Intraneuronal Amyloid Beta Accumulation Disrupts Hippocampal CRTC1-Dependent Gene Expression and Cognitive Function in a Rat Model of Alzheimer Disease.
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SUBMITTER: Wilson EN
PROVIDER: S-EPMC5378482 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The prevalence of HIV-1 associated neurocognitive disorders (HAND) is significantly greater in older, relative to younger, HIV-1 seropositive individuals; the neural pathogenesis of HAND in older HIV-1 seropositive individuals, however, remains elusive. To address this knowledge gap, abnormal protein aggregates (i.e., β-amyloid) were investigated in the brains of aging (>12 months of age) HIV-1 transgenic (Tg) rats. In aging HIV-1 Tg rats, double immunohistochemistry staining revealed abnormal intraneuronal β-amyloid accumulation in the prefrontal cortex (PFC) and hippocampus, relative to F344/N control rats. Notably, in HIV-1 Tg animals, increased β-amyloid accumulation occurred in the absence of any genotypic changes in amyloid precursor protein (APP). Furthermore, no clear amyloid plaque deposition was observed in HIV-1 Tg animals. Critically, β-amyloid was co-localized with neurons in the cortex and hippocampus, supporting a potential mechanism underlying synaptic dysfunction in the HIV-1 Tg rat. Consistent with these neuropathological findings, HIV-1 Tg rats exhibited prominent alterations in the progression of temporal processing relative to control animals; temporal processing relies, at least in part, on the integrity of the PFC and hippocampus. In addition, in post-mortem HIV-1 seropositive individuals with HAND, intraneuronal β-amyloid accumulation was observed in the dorsolateral PFC and hippocampal dentate gyrus. Consistent with observations in the HIV-1 Tg rat, no amyloid plaques were found in these post-mortem HIV-1 seropositive individuals with HAND. Collectively, intraneuronal β-amyloid aggregation observed in the PFC and hippocampus of HIV-1 Tg rats supports a potential factor underlying HIV-1 associated synaptodendritic damage. Further, the HIV-1 Tg rat provides a biological system to model HAND in older HIV-1 seropositive individuals.
| S-EPMC9230035 | biostudies-literature
Project description:ObjectiveTo test the hypotheses predicted in a hypothetical model of Alzheimer disease (AD) biomarkers that rates of β-amyloid (Aβ) accumulation on PET imaging are not related to hippocampal neurodegeneration whereas rates of neurodegenerative brain atrophy depend on the presence of both amyloid and neurodegeneration in a population-based sample.MethodsA total of 252 cognitively normal (CN) participants from the Mayo Clinic Study of Aging had 2 or more serial visits with both amyloid PET and MRI. Subjects were classified into 4 groups based on baseline positive/negative amyloid PET (A+ or A-) and baseline hippocampal volume (N+ or N-). We compared rates of amyloid accumulation and rates of brain atrophy among the 4 groups.ResultsAt baseline, 148 (59%) were amyloid negative and neurodegeneration negative (A-N-), 29 (12%) amyloid negative and neurodegeneration positive (A-N+), 56 (22%) amyloid positive and neurodegeneration negative (A+N-), and 19 (8%) amyloid positive and neurodegeneration positive (A+N+). High rates of Aβ accumulation were found in those with abnormal amyloid at baseline and were not influenced by hippocampal neurodegeneration at baseline. In contrast, rates of brain atrophy were greatest in A+N+.ConclusionsWe describe a 2-feature biomarker approach to classifying elderly CN subjects that is complementary to the National Institute on Aging-Alzheimer's Association preclinical staging criteria. Our results support 2 key concepts in a model of the temporal evolution of AD biomarkers. First, the rate of Aβ accumulation is not influenced by neurodegeneration and thus may be a biologically independent process. Second, Aβ pathophysiology increases or catalyzes neurodegeneration.
| S-EPMC4013810 | biostudies-literature
Project description:The amyloid hypothesis suggests that beta-amyloid (Aβ) deposition leads to alterations in neural function and ultimately to cognitive decline in Alzheimer's disease. However, factors that underlie Aβ deposition are incompletely understood. One proposed model suggests that synaptic activity leads to increased Aβ deposition. More specifically, hyperactivity in the hippocampus may be detrimental and could be one factor that drives Aβ deposition. To test this model, we examined the relationship between hippocampal activity during a memory task using fMRI and subsequent longitudinal change in Aβ using PIB-PET imaging in cognitively normal older adults. We found that greater hippocampal activation at baseline was associated with increased Aβ accumulation. Furthermore, increasing Aβ accumulation mediated the influence of hippocampal activation on declining memory performance, demonstrating a crucial role of Aβ in linking hippocampal activation and memory. These findings support a model linking increased hippocampal activation to subsequent Aβ deposition and cognitive decline.
