Aged 3xTg-AD Mice Research Articles

Cell type-specific impact of aging and Alzheimer disease on hippocampal CA1 perforant path input.

The perforant path (PP) carries direct inputs from entorhinal cortex to CA1 pyramidal neurons (PNs), with an impact dependent on PN position across transverse (CA1a-CA1c) and radial (superficial/deep) axes. It remains unclear how aging and Alzheimer disease (AD) affect PP input, despite its critical role in memory and early AD. Applying ex vivo recordings and two-photon microscopy in slices from mice up to 30 months old, we interrogated PP responses across PN subpopulations and compared them to Schaffer collateral and intrinsic excitability changes. We found that aging uniquely impacts PP excitatory responses, abolishing transverse and radial differences via a mechanism independent of presynaptic and membrane excitability change. This is amplified in aged 3xTg-AD mice, with further weakening of PP inputs to CA1a superficial PNs associated with distal dendritic spine loss. This demonstrates a unique feature of aging-related circuit dysfunction, with mechanistic implications related to memory impairment and synaptic vulnerability.

KIR channel regulation of electrical conduction along cerebrovascular endothelium: Enhanced modulation during Alzheimer's disease.

Endothelial cell (EC) coupling occurs through gap junctions and underlies cerebral blood flow regulation governed by inward-rectifying (KIR ) channels. This study addressed effects of KIR channel activity on EC coupling before and during Alzheimer's disease (AD). Intact EC tubes (width: ~90-100 μm; length: ~0.5 mm) were freshly isolated from posterior cerebral arteries of young Pre-AD (1-3 months) and aged AD (13-18 months) male and female 3xTg-AD mice. Dual intracellular microelectrodes applied simultaneous current injections (±0.5-3 nA) and membrane potential (Vm ) recordings in ECs at distance ~400 μm. Elevated extracellular potassium ([K+ ]E ; 8-15 mmol L-1 ; reference, 5 mmol L-1 ) activated KIR channels. Conducted Vm (∆Vm ) responses ranged from ~-30 to 30 mV in response to -3 to +3 nA (linear regression, R2 ≥0.99) while lacking rectification for charge polarity or axial direction of spread. Conduction slope decreased ~10-20% during 15 mmol L-1 [K+ ]E in Pre-AD males and AD females. 15 mmol L-1 [K+ ]E decreased conduction at lower thresholds in AD animals (~±20 mV) versus Pre-AD (~±25 mV). AD increased (~10-15%) conducted hyperpolarization during 8-12 mmol L-1 [K+ ]E . Brain endothelial KIR channel activity modulates bidirectional spread of vasoreactive signals with enhanced regulation of EC coupling during AD pathology.

Sex- and Neuropsychiatric-Dependent Circadian Alterations in Daily Voluntary Physical Activity Engagement and Patterns in Aged 3xTg-AD Mice.

Alzheimer's disease (AD) patients suffer from circadian rhythm alterations affecting their daily physical activity patterns with less willingness to perform a voluntary exercise. In preclinical studies, there is no clarity on whether animal models of AD can replicate these impairments. Here, we provide a proof of concept of the performance and behavioral effects of four weeks of voluntary wheel running (VWR) in a group of 14-month-old male and female 3xTg-AD mice at advanced stages of AD and the daily variance (behavioral circadian rhythmicity) of VWR associated with sex and their neuropsychiatric-like phenotype. Higher levels of horizontal exploration in the open field (OF) test were found in mice submitted to exercise. A linear mixed effect model showed significant sex-dependent differences in the VWR activity performed on the first night of follow-up, with high-NIBI males running less than high-NIBI females. Thus, an influence of NPS-like symptoms on the circadian patterns of VWR may account for such differences. In addition, males remained more active than females during diurnal periods. We hypothesize that this increment in energy expenditure during resting periods may be related to hyperactive behavior, similar to that observed in humans' exacerbated agitation or sundowning behavior. These findings support the usage of the 3xTg-AD mouse as a reliable model for studying circadian rhythm alterations in AD and, at the translational level, the importance of tailored and individualized physical activity programs in clinical settings.

Liver and White/Brown Fat Dystrophy Associates with Gut Microbiota and Metabolomic Alterations in 3xTg Alzheimer's Disease Mouse Model.

