Abeta solubility and deposition during AD progression and in APPxPS-1 knock-in mice

Thermoneutral temperature exposure enhances slow-wave sleep with a correlated improvement in amyloid pathology in a triple-transgenic mouse model of Alzheimer's disease

Accumulation of amyloid-β (Aβ) plays an important role in Alzheimer's disease (AD) pathology. There is growing evidence that disordered sleep may accelerate AD pathology by impeding the physiological clearance of Aβ from the brain that occurs in normal sleep. Therapeutic strategies for improving sleep quality may therefore help slow disease progression. It is well documented that the composition and dynamics of sleep are sensitive to ambient temperature. We therefore compared Aβ pathology and sleep metrics derived from polysomnography in 12-month-old female 3xTg-AD mice (n = 8) exposed to thermoneutral temperatures during the light period over 4 weeks to those of age- and sex-matched controls (n = 8) that remained at normal housing temperature (22°C) during the same period. The treated group experienced greater proportions of slow wave sleep (SWS)-i.e. epochs of elevated 0.5-2 Hz EEG slow wave activity during non-rapid eye movement (NREM) sleep-compared to controls. Assays performed on mouse brain tissue harvested at the end of the experiment showed that exposure to thermoneutral temperatures significantly reduced levels of DEA-soluble (but not RIPA- or formic acid-soluble) Aβ40 and Aβ42 in the hippocampus, though not in the cortex. With both groups pooled together and without regard to treatment condition, NREM sleep continuity and any measure of SWS within NREM at the end of the treatment period were inversely correlated with DEA-soluble Aβ40 and Aβ42 levels, again in the hippocampus but not in the cortex. These findings suggest that experimental manipulation of SWS could offer useful clues into the mechanisms and treatment of AD.

A comprehensive review of the literature on CD10: its function, clinical application, and prospects

CD10, a zinc-dependent metalloprotease found on the cell surface, plays a pivotal role in an array of physiological and pathological processes including cardiovascular regulation, immune function, fetal development, pain response, oncogenesis, and aging. Recognized as a biomarker for hematopoietic and tissue stem cells, CD10 has garnered attention for its prognostic potential in the progression of leukemia and various solid tumors. Recent studies underscore its regulatory significance and therapeutic promise in combating Alzheimer's disease (AD), and it is noted for its protective role in preventing heart failure (HF), obesity, and type-2 diabetes. Furthermore, CD10/substance P interaction has also been shown to contribute to the pain signaling regulation and immunomodulation in diseases such as complex regional pain syndrome (CRPS) and osteoarthritis (OA). The emergence of COVID-19 has sparked interest in CD10's involvement in the disease's pathogenesis. Given its association with multiple disease states, CD10 is a prime therapeutic target; inhibitors targeting CD10 are now being advanced as therapeutic agents. This review compiles recent and earlier literature on CD10, elucidating its physicochemical attributes, tissue-specific expression, and molecular functions. Furthermore, it details the association of CD10 with various diseases and the clinical advancements of its inhibitors, providing a comprehensive overview of its growing significance in medical research.

The amyloid-β peptide: Guilty as charged?

Recent years have seen both considerable progress and controversy in the Alzheimer's disease (AD) field. After decades of slow to negligible movement towards the development of disease modifying therapies, promising outcomes in recent clinical trials with several monoclonal antibodies targeting various forms of the amyloid-β (Aβ) peptide have at last opened a possible way forward. In fact, at this point multiple anti-Aβ therapeutics are close to receiving (or have already received) regulatory approval. Although these outcomes are not without some degree of divisiveness, the fact remains that targeting amyloid for removal has finally shown at least modest efficacy in slowing the otherwise relentless progression of the disease. Although the validation of the long standing amyloid cascade hypothesis would seem to be at hand, what remains is the puzzling issue of why - if Aβ indeed causes AD - does removing it from the brain not stop the disease entirely.

Exposure to Lead in Drinking Water Causes Cognitive Impairment via an Alzheimer's Disease Gene-Dependent Mechanism in Adult Mice

Background

Exposure to lead (Pb) is a major public health problem that could occur through contaminated soil, air, food, or water, either during the course of everyday life, or while working in hazardous occupations. Although Pb has long been known as a neurodevelopmental toxicant in children, a recent and growing body of epidemiological research indicates that cumulative, low-level Pb exposure likely drives age-related neurologic dysfunction in adults. Environmental Pb exposure in adulthood has been linked to risk of late-onset Alzheimer's disease (AD) and dementia.

Objective

Although the biological mechanism underlying this link is unknown, it has been proposed that Pb exposure may increase the risk of AD via altering the expression of AD-related genes and, possibly, by activating the molecular pathways underlying AD-related pathology.

Methods

We investigated Pb exposure using a line of genetically modified mice with AD-causing knock-in mutations in the amyloid precursor protein and presenilin 1 (APPΔNL/ΔNL x PS1P264L/P264L) that had been crossed with Leprdb/db mice to impart vulnerability to vascular pathology.

Results

Our data show that although Pb exposure in adult mice impairs cognitive function, this effect is not related to either an increase in amyloid pathology or to changes in the expression of common AD-related genes. Pb exposure also caused a significant increase in blood pressure, a well known effect of Pb. Interestingly, although the increase in blood pressure was unrelated to genotype, only mice that carried AD-related mutations developed cognitive dysfunction, in spite of showing no significant change in cerebrovascular pathology.

Conclusions

These results raise the possibility that the increased risk of dementia associated with Pb exposure in adults may be tied to its subsequent interaction with either pre-existing or developing AD-related neuropathology.

Mammalian Models in Alzheimer's Research: An Update

A form of dementia distinct from healthy cognitive aging, Alzheimer's disease (AD) is a complex multi-stage disease that currently afflicts over 50 million people worldwide. Unfortunately, previous therapeutic strategies developed from murine models emulating different aspects of AD pathogenesis were limited. Consequently, researchers are now developing models that express several aspects of pathogenesis that better reflect the clinical situation in humans. As such, this review seeks to provide insight regarding current applications of mammalian models in AD research by addressing recent developments and characterizations of prominent transgenic models and their contributions to pathogenesis as well as discuss the advantages, limitations, and application of emerging models that better capture genetic heterogeneity and mixed pathologies observed in the clinical situation.

Depletion of Paraoxonase 1 (Pon1) Dysregulates mTOR, Autophagy, and Accelerates Amyloid Beta Accumulation in Mice

Paraoxonase 1 (PON1), a homocysteine (Hcy)-thiolactone detoxifying enzyme, has been associated with Alzheimer's disease (AD), suggesting that PON1 plays an important protective role in the brain. To study the involvement of PON1 in the development of AD and to elucidate the mechanism involved, we generated a new mouse model of AD, the Pon1^-/-xFAD mouse, and examined how Pon1 depletion affects mTOR signaling, autophagy, and amyloid beta (Aβ) accumulation. To elucidate the mechanism involved, we examined these processes in N2a-APP_swe cells. We found that Pon1 depletion significantly downregulated Phf8 and upregulated H4K20me1; mTOR, phospho-mTOR, and App were upregulated while autophagy markers Bcln1, Atg5, and Atg7 were downregulated at the protein and mRNA levels in the brains of Pon1^─/─5xFAD vs. Pon1^+/+5xFAD mice. Pon1 depletion in N2a-APP_swe cells by RNA interference led to downregulation of Phf8 and upregulation of mTOR due to increased H4K20me1-mTOR promoter binding. This led to autophagy downregulation and significantly increased APP and Aβ levels. Phf8 depletion by RNA interference or treatments with Hcy-thiolactone or N-Hcy-protein metabolites similarly increased Aβ levels in N2a-APP_swe cells. Taken together, our findings define a neuroprotective mechanism by which Pon1 prevents Aβ generation.

Deletion of the Homocysteine Thiolactone Detoxifying Enzyme Bleomycin Hydrolase, in Mice, Causes Memory and Neurological Deficits and Worsens Alzheimer's Disease-Related Behavioral and Biochemical Traits in the 5xFAD Model of Alzheimer's Disease

BACKGROUND

Bleomycin hydrolase (BLMH), a homocysteine (Hcy)-thiolactone detoxifying enzyme, is attenuated in Alzheimer's disease (AD) brains. Blmh loss causes astrogliosis in mice while the loss of histone demethylase Phf8, which controls mTOR signaling, causes neuropathy in mice and humans.

OBJECTIVE

To examine how Blmh gene deletion affects the Phf8/H4K20me1/mTOR/autophagy pathway, amyloid-β (Aβ) accumulation, and cognitive/neuromotor performance in mice.

METHODS

We generated a new mouse model of AD, the Blmh-/-5xFAD mouse. Behavioral assessments were conducted by cognitive/neuromotor testing. Blmh and Phf8 genes were silenced in mouse neuroblastoma N2a-APPswe cells by RNA interference. mTOR- and autophagy-related proteins, and AβPP were quantified by western blotting and the corresponding mRNAs by RT-qPCR. Aβ was quantified by western blotting (brains) and by confocal microscopy (cells).

