Role of PI3K/Akt signaling pathway in mild head hypothermia-induced reduction of global cerebral ischemia-reperfusion injury in rats

Objective To evaluate the role of phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway in mild head hypothermia-induced reduction of global cerebral ischemia-reperfusion (I/R) injury in rats. Methods Sixty male Sprague-Dawley rats, weighing 250-280 g, were randomly divided into 5 groups (n=12 each) using a random number table: sham operation group (group S), group I/R, mild hypothermia + I/R group (group H), mild hypothermia + I/R + solvent control group (group DM), and mild hypothermia + I/R + PI3K inhibitor LY294002 group (group LY). Global cerebral I/R was induced by modified four-vessel occlusion method described by Pulsinelli. In H group, when the hippocampal temperature was decreased to 33℃ using nasopharyngeal cooling, the bilateral common carotid arteries were occluded for 15 min followed by reperfusion, and hippocampal hypothermia was maintained at 32.5-33.5 ℃ for 1 h. In DM and LY groups, DMSO and LY294002 5 μl were injected into the left ventricle, respectively, and 20 min later the other procedures were similar to those previously described in group H. At 8 h of reperfusion, 6 rats were sacrificed, and hippocampal specimens were obtained to detect the expression of pFoxO3a, Bcl-2 and Bax (by immuno-histochemistry). The expression of phosphor-Akt (p-Akt) was determined by Western blot. Results Compared with group S, the expression of p-Akt, pFoxO3a and Bcl-2 was significantly up-regulated in I/R, H and DM groups, the expression of Bcl-2 was down-regulated, and the ratio of Bcl-2/Bax was increased in H and DM groups, and the ratio of Bcl-2/Bax was decreased in I/R and LY groups. Compared with group I/R, the expression of p-Akt, pFoxO3a and Bcl-2 was significantly up-regulated, the expression of Bcl-2 was down-regulated, and the ratio of Bcl-2/Bax was increased in H and DM groups. Compared with H and DM groups, the expression of p-Akt, pFoxO3a and Bcl-2 was down-regulated, the expression of Bax was up-regulated, and the ratio of Bcl-2/Bax was decreased in group LY. Conclusion PI3K/Akt signaling pathway is involved in reduction of global cerebral I/R injury by mild head hypothermia in rats. Key words: Phosphoinositide-3-kinase; Protein-serine-threonine kinases; Hypothermia, induced; Reperfusion injury; Brain