Single App knock-in mouse models of Alzheimer's disease

Strategies to dissect microglia-synaptic interactions during aging and in Alzheimer's disease

Age is the largest risk factor for developing Alzheimer's disease (AD), a neurodegenerative disorder that causes a progressive and severe dementia. The underlying cause of cognitive deficits seen in AD is thought to be the disconnection of neural circuits that control memory and executive functions. Insight into the mechanisms by which AD diverges from normal aging will require identifying precisely which cellular events are driven by aging and which are impacted by AD-related pathologies. Since microglia, the brain-resident macrophages, are known to have critical roles in the formation and maintenance of neural circuits through synaptic pruning, they are well-positioned to modulate synaptic connectivity in circuits sensitive to aging or AD. In this review, we provide an overview of the current state of the field and on emerging technologies being employed to elucidate microglia-synaptic interactions in aging and AD. We also discuss the importance of leveraging genetic diversity to study how these interactions are shaped across more realistic contexts. We propose that these approaches will be essential to define specific aging- and disease-relevant trajectories for more personalized therapeutics aimed at reducing the effects of age or AD pathologies on the brain. This article is part of the Special Issue on "Microglia".

Downregulated expression of lactate dehydrogenase in adult oligodendrocytes and its implication for the transfer of glycolysis products to axons

Oligodendrocytes and astrocytes are metabolically coupled to neuronal compartments. Pyruvate and lactate can shuttle between glial cells and axons via monocarboxylate transporters. However, lactate can only be synthesized or used in metabolic reactions with the help of lactate dehydrogenase (LDH), a tetramer of LDHA and LDHB subunits in varying compositions. Here we show that mice with a cell type-specific disruption of both Ldha and Ldhb genes in oligodendrocytes lack a pathological phenotype that would be indicative of oligodendroglial dysfunctions or lack of axonal metabolic support. Indeed, when combining immunohistochemical, electron microscopical, and in situ hybridization analyses in adult mice, we found that the vast majority of mature oligodendrocytes lack detectable expression of LDH. Even in neurodegenerative disease models and in mice under metabolic stress LDH was not increased. In contrast, at early development and in the remyelinating brain, LDHA was readily detectable in immature oligodendrocytes. Interestingly, by immunoelectron microscopy LDHA was particularly enriched at gap junctions formed between adjacent astrocytes and at junctions between astrocytes and oligodendrocytes. Our data suggest that oligodendrocytes metabolize lactate during development and remyelination. In contrast, for metabolic support of axons mature oligodendrocytes may export their own glycolysis products as pyruvate rather than lactate. Lacking LDH, these oligodendrocytes can also "funnel" lactate through their "myelinic" channels between gap junction-coupled astrocytes and axons without metabolizing it. We suggest a working model, in which the unequal cellular distribution of LDH in white matter tracts facilitates a rapid and efficient transport of glycolysis products among glial and axonal compartments.

Alzheimer's disease and epilepsy: Research hotspots for comorbidity in the era of global aging

Neurological conditions such as Alzheimer's disease (AD) and epilepsy share a significant clinical overlap, particularly in the elderly, with each disorder potentiating the risk of the other. This interplay is significant amidst an aging global demographic. The review explores the classical pathologies of AD, including amyloid-beta plaques and hyperphosphorylated tau, and their potential role in the genesis of epilepsy. It also delves into the imbalance of glutamate and gamma-amino butyric acid activities, a key mechanism in epilepsy that may be influenced by AD pathology. The impact of age of onset on comorbidity is examined, with early-onset AD and Down syndrome presenting higher risks of epilepsy. The review suggests that epilepsy might precede cognitive symptoms in AD, indicating a complex interaction. Sleep modulation is highlighted as a factor, with sleep disturbances potentially contributing to AD progression. The necessity for cautious medication management is emphasized due to the cognitive effects of certain antiepileptic drugs. Animal models are recognized for their importance in understanding the relationship between AD and epilepsy, though creating fully representative models presents a challenge. The review concludes by noting the efficacy of medications such as lamotrigine, levetiracetam, and memantine in managing both conditions and suggests the ketogenic diet and cannabidiol as emerging treatment options, warranting further investigation for comprehensive patient care strategies.

Improving Cognition Without Clearing Amyloid: Effects of Tau and Ultrasound Neuromodulation

Alzheimer's disease is characterized by progressive impairment of neuronal functions culminating in neuronal loss and dementia. A universal feature of dementia is protein aggregation, a process by which a monomer forms intermediate oligomeric assembly states and filaments that develop into end-stage hallmark lesions. In Alzheimer's disease, this is exemplified by extracellular amyloid-β (Aβ) plaques which have been placed upstream of tau, found in intracellular neurofibrillary tangles and dystrophic neurites. This implies causality that can be modeled as a linear activation cascade. When Aβ load is reduced, for example, in response to an anti-Aβ immunotherapy, cognitive functions improve in plaque-forming mice. They also deteriorate less in clinical trial cohorts although real-world clinical benefits remain to be demonstrated. Given the existence of aged humans with unimpaired cognition despite a high plaque load, the central role of Aβ has been challenged. A counter argument has been that clinical symptoms would eventually develop if these aged individuals were to live long enough. Alternatively, intrinsic mechanisms that protect the brain in the presence of pathology may exist. In fact, Aβ toxicity can be abolished by either reducing or manipulating tau (through which Aβ signals), at least in preclinical models. In addition to manipulating steps in this linear pathocascade model, mechanisms of restoring brain reserve can also counteract Aβ toxicity. Low-intensity ultrasound is a neuromodulatory modality that can improve cognitive functions in Aβ-depositing mice without the need for removing Aβ. Together, this highlights a dissociation of Aβ and cognition, with important implications for therapeutic interventions.

Involvement of the choroid plexus in Alzheimer's disease pathophysiology: findings from mouse and human proteomic studies

BACKGROUND

Structural and functional changes of the choroid plexus (ChP) have been reported in Alzheimer's disease (AD). Nonetheless, the role of the ChP in the pathogenesis of AD remains largely unknown. We aim to unravel the relation between ChP functioning and core AD pathogenesis using a unique proteomic approach in mice and humans.

METHODS

We used an APP knock-in mouse model, APPNL-G-F, exhibiting amyloid pathology, to study the association between AD brain pathology and protein changes in mouse ChP tissue and CSF using liquid chromatography mass spectrometry. Mouse proteomes were investigated at the age of 7 weeks (n = 5) and 40 weeks (n = 5). Results were compared with previously published human AD CSF proteomic data (n = 496) to identify key proteins and pathways associated with ChP changes in AD.

RESULTS

ChP tissue proteome was dysregulated in APPNL-G-F mice relative to wild-type mice at both 7 and 40 weeks. At both ages, ChP tissue proteomic changes were associated with epithelial cells, mitochondria, protein modification, extracellular matrix and lipids. Nonetheless, some ChP tissue proteomic changes were different across the disease trajectory; pathways related to lysosomal function, endocytosis, protein formation, actin and complement were uniquely dysregulated at 7 weeks, while pathways associated with nervous system, immune system, protein degradation and vascular system were uniquely dysregulated at 40 weeks. CSF proteomics in both mice and humans showed similar ChP-related dysregulated pathways.

CONCLUSIONS

Together, our findings support the hypothesis of ChP dysfunction in AD. These ChP changes were related to amyloid pathology. Therefore, the ChP could become a novel promising therapeutic target for AD.

