Objective:To study the role of SUMOylation in the process of therapeutic hypothermia on neural stem cells (NSCs) in neonatal hypoxic-ischemic encephalopathy.Methods:SUMOylation is an essential post-translational modification involving small ubiquitin-like modifiers (SUMOs). Primary-cultured NSCs from mice were assigned into four groups: control group, hypoxia group, hypothermia group and hypoxia+hypothermia group. Western Blot was used to detect the protein levels of SUMO2/3, hypoxia-inducible factor-1α (HIF-1α), peroxisome proliferator-activated receptor γ coactivator factor 1α (PGC-1α) and octamer binding transcription factor 4 (Oct4). The diameters of NSCs were compared. ELISA was used to detect lactate dehydrogenase (LDH) level. Apoptosis was examined using flow cytometry. Immunofluorescence method was used to measure the differentiation of NSCs into neuronal cells.Results:Compared with the control group, the levels of SUMO2/3, HIF-1αand PGC-1α in NSCs of the hypoxia group increased 33%, 126% and 140%, respectively ( P<0.05). Compared with the control group, the levels of SUMO2/3 and PGC-1α in NSCs of the hypothermia group increased 52% and 536%, respectively ( P<0.05). Compared with the hypoxia group, the levels of SUMO2/3, HIF-1α, PGC-1α and Oct4 in the hypoxia+hypothermia group increased 44%, 40%, 230% and 59%, respectively ( P<0.05). The diameters of NSCs in hypoxia group, hypothermia group and hypoxia+hypothermia group were smaller than control group, and hypoxia+hypothermia group smaller than hypoxia group ( P<0.05). No significant differences existed in LDH levels between hypothermia group and control group ( P>0.05). LDH level in hypoxia+hypothermia group were significantly lower than hypoxia group ( P<0.05). No significant differences existed in the cell death rates between hypothermia group and control group ( P>0.05). The cell death rate in hypoxia+hypothermia group was significantly lower than hypoxia group ( P<0.05). Compared with the control group, the expressions of Nestin in both hypoxia group and hypothermia group were increased, but neuron specific enolase (NSE) were decreased ( P<0.05). Compared with hypoxia group and hypothermia group, the level of Nestin in hypoxia+hypothermia group was further increased, while NSE was further decreased ( P<0.05). Conclusions:Therapeutic hypothermia may increase the tolerance of NSCs to hypoxia by enhancing SUMO modification of proteins, providing theoretical basis for the treatment of hypoxic-ischemic encephalopathy with therapeutic hypothermia.