Amyloid beta protein (A beta) in Alzheimer's disease brain. Biochemical and immunocytochemical analysis with antibodies specific for forms ending at A beta 40 or A beta 42(43)

Deciphering the role of APOE in cerebral amyloid angiopathy: from genetic insights to therapeutic horizons

Cerebral amyloid angiopathy (CAA), characterized by the deposition of amyloid-β (Aβ) peptides in the walls of medium and small vessels of the brain and leptomeninges, is a major cause of lobar hemorrhage in elderly individuals. Among the genetic risk factors for CAA that continue to be recognized, the apolipoprotein E (APOE) gene is the most significant and prevalent, as its variants have been implicated in more than half of all patients with CAA. While the presence of the APOE ε4 allele markedly increases the risk of CAA, the ε2 allele confers a protective effect relative to the common ε3 allele. These allelic variants encode three APOE isoforms that differ at two amino acid positions. The primary physiological role of APOE is to mediate lipid transport in the brain and periphery; however, it has also been shown to be involved in a wide array of biological functions, particularly those involving Aβ, in which it plays a known role in processing, production, aggregation, and clearance. The challenges posed by the reliance on postmortem histological analyses and the current absence of an effective intervention underscore the urgency for innovative APOE-targeted strategies for diagnosing CAA. This review not only deepens our understanding of the impact of APOE on the pathogenesis of CAA but can also help guide the exploration of targeted therapies, inspiring further research into the therapeutic potential of APOE.

Mouse models of Anti-Aβ immunotherapies

BACKGROUND

The development of anti-amyloid-beta (Aβ) immunotherapies as the first disease modifying therapy for Alzheimer's Disease (AD) is a breakthrough of basic research and translational science.

MAIN TEXT

Genetically modified mouse models developed to study AD neuropathology and physiology were used for the discovery of Aβ immunotherapies and helped ultimately propel therapies to FDA approval. Nonetheless, the combination of modest efficacy and significant rates of an adverse side effect (amyloid related imaging abnormalities, ARIA), has prompted reverse translational research in these same mouse models to better understand the mechanism of the therapies.

CONCLUSION

This review considers the use of these mouse models in understanding the mechanisms of Aβ clearance, cerebral amyloid angiopathy (CAA), blood brain barrier breakdown, neuroinflammation, and neuronal dysfunction in response to Aβ immunotherapy.

Multi-omic analysis of meningeal cerebral amyloid angiopathy reveals enrichment of unsubstituted glucosamine and extracellular proteins

Cerebral amyloid angiopathy (CAA) is a common feature of Alzheimer's disease in which amyloid-β (Aβ) deposits in cerebral and leptomeningeal vessel walls, predisposing vessels to micro- and macro-hemorrhages. The vessel walls contain distinct proteins and heparan sulfate (HS), yet how vascular proteins and HS jointly associate with Aβ is unknown. We conducted the first multi-omics study to systematically characterize the proteins as well as the HS abundance, sulfation level, and disaccharide composition of leptomeninges from 23 moderate to severe CAA cases and controls. We then analyzed the associations between Aβ and other proteins, HS, and apolipoprotein E genotype. We found an increase in a minor HS disaccharide containing unsubstituted glucosamine, as well as 6-O sulfated disaccharides; Aβ40 levels positively correlated with unsubstituted glucosamine. There was also an increase in extracellular proteins derived from brain parenchyma or plasma, including olfactomedin-like protein 3, fibrinogen, serum amyloid protein, apolipoprotein E, and secreted frizzled related protein-3. Our findings of vascular HS and protein alterations specific to CAA-affected leptomeningeal vessels provide molecular insight into the extracellular remodeling that co-occurs with Aβ deposits and may indicate a basis for antemortem diagnostic assay development and therapeutic strategies to impede Aβ-HS interactions.

Traumatic Brain Injury and Alzheimer's Disease: A Shared Neurovascular Hypothesis

Traumatic brain injury (TBI) is a modifiable risk factor for Alzheimer's disease (AD). TBI and AD share several histopathological hallmarks: namely, beta-amyloid aggregation, tau hyperphosphorylation, and plasma protein infiltration. The relative contributions of these proteinopathies and their interplay in the pathogenesis of both conditions remains unclear although important differences are emerging. This review synthesises emerging evidence for the critical role of the neurovascular unit in mediating protein accumulation and neurotoxicity in both TBI and AD. We propose a shared pathogenic cascade centred on a neurovascular unit, in which increased blood-brain barrier permeability induces a series of noxious mechanisms leading to neuronal loss, synaptic dysfunction and ultimately cognitive dysfunction in both conditions. We explore the application of this hypothesis to outstanding research questions and potential treatments for TBI and AD, as well as other neurodegenerative and neuroinflammatory conditions. Limitations of this hypothesis, including the challenges of establishing a causal relationship between neurovascular damage and proteinopathies, are also discussed.

Decoding TGR5: A comprehensive review of its impact on cerebral diseases

Currently, unraveling the enigmatic realm of drug targets for cerebral disorders poses a formidable challenge. Takeda G protein-coupled receptor 5 (TGR5), also known as G protein-coupled bile acid receptor 1, is a specific bile acid receptor. Widely distributed across various tissues, TGR5 orchestrates a myriad of biological functions encompassing inflammation, energy metabolism, fatty acid metabolism, immune responses, cellular proliferation, apoptosis, and beyond. Alongside its well-documented implications in liver diseases, obesity, type 2 diabetes, tumors, and cardiovascular diseases, a growing body of evidence accentuates the pivotal role of TGR5 in cerebral diseases. Thus, this comprehensive review aimed to scrutinize the current insights into the pathological mechanisms involving TGR5 in cerebral diseases, while contemplating its potential as a promising therapeutic target for cerebral diseases.

Plasma Biomarkers for Cerebral Amyloid Angiopathy and Implications for Amyloid-Related Imaging Abnormalities: A Comprehensive Review

Anti-amyloid therapies (AATs) are increasingly being recognized as promising treatment options for Alzheimer's disease (AD). Amyloid-related imaging abnormalities (ARIAs), small areas of edema and microbleeds in the brain presenting as abnormal signals in MRIs of the brain for patients with AD, are the most common side effects of AATs. While most ARIAs are asymptomatic, they can be associated with symptoms like nausea, headache, confusion, and gait instability and, less commonly, with more serious complications such as seizures and death. Cerebral amyloid angiopathy (CAA) has been found to be a major risk for ARIA development. The identification of sensitive and reliable non-invasive biomarkers for CAA has been an area of AD research over the years, but with the approval of AATs, this area has taken on a new urgency. This comprehensive review highlights several potential biomarkers, such as Aβ40, Aβ40/42, phosphorylated-tau217, neurofilament light chain, glial fibrillary acidic protein, secreted phosphoprotein 1, placental growth factor, triggering receptor expressed on myeloid cells 2, cluster of differentiation 163, proteomics, and microRNA. Identifying and staging CAA even before its consequences can be detected via neuroimaging are critical to allow clinicians to judiciously select appropriate candidates for AATs, stratify monitoring, properly manage therapeutic regimens for those experiencing symptomatic ARIAs, and optimize the treatment to achieve the best outcomes. Future studies can test potential plasma biomarkers in human beings and evaluate predictive values of individual markers for CAA severity.

The Contribution of the Renin-Angiotensin System to Alzheimer's Disease

The renin-angiotensin system (RAS) is becoming increasingly recognised as a biochemical pathway relevant to the development and progression of Alzheimer's disease (AD). RAS involvement in AD was initially linked to AD via numerous genetic association studies and more recent Genome-Wide Association Studies (GWAS), and in some cases in relation to classical hallmarks of AD pathology. Since these initial findings, which will be summarised here, several complementary areas of research are converging in support of what has been proposed as the Angiotensin Hypothesis for Alzheimer's disease. This hypothesis proposes how the RAS and disease-associated changes to the normal balance between opposing regulatory pathways within RAS warrant careful consideration in the pathogenesis of AD and its pathology. We discuss some of these in relation to RAS-targeting therapeutics, originally developed for the treatment of cardiovascular conditions, and how they might be repurposed as interventions for AD.