The Brain-Gut Axis, an Important Player in Alzheimer and Parkinson Disease: A Narrative Review

Neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD), are severe age-related disorders with complex and multifactorial causes. Recent research suggests a critical link between neurodegeneration and the gut microbiome, via the gut-brain communication pathway. This review examines the role of trimethylamine N-oxide (TMAO), a gut microbiota-derived metabolite, in the development of AD and PD, and investigates its interaction with microRNAs (miRNAs) along this bidirectional pathway. TMAO, which is produced from dietary metabolites like choline and carnitine, has been linked to increased neuroinflammation, protein misfolding, and cognitive decline. In AD, elevated TMAO levels are associated with amyloid-beta and tau pathologies, blood-brain barrier disruption, and neuronal death. TMAO can cross the blood-brain barrier and promote the aggregation of amyloid and tau proteins. Similarly, TMAO affects alpha-synuclein conformation and aggregation, a hallmark of PD. TMAO also activates pro-inflammatory pathways such as NF-kB signaling, exacerbating neuroinflammation further. Moreover, TMAO modulates the expression of various miRNAs that are involved in neurodegenerative processes. Thus, the gut microbiome-miRNA-brain axis represents a newly discovered mechanistic link between gut dysbiosis and neurodegeneration. MiRNAs regulate the key pathways involved in neuroinflammation, oxidative stress, and neuronal death, contributing to disease progression. As a direct consequence, specific miRNA signatures may serve as potential biomarkers for the early detection and monitoring of AD and PD progression. This review aims to elucidate the complex interrelationships between the gut microbiota, trimethylamine-N-oxide (TMAO), microRNAs (miRNAs), and the central nervous system, and the implications of these connections in neurodegenerative diseases. In this context, an overview of the current neuroradiology techniques available for studying neuroinflammation and of the animal models used to investigate these intricate pathologies will also be provided. In summary, a bulk of evidence supports the concept that modulating the gut-brain communication pathway through dietary changes, the manipulation of the microbiome, and/or miRNA-based therapies may offer novel approaches for implementing the treatment of debilitating neurological disorders.

Hypothalamic and hippocampal transcriptome changes in AppNL-G-F mice as a function of metabolic and inflammatory dysfunction

The progression of Alzheimer's disease (AD) has a silent phase that predates characteristic cognitive decline and eventually leads to active cognitive deficits. Metabolism, diet, and obesity have been correlated to the development of AD but is poorly understood. The hypothalamus is a brain region that exerts homeostatic control on food intake and metabolism and has been noted to be impacted during the active phase of Alzheimer's disease. This study, in using an amyloid overexpression AppNL-G-F mouse model under normal metabolic conditions, examines blood markers in young and old male AppNL-G-F mice (n = 5) that corresponds to the silent and active phases of AD, and bulk gene expression changes in the hypothalamus and the hippocampus. The results show a large panel of inflammatory mediators, leptin, and other proteins that may be involved in weakening the blood brain barrier, to be increased in the young AppNL-G-F mice but not in the old AppNL-G-F mice. There were also several differentially expressed genes in both the hypothalamus and the hippocampus in the young AppNL-G-F mice prior to amyloid plaque formation and cognitive decline that persisted in the old AppNL-G-F mice, including GABRa2 receptor, Wdfy1, and several pseudogenes with unknown function. These results suggests that a larger panel of inflammatory mediators may be used as blood markers to detect silent AD, and that a change in leptin and gene expression in the hypothalamus exist prior to cognitive effects, suggesting a coupling of metabolism with amyloid plaque induced cognitive decline.

Apolipoprotein E polymorphisms and female fertility in a transgenic mouse model of Alzheimer's disease

Apolipoprotein E (APOE) is a major cholesterol carrier responsible for lipid transport and injury repair in the brain. The human APOE gene (h-APOE) has 3 naturally occurring alleles: ε3, the common allele; ε4, which increases Alzheimer's disease (AD) risk up to 15-fold; and ε2, the rare allele which protects against AD. Although APOE4 has negative effects on neurocognition in old age, its persistence in the population suggests a survival advantage. We investigated the relationship between APOE genotypes and fertility in EFAD mice, a transgenic mouse model expressing h-APOE. We show that APOE4 transgenic mice had the highest level of reproductive performance, followed by APOE3 and APOE2. Intriguingly, APOE3 pregnancies had more fetal resorptions and reduced fetal weights relative to APOE4 pregnancies. In conclusion, APOE genotypes impact fertility and pregnancy outcomes in female mice, in concordance with findings in human populations. These mouse models may help elucidate how h-APOE4 promotes reproductive fitness at the cost of AD in later life.

Retinal Vascular and Structural Changes in the Murine Alzheimer's APPNL-F/NL-F Model from 6 to 20 Months

Alzheimer's disease (AD) may manifest retinal changes preceding brain pathology. A transversal case-control study utilized spectral-domain OCT angiography (SD-OCTA) and Angio-Tool software 0.6a to assess retinal vascular structures and OCT for inner and outer retina thickness in the APPNL-F/NL-F AD model at 6, 9, 12, 15, 17, and 20 months old. Comparisons to age-matched wild type (WT) were performed. The analysis focused on the three vascular plexuses using AngiooTool and on retinal thickness, which was represented with the Early Treatment Diabetic Retinopathy Study (ETDRS) sectors. Compared to WT, the APPNL-F/NL-F group exhibited both vascular and structural changes as early as 6 months persisting and evolving at 15, 17, and 20 months. Significant vascular alterations, principally in the superficial vascular complex (SVC), were observed. There was a significant decrease in the vessel area and the total vessel length in SVC, intermediate, and deep capillary plexus. The inner retina in the APPNL-F/NL-F group predominantly decreased in thickness while the outer retina showed increased thickness in most analyzed time points compared to the control group. There are early vascular and structural retinal changes that precede the cognitive changes, which appear at later stages. Therefore, the natural history of the APPNL-F/NL-F model may be more similar to human AD than other transgenic models.

Microglia Gravitate toward Amyloid Plaques Surrounded by Externalized Phosphatidylserine via TREM2

Microglia play a crucial role in synaptic elimination by engulfing dystrophic neurons via triggering receptors expressed on myeloid cells 2 (TREM2). They are also involved in the clearance of beta-amyloid (Aβ) plaques in Alzheimer's disease (AD); nonetheless, the driving force behind TREM2-mediated phagocytosis of beta-amyloid (Aβ) plaques remains unknown. Here, using advanced 2D/3D/4D co-culture systems with loss-of-function mutations in TREM2 (a frameshift mutation engineered in exon 2) brain organoids/microglia/assembloids, it is identified that the clearance of Aβ via TREM2 is accelerated by externalized phosphatidylserine (ePtdSer) generated from dystrophic neurons surrounding the Aβ plaques. Moreover, it is investigated whether microglia from both sporadic (CRISPR-Cas9-based APOE4 lines) and familial (APPNL-G-F/MAPT double knock-in mice) AD models show reduced levels of TREM2 and lack of phagocytic activity toward ePtdSer-positive Aβ plaques. Herein new insight is provided into TREM2-dependent microglial phagocytosis of Aβ plaques in the context of the presence of ePtdSer during AD progression.

Exploring advancements in early detection of Alzheimer's disease with molecular assays and animal models

Alzheimer's Disease (AD) is a challenging neurodegenerative condition, with overwhelming implications for affected individuals and healthcare systems worldwide. Animal models have played a crucial role in studying AD pathogenesis and testing therapeutic interventions. Remarkably, studies on the genetic factors affecting AD risk, such as APOE and TREM2, have provided valuable insights into disease mechanisms. Early diagnosis has emerged as a crucial factor in effective AD management, as demonstrated by clinical studies emphasizing the benefits of initiating treatment at early stages. Novel diagnostic technologies, including RNA sequencing of microglia, offer promising avenues for early detection and monitoring of AD progression. Therapeutic strategies remain to evolve, with a focus on targeting amyloid beta (Aβ) and tau pathology. Advances in animal models, such as APP-KI mice, and the advancement of anti-Aβ drugs signify progress towards more effective treatments. Therapeutically, the focus has shifted towards intricate approaches targeting multiple pathological pathways simultaneously. Strategies aimed at reducing Aβ plaque accumulation, inhibiting tau hyperphosphorylation, and modulating neuroinflammation are actively being explored, both in preclinical models and clinical trials. While challenges continue in developing validated animal models and translating preclinical findings to clinical success, the continuing efforts in understanding AD at molecular, cellular, and clinical levels offer hope for improved management and eventual prevention of this devastating disease.

The Inflammation-Induced Dysregulation of Reelin Homeostasis Hypothesis of Alzheimer's Disease

Alzheimer's disease (AD) accounts for most dementia cases, but we lack a complete understanding of the mechanisms responsible for the core pathology associated with the disease (e.g., amyloid plaque and neurofibrillary tangles). Inflammation has been identified as a key contributor of AD pathology, with recent evidence pointing towards Reelin dysregulation as being associated with inflammation. Here we describe Reelin signaling and outline existing research involving Reelin signaling in AD and inflammation. Research is described pertaining to the inflammatory and immunological functions of Reelin before we propose a mechanism through which inflammation renders Reelin susceptible to dysregulation resulting in the induction and exacerbation of AD pathology. Based on this hypothesis, it is predicted that disorders of both inflammation (including peripheral inflammation and neuroinflammation) and Reelin dysregulation (including disorders associated with upregulated Reelin expression and disorders of Reelin downregulation) have elevated risk of developing AD. We conclude with a description of AD risk in various disorders involving Reelin dysregulation and inflammation.

