Mapping genetic modulators of amyloid plaque deposition in TgCRND8 transgenic mice

Alzheimer's disease (AD) is a complex disorder for which various in vivo models exist. The TgCRND8 mouse, transgenic for the human amyloid precursor protein, is an aggressive early onset model of brain amyloid deposition. Preliminary studies revealed that when the transgene is expressed on an A/J genetic background, these mice not only survive longer but also deposit less parenchymal amyloid-beta (Abeta) peptides as compared to those on a C57BL/6 background. We performed a genome-wide study of an F2 intercross between TgCRND8 on an A/J background and C57BL/6 mice, to identify genetic modulators of amyloid accumulation and deposition. We identified four highly significant QTLs that together account for 55% of the phenotypic variance in the number of plaques (Thioflavin S). QTLs were found on the distal part of chromosome 4 with an LOD score of 8.1 at D4Mit251, on chromosome 11 with an LOD score of 5.5 at D11Mit242, on chromosome 9 with an LOD score of 5.0 at D9Mit336 and on the proximal part of chromosome 8 with an LOD score of 4.5 at D8Mit223. A/J alleles at these loci are protective and all decreased the amount of Abeta deposition. Interestingly, the QTL on chromosome 11 is also significantly linked to the levels of brain Abeta(42) and Abeta(40). Although these QTLs do not control the levels of plasmatic Abeta, other regions on chromosomes 1 and 6 show significant linkage. Further characterization of these QTL regions may lead to the identification of genes involved in the pathogenesis of AD.     

Targeting soluble Abeta peptide with Tramiprosate for the treatment of brain amyloidosis

Amyloid beta-peptide (Abeta) is a major constituent of senile plaques in Alzheimer's disease (AD). Neurotoxicity results from the conformational transition of Abeta from random-coil to beta-sheet and its oligomerization. Among a series of ionic compounds able to interact with soluble Abeta, Tramiprosate (3-amino-1-propanesulfonic acid; 3APS; Alzhemedtrade mark) was found to maintain Abeta in a non-fibrillar form, to decrease Abeta(42)-induced cell death in neuronal cell cultures, and to inhibit amyloid deposition. Tramiprosate crosses the murine blood-brain barrier (BBB) to exert its activity. Treatment of TgCRND8 mice with Tramiprosate resulted in significant reduction (approximately 30%) in the brain amyloid plaque load and a significant decrease in the cerebral levels of soluble and insoluble Abeta(40) and Abeta(42) (approximately 20-30%). A dose-dependent reduction (up to 60%) of plasma Abeta levels was also observed, suggesting that Tramiprosate influences the central pool of Abeta, changing either its efflux or its metabolism in the brain. We propose that Tramiprosate, which targets soluble Abeta, represents a new and promising therapeutic class of drugs for the treatment of AD.     

Reduced effectiveness of Abeta1-42 immunization in APP transgenic mice with significant amyloid deposition.

Vaccinations with Abeta1-42 have been shown to reduce amyloid burden in transgenic models of Alzheimer's disease (AD). We have further tested the efficacy of Abeta1-42 immunization in the Tg2576 mouse model of AD by immunizing one group of mice with minimal Abeta deposition, one group of mice with modest Abeta deposition, and one group with significant Abeta deposition. The effects of immunization on Abeta deposition were examined using biochemical and immunohistochemical methods. In Tg2576 mice immunized prior to significant amyloid deposition, Abeta1-42 immunization was highly effective. Biochemically extracted Abeta40 and Abeta42 levels were significantly reduced and immunohistochemical plaque load was also reduced. Immunization of mice with modest amounts of pre-existing Abeta deposits selectively reduced Abeta42 without altering Abeta40, although plaque load was reduced. In contrast, in Tg2576 mice with significant pre-existing Abeta loads, Abeta1-42 immunization only minimally decreased Abeta42 levels, whereas no alteration in Abeta40 levels or in plaque load was observed. These results indicate that in Tg2576 mice, Abeta1-42 immunization is more effective at preventing additional Abeta accumulation and does not result in significant clearance of pre-existing Abeta deposits.     