The stability and dynamics of the Aβ40/Aβ42 interlaced mixed fibrils

The accumulation of fibrillar amyloid-β (Aβ) aggregates in the brain, predominantly comprising 40- and 42-residue amyloid-β (Aβ40 and Aβ42), is a major pathological hallmark of Alzheimer's disease (AD). Aβ40 and Aβ42 naturally coexist in the brain under normal physiological conditions, and their interplay is generally considered to be a critical factor in the progression of AD. In addition to forming homogeneous oligomers and fibrils, Aβ40 and Aβ42 are also reported to co-assemble into hetero-oligomers and interlaced mixed fibrils, as evidenced by solid-state nuclear magnetic resonance spectroscopy (NMR), high molecular weight mass spectrometry and cross-seeding experiments. However, the exact molecular mechanisms underlying these processes remain unclear. In this study, we have used a recently resolved structurally uniform 1:1 mixture of Aβ40/Aβ42 interlaced mixed fibril as a prototype to gain insights into the molecular-level interactions between Aβ40 and Aβ42. We employed fully atomistic molecular dynamics simulation and compared the results with a homogeneous U-shaped Aβ40 fibrillar model. Our simulations using two different force fields provide conclusive evidence that the Aβ40/Aβ42 interlaced mixed fibril is energetically more favorable than the homogeneous Aβ40 fibrillar model. Furthermore, we also show that the increase in stability observed in the mixed model stems primarily from the packing interfaces and the stacking interfaces between C-termini. Our simulation results provide valuable mechanistic insights that are not readily accessible in experiment and could have significant implications for both the pathogenesis of AD and the development of current therapeutic strategies.Communicated by Ramaswamy H. Sarma.

Amyloid beta Aβ1-40 activates Piezo1 channels in brain capillary endothelial cells

Amyloid beta (Aβ) peptide accumulation on blood vessels in the brain is a hallmark of neurodegeneration. While Aβ peptides constrict cerebral arteries and arterioles, their impact on capillaries is less understood. Aβ was recently shown to constrict brain capillaries through pericyte contraction, but whether-and if so how-Aβ affects endothelial cells (ECs) remains unknown. ECs represent the predominant vascular cell type in the cerebral circulation, and we recently showed that the mechanosensitive ion channel Piezo1 is functionally expressed in the plasma membrane of ECs. Since Aβ disrupts membrane structures, we hypothesized that Aβ1-40, the predominantly deposited isoform in the cerebral circulation, alters endothelial Piezo1 function. Using patch-clamp electrophysiology and freshly isolated capillary ECs, we assessed the impact of the Aβ1-40 peptide on single-channel Piezo1 activity. We show that Aβ1-40 increased Piezo1 open probability and channel open time. Aβ1-40 effects were absent when Piezo1 was genetically deleted or when a superoxide dismutase/catalase mimetic was used. Further, Aβ1-40 enhanced Piezo1 mechanosensitivity and lowered the pressure of half-maximal Piezo1 activation. Our data collectively suggest that Aβ1-40 facilitates higher Piezo1-mediated cation influx in brain ECs. These novel findings have the potential to unravel the possible involvement of Piezo1 modulation in the pathophysiology of neurodegenerative diseases characterized by Aβ accumulation.

Dementia with lewy bodies patients with high tau levels display unique proteome profiles

BACKGROUND

Clinical studies have long observed that neurodegenerative disorders display a range of symptoms and pathological features and, in some cases, overlap, suggesting that these diseases exist on a spectrum. Dementia with Lewy Bodies (DLB), a synucleinopathy, is a prominent example, where symptomatic similarities with tauopathy, Alzheimer's disease, are observed. Although tau pathology has been observed in DLB, the interplay between tau and α-synuclein is poorly understood at a molecular level.

METHODS

Quantitative mass spectrometry analysis was used to measure protein abundance in the insoluble fraction from cortical brain tissue from pathologically diagnosed DLB subjects (n = 30) and age-matched controls (n = 29). Using tau abundance, we stratified the DLB subjects into two subgroups termed DLBTau+ (higher abundance) and DLBTau- (lower abundance). We conducted proteomic analysis to characterize and compare the cortical proteome of DLB subjects exhibiting elevated tau, as well as the molecular modifications of tau and α-synuclein to explore the dynamic between tau and α-synuclein pathology in these patients.

RESULTS

Proteomic analyses revealed distinct global protein dysregulations in DLBTau+ and DLBTau- subjects when compared to controls. Notably, DLBTau+ patients exhibited increased levels of tau, along with ubiquitin, and APOE, indicative of cortical proteome alterations associated with elevated tau. Comparing DLBTau+ and DLBTau- groups, we observed significant upregulation of cytokine signaling and metabolic pathways in DLBTau- patients, while DLBTau+ subjects showed increases in protein ubiquitination processes and regulation of vesicle-mediated transport. Additionally, we examined the post-translational modification patterns of tau and α-synuclein. Our analysis revealed distinct phosphorylation and ubiquitination sites on α-synuclein between groups. Moreover, we observed increased modifications on tau specifically within the DLBTau+ subgroup.

CONCLUSION

This molecular-level data supports the idea of neurodegenerative disease as a continuum of diseases with distinct PTM profiles DLBTau+ and DLBTau- patients in comparison to AD. These findings further emphasize the importance of identifying specific and tailored therapeutic approaches targeting the involved proteopathies in the neurodegenerative disease spectrum.

Aggregation dynamics of a 150 kDa Aβ42 oligomer: Insights from cryo electron microscopy and multimodal analysis

Protein misfolding is a widespread phenomenon that can result in the formation of protein aggregates, which are markers of various disease states, including Alzheimer's disease (AD). In AD, amyloid beta (Aβ) peptides are key players in the disease's progression, particularly the 40- and 42- residue variants, Aβ40 and Aβ42. These peptides aggregate to form amyloid plaques and contribute to neuronal toxicity. Recent research has shifted attention from solely Aβ fibrils to also include Aβ protofibrils and oligomers as potentially critical pathogenic agents. Particularly, oligomers demonstrate more significant toxicity compared to other Aβ specie. Hence, there is an increased interest in studying the correlation between toxicity and their structure and aggregation pathway. The present study investigates the aggregation of a 150 kDa Aβ42 oligomer that does not lead to fibril formation. Using negative stain transmission electron microscopy (TEM), size exclusion chromatography (SEC), dynamic light scattering (DLS), and cryo-electron microscopy (cryo-EM), we demonstrate that 150 kDa Aβ42 oligomers form higher-order string-like assemblies over time. These strings are unique from the classical Aβ fibrils. The significance of our work lies in elucidating molecular behavior of a novel non-fibrillar form of Aβ42 aggregate.

Metabolic resistance of Aβ3pE-42, a target epitope of the anti-Alzheimer therapeutic antibody, donanemab

The amyloid β peptide (Aβ), starting with pyroglutamate (pE) at position 3 and ending at position 42 (Aβ3pE-42), predominantly accumulates in the brains of Alzheimer's disease. Consistently, donanemab, a therapeutic antibody raised against Aβ3pE-42, has been shown to be effective in recent clinical trials. Although the primary Aβ produced physiologically is Aβ1-40/42, an explanation for how and why this physiological Aβ is converted to the pathological form remains elusive. Here, we present experimental evidence that accounts for the aging-associated Aβ3pE-42 deposition: Aβ3pE-42 was metabolically more stable than other Aβx-42 variants; deficiency of neprilysin, the major Aβ-degrading enzyme, induced a relatively selective deposition of Aβ3pE-42 in both APP transgenic and App knock-in mouse brains; Aβ3pE-42 deposition always colocalized with Pittsburgh compound B-positive cored plaques in APP transgenic mouse brains; and under aberrant conditions, such as a significant reduction in neprilysin activity, aminopeptidases, dipeptidyl peptidases, and glutaminyl-peptide cyclotransferase-like were up-regulated in the progression of aging, and a proportion of Aβ1-42 may be processed to Aβ3pE-42. Our findings suggest that anti-Aβ therapies are more effective if given before Aβ3pE-42 deposition.

Adverse Effects of Aβ1-42 Oligomers: Impaired Contextual Memory and Altered Intrinsic Properties of CA1 Pyramidal Neurons

Aβ1-42 (amyloid beta) oligomers, the major neurotoxic culprits in Alzheimer's disease, initiate early pathophysiological events, including neuronal hyperactivity, that underlie aberrant network activity and cognitive impairment. Although several synaptotoxic effects have been extensively studied, neuronal hyperexcitability, which may also contribute to cognitive deficits, is not fully understood. Here, we found several adverse effects of in vivo injection of Aβ1-42 oligomers on contextual memory and intrinsic properties of CA1 pyramidal neurons. Male rats underwent behavioral and electrophysiological studies 1 week after microinjections into the dorsal CA1 region, followed by histological analysis. After 1 week, Aβ1-42 oligomers impaired contextual learning without affecting basic physiological functions and triggered training-induced neuronal excitability. Furthermore, riluzole, a persistent sodium current (INaP) blocker, dose-dependently reduced Aβ1-42 oligomer-induced hyperexcitability. Congo red staining, which detects insoluble amyloid deposits, further identified labeling of CA1 pyramidal neurons while immunohistochemistry with lecanemab, which detects soluble Aβ oligomers, revealed immunoreactivity of both pyramidal and non-pyramidal cells in the target area. Therefore, our study suggests that a single injection of Aβ1-42 oligomers resulted in contextual memory deficits along with concomitant neuronal hyperexcitability and amyloid deposition in the CA1 region after 1 week.

