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  • 11
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Accumulation of theβ-amyloid protein (Aβ) in the brain is an important step in the pathogenesis of Alzheimer's disease. However, the mechanism of Aβ toxicity remains unclear. Aβ can bind to the extracellular matrix, a structure that regulates adhesive events such as neurite outgrowth and synaptogenesis. The binding of Aβ to the extracellular matrix suggests that Aβ may disrupt cell-substrate interactions. Therefore, the effect of substrate-bound Aβ on the growth of isolated chick sympathetic and mouse cortical neurons was examined. Aβ1-40 and Aβ1-42 had dose-dependent effects on cell morphology. When tissue culture plates were coated with 0.1-10 ng/well Aβ, neurite outgrowth increased. Higher amounts of Aβ peptides (≥μg/well) inhibited outgrowth. The inhibitory effect was related to aggregation of the peptide, as preincubation of Aβ1-40 for 24 h at 37 °C (a process known to increase amyloid fibril formation) was necessary for inhibition of neurite outgrowth. Aβ29-42, but not Aβ1-28, also inhibited neurite outgrowth at high concentrations, demonstrating that the inhibitory domain is located within the hydrophobic C-terminal region. Aβ1-40, Aβ1-42, and Aβ29-42 also inhibited cell-substrate adhesion, indicating that the effect on neurite outgrowth may have been due to inhibition of cell adhesion. The results suggest that accumulation of Aβ may disrupt cell-adhesion mechanisms in vivo.
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  • 12
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 72 (1999), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Perturbations to glutathione (GSH) metabolism may play an important role in neurodegenerative disorders such as Alzheimer's, Parkinson's, and prion diseases. A primary function of GSH is to prevent the toxic interaction between free radicals and reactive transition metals such as copper (Cu). Due to the potential role of Cu in neurodegeneration, we examined the effect of GSH depletion on Cu toxicity in murine primary neuronal cultures. Depletion of cellular GSH with L-buthionine-[S,R]-sulfoximine resulted in a dramatic potentiation of Cu toxicity in neurons without effect on iron (Fe) toxicity. Similarly, inhibition of glutathione reductase (GR) activity with 1,3-bis(2-chloroethyl)-1-nitrosurea also increased Cu toxicity in neurons. To determine if the Alzheimer's amyloid-β (Aβ) peptide can affect neuronal resistance to transition metal toxicity, we exposed cultures to nontoxic concentrations of Aβ25-35 in the presence or absence of Cu or Fe. Aβ25-35 pretreatment was found to deplete neuronal GSH and increase GR activity, confirming the ability of Aβ to perturb neuronal GSH homeostasis. Aβ25-35 pretreatment potently increased Cu toxicity but had no effect on Fe toxicity. These studies demonstrate an important role for neuronal GSH homeostasis in selective protection against Cu toxicity, a finding with widespread implications for neurodegenerative disorders.
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  • 13
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Oxidative stress may have an important role in the progression of neurodegenerative disorders such as Alzheimer's disease (AD) and prion diseases. Oxidative damage could result from interactions between highly reactive transition metals such as copper (Cu) and endogenous reducing and/or oxidizing molecules in the brain. One such molecule, homocysteine, a thiol-containing amino acid, has previously been shown to modulate Cu toxicity in HeLa and endothelial cells in vitro. Due to a possible link between hyperhomocysteinemia and AD, we examined whether interaction between homocysteine and Cu could potentiate Cu neurotoxicity. Primary mouse neuronal cultures were treated with homocysteine and either Cu (II), Fe (II or III) or Zn (II). Homocysteine was shown to selectively potentiate toxicity from low micromolar concentrations of Cu. The toxicity of homocysteine/Cu coincubation was dependent on the ability of homocysteine to reduce Cu (II) as reflected by the inhibition of toxicity with the Cu (I)-specific chelator, bathocuproine disulphonate. This was supported by data showing that homocysteine reduced Cu (II) more effectively than cysteine or methionine but did not reduce Fe (III) to Fe (II). Homocysteine also generated high levels of hydrogen peroxide in the presence of Cu (II) and promoted Aβ/Cu-mediated hydrogen peroxide production and neurotoxicity. The potentiation of metal toxicity did not involve excitotoxicity as ionotropic glutamate receptor antagonists had no effect on neurotoxicity. Homocysteine alone also had no effect on neuronal glutathione levels. These studies suggest that increased copper and/or homocysteine levels in the elderly could promote significant oxidant damage to neurons and may represent additional risk factor pathways which conspire to produce AD or related neurodegenerative conditions.
