Role of water-soluble amyloid-beta in the pathogenesis of Alzheimer's disease

Exploring the nexus: Sleep disorders, circadian dysregulation, and Alzheimer's disease

We reviewed the connections among Alzheimer's disease (AD), sleep deprivation, and circadian rhythm disorders. Evidence is mounting that disrupted sleep and abnormal circadian rhythms are not merely symptoms of AD, but are also involved in accelerating the disease. Amyloid-beta (Aβ) accumulates, a feature of AD, and worsens with sleep deprivation because glymphatic withdrawal is required to clear toxic proteins from the brain. In addition, disturbances in circadian rhythm can contribute to the induction of neuroinflammation and oxidative stress, thereby accelerating neurodegenerative processes. While these interactions are bidirectional, Alzheimer's pathology further disrupts sleep and circadian function in a vicious cycle that worsens cognitive decline, which is emphasized in the review. The evidence that targeting sleep and circadian mechanisms may serve as therapeutic strategies for AD was strengthened by this study through the analysis of the molecular and physiological pathways. Further work on this nexus could help unravel the neurobiological mechanisms common to the onset of Alzheimer's and disrupted sleep and circadian regulation, which could result in earlier intervention to slow or prevent the onset of the disease.

Mind Gaps and Bone Snaps: Exploring the Connection Between Alzheimer's Disease and Osteoporosis

PURPOSE OF REVIEW

This comprehensive review discusses the complex relationship between Alzheimer's disease (AD) and osteoporosis, two conditions that are prevalent in the aging population and result in adverse complications on quality of life. The purpose of this review is to succinctly elucidate the many commonalities between the two conditions, including shared pathways, inflammatory and oxidative mechanisms, and hormonal deficiencies.

RECENT FINDINGS

AD and osteoporosis share many aspects of their respective disease-defining pathophysiology. These commonalities include amyloid beta deposition, the Wnt/β-catenin signaling pathway, and estrogen deficiency. The shared mechanisms and risk factors associated with AD and osteoporosis result in a large percentage of patients that develop both diseases. Previous literature has established that the progression of AD increases the risk of sustaining a fracture. Recent findings demonstrate that the reverse may also be true, suggesting that a fracture early in the life course can predispose one to developing AD due to the activation of these shared mechanisms. The discovery of these commonalities further guides the development of novel therapeutics in which both conditions are targeted. This detailed review delves into the commonalities between AD and osteoporosis to uncover the shared players that bring these two seemingly unrelated conditions together. The discussion throughout this review ultimately posits that the occurrence of fractures and the mechanism behind fracture healing can predispose one to developing AD later on in life, similar to how AD patients are at an increased risk of developing fractures. By focusing on the shared mechanisms between AD and osteoporosis, one can better understand the conditions individually and as a unit, thus informing therapeutic approaches and further research. This review article is part of a series of multiple manuscripts designed to determine the utility of using artificial intelligence for writing scientific reviews.

Ferroptosis: A new strategy for targeting Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a complex pathogenesis, which involves the formation of amyloid plaques and neurofibrillary tangles. Many recent studies have revealed a close association between ferroptosis and the pathogenesis of AD. Factors such as ferroptosis-associated iron overload, lipid peroxidation, disturbances in redox homeostasis, and accumulation of reactive oxygen species have been found to contribute to the pathological progression of AD. In this review, we explore the mechanisms underlying ferroptosis, describe the link between ferroptosis and AD, and examine the reported efficacy of ferroptosis inhibitors in treating AD. Finally, we discuss the potential challenges to ferroptosis inhibitors use in the clinic, enabling their faster use in clinical treatment.

Impact of GSK-3β and CK-1δ on Wnt signaling pathway in alzheimer disease: A dual target approach

Alzheimer's disease (AD) is an enigmatic neurological illness that offers few treatment options. Recent exploration has highlighted the crucial connection of the Wnt signaling pathway in AD pathogenesis, shedding light on potential therapeutic targets. The present study focuses on the dual targeting of glycogen synthase kinase-3β (GSK-3β) and casein kinase-1δ (CK-1δ) within the framework of the Wnt signaling pathway as a possible technique for AD intervention. GSK-3β and CK-1δ are multifunctional kinases known for their roles in tau hyperphosphorylation, amyloid processing, and synaptic dysfunction, all of which are major hallmarks of Alzheimer's disease. They are intricately linked to Wnt signaling, which plays a pivotal part in sustaining neuronal function and synaptic plasticity. Dysregulation of the Wnt pathway in AD contributes to cognitive decline and neurodegeneration. This review delves into the molecular mechanisms by which GSK-3β and CK-1δ impact the Wnt signaling pathway, elucidating their roles in AD pathogenesis. We discuss the potential of small-molecule inhibitors along with their SAR studies along with the multi-targetd approach targeting GSK-3β and CK-1δ to modulate Wnt signaling and mitigate AD-related pathology. In summary, the dual targeting of GSK-3β and CK-1δ within the framework of the Wnt signaling pathway presents an innovative and promising avenue for future AD therapies, offering new hope for patients and caregivers in the quest to combat this challenging condition.

From the Mind to the Spine: The Intersecting World of Alzheimer's and Osteoporosis

PURPOSE OF REVIEW

This comprehensive review delves into the intricate interplay between Alzheimer's disease (AD) and osteoporosis, two prevalent conditions with significant implications for individuals' quality of life. The purpose is to explore their bidirectional association, underpinned by common pathological processes such as aging, genetic factors, inflammation, and estrogen deficiency.

