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.     

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.     

Chronic dietary alpha-lipoic acid reduces deficits in hippocampal memory of aged Tg2576 mice

Oxidative stress may play a key role in Alzheimer's disease (AD) neuropathology. Here, the effects of the antioxidant, alpha-lipoic acid (ALA) were tested on the Tg2576 mouse, a transgenic model of cerebral amyloidosis associated with AD. Ten-month old Tg2576 and wild type mice were fed an ALA-containing diet (0.1%) or control diet for 6 months and then assessed for the influence of diet on memory and neuropathology. ALA-treated Tg2576 mice exhibited significantly improved learning, and memory retention in the Morris water maze task compared to untreated Tg2576 mice. Twenty-four hours after contextual fear conditioning, untreated Tg2576 mice exhibited significantly impaired context-dependent freezing. ALA-treated Tg2576 mice exhibited significantly more context freezing than the untreated Tg2576 mice. Assessment of brain soluble and insoluble beta-amyloid levels revealed no differences between ALA-treated and untreated Tg2576 mice. Brain levels of nitrotyrosine, a marker of nitrative stress, were elevated in Tg2576 mice, while F2 isoprostanes and neuroprostanes, oxidative stress markers, were not elevated in the Tg2576 mice relative to wild type. These data indicate that chronic dietary ALA can reduce hippocampal-dependent memory deficits of Tg2576 mice without affecting beta-amyloid levels or plaque deposition.     

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.     

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.     

Lack of LDL receptor aggravates learning deficits and amyloid deposits in Alzheimer transgenic mice

Emerging evidence indicates that cholesterol metabolism affects the pathogenesis of Alzheimer's disease (AD). The LDL receptor (LDLR) is obligatory in maintaining cholesterol homeostasis in the periphery. To investigate the role of LDLR in the development of AD-like behavior and pathology, Tg2576 mice, a well-characterized transgenic mouse model of AD, with different genotypes of LDLR were generated. Here we show that LDLR-deficient Tg2576 mice developed hypercholesterolemia and age-dependent cerebral beta-amyloidosis. Before the manifestation of amyloid-beta (Abeta) deposition, these mice displayed hyperactivity, reduced anxiety, and impaired spatial learning regardless of LDLR genotypes. After the manifestation of Abeta deposition, LDLR-deficient Tg2576 mice showed more spatial learning deficits than LDLR-intact Tg2576 mice. Although LDLR genotypes did not affect the expression level of the amyloid-beta precursor protein transgene, there was a significant increase in Abeta deposition accompanied with an increase of apoE expression in LDLR-deficient Tg2576 mice. Our results suggest that the LDLR plays a role in the development of Alzheimer-type learning impairment and amyloidosis and can be a novel therapeutic target for AD.     

Association of aortic atherosclerosis with cerebral beta-amyloidosis and learning deficits in a mouse model of Alzheimer's disease

High fat/high cholesterol diets exacerbate beta-amyloidosis in mouse models of Alzheimer's disease (AD). It has been impossible, however, to study the relationship between atherosclerosis and beta-amyloidosis in those models because such mice were on atherosclerosis-resistant genetic backgrounds. Here we report the establishment of AD model mice, B6Tg2576, that are prone to atherosclerosis. B6Tg2576 mice were produced by back-crossing Tg2576 mice, an AD mouse model overexpressing human amyloid beta-protein precursor with the Swedish double mutation, to C57BL/6 mice, a strain susceptible to diet-induced atherosclerosis. An atherogenic diet induced aortic atherosclerosis and exacerbated cerebral beta-amyloidosis in B6Tg2576 mice. Compared with age-matched non-transgenic littermates, B6Tg2576 mice developed significantly more diet-induced aortic atherosclerosis. Unexpectedly, normal diet-fed B6Tg2576 mice also developed fatty streak lesions (early atherosclerosis) in the aorta. The aortic atherosclerotic lesion area positively correlated with cerebral beta-amyloid deposits in B6Tg2576 mice on both atherogenic and normal diets. Furthermore, behavioral assessments demonstrated that B6Tg2576 mice fed an atherogenic diet had more spatial learning impairment than those fed a normal diet. Our results suggest that synergistic mechanisms may be involved in the pathogenesis of atherosclerosis and AD. These findings may have important implications in the prevention and treatment of cardiovascular diseases as well as AD.     