Corticosterone and related receptor expression are associated with increased beta-amyloid plaques in isolated Tg2576 mice

Previously, we reported that the stress associated with chronic isolation was associated with increased beta-amyloid (Abeta) plaque deposition and memory deficits in the Tg2576 transgenic animal model of Alzheimer's disease (AD) [Dong H, Goico B, Martin M, Csernansky CA, Bertchume A, Csernansky JG (2004) Effects of isolation stress on hippocampal neurogenesis, memory, and amyloid plaque deposition in APP (Tg2576) mutant mice. Neuroscience 127:601-609]. In this study, we investigated the potential mechanisms of stress-accelerated Abeta plaque deposition in this Tg2576 mice by examining the relationship between plasma corticosterone levels, expression of glucocorticoid receptor (GR) and corticotropin-releasing factor receptor-1 (CRFR1) in the brain, brain tissue Abeta levels and Abeta plaque deposition during isolation or group housing from weaning (i.e. 3 weeks of age) until 27 weeks of age. We found that isolation housing significantly increased plasma corticosterone levels as compared with group-housing in both Tg+ mice (which contain and overexpress human amyloid precursor protein (hAPP) gene) and Tg- mice (which do not contain hAPP gene as control). Also, isolated, but not group-housed animals showed increases in the expression of GR in the cortex. Furthermore, the expression of CRFR1 was increased in isolated Tg+ mice, but decreased in isolated Tg- mice in both cortex and hippocampus. Changes in the components of hypothalamic-pituitary-adrenal (HPA) axis were accompanied by increases in brain tissue Abeta levels and Abeta plaque deposition in the hippocampus and overlying cortex in isolated Tg+ mice. These results suggest that isolation stress increases corticosterone levels and GR and CRFR1 expression in conjunction with increases in brain tissue Abeta levels and Abeta plaque deposition in the Tg2576 mouse model of AD.     

Reduction of amyloid angiopathy and Abeta plaque burden after enriched housing in TgCRND8 mice: involvement of multiple pathways

Diversity and intensity of intellectual and physical activities seem to have an inverse relationship with the extent of cognitive decline in Alzheimer's disease (AD). To study the interaction between an active lifestyle and AD pathology, female TgCRND8 mice carrying human APPswe+ind were transferred into enriched housing. Four months of continuous and diversified environmental stimulation resulted in a significant reduction of beta-amyloid (Abeta) plaques and in a lower extent of amyloid angiopathy. Neither human amyloid precursor protein (APP) mRNA/protein levels nor the level of carboxy-terminal fragments of APP nor soluble Abeta content differed between both groups, making alterations in APP expression or processing unlikely as a cause of reduced Abeta deposition. Moreover, DNA microarray analysis revealed simultaneous down-regulation of proinflammatory genes as well as up-regulation of molecules involved in anti-inflammatory processes, proteasomal degradation, and cholesterol binding, possibly explaining reduced Abeta burden by lower aggregation and enhanced clearance of Abeta. Additionally, immunoblotting against F4/80 antigen and morphometric analysis of microglia (Mac-3) revealed significantly elevated microgliosis in the enriched brains, which suggests increased amyloid phagocytosis. In summary, this study demonstrates that the environment interacts with AD pathology at dif-ferent levels.     