RECENT FINDINGS

Recent advances have shown promise in treating both Alzheimer's disease (AD) and osteoporosis by targeting disease-specific proteins and bone metabolism regulators. Monoclonal antibodies against beta-amyloid and tau for AD, as well as RANKL and sclerostin for osteoporosis, have displayed therapeutic potential. Additionally, ongoing research has identified neuroinflammatory genes shared between AD and osteoporosis, offering insight into the interconnected inflammatory mechanisms. This knowledge opens avenues for innovative dual-purpose therapies that could address both conditions, potentially revolutionizing treatment approaches for AD and osteoporosis simultaneously. This review underscores the potential for groundbreaking advancements in early diagnosis and treatment by unraveling the intricate connection between AD and bone health. It advocates for a holistic, patient-centered approach to medical care that considers both cognitive and bone health, ultimately aiming to enhance the overall well-being of individuals affected by these conditions. This review article is part of a series of multiple manuscripts designed to determine the utility of using artificial intelligence for writing scientific reviews.

Lithium Benzoate Exerts Neuroprotective Effect by Improving Mitochondrial Function, Attenuating Reactive Oxygen Species, and Protecting Cognition and Memory in an Animal Model of Alzheimer’s Disease

Background:

Alzheimer’s disease (AD) is a multifactorial neurodegenerative disease affecting many cellular pathways, including protein aggregation, mitochondrial dysfunction, oxidative stress (OS), and neuroinflammation. Currently, no effective treatment for AD exists.

Objective:

We aim to determine the effect of lithium benzoate (LiBen) in protecting neurons from amyloid-β (Aβ) or other neurotoxin insults.

Methods:

Primary rat cortical neurons co-treated with neurotoxins and LiBen were used to examine its effect in cell viability, reactive oxygen species (ROS) clearance, and mitochondrial functions by MTT, CellRox fluorescence staining, and seahorse assay. Then, Barnes maze and prepulse inhibition test were performed in APP/PS1 mice that received chronic LiBen treatment to assess its effect on cognitive protection. Oral bioavailability of LiBen was also assessed by pharmacokinetic study in rat plasma.

Results:

In this study, we discovered that LiBen can attenuate cellular ROS level, improve mitochondrial function, increase cell viability against multiple different insults of mitochondrial dysfunction, Aβ accumulation, and neuroinflammation, and promote neurogenesis. We demonstrated that LiBen has advantages over lithium or sodium benzoate alone as LiBen displays superior neuroprotective efficacy and oral bioavailability than the other two agents when being applied either alone or in combination. Furthermore, chronic administration of LiBen showed protection for cognition as well as spatial memory and reduced the senile plaque deposition in brains of AD animal models.

Conclusion:

LiBen stands as a promising therapeutic agent for improving cognition and delaying the progression of AD.

Microglial amyloid beta clearance is driven by PIEZO1 channels

Background

Microglia are the endogenous immune cells of the brain and act as sensors of pathology to maintain brain homeostasis and eliminate potential threats. In Alzheimer's disease (AD), toxic amyloid beta (Aβ) accumulates in the brain and forms stiff plaques. In late-onset AD accounting for 95% of all cases, this is thought to be due to reduced clearance of Aβ. Human genome-wide association studies and animal models suggest that reduced clearance results from aberrant function of microglia. While the impact of neurochemical pathways on microglia had been broadly studied, mechanical receptors regulating microglial functions remain largely unexplored.

Methods

Here we showed that a mechanotransduction ion channel, PIEZO1, is expressed and functional in human and mouse microglia. We used a small molecule agonist, Yoda1, to study how activation of PIEZO1 affects AD-related functions in human induced pluripotent stem cell (iPSC)-derived microglia-like cells (iMGL) under controlled laboratory experiments. Cell survival, metabolism, phagocytosis and lysosomal activity were assessed using real-time functional assays. To evaluate the effect of activation of PIEZO1 in vivo, 5-month-old 5xFAD male mice were infused daily with Yoda1 for two weeks through intracranial cannulas. Microglial Iba1 expression and Aβ pathology were quantified with immunohistochemistry and confocal microscopy. Published human and mouse AD datasets were used for in-depth analysis of PIEZO1 gene expression and related pathways in microglial subpopulations.

Results

We show that PIEZO1 orchestrates Aβ clearance by enhancing microglial survival, phagocytosis, and lysosomal activity. Aβ inhibited PIEZO1-mediated calcium transients, whereas activation of PIEZO1 with a selective agonist, Yoda1, improved microglial phagocytosis resulting in Aβ clearance both in human and mouse models of AD. Moreover, PIEZO1 expression was associated with a unique microglial transcriptional phenotype in AD as indicated by assessment of cellular metabolism, and human and mouse single-cell datasets.

Conclusion

These results indicate that the compromised function of microglia in AD could be improved by controlled activation of PIEZO1 channels resulting in alleviated Aβ burden. Pharmacological regulation of these mechanoreceptors in microglia could represent a novel therapeutic paradigm for AD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02486-y.

Glymphatic System Dysfunction in Central Nervous System Diseases and Mood Disorders

The glymphatic system, a recently discovered macroscopic waste removal system in the brain, has many unknown aspects, especially its driving forces and relationship with sleep, and thus further explorations of the relationship between the glymphatic system and a variety of possible related diseases are urgently needed. Here, we focus on the progress in current research on the role of the glymphatic system in several common central nervous system diseases and mood disorders, discuss the structural and functional abnormalities of the glymphatic system which may occur before or during the pathophysiological progress and the possible underlying mechanisms. We emphasize the relationship between sleep and the glymphatic system under pathological conditions and summarize the common imaging techniques for the glymphatic system currently available. The perfection of the glymphatic system hypothesis and the exploration of the effects of aging and endocrine factors on the central and peripheral regulatory pathways through the glymphatic system still require exploration in the future.