Amyloid-Beta, Tau, and Microglial Activation in Aged Felid Brains

Alzheimer's disease (AD) and its associated pathology have been primarily identified in humans, who have relatively large brains and long lifespans. To expand what is known about aging and neurodegeneration across mammalian species, we characterized amyloid-beta (Aβ) and tau lesions in five species of aged felids (n = 9; cheetah, clouded leopard, African lion, serval, Siberian tiger). We performed immunohistochemistry to detect Aβ40 and Aβ42 in plaques and vessels and hyperphosphorylated tau in the temporal lobe gyrus sylvius and in the CA1 and CA3 subfields of the hippocampus. We also quantified the densities and morphological types of microglia expressing IBA1. We found that diffuse Aβ42 plaques, but not dense-core plaques, were present more frequently in the temporal cortex and tended to be more common than Aβ40 plaques across species. Conversely, vascular Aβ was labeled more consistently with Aβ40 for each species on average. Although all individuals showed some degree of Aβ40 and/or Aβ42 immunoreactivity, only the cheetahs and clouded leopards exhibited intraneuronal hyperphosphorylated tau (i.e., pretangles), which was more common in the hippocampus. Reactive, intermediate microglia were significantly associated with total Aβ40 vessel area and pretangle load in the hippocampus. This study demonstrates the co-occurrence of Aβ and tau pathology in two felid species, cheetahs and clouded leopards. Overall, these results provide an initial view of the manifestation of Aβ and tau pathology in aged, large-brained felids, which can be compared with markers of neurodegeneration across different taxa, including domestic cats, nonhuman primates, and humans.

Loss of TREM2 diminishes CAA despite an overall increase of amyloid load in Tg-SwDI mice

INTRODUCTION

The microglial receptor triggering receptor expressed on myeloid cells 2 (TREM2) is a major risk factor for Alzheimer's disease (AD). Experimentally, Trem2 deficiency affects parenchymal amyloid beta (Aβ) deposition. However, the role of TREM2 in cerebrovascular amyloidosis, especially cerebral amyloid angiopathy (CAA), remains unexplored.

METHODS

Tg-SwDI (SwDI) mice, a CAA-prone model of AD, and Trem2 knockout mice were crossed to generate SwDI/TWT, SwDI/THet, and SwDI/TKO mice, followed by pathological and biochemical analyses at 16 months of age.

RESULTS

Loss of Trem2 led to a dramatic decrease in CAA and microglial association, despite a marked increase in overall brain Aβ load. Single nucleus RNA sequencing analysis revealed that in the absence of Trem2, microglia were activated but trapped in transition to the fully reactive state, with distinct responses of vascular cells.

DISCUSSION

Our study provides the first evidence that TREM2 differentially modulates parenchymal and vascular Aβ pathologies, offering significant implications for both TREM2- and Aβ-targeting therapies for AD.

HIGHLIGHTS

Triggering receptor expressed on myeloid cells 2 (TREM2) differentially modulates brain parenchymal and vascular amyloidosis. Loss of Trem2 markedly reduces cerebral amyloid angiopathy despite an overall increase of amyloid beta load in Tg-SwDI mice. Microglia are trapped in transition to the fully reactive state without Trem2. Perivascular macrophages and other vascular cells have distinct responses to Trem2 deficiency. Balanced TREM2-targeting therapies may be required for optimal outcomes.

Amyloid beta 1-40 and 1-42 fibril ratios and maturation level cause conformational differences with minimal impact on autophagy and cytotoxicity

The amyloid β (Aβ) peptide has a central role in Alzheimer's disease (AD) pathology. The peptide length can vary between 37 and 49 amino acids, with Aβ1-42 being considered the most disease-related length. However, Aβ1-40 is also found in Aβ plaques and has shown to form intertwined fibrils with Aβ1-42. The peptides have previously also shown to form different fibril conformations, proposed to be related to disease phenotype. To conduct more representative in vitro experiments, it is vital to uncover the impact of different fibril conformations on neurons. Hence, we fibrillized different Aβ1-40:42 ratios in concentrations of 100:0, 90:10, 75:25, 50:50, 25:75, 10:90 and 0:100 for either 24 h (early fibrils) or 7 days (aged fibrils). These were then characterized based on fibril width, LCO-staining and antibody-staining. We further challenged differentiated neuronal-like SH-SY5Y human cells with the different fibrils and measured Aβ content, cytotoxicity and autophagy function at three different time-points: 3, 24, and 72 h. Our results revealed that both Aβ1-40:42 ratio and fibril maturation affect conformation of fibrils. We further show the impact of these conformation changes on the affinity to commonly used Aβ antibodies, primarily affecting Aβ1-40 rich aggregates. In addition, we demonstrate uptake of the aggregates by neuronally differentiated human cells, where aggregates with higher Aβ1-42 ratios generally caused higher cellular levels of Aβ. These differences in Aβ abundance did not cause changes in cytotoxicity nor in autophagy activation. Our results show the importance to consider conformational differences of Aβ fibrils, as this can have fundamental impact on Aβ antibody detection. Overall, these insights underline the need for further exploration of the impact of conformationally different fibrils and the need to reliably produce disease relevant Aβ aggregates.

Aggregation Dynamics of a 150 kDa Aβ42 Oligomer: Insights from Cryo Electron Microscopy and Multimodal Analysis

Protein misfolding is a widespread phenomenon that can result in the formation of protein aggregates, which are markers of various disease states, including Alzheimer's disease (AD). In AD, amyloid beta (Aβ) peptides, particularly Aβ40 and Aβ42, are key players in the disease's progression, as they aggregate to form amyloid plaques and contribute to neuronal toxicity. Recent research has shifted attention from solely Aβ fibrils to also include Aβ protofibrils and oligomers as potentially critical pathogenic agents. Particularly, oligomers demonstrate greater toxicity compared to other Aβ specie. Hence, there is an increased interest in studying the correlation between toxicity and their structure and aggregation pathway. The present study investigates the aggregation of a 150 kDa Aβ42 oligomer that does not lead to fibril formation over time. Using negative stain transmission electron microscopy (TEM), size exclusion chromatography (SEC), dynamic light scattering (DLS), and cryo-electron microscopy (cryo-EM), we demonstrate that 150 kDa Aβ42 oligomers form higher-order string-like assemblies over time. The strings are unique from the classical Aβ fibril structures. The significance of our work lies in elucidating molecular behavior of a novel non-fibrillar form of Aβ42 aggregate.

Cryo-EM structures of pathogenic fibrils and their impact on neurodegenerative disease research

Neurodegenerative diseases are commonly associated with the formation of aberrant protein aggregates within the brain, and ultrastructural analyses have revealed that the proteins within these inclusions often assemble into amyloid filaments. Cryoelectron microscopy (cryo-EM) has emerged as an effective method for determining the near-atomic structure of these disease-associated filamentous proteins, and the resulting structures have revolutionized the way we think about aberrant protein aggregation and propagation during disease progression. These structures have also revealed that individual fibril conformations may dictate different disease conditions, and this newfound knowledge has improved disease modeling in the lab and advanced the ongoing pursuit of clinical tools capable of distinguishing and targeting different pathogenic entities within living patients. In this review, we summarize some of the recently developed cryo-EM structures of ex vivo α-synuclein, tau, β-amyloid (Aβ), TAR DNA-binding protein 43 (TDP-43), and transmembrane protein 106B (TMEM106B) fibrils and discuss how these structures are being leveraged toward mechanistic research and therapeutic development.

Genomic stress and impaired DNA repair in Alzheimer disease

Alzheimer disease (AD) is the most prominent form of dementia and has received considerable attention due to its growing burden on economic, healthcare and basic societal infrastructures. The two major neuropathological hallmarks of AD, i.e., extracellular amyloid beta (Aβ) peptide plaques and intracellular hyperphosphorylated Tau neurofibrillary tangles, have been the focus of much research, with an eye on understanding underlying disease mechanisms and identifying novel therapeutic avenues. One often overlooked aspect of AD is how Aβ and Tau may, through indirect and direct mechanisms, affect genome integrity. Herein, we review evidence that Aβ and Tau abnormalities induce excessive genomic stress and impair genome maintenance mechanisms, events that can promote DNA damage-induced neuronal cell loss and associated brain atrophy.

