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[Phosphoinositide 3-kinase/Akt pathway involved in regulation of hypoxia inducible factor 1alpha in hypoxia ischemia brain damage of neonatal rats].

OBJECTIVE
To investigate the expression of hypoxia inducible factor 1alpha (HIF-1alpha) protein and the activation of phosphoinositide 3-kinase/Akt (PI3K/Akt) signaling pathway in neurons under hypoxia ischemia condition, and to elucidate the role of PI3K/Akt on HIF-1alpha regulation in the developing neurons after hypoxia ischemia brain damage (HIBD).


METHODS
Fifty-six SD rats aged 10 days were randomly divided into normal control group (n=12), sham operation group (n=12), experimental group (n=24), wortmannin treated group (n=4) and DMSO/PBS treated group (n=4). In the experimental group, the rats were anesthetized with ethyl ether. The right common carotid artery was exposed and ligated. Then, they were exposed to hypoxia in a normobaric chamber filled with 8% oxygen and 92% nitrogen for 2.5 hours. In the sham control group, the right common carotid artery was exposed but was not ligated or exposed hypoxia. In the normal control group, the rats received no further processing. For wortmannin treated group and DMSO/PBS treated group, the rats received intraventricular injection of wortmannin or DMSO/PBS 30 minutes before hypoxia ischemia. The brain tissues were harvested from the rats in the normal control, sham operation and experimental groups at 4, 8 and 24 hours after hypoxia ischemia, but in the wortmannin and DMSO/PBS treated groups only at 4 hours. The HIF-1alpha protein expression and Akt protein expression were detected with immunohistochemistry method. HIF-1alpha, Akt and p-Akt protein expression were measured by Western blot analysis.


RESULTS
In the experimental group, the HIF-1alpha expression was significantly increased at 4 hours after operation, reached the peak level at 8 hours, and began to decrease at 24 hours. The p-Akt protein was significantly increased at 4 hours, and began to decrease at 8 hours. However, the expression levels of HIF-1alpha and p-Akt protein in the normal control group were extremely low at each time point. So, the expression levels of HIF-1alpha in the experimental group was significantly higher than that in the normal control groups (P < 0.01), the expression of p-Akt protein in the experimental group at 4 and 8 hours was significant higher than that in the normal control group (P < 0.05). The change of Akt protein in the experimental group was not time-dependent, and no significant difference was evident when compared with that of the normal control group (P > 0.05). Using wortmannin, the PI3K/Akt specific inhibitor, HIF-1alpha protein expression was significantly decreased when compared with the DMSO/PBS treated group and experimental group (P < 0.01).


CONCLUSION
These results suggested that the HIBD of neonatal rats may activate PI3K/Akt signaling pathway and further induce the expression of HIF-1alpha, indicating PI3K/Akt signaling pathway and HIF-1alpha could be a potential target for treatment of neonatal HIBD.