Age-related amyloid beta deposition in transgenic mice overexpressing both Alzheimer mutant presenilin 1 and amyloid beta precursor protein Swedish mutant is not associated with global neuronal loss

Binding of the positron emission tomography tracer Pittsburgh compound-B reflects the amount of amyloid-beta in Alzheimer's disease brain but not in transgenic mouse brain

During the development of in vivo amyloid imaging agents, an effort was made to use micro-positron emission tomography (PET) imaging in the presenilin-1 (PS1)/amyloid precursor protein (APP) transgenic mouse model of CNS amyloid deposition to screen new compounds and further study Pittsburgh Compound-B (PIB), a PET tracer that has been shown to be retained well in amyloid-containing areas of Alzheimer's disease (AD) brain. Unexpectedly, we saw no significant retention of PIB in this model even at 12 months of age when amyloid deposition in the PS1/APP mouse typically exceeds that seen in AD. This study describes a series of ex vivo and postmortem in vitro studies designed to explain this low retention. Ex vivo brain pharmacokinetic studies confirmed the low in vivo PIB retention observed in micro-PET experiments. In vitro binding studies showed that PS1/APP brain tissue contained less than one high-affinity (K(d) = 1-2 nm) PIB binding site per 1000 molecules of amyloid-beta (Abeta), whereas AD brain contained >500 PIB binding sites per 1000 molecules of Abeta. Synthetic Abeta closely resembled PS1/APP brain in having less than one high-affinity PIB binding site per 1000 molecules of Abeta, although the characteristics of the few high-affinity PIB binding sites found on synthetic Abeta were very similar to those found in AD brain. We hypothesize that differences in the time course of deposition or tissue factors present during deposition lead to differences in secondary structure between Abeta deposited in AD brain and either synthetic Abeta or Abeta deposited in PS1/APP brain.

Hyperhomocysteinemic Alzheimer's mouse model of amyloidosis shows increased brain amyloid beta 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.

Quantitative analysis of amyloid plaques in a mouse model of Alzheimer's disease by phase-contrast X-ray computed tomography

Densely aggregated beta-amyloid peptides are believed to play a key role in the pathogenesis of Alzheimer's disease. Amyloid plaques are a potential target for molecular imaging to determine the clinical status of Alzheimer's disease. Phase-contrast X-ray imaging combined with computed tomography is a promising technique that can be used to visualize the physical density of structures in biological tissues non-invasively, and without the use of imaging agents. Using brain tissue isolated from a mouse model of Alzheimer's disease, we show that beta-amyloid 40-positive/beta-amyloid 42-positive amyloid plaques, but not beta-amyloid 40-negative/beta-amyloid 42-positive amyloid plaques, exist as high-density aggregates that can be specifically detected by phase-contrast X-ray computed tomography. The phase-contrast X-ray computed tomography detected beta-amyloid 40-positive/beta-amyloid 42-positive amyloid plaques in three-dimensions with an extremely high sensitivity comparable to that of histological analysis, and also enabled the load of amyloid plaques to be quantified. Furthermore, the use of phase-contrast X-ray computed tomography reveals that the physical density of beta-amyloid 40-positive/beta-amyloid 42-positive amyloid plaques increases with age, and that the large volume, high-density, amyloid plaques that are specifically observed in aged Alzheimer's disease mice are closely associated with neuritic dystrophy. These results demonstrate that phase-contrast X-ray computed tomography is a highly sensitive imaging technique for analyzing dense-cored amyloid plaques in postmortem samples, and is beneficial in elucidating amyloid pathophysiology in Alzheimer's disease.

Transgenic models of Alzheimer's disease: learning from animals

As the scope of the problem of Alzheimer's disease (AD) grows due to an aging population, research into the devastating condition has taken on added urgency. Rare inherited forms of AD provide insight into the molecular pathways leading to degeneration and have made possible the development of transgenic animal models. Several of these models are based on the overexpression of amyloid precursor protein (APP), presenilins, or tau to cause production and accumulation of amyloid-beta into plaques or hyperphosphorylated tau into neurofibrillary tangles. Producing these characteristic neuropathological lesions in animals causes progressive neurodegeneration and in some cases similar behavioral disruptions to those seen in AD patients. Knockout models of proteins involved in AD have also been generated to explore the native functions of these genes and examine whether pathogenesis is due to loss of function or toxic gain of function in these systems. Although none of the transgenic lines models the human condition exactly, the ability to study similar pathological processes in living animals have provided numerous insights into disease mechanisms and opportunities to test therapeutic agents. This chapter reviews animal models of AD and their contributions to developing therapeutic approaches for AD.

In vivo magnetic resonance microimaging of individual amyloid plaques in Alzheimer's transgenic mice

The ability to detect individual Alzheimer's amyloid plaques in vivo by magnetic resonance microimaging (MRI) should improve diagnosis and also accelerate discovery of effective therapeutic agents for Alzheimer's disease (AD). Here, we perform in vivo and ex vivo MRI on double transgenic AD mice as well as wild-type mice at varying ages and correlate these with thioflavin-S and iron staining histology. Quantitative counts of individual plaques on MRI increase with age and correlate with histologically determined plaque burden. Plaques 20 microm in diameter can be detected in AD mice as young as 3 months of age with ex vivo MRI. Plaques 35 microm in diameter can be detected by 9 months of age with in vivo MRI. In vivo MRI of individual Alzheimer's amyloid plaques provides a noninvasive estimate of plaque burden in transgenic AD mice that might be useful in assessing the efficacy of amyloid reduction therapies.

Cyclin-dependent kinase 5, Munc18a and Munc18-interacting protein 1/X11α protein up-regulation in Alzheimer’s disease

Besides formation of neurofibrillary tangles and neuron loss, the Alzheimer's disease brain is characterized by neuritic plaques consisting of beta-amyloid peptide deposits and impaired neurotransmission. The proteins Munc18a, Munc18-interacting protein 1 and Munc18-interacting protein 2 mediate exocytosis and decrease beta-amyloid peptide formation. Cyclin-dependent kinase 5 and its activator p35 disrupt Munc18a-syntaxin 1 binding, thereby promoting synaptic vesicle fusion during exocytosis. We investigated protein levels of the signaling pathway: p35, cyclin-dependent kinase 5, Munc18a, syntaxin 1A and 1B, Munc18-interacting protein 1 and Munc18-interacting protein 2 in Alzheimer's disease cortex and found that this pathway was up-regulated in the Alzheimer's disease parietal and occipital cortex. In the cortex of transgenic Tg2576 mice over-expressing human beta-amyloid precursor protein with the Swedish mutation known to lead to familial Alzheimer's disease, which have substantial levels of beta-amyloid peptide but lack neurofibrillary tangles and neuron loss, no alterations of protein levels were detected. These data suggest that the pathway is enhanced in dying or surviving neurons and might serve a protective role by compensating for decreased neurotransmission and decreasing beta-amyloid peptide levels early during the progression of Alzheimer's disease.

