Amyloid beta and impairment in multiple memory systems in older transgenic APP TgCRND8 mice

Ultrasound delivery of a TrkA agonist confers neuroprotection to Alzheimer-associated pathologies

Early degeneration of basal forebrain cholinergic neurons (BFCNs) contributes substantially to cognitive decline in Alzheimer's disease (AD). Evidence from preclinical models of neuronal injury and aging support a pivotal role for nerve growth factor (NGF) in neuroprotection, resilience, and cognitive function. However, whether NGF can provide therapeutic benefit in the presence of AD-related pathologies remains unresolved. Perturbations in the NGF signaling system in AD may render neurons unable to benefit from NGF administration. Additionally, challenges related to brain delivery remain for clinical translation of NGF-based therapies in AD. To be safe and efficient, NGF-related agents should stimulate the NGF receptor, tropomyosin receptor kinase A (TrkA), avoid activation through the p75 neurotrophin receptor (p75NTR), and be delivered non-invasively to targeted brain areas using real-time monitoring. We addressed these limitations using MRI-guided focused ultrasound (MRIgFUS) to increase blood-brain barrier (BBB) permeability locally and transiently, allowing an intravenously administered TrkA agonist that does not activate p75NTR, termed D3, to enter targeted brain areas. Here, we report the therapeutic potential of selective TrkA activation in a transgenic mouse model that recapitulates numerous AD-associated pathologies. Repeated MRIgFUS-mediated delivery of D3 (D3/FUS) improved cognitive function in the TgCRND8 model of AD. Mechanistically, D3/FUS treatment effectively attenuated cholinergic degeneration and promoted functional recovery. D3/FUS treatment also resulted in widespread reduction of brain amyloid pathology and dystrophic neurites surrounding amyloid plaques. Furthermore, D3/FUS markedly enhanced hippocampal neurogenesis in TgCRND8 mice, implicating TrkA agonism as a novel therapeutic target to promote neurogenesis in the context of AD-related pathology. Thus, this study provides evidence that selective TrkA agonism confers neuroprotection to effectively counteract AD-related vulnerability. Recent clinical trials demonstrate that non-invasive BBB modulation using MRIgFUS is safe, feasible and reversible in AD patients. TrkA receptor agonists coupled with MRIgFUS delivery constitute a promising disease-modifying strategy to foster brain health and counteract cognitive decline in AD.

Progressive impairments in executive function in the APP/PS1 model of Alzheimer's disease as measured by translatable touchscreen testing

Executive function deficits in Alzheimer's disease (AD) occur early in disease progression and may be predictive of cognitive decline. However, no preclinical studies have identified deficits in rewarded executive function in the commonly used APPSwe/PS1∆E9 (APP/PS1) mouse model. To address this, we assessed 12-26 month old APP/PS1 mice on rewarded reversal and/or extinction tasks. 16-month-old, but not 13- or 26-month-old, APP/PS1 mice showed an attenuated rate of extinction. Reversal deficits were seen in 22-month-old, but not 13-month-old APP/PS1 animals. We then confirmed that impairments in reversal were unrelated to previously reported visual impairments in both AD mouse models and humans. Age, but not genotype, had a significant effect on markers of retinal health, indicating the deficits seen in APP/PS1 mice were directly related to cognition. This is the first characterisation of rewarded executive function in APP/PS1 mice, and has great potential to facilitate translation from preclinical models to the clinic.

Time course of focused ultrasound effects on β-amyloid plaque pathology in the TgCRND8 mouse model of Alzheimer's disease

Previous studies have demonstrated that temporarily increasing the permeability of the blood-brain barrier using focused ultrasound can reduce β-amyloid plaque load and improve cognitive function in animal models of Alzheimer’s disease. However, the underlying mechanism and duration for which the effects of one treatment persists for are unknown. Here, we used in vivo two-photon fluorescence microscopy to track changes in β-amyloid plaque sizes in the TgCRND8 mouse model of Alzheimer’s disease after one focused ultrasound treatment. We found that one treatment reduced plaques to 62 ± 16% (p ≤ 0.001) of their original volume two days post-sonication; this decrease in size persisted for two weeks. We then sought to evaluate the effectiveness of biweekly focused ultrasound treatments using magnetic resonance imaging-guided focused ultrasound treatments. Three to five biweekly treatments resulted in a 27 ± 7% (p ≤ 0.01) decrease in plaque number and 40 ± 10% (p ≤ 0.01) decrease in plaque surface area compared to untreated littermates. This study demonstrates that one focused ultrasound treatment reduces the size of existing β-amyloid plaques for two weeks, and that repeated biweekly focused ultrasound treatments is an effective method of reducing β-amyloid pathology in moderate-to-late stages of Alzheimer’s disease.

