Cyclooxygenase (COX)-2 and cell cycle activity in a transgenic mouse model of Alzheimer's disease neuropathology

Prior studies have shown that cyclooxygenase (COX)-2, an enzyme involved in inflammatory mechanisms as well as neuronal activities, is up-regulated in the Alzheimer's disease (AD) brain and may represent a therapeutic target for anti-inflammatory treatments. We report the effect of neuronal overexpression of human (h)COX-2 in a murine model of AD neuropathology. Transgenic mice expressing both the human amyloid precursor protein mutation (APPswe) and the human presenilin (PS1-A246E) mutation, with resultant AD plaque pathology, were crossed with transgenic mice expressing human (h)COX-2 in neurons. At 12 months of age, the APPswe/PS1-A246E/hCOX-2 triple-transgenic mice showed an elevation in the number of phosphorylated retinoblastoma (pRb) tumor suppressor protein and active caspase-3 immunopositive neurons, compared to double APPswe/PS1-A246E or single hCOX-2 transgenic controls. No detectable influence of neuronal hCOX-2 on AD neuropathology was found in the brain of APPswe/PS1-A246E/hCOX-2 triple-transgenic mice, compared to double APPswe/PS1-A246E. In vitro studies revealed that hCOX-2 overexpression in primary cortico-hippocampal neurons derived from the hCOX-2 transgenics accelerates beta-amyloid (Abeta)(1-42)-mediated apoptotic damage which was prevented by the cell cycle dependent (CDK) inhibitor, flavoperidol. The data indicates that COX-2 overexpression causes alteration of neuronal cell cycle in a murine model of AD neuropathology, and provides a rational basis for targeting neuronal COX-2 in therapeutic research aimed at slowing the clinical progression of AD.     

Ultrastructural studies in APP/PS1 mice expressing human ApoE isoforms: implications for Alzheimer's disease

Alzheimer's disease is characterized in part by extracellular aggregation of the amyloid-β peptide in the form of diffuse and fibrillar plaques in the brain. Electron microscopy (EM) has made an important contribution in understanding of the structure of amyloid plaques in humans. Classical EM studies have revealed the architecture of the fibrillar core, characterized the progression of neuritic changes, and have identified the neurofibrillary tangles formed by paired helical filaments (PHF) in degenerating neurons. Clinical data has strongly correlated cognitive impairment in AD with the substantial synapse loss observed in these early ultrastructural studies. Animal models of AD-type brain amyloidosis have provided excellent opportunities to study amyloid and neuritic pathology in detail and establish the role of neurons and glia in plaque formation. Transgenic mice overexpressing mutant amyloid precursor protein (APP) alone with or without mutant presenilin 1 (PS1), have shown that brain amyloid plaque development and structure grossly recapitulate classical findings in humans. Transgenic APP/PS1 mice expressing human apolioprotein E isoforms also develop amyloid plaque deposition. However no ultrastructural data has been reported for these animals. Here we show results from detailed EM analysis of amyloid plaques in APP/PS1 mice expressing human isoforms of ApoE and compare these findings with EM data in other transgenic models and in human AD. Our results show that similar to other transgenic animals, APP/PS1 mice expressing human ApoE isoforms share all major cellular and subcellular degenerative features and highlight the identity of the cellular elements involved in Aβ deposition and neuronal degeneration.     

Amyloid precursor protein-induced axonopathies are independent of amyloid-beta peptides

Overexpression of amyloid precursor protein (APP), as well as mutations in the APP and presenilin genes, causes rare forms of Alzheimer's disease (AD). These genetic changes have been proposed to cause AD by elevating levels of amyloid-beta peptides (Abeta), which are thought to be neurotoxic. Since overexpression of APP also causes defects in axonal transport, we tested whether defects in axonal transport were the result of Abeta poisoning of the axonal transport machinery. Because directly varying APP levels also alters APP domains in addition to Abeta, we perturbed Abeta generation selectively by combining APP transgenes in Drosophila and mice with presenilin-1 (PS1) transgenes harboring mutations that cause familial AD (FAD). We found that combining FAD mutant PS1 with FAD mutant APP increased Abeta42/Abeta40 ratios and enhanced amyloid deposition as previously reported. Surprisingly, however, this combination suppressed rather than increased APP-induced axonal transport defects in both Drosophila and mice. In addition, neuronal apoptosis induced by expression of FAD mutant human APP in Drosophila was suppressed by co-expressing FAD mutant PS1. We also observed that directly elevating Abeta with fusions to the Familial British and Danish Dementia-related BRI protein did not enhance axonal transport phenotypes in APP transgenic mice. Finally, we observed that perturbing Abeta ratios in the mouse by combining FAD mutant PS1 with FAD mutant APP did not enhance APP-induced behavioral defects. A potential mechanism to explain these findings was suggested by direct analysis of axonal transport in the mouse, which revealed that axonal transport or entry of APP into axons is reduced by FAD mutant PS1. Thus, we suggest that APP-induced axonal defects are not caused by Abeta.     

