title: TGF-beta dependent regulation of oxygen radicals during transdifferentiation of activated hepatic stellate cells to myofibroblastoid cells.
abstract: BACKGROUND
  The activation of hepatic stellate cells (HSCs) plays a pivotal role during liver injury because the resulting myofibroblasts (MFBs) are mainly responsible for connective tissue re-assembly. MFBs represent therefore cellular targets for anti-fibrotic therapy. In this study, we employed activated HSCs, termed M1-4HSCs, whose transdifferentiation to myofibroblastoid cells (named M-HTs) depends on transforming growth factor (TGF)-beta. We analyzed the oxidative stress induced by TGF-beta and examined cellular defense mechanisms upon transdifferentiation of HSCs to M-HTs.
  
  
  RESULTS
  We found reactive oxygen species (ROS) significantly upregulated in M1-4HSCs within 72 hours of TGF-beta administration. In contrast, M-HTs harbored lower intracellular ROS content than M1-4HSCs, despite of elevated NADPH oxidase activity. These observations indicated an upregulation of cellular defense mechanisms in order to protect cells from harmful consequences caused by oxidative stress. In line with this hypothesis, superoxide dismutase activation provided the resistance to augmented radical production in M-HTs, and glutathione rather than catalase was responsible for intracellular hydrogen peroxide removal. Finally, the TGF-beta/NADPH oxidase mediated ROS production correlated with the upregulation of AP-1 as well as platelet-derived growth factor receptor subunits, which points to important contributions in establishing antioxidant defense.
  
  
  CONCLUSIONS
  The data provide evidence that TGF-beta induces NADPH oxidase activity which causes radical production upon the transdifferentiation of activated HSCs to M-HTs. Myofibroblastoid cells are equipped with high levels of superoxide dismutase activity as well as glutathione to counterbalance NADPH oxidase dependent oxidative stress and to avoid cellular damage.
authors.affiliation: Department of Medicine I, Division Institute of Cancer Research, Medical University of Vienna, Borschke-Gasse 8a, A-1090 Vienna, Austria. verena.proell@meduniwien.ac.at
authors.forename: Verena
authors.initials: V
authors.lastname: Proell
authors.forename: Irene
authors.initials: I
authors.lastname: Carmona-Cuenca
authors.forename: Miguel M
authors.initials: MM
authors.lastname: Murillo
authors.forename: Heidemarie
authors.initials: H
authors.lastname: Huber
authors.forename: Isabel
authors.initials: I
authors.lastname: Fabregat
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Mikulits