Shenker B J, Guo T L, Shapiro I M
Department of Pathology, School of Dental Medicine, University of Pennsylvania, Philadelphia 19104, USA.
Environ Res. 2000 Oct;84(2):89-99. doi: 10.1006/enrs.2000.4078.
There is growing evidence that heavy metals, in general, and mercurial compounds, in particular, are toxic to the human immune system. In this regard, we have previously shown that both inorganic and organic mercurials are potent human T-cell apoptogens; moreover, mitochondria appear to be a target organelle for the induction of cell death. To ascertain whether both mercury species utilize the same molecular pathway to trigger the apoptotic cascade, cells were treated with MeHgCl or HgCl2 and mitochondrial activity was examined. We show that both mercury species affect mitochondrial activity by inducing the development of a membrane permeability transition. This state is characterized by a decline in both the transmembrane potential and the intracellular pH, as well as the generation of reactive oxygen species. We also determined that mercury exposure results in a decline in the T-cell GSH content. Since mitochondrial dysfunction and the development of a permeability transition may result in the release of cytochrome c, a factor that promotes apoptosis, we assessed the abilities of both species of mercury to induce the translocation of cytochrome c from mitochondria to the cytosol. We noted that MeHgCl caused a significant increase in cytosolic cytochrome c. Surprisingly, however, HgCl2 did not alter the level of cytosolic cytochrome c. We next determined whether the mercurials could alter the level of the anti-apoptotic protein Bcl-2. Our results demonstrate that HgCl2 induces a significant elevation in the Bcl-2 content of T-cells; in contrast, T-cells treated with MeHgCl did not exhibit altered levels of this anti-apoptotic protein. Regardless of whether cytochrome c is released from the mitochondria, both mercurial species were capable of activating the caspase cascade, as evident by cleavage of poly (ADP-ribose) polymerase. Thus, our study shows that, whereas each of the mercury species shares common features in the apoptotic process, profound differences exist in a number of key steps in the pathway. The significance of these differences is discussed.
越来越多的证据表明，一般而言重金属，尤其是汞化合物，对人体免疫系统有毒性。在这方面，我们之前已经表明，无机汞和有机汞都是强效的人类T细胞凋亡诱导剂；此外，线粒体似乎是诱导细胞死亡的靶细胞器。为了确定这两种汞是否利用相同的分子途径触发凋亡级联反应，用甲基汞氯化物或氯化汞处理细胞并检测线粒体活性。我们表明，这两种汞都通过诱导膜通透性转变的发生来影响线粒体活性。这种状态的特征是跨膜电位和细胞内pH值下降，以及活性氧的产生。我们还确定，汞暴露会导致T细胞谷胱甘肽含量下降。由于线粒体功能障碍和通透性转变的发生可能导致细胞色素c的释放，而细胞色素c是一种促进凋亡的因子，我们评估了这两种汞诱导细胞色素c从线粒体转运到细胞质的能力。我们注意到甲基汞氯化物导致细胞质中细胞色素c显著增加。然而，令人惊讶的是，氯化汞并没有改变细胞质中细胞色素c的水平。接下来，我们确定汞是否会改变抗凋亡蛋白Bcl-2的水平。我们的结果表明，氯化汞会导致T细胞中Bcl-2含量显著升高；相比之下，用甲基汞氯化物处理的T细胞中这种抗凋亡蛋白的水平没有变化。无论细胞色素c是否从线粒体中释放，这两种汞都能够激活半胱天冬酶级联反应，这从聚（ADP-核糖）聚合酶的裂解可以明显看出。因此，我们的研究表明，虽然这两种汞在凋亡过程中具有共同特征，但在该途径的一些关键步骤中存在深刻差异。讨论了这些差异的意义。
