Alzheimer's Disease Mouse Brain Research Articles

11C-labelled PIB analogues as potential tracer agents for in vivo imaging of amyloid β in Alzheimer's disease

Pittsburgh Compound-B (PIB) is currently being evaluated clinically for in vivo visualization of amyloid plaques in patients with Alzheimer's disease (AD). We have synthesized three structural isomers of 6-hydroxy-2-(4′-aminophenyl)-1,3-benzothiazole, performed radiolabelling with carbon-11 and investigated their in vivo and in vitro properties. Specific binding to amyloid plaques was demonstrated in vitro using post-mortem brain homogenates of AD patients, transgenic AD mice brain sections and post-mortem human AD brain sections. In normal mice, initial brain uptake (at 2 min p.i.) was high and was followed by a fast wash-out. The three structural analogues have a high potential as tracer agents for in vivo visualization of amyloid plaques in AD patients.

Toll-like receptor 4-dependent upregulation of cytokines in a transgenic mouse model of Alzheimer's disease

BackgroundAβ deposits in the brains of patients with Alzheimer's disease (AD) are closely associated with innate immune responses such as activated microglia and increased cytokines. Accumulating evidence supports the hypothesis that innate immune/inflammatory responses play a pivotal role in the pathogenesis of AD: either beneficial or harmful effects on the AD progression. The molecular mechanisms by which the innate immune system modulates the AD progression are not well understood. Toll-like receptors (TLRs) are first-line molecules for initiating the innate immune responses. When activated through TLR signaling, microglia respond to pathogens and damaged host cells by secreting chemokines and cytokines and express the co-stimulatory molecules needed for protective immune responses to pathogens and efficient clearance of damaged tissues. We previously demonstrated that an AD mouse model homozygous for a destructive mutation of TLR4 has increases in diffuse and fibrillar Aβ deposits as well as buffer-soluble and insoluble Aβ in the brain as compared with a TLR4 wild-type AD mouse model. Here, we investigated the roles of TLR4 in Aβ-induced upregulation of cytokines and chemokines, Aβ-induced activation of microglia and astrocytes and Aβ-induced immigration of leukocytes.MethodsUsing the same model, levels of cytokines and chemokines in the brain were determined by multiplex cytokine/chemokine array. Activation of microglia and astrocytes and immigration of leukocytes were determined by immunoblotting and immunohistochemistry followed by densitometry and morphometry, respectively.ResultsLevels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-10 and IL-17 in the brains of TLR4 wild-type AD mice were significantly higher than those in TLR4 wild-type non-transgenic littermates. Such increases in cytokines were not found in TLR4 mutant AD mice as compared with TLR4 mutant non-transgenic littermates. Although expression levels of CD11b (a microglia marker) and GFAP (a reactive astrocyte marker) in the brains of TLR4 mutant AD mice were higher than those in TLR4 wild type AD mice, no difference was found in levels of CD45 (common leukocyte antigen).ConclusionThis is the first demonstration of TLR4-dependent upregulation of cytokines in an AD mouse model. Our results suggest that TLR4 signaling is involved in AD progression and that TLR4 signaling can be a new therapeutic target for AD.

Transgenic mice overexpressing reticulon 3 develop neuritic abnormalities

Dystrophic neurites are swollen dendrites or axons recognizable near amyloid plaques as a part of important pathological feature of Alzheimer's disease (AD). We report herein that reticulon 3 (RTN3) is accumulated in a distinct population of dystrophic neurites named as RTN3 immunoreactive dystrophic neurites (RIDNs). The occurrence of RIDNs is concomitant with the formation of high-molecular-weight RTN3 aggregates in brains of AD cases and mice expressing mutant APP. Ultrastructural analysis confirms accumulation of RTN3-containing aggregates in RIDNs. It appears that the protein level of RTN3 governs the formation of RIDNs because transgenic mice expressing RTN3 will develop RIDNs, initially in the hippocampal CA1 region, and later in other hippocampal and cortical regions. Importantly, we show that the presence of dystrophic neurites in Tg-RTN3 mice causes impairments in spatial learning and memory, as well as synaptic plasticity, implying that RIDNs potentially contribute to AD cognitive dysfunction. Together, we demonstrate that aggregation of RTN3 contributes to AD pathogenesis by inducing neuritic dystrophy. Inhibition of RTN3 aggregation is likely a therapeutic approach for reducing neuritic dystrophy.

