Mouse Model Of Amyloidosis Research Articles

Stratégie de recherche translationnelle sur la maladie d’Alzheimer : cibles, modèles animaux et biomarqueurs

Alzheimer's disease causes severe cognitive alterations in humans and is associated with two main pathologic processes: the β-amyloid and tau pathologies. Imaging biomarkers can reveal the natural history of the disease and show an alteration of glucose metabolism and an evolving cerebral atrophy process. The discovery of new therapies against this disease relies on early stages of drug development that can be evaluated precisely only in animals. Our review focuses on transgenic mouse models of amyloidosis and on the mouse lemur primate model. Biomarkers in these animals may reveal endophenotypes that can be compared to human endophenotypes and help rationalizing decision-making during the development of new therapies. Animal models can also help to validate new hypotheses on disease mechanisms. We focus here on the protein misfolding hypothesis of Alzheimer as it will probably modulate our vision of the disease in forthcoming years. This hypothesis suggests that native Aβ peptides become toxic when their conformation in alpha helices evolves into a beta-sheet conformation and also suggests that misfolded proteins can transmit their misfolded conformation to normal proteins.

Behavioral abnormalities in APPSwe/PS1dE9 mouse model of AD-like pathology: comparative analysis across multiple behavioral domains

Alzheimer's disease (AD) is characterized by dysfunction in cognitive and noncognitive domains with clinical diagnosis based on multiple neuropsychological tests. Here, we evaluated cognitive and noncognitive behaviors in 2 age cohorts (8 and 14 months at the start of the study) of APPSwe/PS1dE9 transgenic mice that model AD-like amyloidosis. We used a battery of tests that included fear-conditioned context and tone memories, swimming activity, and orientation to a proximal cue in a visible platform water maze test and burrowing and nest building activity. To compare the performance of mice across all tests, we used z-score normalization of data. The analyses revealed that the behavior of the transgenic mice was significantly compromised in cognitive as well as in noncognitive domains. Combining scores across multiple behavioral tests produced an integrated index characterizing the overall phenotypic abnormality in this model of AD-like amyloidosis. Assessing multiple behavioral domains provides a broader view of the breadth of impairments in multiple behavioral systems. Greater implementation of such approaches could enable reliable and clinically predictive evaluation of therapeutics in mouse models of amyloidosis.

An ER-directed gelsolin nanobody targets the first step in amyloid formation in a gelsolin amyloidosis mouse model.

Hereditary gelsolin amyloidosis is an autosomal dominantly inherited amyloid disorder. A point mutation in the GSN gene (G654A being the most common one) results in disturbed calcium binding by the second gelsolin domain (G2). As a result, the folding of G2 is hampered, rendering the mutant plasma gelsolin susceptible to a proteolytic cascade. Consecutive cleavage by furin and MT1-MMP-like proteases generates 8 and 5 kDa amyloidogenic peptides that cause neurological, ophthalmological and dermatological findings. To this day, no specific treatment is available to counter the pathogenesis. Using GSN nanobody 11 as a molecular chaperone, we aimed to protect mutant plasma gelsolin from furin proteolysis in the trans-Golgi network. We report a transgenic, GSN nanobody 11 secreting mouse that was used for crossbreeding with gelsolin amyloidosis mice. Insertion of the therapeutic nanobody gene into the gelsolin amyloidosis mouse genome resulted in improved muscle contractility. X-ray crystal structure determination of the gelsolin G2:Nb11 complex revealed that Nb11 does not directly block the furin cleavage site. We conclude that nanobodies can be used to shield substrates from aberrant proteolysis and this approach might establish a novel therapeutic strategy in amyloid diseases.

