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  • MAPT Genetic Variation and Neuronal Maturity Alter Isoform Expression Affecting Axonal Transport in iPSC-Derived Dopamine Neurons.

    3 July 2018

    The H1 haplotype of the microtubule-associated protein tau (MAPT) locus is genetically associated with neurodegenerative diseases, including Parkinson's disease (PD), and affects gene expression and splicing. However, the functional impact on neurons of such expression differences has yet to be fully elucidated. Here, we employ extended maturation phases during differentiation of induced pluripotent stem cells (iPSCs) into mature dopaminergic neuronal cultures to obtain cultures expressing all six adult tau protein isoforms. After 6 months of maturation, levels of exon 3+ and exon 10+ transcripts approach those of adult brain. Mature dopaminergic neuronal cultures display haplotype differences in expression, with H1 expressing 22% higher levels of MAPT transcripts than H2 and H2 expressing 2-fold greater exon 3+ transcripts than H1. Furthermore, knocking down adult tau protein variants alters axonal transport velocities in mature iPSC-derived dopaminergic neuronal cultures. This work links haplotype-specific MAPT expression with a biologically functional outcome relevant for PD.

  • Advances in noninvasive myelin imaging.

    3 July 2018

    Myelin is important for the normal development and healthy function of the nervous system. Recent developments in MRI acquisition and tissue modeling aim to provide a better characterization and more specific markers for myelin. This allows for specific monitoring of myelination longitudinally and noninvasively in the healthy brain as well as assessment of treatment and intervention efficacy. Here, we offer a nontechnical review of MRI techniques developed to specifically monitor myelin such as magnetization transfer (MT) and myelin water imaging (MWI). We further summarize recent studies that employ these methods to measure myelin in relation to development and aging, learning and experience, and neuropathology and psychiatric disorders. © 2017 The Authors. Developmental Neurobiology Published by Wiley Periodicals, Inc. Develop Neurobiol 78: 136-151, 2018.

  • Myelin plasticity and behaviour-connecting the dots.

    3 July 2018

    Myelin sheaths in the vertebrate nervous system enable faster impulse propagation, while myelinating glia provide vital support to axons. Once considered a static insulator, converging evidence now suggests that myelin in the central nervous system can be dynamically regulated by neuronal activity and continues to participate in nervous system plasticity beyond development. While the link between experience and myelination gains increased recognition, it is still unclear what role such adaptive myelination plays in facilitating and shaping behaviour. Additionally, fundamental mechanisms and principles underlying myelin remodelling remain poorly understood. In this review, we will discuss new insights into the link between myelin plasticity and behaviour, as well as mechanistic aspects of myelin remodelling that may help to elucidate this intriguing process.

  • Routine screening in the general hospital: What happens after discharge to those identified as at risk of dementia?

    3 July 2018

    © Royal College of Physicians 2017. All rights reserved. Cognitive screening is recommended for older patients with unplanned hospital admission. We determined rates of reassessment/specialist memory referral after routine inclusion of at risk of dementia status in discharge documentation to primary care. Questionnaires were sent to relevant GP practices on consecutive patients aged ≥75 years identified as at risk and discharged 6 months earlier. Among 53 patients (mean age ±SD = 87.3±6.0 years, mean±SD Abbreviated Mental Test Score = 4.4±2.7), 49 (92%) patients had been reviewed since discharge, and 12/43 (28%) without previously known cognitive problem had had a cognitive reassessment. The most common reasons for non-assessment/referral included clinical factors (eg terminal illness/comorbidities) (n=15) and patient/ family wishes (n=5) and that confusion was expected in unwell older patients (n=5). Routine cognitive reassessment/specialist referral appears unjustified in patients identified as at risk of dementia during unplanned hospital admission. However, the prognostic value of delirium/confusion in acute illness is under-recognised and could be used to highlight those at risk.

  • Increased rostral anterior cingulate activity following positive mental imagery training in healthy older adults.

