Transgenic mouse models of Alzheimer's disease

Behaviour Hallmarks in Alzheimer's Disease 5xFAD Mouse Model

The 5xFAD transgenic mouse model widely used in Alzheimer's disease (AD) research recapitulates many AD-related phenotypes with a relatively early onset and aggressive age-dependent progression. Besides developing amyloid peptide deposits alongside neuroinflammation by the age of 2 months, as well as exhibiting neuronal decline by the age of 4 months that intensifies by the age of 9 months, these mice manifest a broad spectrum of behavioural impairments. In this review, we present the extensive repertoire of behavioural dysfunctions in 5xFAD mice, organised into four categories: motor skills, sensory function, learning and memory abilities, and neuropsychiatric-like symptoms. The motor problems, associated with agility and reflex movements, as well as balance and coordination, and skeletal muscle function, typically arise by the time mice reach 9 months of age. The sensory function (such as taste, smell, hearing, and vision) starts to deteriorate when amyloid peptide buildups and neuroinflammation spread into related anatomical structures. The cognitive functions, encompassing learning and memory abilities, such as visual recognition, associative, spatial working, reference learning, and memory show signs of decline from 4 to 6 months of age. Concerning neuropsychiatric-like symptoms, comprising apathy, anxiety and depression, and the willingness for exploratory behaviour, it is believed that motivational changes emerge by approximately 6 months of age. Unfortunately, numerous studies from different laboratories are often contradictory on the conclusions drawn and the identification of onset age, making preclinical studies in rodent models not easily translatable to humans. This variability is likely due to a range of factors associated with animals themselves, housing and husbandry conditions, and experimental settings. In the forthcoming studies, greater clarity in experimental details when conducting behavioural testing in 5xFAD transgenic mice could minimise the inconsistencies and could ensure the reliability and the reproducibility of the results.

Gut instincts: Unveiling the connection between gut microbiota and Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder marked by neuroinflammation and gradual cognitive decline. Recent research has revealed that the gut microbiota (GM) plays an important role in the pathogenesis of AD through the microbiota-gut-brain axis. However, the mechanism by which GM and microbial metabolites alter brain function is not clearly understood. GM dysbiosis increases the permeability of the intestine, alters the blood-brain barrier permeability, and elevates proinflammatory mediators causing neurodegeneration. This review article introduced us to the composition and functions of GM along with its repercussions of dysbiosis in relation to AD. We also discussed the importance of the gut-brain axis and its role in communication. Later we focused on the mechanism behind gut dysbiosis and the progression of AD including neuroinflammation, oxidative stress, and changes in neurotransmitter levels. Furthermore, we highlighted recent developments in AD management, such as microbiota-based therapy, dietary interventions like prebiotics, probiotics, and fecal microbiota transplantation. Finally, we concluded with challenges and future directions in AD research based on GM.

A novel mouse model for N-terminal truncated Aβ2-x generation through meprin β overexpression in astrocytes

Neurotoxic amyloid-β (Aβ) peptides cause neurodegeneration in Alzheimer's disease (AD) patients' brains. They are released upon proteolytic processing of the amyloid precursor protein (APP) extracellularly at the β-secretase site and intramembranously at the γ-secretase site. Several AD mouse models were developed to conduct respective research in vivo. Most of these classical models overexpress human APP with mutations driving AD-associated pathogenic APP processing. However, the resulting pattern of Aβ species in the mouse brains differs from those observed in AD patients' brains. Particularly mutations proximal to the β-secretase cleavage site (e.g., the so-called Swedish APP (APPswe) fostering Aβ1-x formation) lead to artificial Aβ production, as N-terminally truncated Aβ peptides are hardly present in these mouse brains. Meprin β is an alternative β-secretase upregulated in brains of AD patients and capable of generating N-terminally truncated Aβ2-x peptides. Therefore, we aimed to generate a mouse model for the production of so far underestimated Aβ2-x peptides by conditionally overexpressing meprin β in astrocytes. We chose astrocytes as meprin β was detected in this cell type in close proximity to Aβ plaques in AD patients' brains. The meprin β-overexpressing mice showed elevated amyloidogenic APP processing detected with a newly generated neo-epitope-specific antibody. Furthermore, we observed elevated Aβ production from endogenous APP as well as AD-related behavior changes (hyperlocomotion and deficits in spatial memory). The novel mouse model as well as the established tools and methods will be helpful to further characterize APP cleavage and the impact of different Aβ species in future studies.

Cognitive trajectories in longitudinally trained 3xTg-AD mice

Preclinical studies in Alzheimer's disease (AD) often rely on cognitively naïve animal models in cross-sectional designs that can fail to reflect the cognitive exposures across the lifespan and heterogeneous neurobehavioral features observed in humans. To determine whether longitudinal cognitive training may affect cognitive capacities in a well-characterized AD mouse model, 3xTg and wild-type mice (n = 20) were exposed daily to a training variant of the Go-No-Go (GNG) operant task from 3 to 9 months old. At 3, 6, and 9 months, performance on a testing variant of the GNG task and anxiety-like behaviors were measured, while long-term recognition memory was also assessed at 9 months. In general, GNG training improved performance with increasing age across genotypes. At 3 months old, 3xTg mice showed slight deficits in inhibitory control that were accompanied by minor improvements in signal detection and decreased anxiety-like behavior, but these differences did not persist at 6 and 9 months old. At 9 months old, 3xTg mice displayed minor deficits in signal detection, and long-term recognition memory capacity was comparable with wild-type subjects. Our findings indicate that longitudinal cognitive training can render 3xTg mice with cognitive capacities that are on par with their wild-type counterparts, potentially reflecting functional compensation in subjects harboring AD genetic mutations.

Insights on the Use of Transgenic Mice Models in Alzheimer's Disease Research

Alzheimer's disease (AD), the leading cause of dementia, presents a significant global health challenge with no known cure to date. Central to our understanding of AD pathogenesis is the β-amyloid cascade hypothesis, which underlies drug research and discovery efforts. Despite extensive studies, no animal models of AD have completely validated this hypothesis. Effective AD models are essential for accurately replicating key pathological features of the disease, notably the formation of β-amyloid plaques and neurofibrillary tangles. These pathological markers are primarily driven by mutations in the amyloid precursor protein (APP) and presenilin 1 (PS1) genes in familial AD (FAD) and by tau protein mutations for the tangle pathology. Transgenic mice models have been instrumental in AD research, heavily relying on the overexpression of mutated APP genes to simulate disease conditions. However, these models do not entirely replicate the human condition of AD. This review aims to provide a comprehensive evaluation of the historical and ongoing research efforts in AD, particularly through the use of transgenic mice models. It is focused on the benefits gathered from these transgenic mice models in understanding β-amyloid toxicity and the broader biological underpinnings of AD. Additionally, the review critically assesses the application of these models in the preclinical testing of new therapeutic interventions, highlighting the gap between animal models and human clinical realities. This analysis underscores the need for refinement in AD research methodologies to bridge this gap and enhance the translational value of preclinical studies.

Memantine: Updating a rare success story in pro-cognitive therapeutics

The great potential for NMDA receptor modulators as druggable targets in neurodegenerative disorders has been met with limited success. Considered one of the rare exceptions, memantine has consistently demonstrated restorative and prophylactic properties in many AD models. In clinical trials memantine slows the decline in cognitive performance associated with AD. Here, we provide an overview of the basic properties including pharmacological targets, toxicology and cellular effects of memantine. Evidence demonstrating reductions in molecular, physiological and behavioural indices of AD-like impairments associated with memantine treatment are also discussed. This represents both an extension and homage to Dr. Chris Parson's considerable contributions to our fundamental understanding of a success story in the AD treatment landscape.

Impact of Long-Term Dietary High Fat and Eicosapentaenoic Acid on Behavior and Hypothalamic-Pituitary-Adrenal Axis Activity in Amyloidogenic APPswe/PSEN1dE9 Mice

INTRODUCTION

Alzheimer's disease (AD) alters neurocognitive and emotional function and causes dysregulation of multiple homeostatic processes. The leading AD framework pins amyloid beta plaques and tau tangles as primary drivers of dysfunction. However, many additional variables, including diet, stress, sex, age, and pain tolerance, interact in ways that are not fully understood to impact the onset and progression of AD pathophysiology. We asked: (1) does high-fat diet, compared to low-fat diet, exacerbate AD pathophysiology and behavioral decline? And, (2) can supplementation with eicosapentaenoic (EPA)-enriched fish oil prevent high-fat-diet-induced changes?