Correction: Resting State fMRI Reveals Diminished Functional Connectivity in a Mouse Model of Amyloidosis

Figure 2, Results of the whole brain seed correlation analysis for the WT and TG groups, was mistakenly replaced by a duplicate of Figure S2. The Figure 2 legend is correct. Please see the correct Figure 2 here:

Resting State fMRI Reveals Diminished Functional Connectivity in a Mouse Model of Amyloidosis

IntroductionFunctional connectivity (FC) studies have gained immense popularity in the evaluation of several neurological disorders, such as Alzheimer’s disease (AD). AD is a complex disorder, characterised by several pathological features. The problem with FC studies in patients is that it is not straightforward to focus on a specific aspect of pathology. In the current study, resting state functional magnetic resonance imaging (rsfMRI) is applied in a mouse model of amyloidosis to assess the effects of amyloid pathology on FC in the mouse brain.MethodsNine APP/PS1 transgenic and nine wild-type mice (average age 18.9 months) were imaged on a 7T MRI system. The mice were anesthetized with medetomidine and rsfMRI data were acquired using a gradient echo EPI sequence. The data were analysed using a whole brain seed correlation analysis and interhemispheric FC was evaluated using a pairwise seed analysis. Qualitative histological analyses were performed to assess amyloid pathology, inflammation and synaptic deficits.ResultsThe whole brain seed analysis revealed an overall decrease in FC in the brains of transgenic mice compared to wild-type mice. The results showed that interhemispheric FC was relatively preserved in the motor cortex of the transgenic mice, but decreased in the somatosensory cortex and the hippocampus when compared to the wild-type mice. The pairwise seed analysis confirmed these results. Histological analyses confirmed the presence of amyloid pathology, inflammation and synaptic deficits in the transgenic mice. ConclusionsIn the current study, rsfMRI demonstrated decreased FC in APP/PS1 transgenic mice compared to wild-type mice in several brain regions. The APP/PS1 transgenic mice had advanced amyloid pathology across the brain, as well as inflammation and synaptic deficits surrounding the amyloid plaques. Future studies should longitudinally evaluate APP/PS1 transgenic mice and correlate the rsfMRI findings to specific stages of amyloid pathology.

Fast in vivo imaging of amyloid plaques using μ-MRI Gd-staining combined with ultrasound-induced blood–brain barrier opening

Amyloid plaques are one of the major microscopic lesions that characterize Alzheimer's disease. Current approaches to detect amyloid plaques by using magnetic resonance imaging (MRI) contrast agents require invasive procedures to penetrate the blood-brain barrier (BBB) and to deliver the contrast agent into the vicinity of amyloid plaques. Here we have developed a new protocol (US-Gd-staining) that enables the detection of amyloid plaques in the brain of an APP/PS1 transgenic mouse model of amyloidosis after intra-venous injection of a non-targeted, clinically approved MRI contrast agent (Gd-DOTA, Dotarem®) by transiently opening the BBB with unfocused ultrasound (1 MHz) and clinically approved microbubbles (Sonovue®, Bracco). This US-Gd-staining protocol can detect amyloid plaques with a short imaging time (32 min) and high in-plane resolution (29 μm). The sensitivity and resolution obtained is at least equal to that provided by MRI protocols using intra-cerebro-ventricular injection of contrast agents, a reference method used to penetrate the BBB. To our knowledge this is the first study to demonstrate the ability of MR imaging to detect amyloid plaques by using a peripheral intra-venous injection of a clinically approved NMR contrast agent.

Molecular Differences and Similarities Between Alzheimer's Disease and the 5XFAD Transgenic Mouse Model of Amyloidosis.

Transgenic (Tg) mouse models of Alzheimer’s disease (AD) have been extensively used to study the pathophysiology of this dementia and to test the efficacy of drugs to treat AD. The 5XFAD Tg mouse, which contains two presenilin-1 and three amyloid precursor protein (APP) mutations, was designed to rapidly recapitulate a portion of the pathologic alterations present in human AD. APP and its proteolytic peptides, as well as apolipoprotein E and endogenous mouse tau, were investigated in the 5XFAD mice at 3 months, 6 months, and 9 months. AD and nondemented subjects were used as a frame of reference. APP, amyloid-beta (Aβ) peptides, APP C-terminal fragments (CT99, CT83, AICD), β-site APP-cleaving enzyme, and APLP1 substantially increased with age in the brains of 5XFAD mice. Endogenous mouse tau did not show age-related differences. The rapid synthesis of Aβ and its impact on neuronal loss and neuroinflammation make the 5XFAD mice a desirable paradigm to model AD.