Distinctive contribution of two additional residues in protein aggregation of Aβ42 and Aβ40 isoforms

Amyloid-β (Aβ) is one of the amyloidogenic intrinsically disordered proteins (IDPs) that self-assemble to protein aggregates, incurring cell malfunction and cytotoxicity. While Aβ has been known to regulate multiple physiological functions, such as enhancing synaptic functions, aiding in the recovery of the blood-brain barrier/brain injury, and exhibiting tumor suppression/antimicrobial activities, the hydrophobicity of the primary structure promotes pathological aggregations that are closely associated with the onset of Alzheimer's disease (AD). Aβ proteins consist of multiple isoforms with 37-43 amino acid residues that are produced by the cleavage of amyloid-β precursor protein (APP). The hydrolytic products of APP are secreted to the extracellular regions of neuronal cells. Aβ 1-42 (Aβ42) and Aβ 1-40 (Aβ40) are dominant isoforms whose significance in AD pathogenesis has been highlighted in numerous studies to understand the molecular mechanism and develop AD diagnosis and therapeutic strategies. In this review, we focus on the differences between Aβ42 and Aβ40 in the molecular mechanism of amyloid aggregations mediated by the two additional residues (Ile41 and Ala42) of Aβ42. The current comprehension of Aβ42 and Aβ40 in AD progression is outlined, together with the structural features of Aβ42/Aβ40 amyloid fibrils, and the aggregation mechanisms of Aβ42/Aβ40. Furthermore, the impact of the heterogeneous distribution of Aβ isoforms during amyloid aggregations is discussed in the system mimicking the coexistence of Aβ42 and Aβ40 in human cerebrospinal fluid (CSF) and plasma. [BMB Reports 2024; 57(6): 263-272].

Particulate matter constituents trigger the formation of extracellular amyloid β and Tau -containing plaques and neurite shortening in vitro

Air pollution is an environmental factor associated with an increased risk of neurodegenerative diseases, such as Alzheimer's and Parkinson's, characterized by decreased cognitive abilities and memory. The limited models of sporadic Alzheimer's disease fail to replicate all pathological hallmarks of the disease, making it challenging to uncover potential environmental causes. Environmentally driven models of Alzheimer's disease are thus timely and necessary. We used live-cell confocal fluorescent imaging combined with high-resolution stimulated emission depletion (STED) microscopy to follow the response of retinoic acid-differentiated human neuroblastoma SH-SY5Y cells to nanomaterial exposure. Here, we report that exposure of the cells to some particulate matter constituents reproduces a neurodegenerative phenotype, including extracellular amyloid beta-containing plaques and decreased neurite length. Consistent with the existing in vivo research, we observed detrimental effects, specifically a substantial reduction in neurite length and formation of amyloid beta plaques, after exposure to iron oxide and diesel exhaust particles. Conversely, after exposure to engineered cerium oxide nanoparticles, the lengths of neurites were maintained, and almost no extracellular amyloid beta plaques were formed. Although the exact mechanism behind this effect remains to be explained, the retinoic acid differentiated SH-SY5Y cell in vitro model could serve as an alternative, environmentally driven model of neurodegenerative diseases, including Alzheimer's disease.

Vascular Heparan Sulfate and Amyloid-β in Alzheimer's Disease Patients

Alzheimer's disease (AD) is a debilitating neurodegenerative disease characterized by the accumulation of extracellular amyloid-β peptides (Aβ) within the cerebral parenchyma and vasculature, which is known as cerebral amyloid angiopathy (CAA). This study utilized confocal imaging to investigate heparan sulfate (HS) expression within the cerebrovasculature and its associations with Aβ, gender, and ApoE4 genotype in AD. Our investigation revealed elevated levels of HS in the cerebrovasculature of AD patients with severe CAA. Additionally, these patients exhibited higher HS colocalization with Aβ in the cerebrovasculature, including both endothelial and vascular smooth muscle cell compartments. Intriguingly, a reversal in the polarized expression of HS within the cerebrovasculature was detected in AD patients with severe CAA. Furthermore, male patients exhibited lower levels of both parenchymal and cerebrovascular HS. Additionally, ApoE4 carriers displayed heightened cerebrovascular Aβ expression and a tendency of elevated cerebrovascular HS levels in AD patients with severe CAA. Overall, these findings reveal potential intricate interplay between HS, Aβ, ApoE, and vascular pathology in AD, thereby underscoring the potential roles of cerebrovascular HS in CAA development and AD pathology. Further study of the underlying mechanisms may present novel therapeutic avenues for AD treatment.

Amyloid Modifier SERF1a Accelerates Alzheimer's Amyloid-β Fibrillization and Exacerbates the Cytotoxicity

Alzheimer's disease (AD) is a devastating, progressive neurodegenerative disease affecting the elderly in the world. The pathological hallmark senile plaques are mainly composed of amyloid-β (Aβ), in which the main isoforms are Aβ40 and Aβ42. Aβ is prone to aggregate and ultimately forms amyloid fibrils in the brains of AD patients. Factors that alter the Aβ aggregation process have been considered to be potential targets for treatments of AD. Modifier of aggregation 4 (MOAG-4)/small EDRK-rich factor (SERF) was previously selected from a chemical mutagenesis screen and identified as an amyloid modifier that promotes amyloid aggregation for α-synuclein, huntingtin, and Aβ40. The interaction and effect of yeast ScSERF on Aβ40 were previously described. Here, we examined the human SERF1a effect on Aβ40 and Aβ42 fibrillization by the Thioflavin T assay and found that SERF1a accelerated Aβ fibrillization in a dose-dependent manner without changing the fibril amount and without incorporation. By Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM), we found that SERF1a altered the secondary structures and the morphology of Aβ fibrils. The electrospray ionization mass spectrometry (ESI-MS) and analytical ultracentrifugation (AUC) results showed that SERF1a binds to Aβ in a 1:1 stoichiometry. Moreover, the NMR study showed that SERF1a interacts with Aβ via its N-terminal region. Cytotoxicity assay demonstrated that SERF1a enhanced toxicity of Aβ intermediates, and the effect can be rescued by SERF1a antibody. Overall, our study provides the underlying molecular mechanism for the SERF1a effect on Aβ fibrillization and facilitates the therapeutic development of AD.

Loss of TREM2 exacerbates parenchymal amyloid pathology but diminishes CAA in Tg-SwDI mice

Alzheimer's disease (AD) is a progressive neurodegenerative disease, and it is the most common cause of dementia worldwide. Recent genome-wide association studies (GWAS) identified TREM2 (triggering receptor expressed on myeloid cells 2) as one of the major risk factors for AD. TREM2 is a surface receptor expressed on microglia and largely mediates microglial functions and immune homeostasis in the brain. The functions of TREM2 in AD pathogenesis, including in the formation of the key pathology parenchymal amyloid-β (Aβ) plaques, have been investigated by introducing Trem2 deficiency in AD mouse models. However, the role of TREM2 in cerebrovascular amyloidosis, in particular cerebral amyloid angiopathy (CAA) remains unexplored. CAA features Aβ deposition along the cerebral vessels, signifying an intersection between AD and vascular dysfunction. Using a well-characterized CAA-prone, transgenic mouse model of AD, Tg-SwDI (SwDI), we found that loss of TREM2 led to a marked increase in overall Aβ load in the brain, but a dramatic decrease in CAA in microvessel-rich regions, along with reduced microglial association with CAA. Transcriptomic analysis revealed that in the absence of Trem2 , microglia were activated but trapped in transition to the fully reactive state. Like microglia, perivascular macrophages were activated with upregulation of cell junction related pathways in Trem2 -deficient SwDI mice. In addition, vascular mural cells and astrocytes exhibited distinct responses to Trem2 deficiency, contributing to the pathological changes in the brain of Trem2 -null SwDI mice. Our study provides the first evidence that TREM2 differentially modulates parenchymal and vascular Aβ pathologies, which may have significant implications for both TREM2- and Aβ-targeting therapies for AD.