RESULTS

Behavioral testing showed cognitive/neuromotor deficits in Blmh-/- and Blmh-/-5xFAD mice. Phf8 was transcriptionally downregulated in Blmh-/- and Blmh-/-5xFAD brains. H4K20me1, mTOR, phospho-mTOR, and AβPP were upregulated while autophagy markers Becn1, Atg5, and Atg7 were downregulated in Blmh-/- and Blmh-/-5xFAD brains. Aβ was elevated in Blmh-/-5xFAD brains. These biochemical changes were recapitulated in Blmh-silenced N2a-APPswe cells, which also showed increased H4K20me1-mTOR promoter binding and impaired autophagy flux (Lc3-I, Lc3-II, p62). Phf8-silencing or treatments with Hcy-thiolactone or N-Hcy-protein, metabolites elevated in Blmh-/- mice, induced biochemical changes in N2a-APPswe cells like those induced by the Blmh-silencing. However, Phf8-silencing elevated Aβ without affecting AβPP.

CONCLUSIONS

Our findings show that Blmh interacts with AβPP and the Phf8/H4K20me1/mTOR/autophagy pathway, and that disruption of those interactions causes Aβ accumulation and cognitive/neuromotor deficits.

Anodal transcranial direct current stimulation alleviates cognitive impairment in an APP/PS1 model of Alzheimer's disease in the preclinical stage

Anodal transcranial direct current stimulation (AtDCS) has been shown to alleviate cognitive impairment in an APP/PS1 model of Alzheimer's disease in the preclinical stage. However, this enhancement was only observed immediately after AtDCS, and the long-term effect of AtDCS remains unknown. In this study, we treated 26-week-old mouse models of Alzheimer's disease in the preclinical stage with 10 AtDCS sessions or sham stimulation. The Morris water maze, novel object recognition task, and novel object location test were implemented to evaluate spatial learning memory and recognition memory of mice. Western blotting was used to detect the relevant protein content. Morphological changes were observed using immunohistochemistry and immunofluorescence staining. Six weeks after treatment, the mice subjected to AtDCS sessions had a shorter escape latency, a shorter path length, more platform area crossings, and spent more time in the target quadrant than sham-stimulated mice. The mice subjected to AtDCS sessions also performed better in the novel object recognition and novel object location tests than sham-stimulated mice. Furthermore, AtDCS reduced the levels of amyloid-β42 and glial fibrillary acidic protein, a marker of astrocyte activation, and increased the level of neuronal marker NeuN in hippocampal tissue. These findings suggest that AtDCS can improve the spatial learning and memory abilities and pathological state of an APP/PS1 mouse model of Alzheimer's disease in the preclinical stage, with improvements that last for at least 6 weeks.

Chronic Fragmentation of the Daily Sleep-Wake Rhythm Increases Amyloid-beta Levels and Neuroinflammation in the 3xTg-AD Mouse Model of Alzheimer's Disease

Fragmentation of the daily sleep-wake rhythm with increased nighttime awakenings and more daytime naps is correlated with the risk of development of Alzheimer's disease (AD). To explore whether a causal relationship underlies this correlation, the present study tested the hypothesis that chronic fragmentation of the daily sleep-wake rhythm stimulates brain amyloid-beta (Aβ) levels and neuroinflammation in the 3xTg-AD mouse model of AD. Female 3xTg-AD mice were allowed to sleep undisturbed or were subjected to chronic sleep fragmentation consisting of four daily sessions of enforced wakefulness (one hour each) evenly distributed during the light phase, five days a week for four weeks. Piezoelectric sleep recording revealed that sleep fragmentation altered the daily sleep-wake rhythm to resemble the pattern observed in AD. Levels of amyloid-beta (Aβ₄₀ and Aβ₄₂) determined by ELISA were higher in hippocampal tissue collected from sleep-fragmented mice than from undisturbed controls. In contrast, hippocampal levels of tau and phospho-tau differed minimally between sleep fragmented and undisturbed control mice. Sleep fragmentation also stimulated neuroinflammation as shown by increased expression of markers of microglial activation and proinflammatory cytokines measured by q-RT-PCR analysis of hippocampal samples. No significant effects of sleep fragmentation on Aβ, tau, or neuroinflammation were observed in the cerebral cortex. These studies support the concept that improving sleep consolidation in individuals at risk for AD may be beneficial for slowing the onset or progression of this devastating neurodegenerative disease.

Necrostatin-1 Relieves Learning and Memory Deficits in a Zebrafish Model of Alzheimer's Disease Induced by Aluminum

Aluminum (Al) is considered one of the environmental risk factors for Alzheimer's disease (AD). The present study aims to establish a zebrafish AD model induced by Al and explore if necrostation-1 (Nec-1), a specific inhibitor of necroptosis, is effective in relieving learning and memory deficits in the zebrafish AD models. We treated adult zebrafish with aluminum trichloride at various doses for 1 month, followed by a T-maze test to evaluate learning and memory performance. Al concentration, levels of acetylcholine (Ach), and AD-related protein and gene expression in the brain tissue were evaluated in the zebrafish AD models. Our results demonstrated that in the brain tissue of Al-treated zebrafish, Al accumulated, Ach levels decreased, and AD-related genes and proteins increased. As a result, the learning and memory performance of Al-treated zebrafish was impaired. This suggested that a zebrafish AD model was established. To test the effect of Nec-1 on the zebrafish AD model, we added Nec-1 into the culture medium of the Al-treated adult zebrafish. The results demonstrated that Nec-1 could relive the learning and memory deficits, enhance Ach levels and the numbers of neural cells, and impact necroptosis-related gene expression. We concluded that Nec-1 could reverse Al-induced learning and memory impairment and had potential theoretical value in the zebrafish AD model.

MUTYH Actively Contributes to Microglial Activation and Impaired Neurogenesis in the Pathogenesis of Alzheimer's Disease

Oxidative stress is a major risk factor for Alzheimer's disease (AD), which is characterized by brain atrophy, amyloid plaques, neurofibrillary tangles, and loss of neurons. 8-Oxoguanine, a major oxidatively generated nucleobase highly accumulated in the AD brain, is known to cause neurodegeneration. In mammalian cells, several enzymes play essential roles in minimizing the 8-oxoguanine accumulation in DNA. MUTYH with adenine DNA glycosylase activity excises adenine inserted opposite 8-oxoguanine in DNA. MUTYH is reported to actively contribute to the neurodegenerative process in Parkinson and Huntington diseases and some mouse models of neurodegenerative diseases by accelerating neuronal dysfunction and microgliosis under oxidative conditions; however, whether or not MUTYH is involved in AD pathogenesis remains unclear. In the present study, we examined the contribution of MUTYH to the AD pathogenesis. Using postmortem human brains, we showed that various types of MUTYH transcripts and proteins are expressed in most hippocampal neurons and glia in both non-AD and AD brains. We further introduced MUTYH deficiency into App ^{NL-G-F/NL-G-F} knock-in AD model mice, which produce humanized toxic amyloid-β without the overexpression of APP protein, and investigated the effects of MUTYH deficiency on the behavior, pathology, gene expression, and neurogenesis. MUTYH deficiency improved memory impairment in App ^{NL-G-F/NL-G-F} mice, accompanied by reduced microgliosis. Gene expression profiling strongly suggested that MUTYH is involved in the microglial response pathways under AD pathology and contributes to the phagocytic activity of disease-associated microglia. We also found that MUTYH deficiency ameliorates impaired neurogenesis in the hippocampus, thus improving memory impairment. In conclusion, we propose that MUTYH, which is expressed in the hippocampus of AD patients as well as non-AD subjects, actively contributes to memory impairment by inducing microgliosis with poor neurogenesis in the preclinical AD phase and that MUTYH is a novel therapeutic target for AD, as its deficiency is highly beneficial for ameliorating AD pathogenesis.

Translational animal models for Alzheimer's disease: An Alzheimer's Association Business Consortium Think Tank

Over 5 million Americans and 50 million individuals worldwide are living with Alzheimer's disease (AD). The progressive dementia associated with AD currently has no cure. Although clinical trials in patients are ultimately required to find safe and effective drugs, animal models of AD permit the integration of brain pathologies with learning and memory deficits that are the first step in developing these new drugs. The purpose of the Alzheimer's Association Business Consortium Think Tank meeting was to address the unmet need to improve the discovery and successful development of Alzheimer's therapies. We hypothesize that positive responses to new therapies observed in validated models of AD will provide predictive evidence for positive responses to these same therapies in AD patients. To achieve this goal, we convened a meeting of experts to explore the current state of AD animal models, identify knowledge gaps, and recommend actions for development of next-generation models with better predictability. Among our findings, we all recognize that models reflecting only single aspects of AD pathogenesis do not mimic AD. Models or combinations of new models are needed that incorporate genetics with environmental interactions, timing of disease development, heterogeneous mechanisms and pathways, comorbidities, and other pathologies that lead to AD and related dementias. Selection of the best models requires us to address the following: (1) which animal species, strains, and genetic backgrounds are most appropriate; (2) which models permit efficient use throughout the drug development pipeline; (3) the translatability of behavioral-cognitive assays from animals to patients; and (4) how to match potential AD therapeutics with particular models. Best practice guidelines to improve reproducibility also need to be developed for consistent use of these models in different research settings. To enhance translational predictability, we discuss a multi-model evaluation strategy to de-risk the successful transition of pre-clinical drug assets to the clinic.