Pyrrolidine Dithiocarbamate Activates Akt and Improves Spatial Learning in APP/PS1 Mice without Affecting β-Amyloid Burden

Pyrrolidine dithiocarbamate (PDTC) is a clinically tolerated inhibitor of nuclear factor-kappaB (NF-kappaB), antioxidant and antiinflammatory agent, which provides protection in brain ischemia models. In neonatal hypoxia-ischemia model, PDTC activates Akt and reduces activation of glycogen synthase kinase 3beta (GSK-3beta). Because chronic inflammation, oxidative stress, and increased GSK-3beta activity are features of Alzheimer's disease (AD) pathology, we tested whether PDTC reduces brain pathology and improves cognitive function in a transgenic animal model of AD. A 7 month oral treatment with PDTC prevented the decline in cognition in AD mice without altering beta-amyloid burden or gliosis. Moreover, marked oxidative stress and activation of NF-kappaB were not part of the brain pathology. Instead, the phosphorylated form of GSK-3beta was decreased in the AD mouse brain, and PDTC treatment increased the phosphorylation of Akt and GSK-3beta. Also, PDTC treatment increased the copper concentration in the brain. In addition, PDTC rescued cultured hippocampal neurons from the toxicity of oligomeric Abeta and reduced tau phosphorylation in the hippocampus of AD mice. Finally, astrocytic glutamate transporter GLT-1, known to be regulated by Akt pathway, was decreased in the transgenic AD mice but upregulated back to the wild-type levels by PDTC treatment. Thus, PDTC may improve spatial learning in AD by interfering with Akt-GSK pathway both in neurons and astrocytes. Because PDTC is capable of transferring external Cu2+ into a cell, and, in turn, Cu2+ is able to activate Akt, we hypothesize that PDTC provides the beneficial effect in transgenic AD mice through Cu2+-activated Akt pathway.

Deposition of mouse amyloid β in human APP/PS1 double and single AD model transgenic mice

The deposition of amyloid beta (Abeta) peptides and neurofibrillary tangles are the two characteristic pathological features of Alzheimer's disease (AD). To investigate the relation between amyloid precursor protein (APP) production, amyloid beta deposition and the type of Abeta in deposits, i.e., human and/or mouse, we performed a histopathological analysis, using mouse and human specific antibodies, of the neocortex and hippocampus in 6, 12 and 19 months old APP/PS1 double and APP and PS1 single transgenic mice. There was a significant correlation between the human amyloid beta deposits and the intrinsic rodent amyloid beta deposits, that is, all plaques contained both human and mouse Abeta, and the diffuse amyloid beta deposits also colocalized human and mouse Abeta. Furthermore, some blood vessels (mainly leptomeningeal vessels) show labeling with human Abeta, and most of these vessels also label with mouse Abeta. Our findings demonstrate that the human amyloid deposits in APP/PS1 transgenic mice are closely associated with mouse Abeta, however, they do not precisely overlap. For instance, the core of plaques consists of primarily human Abeta, whereas the rim of the plaque contains both human and mouse amyloid beta, similarly, human and mouse Abeta are differentially localized in the blood vessel wall. Finally, as early as amyloid beta deposits can be detected, they show the presence of both human and mouse Abeta. Together, these data indicate that mouse Abeta is formed and deposited in significant amounts in the AD mouse brain and that it is deposited together with the human Abeta.

The creatine kinase/creatine connection to Alzheimer's disease: CK-inactivation, APP-CK complexes and focal creatine deposits.