Anti-Amyloid Therapy, AD, and ARIA: Untangling the Role of CAA

Anti-amyloid therapies (AATs), such as anti-amyloid monoclonal antibodies, are emerging treatments for people with early Alzheimer's disease (AD). AATs target amyloid β plaques in the brain. Amyloid-related imaging abnormalities (ARIA), abnormal signals seen on magnetic resonance imaging (MRI) of the brain in patients with AD, may occur spontaneously but occur more frequently as side effects of AATs. Cerebral amyloid angiopathy (CAA) is a major risk factor for ARIA. Amyloid β plays a key role in the pathogenesis of AD and of CAA. Amyloid β accumulation in the brain parenchyma as plaques is a pathological hallmark of AD, whereas amyloid β accumulation in cerebral vessels leads to CAA. A better understanding of the pathophysiology of ARIA is necessary for early detection of those at highest risk. This could lead to improved risk stratification and the ultimate reduction of symptomatic ARIA. Histopathological confirmation of CAA by brain biopsy or autopsy is the gold standard but is not clinically feasible. MRI is an available in vivo tool for detecting CAA. Cerebrospinal fluid amyloid β level testing and amyloid PET imaging are available but do not offer specificity for CAA vs amyloid plaques in AD. Thus, developing and testing biomarkers as reliable and sensitive screening tools for the presence and severity of CAA is a priority to minimize ARIA complications.

Mechanistic Intimate Insights into the Role of Hydrogen Sulfide in Alzheimer's Disease: A Recent Systematic Review

In the rapidly evolving field of Alzheimer's Disease (AD) research, the intricate role of Hydrogen Sulfide (H2S) has garnered critical attention for its diverse involvement in both pathological substrates and prospective therapeutic paradigms. While conventional pathophysiological models of AD have primarily emphasized the significance of amyloid-beta (Aβ) deposition and tau protein hyperphosphorylation, this targeted systematic review meticulously aggregates and rigorously appraises seminal contributions from the past year elucidating the complex mechanisms of H2S in AD pathogenesis. Current scholarly literature accentuates H2S's dual role, delineating its regulatory functions in critical cellular processes-such as neurotransmission, inflammation, and oxidative stress homeostasis-while concurrently highlighting its disruptive impact on quintessential AD biomarkers. Moreover, this review illuminates the nuanced mechanistic intimate interactions of H2S in cerebrovascular and cardiovascular pathology associated with AD, thereby exploring avant-garde therapeutic modalities, including sulfurous mineral water inhalations and mud therapy. By emphasizing the potential for therapeutic modulation of H2S via both donors and inhibitors, this review accentuates the imperative for future research endeavors to deepen our understanding, thereby potentially advancing novel diagnostic and therapeutic strategies in AD.

Border-associated macrophages promote cerebral amyloid angiopathy and cognitive impairment through vascular oxidative stress

BACKGROUND

Cerebral amyloid angiopathy (CAA) is a devastating condition common in patients with Alzheimer's disease but also observed in the general population. Vascular oxidative stress and neurovascular dysfunction have been implicated in CAA but the cellular source of reactive oxygen species (ROS) and related signaling mechanisms remain unclear. We tested the hypothesis that brain border-associated macrophages (BAM), yolk sac-derived myeloid cells closely apposed to parenchymal and leptomeningeal blood vessels, are the source of radicals through the Aβ-binding innate immunity receptor CD36, leading to neurovascular dysfunction, CAA, and cognitive impairment.

METHODS

Tg2576 mice and WT littermates were transplanted with CD36-/- or CD36+/+ bone marrow at 12-month of age and tested at 15 months. This approach enables the repopulation of perivascular and leptomeningeal compartments with CD36-/- BAM. Neurovascular function was tested in anesthetized mice equipped with a cranial window in which cerebral blood flow was monitored by laser-Doppler flowmetry. Amyloid pathology and cognitive function were also examined.

RESULTS

The increase in blood flow evoked by whisker stimulation (functional hyperemia) or by endothelial and smooth muscle vasoactivity was markedly attenuated in WT → Tg2576 chimeras but was fully restored in CD36-/- → Tg2576 chimeras, in which BAM ROS production was suppressed. CAA-associated Aβ1-40, but not Aβ1-42, was reduced in CD36-/- → Tg2576 chimeras. Similarly, CAA, but not parenchymal plaques, was reduced in CD36-/- → Tg2576 chimeras. These beneficial vascular effects were associated with cognitive improvement. Finally, CD36-/- mice were able to more efficiently clear exogenous Aβ1-40 injected into the neocortex or the striatum.

CONCLUSIONS

CD36 deletion in BAM suppresses ROS production and rescues the neurovascular dysfunction and damage induced by Aβ. CD36 deletion in BAM also reduced brain Aβ1-40 and ameliorated CAA without affecting parenchyma plaques. Lack of CD36 enhanced the vascular clearance of exogenous Aβ. Restoration of neurovascular function and attenuation of CAA resulted in a near complete rescue of cognitive function. Collectively, these data implicate brain BAM in the pathogenesis of CAA and raise the possibility that targeting BAM CD36 is beneficial in CAA and other conditions associated with vascular Aβ deposition and damage.

Mass Spectrometry Imaging in Alzheimer's Disease

Introduction: Amyloid-beta (Aβ) pathology is the precipitating histopathological characteristic of Alzheimer's disease (AD). Although the formation of amyloid plaques in human brains is suggested to be a key factor in initiating AD pathogenesis, it is still not fully understood the upstream events that lead to Aβ plaque formation and its metabolism inside the brains. Methods: Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) has been successfully introduced to study AD pathology in brain tissue both in AD mouse models and human samples. By using MALDI-MSI, a highly selective deposition of Aβ peptides in AD brains with a variety of cerebral amyloid angiopathy (CAA) involvement was observed. Results: MALDI-MSI visualized depositions of shorter peptides in AD brains; Aβ1-36 to Aβ1-39 were quite similarly distributed with Aβ1-40 as a vascular pattern, and deposition of Aβ1-42 and Aβ1-43 was visualized with a distinct senile plaque pattern distributed in parenchyma. Moreover, how MALDI-MSI covered in situ lipidomics of plaque pathology has been reviewed, which is of interest as aberrations in neuronal lipid biochemistry have been implicated in AD pathogenesis. Discussion: In this study, we introduce the methodological concepts and challenges of MALDI-MSI for the studies of AD pathogenesis. Diverse Aβ isoforms including various C- and N-terminal truncations in AD and CAA brain tissues will be visualized. Despite the close relationship between vascular and plaque Aβ deposition, the current strategy will define cross talk between neurodegenerative and cerebrovascular processes at the level of Aβ metabolism.

Receptor Recycling by Retromer

The highly conserved retromer complex controls the fate of hundreds of receptors that pass through the endolysosomal system and is a central regulatory node for diverse metabolic programs. More than 20 years ago, retromer was discovered as an essential regulator of endosome-to-Golgi transport in yeast; since then, significant progress has been made to characterize how metazoan retromer components assemble to enable its engagement with endosomal membranes, where it sorts cargo receptors from endosomes to the trans-Golgi network or plasma membrane through recognition of sorting motifs in their cytoplasmic tails. In this review, we examine retromer regulation by exploring its assembled structure with an emphasis on how a range of adaptor proteins shape the process of receptor trafficking. Specifically, we focus on how retromer is recruited to endosomes, selects cargoes, and generates tubulovesicular carriers that deliver cargoes to target membranes. We also examine how cells adapt to distinct metabolic states by coordinating retromer expression and function. We contrast similarities and differences between retromer and its related complexes: retriever and commander/CCC, as well as their interplay in receptor trafficking. We elucidate how loss of retromer regulation is central to the pathology of various neurogenerative and metabolic diseases, as well as microbial infections, and highlight both opportunities and cautions for therapeutics that target retromer. Finally, with a focus on understanding the mechanisms that govern retromer regulation, we outline new directions for the field moving forward.

Imaging Amyloid-β Membrane Interactions: Ion-Channel Pores and Lipid-Bilayer Permeability in Alzheimer's Disease

The accumulation of the amyloid-β peptides (Aβ) is central to the development of Alzheimer's disease. The mechanism by which Aβ triggers a cascade of events that leads to dementia is a topic of intense investigation. Aβ self-associates into a series of complex assemblies with different structural and biophysical properties. It is the interaction of these oligomeric, protofibril and fibrillar assemblies with lipid membranes, or with membrane receptors, that results in membrane permeability and loss of cellular homeostasis, a key event in Alzheimer's disease pathology. Aβ can have an array of impacts on lipid membranes, reports have included: a carpeting effect; a detergent effect; and Aβ ion-channel pore formation. Recent advances imaging these interactions are providing a clearer picture of Aβ induced membrane disruption. Understanding the relationship between different Aβ structures and membrane permeability will inform therapeutics targeting Aβ cytotoxicity.