Entorhinal cortex vulnerability to human APP expression promotes hyperexcitability and tau pathology

Preventative treatment for Alzheimer's Disease is of dire importance, and yet, cellular mechanisms underlying early regional vulnerability in Alzheimer's Disease remain unknown. In human patients with Alzheimer's Disease, one of the earliest observed pathophysiological correlates to cognitive decline is hyperexcitability. In mouse models, early hyperexcitability has been shown in the entorhinal cortex, the first cortical region impacted by Alzheimer's Disease. The origin of hyperexcitability in early-stage disease and why it preferentially emerges in specific regions is unclear. Using cortical-region and cell-type-specific proteomics coupled with ex vivo and in vivo electrophysiology, we uncovered differential susceptibility to human-specific amyloid precursor protein (hAPP) in a model of sporadic Alzheimer's. Unexpectedly, our findings reveal that early entorhinal hyperexcitability may result from intrinsic vulnerability of parvalbumin (PV) interneurons, rather than the suspected layer II excitatory neurons. This vulnerability of entorhinal PV interneurons is specific to hAPP, as it could not be recapitulated with increased murine APP expression. However, partial replication of the findings could be seen after introduction of a murine APP chimera containing a humanized amyloid-beta sequence. Surprisingly, neurons in the Somatosensory Cortex showed no such vulnerability to adult-onset hAPP expression. hAPP-induced hyperexcitability in entorhinal cortex could be ameliorated by enhancing PV interneuron excitability in vivo. Co-expression of human Tau with hAPP decreased circuit hyperexcitability, but at the expense of increased pathological tau species. This study suggests early disease interventions targeting non-excitatory cell types may protect regions with early vulnerability to pathological symptoms of Alzheimer's Disease and downstream cognitive decline.

Early Astrocytic Dysfunction Is Associated with Mistuned Synapses as well as Anxiety and Depressive-Like Behavior in the AppNL-F Mouse Model of Alzheimer's Disease

Background

Alzheimer's disease (AD) is the most common neurodegenerative disease. Unfortunately, efficient and affordable treatments are still lacking for this neurodegenerative disorder, it is therefore urgent to identify new pharmacological targets. Astrocytes are playing a crucial role in the tuning of synaptic transmission and several studies have pointed out severe astrocyte reactivity in AD. Reactive astrocytes show altered physiology and function, suggesting they could have a role in the early pathophysiology of AD.

Objective

We aimed to characterize early synaptic impairments in the AppNL-F knock-in mouse model of AD, especially to understand the contribution of astrocytes to early brain dysfunctions.

Methods

The AppNL-F mouse model carries two disease-causing mutations inserted in the amyloid precursor protein gene. This strain does not start to develop amyloid-β plaques until 9 months of age. Thanks to electrophysiology, we investigated synaptic function, at both neuronal and astrocytic levels, in 6-month-old animals and correlate the synaptic activity with emotional behavior.

Results

Electrophysiological recordings in the hippocampus revealed an overall synaptic mistuning at a pre-plaque stage of the pathology, associated to an intact social memory but a stronger depressive-like behavior. Astrocytes displayed a reactive-like morphology and a higher tonic GABA current compared to control mice. Interestingly, we here show that the synaptic impairments in hippocampal slices are partially corrected by a pre-treatment with the monoamine oxidase B blocker deprenyl or the fast-acting antidepressant ketamine (5 mg/kg).

Conclusions

We propose that reactive astrocytes can induce synaptic mistuning early in AD, before plaques deposition, and that these changes are associated with emotional symptoms.

Senolytic Intervention Improves Cognition, Metabolism, and Adiposity in Female APP NL-F/NL-F Mice

Senescent cells accumulate throughout the body and brain contributing to unhealthy aging and Alzheimer's disease (AD). The APP NL-F/NL-F amyloidogenic AD mouse model exhibits increased markers of senescent cells and the senescence-associated secretory phenotype (SASP) in visceral white adipose tissue before plaque accumulation and cognitive decline. We hypothesized that senolytic intervention would alleviate cellular senescence thereby improving spatial memory in APP NL-F/NL-F mice. Thus, four month old male and female APP NL-F/NL-F mice were treated monthly with vehicle, 5 mg/kg Dasatinib + 50 mg/kg Quercetin, or 100 mg/kg Fisetin. Blood glucose levels, energy metabolism, spatial memory, amyloid burden, and senescent cell markers were assayed. Dasatinib + Quercetin treatment in female APP NL-F/NL-F mice increased oxygen consumption and energy expenditure resulting in decreased body mass. White adipose tissue mass was decreased along with senescence markers, SASP, blood glucose, and plasma insulin and triglycerides. Hippocampal senescence markers and SASP were reduced along with soluble and insoluble amyloid-β (Aβ) 42 and senescence associated-β-gal activity leading to improved spatial memory. Fisetin had negligible effects on these measures in female APP NL-F/NL-F mice while neither senolytic intervention altered these parameters in the male mice. Considering women have a greater risk of dementia, identifying senotherapeutics appropriate for sex and disease stage is necessary for personalized medicine.

Dynamic microglia alterations associate with hippocampal network impairments: A turning point in amyloid pathology progression

Alzheimer's disease is a progressive neurological disorder causing memory loss and cognitive decline. The underlying causes of cognitive deterioration and neurodegeneration remain unclear, leading to a lack of effective strategies to prevent dementia. Recent evidence highlights the role of neuroinflammation, particularly involving microglia, in Alzheimer's disease onset and progression. Characterizing the initial phase of Alzheimer's disease can lead to the discovery of new biomarkers and therapeutic targets, facilitating timely interventions for effective treatments. We used the AppNL-G-F knock-in mouse model, which resembles the amyloid pathology and neuroinflammatory characteristics of Alzheimer's disease, to investigate the transition from a pre-plaque to an early plaque stage with a combined functional and molecular approach. Our experiments show a progressive decrease in the power of cognition-relevant hippocampal gamma oscillations during the early stage of amyloid pathology, together with a modification of fast-spiking interneuron intrinsic properties and postsynaptic input. Consistently, transcriptomic analyses revealed that these effects are accompanied by changes in synaptic function-associated pathways. Concurrently, homeostasis- and inflammatory-related microglia signature genes were downregulated. Moreover, we found a decrease in Iba1-positive microglia in the hippocampus that correlates with plaque aggregation and neuronal dysfunction. Collectively, these findings support the hypothesis that microglia play a protective role during the early stages of amyloid pathology by preventing plaque aggregation, supporting neuronal homeostasis, and overall preserving the oscillatory network's functionality. These results suggest that the early alteration of microglia dynamics could be a pivotal event in the progression of Alzheimer's disease, potentially triggering plaque deposition, impairment of fast-spiking interneurons, and the breakdown of the oscillatory circuitry in the hippocampus.

Lipid imaging of Alzheimer's disease pathology

Alzheimer's disease (AD) affects one in eight individuals over 65 and poses an immense societal challenge. AD pathology is characterized by the formation of beta-amyloid plaques and Tau tangles in the brain. While some disease-modifying treatments targeting beta-amyloid are emerging, the exact chain of events underlying the pathogenesis of this disease remains unclear. Brain lipids have long been implicated in AD pathology, though their role in AD pathogenesis remains not fully resolved. Significant advancements in mass spectrometry imaging (MSI) allow to detail spatial lipid regulations in biological tissues at the low um scale. In this issue, Huang et al. resolve spatial lipid patterns in human AD brain and genetic mouse models using desorption electrospray ionization (DESI)-based MSI integrated with other spatial techniques such as imaging mass cytometry of correlative protein signatures. Those spatial multiomics experiments identify plaque-associated lipid regulations that are dependent on progressing plaque pathology in both mouse models and the human brain. Of those lipid species, particularly pro-inflammatory lysophospholipids have been implicated in AD pathology through their interaction with both aggregating Aβ and microglial activation through lipid sensing surface receptors. Together, this study provides further insight into how brain lipid homeostasis is linked to progressing AD pathology, and thereby highlights the potential of MSI-based spatial lipidomics as an emerging spatial biology technology for biomedical research.

