Temporal memory deficits in Alzheimer's mouse models: rescue by genetic deletion of BACE1

Alzheimer's-linked axonal changes accompany elevated antidromic action potential failure rate in aged mice

Alzheimer's disease (AD) affects both grey and white matter (WM), but considerably more is known about the former. Interestingly, WM disruption has been consistently observed and thoroughly described using imaging modalities, particularly MRI which has shown WM functional disconnections between the hippocampus and other brain regions during AD pathogenesis when early neurodegeneration and synapse loss are also evident. Nonetheless, high-resolution structural and functional analyses of WM during AD pathogenesis remain scarce. Given the importance of the myelinated axons in the WM for conveying information across brain regions, such studies will provide valuable information on the cellular drivers and consequences of WM disruption that contribute to the characteristic cognitive decline of AD. Here, we employed a multi-scale approach to investigate hippocampal WM disruption during AD pathogenesis and determine whether hippocampal WM changes accompany the well-documented grey matter losses. Our data indicate that ultrastructural myelin disruption is elevated in the alveus in human AD cases and increases with age in 5xFAD mice. Unreliable action potential propagation and changes to sodium channel expression at the node of Ranvier co-emerged with this deterioration. These findings provide important insight to the neurobiological substrates and functional consequences of decreased WM integrity and are consistent with the notion that hippocampal disconnection contributes to cognitive changes in AD.

The duality of amyloid-β: its role in normal and Alzheimer's disease states

Alzheimer's disease (AD) is a degenerative neurological condition that gradually impairs cognitive abilities, disrupts memory retention, and impedes daily functioning by impacting the cells of the brain. A key characteristic of AD is the accumulation of amyloid-beta (Aβ) plaques, which play pivotal roles in disease progression. These plaques initiate a cascade of events including neuroinflammation, synaptic dysfunction, tau pathology, oxidative stress, impaired protein clearance, mitochondrial dysfunction, and disrupted calcium homeostasis. Aβ accumulation is also closely associated with other hallmark features of AD, underscoring its significance. Aβ is generated through cleavage of the amyloid precursor protein (APP) and plays a dual role depending on its processing pathway. The non-amyloidogenic pathway reduces Aβ production and has neuroprotective and anti-inflammatory effects, whereas the amyloidogenic pathway leads to the production of Aβ peptides, including Aβ40 and Aβ42, which contribute to neurodegeneration and toxic effects in AD. Understanding the multifaceted role of Aβ, particularly in AD, is crucial for developing effective therapeutic strategies that target Aβ metabolism, aggregation, and clearance with the aim of mitigating the detrimental consequences of the disease. This review aims to explore the mechanisms and functions of Aβ under normal and abnormal conditions, particularly in AD, by examining both its beneficial and detrimental effects.

Reactivation of encoding ensembles in the prelimbic cortex supports temporal associations

Fear conditioning is encoded by strengthening synaptic connections between the neurons activated by a conditioned stimulus (CS) and those activated by an unconditioned stimulus (US), forming a memory engram, which is reactivated during memory retrieval. In temporal associations, activity within the prelimbic cortex (PL) plays a role in sustaining a short-term, transient memory of the CS, which is associated with the US after a temporal gap. However, it is unknown whether the PL has only a temporary role, transiently representing the CS, or is part of the neuronal ensembles that support the retrieval, i.e., whether PL neurons support both transient, short-term memories and stable, long-term memories. We investigated neuronal ensembles underlying temporal associations using fear conditioning with a 5-s interval between the CS and US (CFC-5s). Controls were trained in contextual fear conditioning (CFC), in which the CS-US overlaps. We used Robust Activity Marking (RAM) to selectively manipulate PL neurons activated by CFC-5s learning and Targeted Recombination in Active Populations (TRAP2) mice to label neurons activated by CFC-5s learning and reactivated by memory retrieval in the amygdala, medial prefrontal cortex, hippocampus, perirhinal cortices (PER) and subiculum. We also computed their co-reactivation to generate correlation-based networks. The optogenetic reactivation or silencing of PL encoding ensembles either promoted or impaired the retrieval of CFC-5s but not CFC. CFC-5s retrieval reactivated encoding ensembles in the PL, PER, and basolateral amygdala. The engram network of CFC-5s had higher amygdala and PER centralities and interconnectivity. The same PL neurons support learning and stable associative memories.

Intranasal insulin treatment ameliorates spatial memory, muscular strength, and frailty deficits in 5xFAD mice

The 5xFAD mouse model shows age-related weight loss as well as cognitive and motor deficits. Metabolic dysregulation, especially impaired insulin signaling, is also present in AD. This study examined whether intranasal delivery of insulin (INI) at low (0.875 U) or high (1.750 U) doses would ameliorate these deficits compared to saline in 10-month-old female 5xFAD and B6SJL wildtype (WT) mice. INI increased forelimb grip strength in the wire hang test in 5xFAD mice in a dose-dependent manner but did not improve the performance of 5xFAD mice on the balance beam. High INI doses reduced frailty scores in 5xFAD mice and improved spatial memory in both acquisition and reversal probe trials in the Morris water maze. INI increased swim speed in 5xFAD mice but had no effect on object recognition memory or working memory in the spontaneous alternation task, nor did it improve memory in the contextual or cued fear memory tasks. High doses of insulin increased the liver, spleen, and kidney weights and reduced brown adipose tissue weights. P-Akt signaling in the hippocampus was increased by insulin in a dose-dependent manner. Altogether, INI increased strength, reduced frailty scores, and improved visual spatial memory. Hypoglycemia was not present after INI, however alterations in tissue and organ weights were present. These results are novel and important as they indicate that intra-nasal insulin can reverse cognitive, motor and frailty deficits found in this mouse model of AD.

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.

M2 receptors are required for spatiotemporal sequence learning in mouse primary visual cortex

Acetylcholine is a neurotransmitter that plays a variety of roles in the central nervous system. It was previously shown that blocking muscarinic receptors with a nonselective antagonist prevents a form of experience-dependent plasticity termed "spatiotemporal sequence learning" in the mouse primary visual cortex (V1). Muscarinic signaling is a complex process involving the combined activities of five different G protein-coupled receptors, M1-M5, all of which are expressed in the murine brain but differ from each other functionally and in anatomical localization. Here we present electrophysiological evidence that M2, but not M1, receptors are required for spatiotemporal sequence learning in mouse V1. We show in male mice that M2 is highly expressed in the neuropil in V1, especially in thalamorecipient layer 4, and colocalizes with the soma in a subset of somatostatin-expressing neurons in deep layers. We also show that expression of M2 receptors is higher in the monocular region of V1 than it is in the binocular region but that the amount of experience-dependent sequence potentiation is similar in both regions and that blocking muscarinic signaling after visual stimulation does not prevent plasticity. This work establishes a new functional role for M2-type receptors in processing temporal information and demonstrates that monocular circuits are modified by experience in a manner similar to binocular circuits.NEW & NOTEWORTHY Muscarinic acetylcholine receptors are required for multiple forms of plasticity in the brain and support perceptual functions, but the precise role of the five subtypes (M1-M5) are unclear. Here we show that the M2 receptor is specifically required to encode experience-dependent representations of spatiotemporal relationships in both monocular and binocular regions of mouse V1. This work identifies a novel functional role for M2 receptors in coding temporal information into cortical circuits.

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.

Combination strategy employing BACE1 inhibitor and memantine to boost cognitive benefits in Alzheimer's disease therapy

RATIONALE

The β-secretase BACE1 initiates amyloid-β (Aβ) generation and represents a long-standing prime therapeutic target for the treatment of Alzheimer's disease (AD). However, BACE1 inhibitors tested to date in clinical trials have yielded no beneficial outcomes. In fact, prior BACE1 inhibitor trials targeted at ~ 50-90% Aβ reductions in symptomatic or prodromal AD stages have ended in the discontinuation due to futility and/or side effects, including cognitive worsening rather than expected improvement at the highest dose.

OBJECTIVES

We tested whether a combination strategy with the selective BACE1 inhibitor GRL-8234 and the FDA-approved symptomatic drug memantine may provide synergistic cognitive benefits within their safe dose range.

