Biphasic role of nuclear factor-kappa B on cell survival and COX-2 expression in SOD1 Tg astrocytes after oxygen glucose deprivation.

In cytoplasm, nuclear factor-kappaB (NF-kappaB) is associated with the inhibitory protein, IkappaBalpha. On activation by H2O2, IkappaBalpha is phosphorylated and degraded, exposing the nuclear localization signals on the NF-kappaB heterodimer. Cyclooxygenase-2 (COX-2), which mediates prostaglandin synthesis during inflammation, is induced by oxidative stress mediated by NF-kappaB. We investigated whether the NF-kappaB signaling pathway affected cell death and COX-2 expression after hypoxia-induced oxidative stress in wild-type (WT) and copper/zinc-superoxide dismutase transgenic (SOD1 Tg) astrocytes. In WT astrocytes, phospho-IkappaBalpha was highly expressed after oxygen-glucose deprivation (OGD) and 2 h of reperfusion, concomitant with the decrease in IkappaBalpha. The NF-kappaB p50 level increased similarly in WT and SOD1 Tg astrocytes (1.2-/1.4-fold) after OGD. Electrophoretic mobility shift assay showed higher DNA-binding activity of NF-kappaB p50 in WT than in SOD1 Tg astrocytes 6 h after 4 h of OGD. The COX-2 level was induced by 2.7- and 1.3-fold after OGD in WT and SOD1 Tg astrocytes, and an antioxidant protected both groups against OGD injury. Superoxide dismutase transgenic cells were 23% more protective against OGD injury than WTs when assessed by lactate dehydrogenase release. However, transfection of NF-kappaB small interfering RNAs in SOD1 Tg astrocytes aggravated cell death and increased COX-2 expression. These results suggest that the NF-kappaB signaling pathway induced COX-2 expression and promoted cell death in WTs after OGD injury; however, NF-kappaB activation protected cells and decreased COX-2 expression in SOD1 Tg astrocytes. This biphasic role of NF-kappaB might be coordinately regulated by reactive oxygen species levels in astrocytes, thereby functioning as a regulator of cell death/survival.