Preventive effect of propolis on cognitive decline in Alzheimer's disease model mice

Brazilian green propolis (propolis) is a chemically complex resinous substance that is a potentially viable therapeutic agent for Alzheimer's disease. Herein, propolis induced a transient increase in intracellular Ca2+ concentration ([Ca2+]i) in Neuro-2A cells; moreover, propolis-induced [Ca2+]i elevations were suppressed prior to 24-h pretreatment with amyloid-β. To reveal the effect of [Ca2+]i elevation on impaired cognition, we performed memory-related behavioral tasks in APP-KI mice relative to WT mice at 4 and 12 months of age. Propolis, at 300-1000 mg/kg/d for 8 wk, significantly ameliorated cognitive deficits in APP-KI mice at 4 months, but not at 12 months of age. Consistent with behavioral observations, injured hippocampal long-term potentiation was markedly ameliorated in APP-KI mice at 4 months of age following repeated propolis administration. In addition, repeated administration of propolis significantly activated intracellular calcium signaling pathway in the CA1 region of APP-KI mice. These results suggest a preventive effect of propolis on cognitive decline through the activation of intracellular calcium signaling pathways in CA1 region of AD mice model.

Leuco Ethyl Violet as Self-Activating Prodrug Photocatalyst for In Vivo Amyloid-Selective Oxygenation

Aberrant aggregates of amyloid-β (Aβ) and tau protein (tau), called amyloid, are related to the etiology of Alzheimer disease (AD). Reducing amyloid levels in AD patients is a potentially effective approach to the treatment of AD. The selective degradation of amyloids via small molecule-catalyzed photooxygenation in vivo is a leading approach; however, moderate catalyst activity and the side effects of scalp injury are problematic in prior studies using AD model mice. Here, leuco ethyl violet (LEV) is identified as a highly active, amyloid-selective, and blood-brain barrier (BBB)-permeable photooxygenation catalyst that circumvents all of these problems. LEV is a redox-sensitive, self-activating prodrug catalyst; self-oxidation of LEV through a hydrogen atom transfer process under photoirradiation produces catalytically active ethyl violet (EV) in the presence of amyloid. LEV effectively oxygenates human Aβ and tau, suggesting the feasibility for applications in humans. Furthermore, a concept of using a hydrogen atom as a caging group of a reactive catalyst functional in vivo is postulated. The minimal size of the hydrogen caging group is especially useful for catalyst delivery to the brain through BBB.

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

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

Selective suppression of oligodendrocyte-derived amyloid beta rescues neuronal dysfunction in Alzheimer's disease

Reduction of amyloid beta (Aβ) has been shown to be effective in treating Alzheimer's disease (AD), but the underlying assumption that neurons are the main source of pathogenic Aβ is untested. Here, we challenge this prevailing belief by demonstrating that oligodendrocytes are an important source of Aβ in the human brain and play a key role in promoting abnormal neuronal hyperactivity in an AD knock-in mouse model. We show that selectively suppressing oligodendrocyte Aβ production improves AD brain pathology and restores neuronal function in the mouse model in vivo. Our findings suggest that targeting oligodendrocyte Aβ production could be a promising therapeutic strategy for treating AD.

Advances in Alzheimer's disease: A multifaceted review of potential therapies and diagnostic techniques for early detection

Alzheimer's disease (AD) remains one of the most formidable neurological disorders, affecting millions globally. This review provides a holistic overview of the therapeutic strategies, both conventional and novel, aimed at mitigating the impact of AD. Initially, we delve into the conventional approach, emphasizing the role of Acetylcholinesterase (AChE) inhibition, which has been a cornerstone in AD management. As our understanding of AD evolves, several novel potential approaches emerge. We discuss the promising roles of Butyrylcholinesterase (BChE) inhibition, Tau Protein inhibitors, COX-2 inhibition, PPAR-γ agonism, and FAHH inhibition, among others. The potential of the endocannabinoids (eCB) system, cholesterol-lowering drugs, metal chelators, and MMPs inhibitors are also explored, culminating in the exploration of the pivotal role of microRNA in AD progression. Parallel to these therapeutic insights, we shed light on the novel tools and methodologies revolutionizing AD research. From the quantitative analysis of gene expression by qRTPCR to the evaluation of mitochondrial function using induced pluripotent stem cells (iPSCs), the advances in diagnostic and research tools offer renewed hope. Moreover, we explore the current landscape of clinical trials, highlighting the leading drug interventions and their respective stages of development. This comprehensive review concludes with a look into the future perspectives, capturing the potential breakthroughs and innovations on the horizon. Through a synthesis of current knowledge and emerging research, this article aims to provide a consolidated resource for clinicians, researchers, and academicians in the realm of Alzheimer's disease.

Neuronal glutathione depletion elevates the Aβ42/Aβ40 ratio and tau aggregation in Alzheimer's disease mice

Alzheimer's disease (AD) involves reduced glutathione levels, causing oxidative stress and contributing to neuronal cell death. Our prior research identified diminished glutamate-cysteine ligase catalytic subunit (GCLC) as linked to cell death. However, the effect of GCLC on AD features such as amyloid and tau pathology remained unclear. To address this, we investigated amyloid pathology and tau pathology in mice by combining neuron-specific conditional GCLC knockout mice with amyloid precursor protein (App) knockin (KI) or microtubule-associated protein tau (MAPT) KI mice. Intriguingly, GCLC knockout resulted in an increased Aβ42/40 ratio. Additionally, GCLC deficiency in MAPT KI mice accelerated the oligomerization of tau through intermolecular disulfide bonds. These findings suggest that the decline in glutathione levels, due to aging or AD pathology, may contribute to the progression of AD.

Neural circuits expressing the serotonin 2C receptor regulate memory in mice and humans

Declined memory is a hallmark of Alzheimer's disease (AD). Experiments in rodents and human postmortem studies suggest that serotonin (5-hydroxytryptamine, 5-HT) plays a role in memory, but the underlying mechanisms are unknown. Here, we investigate the role of 5-HT 2C receptor (5-HT2CR) in regulating memory. Transgenic mice expressing a humanized HTR2C mutation exhibit impaired plasticity of hippocampal ventral CA1 (vCA1) neurons and reduced memory. Further, 5-HT neurons project to and synapse onto vCA1 neurons. Disruption of 5-HT synthesis in vCA1-projecting neurons or deletion of 5-HT2CRs in the vCA1 impairs neural plasticity and memory. We show that a selective 5-HT2CR agonist, lorcaserin, improves synaptic plasticity and memory in an AD mouse model. Cumulatively, we demonstrate that hippocampal 5-HT2CR signaling regulates memory, which may inform the use of 5-HT2CR agonists in the treatment of dementia.

The link between gut microbiome and Alzheimer's disease: From the perspective of new revised criteria for diagnosis and staging of Alzheimer's disease

Over the past decades, accumulating evidence suggests that the gut microbiome exerts a key role in Alzheimer's disease (AD). The Alzheimer's Association Workgroup is updating the diagnostic criteria for AD, which changed the profiles and categorization of biomarkers from "AT(N)" to "ATNIVS." Previously, most of studies focus on the correlation between the gut microbiome and amyloid beta deposition ("A"), the initial AD pathological feature triggering the "downstream" tauopathy and neurodegeneration. However, limited research investigated the interactions between the gut microbiome and other AD pathogenesis ("TNIVS"). In this review, we summarize current findings of the gut microbial characteristics in the whole spectrum of AD. Then, we describe the association of the gut microbiome with updated biomarker categories of AD pathogenesis. In addition, we outline the gut microbiome-related therapeutic strategies for AD. Finally, we discuss current key issues of the gut microbiome research in the AD field and future research directions. HIGHLIGHTS: The new revised criteria for Alzheimer's disease (AD) proposed by the Alzheimer's Association Workgroup have updated the profiles and categorization of biomarkers from "AT(N)" to "ATNIVS." The associations of the gut microbiome with updated biomarker categories of AD pathogenesis are described. Current findings of the gut microbial characteristics in the whole spectrum of AD are summarized. Therapeutic strategies for AD based on the gut microbiome are proposed.

