However, in vasogenic brain edema, the BBB integrity is seriously damaged, and water molecules leak directly from blood vessels into brain tissue space and lead to brain edema without the participation of AQP-4, and there was no direct relationship between the severity of brain edema and the expression level of AQP-4 (Tait et al., 2008), while the removal of water molecules from brain requires the mediation of AQP-4 channel, and this result may explain the differences of AQP-4 expression in many hypoxia models and CO poisoning experiments. The gene discussed is AQP4; the disease is brain edema.