Effects of Aged Garlic Extract on Cholinergic, Glutamatergic and GABAergic Systems with Regard to Cognitive Impairment in Aβ-Induced Rats

Alzheimer’s disease (AD) has been linked to the degeneration of central cholinergic and glutamatergic transmission, which correlates with progressive memory loss and the accumulation of amyloid-β (Aβ). It has been claimed that aged garlic extract (AGE) has a beneficial effect in preventing neurodegeneration in AD. Therefore, the objective of this study was to investigate the effects of AGE on Aβ-induced cognitive dysfunction with a biochemical basis in the cholinergic, glutamatergic, and GABAergic systems in rats. Adult male Wistar rats were orally administered three doses of AGE (125, 250, and 500 mg/kg) daily for 65 days. At day 56, they were injected with 1 μL of aggregated Aβ (1–42) into each lateral ventricle, bilaterally. After six days of Aβ injection, the rats’ working and reference memory was tested using a radial arm maze. The rats were then euthanized to investigate any changes to the cholinergic neurons, vesicular glutamate transporter 1 and 2 proteins (VGLUT1 and VGLUT2), and glutamate decarboxylase (GAD) in the hippocampus. The results showed that AGE significantly improved the working memory and tended to improve the reference memory in cognitively-impaired rats. In addition, AGE significantly ameliorated the loss of cholinergic neurons and increased the VGLUT1 and GAD levels in the hippocampus of rat brains with Aβ-induced toxicity. In contrast, the VGLUT2 protein levels did not change in any of the treated groups. We concluded that AGE was able to attenuate the impairment of working memory via the modification of cholinergic neurons, VGLUT1, and GAD in the hippocampus of Aβ-induced rats.

Behavioral abnormalities in APPSwe/PS1dE9 mouse model of AD-like pathology: comparative analysis across multiple behavioral domains

Alzheimer's disease (AD) is characterized by dysfunction in cognitive and noncognitive domains with clinical diagnosis based on multiple neuropsychological tests. Here, we evaluated cognitive and noncognitive behaviors in 2 age cohorts (8 and 14 months at the start of the study) of APPSwe/PS1dE9 transgenic mice that model AD-like amyloidosis. We used a battery of tests that included fear-conditioned context and tone memories, swimming activity, and orientation to a proximal cue in a visible platform water maze test and burrowing and nest building activity. To compare the performance of mice across all tests, we used z-score normalization of data. The analyses revealed that the behavior of the transgenic mice was significantly compromised in cognitive as well as in noncognitive domains. Combining scores across multiple behavioral tests produced an integrated index characterizing the overall phenotypic abnormality in this model of AD-like amyloidosis. Assessing multiple behavioral domains provides a broader view of the breadth of impairments in multiple behavioral systems. Greater implementation of such approaches could enable reliable and clinically predictive evaluation of therapeutics in mouse models of amyloidosis.

α-Melanocyte stimulating hormone prevents GABAergic neuronal loss and improves cognitive function in Alzheimer's disease