METHODS

The drug effects were evaluated in the advanced symptomatic stage of 5XFAD mice that developed extensive cerebral Aβ deposition.

RESULTS

Chronic combination treatment with 33.4-mg/kg GRL-8234 and 10-mg/kg memantine, but not either drug alone, rescued cognitive deficits in 5XFAD mice at 12 months of age (the endpoint after 60-day drug treatment), as assessed by the contextual fear conditioning, spontaneous alternation Y-maze and nest building tasks. Intact baseline performances of wild-type control mice on three cognitive paradigms demonstrated that combination treatment did not augment potential cognitive side effects of individual drugs. Biochemical and immunohistochemical examination showed that combination treatment did not synergistically reduce the β-amyloidogenic processing of amyloid precursor protein or Aβ levels in 5XFAD mouse brains.

CONCLUSIONS

A combination strategy with BACE1 inhibitors and memantine may be able to increase the effectiveness of individual drugs within their safe dose range in AD therapy.

Age dependent path integration deficit in 5xFAD mice

Alzheimer's disease (AD) is a severe neurodegenerative disorder and the most common form of dementia in elderly individuals, characterized by memory deficits, cognitive decline, and neuropathology. The identification of preclinical markers for AD remains elusive. We employed an ultrasound-evoked spatial memory assay to investigate path integration (PI) in wild type C57BL/6 J and 5xFAD mice. We observed significant recruitment of the mammillary bodies (MB) and subiculum (Sub) - core regions of the Papez circuit during PI, as indicated by increased expression of the immediate early gene c-Fos in C57BL/6 J mice. In 5xFAD mice, amyloid-beta (Aβ) vulnerability in the MB and Sub was evident at 3-months of age, preceding widespread pathology at 5-months of age. In parallel, we detected significant behavioral deficits in PI in the 5XFAD mice at 5- but not 3-months of age. Sex based analysis revealed a more profound deficit in males compared to females at 5-months of age. Our data suggest PI may be as an early indicator of AD, potentially associated with dysfunction within the Papez circuit.

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.

7,8-Dihydroxy Efavirenz Is Not as Effective in CYP46A1 Activation In Vivo as Efavirenz or Its 8,14-Dihydroxy Metabolite

High dose (S)-efavirenz (EFV) inhibits the HIV reverse transcriptase enzyme and is used to lower HIV load. Low-dose EFV allosterically activates CYP46A1, the key enzyme for cholesterol elimination from the brain, and is investigated as a potential treatment for Alzheimer's disease. Simultaneously, we evaluate EFV dihydroxymetabolites for in vivo brain effects to compare with those of (S)-EFV. We have already tested (rac)-8,14dihydroxy EFV on 5XFAD mice, a model of Alzheimer's disease. Herein, we treated 5XFAD mice with (rac)-7,8dihydroxy EFV. In both sexes, the treatment modestly activated CYP46A1 in the brain and increased brain content of acetyl-CoA and acetylcholine. Male mice also showed a decrease in the brain levels of insoluble amyloid β40 peptides. However, the treatment had no effect on animal performance in different memory tasks. Thus, the overall brain effects of (rac)-7,8dihydroxy EFV were weaker than those of EFV and (rac)-8,14dihydroxy EFV and did not lead to cognitive improvements as were seen in treatments with EFV and (rac)-8,14dihydroxy EFV. An in vitro study assessing CYP46A1 activation in co-incubations with EFV and (rac)-7,8dihydroxy EFV or (rac)-8,14dihydroxy EFV was carried out and provided insight into the compound doses and ratios that could be used for in vivo co-treatments with EFV and its dihydroxymetabolite.

Aberrant Cortical Activity in 5xFAD Mice in Response to Social and Non-Social Olfactory Stimuli

BACKGROUND

Neuroimaging studies investigating the behavioral and psychological symptoms of dementia (BPSD)- such as apathy, anxiety, and depression- have linked some of these symptoms with altered neural activity. However, inconsistencies in operational definitions and rating scales, limited scope of assessments, and poor temporal resolution of imaging techniques have hampered human studies. Many transgenic (Tg) mouse models of Alzheimer's disease (AD) exhibit BPSD-like behaviors concomitant with AD-related neuropathology, allowing examination of how neural activity may relate to BPSD-like behaviors with high temporal and spatial resolution.

OBJECTIVE

To examine task-dependent neural activity in the medial prefrontal cortex (mPFC) of AD-model mice in response to social and non-social olfactory stimuli.

METHODS

We previously demonstrated age-related decreases in social investigation in Tg 5xFAD females, and this reduced social investigation is evident in Tg 5xFAD females and males by 6 months of age. In the present study, we examine local field potential (LFP) in the mPFC of awake, behaving 5xFAD females and males at 6 months of age during exposure to social and non-social odor stimuli in a novel olfactometer.

RESULTS

Our results indicate that Tg 5xFAD mice exhibit aberrant baseline and task-dependent LFP activity in the mPFC- including higher relative delta (1-4 Hz) band power and lower relative power in higher bands, and overall stronger phase-amplitude coupling- compared to wild-type controls.

CONCLUSIONS

These results are consistent with previous human and animal studies examining emotional processing, anxiety, fear behaviors, and stress responses, and suggest that Tg 5xFAD mice may exhibit altered arousal or anxiety.

A Strategy for Allowing Earlier Diagnosis and Rigorous Evaluation of BACE1 Inhibitors in Preclinical Alzheimer's Disease

Given continued failure of BACE1 inhibitor programs at symptomatic and prodromal stages of Alzheimer's disease (AD), clinical trials need to target the earlier preclinical stage. However, trial design is complex in this population with negative diagnosis of classical hippocampal amnesia on standard memory tests. Besides recent advances in brain imaging, electroencephalogram, and fluid-based biomarkers, new cognitive markers should be established for earlier diagnosis that can optimize recruitment to BACE1 inhibitor trials in presymptomatic AD. Notably, accelerated long-term forgetting (ALF) is emerging as a sensitive cognitive measure that can discriminate between asymptomatic individuals with high risks for developing AD and healthy controls. ALF is a form of declarative memory impairment characterized by increased forgetting rates over longer delays (days to months) despite normal storage within the standard delays of testing (20-60 min). Therefore, ALF may represent a harbinger of preclinical dementia and the impairment of systems memory consolidation, during which memory traces temporarily stored in the hippocampus become gradually integrated into cortical networks. This review provides an overview of the utility of ALF in a rational design of next-generation BACE1 inhibitor trials in preclinical AD. I explore potential mechanisms underlying ALF and relevant early-stage biomarkers useful for BACE1 inhibitor evaluation, including synaptic protein alterations, astrocytic dysregulation and neuron hyperactivity in the hippocampal-cortical network. Furthermore, given the physiological role of the isoform BACE2 as an AD-suppressor gene, I also discuss the possible association between the poor selectivity of BACE1 inhibitors and their side effects (e.g., cognitive worsening) in prior clinical trials.

Electrochemiluminescence and electrochemical dual-mode detection of BACE1 activity based on the assembly of peptide and luminol co-functionalized silver nanoparticles induced by cucurbit[8]uril

A novel electrochemiluminescence (ECL) and electrochemical dual-mode sensor was developed for detecting the activity of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) and screening its inhibitor. Specifically, the adamantane (ADA)-functionalized peptide (P1), a designed substrate peptide for BACE1, was immobilized on the electrode surface via host-guest interaction between β-cyclodextrin (β-CD) and ADA. The aggregation of the peptide (P2) and luminol co-functionalized silver nanoparticles could be induced by cucurbit [8]uril (CB[8] due to the ability of CB[8] to accommodate two aromatic residues simultaneously. The obtained (CB[8]-P2-AgNPs-luminol)n aggregates with both ECL and electrochemical activity, used as the dual-mode signal probe, could be captured to the N-terminal of P1 through CB[8]. Once the substrate P1 was cleaved by BACE1, the probe-binding polypeptide fragment detached from the electrode surface, resulting in a remarkable decrease in the ECL and electrochemical signals. Taking advantage of the signal amplification function of the signal probe, the sensitive dual-mode assay for BACE1 activity can be achieved with the low detection limits of 33.11 pM for ECL and 53.19 pM for electrochemical mode. The superior analytical performance of this novel dual-mode sensor toward BACE1 activity suggested the promising application in early diagnosis of Alzheimer's disease (AD).

