Stable beta-secretase activity and presynaptic cholinergic markers during progressive central nervous system amyloidogenesis in Tg2576 mice

We examined presynaptic cholinergic markers and beta-secretase activity during progressive central nervous system amyloidogenesis in Tg2576 Alzheimer mice (transgenic for human amyloid precursor protein Swedish mutation; hAPPswe). At 14, 18, and 23 months of age there were no significant differences between wild-type and transgenic mice in four distinct central nervous system cholinergic indices--choline acetyltransferase and acetylcholinesterase activities, and binding to vesicular acetylcholine transporter and Na(+)-dependent high-affinity choline uptake sites. A novel enzyme-linked immunosorbent assay measuring only the secreted human beta-secretase cleavage product (APPsbetaswe) of APPswe also revealed no change with aging in Tg2576 mouse brain. In contrast, transgenic but not wild-type mice exhibited an age-dependent increase in soluble Abeta40 and Abeta42 levels and progressive amyloid deposition in brain. Thus, aging Tg2576 mice exhibited presynaptic cholinergic integrity despite progressively increased soluble Abeta40 and Abeta42 levels and amyloid plaque density in brain. Older Tg2576 mice may best resemble preclinical or early stages of human Alzheimer's disease with preserved presynaptic cholinergic innervation. Homeostatic APPsbetaswe levels with aging suggest that progressive amyloid deposition in brain results not from increased beta-secretase cleavage of APP but from impaired Abeta/amyloid clearance mechanisms.     

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.     

Intact spatial learning in adult Tg2576 mice

Tg2576 mice, a transgenic model of amyloid pathology associated with Alzheimer's disease (AD), develop measurable levels of soluble amyloid beta1-40 and 1-42 by 6 months of age and amyloid plaque deposition in cortex, hippocampus and amygdala by 10 months of age. To investigate whether non-hippocampal learning strategies would predominate coincident with the age-related increase in Abeta load in the hippocampal region, we measured learning strategies in the T-maze and a redundant cued version of the water maze. Each of these tasks can be solved using either hippocampal or non-hippocampal learning strategies and has proved sensitive to hippocampal disruption in other settings. The results revealed subtle differences in T-maze and water maze performance in Tg2576 mice compared to controls. Surprisingly, however, Tg2576 mice were not impaired relative to non-transgenic littermates on any measures of hippocampal dependent behavior assessed in these tasks. These data suggest that the medial temporal lobe retains considerable function in 15-month-old Tg2576 mice despite significant Abeta pathology.     

Lovastatin enhances Abeta production and senile plaque deposition in female Tg2576 mice

A recent clinical study showed that statins, which are inhibitors of cholesterol biosynthesis pathway, reduced the prevalence of Alzheimer's disease (AD). Animal studies that have employed high cholesterol diet indicate significant relationship between cholesterol level and senile plaque deposition. Here, we investigated the effects of lovastatin on beta-amyloid production and senile plaque deposition in an animal model of AD (Tg2576 mice). As expected, lovastatin treatment reduced plasma cholesterol level in both male and female mice. However, lovastatin enhanced the amounts of beta-amyloid and other beta-secretase derived peptides in females, but not in males. Likewise, lovastatin increased the number of plaques in the hippocampus and cortex of females, but not in males. Lovastatin did not change the amounts of full-length or alpha-secretase processed amyloid precursor protein (APP), or presenilin 1 (PS1) in either sex. Thus, lovastatin lowers cholesterol level in both genders, but enhances beta-amyloid production and senile plaque deposition only in brains of female Tg2576 mice. Our results suggest that low plasma cholesterol levels might be a risk factor for AD in females.     

