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-xL against both apoptotic and necrotic cell death, but the mode of action of Bcl-xL remains unclear. This work analyzed effects of Bcl-xL overexpression on cellular levels of reactive oxygen species (ROS), intracellular calcium ([Ca2+]i), and mitochondrial membrane potential (ΔΨm) 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-xL. Changes in ΔΨm in response to the two insults differed. H2O2 induced a decrease in ΔΨm that was initially greater in Bcl-xL cells, but then held stable. ΔΨm 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 ΔΨm, which was not observed with Bcl-xL overexpression. Bcl-xL failed to inhibit the calcium dysregulation seen in control cells exposed to 400 μM 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-xL on calcium homeostasis from effects on ROS, ΔΨm, and for H2O2 exposure, cell survival.