Effect of Bcl-xL overexpression on reactive oxygen species, intracellular calcium, and mitochondrial membrane potential following injury in astrocytes

Many studies have demonstrated the protective effects of Bcl-x(L) against both apoptotic and necrotic cell death, but the mode of action of Bcl-x(L) remains unclear. This work analyzed effects of Bcl-x(L) overexpression on cellular levels of reactive oxygen species (ROS), intracellular calcium ([Ca2+](i)), and mitochondrial membrane potential (DeltaPsi(m)) in cultured mouse primary astrocytes after exposure to glucose deprivation (GD) or hydrogen peroxide (H2O2). Upon exposure to GD or H2O2, uninfected and Lac-Z-expressing astrocytes showed an immediate, rapid increase in ROS accumulation that was slowed and or reduced by Bcl-X-L. Changes in DeltaPsi(m) in response to the two insults differed. H2O2 induced a decrease in DeltaPsi(m) that was initially greater in Bcl-X-L cells, but then held stable. DeltaPsi(m) in control and Lac-Z-expressing cells initially declined more slowly, but after about 20 min showed rapid deterioration. Five hours of GD caused mitochondrial membrane hyperpolarization followed by a decrease in DeltaPsi(m), which was not observed with Bcl-X-L overexpression. Bcl-X-L failed to inhibit the calcium dysregulation seen in control cells exposed to 400 muM H2O2, but still improved cell survival. There was no increase in [Ca2+](i) with 5 h of GD. These data thus dissociate the effect of Bcl-X-L on calcium homeostasis from effects on ROS, DeltaPsi(m), and for H2O2 exposure, cell survival. (C) 2002 Elsevier Science Inc.