T cell-mediated microglial activation triggers myelin pathology in a mouse model of amyloidosis

Age-related myelin damage induces inflammatory responses, yet its involvement in Alzheimer's disease remains uncertain, despite age being a major risk factor. Using a mouse model of Alzheimer's disease, we found that amyloidosis itself triggers age-related oligodendrocyte and myelin damage. Mechanistically, CD8+ T cells promote the progressive accumulation of abnormally interferon-activated microglia that display myelin-damaging activity. Thus, our data suggest that immune responses against myelinating oligodendrocytes may contribute to neurodegenerative diseases with amyloidosis.

Xenografted human iPSC-derived neurons with the familial Alzheimer's disease APPV717I mutation reveal dysregulated transcriptome signatures linked to synaptic function and implicate LINGO2 as a disease signaling mediator

Alzheimer's disease (AD) is the most common cause of dementia, and disease mechanisms are still not fully understood. Here, we explored pathological changes in human induced pluripotent stem cell (iPSC)-derived neurons carrying the familial AD APPV717I mutation after cell injection into the mouse forebrain. APPV717I mutant iPSCs and isogenic controls were differentiated into neurons revealing enhanced Aβ42 production, elevated phospho-tau, and impaired neurite outgrowth in APPV717I neurons. Two months after transplantation, APPV717I and control neural cells showed robust engraftment but at 12 months post-injection, APPV717I grafts were smaller and demonstrated impaired neurite outgrowth compared to controls, while plaque and tangle pathology were not seen. Single-nucleus RNA-sequencing of micro-dissected grafts, performed 2 months after cell injection, identified significantly altered transcriptome signatures in APPV717I iPSC-derived neurons pointing towards dysregulated synaptic function and axon guidance. Interestingly, APPV717I neurons showed an increased expression of genes, many of which are also upregulated in postmortem neurons of AD patients including the transmembrane protein LINGO2. Downregulation of LINGO2 in cultured APPV717I neurons rescued neurite outgrowth deficits and reversed key AD-associated transcriptional changes related but not limited to synaptic function, apoptosis and cellular senescence. These results provide important insights into transcriptional dysregulation in xenografted APPV717I neurons linked to synaptic function, and they indicate that LINGO2 may represent a potential therapeutic target in AD.

Associations of amyloid-β oligomers and plaques with neuropathology in the App NL-G-F mouse

Amyloid-β pathology and neurofibrillary tangles lead to glial activation and neurodegeneration in Alzheimer's disease. In this study, we investigated the relationships between the levels of amyloid-β oligomers, amyloid-β plaques, glial activation and markers related to neurodegeneration in the App NL-G-F triple mutation mouse line and in a knock-in line homozygous for the common human amyloid precursor protein (App hu mouse). The relationships between neuropathological features were characterized with immunohistochemistry and imaging mass cytometry. Markers assessing human amyloid-β proteins, microglial and astrocytic activation and neuronal and synaptic densities were used in mice between 2.5 and 12 months of age. We found that amyloid-β oligomers were abundant in the brains of App hu mice in the absence of classical amyloid-β plaques. These brains showed morphological changes consistent with astrocyte activation but no evidence of microglial activation or synaptic or neuronal pathology. In contrast, both high levels of amyloid-β oligomers and numerous plaques accumulated in App NL-G-F mice in association with substantial astrocytic and microglial activation. The increase in amyloid-β oligomers over time was more strongly correlated with astrocytic than with microglia activation. Spatial analyses suggested that activated microglia were more closely associated with amyloid-β oligomers than with amyloid-β plaques in App NL-G-F mice, which also showed age-dependent decreases in neuronal and synaptic density markers. A comparative study of the two models highlighted the dependence of glial and neuronal pathology on the nature and aggregation state of the amyloid-β peptide. Astrocyte activation and neuronal pathology appeared to be more strongly associated with amyloid-β oligomers than with amyloid-β plaques, although amyloid-β plaques were associated with microglia activation.

Microglia-astrocyte crosstalk in the amyloid plaque niche of an Alzheimer's disease mouse model, as revealed by spatial transcriptomics

The amyloid plaque niche is a pivotal hallmark of Alzheimer's disease (AD). Here, we employ two high-resolution spatial transcriptomics (ST) platforms, CosMx and Spatial Enhanced Resolution Omics-sequencing (Stereo-seq), to characterize the transcriptomic alterations, cellular compositions, and signaling perturbations in the amyloid plaque niche in an AD mouse model. We discover heterogeneity in the cellular composition of plaque niches, marked by an increase in microglial accumulation. We profile the transcriptomic alterations of glial cells in the vicinity of plaques and conclude that the microglial response to plaques is consistent across different brain regions, while the astrocytic response is more heterogeneous. Meanwhile, as the microglial density of plaque niches increases, astrocytes acquire a more neurotoxic phenotype and play a key role in inducing GABAergic signaling and decreasing glutamatergic signaling in hippocampal neurons. We thus show that the accumulation of microglia around hippocampal plaques disrupts astrocytic signaling, in turn inducing an imbalance in neuronal synaptic signaling.

Androgen deprivation therapy exacerbates Alzheimer's-associated cognitive decline via increased brain immune cell infiltration

Androgen deprivation therapy (ADT) for prostate cancer is associated with an increased risk of dementia, including Alzheimer's disease (AD). The mechanistic connection between ADT and AD-related cognitive impairment in patients with prostate cancer remains elusive. We established a clinically relevant prostate cancer-bearing AD mouse model to explore this. Both tumor-bearing and ADT induce complex changes in immune and inflammatory responses in peripheral blood and in the brain. ADT disrupts the integrity of the blood-brain barrier (BBB) and promotes immune cell infiltration into the brain, enhancing neuroinflammation and gliosis without affecting the amyloid plaque load. Moreover, treatment with natalizumab, an FDA-approved drug targeting peripheral immune cell infiltration, reduces neuroinflammation and improves cognitive function in this model. Our study uncovers an inflammatory mechanism, extending beyond amyloid pathology, that underlies ADT-exacerbated cognitive deficits, and suggests natalizumab as a potentially effective treatment in alleviating the detrimental effects of ADT on cognition.

Decreased extrasynaptic δ-GABAA receptors in PNN-associated parvalbumin interneurons correlates with anxiety in APP and tau mouse models of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is associated with gradual memory loss and anxiety which affects ~75% of AD patients. This study investigated whether AD-associated anxiety correlated with modulation of extrasynaptic δ-subunit-containing GABAA receptors (δ-GABAARs) in experimental mouse models of AD.

EXPERIMENTAL APPROACH

We combined behavioural experimental paradigms to measure cognition performance, and anxiety with neuroanatomy and molecular biology, using familial knock-in (KI) mouse models of AD that harbour β-amyloid (Aβ) precursor protein App (AppNL-F) with or without humanized microtubule-associated protein tau (MAPT), age-matched to wild-type control mice at three different age windows.

RESULTS

AppNL-F KI and AppNL-F/MAPT AD models showed a similar magnitude of cognitive decline and elevated magnitude of anxiety correlated with neuroinflammatory hallmarks, including triggering receptor expressed on myeloid cells 2 (TREM2), reactive astrocytes and activated microglia consistent with accumulation of Aβ, tau and down-regulation of Wnt/β-catenin signalling compared to aged-matched WT controls. In both the CA1 region of the hippocampus and dentate gyrus, there was an age-dependent decline in the expression of δ-GABAARs selectively expressed in parvalbumin (PV)-expressing interneurons, encapsulated by perineuronal nets (PNNs) in the AD mouse models compared to WT mice. In vivo positive allosteric modulation of the δ-GABAARs, using a δ-selective-compound DS2, decreased the level of anxiety in the AD mouse models, which was correlated with reduced hallmarks of neuroinflammation, and 'normalisation' of the expression of δ-GABAARs.

CONCLUSIONS

Our data show that the δ-GABAARs could potentially be targeted for alleviating symptoms of anxiety, which would greatly improve the quality of life of AD individuals.

Sexual Dimorphism, Altered Hippocampal Glutamatergic Neurotransmission and Cognitive Impairment in APP Knock-In Mice

Background

It is well established that glutamatergic neurotransmission plays an essential role in learning and memory. Previous studies indicate that glutamate dynamics shift with Alzheimer's disease (AD) progression, contributing to negative cognitive outcomes.

Objective

In this study, we characterized hippocampal glutamatergic signaling with age and disease progression in a knock-in mouse model of AD (APPNL-F/NL-F).