METHODS

Male and female APPswePSdE9 mice, and their non-transgenic littermates, were randomly assigned to a diet condition (low-fat, high-fat, high-fat with EPA) and followed from 2 to 10 months of age. We assessed baseline corticosterone concentration during aging, pain tolerance, cognitive function, stress coping, and corticosterone response to a stressor.

RESULTS

Transgenic mice were consistently more active than non-transgenic mice but did not perform worse on either cognitive task, even though we recently reported that these same transgenic mice exhibited metabolic changes and had increased amyloid beta. Mice fed high-fat diet had higher baseline and post-stressor corticosterone, but diet did not impact cognition or pain tolerance. Sex had the biggest influence, as female mice were consistently more active and had higher corticosterone than males.

CONCLUSION

Overall, diet, genotype, and sex did not have consistent impacts on outcomes. We found little support for predicted interactions and correlations, suggesting diet impacts metabolic function and amyloid beta levels, but these outcomes do not translate to changes in behaviors measured here.

Therapeutic Effects of Aβ-Specific Regulatory T Cells in Alzheimer's Disease: A Study in 5xFAD Mice

The aging global population is placing an increasing burden on healthcare systems, and the social impact of Alzheimer's disease (AD) is on the rise. However, the availability of safe and effective treatments for AD remains limited. Adoptive Treg therapy has been explored for treating neurodegenerative diseases, including AD. To facilitate the clinical application of Treg therapy, we developed a Treg preparation protocol and highlighted the therapeutic effects of Tregs in 5xFAD mice. CD4+CD25+ Tregs, isolated after Aβ stimulation and expanded using a G-rex plate with a gas-permeable membrane, were adoptively transferred into 5xFAD mice. Behavioral analysis was conducted using Y-maze and passive avoidance tests. Additionally, we measured levels of Aβ, phosphorylated tau (pTAU), and nitric oxide synthase 2 (NOS2) in the hippocampus. Real-time RT-PCR was employed to assess the mRNA levels of pro- and anti-inflammatory markers. Our findings indicate that Aβ-specific Tregs not only improved cognitive function but also reduced Aβ and pTAU accumulation in the hippocampus of 5xFAD mice. They also inhibited microglial neuroinflammation. These effects were observed at doses as low as 1.5 × 103 cells/head. Collectively, our results demonstrate that Aβ-specific Tregs can mitigate AD pathology in 5xFAD mice.

9-cis beta-carotene-enriched diet significantly improved cognition and decreased Alzheimer's disease neuropathology and neuroinflammation in Alzheimer's disease-like mouse models

A significant progressive decline in beta-carotene (βC) levels in the brain is associated with cognitive impairment and a higher prevalence of Alzheimer's disease (AD). In this study, we investigated whether the administration of 9-cis beta-carotene (9CBC)-rich powder of the alga Dunaliella bardawil, the best-known source of βC in nature, inhibits the development of AD-like neuropathology and cognitive deficits. We demonstrated that in 3 AD mouse models, Tg2576, 5xFAD, and apoE4, 9CBC treatment improved long- and short-term memory, decreased neuroinflammation, and reduced the prevalence of β-amyloid plaques and tau hyperphosphorylation. These findings suggest that 9CBC has the potential to be an effective preventive and symptomatic AD therapy.

Histological and Memory Alterations in an Innovative Alzheimer's Disease Animal Model by Vanadium Pentoxide Inhalation

Background

Previous work from our group has shown that chronic exposure to Vanadium pentoxide (V2O5) causes cytoskeletal alterations suggesting that V2O5 can interact with cytoskeletal proteins through polymerization and tyrosine phosphatases inhibition, causing Alzheimer's disease (AD)-like hippocampal cell death.

Objective

This work aims to characterize an innovative AD experimental model through chronic V2O5 inhalation, analyzing the spatial memory alterations and the presence of neurofibrillary tangles (NFTs), amyloid-β (Aβ) senile plaques, cerebral amyloid angiopathy, and dendritic spine loss in AD-related brain structures.

Methods

20 male Wistar rats were divided into control (deionized water) and experimental (0.02 M V2O5 1 h, 3/week for 6 months) groups (n = 10). The T-maze test was used to assess spatial memory once a month. After 6 months, histological alterations of the frontal and entorhinal cortices, CA1, subiculum, and amygdala were analyzed by performing Congo red, Bielschowsky, and Golgi impregnation.

Results

Cognitive results in the T-maze showed memory impairment from the third month of V2O5 inhalation. We also noted NFTs, Aβ plaque accumulation in the vascular endothelium and pyramidal neurons, dendritic spine, and neuronal loss in all the analyzed structures, CA1 being the most affected.

Conclusions

This model characterizes neurodegenerative changes specific to AD. Our model is compatible with Braak AD stage IV, which represents a moment where it is feasible to propose therapies that have a positive impact on stopping neuronal damage.

Pharmacological Potential of Bioactive Peptides for the Treatment of Diseases Associated with Alzheimer's and Brain Disorders

Bioactive peptides are a promising class of therapeutics for the treatment of diseases associated with Alzheimer's and brain disorders. These peptides are derived from naturally occurring proteins and have been shown to possess a variety of beneficial properties. They may modulate neurotransmitter systems, reduce inflammation, and improve cognitive performance. In addition, bioactive peptides have the potential to target specific molecular pathways involved in the pathogenesis of Alzheimer's and brain disorders. For example, peptides have been shown to interact with amyloid-beta, a major component of amyloid plaques found in Alzheimer's disease, and have been shown to reduce its accumulation in the brain. Furthermore, peptides have been found to modulate the activity of glutamate receptors, which are important for memory and learning, as well as to inhibit the activity of enzymes involved in the formation of toxic amyloid-beta aggregates. Finally, bioactive peptides have the potential to reduce oxidative stress and inflammation, two major components of many neurological disorders. These peptides could be used alone or in combination with traditional pharmacological treatments to improve the management of diseases associated with Alzheimer's and brain disorders.

Insight into the emerging and common experimental in-vivo models of Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial, rapidly progressing neurodegenerative disorder. As the exact cause of the disease is still unclear, the drug development is very challenging. This review encompasses the commonly used AD models involving various chemicals, heavy metals and endogenous substances induced models and the transgenic models. It also provides insight into the reliable emerging models of AD that may overcome the shortcomings associated with available models. Chemicals like streptozotocin, scopolamine, colchicine and okadaic acid render the animal susceptible to neuroinflammation and oxidative stress induced neurodegeneration along with amyloid-β deposition and tau hyperphosphorylation. Similarly, endogenous substances like acrolein and amyloid-β 1-42 are efficient in inducing the major pathologies of AD. Heavy metals like aluminum and fluoride and mixture of these have been reported to induce neurotoxicity therefore are used as animal models for AD. Transgenic models developed as a result of knock-in or knock-out of certain genes associated with AD including PDAPP, APP23, Tg2576, APP/PS1, 3 × Tg and 5 × FAD have also been incorporated in this study. Further, emerging and advanced pathomimetic models of AD are provided particular interest here which will add on to the current knowledge of animal models and may aid in the drug development process and deepen our understanding related to AD pathogenesis. These newly discovered models include oAβ25-35 model, transgenic model expressing 82-kDa ChAT, oDGal mouse and APP knock-in rat. This study may aid in the selection of suitable model for development of novel potent therapeutics and for exploring detailed pathogenic mechanism of AD.

Astrocyte-specific knockout of YKL-40/Chi3l1 reduces Aβ burden and restores memory functions in 5xFAD mice

Glial cell-mediated neuroinflammation and neuronal attrition are highly correlated with cognitive impairment in Alzheimer's disease. YKL-40 is a secreted astrocytic glycoprotein that serves as a diagnostic biomarker of Alzheimer's disease. High levels of YKL-40 are associated with either advanced Alzheimer's disease or the normal aging process. However, the functional role of YKL-40 in Alzheimer's disease development has not been firmly established. In a 5xFAD mouse model of Alzheimer's disease, we observed increased YKL-40 expression in the cerebrospinal fluid of 7-month-old mice and was correlated with activated astrocytes. In primary astrocytes, Aβ1-42 upregulated YKL-40 in a dose-dependent manner and was correlated with PI3-K signaling pathway activation. Furthermore, primary neurons treated with YKL-40 and/or Aβ1-42 resulted in significant synaptic degeneration, reduced dendritic complexity, and impaired electrical parameters. More importantly, astrocyte-specific knockout of YKL-40 over a period of 7 days in symptomatic 5xFAD mice could effectively reduce amyloid plaque deposition in multiple brain regions. This was also associated with attenuated glial activation, reduced neuronal attrition, and restored memory function. These biological phenotypes could be explained by enhanced uptake of Aβ1-42 peptides, increased rate of Aβ1-42 degradation and acidification of lysosomal compartment in YKL-40 knockout astrocytes. Our results provide new insights into the role of YKL-40 in Alzheimer's disease pathogenesis and demonstrate the potential of targeting this soluble biomarker to alleviate cognitive defects in symptomatic Alzheimer's disease patients.

