Progressive neuropathology and cognitive decline in a single Arctic APP transgenic mouse model

The Arctic APP mutation (E693G) leads to dementia with clinical features similar to Alzheimer disease (AD), but little is known about the pathogenic mechanism of this mutation. To address this question, we have generated a transgenic mouse model, TgAPParc, with neuron-specific expression of human APP with the Arctic mutation (hAPParc). Heterozygous mice from two separate founder lines with different levels of expression of hAPParc were analyzed with respect to brain morphology and behavior every 3 months until the age of 18 months. Standard histological stainings and immunohistochemistry using a panel of Aβ antibodies showed an age- and dose-dependant progression of amyloid deposition in the brain, starting in the subiculum and spreading to the thalamus. Cognitive behavioral testing revealed deficits in hippocampus-dependent spatial learning and memory in the Barnes maze test. This study demonstrates that the Arctic APP mutation is sufficient to cause amyloid deposition and cognitive dysfunction, and thus the TgAPParc mouse model provides a valuable tool to study the effect of the Arctic mutation in vivo without possible confounding effect of other APP mutations.     

A highly insoluble state of Abeta similar to that of Alzheimer's disease brain is found in Arctic APP transgenic mice

Amyloid-β (Aβ) is a major drug target in Alzheimer's disease. Here, we demonstrate that deposited Aβ is SDS insoluble in tgAPP-ArcSwe, a transgenic mouse model harboring the Arctic (E693G) and Swedish (KM670/671NL) APP mutations. Formic acid was needed to extract the majority of deposited Aβ in both tgAPP-ArcSwe and Alzheimer's disease brain, but not in a commonly used type of mouse model with the Swedish mutation alone. Interestingly, the insoluble state of Arctic Aβ was determined early on and did not gradually evolve with time. In tgAPP-ArcSwe, Aβ plaques displayed a patchy morphology with bundles of Aβ fibrils, whereas amyloid cores in tgAPP-Swe were circular with radiating fibrils. Amyloid was more densely stacked in tgAPP-ArcSwe, as demonstrated with a conformation sensitive probe. A reduced increase in plasma Aβ was observed following acute administration of an Aβ antibody in tgAPP-ArcSwe, results that might imply reduced brain to plasma Aβ efflux. TgAPP-ArcSwe, with its insoluble state of deposited Aβ, could serve as a complementary model to better predict the outcome of clinical trials.     

Prenatal hypoxia may aggravate the cognitive impairment and Alzheimer’s disease neuropathology in APP/PS1 transgenic mice

Most cases of Alzheimer's disease (AD) arise through interactions between genetic and environmental factors. It is believed that hypoxia is an important environmental factor influencing the development of AD. Our group has previously demonstrated that hypoxia increased β-amyloid (Aβ) generation in aged AD mice. Here, we further investigate the pathological role of prenatal hypoxia in AD. We exposed the pregnant APP^Swe/PS1^A246E transgenic mice to high-altitude hypoxia in a hypobaric chamber during days 7–20 of gestation. We found that prenatal hypoxic mice exhibited a remarkable deficit in spatial learning and memory and a significant decrease in synapses. We also documented a significantly higher level of amyloid precursor protein, lower level of the Aβ-degrading enzyme neprilysin, and increased Aβ accumulation in the brain of prenatal hypoxic mice. Finally, we demonstrated striking neuropathologic changes in prenatal hypoxic AD mice, showing increased phosphorylation of tau, decreased hypoxia-induced factor, and enhanced activation of astrocytes and microglia. These data suggest that although the characteristic features of AD appear later in life, hypoxemia in the prenatal stage may contribute to the pathogenesis of the disease, supporting the notion that environmental factors can trigger or aggravate AD.     

Alzheimer-associated APP+1 transgenic mice: frameshift beta-amyloid precursor protein is secreted in cerebrospinal fluid without inducing neuropathology

Biomarkers present in the cerebrospinal fluid (CSF) of Alzheimer Disease patients could be instrumental in guiding diagnosis and monitoring of progression of the disease. We have previously reported on the secretion of a frameshifted form of amyloid-beta precursor protein, APP+1, into the CSF of Alzheimer patients and controls. APP+1 is secreted efficiently in controls, but during the progression of Alzheimer Disease, its secretion is reduced and APP+1 accumulates in tangle-bearing neurons. Here we describe the generation of a transgenic mouse line expressing APP+1 in the brain. These mice do not suffer from overt pathology or neurodegeneration, suggesting that APP+1 is not neurotoxic. To measure APP+1 levels in the CSF, we serially sampled CSF from the cisterna magna in the same mouse over a period of months. Indeed, APP+1 is secreted into the CSF of the transgenic mice, and APP+1 levels are stable over 1 year. This mouse model may guide the study of secretion deficits as found in Alzheimer Disease.     