Brain-Derived Exosomal Proteins as Effective Biomarkers for Alzheimer's Disease: A Systematic Review and Meta-Analysis

Alzheimer's disease (AD), a progressive neurodegenerative disease, affects approximately 50 million people worldwide, which warrants the search for reliable new biomarkers for early diagnosis of AD. Brain-derived exosomal (BDE) proteins, which are extracellular nanovesicles released by all cell lineages of the central nervous system, have been focused as biomarkers for diagnosis, screening, prognosis prediction, and monitoring in AD. This review focused on the possibility of BDE proteins as AD biomarkers. The articles published prior to 26 January 2021 were searched in PubMed, EMBASE, Web of Science, and Cochrane Library to identify all relevant studies that reported exosome biomarkers in blood samples of patients with AD. From 342 articles, 20 studies were selected for analysis. We conducted a meta-analysis of six BDE proteins and found that levels of amyloid-β42 (standardized mean difference (SMD) = 1.534, 95% confidence interval [CI]: 0.595-2.474), total-tau (SMD = 1.224, 95% CI: 0.534-1.915), tau phosphorylated at threonine 181 (SMD = 4.038, 95% CI: 2.312-5.764), and tau phosphorylated at serine 396 (SMD = 2.511, 95% CI: 0.795-4.227) were significantly different in patients with AD compared to those in control. Whereas, those of p-tyrosine-insulin receptor substrate-1 and heat shock protein 70 did not show significant differences. This review suggested that Aβ42, t-tau, p-T181-tau, and p-S396-tau could be effective in diagnosing AD as blood biomarkers, despite the limitation in the meta-analysis based on the availability of data. Therefore, certain BDE proteins could be used as effective biomarkers for AD.

Comprehensive Review on Alzheimer's Disease: Causes and Treatment

Alzheimer's disease (AD) is a disorder that causes degeneration of the cells in the brain and it is the main cause of dementia, which is characterized by a decline in thinking and independence in personal daily activities. AD is considered a multifactorial disease: two main hypotheses were proposed as a cause for AD, cholinergic and amyloid hypotheses. Additionally, several risk factors such as increasing age, genetic factors, head injuries, vascular diseases, infections, and environmental factors play a role in the disease. Currently, there are only two classes of approved drugs to treat AD, including inhibitors to cholinesterase enzyme and antagonists to N-methyl d-aspartate (NMDA), which are effective only in treating the symptoms of AD, but do not cure or prevent the disease. Nowadays, the research is focusing on understanding AD pathology by targeting several mechanisms, such as abnormal tau protein metabolism, β-amyloid, inflammatory response, and cholinergic and free radical damage, aiming to develop successful treatments that are capable of stopping or modifying the course of AD. This review discusses currently available drugs and future theories for the development of new therapies for AD, such as disease-modifying therapeutics (DMT), chaperones, and natural compounds.

The Erythrocytic Hypothesis of Brain Energy Crisis in Sporadic Alzheimer Disease: Possible Consequences and Supporting Evidence

Alzheimer’s disease (AD) is a fatal form of dementia of unknown etiology. Although amyloid plaque accumulation in the brain has been the subject of intensive research in disease pathogenesis and anti-amyloid drug development; the continued failures of the clinical trials suggest that amyloids are not a key cause of AD and new approaches to AD investigation and treatment are needed. We propose a new hypothesis of AD development based on metabolic abnormalities in circulating red blood cells (RBCs) that slow down oxygen release from RBCs into brain tissue which in turn leads to hypoxia-induced brain energy crisis; loss of neurons; and progressive atrophy preceding cognitive dysfunction. This review summarizes current evidence for the erythrocytic hypothesis of AD development and provides new insights into the causes of neurodegeneration offering an innovative way to diagnose and treat this systemic disease.

20S proteasome and glyoxalase 1 activities decrease in erythrocytes derived from Alzheimer's disease patients

As a result of accumulating methylglyoxal and advanced glycation end products in the brains of patients with Alzheimer's disease, it is considered a protein precipitation disease. The ubiquitin proteasome system is one of the most important mechanisms for cells to degrade proteins, and thus is very important for maintaining normal physiological function of the nervous system. This study recruited 48 individuals with Alzheimer's disease (20 males and 28 females aged 75 ± 6 years) and 50 healthy volunteers (21 males and 29 females aged 72 ± 7 years) from the Affiliated Hospital of Youjiang Medical University for Nationalities (Baise, China) between 2014 and 2017. Plasma levels of malondialdehyde and H₂O₂ were measured by colorimetry, while glyoxalase 1 activity was detected by spectrophotometry. In addition, 20S proteasome activity in erythrocytes was measured with a fluorescent substrate method. Ubiquitin and glyoxalase 1 protein expression in erythrocyte membranes was detected by western blot assay. The results demonstrated that compared with the control group, patients with Alzheimer's disease exhibited increased plasma malondialdehyde and H₂O₂ levels, and decreased glyoxalase 1 activity; however, expression level of glyoxalase 1 protein remained unchanged. Moreover, activity of the 20S proteasome was decreased and expression of ubiquitin protein was increased in erythrocytes. These findings indicate that proteasomal and glyoxalase activities may be involved in the occurrence of Alzheimer's disease, and erythrocytes may be a suitable tissue for Alzheimer's disease studies. This study was approved by the Ethics Committee of Youjiang Medical University for Nationalities (approval No. YJ12017013) on May 3, 2017.

Cajaninstilbene Acid Ameliorates Cognitive Impairment Induced by Intrahippocampal Injection of Amyloid-β1-42 Oligomers

Amyloid-β_1-42 (Aβ_1-42) oligomers play an important role at the early stage of Alzheimer's disease (AD) and have been a vital target in the development of therapeutic drugs for AD. Cajaninstilbene acid (CSA), a major bioactive stilbene isolated from pigeon pea (Cajanus cajan) leaves, exerted the neuroprotective property in our previous studies. The present study utilized a validated mouse model of early-stage AD induced by bilateral injection of Aβ_1-42 oligomers into hippocampal CA1 regions (100 pmol/mouse) to investigate the cognitive enhancing effects of CSA and the underlying mechanism, by a combination of animal behavioral tests, immunohistochemistry, liquid chromatography-tandem mass spectrometry analysis, and Western blot methods. Intragastric administration of CSA (7.5, 15, and 30 mg/kg) attenuated the impairment of learning and memory induced by Aβ_1-42 oligomers. CSA stimulated Aβ clearance and prevented microglial activation and astrocyte reactivity in the hippocampus of model mice. It also decreased the high levels of Glu but increased the low levels of GABA. In addition, CSA inhibited excessive expression of GluN2B-containing NMDARs and upregulated the downstream PKA/CREB/BDNF/TrkB signaling pathway. These results suggest that CSA could be a potential therapeutic agent at the early stage of AD.

