Beyond the neuron-cellular interactions early in Alzheimer disease pathogenesis

A review of the application of exercise intervention on improving cognition in patients with Alzheimer's disease: mechanisms and clinical studies

Alzheimer's disease (AD) is the most common form of dementia, leading to sustained cognitive decline. An increasing number of studies suggest that exercise is an effective strategy to promote the improvement of cognition in AD. Mechanisms of the benefits of exercise intervention on cognitive function may include modulation of vascular factors by affecting cardiovascular risk factors, regulating cardiorespiratory health, and enhancing cerebral blood flow. Exercise also promotes neurogenesis by stimulating neurotrophic factors, affecting neuroplasticity in the brain. Additionally, regular exercise improves the neuropathological characteristics of AD by improving mitochondrial function, and the brain redox status. More and more attention has been paid to the effect of Aβ and tau pathology as well as sleep disorders on cognitive function in persons diagnosed with AD. Besides, there are various forms of exercise intervention in cognitive improvement in patients with AD, including aerobic exercise, resistance exercise, and multi-component exercise. Consequently, the purpose of this review is to summarize the findings of the mechanisms of exercise intervention on cognitive function in patients with AD, and also discuss the application of different exercise interventions in cognitive impairment in AD to provide a theoretical basis and reference for the selection of exercise intervention in cognitive rehabilitation in AD.

Shedding light on microglial dysregulation in Alzheimer's disease: exploring molecular mechanisms and therapeutic avenues

Alzheimer's disease (AD) stands out as the foremost prevalent neurodegenerative disorder, characterized by a complex etiology. Various mechanisms have been proposed to elucidate its onset, encompassing amyloid-beta (Aβ) toxicity, tau hyperphosphorylation, oxidative stress and reactive gliosis. The hallmark of AD comprises Aβ and tau aggregation. These misfolded protein aggregates trigger the activation of glial cells, primarily microglia. Microglial cells serve as a major source of inflammatory mediators and their cytotoxic activation has been implicated in various aspects of AD pathology. Activated microglia can adopt M1 or M2 phenotypes, where M1 promotes inflammation by increasing pro-inflammatory cytokines and M2 suppresses inflammation by boosting anti-inflammatory factors. Overexpressed pro-inflammatory cytokines include interleukin (IL)-1β, IL-6 and tumor necrosis factor-α (TNF-α) in adjacent brain regions. Furthermore, microglial signaling pathways dysregulated in AD are myeloid differentiation primary-response protein 88 (Myd 88), colony-stimulating factor-1 receptor (CSF1R) and dedicator of cytokinesis 2 (DOCK2), which alter the physiology. Despite numerous findings, the causative role of microglia-mediated neuroinflammation in AD remains elusive. This review concisely explores cellular and molecular mechanisms of activated microglia and their correlation with AD pathogenesis. Additionally, it highlights promising therapeutics targeting microglia modulation, currently undergoing preclinical and clinical studies, for developing effective treatment for AD.

A biphasic drug-releasing microneedle with ROS scavenging and angiogenesis for the treatment of diabetic ulcers

Diabetic ulcers are one of the common complications in diabetic patients. Delayed wound healing is associated with persistent pro-inflammatory M1 polarization, reduced angiogenesis and increased reactive oxygen species (ROS) in the microenvironment. Wound healing consists of multiple phases and therefore requires treatment tailored to each phase. In this study, a biphasic drug-releasing microneedle (MN) was fabricated to achieve early ROS scavenging and late accelerated angiogenesis to promote wound healing. Vascular endothelial growth factor (VEGF) was first encapsulated in methacryloylated sulfonated chitosan (SCSMA) microspheres (V@MP), and then V@MP was loaded into hyaluronic acid (HA) microneedles along with cerium dioxide nanoparticles (CONPs). Rapid dissolution of HA rapidly releases the CONPs to clear ROS, whereas the V@MP stays in the wound. SCSMA slow degradation prolongs the release of VEGF, thereby promoting angiogenesis. In vitro and in vivo studies have shown that this biphasic drug-releasing smart microneedle improves cell proliferation and migration, effectively scavenges ROS, promotes angiogenesis and tissue regeneration, and synergistically promotes M2 macrophage polarization. It provides a new delivery mode for nano-enzymes and growth factors that could be multifunctional and synergistic in the treatment of diabetic ulcers. STATEMENT OF SIGNIFICANCE: In our study, we present a microneedle (V@MP/C@MN) that can release drugs biphasically, which showed good repair ability in diabetic ulcer model. Large amounts of CONPs were rapidly released to alleviate oxidative stress during the inflammation of the wound, and V@MP stayed in the wound for a long period of time to release VEGF and promote angiogenesis in the late stage of wound healing. The results indicated that V@MP/C@MN could promote cell proliferation and migration, effectively scavenge ROS, promote angiogenesis and tissue regeneration, and synergistically promote M2 macrophage polarization, which could play a multifunctional and synergistic role in the treatment of diabetic ulcers.

Spatiotemporal Dysregulation of Neuron-Glia Related Genes and Pro-/Anti-Inflammatory miRNAs in the 5xFAD Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD), the leading cause of dementia, is a multifactorial disease influenced by aging, genetics, and environmental factors. miRNAs are crucial regulators of gene expression and play significant roles in AD onset and progression. This exploratory study analyzed the expression levels of 28 genes and 5 miRNAs (miR-124-3p, miR-125b-5p, miR-21-5p, miR-146a-5p, and miR-155-5p) related to AD pathology and neuroimmune responses using RT-qPCR. Analyses were conducted in the prefrontal cortex (PFC) and the hippocampus (HPC) of the 5xFAD mouse AD model at 6 and 9 months old. Data highlighted upregulated genes encoding for glial fibrillary acidic protein (Gfap), triggering receptor expressed on myeloid cells (Trem2) and cystatin F (Cst7), in the 5xFAD mice at both regions and ages highlighting their roles as critical disease players and potential biomarkers. Overexpression of genes encoding for CCAAT enhancer-binding protein alpha (Cebpa) and myelin proteolipid protein (Plp) in the PFC, as well as for BCL2 apoptosis regulator (Bcl2) and purinergic receptor P2Y12 (P2yr12) in the HPC, together with upregulated microRNA(miR)-146a-5p in the PFC, prevailed in 9-month-old animals. miR-155 positively correlated with miR-146a and miR-21 in the PFC, and miR-125b positively correlated with miR-155, miR-21, while miR-146a in the HPC. Correlations between genes and miRNAs were dynamic, varying by genotype, region, and age, suggesting an intricate, disease-modulated interaction between miRNAs and target pathways. These findings contribute to our understanding of miRNAs as therapeutic targets for AD, given their multifaceted effects on neurons and glial cells.

Recent Insights into the Neurobiology of Alzheimer's Disease and Advanced Treatment Strategies

In recent years, significant advancements have been made in understanding Alzheimer's disease from both neurobiological and clinical perspectives. Exploring the complex systems underlying AD has unveiled insights that could potentially revolutionize therapeutic approaches. Recent investigations have highlighted intricate interactions among genetic, molecular, and environmental factors in AD. Optimism arises from neurobiological advancements and diverse treatment options, potentially slowing or halting disease progression. Amyloid-beta plaques and tau protein tangles crucially influence AD onset and progression. Emerging treatments involve diverse strategies, such as approaches targeting multiple pathways involved in AD pathogenesis, such as inflammation, oxidative stress, and synaptic dysfunction pathways. Clinical trials using humanized monoclonal antibodies, focusing on immunotherapies eliminating amyloid-beta, have shown promise. Nonpharmacological interventions such as light therapy, electrical stimulation, cognitive training, physical activity, and dietary changes have drawn attention for their potential to slow cognitive aging and enhance brain health. Precision medicine, which involves tailoring therapies to individual genetic and molecular profiles, has gained traction. Ongoing research and interdisciplinary collaboration are expected to yield more effective treatments.

Microglial modulation as a therapeutic strategy in Alzheimer's disease: Focus on microglial preconditioning approaches

Alzheimer's disease (AD) is a progressive disease that causes an impairment of learning and memory. Despite the highly complex pathogenesis of AD, amyloid beta (Aβ) deposition and neurofibrillary tangles (NFTs) formation are the main hallmarks of AD. Neuroinflammation also has a crucial role in the development of AD. As the central nervous system's innate immune cells, microglial cells are activated in AD and induce inflammation by producing pro-inflammatory mediators. However, microglial activation is not always deleterious. M2-activated microglial cells are considered anti-inflammatory cells, which develop neuroprotection. Various approaches are proposed for managing AD, yet no effective therapy is available for this disorder. Considering the potential protective role of M2 microglia in neurodegenerative disorders and the improvement of these disorders by preconditioning approaches, it can be suggested that preconditioning of microglial cells may be beneficial for managing AD progression. Therefore, this study review microglial preconditioning approaches for preventing and improving AD.

Tau-mediated synaptic dysfunction is coupled with HCN channelopathy

INTRODUCTION

In tauopathies, altered tau processing correlates with impairments in synaptic density and function. Changes in hyperpolarization-activated cyclic nucleotide-gated (HCN) channels contribute to disease-associated abnormalities in multiple neurodegenerative diseases.

METHODS

To investigate the link between tau and HCN channels, we performed histological, biochemical, ultrastructural, and functional analyses of hippocampal tissues from Alzheimer's disease (AD), age-matched controls, Tau35 mice, and/or Tau35 primary hippocampal neurons.