Selective degeneration of septal and hippocampal GABAergic neurons in a mouse model of amyloidosis and tauopathy

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by brain accumulation of amyloid-β peptide and neurofibrillary tangles, which are believed to initiate a pathological cascade that results in progressive impairment of cognitive functions and eventual neuronal death. To obtain a mouse model displaying the typical AD histopathology of amyloidosis and tauopathy, we generated a triple-transgenic mouse line (TauPS2APP) by overexpressing human mutations of the amyloid precursor protein, presenilin2 and tau genes. Stereological analysis of TauPS2APP mice revealed significant neurodegeneration of GABAergic septo-hippocampal projection neurons as well as their target cells, the GABAergic hippocampal interneurons. In contrast, the cholinergic medial septum neurons remained unaffected. Moreover, the degeneration of hippocampal GABAergic interneurons was dependent on the hippocampal subfield and interneuronal subtype investigated, whereby the dentate gyrus and the NPY-positive interneurons, respectively, were most strongly affected. Neurodegeneration was also accompanied by a change in the mRNA expression of markers for inhibitory interneurons. In line with the loss of inhibitory neurons, we observed functional changes in TauPS2APP mice relative to WT mice, with strongly enhanced long-term potentiation in the medial-perforant pathway input to the dentate gyrus, and stereotypic hyperactivity. Our data indicate that inhibitory neurons are the targets of neurodegeneration in a mouse model of amyloidosis and tauopathy, thus pointing to a possible role of the inhibitory network in the pathophysiological and functional cascade of Alzheimer's disease.

Age-related increase in amyloid plaque burden is associated with impairment in conditioned fear memory in CRND8 mouse model of amyloidosis

IntroductionThe current pathological confirmation of the diagnosis of Alzheimer's disease (AD) is still based on postmortem identification of parenchymal amyloid beta (Aβ) plaques, intra-neuronal neurofibrillary tangles, and neuronal loss. The memory deficits that are present in the early stages of AD are linked to the dysfunction of structures in the entorhinal cortex and limbic system, especially the hippocampus and amygdala. Using the CRND8 transgenic mouse model of amyloidosis, which over-expresses a mutant human amyloid precursor protein (APP) gene, we evaluated hippocampus-dependent contextual and amygdala-dependent tone fear conditioned (FC) memory, and investigated the relationship between the fear memory indices and Aβ plaque burden.MethodsMice were tested at three, six, and 12 months of age, which corresponds to early, mild, and severe Aβ plaque deposition, following a cross-sectional experimental design. We used a delay version of the fear conditioning paradigm in which tone stimulus was co-terminated with foot-shocks during exploration of the training chamber. The Aβ plaque burden was evaluated at each age after the completion of the behavioral tests.ResultsCRDN8 mice showed context fear memory comparable to control mice at three and six months, but were significantly impaired at 12 months of age. In contrast, the tone fear memory was significantly impaired in the model at each age of testing. The Aβ plaque burden significantly increased with age, and was correlated with the overall impairment in context and tone fear memory in the CRND8 mice within the studied age.ConclusionsOur data extend previous studies showing that other APP mouse models exhibit impairment in fear conditioned memory, by demonstrating that this impairment is progressive and correlates well with an overall increase in Aβ burden. Also, the demonstrated greater sensitivity of the tone conditioning test in the identification of age dependent differences between CRND8 and control mice suggests that this paradigm might be particularly suitable in studies evaluating potential therapeutics related to memory improvement in mouse models of amyloidosis.