Modulation of LPS-Induced Neurodegeneration by Intestinal Helminth Infection in Ageing Mice

Parasitic helminths induce a transient, short-term inflammation at the beginning of infection, but in persistent infection may suppress the systemic immune response by enhancing the activity of regulatory M2 macrophages. The aim of the study was to determine how nematode infection affects age-related neuroinflammation, especially macrophages in the nervous tissue. Here, intraperitoneal LPS-induced systemic inflammation resulting in brain neurodegeneration was enhanced by prolonged Heligmosomoides polygyrus infection in C57BL/6 mice. The changes in the brain coincided with the increase in M1 macrophages, reduced survivin level, enhanced APP and GFAP expression, chitin-like chains deposition in the brain and deterioration behaviour manifestations. These changes were also observed in transgenic C57BL/6 mice predisposed to develop neurodegeneration typical for Alzheimer's disease in response to pathogenic stimuli. Interestingly, in mice infected with the nematode only, the greater M2 macrophage population resulted in better results in the forced swim test. Given the growing burden of neurodegenerative diseases, understanding such interactive associations can have significant implications for ageing health strategies and disease monitoring.

Aberrant accumulation of age- and disease-associated factors following neural probe implantation in a mouse model of Alzheimer's disease

Objective. Electrical stimulation has had a profound impact on our current understanding of nervous system physiology and provided viable clinical options for addressing neurological dysfunction within the brain. Unfortunately, the brain's immune suppression of indwelling microelectrodes currently presents a major roadblock in the long-term application of neural recording and stimulating devices. In some ways, brain trauma induced by penetrating microelectrodes produces similar neuropathology as debilitating brain diseases, such as Alzheimer's disease (AD), while also suffering from end-stage neuron loss and tissue degeneration. The goal of the present study was to understand whether there may be any parallel mechanisms at play between brain injury from chronic microelectrode implantation and those of neurodegenerative disorder.Approach. We used two-photon microscopy to visualize the accumulation, if any, of age- and disease-associated factors around chronically implanted electrodes in both young and aged mouse models of AD.Main results. We determined that electrode injury leads to aberrant accumulation of lipofuscin, an age-related pigment, in wild-type and AD mice alike. Furthermore, we reveal that chronic microelectrode implantation reduces the growth of pre-existing Alzheimer's plaques while simultaneously elevating amyloid burden at the electrode-tissue interface. Lastly, we uncover novel spatial and temporal patterns of glial reactivity, axonal and myelin pathology, and neurodegeneration related to neurodegenerative disease around chronically implanted microelectrodes.Significance. This study offers multiple novel perspectives on the possible neurodegenerative mechanisms afflicting chronic brain implants, spurring new potential avenues of neuroscience investigation and design of more targeted therapies for improving neural device biocompatibility and treatment of degenerative brain disease.

Discovery of Multitarget-Directed Ligands from Piperidine Alkaloid Piperine as a Cap Group for the Management of Alzheimer's Disease

The naturally inspired multitarget-directed ligands (PC01-PC10 and PD01-PD26) were synthesized from piperine for the management of Alzheimer's disease (AD). The compound PD07 showed significant inhibitory activity on ChEs, BACE1, and Aβ1-42 aggregation in in vitro studies. Further, compound PD07 effectively displaced the propidium iodide at the AChE PAS site. The compound PD07 exhibited significant lipophilicity in PAMPA studies. Additionally, PD07 demonstrated neuroprotective properties in the Aβ1-42 induced SH-SY5Y cell line. Furthermore, DFT calculations were performed using B3LYP/6-311G(d,p) basis sets to explore the PD07 physical and chemical properties. The compound PD07 showed a similar binding interaction profile at active sites of AChE, BuChE, and BACE1 proteins as compared to reference ligands (donepezil, tacrine, and BSD) in molecular docking and dynamic simulation studies. In acute oral toxicity studies, compound PD07 exhibited no toxicity symptoms up to 300 mg/kg, po. The compound PD07 (10 mg/kg, po) improved memory and cognition in scopolamine-induced amnesia rats. Further, PD07 increased ACh levels in the brain by inhibiting the AChE activity. The results from in vitro, in silico, and in vivo studies suggested that compound PD07 is a potent multitarget-directed lead from piperine to overcome Alzheimer's disease.

Antidiabetic agents as a novel treatment for Alzheimer's and Parkinson's disease

Therapeutic strategies for neurodegenerative disorders have commonly targeted individual aspects of the disease pathogenesis to little success. Neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD), are characterized by several pathological features. In AD and PD, there is an abnormal accumulation of toxic proteins, increased inflammation, decreased synaptic function, neuronal loss, increased astrocyte activation, and perhaps a state of insulin resistance. Epidemiological evidence has revealed a link between AD/PD and type 2 diabetes mellitus, with these disorders sharing some pathological commonalities. Such a link has opened up a promising avenue for repurposing antidiabetic agents in the treatment of neurodegenerative disorders. A successful therapeutic strategy for AD/PD would likely require a single or several agents which target the separate pathological processes in the disease. Targeting cerebral insulin signalling produces numerous neuroprotective effects in preclinical AD/PD brain models. Clinical trials have shown the promise of approved diabetic compounds in improving motor symptoms of PD and preventing neurodegenerative decline, with numerous further phase II trials and phase III trials underway in AD and PD populations. Alongside insulin signalling, targeting incretin receptors in the brain represents one of the most promising strategies for repurposing currently available agents for the treatment of AD/PD. Most notably, glucagon-like-peptide-1 (GLP-1) receptor agonists have displayed impressive clinical potential in preclinical and early clinical studies. In AD the GLP-1 receptor agonist, liraglutide, has been demonstrated to improve cerebral glucose metabolism and functional connectivity in small-scale pilot trials. Whilst in PD, the GLP-1 receptor agonist exenatide is effective in restoring motor function and cognition. Targeting brain incretin receptors reduces inflammation, inhibits apoptosis, prevents toxic protein aggregation, enhances long-term potentiation and autophagy as well as restores dysfunctional insulin signalling. Support is also increasing for the use of additional approved diabetic treatments, including intranasal insulin, metformin hydrochloride, peroxisome proliferator-activated nuclear receptor γ agonists, amylin analogs, and protein tyrosine phosphatase 1B inhibitors which are in the investigation for deployment in PD and AD treatment. As such, we provide a comprehensive review of several promising anti-diabetic agents for the treatment of AD and PD.

Glucagon-like peptide-1: a multi-faceted anti-inflammatory agent

Inflammation contributes to many chronic conditions. It is often associated with circulating pro-inflammatory cytokines and immune cells. GLP-1 levels correlate with disease severity. They are often elevated and can serve as markers of inflammation. Previous studies have shown that oxytocin, hCG, ghrelin, alpha-MSH and ACTH have receptor-mediated anti-inflammatory properties that can rescue cells from damage and death. These peptides have been studied well in the past century. In contrast, GLP-1 and its anti-inflammatory properties have been recognized only recently. GLP-1 has been proven to be a useful adjuvant therapy in type-2 diabetes mellitus, metabolic syndrome, and hyperglycemia. It also lowers HbA1C and protects cells of the cardiovascular and nervous systems by reducing inflammation and apoptosis. In this review we have explored the link between GLP-1, inflammation, and sepsis.

