Oligomeric Aggregates Research Articles

Mechanistic insights into the role of amyloid-β in innate immunity

Colocalization of microbial pathogens and the β-amyloid peptide (Aβ) in the brain of Alzheimer’s disease (AD) patients suggests that microbial infection may play a role in sporadic AD. Aβ exhibits antimicrobial activity against numerous pathogens, supporting a potential role for Aβ in the innate immune response. While mammalian amyloid is associated with disease, many bacteria form amyloid fibrils to fortify the biofilm that protects the cells from the surrounding environment. In the microbial AD hypothesis, Aβ aggregates in response to infection to combat the pathogen. We hypothesize that this occurs through toxic Aβ oligomers that contain α-sheet structure and form prior to fibrillization. De novo designed α-sheet peptides specifically bind to the α-sheet structure present in the oligomers of both bacterial and mammalian amyloidogenic proteins to neutralize toxicity and inhibit aggregation. Here, we measure the effect of E. coli on Aβ, including upregulation, aggregation, and toxicity. Additionally, we determined the effect of Aβ structure on E. coli amyloid fibrils, or curli comprised of the CsgA protein, and biofilm formation. We found that curli formation by E. coli increased Aβ oligomer production, and Aβ oligomers inhibited curli biogenesis and reduced biofilm cell density. Further, curli and biofilm inhibition by Aβ oligomers increased E. coli susceptibility to gentamicin. Toxic oligomers of Aβ and CsgA interact via α-sheet interactions, neutralizing their toxicity. These results suggest that exposure to toxic oligomers formed by microbial pathogens triggers Aβ oligomer upregulation and aggregation to combat infection via selective interactions between α-sheet oligomers to neutralize toxicity of both species with subsequent inhibition of fibrillization.

Aggregate-prone brain regions in Parkinson’s disease are rich in unique N-terminus α-synuclein conformers with high proteolysis susceptibility

In Parkinson’s disease (PD), and other α-synucleinopathies, α-synuclein (α-Syn) aggregates form a myriad of conformational and truncational variants. Most antibodies used to detect and quantify α-Syn in the human brain target epitopes within the C-terminus (residues 96–140) of the 140 amino acid protein and may fail to capture the diversity of α-Syn variants present in PD. We sought to investigate the heterogeneity of α-Syn conformations and aggregation states in the PD human brain by labelling with multiple antibodies that detect epitopes along the entire length of α-Syn. We used multiplex immunohistochemistry to simultaneously immunolabel tissue sections with antibodies mapping the three structural domains of α-Syn. Discrete epitope-specific immunoreactivities were visualised and quantified in the olfactory bulb, medulla, substantia nigra, hippocampus, entorhinal cortex, middle temporal gyrus, and middle frontal gyrus of ten PD cases, and the middle temporal gyrus of 23 PD, and 24 neurologically normal cases. Distinct Lewy neurite and Lewy body aggregate morphologies were detected across all interrogated regions/cases. Lewy neurites were the most prominent in the olfactory bulb and hippocampus, while the substantia nigra, medulla and cortical regions showed a mixture of Lewy neurites and Lewy bodies. Importantly, unique N-terminus immunoreactivity revealed previously uncharacterised populations of (1) perinuclear, (2) glial (microglial and astrocytic), and (3) neuronal lysosomal α-Syn aggregates. These epitope-specific N-terminus immunoreactive aggregate populations were susceptible to proteolysis via time-dependent proteinase K digestion, suggesting a less stable oligomeric aggregation state. Our identification of unique N-terminus immunoreactive α-Syn aggregates adds to the emerging paradigm that α-Syn pathology is more abundant and complex in human brains with PD than previously realised. Our findings highlight that labelling multiple regions of the α-Syn protein is necessary to investigate the full spectrum of α-Syn pathology and prompt further investigation into the functional role of these N-terminus polymorphs.

Aggregation, structure and water permeability of membrane-embedded helical Aβ oligomers.