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.

Apolipoprotein E genotype-dependent accumulation of amyloid β in APP-knock-in mouse model of Alzheimer's disease

Apolipoprotein E4 (APOE4), the strongest risk factor for late-onset Alzheimer's disease (AD), has been revealed to cause greater accumulation of extracellular amyloid β (Aβ) aggregates than does APOE3 in traditional transgenic mouse models of AD. However, concerns that the overexpression paradigm might have affected the phenotype remain. Amyloid precursor protein (APP)-knock-in (KI) mice, incorporating APP mutations associated with AD development, offer an alternative approach for overproducing pathogenic Aβ without needing overexpression of APP. Here, we present the results of comprehensive analyses of pathological and biochemical traits in the brains of APP-KI mice harboring APP-associated familial AD mutations (APPNL-G-F/NL-G-F mice) crossed with human APOE-KI mice. Immunohistochemical and biochemical analyses revealed the APOE genotype-dependent increase in Aβ pathology and glial activation, which was evident within 8 months in the mouse model. These results suggested that this mouse model may be valuable for investigating APOE pathobiology within a reasonable experimental time frame. Thus, this model can be considered in investigating the interaction between APOE and Aβ in vivo, which may not be addressed appropriately by using other transgenic mouse models.

Amyloid Precursor Protein and Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders associated with age or inherited mutations. It is characterized by severe dementia in the late stages that affect memory, cognitive functions, and daily life overall. AD progression is linked to the accumulation of cytotoxic amyloid beta (Aβ) and hyperphosphorylated tau protein combined with other pathological features such as synaptic loss, defective energy metabolism, imbalances in protein, and metal homeostasis. Several treatment options for AD are under investigation, including antibody-based therapy and stem cell transplantation. Amyloid precursor protein (APP) is a membrane protein considered to play a main role in AD pathology. It is known that APP in physiological conditions follows a non-amyloidogenic pathway; however, it can proceed to an amyloidogenic scenario, which leads to the generation of extracellular deleterious Aβ plaques. Not all steps of APP biogenesis are clear so far, and these questions should be addressed in future studies. AD is a complex chronic disease with many factors that contribute to disease progression.

Deficiency in the neural cell adhesion molecule 2 (NCAM2) reduces axonal levels of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), affects axonal organization in the hippocampus, and leads to behavioral deficits

The neural cell adhesion molecule 2 (NCAM2) regulates axonal organization in the central nervous system via mechanisms that have remained poorly understood. We now show that NCAM2 increases axonal levels of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), a protease that regulates axonal guidance. In brains of NCAM2-deficient mice, BACE1 levels are reduced in hippocampal mossy fiber projections, and the infrapyramidal bundle of these projections is shortened. This abnormal axonal organization correlates with impaired short-term spatial memory and cognitive flexibility in NCAM2-deficient male and female mice. Self-grooming, rearing, digging and olfactory acuity are increased in NCAM2-deficient male mice, when compared with littermate wild-type mice of the same sex. NCAM2-deficient female mice also show increased self-grooming, but are reduced in rearing, and do not differ from female wild-type mice in olfactory acuity and digging behavior. Our results indicate that errors in axonal guidance and organization caused by impaired BACE1 function can underlie the manifestation of neurodevelopmental disorders, including autism as found in humans with deletions of the NCAM2 gene.

The unfolded protein response transcription factor XBP1s ameliorates Alzheimer's disease by improving synaptic function and proteostasis

Alteration in the buffering capacity of the proteostasis network is an emerging feature of Alzheimer's disease (AD), highlighting the occurrence of endoplasmic reticulum (ER) stress. The unfolded protein response (UPR) is the main adaptive pathway to cope with protein folding stress at the ER. Inositol-requiring enzyme-1 (IRE1) operates as a central ER stress sensor, enabling the establishment of adaptive and repair programs through the control of the expression of the transcription factor X-box binding protein 1 (XBP1). To artificially enforce the adaptive capacity of the UPR in the AD brain, we developed strategies to express the active form of XBP1 in the brain. Overexpression of XBP1 in the nervous system using transgenic mice reduced the load of amyloid deposits and preserved synaptic and cognitive function. Moreover, local delivery of XBP1 into the hippocampus of an 5xFAD mice using adeno-associated vectors improved different AD features. XBP1 expression corrected a large proportion of the proteomic alterations observed in the AD model, restoring the levels of several synaptic proteins and factors involved in actin cytoskeleton regulation and axonal growth. Our results illustrate the therapeutic potential of targeting UPR-dependent gene expression programs as a strategy to ameliorate AD features and sustain synaptic function.

The Expression of the Endocannabinoid Receptors CB2 and GPR55 Is Highly Increased during the Progression of Alzheimer's Disease in AppNL-G-F Knock-In Mice

BACKGROUND

The endocannabinoid system (ECS) and associated lipid transmitter-based signaling systems play an important role in modulating brain neuroinflammation. ECS is affected in neurodegenerative disorders, such as Alzheimer's disease (AD). Here we have evaluated the non-psychotropic endocannabinoid receptor type 2 (CB2) and lysophosphatidylinositol G-protein-coupled receptor 55 (GPR55) localization and expression during Aβ-pathology progression.

METHODS

Hippocampal gene expression of CB2 and GPR55 was explored by qPCR analysis, and brain distribution was evaluated by immunofluorescence in the wild type (WT) and APP knock-in App^NL-G-F AD mouse model. Furthermore, the effects of Aβ42 on CB2 and GPR55 expression were assessed in primary cell cultures.

RESULTS

CB2 and GPR55 mRNA levels were significantly upregulated in App^NL-G-F mice at 6 and 12 months of age, compared to WT. CB2 was highly expressed in the microglia and astrocytes surrounding the Aβ plaques. Differently, GPR55 staining was mainly detected in neurons and microglia but not in astrocytes. In vitro, Aβ42 treatment enhanced CB2 receptor expression mainly in astrocytes and microglia cells, whereas GPR55 expression was enhanced primarily in neurons.

CONCLUSIONS

These data show that Aβ pathology progression, particularly Aβ42, plays a crucial role in increasing the expression of CB2 and GPR55 receptors, supporting CB2 and GPR55 implications in AD.

Lateral mammillary body neurons in mouse brain are disproportionately vulnerable in Alzheimer's disease

The neural circuits governing the induction and progression of neurodegeneration and memory impairment in Alzheimer's disease (AD) are incompletely understood. The mammillary body (MB), a subcortical node of the medial limbic circuit, is one of the first brain regions to exhibit amyloid deposition in the 5xFAD mouse model of AD. Amyloid burden in the MB correlates with pathological diagnosis of AD in human postmortem brain tissue. Whether and how MB neuronal circuitry contributes to neurodegeneration and memory deficits in AD are unknown. Using 5xFAD mice and postmortem MB samples from individuals with varying degrees of AD pathology, we identified two neuronal cell types in the MB harboring distinct electrophysiological properties and long-range projections: lateral neurons and medial neurons. lateral MB neurons harbored aberrant hyperactivity and exhibited early neurodegeneration in 5xFAD mice compared with lateral MB neurons in wild-type littermates. Inducing hyperactivity in lateral MB neurons in wild-type mice impaired performance on memory tasks, whereas attenuating aberrant hyperactivity in lateral MB neurons ameliorated memory deficits in 5xFAD mice. Our findings suggest that neurodegeneration may be a result of genetically distinct, projection-specific cellular dysfunction and that dysregulated lateral MB neurons may be causally linked to memory deficits in AD.