Associations between physical activity and cognitive dysfunction in older companion dogs: results from the Dog Aging Project

Canine cognitive dysfunction (CCD) is a form of dementia that shares many similarities with Alzheimer's disease. Given that physical activity is believed to reduce risk of Alzheimer's disease in humans, we explored the association between physical activity and cognitive health in a cohort of companion dogs, aged 6-18 years. We hypothesized that higher levels of physical activity would be associated with lower (i.e., better) scores on a cognitive dysfunction rating instrument and lower prevalence of dementia, and that this association would be robust when controlling for age, comorbidities, and other potential confounders. Our sample included 11,574 companion dogs enrolled through the Dog Aging Project, of whom 287 had scores over the clinical threshold for CCD. In this observational, cross-sectional study, we used owner-reported questionnaire data to quantify dog cognitive health (via a validated scale), physical activity levels, health conditions, training history, and dietary supplements. We fit regression models with measures of cognitive health as the outcome, and physical activity-with several important covariates-as predictors. We found a significant negative relationship between physical activity and current severity of cognitive dysfunction symptoms (estimate =  - 0.10, 95% CI: - 0.11 to - 0.08, p < 0.001), extent of symptom worsening over a 6-month interval (estimate =  - 0.07, 95% CI: - 0.09 to - 0.05, p < 0.001), and whether a dog reached a clinical level of CCD (odds ratio = 0.53, 95% CI: 0.45 to 0.63, p < 0.001). Physical activity was robustly associated with better cognitive outcomes in dogs. Our findings illustrate the value of companion dogs as a model for investigating relationships between physical activity and cognitive aging, including aspects of dementia that may have translational potential for Alzheimer's disease. While the current study represents an important first step in identifying a relationship between physical activity and cognitive function, it cannot determine causality. Future studies are needed to rule out reverse causation by following the same dogs prospectively over time, and to evaluate causality by administering physical activity interventions.

Perinatal diesel exhaust exposure causes persistent changes in the brains of aged mice: An assessment of behavioral and biochemical endpoints related to neurodegenerative disease

Epidemiological studies support an association between air pollution exposure, specifically particulate matter (PM), and neurodegenerative disease. Diesel exhaust (DE) is a principal component of ambient air pollution and a major contributor of PM. Our study aimed to examine whether early-life perinatal DE exposure is sufficient to affect behavioral and biochemical endpoints related to Alzheimer's disease later in life. To achieve this, mice were perinatally exposed (embryonic day 0-postnatal day 21) to DE (250-300 μg/m3 ) or filtered air (FA), and allowed to reach aged status (>18 months). Mice underwent behavioral assessment at 6 and 20 months of age, with tissue collected at 22 months for biochemical endpoints. At 6 months, minimal changes were noted in home-cage behavior of DE treated animals. At 20 months, an alternation deficit was noted with the T-maze, although no difference was seen in the object location task or any home-cage metrics. DE exposure did not alter the expression of Aβ42, phosphorylated tau S199, or total tau. However, IBA-1 protein, a microglial activation marker, was significantly higher in DE exposed animals. Further, lipid peroxidation levels were significantly higher in the DE exposed animals compared to FA controls. Cytokine levels were largely unchanged with DE exposure, suggesting a lack of inflammation despite persistent lipid peroxidation. Taken together, the findings of this study support that perinatal exposure alone is sufficient to cause lasting changes in the brain, although the effects appear to be less striking than those previously reported in younger animals, suggesting some effects do not persist over time. These findings are encouraging from a public health standpoint and support the aggressive reduction of DE emissions to reduce lifetime exposure and potentially reduce disease outcome.

Aberrant accumulation of age- and disease-associated factors following neural probe implantation in a mouse model of Alzheimer's disease

Electrical stimulation has had a profound impact on our current understanding of nervous system physiology and provided viable clinical options for addressing neurological dysfunction within the brain. Unfortunately, the brain's immune suppression of indwelling microelectrodes currently presents a major roadblock in the long-term application of neural recording and stimulating devices. In some ways, brain trauma induced by penetrating microelectrodes produces similar neuropathology as debilitating brain diseases, such as Alzheimer's disease (AD), while also suffering from end-stage neuron loss and tissue degeneration. To understand whether there may be any parallel mechanisms at play between brain injury from chronic microelectrode implantation and those of neurodegenerative disorder, we used two-photon microscopy to visualize the accumulation, if any, of age- and disease-associated factors around chronically implanted electrodes in both young and aged mouse models of AD. With this approach, we determined that electrode injury leads to aberrant accumulation of lipofuscin, an age-related pigment, in wild-type and AD mice alike. Furthermore, we reveal that chronic microelectrode implantation reduces the growth of pre-existing amyloid plaques while simultaneously elevating amyloid burden at the electrode-tissue interface. Lastly, we uncover novel spatial and temporal patterns of glial reactivity, axonal and myelin pathology, and neurodegeneration related to neurodegenerative disease around chronically implanted microelectrodes. This study offers multiple novel perspectives on the possible neurodegenerative mechanisms afflicting chronic brain implants, spurring new potential avenues of neuroscience investigation and design of more targeted therapies for improving neural device biocompatibility and treatment of degenerative brain disease.

Spatial Disorientation Under Dark Conditions Across Development in an Alzheimer's Disease Mouse Model

Alzheimer's disease (AD) is associated with hippocampal neuropathology and cognitive impairments, including wandering behavior or becoming lost in a familiar environment. Wandering behavior is severe and manifests early in life for people with specific genetic mutations. Genetic mouse models of AD have been developed to characterize the onset and progression of behavioral deficits that represent human behaviors, such as wandering, to test the efficacy of therapeutics. It is not clear if current assessments of mouse models capture the onset of AD or a snapshot of its progression. Sequential analysis of open field behavior provides a robust, quick test to dissociate navigation cues that contribute to spatial disorientation, a feature of wandering. Despite potential utility in evaluating this feature of AD, little work has been reported using animal models of dementia in this task. Thus, we examined the use of different sources of information to maintain spatial orientation at two prodromal ages in female transgenic CRND8 AD (n = 17) and Control mice (n = 16). These mice exhibit amyloid plaques, a hallmark neuropathological feature of AD, that are associated with cognitive dysfunction at ∼three months of age. Spatial disorientation was observed at two months and more severely at four months under dark conditions, but performance was spared when visual environmental cues were available. This study provides documentation of impaired self-movement cue processing in AD mice, establishing the dark open field as a behavioral tool to characterize spatial disorientation associated with AD. These findings may accelerate future assessments of novel therapeutic interventions for neurological disorders.

Maitake Medicinal Mushroom, Grifola frondosa (Agaricomycetes), and Its Neurotrophic Properties: A Mini-Review

Neurodegeneration is one of the most common manifestations in an aging population. The occurrence of oxidative stress and neuroinflammation are the main contributors to the phenomenon. Neurologic conditions such as Alzheimer's disease (AD) and Parkinson's disease (PD) are challenging to treat due to their irreversible manner as well as the lack of effective treatment. Grifola frondosa (Dicks.: Fr.) S.F. Gray, or maitake mushroom, is believed to be a potential choice as a therapeutic agent for neurodegenerative diseases. G. frondosa is known to be a functional food that has a wide variety of medicinal purposes. Thus, this review emphasizes the neuroprotective effects and the chemical composition of G. frondosa. Various studies have described that G. frondosa can protect and proliferate neuronal cells through neurogenesis, antioxidative, anti-inflammatory, and anti-β-amyloid activities. The mechanism of action behind these therapeutic findings in various in vitro and in vivo models has also been intensively studied. In this mini review, we also summarized the chemical composition of G. frondosa to provide a better understanding of the presence of nutritional compounds in G. frondosa.

Costs and Benefits of Popular P-Value Correction Methods in Three Models of Quantitative Omic Experiments

The multiple hypothesis testing problem is inherent in large-scale quantitative "omic" experiments such as mass spectrometry-based proteomics. Yet, tools for comparing the costs and benefits of different p-value correction methods under different experimental conditions are lacking. We performed thousands of simulations of omic experiments under a range of experimental conditions and applied correction using the Benjamini-Hochberg (BH), Bonferroni, and permutation-based false discovery proportion (FDP) estimation methods. The tremendous false discovery rate (FDR) benefit of correction was confirmed in a range of different contexts. No correction method can guarantee a low FDP in a single experiment, but the probability of a high FDP is small when a high number and proportion of corrected p-values are significant. On average, correction decreased sensitivity, but the sensitivity costs of BH and permutation were generally modest compared to the FDR benefits. In a given experiment, observed sensitivity was always maintained or decreased by BH and Bonferroni, whereas it was often increased by permutation. Overall, permutation had better FDR and sensitivity than BH. We show how increasing sample size, decreasing variability, or increasing effect size can enable the detection of all true changes while still correcting p-values, and we present basic guidelines for omic experimental design. Analysis of an experimental proteomic data set with defined changes corroborated these trends. We developed an R Shiny web application for further exploration and visualization of these models, which we call the Simulator of P-value Multiple Hypothesis Correction (SIMPLYCORRECT) and a high-performance R package, permFDP, for easy use of the permutation-based FDP estimation method.

