu-based PET imaging of AD through radiolabeling and autoradiography studies. We believe our findings provide molecular insights into the design of bifunctional Cu chelators that can effectively stabilize both Cu(II) and Cu(I) and, thus, can have significant implications for the development of 64Cu PET imaging as a diagnostic tool for AD.

Ligand Profiling to Characterize Different Polymorphic Forms of α-Synuclein Aggregates

The presence of amyloid fibrils is a characteristic feature of many diseases, most famously neurodegenerative disease. The supramolecular structure of these fibrils appears to be disease-specific. Identifying the unique morphologies of amyloid fibrils could, therefore, form the basis of a diagnostic tool. Here we report a method to characterize the morphology of α-synuclein (αSyn) fibrils based on profiling multiple different ligand binding sites that are present on the surfaces of fibrils. By employing various competition binding assays, seven different types of binding sites were identified on four different morphologies of αSyn fibrils. Similar binding sites on different fibrils were shown to bind ligands with significantly different affinities. We combined this information to construct individual profiles for different αSyn fibrils based on the distribution of binding sites and ligand interactions. These results demonstrate that ligand-based profiling can be used as an analytical method to characterize fibril morphologies with operationally simple fluorescence binding assays.

An in situ and in vitro investigation of cytoplasmic TDP-43 inclusions reveals the absence of a clear amyloid signature

Introduction: Several neurodegenerative conditions are associated with a common histopathology within neurons of the central nervous system, consisting of the deposition of cytoplasmic inclusions of TAR DNA-binding protein 43 (TDP-43). Such inclusions have variably been described as morphologically and molecularly ordered aggregates having amyloid properties, as filaments without the cross-β-structure and dye binding specific for amyloid, or as amorphous aggregates with no defined structure and fibrillar morphology.Aims and Methods: Here we have expressed human full-length TDP-43 in neuroblastoma x spinal cord 34 (NSC-34) cells to investigate the morphological, structural, and tinctorial properties of TDP-43 inclusions in situ. We have used last-generation amyloid diagnostic probes able to cross the cell membrane and detect amyloid in the cytoplasm and have adopted Raman and Fourier transform infrared microspectroscopies to study in situ the secondary structure of the TDP-43 protein in the inclusions. We have then used transmission electron microscopy to study the morphology of the TDP-43 inclusions.Results: The results show the absence of amyloid dye binding, the lack of an enrichment of cross-β structure in the inclusions, and of a fibrillar texture in the round inclusions. The aggregates formed in vitro from the purified protein under conditions in which it is initially native also lack all these characteristics, ruling out a clear amyloid-like signature.Conclusions: These findings indicate a low propensity of TDP-43 to form amyloid fibrils and even non-amyloid filaments, under conditions in which the protein is initially native and undergoes its typical nucleus-to-cell mislocalization. It cannot be excluded that filaments emerge on the long time scale from such inclusions, but the high propensity of the protein to form initially other types of inclusions appear to be an essential characteristic of TDP-43 proteinopathies.KEY MESSAGESCytoplasmic inclusions of TDP-43 formed in NSC-34 cells do not stain with amyloid-diagnostic dyes, are not enriched with cross-β structure, and do not show a fibrillar morphology.TDP-43 assemblies formed in vitro from pure TDP-43 do not have any hallmarks of amyloid.