Cytosolic brain-type creatine kinase (BB-CK), which is coexpressed with ubiquitous mitochondrial uMtCK, is significantly inactivated by oxidation in Alzheimer's disease (AD) patients. Since CK has been shown to play a fundamental role in cellular energetics of the brain, any disturbance of this enzyme may exasperate the AD disease process. Mutations in amyloid precursor protein (APP) are associated with early onset AD and result in abnormal processing of APP, and accumulation of Aβ peptide, the main constituent of amyloid plaques in AD brain. Recent data on a direct interaction between APP and the precursor of uMtCK support an emerging relationship between AD, cellular energy levels, and mitochondrial function. In addition, recently discovered creatine (Cr) deposits in the brain of transgenic AD mice, as well as in the hippocampus from AD patients, indicate a direct link between perturbed energy state, Cr metabolism, and AD. Here, we review the roles of Cr and Cr-related enzymes and consider the potential value of supplementation with Cr, a potent neuroprotective substance. As a hypothesis, we consider whether Cr, if given at an early time point of the disease, may prevent or delay the course of AD-related neurodegeneration.

Amyloid‐β induces disulfide bonding and aggregation of GAPDH in Alzheimer's disease

GAPDH is a redox-sensitive glycolytic enzyme that also promotes apoptosis when translocated to the nucleus and associates with aggregate-prone proteins involved in neurodegenerative disorders. Recent evidence indicates that polymorphic variation within GAPDH genes is associated with an elevated risk of developing Alzheimer's disease (AD). We previously demonstrated that GAPDH readily undergoes disulfide bonding following oxidant exposure, although the consequence of disulfide bonding on GAPDH activity or function is unknown. Here we show that increased GAPDH disulfide bonding is observed in detergent-insoluble extracts from AD patient and transgenic AD mouse brain tissue compared with age-matched controls. Exposure of primary rat cortical neurons to the pro-oxidant amyloid beta peptide promotes nuclear accumulation of a disulfide-linked form of GAPDH, which becomes detergent-insoluble. Disulfide bonding leads to a reduction in GAPDH enzymatic activity and correlates with the appearance of punctate aggregate-like GAPDH staining within the cytoplasm of both oxidant-treated HT22 cells and amyloid beta-treated primary cortical neurons. Our findings suggest that disulfide bonding of GAPDH and subsequent protein aggregate formation may have relevance to the pathophysiology of AD.

Curcumin Inhibits Formation of Amyloid β Oligomers and Fibrils, Binds Plaques, and Reduces Amyloid in Vivo

Alzheimer's disease (AD) involves amyloid beta (Abeta) accumulation, oxidative damage, and inflammation, and risk is reduced with increased antioxidant and anti-inflammatory consumption. The phenolic yellow curry pigment curcumin has potent anti-inflammatory and antioxidant activities and can suppress oxidative damage, inflammation, cognitive deficits, and amyloid accumulation. Since the molecular structure of curcumin suggested potential Abeta binding, we investigated whether its efficacy in AD models could be explained by effects on Abeta aggregation. Under aggregating conditions in vitro, curcumin inhibited aggregation (IC(50) = 0.8 microM) as well as disaggregated fibrillar Abeta40 (IC(50) = 1 microM), indicating favorable stoichiometry for inhibition. Curcumin was a better Abeta40 aggregation inhibitor than ibuprofen and naproxen, and prevented Abeta42 oligomer formation and toxicity between 0.1 and 1.0 microM. Under EM, curcumin decreased dose dependently Abeta fibril formation beginning with 0.125 microM. The effects of curcumin did not depend on Abeta sequence but on fibril-related conformation. AD and Tg2576 mice brain sections incubated with curcumin revealed preferential labeling of amyloid plaques. In vivo studies showed that curcumin injected peripherally into aged Tg mice crossed the blood-brain barrier and bound plaques. When fed to aged Tg2576 mice with advanced amyloid accumulation, curcumin labeled plaques and reduced amyloid levels and plaque burden. Hence, curcumin directly binds small beta-amyloid species to block aggregation and fibril formation in vitro and in vivo. These data suggest that low dose curcumin effectively disaggregates Abeta as well as prevents fibril and oligomer formation, supporting the rationale for curcumin use in clinical trials preventing or treating AD.