Metabolic impairments and liver and adipose depots alterations were reported in subjects with Alzheimer’s disease (AD), highlighting the role of the liver–adipose–tissue–brain axis in AD pathophysiology. The gut microbiota might play a modulating role. We investigated the alterations to the liver and white/brown adipose tissues (W/BAT) and their relationships with serum and gut metabolites and gut bacteria in a 3xTg mouse model during AD onset (adulthood) and progression (aging) and the impact of high-fat diet (HFD) and intranasal insulin (INI). Glucose metabolism (18FDG-PET), tissue radiodensity (CT), liver and W/BAT histology, BAT-thermogenic markers were analyzed. 16S-RNA sequencing and mass-spectrometry were performed in adult (8 months) and aged (14 months) 3xTg-AD mice with a high-fat or control diet. Generalized and HFD resistant deficiency of lipid accumulation in both liver and W/BAT, hypermetabolism in WAT (adulthood) and BAT (aging), abnormal cytokine–hormone profiles, and liver inflammation were observed in 3xTg mice; INI could antagonize all these alterations. Specific gut microbiota–metabolome profiles correlated with a significant disruption of the gut–microbiota–liver–adipose axis in AD mice. In conclusion, fat dystrophy in liver and adipose depots contributes to AD progression, and associates with altered profiles of the gut microbiota, which candidates as an appealing early target for preventive intervention.

Influence of fecal microbiota transplantation on gut microbiota composition and neuroinflammation of 3xTg-AD mice.

The gut microbiota, the aggregate of all microbial cells that inhabit the gut, bidirectionally communicates with the brain via cytokines, neurotransmitters, hormones, and secondary metabolites via the gut-brain axis. The gut microbiota is thought to contribute to the development of Alzheimer's disease (AD), characterized by plaque deposition, neurofibrillary tangles, and neuroinflammation. We hypothesize that manipulation of the gut microbiota can alter development of AD pathologies and neuroinflammation via the gut microbiota-brain axis. To further elucidate the role of the gut-brain axis in AD, we performed fecal microbiota transplants (FMT) from aged (52-64 weeks) 3xTg-AD mice, modeling plaques and neurofibrillary tangles, to young 3xTg-AD (n=5) or wild-type mice (n=10). Phosphate buffered saline (PBS) was gavaged into 3xTg-AD (n=5) and wild-type mice (n=10) as a control. For FMT, a fecal slurry from aged 3xTg-AD mice was prepared and given to experimental mice via oral gavage. At 8 weeks, mice were gavaged with FMT or PBS for 5 consecutive days, followed by fortnightly maintenance transplants for 24 weeks. The V4 region of the 16S rRNA gene was sequenced on the Illumina MiSeq. Data were analyzed using QIIME 2. Reverse transcriptase qPCR was used to assess microgliosis, astrocytosis, and Th1/Th2 inflammation in the hippocampus of the FMT cohort at 24 weeks of age. Our results show a shift in microbiome composition in FMT-treated mice when compared to control (PBS-treated) mice. Bacteroides were increased in 3xTg-AD and wild-type mice receiving FMT. At 24 weeks of age, there was no difference in neuroinflammation between mice treated with FMT compared to control (PBS) in 3xTg-AD or wild type mice. We observed partial engraftment of the gut microbiota from aged 3xTg-AD mice in all FMT-treated mice. We demonstrate the ability to transplant an aged gut microbiome into young mice, however we did not observe changes in neuroinflammation at 24 weeks of age. Future studies will evaluate neuroinflammation and neuropathologies at later time points. These studies will contribute to our understanding of how features of the gut microbiota may contribute to AD development.