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  • 14
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: One of the characteristic changes that occurs in Alzheimer's disease is the loss of acetylcholinesterase (AChE) from both cholinergic and noncholinergic neurons of the brain. However, AChE activity is increased around amyloid plaques. This increase in AChE may be of significance for therapeutic strategies using AChE inhibitors. The aim of this study was to examine the effect of amyloid β-protein (Aβ), the major component of amyloid plaques, on AChE expression. Aβ peptides spanning residues 1–40 or 25–35 increased AChE activity in P19 embryonal carcinoma cells. A peptide containing a scrambled Aβ25–35 sequence did not stimulate AChE expression. To examine the possibility that the increase in AChE expression was mediated by an influx of calcium through voltage-dependent calcium channels (VDCCs), drugs acting on VDCCs were tested for their effects. Inhibitors of L-type VDCCs (diltiazem, nifedipine, and verapamil), but not N- or P- or Q-type VDCCs, resulted in a decrease in AChE expression. Agonists of L-type VDCCs (maitotoxin and S(−)-Bay K 8644) increased AChE expression. As L-type VDCCs are known to be modulated by cyclic AMP-dependent protein kinase, the effect of the adenylate cyclase activator forskolin was also examined. Forskolin stimulated AChE expression, an action that was blocked by the L-type VDCC antagonist nifedipine. The Aβ25–35-induced increase in AChE expression was mediated by an L-type VDCC, as the effect was also blocked by nifedipine. The results suggest that the increase in AChE expression around amyloid plaques could be due to a disturbance in calcium homeostasis involving the opening of L-type VDCCs.
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  • 15
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
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  • 16
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: We and colleagues have shown that the amyloid protein precursor of Alzheimer’s disease (APP) is distributed along the surface of neurites of fixed but nonpermeabilized neurons in primary culture in a segmental pattern, which shows colocalization with some markers of adhesion patches. This is in contrast to the diffuse pattern of immunoreactivity seen after permeabilization. We have also recently demonstrated that the APP in these surface patches is likely to be integral to the membrane rather than secreted and re-adsorbed, based on alkali stripping experiments and on soluble APP adsorption experiments. Total cellular APP has previously been shown to have a short half-life of ≈ 30–60 min. We confirm this in neurons in primary culture in pulse-chase experiments using short labelling times. Additionally, we provide evidence that a separate, stable pool of neuronal APP can be demonstrated in pulse-chase experiments using long labelling times. Experiments involving inhibition of protein synthesis suggest that this corresponds with the surface, segmental pool. Metabolic labelling followed by surface biotinylation and two-stage precipitation demonstrates that the surface APP is trans-membrane and full-length (not carboxyl-terminal truncated), and confirms that the surface APP belongs to the stable pool. This two-stage procedure is necessary as the surface APP appears to be present in low copy number, and is difficult to detect by direct labelling. This information is consistent with a role for APP in stable cell-matrix or cell–cell interactions.
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  • 17
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Previous studies have shown that a minor glycoform of acetylcholinesterase (AChE) is increased in Alzheimer's disease brain and cerebrospinal fluid. This glycoform can be distinguished from other AChE species by its lack of binding to concanavalin A (Con A). In this study, the temporal relationship between AChE glycosylation and Aβ deposition was examined in Tg2576 mice. There was a significant (p 〈 0.05) difference in AChE glycosylation in Tg2576 mice compared with age-matched background strain control mice at 4 months of age. This difference in glycosylation was also observed in 8- and 12-month-old Tg2576 mice. In contrast, Aβ plaques were only seen in the Tg2576 mice at 12 months of age, and were not detected at 4 and 8 months of age. Soluble human-sequence Aβ was detected as early as 4 months of age in the transgenic mice. The altered AChE glycosylation was due to an increase in a minor AChE isoform, which did not bind Con A, similar to that previously observed to be increased in Alzheimer's disease brain and cerebrospinal fluid. The results demonstrate that in transgenic mice altered AChE glycosylation is associated with very early events in the development of AD-like pathology. The study supports the possibility that glycosylation may also be a useful biomarker of AD.
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  • 18
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature medicine 3 (1997), S. 723-725 
    ISSN: 1546-170X
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] MUTATIONS IN THE presenilin 1 gene (PS1) are associated with early-onset auto-somal dominant familial Alzheimer's disease (FAD)1. Three recent reports2–4including one in thisissue of Nature Medicine2 use transgenic and knockout mice to elucidate how mutations in PS1 contribute to amyloid ...
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  • 19
    ISSN: 1546-170X
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] The Alzheimer amyloid precursor protein (APP) is cleaved by several proteases, the most studied, but still unidentified ones, are those involved in the release of a fragment of APP, the amyloidogenic β-protein Aβ. Proteolysis by γ-secretase is the last processing step resulting in ...
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  • 20
    ISSN: 1432-0533
    Keywords: Key words Alzheimer’s disease ; Amyloid ; precursor-like protein 1 ; Amyloid precursor protein ; Plaques
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The Alzheimer’s disease (AD) β-amyloid precursor protein (APP) and the amyloid precursor-like protein 1 (APLP1) and 2 (APLP2) are members of a superfamily of proteins that appear functionally related. Although APLPs are highly homologous to APP in the N- and C-terminal domains, they lack the βA4/amyloid peptide, i.e., the main constituent of neuritic plaques in AD. To assess a potential role of APLP1 in AD, we have determined its immunohistochemical distribution in human hippocampal formation, a structure which is strongly affected in AD, and compared it with APP immunoreactivity. There was a considerable overlap of APP and APLP1 regional expression patterns. Significant APLP1 immunoreactivity was observed in neuritic plaques. Large pyramidal neurons of the subiculum showed an accumulation of APLP1 protein in their dendritic compartment. Some astrocytes elicited perinuclear APLP1 staining, but this was observed in both AD and control brains. These findings raise the possibility that APLP1 may contribute to the pathogenesis of AD-associated neurodegeneration.
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