Age-related loss of synaptophysin immunoreactive presynaptic boutons within the hippocampus of APP751SL, PS1M146L, and APP751SL/PS1M146L transgenic mice

Neuron and synapse loss are important features of the neuropathology of Alzheimer's disease (AD). Recently, we observed substantial age-related hippocampal neuron loss in APP751SL/PS1M146L transgenic mice but not in PS1M146L mice. Here, we investigated APP751SL mice, PS1M146L mice, and APP751SL/PS1M146L mice for age-related alterations in synaptic integrity within hippocampal stratum moleculare of the dentate gyrus (SM), stratum lucidum of area CA3 (SL), and stratum radiatum of area CA1-2 (SR) by analyzing densities and numbers of synaptophysin-immunoreactive presynaptic boutons (SIPBs). Wild-type mice, APP751SL mice and PS1M146L mice showed similar amounts of age-related SIPB loss within SM, and no SIPB loss within SL. Both APP751SL mice and PS1M146L mice showed age-related SIPB loss within SR. Importantly, APP751SL/PS1M146L) mice displayed the severest age-related SIPB loss within SM, SL, and SR, even in regions free of extracellular Abeta deposits. Together, these mouse models offer a unique framework to study the impact of several molecular and cellular events caused by mutant APP and/or mutant PS1 on age-related alterations in synaptic integrity. The observation of age-related SIPB loss within SR of PS1M146L mice supports a role of mutant PS1 in neurodegeneration apart from its contribution to alterations in Abeta generation.

Dendritic spine abnormalities in amyloid precursor protein transgenic mice demonstrated by gene transfer and intravital multiphoton microscopy

Accumulation of amyloid-beta (Abeta) into senile plaques in Alzheimer's disease (AD) is a hallmark neuropathological feature of the disorder, which likely contributes to alterations in neuronal structure and function. Recent work has revealed changes in neurite architecture associated with plaques and functional changes in cortical signaling in amyloid precursor protein (APP) expressing mouse models of AD. Here we developed a method using gene transfer techniques to introduce green fluorescent protein (GFP) into neurons, allowing the investigation of neuronal processes in the vicinity of plaques. Multiphoton imaging of GFP-labeled neurons in living Tg2576 APP mice revealed disrupted neurite trajectories and reductions in dendritic spine density compared with age-matched control mice. A profound deficit in spine density (approximately 50%) extends approximately 20 mum from plaque edges. Importantly, a robust decrement (approximately 25%) also occurs on dendrites not associated with plaques, suggesting widespread loss of postsynaptic apparatus. Plaques and dendrites remained stable over the course of weeks of imaging. Postmortem analysis of axonal immunostaining and colocalization of synaptophysin and postsynaptic density 95 protein staining around plaques indicate a parallel loss of presynaptic and postsynaptic partners. These results show considerable changes in dendrites and dendritic spines in APP transgenic mice, demonstrating a dramatic synaptotoxic effect of dense-cored plaques. Decreased spine density will likely contribute to altered neural system function and behavioral impairments observed in Tg2576 mice.

Early Changes in Behavior Deficits, Amyloid β-42 Deposits and MAPK Activation in Doubly Transgenic Mice Co-expressing NSE-Controlled Human Mutant PS2 and APPsw

1. Doubly transgenic mice were some differences in the period proceeding of the development of Abeta-42 deposits and behavioral deficits. It was not characterized human mutant PS2 (hPS2) with APPsw in the brains of double transgenic mice. The aim of this study was to examine whether doubly transgenic mice co-expressing NSE-controlled APPsw and hPS2m develop AD-like phenotypes much earlier than singly APPsw or hPS2m alone. 2. We produced doubly transgenic mice from a cross between our previously created NSE-controlled hPS2m and an APPsw transgenic line. This doubly transgenic line was quantitatively produced by cross with age-matched control mice, and the produced mice were separated into 5, 6, 7 and 8-month old age groups. At the age of 8 months, the four groups of mice were tested for behavioral function, levels of Abeta-42 deposition, and potential signaling events. 3. It was shown that all the AD-like phenotypes, including behavior deficits, Abeta-42 levels, MAPK activation and ER expressions in doubly transgenic mice develop much earlier in the early time of AD development than their singly transgenic and non-transgenic littermates. 4. The results suggest that elevated Abeta-42 levels, and MAPK activation in doubly transgenic mice are model for early diagnosis and treatment of AD with therapeutic drug.

Behavioral phenotypes of amyloid-based genetically modified mouse models of Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative affliction of the elderly, presenting with progressive memory loss and dementia and terminating with death. There have been significant advances in understanding the biology and subsequent diagnosis of AD; however, the furious pace of research has not yet translated into a disease-modifying treatment. While scientific inquiry in AD is largely centered on identifying biological players and pathological mechanisms, the day-to-day realities of AD patients and their caregivers revolve around their steady and heartbreaking cognitive decline. In the past decade, AD research has been fundamentally transformed by the development of genetically modified animal models of amyloid-driven neurodegeneration. These important in vivo models not only replicate some of the hallmark pathology of the disease, such as plaque-like amyloid accumulations and astrocytic inflammation, but also some of the cognitive impairments relevant to AD. In this article, we will provide a detailed review of the behavioral and cognitive deficits present in several transgenic mouse models of AD and discuss their functional changes in response to experimental treatments.

Amyloid-beta in Alzheimer's disease: the horse or the cart? Pathogenic or protective?

While the pathogenesis of Alzheimer's disease (AD) is unclear, amyloid-beta plaques remain major lesions in the brain of individuals with AD. Likewise, amyloid-beta is one of the best-studied proteins relating to the pathogenesis of AD. Indeed, the pathological diagnosis of AD tends to be congruous with the quantity of amyloid-beta. However, it is important to recognize that pathological diagnosis merely represents the association of a pattern of pathological changes with a clinical phenotype. Therefore, it should be acknowledged that, although amyloid-beta detection and semiquantification have some diagnostic utility, the simple presence of amyloid plaques, as with proteinaceous accumulations in essentially all neurodegenerative diseases, does not presume aetiology. Thus, in this review, we discuss the role of amyloid-beta in the pathogenesis of AD and provide an alternative view to the widely accepted dogma.

Progression of Cerebral Amyloid Angiopathy in Transgenic Mouse Models of Alzheimer Disease

Cerebral amyloid angiopathy (CAA), the deposition of beta-amyloid (Abeta3) in cerebral vessels, has been implicated as a common cause of hemorrhagic stroke and other forms of vascular disease. CAA is also a frequent concomitant of Alzheimer disease (AD). While the longterm consequences of CAA are well recognized from clinical and pathologic studies, numerous questions remain unanswered regarding the progression of the disease. Examination of CAA in traditional histologic sections does not easily allow for characterization of CAA, particularly in leptomeningeal vessels. In order to approach this topic, we used low magnification imaging of intact, postmortem brains from transgenic mouse models of AD-like pathology to define the spatial and temporal characteristics of CAA in leptomeningeal vessels. Imaging of brains from 10- to 26-month-old animals demonstrated a stereotypical pattern to the development of CAA, with vessels over the dorsal surface of the brain showing an anterior-to-posterior and large-to-small vessel gradient of involvement. High magnification imaging revealed that CAA deposition began with a banding pattern determined by the organization of the vascular smooth muscle cells. Further analysis of the pattern of amyloid deposits showed shrinkage and disappearance of the gaps between clusters of amyloid bands, gradually reaching a confluent pattern. These data led to a classification system to describe the severity of CAA deposition and demonstrate the potential of using intact brains to generate maps defining the progression and kinetics of CAA. This approach should lead to more informed analysis of the consequences of evolving therapeutic options for AD on this related form of vascular pathology.

