Opposite roles of selenium-dependent glutathione peroxidase-1 in superoxide generator diquat- and peroxynitrite-induced apoptosis and signaling.

Yangxin Fu,Helmut Sies,Xin Gen Lei

doi:10.1074/jbc.m106946200

Abstract

Oxidative injuries including apoptosis can be induced by reactive oxygen species (ROS) and reactive nitrogen species (RNS) in aerobic metabolism. We determined impacts of a selenium-dependent glutathione peroxidase-1 (GPX1) on apoptosis induced by diquat (DQ), a ROS (superoxide) generator, and peroxynitrite (PN), a potent RNS. Hepatocytes were isolated from GPX1 knockout (GPX1-/-) or wild-type (WT) mice, and treated with 0.5 mm DQ or 0.1-0.8 mm PN for up to 12 h. Loss of cell viability, high levels of apoptotic cells, and severe DNA fragmentation were produced by DQ in only GPX1-/- cells and by PN in only WT cells. These two groups of cells shared similar cytochrome c release, caspase-3 activation, and p21(WAF1/CIP1) cleavage. Higher levels of protein nitration were induced by PN in WT than GPX1-/- cells. Much less and/or slower cellular GSH depletion was caused by DQ or PN in GPX1-/- than in WT cells, and corresponding GSSG accumulation occurred only in the latter. In conclusion, it is most striking that, although GPX1 protects against apoptosis induced by superoxide-generator DQ, the enzyme actually promotes apoptosis induced by PN in murine hepatocytes. Indeed, GSH is a physiological substrate for GPX1 in coping with ROS in these cells.

Highlights

Reactive oxygen species (ROS)1 and reactive nitrogen species (RNS) are constantly generated in aerobic metabolism and involved in pathogenesis of many diseases [1, 2]
glutathione peroxidase-1 (GPX1) Knockout Renders Mouse Hepatocytes Susceptible to DQ-induced, but Resistant to PN-induced, Apoptotic Death— Compared with the untreated controls, viability of GPX1Ϫ/Ϫ hepatocytes was decreased by 0.5 mM DQ from 82% at 3 h to 4.9% at 12 h, whereas that of WT remained Ͼ84% throughout (Fig. 1A)
DNA fragmentation was produced by 0.5 mM DQ in only GPX1Ϫ/Ϫ cells and by 0.4 mM PN in only WT cells at 9 h, and the DNA ladder became pronounced at 12 h in these two groups (Fig. 2A)

Summary

Introduction

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are constantly generated in aerobic metabolism and involved in pathogenesis of many diseases [1, 2]. (16), we have demonstrated that GPX1 is the metabolic mediator of body selenium to protect mice against pro-oxidantinduced death and oxidative injuries [17, 18]. In contrast to such strong evidence for the long-assumed role of GPX1 in coping with ROS in vivo [19], the impact of GPX1 on RNS-. C-Jun NH2-terminal protein kinase (JNK) and p38 kinase, two mitogen-activated protein kinases (MAPK), are activated in apoptosis induced by diverse stimuli [32] It is unknown how GPX1 affects the DQ- and PN-induced apoptosis and related signaling

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Conclusion