It is widely recognized that membranes can facilitate the aggregation of amyloid-β (Aβ) peptides, while Aβ can in turn cause membrane damage. Many studies focus on the peptide-membrane interactions of Aβ oligomers with β-rich structures. However, the exact aggregation and toxicity mechanism of the membrane-embedded helical Aβ oligomers remain ambiguous. Herein, the molecular dynamics simulations were performed on membrane-embedded helical Aβ42 peptides. Initiated by eight Aβ42 monomers embedded in a lipid bilayer, the monomers aggregate into oligomers with stable transmembrane helix structures. With the aggregation of peptides, the membrane perturbations caused by Aβ aggregates decrease. The molecular architectures of oligomers were characterized and a helix-rich octamer stabilized by an annular network of hydrogen bonds was observed. The oligomers demonstrate the capability to assist transmembrane water transport. Our study may provide new insights for the investigation of transmembrane Aβ oligomers.

Circadian and sleep phenotypes in a mouse model of Alzheimer's disease characterized by intracellular accumulation of amyloid β oligomers.

Disturbances in sleep-wake and circadian rhythms may reportedly precede the onset of cognitive symptoms in the early stages of Alzheimer's disease (AD); however, the underlying mechanisms of these AD-induced sleep disturbances remain unelucidated. To specifically evaluate the involvement of amyloid beta (Aβ) oligomers in AD-induced sleep disturbances, we examined circadian and sleep phenotypes using an Aβ-GFP transgenic (Aβ-GFP Tg) mouse characterized by intracellular accumulation of Aβ oligomers. The circadian rhythm and free-running period of wheel running activity were identical between Aβ-GFP Tg and littermate wild-type mice. The durations of rapid eye movement (REM) sleep were elongated in Aβ-GFP Tg mice; however, the durations of non-REM sleep and wakefulness were unaffected. The Aβ-GFP Tg mice exhibited shifts in the electroencephalogram (EEG) power spectra toward higher frequencies in the inactive light phase. These findings suggest that the intracellular accumulation of Aβ oligomers might be associated with sleep quality; however, its impact on circadian systems is limited.

Prediction of the 3D conformation of a small peptide vaccine targeting Aβ42 oligomers.

The original etiology of Alzheimer's disease (AD) is the deposition of amyloid-beta (Aβ) proteins, which starts from the aggregation of the Aβ oligomers. The optimal therapeutic strategy targeting Aβ oligomer aggregation is the development of AD vaccines. Despite the fact that positive progress has been made for experimental attempts at AD vaccines, the physicochemical and even structural properties of these AD vaccines remain unclear. In this study, through immunoinformatic and molecular dynamics (MD) simulations, we first designed and simulated an alternative of vaccine TAPAS and found that the structure of the alternative can reproduce the 3D conformation of TAPAS determined experimentally. Meanwhile, immunoinformatic methods were used to analyze the physicochemical properties of TAPAS, including immunogenicity, antigenicity, thermal stability, and solubility, which confirm well the efficacy and safety of the vaccine, and validate the scheme reliability of immunoinformatic and MD simulations in designing and simulating the TAPAS vaccine. Using the same scheme, we predicted the 3D conformation of the optimized ACI-24 peptide vaccine, an Aβ peptide with the first 15 residues of Aβ42 (Aβ1-15). The vaccine was verified once to be effective against both full-length Aβ1-42 and truncated Aβ4-42 aggregates, but an experimental 3D structure was absent. We have also explored the immune mechanism of the vaccine at the molecular level and found that the optimized ACI-24 and its analogues can block the growth of either full-length Aβ1-42 or truncated Aβ4-42 pentamer by contacting the hydrophobic residues within the N-terminus and β1 region on the contact surface of either pentamer. Additionally, residues (D1, D7, S8, H13, and Q15) were identified as the key residues of the vaccine to contact either of the two Aβ oligomers. This work provides a feasible implementation scheme of immunoinformatic and MD simulations for the development of AD small peptide vaccines, validating the power of the scheme as a parallel tool to the experimental approaches and injecting molecular-level information into the understanding and design of anti-AD vaccines.

Fusion of amyloid beta with ferritin yields an isolated oligomeric beta-sheet-rich aggregate inside the ferritin cage.

