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  • Utrophin influences mitochondrial pathology and oxidative stress in dystrophic muscle.

    12 January 2018

    BACKGROUND: Duchenne muscular dystrophy (DMD) is a lethal X-linked muscle wasting disorder caused by the absence of dystrophin, a large cytoskeletal muscle protein. Increasing the levels of the dystrophin-related-protein utrophin is a highly promising therapy for DMD and has been shown to improve pathology in dystrophin-deficient mice. One contributing factor to muscle wasting in DMD is mitochondrial pathology that contributes to oxidative stress and propagates muscle damage. The purpose of this study was to assess whether utrophin could attenuate mitochondria pathology and oxidative stress. METHODS: Skeletal muscles from wildtype C57BL/10, dystrophin-deficient mdx, dystrophin/utrophin double knockout (dko) and dystrophin-deficient mdx/utrophin over-expressing mdx-Fiona transgenic mice were assessed for markers of mitochondrial damage. RESULTS: Using transmission electron microscopy, we show that high levels of utrophin ameliorate the aberrant structure and localisation of mitochondria in mdx mice whereas absence of utrophin worsened these features in dko mice. Elevated utrophin also reverts markers of protein oxidation and oxidative stress, elevated in mdx and dko mice, to wildtype levels. These changes were observed independently of a shift in oxidative phenotype. CONCLUSION: These findings show that utrophin levels influence mitochondrial pathology and oxidative stress. While utrophin deficiency worsens the pathology, utrophin over-expression in dystrophic muscle benefits mitochondria and attenuates the downstream pathology associated with aberrant mitochondrial function.

  • The evolution of non-visual photopigments in the central nervous system of vertebrates

    28 November 2017

    © Springer Science+Business Media New York 2014. In addition to classical image-forming vision, the vertebrates exhibit a range of non-image-forming light detection systems that utilise opsin photopigments. Within the CNS these systems are present in a range of anatomical locations that include both eye and brain. In mammals the eye is both responsible and required for all commonly measured responses to light. By contrast, non-mammalian vertebrates possess a wide range of intrinsically photoreceptive sites. Members of the non-visual opsin family include exorhodopsin, pinopsin, vertebrate ancient opsin (VA), parietopsin, parapinopsin, teleost multiple tissue opsin (TMT), encephalopsin (OPN3), neuropsin (OPN5), peropsin, retinal G protein-coupled receptor (RGR) and melanopsin (OPN4). Opsin-based photopigments have evolved to mediate specific photoreceptive tasks in different light environments, each exhibit functional properties that are tuned to the biological task in which they are involved. Examination of the classes of opsin involved reveals a range of adaptions particularly in spectral sensitivity, chromophore handling and signalling mechanisms. The loss of extraocular light detection in the mammals is associated with an evolutionary reduction in the non-visual opsin representation in the mammalian genome. One clear exception to this is the retention of the melanopsin (OPN4M) gene and the expression of this opsin protein in a single class of mammalian retinal ganglion cell. Exploring the diversity of melanopsin proteins in the lower vertebrates suggests that the property of chromophore biochemistry and bistability does not necessarily define an opsin class and may have evolved more than once.

  • The evolution and function of melanopsin in craniates

    28 November 2017

    © Springer Science+Business Media New York 2014. In addition to well-characterised visual systems, many organisms, including the craniates, possess a complex sensory system of non-visual photoreceptors that detect light for a diverse array of non-image-forming tasks. Like the photoreceptors of image-forming systems, the pigments contained within nonvisual photoreceptive cells comprise a protein component (opsin) linked to a lightsensitive retinal chromophore derived from vitamin A. In mammals, one of the most important of these non-visual pigments is melanopsin (encoded by the OPN4 gene, specifically that of the "mammal-like" or "m-class"), which is restricted in expression to a subset of retinal ganglion cells and has been shown to be the conduit through which light regulates many physiological activities, including the photoentrainment of circadian systems (e.g. the sleep cycle) and the pupillary reflex response. In non-mammals, melanopsin exists as two distinct gene lineages, namely the m-class and x-class (" Xenopus - like"), and both are expressed in many different tissues, including the eyes, skin, fins, gills, brain and pineal gland, however, the functional roles mediated by melanopsin in these "lower" vertebrates remain to be fully elucidated. In this review, we discuss the evolutionary history of the melanopsin gene, its diverse patterns of expression and transcriptional output, the functional roles so far determined, and the clinical significance of this critical and phylogenetically most ancient opsin-based system of irradiance detection.

  • The transcellular propagation and intracellular trafficking of α-synuclein

    18 January 2018

    © 2017 Cold Spring Harbor Laboratory Press. Parkinson’s disease is the second most common neurodegenerative disorder, with only partial symptomatic therapy and no mechanism-based therapies. The accumulation and aggregation of α-synuclein is causatively linked to the sporadic form of the disease, which accounts for 95% of cases. The pathology is a result of a gain of toxic function of misfolded α-synuclein conformers, which can template the aggregation of soluble monomers and lead to cellular dysfunction, at least partly by interfering with membrane fusion events at synaptic terminals. Here, we discuss the transcellular propagation and intracellular trafficking of α-synuclein and posit that endosomal processing could be a point of convergence between these two routes. Understanding these events will clarify the therapeutic potential of enzymes that regulate protein trafficking and degradation in synucleinopathies.