In Alzheimer's disease (AD), appropriate excitatory-inhibitory balance required for memory formation is impaired. Our objective was to elucidate deficits in the inhibitory GABAergic system in the TgCRND8 mouse model of AD to establish a link between GABAergic dysfunction and cognitive function. We sought to determine whether the neuroprotective peptide α-melanocyte stimulating hormone (α-MSH) attenuates GABAergic loss and thus improves cognition. TgCRND8 mice with established β-amyloid peptide pathology and nontransgenic littermates were treated with either α-MSH or vehicle via daily intraperitoneal injections for 28 d. TgCRND8 mice exhibited spatial memory deficits and altered anxiety that were rescued after α-MSH treatment. The expression of GABAergic marker glutamic acid decarboxylase 67 (GAD67) and the number of GABAergic GAD67+ interneurons expressing neuropeptide Y and somatostatin are reduced in the hippocampus in vehicle-treated TgCRND8 mice. In the septohippocampal pathway, GABAergic deficits are observed before cholinergic deficits, suggesting that GABAergic loss may underlie behavior deficits in vehicle-treated TgCRND8 mice. α-MSH preserves GAD67 expression and prevents loss of the somatostatin-expressing subtype of GABAergic GAD67+ inhibitory interneurons. Without decreasing β-amyloid peptide load in the brain, α-MSH improves spatial memory in TgCRND8 mice and prevents alterations in anxiety. α-MSH modulated the excitatory-inhibitory balance in the brain by restoring GABAergic inhibition and, as a result, improved cognition in TgCRND8 mice.

Using mice to model Alzheimer's dementia: an overview of the clinical disease and the preclinical behavioral changes in 10 mouse models

The goal of this review is to discuss how behavioral tests in mice relate to the pathological and neuropsychological features seen in human Alzheimer's disease (AD), and present a comprehensive analysis of the temporal progression of behavioral impairments in commonly used AD mouse models that contain mutations in amyloid precursor protein (APP). We begin with a brief overview of the neuropathological changes seen in the AD brain and an outline of some of the clinical neuropsychological assessments used to measure cognitive deficits associated with the disease. This is followed by a critical assessment of behavioral tasks that are used in AD mice to model the cognitive changes seen in the human disease. Behavioral tests discussed include spatial memory tests [Morris water maze (MWM), radial arm water maze (RAWM), Barnes maze], associative learning tasks (passive avoidance, fear conditioning), alternation tasks (Y-Maze/T-Maze), recognition memory tasks (Novel Object Recognition), attentional tasks (3 and 5 choice serial reaction time), set-shifting tasks, and reversal learning tasks. We discuss the strengths and weaknesses of each of these behavioral tasks, and how they may correlate with clinical assessments in humans. Finally, the temporal progression of both cognitive and non-cognitive deficits in 10 AD mouse models (PDAPP, TG2576, APP23, TgCRND8, J20, APP/PS1, TG2576 + PS1 (M146L), APP/PS1 KI, 5×FAD, and 3×Tg-AD) are discussed in detail. Mouse models of AD and the behavioral tasks used in conjunction with those models are immensely important in contributing to our knowledge of disease progression and are a useful tool to study AD pathophysiology and the resulting cognitive deficits. However, investigators need to be aware of the potential weaknesses of the available preclinical models in terms of their ability to model cognitive changes observed in human AD. It is our hope that this review will assist investigators in selecting an appropriate mouse model, and accompanying behavioral paradigms to investigate different aspects of AD pathology and disease progression.

Dose-dependent improvements in learning and memory deficits in APPPS1-21 transgenic mice treated with the orally active Aβ toxicity inhibitor SEN1500

In the Alzheimer's disease (AD) brain, accumulation of Aβ1-42 peptides is suggested to initiate a cascade of pathological events. To date, no treatments are available that can reverse or delay AD-related symptoms in patients. In the current study, we introduce a new Aβ toxicity inhibitor, SEN1500, which in addition to its block effect on Aβ1-42 toxicity in synaptophysin assays, can be administered orally and cross the blood-brain barrier without adverse effects in mice. In a different set of animals, APPPS1-21 mice were fed with three different doses of SEN1500 (1 mg/kg, 5 mg/kg and 20 mg/kg) for a period of 5 months. Cognition was assessed in a variety of behavioral tests (Morris water maze, social recognition, conditioned taste aversion and passive avoidance). Results suggest a positive effect on cognition with 20 mg/kg SEN1500 compared to control APPPS1-21 mice. However, no changes in soluble or insoluble Aβ1-40 and Aβ1-42 were detected in the brains of SEN1500-fed mice. SEN1500 also attenuated the effect of Aβ1-42 on synaptophysin levels in mouse cortical neurons, which indicated that the compound blocked the synaptic toxicity of Aβ1-42. In vitro and in vivo effects presented here suggest that SEN1500 could be an interesting AD therapeutic.

