Transgenic Mouse Models of Alzheimer's Disease: An Integrative Analysis

Measuring the replicability of our own research

In the study of transgenic mouse models of neurodevelopmental and neurodegenerative disorders, we use batteries of tests to measure deficits in behaviour and from the results of these tests, we make inferences about the mental states of the mice that we interpret as deficits in "learning", "memory", "anxiety", "depression", etc. This paper discusses the problems of determining whether a particular transgenic mouse is a valid mouse model of disease X, the problem of background strains, and the question of whether our behavioural tests are measuring what we say they are. The problem of the reliability of results is then discussed: are they replicable between labs and can we replicate our results in our own lab? This involves the study of intra- and inter- experimenter reliability. The variables that influence replicability and the importance of conducting a complete behavioural phenotype: sensory, motor, cognitive and social emotional behaviour are discussed. Then the thorny question of failure to replicate is examined: Is it a curse or a blessing? Finally, the role of failure in research and what it tells us about our research paradigms is examined.

Microglia and amyloid plaque formation in Alzheimer's disease - Evidence, possible mechanisms, and future challenges

Alzheimer's disease (AD) is a neurodegenerative disease characterized by cognitive decline that severely affects patients and their families. Genetic and environmental risk factors, such as viral infections, synergize to accelerate the aging-associated neurodegeneration. Genetic risk factors for late-onset AD (LOAD), which accounts for most AD cases, are predominantly implicated in microglial and immune cell functions. As such, microglia play a major role in formation of amyloid beta (Aβ) plaques, the major pathological hallmark of AD. This review aims to provide an overview of the current knowledge regarding the role of microglia in Aβ plaque formation, as well as their impact on morphological and functional diversity of Aβ plaques. Based on this discussion, we seek to identify challenges and opportunities in this field with potential therapeutic implications.

Age-related changes in species-typical behaviours in the 5xFAD mouse model of Alzheimer's disease from 4 to 16 months of age

Alzheimer's disease (AD) patients show age-related decreases in the ability to perform activities of daily living and the decline in these activities is related to the severity of neurobiological deterioration underlying the disease. The 5xFAD mouse model of AD shows age-related impairments in sensory- motor and cognitive function, but little is known about changes in species-typical behaviours that may model activities of daily living in AD patients. Therefore, we examined species-typical behaviours used as indices of exploration (rearing) and compulsivity (grooming) across six tests of anxiety-like behaviour or motor function in female 5xFAD mice from 3 to 16 months of age. Robust decreases in rearing were found in 5xFAD mice across all tests after 9 months of age, although few differences were observed in grooming. A fine-scale analysis of grooming, however, revealed a previously unresolved and spatially restricted pattern of grooming in 5xFAD mice at 13-16 months of age. We then examined changes in species-typical behaviours in the home-cage, and show impaired nest building in 5xFAD mice at all ages tested. Lastly, we examined the relationship between reduced species typical behaviours in 5xFAD mice and the presentation of freezing behaviour, a commonly used measure of memory for conditioned fear. These results showed that along with cognitive and sensory-motor behaviour, 5xFAD mice have robust age-related impairments in species-typical behaviours. Therefore, species typical behaviours in 5xFAD mice may help to model the decline in activities of daily living observed in AD patients, and may provide useful behavioural phenotypes for evaluating the pre-clinical efficacy of novel therapeutics for AD.

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.

Choline Metabolites Reverse Differentially the Habituation Deficit and Elevated Memory of Tau Null Drosophila

Impaired neuronal plasticity and cognitive decline are cardinal features of Alzheimer's disease and related Tauopathies. Aberrantly modified Tau protein and neurotransmitter imbalance, predominantly involving acetylcholine, have been linked to these symptoms. In Drosophila, we have shown that dTau loss specifically enhances associative long-term olfactory memory, impairs foot shock habituation, and deregulates proteins involved in the regulation of neurotransmitter levels, particularly acetylcholine. Interestingly, upon choline treatment, the habituation and memory performance of mutants are restored to that of control flies. Based on these surprising results, we decided to use our well-established genetic model to understand how habituation deficits and memory performance correlate with different aspects of choline physiology as an essential component of the neurotransmitter acetylcholine, the lipid phosphatidylcholine, and the osmoregulator betaine. The results revealed that the two observed phenotypes are reversed by different choline metabolites, implying that they are governed by different underlying mechanisms. This work can contribute to a broader knowledge about the physiologic function of Tau, which may be translated into understanding the mechanisms of Tauopathies.

What Threshold of Amyloid Reduction Is Necessary to Meaningfully Improve Cognitive Function in Transgenic Alzheimer's Disease Mice?

Background

Amyloid-β plaques (Aβ) are associated with Alzheimer's disease (AD). Pooled assessment of amyloid reduction in transgenic AD mice is critical for expediting anti-amyloid AD therapeutic research.

Objective

The mean threshold of Aβ reduction necessary to achieve cognitive improvement was measured via pooled assessment (n = 594 mice) of Morris water maze (MWM) escape latency of transgenic AD mice treated with substances intended to reduce Aβ via reduction of beta-secretase cleaving enzyme (BACE).