Targeting BACE1 with siRNAs ameliorates Alzheimer disease neuropathology in a transgenic model

In Alzheimer disease, increased beta-secretase (BACE1) activity has been associated with neurodegeneration and accumulation of amyloid precursor protein (APP) products. Thus, inactivation of BACE1 could be important in the treatment of Alzheimer disease. In this study, we found that lowering BACE1 levels using lentiviral vectors expressing siRNAs targeting BACE1 reduced amyloid production and the neurodegenerative and behavioral deficits in APP transgenic mice, a model of Alzheimer disease. Our results suggest that lentiviral vector delivery of BACE1 siRNA can specifically reduce the cleavage of APP and neurodegeneration in vivo and indicate that this approach could have potential therapeutic value for treatment of Alzheimer disease.     

Amyloid deposition precedes tangle formation in a triple transgenic model of Alzheimer's disease

Amyloid-β (Aβ) containing plaques and tau-laden neurofibrillary tangles are the defining neuropathological features of Alzheimer’s disease (AD). To better mimic this neuropathology, we generated a novel triple transgenic model of AD (3xTg-AD) harboring three mutant genes: β-amyloid precursor protein (βAPP_Swe), presenilin-1 (PS1_M146V), and tau_P301L. The 3xTg-AD mice progressively develop Aβ and tau pathology, with a temporal- and regional-specific profile that closely mimics their development in the human AD brain. We find that Aβ deposits initiate in the cortex and progress to the hippocampus with aging, whereas tau pathology is first apparent in the hippocampus and then progresses to the cortex. Despite equivalent overexpression of the human βAPP and human tau transgenes, Aβ deposition develops prior to the tangle pathology, consistent with the amyloid cascade hypothesis. As these 3xTg-AD mice phenocopy critical aspects of AD neuropathology, this model will be useful in pre-clinical intervention trials, particularly because the efficacy of anti-AD compounds in mitigating the neurodegenerative effects mediated by both signature lesions can be evaluated.     

Altered expression and distribution of zinc transporters in APP/PS1 transgenic mouse brain

Pathological accumulation of beta-amyloid peptide (Abeta) is an early and common feature of Alzheimer's disease (AD). An increased zinc concentration can initiate the deposition of Abeta. The present study aimed to study the expression and distribution patterns of six members of the zinc transporter (ZnT) family, ZnT1, ZnT3, ZnT4, ZnT5, ZnT6, and ZnT7, in the APPswe/PS1dE9 transgenic mouse brain. Our results demonstrated a statistically significant (P<0.05) increase of ZnT1, ZnT3, ZnT4, ZnT6, and ZnT7 in both hippocampus and neo-cortex using Western blot method and an abundant distribution of zinc ions in the plaques and amyloid angiopathic vessels using immersion autometallography. Furthermore, all ZnT immunoreactions were detected in most amyloid plaques and amyloid angiopathic vessels. ZnT1 and ZnT4 were extensively expressed in all parts of the plaques. ZnT3, ZnT5, and ZnT6 were expressed most prominently in the degenerating neurites in the peripheral part of the plaques, while ZnT7 was present in the core of the plaques. The amyloid angiopathic vessels showed a strong ZnT3 immunoreactivity. These results might suggest multiple roles of ZnTs in the deposition and organization of the Abeta composition.     

APP转基因拟痴呆小鼠模型脑内α synuclein的增龄改变

目的： 观察不同时程APP转基因拟痴呆小鼠脑内α synuclein的改变，以探讨α synuclein在AD发病中的作用。方法: 拟AD动物模型为4 月龄、10月龄和16月龄APP695V717I转基因小鼠；同背景同月龄C57BL/6J小鼠设为正常对照组。表达谱基因芯片、RT PCR方法检测皮层、海马mRNA表达改变；Western blotting、免疫组化法检测蛋白表达的改变。结果: α-synuclein mRNA表达在不同时程APP转基因小鼠脑内均明显增多。α-synuclein蛋白表达在早期4月龄APP转基因小鼠即显著上调，10月龄继续增多，16月龄继续上调并形成蛋白的异常聚集。结论: APP转基因小鼠脑内AD老年斑非Aβ主要成分α-synuclein表达明显增多，并随增龄不断加重，可能是模型小鼠学习记忆障碍及AD发病的重要因素。     