RESULTS

Expression of specific HCN channels is elevated in post mortem AD hippocampus. Tau35 mice develop progressive abnormalities including increased phosphorylated tau, enhanced HCN channel expression, decreased dendritic branching, reduced synapse density, and vesicle clustering defects. Tau35 primary neurons show increased HCN channel expression enhanced hyperpolarization-induced membrane voltage "sag" and changes in the frequency and kinetics of spontaneous excitatory postsynaptic currents.

DISCUSSION

Our findings are consistent with a model in which pathological changes in tauopathies impact HCN channels to drive network-wide structural and functional synaptic deficits.

HIGHLIGHTS

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are functionally linked to the development of tauopathy. Expression of specific HCN channels is elevated in the hippocampus in Alzheimer's disease and the Tau35 mouse model of tauopathy. Increased expression of HCN channels in Tau35 mice is accompanied by hyperpolarization-induced membrane voltage "sag" demonstrating a detrimental effect of tau abnormalities on HCN channel function. Tau35 expression alters synaptic organization, causing a loosened vesicle clustering phenotype in Tau35 mice.

Proteomic analysis identifies HSP90AA1, PTK2B, and ANXA2 in the human entorhinal cortex in Alzheimer's disease: Potential role in synaptic homeostasis and Aβ pathology through microglial and astroglial cells

Alzheimer's disease (AD), the most prevalent neurodegenerative disorder worldwide, is clinically characterized by cognitive deficits. Neuropathologically, AD brains accumulate deposits of amyloid-β (Aβ) and tau proteins. Furthermore, these misfolded proteins can propagate from cell to cell in a prion-like manner and induce native proteins to become pathological. The entorhinal cortex (EC) is among the earliest areas affected by tau accumulation along with volume reduction and neurodegeneration. Neuron-glia interactions have recently come into focus; however, the role of microglia and astroglia in the pathogenesis of AD remains unclear. Proteomic approaches allow the determination of changes in the proteome to better understand the pathology underlying AD. Bioinformatic analysis of proteomic data was performed to compare ECs from AD and non-AD human brain tissue. To validate the proteomic results, western blot, immunofluorescence, and confocal studies were carried out. The findings revealed that the most disturbed signaling pathway was synaptogenesis. Because of their involvement in synapse function, relationship with Aβ and tau proteins and interactions in the pathway analysis, three proteins were selected for in-depth study: HSP90AA1, PTK2B, and ANXA2. All these proteins showed colocalization with neurons and/or astroglia and microglia and with pathological Aβ and tau proteins. In particular, ANXA2, which is overexpressed in AD, colocalized with amoeboid microglial cells and Aβ plaques surrounded by astrocytes. Taken together, the evidence suggests that unbalanced expression of HSP90AA1, PTK2B, and ANXA2 may play a significant role in synaptic homeostasis and Aβ pathology through microglial and astroglial cells in the human EC in AD.

Molecular mechanisms linking type 2 diabetes mellitus and late-onset Alzheimer's disease: A systematic review and qualitative meta-analysis

Research evidence indicating common metabolic mechanisms through which type 2 diabetes mellitus (T2DM) increases risk of late-onset Alzheimer's dementia (LOAD) has accumulated over recent decades. The aim of this systematic review is to provide a comprehensive review of common mechanisms, which have hitherto been discussed in separate perspectives, and to assemble and evaluate candidate loci and epigenetic modifications contributing to polygenic risk linkages between T2DM and LOAD. For the systematic review on pathophysiological mechanisms, both human and animal studies up to December 2023 are included. For the qualitative meta-analysis of genomic bases, human association studies were examined; for epigenetic mechanisms, data from human studies and animal models were accepted. Papers describing pathophysiological studies were identified in databases, and further literature gathered from cited work. For genomic and epigenomic studies, literature mining was conducted by formalised search codes using Boolean operators in search engines, and augmented by GeneRif citations in Entrez Gene, and other sources (WikiGenes, etc.). For the systematic review of pathophysiological mechanisms, 923 publications were evaluated, and 138 gene loci extracted for testing candidate risk linkages. 3 57 publications were evaluated for genomic association and descriptions of epigenomic modifications. Overall accumulated results highlight insulin signalling, inflammation and inflammasome pathways, proteolysis, gluconeogenesis and glycolysis, glycosylation, lipoprotein metabolism and oxidation, cell cycle regulation or survival, autophagic-lysosomal pathways, and energy. Documented findings suggest interplay between brain insulin resistance, neuroinflammation, insult compensatory mechanisms, and peripheral metabolic dysregulation in T2DM and LOAD linkage. The results allow for more streamlined longitudinal studies of T2DM-LOAD risk linkages.

Microglia target synaptic sites early during excitatory circuit disassembly in neurodegeneration

During development, microglia prune excess synapses to refine neuronal circuits. In neurodegeneration, the role of microglia-mediated synaptic pruning in circuit remodeling and dysfunction is important for developing therapies aimed at modulating microglial function. Here we analyzed the role of microglia in the synapse disassembly of degenerating postsynaptic neurons in the inner retina. After inducing transient intraocular pressure elevation to injure retinal ganglion cells, microglia increase in number, shift to ameboid morphology, and exhibit greater process movement. Furthermore, due to the greater number of microglia, there is increased colocalization of microglia with synaptic components throughout the inner plexiform layer and with excitatory synaptic sites along individual ganglion cell dendrites. Microglia depletion partially restores ganglion cell function, suggesting that microglia activation may be neurotoxic in early neurodegeneration. Our results demonstrate the important role of microglia in synapse disassembly in degenerating circuits, highlighting their recruitment to synaptic sites early after neuronal injury.

Heparan sulfate proteoglycans: Mediators of cellular and molecular Alzheimer's disease pathogenic factors via tunnelling nanotubes?

Neurological disorders impact around one billion individuals globally (15 % approx.), with significant implications for disability and mortality with their impact in Australia currently amounts to 6.8 million deaths annually. Heparan sulfate proteoglycans (HSPGs) are complex extracellular molecules implicated in promoting Tau fibril formation resulting in Tau tangles, a hallmark of Alzheimer's disease (AD). HSPG-Tau protein interactions contribute to various AD stages via aggregation, toxicity, and clearance, largely via interactions with the glypican 1 and syndecan 3 core proteins. The tunnelling nanotubes (TNTs) pathway is emerging as a facilitator of intercellular molecule transport, including Tau and Amyloid β proteins, across extensive distances. While current TNT-associated evidence primarily stems from cancer models, their role in Tau propagation and its effects on recipient cells remain unclear. This review explores the interplay of TNTs, HSPGs, and AD-related factors and proposes that HSPGs influence TNT formation in neurodegenerative conditions such as AD.

Mitochondrial calcium signaling in non-neuronal cells: Implications for Alzheimer's disease pathogenesis

Mitochondrial dysregulation is pivotal in Alzheimer's disease (AD) pathogenesis. Calcium governs vital mitochondrial processes impacting energy conversion, oxidative stress, and cell death signaling. Disruptions in mitochondrial calcium (mCa2+) handling induce calcium overload and trigger the opening of mitochondrial permeability transition pore, ensuing energy deprivation and resulting in AD-related neuronal cell death. However, the role of mCa2+ in non-neuronal cells (microglia, astrocytes, oligodendrocytes, endothelial cells, and pericytes) remains elusive. This review provides a comprehensive exploration of mitochondrial heterogeneity and calcium signaling, offering insights into specific differences among various brain cell types in AD.

Clinicopathologic Heterogeneity and Glial Activation Patterns in Alzheimer Disease

Importance

Factors associated with clinical heterogeneity in Alzheimer disease (AD) lay along a continuum hypothesized to associate with tangle distribution and are relevant for understanding glial activation considerations in therapeutic advancement.

Objectives

To examine clinicopathologic and neuroimaging characteristics of disease heterogeneity in AD along a quantitative continuum using the corticolimbic index (CLix) to account for individuality of spatially distributed tangles found at autopsy.

Design, Setting, and Participants

This cross-sectional study was a retrospective medical record review performed on the Florida Autopsied Multiethnic (FLAME) cohort accessioned from 1991 to 2020. Data were analyzed from December 2022 to December 2023. Structural magnetic resonance imaging (MRI) and tau positron emission tomography (PET) were evaluated in an independent neuroimaging group. The FLAME cohort includes 2809 autopsied individuals; included in this study were neuropathologically diagnosed AD cases (FLAME-AD). A digital pathology subgroup of FLAME-AD cases was derived for glial activation analyses.

Main Outcomes and Measures

Clinicopathologic factors of heterogeneity that inform patient history and neuropathologic evaluation of AD; CLix score (lower, relative cortical predominance/hippocampal sparing vs higher, relative cortical sparing/limbic predominant cases); neuroimaging measures (ie, structural MRI and tau-PET).