Transthyretin accelerates vascular Abeta deposition in a mouse model of Alzheimer's disease

Transthyretin (TTR) binds amyloid-β (Aβ) and prevents Aβ fibril formation in vitro . It was reported that the lack of neurodegeneration in a transgenic mouse model of Alzheimer's disease (AD) (Tg2576 mouse) was associated with increased TTR level in the hippocampus, and that chronic infusion of anti-TTR antibody into the hippocampus of Tg2576 mice led to increased local Aβ deposits, tau hyperphosphorylation and apoptosis. TTR is, therefore, speculated to prevent Aβ pathology in AD. However, a role for TTR in Aβ deposition is not yet known. To investigate the relationship between TTR and Aβ deposition, we generated a mouse line carrying a null mutation at the endogenous TTR locus and the human mutant amyloid precursor protein cDNA responsible for familial AD (Tg2576 /TTR ^−/− mouse) by crossing Tg2576 mice with TTR-deficient mice. We asked whether Aβ deposition was accelerated in Tg2576/ TTR ^−/− mice relative to the heterozygous mutant Tg2576 (Tg2576/ TTR ^+/−) mice. Contrary to our expectations, the degree of total and vascular Aβ burdens in the aged Tg2576/ TTR ^−/− mice was significantly reduced relative to the age-matched Tg2576/ TTR ^+/− mice. Our experiments present, for the first time, compelling evidence that TTR does not suppress but rather accelerates vascular Aβ deposition in the mouse model of AD.     

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。     

Outcome-specific satiety reveals a deficit in context-outcome, but not stimulus- or action-outcome, associations in aged Tg2576 mice

The onset of Alzheimer's disease (AD) is often accompanied by changes in emotion, motivation, and goal-directed behavior. The production of beta-amyloid is thought to be a major and early contributor to the pathogenesis of AD. The present study tested the hypothesis that amyloid pathology present in the amygdala, frontal cortex, and hippocampus of Tg2576 mice would disrupt the development of instrumental- and/or Pavlovian-outcome associations. The results showed that both instrumental- and Pavlovian-conditioned behaviors were sensitive to outcome devaluation (Experiments 1 & 2) and that Pavlovian cues influenced goal-directed actions associated with the same outcome (Experiment 2) in Tg2576 mice. In contrast, context mediated Pavlovian-conditioned behaviors in aged (Experiment 3a) but not young (Experiment 3b) Tg2576 mice were insensitive to outcome devaluation. Aged Tg2576, nevertheless, successfully acquired a simple context discrimination at the same rate as control mice. We conclude that amyloid pathology in aged Tg2576 mice may specifically disrupt context-outcome associations supported by the hippocampus and/or its interaction with the amygdala.     

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.     

Progressive impairment in olfactory working memory in a mouse model of Mild Cognitive Impairment

Patients with Mild Cognitive Impairment (MCI), exhibiting both working memory and olfactory deficits are likely to progress to Alzheimer's disease (AD). Targeting this pre-clinical AD population with disease modifying agents or cognitive enhancers represents the best strategy for halting or delaying the impact of this pernicious disease. However, there is a paucity of animal models of MCI with which to assess putative therapeutic strategies.We describe an odour span task which assesses the ability of mice to remember lists of odours, and report subtle cognitive deficits in human amyloid over-expressing (Tg2576) mice, at an age prior to plaque deposition. Four-month-old Tg2576 mice exhibited normal acquisition and performance in the standard 12-span task, but were significantly impaired when memory load was increased to 22 odours. By 8-months, a performance deficit was apparent in the 12-span task and by 1-year mice also exhibited significant acquisition deficits.Thus, by assessing olfactory working memory in Tg2576 mice we can model aspects of MCI in rodents and aid development of future therapeutic strategies for AD.     

Microglial response to amyloid plaques in APPsw transgenic mice.

Microglial activation is central to the inflammatory response in Alzheimer's Disease (AD). A recently described mouse line, Tg(HuAPP695.K670N/M671L)2576, expressing human amyloid precursor protein with a familial AD gene mutation, age-related amyloid deposits, and memory deficits, was found to develop a significant microglial response using Griffonia simplicifolia lectin or phosphotyrosine probe to identify microglia Both Griffonia simplicifolia lectin and phosphotyrosine staining showed increased numbers of intensely labeled, often enlarged microglia clustered in and around plaques, consistent with microglial activation related to beta-amyloid formation. Using quantitative image analysis of coronal phosphotyrosine-immunostained sections, transgene-positive 10- to 16-month-old, hemizygous, hybrid Tg2576 (APPsw) animals showed significantly increased microglial density and size in plaque-forming areas of hippocampus and frontal, entorhinal, and occipital cortex. Quantitative analysis of microglia as a function of distance from the center of plaques (double labeled for A beta peptide and microglia) revealed highly significant, two- to fivefold elevations in microglial number and area within plaques compared with neighboring regions. Tg2576 beta-amyloid-plaque-forming mice should be a useful system for assessing the consequences of the microglial-mediated inflammatory response to beta-amyloid and developing anti-inflammatory therapeutic strategies for Alzheimer's disease. These results provide the first quantitative link between beta-amyloid plaque formation and microglial activation in an animal model with neuritic plaques and memory deficits.     

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.     