Neutralization of transthyretin reverses the neuroprotective effects of secreted amyloid precursor protein (APP) in APPSW mice resulting in tau phosphorylation and loss of hippocampal neurons: support for the amyloid hypothesis

Alzheimer's disease (AD) may be caused by the abnormal processing of the amyloid precursor protein (APP) and the accumulation of beta-amyloid (Abeta). The amyloid precursor protein can be proteolytically cleaved into multiple fragments, many of which have distinct biological actions. Although a high level of Abeta can be toxic, the alpha-secretase cleaved APP (sAPPalpha) is neuroprotective. However, the mechanism of sAPPalpha protection is unknown. Here, we show that sAPPalpha increases the expression levels of several neuroprotective genes and protects organotypic hippocampal cultures from Abeta-induced tau phosphorylation and neuronal death. Antibody interference and small interfering RNA knock-down demonstrate that the sAPPalpha-driven expression of transthyretin and insulin-like growth factor 2 is necessary for protection against Abeta-induced neuronal death. Mice overexpressing mutant APP possess high levels of sAPPalpha and transthyretin and do not develop the tau phosphorylation or neuronal loss characteristic of human AD. Chronic infusion of an antibody against transthyretin into the hippocampus of mice overexpressing APP with the Swedish mutation (APP(Sw)) leads to increased Abeta, tau phosphorylation, and neuronal loss and apoptosis within the CA1 neuronal field. Therefore, the elevated expression of transthyretin is mediated by sAPPalpha and protects APP(Sw) mice from developing many of the neuropathologies observed in AD.

Absence of C1q leads to less neuropathology in transgenic mouse models of Alzheimer's disease

C1q, the recognition component of the classical complement activation pathway, is a multifunctional protein known to be expressed in brain of Alzheimer's disease (AD) patients. To experimentally address the role of C1q in AD, a mouse model lacking C1q (APPQ-/-) was generated by crossing Tg2576 animals (APP) with C1q-deficient mice. The pathology of APPQ-/- was compared with that of APP mice and B6SJL controls at 3-16 months of age by immunohistochemistry and Western blot analysis. At younger ages (3-6 months), when no plaque pathology was present, no significant differences were seen in any of the neuronal or glial markers tested. At older ages (9-16 months), the APP and APPQ-/- mice developed comparable total amyloid and fibrillar beta-amyloid in frontal cortex and hippocampus; however, the level of activated glia surrounding the plaques was significantly lower in the APPQ-/- mice at 12 and 16 months. In addition, although Tg2576 mice showed a progressive decrease in synaptophysin and MAP2 in the CA3 area of hippocampus compared with control B6SJL at 9, 12, and 16 months, the APPQ-/- mice had significantly less of a decrease in these markers at 12 and 16 months. In a second murine model for AD containing transgenes for both APP and mutant presenilin 1 (APP/PS1), a similar reduction of pathology was seen in the APPPS1Q-/- mice. These data suggest that at ages when the fibrillar plaque pathology is present, C1q exerts a detrimental effect on neuronal integrity, most likely through the activation of the classical complement cascade and the enhancement of inflammation.

Inflammatory cytokine levels correlate with amyloid load in transgenic mouse models of Alzheimer's disease

BACKGROUND: Inflammation is believed to play an important role in the pathology of Alzheimer's disease (AD) and cytokine production is a key pathologic event in the progression of inflammatory cascades. The current study characterizes the cytokine expression profile in the brain of two transgenic mouse models of AD (TgAPPsw and PS1/APPsw) and explores the correlations between cytokine production and the level of soluble and insoluble forms of Abeta. METHODS: Organotypic brain slice cultures from 15-month-old mice (TgAPPsw, PS1/APPsw and control littermates) were established and multiple cytokine levels were analyzed using the Bio-plex multiple cytokine assay system. Soluble and insoluble forms of Abeta were quantified and Abeta-cytokine relationships were analyzed. RESULTS: Compared to control littermates, transgenic mice showed a significant increase in the following pro-inflammatory cytokines: TNF-alpha, IL-6, IL-12p40, IL-1beta, IL-1alpha and GM-CSF. TNF-alpha, IL-6, IL-1alpha and GM-CSF showed a sequential increase from control to TgAPPsw to PS1/APPsw suggesting that the amplitude of this cytokine response is dependent on brain Abeta levels, since PS1/APPsw mouse brains accumulate more Abeta than TgAPPsw mouse brains. Quantification of Abeta levels in the same slices showed a wide range of Abeta soluble:insoluble ratio values across TgAPPsw and PS1/APPsw brain slices. Abeta-cytokine correlations revealed significant relationships between Abeta1-40, 1-42 (both soluble and insoluble) and all the above cytokines that changed in the brain slices. CONCLUSION: Our data confirm that the brains of transgenic APPsw and PS1/APPsw mice are under an active inflammatory stress, and that the levels of particular cytokines may be directly related to the amount of soluble and insoluble Abeta present in the brain suggesting that pathological accumulation of Abeta is a key driver of the neuroinflammatory response.

Exercise Your Amyloid

The interplay of genetics and the environment in the etiology of Alzheimer's disease (AD) is not well understood. Now, Lazarov and coworkers show that a simple paradigm of environmental enrichment alleviates amyloid burden and alters disease-associated gene expression changes in a double transgenic mouse model of AD.

Dysregulation of Na+/K+ ATPase by amyloid in APP+PS1 transgenic mice

Background

The pathology of Alzheimer's disease (AD) is comprised of extracellular amyloid plaques, intracellular tau tangles, dystrophic neurites and neurodegeneration. The mechanisms by which these various pathological features arise are under intense investigation. Here, expanding upon pilot gene expression studies, we have further analyzed the relationship between Na+/K+ ATPase and amyloid using APP+PS1 transgenic mice, a model that develops amyloid plaques and memory deficits in the absence of tangle formation and neuronal or synaptic loss.

Results

We report that in addition to decreased mRNA expression, there was decreased overall Na+/K+ ATPase enzyme activity in the amyloid-containing hippocampi of the APP+PS1 mice (although not in the amyloid-free cerebellum). In addition, dual immunolabeling revealed an absence of Na+/K+ ATPase staining in a zone surrounding congophilic plaques that was occupied by dystrophic neurites. We also demonstrate that cerebral Na+/K+ ATPase activity can be directly inhibited by high concentrations of soluble Aβ.

Conclusions

The data suggest that the reductions in Na+/K+ ATPase activity in Alzheimer tissue may not be purely secondary to neuronal loss, but may results from direct effects of amyloid on this enzyme. This disruption of ion homeostasis and osmotic balance may interfere with normal electrotonic properties of dendrites, blocking intraneuronal signal processing, and contribute to neuritic dystrophia. These results suggest that therapies aimed at enhancing Na+/K+ ATPase activity in AD may improve symptoms and/or delay disease progression.