THE USE OF RESTING STATE FUNCTIONAL MRI TO STUDY FUNCTIONAL CONNECTIVITY IN A MOUSE MODEL OF ALZHEIMER’S DISEASE

Event Abstract Back to Event THE USE OF RESTING STATE FUNCTIONAL MRI TO STUDY FUNCTIONAL CONNECTIVITY IN A MOUSE MODEL OF ALZHEIMER’S DISEASE Disha Shah1*, Elisabeth Jonckers1, Christian Bigot1, Greetje Vanhoutte1, Marleen Verhoye1 and Annemie Van Der Linden1 1 Bio-Imaging Lab, University of Antwerp, Belgium Objectives: The goal of this study is to assess functional connectivity (FC) in an APPPS1 mouse model of Alzheimer’s disease (AD) using resting state functional MRI (rsfMRI). Background: AD pathology is characterized by amyloid pathology, the formation of tau-fibrils and neurodegeneration. Amyloid pathology is hypothesized to be the driving force behind AD. RsfMRI in human research has shown that amyloid pathology and altered FC occur in the same brain regions (1), suggesting a possible relation between these two events. Human rsfMRI studies are limited in studying correlations, as AD manifests many pathological alterations. Using a mouse model of amyloidosis, e.g. the APPPS1 mice (2), facilitates the assessment of a correlation between FC alterations and amyloid. The hypothesis of this study is that old APPPS1 mice show FC alterations in the brain, which could be related to amyloidosis. RsfMRI data of 10 male APPswePS1 mice and 9 male control C57BL6 mice of (18.9 ±1.3) months old were acquired on a 7T Pharmascan (Bruker BioSpin, Germany) using a gradient echo EPI sequence. For the analysis we have opted for independent component analysis (ICA), a technique that divides the blood-oxygenation-level-dependent (BOLD) signal into a number of components, each consistent with a certain time course of the BOLD-signal. For every component a map is obtained consisting of regions of which the time course is correlated to the time course of the component i.e. a functional connectivity map. Results: ICA revealed differences in FC between the APPPS1 and control groups. FC was deteriorated between the retrosplenial cortex and the hippocampus, which are regions associated with spatial memory. Conclusion: These results are in accordance with literature (2), reporting diminished spatial memory in the APPPS1 mice. The observation of altered FC in the same regions that show amyloid plaques suggest that these two events are related. The next step would be to study mice longitudinally to assess the exact relation between FC changes and amyloid pathology. Acknowledgements The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 278850 (INMiND). The APPPS1 mice were kindly provided by the Department of molecular genetics, University of Antwerp, Belgium. References 1) Sheline et al., (2010), Biol. psych. 67 (6): 584–587. 2) Radde et al., (2006), EMBO reports 7: 940-946. Keywords: Alzheimer's disease, resting state functional MRI, functional connectivity, APPPS1 mice, Amyloid Conference: Belgian Brain Council, Liège, Belgium, 27 Oct - 27 Oct, 2012. Presentation Type: Poster Presentation Topic: Higher Brain Functions in health and disease: cognition and memory Citation: Shah D, Jonckers E, Bigot C, Vanhoutte G, Verhoye M and Van Der Linden A (2012). THE USE OF RESTING STATE FUNCTIONAL MRI TO STUDY FUNCTIONAL CONNECTIVITY IN A MOUSE MODEL OF ALZHEIMER’S DISEASE. Conference Abstract: Belgian Brain Council. doi: 10.3389/conf.fnhum.2012.210.00045 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 03 Sep 2012; Published Online: 12 Sep 2012. * Correspondence: Miss. Disha Shah, Bio-Imaging Lab, University of Antwerp, Antwerp, Belgium, disha.shah@ua.ac.be Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Disha Shah Elisabeth Jonckers Christian Bigot Greetje Vanhoutte Marleen Verhoye Annemie Van Der Linden Google Disha Shah Elisabeth Jonckers Christian Bigot Greetje Vanhoutte Marleen Verhoye Annemie Van Der Linden Google Scholar Disha Shah Elisabeth Jonckers Christian Bigot Greetje Vanhoutte Marleen Verhoye Annemie Van Der Linden PubMed Disha Shah Elisabeth Jonckers Christian Bigot Greetje Vanhoutte Marleen Verhoye Annemie Van Der Linden Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Finally, a transgenic light chain amyloidosis mouse model

Ward and colleagues report the first transgenic light chain amyloidosis mouse model in this issue of Blood and demonstrate that it can be used to test pharmaceutical candidates.

