Transforming growth factor beta mediates hepatocyte apoptosis through Smad3 generation of reactive oxygen species

Abstract

TGFβ induces hepatocyte apoptosis via reactive oxygen species (ROS) generation, the mitochondrial permeability transition (MPT), and caspase activation. The role of the Smad pathway in these events is unknown. In this study primary hepatocytes were isolated from Smad3 wild-type (+/+) and knockout (−/−) mice, and were treated with TGFβ (5 ng/ml) and/or trolox (2 mM). ROS generation, MPT, TGFβ-dependent transcription, and apoptosis were assessed in the presence or absence of Smad3 wild-type (WT) and dominant-negative (DN) plasmids. With TGFβ treatment, Smad3 (−/−) hepatocytes did not generate ROS activity, exhibit MPT, activate caspases, or undergo apoptosis when compared to Smad 3 (+/+) hepatocytes. Similarly, transfection of Smad3 (+/+) hepatocytes with DN-Smad3 inhibited TGFβ-mediated transcription, ROS generation, MPT, and apoptosis. However, Smad3 (−/−) cells transfected with WT-Smad3 and treated with TGFβ demonstrated increased transcriptional activity, the MPT, and TGFβ-induced apoptosis. TGFβ-mediated ROS generation occurred through an NADPH-like oxidase pathway since diphenyleneiodonium chloride inhibited ROS induction. In conclusion, TGFβ-induced hepatocyte apoptosis occurs through Smad3 dependent activation of ROS with subsequent activation of the MPT and caspases.

High glucose activates PKC-ζ and NADPH oxidase through autocrine TGF-β1 signaling in mesangial cells

“…We extend these observations further in the present study by showing that high glucosestimulated ROS generation by NADPH oxidase is dependent on extracellular TGF-␤ 1 . This agrees with the previously reported generation of ROS by TGF-␤ 1 through NADPH oxidase in lung fibroblasts and hepatocytes (4,5,36). The capacity of antisense p22 phox oligonucleotides to repress the effects of high glucose and TGF-␤ 1 on ROS levels confirmed NADPH oxidase as the target of TGF-␤ 1 in mesangial cells.…”

“…TGF-␤ 1 strongly enhances reactive oxygen species (ROS) production by NADPH oxidase in fibroblasts and hepatocytes (4,5,36). While the mechanisms are incompletely defined, this effect may be mediated in part through Smadinduced increases in the expression of Nox4 or other NADPH oxidase subunits (4). It could also involve PKC isozymes.…”

Mitochondrial Reactive Oxygen Species Regulate Transforming Growth Factor-β Signaling

“…Consistent with these reports, we detected an increase in ROS generation 30 min after TGF-␤ stimulation in NHLFs (22)(23)(24). Using oxidant-sensitive fluorescent proteins localized to the mitochondria or cytosol, we were able to localize the source of these ROS to the mitochondria.…”

Pleiotrophin inhibits transforming growth factor β1‐induced apoptosis in hepatoma cell lines

“…TGFb1 is the most effective apoptotic cytokine during hepatocarcinogenesis [22]. TGFb1 generated the reactive oxygen species and induced apoptosis of Huh-7 cells and activates first caspase-8, -9, and finally -3 [23,24]. Furthermore, a study on ''the loss of TGFb receptor'' showed that the hepatocytes in diethylnitrosamine and nodularin-induced-hyperplastic liver nodules escaped from the TGFb1-induced apoptosis and continued to proliferate [21].…”