Methods

At 2-4 and 18+ months old, male and female APPNL/NL, APPNL-F/NL-F, and C57BL/6 mice underwent cognitive assessment using Morris water maze (MWM) and Novel Object Recognition (NOR). Then, basal and 70 mM KCl stimulus-evoked glutamate release was measured in the dentate gyrus (DG), CA3, and CA1 regions of the hippocampus using a glutamate-selective microelectrode in anesthetized mice.

Results

Glutamate recordings support elevated stimulus-evoked glutamate release in the DG and CA3 of young APPNL-F/NL-F male mice that declined with age compared to age-matched control mice. Young female APPNL-F/NL-F mice exhibited increased glutamate clearance in the CA1 that slowed with age compared to age-matched control mice. Male and female APPNL-F/NL-F mice exhibited decreased CA1 basal glutamate levels, while males also showed depletion in the CA3. Cognitive assessment demonstrated impaired spatial cognition in aged male and female APPNL-F/NL-F mice, but only aged females displayed recognition memory deficits compared to age-matched control mice. Conclusions: These findings confirm a sex-dependent hyper-to-hypoactivation glutamatergic paradigm in APPNL-F/NL-F mice. Further, data illustrate a sexually dimorphic biological aging process resulting in a more severe cognitive phenotype for female APPNL-F/NL-F mice than their male counterparts. Research outcomes mirror that of human AD pathology and provide further evidence of divergent AD pathogenesis between sexes.

Long term rescue of Alzheimer's deficits in vivo by one-time gene-editing of App C-terminus

Gene-editing technologies promise to create a new class of therapeutics that can achieve permanent correction with a single intervention. Besides eliminating mutant alleles in familial disease, gene-editing can also be used to favorably manipulate upstream pathophysiologic events and alter disease-course in wider patient populations, but few such feasible therapeutic avenues have been reported. Here we use CRISPR-Cas9 to edit the last exon of amyloid precursor protein (App), relevant for Alzheimer's disease (AD). Our strategy effectively eliminates an endocytic (YENPTY) motif at APP C-terminus, while preserving the N-terminus and compensatory APP-homologues. This manipulation favorably alters events along the amyloid-pathway - inhibiting toxic APP-β-cleavage fragments (including Aβ) and upregulating neuroprotective APP-α-cleavage products. AAV-driven editing ameliorates neuropathologic, electrophysiologic, and behavioral deficits in an AD knockin mouse model. Effects persist for many months, and no abnormalities are seen in WT mice even after germline App-editing; underlining overall efficacy and safety. Pathologic alterations in the glial-transcriptome of App-KI mice, as seen by single nuclei RNA-sequencing (sNuc-Seq), are also normalized by App C-terminus editing. Our strategy takes advantage of innate transcriptional rules that render terminal exons insensitive to nonsense-decay, and the upstream manipulation is expected to be effective for all forms of AD. These studies offer a path for a one-time disease-modifying treatment for AD.

The landscape of programmed cell death-related lncRNAs in Alzheimer's disease and Parkinson's disease

This study delivers a thorough analysis of long non-coding RNAs (lncRNAs) in regulating programmed cell death (PCD), vital for neurodegenerative diseases like Alzheimer's disease (AD) and Parkinson's disease (PD). We propose a new framework PCDLnc, and identified 20 significant lncRNAs, including HEIH, SNHG15, and SNHG5, associated with PCD gene sets, which were known for roles in proliferation and apoptosis in neurodegenerative diseases. By using GREAT software, we identified regulatory functions of top lncRNAs in different neurodegenerative diseases. Moreover, lncRNAs cis-regulated mRNAs linked to neurodegeneration, including JAK2, AKT1, EGFR, CDC42, SNCA, and ADIPOQ, highlighting their therapeutic potential in neurodegenerative diseases. A further exploration into the differential expression of mRNA identified by PCDLnc revealed a role in apoptosis, ferroptosis and autophagy. Additionally, protein-protein interaction (PPI) network analysis exposed abnormal interactions among key genes, despite their consistent expression levels between disease and normal samples. The randomforest model effectively distinguished between disease samples, indicating a high level of accuracy. Shared gene subsets in AD and PD might serve as potential biomarkers, along with disease-specific gene sets. Besides, we also found the strong relationship between AD and immune infiltration. This research highlights the role of lncRNAs and their associated genes in PCD in neurodegenerative diseases, offering potential therapeutic targets and diagnostic markers for future study and clinical application.

Rodent Models of Alzheimer's Disease: Past Misconceptions and Future Prospects

Alzheimer's disease (AD) is a progressive neurodegenerative disease with no effective treatments, not least due to the lack of authentic animal models. Typically, rodent models recapitulate the effects but not causes of AD, such as cholinergic neuron loss: lesioning of cholinergic neurons mimics the cognitive decline reminiscent of AD but not its neuropathology. Alternative models rely on the overexpression of genes associated with familial AD, such as amyloid precursor protein, or have genetically amplified expression of mutant tau. Yet transgenic rodent models poorly replicate the neuropathogenesis and protein overexpression patterns of sporadic AD. Seeding rodents with amyloid or tau facilitates the formation of these pathologies but cannot account for their initial accumulation. Intracerebral infusion of proinflammatory agents offer an alternative model, but these fail to replicate the cause of AD. A novel model is therefore needed, perhaps similar to those used for Parkinson's disease, namely adult wildtype rodents with neuron-specific (dopaminergic) lesions within the same vulnerable brainstem nuclei, 'the isodendritic core', which are the first to degenerate in AD. Site-selective targeting of these nuclei in adult rodents may recapitulate the initial neurodegenerative processes in AD to faithfully mimic its pathogenesis and progression, ultimately leading to presymptomatic biomarkers and preventative therapies.

Development of Triphenylmethane Dyes for In Vivo Fluorescence Imaging of Aβ Oligomers

Detection of amyloid β (Aβ) oligomers, regarded as the most toxic aggregated forms of Aβ, can contribute to the diagnosis and treatment of Alzheimer's disease (AD). Thus, the development of imaging probes for in vivo visualization of Aβ oligomers is crucial. However, the structural uncertainty regarding Aβ oligomers makes it difficult to design imaging probes with high sensitivity to Aβ oligomers against highly aggregated Aβ fibrils. In this study, we developed Aβ oligomer-selective fluorescent probes based on triphenylmethane dyes through screening of commercially available compounds followed by structure-activity relationship (SAR) studies on cyclic or acyclic 4-dialkylamino groups. We synthesized 11 triarylmethane-based Aβ oligomer probe (TAMAOP) derivatives. In vitro evaluation of fluorescence properties, TAMAOP-9, which had bulky 4-diisobutylamino groups introduced into three benzenes of a twisted triphenylmethane backbone, showed marked fluorescence enhancement in the presence of Aβ oligomers and demonstrated high selectivity for Aβ oligomers against Aβ fibrils. In docking studies using the Aβ trimer model, TAMAOP-9 bound to the hydrophobic surface and interacted with the side chain of Phe20. In vitro section staining revealed that TAMAOP-9 could visualize Aβ oligomers in the brains of AD model mice. An in vivo fluorescence imaging study using TAMAOP-9 showed significantly higher fluorescence signals from the brains of AD model mice than those of age-matched wild-type mice, confirmed by ex vivo section observation. These results suggest that TAMAOP-9 is a promising Aβ oligomer-targeting fluorescent probe applicable to in vivo imaging.

Clioquinol rescues yeast cells from Aβ42 toxicity via the inhibition of oxidative damage

Alzheimer's disease (AD), the most common form of dementia, has gotten considerable attention. Previous studies have demonstrated that clioquinol (CQ) as a metal chelator is a potential drug for the treatment of AD. However, the mode of action of CQ in AD is still unclear. In our study, the antioxidant effects of CQ on yeast cells expressing Aβ42 were investigated. We found that CQ could reduce Aβ42 toxicity by alleviating reactive oxygen species (ROS) generation and lipid peroxidation level in yeast cells. These alterations were mainly attributable to the increased reduced glutathione (GSH) content and independent of activities of superoxide dismutase (SOD) and/or catalase (CAT). CQ could affect antioxidant enzyme activity by altering the transcription level of related genes. Interestingly, it was noted for the first time that CQ could combine with antioxidant enzymes to reduce their enzymatic activities by molecular docking and circular dichroism spectroscopy. In addition, CQ restored Aβ42-mediated disruption of GSH homeostasis via regulating YAP1 expression to protect cells against oxidative stress. Our findings not only improve the current understanding of the mechanism of CQ as a potential drug for AD treatment but also provide ideas for subsequent drug research and development.