Results

Of the 2809 autopsied individuals in the FLAME cohort, 1361 neuropathologically diagnosed AD cases were evaluated. A digital pathology subgroup included 60 FLAME-AD cases. The independent neuroimaging group included 93 cases. Among the 1361 FLAME-AD cases, 633 were male (47%; median [range] age at death, 81 [54-96] years) and 728 were female (53%; median [range] age at death, 81 [53-102] years). A younger symptomatic onset (Spearman ρ = 0.39, P < .001) and faster decline on the Mini-Mental State Examination (Spearman ρ = 0.27; P < .001) correlated with a lower CLix score in FLAME-AD series. Cases with a nonamnestic syndrome had lower CLix scores (median [IQR], 13 [9-18]) vs not (median [IQR], 21 [15-27]; P < .001). Hippocampal MRI volume (Spearman ρ = -0.45; P < .001) and flortaucipir tau-PET uptake in posterior cingulate and precuneus cortex (Spearman ρ = -0.74; P < .001) inversely correlated with CLix score. Although AD cases with a CLix score less than 10 had higher cortical tangle count, we found lower percentage of CD68-activated microglia/macrophage burden (median [IQR], 0.46% [0.32%-0.75%]) compared with cases with a CLix score of 10 to 30 (median [IQR], 0.75% [0.51%-0.98%]) and on par with a CLix score of 30 or greater (median [IQR], 0.40% [0.32%-0.57%]; P = .02).

Conclusions and Relevance

Findings show that AD heterogeneity exists along a continuum of corticolimbic tangle distribution. Reduced CD68 burden may signify an underappreciated association between tau accumulation and microglia/macrophages activation that should be considered in personalized therapy for immune dysregulation.

Machine Learning Model for Mild Cognitive Impairment Stage Based on Gait and MRI Images

In patients with mild cognitive impairment (MCI), a lower level of cognitive function is associated with a higher likelihood of progression to dementia. In addition, gait disturbances and structural changes on brain MRI scans reflect cognitive levels. Therefore, we aimed to classify MCI based on cognitive level using gait parameters and brain MRI data. Eighty patients diagnosed with MCI from three dementia centres in Gangwon-do, Korea, were recruited for this study. We defined MCI as a Clinical Dementia Rating global score of ≥0.5, with a memory domain score of ≥0.5. Patients were classified as early-stage or late-stage MCI based on their mini-mental status examination (MMSE) z-scores. We trained a machine learning model using gait and MRI data parameters. The convolutional neural network (CNN) resulted in the best classifier performance in separating late-stage MCI from early-stage MCI; its performance was maximised when feature patterns that included multimodal features (GAIT + white matter dataset) were used. The single support time was the strongest predictor. Machine learning that incorporated gait and white matter parameters achieved the highest accuracy in distinguishing between late-stage MCI and early-stage MCI.

A nonlinear meccano for Alzheimer's emergence by amyloid β-mediated glutamatergic hyperactivity

The pathophysiological process of Alzheimer's disease (AD) is believed to begin many years before the formal diagnosis of AD dementia. This protracted preclinical phase offers a crucial window for potential therapeutic interventions, yet its comprehensive characterization remains elusive. Accumulating evidence suggests that amyloid-β (Aβ) may mediate neuronal hyperactivity in circuit dysfunction in the early stages of AD. At the same time, neural activity can also facilitate Aβ accumulation through intricate feed-forward interactions, complicating elucidating the conditions governing Aβ-dependent hyperactivity and its diagnostic utility. In this study, we use biophysical modeling to shed light on such conditions. Our analysis reveals that the inherently nonlinear nature of the underlying molecular interactions can give rise to the emergence of various modes of hyperactivity. This diversity in the mechanisms of hyperactivity may ultimately account for a spectrum of AD manifestations.

Could protein phosphatase 2A and glycogen synthase kinase-3 beta be targeted by natural compounds to ameliorate Alzheimer's pathologies?

Alzheimer's disease (AD) is a progressive neurological disorder that impairs memory and cognitive abilities, primarily in the elderly. The burden of AD extends beyond patients, impacting families and caregivers due to the patients' reliance on assistance for daily tasks. The main features of the pathogenesis of AD are beta-amyloid plaques and neurofibrillary tangles (NFTs), that strongly correlate with oxidative stress and inflammation. NFTs result from misfolded and hyperphosphorylated tau proteins. Various studies have focused on tau phosphorylation, indicating protein phosphatase 2A (PP2A) as the primary tau phosphatase and glycogen synthase kinase-3 beta (GSK-3β) as the leading tau kinase. Experimental evidence suggests that inhibition of PP2A and increased GSK-3β activity contribute to neuroinflammation, oxidative stress, and cognitive impairment. Hence, targeting PP2A and GSK-3β with pharmacological approaches shows promise in treating AD. The use of natural compounds in the drug development for AD have been extensively studied for their antioxidant, anti-inflammatory, anti-cholinesterase, and neuroprotective properties, demonstrating therapeutic advantages in neurological diseases. Alongside the development of PP2A activator and GSK-3β inhibitor drugs, natural compounds are likely to have neuroprotective effects by increasing PP2A activity and decreasing GSK-3β levels. Therefore, based on the preclinical and clinical studies, the potential of PP2A and GSK-3β as therapeutic targets of natural compounds are highlighted in this review.

Synaptic gene expression changes in frontotemporal dementia due to the MAPT 10+16 mutation

Mutations in the MAPT gene encoding tau protein can cause autosomal dominant neurodegenerative tauopathies including frontotemporal dementia (often with Parkinsonism). In Alzheimer's disease, the most common tauopathy, synapse loss is the strongest pathological correlate of cognitive decline. Recently, PET imaging with synaptic tracers revealed clinically relevant loss of synapses in primary tauopathies; however, the molecular mechanisms leading to synapse degeneration in primary tauopathies remain largely unknown. In this study, we examined post-mortem brain tissue from people who died with frontotemporal dementia with tau pathology (FTDtau) caused by the MAPT intronic exon 10+16 mutation, which increases splice variants containing exon 10 resulting in higher levels of tau with four microtubule binding domains. We used RNA sequencing and histopathology to examine temporal cortex and visual cortex, to look for molecular phenotypes compared to age, sex, and RNA integrity matched participants who died without neurological disease (n=12 per group). Bulk tissue RNA sequencing reveals substantial downregulation of gene expression associated with synaptic function. Upregulated biological pathways in human MAPT 10+16 brain included those involved in transcriptional regulation, DNA damage response, and neuroinflammation. Histopathology confirmed increased pathological tau accumulation in FTDtau cortex as well as a loss of presynaptic protein staining, and region-specific increased colocalization of phospho-tau with synapses in temporal cortex. Our data indicate that synaptic pathology likely contributes to pathogenesis in FTDtau caused by the MAPT 10+16 mutation.

Current Insights of Nanocarrier-Mediated Gene Therapeutics to Treat Potential Impairment of Amyloid Beta Protein and Tau Protein in Alzheimer's Disease

Alzheimer's disease (AD), is the major type of dementia and most progressive, irreversible widespread neurodegenerative disorder affecting the elderly worldwide. The prime hallmarks of Alzheimer's disease (AD) are beta-amyloid plaques (Aβ) and neurofibrillary tangles (NFT). In spite of recent advances and developments in targeting the hallmarks of AD, symptomatic medications that promise neuroprotective activity against AD are currently unable to treat degenerating brain clinically or therapeutically and show little efficacy. The extensive progress of AD therapies over time has resulted in the advent of disease-modifying medications with the potential to alleviate AD. However, due to the presence of a defensive connection between the vascular system and the neural tissues known as the blood-brain barrier (BBB), directing these medications to the site of action in the degenerating brain is the key problem. BBB acts as a highly selective semipermeable membrane that prevents any type of foreign substance from entering the microenvironment of neurons. To overcome this limitation, the revolutionary approach of nanoparticle(NP)/nanocarrier-mediated drug delivery system has marked the era with its unique property to cross, avoid, or disrupt the defensive BBB efficiently and release the modified drug at the target site of action. After comprehensive data mining, this review focuses on the detailed understanding of different types of nanoparticle(NP)/nanocarrier-mediated drug delivery system like liposomes, micelles, gold nanoparticles(NP), polymeric NPs, etc. which have promising potential in carrying the desired drug(cargo) to the location in the degenerated brain thus mitigating the Alzheimer's disease.

A Multiscale Closed-Loop Neurotoxicity Model of Alzheimer's Disease Progression Explains Functional Connectivity Alterations

The accumulation of amyloid-β (Aβ) and hyperphosphorylated-tau (hp-tau) are two classical histopathological biomarkers in Alzheimer's disease (AD). However, their detailed interactions with the electrophysiological changes at the meso- and macroscale are not yet fully understood. We developed a mechanistic multiscale model of AD progression, linking proteinopathy to its effects on neural activity and vice-versa. We integrated a heterodimer model of prion-like protein propagation and a brain network model of Jansen-Rit neural masses derived from human neuroimaging data whose parameters varied due to neurotoxicity. Results showed that changes in inhibition guided the electrophysiological alterations found in AD, and these changes were mainly attributed to Aβ effects. Additionally, we found a causal disconnection between cellular hyperactivity and interregional hypersynchrony contrary to previous beliefs. Finally, we demonstrated that early Aβ and hp-tau depositions' location determine the spatiotemporal profile of the proteinopathy. The presented model combines the molecular effects of both Aβ and hp-tau together with a mechanistic protein propagation model and network effects within a closed-loop model. This holds the potential to enlighten the interplay between AD mechanisms on various scales, aiming to develop and test novel hypotheses on the contribution of different AD-related variables to the disease evolution.