Histochemical visualization and diffusion MRI at 7 Tesla in the TgCRND8 transgenic model of Alzheimer’s disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder that has been characterized by gross cortical atrophy, cellular neurodegeneration, reactive gliosis, and the presence of microscopic extracellular amyloid plaques and intracellular neurofibrillary tangles. Earlier diagnoses of AD would be in the best interest of managing the patient and would allow for earlier therapeutic intervention. By measuring the apparent diffusion coefficient (ADC) using diffusion-weighted imaging (DWI), a type of magnetic resonance imaging (MRI), one can quantify alterations in water diffusivity resulting from microscopic structural changes in the cell at early stages that are associated with pathophysiological processes of brain injury and/or disease progression. Whether or not this methodology is useful for AD is a question under examination. For example, DWI in suspected AD patients has shown increases in mean ADC values in the hippocampus and diminished diffusion anisotropy in the posterior white matter. However, in some cases, hippocampal ADC values appear not to change in AD patients. Moreover, to our knowledge, all DWI studies in suspected AD patients to date are technically incomplete in experimental design, because corresponding histological sections demonstrating actual plaque deposition are lacking and so it is not clear that ADC changes actually correspond to plaque deposition. In our study, we used DWI in the TgCRND8 transgenic model of Alzheimer’s disease in conjunction with histological techniques and found robust plaque deposition in the transgenic strain in older animals (12–16 months old). However, we did not find statistically significant changes (p > 0.05) in ADC values (although ADC values in TgCRND8 mice did decrease in all regions examined) in mice 12–16 months old. Collectively, recent results from human studies and in rodent AD transgenic models support our findings and suggest that amyloid beta plaque load is not likely the major or primary component contributing to diffusional changes, if they occur.     

Inflammation occurs early during the Abeta deposition process in TgCRND8 mice

Alzheimer's disease (AD) is characterized by a progressive cognitive decline leading to dementia and involves the deposition of amyloid-beta (Abeta) peptides into senile plaques. Other neuropathological features that accompany progression of the disease include a decrease in synaptic density, neurofibrillary tangles, dystrophic neurites, inflammation, and neuronal cell loss. In this study, we report the early kinetics of brain amyloid deposition and its associated inflammation in an early onset transgenic mouse model of AD (TgCRND8) harboring the human amyloid precursor protein gene with the Indiana and Swedish mutations. Both diffuse and compact plaques were detected as early as 9-10 weeks of age. Abeta-immunoreactive (Abeta-IR) plaques (4G8-positive) appeared first in the neocortex and amygdala, then in the hippocampal formation, and lastly in the thalamus. Compact plaques (ThioS-positive) with an amyloid core were observed as early as diffuse plaques were detected, but in lower numbers. Amyloid deposition increased progressively with age. The formation of plaques was concurrent with the appearance of activated microglial cells and shortly followed by the clustering of activated astrocytes around plaques at 13-14 weeks of age. This TgCRND8 mouse model allows for a rapid, time-dependent study of the relationship between the fibrillogenic process and the inflammatory response during the brain amyloidogenic process.     

Tg-SwDI transgenic mice exhibit novel alterations in AbetaPP processing, Abeta degradation, and resilient amyloid angiopathy

Alzheimer's disease (AD) is characterized by the accumulation of extracellular insoluble amyloid, primarily derived from polymerized amyloid-beta (Abeta) peptides. We characterized the chemical composition of the Abeta peptides deposited in the brain parenchyma and cerebrovascular walls of triple transgenic Tg-SwDI mice that produce a rapid and profuse Abeta accumulation. The processing of the N- and C-terminal regions of mutant AbetaPP differs substantially from humans because the brain parenchyma accumulates numerous, diffuse, nonfibrillar plaques, whereas the thalamic microvessels harbor overwhelming amounts of compact, fibrillar, thioflavine-S- and apolipoprotein E-positive amyloid deposits. The abundant accretion of vascular amyloid, despite low AbetaPP transgene expression levels, suggests that inefficient Abeta proteolysis because of conformational changes and dimerization may be key pathogenic factors in this animal model. The disruption of amyloid plaque cores by immunotherapy is accompanied by increased perivascular deposition in both humans and transgenic mice. This analogous susceptibility and response to the disruption of amyloid deposits suggests that Tg-SwDI mice provide an excellent model in which to study the functional aftermath of immunotherapeutic interventions. These mice might also reveal new avenues to promote amyloidogenic AbetaPP processing and fundamental insights into the faulty degradation and clearance of Abeta in AD, pivotal issues in understanding AD pathophysiology and the assessment of new therapeutic agents.     