Methods

Machine learning and statistical methods identified necessary amyloid reduction levels using mouse data (e.g., APP/PS1, LPS, Tg2576, 3xTg-AD, control, wild type, treated, untreated) curated from 22 published studies.

Results

K-means clustering identified 4 clusters that primarily corresponded with level of Aβ: untreated transgenic AD control mice, wild type mice, and two clusters of transgenic AD mice treated with BACE inhibitors that had either an average 25% "medium reduction" of Aβ or 50% "high reduction" of Aβ compared to untreated control. A 25% Aβ reduction achieved a 28% cognitive improvement, and a 50% Aβ reduction resulted in a significant 32% improvement compared to untreated transgenic mice (p < 0.05). Comparatively, wild type mice had a mean 41% MWM latency improvement over untreated transgenic mice (p < 0.05). BACE reduction had a lesser impact on the ratio of Aβ42 to Aβ40. Supervised learning with an 80% -20% train-test split confirmed Aβ reduction was a key feature for predicting MWM escape latency (R2 = 0.8 to 0.95).

Conclusions

Results suggest a 25% reduction in Aβ as a meaningful treatment threshold for improving transgenic AD mouse cognition.

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.

A novel Zebrafish model of Alzheimer's disease by Aluminium chloride; involving nitro-oxidative stress, neuroinflammation and cholinergic pathway

Alzheimer's disease (AD) is the most common form of dementia and is a progressive neurodegenerative disorder of the brain. Most AD experimental animal models are pharmacological or transgenic in origin. The existing pharmacological approaches for developing AD are poorly developed and most of them fail to replicate the complete characteristics of disease pathology. Developing a cost-effective and reliable experimental animal model will meet this research gap. Zebrafish (ZF) are progressively emerging as a powerful drug discovery disease model to evaluate central nervous system (CNS) disorders due to their homologous similarities to humans as well as cost-effectiveness. The present research is conceptualized to develop and evaluate a reliable ZF AD model using aluminum chloride (AlCl3). Chronic exposure of 0.04 mM of AlCl3 for 28 days increased the expression of amyloid-β, phosphorylated tau protein and senile plaque development in the ZF brain. The observed changes were associated with learning and memory impairment. Furthermore, decreased brain-derived neurotrophic factor (BDNF) level and elevated oxidative stress indices, pro-inflammatory cytokines levels and acetylcholine esterase (AChE) activity was observed upon exposure to AlCl3 in the ZF brain. Chronic exposure to 0.04 mM of AlCl3 would be a cost-effective ZF AD model for pharmacological screening and may also be used to unravel the molecular mechanism underlying the neuropathology of the disease.

Vulnerability of the Hippocampus to Insults: Links to Blood-Brain Barrier Dysfunction

The hippocampus is a critical brain substrate for learning and memory; events that harm the hippocampus can seriously impair mental and behavioral functioning. Hippocampal pathophysiologies have been identified as potential causes and effects of a remarkably diverse array of medical diseases, psychological disorders, and environmental sources of damage. It may be that the hippocampus is more vulnerable than other brain areas to insults that are related to these conditions. One purpose of this review is to assess the vulnerability of the hippocampus to the most prevalent types of insults in multiple biomedical domains (i.e., neuroactive pathogens, neurotoxins, neurological conditions, trauma, aging, neurodegenerative disease, acquired brain injury, mental health conditions, endocrine disorders, developmental disabilities, nutrition) and to evaluate whether these insults affect the hippocampus first and more prominently compared to other brain loci. A second purpose is to consider the role of hippocampal blood-brain barrier (BBB) breakdown in either causing or worsening the harmful effects of each insult. Recent research suggests that the hippocampal BBB is more fragile compared to other brain areas and may also be more prone to the disruption of the transport mechanisms that act to maintain the internal milieu. Moreover, a compromised BBB could be a factor that is common to many different types of insults. Our analysis indicates that the hippocampus is more vulnerable to insults compared to other parts of the brain, and that developing interventions that protect the hippocampal BBB may help to prevent or ameliorate the harmful effects of many insults on memory and cognition.

Quantification of AMPA receptor subunits and RNA editing-related proteins in the J20 mouse model of Alzheimer's disease by capillary western blotting

Introduction

Accurate modelling of molecular changes in Alzheimer's disease (AD) dementia is crucial for understanding the mechanisms driving neuronal pathology and for developing treatments. Synaptic dysfunction has long been implicated as a mechanism underpinning memory dysfunction in AD and may result in part from changes in adenosine deaminase acting on RNA (ADAR) mediated RNA editing of the GluA2 subunit of AMPA receptors and changes in AMPA receptor function at the post synaptic cleft. However, few studies have investigated changes in proteins which influence RNA editing and notably, AD studies that focus on studying changes in protein expression, rather than changes in mRNA, often use traditional western blotting.

