Decreased vulnerability of hippocampal neurons after neonatal hypoxia-ischemia in bis-deficient mice

The Bcl-2-interacting death suppressor (Bis) protein is involved in antiapoptosis and antistress pathways. However, its roles after neonatal hypoxia-ischemia remain obscure. Therefore, we investigated the effects of Bis deletion on hippocampal cell death following neonatal hypoxia-ischemia. We transected the right common carotid artery of bis^+/+ and bis^-/- mice at postnatal Day 7 and subjected them to hypoxia for 35 min. Cresyl violet staining showed that hypoxia-ischemia induced progressive cell death in the hippocampi of bis^+/+ mice. Moreover, Bis was expressed in astrocytes, not microglia, in sham-manipulated hippocampi of bis^+/+ mice, and was markedly enhanced after hypoxia-ischemia. Immunoblotting showed that Bis expression significantly increased 3 and 7 days following hypoxia-ischemia. Unexpectedly, 7 days after hypoxia-ischemia, the number of hippocampal NeuN-positive cells was higher in the bis^-/- mice than in the bis^+/+ mice. We subsequently performed transcriptomic analysis and quantitative real time polymerase chain reaction to search for the underlying genes responsible for resistance to hypoxia-ischemia in the bis^-/- hippocampus. These studies showed that 6 h after hypoxia-ischemia, galectin 3 and filamin C levels increased to a lesser extent in the bis^-/- hippocampi compared with the bis^+/+ hippocampi. Finally, our in vitro hypoxia-ischemia model, using A172 glioma cells and primary astrocytes, showed that downregulation of Bis blocked the enhanced expression of galectin 3 after oxygen-glucose deprivation. This study demonstrated that Bis was upregulated in the astrocytes after hypoxia-ischemia. In addition, we showed that hippocampal neurons are less vulnerable to hypoxia-ischemia in mice lacking Bis, possibly because of the modulation of galectin 3 induction.