Alzheimer's disease is a severe brain condition caused by the formation of amyloid plaques composed of amyloid beta (Aβ) peptides. These peptides form oligomers, protofibrils, and fibrils before deposition into amyloid plaques. Among these intermediates, Aβ oligomers (AβOs) were found to be the most toxic and therefore an appealing target for drug development and understanding their role in the disease. However, precise isolation and characterization of AβOs have proven challenging because AβOs tend to aggregate and form heterogeneous mixtures in solution. As a solution, we genetically fused the Aβ peptide with a ferritin monomer. Such fusion allowed the encapsulation of precisely 24 Aβ peptides inside the 24-mer ferritin cage. Using high-speed atomic force microscopy (HS-AFM), we disassembled ferritin and directly visualized the Aβ core enclosed within the cage. The thioflavin-T assay (ThT) and attenuated total reflection infrared spectroscopy (ATR-IR) revealed the presence of a β-sheet structure in the encapsulated oligomeric aggregate. Gallic acid, an amyloid inhibitor, can inhibit the fluorescence of ThT bound AβOs. Our approach represents a significant advancement in the isolation and characterization of β-sheet rich AβOs and is expected to be useful for future studies of other disordered peptides such as α-synuclein and tau.

Discovery of Quinolinone Hybrids as Dual Inhibitors of Acetylcholinesterase and Aβ Aggregation for Alzheimer's Disease Therapy.

The development of multitargeted therapeutics has evolved as a promising strategy to identify efficient therapeutics for neurological disorders. We report herein new quinolinone hybrids as dual inhibitors of acetylcholinesterase (AChE) and Aβ aggregation that function as multitargeted ligands for Alzheimer's disease. The quinoline hybrids (AM1-AM16) were screened for their ability to inhibit AChE, BACE1, amyloid fibrillation, α-syn aggregation, and tau aggregation. Among the tested compounds, AM5 and AM10 inhibited AChE activity by more than 80% at single-dose screening and possessed a remarkable ability to inhibit the fibrillation of Aβ42 oligomers at 10 μM. In addition, dose-dependent screening of AM5 and AM10 was performed, giving half-maximal AChE inhibitory concentration (IC50) values of 1.29 ± 0.13 and 1.72 ± 0.18 μM, respectively. In addition, AM5 and AM10 demonstrated concentration-dependent inhibitory profiles for the aggregation of Aβ42 oligomers with estimated IC50 values of 4.93 ± 0.8 and 1.42 ± 0.3 μM, respectively. Moreover, the neuroprotective properties of the lead compounds AM5 and AM10 were determined in SH-SY5Y cells incubated with Aβ oligomers. This work would enable future research efforts aiming at the structural optimization of AM5 and AM10 to develop potent dual inhibitors of AChE and amyloid aggregation. Furthermore, the in vivo assay confirmed the antioxidant activity of compounds AM5 and AM10 through increasing GSH, CAT, and SOD activities that are responsible for scavenging the ROS and restoring its normal level. Blood investigation illustrated the protective activity of the two compounds against lead-induced neurotoxicity through retaining hematological and liver enzymes near normal levels. Finally, immunohistochemistry investigation revealed the inhibitory activity of β-amyloid (Aβ) aggregation.

Development of fluorophores for the detection of oligomeric aggregates of amyloidogenic proteins found in neurodegenerative diseases.

Alzheimer's disease and Parkinson's disease are the two most common neurodegenerative diseases globally. These neurodegenerative diseases have characteristic late-stage symptoms allowing for differential diagnosis; however, they both share the presence of misfolded protein aggregates which appear years before clinical manifestation. Historically, research has focused on the detection of higher-ordered aggregates (or amyloids); however, recent evidence has shown that the oligomeric state of these protein aggregates plays a greater role in disease pathology, resulting in increased efforts to detect oligomers to aid in disease diagnosis. In this review, we summarize some of the exciting new developments towards the development of fluorescent probes that can detect oligomeric aggregates of amyloidogenic proteins present in Alzheimer's and Parkinson's disease patients.

Neuroprotective Profile of Triazole Grandisin Analogue against Amyloid-Beta Oligomer-Induced Cognitive Impairment.