Alterations in beta-amyloid production and deposition in brain regions of two transgenic models

Mutations in the amyloid precursor protein (APP) gene are associated with altered production and deposition of amyloid beta (Abeta) peptide in the Alzheimer's disease (AD) brain. The pathways that regulate APP processing, Abeta production and Abeta deposition in different tissues and brain regions remain unclear. To address this, we examined levels of various APP processing products as well as Abeta deposition in a genomic-based (R1.40) and a cDNA-based (Tg2576) transgenic mouse model of AD. In tissues, only brain generated detectable levels of the penultimate precursor to Abeta, APP C-terminal fragment-beta. In brain regions, holoAPP levels remained constant, but ratios of APP C-terminal fragments and levels of Abeta differed significantly. Surprisingly, cortex had the lowest steady-state levels of Abeta compared to other brain regions. Comparison of Abeta deposition in Tg2576 and R1.40 animals revealed that R1.40 exhibited more abundant deposition in cortex while Tg2576 exhibited extensive deposition in the hippocampus. Our results suggest that AD transgenic models are not equal; their unique characteristics must be considered when studying AD pathogenesis and therapies.     

In vivo MRI and histological evaluation of brain atrophy in APP/PS1 transgenic mice

Regional cerebral atrophy was evaluated in APP/PS1 mice harboring mutated transgenes linked to familial Alzheimer's disease, using complementary methods. In vivo high resolution MRI was selected for measurements of brain atrophy and associated cerebrospinal fluid dilation; histological analysis was performed to reveal localized atrophies and to evaluate amyloid burden. Young APP/PS1 mice examined at a pre-amyloid stage (10 weeks) showed disruption in development (reduced intracranial and brain volumes). Comparison of young and old (24 months) mice, indicated that both APP/PS1 and control brains endure growth during adulthood. Aged APP/PS1 animals showed a moderate although significant global brain atrophy and a dilation of CSF space in posterior brain regions. The locus of this atrophy was identified in the midbrain area and not, as expected, at isocortical/hippocampal levels. Atrophy was also detected in fiber tracts. The severity of brain atrophy in old APP/PS1 mice was not correlated with the extent of cerebral amyloidosis. The relevance of current transgenic mouse models for the study of brain atrophy related to Alzheimer's disease is discussed.     

Amyloid plaques arise from zinc-enriched cortical layers in APP/PS1 transgenic mice and are paradoxically enlarged with dietary zinc deficiency

The ZnT3 zinc transporter is uniquely expressed in cortical glutamatergic synapses where it organizes zinc release into the synaptic cleft and mediates beta-amyloid deposition in transgenic mice. We studied the association of zinc in plaques in relation to cytoarchitectural zinc localization in the APP/PS1 transgenic mouse model of Alzheimer's disease. The effects of low dietary zinc for 3 months upon brain pathology were also studied. We determined that synaptic zinc distribution within cortical layers is paralleled by amyloid burden, which is heaviest for both in layers 2-3 and 5. ZnT3 immunoreactivity is prominent in dystrophic neurites within amyloid plaques. Low dietary zinc caused a significant 25% increase in total plaque volume in Alzheimer's mice using stereological measures. The level of oxidized proteins in brain tissue did not changed in animals on a zinc-deficient diet compared with controls. No obvious changes were observed in the autometallographic pattern of zinc-enriched terminals in the neocortex or in the expression levels of zinc transporters, zinc importers or metallothioneins. A small decrease in plasma zinc induced by the low-zinc diet was consistent with the subclinical zinc deficiency that is common in older human populations. While the mechanism remains uncertain, our findings indicate that subclinical zinc deficiency may be a risk factor for Alzheimer's pathology.     

Pathogenic accumulation of APP in fast twitch muscle of IBM patients and a transgenic model

Inclusion body myositis (IBM) is the most common age-related degenerative skeletal muscle disorder. The aberrant intracellular accumulation of the beta-amyloid (Abeta) peptide within skeletal muscle is a pathological hallmark of IBM. Skeletal muscle is comprised of both slow and fast twitch fibers, which are present in different proportions in various muscles. It remains unclear if fast and/or slow twitch fibers are differentially involved in IBM pathogenesis. To better understand the molecular pathogenesis of IBM, we analyzed human IBM muscle biopsies and muscle from a transgenic mouse model of IBM (MCK-betaAPP). Here we report that the majority of histopathologically-affected fibers in human IBM biopsies were type II fast fibers. Skeletal muscle from MCK-betaAPP mice exhibited higher transgene expression and steady-state levels of human betaAPP in fast type IIB fibers compared to slow type I fibers. These findings indicate that fast twitch fibers may selectively accumulate and be more vulnerable to betaAPP- and Abeta-mediated damage in IBM. These findings also highlight parallels between the MCK-betaAPP mice and the human IBM condition.     