High mobility group box protein-1 inhibits microglial A? clearance and enhances A? neurotoxicity

One pathogenic characteristic of Alzheimer's disease (AD) is the formation of extracellular senile plaques with accumulated microglia. According to the amyloid hypothesis, the increase or accumulation of amyloid-beta (Abeta) peptides in the brain parenchyma is the primary event that influences AD pathology. Although the role of microglia in AD pathology has not been clarified, their involvement in Abeta clearance has been noted. High mobility group box protein-1 (HMGB1) is an abundant nonhistone chromosomal protein. We reported recently that HMGB1 was associated with senile plaques and the total protein level significantly increased in AD brain. In this study, diffuse HMGB1 immunoreactivity was observed around dying neurons in the kainic acid- and Abeta1-42 (Abeta42)-injected rat hippocampi. HMGB1 also colocalized with Abeta in the Abeta42-injected rats but not in transgenic mice, which show massive Abeta production without neuronal loss in their brains. Furthermore, coinjection of HMGB1 delayed the clearance of Abeta42 and accelerated neurodegeneration in Abeta42-injected rats. These results suggest that HMGB1 released from dying neurons may inhibit microglial Abeta42 clearance and enhance the neurotoxicity of Abeta42. HMGB1 may thus be another target in the investigation of a therapeutic strategy for AD.

Visualization of beta-amyloid plaques in a transgenic mouse model of Alzheimer's disease using MR microscopy without contrast reagents

The visualization of beta-amyloid plaque deposition in brain, a key feature of Alzheimer's disease (AD), is important for the evaluation of disease progression and the efficacy of therapeutic interventions. In this study, beta-amyloid plaques in the PS/APP transgenic mouse brain, a model of human AD pathology, were detected using MR microscopy without contrast reagents. beta-Amyloid plaques were clearly visible in the cortex, thalamus, and hippocampus of fixed brains of PS/APP mice. The distribution of plaques identified by MRI was in excellent agreement with those found in the immunohistological analysis of the same brain sections. It was also demonstrated that image contrast for beta-amyloid plaques was present in freshly excised nonfixed brains. Furthermore, the detection of beta-amyloid plaques was achieved with a scan time as short as 2 hr, approaching the scan time considered reasonable for in vivo imaging.

Exclusive association and simultaneous appearance of congophilic plaques and AT8-positive dystrophic neurites in Tg2576 mice suggest a mechanism of senile plaque formation and progression of neuritic dystrophy in Alzheimer's disease

Progression of neuritic dystrophy is a histological hallmark of Alzheimer's disease (AD) in addition to amyloid deposition and neurofibrillary tangle formation. Dystrophic neurites (DNs) are abnormal neurites, and are closely associated with amyloid deposits. To clarify the process of DN formation, we immunohistochemically investigated phosphorylated tau (AT8 and Ser396)-positive DNs and plaques in Tg2576 mice overexpressing human beta-amyloid precursor protein (APP) with the Swedish type mutation (K670N/M671L). AT8-positive DNs were exclusively associated with the Congo red-positive plaques examined, and all Abeta(1-40)-positive plaques appeared to be associated with AT8-positive DNs, whereas there were no AT8-positive DNs with Abeta(1-42)-positive/Abeta(1-40)-negative plaques. Since we have previously shown that Abeta(1-42)-positive plaque precede Abeta(1-40) deposition, the appearance of congophilic structures is also late. Quantitative analyses were performed on AT8-positive DNs that were associated with congophilic plaques in the cerebral cortex and hippocampus (more than 1,000 plaques). The number of congophilic plaques increased dramatically with age. The area of DNs in the cerebral cortex and hippocampus increased 120- and 60-fold from 11-13 to 20.5 months of age, respectively. Interestingly, the mean ratio of DN area to congophilic plaque area in every plaque was unchanged, approximately 10%, through the ages examined. The mean plaque size was stable with age in both the cortex and hippocampus. These data suggest that the formation of AT8-positive DNs is simultaneous with Congo red-positive plaque development, and that the event may be closely related in the pathological progression of AD.

Mostly separate distributions of CLAC- versus Abeta40- or thioflavin S-reactivities in senile plaques reveal two distinct subpopulations of beta-amyloid deposits

Collagenous Alzheimer amyloid plaque component (CLAC) is a unique non-Abeta amyloid component of senile plaques (SP) derived from a transmembrane collagen termed CLAC-precursor. Here we characterize the chronological and spatial relationship of CLAC with other features of SP amyloid in the brains of patients with Alzheimer's disease (AD), Down syndrome (DS), and of PSAPP transgenic mice. In AD and DS cerebral cortex, CLAC invariably colocalized with Abeta42 but often lacked Abeta40- or thioflavin S (thioS)-reactivities. Immunoelectron microscopy of CLAC-positive SP showed labeling of fibrils that are more loosely dispersed compared to typical amyloid fibrils in CLAC-negative SP. In DS cerebral cortex, diffuse plaques in young patients were negative for CLAC, whereas a subset of SP became CLAC-positive in patients aged 35 to 50 years, before the appearance of Abeta40. In DS cases over 50 years of age, Abeta40-positive SP dramatically increased, whereas CLAC burden remained at a constant level. In PSAPP transgenic mice, CLAC was positive in the diffuse Abeta deposits surrounding huge-cored plaques. Thus, CLAC and Abeta40 or thioS exhibit mostly separate distribution patterns in SP, suggesting that CLAC is a relatively early component of SP in human brains that may have inhibitory effects against the maturation of SP into beta-sheet-rich amyloid deposits.

Amyloid-beta deposition is associated with decreased hippocampal glucose metabolism and spatial memory impairment in APP/PS1 mice

In Alzheimer disease (AD) patients, early memory dysfunction is associated with glucose hypometabolism and neuronal loss in the hippocampus. Double transgenic (Tg) mice co-expressing the M146L presenilin 1 (PS1) and K670N/M671L, the double "Swedish" amyloid precursor protein (APP) mutations, are a model of AD amyloid-beta deposition (Abeta) that exhibits earlier and more profound impairments of working memory and learning than single APP mutant mice. In this study we compared performance on spatial memory tests, regional glucose metabolism, Abeta deposition, and neuronal loss in APP/PS1, PS1, and non-Tg (nTg) mice. At the age of 2 months no significant morphological and metabolic differences were detected between 3 studied genotypes. By 8 months, however, APP/PS1 mice developed selective impairment of spatial memory, which was significantly worse at 22 months and was accompanied by reduced glucose utilization in the hippocampus and a 35.8% dropout of neurons in the CA1 region. PS1 mice exhibited a similar degree of neuronal loss in CA1 but minimal memory deficit and no impairment of glucose utilization compared to nTg mice. Deficits in 22 month APP/PS1 mice were accompanied by a substantially elevated Abeta load, which rose from 2.5% +/- 0.4% at 8 months to 17.4% +/- 4.6%. These findings implicate Abeta or APP in the behavioral and metabolic impairments in APP/PS1 mice and the failure to compensate functionally for PS1-related hippocampal cell loss.

