Increased endogenous reactive oxygen species normalizes proliferation defects of Bmi1 heterozygous knockout neural stem cells

The Bmi1gene, one of transcriptional suppressor genes in multi-comb family, maintains proliferation of neural stem cells (NSCs) and redox homeostasis. However, heterozygous deletion of the Bmi1 gene (Bmi1+/-) does not reduce the proliferative ability of NSCs. The aim of the present study was to reveal the underlying mechanism of this phenotype.NSCs derived from the cortex of newborn Bmi1+/- and wild-type (WT) mice were treated with different concentrations of hydrogen peroxide (H2O2) and antioxidant N-acetyl-L-cysteine (NAC) for 24 h followed by analyses of NSC proliferation and oxidative stress-related indexes.The levels of reactive oxygen species (ROS) of Bmi1+/--NSCs were slightly higher than that of WT-NSCs at baseline. H2O2 increased ROS and NAC reduced ROS in a concentration-dependent pattern, but the change was significantly greater in Bmi1+/--NSCs than WT-NSCs. The proliferation and self-renewal ability of Bmi1+/--NSCs and WT-NSCs were comparable in a basic state. After 1 μM H2O2 treatment, Brdu incorporation ratio, cell viability, total antioxidant capacity (T-AOC) and total superoxide dismutase activity were increased slightly in WT-NSCs, but decreased in Bmi1+/--NSCs. H2O2 at 10 μM decreased proliferation and self-renewal ability of both genotype NSCs, with greater effect in Bmi1+/-. After treatment with 1 mM NAC, the number and diameter of neurospheres, Brdu incorporation rate, cell viability, T-AOC and total superoxide dismutase activity of Bmi1+/--NSCs were lower than those of WT-NSCs.These results suggest that Bmi1+/--NSCs exhibit normal proliferation and self-renewal due to a slight increase in ROS, but are more vulnerable to changes in redox status.