Beta-amyloid-associated expression of intercellular adhesion molecule-1 in brain cortical tissue of transgenic Tg2576 mice

To study the relationship of beta-amyloid-mediated micro- and astrogliosis and inflammation-induced proteins including intercellular adhesion molecule (ICAM-1), brain tissue from transgenic Tg2576 mice expressing the Swedish mutation of the human amyloid precursor protein were examined for ICAM-1 expression. Immunocytochemistry demonstrated a diffuse immunostaining of ICAM-1 in the corona around fibrillary beta-amyloid plaques and an upregulation of ICAM-1 in activated microglial cells located in close proximity to the plaques, an ICAM-1 distribution pattern that partly mimics the situation in the brain of Alzheimer patients. The developmental time course revealed that the rate of cortical ICAM-1 induction was somewhat behind that of the progression of beta-amyloid plaque deposition. The microglial expression of ICAM-1 is a further indicator of the presence of inflammatory reactions in aged transgenic Tg2576 mouse brain, and may be a result of plaque-mediated astrocytic interleukin-1beta upregulation.     

Age-dependent differential expression of BACE splice variants in brain regions of tg2576 mice

Plaques found in the brains of patients suffering from Alzheimer's disease (AD) mainly consist of beta-amyloid (Abeta), which is produced by sequential cleaving of amyloid precursor protein (APP) by two proteolytic enzymes, beta- and gamma-secretases. Any change in the fine balance between these enzymes and their substrate may contribute to the etio-pathogenesis of AD. Indeed, the protein level and enzymatic activity of beta-secretase (BACE), but not its mRNA level, were found elevated in brain areas of AD patients who suffer a high load of Abeta plaque formation. Similarly, increased BACE activity but no mRNA change was observed in a transgenic mouse model of AD, tg2576, in which over expression of the Swedish mutated human APP leads to Abeta plaque formation and learning deficits. Based on the recent demonstration of four BACE splice variants with different enzymatic activity, the discrepancy between BACE activity and mRNA expression may be explained by the altered BACE alternative splicing. To test this hypothesis, we studied the expression of all BACE splice variants in different brain areas of tg2576 mice at age of 4 months and 1 year old. We found developmental and regional differences between wild-type and tg2576 mice. Our results indicate that over expression of APP in tg2576 mice leads to the altered alternative splicing of BACE and the increase of its enzymatically more active splice variant (I-501).     

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.     

Tissue plasminogen activator arrests Alzheimer's disease pathogenesis

The progressive deposition of amyloid-β (Aβ) in the brain is a pathologic feature of Alzheimer's disease (AD). This study was aimed to determine whether endogenous tissue plasminogen activator (tPA) modulates the pathogenic process of AD. tPA expression and activity developed around amyloid plaques in the brains of human amyloid precursor protein–overexpressing Tg2576 mice, which were weakened by the genetic ablation of tPA. Although the complete loss of tPA was developmentally fatal to Tg2576 mice, tPA-heterozygous Tg2576 mice expressed the more severe degenerative phenotypes than tPA wild-type Tg2576 mice, including abnormal and unhealthy growth, shorter life spans, significantly enhanced Aβ levels, and the deposition of more and larger amyloid plaques in the brain. In addition, the expression of synaptic function–associated proteins was significantly reduced, which in turn caused a more severe impairment in learning and memory performance in Tg2576 mice. Thus, endogenous tPA, preferentially its aggregate form, could degrade Aβ molecules and maintain low levels of brain Aβ, resulting in the delay of AD pathogenesis.     

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.     

Profiles of SUMO and ubiquitin conjugation in an Alzheimer's disease model

Alzheimer's disease (AD) is a major cause of disability in the elderly. The formation of senile plaques and neurofibrillary tangles are the main hallmarks of the disorder, whereas synaptic loss best correlates to the progressive cognitive decline. Interestingly, some of the proteins involved in these pathophysiological processes have been reported to be subject to posttranslational modification by ubiquitin and/or the small ubiquitin-like modifier (SUMO). Here we investigated global changes in protein SUMOylation and ubiquitination in vivo in a model of AD. We used Tg2576 transgenic mice, which overexpress a mutated human amyloid precursor protein (APP) gene implicated in familial AD. As expected, APP protein levels were dramatically increased in the hippocampus, cortex and cerebellum of Tg2576 mice. A significant increase in the global level of ubiquitinated proteins was observed in the hippocampus of Tg2576 mice. Significant or close to significant changes in individual bands of SUMO-1 or SUMO-2/3 conjugation were apparent in all brain regions investigated, although global levels were unaltered between wild-type and transgenic mice. Levels of SUMO-specific conjugating and deconjugating enzymes, UBC9 and SENP-1 were also unaltered in any of the brain regions analysed. Surprisingly, given the well-documented loss of synaptic function, total levels of the excitatory AMPA and kainate receptors were unaffected in the Tg2576 mice. These results suggest that alterations in SUMO substrate conjugation may occur and that global posttranslational modifications by ubiquitin may play an important role in the mechanisms underlying AD.