Accelerated long-term forgetting: A sensitive paradigm for detecting subtle cognitive impairment and evaluating BACE1 inhibitor efficacy in preclinical Alzheimer's disease

Given a long preclinical stage of Alzheimer's disease (AD) continuum before the onset of dementia, there is a growing demand for tools capable of detecting the earliest feature of subtle cognitive impairment and optimizing recruitment to clinical trials for potentially disease-modifying therapeutic interventions such as BACE1 inhibitors. Now that all BACE1 inhibitor programs in symptomatic and prodromal AD populations have ended in failure, trials need to shift to target the earlier preclinical stage. However, evaluating cognitive efficacy (if any) in asymptomatic AD individuals is a great challenge. In this context, accelerated long-term forgetting (ALF) is emerging as a sensitive cognitive measure that can discriminate between presymptomatic individuals with high risks for developing AD and healthy controls. ALF is characterized by increased forgetting rates over extended delays (e.g., days, weeks, months) despite normal learning and short-term retention on standard memory assessments that typically use around 30-min delays. This review provides an overview of recent progress in animal model and clinical studies on this topic, focusing on the utility and underlying mechanism of ALF that may be applicable to earlier diagnosis and BACE1 inhibitor efficacy evaluation at a preclinical stage of AD.

Proteomic alterations in the cerebellum and hippocampus in an Alzheimer's disease mouse model: Alleviating effect of palmatine

Alzheimer's disease (AD) is one of the most prevalent diseases that lead to memory deficiencies, severe behavioral abnormalities, and ultimately death. The need for more appropriate treatment of AD continues, and remains a sought-after goal. Previous studies showed palmatine (PAL), an isoquinoline alkaloid, might have the potential for combating AD because of its in vitro and in vivo activities. In this study, we aimed to assess PAL's therapeutic potential and gain insights into the working mechanism on protein level in the AD mouse model brain, for the first time. To this end, PAL was administered to 12-month-old 5xFAD mice at two doses after its successful isolation from the Siberian barberry shrub. PAL (10 mg/kg) showed statistically significant improvement in the memory and learning phase on the Morris water maze test. The PAL's ability to pass through the blood-brain barrier was verified via Multiple Reaction Monitoring (MRM). Label-free proteomics analysis revealed PAL administration led to changes most prominently in the cerebellum, followed by the hippocampus, but none in the cortex. Most of the differentially expressed proteins in PAL compared to the 5xFAD control group (ALZ) were the opposite of those in ALZ in comparison to healthy Alzheimer's littermates (ALM) group. HS105, HS12A, and RL12 were detected as hub proteins in the cerebellum. Collectively, here we present PAL as a potential therapeutic candidate owing to its alleviating effect in 5xFAD mice on not only cognitive impairment but also proteomes in the cerebellum and hippocampus.

Effects of Striatal Amyloidosis on the Dopaminergic System and Behavior: A Comparative Study in Male and Female 5XFAD Mice

BACKGROUND

Nearly two-thirds of patients diagnosed with Alzheimer's disease (AD) are female. In addition, female patients with AD have more significant cognitive impairment than males at the same disease stage. This disparity suggests there are sex differences in AD progression. While females appear to be more affected by AD, most published behavioral studies utilize male mice. In humans, there is an association between antecedent attention-deficit/hyperactivity disorder and increased risk of dementia. Functional connectivity studies indicate that dysfunctional cortico-striatal networks contribute to hyperactivity in attention deficit hyperactivity disorder. Higher plaque density in the striatum accurately predicts the presence of clinical AD pathology. In addition, there is a link between AD-related memory dysfunction and dysfunctional dopamine signaling.

OBJECTIVE

With the need to consider sex as a biological variable, we investigated the influence of sex on striatal plaque burden, dopaminergic signaling, and behavior in prodromal 5XFAD mice.

METHODS

Six-month-old male and female 5XFAD and C57BL/6J mice were evaluated for striatal amyloid plaque burden, locomotive behavior, and changes in dopaminergic machinery in the striatum.

RESULTS

5XFAD female mice had a higher striatal amyloid plaque burden than male 5XFAD mice. 5XFAD females, but not males, were hyperactive. Hyperactivity in female 5XFAD mice was associated with increased striatal plaque burden and changes in dopamine signaling in the dorsal striatum.

CONCLUSION

Our results indicate that the progression of amyloidosis involves the striatum in females to a greater extent than in males. These studies have significant implications for using male-only cohorts in the study of AD progression.

5xFAD mice do not have myenteric amyloidosis, dysregulation of neuromuscular transmission or gastrointestinal dysmotility

BACKGROUND

Alterations in gastrointestinal (GI) function and the gut-brain axis are associated with progression and pathology of Alzheimer's Disease (AD). Studies in AD animal models show that changes in the gut microbiome and inflammatory markers can contribute to AD development in the central nervous system (CNS). Amyloid-beta (Aβ) accumulation is a major AD pathology causing synaptic dysfunction and neuronal death. Current knowledge of the pathophysiology of AD in enteric neurons is limited, and whether Aβ accumulation directly disrupts enteric neuron function is unknown.

METHODS

In 6-month-old 5xFAD (transgenic AD) and wildtype (WT) male and female mice, GI function was assessed by colonic transit in vivo; propulsive motility and GI smooth muscle contractions ex vivo; electrochemical detection of enteric nitric oxide release in vitro, and changes in myenteric neuromuscular transmission using smooth muscle intracellular recordings. Expression of Aβ in the brain and colonic myenteric plexus in these mice was determined by immunohistochemistry staining and ELISA assay.

KEY RESULTS

At 6 months, 5xFAD mice did not show significant changes in GI motility or synaptic neurotransmission in the small intestine or colon. 5xFAD mice, but not WT mice, showed abundant Aβ accumulation in the brain. Aβ accumulation was undetectable in the colonic myenteric plexus of 5xFAD mice.

CONCLUSIONS

5xFAD AD mice are not a robust model to study amyloidosis in the gut as these mice do not mimic myenteric neuronal dysfunction in AD patients with GI dysmotility. An AD animal model with enteric amyloidosis is required for further study.

Single Nucleus Transcriptome Data from Alzheimer’s Disease Mouse Models Yield New Insight into Pathophysiology

Background: 5XFAD humanized mutant mice and Trem2 knockout (T2KO) mice are two mouse models relevant to the study of Alzheimer’s disease (AD)-related pathology. Objective: To determine hippocampal transcriptomic and polyadenylation site usage alterations caused by genetic mutations engineered in 5XFAD and T2KO mice. Methods: Employing a publicly available single-nucleus RNA sequencing dataset, we used Seurat and Sierra analytic programs to identify differentially expressed genes (DEGs) and differential transcript usage (DTU), respectively, in hippocampal cell types from each of the two mouse models. We analyzed cell type-specific DEGs further using Ingenuity Pathway Analysis (IPA). Results: We identified several DEGs in both neuronal and glial cell subtypes in comparisons of wild type (WT) versus 5XFAD and WT versus T2KO mice, including Ttr, Fth1, Pcsk1n, Malat1, Rpl37, Rtn1, Sepw1, Uba52, Mbp, Arl6ip5, Gm26917, Vwa1, and Pgrmc1. We also observed DTU in common between the two comparisons in neuronal and glial subtypes, specifically in the genes Prnp, Rbm4b, Pnisr, Opcml, Cpne7, Adgrb1, Gabarapl2, Ubb, Ndfip1, Car11, and Stmn4. IPA identified three statistically significant canonical pathways that appeared in multiple cell types and that overlapped between 5XFAD and T2KO comparisons to WT, including ‘FXR/RXR Activation’, ‘LXR/RXR Activation’, and ‘Acute Phase Response Signaling’. Conclusion: DEG, DTU, and IPA findings, derived from two different mouse models of AD, highlight the importance of energy imbalance and inflammatory processes in specific hippocampal cell types, including subtypes of neurons and glial cells, in the development of AD-related pathology. Additional studies are needed to further characterize these findings.