The Aβ(1-38) peptide is a negative regulator of the Aβ(1-42) peptide implicated in Alzheimer disease progression

The pool of β-Amyloid (Aβ) length variants detected in preclinical and clinical Alzheimer disease (AD) samples suggests a diversity of roles for Aβ peptides. We examined how a naturally occurring variant, e.g. Aβ(1-38), interacts with the AD-related variant, Aβ(1-42), and the predominant physiological variant, Aβ(1-40). Atomic force microscopy, Thioflavin T fluorescence, circular dichroism, dynamic light scattering, and surface plasmon resonance reveal that Aβ(1-38) interacts differently with Aβ(1-40) and Aβ(1-42) and, in general, Aβ(1-38) interferes with the conversion of Aβ(1-42) to a β-sheet-rich aggregate. Functionally, Aβ(1-38) reverses the negative impact of Aβ(1-42) on long-term potentiation in acute hippocampal slices and on membrane conductance in primary neurons, and mitigates an Aβ(1-42) phenotype in Caenorhabditis elegans. Aβ(1-38) also reverses any loss of MTT conversion induced by Aβ(1-40) and Aβ(1-42) in HT-22 hippocampal neurons and APOE ε4-positive human fibroblasts, although the combination of Aβ(1-38) and Aβ(1-42) inhibits MTT conversion in APOE ε4-negative fibroblasts. A greater ratio of soluble Aβ(1-42)/Aβ(1-38) [and Aβ(1-42)/Aβ(1-40)] in autopsied brain extracts correlates with an earlier age-at-death in males (but not females) with a diagnosis of AD. These results suggest that Aβ(1-38) is capable of physically counteracting, potentially in a sex-dependent manner, the neuropathological effects of the AD-relevant Aβ(1-42).

Can Healthy Diets, Regular Exercise, and Better Lifestyle Delay the Progression of Dementia in Elderly Individuals?

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by memory loss and multiple cognitive impairments. Current healthcare costs for over 50 million people afflicted with AD are about $818 million and are projected to be $2 billion by 2050. Unfortunately, there are no drugs currently available that can delay and/or prevent the progression of disease in elderly individuals and in AD patients. Loss of synapses and synaptic damage are largely correlated with cognitive decline in AD patients. Women are at a higher lifetime risk of developing AD encompassing two-thirds of the total AD afflicted population. Only about 1-2% of total AD patients can be explained by genetic mutations in APP, PS1, and PS2 genes. Several risk factors have been identified, such as Apolipoprotein E4 genotype, type 2 diabetes, traumatic brain injury, depression, and hormonal imbalance, are reported to be associated with late-onset AD. Strong evidence reveals that antioxidant enriched diets and regular exercise reduces toxic radicals, enhances mitochondrial function and synaptic activity, and improves cognitive function in elderly populations. Current available data on the use of antioxidants in mouse models of AD and antioxidant(s) supplements in diets of elderly individuals were investigated. The use of antioxidants in randomized clinical trials in AD patients was also critically assessed. Based on our survey of current literature and findings, we cautiously conclude that healthy diets, regular exercise, and improved lifestyle can delay dementia progression and reduce the risk of AD in elderly individuals and reverse subjects with mild cognitive impairment to a non-demented state.

Redox proteomics and amyloid β-peptide: insights into Alzheimer disease

Alzheimer disease (AD) is a progressive neurodegenerative disorder associated with aging and characterized pathologically by the presence of senile plaques, neurofibrillary tangles, and neurite and synapse loss. Amyloid beta-peptide (1-42) [Aβ(1-42)], a major component of senile plaques, is neurotoxic and induces oxidative stress in vitro and in vivo. Redox proteomics has been used to identify proteins oxidatively modified by Aβ(1-42) in vitro and in vivo. In this review, we discuss these proteins in the context of those identified to be oxidatively modified in animal models of AD, and human studies including familial AD, pre-clinical AD (PCAD), mild cognitive impairment (MCI), early AD, late AD, Down syndrome (DS), and DS with AD (DS/AD). These redox proteomics studies indicate that Aβ(1-42)-mediated oxidative stress occurs early in AD pathogenesis and results in altered antioxidant and cellular detoxification defenses, decreased energy yielding metabolism and mitochondrial dysfunction, excitotoxicity, loss of synaptic plasticity and cell structure, neuroinflammation, impaired protein folding and degradation, and altered signal transduction. Improved access to biomarker imaging and the identification of lifestyle interventions or treatments to reduce Aβ production could be beneficial in preventing or delaying the progression of AD. This article is part of the special issue "Proteomics".

The db mutation improves memory in younger mice in a model of Alzheimer's disease

Alzheimer's disease (AD) is the most common age-related neurodegenerative disease, while obesity is a major global public health problem associated with the metabolic disorder type 2 diabetes mellitus (T2DM). Chronic obesity and T2DM have been identified as invariant risk factors for dementia and late-onset AD, while their impacts on the occurrence and development of AD remain unclear. As shown in our previous study, the diabetic mutation (db, Lepr^db/db) induces mixed or vascular dementia in mature to middle-aged APP^ΔNL/ΔNL x PS1^P264L/P264L knock-in mice (db/AD). In the present study, the impacts of the db mutation on young AD mice at 10 weeks of age were evaluated. The db mutation not only conferred young AD mice with severe obesity, impaired glucose regulation and activated mammalian target of rapamycin (mTOR) signaling pathway in the mouse cortex, but lead to a surprising improvement in memory. At this young age, mice also had decreased cerebral Aβ content, which we have not observed at older ages. This was unlikely to be related to altered Aβ synthesis, as both β- and γ-secretase were unchanged. The db mutation also reduced the cortical IL-1β mRNA level and IBA1 protein level in young AD mice, with no significant effect on the activation of microglia and astrocytes. We conclude that the db mutation could transitorily improve the memory of young AD mice, a finding that may be partially explained by the relatively improved glucose homeostasis in the brains of db/AD mice compared to their counterpart AD mice, suggesting that glucose regulation could be a strategy for prevention and treatment of neurodegenerative diseases like AD.

Emergence of synaptic and cognitive impairment in a mature-onset APP mouse model of Alzheimer's disease

The synaptic changes underlying the onset of cognitive impairment in Alzheimer’s disease (AD) are poorly understood. In contrast to the well documented inhibition of long-term potentiation (LTP) in CA3-CA1 synapses by acute Aβ application in adult neurons from rodents, young amyloid precursor protein (APP) transgenic mouse models often, surprisingly, show normal LTP. This suggests that there may be important differences between mature-onset and developmental-onset APP expression/ Aβ accumulation and the ensuing synaptic and behavioural phenotype. Here, in agreement with previous studies, we observed that developmental expression of APP_Sw,Ind (3–4 month old mice from line 102, PLoS Med 2:e355, 2005), resulted in reduced basal synaptic transmission in CA3-CA1 synapses, normal LTP, impaired spatial working memory, but normal spatial reference memory. To analyse early Aβ-mediated synaptic dysfunction and cognitive impairment in a more mature brain, we used controllable mature-onset APP_Sw,Ind expression in line 102 mice. Within 3 weeks of mature-onset APP_Sw,Ind expression and Aβ accumulation, we detected the first synaptic dysfunction: an impairment of LTP in hippocampal CA3-CA1 synapses. Cognitively, at this time point, we observed a deficit in short-term memory. A reduction in basal synaptic strength and deficit in long-term associative spatial memory were only evident following 12 weeks of APP_Sw,Ind expression. Importantly, the plasticity impairment observed after 3 weeks of mature-onset APP expression is reversible. Together, these findings demonstrate important differences between developmental and mature-onset APP expression. Further research targeted at this early stage of synaptic dysfunction could help identify mechanisms to treat cognitive impairment in mild cognitive impairment (MCI) and early AD.

Chronic Intermittent Hypoxia Induces Robust Astrogliosis in an Alzheimer's Disease-Relevant Mouse Model

Sleep disturbances are a common early symptom of neurodegenerative diseases, including Alzheimer's disease (AD) and other age-related dementias, and emerging evidence suggests that poor sleep may be an important contributor to development of amyloid pathology. Of the causes of sleep disturbances, it is estimated that 10-20% of adults in the United States have sleep-disordered breathing (SDB) disorder, with obstructive sleep apnea accounting for the majority of the SBD cases. The clinical and epidemiological data clearly support a link between sleep apnea and AD; yet, almost no experimental research is available exploring the mechanisms associated with this correlative link. Therefore, we exposed an AD-relevant mouse model (APP/PS1 KI) to chronic intermittent hypoxia (IH) (an experimental model of sleep apnea) to begin to describe one of the potential mechanisms by which SDB could increase the risk of dementia. Previous studies have found that astrogliosis is a contributor to neuropathology in models of chronic IH and AD; therefore, we hypothesized that a reactive astrocyte response might be a contributing mechanism in the neuroinflammation associated with sleep apnea. To test this hypothesis, 10-11-month-old wild-type (WT) and APP/PS1 KI mice were exposed to 10 hours of IH, daily for four weeks. At the end of four weeks brains were analyzed from amyloid burden and astrogliosis. No effect was found for chronic IH exposure on amyloid-beta levels or plaque load in the APP/PS1 KI mice. A significant increase in GFAP staining was found in the APP/PS1 KI mice following chronic IH exposure, but not in the WT mice. Profiling of genes associated with different phenotypes of astrocyte activation identified GFAP, CXCL10, and Ggta1 as significant responses activated in the APP/PS1 KI mice exposed to chronic IH.