Increased regional cerebral glucose uptake in an APP/PS1 model of Alzheimer's disease

Alzheimer's disease (AD), the most common age-related neurodegenerative disorder, is characterized by the invariant cerebral accumulation of β-amyloid peptide. This event occurs early in the disease process. In humans, [18F]-fluoro-2-deoxy-D-glucose ([18F]-FDG) positron emission tomography (PET) is largely used to follow-up in vivo cerebral glucose utilization (CGU) and brain metabolism modifications associated with the Alzheimer's disease pathology. Here, [18F]-FDG positron emission tomography was used to study age-related changes of cerebral glucose utilization under resting conditions in 3-, 6-, and 12-month-old APPSweLon/PS1M146L, a mouse model of amyloidosis. We showed an age-dependent increase of glucose uptake in several brain regions of APP/PS1 mice but not in control animals and a higher [18F]-FDG uptake in the cortex and the hippocampus of 12-month-old APP/PS1 mice as compared with age-matched control mice. We then developed a method of 3-D microscopic autoradiography to evaluate glucose uptake at the level of amyloid plaques and showed an increased glucose uptake close to the plaques rather than in amyloid-free cerebral tissues. These data suggest a macroscopic and microscopic reorganization of glucose uptake in relation to cerebral amyloidosis.

Enhanced dentate gyrus synaptic plasticity but reduced neurogenesis in a mouse model of amyloidosis

Long-term potentiation (LTP) and neurogenesis in the dentate gyrus (DG) are correlated forms of hippocampal plasticity which share, under physiological conditions, common regulatory mechanisms. In Alzheimer's disease (AD), their alterations are potentially associated with the early cellular pathology and cognitive decline. We analyzed DG LTP and neurogenesis in B6.152H mice, an amyloid precursor protein and presenilin 2 double-transgenic mouse model of amyloidosis and observed that DG LTP was strongly enhanced before and after amyloid plaque formation. Whereas proliferation of DG neuronal progenitor cells was unchanged, survival of newborn neurons was strongly decreased already before plaque formation. As similar alteration of neurogenesis was observed in PS2APP mice without changes in DG LTP (Richards et al. 2003), this study suggests that enhanced synaptic plasticity did not rescue impaired neurogenesis, and supports decreased survival of newborn neurons as an early event associated with AD detectable even before plaque formation.

Fractal analysis of amyloid plaques in Alzheimer's disease patients and mouse models

The varied morphological and biochemical forms in which amyloid deposits in brain of Alzheimer's disease (AD) patients are complex and their mechanisms of formation are not completely understood. Here we investigated the ability of fractal dimension (FD) to differentiate between the textures of commonly observed amyloid plaques in sporadic and familial AD patients and aged-control individuals as well as in transgenic mouse models of amyloidosis. Studying more than 6000 amyloid plaques immunostained for total Aβ (Aβt), Aβ40 or Aβ42, we show here that Aβ40 FD could efficiently differentiate between (i) AD patients and aged-control individuals (P<0.001); (ii) sporadic and familial AD due to presenilin-1 or APP (A692G) mutations (P<0.001); and (iii) three transgenic mouse models of different genotypes (P<0.001). Furthermore, while diffuse and dense-core plaques present in humans and transgenic mice had comparable FDs, both Aβt and Aβ42 FD could also differentiate diffuse plaques from other plaque types in both species (P<0.001). Our data suggest that plaque FD could be a valuable tool for objective, computer-oriented AD diagnosis as well as for genotype-phenotype correlations of AD.

Hyperhomocysteinemia Increases β-Amyloid by Enhancing Expression of γ-Secretase and Phosphorylation of Amyloid Precursor Protein in Rat Brain