Hypoxia increases Abeta generation by altering beta- and gamma-cleavage of APP

Environmental factors are significant contributors for the development of Alzheimer's disease (AD). The greatly increased incidence of AD following stroke and cerebral ischemia suggests that hypoxia is a risk factor which may accelerate AD pathogenesis by altering amyloid precursor protein (APP) processing. However, the molecular mechanisms underlying the hypoxia mediated AD pathogenesis have not been fully elucidated. In the present study we demonstrated that repeated hypoxia increased beta-amyloid (Abeta) generation and neuritic plaques formation by elevating beta-cleavage of APP in APP(swe)+PS1(A246E) transgenic mice. We also found that hypoxia enhanced the expression of APH-1a, a component of gamma-secretase complex, which in turn may lead to increase in gamma-cleavage activity. Furthermore, we demonstrated that repeated hypoxia treatment can activate macroautophagy, which may contribute to the increases in Abeta production since pretreatment with macroautophagy inhibitor 3-methyladenine significantly blocked chemical hypoxic condition-induced increase in Abeta production in SH-SY5Y cells. Taken together, our results suggest an important role of hypoxia in modulating the APP processing by facilitating both beta- and gamma-cleavage which may result in a significant increase of Abeta generation.     

Mutant presenilins specifically elevate the levels of the 42 residue beta-amyloid peptide in vivo: evidence for augmentation of a 42-specific gamma secretase

Amyloid precursor protein (APP) is endoproteolytically processed by BACE1 and gamma-secretase to release amyloid peptides (Abeta40 and 42) that aggregate to form senile plaques in the brains of patients with Alzheimer's disease (AD). The C-terminus of Abeta40/42 is generated by gamma-secretase, whose activity is dependent upon presenilin (PS 1 or 2). Missense mutations in PS1 (and PS2) occur in patients with early-onset familial AD (FAD), and previous studies in transgenic mice and cultured cell models demonstrated that FAD-PS1 variants shift the ratio of Abeta40 : 42 to favor Abeta42. One hypothesis to explain this outcome is that mutant PS alters the specificity of gamma-secretase to favor production of Abeta42 at the expense of Abeta40. To test this hypothesis in vivo, we studied Abeta40 and 42 levels in a series of transgenic mice that co-express the Swedish mutation of APP (APPswe) with two FAD-PS1 variants that differentially accelerate amyloid pathology in the brain. We demonstrate a direct correlation between the concentration of Abeta42 and the rate of amyloid deposition. We further show that the shift in Abeta42 : 40 ratios associated with the expression of FAD-PS1 variants is due to a specific elevation in the steady-state levels of Abeta42, while maintaining a constant level of Abeta40. These data suggest that PS1 variants do not simply alter the preferred cleavage site for gamma-secretase, but rather that they have more complex effects on the regulation of gamma-secretase and its access to substrates.     

Therapeutic actions of insulin-like growth factor I on APP/PS2 mice with severe brain amyloidosis

Transgenic mice expressing mutant forms of both amyloid-beta (Abeta) precursor protein (APP) and presenilin (PS) 2 develop severe brain amyloidosis and cognitive deficits, two pathological hallmarks of Alzheimer's disease (AD). One-year-old APP/PS2 mice with high brain levels of Abeta and abundant Abeta plaques show disturbances in spatial learning and memory. Treatment of these deteriorated mice with a systemic slow-release formulation of insulin-like growth factor I (IGF-I) significantly ameliorated AD-like disturbances. Thus, IGF-I enhanced cognitive performance, decreased brain Abeta load, increased the levels of synaptic proteins, and reduced astrogliosis associated to Abeta plaques. The beneficial effects of IGF-I were associated to a significant increase in brain Abeta complexed to protein carriers such as albumin, apolipoprotein J or transthyretin. Since levels of APP were not modified after IGF-I therapy, and in vitro data showed that IGF-I increases the transport of Abeta/carrier protein complexes through the choroid plexus barrier, it seems that IGF-I favors elimination of Abeta from the brain, supporting a therapeutic use of this growth factor in 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.     