Alzheimer's disease (AD) is a neurodegenerative disorder caused by accumulation of amyloid-β oligomers (AβO) in the brain, neuroinflammation, oxidative stress, and cognitive decline. Grandisin, a tetrahydrofuran neolignan, exhibits relevant anti-inflammatory and antioxidant properties. Interestingly, grandisin-based compounds were shown to prevent AβO-induced neuronal death in vitro. However, no study has assessed the effect of these compounds on the AD animal model. This study focuses on a triazole grandisin analogue (TGA) synthesized using simplification and bioisosteric drug design, which resulted in improved potency and solubility compared with the parent compound. This study aimed to investigate the possible in vivo effects of TGA against AβO-induced AD. Male C57/Bl6 mice underwent stereotaxic intracerebroventricular AβO (90 μM) or vehicle injections. 24 h after surgery, animals received intraperitoneal treatment with TGA (1 mg/kg) or vehicle, administered on a 14 day schedule. One day after treatment completion, a novel object recognition task (NORT) was performed. Memantine (10 mg/kg) was administered as a positive control. NORT retention sessions were performed on days 8 and 16 after AβO injection. Immediately after retention sessions, animals were euthanized for cortex and hippocampus collection. Specimens were subjected to oxidative stress and cytokine analyses. TGA reduced the level of cortex/hippocampus lipoperoxidation and prevented cognitive impairment in AβO-injected mice. Additionally, TGA reduced tumor necrosis factor (TNF) and interferon-γ (IFN-γ) levels in the hippocampus. By contrast, memantine failed to prevent cortex/hippocampus lipid peroxidation, recognition memory decline, and AβO-induced increases in TNF and IFN-γ levels in the hippocampus. Thus, memantine was unable to avoid the AβO-induced persistent cognitive impairment. The results showed that TGA may prevent memory impairment by exerting antioxidant and anti-inflammatory effects in AβO-injected mice. Moreover, TGA exhibited a persistent neuroprotective effect compared to memantine, reflecting an innovative profile of this promising agent against neurodegenerative diseases, such as AD.

The AD/ADRD Interdisciplinary Research Network on Biologically Active Tau Aggregate Polymorphs from Alzheimer’s Disease and Related Dementias

AbstractBackgroundTauopathies, including Alzheimer’s disease (AD), are characterized by intracellular lesions composed of aggregated and post‐translationally modified tau proteins. Methods for preparation and biochemical characterization of stable filaments from various tauopathies are well established. In contrast, methods for preparation of soluble oligomeric tau aggregates have not been standardized to the same degree. Additionally, the structures of oligomers which associate most closely with disease propagation and toxicity, are not fully established. The AD/ADRD Resource Network aims to isolate structurally vetted tau filaments and oligomers from human tauopathy cases and distribute them to the research community. In addition, it seeks to bank and distribute detection reagents and associated protocols. The overall mission of the network is to support impactful tauopathy research.MethodTauopathies, including Alzheimer’s disease (AD), are characterized by intracellular lesions composed of aggregated and post‐translationally modified tau proteins. Methods for preparation and biochemical characterization of stable filaments from various tauopathies are well established. In contrast, methods for preparation of soluble oligomeric tau aggregates have not been standardized to the same degree. Additionally, the structures of oligomers which associate most closely with disease propagation and toxicity, are not fully established. The AD/ADRD Resource Network aims to isolate structurally vetted tau filaments and oligomers from human tauopathy cases and distribute them to the research community. In addition, it seeks to bank and distribute detection reagents and associated protocols. The overall mission of the network is to support impactful tauopathy research.ResultProtocols for simultaneous isolation of oligomeric and filamentous tau aggregates have been developed along with analytical and quantitative methods to estimate sample heterogenicity and stability. Resource Network members are establishing cross‐laboratory analytical benchmarks for experiments to ensure rigor and reproducibility of results.ConclusionThe AD/ADRD Research Network banks rigorously validated preparations of structurally vetted tau aggregates along with directed protocols and reagents. Dissemination of these reagents is expected to maximize rigor and reproducibility of basic research involving tau protein aggregates.