Effects of concentrated ambient ultrafine particulate matter on hallmarks of Alzheimer’s disease in the 3xTgAD mouse model

BackgroundExposure to air pollution has been identified as a possible environmental contributor to Alzheimer’s Disease (AD) risk. As the number of people with AD worldwide continues to rise, it becomes vital to understand the nature of this potential gene-environment interaction. This study assessed the effects of short-term exposures to concentrated ambient ultrafine particulates (UFP, <100 nm) on measurements of amyloid-β, tau, and microglial morphology. MethodsTwo cohorts of aged (12.5–14 months) 3xTgAD and NTg mice were exposed to concentrated ambient UFP or filtered air for 2 weeks (4-h/day, 4 days/week). Bronchoalveolar lavage fluid and brain tissue were collected twenty-four hours following the last exposure to evaluate lung inflammation, tau pathology, amyloid-β pathology, and glial cell morphology. ResultsNo exposure- or genotype-related changes were found with any of the measures of lung inflammation or in the hippocampal staining density of astrocyte marker glial fibrillary acidic protein. The microglia marker, ionized calcium binding adaptor molecule 1, and amyloid-β marker, 6E10, exhibited significant genotype by exposure interactions such that levels were lower in the UFP-exposed as compared to filtered air-exposed 3xTgAD mice. When microglia morphology was assessed by Sholl analysis, microglia from both NTg mouse groups were ramified. The 3xTgAD air-exposed mice had the most ameboid microglia, while the 3xTgAD UFP-exposed mice had microglia that were comparatively more ramified. The 3xTgAD air-exposed mice had more plaques per region of interest as measured by Congo red staining as well as more plaque-associated microglia than the 3xTgAD UFP-exposed mice. The number of non-plaque-associated microglia was not affected by genotype or exposure. Levels of soluble and insoluble human amyloid-β42 protein were measured in both 3xTgAD groups and no exposure effect was found. In contrast, UFP-exposure led to significant elevations in phosphorylated tau in 3xTgAD mice as compared to those that were exposed to air, as measured by pT205 staining. ConclusionsExposure to environmentally relevant levels of ultrafine particulates led to changes in tau phosphorylation and microglial morphology in the absence of overt lung inflammation. Such changes highlight the need to develop greater mechanistic understanding of the link between air pollution exposure and Alzheimer’s disease.

Accumulation of\xa0amyloid precursor protein C-terminal fragments triggers mitochondrial structure, function, and mitophagy defects in Alzheimer\u2019s disease models and human brains

Several lines of recent evidence indicate that the amyloid precursor protein-derived C-terminal fragments (APP-CTFs) could correspond to an etiological trigger of Alzheimer’s disease (AD) pathology. Altered mitochondrial homeostasis is considered an early event in AD development. However, the specific contribution of APP-CTFs to mitochondrial structure, function, and mitophagy defects remains to be established. Here, we demonstrate in neuroblastoma SH-SY5Y cells expressing either APP Swedish mutations, or the β-secretase-derived APP-CTF fragment (C99) combined with β- and γ-secretase inhibition, that APP-CTFs accumulation independently of Aβ triggers excessive mitochondrial morphology alteration (i.e., size alteration and cristae disorganization) associated with enhanced mitochondrial reactive oxygen species production. APP-CTFs accumulation also elicit basal mitophagy failure illustrated by enhanced conversion of LC3, accumulation of LC3-I and/or LC3-II, non-degradation of SQSTM1/p62, inconsistent Parkin and PINK1 recruitment to mitochondria, enhanced levels of membrane and matrix mitochondrial proteins, and deficient fusion of mitochondria with lysosomes. We confirm the contribution of APP-CTFs accumulation to morphological mitochondria alteration and impaired basal mitophagy in vivo in young 3xTgAD transgenic mice treated with γ-secretase inhibitor as well as in adeno-associated-virus-C99 injected mice. Comparison of aged 2xTgAD and 3xTgAD mice indicates that, besides APP-CTFs, an additional contribution of Aβ to late-stage mitophagy activation occurs. Importantly, we report on mitochondrial accumulation of APP-CTFs in human post-mortem sporadic AD brains correlating with mitophagy failure molecular signature. Since defective mitochondria homeostasis plays a pivotal role in AD pathogenesis, targeting mitochondrial dysfunctions and/or mitophagy by counteracting early APP-CTFs accumulation may represent relevant therapeutic interventions in AD.

Microglia facilitate loss of perineuronal nets in the Alzheimer's disease brain.