Imaging Amyloid-β Membrane Interactions: Ion-Channel Pores and Lipid-Bilayer Permeability in Alzheimer's Disease

The accumulation of the amyloid-β peptides (Aβ) is central to the development of Alzheimer's disease. The mechanism by which Aβ triggers a cascade of events that leads to dementia is a topic of intense investigation. Aβ self-associates into a series of complex assemblies with different structural and biophysical properties. It is the interaction of these oligomeric, protofibril and fibrillar assemblies with lipid membranes, or with membrane receptors, that results in membrane permeability and loss of cellular homeostasis, a key event in Alzheimer's disease pathology. Aβ can have an array of impacts on lipid membranes, reports have included: a carpeting effect; a detergent effect; and Aβ ion-channel pore formation. Recent advances imaging these interactions are providing a clearer picture of Aβ induced membrane disruption. Understanding the relationship between different Aβ structures and membrane permeability will inform therapeutics targeting Aβ cytotoxicity.

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

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

Discoveries and future significance of research into amyloid-beta/α7-containing nicotinic acetylcholine receptor (nAChR) interactions

Initiated by findings that Alzheimer's disease is associated with a profound loss of cholinergic markers in human brain, decades of studies have examined the interactions between specific subtypes of nicotinic acetylcholine receptors and amyloid-β [derived from the amyloid precursor protein (APP), which is cleaved to yield variable isoforms of amyloid-β]. We review the evolving understanding of amyloid-β's roles in Alzheimer's disease and pioneering studies that highlighted a role of nicotinic acetylcholine receptors in mediating important aspects of amyloid-β's effects. This review also surveys the current state of research into amyloid-β / nicotinic acetylcholine receptor interactions. The field has reached an exciting point in which common themes are emerging from the wide range of prior research and a range of accessible, relevant model systems are available to drive further progress. We highlight exciting new areas of inquiry and persistent challenges that need to be considered while conducting this research. Studies of amyloid-β and the nicotinic acetylcholine receptor populations that it interacts with provide opportunities for innovative basic and translational scientific breakthroughs related to nicotinic receptor biology, Alzheimer's disease, and cholinergic contributions to cognition more broadly.

Sodium Oligomannate Electrostatically Binds to Aβ and Blocks Its Aggregation

GV-971 (sodium oligomannate) is a China Food and Drug Administration (CFDA)-approved drug for treating Alzheimer's disease, and it could inhibit Aβ fibril formation in vitro and in mouse studies. To elucidate the mechanisms for understanding how GV-971 modulates Aβ's aggregation, we conducted a systematic biochemical and biophysical study of Aβ40/Aβ42:GV-971 systems. The integrating analysis of previously published data and our results suggests that the multisite electrostatic interactions between GV-971's carboxylic groups and Aβ40/Aβ42's three histidine residues might play a dominant role in driving the binding of GV-971 to Aβ. The fuzzy-type electrostatic interactions between GV-971 and Aβ are expected to protect Aβ from aggregation potentially through breaking the histidine-mediated inter-Aβ electrostatic interactions. Meanwhile, since GV-971's binding exhibited a slight downregulation effect on the flexibility of Aβ's histidine-colonized fragment, which potentially favors Aβ aggregation, we conclude that the dynamics alteration plays a minor role in GV-971's modulation on Aβ aggregation.

Stability of the Aβ42 Peptide in Mixed Solutions of Denaturants and Proline

Amyloid β-peptide (Aβ) is responsible for the neuronal damage and death of a patient with Alzheimer's disease (AD). Aβ42 oligomeric forms are dominant neurotoxins and are related to neurodegeneration. Their different forms are related to various pathological conditions in the brain. We investigated Aβ42 peptides in different environments of proline, urea, and GdmCl solutions (in pure and mixed binary forms) through atomistic molecular dynamics simulations. Preferential exclusion from the protein surface and facile formation of a large number of weak molecular interactions are the driving forces for the osmolyte's action. We have focused on these interactions between peptide monomers and pure/mixed osmolytes and denaturants. Urea, as usual, denatures the peptide strongly compared to the GdmCl by accumulation around the peptide. GdmCl shows lesser build-up around protein in contrast to urea but is involved in destabilizing the salt bridge formation of Asp23 and Lys28. Proline as an osmolyte protects the peptide from aggregation when mixed with urea and GdmCl solutions. In mixed solutions of two denaturants and osmolyte plus denaturant, the peptide shows enhanced stability as compared to pure denaturant urea solution. The enhanced stability of peptides in proline may be attributed to its exclusion from the peptide surface and favoring salt bridge formation.

Towards early detection of neurodegenerative diseases: A gut feeling

The gastrointestinal tract communicates with the nervous system through a bidirectional network of signaling pathways called the gut-brain axis, which consists of multiple connections, including the enteric nervous system, the vagus nerve, the immune system, endocrine signals, the microbiota, and its metabolites. Alteration of communications in the gut-brain axis is emerging as an overlooked cause of neuroinflammation. Neuroinflammation is a common feature of the pathogenic mechanisms involved in various neurodegenerative diseases (NDs) that are incurable and debilitating conditions resulting in progressive degeneration and death of neurons, such as in Alzheimer and Parkinson diseases. NDs are a leading cause of global death and disability, and the incidences are expected to increase in the following decades if prevention strategies and successful treatment remain elusive. To date, the etiology of NDs is unclear due to the complexity of the mechanisms of diseases involving genetic and environmental factors, including diet and microbiota. Emerging evidence suggests that changes in diet, alteration of the microbiota, and deregulation of metabolism in the intestinal epithelium influence the inflammatory status of the neurons linked to disease insurgence and progression. This review will describe the leading players of the so-called diet-microbiota-gut-brain (DMGB) axis in the context of NDs. We will report recent findings from studies in model organisms such as rodents and fruit flies that support the role of diets, commensals, and intestinal epithelial functions as an overlooked primary regulator of brain health. We will finish discussing the pivotal role of metabolisms of cellular organelles such as mitochondria and peroxisomes in maintaining the DMGB axis and how alteration of the latter can be used as early disease makers and novel therapeutic targets.

Quantitative proteomics of tau and Aβ in detergent fractions from Alzheimer's disease brains

The two hallmarks of Alzheimer's disease (AD) are amyloid-β (Aβ) plaques and neurofibrillary tangles marked by phosphorylated tau. Increasing evidence suggests that aggregating Aβ drives tau accumulation, a process that involves synaptic degeneration leading to cognitive impairment. Conversely, there is a realization that non-fibrillar (oligomeric) forms of Aβ mediate toxicity in AD. Fibrillar (filamentous) aggregates of proteins across the spectrum of the primary and secondary tauopathies were the focus of recent structural studies with a filament structure-based nosologic classification, but less emphasis was given to non-filamentous co-aggregates of insoluble proteins in the fractions derived from post-mortem human brains. Here, we revisited sarkosyl-soluble and -insoluble extracts to characterize tau and Aβ species by quantitative targeted mass spectrometric proteomics, biochemical assays, and electron microscopy. AD brain sarkosyl-insoluble pellets were greatly enriched with Aβ₄₂ at almost equimolar levels to N-terminal truncated microtubule-binding region (MTBR) isoforms of tau with multiple site-specific post-translational modifications (PTMs). MTBR R3 and R4 tau peptides were most abundant in the sarkosyl-insoluble materials with a 10-fold higher concentration than N-terminal tau peptides. This indicates that the major proportion of the enriched tau was the aggregation-prone N-terminal and proline-rich region (PRR) of truncated mixed 4R and 3R tau with more 4R than 3R isoforms. High concentration and occupancies of site-specific phosphorylation pT₁₈₁ (~22%) and pT₂₁₇ (~16%) (key biomarkers of AD) along with other PTMs in the PRR and MTBR indicated a regional susceptibility of PTMs in aggregated tau. Immunogold labelling revealed that tau may exist in globular non-filamentous form (N-terminal intact tau) co-localized with Aβ in the sarkosyl-insoluble pellets along with tau filaments (N-truncated MTBR tau). Our results suggest a model that Aβ and tau interact forming globular aggregates, from which filamentous tau and Aβ emerge. These characterizations contribute towards unravelling the sequence of events which lead to end-stage AD changes.

Time-Resolved In Situ AFM Measurement of Growth Rates of Aβ40 Fibrils

We employ time-resolved in situ atomic force microcopy to monitor the growth of individual Aβ40 fibrils and thereby directly measure the fibril growth rates. We describe procedures to express and purify the Aβ peptide and verify its identity, prepare solutions and seeds, quantify the displacements of the growing tips of individual fibrils, and determine their respective growth rates. We discuss approaches to evaluate and minimize the impact of the scanning tip on the monitored processes. We use the distribution of fibril thickness to characterize approximately the fibril structure. The ability to quantify faithfully the growth kinetics of amyloid fibrils empowers exploration of the molecular-level processes of fibril growth that relate to behaviors of amyloid species of laboratory and clinical interest.