Amyloid Pathology in the Central Auditory Pathway of 5XFAD Mice Appears First in Auditory Cortex

Background: Effective treatment of Alzheimer’s disease (AD) will hinge on early detection. This has led to the search for early biomarkers that use non-invasive testing. One possible early biomarker is auditory temporal processing deficits, which reflect central auditory pathway dysfunction and precede cognitive and memory declines in AD. Gap detection is a measure of auditory temporal processing, is impaired in human AD, and is also impaired in the 5XFAD mouse model of AD. Gap detection deficits appear as early as postnatal day 60 in 5XFAD mice, months before cognitive deficits or cell death, supporting gap detection as an early biomarker. However, it remains unclear how gap detection deficits relate to the progression of amyloid pathology in the auditory system. Objective: To determine the progression of amyloid pathology throughout the central auditory system and across age in 5XFAD mice. Methods: We quantified intracellular and extracellular antibody labelling of Aβ 42 in 6 regions of the central auditory system from p14 to p150. Results: Pathology appeared first in primary auditory cortex (A1) as intracellular accumulation of Aβ 42 in layer 5 pyramidal neurons by age p21. Extracellular plaques appeared later, by age p90, in A1, medial geniculate body, and inferior colliculus. Auditory brainstem structures showed minimal amyloid pathology. We also observed pathology in the caudal pontine reticular nucleus, a brainstem structure that is outside of the central auditory pathway but which is involved in the acoustic startle reflex. Conclusion: These results suggest that Aβ 42 accumulation, but not plaques, may impair gap detection.

Dietary administration of D-chiro-inositol attenuates sex-specific metabolic imbalances in the 5xFAD mouse model of Alzheimer's disease

Increasing evidence shows that hypothalamic dysfunction, insulin resistance, and weight loss precede and progress along with the cognitive decline in sporadic Alzheimer's Disease (AD) with sex differences. This study aimed to determine the effect of oral dietary administration of D-Chiro-inositol (DCI), an inositol used against insulin resistance associated with polycystic ovary, on the occurrence of metabolic disorders in the transgenic 5xFAD mouse model of AD (FAD: Family Alzheimer's Disease). DCI was administered from 6 to 10 months of age to male and female 5xFAD mice and control (non-Tg) littermates. Energy balance and multiple metabolic and inflammatory parameters in the hypothalamus, liver and plasma were evaluated to assess the central and peripheral effects of DCI. Results indicated that weight loss and reduced food intake in 5xFAD mice were associated with decreased neuropeptides controlling food intake and the appearance of a pro-inflammatory state in the hypothalamus. Oral administration of DCI partially restored energy balance and hypothalamic parameters, highlighting an increased expression of Npy and Agrp and female-specific downregulation of Gfap and Igf1. DCI also partially normalized impaired insulin signaling and circulating insulin, GLP-1, and GIP deficiencies in 5xFAD mice. Principal component analysis of metabolic parameters indicated the presence of a female-specific fatty liver in 5xFAD mice: DCI administration reversed hepatic fat accumulation, β-oxidation, inflammation and increased GOT and GPT levels. Our study depicts that metabolic impairment along with the cognitive decline in a mouse model of AD, which is exacerbated in females, can be ameliorated by oral supplementation with insulin-sensitizing DCI.

PCSK9 acts as a key regulator of Aβ clearance across the blood-brain barrier

Despite the neurodegenerative disorder Alzheimer's disease (AD) is the most common form of dementia in late adult life, there is currently no therapy available to prevent the onset or slow down the progression of AD. The progressive cognitive decline in AD correlates with a successive accumulation of cerebral amyloid-β (Aβ) due to impaired clearance mechanisms. A significant percentage is removed by low-density lipoprotein receptor-related protein 1 (LRP1)-mediated transport across the blood-brain barrier (BBB) into the periphery. Circulating proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to members of the low-density lipoprotein receptor protein family at the cell surface and targets them for lysosomal degradation, which reduces the number of functional receptors. However, the adverse impact of PCSK9 on LRP1-mediated brain Aβ clearance remains elusive. By using an established BBB model, we identified reduced LRP1-mediated brain-to-blood Aβ clearance due to PCSK9 across different endothelial monolayer in vitro. Consequently, the repetitive application of FDA-approved monoclonal anti-PCSK9 antibodies into 5xFAD mice decreased the cerebral Aβ burden across variants and aggregation state, which was not reproducible in brain endothelial-specific LRP1^-/- 5xFAD mice. The peripheral PCSK9 inhibition reduced Aβ pathology in prefrontal cortex and hippocampus-brain areas critically involved in memory processing-and prevented disease-related impairment in hippocampus-dependent memory formation. Our data suggest that peripheral inhibition of PCSK9 by already available therapeutic antibodies may be a novel and easily applicable potential AD treatment.

A Mutant Variant of E2F4 Triggers Multifactorial Therapeutic Effects in 5xFAD Mice

Alzheimer’s disease (AD) has a complex etiology, which requires a multifactorial approach for an efficient treatment. We have focused on E2 factor 4 (E2F4), a transcription factor that regulates cell quiescence and tissue homeostasis, controls gene networks affected in AD, and is upregulated in the brains of Alzheimer’s patients and of APP^swe/PS1^dE9 and 5xFAD transgenic mice. E2F4 contains an evolutionarily conserved Thr-motif that, when phosphorylated, modulates its activity, thus constituting a potential target for intervention. In this study, we generated a knock-in mouse strain with neuronal expression of a mouse E2F4 variant lacking this Thr-motif (E2F4DN), which was mated with 5xFAD mice. Here, we show that neuronal expression of E2F4DN in 5xFAD mice potentiates a transcriptional program consistent with the attenuation of the immune response and brain homeostasis. This correlates with reduced microgliosis and astrogliosis, modulation of amyloid-β peptide proteostasis, and blocking of neuronal tetraploidization. Moreover, E2F4DN prevents cognitive impairment and body weight loss, a known somatic alteration associated with AD. We also show that our finding is significant for AD, since E2F4 is expressed in cortical neurons from Alzheimer patients in association with Thr-specific phosphorylation, as evidenced by an anti-E2F4/anti-phosphoThr proximity ligation assay. We propose E2F4DN-based gene therapy as a promising multifactorial approach against AD.

Visuo-spatial learning and memory impairments in the 5xFAD mouse model of Alzheimer's disease: Effects of age, sex, albinism, and motor impairments

The 5xFAD mouse model of Alzheimer's disease (AD) rapidly develops AD-related neuro-behavioral pathology. Learning and memory impairments in 5xFAD mice, however, are not always replicated and the size of impairments varies considerably across studies. To examine possible sources of this variability, we analyzed the effects of age, sex, albinism due to background genes (Tyr^c , Oca2^p ) and motor impairment on learning and memory performance of wild type and 5xFAD mice on the Morris water maze, from 3 to 15 months of age. The 5xFAD mice showed impaired learning at 6-9 months of age, but memory impairments were not detected with the test procedure used in this study. Performance of 5xFAD mice was profoundly impaired at 12-15 months of age, but was accompanied by slower swim speeds than wild-type mice and a frequent failure to locate the escape platform. Overall female mice performed worse than males, and reversal learning impairments in 5xFAD mice were more pronounced in females than males. Albino mice performed worse than pigmented mice, confirming that albinism can impair performance of 5xFAD mice independently of AD-related transgenes. Overall, these results show that 5xFAD mice have impaired learning performance at 6-9 months of age, but learning and memory performance at 12-15 months is confounded with motor impairments. Furthermore, sex and albinism should be controlled to provide an accurate assessment of AD-related transgenes on learning and memory. These results will help reduce variability across pre-clinical experiments with 5xFAD mice, and thus enhance the reliability of studies developing new therapeutics for AD.

The Therapeutic and Diagnostic Potential of Amyloid β Oligomers Selective Antibodies to Treat Alzheimer's Disease

Improvements have been made in the diagnosis of Alzheimer’s disease (AD), manifesting mostly in the development of in vivo imaging methods that allow for the detection of pathological changes in AD by magnetic resonance imaging (MRI) and positron emission tomography (PET) scans. Many of these imaging methods, however, use agents that probe amyloid fibrils and plaques–species that do not correlate well with disease progression and are not present at the earliest stages of the disease. Amyloid β oligomers (AβOs), rather, are now widely accepted as the Aβ species most germane to AD onset and progression. Here we report evidence further supporting the role of AβOs as pathological instigators of AD and introduce promising anti-AβO diagnostic probes capable of distinguishing the 5xFAD mouse model from wild type mice by PET and MRI. In a developmental study, Aβ oligomers in 5xFAD mice were found to appear at 3 months of age, just prior to the onset of memory dysfunction, and spread as memory worsened. The increase of AβOs is prominent in the subiculum and correlates with concomitant development of reactive astrocytosis. The impact of these AβOs on memory is in harmony with findings that intraventricular injection of synthetic AβOs into wild type mice induced hippocampal dependent memory dysfunction within 24 h. Compelling support for the conclusion that endogenous AβOs cause memory loss was found in experiments showing that intranasal inoculation of AβO-selective antibodies into 5xFAD mice completely restored memory function, measured 30–40 days post-inoculation. These antibodies, which were modified to give MRI and PET imaging probes, were able to distinguish 5xFAD mice from wild type littermates. These results provide strong support for the role of AβOs in instigating memory loss and salient AD neuropathology, and they demonstrate that AβO selective antibodies have potential both for therapeutics and for diagnostics.