BackgroundMicroglia, the brain's principal immune cell, are increasingly implicated in Alzheimer's disease (AD), but the molecular interfaces through which these cells contribute to amyloid beta (Aβ)-related neurodegeneration are unclear. We recently identified microglial contributions to the homeostatic and disease-associated modulation of perineuronal nets (PNNs), extracellular matrix structures that enwrap and stabilize neuronal synapses, but whether PNNs are altered in AD remains controversial.MethodsExtensive histological analysis was performed on male and female 5xFAD mice at 4, 8, 12, and 18 months of age to assess plaque burden, microgliosis, and PNNs. Findings were validated in postmortem AD tissue. The role of neuroinflammation in PNN loss was investigated via LPS treatment, and the ability to prevent or rescue disease-related reductions in PNNs was assessed by treating 5xFAD and 3xTg-AD model mice with colony-stimulating factor 1 receptor (CSF1R) inhibitor PLX5622 to deplete microglia.FindingsUtilizing the 5xFAD mouse model and human cortical tissue, we report that PNNs are extensively lost in AD in proportion to plaque burden. Activated microglia closely associate with and engulf damaged nets in the 5xFAD brain, and inclusions of PNN material are evident in mouse and human microglia, while aggrecan, a critical PNN component, deposits within human dense-core plaques. Disease-associated reductions in parvalbumin (PV)+ interneurons, frequently coated by PNNs, are preceded by PNN coverage and integrity impairments, and similar phenotypes are elicited in wild-type mice following microglial activation with LPS. Chronic pharmacological depletion of microglia prevents 5xFAD PNN loss, with similar results observed following depletion in aged 3xTg-AD mice, and this occurs despite plaque persistence.InterpretationWe conclude that phenotypically altered microglia facilitate plaque-dependent PNN loss in the AD brain.FundingThe NIH (NIA, NINDS) and the Alzheimer's Association.

The Accumulation of Tau-Immunoreactive Hippocampal Granules and Corpora Amylacea Implicates Reactive Glia in Tau Pathogenesis during Aging.

SummaryThe microtubule-associated tau protein forms pathological inclusions that accumulate in an age-dependent manner in tauopathies including Alzheimer's disease (AD). Since age is the major risk factor for AD, we examined endogenous tau species that evolve during aging in physiological and diseased conditions. In aged mouse brain, we found tau-immunoreactive clusters embedded within structures that are reminiscent of periodic acid-Schiff (PAS) granules. We showed that PAS granules harbor distinct tau species that are more prominent in 3xTg-AD mice. Epitope profiling revealed hypo-phosphorylated rather than hyper-phosphorylated tau commonly observed in tauopathies. High-resolution imaging and 3D reconstruction suggest a link between tau clusters, reactive astrocytes, and microglia, indicating that early tau accumulation may promote neuroinflammation during aging. Using postmortem human brain, we identified tau as a component of corpora amylacea (CA), age-related structures that are functionally analogous to PAS granules. Overall, our study supports neuroimmune dysfunction as a precipitating event in tau pathogenesis.

Selective memory and behavioral alterations after ambient ultrafine particulate matter exposure in aged 3xTgAD Alzheimer\u2019s disease mice

BackgroundA growing body of epidemiological literature indicates that particulate matter (PM) air pollution exposure is associated with elevated Alzheimer’s disease (AD) risk and may exacerbate AD-related cognitive decline. Of concern is exposure to the ultrafine PM (UFP) fraction (≤100 nm), which deposits efficiently throughout the respiratory tract, has higher rates of translocation to secondary organs, like brain, and may induce inflammatory changes. We, therefore, hypothesize that exposure to UFPs will exacerbate cognitive deficits in a mouse model of AD. The present study assessed alterations in learning and memory behaviors in aged (12.5 months) male 3xTgAD and non-transgenic mice following a 2-week exposure (4-h/day, 4 days/week) to concentrated ambient UFPs using the Harvard ultrafine concentrated ambient particle system (HUCAPS) or filtered air. Beginning one month following exposure, locomotor activity, spatial learning and memory, short-term recognition memory, appetitive motivation, and olfactory discrimination were assessed.ResultsNo effects on locomotor activity were found following HUCAPS exposure (number concentration, 1 × 104–4.7 × 105 particles/cm3; mass concentration, 29–132 μg/m3). HUCAPS-exposed mice, independent of AD background, showed a significantly decreased spatial learning, mediated through reference memory deficits, as well as short-term memory deficits in novel object recognition testing. AD mice displayed diminished spatial working memory, potentially a result of olfactory deficits, and short-term memory. AD background modulated HUCAPS-induced changes on appetitive motivation and olfactory discrimination, specifically enhancing olfactory discrimination in NTg mice. Modeling variation in appetitive motivation as a covariate in spatial learning and memory, however, did not support the conclusion that differences in motivation significantly underlie changes in spatial learning and memory.ConclusionsA short-term inhalation exposure of aged mice to ambient UFPs at human-relevant concentrations resulted in protracted (testing spanning 1–6.5 months post-exposure) adverse effects on multiple memory domains (reference and short-term memory) independent of AD background. Impairments in learning and memory were present when accounting for potential covariates like motivational changes and locomotor activity. These results highlight the need for further research into the potential mechanisms underlying the cognitive effects of UFP exposure in adulthood.