Dense-core senile plaques in the Flemish variant of Alzheimer's disease are vasocentric

Alzheimer's disease (AD) is characterized by deposition of beta-amyloid (Abeta) in diffuse and senile plaques, and variably in vessels. Mutations in the Abeta-encoding region of the amyloid precursor protein (APP) gene are frequently associated with very severe forms of vascular Abeta deposition, sometimes also accompanied by AD pathology. We earlier described a Flemish APP (A692G) mutation causing a form of early-onset AD with a prominent cerebral amyloid angiopathy and unusually large senile plaque cores. The pathogenic basis of Flemish AD is unknown. By image and mass spectrometric Abeta analyses, we demonstrated that in contrast to other familial AD cases with predominant brain Abeta42, Flemish AD patients predominantly deposit Abeta40. On serial histological section analysis we further showed that the neuritic senile plaques in APP692 brains were centered on vessels. Of a total of 2400 senile plaque cores studied from various brain regions from three patients, 68% enclosed a vessel, whereas the remainder were associated with vascular walls. These observations were confirmed by electron microscopy coupled with examination of serial semi-thin plastic sections, as well as three-dimensional observations by confocal microscopy. Diffuse plaques did not associate with vessels, or with neuritic or inflammatory pathology. Together with earlier in vitro data on APP692, our analyses suggest that the altered biological properties of the Flemish APP and Abeta facilitate progressive Abeta deposition in vascular walls that in addition to causing strokes, initiates formation of dense-core senile plaques in the Flemish variant of AD.     

Reactive astrocytes and alpha1-antichymotrypsin in Alzheimer's disease.

There is ample genetic, biochemical, cellular and molecular evidence to show that the amyloid beta peptide (Abeta), a proteolytic fragment of the amyloid precursor protein (APP), plays an important, if not causative role in Alzheimer's disease (AD). An additional hallmark of AD is the neuroinflammatory response that is associated with the amyloid deposition. We discovered that the acute phase protein alpha1-antichymotrypsin (ACT) is overexpressed by reactive astrocytes, and is tightly associated with virtually all amyloid plaques in the AD brain. It has also been shown that Abeta and ACT bind in vitro. Recently, we have reported that astrocytic expression of ACT in APP transgenic mice leads to an increased plaque deposition in ACT/APP doubly transgenic mice compared to the APP mice alone, suggesting that ACT interferes with Abeta clearance. The main objective of this review is to summarize the role of astrocytosis and ACT in the pathogenesis of AD.     

TGF-beta1 is increased in a transgenic mouse model of familial Alzheimer's disease and causes neuronal apoptosis

Alzheimer's disease (AD) is a neurodegenerative disorder, due to excess amyloid-beta peptide (Abeta). TGF-beta1 and beta-catenin signaling pathways have been separately implicated in modulating Abeta-neurotoxicity. However, the underlying mechanisms remain unclear. Here, we report that TGF-beta1 and nuclear Smad7 and beta-catenin levels were markedly upregulated in cortical brain regions of the TgCRND8 mice, a mouse model of familial Alzheimer's disease. Coimmunoprecipitation of cortical brain tissue lysates revealed an interaction between Smad7 and beta-catenin. This interaction which was significantly enhanced in the TgCRND8 mice was also associated with an increase in TCF/LEF DNA-shift binding activity. TCF/LEF reporter gene activity was significantly increased in mouse primary cortical neuronal cultures (MCN) from the TgCRND8 mice, compared to controls. Interestingly, exposure of MCN to Abeta(1-42) led to an increase in TGF-beta1 and nuclear levels of both beta-catenin and Smad7. Furthermore, addition of TGF-beta1 to the MCN caused an increase in apoptosis and Smad7 levels. When Smad7 or beta-catenin levels were reduced by siRNA, TGF-beta1-induced apoptosis was suppressed, indicating that both Smad7 and beta-catenin are required for TGF-beta1-induced neurotoxicity. Since Abeta(1-42)-induced TGF-beta1, we suggest that TGF-beta1 may amplify Abeta(1-42)-mediated neurodegeneration in AD via Smad7 and beta-catenin interaction and nuclear localization.     