7B2 chaperone knockout in APP model mice results in reduced plaque burden

Impairment of neuronal proteostasis is a hallmark of Alzheimer's and other neurodegenerative diseases. However, the underlying molecular mechanisms leading to pathogenic protein aggregation, and the role of secretory chaperone proteins in this process, are poorly understood. We have previously shown that the neural-and endocrine-specific secretory chaperone 7B2 potently blocks in vitro fibrillation of Aβ42. To determine whether 7B2 can function as a chaperone in vivo, we measured plaque formation and performed behavioral assays in 7B2-deficient mice in an hAPPswe/PS1dE9 Alzheimer's model mouse background. Surprisingly, immunocytochemical analysis of cortical levels of thioflavin S- and Aβ-reactive plaques showed that APP mice with a partial or complete lack of 7B2 expression exhibited a significantly lower number and burden of thioflavin S-reactive, as well as Aβ-immunoreactive, plaques. However, 7B2 knockout did not affect total brain levels of either soluble or insoluble Aβ. While hAPP model mice performed poorly in the Morris water maze, their brain 7B2 levels did not impact performance. Since 7B2 loss reduced amyloid plaque burden, we conclude that brain 7B2 can impact Aβ disposition in a manner that facilitates plaque formation. These results are reminiscent of prior findings in hAPP model mice lacking the ubiquitous secretory chaperone clusterin.

Calcineurin/NFAT Signaling in Activated Astrocytes Drives Network Hyperexcitability in Aβ-Bearing Mice

Hyperexcitable neuronal networks are mechanistically linked to the pathologic and clinical features of Alzheimer's disease (AD). Astrocytes are a primary defense against hyperexcitability, but their functional phenotype during AD is poorly understood. Here, we found that activated astrocytes in the 5xFAD mouse model were strongly associated with proteolysis of the protein phosphatase calcineurin (CN) and the elevated expression of the CN-dependent transcription factor nuclear factor of activated T cells 4 (NFAT4). Intrahippocampal injections of adeno-associated virus vectors containing the astrocyte-specific promoter Gfa2 and the NFAT inhibitory peptide VIVIT reduced signs of glutamate-mediated hyperexcitability in 5xFAD mice, measured in vivo with microelectrode arrays and ex vivo brain slices, using whole-cell voltage clamp. VIVIT treatment in 5xFAD mice led to increased expression of the astrocytic glutamate transporter GLT-1 and to attenuated changes in dendrite morphology, synaptic strength, and NMDAR-dependent responses. The results reveal astrocytic CN/NFAT4 as a key pathologic mechanism for driving glutamate dysregulation and neuronal hyperactivity during AD.SIGNIFICANCE STATEMENT Neuronal hyperexcitability and excitotoxicity are increasingly recognized as important mechanisms for neurodegeneration and dementia associated with Alzheimer's disease (AD). Astrocytes are profoundly activated during AD and may lose their capacity to regulate excitotoxic glutamate levels. Here, we show that a highly active calcineurin (CN) phosphatase fragment and its substrate transcription factor, nuclear factor of activated T cells (NFAT4), appear in astrocytes in direct proportion to the extent of astrocyte activation. The blockade of astrocytic CN/NFAT signaling in a common mouse model of AD, using adeno-associated virus vectors normalized glutamate signaling dynamics, increased astrocytic glutamate transporter levels and alleviated multiple signs of neuronal hyperexcitability. The results suggest that astrocyte activation drives hyperexcitability during AD through a mechanism involving aberrant CN/NFAT signaling and impaired glutamate transport.

Oxidative stress and hippocampal synaptic protein levels in elderly cognitively intact individuals with Alzheimer's disease pathology

Neuritic amyloid plaques and neurofibrillary tangles are hallmarks of Alzheimer's disease (AD) and are major components used for the clinical diagnosis of this disorder. However, many individuals with no cognitive impairment (NCI) also present at autopsy with high levels of these AD pathologic hallmarks. In this study, we evaluated 15 autopsy cases from NCI individuals with high levels of AD-like pathology (high pathology no cognitive impairment) and compared them to age- and postmortem-matched cohorts of individuals with amnestic mild cognitive impairment and NCI cases with low AD-like pathology (low pathology no cognitive impairment [LPNCI]). Individuals classified as high pathology no cognitive impairment or amnestic mild cognitive impairment had a significant loss of both presynaptic and postsynaptic proteins in the hippocampus compared with those in the LPNCI cohort. In addition, these 2 groups had a significant increase in 3 different markers of oxidative stress compared with that in the LPNCI group. The changes in levels of synaptic proteins are strongly associated with levels of oxidative stress. These data suggest that cognitively older subjects without dementia but with increased levels of AD-like pathology may represent a very early preclinical stage of AD.

Extra-virgin olive oil attenuates amyloid-β and tau pathologies in the brains of TgSwDI mice

Extra-virgin olive oil (EVOO) is one of the main elements of Mediterranean diet. Several studies have suggested that EVOO has several health promoting effects that could protect from and decrease the risk of Alzheimer's disease (AD). In this study, we investigated the effect of consumption of EVOO-enriched diet on amyloid- and tau-related pathological alterations that are associated with the progression of AD and cerebral amyloid angiopathy (CAA) in TgSwDI mice. Feeding mice with EVOO-enriched diet for 6months, beginning at an age before amyloid-β (Aβ) accumulation starts, has significantly reduced total Aβ and tau brain levels with a significant improvement in mouse cognitive behavior. This reduction in brain Aβ was explained by the enhanced Aβ clearance pathways and reduced brain production of Aβ via modulation of amyloid-β precursor protein processing. On the other hand, although feeding mice with EVOO-enriched diet for 3months, beginning at an age after Aβ accumulation starts, showed improved clearance across the blood-brain barrier and significant reduction in Aβ levels, it did not affect tau levels or improve cognitive functions of TgSwDI mouse. Collectively, results of this study suggest that the long-term consumption of EVOO-containing diet starting at early age provides a protective effect against AD and its related disorder CAA.

Synaptic change in the posterior cingulate gyrus in the progression of Alzheimer's disease

Mild cognitive impairment (MCI) is considered to be an early stage in the progression of Alzheimer's disease (AD) providing an opportunity to investigate brain pathogenesis prior to the onset of dementia. Neuroimaging studies have identified the posterior cingulate gyrus (PostC) as a cortical region affected early in the onset of AD. This association cortex is involved in a variety of different cognitive tasks and is intimately connected with the hippocampal/entorhinal cortex region, a component of the medial temporal memory circuit that displays early AD pathology. We quantified the total number of synapses in lamina 3 of the PostC using unbiased stereology coupled with electron microscopy from short postmortem autopsy tissue harvested from cases at different stage of AD progression. Individuals in the early stages of AD showed a significant decline in synaptic numbers compared to individuals with no cognitive impairment (NCI). Subjects with MCI exhibited synaptic numbers that were between the AD and NCI cohorts. Adjacent tissue was evaluated for changes in both pre and postsynaptic proteins levels. Individuals with MCI demonstrated a significant loss in presynaptic markers synapsin-1 and synaptophysin and postsynaptic markers PSD-95 and SAP-97. Levels of [3H]PiB binding was significantly increased in MCI and AD and correlated strongly with levels of synaptic proteins. All synaptic markers showed a significant association with Mini-Mental Status Examination scores. These results support the idea that the PostC synaptic function is affected during the prodromal stage of the disease and may underlie some of the early clinical sequelae associated with AD.

Human umbilical cord blood-derived monocytes improve cognitive deficits and reduce amyloid-β pathology in PSAPP mice

Alzheimer's disease (AD) is the fourth major cause of mortality in the elderly in the US and the leading cause of dementia worldwide. While pharmacological targets have been discovered, there are no true disease-modifying therapies. We have recently discovered that multiple low-dose infusions of human umbilical cord blood cells (HUCBCs) ameliorate cognitive impairments and reduce Aβ-associated neuropathology in PSAPP transgenic mice. However, the mechanism for these effects of HUCBCs remains unclear. In the present study, we examined whether monocytes, as important components of HUCBCs, would have beneficial outcomes on the reduction of AD-like pathology and associated cognitive impairments in PSAPP transgenic AD model mice. PSAPP mice and their wild-type littermates were treated monthly with an infusion of peripheral human umbilical cord blood cell (HUCBC)-derived monocytes over a period of 2 and 4 months, followed by behavioral evaluations, biochemical, and histological analyses. The principal findings of the present study confirmed that monocytes derived from HUCBCs (CB-M) play a central role in HUCBC-mediated cognition-enhancing and Aβ pathology-ameliorating activities. Most importantly, we found that compared with CB-M, aged monocytes showed an ineffective phagocytosis of Aβ, while exogenous soluble amyloid precursor protein α (sAPPα) could reverse this deficiency. Pretreating monocytes with sAPPα upregulates Aβ internalization. Our further studies suggested that sAPPα could form a heterodimer with Aβs, with the APP672-688 (Aβ1-16) region being responsible for this effect. This in turn promoted binding of these heterodimers to monocyte scavenger receptors and thus promoted enhanced Aβ clearance. In summary, our findings suggest an interesting hypothesis that peripheral monocytes contribute to Aβ clearance through heterodimerization of sAPPα with Aβ. Further, declined or impaired sAPPα production, or reduced heterodimerization with Aβ, would cause a deficiency in Aβ clearance and thus accelerate the pathogenesis of AD.