Transgenic animal models of Alzheimer's disease and related disorders: histopathology, behavior and therapy

Alzheimer's disease (AD) is a devastating neurodegenerative disease that affects more than 15 million people worldwide. Within the next generation, these numbers will more than double. To assist in the elucidation of pathogenic mechanisms of AD and related disorders, such as frontotemporal dementia (FTDP-17), genetically modified mice, flies, fish and worms were developed, which reproduce aspects of the human histopathology, such as beta-amyloid-containing plaques and tau-containing neurofibrillary tangles (NFT). In mice, the tau pathology caused selective behavioral impairment, depending on the distribution of the tau aggregates in the brain. Beta-amyloid induced an increase in the numbers of NFT, whereas the opposite was not observed in mice. In beta-amyloid-producing transgenic mice, memory impairment was associated with increased levels of beta-amyloid. Active and passive beta-amyloid-directed immunization caused the removal of beta-amyloid plaques and restored memory functions. These findings have since been translated to human therapy. This review aims to discuss the suitability and limitations of the various animal models and their contribution to an understanding of the pathophysiology of AD and related disorders.

Hippocampal neuron loss exceeds amyloid plaque load in a transgenic mouse model of Alzheimer's disease

According to the "amyloid hypothesis of Alzheimer's disease," beta-amyloid is the primary driving force in Alzheimer's disease pathogenesis. Despite the development of many transgenic mouse lines developing abundant beta-amyloid-containing plaques in the brain, the actual link between amyloid plaques and neuron loss has not been clearly established, as reports on neuron loss in these models have remained controversial. We investigated transgenic mice expressing human mutant amyloid precursor protein APP751 (KM670/671NL and V717I) and human mutant presenilin-1 (PS-1 M146L). Stereologic and image analyses revealed substantial age-related neuron loss in the hippocampal pyramidal cell layer of APP/PS-1 double-transgenic mice. The loss of neurons was observed at sites of Abeta aggregation and surrounding astrocytes but, most importantly, was also clearly observed in areas of the parenchyma distant from plaques. These findings point to the potential involvement of more than one mechanism in hippocampal neuron loss in this APP/PS-1 double-transgenic mouse model of Alzheimer's disease.

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.

MRI assessment of neuropathology in a transgenic mouse model of Alzheimer's disease

The cerebral deposition of amyloid beta-peptide, a central event in Alzheimer's disease (AD) pathogenesis, begins several years before the onset of clinical symptoms. Noninvasive detection of AD pathology at this initial stage would facilitate intervention and enhance treatment success. In this study, high-field MRI was used to detect changes in regional brain MR relaxation times in three types of mice: 1). transgenic mice (PS/APP) carrying both mutant genes for amyloid precursor protein (APP) and presenilin (PS), which have high levels and clear accumulation of beta-amyloid in several brain regions, starting from 10 weeks of age; 2). transgenic mice (PS) carrying only a mutant gene for presenilin (PS), which show subtly elevated levels of Abeta-peptide without beta-amyloid deposition; and 3). nontransgenic (NTg) littermates as controls. The transverse relaxation time T(2), an intrinsic MR parameter thought to reflect impaired cell physiology, was significantly reduced in the hippocampus, cingulate, and retrosplenial cortex, but not the corpus callosum, of PS-APP mice compared to NTg. No differences in T(1) values or proton density were detected between any groups of mice. These results indicate that T(2) may be a sensitive marker of abnormalities in this transgenic mouse model of AD.

Progressive age-related development of Alzheimer-like pathology in APP/PS1 mice

Increasing evidence points to synaptic plasticity impairment as one of the first events in Alzheimer's disease (AD). However, studies on synaptic dysfunction in different transgenic AD models that overexpress familial AD mutant forms of amyloid precursor protein (APP) and/or presenilin (PS) have provided conflicting results. Both long-term potentiation (LTP) and basal synaptic transmission (BST) have been found to be both unchanged and altered in different models and under differing experimental conditions. Because of their more robust amyloid-beta (Abeta) deposition, double transgenic mice currently are used by several laboratories as an AD model. Here, we report that mice overexpressing APP (K670N:M671L) together with PS1 (M146L) have abnormal LTP as early as 3 months of age. Interestingly, reduced LTP paralleled plaque appearance and increased Abeta levels and abnormal short-term memory (working memory). BST and long-term memory (reference memory) are impaired only later (approximately 6 months) as amyloid burden increases. Abeta pathology across different ages did not correlate with synaptic and cognitive deficits, suggesting that Abeta levels are not a marker of memory decline. In contrast, progression of LTP impairment correlated with the deterioration of working memory, suggesting that percentage of potentiation might be an indicator of the cognitive decline and disease progression in the APP/PS1 mice.

Genetic programming by the proteolytic fragments of the amyloid precursor protein: somewhere between confusion and clarity

Mice engineered to overexpress disease-causing mutant amyloid precursor proteins (APP) display plaque deposition, but lack the hyperphosphorylated tau and massive neuronal loss characteristic of Alzheimer's disease (AD). Global gene expression profiles of brain regions from AD patients show upregulation of proapoptotic and inflammatory genes and down-regulation of neurotrophic, MAPK, phosphatase, and synaptic genes, while a profile of mice overexpressing a mutant APP shows the opposite trends in apoptotic and neurotrophic genes. The proteolytic fragments of the amyloid precursor protein have distinct biological actions. Both the gamma-secretase cleaved COOH-terminal fragment (CTFgamma) and the alpha-secretase cleaved NH2-terminal of APP (sAPPalpha) can regulate gene expression. While Abeta and CTFgamma can lead to toxicity and cell death, sAPPalpha promotes neurite outgrowth, enhances memory, and protects against a variety of insults, including Abeta toxicity. In AD, Abeta levels increase while sAPPalpha levels decrease. These subtleties in the levels of APP cleavage products are not reproduced in mice overexpressing mutant APP. In fact, the gene expression changes driven by sAPPalpha, such as increases in transthyretin and insulin-like growth factor 2, may protect these mice from high levels of Abeta.

FGF-2 regulates neurogenesis and degeneration in the dentate gyrus after traumatic brain injury in mice

We studied the role of FGF-2 on regulation of neurogenesis and cell loss in the granule cell layer (GCL) of the hippocampal dentate gyrus after experimental traumatic brain injury (TBI). In both FGF-2(-/-) and FGF-2(+/+) mice subjected to controlled cortical impact, the number of dividing cells labeled with BrdU, injected on posttrauma days 6 through 8, increased at 9 days after TBI, and the number of BrdU-positive cells colabeled with neuron-specific nuclear antigen significantly increased at 35 days. However, in injured FGF-2-/- mice, BrdU-positive cells and BrdU-positive neurons (days 9, 35) were fewer compared with FGF-2(+/+) mice. There was also a decrease in the volume of the GCL and the number of GCL neurons after TBI in both FGF-2(-/-) and FGF-2(+/+) mice, but the decrease in both was greater in FGF-2-/- mice at 35 days. Overexpression of FGF-2 by intracerebral injection of herpes simplex virus-1 amplicon vectors encoding this factor increased numbers of dividing cells (day 9) and BrdU-positive neurons (day 35) significantly in C57BL/6 mice. Furthermore, the decrease in GCL volume was also attenuated. These results suggest that FGF-2 upregulates neurogenesis and protects neurons against degeneration in the adult hippocampus after TBI, and that FGF-2 supplementation via gene transfer can reduce GCL degeneration after TBI.