Abeta-degrading endopeptidase,neprilysin, in mouse brain: synaptic and axonal localization inversely correlating with Abeta pathology

Metabolism of amyloid-beta peptide (Abeta) is closely associated with the pathology and etiology of Alzheimer's disease (AD). Since neprilysin is the only rate-limiting catabolic peptidase proven by reverse genetics to participate in Abeta metabolism in vivo, we performed detailed immunohistochemical analysis of neprilysin in mouse brain using neprilysin-deficient mice as a negative control. The aim was to assess, at both the cellular and subcellular levels, where Abeta undergoes neprilysin-dependent degradation in the brain and how neprilysin localization relates to Abeta pathology in amyloid precursor protein (APP)-transgenic mice. In hippocampus, neprilysin was present in the stratum pyramidale and stratum lacunosum-moleculare of the CA1-3 fields and the molecular layer of the dentate gyrus. Confocal double immunofluorescence analyses revealed the subcellular localization of neprilysin along axons and at synapses. This observation suggests that after synthesis in the soma, neprilysin, a type II membrane-associated protein, is axonally transported to the terminals, where Abeta degradation is likely to take place. Among various cell types, GABAergic and metabotropic glutamate 2/3 receptor-positive neurons but not catecholaminergic or cholinergic neurons, expressed neprilysin in hippocampus and neocortex, implying the presence of a cell type-specific mechanism that regulates neprilysin gene expression. As expected, Abeta deposition correlated inversely with neprilysin expression in TgCRND8 APP-transgenic mice. These observations not only support the notion that neprilysin functions as a major Abeta-degrading enzyme in the brain but also suggest that down-regulation of neprilysin activity, which may be caused by aging, is likely to elevate local concentrations of Abeta at and around neuronal synapses.     

Metallothionein-I and -III expression in animal models of Alzheimer disease

Previous studies have described altered expression of metallothioneins (MTs) in neurodegenerative diseases like multiple sclerosis (MS), Down syndrome, and Alzheimer's disease (AD). In order to gain insight into the possible role of MTs in neurodegenerative processes and especially in human diseases, the use of animal models is a valuable tool. Several transgenic mouse models of AD amyloid deposits are currently available. These models express human beta-amyloid precursor protein (AbetaPP) carrying different mutations that subsequently result in a varied pattern of beta-amyloid (Abeta) deposition within the brain. We have evaluated the expression of MT-I and MT-III mRNA by in situ hybridization in three different transgenic mice models of AD: Tg2576 (carrying AbetaPP harboring the Swedish K670N/M671L mutations), TgCRND8 (Swedish and the Indiana V717F mutations), and Tg-SwDI (Swedish and Dutch/Iowa E693Q/D694N mutations). MT-I mRNA levels were induced in all transgenic lines studied, although the pattern of induction differed between the models. In the Tg2576 mice MT-I was weakly upregulated in cells surrounding Congo Red-positive plaques in the cortex and hippocampus. A more potent induction of MT-I was observed in the cortex and hippocampus of the TgCRND8 mice, likely reflecting their higher amyloid plaques content. MT-I upregulation was also more significant in Tg-SwDI mice, especially in the subiculum and hippocampus CA1 area. Immunofluorescence stainings demonstrate that astrocytes and microglia/macrophages surrounding the plaques express MT-I&II. In general, MT-I regulation follows a similar but less potent response than glial fibrillary acidic protein (GFAP) expression. In contrast to MT-I, MT-III mRNA expression was not significantly altered in any of the models examined suggesting that the various MT isoforms may have different roles in these experimental systems, and perhaps also in human AD.     