Bridging integrator 1 (BIN1) protein expression increases in the Alzheimer's disease brain and correlates with neurofibrillary tangle pathology

Recent genome wide association studies have implicated bridging integrator 1 (BIN1) as a late-onset Alzheimer's disease (AD) susceptibility gene. There are at least 15 different known isoforms of BIN1, with many being expressed in the brain including the longest isoform (iso1), which is brain-specific and localizes to axon initial segments and nodes of Ranvier. It is currently unknown what role BIN1 plays in AD. We analyzed BIN1 protein expression from a large number (n = 71) of AD cases and controls from five different brain regions (hippocampus, inferior parietal cortex, inferior temporal cortex, frontal cortex (BA9), and superior and middle temporal gyri). We found that the amount of the largest isoform of BIN1 was significantly reduced in the AD brain compared to age-matched controls, and smaller BIN1 isoforms were significantly increased. Further, BIN1 was significantly correlated with the amount of neurofibrillary tangle (NFT) pathology but not with either diffuse or neuritic plaques, or with the amount of amyloid-β peptide. BIN1 is known to be abnormally expressed in another human disease, myotonic dystrophy, which also features prominent NFT pathology. These data suggest that BIN1 is likely involved in AD as a modulator of NFT pathology, and that this role may extend to other human diseases that feature tau pathology.

Closed head injury in an age-related Alzheimer mouse model leads to an altered neuroinflammatory response and persistent cognitive impairment

Epidemiological studies have associated increased risk of Alzheimer's disease (AD)-related clinical symptoms with a medical history of head injury. Currently, little is known about pathophysiology mechanisms linked to this association. Persistent neuroinflammation is one outcome observed in patients after a single head injury. Neuroinflammation is also present early in relevant brain regions during AD pathology progression. In addition, previous mechanistic studies in animal models link neuroinflammation as a contributor to neuropathology and cognitive impairment in traumatic brain injury (TBI) or AD-related models. Therefore, we explored the potential interplay of neuroinflammatory responses in TBI and AD by analysis of the temporal neuroinflammatory changes after TBI in an AD model, the APP/PS1 knock-in (KI) mouse. Discrete temporal aspects of astrocyte, cytokine, and chemokine responses in the injured KI mice were delayed compared with the injured wild-type mice, with a peak neuroinflammatory response in the injured KI mice occurring at 7 d after injury. The neuroinflammatory responses were more persistent in the injured KI mice, leading to a chronic neuroinflammation. At late time points after injury, KI mice exhibited a significant impairment in radial arm water maze performance compared with sham KI mice or injured wild-type mice. Intervention with a small-molecule experimental therapeutic (MW151) that selectively attenuates proinflammatory cytokine production yielded improved cognitive behavior outcomes, consistent with a link between neuroinflammatory responses and altered risk for AD-associated pathology changes with head injury.

Obesity and diabetes cause cognitive dysfunction in the absence of accelerated β-amyloid deposition in a novel murine model of mixed or vascular dementia

Mid-life obesity and type 2 diabetes mellitus (T2DM) confer a modest, increased risk for Alzheimer's disease (AD), though the underlying mechanisms are unknown. We have created a novel mouse model that recapitulates features of T2DM and AD by crossing morbidly obese and diabetic db/db mice with APPΔNL/ΔNLx PS1P264L/P264L knock-in mice. These mice (db/AD) retain many features of the parental lines (e.g. extreme obesity, diabetes, and parenchymal deposition of β-amyloid (Aβ)). The combination of the two diseases led to additional pathologies-perhaps most striking of which was the presence of severe cerebrovascular pathology, including aneurysms and small strokes. Cortical Aβ deposition was not significantly increased in the diabetic mice, though overall expression of presenilin was elevated. Surprisingly, Aβ was not deposited in the vasculature or removed to the plasma, and there was no stimulation of activity or expression of major Aβ-clearing enzymes (neprilysin, insulin degrading enzyme, or endothelin-converting enzyme). The db/AD mice displayed marked cognitive impairment in the Morris Water Maze, compared to either db/db or APPΔNLx PS1P264L mice. We conclude that the diabetes and/or obesity in these mice leads to a destabilization of the vasculature, leading to strokes and that this, in turn, leads to a profound cognitive impairment and that this is unlikely to be directly dependent on Aβ deposition. This model of mixed or vascular dementia provides an exciting new avenue of research into the mechanisms underlying the obesity-related risk for age-related dementia, and will provide a useful tool for the future development of therapeutics.

Nucleic acid oxidation: an early feature of Alzheimer's disease

Studies of oxidative damage during the progression of Alzheimer's disease (AD) suggest its central role in disease pathogenesis. To investigate levels of nucleic acid oxidation in both early and late stages of AD, levels of multiple base adducts were quantified in nuclear and mitochondrial DNA from the superior and middle temporal gyri (SMTG), inferior parietal lobule (IPL), and cerebellum (CER) of age-matched normal control subjects, subjects with mild cognitive impairment, preclinical AD, late-stage AD, and non-AD neurological disorders (diseased control; DC) using gas chromatography/mass spectrometry. Median levels of multiple DNA adducts in nuclear and mitochondrial DNA were significantly (p ≤ 0.05) elevated in the SMTG, IPL, and CER in multiple stages of AD and in DC subjects. Elevated levels of fapyguanine and fapyadenine in mitochondrial DNA suggest a hypoxic environment early in the progression of AD and in DC subjects. Overall, these data suggest that oxidative damage is an early event not only in the pathogenesis of AD but is also present in neurodegenerative diseases in general. Levels of oxidized nucleic acids in nDNA and mtDNA were found to be significantly elevated in mild cognitive impairment (MCI), preclinical Alzheimer's disease (PCAD), late-stage AD (LAD), and a pooled diseased control group (DC) of frontotemporal dementia (FTD) and dementia with Lewy bodies (DLB) subjects compared to normal control (NC) subjects. Nucleic acid oxidation peaked early in disease progression and remained elevated. The study suggests nucleic acid oxidation is a general event in neurodegeneration.

MER5101, a novel Aβ1-15:DT conjugate vaccine, generates a robust anti-Aβ antibody response and attenuates Aβ pathology and cognitive deficits in APPswe/PS1ΔE9 transgenic mice

Active amyloid-β (Aβ) immunotherapy is under investigation to prevent or treat early Alzheimer's disease (AD). In 2002, a Phase II clinical trial (AN1792) was halted due to meningoencephalitis in ∼6% of the AD patients, possibly caused by a T-cell-mediated immunological response. Thus, generating a vaccine that safely generates high anti-Aβ antibody levels in the elderly is required. In this study, MER5101, a novel conjugate of Aβ1-15 peptide (a B-cell epitope fragment) conjugated to an immunogenic carrier protein, diphtheria toxoid (DT), and formulated in a nanoparticular emulsion-based adjuvant, was administered to 10-month-old APPswe/PS1ΔE9 transgenic (Tg) and wild-type (Wt) mice. High anti-Aβ antibody levels were observed in both vaccinated APPswe/PS1ΔE9 Tg and Wt mice. Antibody isotypes were mainly IgG1 and IgG2b, suggesting a Th2-biased response. Restimulation of splenocytes with the Aβ1-15:DT conjugate resulted in a strong proliferative response, whereas proliferation was absent after restimulation with Aβ1-15 or Aβ1-40/42 peptides, indicating a cellular immune response against DT while avoiding an Aβ-specific T-cell response. Moreover, significant reductions in cerebral Aβ plaque burden, accompanied by attenuated microglial activation and increased synaptic density, were observed in MER5101-vaccinated APPswe/PS1ΔE9 Tg mice compared with Tg adjuvant controls. Last, MER5101-immunized APPswe/PS1ΔE9 Tg mice showed improvement of cognitive deficits in both contextual fear conditioning and the Morris water maze. Our novel, highly immunogenic Aβ conjugate vaccine, MER5101, shows promise for improving Aβ vaccine safety and efficacy and therefore, may be useful for preventing and/or treating early AD.

Comprehensive behavioral characterization of an APP/PS-1 double knock-in mouse model of Alzheimer's disease

INTRODUCTION

Despite the extensive mechanistic and pathological characterization of the amyloid precursor protein (APP)/presenilin-1 (PS-1) knock-in mouse model of Alzheimer's disease (AD), very little is known about the AD-relevant behavioral deficits in this model. Characterization of the baseline behavioral performance in a variety of functional tasks and identification of the temporal onset of behavioral impairments are important to provide a foundation for future preclinical testing of AD therapeutics. Here we perform a comprehensive behavioral characterization of this model, discuss how the observed behavior correlates with the mechanistic and pathological observations of others, and compare this model with other commonly used AD mouse models.

METHODS

FOUR DIFFERENT GROUPS OF MICE RANGING ACROSS THE LIFESPAN OF THIS MODEL (TEST GROUPS: 7, 11, 15, and 24 months old) were run in a behavioral test battery consisting of tasks to assess motor function (grip strength, rotor rod, beam walk, open field ambulatory movement), anxiety-related behavior (open field time spent in peripheral zone vs. center zone, elevated plus maze), and cognitive function (novel object recognition, radial arm water maze).

RESULTS

There were no differences in motor function or anxiety-related behavior between APP/PS-1 knock-in mice and wild-type counterpart mice for any age group. Cognitive deficits in both recognition memory (novel object recognition) and spatial reference memory (radial arm water maze) became apparent for the knock-in animals as the disease progressed.

CONCLUSION

This is the first reported comprehensive behavioral analysis of the APP/PS1 knock-in mouse model of AD. The lack of motor/coordination deficits or abnormal anxiety levels, coupled with the age/disease-related cognitive decline and high physiological relevance of this model, make it well suited for utilization in preclinical testing of AD-relevant therapeutics.