RNA‐Binding Proteins Musashi and Tau Aggresome in Alzheimer’s disease

AbstractBackgroundTauopathies, such as Alzheimer’s disease (AD), are characterized by the accumulation of toxic tau oligomers in the brain and accumulation of proteinaceous inclusions stored in cellular structures called aggresomes. Recent studies suggest that AD also exhibits pathology related to RNA binding proteins (RBPs), including Musashi proteins. Our lab has previously discovered that Musashi 1 (MSI1) and Musashi 2 (MSI2) aggregate in human AD brains and we have also visualized co‐localization with tau oligomers, suggesting toxic direct crosstalk between tau and MSI proteins. With this discovery and the growing evidence indicating MSI proteins as contributors to AD pathology, through their loss of functions it is crucial to elucidate how the interactions between misfolded tau and MSI influence tau aggregation and perhaps formation of cellular aggresomes.MethodIn this study, we characterize which tau oligomeric species, including phosphorylated and ubiquitinated ones, interact with MSI within the human AD brain (Braak Stage V‐VI). We investigate the deposition and cellular location of MSI and tau aggregates in AD and age‐matched control human cortical brain tissues by biochemical, immunohistochemistry and co‐immunofluorescence assays. Using high‐resolution microscopy and imaging analysis we measured the differences in size and morphology of MSI/tau co‐aggregates.ResultInvestigation of these co‐aggregates showed specific accumulation in neurons as well as in glial cells (astrocytes and microglia). We performed biochemical assays using commercial and in‐house antibodies to qualitatively investigate MSI1, MSI2, and tau across in AD brains. Co‐IF was performed to investigate the spatial and quantitative distribution of MSI1, MSI2, and tau aggregates. MSI/tau aggregate morphological characterization was conducted to profile their size and shape in AD cortices.ConclusionFor the first time, we show that the presence and quantity of tau oligomeric species and MSI co‐aggregates vary across the AD brains, showing inter‐subjects’ variability in size and deposition density. We also identify that tau conformers with MSI1 and MSI2 form different co‐aggregates in size and morphology quantifying their colocalization in high‐resolution 3D imaging. Further investigations are warranted to determine the temporal and regional distribution of these tau species in association with MSI proteins as well as the mechanisms underlying their aggregation.

APP/AICD‐dependent expression of Glypican 4 mediates accumulation of tau oligomers in astrocytes and their synaptotoxic action

AbstractBackgroundSeveral studies including ours reported the detrimental effects of extracellular tau oligomers (ex‐oTau) on glutamatergic synaptic transmission and plasticity. Astrocytes greatly internalize ex‐oTau thus contributing to their clearance. However, glial cell engulfment of oTau leads to alteration of neuro/gliotransmitter handling that negatively affects synaptic function. We previously reported that amyloid precursor protein (APP) is required for oTau internalization in astrocytes but the molecular mechanisms underlying this phenomenon has not been clearly identified yet. Here we investigated the role of glypican 4 (GPC4), a member of the large family of heparan sulfate proteoglycans that are membrane glycoproteins highly expressed in astrocytes playing a critical role in protein trafficking through the plasma membrane.MethodThe role of GPC4 in ex‐oTau accumulation in astrocytes and the resulting synaptotoxic action were studied in in vitro and ex‐vivo models obtained from wild‐type C57/bl6 and transgenic mice in which either APP was knocked‐out or it contained the non‐phosphorylatable amino acid alanine replacing threonine 688 (APPTA mice). In these experimental models we performed immunofluorescence analyses, Western blot and real‐time PCR experiments, confocal Ca2+ imaging, high‐pressure liquid chromatography, FM1‐43 imaging, electrophysiological recordings and Chromatin immunoprecipitation assays.ResultTreatment of cultured astrocytes with a specific anti‐GPC4 antibody significantly reduced oTau internalization in astrocytes and prevented oTau‐induced alterations of intracellular Ca2+ signaling and gliotransmitter release. As such, anti‐GPC4 treatment spared neurons from the astrocyte‐mediated synaptotoxic action of ex‐oTau. Specifically, after counteracting the interaction between ex‐oTau and GPC4 no significant decreases in synaptic vesicular release and synaptic protein expression were observed in neurons co‐cultured with astrocytes following exposure to ex‐oTau. The latter also failed to inhibit hippocampal LTP at CA3‐CA1 synapses. Of note, we found that the expression of GPC4 depended on APP and, in particular, on its C‐terminal domain, AICD, generated by γ‐secretase‐dependent cleavage of APP, that can bind Gpc4 promoter. Accordingly, GPC4 expression was significantly reduced in both APP‐KO ad APPTA mice, and ex‐oTau did not exert any significant detrimental action on synaptic function in APP‐KO mice.ConclusionCollectively, our data indicate that GPC4 expression is APP/AICD‐dependent, it mediates oTau accumulation in astrocytes and the resulting synaptotoxic effects.

