Behavioral stress fails to accelerate the onset and progression of plaque pathology in the brain of a mouse model of Alzheimer's disease.
ABSTRACT: Conflicting findings exist regarding the link between environmental factors and development of Alzheimer's disease (AD) in a variety of transgenic mouse models of AD. In the present study, we investigated the effect of behavioral stress on the onset and progression of A? pathology in the brains of TgCRND8 mice, a transgenic mouse model of AD. One group of TgCRND8 mice was subjected to restraint stress starting at 1 month of age until they were 3 months old, while restraint stress in the second group started at 4 months of age until they were 6 months old. After 2 months of treatment, no differences in the soluble, formic acid extracted, or histologically detected A? deposition in the cortical and hippocampal levels were found between non-stressed and stressed mice. These results showed that restraint stress alone failed to aggravate amyloid pathology when initiated either before or after the age of amyloid plaque deposition in TgCRND8 mice, suggesting that if stress aggravated AD phenotype, it may not be via an amyloid-related mechanism in the TgCRND8 mice. These findings are indicative that plaque load per se may not be used as a significant criterion for evaluating the effect of stress on AD patients.
Project description:Alzheimer's disease (AD) is a chronic neurodegenerative disease with pathological hallmarks including the formation of extracellular aggregates of amyloid-beta (A?) known as plaques and intracellular tau tangles. Coincident with the formation of A? plaques is recruitment and activation of glial cells to the plaque forming a plaque niche. In addition to histological data showing the formation of the niche, AD genetic studies have added to the growing appreciation of how dysfunctional glia pathways drive neuropathology, with emphasis on microglia pathways. Genomic approaches enable comparisons of human disease profiles between different mouse models informing on their utility to evaluate secondary changes to triggers such as A? deposition.In this study, we utilized two animal models of AD to examine and characterize the AD-associated pathology: the Tg2576 Swedish APP (KM670/671NL) and TgCRND8 Swedish plus Indiana APP (KM670/671NL?+?V717F) lines. We used laser capture microscopy (LCM) to isolate samples surrounding Thio-S positive plaques from distal non-plaque tissue. These samples were then analyzed using RNA sequencing.We determined age-associated transcriptomic differences between two similar yet distinct APP transgenic mouse models, known to differ in proportional amyloidogenic species and plaque deposition rates. In Tg2576, human AD gene signatures were not observed despite profiling mice out to 15 months of age. TgCRND8 mice however showed progressive and robust induction of lysomal, neuroimmune, and ITIM/ITAM-associated gene signatures overlapping with prior human AD brain transcriptomic studies. Notably, RNAseq analyses highlighted the vast majority of transcriptional changes observed in aging TgCRND8 cortical brain homogenates were in fact specifically enriched within the plaque niche samples. Data uncovered plaque-associated enrichment of microglia-related genes such as ITIM/ITAM-associated genes and pathway markers of phagocytosis.This work may help guide improved translational value of APP mouse models of AD, particularly for strategies aimed at targeting neuroimmune and neurodegenerative pathways, by demonstrating that TgCRND8 more closely recapitulates specific human AD-associated transcriptional responses.
Project description:In addition to cognitive decline, individuals affected by Alzheimer's disease (AD) can experience important neuropsychiatric symptoms including sleep disturbances. We characterized the sleep-wake cycle in the TgCRND8 mouse model of AD, which overexpresses a mutant human form of amyloid precursor protein resulting in high levels of ?-amyloid and plaque formation by 3 months of age. Polysomnographic recordings in freely-moving mice were conducted to study sleep-wake cycle architecture at 3, 7 and 11 months of age and corresponding levels of ?-amyloid in brain regions regulating sleep-wake states were measured. At all ages, TgCRND8 mice showed increased wakefulness and reduced non-rapid eye movement (NREM) sleep during the resting and active phases. Increased wakefulness in TgCRND8 mice was accompanied by a shift in the waking power spectrum towards fast frequency oscillations in the beta (14-20 Hz) and low gamma range (20-50 Hz). Given the phenotype of hyperarousal observed in TgCRND8 mice, the role of noradrenergic transmission in the promotion of arousal, and previous work reporting an early disruption of the noradrenergic system in TgCRND8, we tested the effects of the alpha-1-adrenoreceptor antagonist, prazosin, on sleep-wake patterns in TgCRND8 and non-transgenic (NTg) mice. We found that a lower dose (2 mg/kg) of prazosin increased NREM sleep in NTg but not in TgCRND8 mice, whereas a higher dose (5 mg/kg) increased NREM sleep in both genotypes, suggesting altered sensitivity to noradrenergic blockade in TgCRND8 mice. Collectively our results demonstrate that amyloidosis in TgCRND8 mice is associated with sleep-wake cycle dysfunction, characterized by hyperarousal, validating this model as a tool towards understanding the relationship between ?-amyloid overproduction and disrupted sleep-wake patterns in AD.