Metabolic Abnormalities of Erythrocytes as a Risk Factor for Alzheimer's Disease

Alzheimer's disease (AD) is a slowly progressive, neurodegenerative disorder of uncertain etiology. According to the amyloid cascade hypothesis, accumulation of non-soluble amyloid β peptides (Aβ) in the Central Nervous System (CNS) is the primary cause initiating a pathogenic cascade leading to the complex multilayered pathology and clinical manifestation of the disease. It is, therefore, not surprising that the search for mechanisms underlying cognitive changes observed in AD has focused exclusively on the brain and Aβ-inducing synaptic and dendritic loss, oxidative stress, and neuronal death. However, since Aβ depositions were found in normal non-demented elderly people and in many other pathological conditions, the amyloid cascade hypothesis was modified to claim that intraneuronal accumulation of soluble Aβ oligomers, rather than monomer or insoluble amyloid fibrils, is the first step of a fatal cascade in AD. Since a characteristic reduction of cerebral perfusion and energy metabolism occurs in patients with AD it is suggested that capillary distortions commonly found in AD brain elicit hemodynamic changes that alter the delivery and transport of essential nutrients, particularly glucose and oxygen to neuronal and glial cells. Another important factor in tissue oxygenation is the ability of erythrocytes (red blood cells, RBC) to transport and deliver oxygen to tissues, which are first of all dependent on the RBC antioxidant and energy metabolism, which finally regulates the oxygen affinity of hemoglobin. In the present review, we consider the possibility that metabolic and antioxidant defense alterations in the circulating erythrocyte population can influence oxygen delivery to the brain, and that these changes might be a primary mechanism triggering the glucose metabolism disturbance resulting in neurobiological changes observed in the AD brain, possibly related to impaired cognitive function. We also discuss the possibility of using erythrocyte biochemical aberrations as potential tools that will help identify a risk factor for AD.

Genistein protects against Aβ25-35 induced apoptosis of PC12 cells through JNK signaling and modulation of Bcl-2 family messengers

Background

Deposition of aggregated amyloid beta (Aβ) protein is hallmark of Alzheimer’s disease, leading to dysfunction and apoptosis of neurons. The isoflavone phytoestrogen compound genistein (Gen) exerts a significant protective effect against Aβ_25–35 induced neurotoxicity and mitochondrial damage in rat pheochromocytoma (PC12) cells. However, the mechanisms underlying Gen’s rescue remain elusive. Therefore we endeavored to research further the molecular mechanisms underlying Gen’s inhibition of Aβ_25–35 induced apoptosis of neurons.

Results

We found that Gen dramatically suppressed the activation by Aβ_25–35 of p-c-Jun N-terminal kinase (p-JNK), and also inhibited the JNK-dependent decreased of Bcl-w and increased of Bim. Furthermore, Gen significantly reduced the cytoplasmic concentrations of cytochrome c and Smac protein as well as caspase-3 activity. Additionally, pretreatment with JNK inhibitor SP600125 effectively suppressed Aβ_25–35 induced PC12 cell cytotoxicity.

Conclusion

Taken together, the results suggested that Gen protects PC12 cells from Aβ_25–35 induced neurotoxicity by interfering with p-JNK activation, thus attenuating the JNK-dependent apoptosis through the mitochondrial pathway. These findings constitute novel insights into the pathway for Aβ_25–35 toxicity, and the neuroprotective action of Gen.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-016-0329-9) contains supplementary material, which is available to authorized users.

Increasing anti-Aβ-induced neurotoxicity ability of Antrodia camphorata-fermented product with deep ocean water supplementary

BACKGROUND

Antrodia camphorata is proven to probably inhibit the neurotoxicity of amyloid β-peptide (Aβ), known as a risk factor toward the development of Alzheimer's disease. Deep ocean water (DOW), drawn from an ocean depth of more than 200 m, has proven to stimulate the growth and metabolite biosynthesis of fungi owing to its rich minerals and trace elements. Based on these advantages of DOW, this study used statistical response surface methodology (RSM) to investigate the effects of DOW on the growth and anti-Aβ-induced neurocytotoxicity ability of A. camphorata.

RESULTS

The results showed that DOW was useful for increasing the biomass of A. camphorata and enhancing its neuroprotective capability. The anti-Aβ40-induced neurocytotoxicity ability of filtrate was increased via raising the mycelium-secreted components. Furthermore, the anti-Aβ40-induced neurocytotoxicity ability of mycelium was also increased by the DOW-stimulated intracellular antioxidants. Using 80% DOW concentration, initial pH 3.3 and 20% inoculum size as the optimal culture conditions of A. camphorata significantly stimulated the biomass and mycelium-mediated Aβ40-induced cell viability from 302 ± 14 mg per 100 mL and 49.2 ± 2.2% to 452 ± 33 mg per 100 mL and 65.0 ± 7.4% respectively.

CONCLUSION

This study indicated that DOW could be used as a promising supplementary for the production of A. camphorata secondary metabolites with strong antioxidant activity to protect neuron cells from damage based on Aβ stimulation cytotoxicity. © 2016 Society of Chemical Industry.