Comprehensive behavioral characterization of an APP/PS-1 double knock-in mouse model of Alzheimer's disease

INTRODUCTION

Despite the extensive mechanistic and pathological characterization of the amyloid precursor protein (APP)/presenilin-1 (PS-1) knock-in mouse model of Alzheimer's disease (AD), very little is known about the AD-relevant behavioral deficits in this model. Characterization of the baseline behavioral performance in a variety of functional tasks and identification of the temporal onset of behavioral impairments are important to provide a foundation for future preclinical testing of AD therapeutics. Here we perform a comprehensive behavioral characterization of this model, discuss how the observed behavior correlates with the mechanistic and pathological observations of others, and compare this model with other commonly used AD mouse models.

METHODS

FOUR DIFFERENT GROUPS OF MICE RANGING ACROSS THE LIFESPAN OF THIS MODEL (TEST GROUPS: 7, 11, 15, and 24 months old) were run in a behavioral test battery consisting of tasks to assess motor function (grip strength, rotor rod, beam walk, open field ambulatory movement), anxiety-related behavior (open field time spent in peripheral zone vs. center zone, elevated plus maze), and cognitive function (novel object recognition, radial arm water maze).

RESULTS

There were no differences in motor function or anxiety-related behavior between APP/PS-1 knock-in mice and wild-type counterpart mice for any age group. Cognitive deficits in both recognition memory (novel object recognition) and spatial reference memory (radial arm water maze) became apparent for the knock-in animals as the disease progressed.

CONCLUSION

This is the first reported comprehensive behavioral analysis of the APP/PS1 knock-in mouse model of AD. The lack of motor/coordination deficits or abnormal anxiety levels, coupled with the age/disease-related cognitive decline and high physiological relevance of this model, make it well suited for utilization in preclinical testing of AD-relevant therapeutics.

Normal cognition in transgenic BRI2-Aβ mice

BACKGROUND

Recent research in Alzheimer's disease (AD) field has been focused on the potential role of the amyloid-β protein that is derived from the transmembrane amyloid precursor protein (APP) in directly mediating cognitive impairment in AD. Transgenic mouse models overexpressing APP develop robust AD-like amyloid pathology in the brain and show various levels of cognitive decline. In the present study, we examined the cognition of the BRI2-Aβ transgenic mouse model in which secreted extracellular Aβ1-40, Aβ1-42 or both Aβ1-40/Aβ1-42 peptides are generated from the BRI-Aβ fusion proteins encoded by the transgenes. BRI2-Aβ mice produce high levels of Aβ peptides and BRI2-Aβ1-42 mice develop amyloid pathology that is similar to the pathology observed in mutant human APP transgenic models.

RESULTS

Using established behavioral tests that reveal deficits in APP transgenic models, BRI2-Aβ1-42 mice showed completely intact cognitive performance at ages both pre and post amyloid plaque formation. BRI2-Aβ mice producing Aβ1-40 or both peptides were also cognitively intact.

CONCLUSIONS

These data indicate that high levels of Aβ1-40 or Aβ1-42, or both produced in the absence of APP overexpression do not reproduce memory deficits observed in APP transgenic mouse models. This outcome is supportive of recent data suggesting that APP processing derivatives or the overexpression of full length APP may contribute to cognitive decline in APP transgenic mouse models. Alternatively, Aβ aggregates may impact cognition by a mechanism that is not fully recapitulated in these BRI2-Aβ mouse models.