Curcumin Reduces Amyloid Beta Oligomer Interactions with Anionic Membranes

Many neurodegenerative diseases involve amyloidogenic proteins forming surface-bound aggregates on anionic membranes, and the peptide amyloid β (Aβ) in Alzheimer's disease is one prominent example of this. Curcumin is a small polyphenolic molecule that provides an interesting opportunity to understand the fundamental mechanisms of membrane-mediated aggregation because it embeds into membranes to alter their structure while also altering Aβ aggregation in an aqueous environment. The purpose of this work was to understand interactions among curcumin, β-sheet-rich Aβ fibrillar oligomers (FO), and a model anionic membrane. From a combination of liquid surface X-ray scattering experiments and molecular dynamics simulations, we found that curcumin embedded into an anionic 1,2-dimyristoyl-sn-glycero-3-phosphorylglycerol (DMPG) membrane to rest between the lipid headgroups and the tails, causing disorder and membrane thinning. FO accumulation on the membrane was reduced by ∼66% in the presence of curcumin, likely influenced by membrane thinning. Simulation results suggested curcumin clusters near exposed phenylalanine residues on a membrane-embedded FO structure. Altogether, curcumin inhibited FO interactions with a DMPG membrane, likely through a combination of altered membrane structure and interactions with the FO surface. This work elucidates the mechanism of curcumin as a small molecule that inhibits amyloidogenesis through a combination of both membrane and protein interactions.

The bexarotene derivative OAB-14 ameliorates cognitive decline in APP/PS1 transgenic mice by suppressing microglia-mediated neuroinflammation through the PPAR-γ pathway

Neuroinflammation is believed to be a critical process involved in the pathophysiology of Alzheimer's disease (AD). In this study, we investigated the pharmacological ability of OAB-14, a small molecule compound derived from bexarotene, to reduce neuroinflammation and improve cognitive decline in an AD mouse model (in vivo) and its ability to regulate signaling pathways implicated in neuroinflammation in vitro. It was found that OAB-14 significantly improved the cognitive function of 11-month-old AD mice (APP/PS1 transgenic mice) in a dose-dependent manner. Simultaneously, OAB-14 dramatically inhibited the activation of microglia in the cerebral cortex and hippocampus of AD mice and dose-dependently downregulated the expression of nuclear factor kappa B (NF-κB) and NOD-like receptor protein 3 (NLRP3) in the cerebral cortex. At the cellular level, OAB-14 reversed the downregulation of M2 phenotypic markers, including mannose receptor C-type 1 (MRC1) and arginase 1 (ARG1), in lipopolysaccharide (LPS)- or amyloid-β protein oligomer (oAβ1-42)-activated BV2 microglial cells and partially restored their ability to clear Aβ. However, these effects were suppressed when peroxisome proliferator-activated receptor-γ (PPAR-γ) was specifically inhibited by GW9662, a selective PPAR-γ antagonist. These results suggested that OAB-14 could regulate microglial polarization by regulating PPAR-γ signaling, thereby mitigating neuroinflammation and improving cognitive function in AD mice.

Administration of amyloid-β oligomer to the buccal ganglia may reduce food intake and cholinergic synaptic responses within the feeding neural circuit in Aplysia kurodai

Anorexia is a behavioral change caused by functional brain disorders in patients with Alzheimer's disease (AD). Amyloid-β (1-42) oligomers (o-Aβ) are possible causative agents of AD that impair signaling via synaptic dysfunction. In this study, we used Aplysia kurodai to study functional disorders of the brain through o-Aβ. Administration of o-Aβ to the buccal ganglia (feeding brain for oral movements) by surgical treatment significantly reduced food intake for at least five days. Furthermore, we explored the effects of o-Aβ on the synaptic function in the feeding neural circuit, focusing on a specific inhibitory synaptic response in jaw-closing motor neurons produced by cholinergic buccal multi-action neurons because we recently found that this cholinergic response decreases with aging, which is consistent with the cholinergic hypothesis for aging. Administration of o-Aβ to the buccal ganglia significantly reduced the synaptic response within minutes, whereas administration of amyloid-β (1-42) monomers did not. These results suggest that o-Aβ may impair the cholinergic synapses, even in Aplysia, which is consistent with the cholinergic hypothesis for AD.

PACAP-Sirtuin3 alleviates cognitive impairment through autophagy in Alzheimer's disease

BACKGROUND

Autophagy is vital in the pathogenesis of neurodegeneration. Thus far, no studies have specifically investigated the relationship between pituitary adenylate cyclase-activating polypeptide (PACAP) and autophagy, particularly in the context of Alzheimer's disease (AD). This study used in vitro and in vivo models, along with clinical samples, to explore interactions between PACAP and autophagy in AD.

