The role of STAT1/IRF-1 on synergistic ROS production and loss of mitochondrial transmembrane potential during hepatic cell death induced by LPS/D-GaIN

Previously, we demonstrated that signal transducer and activator of transcription factor 1 (STAT1) plays an essential role in liver injury induced by lipopolysaccharide (LPS)/D-galactosamine (D-GalN); however, the underlying mechanism involved remains unclear. Here, we showed that LPS/D-GalN administration induced secretion of tumor necrosis factor alpha (TNF-alpha) and interferon gamma (lFN-gamma), which mediated apoptosis synergistically. Moreover, LPS/D-GalN-induced apoptosis was associated with increased inducible nitric oxide synthase (iNOS) and nitric oxide (NO) production, as well as elevated reactive oxygen species (ROS) production, which were all strongly inhibited by treatment with the antioxidant N-acetyl-L-cysteine (NAC) and an iNOS/NO inhibitor, L-NMMA. Although STAT1 activation and expression did not change significantly in TNF-alpha/IFN-gamma-cotreated cells compared with cells treated with IFN-gamma alone, the absence of STAT1 or interferon regulatory factor I (IRF-1) in genetic knockout mice strongly abrogated the observed effects of TNF(alpha/IFN-gamma on iNOS/NO induction, ROS production, loss of mitochondrial transmembrane potential (Delta Psi m), and apoptosis compared with STAT1 (+/+) and IRF-1(+/+) mice. Additionally, the synergistic effects of TNF(alpha/IFN-gamma on iNOS/NO induction, ROS production, and apoptosis were significantly inhibited by overexpression of dominant negative STAT1 in contrast to overexpression of wild-type STAT1. In STAT1-deficient mice, nuclear factor KB (NF-KB) activation by TNF-alpha/IFN-gamma, was attenuated and strongly inhibited by both NAC and L-NMMA. Moreover, the proteasome inhibitor, MG132, inhibited NF-KB activation and strongly inhibited iNOS/NO induction, ROS production, and loss of Delta Psi m induced by TNF-alpha-/IFN-gamma, thereby inhibiting apoptosis. Interestingly, it appears peroxynitrite, which is produced by TNF-alpha/IFN-, may interfere with STAT1 phosphorylation by inducing STAT1. nitration. Collectively, these findings demonstrate that TNF-alpha/IFN-gamma synergisti cally potentiates iNOS/NO induction, ROS production, and loss of Delta Psi m via STAT1 overexpression, Playing an important role in promoting apoptosis and liver injury induced by LPS/D-GalN. (C) 2007 Elsevier Ltd. All rights reserved.