Dual functional antioxidant and butyrylcholinesterase inhibitors for the treatment of Alzheimer's disease: Design, synthesis and evaluation of novel melatonin-alkylbenzylamine hybrids

Here, we have designed and synthesized a series of melatonin-alkylbenzylamine hybrids as multitarget agents for the treatment of Alzheimer's disease (AD). Most of them exhibited a potent multifunctional profile involving cholinesterase inhibition and antioxidant effects. Among these compounds, compound 5 was most the potent antioxidant (ORAC = 5.13) and also an excellent selective inhibitor of BuChE (huBuChE IC₅₀ = 1.20 μM, huAChE IC₅₀ = 177.49 μM, SI = 147.91). Moreover, kinetic study indicated compound 5 was a mixed-type inhibitor for huBuChE. Furthermore, it could induce expression of the Nrf2 as well as its downstream markers at the protein level in cells. More importantly, compound 5 display no acute toxicity in mice at doses up to 2500 mg/kg. And we found compound 5 could improve memory function of scopolamine-induced amnesia mice. These results highlighted compound 5 as a possible hit molecule for further investigation of new anti-AD drugs.

A three-dimensional spheroid co-culture system of neurons and astrocytes derived from Alzheimer's disease patients for drug efficacy testing

Cell culture systems derived from the progenitor cells of human patients have many advantages over animal models for therapeutic drug testing and studies of disease pathogenesis. Here we describe a three-dimensional (3D) spheroid co-culture system of neurons and astrocytes derived from induced pluripotent stem cells-neural precursor cells (iPSCs-NPCs) of Alzheimer's disease (AD) patients or healthy individuals that can provide information on drug efficacy unobtainable by 2D co-culture or monoculture approaches. iPSCs-NPCs of healthy controls or AD patients were seeded onto 96-well U-bottom plates and incubated with neuronal differentiation medium for one week and with astrocytic medium for two weeks to replicate the temporal order of cell maturation during brain development. These 3D spheroid models expressed marker proteins for mature neurons and astrocytes. In particular, patient-derived spheroids showed beta-amyloid (Aβ) accumulation as revealed by thioflavin T (ThT) staining and ELISA. Aggregation of Aβ induced caspase activation and cell death, while the neuroprotectants nordihydroguaiaretic acid (NDGA) and curcumin (CU) reduced the levels of both ThT and caspase staining. Taken together, these results demonstrate the feasibility of our 3D spheroids combined with ThT and caspase staining as a patient-based anti-AD drug screening platform.

Microglial Expression of the Wnt Signaling Modulator DKK2 Differs between Human Alzheimer's Disease Brains and Mouse Neurodegeneration Models

Wnt signaling is crucial for synapse and cognitive function. Indeed, deficient Wnt signaling is causally related to increased expression of DKK1, an endogenous negative Wnt regulator, and synapse loss, both of which likely contribute to cognitive decline in Alzheimer's disease (AD). Increasingly, AD research efforts have probed the neuroinflammatory role of microglia, the resident immune cells of the CNS, which have furthermore been shown to be modulated by Wnt signaling. The DKK1 homolog DKK2 has been previously identified as an activated response and/or disease-associated microglia (DAM/ARM) gene in a mouse model of AD. Here, we performed a detailed analysis of DKK2 in mouse models of neurodegeneration, and in human AD brain. In APP/PS1 and APP^NL-G-F AD mouse model brains as well as in SOD1^G93A ALS mouse model spinal cords, but not in control littermates, we demonstrated significant microgliosis and microglial Dkk2 mRNA upregulation in a disease-stage-dependent manner. In the AD models, these DAM/ARM Dkk2⁺ microglia preferentially accumulated close to βAmyloid plaques. Furthermore, recombinant DKK2 treatment of rat hippocampal primary neurons blocked WNT7a-induced dendritic spine and synapse formation, indicative of an anti-synaptic effect similar to that of DKK1. In stark contrast, no such microglial DKK2 upregulation was detected in the postmortem human frontal cortex from individuals diagnosed with AD or pathologic aging. In summary, the difference in microglial expression of the DAM/ARM gene DKK2 between mouse models and human AD brain highlights the increasingly recognized limitations of using mouse models to recapitulate facets of human neurodegenerative disease.

Inflammation context in Alzheimer's disease, a relationship intricate to define

Alzheimer's disease (AD), the most common form of dementia, is characterized by the accumulation of amyloid β (Aβ) and hyperphosphorylated tau protein aggregates. Importantly, Aβ and tau species are able to activate astrocytes and microglia, which release several proinflammatory cytokines, such as tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β), together with reactive oxygen (ROS) and nitrogen species (RNS), triggering neuroinflammation. However, this inflammatory response has a dual function: it can play a protective role by increasing Aβ degradation and clearance, but it can also contribute to Aβ and tau overproduction and induce neurodegeneration and synaptic loss. Due to the significant role of inflammation in the pathogenesis of AD, several inflammatory mediators have been proposed as AD markers, such as TNF-α, IL-1β, Iba-1, GFAP, NF-κB, TLR2, and MHCII. Importantly, the use of anti-inflammatory drugs such as NSAIDs has emerged as a potential treatment against AD. Moreover, diseases related to systemic or local inflammation, including infections, cerebrovascular accidents, and obesity, have been proposed as risk factors for the development of AD. In the following review, we focus on key inflammatory processes associated with AD pathogenesis.

Modelling Alzheimer's disease using human brain organoids: current progress and challenges

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterised by gradual memory loss and declining cognitive and executive functions. AD is the most common cause of dementia, affecting more than 50 million people worldwide, and is a major health concern in society. Despite decades of research, the cause of AD is not well understood and there is no effective curative treatment so far. Therefore, there is an urgent need to increase understanding of AD pathophysiology in the hope of developing a much-needed cure. Dissecting the cellular and molecular mechanisms of AD pathogenesis has been challenging as the most commonly used model systems such as transgenic animals and two-dimensional neuronal culture do not fully recapitulate the pathological hallmarks of AD. The recent advent of three-dimensional human brain organoids confers unique opportunities to study AD in a humanised model system by encapsulating many aspects of AD pathology. In the present review, we summarise the studies of AD using human brain organoids that recapitulate the major pathological components of AD including amyloid-β and tau aggregation, neuroinflammation, mitochondrial dysfunction, oxidative stress and synaptic and circuitry dysregulation. Additionally, the current challenges and future directions of the brain organoids modelling system are discussed.

Artificial intelligence-driven meta-analysis of brain gene expression identifies novel gene candidates and a role for mitochondria in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia. There is no treatment and AD models have focused on a small subset of genes identified in familial AD. Microarray studies have identified thousands of dysregulated genes in the brains of patients with AD yet identifying the best gene candidates to both model and treat AD remains a challenge. We performed a meta-analysis of microarray data from the frontal cortex (n = 697) and cerebellum (n = 230) of AD patients and healthy controls. A two-stage artificial intelligence approach, with both unsupervised and supervised machine learning, combined with a functional network analysis was used to identify functionally connected and biologically relevant novel gene candidates in AD. We found that in the frontal cortex, genes involved in mitochondrial energy, ATP, and oxidative phosphorylation, were the most significant dysregulated genes. In the cerebellum, dysregulated genes were involved in mitochondrial cellular biosynthesis (mitochondrial ribosomes). Although there was little overlap between dysregulated genes between the frontal cortex and cerebellum, machine learning models comprised of this overlap. A further functional network analysis of these genes identified that two downregulated genes, ATP5L and ATP5H, which both encode subunits of ATP synthase (mitochondrial complex V) may play a role in AD. Combined, our results suggest that mitochondrial dysfunction, particularly a deficit in energy homeostasis, may play an important role in AD.