METHODS

AD model mice were administered 6 μl of 0.1 mg/ml PACAP liquid intranasally for 4 weeks, then subjected to behavioral analyses to assess the benefits of PACAP treatment. The underlying mechanisms of PACAP-induced effects were investigated by methods including real-time quantitative polymerase chain reaction, RNA sequencing, immunofluorescence, and western blotting. Exosomes were extracted from human serum and subjected to enzyme-linked immunosorbent assays to examine autophagy pathways. The clinical and therapeutic implications of PACAP and autophagy were extensively investigated throughout the experiment.

RESULTS

Impaired autophagy was a critical step in amyloid β (Aβ) and Tau deposition; PACAP enhanced autophagy and attenuated cognitive impairment. RNA sequencing revealed three pathways that may be involved in AD progression: PI3K-AKT, mTOR, and AMPK. In vivo and in vitro studies showed that sirtuin3 knockdown diminished the ability of PACAP to restore normal autophagy function, resulting in phagocytosis dysregulation and the accumulation of pTau, Tau, and Aβ. Additionally, the autophagic biomarker MAP1LC3 demonstrated a positive association with PACAP in human serum.

CONCLUSIONS

PACAP reverses AD-induced cognitive impairment through autophagy, using sirtuin3 as a key mediator. MAP1LC3 has a positive relationship with PACAP in humans. These findings provide insights regarding potential uses of intranasal PACAP and sirtuin3 agonists in AD treatment.

TRIAL REGISTRATION

NCT04320368.

IM-MS and ECD-MS/MS Provide Insight into Modulation of Amyloid Proteins Self-Assembly by Peptides and Small Molecules

Neurodegenerative proteinopathies are characterized by formation and deposition of misfolded, aggregated proteins in the nervous system leading to neuronal dysfunction and death. It is widely believed that metastable oligomers of the offending proteins, preceding the fibrillar aggregates found in the tissue, are the proximal neurotoxins. There are currently almost no disease-modifying therapies for these diseases despite an active pipeline of preclinical development and clinical trials for over two decades, largely because studying the metastable oligomers and their interaction with potential therapeutics is notoriously difficult. Mass spectrometry (MS) is a powerful analytical tool for structural investigation of proteins, including protein-protein and protein-ligand interactions. Specific MS tools have been useful in determining the composition and conformation of abnormal protein oligomers involved in proteinopathies and the way they interact with drug candidates. Here, we analyze critically the utilization of ion-mobility spectroscopy-MS (IM-MS) and electron-capture dissociation (ECD) MS/MS for analyzing the oligomerization and conformation of multiple amyloidogenic proteins. We also discuss IM-MS investigation of their interaction with two classes of compounds developed by our group over the last two decades: C-terminal fragments derived from the 42-residue form of amyloid β-protein (Aβ42) and molecular tweezers. Finally, we review the utilization of ECD-MS/MS for elucidating the binding sites of the ligands on multiple proteins. These approaches are readily applicable to future studies addressing similar questions and hold promise for facilitating the development of successful disease-modifying drugs against neurodegenerative proteinopathies.

APPI-Derived Cyclic Peptide Enhances Aβ42 Aggregation and Reduces Aβ42-Mediated Membrane Destabilization and Cytotoxicity

An amyloid precursor protein inhibitor (APPI) and amyloid beta 42 (Aβ42) are both subdomains of the human transmembrane amyloid precursor protein (APP). In the brains of patients with Alzheimer's disease (AD), Aβ42 oligomerizes into aggregates of various sizes, with intermediate, low-molecular-weight Aβ42 oligomers currently being held to be the species responsible for the most neurotoxic effects associated with the disease. Strategies to ameliorate the toxicity of these intermediate Aβ42 oligomeric species include the use of short, Aβ42-interacting peptides that either inhibit the formation of the Aβ42 oligomeric species or promote their conversion to high-molecular-weight aggregates. We therefore designed such an Aβ42-interacting peptide that is based on the β-hairpin amino acid sequence of the APPI, which exhibits high similarity to the β-sheet-like aggregation site of Aβ42. Upon tight binding of this 20-mer cyclic peptide to Aβ42 (in a 1:1 molar ratio), the formation of Aβ42 aggregates was enhanced, and consequently, Aβ42-mediated cell toxicity was ameliorated. We showed that in the presence of the cyclic peptide, interactions of Aβ42 with both plasma and mitochondrial membranes and with phospholipid vesicles that mimic these membranes were inhibited. Specifically, the cyclic peptide inhibited Aβ42-mediated mitochondrial membrane depolarization and reduced Aβ42-mediated apoptosis and cell death. We suggest that the cyclic peptide modulates Aβ42 aggregation by enhancing the formation of large aggregates─as opposed to low-molecular-weight intermediates─and as such has the potential for further development as an AD therapeutic.