| S-EPMC5325620 | biostudies-literature
Project description:Abnormal folding and aggregation of the microtubule-associated protein, tau, is a hallmark of several neurodegenerative disorders, including Alzheimer's disease (AD). Although normal tau is an intrinsically disordered protein, it does exhibit tertiary structure whereby the N- and C-termini are often in close proximity to each other and to the contiguous microtubule-binding repeat domains that extend C-terminally from the middle of the protein. Unfolding of this paperclip-like conformation might precede formation of toxic tau oligomers and filaments, like those found in AD brain. While there are many ways to monitor tau aggregation, methods to monitor changes in tau folding are not well established. Using full length human 2N4R tau doubly labeled with the Förster resonance energy transfer (FRET) compatible fluorescent proteins, Venus and Teal, on the N- and C-termini, respectively (Venus-Tau-Teal), intensity and lifetime FRET measurements were able to distinguish folded from unfolded tau in living cells independently of tau-tau intermolecular interactions. When expression was restricted to low levels in which tau-tau aggregation was minimized, Venus-Tau-Teal was sensitive to microtubule binding, phosphorylation, and pathogenic oligomers. Of particular interest is our finding that amyloid-β oligomers (AβOs) trigger Venus-Tau-Teal unfolding in cultured mouse neurons. We thus provide direct experimental evidence that AβOs convert normally folded tau into a conformation thought to predominate in toxic tau aggregates. This finding provides further evidence for a mechanistic connection between Aβ and tau at seminal stages of AD pathogenesis.
| S-EPMC7464573 | biostudies-literature
Project description:The prevention or delay of brain senescence would enhance the quality of life for older persons. We investigated the effects of soybean extracts in senescence-accelerated (SAMP10) mice. This mouse is a model of brain senescence with a short life span, cerebral atrophy and cognitive dysfunction. Mice were fed a diet containing soybean extracts from 1 to 12 months of age. The effects of green and yellow soybean extracts were compared with a control diet without soybean extracts. Cognitive functions were higher in aged mice fed green soybean than age-matched control mice and mice fed yellow soybean. We further investigated transcriptome of the SAMP10 hippocampus indicated that expression levels of 36 genes were significantly higher and 19 genes were lower in mice that ingested green soybean than in mice that ingested yellow soybean. Some of the evidences were reconfirmed by real time PCR analysis; the levels of Cdh1 and Ptgds mRNA were significantly higher and that the level of Aplp1 was significantly lower in aged SAMP10 mice fed green soybean than mice ingested yellow soybean and control mice. Additionally, the amount of amyloid beta 40 and 42 was lower in the insoluble fraction of aged SAMP10 mice fed green soybean than control mice and mice fed yellow soybean, although the levels of amyloid beta 40 and 42 in the soluble fraction were not different. Lipocalin-type prostaglandin D2 synthase (L-PGDS) has been proposed as the endogenous amyloid beta - chaperone, suggesting that amyloid aggregation was lower in mice fed green soybean than control mice and mice fed yellow soybean. These results indicate that the intake of green soybean improved cognitive function in aged mice, and suppressed amyloid beta accumulation. Green soybean might help healthy aging of the brain in older persons. The effect of green and yellow soybean extracts on cognitive function in aged SAMP10 mice. Mice were fed a CE-2 diet containing 3.0% soybean extracts taken from both yellow and green soybean species, from 1 to 12 months of age. Total RNA was extracted from the stored hippocampus for DNA microarray analysis.
2014-06-26 | E-GEOD-58811 | biostudies-arrayexpress
Project description:The apolipoprotein (apo) E4 isoform is the strongest risk factor for late-onset Alzheimer's disease (AD). ApoE4 is more susceptible to proteolysis than apoE2 and apoE3 isoforms and carboxyl-terminal truncated apoE4 forms have been found in AD patients' brain. We have previously shown that a specific apoE4 fragment, apoE4-165, promotes amyloid-peptide beta 42 (Aβ42) accumulation in human neuroblastoma SK-N-SH cells and increased intracellular reactive oxygen species formation, two events considered to occur early in AD pathogenesis. Here, we show that these effects are allele-dependent and absolutely require the apoE4 background. Furthermore, the exact length of the fragment is critical since longer or shorter length carboxyl-terminal truncated apoE4 forms do not elicit the same effects. Structural and thermodynamic analyses showed that apoE4-165 has a compact structure, in contrast to other carboxyl-terminal truncated apoE4 forms that are instead destabilized. Compared however to other allelic backgrounds, apoE4-165 is structurally distinct and less thermodynamically stable suggesting that the combination of a well-folded structure with structural plasticity is a unique characteristic of this fragment. Overall, our findings suggest that the ability of apoE fragments to promote Aβ42 intraneuronal accumulation is specific for both the apoE4 isoform and the particular structural and thermodynamic properties of the fragment.
