Expressions of Omi/HtrA2 in parietal cortex of neonatal rats with hypoxic-ischemic brain damage

Abstract

Objective To study the dynamic changes of Omi/HtrA2 in the cytoplasm of cerebral parietal cortex in neonatal rats with hypoxic-ischemic brain damage (HIBD),and explore the role of Omi/HtrA2 in HIBD.Methods Seven-day-old SD rats were randomly assigned to sham-operated group and vehicle group; and HIBD models were established by the Rice and CHEN Hui-jin methods.Each group was further divided into 4 subgroups (n=8) according to the observation time points (6,12,24and 72 h).In each subgroup,the turnover ability and dextrorotatory ability when their tails were gripped were observed before the experiment and 1 h after hypoxic-ischemia (HI).The appearance of the brain was observed,and the protein levels of Omi/HtrA2 in the brain tissues or homogenates were examined by immunohistochemistry and Western blotting.Results (1) Changes of behavior of the rats:before the experiment,all rats were healthy; 1 h after HI,the rats in sham-operated group were still healthy,while out of 32 rats which bared HI injury,18 could not turn themselves over,20 became dextrorotatory when their tails were gripped and 14 exhibited both behavior problems.(2) General examination of the brain:the ligated brain hemisphere in the vehicle group showed obvious pallor and edema at 24 h; the two brain hemispheres in sham-operated group showed no pathological change.(3) Western blotting results showedthat the protein levels of Omi/HtrA2 in the vehicle group were significantly higher than those in the sham-operated group at each observation time points (P＜0.05); the expressions of Omi/HtrA2 in the vehicle group began to increase at 6 h,peaked at 24 h after HI insult and decreased thereafter.(4) By immunohistochemistry,it showed that the Omi/HtrA2 positive cells in cytoplasm and membrane of cerebral cortex in the vehicle group peaked at 24 h after HI insult and decreased thereafter; the quantity of positive cells in the vehicle group was larger than that in the sham-operated group (P＜0.05).Conclusion The levels of Omi/HtrA2 in the cerebral cortex increase after HI insult in neonatal rats,showing time-difference expression,which may play important roles in cell apoptosis induced by HIBD. Key words: Hypoxic-ischemic brain damage; Omi/HtrA2; Cerebral cortex; Neonatal rat