Neuronal or glial expression of human apolipoprotein e4 affects parenchymal and vascular amyloid pathology differentially in different brain regions of double- and triple-transgenic mice

Apolipoprotein E4 (ApoE4) is associated with Alzheimer's disease by unknown mechanisms. We generated six transgenic mice strains expressing human ApoE4 in combination with mutant amyloid precursor protein (APP) and mutant presenilin-1 (PS1) in single-, double-, or triple-transgenic combinations. Diffuse, but not dense, amyloid plaque-load in subiculum and cortex was increased by neuronal but not glial ApoE4 in old (15 months) double-transgenic mice, whereas both diffuse and dense plaques formed in thalamus in both genotypes. Neuronal and glial ApoE4 promoted cerebral amyloid angiopathy as extensively as mutant PS1 but with pronounced regional differences: cortical angiopathy was induced by neuronal ApoE4 while thalamic angiopathy was again independent of ApoE4 source. Angiopathy correlated more strongly with soluble Abeta40 and Abeta42 levels in cortex than in thalamus throughout the six genotypes. Neither neuronal nor glial ApoE4 affected APP proteolytic processing, as opposed to mutant PS1. Neuronal ApoE4 increased soluble amyloid levels more than glial ApoE4, but the Abeta42/40 ratios were similar, although significantly higher than in single APP transgenic mice. We conclude that although the cellular origin of ApoE4 differentially affects regional amyloid pathology, ApoE4 acts on the disposition of amyloid peptides downstream from their excision from APP but without induction of tauopathy.     

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.     

Thiamine deficiency induces oxidative stress and exacerbates the plaque pathology in Alzheimer's mouse model

Mitochondrial dysfunction, oxidative stress and reductions in thiamine-dependent enzymes have been implicated in multiple neurological disorders including Alzheimer's disease (AD). Experimental thiamine deficiency (TD) is an established model for reducing the activities of thiamine-dependent enzymes in brain. TD diminishes thiamine-dependent enzymes throughout the brain, but produces a time-dependent selective neuronal loss, glial activation, inflammation, abnormalities in oxidative metabolism and clusters of degenerating neurites in only specific thalamic regions. The present studies tested how TD alters brain pathology in Tg19959 transgenic mice over expressing a double mutant form of the amyloid precursor protein (APP). TD exacerbated amyloid plaque pathology in transgenic mice and enlarged the area occupied by plaques in cortex, hippocampus and thalamus by 50%, 200% and 200%, respectively. TD increased Abeta(1-42) levels by about three fold, beta-CTF (C99) levels by 33% and beta-secretase (BACE1) protein levels by 43%. TD-induced inflammation in areas of plaque formation. Thus, the induction of mild impairment of oxidative metabolism, oxidative stress and inflammation induced by TD alters metabolism of APP and/or Abeta and promotes accumulation of plaques independent of neuron loss or neuritic clusters.     

Inflammatory responses to amyloidosis in a transgenic mouse model of Alzheimer's disease

Mutations in the amyloid precursor protein (APP) and presenilin-1 and -2 genes (PS-1, -2) cause Alzheimer's disease (AD). Mice carrying both mutant genes (PS/APP) develop AD-like deposits composed of beta-amyloid (Abeta) at an early age. In this study, we have examined how Abeta deposition is associated with immune responses. Both fibrillar and nonfibrillar Abeta (diffuse) deposits were visible in the frontal cortex by 3 months, and the amyloid load increased dramatically with age. The number of fibrillar Abeta deposits increased up to the oldest age studied (2.5 years old), whereas there were less marked changes in the number of diffuse deposits in mice over 1 year old. Activated microglia and astrocytes increased synchronously with amyloid burden and were, in general, closely associated with deposits. Cyclooxygenase-2, an inflammatory response molecule involved in the prostaglandin pathway, was up-regulated in astrocytes associated with some fibrillar deposits. Complement component 1q, an immune response component, strongly colocalized with fibrillar Abeta, but was also up-regulated in some plaque-associated microglia. These results show: i) an increasing proportion of amyloid is composed of fibrillar Abeta in the aging PS/APP mouse brain; ii) microglia and astrocytes are activated by both fibrillar and diffuse Abeta; and iii) cyclooxygenase-2 and complement component 1q levels increase in response to the formation of fibrillar Abeta in PS/APP mice.     