Project description:Proinflammatory stimuli, after amyloid beta (Abeta) deposition, have been hypothesized to create a self-reinforcing positive feedback loop that increases amyloidogenic processing of the Abeta precursor protein (APP), promoting further Abeta accumulation and neuroinflammation in Alzheimer's disease (AD). Interleukin-6 (IL-6), a proinflammatory cytokine, has been shown to be increased in AD patients implying a pathological interaction. To assess the effects of IL-6 on Abeta deposition and APP processing in vivo, we overexpressed murine IL-6 (mIL-6) in the brains of APP transgenic TgCRND8 and TG2576 mice. mIL-6 expression resulted in extensive gliosis and concurrently attenuated Abeta deposition in TgCRND8 mouse brains. This was accompanied by up-regulation of glial phagocytic markers in vivo and resulted in enhanced microglia-mediated phagocytosis of Abeta aggregates in vitro. Further, mIL-6-induced neuroinflammation had no effect on APP processing in TgCRND8 and had no effect on APP processing or steady-state levels of Abeta in young Tg2576 mice. These results indicate that mIL-6-mediated reactive gliosis may be beneficial early in the disease process by potentially enhancing Abeta plaque clearance rather than mediating a neurotoxic feedback loop that exacerbates amyloid pathology. This is the first study that methodically dissects the contribution of mIL-6 with regard to its potential role in modulating Abeta deposition in vivo.
Project description:Recent evidence emphasizes the role of dysregulated one-carbon metabolism in Alzheimer's Disease (AD). Exploiting a nutritional B-vitamin deficiency paradigm, we have previously shown that PSEN1 and BACE1 activity is modulated by one-carbon metabolism, leading to increased amyloid production. We have also demonstrated that S-adenosylmethionine (SAM) supplementation contrasted the AD-like features, induced by B-vitamin deficiency. In the present study, we expanded these observations by investigating the effects of SAM and SOD (Superoxide dismutase) association. TgCRND8 AD mice were fed either with a control or B-vitamin deficient diet, with or without oral supplementation of SAM + SOD. We measured oxidative stress by lipid peroxidation assay, PSEN1 and BACE1 expression by Real-Time Polymerase Chain Reaction (PCR), amyloid deposition by ELISA assays and immunohistochemistry. We found that SAM + SOD supplementation prevents the exacerbation of AD-like features induced by B vitamin deficiency, showing synergistic effects compared to either SAM or SOD alone. SAM + SOD supplementation also contrasts the amyloid deposition typically observed in TgCRND8 mice. Although the mechanisms underlying the beneficial effect of exogenous SOD remain to be elucidated, our findings identify that the combination of SAM + SOD could be carefully considered as co-adjuvant of current AD therapies.
Project description:Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive decline. Deep brain stimulation (DBS) has been used to treat a variety of brain disorders and shows promise in alleviating cognitive symptoms in some AD patients (Laxton et al, 2010). We previously showed that DBS of the entorhinal cortex (EC) enhances spatial memory formation in normal (wild-type) mice (Stone et al, 2011). Here we tested the effects of EC-DBS on the progressive cognitive deficits in a genetically-based mouse model of AD. TgCRND8 (Tg) transgenic mice express human amyloid precursor protein harboring the Swedish and Indiana familial AD mutations. These mice exhibit age-related increases in A? production, plaque deposition, as well as contextual fear and spatial memory impairments. Here, we found EC stimulation in young mice (6 weeks old) rescued the early contextual fear and spatial memory deficits and decreased subsequent plaque load in Tg mice. Moreover, stimulation in older mice (6 months old) was also sufficient to rescue the memory deficits in Tg mice. The memory enhancement induced by DBS emerged gradually (over the course of weeks) and was both persistent and specific to hippocampal-based memories. These results provide further support for the development of novel therapeutics aimed to resolve the cognitive decline and memory impairment in AD using DBS of hippocampal afferents.
Project description:Alzheimer's disease (AD) is characterized by neuronal atrophy caused by soluble amyloid beta protein (Abeta) peptide "oligomers" and a microglial-mediated inflammatory response elicited by extensive amyloid deposition in the brain. We show that CNI-1493, a tetravalent guanylhydrazone with established antiinflammatory properties, interferes with Abeta assembly and protects neuronal cells from the toxic effect of soluble Abeta oligomers. Administration of CNI-1493 to TgCRND8 mice overexpressing human amyloid precursor protein (APP) for a treatment period of 8 wk significantly reduced Abeta deposition. CNI-1493 treatment resulted in 70% reduction of amyloid plaque area in the cortex and 87% reduction in the hippocampus of these animals. Administration of CNI-1493 significantly improved memory performance in a cognition task compared with vehicle-treated mice. In vitro analysis of CNI-1493 on APP processing in an APP-overexpressing cell line revealed a significant dose-dependent decrease of total Abeta accumulation. This study indicates that the antiinflammatory agent CNI-1493 can ameliorate the pathophysiology and cognitive defects in a murine model of AD.
