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Lack of UCP2 reduces fas-mediated liver injury in ob/ob mice and reveals importance of cell-specific UCP2 expression

Authors

  • Péter Fülöp,

    1. Division of Gastroenterology & Liver Research Center, Brown Medical School and Rhode Island Hospital, Providence, Rhode Island
    2. First Department of Medicine, University of Debrecen Medical and Health Science Center, Debrecen, Hungary
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    • Péter Fülöp and Zoltán Derdák contributed equally to this work.

  • Zoltán Derdák,

    1. Division of Gastroenterology & Liver Research Center, Brown Medical School and Rhode Island Hospital, Providence, Rhode Island
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    • Péter Fülöp and Zoltán Derdák contributed equally to this work.

  • Anthony Sheets,

    1. Division of Gastroenterology & Liver Research Center, Brown Medical School and Rhode Island Hospital, Providence, Rhode Island
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  • Edmond Sabo,

    1. Department of Pathology, Brown Medical School and Rhode Island Hospital, Providence, Rhode Island
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  • Eric P. Berthiaume,

    1. Division of Gastroenterology & Liver Research Center, Brown Medical School and Rhode Island Hospital, Providence, Rhode Island
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  • Murray B. Resnick,

    1. Department of Pathology, Brown Medical School and Rhode Island Hospital, Providence, Rhode Island
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  • Jack R. Wands,

    1. Division of Gastroenterology & Liver Research Center, Brown Medical School and Rhode Island Hospital, Providence, Rhode Island
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  • György Paragh,

    1. First Department of Medicine, University of Debrecen Medical and Health Science Center, Debrecen, Hungary
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  • György Baffy

    Corresponding author
    1. Division of Gastroenterology & Liver Research Center, Brown Medical School and Rhode Island Hospital, Providence, Rhode Island
    • Liver Research Center, Brown Medical School and Rhode Island Hospital, 55 Claverick Street, 4th Floor, Providence, RI 02903
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    • fax: 401-444-2939


  • Potential conflict of interest: Nothing to report.

Abstract

Fatty liver is vulnerable to conditions that challenge hepatocellular energy homeostasis. Lipid-laden hepatocytes highly express uncoupling protein-2 (UCP2), a mitochondrial carrier that competes with adenosine triphosphate (ATP) synthesis by mediating proton leak. However, evidence for a link between UCP2 expression and susceptibility of liver to acute injury is lacking. We asked whether absence of UCP2 protects ob/ob mice from Fas-mediated acute liver damage. UCP2-deficient ob/ob mice (ob/ob:ucp2−/−) and UCP2-competent littermates (ob/ob:ucp2+/+) received a single dose of agonistic anti-Fas antibody (Jo2). Low-dose Jo2 (0.15 mg/kg intraperitoneally) caused less serum alanine aminotransferase (ALT) elevation and lower apoptosis rates in ob/ob:ucp2−/− mice. High-dose Jo2 (0.40 mg/kg intraperitoneally) proved uniformly fatal; however, ob/ob:ucp2−/− mice survived longer with less depletion of liver ATP stores, indicating that fatty hepatocytes may benefit from lack of UCP2 during Jo2 challenge. Although UCP2 reportedly controls mitochondrial oxidant production, its absence had no apparent effect on fatty liver tissue malondialdehyde levels augmented by Jo2. This finding prompted us to determine UCP2 expression in Kupffer cells, a major source of intrahepatic oxidative stress. UCP2 expression was found diminished in Kupffer cells of untreated ob/ob:ucp2+/+ mice, conceivably contributing to increased oxidative stress in fatty liver and limiting the impact of UCP2 ablation. In conclusion, whereas UCP2 abundance in fatty hepatocytes exacerbates Fas-mediated injury by compromising ATP stores, downregulation of UCP2 in Kupffer cells may account for persistent oxidative stress in fatty liver. Our data support a cell-specific approach when considering the therapeutic effects of mitochondrial uncoupling in fatty liver disease. (HEPATOLOGY 2006;44:592–601.)

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