APP/PS1转基因小鼠脑内铁死亡参与阿尔茨海默病病理改变的研究

目的 研究APP/PS1转基因小鼠脑内铁死亡与阿尔茨海默病病理改变的相关性.方法 选择不同月龄的野生型C57BL/6和APP/PS1小鼠,利用普鲁士蓝染色检测小鼠脑内铁累积情况;采用蛋白免疫印迹、免疫组织化学染色和免疫组织荧光法观察铁运输、储存、调节和铁死亡相关蛋白的表达及分布情况.结果 野生型小鼠海马和前额叶中铁死亡...     

HuD在N2aAPP细胞和APP/PS1转基因小鼠中的表达

目的研究RNA结合蛋白HuD在AD细胞和动物模型中的表达水平,探讨HuD与AD的关系;明确PI3K/AKT通路对神经细胞HuD表达的调控作用。方法免疫荧光检测HuD在C57BL/6小鼠脑组织中的表达水平;构建过表达APP的N2a APP细胞模型,Western blot检测HuD的表达情况;购买APP/PS1转基因小鼠,Western blot检测HuD在脑组织中的表达情况;应用LY294002处理3种神经细胞(N2a、SH-SY5Y和HT22),阻断PI3K/AKT通路,观察该通路对HuD的调控作用。结果 HuD在整个C57BL/6小鼠脑组织中均有表达,且在海马体的颗粒细胞尤为明显;在N2a APP细胞,HuD的表达水平明显低于对照组;APP/PS1转基因小鼠脑组织中的HuD水平也低于野生对照鼠;LY294002处理下调了HuD在神经细胞中的表达水平。结论 HuD在N2a APP细胞和APP/PS1转基因小鼠中均呈低表达;HuD在神经细胞中受PI3K/AKT通路的调控,为研究HuD与AD的关系及寻找新的AD诊断和治疗靶点提供了理论基础。     

Differential regulation of toll-like receptor mRNAs in amyloid plaque-associated brain tissue of aged APP23 transgenic mice

Alzheimer's disease (AD) is characterized by the pathological deposition of amyloid-β protein in the aged brain. Inefficient clearance of amyloid-β from brain tissue is believed to play a major role in the pathogenesis of these deposits. Since amyloid-β clearance likely involves activation of microglial cells via toll-like receptors and since these receptors and their signaling pathways are regarded as potential therapeutic targets, we have studied the expression of toll-like receptor (tlr) mRNAs in an animal model of AD (APP23 transgenic mice). Laser microdissection was used to harvest plaques, tissue surrounding plaques and plaque-free tissue from cortex of aged APP23 transgenic mice and age-matched controls. Real-time RT-PCR was employed to quantify expression levels of different tlr mRNAs in these tissues. This revealed a strong upregulation of tlr2, tlr4, tlr5, tlr7 and tlr9 mRNAs in plaque material compared to plaque-free tissue. In contrast, tlr3 was not significantly upregulated. Plaque-free tissue did not show an increased expression of any tlr mRNAs compared to age-matched control mice. Double-immunofluorescence for TLR2 and the microglial marker Iba1 was used to demonstrate localization of TLR2 on plaque-associated microglia. Taken together, these data show a strong upregulation of mRNAs encoding surface TLRs in plaque-associated brain tissue of aged APP23 transgenic mice. Since TLR-upregulation is restricted to plaques, modifying TLR-signaling may be a promising therapeutic strategy for plaque removal.     

Amyloid precursor protein (APP) processing genes and cerebrospinal fluid APP cleavage product levels in Alzheimer's disease

The aim of this exploratory investigation was to determine if genetic variation within amyloid precursor protein (APP) or its processing enzymes correlates with APP cleavage product levels: APPα, APPβ or Aβ42, in cerebrospinal fluid (CSF) of cognitively normal subjects or Alzheimer's disease (AD) patients. Cognitively normal control subjects (n = 170) and AD patients (n = 92) were genotyped for 19 putative regulatory tagging SNPs within 9 genes (APP, ADAM10, BACE1, BACE2, PSEN1, PSEN2, PEN2, NCSTN and APH1B) involved in the APP processing pathway. SNP genotypes were tested for their association with CSF APPα, APPβ, and Aβ42, AD risk and age-at-onset while taking into account age, gender, race and APOE ε4. After adjusting for multiple comparisons, a significant association was found between ADAM10 SNP rs514049 and APPα levels. In controls, the rs514049 CC genotype had higher APPα levels than the CA, AA collapsed genotype, whereas the opposite effect was seen in AD patients. These results suggest that genetic variation within ADAM10, an APP processing gene, influences CSF APPα levels in an AD specific manner.     