Dementia-linked amyloidosis is associated with brain protein deamidation as revealed by proteomic profiling of human brain tissues

Background

Aggregation of malformed proteins is a key feature of many neurodegenerative diseases, but the mechanisms that drive proteinopathy in the brain are poorly understood. We aimed to characterize aggregated proteins in human brain tissues affected by dementia.

Results

To characterize amyloidal plaque purified from post-mortem brain tissue of dementia patient, we applied ultracentrifugation-electrostatic repulsion hydrophilic interaction chromatography (UC-ERLIC) coupled mass spectrometry-based proteomics technologies. Proteomics profiling of both soluble and aggregated amyloidal plaque demonstrated significant enrichment and deamidation of S100A9, ferritin, hemoglobin subunits, creatine kinase and collagen protein among the aggregated brain proteins. Amyloidal plaques were enriched in the deamidated variant of protein S100A9, and structural analysis indicated that both the low- and high-affinity calcium binding motifs of S100A9 were deamidated exclusively in the aggregated fraction, suggesting altered charge state and function of this protein in brain tissues affected by dementia. The multiple deamidated residues of S100A9 predicts introduction of negative charge that alter Ca⁺⁺ binding, suggesting increased capacity to form pathological aggregates in the brain.

Conclusion

UC-coupled proteomics revealed that brain amyloidal plaques are enriched in deamidated proteins, and suggested that altered charge state and calcium-binding capacity of S100A9 may enhance protein aggregation and promote neurodegeneration in the human brain.

Electronic supplementary material

The online version of this article (doi:10.1186/s13041-016-0200-z) contains supplementary material, which is available to authorized users.

The effect of geniste on Aβ25–35-induced PC12 cell apoptosis through the JNK-dependent Fas pathway

The β-amyloid protein (Aβ) is considered to be the key factor for inducing Alzheimer's disease (AD).

Activity and architecture of pyroglutamate-modified amyloid-β (AβpE3-42) pores

Among the family of Aβ peptides, pyroglutamate-modified Aβ (AβpE) peptides are particularly associated with cytotoxicity in Alzheimer's disease (AD). They represent the dominant fraction of Aβ oligomers in the brains of AD patients, but their accumulation in the brains of elderly individuals with normal cognition is significantly lower. Accumulation of AβpE plaques precedes the formation of plaques of full-length Aβ (Aβ1-40/42). Most of these properties appear to be associated with the higher hydrophobicity of AβpE as well as an increased resistance to enzymatic degradation. However, the important question of whether AβpE peptides induce pore activity in lipid membranes and their potential toxicity compared with other Aβ pores is still open. Here we examine the activity of AβpE pores in anionic membranes using planar bilayer electrical recording and provide their structures using molecular dynamics simulations. We find that AβpE pores spontaneously induce ionic current across the membrane and have some similar properties to the other previously studied pores of the Aβ family. However, there are also some significant differences. The onset of AβpE3-42 pore activity is generally delayed compared with Aβ1-42 pores. However, once formed, AβpE3-42 pores produce increased ion permeability of the membrane, as indicated by a greater occurrence of higher conductance electrical events. Structurally, the lactam ring of AβpE peptides induces a change in the conformation of the N-terminal strands of the AβpE3-42 pores. While the N-termini of wild-type Aβ1-42 peptides normally reside in the bulk water region, the N-termini of AβpE3-42 peptides tend to reside in the hydrophobic lipid core. These studies provide a first step to an understanding of the enhanced toxicity attributed to AβpE peptides.

Oligomers, fact or artefact? SDS-PAGE induces dimerization of β-amyloid in human brain samples

The formation of low-order oligomers of β-amyloid (Aβ) within the brain is widely believed to be a central component of Alzheimer's disease (AD) pathogenesis. However, despite advances in high-throughput and high-resolution techniques such as xMAP and mass spectrometry (MS), investigations into these oligomeric species have remained reliant on low-resolution Western blots and enzyme-linked immunosorbent assays. The current investigation compared Aβ profiles within human cortical tissue using sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis (PAGE), xMAP and surface enhanced laser desorption/ionization time-of-flight MS and found that whilst there was significant correlation across the techniques regarding levels of monomeric Aβ, only SDS-PAGE was capable of detecting dimeric isoforms of Aβ. The addition of synthetic di-tyrosine cross-linked Aβ(1-40)Met(35)(O) to the AD tissue demonstrated that the MS methodology was capable of observing dimeric Aβ at femto-molar concentrations, with no noticeable effect on monomeric Aβ levels. Focus turned to the association between SDS-PAGE and levels of observable dimeric Aβ within the AD brain tissue. These investigations revealed that increased levels of dimeric Aβ were observed with increasing concentrations of SDS in the sample buffer. This finding was subsequently confirmed using synthetic Aβ(1-42) and suggests that SDS was inducing the formation of dimeric Aβ. The findings that SDS promotes Aβ dimerization have significant implications for the putative role of low-order oligomers in AD pathogenesis and draw into question the utility of oligomeric Aβ as a therapeutic target.

