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  • 1
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The extent of τ phosphorylation is thought to regulate the binding of τ to microtubules: Highly phosphorylated τ does not bind to tubules, whereas dephosphorylated τ can bind to microtubules. It is interesting that the extent of τ phosphorylation in vivo has not been accurately determined. τ was rapidly isolated from human temporal neocortex and hippocampus, rhesus monkey temporal neocortex, and rat temporal neocortex and hippocampus under conditions that minimized dephosphorylation. In brain slices, we observed that τ isolated under such conditions largely existed in several phosphorylated states, including a pool that was highly phosphorylated; this was determined using epitope-specific monoclonal and polyclonal antibodies. This highly phosphorylated τ was dephosphorylated during a 120-min time course in vitro, presumably as a result of neuronal phosphatase activity. The slow-mobility forms of τ were shifted to faster-mobility forms following in vitro incubation with alkaline phosphatase. Laser densitometry was used to estimate the percent of τ in slow-mobility, highly phosphorylated forms. Approximately 25% of immunoreactive τ was present as slow-mobility (66- and 68-kDa) forms of τ. The percentage of immunoreactive τ in faster-mobility pools (42–54 kDa) increased in proportion to the decrease in content of 66–68-kDa τ as a function of neuronal phosphatases or alkaline phosphatase treatment. These data suggest that the turnover of phosphorylated sites on τ is rapid and depends on neuronal phosphatases. Furthermore, τ is highly phosphorylated in normal-appearing human, primate, and rodent brain. The presence of a highly phosphorylated pool of τ in adult brain may modify the present hypotheses on how paired helical filaments of Alzheimer's disease are formed.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: We examined the short-term regulation of the phosphorylation of the mid-sized neurofilament subunit (NF-M) by kinases which were activated in rat pheochromocytoma (PC12) cells by nerve growth factor (NGF) and/or 12-O-tet-radecanoylphorbol 13-acetate (TPA). We found that NGF and TPA, alone or in combination, increased (a) the incorporation of [32P]Pi into NF-M and (b) the rate of conversion of NF-M from a poorly phosphorylated to a more highly phosphorylated form. This was not due to increased synthesis of NF-M, because NGF alone did not increase NF-M synthesis and TPA alone or TPA and NGF together inhibited the synthesis of NF-M. Further, an increase in calcium/phospholipid-dependent kinase (PKC) activity resulting from the treatment of PC12 cells with NGF and TPA was observed concomitant with the increased phosphorylation of NF-M. This PKC activity was determined to be derived from the PKCα and PKCβ isozyme. Finally, when PC12 cells were rendered PKC-deficient by treatment with 1 μM TPA for 24 h, NGF maintained the ability to induce an increase in NF-M phosphorylation, though not to the level attained in cells which were not PKC-deficient. These data suggest (hat NGF with or without TPA stimulates NF-M phosphorylation as a result of a complex series of events which include PKC-in-dependent and PKC-dependent pathways.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1520-4812
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Proteinaceous inclusions with amyloidogenic properties are a common link between many neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. Histological and in vitro studies of amyloid fibrils have advanced the understanding of protein aggregation, and provided important insights into pathogenic mechanisms of these neurodegenerative brain amyloidoses. The classical amyloid dyes Congo Red (CR) and thioflavin T and S, have been used extensively to detect amyloid inclusions in situ. These dyes have also been utilized to monitor the maturation of amyloid fibrils assembled from monomer subunits in vitro. Recently, the compound (trans,trans)-1-bromo-2,5-bis-(3- hydroxycarbonyl-4-hydroxy)styrylbenzene (BSB), derived from the structure of CR, was shown to bind to a wide range of amyloid inclusions in situ. More importantly it was also used to label brain amyloids in live animals. Herein, we show that an analogue of BSB, (trans,trans)-1-bromo-2,5-bis-(4-hydroxy)styrylbenzene (K114), recognizes amyloid lesions, and has distinctive properties which allowed the quantitative monitoring of the formation of amyloid fibrils assembled from the amyloid-β peptide, α-synuclein, and tau.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Parkinson's disease (PD) is characterized by fibrillary neuronal inclusions called Lewy bodies (LBs) consisting largely of alpha-synuclein (α-syn), the protein mutated in some patients with familial PD. The mechanisms of α-syn fibrillization and LB formation are unknown, but may involve aberrant degradation or turnover. We examined the ability of calpain I to cleave α-syn in vitro. Calpain I cleaved wild-type α-syn predominantly after amino acid 57 and within the non-amyloid component (NAC) region. In contrast, calpain I cleaved fibrillized α-syn primarily in the region of amino acid 120 to generate fragments like those that increase susceptibility to dopamine toxicity and oxidative stress. Further, while calpain I cleaved wild-type α-syn after amino acid 57, this did not occur in mutant A53T α-syn. This paucity of proteolysis could increase the stability of A53T α-syn, suggesting that calpain I might protect cells from forming LBs by specific cleavages of soluble wild-type α-syn. However, once α-syn has polymerized into fibrils, calpain I may contribute to toxicity of these forms of α-syn by cleaving at aberrant sites within the C-terminal region. Elucidating the role of calpain I in the proteolytic processing of α-syn in normal and diseased brains may clarify mechanisms of neurodegenerative α-synucleinopathies.