Estimating the synaptic density deficit in Alzheimer's disease using multi-contrast CEST imaging

In vivo noninvasive imaging of neurometabolites is crucial to improve our understanding of the underlying pathophysiological mechanism in neurodegenerative diseases. Abnormal changes in synaptic organization leading to synaptic degradation and neuronal loss is considered as one of the primary factors driving Alzheimer's disease pathology. Magnetic resonance based molecular imaging techniques such as chemical exchange saturation transfer (CEST) and magnetic resonance spectroscopy (MRS) can provide neurometabolite specific information which may relate to underlying pathological and compensatory mechanisms. In this study, CEST and short echo time single voxel MRS was performed to evaluate the sensitivity of cerebral metabolites to beta-amyloid (Aβ) induced synaptic deficit in the hippocampus of a mouse model of Alzheimer's disease. The CEST based spectra (Z-spectra) were acquired on a 9.4 Tesla small animal MR imaging system with two radiofrequency (RF) saturation amplitudes (1.47 μT and 5.9 μT) to obtain creatine-weighted and glutamate-weighted CEST contrasts, respectively. Multi-pool Lorentzian fitting and quantitative T1 longitudinal relaxation maps were used to obtain metabolic specific apparent exchange-dependent relaxation (AREX) maps. Short echo time (TE = 12 ms) single voxel MRS was acquired to quantify multiple neurometabolites from the right hippocampus region. AREX contrasts and MRS based metabolite concentration levels were examined in the ARTE10 animal model for Alzheimer's disease and their wild type (WT) littermate counterparts (age = 10 months). Using MRS voxel as a region of interest, group-wise analysis showed significant reduction in Glu-AREX and Cr-AREX in ARTE10, compared to WT animals. The MRS based results in the ARTE10 mice showed significant decrease in glutamate (Glu) and glutamate-total creatine (Glu/tCr) ratio, compared to WT animals. The MRS results also showed significant increase in total creatine (tCr), phosphocreatine (PCr) and glutathione (GSH) concentration levels in ARTE10, compared to WT animals. In the same ROI, Glu-AREX and Cr-AREX demonstrated positive associations with Glu/tCr ratio. These results indicate the involvement of neurotransmitter metabolites and energy metabolism in Aβ-mediated synaptic degradation in the hippocampus region. The study also highlights the feasibility of CEST and MRS to identify and track multiple competing and compensatory mechanisms involved in heterogeneous pathophysiology of Alzheimer's disease in vivo.

Ceria-Based Therapeutic Antioxidants for Biomedical Applications

The growing interest in nanomedicine over the last 20 years has carved out a research field called "nanocatalytic therapy," where catalytic reactions mediated by nanomaterials are employed to intervene in disease-critical biomolecular processes. Among many kinds of catalytic/enzyme-mimetic nanomaterials investigated thus far, ceria nanoparticles stand out from others owing to their unique scavenging properties against biologically noxious free radicals, including reactive oxygen species (ROS) and reactive nitrogen species (RNS), by exerting enzyme mimicry and nonenzymatic activities. Much effort has been made to utilize ceria nanoparticles as self-regenerating antioxidative and anti-inflammatory agents for various kinds of diseases, given the detrimental effects of ROS and RNS therein that need alleviation. In this context, this review is intended to provide an overview as to what makes ceria nanoparticles merit attention in disease therapy. The introductory part describes the characteristics of ceria nanoparticles as an oxygen-deficient metal oxide. The pathophysiological roles of ROS and RNS are then presented, as well as their scavenging mechanisms by ceria nanoparticles. Representative examples of recent ceria-nanoparticle-based therapeutics are summarized by categorization into organ and disease types, followed by the discussion on the remaining challenges and future research directions.

Emergence of Extracellular Vesicles as "Liquid Biopsy" for Neurological Disorders: Boom or Bust

Extracellular vesicles (EVs) have emerged as an attractive liquid biopsy approach in the diagnosis and prognosis of multiple diseases and disorders. The feasibility of enriching specific subpopulations of EVs from biofluids based on their unique surface markers has opened novel opportunities to gain molecular insight from various tissues and organs, including the brain. Over the past decade, EVs in bodily fluids have been extensively studied for biomarkers associated with various neurological disorders, such as Alzheimer's disease, Parkinson's disease, schizophrenia, bipolar disorder, major depressive disorders, substance use disorders, human immunodeficiency virus-associated neurocognitive disorder, and cancer/treatment-induced neurodegeneration. These studies have focused on the isolation and cargo characterization of either total EVs or brain cells, such as neuron-, astrocyte-, microglia-, oligodendrocyte-, pericyte-, and endothelial-derived EVs from biofluids to achieve early diagnosis and molecular characterization and to predict the treatment and intervention outcomes. The findings of these studies have demonstrated that EVs could serve as a repetitive and less invasive source of valuable molecular information for these neurological disorders, supplementing existing costly neuroimaging techniques and relatively invasive measures, like lumbar puncture. However, the initial excitement surrounding blood-based biomarkers for brain-related diseases has been tempered by challenges, such as lack of central nervous system specificity in EV markers, lengthy protocols, and the absence of standardized procedures for biological sample collection, EV isolation, and characterization. Nevertheless, with rapid advancements in the EV field, supported by improved isolation methods and sensitive assays for cargo characterization, brain cell-derived EVs continue to offer unparallel opportunities with significant translational implications for various neurological disorders. SIGNIFICANCE STATEMENT: Extracellular vesicles present a less invasive liquid biopsy approach in the diagnosis and prognosis of various neurological disorders. Characterizing these vesicles in biofluids holds the potential to yield valuable molecular information, thereby significantly impacting the development of novel biomarkers for various neurological disorders. This paper has reviewed the methodology employed to isolate extracellular vesicles derived from various brain cells in biofluids, their utility in enhancing the molecular understanding of neurodegeneration, and the potential challenges in this research field.

Transmembrane protein 97 is a potential synaptic amyloid beta receptor in human Alzheimer's disease

Synapse loss correlates with cognitive decline in Alzheimer's disease, and soluble oligomeric amyloid beta (Aβ) is implicated in synaptic dysfunction and loss. An important knowledge gap is the lack of understanding of how Aβ leads to synapse degeneration. In particular, there has been difficulty in determining whether there is a synaptic receptor that binds Aβ and mediates toxicity. While many candidates have been observed in model systems, their relevance to human AD brain remains unknown. This is in part due to methodological limitations preventing visualization of Aβ binding at individual synapses. To overcome this limitation, we combined two high resolution microscopy techniques: array tomography and Förster resonance energy transfer (FRET) to image over 1 million individual synaptic terminals in temporal cortex from AD (n = 11) and control cases (n = 9). Within presynapses and post-synaptic densities, oligomeric Aβ generates a FRET signal with transmembrane protein 97. Further, Aβ generates a FRET signal with cellular prion protein, and post-synaptic density 95 within post synapses. Transmembrane protein 97 is also present in a higher proportion of post synapses in Alzheimer's brain compared to controls. We inhibited Aβ/transmembrane protein 97 interaction in a mouse model of amyloidopathy by treating with the allosteric modulator CT1812. CT1812 drug concentration correlated negatively with synaptic FRET signal between transmembrane protein 97 and Aβ. In human-induced pluripotent stem cell derived neurons, transmembrane protein 97 is present in synapses and colocalizes with Aβ when neurons are challenged with human Alzheimer's brain homogenate. Transcriptional changes are induced by Aβ including changes in genes involved in neurodegeneration and neuroinflammation. CT1812 treatment of these neurons caused changes in gene sets involved in synaptic function. These data support a role for transmembrane protein 97 in the synaptic binding of Aβ in human Alzheimer's disease brain where it may mediate synaptotoxicity.

Cellular junction dynamics and Alzheimer's disease: a comprehensive review

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder characterized by progressive neuronal damage and cognitive decline. Recent studies have shed light on the involvement of not only the blood-brain barrier (BBB) dysfunction but also significant alterations in cellular junctions in AD pathogenesis. In this review article, we explore the role of the BBB and cellular junctions in AD pathology, with a specific focus on the hippocampus. The BBB acts as a crucial protective barrier between the bloodstream and the brain, maintaining brain homeostasis and regulating molecular transport. Preservation of BBB integrity relies on various junctions, including gap junctions formed by connexins, tight junctions composed of proteins such as claudins, occludin, and ZO-1, as well as adherence junctions involving molecules like vascular endothelial (VE) cadherin, Nectins, and Nectin-like molecules (Necls). Abnormalities in these junctions and junctional components contribute to impaired neuronal signaling and increased cerebrovascular permeability, which are closely associated with AD advancement. By elucidating the underlying molecular mechanisms governing BBB and cellular junction dysfunctions within the context of AD, this review offers valuable insights into the pathogenesis of AD and identifies potential therapeutic targets for intervention.

Unraveling the intercellular communication disruption and key pathways in Alzheimer's disease: an integrative study of single-nucleus transcriptomes and genetic association

BACKGROUND

Recently, single-nucleus RNA-seq (snRNA-seq) analyses have revealed important cellular and functional features of Alzheimer's disease (AD), a prevalent neurodegenerative disease. However, our knowledge regarding intercellular communication mediated by dysregulated ligand-receptor (LR) interactions remains very limited in AD brains.