Hyperhomocysteinemia and beta-amyloid (Abeta) overproduction are critical etiological and pathological factors in Alzheimer disease, respectively; however, the intrinsic link between them is still missing. Here, we found that Abeta levels increased and amyloid precursor protein (APP) levels simultaneously decreased in hyperhomocysteinemic rats after a 2-week induction by vena caudalis injection of homocysteine. Concurrently, both the mRNA and protein levels of presenilin-1, a component of gamma-secretase, were elevated, whereas the expression levels of beta-secretase and presenilin-2 were not altered. We also observed that levels of phosphorylated APP at threonine-668, a crucial site facilitating the amyloidogenic cleavage of APP, increased in rats with hyperhomocysteinemia, although the phosphorylation per se did not increase the binding capacity of pT668-APP to the secretases. The enhanced phosphorylation of APP in these rats was not relevant to either c-Jun N-terminal kinase or cyclin-dependent kinase-5. A prominent spatial memory deficit was detected in rats with hyperhomocysteinemia. Simultaneous supplementation of folate and vitamin-B12 attenuated the hyperhomocysteinemia-induced abnormal processing of APP and improved memory. Our data revealed that hyperhomocysteinemia could increase Abeta production through the enhanced expression of gamma-secretase and APP phosphorylation, causing memory deficits that could be rescued by folate and vitamin-B12 treatment in these rats. It is suggested that hyperhomocysteinemia may serve as an upstream factor for increased Abeta production as seen in patients with Alzheimer disease.

Neprilysin Deficiency-Dependent Impairment of Cognitive Functions in a Mouse Model of Amyloidosis

Alzheimer's disease, responsible for the vast majority of dementia cases in the elderly population, is caused by accumulation of toxic levels of amyloid beta peptide (A beta) in the brain. Neprilysin is a major enzyme responsible for the degradation of A beta in vivo. We have previously shown that elevation of neprilysin levels in the brain delays the deposition of A beta-plaques in a mouse model of amyloidosis and that lack of neprilysin leads to increased A beta generation and to signs of incipient neurodegeneration in mouse brains. This study was designed to test whether low brain levels of neprilysin affect the amyloid pathology or perturb the learning and memory performance of mice. Double-mutated mice carrying a targeted depletion of one allele of Mme, the gene encoding neprilysin, and over-expressing human amyloid precursor protein (APP), exhibited a reinforced amyloid pathology in comparison with their APP transgenic littermates. Moreover, in contrast to their parental lines, these mice were impaired in the Morris water maze learning and memory paradigm and showed facilitated extinction in the conditioned taste aversion test. These data suggest that even a partial neprilysin deficiency, as is found during aging, exacerbates amyloid pathology and may impair cognitive functions.

Loss of LR11/SORLA Enhances Early Pathology in a Mouse Model of Amyloidosis: Evidence for a Proximal Role in Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent form of dementia, resulting in progressive neuronal death and debilitating damage to brain loci that mediate memory and higher cognitive function. While pathogenic genetic mutations have been implicated in approximately 2% of AD cases, the proximal events that underlie the common, sporadic form of the disease are incompletely understood. Converging lines of evidence from human neuropathology, basic biology, and genetics have implicated loss of the multifunctional receptor LR11 (also known as SORLA and SORL1) in AD pathogenesis. Cell-based studies suggest that LR11 reduces the formation of beta-amyloid (Abeta), the molecule believed to be a primary toxic species in AD. Recently, mutant mice deficient in LR11 were shown to upregulate murine Abeta in mouse brain. In the current study, LR11-deficient mice were crossed with transgenic mice expressing autosomal-dominant human AD genes, presenilin-1 (PS1DeltaE9) and amyloid precursor protein (APPswe). Here, we show that LR11 deficiency in this AD mouse model significantly increases Abeta levels and exacerbates early amyloid pathology in brain, causing a forward shift in disease onset that is LR11 gene dose-dependent. Loss of LR11 increases the processing of the APP holo-molecule into alpha-, beta-, and gamma-secretase derived metabolites. We propose that LR11 regulates APP processing and Abeta accumulation in vivo and is of proximal importance to the cascade of pathological amyloidosis. The results of the current study support the hypothesis that control of LR11 expression may exert critical effects on Alzheimer's disease susceptibility in humans.