  • A point mutation in the ion conduction pore of AMPA receptor GRIA3 causes dramatically perturbed sleep patterns as well as intellectual disability.

    16 February 2018

    The discovery of genetic variants influencing sleep patterns can shed light on the physiological processes underlying sleep. As part of a large clinical sequencing project, WGS500, we sequenced a family in which the two male children had severe developmental delay and a dramatically disturbed sleep-wake cycle, with very long wake and sleep durations, reaching up to 106-h awake and 48-h asleep. The most likely causal variant identified was a novel missense variant in the X-linked GRIA3 gene, which has been implicated in intellectual disability. GRIA3 encodes GluA3, a subunit of AMPA-type ionotropic glutamate receptors (AMPARs). The mutation (A653T) falls within the highly conserved transmembrane domain of the ion channel gate, immediately adjacent to the analogous residue in the Grid2 (glutamate receptor) gene, which is mutated in the mouse neurobehavioral mutant, Lurcher. In vitro, the GRIA3(A653T) mutation stabilizes the channel in a closed conformation, in contrast to Lurcher. We introduced the orthologous mutation into a mouse strain by CRISPR-Cas9 mutagenesis and found that hemizygous mutants displayed significant differences in the structure of their activity and sleep compared to wild-type littermates. Typically, mice are polyphasic, exhibiting multiple sleep bouts of sleep several minutes long within a 24-h period. The Gria3A653T mouse showed significantly fewer brief bouts of activity and sleep than the wild-types. Furthermore, Gria3A653T mice showed enhanced period lengthening under constant light compared to wild-type mice, suggesting an increased sensitivity to light. Our results suggest a role for GluA3 channel activity in the regulation of sleep behavior in both mice and humans.

  • Meta-analysis of transcriptomic datasets identifies genes enriched in the mammalian circadian pacemaker.

    28 January 2018

    The master circadian pacemaker in mammals is located in the suprachiasmatic nuclei (SCN) which regulate physiology and behaviour, as well as coordinating peripheral clocks throughout the body. Investigating the function of the SCN has often focused on the identification of rhythmically expressed genes. However, not all genes critical for SCN function are rhythmically expressed. An alternative strategy is to characterize those genes that are selectively enriched in the SCN. Here, we examined the transcriptome of the SCN and whole brain (WB) of mice using meta-analysis of publicly deposited data across a range of microarray platforms and RNA-Seq data. A total of 79 microarrays were used (24 SCN and 55 WB samples, 4 different microarray platforms), alongside 17 RNA-Seq data files (7 SCN and 10 WB). 31 684 MGI gene symbols had data for at least one platform. Meta-analysis using a random effects model for weighting individual effect sizes (derived from differential expression between relevant SCN and WB samples) reliably detected known SCN markers. SCN-enriched transcripts identified in this study provide novel insights into SCN function, including identifying genes which may play key roles in SCN physiology or provide SCN-specific drivers.

  • Investigation of Slow-wave Activity Saturation during Surgical Anesthesia Reveals a Signature of Neural Inertia in Humans.

    8 February 2018

    BACKGROUND: Previously, we showed experimentally that saturation of slow-wave activity provides a potentially individualized neurophysiologic endpoint for perception loss during anesthesia. Furthermore, it is clear that induction and emergence from anesthesia are not symmetrically reversible processes. The observed hysteresis is potentially underpinned by a neural inertia mechanism as proposed in animal studies. METHODS: In an advanced secondary analysis of 393 individual electroencephalographic data sets, we used slow-wave activity dose-response relationships to parameterize slow-wave activity saturation during induction and emergence from surgical anesthesia. We determined whether neural inertia exists in humans by comparing slow-wave activity dose responses on induction and emergence. RESULTS: Slow-wave activity saturation occurs for different anesthetics and when opioids and muscle relaxants are used during surgery. There was wide interpatient variability in the hypnotic concentrations required to achieve slow-wave activity saturation. Age negatively correlated with power at slow-wave activity saturation. On emergence, we observed abrupt decreases in slow-wave activity dose responses coincident with recovery of behavioral responsiveness in ~33% individuals. These patients are more likely to have lower power at slow-wave activity saturation, be older, and suffer from short-term confusion on emergence. CONCLUSIONS: Slow-wave activity saturation during surgical anesthesia implies that large variability in dosing is required to achieve a targeted potential loss of perception in individual patients. A signature for neural inertia in humans is the maintenance of slow-wave activity even in the presence of very-low hypnotic concentrations during emergence from anesthesia.