The Molecular Effects of Environmental Enrichment on Alzheimer's Disease

Environmental enrichment (EE) is an environmental paradigm encompassing sensory, cognitive, and physical stimulation at a heightened level. Previous studies have reported the beneficial effects of EE in the brain, particularly in the hippocampus. EE improves cognitive function as well as ameliorates depressive and anxiety-like behaviors, making it a potentially effective neuroprotective strategy against neurodegenerative diseases such as Alzheimer's disease (AD). Here, we summarize the current evidence for EE as a neuroprotective strategy as well as the potential molecular pathways that can explain the effects of EE from a biochemical perspective using animal models. The effectiveness of EE in enhancing brain activity against neurodegeneration is explored with a view to differences present in early and late life EE exposure, with its potential application in human being discussed. We discuss EE as one of the non pharmacological approaches in preventing or delaying the onset of AD for future research.

Building in vitro models of the brain to understand the role of APOE in Alzheimer's disease

Alzheimer's disease (AD) is a devastating, complex, and incurable disease that represents an increasingly problematic global health issue. The etiology of sporadic AD that accounts for a vast majority of cases remains poorly understood, with no effective therapeutic interventions. Genetic studies have identified AD risk genes including the most prominent, APOE, of which the ɛ4 allele increases risk in a dose-dependent manner. A breakthrough discovery enabled the creation of human induced pluripotent stem cells (hiPSCs) that can be differentiated into various brain cell types, facilitating AD research in genetically human models. Herein, we provide a brief background on AD in the context of APOE susceptibility and feature work employing hiPSC-derived brain cell and tissue models to interrogate the contribution of APOE in driving AD pathology. Such models have delivered crucial insights into cellular mechanisms and cell type-specific roles underlying the perturbed biological functions that trigger pathogenic cascades and propagate neurodegeneration. Collectively, hiPSC-based models are envisioned to be an impactful platform for uncovering fundamental AD understanding, with high translational value toward AD drug discovery and testing.

APP Knock-In Mice Produce E22P-Aβ Exhibiting an Alzheimer's Disease-like Phenotype with Dysregulation of Hypoxia-Inducible Factor Expression

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that requires further pathological elucidation to establish effective treatment strategies. We previously showed that amyloid β (Aβ) toxic conformer with a turn at positions 22-23 is essential for forming highly toxic oligomers. In the present study, we evaluated phenotypic changes with aging in AD model AppNL-P-F/NL-P-F (NL-P-F) mice with Swedish mutation (NL), Iberian mutation (F), and mutation (P) overproducing E22P-Aβ, a mimic of toxic conformer utilizing the knock-in technique. Furthermore, the role of the toxic conformer in AD pathology was investigated. NL-P-F mice produced soluble toxic conformers from an early age. They showed impaired synaptic plasticity, glial cell activation, and cognitive decline, followed by the accumulation of Aβ plaques and tau hyperphosphorylation. In addition, the protein expression of hypoxia-inducible factor (HIF)-1α was increased, and gene expression of HIF-3α was decreased in NL-P-F mice. HIF dysregulation due to the production of soluble toxic conformers may be involved in AD pathology in NL-P-F mice. This study could reveal the role of a highly toxic Aβ on AD pathogenesis, thereby contributing to the development of a novel therapeutic strategy targeting the toxic conformer.

Amelioration of intracerebroventricular streptozotocin-induced cognitive dysfunction by Ocimum sanctum L. through the modulation of inflammation and GLP-1 levels

DPP-4 inhibitors have been shown to reverse amyloid deposition in Alzheimer's disease (AD) patients with cognitive impairment. Ocimum sanctum L. leaves reported the presence of important phytoconstituents which are reported to have DPP-4 inhibitory activity. To investigate the effects of petroleum ether extract of Ocimum sanctum L. (PEOS) in Intracerebroventricular streptozotocin (ICV-STZ) induced AD rats. ICV-STZ (3 mg/kg) was injected bilaterally into male Wistar rats, while sham animals received the artificial CSF. The ICV-STZ-induced rats were administered with three doses of PEOS (100, 200, and 400 mg/kg, p.o.) for thirty days. All experimental rats were subjected to behaviour parameters (radial arm maze task and novel object recognition test), neurochemical parameters such as GLP-1, Aβ42, and TNF-α levels, and histopathological examination (Congo red staining) of the left brain hemisphere. PEOS significantly reversed the spatial learning and memory deficit exhibited by ICV-STZ-induced rats. Furthermore, PEOS also shows promising results in retreating Aβ deposition, TNF α, and increasing GLP-1 levels. The histopathological study also showed a significant dose-dependent reduction in amyloid plaque formation and dense granule in PEOS -treated rats as compared to the ICV-STZ induced rats (Negative control). The results show that extract of Ocimum sanctum L. attenuated ICV-STZ-induced learning and memory deficits in rats and has the potential to be employed in the therapy of AD.

Mitochondrial Alterations in Neurons Derived from the Murine AppNL-F Knock-In Model of Alzheimer’s Disease

Background: Alzheimer’s disease (AD) research has relied on mouse models overexpressing human mutant A βPP; however, newer generation knock-in models allow for physiological expression of amyloid-β protein precursor (AβPP) containing familial AD mutations where murine AβPP is edited with a humanized amyloid-β (Aβ) sequence. The AppNL-F mouse model has shown substantial similarities to AD brains developing late onset cognitive impairment. Objective: In this study, we aimed to characterize mature primary cortical neurons derived from homozygous AppNL-F embryos, especially to identify early mitochondrial alterations in this model. Methods: Primary cultures of AppNL-F neurons kept in culture for 12–15 days were used to measure Aβ levels, secretase activity, mitochondrial functions, mitochondrial-ER contacts, synaptic function, and cell death. Results: We detected higher levels of Aβ42 released from AppNL-F neurons as compared to wild-type neurons. AppNL-F neurons, also displayed an increased Aβ42/Aβ40 ratio, similar to adult AppNL-F mouse brain. Interestingly, we found an upregulation in mitochondrial oxygen consumption with concomitant downregulation in glycolytic reserve. Furthermore, AppNL-F neurons were more susceptible to cell death triggered by mitochondrial electron transport chain inhibition. Juxtaposition between ER and mitochondria was found to be substantially upregulated, which may account for upregulated mitochondrial-derived ATP production. However, anterograde mitochondrial movement was severely impaired in this model along with loss in synaptic vesicle protein and impairment in pre- and post-synaptic function. Conclusion: We show that widespread mitochondrial alterations can be detected in AppNL-F neurons in vitro, where amyloid plaque deposition does not occur, suggesting soluble and oligomeric Aβ-species being responsible for these alterations.

Clinical relevance of biomarkers, new therapeutic approaches, and role of post-translational modifications in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder that causes progressive loss of cognitive functions like thinking, memory, reasoning, behavioral abilities, and social skills thus affecting the ability of a person to perform normal daily functions independently. There is no definitive cure for this disease, and treatment options available for the management of the disease are not very effective as well. Based on histopathology, AD is characterized by the accumulation of insoluble deposits of amyloid beta (Aβ) plaques and neurofibrillary tangles (NFTs). Although several molecular events contribute to the formation of these insoluble deposits, the aberrant post-translational modifications (PTMs) of AD-related proteins (like APP, Aβ, tau, and BACE1) are also known to be involved in the onset and progression of this disease. However, early diagnosis of the disease as well as the development of effective therapeutic approaches is impeded by lack of proper clinical biomarkers. In this review, we summarized the current status and clinical relevance of biomarkers from cerebrospinal fluid (CSF), blood and extracellular vesicles involved in onset and progression of AD. Moreover, we highlight the effects of several PTMs on the AD-related proteins, and provide an insight how these modifications impact the structure and function of proteins leading to AD pathology. Finally, for disease-modifying therapeutics, novel approaches, and targets are discussed for the successful treatment and management of AD.

Age-dependent microstructure alterations in 5xFAD mice by high-resolution diffusion tensor imaging

Purpose

To evaluate the age-dependent microstructure changes in 5xFAD mice using high-resolution diffusion tensor imaging (DTI).

Methods

The 5xFAD mice at 4, 7.5, and 12 months and the wild-type controls at 4 months were scanned at 9.4T using a 3D echo-planar imaging (EPI) pulse sequence with the isotropic spatial resolution of 100 μm. The b-value was 3000 s/mm² for all the diffusion MRI scans. The samples were also acquired with a gradient echo pulse sequence at 50 μm isotropic resolution. The microstructure changes were quantified with DTI metrics, including fractional anisotropy (FA) and mean diffusivity (MD). The conventional histology was performed to validate with MRI findings.

