DYSREGULATION OF GSH SYNTHESIS DURING LIVER INJURY AND FIBROSIS

Summary

Principal Investigator: SHELLY CHI LOO LU
Abstract: DESCRIPTION (provided by applicant): Glutathione (GSH) plays a key role in xenobiotic metabolism, defends against oxidative stress and modulates pathological processes such as inflammatory response and fibrogenesis. The activity of glutamate-cysteine ligase (GCL) is a key factor that determines GSH synthesis. GCL is made up of a catalytic and a modifier subunit (GCLC and GCLM), the former exhibits all of the catalytic activity of the holoenzyme but the latter makes the enzyme function more efficiently. GSH synthase (GS), the second enzyme in GSH synthesis, is often regulated in a coordinated manner as GCL subunits and can further enhance the GSH synthetic capacity. Hepatic GSH level is often decreased in chronic liver injury and was thought largely to be due to nutritional deficiency and oxidative stress. However, we showed recently that in chronic cholestatic liver injury, the expression of hepatic GSH synthetic enzymes is reduced markedly due to displacement of transcription factor Nrf2 by MafG and c-Maf from binding to the anti-oxidant response element (ARE) that is important in positive regulation of the GSH synthetic enzymes. The expression of MafG and c-Maf is increased during cholestatic liver injury and this occurs at the transcriptional level. Blocking the increasein expression of MafG and c-Maf prevented the fall in expression of GSH synthetic enzymes and GSH levels and significantly ameliorated cholestatic liver injury. In contrast, lowering GCLC expression markedly worsened cholestatic liver injury and fibrosis. We have also found that expression of GSH synthetic enzymes is inhibited by lipopolysaccharide (LPS). In this proposal, our goals are to understand how GSH synthesis is dysregulated in various liver injuries and elucidate mechanisms for induction of Maf proteins. Hepatoprotective agents such as ursodeoxycholic acid (UDCA) and S-adenosylmethionine (SAMe) prevented the fall in GCL subunits mRNA levels in hepatocytes (UDCA and SAMe) during cholestasis, and in macrophages (SAMe) during LPS treatment. We have cloned or obtained mouse, rat and human GCLC, GCLM and GS promoters. We have also cloned the mouse and human MafG and c-Maf promoters. We are poised with these tools to achieve our goal with the following aims: 1) elucidate the molecular mechanism(s) of Nrf2 to MafG/c-Maf switch in nuclear binding to ARE during cholestatic liver injury;2) elucidate the mechanism(s) by which UDCA and SAMe prevent the fall in expression of GSH synthetic enzymes and the significance of preserving GSH during cholestasis;3) identify molecular mechanisms of LPS-induced inhibition of GSH synthetic enzymes. These studies will use hepatocytes and macrophages from mouse and human. They will complement in vivo studies in mice treated with bile duct ligation or LPS. This is to make sure that findings in rodents also occur in human cells and that in vitro findings are applicable t relevant in vivo models. The ultimate goal is to translate results from the laboratory to bedside i designing more effective therapy against various liver injuries where altered GSH synthesis plays a major pathogenetic role, a topic that is highly relevant to public health.
Funding Period: 2012-04-01 - 2017-03-31
more information: NIH RePORT

Top Publications

  1. pmc Mechanism and significance of changes in glutamate-cysteine ligase expression during hepatic fibrogenesis
    Komal Ramani
    Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, Keck School of Medicine of University of Southern California, Los Angeles, California 90033, USA
    J Biol Chem 287:36341-55. 2012
  2. pmc Glutathione synthesis
    Shelly C Lu
    Keck School of Medicine USC, Los Angeles, CA 90033, USA
    Biochim Biophys Acta 1830:3143-53. 2013
  3. pmc S-adenosylmethionine in liver health, injury, and cancer
    Shelly C Lu
    Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, Southern California Research Center for ALPD and Cirrhosis, Keck School of Medicine, Los Angeles, California 90033, USA
    Physiol Rev 92:1515-42. 2012
  4. pmc Molecular mechanisms of lipopolysaccharide-mediated inhibition of glutathione synthesis in mice
    Maria Lauda Tomasi
    Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, Los Angeles, CA 90033, USA Southern California Research Center for Alcoholic Liver and Pancreatic Diseases and Cirrhosis, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA
    Free Radic Biol Med 68:148-58. 2014

Detail Information

Publications4

  1. pmc Mechanism and significance of changes in glutamate-cysteine ligase expression during hepatic fibrogenesis
    Komal Ramani
    Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, Keck School of Medicine of University of Southern California, Los Angeles, California 90033, USA
    J Biol Chem 287:36341-55. 2012
    ..In conclusion, sumoylation of Nrf2 and MafG enhances heterodimerization and increases GCLC expression, which keeps HSCs in a quiescent state. Antifibrotic agents require activation of GCLC to fully exert their protective effect...
  2. pmc Glutathione synthesis
    Shelly C Lu
    Keck School of Medicine USC, Los Angeles, CA 90033, USA
    Biochim Biophys Acta 1830:3143-53. 2013
    ..The second enzyme of GSH synthesis is GSH synthetase (GS)...
  3. pmc S-adenosylmethionine in liver health, injury, and cancer
    Shelly C Lu
    Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, Southern California Research Center for ALPD and Cirrhosis, Keck School of Medicine, Los Angeles, California 90033, USA
    Physiol Rev 92:1515-42. 2012
    ..In experimental models, it is effective as a chemopreventive agent in HCC and perhaps other forms of cancer as well...
  4. pmc Molecular mechanisms of lipopolysaccharide-mediated inhibition of glutathione synthesis in mice
    Maria Lauda Tomasi
    Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, Los Angeles, CA 90033, USA Southern California Research Center for Alcoholic Liver and Pancreatic Diseases and Cirrhosis, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA
    Free Radic Biol Med 68:148-58. 2014
    ..In conclusion, LPS-mediated lowering of GCL expression in hepatocytes and macrophages is due to lowering of sumoylation of Nrf2 and MafG, leading to reduced heterodimerization, binding, and trans-activation of ARE. ..

Research Grants30

  1. Autocrine/Paracrine Regulation of Intrahepatic Bile Duct Growth
    GIANFRANCO D ALPINI; Fiscal Year: 2013
    ....
  2. Regulation of Hepatic Uptake of Endogenous Signaling Molecules and Xenobiotics
    Ivan Csanaky; Fiscal Year: 2013
    ....
  3. Role of Bile Acids in the Initiation of Liver Regeneration
    Willscott E Naugler; Fiscal Year: 2013
    ....
  4. Phagocytosis and NOX2 in Liver Fibrogenesis
    Natalie J Torok; Fiscal Year: 2013
    ..Information originating from the successful completion of the proposed experiments has the potential to be developed into strategies to prevent and treat liver fibrosis. ..
  5. Signaling pathways and the fate of hepatic progenitor cells
    Linda E Greenbaum; Fiscal Year: 2013
    ..Understanding the biology of hepatic progenitor cells will have wide-ranging implications for the development of therapeutics for acute liver failure, chronic cirrhotic liver disease and hepatocellular carcinoma. ..