Molecular Effects of Pteryxin and Scopoletin in the 5xFAD Alzheimer's Disease Mouse Model

BACKGROUND

Alzheimer's disease (AD) is one of the most prevalent diseases with rapidly increasing numbers, but there is still no medication to treat or stop the disease. Previous data on coumarins suggests that scopoletin may have potential benefits in AD.

OBJECTIVE

Evaluate the therapeutic potential of the coumarins with natural origin - scopoletin and pteryxin in a 5xFAD mouse model of AD Methods: Both compounds were administered at two doses to 12-month-old mice, which represent severe AD pathology. The effects of coumarins were assessed on cognition in mouse experiments. Changes in the overall brain proteome were evaluated using LC-MS/MS analyses.

RESULTS

The Morris water maze test implicated that a higher dose of pteryxin (16 mg/kg) significantly improved learning, and the proteome analysis showed pronounced changes of specific proteins upon pteryxin administration. The amyloid-β precursor protein, glial fibrillary acid protein, and apolipoprotein E protein which are highly associated with AD, were among the differentially expressed proteins at the higher dose of the pteryxin.

CONCLUSION

Overall, pteryxin may be evaluated further as a disease-modifying agent in AD pathology in the late stages of AD.

Amphiphilic Distyrylbenzene Derivatives as Potential Therapeutic and Imaging Agents for Soluble and Insoluble Amyloid β Aggregates in Alzheimer's Disease

Alzheimer's Disease (AD) is the most common neurodegenerative disease, and efficient therapeutic and early diagnostic agents for AD are still lacking. Herein, we report the development of a novel amphiphilic compound, LS-4, generated by linking a hydrophobic amyloid-binding distyrylbenzene fragment with a hydrophilic triazamacrocycle, which dramatically increases the binding affinity toward various amyloid β (Aβ) peptide aggregates, especially for soluble Aβ oligomers. Moreover, upon the administration of LS-4 to 5xFAD mice, fluorescence imaging of LS-4-treated brain sections reveals that LS-4 can penetrate the blood-brain barrier and bind to the Aβ oligomers in vivo. In addition, the treatment of 5xFAD mice with LS-4 reduces the amount of both amyloid plaques and associated phosphorylated tau aggregates vs the vehicle-treated 5xFAD mice, while microglia activation is also reduced. Molecular dynamics simulations corroborate the observation that introducing a hydrophilic moiety into the molecular structure of LS-4 can enhance the electrostatic interactions with the polar residues of the Aβ species. Finally, exploiting the Cu2+-chelating property of the triazamacrocycle, we performed a series of imaging and biodistribution studies that show the 64Cu-LS-4 complex binds to the amyloid plaques and can accumulate to a significantly larger extent in the 5xFAD mouse brains vs the wild-type controls. Overall, these results illustrate that the novel strategy, to employ an amphiphilic molecule containing a hydrophilic moiety attached to a hydrophobic amyloid-binding fragment, can increase the binding affinity for both soluble and insoluble Aβ aggregates and can thus be used to detect and regulate various Aβ species in AD.

Pregabalin Treatment does not Affect Amyloid Pathology in 5XFAD Mice

Background:

Calcium dysregulation has been proposed to play a causative role in the development of Alzheimer’s disease pathology. Pregabalin is a compound already approved for human use, marketed as the prescription drug Lyrica. It binds the α2-δ subunit of P/Q-type voltage-gated calcium channels, lowering calcium influx and providing effective treatment for epilepsy and neuropathic pain.

Objective:

We hypothesize that increased resting calcium in neuronal processes near amyloid plaques plays a role in the development of neuritic dystrophies and further progression of amyloid pathology.

Methods:

5XFAD mice were treated orally for 12 weeks with pregabalin, then immunoblotting and immunofluorescent imaging were used to quantify neuritic dystrophy and amyloid deposition in pregabalin compared to placebo-treated mice.

Results:

The treatment did not decrease markers of neuritic dystrophy or amyloid deposition. The image analysis of neuritic dystrophy on a plaque-by-plaque basis showed a small non-significant increase in the relative proportion of LAMP1 to Aβ42 in plaques with areas of 50-450 μm² in the cortex of pregabalin-treated mice. In addition, there was a statistically significant positive correlation between the measured cerebral concentration of pregabalin and the relative levels of BACE1 and Aβ in the cortex. This relationship was not observed in the hippocampus, and there was no increase in average Aβ levels in pregabalin treated mice compared to placebo. We confirmed previous findings that smaller amyloid plaques are associated with a greater degree of neuritic dystrophy.

Conclusion:

Pregabalin may have an effect on Aβ that merits further investigation, but our study does not suggest that pregabalin contributes substantially to amyloid pathology.

Variability in sub-threshold signaling linked to Alzheimer's disease emerges with age and amyloid plaque deposition in mouse ventral CA1 pyramidal neurons

The hippocampus is vulnerable to deterioration in Alzheimer's disease (AD). It is, however, a heterogeneous structure, which may contribute to the differential volumetric changes along its septotemporal axis during AD progression. Here, we investigated amyloid plaque deposition along the dorsoventral axis in two strains of transgenic AD (ADTg) mouse models. We also used patch-clamp physiology in these mice to probe for functional consequences of AD pathogenesis in ventral hippocampus, which we found bears significantly higher plaque burden in the aged ADTg group compared to corresponding dorsal regions. Despite dorsoventral differences in amyloid load, ventral CA1 pyramidal neurons of aged ADTg mice exhibited subthreshold physiological changes similar to those previously reported in dorsal neurons, indicative of an HCN channelopathy, but lacked exacerbated suprathreshold accommodation. Additionally, HCN channel function could be rescued by pharmacological manipulation of the endoplasmic reticulum. These observations suggest that an AD-linked HCN channelopathy emerges in both dorsal and ventral CA1 pyramidal neurons, but that the former encounter an additional integrative obstacle in the form of reduced intrinsic excitability.

miR-128 as a Regulator of Synaptic Properties in 5xFAD Mice Hippocampal Neurons

Alzheimer's disease (AD) is characterized by progressive synaptic dysfunction, deterioration of neuronal transmission, and consequently neuronal death. Although there is no treatment for AD, exposure to enriched environment (EE) in mice, as well as physical and mental activity in human subjects have been shown to have a protective effect by slowing the disease's progression and reducing AD-like cognitive impairment. However, the molecular mechanism of this mitigating effect is still not understood. One of the mechanisms that has recently been shown to be involved in neuronal degeneration is microRNAs (miRNAs) regulation, which act as a post-transcriptional regulators of gene expression. miR-128 has been shown to be significantly altered in individuals with AD and in mice following exposure to EE. Here, we focused on elucidating the possible role of miR-128 in AD pathology and found that miR-128 regulates the expression of two proteins essential for synaptic transmission, SNAP-25, and synaptotagmin1 (Syt1). Clinically relevant, in 5xFAD mouse model for AD, this miRNA's expression was found as downregulated, resembling the alteration found in the hippocampi of individuals with AD. Interestingly, exposing WT mice to EE also resulted in downregulation of miR-128 expression levels, although EE and AD conditions demonstrate opposing effects on neuronal functioning and synaptic plasticity. We also found that miR-128 expression downregulation in primary hippocampal cultures from 5xFAD mice results in increased neuronal network activity and neuronal excitability. Altogether, our findings place miR-128 as a synaptic player that may contribute to synaptic functioning and plasticity through regulation of synaptic protein expression and function.