Inhibition of AMD-Like Pathology With a Neurotrophic Compound in Aged Rats and 3xTg-AD Mice.

Age-associated macular degeneration (AMD), which leads to loss of vision at its end stage, is one of the most common neurodegenerative diseases among the elderly. However, to date, no effective drug therapy is available for the prevention of AMD. Here, we report the occurrence of AMD pathology and its prevention by chronic treatment with the neurotrophic peptidergic compound P021, in aged rats and 3xTg-AD mice. We found photoreceptor degeneration, lipofuscin granules, vacuoles, and atrophy in retinal pigment epithelium (RPE) as well as Bruch’s membrane (BM) thickening; in aged rats, we even found rosette-like structure formation. Microgliosis and astrogliosis were observed in different retinal layers. In addition, we also found that total tau, phosphorylated tau, Aβ/APP, and VEGF were widely distributed in the sub-retina of aged rats and 3xTg mice. Importantly, chronic treatment with P021 for 3 months in rats and for 18 months in 3xTg mice ameliorated the pathological changes above. These findings indicate the therapeutic potential of P021 for prevention and treatment of AMD and retinal changes associated with aging and Alzheimer’s disease.

The mitochondria-targeted antioxidant MitoQ inhibits memory loss, neuropathology, and extends lifespan in aged 3xTg-AD mice

Oxidative stress, likely stemming from dysfunctional mitochondria, occurs before major cognitive deficits and neuropathologies become apparent in Alzheimer's disease (AD) patients and in mouse models of the disease. We previously reported that treating 2- to 7-month-old 3xTg-AD mice with the mitochondria-targeted antioxidant MitoQ (mitoquinone mesylate: [10-(4,5-Dimethoxy-2-methyl-3,6-dioxo-1,4-cyclohexadien-1-yl)decyl](triphenyl)phosphonium methanesulfonate), a period when AD-like pathologies first manifest in them, prevents AD-like symptoms from developing. To elucidate further a role for mitochondria-derived oxidative stress in AD progression, we examined the ability of MitoQ to inhibit AD-like pathologies in these mice at an age in which cognitive and neuropathological symptoms have fully developed. 3xTg-AD female mice received MitoQ in their drinking water for five months beginning at twelve months after birth. Untreated 18-month-old 3xTg-AD mice exhibited significant learning deficits and extensive AD-like neuropathologies. MitoQ-treated mice showed improved memory retention compared to untreated 3xTg-AD mice as well as reduced brain oxidative stress, synapse loss, astrogliosis, microglial cell proliferation, Aβ accumulation, caspase activation, and tau hyperphosphorylation. Additionally, MitoQ treatment significantly increased the abbreviated lifespan of the 3xTg-AD mice. These findings support a role for the involvement of mitochondria-derived oxidative stress in the etiology of AD and suggest that mitochondria-targeted antioxidants may lessen symptoms in AD patients.