Preparation and Fractionation of Heterogeneous Aβ42 Oligomers with Different Aggregation Properties

Deposition of amyloid-β (Aβ) aggregates in the form of amyloid plaques is a central feature of Alzheimer's disease. The end products of Aβ aggregation are amyloid fibrils. Soluble Aβ aggregates called oligomers are also formed either on or off the pathway of fibril formation. The amyloid fibrils from different clinical subtypes of Alzheimer's disease have been found to adopt different structures, a phenomenon called fibril polymorphism. Meanwhile, different types of Aβ oligomers have also been found. Recently, it has been shown that different types of Aβ42 oligomers may form fibrils of different structures, linking oligomer heterogeneity to fibril polymorphism. In this chapter, we describe methods to prepare heterogeneous Aβ42 oligomers and to quantify the concentration of these oligomers at a low micromolar range using a fluorescamine method. Fractionation of these oligomers by size using ultrafiltration filters allows for the formation of Aβ42 fibrils with different structural properties.

Impact of Aβ40 and Aβ42 Fibrils on the Transcriptome of Primary Astrocytes and Microglia

Fibrillar amyloid β-protein (Aβ) deposits in the brain, which are primarily composed of Aβ40 or Aβ42 peptides, are key pathological features of Alzheimer's disease (AD) and related disorders. Although the underlying mechanisms are still not clear, the Aβ fibrils can trigger a number of cellular responses, including activation of astrocytes and microglia. In addition, fibril structures of the Aβ40 and Aβ42 peptides are known to be polymorphic, which poses a challenge for attributing the contribution of different Aβ sequences and structures to brain pathology. Here, we systematically treated primary astrocytes and microglia with single, well-characterized polymorphs of Aβ40 or Aβ42 fibrils, and performed bulk RNA sequencing to assess cell-specific changes in gene expression. A greater number of genes were up-regulated by Aβ42 fibril-treated glial cells (251 and 2133 genes in astrocyte and microglia, respectively) compared with the Aβ40 fibril-treated glial cells (191 and 251 genes in astrocytes and microglia, respectively). Immunolabeling studies in an AD rat model with parenchymal fibrillar Aβ42 plaques confirmed the expression of PAI-1, MMP9, MMP12, CCL2, and C1r in plaque-associated microglia, and iNOS, GBP2, and C3D in plaque-associated astrocytes, validating markers from the RNA sequence data. In order to better understand these Aβ fibril-induced gene changes, we analyzed gene expression patterns using the Ingenuity pathway analysis program. These analyses further highlighted that Aβ42 fibril treatment up-regulated cellular activation pathways and immune response pathways in glial cells, including IL1β and TNFα in astrocytes, and microglial activation and TGFβ1 in microglia. Further analysis revealed that a number of disease-associated microglial (DAM) genes were surprisingly suppressed in Aβ40 fibril treated microglia. Together, the present findings indicate that Aβ42 fibrils generally show similar, but stronger, stimulating activity of glial cells compared with Aβ40 fibril treatment.

Different Aβ43 deposition patterns in the brains of aged dogs, sea lions, and cats

Cerebral amyloid β (Aβ) deposition is a pathological hallmark of Alzheimer's disease (AD). There are several molecular species of Aβ, including Aβ40, Aβ42, and Aβ43, and the pathological roles of Aβ43 have attracted particular attention in recent years. Aβ43 is mainly deposited as senile plaques (SPs) in AD brains, and is known to be more amyloidogenic and neurotoxic than Aβ42 and Aβ40. Aβ40 and Aβ42 deposition have been demonstrated in several animal species, while Aβ43 deposition has not been studied in animals. The brains of sea lions, dogs, and cats exhibit unique age-related Aβ pathologies. In the present study, the deposition patterns of Aβ40, Aβ42, and Aβ43 were examined immunohistochemically in the brains of aged dogs (n=52), sea lions (n=5), and cats (n=17). In dogs, most cerebral amyloid angiopathy (CAA) lesions and primitive SPs were positive for Aβ42, Aβ43, and Aβ40. However, diffuse SPs and capillary CAA lesions were negative for Aβ40. In sea lions, all SPs and most CAA lesions were positive for Aβ42, Aβ43, and Aβ40, while capillary CAA lesions were negative for Aβ40. In cats, Aβ42-immunopositive granular aggregates and arteriole and capillary CAA lesions were positive for Aβ43, but negative for Aβ40. Double-labelling immunohistochemistry revealed the co-localization of Aβ42 and Aβ43. These findings suggest that Aβ43 and Aβ42 are frequently deposited in the brains of Carnivora animals and may play an important role in Aβ pathology.

Chemical traits of cerebral amyloid angiopathy in familial British-, Danish-, and non-Alzheimer's dementias

Familial British dementia (FBD) and familial Danish dementia (FDD) are autosomal dominant forms of dementia caused by mutations in the integral membrane protein 2B (ITM2B, also known as BRI2) gene. Secretase processing of mutant BRI2 leads to secretion and deposition of BRI2-derived amyloidogenic peptides, ABri and ADan that resemble APP/β-amyloid (Aβ) pathology, which is characteristic of Alzheimer's disease (AD). Amyloid pathology in FBD/FDD manifests itself predominantly in the microvasculature by ABri/ADan containing cerebral amyloid angiopathy (CAA). While ABri and ADan peptide sequences differ only in a few C-terminal amino acids, CAA in FDD is characterized by co-aggregation of ADan with Aβ, while in contrast no Aβ deposition is observed in FBD. The fact that FDD patients display an earlier and more severe disease onset than FBD suggests a potential role of ADan and Aβ co-aggregation that promotes a more rapid disease progression in FDD compared to FBD. It is therefore critical to delineate the chemical signatures of amyloid aggregation in these two vascular dementias. This in turn will increase the knowledge on the pathophysiology of these diseases and the pathogenic role of heterogenous amyloid peptide interactions and deposition, respectively. Herein, we used matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) in combination with hyperspectral, confocal microscopy based on luminescent conjugated oligothiophene probes (LCO) to delineate the structural traits and associated amyloid peptide patterns of single CAA in postmortem brain tissue of patients with FBD, FDD as well as sporadic CAA without AD (CAA+) that show pronounced CAA without parenchymal plaques. The results show that CAA in both FBD and FDD consist of N-terminally truncated- and pyroglutamate-modified amyloid peptide species (ADan and ABri), but that ADan peptides in FDD are also extensively C-terminally truncated as compared to ABri in FBD, which contributes to hydrophobicity of ADan species. Further, CAA in FDD showed co-deposition with Aβ x-42 and Aβ x-40 species. CAA+ vessels were structurally more mature than FDD/FBD CAA and contained significant amounts of pyroglutamated Aβ. When compared with FDD, Aβ in CAA+ showed more C-terminal and less N-terminally truncations. In FDD, ADan showed spatial co-localization with Aβ3pE-40 and Aβ3-40 but not with Aβx-42 species. This suggests an increased aggregation propensity of Aβ in FDD that promotes co-aggregation of both Aβ and ADan. Further, CAA maturity appears to be mainly governed by Aβ content based on the significantly higher 500/580 patterns observed in CAA+ than in FDD and FBD, respectively. Together this is the first study of its kind on comprehensive delineation of Bri2 and APP-derived amyloid peptides in single vascular plaques in both FDD/FBD and sporadic CAA that provides new insight in non-AD-related vascular amyloid pathology. Cover Image for this issue: https://doi.org/10.1111/jnc.15424.

Dual-probe fluorescence spectroscopy for sensitive quantitation of Alzheimer’s amyloid pathology

Protein misfolding is a prominent pathological hallmark of neurodegenerative disorders, including Alzheimer’s disease (AD). Studies have shown that the diversity of β sheet-rich protein deposits (such as amyloid β plaques and neurofibrillary tangles), present across different brain regions, might underlie different disease phenotypes and only certain types of aggregates might be associated with cognitive decline. Conformationally sensitive fluorescent amyloid probes have the ability to report different structures of protein aggregates by virtue of their shifting emission spectra. Here we defined the binding affinity of the fluorescent amyloid probes BSB and MCAAD to disease-relevant protein aggregates, and combined the two probes to examine formalin-fixed paraffin-embedded mouse and human brain samples. Coupled with quantitative spectral phasor analysis, the dual-probe staining approach revealed remarkable heterogeneity of protein aggregates across the samples. Distinct emission spectra were consistent with certain types of deposits present in the mouse and human brain sections. The sensitivity of this staining, imaging and analysis approach outperformed conventional immunohistochemistry with the detected spectral differences between the greater parenchyma of cognitively normal and AD cases indicating a subtle yet widespread proteopathy associated with disease. Our method offers more sensitive, objective, and quantitative examination of protein misfolding pathology using conventional tissue sections.