METHODS

We systematically assessed the intercellular communication networks by using a discovery snRNA-seq dataset comprising 69,499 nuclei from 48 human postmortem prefrontal cortex (PFC) samples. We replicated the findings using an independent snRNA-seq dataset of 56,440 nuclei from 18 PFC samples. By integrating genetic signals from AD genome-wide association studies (GWAS) summary statistics and whole genome sequencing (WGS) data, we prioritized AD-associated Gene Ontology (GO) terms containing dysregulated LR interactions. We further explored drug repurposing for the prioritized LR pairs using the Therapeutic Targets Database.

RESULTS

We identified 190 dysregulated LR interactions across six major cell types in AD PFC, of which 107 pairs were replicated. Among the replicated LR signals, we found globally downregulated communications in the astrocytes-to-neurons signaling axis, characterized, for instance, by the downregulation of APOE-related and Calmodulin (CALM)-related LR interactions and their potential regulatory connections to target genes. Pathway analyses revealed 44 GO terms significantly linked to AD, highlighting Biological Processes such as 'amyloid precursor protein processing' and 'ion transmembrane transport,' among others. We prioritized several drug repurposing candidates, such as cromoglicate, targeting the identified dysregulated LR pairs.

CONCLUSIONS

Our integrative analysis identified key dysregulated LR interactions in a cell type-specific manner and the associated GO terms in AD, offering novel insights into potential therapeutic targets involved in disrupted cell-cell communication in AD.

Effects of Exercise Training on Immune-Related Genes and Pathways in the Cortex of Animal Models of Alzheimer's Disease: A Systematic Review

Background

Alzheimer's disease (AD) is a chronic neurodegenerative disease that affects the immune system due to the accumulation of amyloid-β (Aβ) and tau associated molecular pathology and other pathogenic processes. To address AD pathogenesis, various approaches had been conducted from drug development to lifestyle modification to reduce the prevalence of AD. Exercise is considered a prominent lifestyle modification to combat AD.

Objective

This observation prompted us to review the literature on exercise related to immune genes in the cortex of animal models of AD. We focused on animal model studies due to their prevalence in this domain.

Methods

The systematic review was conducted according to PRISMA standards using Web of Science (WoS) and PubMed databases. Any kind of genes, proteins, and molecular molecules were included in this systematic review. The list of these immune-related molecules was analyzed in the STRING database for functional enrichment analysis.

Results

We found that 17 research studies discussed immune-related molecules and 30 immune proteins. These studies showed that exercise had the ability to ameliorate dysfunction in AD-related pathways, which led to decreasing the expression of microglia-related pathways and Th17-related immune pathways. As a result of decreasing the expression of immune-related pathways, the expression of apoptosis-related pathways was also decreasing, and neuronal survival was increased by exercise activity.

Conclusions

Based on functional enrichment analysis, exercise not only could reduce apoptotic factors and immune components but also could increase cell survival and Aβ clearance in cortex samples. PROSPERO ID: CRD42022326093.

Inhibiting tau-induced elevated nSMase2 activity and ceramides is therapeutic in an Alzheimer's disease mouse model

BACKGROUND

Cognitive decline in Alzheimer's disease (AD) is associated with hyperphosphorylated tau (pTau) propagation between neurons along synaptically connected networks, in part via extracellular vesicles (EVs). EV biogenesis is triggered by ceramide enrichment at the plasma membrane from neutral sphingomyelinase2 (nSMase2)-mediated cleavage of sphingomyelin. We report, for the first time, that human tau expression elevates brain ceramides and nSMase2 activity.

METHODS

To determine the therapeutic benefit of inhibiting this elevation, we evaluated PDDC, the first potent, selective, orally bioavailable, and brain-penetrable nSMase2 inhibitor in the transgenic PS19 AD mouse model. Additionally, we directly evaluated the effect of PDDC on tau propagation in a mouse model where an adeno-associated virus (AAV) encoding P301L/S320F double mutant human tau was stereotaxically-injected unilaterally into the hippocampus. The contralateral transfer of the double mutant human tau to the dentate gyrus was monitored. We examined ceramide levels, histopathological changes, and pTau content within EVs isolated from the mouse plasma.

RESULTS

Similar to human AD, the PS19 mice exhibited increased brain ceramide levels and nSMase2 activity; both were completely normalized by PDDC treatment. The PS19 mice also exhibited elevated tau immunostaining, thinning of hippocampal neuronal cell layers, increased mossy fiber synaptophysin immunostaining, and glial activation, all of which were pathologic features of human AD. PDDC treatment reduced these changes. The plasma of PDDC-treated PS19 mice had reduced levels of neuronal- and microglial-derived EVs, the former carrying lower pTau levels, compared to untreated mice. In the tau propagation model, PDDC normalized the tau-induced increase in brain ceramides and significantly reduced the amount of tau propagation to the contralateral side.

CONCLUSIONS

PDDC is a first-in-class therapeutic candidate that normalizes elevated brain ceramides and nSMase2 activity, leading to the slowing of tau spread in AD mice.

Adeno-associated virus (AAV) 9-mediated gene delivery of Nurr1 and Foxa2 ameliorates symptoms and pathologies of Alzheimer disease model mice by suppressing neuro-inflammation and glial pathology

There is a compelling need to develop disease-modifying therapies for Alzheimer's disease (AD), the most common neuro-degenerative disorder. Together with recent progress in vector development for efficiently targeting the central nervous system, gene therapy has been suggested as a potential therapeutic modality to overcome the limited delivery of conventional types of drugs to and within the damaged brain. In addition, given increasing evidence of the strong link between glia and AD pathophysiology, therapeutic targets have been moving toward those addressing glial cell pathology. Nurr1 and Foxa2 are transcription/epigenetic regulators that have been reported to cooperatively regulate inflammatory and neurotrophic response in glial cells. In this study, we tested the therapeutic potential of Nurr1 and Foxa2 gene delivery to treat AD symptoms and pathologies. A series of functional, histologic, and transcriptome analyses revealed that the combined expression of Nurr1 and Foxa2 substantially ameliorated AD-associated amyloid β and Tau proteinopathy, cell senescence, synaptic loss, and neuro-inflammation in multiple in vitro and in vivo AD models. Intra-cranial delivery of Nurr1 and Foxa2 genes using adeno-associated virus (AAV) serotype 9 improved the memory and cognitive function of AD model mice. The therapeutic benefits of gene delivery were attained mainly by correcting pathologic glial function. These findings collectively indicate that AAV9-mediated Nurr1 and Foxa2 gene transfer could be an effective disease-modifying therapy for AD.

Profiling the autoantibody repertoire reveals autoantibodies associated with mild cognitive impairment and dementia

Background

Dementia is a debilitating neurological disease affecting millions of people worldwide. The exact mechanisms underlying the initiation and progression of the disease remain to be fully defined. There is an increasing body of evidence for the role of immune dysregulation in the pathogenesis of dementia, where blood-borne autoimmune antibodies have been studied as potential markers associated with pathological mechanisms of dementia.

Methods

This study included plasma from 50 cognitively normal individuals, 55 subjects with MCI (mild cognitive impairment), and 22 subjects with dementia. Autoantibody profiling for more than 1,600 antigens was performed using a high throughput microarray platform to identify differentially expressed autoantibodies in MCI and dementia.

Results

The differential expression analysis identified 33 significantly altered autoantibodies in the plasma of patients with dementia compared to cognitively normal subjects, and 38 significantly altered autoantibodies in the plasma of patients with dementia compared to subjects with MCI. And 20 proteins had significantly altered autoantibody responses in MCI compared to cognitively normal individuals. Five autoantibodies were commonly dysregulated in both dementia and MCI, including anti-CAMK2A, CKS1B, ETS2, MAP4, and NUDT2. Plasma levels of anti-ODF3, E6, S100P, and ARHGDIG correlated negatively with the cognitive performance scores (MoCA) (r2 -0.56 to -0.42, value of p < 0.001). Additionally, several proteins targeted by autoantibodies dysregulated in dementia were significantly enriched in the neurotrophin signaling pathway, axon guidance, cholinergic synapse, long-term potentiation, apoptosis, glycolysis and gluconeogenesis.

Conclusion

We have shown multiple dysregulated autoantibodies in the plasma of subjects with MCI and dementia. The corresponding proteins for these autoantibodies are involved in neurodegenerative pathways, suggesting a potential impact of autoimmunity on the etiology of dementia and the possible benefit for future therapeutic approaches. Further investigations are warranted to validate our findings.

Assessing Cannabidiol as a Therapeutic Agent for Preventing and Alleviating Alzheimer's Disease Neurodegeneration

Alzheimer's disease (AD) is a leading neurodegenerative condition causing cognitive and memory decline. With small-molecule drugs targeting Aβ proving ineffective, alternative targets are urgently needed. Neuroinflammation, which is central to AD's pathology, results in synaptic and neuronal damage, highlighting the importance of addressing inflammation and conserving neuronal integrity. Cannabidiol (CBD), derived from cannabis, is noted for its neuroprotective and anti-inflammatory properties, having shown efficacy in neuropathic pain management for epilepsy. To investigate the therapeutic efficacy of CBD in AD and to elucidate its underlying mechanisms, we aimed to contribute valuable insights for incorporating AD prevention recommendations into future CBD nutritional guidelines. Aβ1-42 was employed for in vivo or in vitro model establishment, CBD treatment was utilized to assess the therapeutic efficacy of CBD, and RNA-seq analysis was conducted to elucidate the underlying therapeutic mechanism. CBD mitigates Aβ-induced cognitive deficits by modulating microglial activity, promoting neurotrophic factor release, and regulating inflammatory genes. The administration of CBD demonstrated a protective effect against Aβ toxicity both in vitro and in vivo, along with an amelioration of cognitive impairment in mice. These findings support the potential inclusion of CBD in future nutritional guidelines for Alzheimer's disease prevention.