Motor deficits in 16-month-old male and female 3xTg-AD mice

Motor deficits are some of the most prevalent non-cognitive symptoms of Alzheimer’s disease (AD) with patients showing impairments in speech, gait and fine motor skills. We investigated motor behaviour in 16-month-old male and female 3xTg-AD mice and their B6129SF2 wildtype (WT) controls. The 3xTg-AD mice develop extracellular Aβ plaques and tau tangles in the hippocampus and motor cortex between 6 and 9 months of age. Previously we showed that at 6 months of age, 3xTg-AD mice performed better on tests of motor coordination and motor learning than WT mice. The aim of our experiment was to use a battery of motor behaviour tests to determine if this superior motor performance was present in older mice. On the Rotarod, the aged 3xTg-AD mice showed better motor coordination and learning than WT mice. Although females performed better than males, this sex difference was confounded by body weight as females weighed less than males. There were no significant genotype or sex differences on the wire hang or grid suspension tasks, nor in stride length or stride width, but 3xTg-AD mice performed worse than WT mice on the balance beam. In comparison to the 6-month-old mice, an age-related decline in most aspects of motor behaviour was apparent. These results indicate that different sub-domains of motor function are affected differently in the 3xTg-AD mice and that aging does not have the same effect on all motor behaviours.

TSPO ligand PK11195 improves Alzheimer-related outcomes in aged female 3xTg-AD mice

Alzheimer’s disease (AD) pathogenesis is a multifactorial process that involves numerous pathways within the central nervous system. Thus, interventions that interact with several disease-related pathways may offer an increased opportunity for successful prevention and treatment of AD. Translocator protein 18 kD (TSPO) is a mitochondrial protein that is associated with regulation of many cellular processes including inflammation, steroid synthesis, apoptosis, and mitochondrial respiration. Although TSPO ligands have been shown to be protective in several neurodegenerative paradigms, little work has been done to assess their potential as treatments for AD. Female 3xTg-AD mice were administered the TSPO ligand PK11195 once weekly for 5 weeks beginning at 16 months, an age characterized by extensive β-amyloid pathology and behavioral impairments. Animals treated with PK11195 showed improvements in behavior and modest reductions of in both soluble and deposited β-amyloid. The finding that short-term PK11195 treatment was effective in improving both behavioral and pathological outcomes in a model of late-stage AD supports further investigation of TSPO ligands as potential therapeutics for the treatment of AD.

EFFECT OF ISOFLURANE ON NEUROPATHOLOGY AND COGNITIVE IMPAIRMENT IN THE TRIPLE TRANSGENIC ALZHEIMER’S MOUSE MODEL

This study examines the association between isoflurane mediated effects on neuropathology, cognitive performance, and synaptic physiology in early postnatal and aged triple transgenic Alzheimer's disease (3xTg-AD) mice. Male and female C57BL6/J (NonTg) and 3xTg-AD mice (age: PND 7 and 14+ months) were anesthetized with isoflurane in oxygen/air for 2 hours each day over five consecutive days. Mice from each strain and age groups exposed to just oxygen/air served as controls. Plasma levels of S100β 6 hrs after anesthesia were elevated in both NonTg and 3xTg-AD, which was more profound in the 3xTg-AD mice. Isoflurane increased the number of positive neurons for Aβ deposition and oligomers in 3xTg-AD mice. Morris Water Maze (MWM) test showed that young NonTg and 3xTg-AD mice were slow to learn during reference learning test and performed poorly in short-term and working memory tests compared to age-matched controls. Young 3xTg-AD treated with isoflurane performed significantly worse in these spatial learning tests than the isoflurane-treated NonTg mice. Cognitive impairments in the aged mice were noted in short-term memory test in the aged 3xTg-AD mice and in both strains during the long-term and working memory tests. Extracellular field recordings showed hyperexcitable basal synaptic transmission, unstable LTP, and reduced paired pulse facilitation (PPF) in untreated aged 3xTg-AD mice compared to NonTg mice. Isoflurane depressed basal synaptic transmission, more pronounced in the aged 3xTg-AD group. PPF was significantly reduced in both young and old NonTg and 3xTg-AD mice following isoflurane, but more profound in aged 3xTg-AD mice. Isoflurane impaired LTP in young 3xTg and in both young and aged NonTg mice as reflected in the lack of change in extracellular field potential (fEPSP) slope from baseline. Isoflurane normalized and potentiated fEPSP slope to control levels in aged 3xTg mice . Acute treatment of isoflurane to ex-vivo hippocampal slices from young and aged NonTg and 3xTg-AD mice previously exposed to the same anesthetic in vivo suppressed LTP. Acute application of isoflurane to slices from aged 3xTg-AD mice previously exposed to iso displayed severely reduced LTP. isoflurane-mediated neuropathologic and cognitive defects in AD mice are associated with synaptic pathologies in an age-dependent manner.