Endotoxin accelerates insulin amyloid formation and inactivates insulin signal transduction

Aims and objectivesThe aim of this study is to discuss the influence of endotoxin on insulin amyloid formation, to provide guidance for therapeutic insulin preparation and storage. Materials and methodsThe ThT and ANS binding assays were applied to characterize the dynamics curve of insulin amyloid formation with the presence or absence of endotoxin. The morphological structures of intermediate and mature insulin fibrils were observed with SEM and TEM. Secondary structural changes of insulin during fibriliation were examined with CD, FTIR and Raman spectral analysis. The cytotoxic effects of oligomeric and amyloidogenic insulin aggregates were detected using a cck-8 cell viability assay kit. The influence of endotoxin on insulin efficacy was analyzed by monitoring the activation of insulin signal transduction. Key findingsThT analysis showed that endotoxin, regardless of species, accelerated insulin fibrils formation in a dose-dependent manner, as observed with a shorter lag phase. ANS binding assay demonstrated endotoxin provoked the exposure of insulin hydrophobic patches. The results of SEM and TEM data displayed that endotoxin drove insulin to cluster into dense and viscous form, with thicker and stronger filaments. Based on CD, FTIR and Raman spectra, endotoxin promoted the transition of α-helix to random coil and β-strand secondary structures during insulin aggregation. Insulins in both oligomeric and amyloidogenic forms were cytotoxic to HepG2 cells, with the former being more severe. Finally, the efficacy of endotoxin treated insulin obviously decreased. SignificanceOur studies revealed that endotoxin disrupts the structural integrity of insulin and promotes its amyloidosis. These findings offered theoretical guidance for insulin storage and safe utilization, as well as pointing up a new direction for insulin resistance research.

Genetic Causes of Alzheimer's Disease and the Neuroprotective Role of Melatonin in its Management.

Dementia is a global health concern owing to its complexity, which also poses a great challenge to pharmaceutical scientists and neuroscientists. The global dementia prevalence is approximately 47 million, which may increase by three times by 2050. Alzheimer's disease (AD) is the most common cause of dementia. AD is a severe age-related neurodegenerative disorder characterized by short-term memory loss, aphasia, mood imbalance, and executive function. The etiology of AD is still unknown, and the exact origin of the disease is still under investigation. Aggregation of Amyloid β (Aβ) plaques or neurotoxic Aβo oligomers outside the neuron is the most common cause of AD development. Amyloid precursor protein (APP) processing by β secretase and γ secretase produces abnormal Aβ monomers. This aggregation of Aβ and NFT is promoted by various genes like BACE1, ADAM10, PIN1, GSK-3, APOE, PPARα, etc. Identification of these genes can discover several therapeutic targets that can be useful in studying pathogenesis and underlying treatments. Melatonin modulates the activities of these genes, thereby reducing Aβ production and increasing its clearance. Melatonin also reduces the expression of APP by attenuating cAMP, thereby enhancing the non-amyloidogenic process. Present communication explored and discussed the neuroprotective role of melatonin against Aβ-dependent AD pathogenesis. The manuscript also discussed potential molecular and genetic mechanisms of melatonin in the production and clearance of Aβ that could ameliorate neurotoxicity.

Increased lethality of respiratory infection by Streptococcus pneumoniae in the Dp16 mouse model of Down syndrome.

We sought to investigate whether the Dp16 mouse model of Down syndrome (DS) is more susceptible to severe and lethal respiratory tract infection by Streptococcus pneumoniae. We infected controls and Dp16 mice with Streptococcus pneumoniae and measured survival rates. We compared cytokine production by primary lung cell cultures exposed to Streptococcus pneumoniae. We examined lung protein expression for interferon signaling related pathways. We characterized the histopathology and quantified the extent of bronchus-associated lymphoid tissue. Finally, we examined mouse tissues for the presence of oligomeric tau protein. We found that the Dp16 mouse model of DS displayed significantly higher susceptibility to lethal respiratory infection with Streptococcus pneumoniae compared to control mice. Lung cells cultured from Dp16 mice displayed unique secreted cytokine profiles compared to control mice. The Dp16 mouse lungs were characterized by profound lobar pneumonia with massive diffuse consolidation involving nearly the entire lobe. Marked red hepatization was noted, and Dp16 mice lungs contained numerous bronchus-associated lymphoid tissues that were highly follicularized. Compared to uninfected mice, both control mice and Dp16 mice infected with Streptococcus pneumoniae showed evidence of oligomeric tau aggregates. Increased susceptibility to severe respiratory tract infection with Streptococcus pneumoniae in Dp16 mice closely phenocopies infection in individuals with DS. The increase does not appear to be linked to overexpression of mouse interferon genes syntenic to human chromosome 21.