P2X7R influences tau aggregate burden in human tauopathies and shows distinct signalling in microglia and astrocytes

The purinoceptor P2X7R is a promising therapeutic target for tauopathies, including Alzheimer's disease (AD). Pharmacological inhibition or genetic knockdown of P2X7R ameliorates cognitive deficits and reduces pathological tau burden in mice that model aspects of tauopathy, including mice expressing mutant human frontotemporal dementia (FTD)-causing forms of tau. However, disagreements remain over which glial cell types express P2X7R and therefore the mechanism of action is unresolved. Here, we show that P2X7R protein levels increase in human AD post-mortem brain, in agreement with an upregulation of P2RX7 mRNA observed in transcriptome profiles from the AMP-AD consortium. P2X7R protein increases mirror advancing Braak stage and coincide with synapse loss. Using RNAScope we detect P2RX7 mRNA in microglia and astrocytes in human AD brain, including in the vicinity of senile plaques. In cultured microglia, P2X7R activation modulates the NLRP3 inflammasome pathway by promoting the formation of active complexes and release of IL-1β. In astrocytes, P2X7R activates NFκB signalling and increases production of the cytokines CCL2, CXCL1 and IL-6 together with the acute phase protein Lcn2. To further explore the role of P2X7R in a disease-relevant context, we expressed wild-type or FTD-causing mutant forms of tau in mouse organotypic brain slice cultures. Inhibition of P2X7R reduces insoluble tau levels without altering soluble tau phosphorylation or synaptic localisation, suggesting a non-cell autonomous role of glial P2X7R on pathological tau aggregation. These findings support further investigations into the cell-type specific effects of P2X7R-targeting therapies in tauopathies.

MicroRNA expression in extracellular vesicles as a novel blood-based biomarker for Alzheimer's disease

INTRODUCTION

Brain cell-derived small extracellular vesicles (sEVs) in blood offer unique cellular and molecular information related to the onset and progression of Alzheimer's disease (AD). We simultaneously enriched six specific sEV subtypes from the plasma and analyzed a selected panel of microRNAs (miRNAs) in older adults with/without cognitive impairment.

METHODS

Total sEVs were isolated from the plasma of participants with normal cognition (CN; n = 11), mild cognitive impairment (MCI; n = 11), MCI conversion to AD dementia (MCI-AD; n = 6), and AD dementia (n = 11). Various brain cell-derived sEVs (from neurons, astrocytes, microglia, oligodendrocytes, pericytes, and endothelial cells) were enriched and analyzed for specific miRNAs.

RESULTS

miRNAs in sEV subtypes differentially expressed in MCI, MCI-AD, and AD dementia compared to the CN group clearly distinguished dementia status, with an area under the curve (AUC) > 0.90 and correlated with the temporal cortical region thickness on magnetic resonance imaging (MRI).

DISCUSSION

miRNA analyses in specific sEVs could serve as a novel blood-based molecular biomarker for AD.

HIGHLIGHTS

Multiple brain cell-derived small extracellular vesicles (sEVs) could be isolated simultaneously from blood. MicroRNA (miRNA) expression in sEVs could detect Alzheimer's disease (AD) with high specificity and sensitivity. miRNA expression in sEVs correlated with cortical region thickness on magnetic resonance imaging (MRI). Altered expression of miRNAs in sEVCD31 and sEVPDGFRβ suggested vascular dysfunction. miRNA expression in sEVs could predict the activation state of specific brain cell types.

Ion Channels and Ionotropic Receptors in Astrocytes: Physiological Functions and Alterations in Alzheimer's Disease and Glioblastoma

The human brain is composed of nearly one hundred billion neurons and an equal number of glial cells, including macroglia, i.e., astrocytes and oligodendrocytes, and microglia, the resident immune cells of the brain. In the last few decades, compelling evidence has revealed that glial cells are far more active and complex than previously thought. In particular, astrocytes, the most abundant glial cell population, not only take part in brain development, metabolism, and defense against pathogens and insults, but they also affect sensory, motor, and cognitive functions by constantly modulating synaptic activity. Not surprisingly, astrocytes are actively involved in neurodegenerative diseases (NDs) and other neurological disorders like brain tumors, in which they rapidly become reactive and mediate neuroinflammation. Reactive astrocytes acquire or lose specific functions that differently modulate disease progression and symptoms, including cognitive impairments. Astrocytes express several types of ion channels, including K+, Na+, and Ca2+ channels, transient receptor potential channels (TRP), aquaporins, mechanoreceptors, and anion channels, whose properties and functions are only partially understood, particularly in small processes that contact synapses. In addition, astrocytes express ionotropic receptors for several neurotransmitters. Here, we provide an extensive and up-to-date review of the roles of ion channels and ionotropic receptors in astrocyte physiology and pathology. As examples of two different brain pathologies, we focus on Alzheimer's disease (AD), one of the most diffuse neurodegenerative disorders, and glioblastoma (GBM), the most common brain tumor. Understanding how ion channels and ionotropic receptors in astrocytes participate in NDs and tumors is necessary for developing new therapeutic tools for these increasingly common neurological conditions.

Myeloid cell deficiency of the inflammatory transcription factor Stat4 protects long-term synaptic plasticity from the effects of a high-fat, high-cholesterol diet

Neuroinflammation is associated with neurodegenerative diseases, including Alzheimer's and Parkinson's. The cytokine interleukin-12 activates signal transducer and activator of transcription 4 (Stat4), and consumption of a high-fat, high-cholesterol diet (HFD-C) and Stat4 activity are associated with inflammation, atherosclerosis, and a diabetic metabolic phenotype. In studies of in vitro hippocampal slices from control Stat4fl/flLdlr-/- mice fed a HFD-C diabetogenic diet, we show that Schaffer collateral-CA1 synapses exhibited larger reductions in activity-dependent, long-term potentiation (LTP) of synaptic transmission, compared to mice fed a standard diet. Glucose tolerance and insulin sensitivity shifts produced by HFD-C diet were reduced in Stat4ΔLysMLdlr-/- mice compared to Stat4fl/flLdlr-/- controls. Stat4ΔLysMLdlr-/- mice, which lack Stat4 under control of the LysMCre promoter, were resistant to HFD-C induced impairments in LTP. In contrast, Schaffer collateral-CA1 synapses in Stat4ΔLysMLdlr-/- mice fed the HFD-C diet showed larger LTP than control Stat4fl/flLdlr-/- mice. Expression of a number of neuroinflammatory and synaptic plasticity genes was reduced by HFD-C diet in control mice, and less affected by HFD-C diet in Stat4ΔLysMLdlr-/- mice. These data suggest that suppression of Stat4 activation may protect against effects of Western diet on cognition, type 2 diabetes, and reduce risk of Alzheimer's disease and other neurodegenerative disorders associated with neuroinflammation.

Beyond the amyloid cascade: An update of Alzheimer's disease pathophysiology

Alzheimer's disease (AD) is a multi-etiology disease. The biological system of AD is associated with multidomain genetic, molecular, cellular, and network brain dysfunctions, interacting with central and peripheral immunity. These dysfunctions have been primarily conceptualized according to the assumption that amyloid deposition in the brain, whether from a stochastic or a genetic accident, is the upstream pathological change. However, the arborescence of AD pathological changes suggests that a single amyloid pathway might be too restrictive or inconsistent with a cascading effect. In this review, we discuss the recent human studies of late-onset AD pathophysiology in an attempt to establish a general updated view focusing on the early stages. Several factors highlight heterogenous multi-cellular pathological changes in AD, which seem to work in a self-amplifying manner with amyloid and tau pathologies. Neuroinflammation has an increasing importance as a major pathological driver, and perhaps as a convergent biological basis of aging, genetic, lifestyle and environmental risk factors.

Molecular and Structural Insight into Adenosine A2A Receptor in Neurodegenerative Disorders: A Significant Target for Efficient Treatment Approach

All biological tissues and bodily fluids include the autacoid adenosine. The P1 class of purinergic receptors includes adenosine receptors. Four distinct G-protein-coupled receptors on the cellular membrane mediate the effects of adenosine, whose cytoplasmic content is regulated by producing/degrading enzymes and nucleoside transporters. A2A receptor has received a great deal of attention in recent years because it has a wide range of potential therapeutic uses. A2B and, more significantly, A2A receptors regulate numerous physiological mechanisms in the central nervous system (CNS). The inferior targetability of A2B receptors towards adenosine points that they might portray a promising medicinal target since they are triggered only under pharmacological circumstances (when adenosine levels rise up to micromolar concentrations). The accessibility of specific ligands for A2B receptors would permit the exploration of such a theory. A2A receptors mediate both potentially neurotoxic and neuroprotective actions. Hence, it is debatable to what extent they play a role in neurodegenerative illnesses. However, A2A receptor blockers have demonstrated clear antiparkinsonian consequences, and a significant attraction exists in the role of A2A receptors in other neurodegenerative disorders. Amyloid peptide extracellular accumulation and tau hyperphosphorylation are the pathogenic components of AD that lead to neuronal cell death, cognitive impairment, and memory loss. Interestingly, in vitro and in vivo research has shown that A2A adenosine receptor antagonists may block each of these clinical symptoms, offering a crucial new approach to combat a condition for which, regrettably, only symptomatic medications are currently available. At least two requirements must be met to determine whether such receptors are a target for diseases of the CNS: a complete understanding of the mechanisms governing A2A-dependent processes and the availability of ligands that can distinguish between the various receptor populations. This review concisely summarises the biological effects mediated by A2A adenosine receptors in neurodegenerative disorders and discusses the chemical characteristics of A2A adenosine receptor antagonists undergoing clinical trials. Selective A2A receptor blocker against neurodegenerative disorders.