Early memory deficits precede plaque deposition in APPswe/PS1dE9 mice: involvement of oxidative stress and cholinergic dysfunction

A large body of evidence has shown that cognitive deficits occur early, before amyloid plaque deposition, suggesting that soluble amyloid-β protein (Aβ) contributes to the development of early cognitive dysfunction in Alzheimer disease (AD). However, the underlying mechanism(s) through which soluble Aβ exerts its neurotoxicity responsible for cognitive dysfunction in the early stage of AD remains unclear so far. In this study, we used preplaque APPswe/PS1dE9 mice ages 2.5 and 3.5 months to examine alterations in cognitive function, oxidative stress, and cholinergic function. We found that only soluble Aβ, not insoluble Aβ, was detected in these preplaque APPswe/PS1dE9 mice. APPswe/PS1dE9 mice 2.5 months of age did not show any significant changes in the measures of cognitive function, oxidative stress, and cholinergic function, whereas 3.5-month-old APPswe/PS1dE9 mice exhibited spatial memory impairment in the Morris water maze, accompanied by significantly decreased acetylcholine (ACh), choline acetyltransferase (ChAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-px) as well as increased malondialdehyde (MDA) and protein carbonyls. In 3.5-month-old preplaque APPswe/PS1dE9 mice, correlational analyses revealed that the performance of impaired spatial memory was inversely correlated with soluble Aβ, MDA, and protein carbonyls, as well as being positively correlated with ACh, ChAT, SOD, and GSH-px; soluble Aβ level was inversely correlated with ACh, ChAT, SOD, and GSH-px, as well as being positively correlated with MDA and protein carbonyls; ACh level showed a significant positive correlation with ChAT, SOD, and GSH-px, as well as a significant inverse correlation with MDA and protein carbonyls. Collectively, this study provides direct evidence that increased oxidative damage and cholinergic dysfunction may be early pathological responses to soluble Aβ and involved in early memory deficits in the preplaque stage of AD. These findings suggest that early antioxidant therapy and improving cholinergic function may be a promising strategy to prevent or delay the onset and progression of AD.

Pyroglutamate amyloid-β (Aβ): a hatchet man in Alzheimer disease

Pyroglutamate-modified amyloid-β (Aβ(pE3)) peptides are gaining considerable attention as potential key participants in the pathology of Alzheimer disease (AD) due to their abundance in AD brain, high aggregation propensity, stability, and cellular toxicity. Transgenic mice that produce high levels of Aβ(pE3-42) show severe neuron loss. Recent in vitro and in vivo experiments have proven that the enzyme glutaminyl cyclase catalyzes the formation of Aβ(pE3). In this minireview, we summarize the current knowledge on Aβ(pE3), discussing its discovery, biochemical properties, molecular events determining formation, prevalence in the brains of AD patients, Alzheimer mouse models, and potential as a target for therapy and as a diagnostic marker.

Soluble Aβ levels correlate with cognitive deficits in the 12-month-old APPswe/PS1dE9 mouse model of Alzheimer's disease

Amyloid-beta peptide (Aβ) is believed to be central in the pathogenesis of Alzheimer's disease (AD) characterized by cognitive deficits. However, it remains uncertain which form(s) of Aβ pathology is responsible for the cognitive deficits in AD. In the present study, the cognitive deficits and the profiles of Aβ pathology were characterized in the 12-month-old APPswe/PS1dE9 double transgenic mice, and their correlations were examined. Compared with non-transgenic littermates, the middle-aged APPswe/PS1dE9 mice exhibited spatial learning and memory deficits in the water maze test and long-term contextual memory deficits in the step-down passive avoidance test. Among the middle-aged APPswe/PS1dE9 mice, hippocampal soluble Aβ1-40 and Aβ1-42 levels were highly correlated with spatial learning deficits and long-term contextual memory deficits, as well as cortical and hippocampal soluble Aβ1-40 and Aβ1-42 levels were strongly correlated with spatial memory deficits. By contrast, no significant correlations were observed between three measures of cognitive functions and amyloid plaque burden (total Aβ plaque load and fibrillar Aβ plaque load), total Aβ levels (Aβ1-40 and Aβ1-42), as well as insoluble Aβ levels (Aβ1-40 and Aβ1-42). Stepwise multiple regression analysis identified hippocampal soluble Aβ1-40 and Aβ1-42 levels as independent factors for predicting the spatial learning deficits and the long-term contextual memory deficits, as well as hippocampal and cortical soluble Aβ1-40 and Aβ1-42 levels as independent factors for predicting the spatial memory deficits in transgenic mice. These results demonstrate that cognitive deficits are highly related to the levels of soluble Aβ in middle-aged APPswe/PS1dE9 mice, in which soluble Aβ levels are only a tiny fraction of the amount of total Aβ levels. Consequently, our findings provide further evidence that soluble Aβ might primarily contribute to cognitive deficits in AD, suggesting that reducing the levels of soluble Aβ species would be a therapeutic intervention for AD patients even with large deposits of aggregated, insoluble Aβ.

Reduction of brain beta-amyloid (Abeta) by fluvastatin, a hydroxymethylglutaryl-CoA reductase inhibitor, through increase in degradation of amyloid precursor protein C-terminal fragments (APP-CTFs) and Abeta clearance

Epidemiological studies suggest that statins (hydroxymethylglutaryl-CoA reductase inhibitors) could reduce the risk of Alzheimer disease. Although one possible explanation is through an effect on beta-amyloid (Abeta) metabolism, its effect remains to be elucidated. Here, we explored the molecular mechanisms of how statins influence Abeta metabolism. Fluvastatin at clinical doses significantly reduced Abeta and amyloid precursor protein C-terminal fragment (APP-CTF) levels among APP metabolites in the brain of C57BL/6 mice. Chronic intracerebroventricular infusion of lysosomal inhibitors blocked these effects, indicating that up-regulation of the lysosomal degradation of endogenous APP-CTFs is involved in reduced Abeta production. Biochemical analysis suggested that this was mediated by enhanced trafficking of APP-CTFs from endosomes to lysosomes, associated with marked changes of Rab proteins, which regulate endosomal function. In primary neurons, fluvastatin enhanced the degradation of APP-CTFs through an isoprenoid-dependent mechanism. Because our previous study suggests additive effects of fluvastatin on Abeta metabolism, we examined Abeta clearance rates by using the brain efflux index method and found its increased rates at high Abeta levels from brain. As LRP1 in brain microvessels was increased, up-regulation of LRP1-mediated Abeta clearance at the blood-brain barrier might be involved. In cultured brain microvessel endothelial cells, fluvastatin increased LRP1 and the uptake of Abeta, which was blocked by LRP1 antagonists, through an isoprenoid-dependent mechanism. Overall, the present study demonstrated that fluvastatin reduced Abeta level by an isoprenoid-dependent mechanism. These results have important implications for the development of disease-modifying therapy for Alzheimer disease as well as understanding of Abeta metabolism.