Selenomethionine Mitigates Cognitive Decline by Targeting Both Tau Hyperphosphorylation and Autophagic Clearance in an Alzheimer's Disease Mouse Model.

Tau pathology was recently identified as a key driver of disease progression and an attractive therapeutic target in Alzheimer's disease (AD). Selenomethionine (Se-Met), a major bioactive form of selenium (Se) in organisms with significant antioxidant capacity, reduced the levels of total tau and hyperphosphorylated tau and ameliorated cognitive deficits in younger triple transgenic AD (3xTg-AD) mice. Whether Se-Met has a similar effect on tau pathology and the specific mechanism of action in older 3xTg-AD mice remains unknown. Autophagy is a major self-degradative process to maintain cellular homeostasis and function. Autophagic dysfunction has been implicated in the pathogenesis of multiple age-dependent diseases, including AD. Modulation of autophagy has been shown to retard the accumulation of misfolded and aggregated proteins and to delay the progression of AD. Here, we found that 3xTg-AD mice showed significant improvement in cognitive ability after a 3-month treatment with Se-Met beginning at 8 months of age. In addition to attenuating the hyperphosphorylation of tau by modulating the activity of Akt/glycogen synthase kinase-3β and protein phosphatase 2A, Se-Met-induced reduction of tau was also mediated by an autophagy-based pathway. Specifically, Se-Met improved the initiation of autophagy via the AMP-activated protein kinase-mTOR (mammalian target of rapamycin) signaling pathway and enhanced autophagic flux to promote the clearance of tau in 3xTg-AD mice and primary 3xTg neurons. Thus, our results demonstrate for the first time that Se-Met mitigates cognitive decline by targeting both the hyperphosphorylation of tau and the autophagic clearance of tau in AD mice. These data strongly support Se-Met as a potent nutraceutical for AD therapy.SIGNIFICANCE STATEMENT Selenium has been widely recognized as a vital trace element abundant in the brain with effects of antioxidant, anticancer, and anti-inflammation. In this study, we report that selenomethionine rescues spatial learning and memory impairments in aged 3xTg-AD mice via decreasing the level of tau protein and tau hyperphosphorylation. We find that selenomethionine promotes the initiation of autophagy via the AMPK-mTOR pathway and enhances autophagic flux, thereby facilitating tau clearance in vivo and in vitro We have now identified an additional, novel mechanism by which selenomethionine improves the cognitive function of AD mice. Specifically, our data suggest the effect of selenium/selenomethionine on an autophagic pathway in Alzheimer's disease.

BACE1 RNAi Restores the Composition of Phosphatidylethanolamine-Derivates Related to Memory Improvement in Aged 3xTg-AD Mice.

β-amyloid (Aβ) is produced by the β-secretase 1 (BACE1)-mediated enzymatic cleavage of the amyloid precursor protein through the amyloidogenic pathway, making BACE1 a therapeutic target against Alzheimer’s disease (AD). Alterations in lipid metabolism are a risk factor for AD by an unknown mechanism. The objective of this study was to determine the effect of RNA interference against BACE1 (shBACEmiR) on the phospholipid profile in hippocampal CA1 area in aged 3xTg-AD mice after 6 and 12 months of treatment compared to aged PS1KI mice. The shBACEmiR treatment induced cognitive function recovery and restored mainly the fatty acid composition of lysophosphatidylethanolamine and etherphosphatidylethanolamine, reduced the cPLA2’s phosphorylation, down-regulated the levels of arachidonic acid and COX2 in the hippocampi of 3xTg-AD mice. Together, our findings suggest, for the first time, that BACE1 silencing restores phospholipids composition which could favor the recovery of cellular homeostasis and cognitive function in the hippocampus of triple transgenic AD mice.