Accelerated long-term forgetting is a BACE1 inhibitor-reversible incipient cognitive phenotype in Alzheimer's disease model mice

AIM

After the continued failure of β-secretase (BACE1) inhibitor clinical trials in prodromal as well as mild-to-moderate Alzheimer's disease (AD), they are shifting to further earlier or asymptomatic stages. The aim of this study is to explore a cognitive paradigm that allows us to more sensitively detect beneficial effects of BACE1 inhibitors in presymptomatic AD.

METHODS

GRL-8234 (33.4 mg/kg, ip), a small-molecule BACE1 inhibitor, was administered once daily for 28 days to the 5XAFD transgenic mouse model of AD. The contextual fear conditioning was used to evaluate the effects of GRL-8234 on memory deficits in 5XFAD mice at different ages.

RESULTS

Chronic administration of GRL-8234 to 5XFAD mice rescued their contextual memory deficits, when tested 1 day after training at 6-8 months but not at 12 months of age. Importantly, 4-month-old 5XFAD mice retain the ability to form contextual memory equivalent to wild-type controls, demonstrating that the standard method of 1-day memory assessment is not suitable for evaluating BACE1 inhibitor efficacy in ameliorating cognitive declines during earlier disease stages. Despite normal contextual memory formation, young 5XFAD mice showed faster forgetting when a longer delay (28 days) intervened between training and memory testing. Notably, GRL-8234 administered to 4-month-old 5XFAD mice during the 28-day delay reversed accelerated long-term forgetting almost completely back to wild-type control levels.

CONCLUSION

The results provide experimental evidence that accelerated long-term forgetting represents more sensitive memory testing that can help evaluate BACE1 inhibitor therapy in presymptomatic AD populations.

Alzheimer's Disease Animal Models: Elucidation of Biomarkers and Therapeutic Approaches for Cognitive Impairment

Alzheimer's disease (AD) is an age-related and progressive neurodegenerative disorder. It is widely accepted that AD is mainly caused by the accumulation of extracellular amyloid β (Aβ) and intracellular neurofibrillary tau tangles. Aβ begins to accumulate years before the onset of cognitive impairment, suggesting that the benefit of currently available interventions would be greater if they were initiated in the early phases of AD. To understand the mechanisms of AD pathogenesis, various transgenic mouse models with an accelerated accumulation of Aβ and tau tangles have been developed. However, none of these models exhibit all pathologies present in human AD. To overcome these undesirable phenotypes, APP knock-in mice, which were presented with touchscreen-based tasks, were developed to better evaluate the efficacy of candidate therapeutics in mouse models of early-stage AD. This review assesses several AD mouse models from the aspect of biomarkers and cognitive impairment and discusses their potential as tools to provide novel AD therapeutic approaches.

A Negative Energy Balance Is Associated with Metabolic Dysfunctions in the Hypothalamus of a Humanized Preclinical Model of Alzheimer's Disease, the 5XFAD Mouse

Increasing evidence links metabolic disorders with neurodegenerative processes including Alzheimer’s disease (AD). Late AD is associated with amyloid (Aβ) plaque accumulation, neuroinflammation, and central insulin resistance. Here, a humanized AD model, the 5xFAD mouse model, was used to further explore food intake, energy expenditure, neuroinflammation, and neuroendocrine signaling in the hypothalamus. Experiments were performed on 6-month-old male and female full transgenic (Tg^5xFAD/5xFAD), heterozygous (Tg^5xFAD/-), and non-transgenic (Non-Tg) littermates. Although histological analysis showed absence of Aβ plaques in the hypothalamus of 5xFAD mice, this brain region displayed increased protein levels of GFAP and IBA1 in both Tg^5xFAD/- and Tg^5xFAD/5xFAD mice and increased expression of IL-1β in Tg^5xFAD/5xFAD mice, suggesting neuroinflammation. This condition was accompanied by decreased body weight, food intake, and energy expenditure in both Tg^5xFAD/- and Tg^5xFAD/5xFAD mice. Negative energy balance was associated with altered circulating levels of insulin, GLP-1, GIP, ghrelin, and resistin; decreased insulin and leptin hypothalamic signaling; dysregulation in main metabolic sensors (phosphorylated IRS1, STAT5, AMPK, mTOR, ERK2); and neuropeptides controlling energy balance (NPY, AgRP, orexin, MCH). These results suggest that glial activation and metabolic dysfunctions in the hypothalamus of a mouse model of AD likely result in negative energy balance, which may contribute to AD pathogenesis development.

Phenotypic Differences between the Alzheimer's Disease-Related hAPP-J20 Model and Heterozygous Zbtb20 Knock-Out Mice

Diverse gene products contribute to the pathogenesis of Alzheimer’s disease (AD). Experimental models have helped elucidate their mechanisms and impact on brain functions. Human amyloid precursor protein (hAPP) transgenic mice from line J20 (hAPP-J20 mice) are widely used to simulate key aspects of AD. However, they also carry an insertional mutation in noncoding sequence of one Zbtb20 allele, a gene involved in neural development. We demonstrate that heterozygous hAPP-J20 mice have reduced Zbtb20 expression in some AD-relevant brain regions, but not others, and that Zbtb20 levels are higher in hAPP-J20 mice than heterozygous Zbtb20 knock-out (Zbtb20^+/–) mice. Whereas hAPP-J20 mice have premature mortality, severe deficits in learning and memory, other behavioral alterations, and prominent nonconvulsive epileptiform activity, Zbtb20^+/– mice do not. Thus, the insertional mutation in hAPP-J20 mice does not ablate the affected Zbtb20 allele and is unlikely to account for the AD-like phenotype of this model.

The Potential Role of Protein Kinase R as a Regulator of Age-Related Neurodegeneration

There is a growing evidence describing a decline in adaptive homeostasis in aging-related diseases affecting the central nervous system (CNS), many of which are characterized by the appearance of non-native protein aggregates. One signaling pathway that allows cell adaptation is the integrated stress response (ISR), which senses stress stimuli through four kinases. ISR activation promotes translational arrest through the phosphorylation of the eukaryotic translation initiation factor 2 alpha (eIF2α) and the induction of a gene expression program to restore cellular homeostasis. However, depending on the stimulus, ISR can also induce cell death. One of the ISR sensors is the double-stranded RNA-dependent protein kinase [protein kinase R (PKR)], initially described as a viral infection sensor, and now a growing evidence supports a role for PKR on CNS physiology. PKR has been largely involved in the Alzheimer’s disease (AD) pathological process. Here, we reviewed the antecedents supporting the role of PKR on the efficiency of synaptic transmission and cognition. Then, we review PKR’s contribution to AD and discuss the possible participation of PKR as a player in the neurodegenerative process involved in aging-related pathologies affecting the CNS.

Preservation of dendritic spine morphology and postsynaptic signaling markers after treatment with solid lipid curcumin particles in the 5xFAD mouse model of Alzheimer's amyloidosis

BACKGROUND

Synaptic failure is one of the principal events associated with cognitive dysfunction in Alzheimer's disease (AD). Preservation of existing synapses and prevention of synaptic loss are promising strategies to preserve cognitive function in AD patients. As a potent natural anti-oxidant, anti-amyloid, and anti-inflammatory polyphenol, curcumin (Cur) shows great promise as a therapy for AD. However, hydrophobicity of natural Cur limits its solubility, stability, bioavailability, and clinical utility for AD therapy. We have demonstrated that solid lipid curcumin particles (SLCP) have greater therapeutic potential than natural Cur in vitro and in vivo models of AD. In the present study, we have investigated whether SLCP has any preservative role on affected dendritic spines and synaptic markers in 5xFAD mice.

METHODS

Six- and 12-month-old 5xFAD and age-matched wild-type mice received oral administration of SLCP (100 mg/kg body weight) or equivalent amounts of vehicle for 2 months. Neuronal morphology, neurodegeneration, and amyloid plaque load were investigated from prefrontal cortex (PFC), entorhinal cortex (EC), CA1, CA3, and the subicular complex (SC). In addition, the dendritic spine density from apical and basal branches was studied by Golgi-Cox stain. Further, synaptic markers, such as synaptophysin, PSD95, Shank, Homer, Drebrin, Kalirin-7, CREB, and phosphorylated CREB (pCREB) were studied using Western blots. Finally, cognitive and motor functions were assessed using open-field, novel object recognition (NOR) and Morris water maze (MWM) tasks after treatment with SLCP.