Nicotinic acetylcholine receptor activation induces BACE1 transcription via the phosphorylation and stabilization of nuclear SP1

Epidemiological studies have shown that cigarette smoking increases the risk of Alzheimer disease. However, inconsistent results have been reported regarding the effects of smoking or nicotine on brain amyloid β (Aβ) deposition. In this study, we found that stimulation of the nicotinic acetylcholine receptor (nAChR) increased Aβ production in mouse brains and cultured neuronal cells. nAChR activation triggered the MEK/ERK pathway, which then phosphorylated and stabilized nuclear SP1. Upregulated SP1 acted on two recognition motifs in the BACE1 gene to induce its transcription, resulting in enhanced Aβ production. Mouse brain microdialysis revealed that nAChR agonists increased Aβ levels in the interstitial fluid of the cerebral cortex but caused no delay of Aβ clearance. In vitro assays indicated that nicotine inhibited Aβ aggregation. We also found that nicotine modified the immunoreactivity of anti-Aβ antibodies, possibly through competitive inhibition and Aβ conformation changes. Using anti-Aβ antibody that was carefully selected to avoid these effects, we found that chronic nicotine treatment in Aβ precursor protein knockin mice increased the Aβ content but did not visibly change the aggregated Aβ deposition in the brain. Thus, nicotine influences brain Aβ deposition in the opposite direction, thereby increasing Aβ production and inhibiting Aβ aggregation.

Characterizing molecular and synaptic signatures in mouse models of late-onset Alzheimer's disease independent of amyloid and tau pathology

INTRODUCTION

MODEL-AD (Model Organism Development and Evaluation for Late-Onset Alzheimer's Disease) is creating and distributing novel mouse models with humanized, clinically relevant genetic risk factors to capture the trajectory and progression of late-onset Alzheimer's disease (LOAD) more accurately.

METHODS

We created the LOAD2 model by combining apolipoprotein E4 (APOE4), Trem2*R47H, and humanized amyloid-beta (Aβ). Mice were subjected to a control diet or a high-fat/high-sugar diet (LOAD2+HFD). We assessed disease-relevant outcome measures in plasma and brain including neuroinflammation, Aβ, neurodegeneration, neuroimaging, and multi-omics.

RESULTS

By 18 months, LOAD2+HFD mice exhibited sex-specific neuron loss, elevated insoluble brain Aβ42, increased plasma neurofilament light chain (NfL), and altered gene/protein expression related to lipid metabolism and synaptic function. Imaging showed reductions in brain volume and neurovascular uncoupling. Deficits in acquiring touchscreen-based cognitive tasks were observed.

DISCUSSION

The comprehensive characterization of LOAD2+HFD mice reveals that this model is important for preclinical studies seeking to understand disease trajectory and progression of LOAD prior to or independent of amyloid plaques and tau tangles.

HIGHLIGHTS

By 18 months, unlike control mice (e.g., LOAD2 mice fed a control diet, CD), LOAD2+HFD mice presented subtle but significant loss of neurons in the cortex, elevated levels of insoluble Ab42 in the brain, and increased plasma neurofilament light chain (NfL). Transcriptomics and proteomics showed changes in gene/proteins relating to a variety of disease-relevant processes including lipid metabolism and synaptic function. In vivo imaging revealed an age-dependent reduction in brain region volume (MRI) and neurovascular uncoupling (PET/CT). LOAD2+HFD mice also demonstrated deficits in acquisition of touchscreen-based cognitive tasks.

ER-stress response in retinal Müller glia occurs significantly earlier than amyloid pathology in the Alzheimer's mouse brain and retina

Alzheimer's Disease (AD) pathogenesis is thought to begin up to 20 years before cognitive symptoms appear, suggesting the need for more sensitive diagnostic biomarkers of AD. In this report, we demonstrated pathological changes in retinal Müller glia significantly earlier than amyloid pathology in AD mouse models. By utilizing the knock-in NLGF mouse model, we surprisingly discovered an increase in reticulon 3 (RTN3) protein levels in the NLGF retina as early as postnatal day 30 (P30). Despite RTN3 being a canonically neuronal protein, this increase was noted in the retinal Müller glia, confirmed by immunohistochemical characterization. Further unbiased transcriptomic assays of the P30 NLGF retina revealed that retinal Müller glia were the most sensitive responding cells in this mouse retina, compared with other cell types including photoreceptor cells and ganglion neurons. Pathway analyses of differentially expressed genes in glia cells showed activation of ER stress response via the upregulation of unfolded protein response (UPR) proteins such as ATF4 and CHOP. Early elevation of RTN3 in response to challenges by toxic Aβ likely facilitated UPR. Altogether, these findings suggest that Müller glia act as a sentinel for AD pathology in the retina and should aid for both intervention and diagnosis.

Divergent Age-Dependent Conformational Rearrangement within Aβ Amyloid Deposits in APP23, APPPS1, and AppNL-F Mice

Amyloid plaques composed of fibrils of misfolded Aβ peptides are pathological hallmarks of Alzheimer's disease (AD). Aβ fibrils are polymorphic in their tertiary and quaternary molecular structures. This structural polymorphism may carry different pathologic potencies and can putatively contribute to clinical phenotypes of AD. Therefore, mapping of structural polymorphism of Aβ fibrils and structural evolution over time is valuable to understanding disease mechanisms. Here, we investigated how Aβ fibril structures in situ differ in Aβ plaque of different mouse models expressing familial mutations in the AβPP gene. We imaged frozen brains with a combination of conformation-sensitive luminescent conjugated oligothiophene (LCO) ligands and Aβ-specific antibodies. LCO fluorescence mapping revealed that mouse models APP23, APPPS1, and AppNL-F have different fibril structures within Aβ-amyloid plaques depending on the AβPP-processing genotype. Co-staining with Aβ-specific antibodies showed that individual plaques from APP23 mice expressing AβPP Swedish mutation have two distinct fibril polymorph regions of core and corona. The plaque core is predominantly composed of compact Aβ40 fibrils, and the corona region is dominated by diffusely packed Aβ40 fibrils. Conversely, the AβPP knock-in mouse AppNL-F, expressing the AβPP Iberian mutation along with Swedish mutation has tiny, cored plaques consisting mainly of compact Aβ42 fibrils, vastly different from APP23 even at elevated age up to 21 months. Age-dependent polymorph rearrangement of plaque cores observed for APP23 and APPPS1 mice >12 months, appears strongly promoted by Aβ40 and was hence minuscule in AppNL-F. These structural studies of amyloid plaques in situ can map disease-relevant fibril polymorph distributions to guide the design of diagnostic and therapeutic molecules.

Disturbance in the protein landscape of cochlear perilymph in an Alzheimer's disease mouse model

Hearing loss is a pivotal risk factor for dementia. It has recently emerged that a disruption in the intercommunication between the cochlea and brain is a key process in the initiation and progression of this disease. However, whether the cochlear properties can be influenced by pathological signals associated with dementia remains unclear. In this study, using a mouse model of Alzheimer's disease (AD), we investigated the impacts of the AD-like amyloid β (Aβ) pathology in the brain on the cochlea. Despite little detectable change in the age-related shift of the hearing threshold, we observed quantitative and qualitative alterations in the protein profile in perilymph, an extracellular fluid that fills the path of sound waves in the cochlea. Our findings highlight the potential contribution of Aβ pathology in the brain to the disturbance of cochlear homeostasis.

Multi-omics delineate growth factor network underlying exercise effects in an Alzheimer's mouse model

Physical exercise represents a primary defense against age-related cognitive decline and neurodegenerative disorders like Alzheimer's disease (AD). To impartially investigate the underlying mechanisms, we conducted single-nucleus transcriptomic and chromatin accessibility analyses (snRNA-seq and ATAC-seq) on the hippocampus of mice carrying AD-linked NL-G-F mutations in the amyloid precursor protein gene (APPNL-G-F) following prolonged voluntary wheel-running exercise. Our study reveals that exercise mitigates amyloid-induced changes in both transcriptomic expression and chromatin accessibility through cell type-specific transcriptional regulatory networks. These networks converge on the activation of growth factor signaling pathways, particularly the epidermal growth factor receptor (EGFR) and insulin signaling, correlating with an increased proportion of immature dentate granule cells and oligodendrocytes. Notably, the beneficial effects of exercise on neurocognitive functions can be blocked by pharmacological inhibition of EGFR and the downstream phosphoinositide 3-kinases (PI3K). Furthermore, exercise leads to elevated levels of heparin-binding EGF (HB-EGF) in the blood, and intranasal administration of HB-EGF enhances memory function in sedentary APPNL-G-F mice. These findings offer a panoramic delineation of cell type-specific hippocampal transcriptional networks activated by exercise and suggest EGF-related growth factor signaling as a druggable contributor to exercise-induced memory enhancement, thereby suggesting therapeutic avenues for combatting AD-related cognitive decline.

