Selenium attenuates expression of MnSOD and uncoupling protein 2 in J774.2 macrophages: molecular mechanism for its cell-death and antiinflammatory activity.

Selenium can activate cell death. However, the mechanism of action is not yet fully defined. We hypothesized that selenium may impede mitochondrial superoxide dismutation to H2O2 and O2, leading to cell death in macrophages and that this effect may be relevant to antiinflammatory treatment by selenium. In this study, the mechanism of action of selenium was investigated in nonactivated and activated (immune-stimulated) J774.2 macrophages. Sodium selenite treatment decreased dichlorodihydrofluorescein-reacting intracellular reactive oxygen species (ROS) (mainly peroxides and hydroxyl radicals), with no correlation to glutathione peroxidase activity. However, selenite decreased the transcription and expression of manganese superoxide dismutase (MnSOD) and uncoupling protein 2 (UCP2). This cellular effect was due to inhibition of specificity protein-1 (Sp1) binding to its DNA binding site. Following immune stimulation of macrophages using lipopolysaccharides plus interferon-gamma, MnSOD was up-regulated. Activated macrophages showed higher mitochondrial membrane potential, intracellular ROS levels, and cellular resistance to cell death. Selenite treatment attenuated all of these parameters. Selenite prevented nuclear factor-kappaB (NF-kappaB) activation as a mechanism of its inhibitory activity on MnSOD expression in the immune-stimulated cells. In addition, overexpression of human MnSOD protected against death induced by selenite treatment. It is therefore concluded that selenium at high nanomolar to low micromolar concentrations shifts the balance between inflammatory response and cell death toward the latter, through a direct effect on the transcription factors Sp1 and NF-kappaB, and down-regulation of MnSOD and UCP2.