Dendritic spine loss in the hippocampus of young PDAPP and Tg2576 mice and its prevention by the ApoE2 genotype

Postmortem AD brains exhibit dendritic spine loss in the hippocampus. To determine whether this pathology may be associated with amyloid burden, the present study used the Golgi stain technique to assess age- and genotype-dependent changes in dendritic spine density in CA1 hippocampus of two transgenic mouse lines that produce high levels of Abeta. Tg2576 and PDAPP mice, as well as a group of Tg2576 mice crossed with human apoE2-expressing transgenic mice, were compared to respective transgene-negative controls. Since the time course of amyloid plaque deposition in the PDAPP and Tg2576 mice is well characterized, we examined changes in spine density at ages that corresponded to different levels of amyloid plaque load. The data show age- and genotype-dependent reductions in spine density in both Tg2576 and PDAPP mice, albeit at somewhat different time courses. The spine loss occurred prior to plaque deposition and was ameliorated by the overexpression of human apoE2. These results suggest that a soluble Abeta species may affect hippocampal synapses and thereby contribute to functional deficits evident in these animals.

Amyloid-beta immunization in Alzheimer's disease transgenic mouse models and wildtype mice

Alzheimer's disease is the most prevalent form of dementia worldwide. Therapies are desperately needed to prevent and cure the disease. Mouse models of amyloid-beta deposition [APP and PSAPP transgenic (tg) mice] have been useful in determining the role of amyloid-beta (A beta) in both the pathogenesis and cognitive changes in AD. In addition, they have allowed scientists to investigate potential AD therapies in living animals. Active and passive A beta immunizations have been employed successfully in APP and PSAPP tg mice to lower cerebral A beta levels and improve cognition. Optimization of immunization protocols and characterization of immune responses in wildtype mice have been reported. Based on the promising results of A beta immunization studies in mice, a clinical trial was initiated for A beta vaccination in humans with AD. Although no adverse effects were reported in the Phase I safety trials, about 5% of AD patients in the phase II clinical trial developed meningoencephalitis, ending the trial prematurely in March 2002. Studies in AD mouse models and wildtype mice may help elucidate the mechanism for these unwanted side effects and will be useful for testing newer, safer vaccines for future use in human clinical trials.

Learning and memory deficits in APP transgenic mouse models of amyloid deposition

Several different transgenic APP mice develop learning and memory deficits. In some cases the mice have deficits very early in life, while in other instances the mice exhibit deficits only after they have aged and amyloid deposits have accumulated. In many cases, there is a correlation in individual mice of the same age and genotype between the extent of learning and memory deficits and the amounts of deposited amyloid found in the central nervous system. While superficially this might imply that the deposited material is somehow toxic to cognition, it is likely that deposited amyloid is also an index of the overall rate of amyloid production in each mouse. Rate of production would be expected to modify not only the amounts of deposited amyloid, but also other amyloid pools, including soluble, oligomeric, conjugated (e.g. ADDLs) and intracellular. Thus, the deposited material may be an integrated reflection of total A beta production, in addition to indicating the amounts in fibrillar forms. As such, it is conceivable that other A beta pools may be more directly linked to memory deficits. Thus far, the one manipulation found to mitigate the learning and memory deficits in APP transgenic mice is immunotherapy for A beta, either using active or passive immunization against the peptide. These data together with other findings are leading to a conclusion that the fibrillar A beta deposits are not directly linked to the memory deficits in mice, and that some other A beta pool, more readily diminished by immunotherapy, is more directly linked to the mechanisms leading to poor performance in learning and memory tasks.

Heat shock protein-90-induced microglial clearance of exogenous amyloid-beta1-42 in rat hippocampus in vivo

Alzheimer's disease is characterized by the accumulation of extracellular amyloid-beta (A beta) fibrils with microglia. In an in vitro microglial culture, we recently found that heat-shock protein-90 (Hsp90) enhanced the microglial phagocytosis and clearance of A beta (1-42) (A beta 42). In this study, we examined the microinjection of A beta 42 in the presence or absence of Hsp90 into the rat hippocampus in vivo. Intrahippocampal injection of A beta 42 alone induced microglial accumulation, and the amount of A beta 42 then gradually decreased. In addition, simultaneous injection with Hsp90 significantly reduced the amount of A beta 42 and increased the production of cytokines. These results suggest that Hsp90 may facilitate microglial A beta 42 clearance in rat brain in vivo.

Involvement of Wiskott-Aldrich syndrome protein family verprolin-homologous protein (WAVE) and Rac1 in the phagocytosis of amyloid-beta(1-42) in rat microglia

Alzheimer's disease (AD) is characterized by the accumulation of extracellular amyloid-beta (A beta) fibrils with microglia. Recently, there has been great interest in the microglial phagocytosis of A beta, because the microglial pathway is considered to be one of the A beta clearance pathways in the brain parenchyma. However, the mechanism of microglial phagocytosis of A beta is not fully understood and, thus, was investigated in this study. At one minute after exposure to A beta(1-42) (A beta 42), A beta immunoreactivity was detected at the cell surface of microglia. After 1 h, marked immunoreactivity was observed in the cytosolic vesicles. At 12 h, delayed phagocytosis of fibrillar A beta 42 was also observed with the formation of a large phagocytic cup. The microglial cell shape rapidly changed to an ameboid form during the process of phagocytosis. Although neither neural Wiskott-Aldrich syndrome protein (N-WASP) nor WASP interacting SH3 protein (WISH) immunoreactivity was co-localized with filamentous actin (F-actin) distribution, both WASP family verprolin-homologous protein (WAVE) and Rac1 immunoreactivity was co-localized with F-actin in the lamellipodia of phogocytic microglia. These results suggest that WAVE and Rac1 participate in the phagocytosis of A beta 42 by microglia.

In vivo imaging of reactive oxygen species specifically associated with thioflavine S-positive amyloid plaques by multiphoton microscopy

Amyloid-beta, the primary constituent of senile plaques in Alzheimer's disease, is hypothesized to cause neuronal damage and cognitive failure, but the mechanisms are unknown. Using multiphoton imaging, we show a direct association between amyloid-beta deposits and free radical production in vivo in live, transgenic mouse models of Alzheimer's disease and in analogous ex vivo experiments in human Alzheimer tissue. We applied two fluorogenic compounds, which become fluorescent only after oxidation, before imaging with a near infrared laser. We observed fluorescence associated with dense core plaques, but not diffuse plaques, as determined by subsequent addition of thioflavine S and immunohistochemistry for amyloid-beta. Systemic administration of N-tert-butyl-alpha-phenylnitrone, a free radical spin trap, greatly reduced oxidation of the probes. These data show directly that a subset of amyloid plaques produces free radicals in living, Alzheimer's models and in human Alzheimer tissue. Antioxidant therapy neutralizes these highly reactive molecules and may therefore be of therapeutic value in Alzheimer's disease.