阿尔茨海默病患者血清中抗淀粉样蛋白抗体的免疫耐受

目的:研究阿尔茨海默病(AD)血清中抗Aβ抗体与淀粉样蛋白结合的特性。方法:以AD患者和健康老人的血清作一抗,①用组织淀粉样斑块免疫反应(TAPIR)观察与Tg2576鼠脑内老年斑结合能力;②Western blot检测与Aβ42-GST融合蛋白的结合能力;③将Aβ42与PC12细胞培养,加入健康老人和AD患者的血清后,MTT法观察PC12细胞存活率。结果:AD患者的血清中抗Aβ抗体与成熟老年斑和Aβ42-GST融合蛋白的结合能力较弱;加入AD血清后,PC12细胞的A值较健康老人血清相比下降明显(P<0.01)。结论:AD血清中抗Aβ抗体对淀粉样蛋白可能存在着免疫耐受。     

Immunization with a nontoxic/nonfibrillar amyloid-beta homologous peptide reduces Alzheimer's disease-associated pathology in transgenic mice

Transgenic mice with brain amyloid-beta (Abeta) plaques immunized with aggregated Abeta1-42 have reduced cerebral amyloid burden. However, the use of Abeta1-42 in humans may not be appropriate because it crosses the blood brain barrier, forms toxic fibrils, and can seed fibril formation. We report that immunization in transgenic APP mice (Tg2576) for 7 months with a soluble nonamyloidogenic, nontoxic Abeta homologous peptide reduced cortical and hippocampal brain amyloid burden by 89% (P = 0.0002) and 81% (P = 0.0001), respectively. Concurrently, brain levels of soluble Abeta1-42 were reduced by 57% (P = 0.0019). Ramified microglia expressing interleukin-1beta associated with the Abeta plaques were absent in the immunized mice indicating reduced inflammation in these animals. These promising findings suggest that immunization with nonamyloidogenic Abeta derivatives represents a potentially safer therapeutic approach to reduce amyloid burden in Alzheimer's disease, instead of using toxic Abeta fibrils.     

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.     

Amyloid cored plaques in Tg2576 transgenic mice are characterized by giant plaques,slightly activated microglia,and the lack of paired helical filament-typed,dystrophic neurites

We examined the brains of Tg2576 transgenic mice carrying human amyloid precursor protein with the Swedish mutation and Alzheimer's disease (AD) by means of immunohistochemistry and electron microscopy to clarify the characteristics of amyloid-associated pathology in the transgenic mice. In 12- to 29-month-old Tg2576 mice, congophilic cored plaques in the neocortex and hippocampus were labeled by all of the Abeta1-, Abeta40- and 42-specific antibodies, as seen in the classical plaques in AD. However, large-sized (>50 micro m in core diameter) plaques were seen more frequently in the older mice (18-29 months) than in those with AD (approximately 20% vs 2% in total cored plaques), and Tg2576 mice contained giant plaques (>75 micro m in core diameter), which were almost never seen in the brain of those with AD. Neither thread-like structures nor peripheral coronas were observed in the cored plaques of the transgenic mice in the silver impregnations. Immunohistochemically, plaque-accompanied microglia showed a slight enlargement of the cytoplasm with consistent labeling of Mac-1 and macrosialin (murine CD68), and with partial labeling of Ia antigen and macrophage-colony stimulating factor receptor. Ultrastructurally, the microglia surrounding the extracellular amyloid fibrils in the large, cored plaques showed some organella with phagocytic activity, such as secondary lysosomal, dense bodies, but intracellular amyloid fibrils were not evident. Dystrophic neurites in the plaques of the transgenic mice contained many dense multilaminar bodies, but no paired helical filaments. Our results suggest that giant cored plaques without coronas or paired helical filament-typed, dystrophic neurites are characteristic in Tg2576 mice, and that plaque-associated microglia in transgenic mice are activated to be in phagocytic function but not sufficient enough to digest extracellularly deposited amyloid fibrils.     

Dense-core plaques in Tg2576 and PSAPP mouse models of Alzheimer's disease are centered on vessel walls

Occurrence of amyloid beta (Abeta) dense-core plaques in the brain is one of the chief hallmarks of Alzheimer's disease (AD). It is not yet clear what factors are responsible for the aggregation of Abeta in the formation of these plaques. Using Tg2576 and PSAPP mouse models that exhibit age-related development of amyloid plaques similar to that observed in AD, we showed that approximately 95% of dense plaques in Tg2576 and approximately 85% in PSAPP mice are centered on vessel walls or in the immediate perivascular regions. Stereoscopy and simulation studies focusing on smaller plaques suggested that vascular associations for both Tg2576 and PSAPP mice were dramatically higher than those encountered by chance alone. We further identified ultrastructural microvascular abnormalities occurring in association with dense plaques. Although occurrence of gross cerebral hemorrhage was infrequent, we identified considerable infiltration of the serum proteins immunoglobulin and albumin in association with dense plaques. Together with earlier evidence of vascular clearance of Abeta, our data suggest that perturbed vascular transport and/or perivascular enrichment of Abeta leads to the formation of vasocentric dense plaques in Tg2576 and PSAPP mouse models of AD.     