Methods

Here, we demonstrate the value of automated capillary western blotting to investigate the protein expression of AMPA receptor subunits (GluA1-4), the ADAR RNA editing proteins (ADAR1-3), and proteins known to regulate RNA editing (PIN1, WWP2, FXR1P, and CREB1), in the J20 AD mouse model. We describe extensive optimisation and validation of the automated capillary western blotting method, demonstrating the use of total protein to normalise protein load, in addition to characterising the optimal protein/antibody concentrations to ensure accurate protein quantification. Following this, we assessed changes in proteins of interest in the hippocampus of 44-week-old J20 AD mice.

Results

We observed an increase in the expression of ADAR1 p110 and GluA3 and a decrease in ADAR2 in the hippocampus of 44-week-old J20 mice. These changes signify a shift in the balance of proteins that play a critical role at the synapse. Regression analysis revealed unique J20-specific correlations between changes in AMPA receptor subunits, ADAR enzymes, and proteins that regulate ADAR stability in J20 mice, highlighting potential mechanisms mediating RNA-editing changes found in AD.

Discussion

Our findings in J20 mice generally reflect changes seen in the human AD brain. This study underlines the importance of novel techniques, like automated capillary western blotting, to assess protein expression in AD. It also provides further evidence to support the hypothesis that a dysregulation in RNA editing-related proteins may play a role in the initiation and/or progression of AD.

Meta-Analysis in Transgenic Alzheimer's Disease Mouse Models Reveals Opposite Brain Network Effects of Amyloid-β and Phosphorylated Tau Proteins

Background

Cognitive deficits observed in Alzheimer's disease (AD) patients have been correlated with altered hippocampal activity. Although the mechanism remains under extensive study, neurofibrillary tangles and amyloid plaques have been proposed as responsible for brain activity alterations. Aiming to unveil the mechanism, researchers have developed several transgenic models of AD. Nevertheless, the variability in hippocampal oscillatory alterations found in different genetic backgrounds and ages remains unclear.

Objective

To assess the oscillatory alterations in relation to animal developmental age and protein inclusion, amyloid-β (Aβ) load, and abnormally phosphorylated tau (pTau), we reviewed and analyzed the published data on peak power, frequency, and quantification of theta-gamma cross-frequency coupling (modulation index values).

Methods

To ensure that the search was as current as possible, a systematic review was conducted to locate and abstract all studies published from January 2000 to February 2023 that involved in vivo hippocampal local field potential recording in transgenic mouse models of AD.

Results

The presence of Aβ was associated with electrophysiological alterations that are mainly reflected in power increases, frequency decreases, and lower modulation index values. Concomitantly, pTau accumulation was associated with electrophysiological alterations that are mainly reflected in power decreases, frequency decreases, and no significant alterations in modulation index values.

Conclusions

In this study, we showed that electrophysiological parameters are altered from prodromal stages to the late stages of pathology. Thus, we found that Aβ deposition is associated with brain network hyperexcitability, whereas pTau deposition mainly leads to brain network hypoexcitability in transgenic models.

Genomic variation in neurons

Neurons born during the fetal period have extreme longevity and survive until the death of the individual because the human brain has highly limited tissue regeneration. The brain is comprised of an enormous variety of neurons each exhibiting different morphological and physiological characteristics and recent studies have further reported variations in their genome including chromosomal abnormalities, copy number variations, and single nucleotide mutations. During the early stages of brain development, the increasing number of neurons generated at high speeds has been proposed to lead to chromosomal instability. Additionally, mutations in the neuronal genome can occur in the mature brain. This observed genomic mosaicism in the brain can be produced by multiple endogenous and environmental factors and careful analyses of these observed variations in the neuronal genome remain central for our understanding of the genetic basis of neurological disorders.

Critical thinking of Alzheimer's transgenic mouse model: current research and future perspective

Transgenic models are useful tools for studying the pathogenesis of and drug development for Alzheimer's Disease (AD). AD models are constructed usually using overexpression or knock-in of multiple pathogenic gene mutations from familial AD. Each transgenic model has its unique behavioral and pathological features. This review summarizes the research progress of transgenic mouse models, and their progress in the unique mechanism of amyloid-β oligomers, including the first transgenic mouse model built in China based on a single gene mutation (PSEN1 V97L) found in Chinese familial AD. We further summarized the preclinical findings of drugs using the models, and their future application in exploring the upstream mechanisms and multitarget drug development in AD.

Impairment of cerebral vascular reactivity and resting blood flow in early-staged transgenic AD mice: in vivo optical imaging studies

Background

Alzheimer's disease (AD) is a neurodegenerative disorder with progressive cognitive decline in aging individuals that poses a significant challenge to patients due to an incomplete understanding of its etiology and lack of effective interventions. While "the Amyloid Cascade Hypothesis," the abnormal accumulation of amyloid-β in the brain, has been the most prevalent theory for AD, mounting evidence from clinical and epidemiological studies suggest that defects in cerebral vessels and hypoperfusion appear prior to other pathological manifestations and might contribute to AD, leading to "the Vascular Hypothesis." However, assessment of structural and functional integrity of the cerebral vasculature in vivo in the brain from AD rodent models has been challenging owing to the limited spatiotemporal resolution of conventional imaging technologies.