Project description:Mitochondrial dysfunction and oxidative stress are involved in Alzheimer disease (AD) pathogenesis. In human AD brains, the activity of the alpha-ketoglutarate dehydrogenase enzyme complex (alpha-KGDHC) is reduced. KGDHC is mostly involved in NADH production. It can also participate in oxidative stress and reactive oxygen species (ROS) production. The mitochondrial dihydrolipoyl succinyltransferase enzyme (DLST) is a key subunit specific to the alpha-KGDHC. In cultured cells, reduction of DLST increased H(2)O(2)-induced ROS generation and cell death. Thus, we asked whether partial genetic deletion of DLST could accelerate the onset of AD pathogenesis, using a transgenic mouse model of amyloid deposition crossed with DLST(+/-) mice. Tg19959 mice, which carry the human amyloid precursor protein with two mutations, develop amyloid deposits and progressive behavioral abnormalities. We compared Tg19959 mice to Tg19959-DLST(+/-) littermates at 2-3 months of age and studied the effects of DLST deficiency on amyloid deposition, spatial learning and memory, and oxidative stress. We found that alpha-KGDHC activity was reduced in DLST(+/-) mice. We also found that DLST deficiency increased amyloid plaque burden, Abeta oligomers, and nitrotyrosine levels and accelerated the occurrence of spatial learning and memory deficits in female Tg19959 mice. Our data suggest that alpha-KGDHC may be involved in AD pathogenesis through increased mitochondrial oxidative stress.
Project description:Alzheimer's disease (AD) is a neurodegenerative pathology commonly characterized by a progressive and irreversible deterioration of cognitive functions, especially memory. Although the etiology of AD remains unknown, a consensus has emerged on the amyloid hypothesis, which posits that increased production of soluble amyloid ? (A?) peptide induces neuronal network dysfunctions and cognitive deficits. However, the relative failures of A?-centric therapeutics suggest that the amyloid hypothesis is incomplete and/or that the treatments were given too late in the course of AD, when neuronal damages were already too extensive. Hence, it is striking to see that very few studies have extensively characterized, from anatomy to behavior, the alterations associated with pre-amyloid stages in mouse models of AD amyloid pathology. To fulfill this gap, we examined memory capacities as well as hippocampal network anatomy and dynamics in young adult pre-plaque TgCRND8 mice when hippocampal A? levels are still low. We showed that TgCRND8 mice present alterations in hippocampal inhibitory networks and ? oscillations at this stage. Further, these mice exhibited deficits only in a subset of hippocampal-dependent memory tasks, which are all affected at later stages. Last, using a pharmacological approach, we showed that some of these early memory deficits were A?-independent. Our results could partly explain the limited efficacy of A?-directed treatments and favor multitherapy approaches for early symptomatic treatment for AD.
Project description:Alzheimer’s disease (AD) is a common form of dementia characterized by amyloid plaque deposition, TAU pathology, neuroinflammation and neurodegeneration. Mouse models recapitulate some key features of AD. For instance, the B6.APP/PS1 model (carrying human transgenes for mutant forms of APP and PSEN1) shows plaque deposition and associated neuroinflammatory responses involving both astrocytes and microglia beginning around 6 months of age. However, in our colony, TAU pathology, significant neurodegeneration and cognitive decline are not apparent in this model even at older ages. Therefore, this model is ideal for studying neuroinflammatory responses to amyloid deposition. Here, RNA sequencing of brain and retinal tissue, generalized linear modeling (GLM), functional annotation followed by validation by immunofluorescence (IF) was performed in B6.APP/PS1 mice to determine the earliest molecular changes prior to and around the onset of plaque deposition (2-6 months of age). Overall design: Brain transcriptomes of 2, 4, 5 and 6-month old, and retina transcriptomes from 2 and 6-month old wild type (WT) and APP/PS1 female mice from C57BL/6J (B6) were generated.
Project description:Fibrillar amyloid ? (fA?) peptide is the major component of A? plaques in the brains of Alzheimer's disease (AD) patients. Inflammatory mediators have previously been proposed to be drivers of A? pathology in AD patients by increasing amyloidogenic processing of APP and promoting A? accumulation, but recent data have shown that expression of various inflammatory cytokines attenuates A? pathology in mouse models. In an effort to further study the role of different inflammatory cytokines on A? pathology in vivo, we explored the effect of murine Tumor Necrosis Factor ? (mTNF?) in regulating A? accumulation. Recombinant adeno-associated virus serotype 1 (AAV2/1) mediated expression of mTNF? in the hippocampus of 4 month old APP transgenic TgCRND8 mice resulted in significant reduction in hippocampal A? burden. No changes in APP levels or APP processing were observed in either mTNF? expressing APP transgenic mice or in non-transgenic littermates. Analysis of A? plaque burden in mTNF? expressing mice showed that even after substantial reduction compared to EGFP expressing age-matched controls, the A? plaque burden levels of the former do not decrease to the levels of 4 month old unmanipulated mice. Taken together, our data suggests that proinflammatory cytokine expression induced robust glial activation can attenuate plaque deposition. Whether such an enhanced microglial response actually clears preexisting deposits without causing bystander neurotoxicity remains an open question.