Intracellular Aβ42 activates p53 promoter: a pathway to neurodegeneration in Alzheimer's disease

The amyloid beta-protein (Abeta) ending at 42 plays a pivotal role in Alzheimer's disease (AD). We have reported previously that intracellular Abeta42 is associated with neuronal apoptosis in vitro and in vivo. Here, we show that intracellular Abeta42 directly activated the p53 promoter, resulting in p53-dependent apoptosis, and that intracellular Abeta40 had a similar but lesser effect. Moreover, oxidative DNA damage induced nuclear localization of Abeta42 with p53 mRNA elevation in guinea-pig primary neurons. Also, p53 expression was elevated in brain of sporadic AD and transgenic mice carrying mutant familial AD genes. Remarkably, accumulation of both Abeta42 and p53 was found in some degenerating-shape neurons in both transgenic mice and human AD cases. Thus, the intracellular Abeta42/p53 pathway may be directly relevant to neuronal loss in AD. Although neurotoxicity of extracellular Abeta is well known and synaptic/mitochondrial dysfunction by intracellular Abeta42 has recently been suggested, intracellular Abeta42 may cause p53-dependent neuronal apoptosis through activation of the p53 promoter; thus demonstrating an alternative pathogenesis in AD.

P2-187 Hippocampal and amygdalal brain changes in young-old and very-old with Alzheimer's disease: associations with neuropsychological functioning

P2-187 Hippocampal and amygdalal brain changes in young-old and very-old with Alzheimer's disease: associations with neuropsychological functioning

Magnetic resonance spectroscopic analysis of Alzheimer's disease mouse brain that express mutant human APP shows altered neurochemical profile

Transgenic mice that express mutant human amyloid precursor protein (APP Tg2576 ) develop β-amyloid (Aβ) plaques throughout the cortex starting at 10–12 months of age. We examined the neurochemical profile of APP Tg2576 mice using in vitro and in vivo magnetic resonance spectroscopy (MRS); gross abnormalities using magnetic resonance imaging (MRI) and plaque distribution; size and number using immunohistochemistry . Transgenic mice were anesthetized with halothane and scanned at 4.7 T using T2-weighted imaging and in vivo MRS of frontal cortex. In vitro MRS was run from brain extracts of frontal cortex in both APP and wild-type mice. Mice were also perfused and brains were collected and cut for immunohistochemistry. We found that N -acetylaspartate (NAA), glutamate and glutathione were decreased by 17%, 22% and 36%, respectively, in the cerebral cortex of APP transgenic mice at 19 months of age when Aβ deposits are widespread. Taurine was increased 21% compared to wild-type. Decreased levels of NAA and increased levels of taurine are consistent with decreased neuronal viability and increased glial volume, and are similar to findings of decreased NAA and increased myo-inositol in human Alzheimer's disease (AD) brains. Correlation between the severity of Aβ deposition and altered neurochemical profile remains to be studied. Nevertheless, the altered neurochemical profile may be a valuable marker to test therapeutics in this mouse model.

Magnetic resonance spectroscopic analysis of Alzheimer's disease mouse brain that express mutant human APP shows altered neurochemical profile

Transgenic mice that express mutant human amyloid precursor protein (APP Tg2576) develop β-amyloid (Aβ) plaques throughout the cortex starting at 10–12 months of age. We examined the neurochemical profile of APP Tg2576 mice using in vitro and in vivo magnetic resonance spectroscopy (MRS); gross abnormalities using magnetic resonance imaging (MRI) and plaque distribution; size and number using immunohistochemistry. Transgenic mice were anesthetized with halothane and scanned at 4.7 T using T2-weighted imaging and in vivo MRS of frontal cortex. In vitro MRS was run from brain extracts of frontal cortex in both APP and wild-type mice. Mice were also perfused and brains were collected and cut for immunohistochemistry. We found that N-acetylaspartate (NAA), glutamate and glutathione were decreased by 17%, 22% and 36%, respectively, in the cerebral cortex of APP transgenic mice at 19 months of age when Aβ deposits are widespread. Taurine was increased 21% compared to wild-type. Decreased levels of NAA and increased levels of taurine are consistent with decreased neuronal viability and increased glial volume, and are similar to findings of decreased NAA and increased myo-inositol in human Alzheimer's disease (AD) brains. Correlation between the severity of Aβ deposition and altered neurochemical profile remains to be studied. Nevertheless, the altered neurochemical profile may be a valuable marker to test therapeutics in this mouse model.