Possible involvement of small oligomers of amyloid-beta peptides in 15-deoxy-delta 12,14 prostaglandin J2-sensitive microglial activation

In Alzheimer's disease, fibrillar amyloid-beta (Abeta) peptides form senile plaques associated with microglia. However, the relationship between Abeta peptides and microglia is not fully understood. In this study, the incubation of Abeta1-40 (Abeta40) produced small oligomers, while incubation with Abeta1-42 (Abeta42) caused large molecular aggregates. Microglial production of nitrite, interleukin-6 and tumor necrosis factor-alpha was induced by Abeta40, but not Abeta42. This production was significantly reduced by 15-deoxy-Delta(12,14) prostaglandin J(2), and it was completely suppressed by beta-sheet breaker peptide, Leu-Pro-Phe-Phe-Asp. These results suggest that small oligomers, rather than large molecular aggregates, mediate microglial activation induced by Abeta peptides.

In vivo imaging of reactive oxygen species specifically associated with thioflavine S-positive amyloid plaques by multiphoton microscopy

Amyloid-beta, the primary constituent of senile plaques in Alzheimer's disease, is hypothesized to cause neuronal damage and cognitive failure, but the mechanisms are unknown. Using multiphoton imaging, we show a direct association between amyloid-beta deposits and free radical production in vivo in live, transgenic mouse models of Alzheimer's disease and in analogous ex vivo experiments in human Alzheimer tissue. We applied two fluorogenic compounds, which become fluorescent only after oxidation, before imaging with a near infrared laser. We observed fluorescence associated with dense core plaques, but not diffuse plaques, as determined by subsequent addition of thioflavine S and immunohistochemistry for amyloid-beta. Systemic administration of N-tert-butyl-alpha-phenylnitrone, a free radical spin trap, greatly reduced oxidation of the probes. These data show directly that a subset of amyloid plaques produces free radicals in living, Alzheimer's models and in human Alzheimer tissue. Antioxidant therapy neutralizes these highly reactive molecules and may therefore be of therapeutic value in Alzheimer's disease.

Tau load is associated with apolipoprotein E genotype and the amount of amyloid beta protein, Abeta40, in sporadic and familial Alzheimer's disease

The total amount of hyperphosphorylated tau protein (p-tau load), present as neurofibrillary tangles (NFTs), neuropil threads or plaque neurites, was quantified in the frontal cortex of 109 cases of sporadic Alzheimer's disease (AD) and 35 cases of familial AD due to missense mutations in the presenilin-1, presenilin-2 and amyloid precursor protein genes. p-tau load was inversely correlated with age at onset of illness in both sporadic and familial AD but not with duration of disease. There was no difference in p-tau load between cases of familial AD and others with sporadic AD, matching the familial cases for apolipoprotein E (APO E) genotype. However, p-tau was greater in cases of familial and sporadic AD in the presence of APO E epsilon4 allele and increased with gene dose. Conversely, p-tau load tended to be lower when epsilon2 allele was present. In sporadic AD, tau load was highly significantly correlated with amyloid beta40 (Abeta40), but not Abeta42(43), load. These data indicate that the burden of pathological tau deposited in the brain in both familial and sporadic AD is favoured in the presence of APO E epsilon4 allele and also related to the amount of Abeta40, this also being higher when epsilon4 allele is present. Abeta40 plaques are rich in microglial cells and it is possible that p-tau pathology in AD is triggered by reaction of microglial cells to the presence of Abeta40 and not this peptide directly.

Stress proteins and glial functions: possible therapeutic targets for neurodegenerative disorders

Recent findings suggest that unfolded or misfolded proteins participate in the pathology of several neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease. Usually, several stress proteins and glial cells act as intracellular molecular chaperones and show chaperoning neuronal function, respectively. In the brains of patients with neurodegenerative disorders, however, stress proteins are expressed and frequently associated with protein aggregates, and glial cells are activated around degenerative regions. In addition, several stress proteins and glial cells may also regulate neuronal cell death and loss. Therefore, some types of stress proteins and glial cells are considered to be neuroprotective targets. We summarize the current findings regarding the neuroprotective effects of stress proteins and glial cells, and discuss the possibility of using this knowledge to develop new therapeutic strategies to treat neurodegeneration.

Risk factors for Alzheimer's disease: role of multiple antioxidants, non-steroidal anti-inflammatory and cholinergic agents alone or in combination in prevention and treatment

The etiology of Alzheimer's disease (AD) is not well understood. Etiologic factors, chronic inflammatory reactions, oxidative and nitrosylative stresses and high cholesterol levels are thought to be important for initiating and promoting neurodegenerative changes commonly found in AD brains. Even in familial AD, oxidative stress plays an important role in the early onset of the disease. Mitochondrial damage and proteasome inhibition represent early events in the pathogenesis of AD, whereas increased processing of amyloid precursor protein (APP) to beta-amyloid (Abeta) fragments (Abeta(40) and Abeta(42)) and formation of senile plaques and neurofibrillary tangles (NFTs) represent late events. We propose a hypothesis that in idiopathic AD, epigenetic components of neurons such as mitochondria, proteasomes and post-translation protein modifications (processing of amyloid precursor protein to beta-amyloid and hyperphosphorylation of tau), rather than nuclear genes, are the primary targets for the action of diverse groups of neurotoxins. Based on epidemiologic, laboratory and limited clinical studies, we propose that a combination of non steroidal anti-inflammatory drugs (NSAIDs) and appropriate levels and types of multiple micronutrients, including antioxidants, may be more effective than the individual agents in the prevention, and they, in combination with a cholinergic agent, may be more effective in the treatment of AD than the individual agents alone. In addition, agents, which can prevent formation of plaques or dissolve these plaques may further enhance the efficacy of our proposed treatment strategy.

Neurotoxic effects of thioflavin S-positive amyloid deposits in transgenic mice and Alzheimer's disease

Despite extensive deposition of putatively neurotoxic amyloid-beta (Abeta) protein in the brain, it has not been possible to demonstrate an association of Abeta deposits with neuronal loss in Alzheimer's disease (AD), and neuronal loss is minimal in transgenic mouse models of AD. Using triple immunostaining confocal microscopy and analyzing the images with the cross-correlation density map method from statistical physics, we directly compared Abeta deposition, Abeta morphology, and neuronal architecture. We found dramatic, focal neuronal toxicity associated primarily with thioflavin S-positive fibrillar Abeta deposits in both AD and PSAPP mice. These results, along with computer simulations, suggest that Abeta develops neurotoxic properties in vivo when it adopts a fibrillar beta-pleated sheet conformation.

Imaging Abeta plaques in living transgenic mice with multiphoton microscopy and methoxy-X04, a systemically administered Congo red derivative

The identification of amyloid deposits in living Alzheimer disease (AD) patients is important for both early diagnosis and for monitoring the efficacy of newly developed anti-amyloid therapies. Methoxy-X04 is a derivative of Congo red and Chrysamine-G that contains no acid groups and is therefore smaller and much more lipophilic than Congo red or Chrysamine-G. Methoxy-X04 retains in vitro binding affinity for amyloid beta (Abeta) fibrils (Ki = 26.8 nM) very similar to that of Chrysamine-G (Ki = 25.3 nM). Methoxy-X04 is fluorescent and stains plaques, tangles, and cerebrovascular amyloid in postmortem sections of AD brain with good specificity. Using multiphoton microscopy to obtain high-resolution (1 microm) fluorescent images from the brains of living PSI/APP mice, individual plaques could be distinguished within 30 to 60 min after a single i.v. injection of 5 to 10 mg/kg methoxy-X04. A single i.p. injection of 10 mg/kg methoxy-X04 also produced high contrast images of plaques and cerebrovascular amyloid in PSI/APP mouse brain. Complementary quantitative studies using tracer doses of carbon- 11-labeled methoxy-X04 show that it enters rat brain in amounts that suggest it is a viable candidate as a positron emission tomography (PET) amyloid-imaging agent for in vivo human studies.