Modulation of hippocampal cell proliferation, memory, and amyloid plaque deposition in APPsw (Tg2576) mutant mice by isolation stress

Tg2576 transgenic mice (mice overexpressing the "Swedish" mutation in the human amyloid precursor protein 695) demonstrated a decreased capacity for cell proliferation in the dentate gyrus of the hippocampus compared with non-transgenic littermates at 3 months, 6 months and 9 months of age. Isolation stress induced by individually housing each mouse from the time of weaning further decreased hippocampal cell proliferation in Tg2576 mice as well as in non-transgenic littermates at 6 months of age. Decreases in hippocampal cell proliferation in isolated Tg2576 mice were associated with impairments in contextual but not cued memory. Fluoxetine administration increased cell proliferation and improved contextual memory in isolated Tg2576 mice. Further, isolation stress accelerated the age-dependent deposition of beta-amyloid 42 plaques in Tg2576 mice. Numerous beta-amyloid plaques were found in isolated but not non-isolated Tg2576 mice at 6 months of age. These results suggest that Tg2576 mice, a mouse model of Alzheimer disease, have an impaired ability to generate new cells in the dentate gyrus of the hippocampus and that the magnitude of this impairment can be modulated by behavioral interventions and drugs known to have effects on hippocampal neurogenesis in normal rodents. Unexpectedly, isolation stress also appeared to accelerate the underlying process of beta-amyloid plaque deposition in Tg2576 mice. These results suggest that stress may have an impact on the underlying disease process associated with Alzheimer's disease.     

Sleep and circadian abnormalities in a transgenic mouse model of Alzheimer's disease: a role for cholinergic transmission

The Tg2576 mouse model of Alzheimer's disease (AD) exhibits age-dependent amyloid beta (Abeta) deposition in the brain. We studied electroencephalographically defined sleep and the circadian regulation of waking activities in Tg2576 mice to determine whether these animals exhibit sleep abnormalities akin to those in AD. In Tg2576 mice at all ages studied, the circadian period of wheel running rhythms in constant darkness was significantly longer than that of wild type mice. In addition, the increase in electroencephalographic delta (1-4 Hz) power that occurs during non-rapid eye movement sleep after sleep deprivation was blunted in Tg2576 mice relative to controls at all ages studied. Electroencephalographic power during non-rapid eye movement sleep was shifted to higher frequencies in plaque-bearing mice relative to controls. The wake-promoting efficacy of the acetylcholinesterase inhibitor donepezil was lower in plaque-bearing Tg2576 mice than in controls. Sleep abnormalities in Tg2576 mice may be due in part to a cholinergic deficit in these mice. At 22 months of age, two additional deficits emerged in female Tg2576 mice: time of day-dependent modulation of sleep was blunted relative to controls and rapid eye movement sleep as a percentage of time was lower in Tg2576 than in wild type controls. The rapid eye movement sleep deficit in 22 month-old female Tg2576 mice was abolished by brief passive immunization with an N-terminal antibody to Abeta. The Tg2576 model provides a uniquely powerful tool for studies on the pathophysiology of and treatments for sleep deficits and associated cholinergic abnormalities in AD.     