Abeta(1-42) stimulates adult SVZ neurogenesis through the p75 neurotrophin receptor

The generation of amyloid-beta peptide (Abeta) and its accumulation in amyloid plaques are generally recognized as key characteristics of Alzheimer's disease. A number of reports have indicated that Abeta can regulate the proliferation of neural precursor cells and adult neurogenesis, suggesting that this may underpin the cognitive decline and compromised olfaction also associated with the condition. Here we report that Abeta(1-42) treatment both in vitro and in vivo, as well as endogenous generation of Abeta in C100 and APP/PS1 transgenic models of Alzheimer's disease, stimulate neurogenesis of young adult subventricular zone precursors. The neurogenic effect of Abeta(1-42) was found to require expression of the p75 neurotrophin receptor (p75(NTR)) by the precursor cells, and activation of p75(NTR) by metalloprotease cleavage. However, precursors from 12-month-old APP/PS1 mice failed to respond to Abeta(1-42). Our results suggest that overstimulation of p75(NTR)-positive progenitors during early life might result in depletion of the stem cell pool and thus a more rapid decline in basal neurogenesis. This, in turn, could lead to impaired neurogenic function in later life.

Deprivation-induced dendritic shrinkage might be oppositely affected by the expression of wild-type and mutated human amyloid precursor protein

The physiological role of the amyloid precursor protein (APP) and its proteolytic fragments in the brain is associated with neuronal survival, neurite outgrowth, synaptic formation, and neuronal plasticity. However, malregulation of APP processing leads to disordered balance of fragments, which may results in opposite, degenerative neuronal effects. In the present study, we analyzed in vivo effects of the expression of wild-type or mutated human APP on afferent deprivation-induced changes of dendritic morphology. After vibrissectomy, expression of wild-type human APP prevented diameter shrinkage of dendritic segments as well as dendritic rarefaction of apical arbors. In contrast, mutant human APP expression exacerbated degenerative changes of deprived barrel neurons. Degradation of apical arbors was especially pronounced. Results demonstrate for the first time opposite effects of the expression of wild-type and mutated human APP on deprivation-induced dendritic restructuring in vivo.

N-truncated amyloid-beta oligomers induce learning impairment and neuronal apoptosis

N-terminal-truncated forms of amyloid-beta (A beta) peptide have been recently suggested to play a pivotal role early in Alzheimer's disease (AD). Among them, A beta 3(pE)-42 peptide, starting with pyroglutamyl at residue Glu-3, is considered as the predominant A beta species in AD plaques and pre-amyloid lesions. Its abundance is reported to be directly proportional to the severity of the clinical phenotype. The present study investigates the effects of soluble oligomeric A beta 3(pE)-42 after intracerebroventricular injection on mice learning ability and the molecular mechanisms of its in vitro neurotoxicity. Mice injected with soluble A beta 3(pE)-42 or A beta(l-42) displayed impaired spatial working memory and delayed memory acquisition in Y-maze and Morris water maze tests, while those injected with soluble A beta(42-1) showed no effect. These cognitive alterations were associated with free radical overproduction in the hippocampus and olfactory bulbs, but not in the cerebral cortex or cerebellum. In vitro, A beta 3(pE)-42 oligomers induced a redox-sensitive neuronal apoptosis involving caspase activation and an arachidonic acid-dependent pro-inflammatory pathway. These data suggest that A beta 3(pE)-42 could mediate the neurodegenerative process and subsequent cognitive alteration occurring in preclinical AD stages.

Apolipoprotein E epsilon 4 is associated with an increased vulnerability to cell death in Alzheimer’s disease

The presumption to suffer from Alzheimer's disease (AD) accelerates with aging. One important risk factor seems to be the isoform epsilon 4 of the apolipoprotein E gene (Apo epsilon 4), which increases the risk to develop AD at an earlier age. Furthermore, convincing evidence is provided that apoptotic cell death mechanisms play an important role in neuronal cell death in AD. In the present study, we investigated whether abnormalities in apoptosis and caspase-3 activity can be found at the level of lymphocytes and a T cell subtype, CD4 T cells, from AD patients compared to aged sex- and ApoE genotype-matched non-demented controls. Under different experimental conditions (at baseline or after in vitro incubation in the presence of proapoptotic stimuli) increased levels of apoptosis and enhanced caspase-3 activity were detected in lymphocytes from AD patients. This difference was most pronounced in the CD4(+) T cell subtype. Notably, we found a significant increase of apoptotic cells and caspase-3 activity in lymphocytes from AD patients bearing one or two alleles of the ApoE4 compared to non-E4 carriers. Again, these effects were strongest in CD4(+) T cells. Circulating amyloid-beta (A beta) levels did not differ between AD patients bearing ApoE4 and non-ApoE4 and age-matched controls. Therefore, it is likely that circulating A beta is not responsible for the observed effects, which might rather reflect an ongoing systemic response in AD, e.g. an increase in CD95 expression.