Modeling of age-related neurological disease: utility of zebrafish

Many age-related neurological diseases still lack effective treatments, making their understanding a critical and urgent issue in the globally aging society. To overcome this challenge, an animal model that accurately mimics these diseases is essential. To date, many mouse models have been developed to induce age-related neurological diseases through genetic manipulation or drug administration. These models help in understanding disease mechanisms and finding potential therapeutic targets. However, some age-related neurological diseases cannot be fully replicated in human pathology due to the different aspects between humans and mice. Although zebrafish has recently come into focus as a promising model for studying aging, there are few genetic zebrafish models of the age-related neurological disease. This review compares the aging phenotypes of humans, mice, and zebrafish, and provides an overview of age-related neurological diseases that can be mimicked in mouse models and those that cannot. We presented the possibility that reproducing human cerebral small vessel diseases during aging might be difficult in mice, and zebrafish has potential to be another animal model of such diseases due to their similarity of aging phenotype to humans.

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

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

Targeting terminal pathway reduces brain complement activation, amyloid load and synapse loss, and improves cognition in a mouse model of dementia

Complement is dysregulated in the brain in Alzheimer's Disease and in mouse models of Alzheimer's disease. Each of the complement derived effectors, opsonins, anaphylatoxins and membrane attack complex (MAC), have been implicated as drivers of disease but their relative contributions remain unclarified. Here we have focussed on the MAC, a lytic and pro-inflammatory effector, in the AppNL-G-F mouse amyloidopathy model. To test the role of MAC, we back-crossed to generate AppNL-G-F mice deficient in C7, an essential MAC component. C7 deficiency ablated MAC formation, reduced synapse loss and amyloid load and improved cognition compared to complement-sufficient AppNL-G-F mice at 8-10 months age. Adding back C7 caused increased MAC formation in brain and an acute loss of synapses in C7-deficient AppNL-G-F mice. To explore whether C7 was a viable therapeutic target, a C7-blocking monoclonal antibody was administered systemically for one month in AppNL-G-F mice aged 8-9 months. Treatment reduced brain MAC and amyloid deposition, increased synapse density and improved cognitive performance compared to isotype control-treated AppNL-G-F mice. The findings implicate MAC as a driver of pathology and highlight the potential for complement inhibition at the level of MAC as a therapy in Alzheimer's disease.

Telomere length and micronuclei trajectories in APP/PS1 mouse model of Alzheimer's disease: Correlating with cognitive impairment and brain amyloidosis in a sexually dimorphic manner

Although studies have demonstrated that genome instability is accumulated in patients with Alzheimer's disease (AD), the specific types of genome instability linked to AD pathogenesis remain poorly understood. Here, we report the first characterization of the age- and sex-related trajectories of telomere length (TL) and micronuclei in APP/PS1 mice model and wild-type (WT) controls (C57BL/6). TL was measured in brain (prefrontal cortex, cerebellum, pituitary gland, and hippocampus), colon and skin, and MN was measured in bone marrow in 6- to 14-month-old mice. Variation in TL was attributable to tissue type, age, genotype and, to a lesser extent, sex. Compared to WT, APP/PS1 had a significantly shorter baseline TL across all examined tissues. TL was inversely associated with age in both genotypes and TL shortening was accelerated in brain of APP/PS1. Age-related increase of micronuclei was observed in both genotypes but was accelerated in APP/PS1. We integrated TL and micronuclei data with data on cognition performance and brain amyloidosis. TL and micronuclei were linearly correlated with cognition performance or Aβ40 and Aβ42 levels in both genotypes but to a greater extent in APP/PS1. These associations in APP/PS1 mice were dominantly driven by females. Together, our findings provide foundational knowledge to infer the TL and micronuclei trajectories in APP/PS1 mice during disease progression, and strongly support that TL attrition and micronucleation are tightly associated with AD pathogenesis in a female-biased manner.

DNA methylation patterns of FKBP5 regulatory regions in brain and blood of humanized mice and humans

Humanized mouse models can be used to explore human gene regulatory elements (REs), which frequently lie in non-coding and less conserved genomic regions. Epigenetic modifications of gene REs, also in the context of gene x environment interactions, have not yet been explored in humanized mouse models. We applied high-accuracy measurement of DNA methylation (DNAm) via targeted bisulfite sequencing (HAM-TBS) to investigate DNAm in three tissues/brain regions (blood, prefrontal cortex and hippocampus) of mice carrying the human FK506-binding protein 5 (FKBP5) gene, an important candidate gene associated with stress-related psychiatric disorders. We explored DNAm in three functional intronic glucocorticoid-responsive elements (at introns 2, 5, and 7) of FKBP5 at baseline, in cases of differing genotype (rs1360780 single nucleotide polymorphism), and following application of the synthetic glucocorticoid dexamethasone. We compared DNAm patterns in the humanized mouse (N = 58) to those in human peripheral blood (N = 447 and N = 89) and human postmortem brain prefrontal cortex (N = 86). Overall, DNAm patterns in the humanized mouse model seem to recapitulate DNAm patterns observed in human tissue. At baseline, this was to a higher extent in brain tissue. The animal model also recapitulated effects of dexamethasone on DNAm, especially in peripheral blood and to a lesser extent effects of genotype on DNAm. The humanized mouse model could thus assist in reverse translation of human findings in psychiatry that involve genetic and epigenetic regulation in non-coding elements.

Xenografted human microglia display diverse transcriptomic states in response to Alzheimer's disease-related amyloid-β pathology

Microglia are central players in Alzheimer's disease pathology but analyzing microglial states in human brain samples is challenging due to genetic diversity, postmortem delay and admixture of pathologies. To circumvent these issues, here we generated 138,577 single-cell expression profiles of human stem cell-derived microglia xenotransplanted in the brain of the AppNL-G-F model of amyloid pathology and wild-type controls. Xenografted human microglia adopt a disease-associated profile similar to that seen in mouse microglia, but display a more pronounced human leukocyte antigen or HLA state, likely related to antigen presentation in response to amyloid plaques. The human microglial response also involves a pro-inflammatory cytokine/chemokine cytokine response microglia or CRM response to oligomeric Aβ oligomers. Genetic deletion of TREM2 or APOE as well as APOE polymorphisms and TREM2R47H expression in the transplanted microglia modulate these responses differentially. The expression of other Alzheimer's disease risk genes is differentially regulated across the distinct cell states elicited in response to amyloid pathology. Thus, we have identified multiple transcriptomic cell states adopted by human microglia in a multipronged response to Alzheimer's disease-related pathology, which should be taken into account in translational studies.

Adenosine deficiency facilitates CA1 synaptic hyperexcitability in the presymptomatic phase of a knock in mouse model of Alzheimer's disease

The disease's trajectory of Alzheimer's disease (AD) is associated with and worsened by hippocampal hyperexcitability. Here we show that during the asymptomatic stage in a knock in mouse model of Alzheimer's disease (APPNL-G-F/NL-G-F; APPKI), hippocampal hyperactivity occurs at the synaptic compartment, propagates to the soma and is manifesting at low frequencies of stimulation. We show that this aberrant excitability is associated with a deficient adenosine tone, an inhibitory neuromodulator, driven by reduced levels of CD39/73 enzymes, responsible for the extracellular ATP-to-adenosine conversion. Both pharmacologic (adenosine kinase inhibitor) and non-pharmacologic (ketogenic diet) restorations of the adenosine tone successfully normalize hippocampal neuronal activity. Our results demonstrated that neuronal hyperexcitability during the asymptomatic stage of a KI model of Alzheimer's disease originated at the synaptic compartment and is associated with adenosine deficient tone. These results extend our comprehension of the hippocampal vulnerability associated with the asymptomatic stage of Alzheimer's disease.