Elaine D O'Neill

Publications (2)11.05 Total impact

• Article: Absence of insulin signalling in skeletal muscle is associated with reduced muscle mass and function: evidence for decreased protein synthesis and not increased degradation.

  Elaine D O'Neill, John P H Wilding, C Ronald Kahn, Holly Van Remmen, Anne McArdle, Malcolm J Jackson, Graeme L Close
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  ABSTRACT: Loss of skeletal muscle mass and function is observed in many insulin-resistant disease states such as diabetes, cancer cachexia, renal failure and ageing although the mechanisms for this remain unclear. We hypothesised that impaired insulin signalling results in reduced muscle mass and function and that this decrease in muscle mass and function is due to both increased production of atrogenes and aberrant reactive oxygen species (ROS) generation. Maximum tetanic force of the extensor digitorum longus of muscle insulin receptor knockout (MIRKO) and lox/lox control mice was measured in situ. Muscles were removed for the measurement of mass, histological examination and ROS production. Activation of insulin signalling pathways, markers of muscle atrophy and indices of protein synthesis were determined in a separate group of MIRKO and lox/lox mice 15 min following treatment with insulin. Muscles from MIRKO mice had 36% lower maximum tetanic force generation compared with muscles of lox/lox mice. Muscle fibres of MIRKO mice were significantly smaller than those of lox/lox mice with no apparent structural abnormalities. Muscles from MIRKO mice demonstrated absent phosphorylation of AKT in response to exogenous insulin along with a failure to phosphorylate ribosomal S6 compared with lox/lox mice. Atrogin-1 and MuRF1 relative mRNA expression in muscles from MIRKO mice were decreased compared with muscles from lox/lox mice following insulin treatment. There were no differences in markers of reactive oxygen species damage between muscles from MIRKO mice and lox/lox mice. These data support the hypothesis that the absence of insulin signalling contributes to reduced muscle mass and function though decreased protein synthesis rather than proteasomal atrophic pathways.
  Age 06/2010; 32(2):209-22. · 6.28 Impact Factor
• Article: Splice variants of the human zinc transporter ZnT5 (SLC30A5) are differentially localized and regulated by zinc through transcription and mRNA stability.

  Kelly A Jackson, Rachel M Helston, Jill A McKay, Elaine D O'Neill, John C Mathers, Dianne Ford
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  ABSTRACT: Maintenance of cellular zinc homeostasis includes regulating the expression of cell membrane zinc transporters. Knowledge about the mechanisms underlying changes in mammalian zinc transporter mRNA abundance is poor. We demonstrated that when expressed in Chinese hamster ovary cells as N-terminal fusions to green fluorescent protein, two splice variants of ZnT5 adopt different subcellular locations (either in the Golgi apparatus or throughout the cell, including at the plasma membrane) indicating discrete roles in cellular zinc homeostasis. We demonstrated, using a beta-galactosidase reporter gene, that both splice variants were expressed from a promoter region that was transcriptionally repressed by increased extracellular zinc (150 microM compared with 3 mum; approximately 40%) and by extracellular zinc depletion, using the chelator N,N,N',N'-tetrakis(2-pyridylmethyl) ethylenediamine ( approximately 20%). We mapped the zinc-responsive element to the region -154 to +50, relative to the predicted start of transcription, and showed that a consensus metal response element sequence (-410 to -404) was not responsible for these effects. Changes in ZnT5 mRNA abundance in Caco-2 cells at different zinc concentrations were in parallel to the changes in promoter activity ( approximately 40% reduction at 150 microM zinc) but in the presence of actinomycin D, to prevent transcription, we observed a marked stabilization (1.7-2-fold accumulation over 24 h) of ZnT5 mRNA. We conclude that effects of zinc on ZnT5 transcription and mRNA stability act in opposition to balance mRNA abundance for cellular zinc homeostasis. To our knowledge, this is the first report that zinc affects the stability of a transcript with a direct role in cellular zinc homeostasis.
  Journal of Biological Chemistry 05/2007; 282(14):10423-31. · 4.77 Impact Factor