Transgenic models of Alzheimer's disease: better utilization of existing models through viral transgenesis

Animal models have been used for decades in the Alzheimer's disease (AD) research field and have been crucial for the advancement of our understanding of the disease. Most models are based on familial AD mutations of genes involved in the amyloidogenic process, such as the amyloid precursor protein (APP) and presenilin 1 (PS1). Some models also incorporate mutations in tau (MAPT) known to cause frontotemporal dementia, a neurodegenerative disease that shares some elements of neuropathology with AD. While these models are complex, they fail to display pathology that perfectly recapitulates that of the human disease. Unfortunately, this level of pre-existing complexity creates a barrier to the further modification and improvement of these models. However, as the efficacy and safety of viral vectors improves, their use as an alternative to germline genetic modification is becoming a widely used research tool. In this review we discuss how this approach can be used to better utilize common mouse models in AD research. This article is part of a Special Issue entitled: Animal Models of Disease.

Postmortem Pittsburgh Compound B (PiB) binding increases with Alzheimer's disease progression

The development of imaging reagents is of considerable interest in the Alzheimer's disease (AD) field. Some of these, such as Pittsburgh Compound B (PiB), were designed to bind to the amyloid-β peptide (Aβ), the major component of amyloid deposits in the AD brain. Although these agents were designed for imaging amyloid deposits in vivo, a major avenue of evaluation relies on postmortem cross validation with established indices of AD pathology. In this study, we evaluated changes in the postmortem binding of PiB and its relationship to other aspects of Aβ-related pathology in a series of AD cases and age-matched controls. We also examined cases of preclinical AD (PCAD) and amnestic mild cognitive impairment (MCI), both considered early points in the AD continuum. PiB binding was found to increase with the progression of the disease and paralleled increases in the less soluble forms of Aβ, including SDS-stable Aβ oligomers. Increased PiB binding and its relationship to Aβ was only significant in a brain region vulnerable to the development of AD pathology (the superior and middle temporal gyri) but not in an unaffected region (cerebellum). This implies that the amyloid deposited in disease-affected regions may possess fundamental, brain region specific characteristics that may not as yet be fully appreciated. These data support the idea that PiB is a useful diagnostic tool for AD, particularly in the early stage of the disease, and also show that PiB could be a useful agent for the discovery of novel disease-related properties of amyloid.

A ketogenic diet improves motor performance but does not affect β-amyloid levels in a mouse model of Alzheimer's disease

β-Amyloid (Aβ), a small, fibrillogenic peptide, is known to play an important role in the pathogenesis of Alzheimer's disease (AD) in the brain. In addition, Aβ accumulates in skeletal muscle cells in individuals with sporadic inclusion body myositis (sIBM), an age-related muscle disease. Because of the socioeconomic burden associated with age-related diseases, particularly AD, there has been considerable emphasis on studying potential therapeutic strategies. The high-fat, low carbohydrate ketogenic diet has been used extensively to treat refractory childhood epilepsy and has been studied as a potential treatment for other neurological diseases, including Parkinson's disease and AD. In this study, we fed young APP/PS1 knock-in mice, which have a whole body knock-in of AD-related genes, a ketogenic diet and determined the effect on Aβ levels in the brain and skeletal muscle, as well motor performance and oxidative stress. Aβ and its precursor, the β-C-terminal fragment of amyloid precursor protein (CTFβ), were unchanged overall in both the brain and quadriceps after 1 month on the ketogenic diet, and there was no effect on nitrotyrosine, a product of oxidative stress. The ketogenic diet improved performance on the Rota-rod apparatus (p=0.007), however. These data indicate that the ketogenic diet may have some efficacy in the treatment of both neurologic and muscle diseases though the underlying mechanisms do not involve amelioration of Aβ pathology.

Targeting astrocytes ameliorates neurologic changes in a mouse model of Alzheimer's disease

Astrocytes are the most abundant cell type in the brain and play a critical role in maintaining healthy nervous tissue. In Alzheimer's disease (AD) and most other neurodegenerative disorders, many astrocytes convert to a chronically "activated" phenotype characterized by morphologic and biochemical changes that appear to compromise protective properties and/or promote harmful neuroinflammatory processes. Activated astrocytes emerge early in the course of AD and become increasingly prominent as clinical and pathological symptoms progress, but few studies have tested the potential of astrocyte-targeted therapeutics in an intact animal model of AD. Here, we used adeno-associated virus (AAV) vectors containing the astrocyte-specific Gfa2 promoter to target hippocampal astrocytes in APP/PS1 mice. AAV-Gfa2 vectors drove the expression of VIVIT, a peptide that interferes with the immune/inflammatory calcineurin/NFAT (nuclear factor of activated T-cells) signaling pathway, shown by our laboratory and others to orchestrate biochemical cascades leading to astrocyte activation. After several months of treatment with Gfa2-VIVIT, APP/PS1 mice exhibited improved cognitive and synaptic function, reduced glial activation, and lower amyloid levels. The results confirm a deleterious role for activated astrocytes in AD and lay the groundwork for exploration of other novel astrocyte-based therapies.

Prolonged diet induced obesity has minimal effects towards brain pathology in mouse model of cerebral amyloid angiopathy: implications for studying obesity-brain interactions in mice

Cerebral amyloid angiopathy (CAA) occurs in nearly every individual with Alzheimer's disease (AD) and Down's syndrome, and is the second largest cause of intracerebral hemorrhage. Mouse models of CAA have demonstrated evidence for increased gliosis contributing to CAA pathology. Nearly two thirds of Americans are overweight or obese, with little known about the effects of obesity on the brain, although increasingly the vasculature appears to be a principle target of obesity effects on the brain. In the current study we describe for the first time whether diet induced obesity (DIO) modulates glial reactivity, amyloid levels, and inflammatory signaling in a mouse model of CAA. In these studies we identify surprisingly that DIO does not significantly increase Aβ levels, astrocyte (GFAP) or microglial (IBA-1) gliosis in the CAA mice. However, within the hippocampal gyri a localized increase in reactive microglia were increased in the CA1 and stratum oriens relative to CAA mice on a control diet. DIO was observed to selectively increase IL-6 in CAA mice, with IL-1β and TNF-α not increased in CAA mice in response to DIO. Taken together, these data show that prolonged DIO has only modest effects towards Aβ in a mouse model of CAA, but appears to elevate some localized microglial reactivity within the hippocampal gyri and selective markers of inflammatory signaling. These data are consistent with the majority of the existing literature in other models of Aβ pathology, which surprisingly show a mixed profile of DIO effects towards pathological processes in mouse models of neurodegenerative disease. The importance for considering the potential impact of ceiling effects in pathology within mouse models of Aβ pathogenesis, and the current experimental limitations for DIO in mice to fully replicate metabolic dysfunction present in human obesity, are discussed. This article is part of a Special Issue entitled: Animal Models of Disease.

Pittsburgh compound B and the postmortem diagnosis of Alzheimer disease

OBJECTIVE

Deposition of the amyloid-β (Aβ) peptide in neuritic plaques is a requirement for the diagnosis of Alzheimer disease (AD). Although the continued development of in vivo imaging agents such as Pittsburgh compound B (PiB) is promising, the diagnosis of AD is still challenging. This can be partially attributed to our lack of a detailed understanding of the interrelationship between the various pools and species of Aβ and other common indices of AD pathology. We hypothesized that recent advances in our ability to accurately measure Aβ postmortem (for example, using PiB), could form the basis of a simple means to deliver an accurate AD diagnosis.

METHODS

We conducted a comprehensive analysis of the amount of Aβ40 and Aβ42 in increasingly insoluble fractions, oligomeric Aβ, and fibrillar Aβ (as defined by PiB binding), as well as plaques (diffuse and neuritic), and neurofibrillary tangles in autopsy specimens from age-matched, cognitively normal controls (n = 23) and AD (n = 22) cases, across multiple brain regions.

RESULTS

Both PiB binding and the amount of sodium dodecyl sulfate (SDS)-soluble Aβ were able to predict disease status; however, SDS-soluble Aβ was a better measure. Oligomeric Aβ was not a predictor of disease status. PiB binding was strongly related to plaque count, although diffuse plaques were a stronger correlate than neuritic plaques.

INTERPRETATION

Although postmortem PiB binding was somewhat useful in distinguishing AD from control cases, SDS-soluble Aβ measured by standard immunoassay was substantially better. These findings have important implications for the development of imaging-based biomarkers of AD.

Leptin regulates amyloid β production via the γ-secretase complex

Alzheimer's disease (AD) is the most common age-related neurodegenerative disease, affecting an estimated 5.3million people in the United States. While many factors likely contribute to AD progression, it is widely accepted that AD is driven by the accumulation of β-amyloid (Aβ), a small, fibrillogenic peptide generated by the sequential proteolysis of the amyloid precursor protein by the β- and γ-secretases. Though the underlying causes of Aβ accumulation in sporadic AD are myriad, it is clear that lifestyle and overall health play a significant role. The adipocyte-derived hormone leptin has varied systemic affects, including neuropeptide release and neuroprotection. A recent study by Lieb et al. (2009) showed that individuals with low plasma leptin levels are at greater risk of developing AD, through unknown mechanisms. In this report, we show that plasma leptin is a strong negative predictor of Aβ levels in the mouse brain, supporting a protective role for the hormone in AD onset. We also show that the inhibition of Aβ accumulation is due to the downregulation of transcription of the γ-secretase components. On the other hand, β-secretase expression is either unchanged (BACE1) or increased (BACE2). Finally, we show that only presenilin 1 (PS1) is negatively correlated with plasma leptin at the protein level (p<0.0001). These data are intriguing and may highlight a role for leptin in regulating the onset of amyloid pathology and AD.