Methods

We employed two in vivo imaging technologies, i.e., Dual-Wavelength Imaging (DWI) and Optical Coherence Tomography (OCT), to evaluate cerebrovascular reactivity (CVR; responsiveness of blood vessels to vasoconstriction as triggered by cocaine) in a relatively large field of view of the cortex in vivo, and 3D quantitative cerebrovascular blood flow (CBF) imaging in living transgenic AD mice at single vessel resolution.

Results

Our results showed significantly impaired CVR and reduced CBF in basal state in transgenic AD mice compared to non-transgenic littermates in an early stage of AD progression. Changes in total hemoglobin (Δ[HbT]) in response to vasoconstriction were significantly attenuated in AD mice, especially in arteries and tissue, and the recovery time of Δ[HbT] after vasoconstriction was shorter for AD than WT in all types of vessels and cortical tissue, thereby indicating hypoperfusion and reduced vascular flexibility. Additionally, our 3D OCT images revealed that CBF velocities in arteries were slower and that the microvascular network was severely disrupted in the brain of AD mice.

Conclusions

These results suggest significant vascular impairment in basal CBF and dynamic CVR in the neurovascular network in a rodent model of AD at an early stage of the disease. These cutting-edge in vivo optical imaging tools offer an innovative venue for detecting early neurovascular dysfunction in relation to AD pathology and pave the way for clinical translation of early diagnosis and elucidation of AD pathogenesis in the future.

Detection of early proteomic alterations in 5xFAD Alzheimer's disease neonatal mouse model via MALDI-MSI

Alzheimer's disease (AD) is a debilitating neurodegenerative disorder, characterized by memory deficit and dementia. AD is considered a multifactorial disorder where multiple processes like amyloid-beta and tau accumulation, axonal degeneration, synaptic plasticity, and autophagic processes plays an important role. In this study, the spatial proteomic differences in the neonatal 5xFAD brain tissue were investigated using MALDI-MSI coupled to LC-MS/MS, and the statistically significantly altered proteins were associated with AD. Thirty-five differentially expressed proteins (DEPs) between the brain tissues of neonatal 5xFAD and their littermate mice were detected via MALDI-MSI technique. Among the 35 proteins identified, 26 of them were directly associated with AD. Our results indicated a remarkable resemblance in the protein expression profiles of neonatal 5xFAD brain when compared to AD patient specimens or AD mouse models. These findings showed that the molecular alterations in the AD brain existed even at birth and that some proteins are neurodegenerative presages in neonatal AD brain. HIGHLIGHTS: Spatial proteomic alterations in the 5xFAD mouse brain compared to the littermate. 26 out of 35 differentially expressed proteins associated with Alzheimer's disease (AD). Molecular alterations and neurodegenerative presages in neonatal AD brain. Alterations in the synaptic function an early and common neurobiological thread.

Systematic characterization of a non-transgenic Aβ1-42 amyloidosis model: synaptic plasticity and memory deficits in female and male mice

BACKGROUND

The amyloid-β (Aβ) cascade is one of the most studied theories linked to AD. In multiple models, Aβ accumulation and dyshomeostasis have shown a key role in AD onset, leading to excitatory/inhibitory imbalance, the impairments of synaptic plasticity and oscillatory activity, and memory deficits. Despite the higher prevalence of Alzheimer's disease (AD) in women compared to men, the possible sex difference is scarcely explored and the information from amyloidosis transgenic mice models is contradictory. Thus, given the lack of data regarding the early stages of amyloidosis in female mice, the aim of this study was to systematically characterize the effect of an intracerebroventricular (icv.) injection of Aβ1-42 on hippocampal-dependent memory, and on associated activity-dependent synaptic plasticity in the hippocampal CA1-CA3 synapse, in both male and female mice.

METHODS

To do so, we evaluated long term potentiation (LTP) with ex vivo electrophysiological recordings as well as encoding and retrieval of spatial (working, short- and long-term) and exploratory habituation memories using Barnes maze and object location, or open field habituation tasks, respectively.

RESULTS

Aβ1-42 administration impaired all forms of memory evaluated in this work, regardless of sex. This effect was displayed in a long-lasting manner (up to 17 days post-injection). LTP was inhibited at a postsynaptic level, both in males and females, and a long-term depression (LTD) was induced for the same prolonged period, which could underlie memory deficits.

CONCLUSIONS

In conclusion, our results provide further evidence on the shifting of LTP/LTD threshold due to a single icv. Aβ1-42 injection, which underly cognitive deficits in the early stages of AD. These long-lasting cognitive and functional alterations in males and females validate this model for the study of early amyloidosis in both sexes, thus offering a solid alternative to the inconsistence of amyloidosis transgenic mice models.

Preclinical Evaluation of Novel PET Probes for Dementia

The development of novel PET imaging agents that selectively bind specific dementia-related targets can contribute significantly to accurate, differential and early diagnosis of dementia causing diseases and support the development of therapeutic agents. Consequently, in recent years there has been a growing body of literature describing the development and evaluation of potential new promising PET tracers for dementia. This review article provides a comprehensive overview of novel dementia PET probes under development, classified by their target, and pinpoints their preclinical evaluation pathway, typically involving in silico, in vitro and ex/in vivo evaluation. Specific target-associated challenges and pitfalls, requiring extensive and well-designed preclinical experimental evaluation assays to enable successful clinical translation and avoid shortcomings observed for previously developed 'well-established' dementia PET tracers are highlighted in this review.