Neuropathology of Alzheimer disease: pathognomonic but not pathogenic

Neuropathological changes in subjects with dementia are, by definition, end-stage phenomena. While such changes allow case characterization and lend themselves to disease classification and modeling, the lesions themselves are not etiological. This truth would appear to be self-evident, yet the medical and scientific literature suggests otherwise. Indeed it is now customary to view amyloid plaques in Alzheimer disease as primary etiological, neurotoxic lesions and, hence, removing them (e.g., by immunotherapy) is believed to lead to clinical improvement. The foundation for this line of thinking lies in the existence of rare kindreds with mutations in amyloid-beta, or mutations believed to be involved in the processing of amyloid-beta, and then the extrapolation of the inherited condition to sporadic disease. We believe that this overall construct ignores early events that are more critical to onset and progression of sporadic disease. Likewise, we have studied subjects with sporadic Alzheimer disease, as well as early onset familial Alzheimer disease and Down's syndrome, over a spectrum of ages, and have found that markers of oxidative stress precede amyloid deposits in all three conditions. Amyloid and neurofibrillary pathology in the Alzheimer brain show a decrease in oxidative stress relative to vulnerable but morphologically intact neurons, suggesting that neurodegenerative lesions are compensatory phenomena, and thus manifestations of cellular adaptation. The pathology of neurodegenerative diseases should be viewed as the end-stage consequence, as opposed to cause, of the disease processes, so that early disease processes that are amenable to intervention can be properly recognized and treated.

Endogenous plastic composite material in the Alzheimer's brain

Accumulation of amyloid beta (Abeta) peptide in brain is the hallmark of Alzheimer's disease (AD). The resulting plaques though fibrous in nature may also consist of additional structures currently poorly defined. We hypothesize that plastic composite material contributes to plaque formation. This material is organized by polymers of acrolein, which is an oxidized lipid fragment found in AD. Acrolein, a 3-carbon compound, contains a carbonyl and a vinyl group that participate in polymerization via fundamental latex chemistry. The redox and surfactant properties of Abeta allow it to catalyze the polymerization of acrolein. We previously reported observations of thin plastic fragments of Abeta-polyacrolein. The current paper outlines the proposed steps in forming these plastic fragments. Endogenous plastic composite material may significantly contribute to the pathogenesis of AD.

Soluble oligomers of amyloid-beta peptide induce neuronal apoptosis by activating a cPLA2-dependent sphingomyelinase-ceramide pathway

Recent data have revealed that soluble oligomeric amyloid-beta peptide (Abeta) may be the proximate effectors of neuronal injuries and death in Alzheimer's disease (AD) by unknown mechanisms. Consistently, we recently demonstrated the critical role of a redox-sensitive cytosolic calcium-dependent phospholipase A2 (cPLA2)-arachidonic acid (AA) pathway in Abeta oligomer-induced cell death. According to the involvement of oxidative stress and polyunsaturated fatty acids like AA in the regulation of sphingomyelinase (SMase) activity, the present study underlines the role of SMases in soluble Abeta-induced apoptosis. Soluble Abeta oligomers induced the activation of both neutral and acidic SMases, as demonstrated by the direct measurement of their enzymatic activities, by the inhibitory effects of both specific neutral and acidic SMase inhibitors, and by gene knockdown using antisense oligonucleotides. Furthermore, soluble Abeta-mediated activation of SMases and subsequent cell death were found to be inhibited by antioxidant molecules and a cPLA2-specific inhibitor or antisense oligonucleotide. We also demonstrate that sphingosine-1-phosphate is a potent neuroprotective factor against soluble Abeta oligomer-induced cell death and apoptosis by inhibiting soluble Abeta-induced activation of acidic sphingomyelinase. These results suggest that Abeta oligomers induce neuronal death by activating neutral and acidic SMases in a redox-sensitive cPLA2-AA pathway.

Abeta and tau form soluble complexes that may promote self aggregation of both into the insoluble forms observed in Alzheimer's disease

To date, there is no reasonable explanation as to why plaques and tangles simultaneously accumulate in Alzheimer's disease (AD). We demonstrate here by Western blotting and ELISA that a stable complex can form between tau and amyloid-beta protein (Abeta). This complex enhances tau phosphorylation by GSK3beta, but the phosphorylation then promotes dissociation of the complex. We have localized the sites of this interaction by using peptide membrane arrays. Abeta binds to multiple tau peptides, especially those in exons 7 and 9. This binding is sharply reduced or abolished by phosphorylation of specific serine and threonine residues. Conversely, tau binds to multiple Abeta peptides in the mid to C-terminal regions of Abeta. This binding is also significantly decreased by GSK3beta phosphorylation of tau. We used surface plasmon resonance to determine the binding affinity of Abeta for tau and found it to be in the low nanomolar range and almost 1,000-fold higher than tau for itself. In soluble extracts from AD and control brain tissue, we detected Abeta bound to tau in ELISAs. We also found by double immunostaining of AD brain tissue that phosphorylated tau and Abeta form separate insoluble complexes within the same neurons and their processes. We hypothesize that in AD, an initial step in the pathogenesis may be the intracellular binding of soluble Abeta to soluble nonphosphorylated tau, thus promoting tau phosphorylation and Abeta nucleation. Blocking the sites where Abeta initially binds to tau might arrest the simultaneous formation of plaques and tangles in AD.

Very long term studies of the seeding of beta-amyloidosis in primates

Cerebral beta-amyloidosis was found in 16/18 marmosets aged <10 yrs and 8/9 marmosets aged >10 yrs, injected intracerebrally with human or marmoset brain homogenate containing beta-amyloid 1-8 years previously. It was found in only 2/12 marmosets aged <10 yrs and 1/15 marmosets aged >10 yrs, injected with synthetic Abeta-peptides, CSF, or brain tissue which did not contain beta-amyloid. Cerebral beta-amyloidosis was found in 0/11 uninjected marmosets aged <10 yrs and in 5/29 uninjected marmosets aged >10 yrs. The beta-amyloidosis comprised small and large vessel angiopathy and some plaques throughout cortex and was qualitatively similar in injected marmosets and, when present, in uninjected marmosets. Of those injected marmosets which were positive, the amount of beta-amyloidosis was unrelated to age or incubation times but the 3 injected marmosets without beta-amyloidosis had incubation times of <3.5 years. We conclude that beta-amyloid, or associated factors, can initiate or accelerate the process of cerebral amyloidosis in primates.