Key Residue for Aggregation of Amyloid-β Peptides

It is known that oligomers of amyloid-β (Aβ) peptide are associated with Alzheimer's disease. Aβ has two isoforms: Aβ40 and Aβ42. Although the difference between Aβ40 and Aβ42 is only two additional C-terminal residues, Aβ42 aggregates much faster than Aβ40. It is unknown what role the C-terminal two residues play in accelerating aggregation. Since Aβ42 is more toxic than Aβ40, its oligomerization process needs to be clarified. Moreover, clarifying the differences between the oligomerization processes of Aβ40 and Aβ42 is essential to elucidate the key factors of oligomerization. Therefore, to investigate the dimerization process, which is the early oligomerization process, Hamiltonian replica-permutation molecular dynamics simulations were performed for Aβ40 and Aβ42. We identified a key residue, Arg5, for the Aβ42 dimerization. The two additional residues in Aβ42 allow the C-terminus to form contact with Arg5 because of the electrostatic attraction between them, and this contact stabilizes the β-hairpin. This β-hairpin promotes dimer formation through the intermolecular β-bridges. Thus, we examined the effects of amino acid substitutions of Arg5, thereby confirming that the mutations remarkably suppressed the aggregation of Aβ42. Moreover, the mutations of Arg5 suppressed the Aβ40 aggregation. It was found by analyzing the simulations that Arg5 is important for Aβ40 to form intermolecular contacts. Thus, it was clarified that the role of Arg5 in the oligomerization process varies due to the two additional C-terminal residues.

Novel molecular mechanisms in Alzheimer's disease: The potential role of DEK in disease pathogenesis

Alzheimer's disease and age-related dementias (AD/ADRD) are debilitating diseases that exact a significant physical, emotional, cognitive, and financial toll on the individual and their social network. While genetic risk factors for early-onset AD have been identified, the molecular and genetic drivers of late-onset AD, the most common subtype, remain a mystery. Current treatment options are limited for the 35 million people in the United States with AD/ADRD. Thus, it is critically important to identify novel molecular mechanisms of dementia-related pathology that may be targets for the development of new interventions. Here, we summarize the overarching concepts regarding AD/ADRD pathogenesis. Then, we highlight one potential molecular driver of AD/ADRD, the chromatin remodeling protein DEK. We discuss in vitro, in vivo, and ex vivo findings, from our group and others, that link DEK loss with the cellular, molecular, and behavioral signatures of AD/ADRD. These include associations between DEK loss and cellular and molecular hallmarks of AD/ADRD, including apoptosis, Tau expression, and Tau hyperphosphorylation. We also briefly discuss work that suggests sex-specific differences in the role of DEK in AD/ADRD pathogenesis. Finally, we discuss future directions for exploiting the DEK protein as a novel player and potential therapeutic target for the treatment of AD/ADRD.

The Potential Neuroprotective Effects of Extracts from Oat Seedlings against Alzheimer's Disease

The physiological or dietary advantages of germinated grains have been the subject of numerous discussions over the past decade. Around 23 million tons of oats are consumed globally, making up a sizeable portion of the global grain market. Oat seedlings contain more protein, beta-glucan, free amino acids, and phenolic compounds than seeds. The progressive neurodegenerative disorder of Alzheimer's is accompanied by worsening memory and cognitive function. A key indicator of this disorder is the unusual buildup of amyloid-beta protein (or Aβ) in human brains. In this context, oat seedling extract (OSE) has been identified as a new therapeutic candidate for AD, due to its antioxidant activity and AD-specific mechanism of action. This study directly investigated how OSE affected AD and its impacts by examining the cognitive function and exploring the inflammatory response mechanism. The dried oat seedlings were grounded finely with a grinder, inserted with 50% fermented ethanol 10 times (w/v), and extracted by stirring for 10 h at 45 °C. After filtering the extract by 0.22 um filter, some of it was used for UHPLC analysis. The results indicated that the treatment with OSE protects against Aβ25-35-induced cytotoxicity in BV2 cells. Tg-5Xfad AD mice had strong deposition of Aβ throughout their brains, while WT mice did not exhibit any such deposition within their brains. A drastic reduction was observed in terms of numbers, as well as the size, of Aβ plaques within Tg-5Xfad AD mice exposed to OSE. This study indicated OSE's neuroprotective impacts against neurodegeneration, synaptic dysfunction, and neuroinflammation induced by amyloid-beta. Our results suggest that OSE acts as a neuroprotective agent to combat AD-specific apoptotic cell death, neuroinflammation, amyloid-beta accumulation, as well as synaptic dysfunction in AD mice's brains. Furthermore, the study indicated that OSE treatment affects JNK/ERK/p38 MAPK signaling, with considerable inhibition in p-JNK, p-p38, and p-ERK levels seen in the brain of OSE-treated Tg-5Xfad AD mice.

Symptomatic and Disease-Modifying Therapy Pipeline for Alzheimer's Disease: Towards a Personalized Polypharmacology Patient-Centered Approach

Since 1906, when Dr. Alois Alzheimer first described in a patient "a peculiar severe disease process of the cerebral cortex", people suffering from this pathology have been waiting for a breakthrough therapy. Alzheimer's disease (AD) is an irreversible, progressive neurodegenerative brain disorder and the most common form of dementia in the elderly with a long presymptomatic phase. Worldwide, approximately 50 million people are living with dementia, with AD comprising 60-70% of cases. Pathologically, AD is characterized by the deposition of amyloid β-peptide (Aβ) in the neuropil (neuritic plaques) and blood vessels (amyloid angiopathy), and by the accumulation of hyperphosphorylated tau in neurons (neurofibrillary tangles) in the brain, with associated loss of synapses and neurons, together with glial activation, and neuroinflammation, resulting in cognitive deficits and eventually dementia. The current competitive landscape in AD consists of symptomatic treatments, of which there are currently six approved medications: three AChEIs (donepezil, rivastigmine, and galantamine), one NMDA-R antagonist (memantine), one combination therapy (memantine/donepezil), and GV-971 (sodium oligomannate, a mixture of oligosaccharides derived from algae) only approved in China. Improvements to the approved therapies, such as easier routes of administration and reduced dosing frequencies, along with the developments of new strategies and combined treatments are expected to occur within the next decade and will positively impact the way the disease is managed. Recently, Aducanumab, the first disease-modifying therapy (DMT) has been approved for AD, and several DMTs are in advanced stages of clinical development or regulatory review. Small molecules, mAbs, or multimodal strategies showing promise in animal studies have not confirmed that promise in the clinic (where small to moderate changes in clinical efficacy have been observed), and therefore, there is a significant unmet need for a better understanding of the AD pathogenesis and the exploration of alternative etiologies and therapeutic effective disease-modifying therapies strategies for AD. Therefore, a critical review of the disease-modifying therapy pipeline for Alzheimer's disease is needed.

α-Enolase reduces cerebrovascular Aβ deposits by protecting Aβ amyloid formation

Cerebral amyloid angiopathy (CAA) is characterized by cerebrovascular amyloid β (Aβ) deposits and causes dementia and cerebral hemorrhage. Although α-enolase (ENO1) was shown to possess multifunctional roles, its exact functions in CAA pathogenesis have not been determined. In this study, we focused on ENO1, a well-known glycolytic enzyme, which was previously identified via a proteomic approach as an upregulated protein in brain samples from patients with Alzheimer's disease (AD). We utilized the thioflavin T fluorescence assay and transmission electron microscopy to monitor the effects of ENO1 on amyloid formation by Aβ peptides. We also cultured murine primary cerebrovascular smooth muscle cells to determine the effects of ENO1 on Aβ cytotoxicity. To investigate the effects of ENO1 in vivo, we infused ENO1 or a vehicle control into the brains of APP23 mice, a transgenic model of AD/CAA, using a continuous infusion system, followed by a cognitive test and pathological and biochemical analyses. We found that novel functions of ENO1 included interacting with Aβ and inhibiting its fibril formation, disrupting Aβ fibrils, and weakening the cytotoxic effects of these fibrils via proteolytic degradation of Aβ peptide. We also demonstrated that infusion of ENO1 into APP23 mouse brains reduced cerebrovascular Aβ deposits and improved cognitive impairment. In addition, we found that enzymatically inactivated ENO1 failed to inhibit Aβ fibril formation and fibril disruption. The proteolytic activity of ENO1 may thus underlie the enzyme's cytoprotective effect and clearance of Aβ from the brain, and ENO1 may be a therapeutic target in CAA.