Results

The FA values (p = 0.028) showed significant differences in the cortex between wild-type (WT) and 5xFAD mice at 4 months, while hippocampus, anterior commissure, corpus callosum, and fornix showed no significant differences for either FA and MD. FA values of 5xFAD mice gradually decreased in cortex (0.140 ± 0.007 at 4 months, 0.132 ± 0.008 at 7.5 months, 0.126 ± 0.013 at 12 months) and fornix (0.140 ± 0.007 at 4 months, 0.132 ± 0.008 at 7.5 months, 0.126 ± 0.013 at 12 months) with aging. Both FA (p = 0.029) and MD (p = 0.037) demonstrated significant differences in corpus callosum between 4 and 12 months age old. FA and MD were not significantly different in the hippocampus or anterior commissure. The age-dependent microstructure alterations were better captured by FA when compared to MD.

Conclusion

FA showed higher sensitivity to monitor amyloid deposition in 5xFAD mice. DTI may be utilized as a sensitive biomarker to monitor beta-amyloid progression for preclinical studies.

Characterization of Early Alzheimer's Disease-Like Pathological Alterations in Non-Human Primates with Aging: A Pilot Study

BACKGROUND

Sporadic or late onset Alzheimer's disease (LOAD) is a multifactorial neurodegenerative disease with aging the most known risk factor. Non-human primates (NHPs) may serve as an excellent model to study LOAD because of their close similarity to humans in many aspects including neuroanatomy and neurodevelopment. Recent studies reveal AD-like pathology in old NHPs.

OBJECTIVE

In this pilot study, we took advantage of brain samples from 6 Cynomolgus macaques that were divided into two groups: middle aged (average age 14.81 years) and older (average age 19.33 years). We investigated whether AD-like brain pathologies are present in the NHPs.

METHODS

We used immunohistochemical method to examine brain Aβ pathology and neuron density. We applied biochemical assays to measure tau phosphorylation and multiple signaling pathways indicated in AD. We performed electron microscopy experiments to study alterations of postsynaptic density and mitochondrial morphology in the brain of NHPs.

RESULTS

We found multiple AD-like pathological alteration in the prefrontal cortex (but not in the hippocampus) of the older NHPs including tau hyperphosphorylation, increased activity of AMP-activated protein kinase (AMPK), decreased expression of protein phosphatase 2A (PP2A), impairments in mitochondrial morphology, and postsynaptic densities formation.

CONCLUSION

These findings may provide insights into the factors contributing to the development of LOAD, particularly during the early stage transitioning from middle to old age. Future endeavors are warranted to elucidate mechanisms underlying the regional (and perhaps cellular) vulnerability with aging and the functional correlation of such pathological changes in NHPs.

APOE4 confers transcriptomic and functional alterations to primary mouse microglia

Common genetic variants in more than forty loci modulate risk for Alzheimer's disease (AD). AD risk alleles are enriched within enhancers active in myeloid cells, suggesting that microglia, the brain-resident macrophages, may play a key role in the etiology of AD. A major genetic risk factor for AD is Apolipoprotein E (APOE) genotype, with the ε4/ε4 (E4) genotype increasing risk for AD by approximately 15 fold compared to the most common ε3/ε3 (E3) genotype. However, the impact of APOE genotype on microglial function has not been thoroughly investigated. To address this, we cultured primary microglia from mice in which both alleles of the mouse Apoe gene have been humanized to encode either human APOE ε3 or APOE ε4. Relative to E3 microglia, E4 microglia exhibit altered morphology, increased endolysosomal mass, increased cytokine/chemokine production, and increased lipid and lipid droplet accumulation at baseline. These changes were accompanied by decreased translation and increased phosphorylation of eIF2ɑ and eIF2ɑ-kinases that participate in the integrated stress response, suggesting that E4 genotype leads to elevated levels of cellular stress in microglia relative to E3 genotype. Using live-cell imaging and flow cytometry, we also show that E4 microglia exhibited increased phagocytic uptake of myelin and other substrates compared to E3 microglia. While transcriptomic profiling of myelin-challenged microglia revealed a largely overlapping response profile across genotypes, differential enrichment of genes in interferon signaling, extracellular matrix and translation-related pathways was identified in E4 versus E3 microglia both at baseline and following myelin challenge. Together, our results suggest E4 genotype confers several important functional alterations to microglia even prior to myelin challenge, providing insight into the molecular and cellular mechanisms by which APOE4 may increase risk for AD.

Bacterial Amyloid Curli Associated Gut Epithelial Neuroendocrine Activation Predominantly Observed in Alzheimer's Disease Mice with Central Amyloid-β Pathology

BACKGROUND

Substantial evidence from recent research suggests an influential and underappreciated force in Alzheimer's disease (AD) pathogenesis: the pathological signals originate from outside the brain. Pathogenic bacteria produce amyloid-like proteins "curli" that form biofilms and show functional similarities to human amyloid-β (Aβ). These proteins may contribute to neurological disease progression via signaling cascade from the gut to the brain.

OBJECTIVE

We propose that curli causes neuroendocrine activation from the gut to brain that promotes central Aβ pathology.

METHODS

PGP9.5 and TLR2 levels in response to curli in the lumen of Tg2576 AD mice were analyzed by immunohistochemical and qRT-PCR analysis. Western blot and human 3D in vitro enteroids culture systems were also used. 16S rRNA gene sequencing was used to investigate bacterial dysbiosis.

RESULTS

We found significant increase in bacterial-amyloid curli with elevated TLR2 at the mRNA level in the pre- and symptomatic Tg-AD gut compared to littermate WT controls. This data associates with increased gram-positive bacterial colonization in the ileum of the symptomatic AD mice. We found fundamental evidence for vagus nerve activation in response to bacterial curli. Neuroendocrine marker PGP9.5 was significantly elevated in the gut epithelium of symptomatic AD mice, and this was colocalized with increased TLR2 expression. Enteroids, 3D-human ileal mini-gut monolayer in vitro model system also revealed increase levels of TLR2 upon stimulation with purified bacterial curli fibrils.

CONCLUSION

These findings reveal the importance of pathological changes within the gut-vagus-brain signaling in response to luminal bacterial amyloid that might play a vital role in central Aβ pathogenesis seen in the AD brain.

DNA Damage Increases Secreted Aβ40 and Aβ42 in Neuronal Progenitor Cells: Relevance to Alzheimer's Disease

BACKGROUND

Recent studies suggest a strong association between neuronal DNA damage, elevated levels of amyloid-β (Aβ), and regions of the brain that degenerate in Alzheimer's disease (AD).

OBJECTIVE

To investigate the nature of this association, we tested the hypothesis that extensive DNA damage leads to an increase in Aβ40 and Aβ42 generation.

METHODS

We utilized an immortalized human neuronal progenitor cell line (NPCs), ReN VM GA2. NPCs or 20 day differentiated neurons were treated with hydrogen peroxide or etoposide and allowed to recover for designated times. Sandwich ELISA was used to assess secreted Aβ40 and Aβ42. Western blotting, immunostaining, and neutral comet assay were used to evaluate the DNA damage response and processes indicative of AD pathology.

RESULTS

We determined that global hydrogen peroxide damage results in increased cellular Aβ40 and Aβ42 secretion 24 h after treatment in ReN GA2 NPCs. Similarly, DNA double strand break (DSB)-specific etoposide damage leads to increased Aβ40 and Aβ42 secretion 2 h and 4 h after treatment in ReN GA2 NPCs. In contrast, etoposide damage does not increase Aβ40 and Aβ42 secretion in post-mitotic ReN GA2 neurons.

CONCLUSION

These findings provide evidence that in our model, DNA damage is associated with an increase in Aβ secretion in neuronal progenitors, which may contribute to the early stages of neuronal pathology in AD.

