Reactive Oxygen as Modulator of TNF and Fas Receptor-Mediated ApoptosisIn Vivo: Studies with Glutathione Peroxidase-Deficient Mice

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Abstract
Reactive oxygen species (ROS) can directly induce or enhance tumor necrosis factor (TNF)-mediated apoptosis in a number of different cell lines. To test the relevance of intracellular ROS in modulating apoptotic signaling in vivo, we evaluated hepatocellular apoptosis mediated by the TNF or Fas receptor in wild-type and glutathione peroxidase-1 (Gpx1-/-)-deficient mice (129SV/B6 background). Apoptosis developed in livers of wild-type animals 4-6 h after intraperitoneal administration of 700 mg/kg galactosamine/100 µg/kg endotoxin. Apoptosis was indicated by processing of procaspases-3 (assessed by western blotting), a fivefold increase in caspase-3 activity (DEVD-AMC as substrate), and a 44-fold increase in DNA fragmentation (ELISA). The time course and magnitude of apoptosis were the same in Gpx1-/- mice. In contrast, Gpx1-/- mice had higher plasma alanine aminotransferase (ALT) levels and more severe hemorrhage compared to wild-type animals at 6 h. Treatment of wild-type mice with the anti-Fas antibody Jo-2 (0.6 mg/kg i.v.) resulted in processing of procaspase-3 and a sevenfold increase in caspase-3 activity in both wild-type and Gpx1-/- mice. However, higher plasma ALT values in Gpx1-/- mice at 3 h may reflect a trend to develop more rapidly secondary necrosis. These data suggest that, under our experimental conditions, intracellular ROS did not modulate the death receptor-initiated apoptotic signaling cascade in hepatocytes. As Gpx1 is located in the cytosol and in mitochondria, which are the main cellular compartments involved in apoptotic signaling, our findings indicate that the oxidant stress in vivo was insufficient to modulate these signaling pathways. However, Gpx1 deficiency enhances the susceptibility for secondary necrosis or neutrophil-induced cell injury.

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