Behavioral effects of Rho GTPase modulation in a model of Alzheimer's disease

Small GTPases of the Rho family, including Rho, Rac and CDC42 subfamilies, play key role in neural connectivity and cognition. The pharmacological modulation of these regulatory proteins is associated with enhancement of learning and memory. We sought to determine whether the modulation of cerebral Rho GTPases may correct behavioral disturbances in a mouse model of Alzheimer's disease (AD). TgCRND8 mice show early-onset Abeta amyloid deposits associated with deficits in several cognitive tasks. We report that four-month old TgCRND8 mice display (a) increased locomotor activity in an open field, (b) mild deficits in the learning of a fixed platform position in a water maze task. More markedly, after displacement of the escape platform, TgCRND8 mice exhibit impairment in the learning of the novel position (reversal learning), as they perseverate searching in the familiar position. The administration of the Rho GTPase activator Cytotoxic Necrotizing Factor 1 (CNF1, 1.0 fmol kg(-1) intracerebroventricularly) reduces locomotor hyperactivity and corrects the deficits in reversal learning, thus re-establishing normal behavioral plasticity. We conclude that the pharmacological modulation of Rho GTPase signaling might be beneficial for the treatment of AD. Reversal learning in TgCRND8 mice may represent a convenient pre-clinical assay for the efficacy of therapeutic interventions in AD.

Age-related increase in amyloid plaque burden is associated with impairment in conditioned fear memory in CRND8 mouse model of amyloidosis

Introduction

The current pathological confirmation of the diagnosis of Alzheimer's disease (AD) is still based on postmortem identification of parenchymal amyloid beta (Aβ) plaques, intra-neuronal neurofibrillary tangles, and neuronal loss. The memory deficits that are present in the early stages of AD are linked to the dysfunction of structures in the entorhinal cortex and limbic system, especially the hippocampus and amygdala. Using the CRND8 transgenic mouse model of amyloidosis, which over-expresses a mutant human amyloid precursor protein (APP) gene, we evaluated hippocampus-dependent contextual and amygdala-dependent tone fear conditioned (FC) memory, and investigated the relationship between the fear memory indices and Aβ plaque burden.

Methods

Mice were tested at three, six, and 12 months of age, which corresponds to early, mild, and severe Aβ plaque deposition, following a cross-sectional experimental design. We used a delay version of the fear conditioning paradigm in which tone stimulus was co-terminated with foot-shocks during exploration of the training chamber. The Aβ plaque burden was evaluated at each age after the completion of the behavioral tests.

Results

CRDN8 mice showed context fear memory comparable to control mice at three and six months, but were significantly impaired at 12 months of age. In contrast, the tone fear memory was significantly impaired in the model at each age of testing. The Aβ plaque burden significantly increased with age, and was correlated with the overall impairment in context and tone fear memory in the CRND8 mice within the studied age.

Conclusions

Our data extend previous studies showing that other APP mouse models exhibit impairment in fear conditioned memory, by demonstrating that this impairment is progressive and correlates well with an overall increase in Aβ burden. Also, the demonstrated greater sensitivity of the tone conditioning test in the identification of age dependent differences between CRND8 and control mice suggests that this paradigm might be particularly suitable in studies evaluating potential therapeutics related to memory improvement in mouse models of amyloidosis.

Reversal of autophagy dysfunction in the TgCRND8 mouse model of Alzheimer's disease ameliorates amyloid pathologies and memory deficits

Autophagy, a major degradative pathway for proteins and organelles, is essential for survival of mature neurons. Extensive autophagic-lysosomal pathology in Alzheimer's disease brain contributes to Alzheimer's disease pathogenesis, although the underlying mechanisms are not well understood. Here, we identified and characterized marked intraneuronal amyloid-β peptide/amyloid and lysosomal system pathology in the Alzheimer's disease mouse model TgCRND8 similar to that previously described in Alzheimer's disease brains. We further establish that the basis for these pathologies involves defective proteolytic clearance of neuronal autophagic substrates including amyloid-β peptide. To establish the pathogenic significance of these abnormalities, we enhanced lysosomal cathepsin activities and rates of autophagic protein turnover in TgCRND8 mice by genetically deleting cystatin B, an endogenous inhibitor of lysosomal cysteine proteases. Cystatin B deletion rescued autophagic-lysosomal pathology, reduced abnormal accumulations of amyloid-β peptide, ubiquitinated proteins and other autophagic substrates within autolysosomes/lysosomes and reduced intraneuronal amyloid-β peptide. The amelioration of lysosomal function in TgCRND8 markedly decreased extracellular amyloid deposition and total brain amyloid-β peptide 40 and 42 levels, and prevented the development of deficits of learning and memory in fear conditioning and olfactory habituation tests. Our findings support the pathogenic significance of autophagic-lysosomal dysfunction in Alzheimer's disease and indicate the potential value of restoring normal autophagy as an innovative therapeutic strategy for Alzheimer's disease.