The Impact of the hAPP695SW Transgene and Associated Amyloid-β Accumulation on Murine Hippocampal Biochemical Pathways

Background: Alzheimer’s disease (AD) is a neurodegenerative disease characterized by the accumulation of amyloid-β (Aβ) peptide in the brain. Objective: Gain a better insight into alterations in major biochemical pathways underlying AD. Methods: We compared metabolomic profiles of hippocampal tissue of 20-month-old female Tg2576 mice expressing the familial AD-associated hAPP695SW transgene with their 20-month-old wild type female littermates. Results: The hAPP695SW transgene causes overproduction and accumulation of Aβ in the brain. Out of 180 annotated metabolites, 54 metabolites differed (30 higher and 24 lower in Tg2576 versus wild-type hippocampal tissue) and were linked to the amino acid, nucleic acid, glycerophospholipid, ceramide, and fatty acid metabolism. Our results point to 1) heightened metabolic activity as indicated by higher levels of urea, enhanced fatty acid β-oxidation, and lower fatty acid levels; 2) enhanced redox regulation; and 3) an imbalance of neuro-excitatory and neuro-inhibitory metabolites in hippocampal tissue of aged hAPP695SW transgenic mice. Conclusion: Taken together, our results suggest that dysregulation of multiple metabolic pathways associated with a concomitant shift to an excitatory-inhibitory imbalance are contributing mechanisms of AD-related pathology in the Tg2576 mouse.

Gamma Oscillations in Alzheimer’s Disease and Their Potential Therapeutic Role

Despite decades of research, Alzheimer’s Disease (AD) remains a lethal neurodegenerative disorder for which there are no effective treatments. This review examines the latest evidence of a novel and newly introduced perspective, which focuses on the restoration of gamma oscillations and investigates their potential role in the treatment of AD. Gamma brain activity (∼25–100 Hz) has been well-known for its role in cognitive function, including memory, and it is fundamental for healthy brain activity and intra-brain communication. Aberrant gamma oscillations have been observed in both mice AD models and human AD patients. A recent line of work demonstrated that gamma entrainment, through auditory and visual sensory stimulation, can effectively attenuate AD pathology and improve cognitive function in mice models of the disease. The first evidence from AD patients indicate that gamma entrainment therapy can reduce loss of functional connectivity and brain atrophy, improve cognitive function, and ameliorate several pathological markers of the disease. Even though research is still in its infancy, evidence suggests that gamma-based therapy may have a disease-modifying effect and has signified a new and promising era in AD research.

Alzheimer's Disease: Current Perspectives and Advances in Physiological Modeling

Though Alzheimer's disease (AD) is the most common cause of dementia, complete disease-modifying treatments are yet to be fully attained. Until recently, transgenic mice constituted most in vitro model systems of AD used for preclinical drug screening; however, these models have so far failed to adequately replicate the disease's pathophysiology. However, the generation of humanized APOE4 mouse models has led to key discoveries. Recent advances in stem cell differentiation techniques and the development of induced pluripotent stem cells (iPSCs) have facilitated the development of novel in vitro devices. These "microphysiological" systems-in vitro human cell culture systems designed to replicate in vivo physiology-employ varying levels of biomimicry and engineering control. Spheroid-based organoids, 3D cell culture systems, and microfluidic devices or a combination of these have the potential to replicate AD pathophysiology and pathogenesis in vitro and thus serve as both tools for testing therapeutics and models for experimental manipulation.

Neural Derivates of Canine Induced Pluripotent Stem Cells-Like Cells From a Mild Cognitive Impairment Dog

Domestic dogs are superior models for translational medicine due to greater anatomical and physiological similarities with humans than rodents, including hereditary diseases with human equivalents. Particularly with respect to neurodegenerative medicine, dogs can serve as a natural, more relevant model of human disease compared to transgenic rodents. Herein we report attempts to develop a canine-derived in vitro model for neurodegenerative diseases through the generation of induced pluripotent stem cells from a 14-year, 9-month-old female West Highland white terrier with mild cognitive impairment (MCI). Canine induced pluripotent stem cells-like cells (ciPSCLC) were generated using human OSKM and characterized by positive expression of pluripotency markers. Due to inefficient viral vector silencing we refer to them as ciPSCLCs. Subsequently, the ciPSCLC were subjected to neural induction according to two protocols both yielding canine neural progenitor cells (cNPCs), which expressed typical NPC markers. The cNPCs were cultured in neuron differentiation media for 3 weeks, resulting in the derivation of morphologically impaired neurons as compared to iPSC-derived human counterparts generated in parallel. The apparent differences encountered in this study regarding the neural differentiation potential of ciPSCLC reveals challenges and new perspectives to consider before using the canine model in translational neurological studies.

Harnessing cerebral organoids for Alzheimer's disease research

Alzheimer's disease (AD) is a devastating neurodegenerative disorder affecting the aging population. Despite many studies, there remains an urgent need to identify the root causes of AD, together with potential treatments. Cerebral organoid technology has made it possible to model human neurophysiology and disease with increasing accuracy in patient-derived tissue cultures. Here, we review the most recent advances in modeling AD in organoids and other engineered three-dimensional cell culture systems. Early studies demonstrated that familial AD patient-derived organoids robustly develop disease pathology. Ongoing work has expanded this focus to investigate the genetic and environmental causes of late-onset sporadic AD and harness organoids for high-throughput drug screens. Future organoid models will need to incorporate additional cell types and tissues implicated in disease pathogenesis, including microglia and vasculature. We anticipate the continuation of this rapid progress in developing cerebral organoid technology toward facilitating our understanding of and informing treatment strategies for AD.

MicroRNA-455-3p improves synaptic, cognitive functions and extends lifespan: Relevance to Alzheimer's disease

BACKGROUND

MicroRNA-455-3p is one of the highly conserved miRNAs involved in multiple cellular functions in humans and we explored its relevance to learning and memory functions in Alzheimer's disease (AD). Our recent in vitro studies exhibited the protective role of miR-455-3p against AD toxicities in reducing full-length APP and amyloid-β (Aβ) levels, and also in reducing defective mitochondrial biogenesis, impaired mitochondrial dynamics and synaptic deficiencies. In the current study, we sought to determine the function of miR-455-3p in mouse models.

METHODS

For the first time we generated both transgenic (TG) and knockout (KO) mouse models of miR-455-3p. We determined the lifespan extension, cognitive function, mitochondrial biogenesis, mitochondrial dynamics, mitochondrial morphology, dendritic spine density, synapse numbers and synaptic activity in miR-455-3p TG and KO mice.

RESULTS

MiR-455-3p TG mice lived 5 months longer than wild-type (WT) counterparts, whereas KO mice lived 4 months shorter than WT mice. Morris water maze test showed improved cognitive behavior, spatial learning and memory in miR-455-3p TG mice relative to age-matched WT mice and miR-455-3p KO mice. Further, mitochondrial biogenesis, dynamics and synaptic activities were enhanced in miR-455-3p TG mice, while these were reduced in KO mice. Overall, overexpressed miR-455-3p in mice displayed protective effects, whereas depleted miR-455-3p in mice exhibited deleterious effects in relation to lifespan, cognitive behavior, and mitochondrial and synaptic activities.

CONCLUSION

Both mouse models could be ideal research tools to understand the molecular basis of aging and its relevance to AD and other age-related diseases.

Exploring the microbiota-Alzheimer's disease linkage using short-term antibiotic treatment followed by fecal microbiota transplantation

Gut microbiota is proven to be involved in the development of beta amyloid (Aβ) pathology in Alzheimer's disease (AD). Since there are difficulties in translating microbiota findings based on germ-free mice into clinical practice, here, we used short-term antibiotic cocktail treatment to develop a novel model with a near-germ-free status and without impacting Aβ pathology. Three months old APP_SWE/PS1_ΔE9 mice were fed with antibiotic cocktails for two weeks by gavage to obtain a near "germ-free" status, and then received the donor fecal matter from the 16 months old APP_SWE/PS1_ΔE9 mice for 7 consecutive days. Fecal pellets were collected prior to antibiotics treatment, following antibiotic exposure, prior to and following fecal microbiota transplantation for gut microbiota analysis. Also, Aβ pathology, astrocyte and microglia morphology were further explored. Pre-antibiotic-treated mice successfully allowed engraftment of gut microbiota following 7 consecutive days gavage with aged APP_SWE/PS1_ΔE9 mice microbiota. Microbiota reconstitution by transplantation was largely attributable to the donor source (e.g. g_Coriobacteriaceae and g_Clostridium) and led to a significant increase in Aβ plaques. Surprisingly, astrocyte activation around Aβ plaques was suppressed rather than microglia, the well-recognized plaque phagocytic cell type in Aβ clearance, following microbiota engraftment. Our findings provide a novel framework for understanding the mechanisms of AD through the gut-brain axis and the translation of gut microbiota manipulation from bench to clinical practice.