Amyloid-β slows cilia movement along the ventricle, impairs fluid flow, and exacerbates its neurotoxicity in explant culture

Alzheimer's disease (AD) is characterized by extensive and selective death of neurons and deterioration of synapses and circuits in the brain. The Aβ1-42 concentration is higher in an AD brain than in cognitively normal elderly individuals, and Aβ1-42 exhibits neurotoxicity. Brain-derived Aβ is transported into the cerebrospinal fluid (CSF), and CSF flow is driven in part by the beating of cilia and CSF secretion into ventricles. Ventricles are lined with ependyma whose apical surface is covered with motile cilia. Herein, we constructed an experimental system to measure the movement of ependymal cilia and examined the effects of Aβ1-42 to the beating of cilia and neurons. The circadian rhythm of the beating frequency of ependymal cilia was detected using brain wall explant-cultures containing ependymal cilia and neurons; the beating frequency was high at midday and low at midnight. Aβ1-42 decreased the peak frequency of ciliary beating at midday and slightly increased it at midnight. Aβ1-42 exhibited neurotoxicity to neurons on the non-ciliated side of the explant culture, while the neurotoxicity was less evident in neurons on the ciliated side. The neurotoxic effect of Aβ1-42 was diminished when 1 mPa of shear stress was generated using a flow chamber system that mimicked the flow by cilia. These results indicate that Aβ1-42 affects the circadian rhythm of ciliary beating, decreases the medium flow by the cilia-beating, and enhances the neurotoxic action of Aβ1-42 in the brain explant culture.

Nanoscale reorganisation of synaptic proteins in Alzheimer's disease

AIMS

Synaptic strength depends strongly on the subsynaptic organisation of presynaptic transmitter release and postsynaptic receptor densities, and their alterations are expected to underlie pathologies. Although synaptic dysfunctions are common pathogenic traits of Alzheimer's disease (AD), it remains unknown whether synaptic protein nano-organisation is altered in AD. Here, we systematically characterised the alterations in the subsynaptic organisation in cellular and mouse models of AD.

METHODS

We used immunostaining and super-resolution stochastic optical reconstruction microscopy imaging to quantitatively examine the synaptic protein nano-organisation in both Aβ1-42-treated neuronal cultures and cortical sections from a mouse model of AD, APP23 mice.

RESULTS

We found that Aβ1-42-treatment of cultured hippocampal neurons decreased the synaptic retention of postsynaptic scaffolds and receptors and disrupted their nanoscale alignment to presynaptic transmitter release sites. In cortical sections, we found that while GluA1 receptors in wild-type mice were organised in subsynaptic nanoclusters with high local densities, receptors in APP23 mice distributed more homogeneously within synapses. This reorganisation, together with the reduced overall receptor density, led to reduced glutamatergic synaptic transmission. Meanwhile, the transsynaptic alignment between presynaptic release-guiding RIM1/2 and postsynaptic scaffolding protein PSD-95 was reduced in APP23 mice. Importantly, these reorganisations were progressive with age and were more pronounced in synapses in close vicinity of Aβ plaques with dense cores.

CONCLUSIONS

Our study revealed a spatiotemporal-specific reorganisation of synaptic nanostructures in AD and identifies dense-core amyloid plaques as the major local inductor in APP23 mice.