Differential Epigenetic Changes in the Dorsal Hippocampus of Male and Female SAMP8 Mice: A Preliminary Study

Alzheimer's disease (AD) is the most common age-related neurodegenerative disease characterized by memory loss and cognitive impairment. The causes of the disease are not well understood, as it involves a complex interaction between genetic, environmental, and epigenetic factors. SAMP8 mice have been proposed as a model for studying late-onset AD, since they show age-related learning and memory deficits as well as several features of AD pathogenesis. Epigenetic changes have been described in SAMP8 mice, although sex differences have never been evaluated. Here we used western blot and qPCR analyses to investigate whether epigenetic markers are differentially altered in the dorsal hippocampus, a region important for the regulation of learning and memory, of 9-month-old male and female SAMP8 mice. We found that H3Ac was selectively reduced in male SAMP8 mice compared to male SAMR1 control mice, but not in female mice, whereas H3K27me3 was reduced overall in SAMP8 mice. Moreover, the levels of HDAC2 and JmjD3 were increased, whereas the levels of HDAC4 and Dnmt3a were reduced in SAMP8 mice compared to SAMR1. In addition, levels of HDAC1 were reduced, whereas Utx and Jmjd3 were selectively increased in females compared to males. Although our results are preliminary, they suggest that epigenetic mechanisms in the dorsal hippocampus are differentially regulated in male and female SAMP8 mice.

Sex-Dependent Altered Expression of Cannabinoid Signaling in Hippocampal Astrocytes of the Triple Transgenic Mouse Model of Alzheimer's Disease: Implications for Controlling Astroglial Activity

Alzheimer's disease (AD) is a common neurodegenerative disease. In AD-associated neuroinflammation, astrocytes play a key role, finding glial activation both in patients and in animal models. The endocannabinoid system (ECS) is a neurolipid signaling system with anti-inflammatory and neuroprotective properties implicated in AD. Astrocytes respond to external cannabinoid signals and also have their own cannabinoid signaling. Our main objective is to describe the cannabinoid signaling machinery present in hippocampal astrocytes from 3×Tg-AD mice to determine if they are actively involved in the neurodegenerative process. Primary cultures of astrocytes from the hippocampus of 3×Tg-AD and non-Tg offspring were carried out. We analyzed the gene expression of astrogliosis markers, the main components of the ECS and Ca2+ signaling. 3×Tg-AD hippocampal astrocytes show low inflammatory activity (Il1b, Il6, and Gls) and Ca2+ flow (P2rx5 and Mcu), associated with low cannabinoid signaling (Cnr1 and Cnr2). These results were more evident in females. Our study corroborates glial involvement in AD pathology, in which cannabinoid signaling plays an important role. 3×Tg-AD mice born with hippocampal astrocytes with differential gene expression of the ECS associated with an innate attenuation of their activity. In addition, we show that there are sex differences from birth in this AD animal, which should be considered when investigating the pathogenesis of the disease.

Microbiome Alterations and Alzheimer's Disease: Modeling Strategies with Transgenic Mice

In the last decade, the role of the microbiota-gut-brain axis has been gaining momentum in the context of many neurodegenerative and metabolic disorders, including Alzheimer's disease (AD) and diabetes, respectively. Notably, a balanced gut microbiota contributes to the epithelial intestinal barrier maintenance, modulates the host immune system, and releases neurotransmitters and/or neuroprotective short-chain fatty acids. However, dysbiosis may provoke immune dysregulation, impacting neuroinflammation through peripheral-central immune communication. Moreover, lipopolysaccharide or detrimental microbial end-products can cross the blood-brain barrier and induce or at least potentiate the neuropathological progression of AD. Thus, after repeated failure to find a cure for this dementia, a necessary paradigmatic shift towards considering AD as a systemic disorder has occurred. Here, we present an overview of the use of germ-free and/or transgenic animal models as valid tools to unravel the connection between dysbiosis, metabolic diseases, and AD, and to investigate novel therapeutical targets. Given the high impact of dietary habits, not only on the microbiota but also on other well-established AD risk factors such as diabetes or obesity, consistent changes of lifestyle along with microbiome-based therapies should be considered as complementary approaches.

