69 research outputs found

    Glutathione-Mediated Neuroprotection Against Methylmercury Neurotoxicity in Cortical Culture is Dependent on MRP1

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    Methylmercury (MeHg) exposure at high concentrations poses significant neurotoxic threat to humans worldwide. The present study investigated the mechanisms of glutathione-mediated attenuation of MeHg neurotoxicity in primary cortical culture. MeHg (5 μM) caused depletion of mono- and disulfide glutathione in neuronal, glial and mixed cultures. Supplementation with exogenous glutathione, specifically glutathione monoethyl ester (GSHME) protected against the MeHg induced neuronal death. MeHg caused increased reactive oxygen species (ROS) formation measured by dichlorodihydrofluorescein (DCF) fluorescence with an early increase at 30 min and a late increase at 6 h. This oxidative stress was prevented by the presence of either GSHME or the free radical scavenger, trolox. While trolox was capable of quenching the ROS, it showed no neuroprotection. Exposure to MeHg at subtoxic concentrations (3 μM) caused an increase in system xc− mediated 14C-cystine uptake that was blocked by the protein synthesis inhibitor, cycloheximide (CHX). Interestingly, blockade of the early ROS burst prevented the functional upregulation of system xc−. Inhibition of multidrug resistance protein-1 (MRP1) potentiated MeHg neurotoxicity and increased cellular MeHg. Taken together, these data suggest glutathione offers neuroprotection against MeHg toxicity in a manner dependent on MRP1-mediated efflux

    Sub-nanosecond signal propagation in anisotropy engineered nanomagnetic logic chains

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    Energy efficient nanomagnetic logic (NML) computing architectures propagate and process binary information by relying on dipolar field coupling to reorient closely-spaced nanoscale magnets. Signal propagation in nanomagnet chains of various sizes, shapes, and magnetic orientations has been previously characterized by static magnetic imaging experiments with low-speed adiabatic operation; however the mechanisms which determine the final state and their reproducibility over millions of cycles in high-speed operation (sub-ns time scale) have yet to be experimentally investigated. Monitoring NML operation at its ultimate intrinsic speed reveals features undetectable by conventional static imaging including individual nanomagnetic switching events and systematic error nucleation during signal propagation. Here, we present a new study of NML operation in a high speed regime at fast repetition rates. We perform direct imaging of digital signal propagation in permalloy nanomagnet chains with varying degrees of shape-engineered biaxial anisotropy using full-field magnetic soft x-ray transmission microscopy after applying single nanosecond magnetic field pulses. Further, we use time-resolved magnetic photo-emission electron microscopy to evaluate the sub-nanosecond dipolar coupling signal propagation dynamics in optimized chains with 100 ps time resolution as they are cycled with nanosecond field pulses at a rate of 3 MHz. An intrinsic switching time of 100 ps per magnet is observed. These experiments, and accompanying macro-spin and micromagnetic simulations, reveal the underlying physics of NML architectures repetitively operated on nanosecond timescales and identify relevant engineering parameters to optimize performance and reliability.Comment: Main article (22 pages, 4 figures), Supplementary info (11 pages, 5 sections

    EPHA2 Is Associated with Age-Related Cortical Cataract in Mice and Humans

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    Age-related cataract is a major cause of blindness worldwide, and cortical cataract is the second most prevalent type of age-related cataract. Although a significant fraction of age-related cataract is heritable, the genetic basis remains to be elucidated. We report that homozygous deletion of Epha2 in two independent strains of mice developed progressive cortical cataract. Retroillumination revealed development of cortical vacuoles at one month of age; visible cataract appeared around three months, which progressed to mature cataract by six months. EPHA2 protein expression in the lens is spatially and temporally regulated. It is low in anterior epithelial cells, upregulated as the cells enter differentiation at the equator, strongly expressed in the cortical fiber cells, but absent in the nuclei. Deletion of Epha2 caused a significant increase in the expression of HSP25 (murine homologue of human HSP27) before the onset of cataract. The overexpressed HSP25 was in an underphosphorylated form, indicating excessive cellular stress and protein misfolding. The orthologous human EPHA2 gene on chromosome 1p36 was tested in three independent worldwide Caucasian populations for allelic association with cortical cataract. Common variants in EPHA2 were found that showed significant association with cortical cataract, and rs6678616 was the most significant in meta-analyses. In addition, we sequenced exons of EPHA2 in linked families and identified a new missense mutation, Arg721Gln, in the protein kinase domain that significantly alters EPHA2 functions in cellular and biochemical assays. Thus, converging evidence from humans and mice suggests that EPHA2 is important in maintaining lens clarity with age

    Impact of Clinical Variables on Borrelia burgdorferi-Specific Antibody Seropositivity in Acute-Phase Sera from Patients in North America with Culture-Confirmed Early Lyme Disease▿

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    Erythema migrans, the most common manifestation of Lyme disease, has been associated with highly variable rates of seropositivity for antibodies to Borrelia burgdorferi. Differences in the sensitivities of serologic assays for the detection of these antibodies, however, may not be the only or even the primary explanation for this observation. We investigated the impacts of four clinical variables on seropositivity—the duration of erythema migrans, the presence of single versus multiple skin lesions, and the gender and age of the patient. In this analysis, three different serologic tests were performed on acute-phase sera from 175 untreated patients with culture-confirmed erythema migrans: the C6 single-peptide enzyme-linked immunosorbent assay (ELISA), a commercially available ELISA in which a whole-cell sonicate of B. burgdorferi was the antigen, and a two-tier procedure. Irrespective of the serologic test performed, the results showed that seropositivity rates increased with the duration of the erythema migrans for patients with single lesions (P < 0.001) but not for those with multiple skin lesions. The variability in seropositivity rates was greatest for the two-tier testing strategy, with a >6-fold-higher rate of seropositivity among patients with a single lesion of 22- to 30-day duration than among those whose skin lesion was of 1- to 7-day duration (85.7 versus 14.1%; P < 0.001). Rates of seropositivity by each of the testing methods were also significantly higher for patients with multiple skin lesions than for those with single lesions (P < 0.001). In contrast, seropositivity rates were not affected by either the gender or the age of the patient. Thus, in patients with erythema migrans, certain clinical variables such as the duration and number of skin lesions had a profound impact on seropositivity rates, irrespective of the serologic assay performed
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