RESULTS

We observed an increased number of pyknotic and degenerated cells in all these brain areas in 5xFAD mice and SLCP treatment partially protected against those losses. Decrease in dendritic arborization and dendritic spine density from primary, secondary, and tertiary apical and basal branches were observed in PFC, EC, CA1, and CA3 in both 6- and 12-month-old 5xFAD mice, and SLCP treatments partially preserved the normal morphology of these dendritic spines. In addition, pre- and postsynaptic protein markers were also restored by SLCP treatment. Furthermore, SLCP treatment improved NOR and cognitive function in 5xFAD mice.

CONCLUSIONS

Overall, these findings indicate that use of SLCP exerts neuroprotective properties by decreasing amyloid plaque burden, preventing neuronal death, and preserving dendritic spine density and synaptic markers in the 5xFAD mice.

The Fragility of Temporal Memory in Alzheimer's Disease

BACKGROUND

Although episodic memory impairment is one of the hallmarks of Alzheimer's disease (AD), the relative decline in the components of episodic memory (What, Where, and When) and the effects of cognitive training on each of them are still unknown.

OBJECTIVE

We aimed to independently assess the impairment in each component of episodic memory in early to moderate AD and address whether it can be enhanced through active, spatiotemporal episodic training.

METHODS

A non-verbal scene-based episodic memory task was developed to assess the ability to remember What, Where, and When information. Experiment 1 tested whether this task can differentiate AD subjects (N = 16) from healthy controls (N = 16). In Experiment 2, 13 AD subjects underwent 16 training sessions, followed by a re-administration of the scene-based memory task. Experiment 3 tested 42 healthy older adults and 51 younger adults on the same task to investigate the effects of normal aging.

RESULTS

Of the three components, When memory had the highest predictive power in distinguishing AD from normal aging. Following training of AD subjects, only Where memory improved. Only What memory revealed a significant decline in healthy subjects from 65-85 years of age.

CONCLUSION

These findings shed new light on the importance of the temporal component of episodic memory as a behavioral marker of AD. The selective improvement of spatial but not temporal memory through training further demonstrates the fragility of temporal memory even in early AD. Neuroscientific research is needed to distinguish whether the Where component was enhanced by improvements in hippocampal spatial representation or by other compensatory mechanisms.

Parvalbumin-Positive Neuron Loss and Amyloid-β Deposits in the Frontal Cortex of Alzheimer's Disease-Related Mice

Alzheimer's disease (AD) has several hallmark features including amyloid-β (Aβ) plaque deposits and neuronal loss. Here, we characterized Aβ plaque aggregation and parvalbumin-positive (PV) GABAergic neurons in 6-9-month-old 5xFAD mice harboring mutations associated with familial AD. We used immunofluorescence staining to compare three regions in the frontal cortex-prelimbic (PrL), cingulate (Cg, including Cg1 and Cg2), and secondary motor (M2) cortices-along with primary somatosensory (S1) cortex. We quantified the density of Aβ plaques, which showed significant laminar and regional vulnerability. There were more plaques of larger sizes in deep layers compared to superficial layers. Total plaque burden was higher in frontal regions compared to S1. We also found layer- and region-specific differences across genotype in the density of PV interneurons. PV neuron density was lower in 5xFAD mice than wild-type, particularly in deep layers of frontal regions, with Cg (-50%) and M2 (-39%) exhibiting the largest reduction. Using in vivo two-photon imaging, we longitudinally visualized the loss of frontal cortical PV neurons across four weeks in the AD mouse model. Overall, these results provide information about Aβ deposits and PV neuron density in a widely used mouse model for AD, implicating deep layers of frontal cortical regions as being especially vulnerable.

Imbalance of Endocannabinoid/Lysophosphatidylinositol Receptors Marks the Severity of Alzheimer's Disease in a Preclinical Model: A Therapeutic Opportunity

Alzheimer's disease (AD) is the most common form of neurodegeneration and dementia. The endocannabinoid (ECB) system has been proposed as a novel therapeutic target to treat AD. The present study explores the expression of the ECB system, the ECB-related receptor GPR55, and cognitive functions (novel object recognition; NOR) in the 5xFAD (FAD: family Alzheimer's disease) transgenic mouse model of AD. Experiments were performed on heterozygous (HTZ) and homozygous (HZ) 11 month old mice. Protein expression of ECB system components, neuroinflammation markers, and β-amyloid (Aβ) plaques were analyzed in the hippocampus. According to the NOR test, anxiety-like behavior and memory were altered in both HTZ and HZ 5xFAD mice. Furthermore, both animal groups displayed a reduction of cannabinoid (CB1) receptor expression in the hippocampus, which is related to memory dysfunction. This finding was associated with indirect markers of enhanced ECB production, resulting from the combination of impaired monoacylglycerol lipase (MAGL) degradation and increased diacylglycerol lipase (DAGL) levels, an effect observed in the HZ group. Regarding neuroinflammation, we observed increased levels of CB2 receptors in the HZ group that positively correlate with Aβ's accumulation. Moreover, HZ 5xFAD mice also exhibited increased expression of the GPR55 receptor. These results highlight the importance of the ECB signaling for the AD pathogenesis development beyond Aβ deposition.

CYP46A1-dependent and independent effects of efavirenz treatment

Cholesterol excess in the brain is mainly disposed via cholesterol 24-hydroxylation catalysed by cytochrome P450 46A1, a CNS-specific enzyme. Cytochrome P450 46A1 is emerging as a promising therapeutic target for various brain diseases with both enzyme activation and inhibition having therapeutic potential. The rate of cholesterol 24-hydroxylation determines the rate of brain cholesterol turnover and the rate of sterol flux through the plasma membranes. The latter was shown to affect membrane properties and thereby membrane proteins and membrane-dependent processes. Previously we found that treatment of 5XFAD mice, an Alzheimer's disease model, with a small dose of anti-HIV drug efavirenz allosterically activated cytochrome P450 46A1 in the brain and mitigated several disease manifestations. Herein, we generated Cyp46a1-/- 5XFAD mice and treated them, along with 5XFAD animals, with efavirenz to ascertain cytochrome P450 46A1-dependent and independent drug effects. Efavirenz-treated versus control Cyp46a1-/- 5XFAD and 5XFAD mice were compared for the brain sterol and steroid hormone content, amyloid β burden, protein and mRNA expression as well as synaptic ultrastructure. We found that the cytochrome P450 46A1-dependent efavirenz effects included changes in the levels of brain sterols, steroid hormones, and such proteins as glial fibrillary acidic protein, Iba1, Munc13-1, post-synaptic density-95, gephyrin, synaptophysin and synapsin-1. Changes in the expression of genes involved in neuroprotection, neurogenesis, synaptic function, inflammation, oxidative stress and apoptosis were also cytochrome P450 46A1-dependent. The total amyloid β load was the same in all groups of animals, except lack of cytochrome P450 46A1 decreased the production of the amyloid β40 species independent of treatment. In contrast, altered transcription of genes from cholinergic, monoaminergic, and peptidergic neurotransmission, steroid sulfation and production as well as vitamin D3 activation was the main CYP46A1-independent efavirenz effect. Collectively, the data obtained reveal that CYP46A1 controls cholesterol availability for the production of steroid hormones in the brain and the levels of biologically active neurosteroids. In addition, cytochrome P450 46A1 activity also seems to affect the levels of post-synaptic density-95, the main postsynaptic density protein, possibly by altering the calcium/calmodulin-dependent protein kinase II inhibitor 1 expression and activity of glycogen synthase kinase 3β. Even at a small dose, efavirenz likely acts as a transcriptional regulator, yet this regulation may not necessarily lead to functional effects. This study further confirmed that cytochrome P450 46A1 is a key enzyme for cholesterol homeostasis in the brain and that the therapeutic efavirenz effects on 5XFAD mice are likely realized via cytochrome P450 46A1 activation.