The Dual Nature of Microglia in Alzheimer's Disease: A Microglia-Neuron Crosstalk Perspective

Microglia are critical players in the neuroimmune system, and their involvement in Alzheimer's disease (AD) pathogenesis is increasingly being recognized. However, whether microglia play a positive or negative role in AD remains largely controversial and the precise molecular targets for intervention are not well defined. This partly results from the opposing roles of microglia in AD pathology, and is mainly reflected in the microglia-neuron interaction. Microglia can prune synapses resulting in excessive synapse loss and neuronal dysfunction, but they can also promote synapse formation, enhancing neural network plasticity. Neuroimmune crosstalk accelerates microglial activation, which induces neuron death and enhances the microglial phagocytosis of β-amyloid to protect neurons. Moreover, microglia have dual opposing roles in developing the major pathological features in AD, such as amyloid deposition and blood-brain barrier permeability. This review summarizes the dual opposing role of microglia in AD from the perspective of the interaction between neurons and microglia. Additionally, current AD treatments targeting microglia and the advantages and disadvantages of developing microglia-targeted therapeutic strategies are discussed.

Weak-hyperactive hippocampal CA1 neurons in the prodromal stage of Alzheimer's disease in hybrid AppNL-G-F/NL-G-F × Thy1-GCaMP6s+/- mice suggest disrupted plasticity

This study investigated the impact of familial Alzheimer's disease (AD)-linked amyloid precursor protein (App) mutations on hippocampal CA1 neuronal activity and function at an early disease stage in AppNL-G-F/NL-G-F × Thy1-GCaMP6s+/- (A-TG) mice using calcium imaging. Longitudinal assessment of spatial behavior at 12 and 18 months of age identified an early disease stage at 12 months when there was significant amyloid beta pathology with mild behavioral deficits. Hippocampal CA1 neuronal activity and event-related encoding of distance and time were therefore assessed at 12 months of age in several configurations of an air-induced running task to assess the dynamics of cellular activity. Neurons in A-TG mice displayed diminished (weaker) and more frequent (hyperactive) neuronal firing that was more pronounced during movement compared to immobility. Responsive neurons showed configuration-specific deficits in distance and time encoding with impairment in adapting their responses to changing configurations. These results suggest that at an early stage of AD in the absence of full-blown behavioral deficits, weak-hyperactive neuronal activity may induce impairments in sensory perception of changing environments.

Generation of Patterned Cocultures in 2D and 3D: State of the Art

Cells inside the body are embedded into a highly structured microenvironment that consists of cells that lie in direct or close contact with other cell types that regulate the overall tissue function. Therefore, coculture models are versatile tools that can generate tissue engineering constructs with improved mimicking of in vivo conditions. While there are many reviews that have focused on pattering a single cell type, very few reviews have been focused on techniques for coculturing multiple cell types on a single substrate with precise control. In this regard, this Review covers various technologies that have been utilized for the development of these patterned coculture models while mentioning the limitations associated with each of them. Further, the application of these models to various tissue engineering applications has been discussed.

Unraveling the intercellular communication disruption and key pathways in Alzheimer's disease: An integrative study of single-nucleus transcriptomes and genetic association

Background

Recently, single-nucleus RNA-seq (snRNA-seq) analyses have revealed important cellular and functional features of Alzheimer's disease (AD), a prevalent neurodegenerative disease. However, our knowledge regarding intercellular communication mediated by dysregulated ligand-receptor (LR) interactions remains very limited in AD brains.

Methods

We systematically assessed the intercellular communication networks by using a discovery snRNA-seq dataset comprising 69,499 nuclei from 48 human postmortem prefrontal cortex (PFC) samples. We replicated the findings using an independent snRNA-seq dataset of 56,440 nuclei from 18 PFC samples. By integrating genetic signals from AD genome-wide association studies (GWAS) summary statistics and whole genome sequencing (WGS) data, we prioritized AD-associated Gene Ontology (GO) terms containing dysregulated LR interactions. We further explored drug repurposing for the prioritized LR pairs using the Therapeutic Targets Database.

Results

We identified 316 dysregulated LR interactions across six major cell types in AD PFC, of which 210 pairs were replicated. Among the replicated LR signals, we found globally downregulated communications in astrocytes-to-neurons signaling axis, characterized, for instance, by the downregulation of APOE-related and Calmodulin (CALM)-related LR interactions and their potential regulatory connections to target genes. Pathway analyses revealed 60 GO terms significantly linked to AD, highlighting Biological Processes such as 'amyloid precursor protein processing' and 'ion transmembrane transport', among others. We prioritized several drug repurposing candidates, such as cromoglicate, targeting the identified dysregulated LR pairs.

Conclusions

Our integrative analysis identified key dysregulated LR interactions in a cell type-specific manner and the associated GO terms in AD, offering novel insights into potential therapeutic targets involved in disrupted cell-cell communication in AD.

Calcium sensor Yellow Cameleon 3.6 as a tool to support the calcium hypothesis of Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) is a neurodegenerative disease with increasing relevance as dementia cases rise. The etiology of AD is widely debated. The Calcium Hypothesis of Alzheimer's disease and brain aging states that the dysfunction of calcium signaling is the final common pathway leading to neurodegeneration. When the Calcium Hypothesis was originally coined, the technology did not exist to test it, but with the advent of Yellow Cameleon 3.6 (YC3.6) we are able to test its validity.

METHODS

Here we review use of YC3.6 in studying Alzheimer's disease using mouse models and discuss whether these studies support or refute the Calcium Hypothesis.

RESULTS

YC3.6 studies showed that amyloidosis preceded dysfunction in neuronal calcium signaling and changes in synapse structure. This evidence supports the Calcium Hypothesis.

DISCUSSION

In vivo YC3.6 studies point to calcium signaling as a promising therapeutic target; however, additional work is necessary to translate these findings to humans.

Optogenetic targeting of astrocytes restores slow brain rhythm function and slows Alzheimer's disease pathology

Patients with Alzheimer's disease (AD) exhibit non-rapid eye movement (NREM) sleep disturbances in addition to memory deficits. Disruption of NREM slow waves occurs early in the disease progression and is recapitulated in transgenic mouse models of beta-amyloidosis. However, the mechanisms underlying slow-wave disruptions remain unknown. Because astrocytes contribute to slow-wave activity, we used multiphoton microscopy and optogenetics to investigate whether they contribute to slow-wave disruptions in APP/PS1 mice. The power but not the frequency of astrocytic calcium transients was reduced in APP/PS1 mice compared to nontransgenic controls. Optogenetic activation of astrocytes at the endogenous frequency of slow waves restored slow-wave power, reduced amyloid deposition, prevented neuronal calcium elevations, and improved memory performance. Our findings revealed malfunction of the astrocytic network driving slow-wave disruptions. Thus, targeting astrocytes to restore circuit activity underlying sleep and memory disruptions in AD could ameliorate disease progression.

How Many Alzheimer-Perusini's Atypical Forms Do We Still Have to Discover?

Alzheimer-Perusini's (AD) disease represents the most spread dementia around the world and constitutes a serious problem for public health. It was first described by the two physicians from whom it took its name. Nowadays, we have extensively expanded our knowledge about this disease. Starting from a merely clinical and histopathologic description, we have now reached better molecular comprehension. For instance, we passed from an old conceptualization of the disease based on plaques and tangles to a more modern vision of mixed proteinopathy in a one-to-one relationship with an alteration of specific glial and neuronal phenotypes. However, no disease-modifying therapies are yet available. It is likely that the only way to find a few "magic bullets" is to deepen this aspect more and more until we are able to draw up specific molecular profiles for single AD cases. This review reports the most recent classifications of AD atypical variants in order to summarize all the clinical evidence using several discrimina (for example, post mortem neurofibrillary tangle density, cerebral atrophy, or FDG-PET studies). The better defined four atypical forms are posterior cortical atrophy (PCA), logopenic variant of primary progressive aphasia (LvPPA), behavioral/dysexecutive variant and AD with corticobasal degeneration (CBS). Moreover, we discuss the usefulness of such classifications before outlining the molecular-genetic aspects focusing on microglial activity or, more generally, immune system control of neuroinflammation and neurodegeneration.

Inhibiting tau-induced elevated nSMase2 activity and ceramides is therapeutic in murine Alzheimer's disease

Background

Cognitive decline in Alzheimer's disease (AD) is associated with prion-like tau propagation between neurons along synaptically connected networks, in part via extracellular vesicles (EV). EV biogenesis is triggered by ceramide enrichment at the plasma membrane from neutral sphingomyelinase2(nSMase2)-mediated cleavage of sphingomyelin. We report, for the first time, that tau expression triggers an elevation in brain ceramides and nSMase2 activity.