Anterograde and Retrograde Propagation of Inoculated Human Tau Fibrils and Tau Oligomers in a Non-Transgenic Rat Tauopathy Model

The tauopathy of Alzheimer's disease (AD) is first observed in the brainstem and entorhinal cortex, spreading trans-synaptically along specific pathways to other brain regions with recognizable patterns. Tau propagation occurs retrogradely and anterogradely (trans-synaptically) along a given pathway and through exosomes and microglial cells. Some aspects of in vivo tau spreading have been replicated in transgenic mice models expressing a mutated human MAPT (tau) gene and in wild-type mice. In this study, we aimed to characterize the propagation of different forms of tau species in non-transgenic 3-4 months old wild-type rats after a single unilateral injection of human tau oligomers and tau fibrils into the medial entorhinal cortex (mEC). We determined whether different variants of the inoculated human tau protein, tau fibrils, and tau oligomers, would induce similar neurofibrillary changes and propagate in an AD-related pattern, and how tau-related pathological changes would correlate with presumed cognitive impairment. We injected human tau fibrils and tau oligomers stereotaxically into the mEC and examined the distribution of tau-related changes at 3 days and 4, 8, and 11 months post-injection using antibodies AT8 and MC1, which reveal early phosphorylation and aberrant conformation of tau, respectively, HT7, anti-synaptophysin, and the Gallyas silver staining method. Human tau oligomers and tau fibrils exhibited some similarities and some differences in their ability to seed and propagate tau-related changes. Both human tau fibrils and tau oligomers rapidly propagated from the mEC anterogradely into the hippocampus and various parts of the neocortex. However, using a human tau-specific HT7 antibody, 3 days post-injection we found inoculated human tau oligomers in the red nucleus, primary motor, and primary somatosensory cortex, a finding not seen in animals inoculated with human tau fibrils. In animals inoculated with human tau fibrils, 3 days post-injection the HT7 antibody showed fibrils in the pontine reticular nucleus, a finding explained only by uptake of human tau fibrils by incoming presynaptic fibers to the mEC and retrograde transport of inoculated human tau fibrils to the brainstem. Rats inoculated with human tau fibrils showed as early as 4 months after inoculation a spread of phosphorylated tau protein at the AT8 epitopes throughout the brain, dramatically faster propagation of neurofibrillary changes than with human tau oligomers. The overall severity of tau protein changes 4, 8, and 11 months after inoculation of human tau oligomers and tau fibrils correlated well with spatial working memory and cognition impairments, as measured by the T-maze spontaneous alternation, novel object recognition, and object location tests. We concluded that this non-trangenic rat model of tauopathy, especially when using human tau fibrils, demonstrates rapidly developing pathologic alterations in neurons, synapses, and identifiable pathways together with cognitive and behavioral changes, through the anterograde and retrograde spreading of neurofibrillary degeneration. Therefore, it represents a promising model for future experimental studies of primary and secondary tauopathies, especially AD.

Poor Translatability of Biomedical Research Using Animals - A Narrative Review

The failure rate for the translation of drugs from animal testing to human treatments remains at over 92%, where it has been for the past few decades. The majority of these failures are due to unexpected toxicity - that is, safety issues revealed in human trials that were not apparent in animal tests - or lack of efficacy. However, the use of more innovative tools, such as organs-on-chips, in the preclinical pipeline for drug testing, has revealed that these tools are more able to predict unexpected safety events prior to clinical trials and so can be used for this, as well as for efficacy testing. Here, we review several disease areas, and consider how the use of animal models has failed to offer effective new treatments. We also make some suggestions as to how the more human-relevant new approach methodologies might be applied to address this.

Novel Strategy for Alzheimer’s Disease Treatment through Oral Vaccine Therapy with Amyloid Beta

Alzheimer’s disease (AD) is a neuropathology characterized by progressive cognitive impairment and dementia. The disease is attributed to senile plaques, which are aggregates of amyloid beta (Aβ) outside nerve cells; neurofibrillary tangles, which are filamentous accumulations of phosphorylated tau in nerve cells; and loss of neurons in the brain tissue. Immunization of an AD mouse model with Aβ-eliminated pre-existing senile plaque amyloids and prevented new accumulation. Furthermore, its effect showed that cognitive function can be improved by passive immunity without side effects, such as lymphocyte infiltration in AD model mice treated with vaccine therapy, indicating the possibility of vaccine therapy for AD. Further, considering the possibility of side effects due to direct administration of Aβ, the practical use of the safe oral vaccine, which expressed Aβ in plants, is expected. Indeed, administration of this oral vaccine to Alzheimer’s model mice reduced Aβ accumulation in the brain. Moreover, almost no expression of inflammatory IgG was observed. Therefore, vaccination prior to Aβ accumulation or at an early stage of accumulation may prevent Aβ from causing AD.

Chaperone-Dependent Mechanisms as a Pharmacological Target for Neuroprotection

Modern pharmacotherapy of neurodegenerative diseases is predominantly symptomatic and does not allow vicious circles causing disease development to break. Protein misfolding is considered the most important pathogenetic factor of neurodegenerative diseases. Physiological mechanisms related to the function of chaperones, which contribute to the restoration of native conformation of functionally important proteins, evolved evolutionarily. These mechanisms can be considered promising for pharmacological regulation. Therefore, the aim of this review was to analyze the mechanisms of endoplasmic reticulum stress (ER stress) and unfolded protein response (UPR) in the pathogenesis of neurodegenerative diseases. Data on BiP and Sigma1R chaperones in clinical and experimental studies of Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease are presented. The possibility of neuroprotective effect dependent on Sigma1R ligand activation in these diseases is also demonstrated. The interaction between Sigma1R and BiP-associated signaling in the neuroprotection is discussed. The performed analysis suggests the feasibility of pharmacological regulation of chaperone function, possibility of ligand activation of Sigma1R in order to achieve a neuroprotective effect, and the need for further studies of the conjugation of cellular mechanisms controlled by Sigma1R and BiP chaperones.