Early stage drug treatment that normalizes proinflammatory cytokine production attenuates synaptic dysfunction in a mouse model that exhibits age-dependent progression of Alzheimer's disease-related pathology

Overproduction of proinflammatory cytokines in the CNS has been implicated as a key contributor to pathophysiology progression in Alzheimer's disease (AD), and extensive studies with animal models have shown that selective suppression of excessive glial proinflammatory cytokines can improve neurologic outcomes. The prior art, therefore, raises the logical postulation that intervention with drugs targeting dysregulated glial proinflammatory cytokine production might be effective disease-modifying therapeutics if used in the appropriate biological time window. To test the hypothesis that early stage intervention with such drugs might be therapeutically beneficial, we examined the impact of intervention with MW01-2-151SRM (MW-151), an experimental therapeutic that selectively attenuates proinflammatory cytokine production at low doses. MW-151 was tested in an APP/PS1 knock-in mouse model that exhibits increases in AD-relevant pathology progression with age, including increases in proinflammatory cytokine levels. Drug was administered during two distinct but overlapping therapeutic time windows of early stage pathology development. MW-151 treatment attenuated the increase in microglial and astrocyte activation and proinflammatory cytokine production in the cortex and yielded improvement in neurologic outcomes, such as protection against synaptic protein loss and synaptic plasticity impairment. The results also demonstrate that the therapeutic time window is an important consideration in efficacy studies of drugs that modulate glia biological responses involved in pathology progression and suggest that such paradigms should be considered in the development of new therapeutic regimens that seek to delay the onset or slow the progression of AD.

Alzheimer's disease: pathological mechanisms and recent insights

Amyloidopathies cause neurodegeneration in a substantial portion of the elderly population. Improvements in long term health care have made elderly individuals a large and growing demographic group, marking these diseases as a major public health concern. Alzheimer's Disease (AD) is the most studied form of neurodegenerative amyloidopathy. Although our understanding of AD is far from complete, several decades of research have advanced our knowledge to the point where it is conceivable that some form of disease modifying therapy may be available in the near future. These advances have been built on a strong mechanistic understanding of the disease from its underlying genetics, molecular biology and clinical pathology. Insights derived from the study of other neurodegenerative diseases, such as some forms of frontotemporal dementia, have been critical to this process. This knowledge has allowed researchers to construct animal models of the disease process that have paved the way towards the development of therapeutics. However, what was once thought to be a straightforward problem has evolved into a series of disappointing outcomes. Examination of pathways common to all neurodegenerative diseases, including the cellular mechanisms that clear misfolded proteins and their regulation, may be the best way to move forward.

High-molecular weight Aβ oligomers and protofibrils are the predominant Aβ species in the native soluble protein fraction of the AD brain

Alzheimer’s disease (AD) is characterized by the aggregation and deposition of amyloid β protein (Aβ) in the brain. Soluble Aβ oligomers are thought to be toxic. To investigate the predominant species of Aβ protein that may play a role in AD pathogenesis, we performed biochemical analysis of AD and control brains. Sucrose buffer-soluble brain lysates were characterized in native form using blue native (BN)-PAGE and also in denatured form using SDS-PAGE followed by Western blot analysis. BN-PAGE analysis revealed a high-molecular weight smear (>1000 kD) of Aβ₄₂-positive material in the AD brain, whereas low-molecular weight and monomeric Aβ species were not detected. SDS-PAGE analysis, on the other hand, allowed the detection of prominent Aβ monomer and dimer bands in AD cases but not in controls. Immunoelectron microscopy of immunoprecipitated oligomers and protofibrils/fibrils showed spherical and protofibrillar Aβ-positive material, thereby confirming the presence of high-molecular weight Aβ (hiMWAβ) aggregates in the AD brain. In vitro analysis of synthetic Aβ₄₀- and Aβ₄₂ preparations revealed Aβ fibrils, protofibrils, and hiMWAβ oligomers that were detectable at the electron microscopic level and after BN-PAGE. Further, BN-PAGE analysis exhibited a monomer band and less prominent low-molecular weight Aβ (loMWAβ) oligomers. In contrast, SDS-PAGE showed large amounts of loMWAβ but no hiMWAβ₄₀ and strikingly reduced levels of hiMWAβ₄₂. These results indicate that hiMWAβ aggregates, particularly Aβ₄₂ species, are most prevalent in the soluble fraction of the AD brain. Thus, soluble hiMWAβ aggregates may play an important role in the pathogenesis of AD either independently or as a reservoir for release of loMWAβ oligomers.

Effects of aging and genotype on circadian rhythms, sleep, and clock gene expression in APPxPS1 knock-in mice, a model for Alzheimer's disease

Profound disruptions of circadian rhythms and sleep/wake cycles constitute a major cause of institutionalization of AD patients. This study investigated whether a rodent model of AD, APP(NLH/NLH)/PS-1(P264L/264L) (APPxPS1) mice, exhibits circadian alterations. The APPxPS1 mice were generated using CD-1/129 mice and Cre-lox knock-in technology to "humanize" the mouse amyloid (A)β sequence and create a presenilin-1 mutation identified in familial early-onset AD patients. APPxPS1 and WT mice of several ages (~4, 11, and 15 months) were monitored for circadian rhythms in wheel running, cage activity, and sleep:wake behavior. After rhythm assessment, the mice were euthanized at zeitgeber time (ZT) 2 or 10 (i.e., 2 or 10 h after lights-on) and brains were dissected. Amyloidβ levels were measured in cortical samples and brain sections of the hypothalamus and hippocampus were prepared and used for in situ hybridization of circadian or neuropeptide genes. The most significant effects of the APPxPS1 transgenes were phase delays of ~2 h in the onset of daytime wakefulness bouts (P<0.005) and peak wakefulness (P<0.02), potentially relevant to phase delays previously reported in AD patients. However, genotype did not affect the major activity peaks or phases of wheel running, wake, or general movement, which were bimodal with dominant dawn and dusk activity. Expression of Period 2 in the suprachiasmatic nucleus was affected by ZT (P<0.0001) with a marginal interaction effect of age, genotype, and ZT (P<0.08). A separate analysis of the old animals indicated a robust interaction between ZT and genotype, as well as main effects of these parameters. Aging also altered sleep (e.g., bout length and amount of daytime sleep) and the amount of wheel running and cage activity. In conclusion, the APPxPS1 knock-in mice exhibit some alterations in their sleep:wake rhythm and clock gene expression, but do not show robust, genotype-related changes in activity rhythms. The prominent daytime activity peaks shown by the background strain complicate the use of these APPxPS1 knock-in mice for investigations of circadian activity rhythms in AD. In addition to this unusual activity pattern, lack of hyperactivity differentiates the APPxPS1 knock-in mice from other transgenic AD models.

Dihydroxybenzoic acid isomers differentially dissociate soluble biotinyl-Aβ(1-42) oligomers

Polyphenolic compounds including a number of natural products such as resveratrol, curcumin, catechin derivatives, and nordihydroguaiaretic acid have effects on the assembly of Aβ fibrils and oligomers as well as on fibril morphology. Based on a lead structure obtained from a screen of a small molecule diversity library, simple benzoic acid derivatives distinguished by the number and position of hydroxyls on the aromatic ring displayed different abilities to dissociate preformed biotinyl-Aβ(1-42) oligomers. The 2,3-, 2,5-, and 3,4-dihydroxybenzoic acid (DHBA) isomers were active oligomer dissociators. The remaining DHBA isomers and the monohydroxy and unsubstituted benzoic acids were inactive and did not compete with the active compounds to block oligomer dissociation. None of the compounds blocked oligomer assembly, indicating that they do not interact with monomeric Aβ to shift the oligomer-monomer equilibrium. Dissociating activity was not associated with quinone redox cycling capacity of the compounds. Gallic acid (3,4,5-trihydroxybenzoic acid) stabilized biotinyl-Aβ(1-42) oligomers against intrinsic dissociation and blocked the effects of the active dissociators, independent of the concentration of dissociator. A model for the mechanism of action of the DHBA dissociators proposes that these compounds destabilize oligomer structure promoting progressive monomer dissociation rather than fissioning oligomers into smaller, but still macromolecular, species. Gallic acid blocks dissociation by stabilizing oligomers against this process.

Proteomic analysis of brain proteins in APP/PS-1 human double mutant knock-in mice with increasing amyloid β-peptide deposition: insights into the effects of in vivo treatment with N-acetylcysteine as a potential therapeutic intervention in mild cognitive impairment and Alzheimer's disease

Proteomics analyses were performed on the brains of wild-type (WT) controls and an Alzheimer's disease (AD) mouse model, APP/PS-1 human double mutant knock-in mice. Mice were given either drinking water or water supplemented with N-acetylcysteine (NAC) (2 mg/kg body weight) for a period of five months. The time periods of treatment correspond to ages prior to Aβ deposition (i.e. 4-9 months), resembling human mild cognitive impairment (MCI), and after Aβ deposition (i.e. 7-12 months), more closely resembling advancing stages of AD. Substantial differences exist between the proteomes of WT and APP/PS-1 mice at 9 or 12 months, indicating that Aβ deposition and oxidative stress lead to downstream changes in protein expression. Altered proteins are involved in energy-related pathways, excitotoxicity, cell cycle signaling, synaptic abnormalities, and cellular defense and structure. Overall, the proteomic results support the notion that NAC may be beneficial for increasing cellular stress responses in WT mice and for influencing the levels of energy- and mitochondria-related proteins in APP/PS-1 mice.