Presenilin transgenic mice as models of Alzheimer’s disease

Mutations in presenilin-1 (PS1) and presenilin-2 (PS2) cause familial Alzheimer’s disease (FAD). Presenilins influence multiple molecular pathways and are best known for their role in the γ-secretase cleavage of type I transmembrane proteins including the amyloid precursor protein (APP). PS1 and PS2 FAD mutant transgenic mice have been generated using a variety of promoters. PS1-associated FAD mutations have also been knocked into the endogenous mouse gene. PS FAD mutant mice consistently show elevations of Aβ42 with little if any effect on Aβ40. When crossed with plaque forming APP FAD mutant lines, the PS1 FAD mutants cause earlier and more extensive plaque deposition. Although single transgenic PS1 or PS2 mice do not form plaques, they exhibit a number of pathological features including age-related neuronal and synaptic loss as well as vascular pathology. They also exhibit increased susceptibility to excitotoxic injury most likely on the basis of exaggerated calcium release from the endoplasmic reticulum. Electrophysiologically long-term potentiation in the hippocampus is increased in young PS1 FAD mutant mice but this effect appears to be lost with aging. In most studies neurogenesis in the adult hippocampus is also impaired by PS1 FAD mutants. Mice in which PS1 has been conditionally knocked out in adult forebrain on a PS2 null background (PS1/2 cDKO) develop a striking neurodegeneration that mimics AD neuropathology in being associated with neuronal and synaptic loss, astrogliosis and hyperphosphorylation of tau, although it is not accompanied by plaque deposits. The relevance of PS transgenic mice as models of AD is discussed.     

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.     

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.     

Age-related changes of neuron numbers in the frontal cortex of a transgenic mouse model of Alzheimer's disease

Alzheimer’s disease (AD) is a neurodegenerative disorder, characterized by amyloid plaque accumulation, intracellular tangles and neuronal loss in selective brain regions. The frontal cortex, important for executive functioning, is one of the regions that are affected. Here, we investigated the neurodegenerative effects of mutant human amyloid precursor protein (APP) and presenilin 1 (PS1) on frontal cortex neurons in APP/PS1KI mice, a transgenic mouse model of AD, expressing two mutations in the human APP, as well as two human PS1 mutations knocked-in into the mouse PS1 gene in a homozygous (ho) manner. Although the hippocampus is significantly affected in these mice, very little is known about the effects of these mutations on selective neuronal populations and plaque load in the frontal cortex. In this study, cytoarchitectural changes were characterized using high precision design-based stereology to evaluate plaque load, total neuron numbers, as well as total numbers of parvalbumin- (PV) and calretinin- (CR) immunoreactive (ir) neurons in the frontal cortex of 2- and 10-month-old APP/PS1KI mice. The frontal cortex was divided into two subfields: layers II–IV and layers V–VI, the latter of which showed substantially more extracellular amyloid-beta aggregates. We found a 34% neuron loss in layers V–VI in the frontal cortex of 10-month-old APP/PS1KI mice compared to 2-month-old, while there was no change in PV- and CR-ir neurons in these mice. In addition, the plaque load in layers V–VI of 10-month-old APP/PS1KI mice was only 11% and did not fully account for the extent of neuronal loss. Interestingly, an increase was found in the total number of PV-ir neurons in all frontal cortical layers of single transgenic APP mice and in layers II–IV of single transgenic PS1ho mice between 2 and 10 months of age. In conclusion, the APP/PS1KI mice provide novel insights into the regional selective vulnerability in the frontal cortex during AD that, together with previous findings in the hippocampus, are remarkably similar to the human situation.     