Plaque-bearing mice with reduced levels of oligomeric amyloid-beta assemblies have intact memory function

The amyloid-beta (Abeta) protein exists in the aging mammalian brain in diverse assembly states, including amyloid plaques and soluble Abeta oligomers. Both forms of Abeta have been shown to impair neuronal function, but their precise roles in Alzheimer's disease (AD) -associated memory loss remain unclear. Both types of Abeta are usually present at the same time in the brain, which has made it difficult to evaluate the effects of plaques and oligomers individually on memory function. Recently, a particular oligomeric Abeta assembly, Abeta 56, was found to impair memory function in the absence of amyloid plaques. Until now it has not been possible to determine the effects of plaques, in the absence of Abeta oligomers, on memory function. We have identified Tg2576 mice with plaques but markedly reduced levels of Abeta oligomers, which enabled us to study the effects of plaques alone on memory function. We found that animals with amyloid plaques have normal memory function throughout an episode of reduced Abeta oligomers, which occurs during a period of accelerated amyloid plaque formation. These observations support the importance of Abeta oligomers in memory loss and indicate that, at least initially, amyloid plaques do not impair memory.     

Part of membrane-bound Abeta exists in rafts within senile plaques in Tg2576 mouse brain

To clarify whether rafts are the site of abnormal amyloid beta protein (Abeta) deposition, we examined the ultrastructural localization of both flotillin-1 (pre-embedding) and Abeta (post-embedding) in Tg2576 mouse brains. After observing the exact areas of senile plaques by reflection contrast microscopy, we observed these same plaques under an electron microscope. Membrane-bound Abeta was predominantly observed on plasma membranes of small processes in diffuse plaques. Non-fibrillar and fibrillar Abeta was increased in primitive plaques, and the fibrillar form was predominant in mature plaques. The number of flotillin-1-positive rafts per field in mature plaques was prominently less than those outside of the plaques, in diffuse plaques and in primitive plaques. The colocalization of flotillin-1 with Abeta42 appeared approximately 10% of flotillin-1-positive rafts within senile plaques, while there was no colocalization found outside of the plaques. This study ultrastructurally demonstrated that part of membrane-bound Abeta exists in lipid rafts within senile plaques, and suggests that rafts could be one of the sites for initial Abeta deposition.     

The role of microglial cells and astrocytes in fibrillar plaque evolution in transgenic APP(SW) mice

Ultrastructural reconstruction of 27 fibrillar plaques in different stages of formation and maturation was undertaken to characterize the development of fibrillar plaques in the brains of human APP(SW) transgenic mice (Tg2576). The study suggests that microglial cells are not engaged in Abeta removal and plaque degradation, but in contrast, are a driving force in plaque formation and development. Fibrillar Abeta deposition at the amyloid pole of microglial cells appears to initiate three types of neuropil response: degeneration of neurons, protective activation of astrocytes, and attraction and activation of microglial cells sustaining plaque growth. Enlargement of neuronal processes and synapses with accumulation of degenerated mitochondria, dense bodies, and Hirano-type bodies is the marker of toxic injury of neurons by fibrillar Abeta. Separation of amyloid cores from neurons and degradation of amyloid cores by cytoplasmic processes of hypertrophic astrocytes suggest the protective and defensive character of astrocytic response to fibrillar Abeta. The growth of cored plaque from a small plaque with one microglial cell with an amyloid star and a few dystrophic neurites to a large plaque formed by several dozen microglial cells seen in old mice is the effect of attraction and activation of microglial cells residing outside of the plaque perimeter. This mechanism of growth of plaques appears to be characteristic of cored plaques in transgenic mice. Other features in mouse microglial cells that are absent in human brain are clusters of vacuoles, probably of lysosomal origin. They evolve into circular cisternae and finally into large vacuoles filled with osmiophilic, amorphous material and bundles of fibrils that are poorly labeled with antibody to Abeta. Microglial cells appear to release large amounts of fibrillar Abeta and accumulate traces of fibrillar Abeta in a lysosomal pathway.     