Stabilization and Reduced Cytotoxicity of Amyloid Beta Aggregates in the Presence of Catechol Neurotransmitters.

Oligomeric aggregates of the amyloid-beta (Aβ) peptide have been implicated as the toxic species for Alzheimer's disease by contributing to oxidative cytotoxicity and physical disruption in cell membranes in the brain. Recent evidence points to the ability of the catecholamine neurotransmitter dopamine in the presence of copper ions to both stabilize oligomers and decrease the toxic effects of these oligomers. Based on these results, physical characterization of aggregates and subsequent cell studies with a neuroblastoma line were performed that show both dopamine and the related neurotransmitter, norepinephrine, can stabilize oligomers and decrease toxicity of Aβ aggregates without copper present. To investigate this reduction of toxicity, structural characterization of oligomers in the presence of neurotransmitters was compared to aggregates formed with Aβ alone. Gel electrophoresis and transmission electron microscopy show higher levels of oligomers in the presence of dopamine and norepinephrine, yet the oligomer structure is largely amorphous. Aβ aggregated alone forms the predicted highly organized fibrillar species, with increased levels of dityrosine covalent linkages, which are largely absent in the presence of the neurotransmitters. A proposed mechanism for the observed decrease in cell death by Aβ in the presence of dopamine and norepinephrine suggests the neurotransmitters both block the formation of organized oligomer structures and dityrosine stabilizing linkages while also behaving as antioxidants, providing a dual mechanism for increased cell viability.

Tau Oligomer–Containing Synapse Elimination by Microglia and Astrocytes in Alzheimer Disease

Factors associated with synapse loss beyond amyloid-β plaques and neurofibrillary tangles may more closely correlate with the emergence of cognitive deficits in Alzheimer disease (AD) and be relevant for early therapeutic intervention. To investigate whether accumulation of tau oligomers in synapses is associated with excessive synapse elimination by microglia or astrocytes and with cognitive outcomes (dementia vs no dementia [hereinafter termed resilient]) of individuals with equal burdens of AD neuropathologic changes at autopsy. This cross-sectional postmortem study included 40 human brains from the Massachusetts Alzheimer Disease Research Center Brain Bank with Braak III to IV stages of tau pathology but divergent antemortem cognition (dementia vs resilient) and cognitively normal controls with negligible AD neuropathologic changes. The visual cortex, a region without tau tangle deposition at Braak III to IV stages, was assessed after expansion microscopy to analyze spatial relationships of synapses with microglia and astrocytes. Participants were matched for age, sex, and apolipoprotein E status. Evidence of Lewy bodies, TDP-43 aggregates, or other lesions different from AD neuropathology were exclusion criteria. Tissue was collected from July 1998 to November 2020, and analyses were conducted from February 1, 2022, through May 31, 2023. Amyloid-β plaques, tau neuropil thread burden, synapse density, tau oligomers in synapses, and internalization of tau oligomer-tagged synapses by microglia and astrocytes were quantitated. Analyses were performed using 1-way analysis of variance for parametric variables and the Kruskal-Wallis test for nonparametric variables; between-group differences were evaluated with Holm-Šídák tests. Of 40 included participants (mean [SD] age at death, 88 [8] years; 21 [52%] male), 19 had early-stage dementia with Braak stages III to IV, 13 had resilient brains with similar Braak stages III to IV, and 8 had no dementia (Braak stages 0-II). Brains with dementia but not resilient brains had substantial loss of presynaptic (43%), postsynaptic (33%), and colocalized mature synaptic elements (38%) compared with controls and significantly higher percentages of mature synapses internalized by IBA1-positive microglia (mean [SD], 13.3% [3.9%] in dementia vs 2.6% [1.9%] in resilient vs 0.9% [0.5%] in control; P < .001) and by GFAP-positive astrocytes (mean [SD], 17.2% [10.9%] in dementia vs 3.7% [4.0%] in resilient vs 2.7% [1.8%] in control; P = .001). In brains with dementia but not in resilient brains, tau oligomers more often colocalized with synapses, and the proportions of tau oligomer-containing synapses inside microglia (mean [SD] for presynapses, mean [SD], 7.4% [1.8%] in dementia vs 5.1% [1.9%] resilient vs 3.7% [0.8%] control; P = .006; and for postsynapses 11.6% [3.6%] dementia vs 6.8% [1.3%] resilient vs 7.4% [2.5%] control; P = .001) and astrocytes (mean [SD] for presynapses, 7.0% [2.1%] dementia vs 4.3% [2.2%] resilient vs 4.0% [0.7%] control; P = .001; and for postsynapses, 7.9% [2.2%] dementia vs 5.3% [1.8%] resilient vs 3.0% [1.5%] control; P < .001) were significantly increased compared with controls. Those changes in brains with dementia occurred in the absence of tau tangle deposition in visual cortex. The findings from this cross-sectional study suggest that microglia and astrocytes may excessively engulf synapses in brains of individuals with dementia and that the abnormal presence of tau oligomers in synapses may serve as signals for increased glial-mediated synapse elimination and early loss of brain function in AD.