P1-067: Relative impact of vascular versus parenchymal amyloid on synaptic plasticity-related gene induction

Alzheimer's disease is characterized by numerous pathological abnormalities including amyloid deposition in the parenchyma and the vasculature. Transgenic mice replicating distinct aspects of Alzheimer pathology are useful models to evaluate contributions of these factors to cognitive decline. Investigate the relative impact of parenchymal versus vascular amyloid on synaptic plasticity–related gene induction. Three different mouse models of amyloidosis were used: a model which exhibits almost exclusively vascular amyloid (APPDutch), one which shows predominantly parenchymal amyloid (APPPS1), and one with a combination of parenchymal and vascular amyloid (APP23). The behavioral induction of Arc (activity–regulated cytoskeleton–associated protein), an effector immediate early gene known to be necessary for memory consolidation and learning was detected via fluorescent in–situ hybridization (ISH). Thus, the functional status of individual neurons and neural systems could be measured following the exploration of a novel environment. The number of Arc positive cells within the neocortex and dentate gyrus was quantified using stereological analysis. Radioactive ISH was also performed to compare relative levels of Arc mRNA. The pattern of activated, Arc mRNA positive cells was clearly disrupted in mice with parenchymal amyloid, while such obvious changes were not observed in vascular–depositing mice. Stereological analysis revealed a decrease in the percentage of Arc positive cells within the neocortex of mice with vascular (∼17%) or parenchymal (∼26%) amyloid compared to aged–matched controls. Interestingly, these reductions were even more pronounced in the dentate gyrus (∼51%; ∼58%), a region critical for relational memory. Taken together, our data indicate that both parenchymal and vascular amyloid impair the induction of an important learning–related gene, suggesting that both pathologies contribute to memory impairment in Alzheimer's disease.

Hyperhomocysteinemic Alzheimer's mouse model of amyloidosis shows increased brain amyloid β peptide levels

Recent epidemiological and clinical data suggest that elevated serum homocysteine levels may increase the risk of developing Alzheimer's disease (AD), but the underlying mechanisms are unknown. We tested the hypothesis that high serum homocysteine concentration may increase amyloid beta-peptide (Abeta) levels in the brain and could therefore accelerate AD neuropathology. For this purpose, we mated a hyperhomocysteinemic CBS(tm1Unc) mouse carrying a heterozygous dominant mutation in cystathionine-beta-synthase (CBS*) with the APP*/PS1* mouse model of brain amyloidosis. The APP*/PS1*/CBS* mice showed significant elevations of serum homocysteine levels compared to the double transgenic APP*/PS1* model of amyloidosis. Results showed that female (but not male) APP*/PS1*/CBS* mice exhibited significant elevations of Abeta40 and Abeta42 levels in the brain. Correlations between homocysteine levels in serum and brain Abeta levels were statistically significant. No increases in beta secretase activity or evidence of neuronal cell loss in the hyperhomocysteinemic mice were found. The causes of neuronal dysfunction and degeneration in AD are not fully understood, but increased production of Abeta seems to be of major importance. By unveiling a link between homocysteine and Abeta levels, these findings advance our understanding on the mechanisms involved in hyperhomocysteinemia as a risk factor for AD.

525. Therapy for Alzheimer's Disease by Neprilysin Gene Transfer

Accumulation of the amyloid beta peptide (A|[beta]|) is believed to be a key component in the pathogenesis of Alzheimer's disease (AD). Deregulation of the anabolism and / or catabolism of A|[beta]| likely contribute to progression of this disease. Endopeptidases expressed in the brain are now thought to control A|[beta]| concentrations. Neprilysin is a metalloendopeptidase that has been shown to be an important mediator of A|[beta]| degradation. This discovery has opened the way for potentially new therapeutic strategies designed to augment protease activity. To investigate this approach we constructed a lentiviral gene transfer vector that efficiently produces biologically active neprilysin (Lenti-Nep), and intracranially injected this vector into mouse models of amyloidosis (APPtg). Previously we had shown that one-month after Lenti-Nep administration amyloid deposits were significantly reduced in mice with advanced amyloidosis (43% reduction) in addition to improvements in dendritic density (16% increase in MAP2 immunoreactivity). We now show that long-term experiments (five to six months) in younger APPtg mice resulted in further reduced amyloid pathology (54% to 65% reductions in deposited amyloid) and improvements in MAP2, synaptophysin, and NeuN immunoreactivity (|[sim]|20%). Memory test performance in the Morris Water Maze was also improved by Lenti-Nep administration. These data further support the potential use of neprilysin gene transfer for the treatment on AD.