RNA oxidation adducts 8-OHG and 8-OHA change with Aβ42 levels in late-stage Alzheimer's disease

While research supports amyloid-β (Aβ) as the etiologic agent of Alzheimer's disease (AD), the mechanism of action remains unclear. Evidence indicates that adducts of RNA caused by oxidation also represent an early phenomenon in AD. It is currently unknown what type of influence these two observations have on each other, if any. We quantified five RNA adducts by gas chromatography/mass spectroscopy across five brain regions from AD cases and age-matched controls. We then used a reductive directed analysis to compare the RNA adducts to common indices of AD neuropathology and various pools of Aβ. Using data from four disease-affected brain regions (Brodmann's Area 9, hippocampus, inferior parietal lobule, and the superior and middle temporal gyri), we found that the RNA adduct 8-hydroxyguanine (8-OHG) decreased, while 8-hydroxyadenine (8-OHA) increased in AD. The cerebellum, which is generally spared in AD, did not show disease related changes, and no RNA adducts correlated with the number of plaques or tangles. Multiple regression analysis revealed that SDS-soluble Aβ₄₂ was the best predictor of changes in 8-OHG, while formic acid-soluble Aβ₄₂ was the best predictor of changes in 8-OHA. This study indicates that although there is a connection between AD related neuropathology and RNA oxidation, this relationship is not straightforward.

Cognitive impairment in humanized APP×PS1 mice is linked to Aβ(1-42) and NOX activation

Cognitive impairment in Alzheimer's disease (AD) is strongly associated with both extensive deposition of amyloid β peptides and oxidative stress, but the exact role of these indices in the development of dementia is not clear. This study was designed to determine the relationship between cognitive impairment, activation of the free radical producing enzyme NADPH oxidase (NOX), and progressive changes in Aβ deposition and solubility in humanized APP×PS1 knock-in mice of increasing age. Data show that cognitive performance and expression of key synaptic proteins were progressively decreased in aging APP×PS1 mice. Likewise, NOX activity and expression of the specific NOX subunit NOX4 were significantly increased in APP×PS1 mice in an age-dependent manner, and NOX activity and cognitive impairment shared a significant linear relationship. Data further show that age-dependent increases in Aβ(1-42) had a significant linear relationship with both NOX activity and cognitive performance in APP×PS1 knock-in mice. Collectively, these data show that NOX expression and activity are significantly upregulated with age in this humanized model of Aβ pathogenesis, and suggest that NOX-associated redox pathways are intimately linked to both the loss of cognitive function and the deposition of Aβ(1-42).

Purified high molecular weight synthetic Aβ(1-42) and biological Aβ oligomers are equipotent in rapidly inducing MTT formazan exocytosis

Synthetic soluble Aβ oligomers are often used as a surrogate for biologic material in a number of model systems. We compared the activity of Aβ oligomers (synthetic and cell culture media derived) on the human SH-SY5Y neuroblastoma and C2C12 mouse myoblast cell lines in a novel, modified MTT assay. Separating oligomers from monomeric peptide by size exclusion chromatography produced effects at peptide concentrations approaching physiologic levels (10-100 nM). Purified oligomers, but not monomers or fibrils, elicited an increase of a detergent-insoluble form of MTT formazan within 2h as opposed to a control toxin (H(2)O(2)). This effect was comparable for biological and synthetic peptide in both cell types. Monomeric Aβ attenuated the effect of soluble oligomers. This study suggests that the activities of biological and synthetic oligomers are indistinguishable during early stages of Aβ oligomer-cell interaction.

Proteolysis of calcineurin is increased in human hippocampus during mild cognitive impairment and is stimulated by oligomeric Abeta in primary cell culture

Recent reports demonstrate that the activation and interaction of the protease calpain (CP) and the protein phosphatase calcineurin (CN) are elevated in the late stages of Alzheimer's disease (AD). However, the extent to which CPs and CN interact during earlier stages of disease progression remains unknown. Here, we investigated CP and CN protein levels in cytosolic, nuclear, and membrane fractions prepared from human postmortem hippocampal tissue from aged non-demented subjects, and subjects diagnosed with mild cognitive impairment (MCI). The results revealed a parallel increase in CP I and the 48 kDa CN-Aα (ΔCN-Aα48) proteolytic fragment in cytosolic fractions during MCI. In primary rat hippocampal cultures, CP-dependent proteolysis and activation of CN was stimulated by application of oligomeric Aβ((1-42)) peptides. Deleterious effects of Aβ on neuronal morphology were reduced by blockade of either CP or CN. NMDA-type glutamate receptors, which help regulate cognition and neuronal viability, and are modulated by CPs and CN, were also investigated in human hippocampus. Relative to controls, MCI subjects showed significantly greater proteolytic levels of the NR2B subunit. Within subjects, the extent of NR2B proteolysis was strongly correlated with the generation of ΔCN-Aα48 in the cytosol. A similar proteolytic pattern for NR2B was also observed in primary rat hippocampal cultures treated with oligomeric Aβ and prevented by inhibition of CP or CN. Together, the results demonstrate that the activation and interaction of CPs and CN are increased early in cognitive decline associated with AD and may help drive other pathologic processes during disease progression.

Oxidative modification to LDL receptor-related protein 1 in hippocampus from subjects with Alzheimer disease: implications for Aβ accumulation in AD brain

Alzheimer disease (AD) is a neurodegenerative disorder characterized histopathologically by the presence of senile plaques (SPs), neurofibrillary tangles, and synapse loss. The main component of SPs is amyloid-β peptide (Aβ), which has been associated with increased oxidative stress, leading to oxidative modification of proteins and consequently to neurotoxicity and neurodegeneration. Low-density lipoprotein receptor-related protein 1 (LRP1) is the primary moiety responsible for the efflux of Aβ from the brain to the blood across the blood-brain barrier. Impaired brain-to-blood transport of Aβ by LRP1 has been hypothesized to contribute to increased levels of Aβ in AD brain. The cause of LRP1 dysfunction is unknown, but we have hypothesized that Aβ oxidizes LRP1, thus damaging its own transporter. Consistent with this notion, we report in this study a significant increase in the levels of the lipid peroxidation product 4-hydroxy-2-nonenal bound to transmembrane LRP1 in AD hippocampus. In contrast, the levels of LRP1-resident 3-nitrotyrosine did not show a significant increase in AD hippocampus compared to age-matched controls. Based on this study, we propose that Aβ impairs its own efflux from the brain by oxidation of its transporter LRP1, leading to increased Aβ deposition in brain, thereby contributing to subsequent cognitive impairment in AD.

Elevated 4-hydroxyhexenal in Alzheimer's disease (AD) progression

Multiple studies have demonstrated elevations of α, β-unsaturated aldehydes including 4-hydroxynonenal (HNE) and acrolein, in vulnerable regions of mild cognitive impairment (MCI), preclinical Alzheimer's disease (PCAD), and late stage Alzheimer's disease (LAD) brain. However, there has been limited study of a third member, 4-hydroxyhexenal (HHE), a diffusible lipid peroxidation product of the ω-3 polyunstataturated fatty acids (PUFAs). In the present study levels of extractable and protein-bound HHE were quantified in the hippocampus/parahippocampal gyrus (HPG), superior and middle temporal gyri (SMTG), and cerebellum (CER) of MCI, PCAD, LAD, and normal control (NC) subjects. Levels of extractable and protein-bound HHE were increased in multiple regions in the progression of Alzheimer's disease (AD). Extractable HHE was significantly elevated in the hippocampus/parahippocampal gyrus (HPG) of PCAD and LAD subjects and protein-bound HHE was significantly higher in MCI, PCAD, and LAD HPG. A time- and concentration-dependent decrease in survival and a concentration-dependent decrease in glucose uptake were observed in primary cortical cultures treated with HHE. Together these data support a role for lipid peroxidation in the progression of Alzheimer's disease.

Gene-environment interaction research and transgenic mouse models of Alzheimer's disease

The etiology of the sporadic form of Alzheimer's disease (AD) remains largely unknown. Recent evidence has suggested that gene-environment interactions (GxE) may play a crucial role in its development and progression. Whereas various susceptibility loci have been identified, like the apolipoprotein E4 allele, these cannot fully explain the increasing prevalence of AD observed with aging. In addition to such genetic risk factors, various environmental factors have been proposed to alter the risk of developing AD as well as to affect the rate of cognitive decline in AD patients. Nevertheless, aside from the independent effects of genetic and environmental risk factors, their synergistic participation in increasing the risk of developing AD has been sparsely investigated, even though evidence points towards such a direction. Advances in the genetic manipulation of mice, modeling various aspects of the AD pathology, have provided an excellent tool to dissect the effects of genes, environment, and their interactions. In this paper we present several environmental factors implicated in the etiology of AD that have been tested in transgenic animal models of the disease. The focus lies on the concept of GxE and its importance in a multifactorial disease like AD. Additionally, possible mediating mechanisms and future challenges are discussed.