A nonhuman primate model of Alzheimer's disease generated by intracranial injection of amyloid-β42 and thiorphan

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive impairment and neuropathological changes, including the deposition of amyloid-beta (Aβ) peptide. Aged monkeys have proven to be invaluable in the study of AD, as their brains naturally develop amyloid plaques similar to those in AD brains. However, spontaneous development of AD-like pathologies in aged monkeys is time-consuming, often taking several years. Here, we created an experimentally induced AD model in middle-aged (16-17 years) rhesus monkeys by intracranial injection of Aβ42 and thiorphan, an inhibitor of neprilysin that is responsible for Aβ clearance. The working memory capacity of the monkeys in a delayed-response task was little affected following the delivery of Aβ42 and thiorphan. However, the administration of Aβ42 and thiorphan resulted in a significant intracellular accumulation of Aβ in the neurons of the basal ganglia, the cortex, and the hippocampus, accompanied by neuronal atrophy and loss. Moreover, immunohistochemistry revealed a degeneration of choline acetyltransferase-positive cholinergic neurons and an increase of glial fibrillary acidic protein-positive astrocytes. In conclusion, our data demonstrate a primate model of AD generated by combined infusion of Aβ42 and thiorphan, which duplicates a subset of neuropathological changes in AD brains, thereby having implications in the elucidation of this disease.

Object recognition memory and BDNF expression are reduced in young TgCRND8 mice

The TgCRND8 mouse model of Alzheimer's disease exhibits progressive cortical and hippocampal β-amyloid accumulation, resulting in plaque pathology and spatial memory impairment by 3 months of age. We tested whether TgCRND8 cognitive function is disrupted prior to the appearance of macroscopic plaques in an object recognition task. We found profound deficits in 8-week-old mice. Animals this age were not impaired on the Morris water maze task. TgCRND8 and littermate controls did not differ in their duration of object exploration or optokinetic responses. Thus, visual and motor dysfunction did not confound the phenotype. Object memory deficits point to the frontal cortex and hippocampus as early targets of functional disruption. Indeed, we observed altered levels of brain-derived neurotrophic factor (BDNF) messenger ribonucleic acid (mRNA) in these brain regions of preplaque TgCRND8 mice. Our findings suggest that object recognition provides an early index of cognitive impairment associated with amyloid exposure and reduced brain-derived neurotrophic factor expression in the TgCRND8 mouse.

Age-dependent increase in lysosome-associated membrane protein 1 and early-onset behavioral deficits in APPSL transgenic mouse model of Alzheimer's disease

Amyloid precursor protein (APP) is strongly related to the onset of Alzheimer's disease. It possesses cleavage sites for beta- and gamma-secretases, and the resulting cleaved products (amyloid-beta peptides) are capable of causing neurotoxicity. Such cleavage is promoted by the Swedish and London mutations (APPSwe/Lon) inside the APP gene. Here, we characterized APPSL transgenic mice (APPSL-Tg) to determine the effects of this mutation. We observed that both the amount of insoluble amyloid-beta and the ratio of amyloid-beta 42/40 increased promptly in the brain during 6-16 months of age. Amyloid-beta plaques were observed in whole brain sections at 12 months. In contrast, the spatial memory assessed by the Morris water maze task was already impaired at 3 months, which suggested that the APPSL-Tg mice may represent an early-onset model of familial Alzheimer's disease. Furthermore, the levels of LAMP-1, a marker protein of lysosome, increased in the brain at 28 months. Such LAMP-1 protein was detected around the amyloid-beta plaques at the hippocampal regions of the APPSL-Tg mice. Our results suggested that the increase in LAMP-1 was enhanced by the accumulation of amyloid-beta occurring during aging. Our findings coincided with the pathological hallmarks of Alzheimer's disease.