The expression changes and role of hypoxia-inducible factor-1α in the early stage of hypoxic-ischemic brain damage in neonatal rats

Objective To study the expression of hypoxia-inducible factor-1a(HIF-1α) at mRNA and protein levels in the early stage of hypoxic-ischemic brain damage(HIBD) in neonatal rats and its role. Methods (1)Experiment 1: thirty-six postnatal 7-day SD rats were divided into Sham group(n=6) and model group(HIBD, n=30) according to the random table method, then the rats in the model group were divided into 5 subgroups according to the time of sacrifice after HIBD(6 h, 12 h, 24 h, 48 h, 72 h, n=6). The expression levels of HIF-1α mRNA and protein were detected by quantitative Real-time PCR(qPCR) and Western blot, respectively.(2) Experiment 2: forty-five postnatal 7-day SD rats were randomized into 3 groups: Sham group(n=15), HIBD group(n=15) and 2-methoxyestradiol(2ME2) group(n=15). According to the experiment 1, at the time point of the highest expression levels of HIF-1α mRNA and protein, rats were killed and the brains were collected.The location and expression of HIF-1α protein were detected by immunofluorescence, histopathological changes of brain were observed by HE staining, brain water content was measured by dry-wet method, cell apoptosis was detected by nick end labeling(TUNEL) method. Results At the early stage of HIBD, the expression levels of HIF-1α mRNA and protein increased at first and then decreased, and the mRNA expression level (3.38±0.21) and protein expression level (2.81±0.36) were the highest at 24 h after HIBD.In Sham group, HIF-1α protein was mainly expressed in the cytoplasm, while in HIBD group it was mainly expressed in the nucleus.The number of HIF-1α staining positive cells, brain water content and apoptosis rate were significantly different among Sham group, HIBD group and 2ME2 group(all P<0.05), and which were significantly lower in 2ME2 group than those in HIBD group(all P<0.05), and the pathological changes were also less serious than those in HIBD group. Conclusions The mRNA and protein levels of HIF-1α are the highest at 24 h after HIBD.Inhibiting the expression of HIF-1α can ameliorate the brain damage of neonatal rats induced by hypoxia-ischemia.Therefore, it is hypothesized that HIF-1α may cause injury in the early stage of HIBD in neonatal rats. Key words: Hypoxic-ischemic brain damage; Hypoxia-inducible factor1α; 2-methoxyestradiol; Rat, newborn