Reversal of amyloid beta toxicity in Alzheimer's disease model Tg2576 by intraventricular antiamyloid beta antibody

There are considerable data on synaptic dysfunction in Alzheimer's disease (AD). However, the precise molecular basis for synaptotoxicity in AD is not known. We tested the hypothesis that amyloid beta (Abeta), as produced in Tg2576 mice overexpressing a mutant form of amyloid precursor protein, leads to changes in SNAP-25, a molecule required for Ca-sensitive neurotransmitter vesicle exocytosis. Anti-Abeta antibody was injected into the third ventricle (icv) of 10-month-old Tg2576 mice, preceding formation of plaques. Immunodensity of glial fibrillary acidic protein (GFAP) and SNAP-25 were quantitated in the hippocampus 1 month later. SNAP-25 was reduced by 96% in the inner molecular layer (SMi) of dentate gyrus, by 95% in the hilum, and by 75-76% in stratum lucidum (SL), stratum oriens (SO), and stratum radiatum (SR) of CA1-CA3 of the Tg2576 mice. GFAP was increased by more than 50-fold, specifically within the neuropil of CA1-CA3, and by twofold in portions of fimbria. One injection of 10 microg of anti-Abeta antibody into the third ventricle at 10 months completely prevented or restored changes in GFAP at 11 months of age. The restoration of SNAP-25 by anti-Abeta antibody compared with wild type was 69% in CA1-SO, 93% in CA1-SR, 85% in CA3-SL, 77% in SMi, and 60-73% in hilum. In addition, whereas control injections of saline or IgG produced greatly increased GFAP diffusely in the hippocampus of Tg2576 animals, there was no increase in GFAP after anti-Abeta injection, suggesting a synergistic interaction of nonspecific trauma with Abeta in the transgenic mice. This is the first report of depleted SNAP-25 immunoreactivity in Tg models and the first report of icv injection of anti-Abeta antibody in this model of AD. The largest reductions of the SNAP-25 are in hilum and SMi, so either reduction in the septal-hilum-SMi path is primary or reduction in this path begins at an earlier age than in CA3-CA1 fields. A single icv injection of anti-Abeta antibody is potent in reversing Abeta effects and, therefore, represents a suitable model for investigating early Abeta toxicity. In addition, intrathecal or icv antibody may be an efficient means of treating or preventing toxicity in AD, particularly under conditions of immune hyporesponsivity.

Intracellular accumulation of beta-amyloid(1-42) in neurons is facilitated by the alpha 7 nicotinic acetylcholine receptor in Alzheimer's disease

Amyloid beta(1-42), a major component of amyloid plaques, binds with exceptionally high affinity to the alpha 7 nicotinic acetylcholine receptor and accumulates intracellularly in neurons of Alzheimer's disease brains. In this study, we investigated the possibility that this binding plays a key role in facilitating intraneuronal accumulation of amyloid beta(1-42). Consecutive section immunohistochemistry and digital imaging were used to reveal the spatial relationship between amyloid beta(1-42) and the alpha 7 receptor in affected neurons of Alzheimer's disease brains. Results showed that neurons containing substantial intracellular accumulations of amyloid beta(1-42) invariably express relatively high levels of the alpha 7 receptor. Furthermore, this receptor is highly co-localized with amyloid beta(1-42) within neurons of Alzheimer's disease brains. To experimentally test the possibility that the binding interaction between exogenous amyloid beta(1-42) and the alpha 7 receptor facilitates internalization and intracellular accumulation of amyloid beta(1-42) in Alzheimer's disease brains, we studied the fate of exogenous amyloid beta(1-42) and its interaction with the alpha 7 receptor in vitro using cultured, transfected neuroblastoma cells that express elevated levels of this receptor. Transfected cells exhibited rapid binding, internalization and accumulation of exogenous amyloid beta(1-42), but not amyloid beta(1-40). Furthermore, the rate and extent of amyloid beta(1-42) internalization was related directly to the alpha 7 receptor protein level, since (1) the rate of amyloid beta(1-42) accumulation was much lower in untransfected cells that express much lower levels of this receptor and (2) internalization was effectively blocked by alpha-bungarotoxin, an alpha 7 receptor antagonist. As in neurons of Alzheimer's disease brains, the alpha 7 receptor in transfected cells was precisely co-localized with amyloid beta(1-42) in prominent intracellular aggregates. Internalization of amyloid beta(1-42) in transfected cells was blocked by phenylarsine oxide, an inhibitor of endocytosis. We suggest that the intraneuronal accumulation of amyloid beta(1-42) in Alzheimer's disease brains occurs predominantly in neurons that express the alpha 7 receptor. In addition, internalization of amyloid beta(1-42) may be facilitated by the high-affinity binding of amyloid beta(1-42) to the alpha 7 receptor on neuronal cell surfaces, followed by endocytosis of the resulting complex. This provides a plausible explanation for the selective vulnerability of neurons expressing the alpha 7 receptor in Alzheimer's disease brains and for the fact that amyloid beta(1-42) is the dominant amyloid beta peptide species in intracellular accumulations and amyloid plaques.

Behavioral characterization of the Tg2576 transgenic model of Alzheimer's disease through 19 months

Behavioral characterization of Alzheimer's disease (AD) transgenic models over multiple time points during aging has been largely inadequate, usually being limited to one or two cognitive-based tasks. In this context, the present study utilized a comprehensive 6-week behavioral battery to characterize sensorimotor and cognitive performance of Tg2576 AD transgenic (Tg+) mice and nontransgenic (Tg-) controls aged 3, 9, 14, and 19 months. Compared collectively to Tg- mice over all four time points, Tg+ mice were impaired in Y-maze spontaneous alternation, visible platform recognition, and several sensorimotor tasks; Tg+ mice also showed an overall increase in activity measures. The deficits in visible platform became evident by 9 months of age, while those in sensorimotor tasks became clearly manifest by 14 months. Although the behavioral impairments exhibited by Tg+ mice were usually progressive through 19 months, Tg- animals also showed similar progressive decline in the same behavioral measures; thus, no task revealed a progressive behavioral decline exclusive to Tg+ mice. Moreover, although the 6-week behavioral battery included six cognitively based tasks (i.e., Y-maze, visible platform, Morris water maze, circular platform, passive avoidance, and active avoidance), behavioral analysis through 19 months revealed Tg+ mice to be impaired in only the Y-maze and visible platform tasks. Consequently, Tg2576 mice do not exhibit widespread, profound cognitive impairment, even into old age. This may reflect their predominant C57BL/6 background and an apparent inability of the mutant transgene to profoundly alter performance therein.

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.