Probing the relevance of the accelerated aging mouse line SAMP8 as a model for certain types of neuropsychiatric symptoms in dementia

INTRODUCTION

People with dementia (PwD) often present with neuropsychiatric symptoms (NPS). NPS are of substantial burden to the patients, and current treatment options are unsatisfactory. Investigators searching for novel medications need animal models that present disease-relevant phenotypes and can be used for drug screening. The Senescence Accelerated Mouse-Prone 8 (SAMP8) strain shows an accelerated aging phenotype associated with neurodegeneration and cognitive decline. Its behavioural phenotype in relation to NPS has not yet been thoroughly investigated. Physical and verbal aggression in reaction to the external environment (e.g., interaction with the caregiver) is one of the most prevalent and debilitating NPS occurring in PwD. Reactive aggression can be studied in male mice using the Resident-Intruder (R-I) test. SAMP8 mice are known to be more aggressive than the Senescence Accelerated Mouse-Resistant 1 (SAMR1) control strain at specific ages, but the development of the aggressive phenotype over time, is still unknown.

METHODS

In our study, we performed a longitudinal, within-subject, assessment of aggressive behaviour of male SAMP8 and SAMR1 mice at 4, 5, 6 and 7 months of age. Aggressive behaviour from video recordings of the R-I sessions was analysed using an in-house developed behaviour recognition software.

RESULTS

SAMP8 mice were more aggressive relative to SAMR1 mice starting at 5 months of age, and the phenotype was still present at 7 months of age. Treatment with risperidone (an antipsychotic frequently used to treat agitation in clinical practice) reduced aggression in both strains. In a three-chamber social interaction test, SAMP8 mice also interacted more fervently with male mice than SAMR1, possibly because of their aggression-seeking phenotype. They did not show any social withdrawal.

DISCUSSION

Our data support the notion that SAMP8 mice might be a useful preclinical tool to identify novel treatment options for CNS disorders associated with raised levels of reactive aggression such as dementia.

Regulatory role of the endocannabinoid system on glial cells toward cognitive function in Alzheimer's disease: A systematic review and meta-analysis of animal studies

Objective: Over the last decade, researchers have sought to develop novel medications against dementia. One potential agent under investigation is cannabinoids. This review systematically appraised and meta-analyzed published pre-clinical research on the mechanism of endocannabinoid system modulation in glial cells and their effects on cognitive function in animal models of Alzheimer's disease (AD). Methods: A systematic review complying with PRISMA guidelines was conducted. Six databases were searched: EBSCOHost, Scopus, PubMed, CINAHL, Cochrane, and Web of Science, using the keywords AD, cannabinoid, glial cells, and cognition. The methodological quality of each selected pre-clinical study was evaluated using the SYRCLE risk of bias tool. A random-effects model was applied to analyze the data and calculate the effect size, while I² and p-values were used to assess heterogeneity. Results: The analysis included 26 original articles describing (1050 rodents) with AD-like symptoms. Rodents treated with cannabinoid agonists showed significant reductions in escape latency (standard mean difference [SMD] = -1.26; 95% confidence interval [CI]: -1.77 to -0.76, p < 0.00001) and ability to discriminate novel objects (SMD = 1.40; 95% CI: 1.04 to 1.76, p < 0.00001) compared to the control group. Furthermore, a significant decrease in Aβ plaques (SMD = -0.91; 95% CI: -1.55 to -0.27, p = 0.006) was observed in the endocannabinoid-treated group compared to the control group. Trends were observed toward neuroprotection, as represented by decreased levels of glial cell markers including glial fibrillary acid protein (SMD = -1.47; 95% CI: -2.56 to -0.38, p = 0.008) and Iba1 (SMD = -1.67; 95% CI: -2.56 to -0.79, p = 0.0002). Studies on the wild-type mice demonstrated significantly decreased levels of pro-inflammatory markers TNF-α, IL-1, and IL-6 (SMD = -2.28; 95% CI: -3.15 to -1.41, p = 0.00001). Despite the non-significant decrease in pro-inflammatory marker levels in transgenic mice (SMD = -0.47; 95% CI: -1.03 to 0.08, p = 0.09), the result favored the endocannabinoid-treated group over the control group. Conclusion: The revised data suggested that endocannabinoid stimulation promotes cognitive function via modulation of glial cells by decreasing pro-inflammatory markers in AD-like rodent models. Thus, cannabinoid agents may be required to modulate the downstream chain of effect to enhance cognitive stability against concurrent neuroinflammation in AD. Population-based studies and well-designed clinical trials are required to characterize the acceptability and real-world effectiveness of cannabinoid agents. Systematic Review Registration: [https://inplasy.com/inplasy-2022-8-0094/], identifier [Inplasy Protocol 3770].