Methods

To determine the therapeutic benefit of inhibiting this elevation, we evaluated the efficacy of PDDC, the first potent, selective, orally bioavailable, and brain-penetrable nSMase2 inhibitor, in the PS19 tau transgenic AD murine model. Changes in brain ceramide and sphingomyelin levels, Tau content, histopathology, and nSMase2 target engagement were monitored, as well as changes in the number of brain-derived EVs in plasma and their Tau content. Additionally, we evaluated the ability of PDDC to impede tau propagation in a murine model where an adeno-associated virus(AAV) encoding for P301L/S320F double mutant human tau was stereotaxically-injected unilaterally into the hippocampus and the contralateral transfer to the dentate gyrus was monitored.

Results

Similar to human AD, PS19 mice exhibited increased brain ceramides and nSMase2 activity; both were completely normalized by PDDC treatment. PS19 mice exhibited elevated tau immunostaining, thinning of hippocampal neuronal cell layers, increased mossy fiber synaptophysin immunostaining, and glial activation, all pathologic features of human AD. PDDC treatment significantly attenuated these aberrant changes. Mouse plasma isolated from PDDC-treated PS19 mice exhibited reduced levels of neuron- and microglia-derived EVs, the former carrying lower phosphorylated Tau(pTau) levels, compared to untreated mice. In the AAV tau propagation model, PDDC normalized the tau-induced increase in brain ceramides and significantly decreased tau spreading to the contralateral side.

Conclusions

PDDC is a first-in-class therapeutic candidate that normalizes elevated brain ceramides and nSMase2 activity leading to the slowing of tau spread in AD mice.

Pathological BBB Crossing Melanin-Like Nanoparticles as Metal-Ion Chelators and Neuroinflammation Regulators against Alzheimer's Disease

Inflammatory responses, manifested in excessive oxidative stress and microglia overactivation, together with metal ion-triggered amyloid-beta (Aβ) deposition, are critical hallmarks of Alzheimer's disease (AD). The intricate pathogenesis causes severe impairment of neurons, which, in turn, exacerbates Aβ aggregation and facilitates AD progression. Herein, multifunctional melanin-like metal ion chelators and neuroinflammation regulators (named PDA@K) were constructed for targeted treatment of AD. In this platform, intrinsically bioactive material polydopamine nanoparticles (PDA) with potent metal ion chelating and ROS scavenging effects were decorated with the KLVFF peptide, endowing the system with the capacity of enhanced pathological blood-brain barrier (BBB) crossing and lesion site accumulation via Aβ hitchhiking. In vitro and in vivo experiment revealed that PDA@K had high affinity toward Aβ and were able to hitch a ride on Aβ to achieve increased pathological BBB crossing. The engineered PDA@K effectively mitigated Aβ aggregate and alleviated neuroinflammation. The modulated inflammatory microenvironment by PDA@K promoted microglial polarization toward the M2-like phenotype, which restored their critical functions for neuron care and plaque removal. After 3-week treatment of PDA@K, spatial learning and memory deficit as well as neurologic changes of FAD4T transgenic mice were largely rescued. Transcriptomics analysis further revealed the therapeutic mechanism of PDA@K. Our study provided an appealing paradigm for directly utilizing intrinsic properties of nanomaterials as therapeutics for AD instead of just using them as nanocarriers, which largely widen the application of nanomaterials in AD therapy.

Alzheimer's Disease Treatment: The Search for a Breakthrough

As the search for modalities to cure Alzheimer's disease (AD) has made slow progress, research has now turned to innovative pathways involving neural and peripheral inflammation and neuro-regeneration. Widely used AD treatments provide only symptomatic relief without changing the disease course. The recently FDA-approved anti-amyloid drugs, aducanumab and lecanemab, have demonstrated unclear real-world efficacy with a substantial side effect profile. Interest is growing in targeting the early stages of AD before irreversible pathologic changes so that cognitive function and neuronal viability can be preserved. Neuroinflammation is a fundamental feature of AD that involves complex relationships among cerebral immune cells and pro-inflammatory cytokines, which could be altered pharmacologically by AD therapy. Here, we provide an overview of the manipulations attempted in pre-clinical experiments. These include inhibition of microglial receptors, attenuation of inflammation and enhancement of toxin-clearing autophagy. In addition, modulation of the microbiome-brain-gut axis, dietary changes, and increased mental and physical exercise are under evaluation as ways to optimize brain health. As the scientific and medical communities work together, new solutions may be on the horizon to slow or halt AD progression.

Predictive network analysis identifies JMJD6 and other potential key drivers in Alzheimer's disease

Despite decades of genetic studies on late-onset Alzheimer's disease, the underlying molecular mechanisms remain unclear. To better comprehend its complex etiology, we use an integrative approach to build robust predictive (causal) network models using two large human multi-omics datasets. We delineate bulk-tissue gene expression into single cell-type gene expression and integrate clinical and pathologic traits, single nucleotide variation, and deconvoluted gene expression for the construction of cell type-specific predictive network models. Here, we focus on neuron-specific network models and prioritize 19 predicted key drivers modulating Alzheimer's pathology, which we then validate by knockdown in human induced pluripotent stem cell-derived neurons. We find that neuronal knockdown of 10 of the 19 targets significantly modulates levels of amyloid-beta and/or phosphorylated tau peptides, most notably JMJD6. We also confirm our network structure by RNA sequencing in the neurons following knockdown of each of the 10 targets, which additionally predicts that they are upstream regulators of REST and VGF. Our work thus identifies robust neuronal key drivers of the Alzheimer's-associated network state which may represent therapeutic targets with relevance to both amyloid and tau pathology in Alzheimer's disease.

Optimization and evaluation of pyridinyl vinyl sulfones as Nrf2 activator for the antioxidant and anti-inflammatory effects

Many studies have reported that chalcone-based compounds exhibit biological activities such as anticancer, antioxidant, anti-inflammatory and neuroprotective effects. Among the published chalcone derivatives, (E)-1-(3-methoxypyridin-2-yl)-3-(2-(trifluoromethyl)phenyl)prop-2-en-1-one (VEDA-1209), which is currently undergoing preclinical study, was selected as a starting compound for the development of new nuclear factor erythroid 2-related factor 2 (Nrf2) activators. Based on our previous knowledge, we attempted to redesign and synthesize VEDA-1209 derivatives by introducing the pyridine ring and sulfone moiety to ameliorate its Nrf2 efficacy and drug-like properties. Among the synthesized compounds, (E)-3-chloro-2-(2-((3-methoxypyridin-2-yl)sulfonyl)vinyl) pyridine (10e) was found to have approximately 16-folds higher Nrf2 activating effects than VEDA-1209 (10e: EC₅₀ = 37.9 nM vs VEDA-1209: EC₅₀ = 625 nM) in functional cell-based assay. In addition, 10e effectively improved drug-like properties such as CYP inhibition probability and metabolic stability. Finally, 10e demonstrated excellent antioxidant and anti-inflammatory effects in BV-2 microglial cells and significantly restored spatial memory deficits in lipopolysaccharide (LPS)-induced neuroinflammatory mouse models.

Optogenetic Targeting of Astrocytes Restores Slow Brain Rhythm Function and Slows Alzheimer's Disease Pathology

Patients with Alzheimer's disease (AD) exhibit non-rapid eye movement (NREM) sleep disturbances in addition to memory deficits. Disruption of NREM slow waves occurs early in the disease progression and is recapitulated in transgenic mouse models of beta-amyloidosis. However, the mechanisms underlying slow-wave disruptions remain unknown. Because astrocytes contribute to slow-wave activity, we used multiphoton microscopy and optogenetics to investigate whether they contribute to slow-wave disruptions in APP mice. The power but not the frequency of astrocytic calcium transients was reduced in APP mice compared to nontransgenic controls. Optogenetic activation of astrocytes at the endogenous frequency of slow waves restored slow-wave power, reduced amyloid deposition, prevented neuronal calcium elevations, and improved memory performance. Our findings revealed malfunction of the astrocytic network driving slow-wave disruptions. Thus, targeting astrocytes to restore circuit activity underlying sleep and memory disruptions in AD could ameliorate disease progression.

Recent Development in the Understanding of Molecular and Cellular Mechanisms Underlying the Etiopathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that leads to dementia and patient death. AD is characterized by intracellular neurofibrillary tangles, extracellular amyloid beta (Aβ) plaque deposition, and neurodegeneration. Diverse alterations have been associated with AD progression, including genetic mutations, neuroinflammation, blood-brain barrier (BBB) impairment, mitochondrial dysfunction, oxidative stress, and metal ion imbalance.Additionally, recent studies have shown an association between altered heme metabolism and AD. Unfortunately, decades of research and drug development have not produced any effective treatments for AD. Therefore, understanding the cellular and molecular mechanisms underlying AD pathology and identifying potential therapeutic targets are crucial for AD drug development. This review discusses the most common alterations associated with AD and promising therapeutic targets for AD drug discovery. Furthermore, it highlights the role of heme in AD development and summarizes mathematical models of AD, including a stochastic mathematical model of AD and mathematical models of the effect of Aβ on AD. We also summarize the potential treatment strategies that these models can offer in clinical trials.