High sensitivity analysis of amyloid-beta peptide composition in amyloid deposits from human and PS2APP mouse brain

Cortical amyloid-beta (Abeta) deposition is considered essential in Alzheimer's disease (AD) and is also detectable in nondemented individuals with pathologic aging (PA). The present work presents a detailed analysis of the Abeta composition in various plaque types from human AD and PA cases, compared with plaque Abeta isolated from PS2APP mice. To determine minute amounts of Abeta from 30 to 50 laser-dissected amyloid deposits, we used a highly sensitive mass spectrometry procedure after restriction protease lysyl endopeptidase (Lys-C) digestion. This approach allowed the analysis of the amino-terminus and, including a novel ionization modifier, for the first time the carboxy-terminus of Abeta at a detection limit of approximately 200 fmol. In addition, full length Abeta 40/42 and pyroglutamate 3-42 were analyzed using a highly sensitive urea-based Western blot procedure. Generally, Abeta fragments were less accessible in human deposits, indicative of more posttranslational modifications. Thioflavine S positive cored plaques in AD were found to contain predominantly Abeta 42, whereas thioflavine S positive compact plaques and vascular amyloid consist mostly of Abeta 40. Diffuse plaques from AD and PA, as well as from PS2APP mice are composed predominantly of Abeta 1-42. Despite biochemical similarities in human and PS2APP mice, immuno-electron microscopy revealed an extensive extracellular matrix associated with Abeta fibrils in AD, specifically in diffuse plaques. Amino-terminal truncations of Abeta, especially pyroglutamate 3-40/42, are more frequently found in human plaques. In cored plaques we measured an increase of N-terminal truncations of approximately 20% between Braak stages IV to VI. In contrast, diffuse plaques of AD and PA cases, show consistently only low levels of amino-terminal truncations. Our data support the concept that diffuse plaques represent initial Abeta deposits but indicate a structural difference for Abeta depositions in human AD compared with PS2APP mice already at the stage of diffuse plaque formation.     

Activity changes and marked stereotypic behavior precede Abeta pathology in TgCRND8 Alzheimer mice

Alzheimer's disease (AD) is not only characterized by cognitive decline and neuropathological changes, but also by non-cognitive behavioral symptoms like restlessness, sleep disturbance, and wandering. These symptoms are categorized in the "Behavioral and Psychological Symptoms of Dementia" (BPSD). We investigated transgenic and wildtype mice of an APP transgenic mouse model of AD (TgCRND8) with respect to 24 h activity and spontaneous home cage behavior at 30, 60, 90 and 120 days of age. At all test days, transgenic and wildtype animals differed significantly with respect to activity patterns. In addition, activity rhythms changed distinctly in transgenic mice with increasing age. Transgenic mice also clearly showed more stereotypic behavior, which correlated significantly at 90 and 120 days of age with elevated corticosterone metabolite concentrations in fecal samples. Activity patterns in TgCRND8 mice resemble altered rhythms of activity in AD patients. Stereotypic behaviors may be caused by the same mechanisms as non-cognitive behavioral symptoms of AD. Thus, it is likely that analogies to BPSD that precede Abeta pathology are found in APP-overexpressing TgCRND8 mice.     

Cyclooxygenase-2 promotes amyloid plaque deposition in a mouse model of Alzheimer's disease neuropathology

Several epidemiologic studies have reported that cyclooxygenase (COX) inhibitors prevent/delay the onset of Alzheimer's disease (AD). Recent experimental studies suggest that these compounds can also diminish amyloid-beta (Abeta) neuropathology in rodent models of AD. To explore the relationship of COX expression to Abeta neuropathology, we crossed mice expressing both mutant amyloid precursor protein [K670N/M671L (APP(swe)] and mutant PS1 (A246E) with mice expressing human COX-2 selectively in neurons. We show here that human COX-2 expression in APP(swe)/PS1/COX-2 mice induces potentiation of brain parenchymal amyloid plaque formation and a greater than twofold increase in prostaglandin E2 production, at 24 months of age. This increased amyloid plaque formation coincided with a preferential elevation of Abeta1-40 and Abeta1-42 with no change in total amyloid precursor protein (APP) expression/content in the brain. Collectively these data suggest that COX-2 influences APP processing and promotes amyloidosis in the brain.     