Fats, Friends or Foes: Investigating the Role of Short- and Medium-Chain Fatty Acids in Alzheimer's Disease

Characterising Alzheimer's disease (AD) as a metabolic disorder of the brain is gaining acceptance based on the pathophysiological commonalities between AD and major metabolic disorders. Therefore, metabolic interventions have been explored as a strategy for brain energetic rescue. Amongst these, medium-chain fatty acid (MCFA) supplementations have been reported to rescue the energetic failure in brain cells as well as the cognitive decline in patients. Short-chain fatty acids (SCFA) have also been implicated in AD pathology. Due to the increasing therapeutic interest in metabolic interventions and brain energetic rescue in neurodegenerative disorders, in this review, we first summarise the role of SCFAs and MCFAs in AD. We provide a comparison of the main findings regarding these lipid species in established AD animal models and recently developed human cell-based models of this devastating disorder.

Populations of Tau Conformers Drive Prion-like Strain Effects in Alzheimer's Disease and Related Dementias

Recent findings of diverse populations of prion-like conformers of misfolded tau protein expand the prion concept to Alzheimer's disease (AD) and monogenic frontotemporal lobar degeneration (FTLD)-MAPT P301L, and suggest that distinct strains of misfolded proteins drive the phenotypes and progression rates in many neurodegenerative diseases. Notable progress in the previous decades has generated many lines of proof arguing that yeast, fungal, and mammalian prions determine heritable as well as infectious traits. The extraordinary phenotypic diversity of human prion diseases arises from structurally distinct prion strains that target, at different progression speeds, variable brain structures and cells. Although human prion research presents beneficial lessons and methods to study the mechanism of strain diversity of protein-only pathogens, the fundamental molecular mechanism by which tau conformers are formed and replicate in diverse tauopathies is still poorly understood. In this review, we summarize up to date advances in identification of diverse tau conformers through biophysical and cellular experimental paradigms, and the impact of heterogeneity of pathological tau strains on personalized structure- and strain-specific therapeutic approaches in major tauopathies.

Disaccharide Trehalose in Experimental Therapies for Neurodegenerative Disorders: Molecular Targets and Translational Potential

Induction of autophagy is a prospective approach to the treatment of neurodegeneration. In the recent decade, trehalose attracted special attention. It is an autophagy inducer with negligible adverse effects and is approved for use in humans according to FDA requirements. Trehalose has a therapeutic effect in various experimental models of diseases. This glucose disaccharide with a flexible α-1-1'-glycosidic bond has unique properties: induction of mTOR-independent autophagy (with kinase AMPK as the main target) and a chaperone-like effect on proteins imparting them natural spatial structure. Thus, it can reduce the accumulation of neurotoxic aberrant/misfolded proteins. Trehalose has an anti-inflammatory effect and inhibits detrimental oxidative stress partially owing to the enhancement of endogenous antioxidant defense represented by the Nrf2 protein. The disaccharide activates lysosome and autophagosome biogenesis pathways through the protein factors TFEB and FOXO1. Here we review various mechanisms of the neuroprotective action of trehalose and touch on the possibility of pleiotropic effects. Current knowledge about specific features of trehalose pharmacodynamics is discussed. The neuroprotective effects of trehalose in animal models of major neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's diseases are examined too. Attention is given to translational transition to clinical trials of this drug, especially oral and parenteral routes of administration. Besides, the possibility of enhancing the therapeutic benefit via a combination of mTOR-dependent and mTOR-independent autophagy inducers is analyzed. In general, trehalose appears to be a promising multitarget tool for the inhibition of experimental neurodegeneration and requires thorough investigation of its clinical capabilities.

Z-Guggulsterone attenuates cognitive defects and decreases neuroinflammation in APPswe/PS1dE9 mice through inhibiting the TLR4 signaling pathway

Growing evidence indicates that inflammatory damage is implicated in the pathogenesis of Alzheimer's disease (AD). Z-Guggulsterone (Z-GS) is a natural steroid, which is extracted from Commiphora mukul and has anti-inflammatory effects in vivo and in vitro. In the present study, we investigated the disease-modifying effects of chronic Z-GS administration on the cognitive and neuropathological impairments in the transgenic mouse models of AD. We found that chronic Z-GS administration prevented learning and memory deficits in the APPswe/PS1dE9 mice. In addition, Z-GS treatment significantly decreased cerebral amyloid-β (Aβ) levels and plaque burden via inhibiting amyloid precursor protein (APP) processing by reducing beta-site APP cleaving enzyme 1 (BACE1) expression in the APPswe/PS1dE9 mice. We also found that Z-GS treatment markedly alleviated neuroinflammation and reduced synaptic defects in the APPswe/PS1dE9 mice. Furthermore, the activated TLR4/NF-κB signaling pathways in APPswe/PS1dE9 mice were remarkably inhibited by Z-GS treatment, which was achieved via suppressing the phosphorylation of JNK. Collectively, our data demonstrate that chronic Z-GS treatment restores cognitive defects and reverses multiple neuropathological impairments in the APPswe/PS1dE9 mice. This study provides novel insights into the neuroprotective effects and neurobiological mechanisms of Z-GS on AD, indicating that Z-GS is a promising disease-modifying agent for the treatment of AD.