Increased platelet adhesion and thrombus formation in a mouse model of Alzheimer's disease

Vascular dysfunctions and Alzheimer's disease show significant similarities and overlaps. Cardiovascular risk factors (hypercholesterolemia, hypertension, obesity, atherosclerosis and diabetes) increase the risk of vascular dementia and Alzheimer's disease. Conversely, Alzheimer's patients have considerably increased predisposition of ischemic and hemorrhagic strokes. Platelets are major players in haemostasis and thrombosis and are involved in inflammation. We have investigated morphology and function of platelets in 3xTg-AD animals, a consolidate murine model for Alzheimer's disease. Platelets from aged 3xTg-AD mice are normal in number and glycoprotein expression, but adhere more avidly on matrices such as fibrillar collagen, von Willebrand factor, fibrinogen and amyloid peptides compared to platelets from age-matching wild type mice. 3xTg-AD washed platelets adherent to collagen also show increased phosphorylation of selected signaling proteins, including tyrosine kinase Pyk2, PI3 kinase effector Akt, p38MAP kinase and myosin light chain kinase, and increased ability to form thrombi under shear. In contrast, aggregation and integrin αIIbβ3 activation induced by several agonists in 3xTg-AD mice are similar to wild type platelets. These results demonstrated that Alzheimer's mutations result in a significant hyper-activated state of circulating platelets, evident with the progression of the disease.

β-Secretase 1's Targeting Reduces Hyperphosphorilated Tau, Implying Autophagy Actors in 3xTg-AD Mice.

β-site APP cleaving enzyme 1 (BACE1) initiates APP cleavage, which has been reported to be an inducer of tau pathology by altering proteasome functions in Alzheimer’s disease (AD). However, the exact relationship between BACE1 and PHF (Paired Helical Filaments) formation is not clear. In this study, we confirm that BACE1 and Hsc70 are upregulated in the brains of AD patients, and we demonstrate that both proteins show enhanced expression in lipid rafts from AD-affected triple transgenic mouse brains. BACE1 targeting increased Hsc70 levels in the membrane and cytoplasm fractions and downregulated Hsp90 and CHIP in the nucleus in the hippocampi of 3xTg-AD mice. However, these observations occurred in a proteasome-independent manner in vitro. The BACE1miR-induced reduction of soluble hyperphosphorylated tau was associated with a decrease in MAPK activity. However, the BACE1 RNAi-mediated reduction of hyperphosphorylated tau was only blocked by 3-MA (3-methyladenine) in vitro, and it resulted in the increase of Hsc70 and LAMP2 in lipid rafts from hippocampi of 3xTg-AD mice, and upregulation of survival and homeostasis signaling. In summary, our findings suggest that BACE1 silencing neuroprotects reducing soluble hyperphosphorylated tau, modulating certain autophagy-related proteins in aged 3xTg-AD mice.

Colony-stimulating factor 1 receptor inhibition prevents microglial plaque association and improves cognition in 3xTg-AD mice.

BackgroundMicroglia are dependent upon colony-stimulating factor 1 receptor (CSF1R) signaling for their survival in the adult brain, with administration of the dual CSF1R/c-kit inhibitor PLX3397 leading to the near-complete elimination of all microglia brainwide. Here, we determined the dose-dependent effects of a specific CSF1R inhibitor (PLX5622) on microglia in both wild-type and the 3xTg-AD mouse model of Alzheimer’s disease.MethodsWild-type mice were treated with PLX5622 for up to 21 days, and the effects on microglial numbers were assessed. 3xTg-AD mice were treated with PLX5622 for 6 or 12 weeks and effects on microglial numbers and pathology subsequently assessed.ResultsHigh doses of CSF1R inhibitor eliminate most microglia from the brain, but a 75 % lower-dose results in sustained elimination of ~30 % of microglia in both wild-type and 3xTg-AD mice. No behavioral or cognitive deficits were found in mice either depleted of microglia or treated with lower CSF1R inhibitor concentrations. Aged 3xTg-AD mice treated for 6 or 12 weeks with lower levels of PLX5622 resulted in improved learning and memory. Aβ levels and plaque loads were not altered, but microglia in treated mice no longer associated with plaques, revealing a role for the CSF1R in the microglial reaction to plaques, as well as in mediating cognitive deficits.ConclusionsWe find that inhibition of CSF1R alone is sufficient to eliminate microglia and that sustained microglial elimination is concentration-dependent. Inhibition of the CSF1R at lower levels in 3xTg-AD mice prevents microglial association with plaques and improves cognition.