Tauopathy promotes spinal cord-dependent production of toxic amyloid-beta in transgenic monkeys

Tauopathy, characterized by the hyperphosphorylation and accumulation of the microtubule-associated protein tau, and the accumulation of Aβ oligomers, constitute the major pathological hallmarks of Alzheimer’s disease. However, the relationship and causal roles of these two pathological changes in neurodegeneration remain to be defined, even though they occur together or independently in several neurodegenerative diseases associated with cognitive and movement impairment. While it is widely accepted that Aβ accumulation leads to tauopathy in the late stages of the disease, it is still unknown whether tauopathy influences the formation of toxic Aβ oligomers. To address this, we generated transgenic cynomolgus monkey models expressing Tau (P301L) through lentiviral infection of monkey embryos. These monkeys developed age-dependent neurodegeneration and motor dysfunction. Additionally, we performed a stereotaxic injection of adult monkey and mouse brains to express Tau (P301L) via AAV9 infection. Importantly, we found that tauopathy resulting from embryonic transgenic Tau expression or stereotaxic brain injection of AAV-Tau selectively promoted the generation of Aβ oligomers in the monkey spinal cord. These Aβ oligomers were recognized by several antibodies to Aβ1–42 and contributed to neurodegeneration. However, the generation of Aβ oligomers was not observed in other brain regions of Tau transgenic monkeys or in the brains of mice injected with AAV9-Tau (P301L), suggesting that the generation of Aβ oligomers is species- and brain region-dependent. Our findings demonstrate for the first time that tauopathy can trigger Aβ pathology in the primate spinal cord and provide new insight into the pathogenesis and treatment of tauopathy.

Exploring the Barriers in the Aggregation of a Hexadecameric Human Prion Peptide through the Markov State Model.

The prefibrillar aggregation kinetics of prion peptides are still an enigma. In this perspective, we employ atomistic molecular dynamics (MD) simulations of the shortest human prion peptide (HPP) (127GYMLGS132) at various temperatures and peptide concentrations and apply the Markov state model to determine the various intermediates and lag phases. Our results reveal that the natural mechanism of prion peptide self-assembly in the aqueous phase is impeded by two significant kinetic barriers with oligomer sizes of 6-9 and 12-13 peptides, respectively. The first one is the aggregation of unstructured lower-order oligomers, and the second is fibril nucleation, which impedes the further growth of prion aggregates. Among these two activation barriers, the second one is found to be dominant irrespective of the increase in temperature and peptide concentration. These lag phases are captured in all three different force-field parameters, namely, GROMOS-54a7, AMBER-99SB-ILDN, and CHARMMS 36m, at different concentrations. The GROMOS-54a7 and AMBER-99SB-ILDN force fields showed a comparatively higher percentage of β-sheet formation in the metastable aggregate that evolved during the aggregation process. In contrast, the CHARMM-36m force field showed mostly coil or turn conformations. The addition of a novel catecholamine derivative (naphthoquinone dopamine (NQDA)) arrests the aggregation process between the lag phases by increasing the activation barrier for the Lag1 and Lag2 phases in all of the force fields, which further validates the existence of these lag phases. The preferential binding of NQDA with the peptides increases the hydration of peptides and eventually disrupts the organized morphology of prefibrillar aggregates. It reduces the dimer dissociation energy by -24.34 kJ/mol.

Beta Amyloid Oligomers with Higher Cytotoxicity have Higher Sidechain Dynamics.

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