    3 July 2018

    The ability to form positive mental images may be an important aspect of mental health and well-being. We have previously demonstrated that the vividness of positive prospective imagery is increased in healthy older adults following positive imagery cognitive training. The rostral anterior cingulate cortex (rACC) is involved in the simulation of future affective episodes. Here, we investigate the effect of positive imagery training on rACC activity during the imagination of novel, ambiguous scenarios vs closely matched control training. Seventy-five participants received 4 weeks of positive imagery or control training. Participants underwent a functional magnetic resonance imaging scan, during which they completed an Ambiguous Sentences Task, which required them to form mental images in response to cues describing ambiguous social events. rACC activity was positively correlated with the pleasantness ratings of images formed. Positive imagery training increased rACC and bilateral hippocampal activity compared with the control training. Here, we demonstrate that rACC activity during positive imagery can be changed by the cognitive training. This is consistent with other evidence that this training enhances the vividness of positive imagery, and suggests the training may be acting to increase the intensity and affective quality of imagery simulating the future.

  • Evaluating the Performance of Fine-Mapping Strategies at Common Variant GWAS Loci.

    3 July 2018

    The growing availability of high-quality genomic annotation has increased the potential for mechanistic insights when the specific variants driving common genome-wide association signals are accurately localized. A range of fine-mapping strategies have been advocated, and specific successes reported, but the overall performance of such approaches, in the face of the extensive linkage disequilibrium that characterizes the human genome, is not well understood. Using simulations based on sequence data from the 1000 Genomes Project, we quantify the extent to which fine-mapping, here conducted using an approximate Bayesian approach, can be expected to lead to useful improvements in causal variant localization. We show that resolution is highly variable between loci, and that performance is severely degraded as the statistical power to detect association is reduced. We confirm that, where causal variants are shared between ancestry groups, further improvements in performance can be obtained in a trans-ethnic fine-mapping design. Finally, using empirical data from a recently published genome-wide association study for ankylosing spondylitis, we provide empirical confirmation of the behaviour of the approximate Bayesian approach and demonstrate that seven of twenty-six loci can be fine-mapped to fewer than ten variants.

  • An ankylosing spondylitis-associated genetic variant in the IL23R-IL12RB2 intergenic region modulates enhancer activity and is associated with increased Th1-cell differentiation.

    3 July 2018

    OBJECTIVES: To explore the functional basis for the association between ankylosing spondylitis (AS) and single-nucleotide polymorphisms (SNPs) in the IL23R-IL12RB2 intergenic region. METHODS: We performed conditional analysis on genetic association data and used epigenetic data on chromatin remodelling and transcription factor (TF) binding to identify the primary AS-associated IL23R-IL12RB2 intergenic SNP. Functional effects were tested in luciferase reporter assays in HEK293T cells and allele-specific TF binding was investigated by electrophoretic mobility gel shift assays. IL23R and IL12RB2 mRNA levels in CD4+ T cells were compared between cases homozygous for the AS-risk 'A' allele and the protective 'G' allele. The proportions of interleukin (IL)-17A+ and interferon (IFN)-γ+ CD4+ T-cells were measured by fluorescence-activated cell sorting and compared between these AS-risk and protective genotypes. RESULTS: Conditional analysis identified rs11209032 as the probable causal SNP within a 1.14 kb putative enhancer between IL23R and IL12RB2. Reduced luciferase activity was seen for the risk allele (p<0.001) and reduced H3K4me1 methylation observed in CD4+ T-cells from 'A/A' homozygotes (p=0.02). The binding of nuclear extract to the risk allele was decreased ∼3.5-fold compared with the protective allele (p<0.001). The proportion of IFN-γ+ CD4+ T-cells was increased in 'A/A' homozygotes (p=0.004), but neither IL23R nor IL12RB2 mRNA was affected. CONCLUSIONS: The rs11209032 SNP downstream of IL23R forms part of an enhancer, allelic variation of which may influence Th1-cell numbers. Homozygosity for the risk 'A' allele is associated with more IFN-γ-secreting (Th1) cells. Further work is necessary to explain the mechanisms for these important observations.