Intraneuronal Abeta accumulation precedes plaque formation in beta-amyloid precursor protein and presenilin-1 double-transgenic mice

beta-Amyloid peptides are key molecules that are involved in the pathology of Alzheimer's disease (AD). The source and place of the neurotoxic action of Abeta, however, is still a matter of controversial debates. In the present report, we studied the neuropathological events in a transgenic mouse model expressing human mutant beta-amyloid precursor protein and human mutant presenilin-1 in neurons. Western blot and immunohistochemical analysis revealed that intracellular Abeta staining preceded plaque deposition, which started in the hippocampal formation. At later stages, many neuritic Abeta positive plaques were found in all cortical, hippocampal and many other brain areas. Interestingly, intraneuronal Abeta staining was no longer detected in the brain of aged double-transgenic mice, which correlates with the typical neuropathology in the brain of chronic AD patients.     

Pro-oxidant diet enhances β/γ secretase-mediated APP processing in APP/PS1 transgenic mice

The etiology of Alzheimer's disease (AD) is complex with oxidative stress being a possible contributory factor to pathogenesis and disease progression. TASTPM transgenic mice expressing familial AD-associated amyloid precursor protein (APPswe) and presenilin transgenes (PS1M146V) show increased brain amyloid beta (Aβ) levels and Aβ plaques from 3 months. We tested if enhancing oxidative stress through diet would accelerate Aβ-related pathology. TASTPM were fed a pro-oxidant diet for 3 months resulting in increased brain levels of protein carbonyls, increased Nrf2, and elevated concentrations of glutathione (GSH). The diet increased both amyloid precursor protein (APP) and Aβ in the cortex of TASTPM but did not alter Aβ plaque load, presenilin 1, or β-secretase (BACE1) expression. TASTPM cortical neurons were cultured under similar pro-oxidant conditions resulting in increased levels of APP and Aβ likely as a result of enhanced β/γ secretase processing of APP. Thus, pro-oxidant conditions increase APP levels and enhance BACE1-mediated APP processing and in doing so might contribute to pathogenesis in AD.     

Antibodies from a DNA peptide vaccination decrease the brain amyloid burden in a mouse model of Alzheimer’s disease

The neuropathology of Alzheimer's disease(AD) is characterized by the accumulation of amyloid peptide Abeta in the brain derived from proteolytic cleavage of the amyloid precursor protein (APP). Vaccination of mice with plasmid DNA coding for the human Abeta42 peptide together with low doses of preaggregated peptide induced antibodies with detectable titers after only 2 weeks. One serum was directed against the four aminoterminal amino acids DAEF and differs from previously described ones. Both immune sera and monoclonal antibodies solubilized preformed aggregates of Abeta42 in vitro and recognized amyloid plaques in brain sections of mice transgenic for human APP. Passive immunization of transgenic AD mice caused a significant and rapid reduction in brain amyloid plaques within 24 h. The combined DNA peptide vaccine may prove useful for active immunization with few inoculations and low peptide dose which may prevent the recently described inflammatory reactions inpatients. The monoclonal antibodies are applicable for passive immunization studies and may lead to a therapy of AD.     

Accumulation of proteolytic fragments of mutant presenilin 1 and accelerated amyloid deposition are co-regulated in transgenic mice.

The activities of presenilin 1 (PS1) and 2 modulate the proteolytic processing of amyloid precursor proteins to produce Abeta1-42, and mutations in these proteins are associated with an accelerated rate of Abeta deposition. PS1 and PS2 themselves are subject to a highly-regulated endoproteolytic cleavage to generate stable 27 kDa N-terminal and 17 kDa C-terminal fragments. Here, we examined the relationship between the regulated cleavage of PS1 and the acceleration of Abeta deposition in transgenic mice that co-express Mo/Hu APPswe and varied levels mutant PS1 (A246E variant). The steady-state levels of the N- and C-terminal fragments of mutant PS1 in mice expressing low levels of mRNA were similar to that of mice expressing high levels of mRNA. Only mice expressing high levels of transgene mRNA accumulated uncleaved full-length protein. In mice co-expressing low levels of PS1A246E mRNA with Mo/Hu APPswe the age of appearance of Abeta deposits was similar to that of mice co-expressing expressing Mo/Hu APPswe with very high levels of mutant PS1. Our findings demonstrate that the levels of accumulated human PS1 N- and C-terminal fragments do not increase in proportion to the level of transgene mRNA and that similarly, the magnitude by which mutant PS1 accelerates the deposition of beta-amyloid is not proportional to the level of transgene expression.