| S-EPMC4967930 | biostudies-literature
Project description:Alzheimer's disease is an irreversible neurodegenerative disorder that is characterized by the abnormal aggregation of amyloid-β into neurotoxic oligomers and plaques. Although many disease-modifying molecules are currently in Alzheimer clinical trials, a small molecule that inhibits amyloid-β aggregation and ameliorates the disorder has not been approved to date. Herein, we report the effects of a potent small molecule, 6-methoxy-2-(4-dimethylaminostyryl) benzofuran (KMS88009), that directly disrupts amyloid-β oligomerization, preserving cognitive behavior when used prophylactically and reversing declines in cognitive behavior when used therapeutically. KMS88009 exhibited excellent pharmacokinetic profiles with extensive brain uptake and a high level of safety. When orally administered before and after the onset of Alzheimer's disease symptoms, KMS88009 significantly reduced assembly of amyloid-β oligomers and improved cognitive behaviors in the APP/PS1 double transgenic mouse model. The unique dual mode of action indicates that KMS88009 may be a powerful therapeutic candidate for the treatment of Alzheimer's disease.
| S-EPMC3997483 | biostudies-literature
Project description:Genome-wide association studies (GWAS) have identified genes in lipid metabolism,inflammation and vesicular trafficking pathways as risk factors for late onset Alzheimer disease (LOAD). The mechanism by which they cause AD and their relationship to the amyloid cascade affected by genes causing early onset familial AD is unknown. Unproven hypotheses are that these LOAD genes modulate the amyloid cascade itself or downstream targets affected by this cascade.If so, it is likely that these genes and/or other genes in the same pathways may show alterations in their expression as an early consequence of misprocessing of amyloid precursor protein (APP) and accumulation of amyloid β-peptides (Aβ). We report that in three independent APP transgenic mouse models of AD, multiple genes in lipid and inflammation pathways show very early changes in mRNA and protein expression. Many of these changes are reversed by treatment with LXR agonists, which regulate transcription of genes in lipid/inflammation pathways, and which we have previously shown can reverse the cognitive deficits and neuropathology in Tg2756 mice. These results suggest that changes in lipid and inflammation pathways are likely to be very early consequences of APP misprocessing and Aβ accumulation in AD. Moreover, genetic variants within these pathways might affect risk for AD by modulating this early response. These pathways are likely to contain biomarkers of early disease and targets for therapies. TgCRND8 mice and wild-type littermate controls at ages 70, 80, and 150 days (n = 4 mice per cohort) were used in the study.
2014-08-12 | E-GEOD-31372 | biostudies-arrayexpress
Project description:Amyloid beta (Aβ), the hallmark of Alzheimer's Disease (AD), now appears to be deleterious in its low number aggregate form as opposed to the macroscopic Aβ fibers historically seen postmortem. While Alzheimer targets, such as the tau protein, amyloid precursor protein (APP) processing, and immune system activation continue to be investigated, the recent discovery that amyloid beta aggregates at lipid rafts and likely forms neurotoxic pores has led to a new paradigm regarding why past therapeutics may have failed and how to design the next round of compounds for clinical trials. An atomic resolution understanding of Aβ aggregates, which appear to exist in multiple conformations, is most desirable for future therapeutic development. The investigative difficulties, structures of these small Aβ aggregates, and current therapeutics are summarized in this review.
| S-EPMC4797837 | biostudies-literature
Project description:BackgroundMany identified mechanisms could be upstream of the prominent amyloid-β (Aβ) plaques in Alzheimer's disease (AD).ObjectiveTo profile the progression of pathology in AD.MethodsWe monitored metabolic signaling, redox stress, intraneuronal amyloid-β (iAβ) accumulation, and extracellular plaque deposition in the brains of 3xTg-AD mice across the lifespan.ResultsIntracellular accumulation of aggregated Aβ in the CA1 pyramidal cells at 9 months preceded extracellular plaques that first presented in the CA1 at 16 months of age. In biochemical assays, brain glutathione (GSH) declined with age in both 3xTg-AD and non-transgenic controls, but the decline was accelerated in 3xTg-AD brains from 2 to 4 months. The decline in GSH correlated exponentially with the rise in iAβ. Integrated metabolic signaling as the ratio of phospho-Akt (pAkt) to total Akt (tAkt) in the PI3kinase and mTOR pathway declined at 6, 9, and 12 months, before rising at 16 and 20 months. These pAkt/tAkt ratios correlated with both iAβ and GSH levels in a U-shaped relationship. Selective vulnerability of age-related AD-genotype-specific pAkt changes was greatest in the CA1 pyramidal cell layer. To demonstrate redox causation, iAβ accumulation was lowered in cultured middle-age adult 3xTg-AD neurons by treatment of the oxidized redox state in the neurons with exogenous cysteine.ConclusionThe order of pathologic progression in the 3xTg-AD mouse was loss of GSH (oxidative redox shift) followed by a pAkt/tAkt metabolic shift in CA1, iAβ accumulation in CA1, and extracellular Aβ deposition. Upstream targets may prove strategically more effective for therapy before irreversible changes.
| S-EPMC9789488 | biostudies-literature