Prominent cerebral amyloid angiopathy in transgenic mice overexpressing the london mutant of human APP in neurons

Deposition of amyloid beta-peptide (Abeta) in cerebral vessel walls (cerebral amyloid angiopathy, CAA) is very frequent in Alzheimer's disease and occurs also as a sporadic disorder. Here, we describe significant CAA in addition to amyloid plaques, in aging APP/Ld transgenic mice overexpressing the London mutant of human amyloid precursor protein (APP) exclusively in neurons. The number of amyloid-bearing vessels increased with age, from approximately 10 to >50 per coronal brain section in APP/Ld transgenic mice, aged 13 to 24 months. Vascular amyloid was preferentially deposited in arterioles and ranged from small focal to large circumferential depositions. Ultrastructural analysis allowed us to identify specific features contributing to weakening of the vessel wall and aneurysm formation, ie, disruption of the external elastic lamina, thinning of the internal elastic lamina, interruption of the smooth muscle layer, and loss of smooth muscle cells. Biochemically, the much lower Abeta42:Abeta40 ratio evident in vascular relative to plaque amyloid, demonstrated that in blood vessel walls Abeta40 was the more abundant amyloid peptide. The exclusive neuronal origin of transgenic APP, the high levels of Abeta in cerebrospinal fluid compared to plasma, and the specific neuroanatomical localization of vascular amyloid strongly suggest specific drainage pathways, rather than local production or blood uptake of Abeta as the primary mechanism underlying CAA. The demonstration in APP/Ld mice of rare vascular amyloid deposits that immunostained only for Abeta42, suggests that, similar to senile plaque formation, Abeta42 may be the first amyloid to be deposited in the vessel walls and that it entraps the more soluble Abeta40. Its ability to diffuse for larger distances along perivascular drainage pathways would also explain the abundance of Abeta40 in vascular amyloid. Consistent with this hypothesis, incorporation of mutant presenilin-1 in APP/Ld mice, which resulted in selectively higher levels of Abeta42, caused an increase in CAA and senile plaques. This mouse model will be useful in further elucidating the pathogenesis of CAA and Alzheimer's disease, and will allow testing of diagnostic and therapeutic strategies.     

Transgenic mice overexpressing human acetylcholinesterase and the Swedish amyloid precursor protein mutation: effect of nicotine treatment

Acetylcholinesterase (AChE) is shown to promote deposition of beta-amyloid (Abeta) peptides and to enhance Abeta toxicity. Tg2576 (transgenic mice carrying the Swedish mutation of amyloid precursor protein, APPswe) mice and mice overexpressing human synaptic acetylcholinesterase (AChE-S) were crossed (hAChE-Tg//APPswe), to study the effects of brain Abeta, from 1 to 10 months of age, under the constant influence of AChE-S. The effect of nicotine treatment was also evaluated in these mice since we have previously shown that nicotine dramatically decreases Abeta levels in single transgenic APPswe mice. Already at 1 and 3 months, hAChE-Tg// APPswe mice showed increased levels of cortical insoluble Abeta1-40 and Abeta1-42 compared with APPswe mice, whereas APPswe mice displayed increased soluble Abeta1-40. Abeta plaques were detected at 7 months, thus before onset of plaque formation in APPswe mice. No differences were found in [125I]alpha-bungarotoxin binding sites or hippocampal glial fibrillary acidic protein (GFAP) immunoreactivity between hAChE-Tg//APPswe, and APPswe mice at either 1 or 10 months of age. L(-)-Nicotine (final dose 0.45 mg/kg) treatment twice daily for 10 days to 14-month-old hAChE-Tg// APPswe mice increased cortical insoluble Abeta1-40 levels, while both L(-)- and D(+)-nicotine (final dose 0.45 mg/kg) increased soluble Abeta1-42. L(-)-Nicotine reduced hippocampal GFAP immunoreactivity both in hAChE-Tg//APPswe mice and non-transgenic controls, while D(+)-nicotine caused a decrease only in hAChE-Tg//APPswe mice. Moreover, D(+)-nicotine increased the [125I]alpha-bungarotoxin binding sites in the hippocampus, and cortex of the hAChE-Tg//APPswe mice. In conclusion, already at a very young age, hAChE-Tg// APPswe mice exhibit increased levels of aggregated Abeta compared with APPswe mice, due to the possible interaction between Abeta and AChE-S, whereas APPswe mice exhibit increased soluble Abeta. The interaction between Abeta and AChE-S may also explain the different effect of nicotine on Abeta pathology in the hAChE-Tg//APPswe mice. The results in this study emphasize the importance of using different transgenic mouse models for evaluating the effect of new drug candidates for the treatment of Alzheimer's disease.     