Berberine ameliorates β-amyloid pathology, gliosis, and cognitive impairment in an Alzheimer's disease transgenic mouse model

The accumulation of β-amyloid (Aβ) peptide derived from abnormal processing of amyloid precursor protein (APP) is a common pathological hallmark of Alzheimer's disease (AD) brains. In this study, we evaluated the therapeutic effect of berberine (BBR) extracted from Coptis chinensis Franch, a Chinese medicinal herb, on the neuropathology and cognitive impairment in TgCRND8 mice, a well established transgenic mouse model of AD. Two-month-old TgCRND8 mice received a low (25 mg/kg per day) or a high dose of BBR (100 mg/kg per day) by oral gavage until 6 months old. BBR treatment significantly ameliorated learning deficits, long-term spatial memory retention, as well as plaque load compared with vehicle control treatment. In addition, enzyme-linked immunosorbent assay (ELISA) measurement showed that there was a profound reduction in levels of detergent-soluble and -insoluble β-amyloid in brain homogenates of BBR-treated mice. Glycogen synthase kinase (GSK)3, a major kinase involved in APP and tau phosphorylation, was significantly inhibited by BBR treatment. We also found that BBR significantly decreased the levels of C-terminal fragments of APP and the hyperphosphorylation of APP and tau via the Akt/glycogen synthase kinase 3 signaling pathway in N2a mouse neuroblastoma cells stably expressing human Swedish mutant APP695 (N2a-SwedAPP). Our results suggest that BBR provides neuroprotective effects in TgCRND8 mice through regulating APP processing and that further investigation of the BBR for therapeutic use in treating AD is warranted.     

Noradrenaline deficiency in brain increases beta-amyloid plaque burden in an animal model of Alzheimer's disease

Loss of Locus coeruleus (LC) noradrenergic (NA) neurons occurs in several neurodegenerative conditions including Alzheimer's disease (AD). In vitro and in vivo studies have shown that NA influences several features of AD disease including inflammation, neurodegeneration, and cognitive function. In the current study we tested if LC loss influenced beta amyloid (Abeta) plaque deposition. LC neuronal degeneration was induced in transgenic mice expressing mutant V717F human amyloid precursor protein (APP) by treatment with the selective neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine DSP4 (5mg/kg every 2 weeks beginning at age 3 months). At 9 months of age, when control mice show low amyloid load, DSP4-treated mice showed an approximately 5-fold increase in the average number of Abeta plaques. This was accompanied by an increase in the levels of APP C-terminal cleavage fragments. DSP4-treatment increased both microglial and astroglial activation. In vivo, DSP4-treatment decreased expression and activity of the Abeta degrading enzyme neprilysin, while in vitro NA increased phagocytosis of Abeta1-42 by microglia. These findings suggest that noradrenergic innervation from LC are needed to maintain adequate Abeta clearance, and therefore that LC degeneration could contribute to AD pathogenesis.     

Augmented senile plaque load in aged female beta-amyloid precursor protein-transgenic mice

Transgenic mice (Tg2576) overexpressing human beta-amyloid precursor protein with the Swedish mutation (APP695SWE) develop Alzheimer's disease-like amyloid beta protein (Abeta) deposits by 8 to 10 months of age. These mice show elevated levels of Abeta40 and Abeta42, as well as an age-related increase in diffuse and compact senile plaques in the brain. Senile plaque load was quantitated in the hippocampus and neocortex of 8- to 19-month-old male and female Tg2576 mice. In all mice, plaque burden increased markedly after the age of 12 months. At 15 and 19 months of age, senile plaque load was significantly greater in females than in males; in 91 mice studied at 15 months of age, the area occupied by plaques in female Tg2576 mice was nearly three times that of males. By enzyme-linked immunosorbent assay, female mice also had more Abeta40 and Abeta42 in the brain than did males, although this difference was less pronounced than the difference in histological plaque load. These data show that senescent female Tg2576 mice deposit more amyloid in the brain than do male mice, and may provide an animal model in which the influence of sex differences on cerebral amyloid pathology can be evaluated.