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Traumatic brain injury is a well-recognized environmental risk factor for developing Alzheimer's disease. Repetitive concussive brain injury (RCBI) exacerbates brain lipid peroxidation, accelerates amyloid (Aβ) formation and deposition, as well as cognitive impairments in Tg2576 mice. This study evaluated the effects of vitamin E on these four parameters in Tg2576 mice following RCBI. Eleven-month-old mice were randomized to receive either regular chow or chow-supplemented with vitamin E for 4 weeks, and subjected to RCBI (two injuries, 24 h apart) using a modified controlled cortical impact model of closed head injury. The same dietary regimens were maintained up to 8 weeks post-injury, when the animals were killed for biochemical and immunohistochemical analyses after behavioral evaluation. Vitamin E-treated animals showed a significant increase in brain vitamin E levels and a significant decrease in brain lipid peroxidation levels. After RBCI, compared with the group on regular chow, animals receiving vitamin E did not show the increase in Aβ peptides, and had a significant attenuation of learning deficits. This study suggests that the exacerbation of brain oxidative stress following RCBI plays a mechanistic role in accelerating Αβ accumulation and behavioral impairments in the Tg2576 mice.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The effects of synthetic β-amyloid (Aβ1–42) on cell viability and cellular Ca2+ homeostasis have been studied in the human neuron-like NT2N cell, which differentiates from a teratocarcinoma cell line, NTera2/C1.D1, by retinoic acid treatment. NT2N viability was measured using morphological criteria and fluorescent live/dead staining and quantified using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide metabolism. Aβ1–42 dose-dependently caused NT2N cell death when it was present in the cell culture for 14 days but had no effect on viability when it was present for 4 days. The lowest effective concentration was 4 µM, and the strongest effect was produced by 40 µM. Control NT2N cells produced spontaneous cytosolic Ca2+ oscillations under basal conditions. These oscillations were inhibited dose-dependently (0.4–40 µM) by Aβ1–42 that was present in the cell culture for 1 or 4 days. Ca2+ wave frequency was decreased from 0.21 ± 0.02 to 0.05 ± 0.02/min, amplitude from 88 ± 8 to 13 ± 4 nM, and average Ca2+ level from 130 ± 8 to 58 ± 3 nM. The Ca2+ responses to 30 mM K+ and 100 µM glutamate were not different between control and Aβ-treated cells. Thus, the results do not support the hypothesis that cytosolic early Ca2+ accumulation mediates Aβ-induced NT2N cell death.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Structural and functional alterations of α-synuclein is a presumed culprit in the demise of dopaminergic neurons in Parkinson's disease (PD). α-Synuclein mutations are found in familial but not in sporadic PD, raising the hypothesis that effects similar to those of familial PD-linked α-synuclein mutations may be achieved by oxidative post-translational modifications. Here, we show that wild-type α-synuclein is a selective target for nitration following peroxynitrite exposure of stably transfected HEK293 cells. Nitration of α-synuclein also occurs in the mouse striatum and ventral midbrain following administration of the parkinsonian neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Conversely, β-synuclein and synaptophysin were not nitrated in MPTP-intoxicated mice. Our data demonstrate that α-synuclein is a target for tyrosine nitration, which, by disrupting its biophysical properties, may be relevant to the putative role of α-synuclein in the neurodegeneration associated with MPTP toxicity and with PD.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: RNA editing plays an important role in determining physiological characteristics of certain glutamate-gated receptor (GluR) channels such as Ca2+ permeability and desensitization kinetics. In one case, the editing changes a gene-encoded glutamine (Q) to an arginine (R) codon located in the channel-forming domain of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor subunit GluR-B and also the kainate receptor subunits GluR5 and GluR6. Another case of RNA editing alters an arginine (R) to a glycine (G) codon at a position termed the “R/G” site of AMPA subunits GluR-B, C, and D. Double-stranded RNA-specific adenosine deaminases (DRADA) have been implicated as agents involved in the editing. By using a human teratocarcinoma cell line, NT2, we investigated the change of the RNA editing of GluR subunits in conjunction with the expression of two DRADA members, DRADA1 and DRADA2 genes, during neuronal differentiation. Whereas Q/R and R/G site RNA editing both become progressively activated in differentiating NT2 cells, the expression of the two DRADA genes can already be detected even in the undifferentiated NT2 cells. Development of the editing machinery appears to require, in addition to DRADA enzymes, a currently unidentified mechanism(s) that may become activated during neuronal differentiation.
    Type of Medium: Electronic Resource
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