Mitochondria are a direct site of A beta accumulation in Alzheimer's disease neurons: implications for free radical generation and oxidative damage in disease progression

Alzheimer's disease (AD) is a complex, neurodegenerative disease characterized by the impairment of cognitive function in elderly individuals. In a recent global gene expression study of APP transgenic mice, we found elevated expression of mitochondrial genes, which we hypothesize represents a compensatory response because of mitochondrial oxidative damage caused by the over-expression of mutant APP and/or amyloid beta (Abeta). We investigated this hypothesis in a series of experiments examining what forms of APP and Abeta localize to the mitochondria, and whether the presence of these species is associated with mitochondrial dysfunction and oxidative damage. Using immunoblotting, digitonin fractionation, immunofluorescence, and electron microscopy techniques, we found a relationship between mutant APP derivatives and mitochondria in brain slices from Tg2576 mice and in mouse neuroblastoma cells expressing mutant human APP. Further, to determine the functional relationship between mutant APP/Abeta and oxidative damage, we quantified Abeta levels, hydrogen peroxide production, cytochrome oxidase activity and carbonyl proteins in Tg2576 mice and age-matched wild-type (WT) littermates. Hydrogen peroxide levels were found to be significantly increased in Tg2576 mice when compared with age-matched WT littermates and directly correlated with levels of soluble Abeta in Tg2576 mice, suggesting that soluble Abeta may be responsible for the production of hydrogen peroxide in AD progression in Tg2576 mice. Cytochrome c oxidase activity was found to be decreased in Tg2576 mice when compared with age-matched WT littermates, suggesting that mutant APP and soluble Abeta impair mitochondrial metabolism in AD development and progression. An increase in hydrogen peroxide and a decrease in cytochrome oxidase activity were found in young Tg2576 mice, prior to the appearance of Abeta plaques. These findings suggest that early mitochondrially targeted therapeutic interventions may be effective in delaying AD progression in elderly individuals and in treating AD patients.     

Early discrimination reversal learning impairment and preserved spatial learning in a longitudinal study of Tg2576 APPsw mice

To understand the relationship between amyloid-beta and cognitive decline in Alzheimer's disease, we evaluated cortical and hippocampal function in a transgenic mouse model of amyloid over-expression in Alzheimer's disease, the Tg2576 mouse. Tg2576 mice and their non-transgenic littermates were assessed at both 6 and 14 months of age in a battery of cognitive tests: attentional set-shifting, water maze spatial reference memory and T-maze working memory. Spatial reference memory was not affected by Tg status at either age. Working memory was only affected by age, with 6-month-old mice performing better than 14-month-old ones. Older mice were also significantly impaired on reversal learning and on the intra- and extra-dimensional shift in attentional set-shifting. A significant transgene effect was apparent in reversal learning, with Tg2576 mice requiring more trials to reach criterion at 6 months old. These data indicate that the effects of normal aging in C57B6xSJL F1 mice are most pronounced on putative frontal cortex-dependent tasks and that increasing Abeta load only affects discrimination reversal learning in our study.     

Acetylcholinesterase promotes beta-amyloid plaques in cerebral cortex

Studies in vitro have suggested that acetylcholinesterase (AChE) may interact with beta-amyloid to promote deposition of amyloid plaques in the brain of patients with Alzheimer's disease. To test that hypothesis in vivo, we crossed Tg2576 mice, which express human amyloid precursor protein and develop plaques at 9 months, with transgenic mice expressing human AChE. The resulting F1 hybrids (FVB/N x [C57B6 x SJL/J]) expressed both transgenes in brain. By 6 months of age, their cerebral cortex showed authentic plaques that stained both by thioflavin S and by beta-amyloid 1-40 and 1-42 immunohistochemistry. The plaques also stained positively for other components including Cd11b, GFAP, and AChE. Plaque onset in the hybrids occurred 30-50% sooner than in the parental lines. Plaque numbers increased with age and plaques remained more numerous in the doubly transgenic animals at 9 and 12 months. Quantitative immunoassay via ELISA also showed an increase of total amyloid content in brain at 9-12 months. These histological and biochemical results support the conclusion that AChE may play a role in pathogenesis of Alzheimer's disease