Impaired conditioned taste aversion learning in APP transgenic mice

Cognition in transgenic mouse models of Alzheimer's disease (AD) has been predominantly characterized in explicit spatial orientation tasks. However, dementia in AD encompasses also implicit memory systems. In the present study a line of transgenic mice (TgCRND8) encoding a double mutated allele of the human amyloid precursor protein (APP) genes was evaluated in an implicit associative learning task of conditioned taste aversion (CTA). CTA is a form of Pavlovian classical conditioning, in which a mouse learns to avoid a novel taste of saccharine (conditioned stimulus) paired with an experimentally induced (systemic injection of lithium chloride) nausea (unconditioned stimulus). In contrast to conditioned non-Tg mice, TgCRND8 APP mice developed weaker aversion against saccharine and quickly increased its consumption in repeated tests. These results indicate that TgCRND8 mice show a significant impairment not only in explicit spatial memory, as has been previously shown [Nature 408 (2000) 979], but also in implicit memory. Control experiments confirmed that TgCRND8 and non-Tg mice had comparable taste sensitivities in response to appetitive as well as aversive tastes. The study suggests that the CTA paradigm can be a sensitive tool to evaluate deficits in implicit associative learning in APP transgenic mouse models of AD.     

锌转运体7基因沉默抑制APP转基因细胞APP表达和Aβ分泌

目的锌转运体7(ZnT7)在阿尔茨海默病(Alzheimer'sdisease,AD)患者脑内高表达并在老年斑内形成聚集效应。但其是否参与AD发病尚不清楚,本实验旨在探讨ZnT7基因沉默对APP转基因细胞APP/Aβ表达水平的影响。方法应用RNAi技术对APP转基因细胞进行ZnT7基因沉默,并采用RT-PCR,WesternBlot,免疫荧光,ELISA,MTT方法,分析ZnT7基因沉默对APP转基因细胞对APP蛋白的表达、Aβ分泌和细胞活力的影响。结果免疫荧光双标结果显示,ZnT7RNAi可明显抑制APP转基因细胞的ZnT7和APP表达;WesternBlot结果显示,ZnT7RNAi可明显抑制APP转基因细胞的APP蛋白表达;ELISA结果显示,ZnT7RNAi可明显抑制APP细胞转基因的Aβ分泌。结论 ZnT7可能参与细胞内APP代谢,ZnT7基因可作为AD治疗的一个潜在靶点。     

还脑益聪方组分对APP转基因小鼠脑组织炎症因子和氧化应激的影响

目的: 研究中药复方-还脑益聪方(HNYCF)组分对阿尔茨海默病(AD)动物模型脑组织炎症因子和氧化应激相关指标的影响,探讨其治疗AD的作用机制。方法: 选用3月龄APP695V717I转基因小鼠AD模型,随机分成4组:模型组、盐酸多奈哌齐组、HNYCE组分大剂量组和HNYCF组分小剂量组。另设立正常对照组(相同遗传背景的C57BL/6J小鼠)。各组小鼠按相应处理连续灌胃6个月后进行相关指标检测。采用Morris水迷宫和跳台实验观测小鼠学习记忆能力,采用免疫组织化学法检测脑组织核因子κB(NF-κB) 和过氧化物酶体增殖物激活受体γ(PPARγ)的表达水平,放射免疫法测定脑组织皮层和海马白细胞介素-6 (IL-6)和高敏C-反应蛋白(hs-CRP)的含量,比色法检测血清超氧化物歧化酶(SOD)活性,硫代巴比妥酸法测定血清丙二醛(MDA)含量。结果: HNYCF小鼠在Morris水迷宫中穿越平台次数、第4象限游泳时间和路程均较模型组显著增多(P<0.05或P<0.01);HNYCF大剂量组小鼠在跳台实验中潜伏期较模型组显著延长(P<0.01);HNYCF小鼠脑组织NF-κB表达下调,PPARγ表达上调,IL-6含量减少,与模型组比较有显著差异(P<0.05或P<0.01);HNYCF小鼠血清SOD活性较模型组显著升高(P<0.05或P<0.01)。结论: HNYCF可以改善APP转基因小鼠的学习记忆能力,其作用机制可能与抗炎、抗氧化作用有关。