Browsing by Author "Ojuka, Edward"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Open Access
    Exercise-induced protection against insulin resistance and type 11 diabetes : the role of calcium
    (2008) Smith, James Antony Harris; Ojuka, Edward; Collins, Malcolm
    Regular exercise protects individuals against developing insulin resistance and type II diabetes. This effect of exercise does not appear to be due to an improvement in the insulin signalling pathway but instead due to an increase in the content of the insulin-regulatable glucose transporter (GLUT4) in skeletal muscle (84). Understanding the mechanisms by which exercise increases GLUT4 levels in skeletal muscle may reveal targets for pharmaceuticals to treat insulin resistance and type II diabetes. Although in vitro binding assays have shown that GLUT4 expression during exercise is mediated by the binding of myocyte enhancer factor-2A (MEF2A) to its cis-element on the Glut4 promoter (122), this has not been demonstrated in vivo. Moreover, the mechanisms by which exercise increases MEF2A binding to the Glut4 promoter have not been fully characterised.
  • Thumbnail Image
    Item
    Open Access
    Involvement of p300 in caffeine-induced hyper-acetylation of histones at the MEF2 binding domain on the Glut4 gene
    (2012) Chetty, Kovin Ashley; Ojuka, Edward
    Includes abstract. Includes bibliographical references.
  • Thumbnail Image
    Item
    Open Access
    Over-expression of NRF-1 in C2C12 myotubes increases GLUT4 content via a transcriptional cascade involving MEF2A
    (2012) Gumede, Dimakatso; Ojuka, Edward
    Previous studies have shown that over-expression of nuclear respiratory factor (NRF)-1 in mice increases glucose transporter (GLUT)-4 and myocyte enhancer factor (MEF-) 2A content, but the mechanisms have not been elucidated. Because NRF-1 has a binding site on the mef2a gene, and MEF2A binds the glut4 gene as a MEF2A-MEF2D heterodimer, the aims of this study were to determine whether NRF-1 over-expression a) enhanced GLUT4 expression indirectly via MEF2A and b) alters MEF2A-MEF2D dimer formation in C2C12 myotubes.
  • Thumbnail Image
    Item
    Open Access
    Regulation of Glut-4 Expression in Skeletal Muscle cells: The Roles of Nuclear Respiratory Factor-1 and calcium/calmodulin dependent protein Kinase
    (2010) Mukwevho, Emmanuel; Ojuka, Edward
    GLUT4 protein is the major glucose transporter in skeletal muscle and is vital in the maintenance of euglycemia (17; 108). Underexpression of GLUT4 or impairement of its translocation from intracellular compartments to the cell surface, are linked to diminished glucose transport, hyperglycemia and type II diabetes (59; 61; 153). Type II diabetes can be alleviated by increasing GLUT4 expression (223). Previous reports have shown that overexpression of NRF-1 and activation of CaMKII increases GLUT4 expression but the mechanisms involved have not be characterized (10; 173). Therefore, the objective of this thesis was to investigate the molecular mechanisms by which NRF-1 and CaMK II regulate GLUT4 expression in C2C12 myocytes. We engineered C2C12 cells that overexpressed NRF-1 in response to doxycycline (Dox) using a Tet-On gene expression system and assessed the effects of NRF-1 overexpression on: a) MEF2A, GLUT4 and δALAS proteins by western blot, and b) the binding of NRF-1 to mef2a and δalas genes and MEF2A to the glut4 gene, by chromatin immunoprecipitation assay (ChIP). The importance of MEF2A in NRF-1-induced increase in GLUT4 expression was investigated by silencing MEF2A expression using small interference RNA (siRNA). CaMK II was activated in wild-type C2C12 myocytes using 10 mM caffeine and was inhibited by 25 μ M KN93. Acetylation of histones in the vicinity of NRF-1 and MEF2A binding sites on the mef2a and glut4 genes, respectively, were assessed by ChIP assay. HDAC5 nuclear export was assessed by immunocytochemistry and mRNA levels by qRT-PCR. Overexpression of NRF-1 resulted in ~3-fold increases in mef2a-bound NRF-1 and glut4 -bound MEF2A at 6 h and 8 h post Dox treatment, respectively. MEF2A and GLUT4 proteins were both increased ~1.6-fold at 6 h and 18 h post Dox treatment. Silencing of MEF2A caused a marked downregulation of GLUT4 expression in NRF-1-overexpressing cells.