Reactive oxygen species (ROS) mediates the mitochondrial-dependent apoptosis induced by transforming growth factor β in fetal hepatocytes

Treatment of fetal rat hepatocytes with transforming growth factor beta (TGF-beta) is followed by apoptotic cell death, Analysis of radical oxygen species (ROS) content and mitochondrial transmembrane potential (Delta Psi (m)), using specific fluorescent probes in FACScan and confocal microscopy, showed that TGF-beta mediates ROS production that precedes the loss of Delta Psi (m), the release of cytochrome c, and the activation of caspase 3. TGF-beta induces a decrease in the protein and mRNA levels of bcl-x(L), an antiapoptotic member of the Bcl-2 family. In contrast, there is no change in the expression and/or translocation of Bax, a proapoptotic member of the same family. EGF maintains Bcl-x(L), preventing Delta Psi (m) collapse and release of cytochrome c, The presence of radical scavengers blocks the decrease in bcl-x(L) levels, Delta Psi (m) collapse, cytochrome c release, and activation of caspase 3; in contrast, the presence of glutathione synthesis inhibitors such as BSO accentuated the effect. The incubation of fetal hepatocytes in the presence of ter-butyl-hydroperoxide alone produces a decrease in bcl-x(L). These results indicate that during the apoptosis mediated by TGF-beta in fetal hepatocytes, ROS may be responsible for the decrease in bcl-x(L) mRNA levels that precedes the loss of Delta Psi (m), the release of cytochrome c, and the activation of caspase 3, culminating in cell death.