Effect Of Ischemia Preconditioning On HIF-1α And VEGF Expression In Rat Focal Cerebral Ischemia Reperfusion

Objective To observe the changes of ischemic preconditioning on effect of the cortical histopathological injury and the expression of HIF-1α and VEGF in cortex area surrounding infarct locus and hippocampus CA1 region after focal cerebral ischemia/reperfusion(I/R) in rats, then discussed the mechanisms of brain protection from BIP.Methods 1 130 adult male SD rats were randomly divided into three groups: SO operation(SO, n=10)group, middle cerebral artery occlusion(MCAO, n=60)group and brain ischemia preconditioning(BIP, n=60)group. The later two groups was further divided into six time points according to 2, 6, 12, 24, 48 and 72 h after I /R(Each time point had 10 rats, among which 5 rats were used for HE staining and Immunohistochemistry, and the let 5 rats were used for western blot. 2 The focal cerebral ischemia models of rats were achieved by middle cerebral artery thread embolism for two times. The model building method was described here: BIP group: middle cerebral artery occlusion 10 min as preconditioning, then middle cerebral artery occlusion 2h after 24 h, the rats were sacrificed at each time point the brain tissue; MCAO group: sham operation to replace preconditioning, the remaining steps with the BIP group; SO group: with two sham operation instead of preconditioning and ischemia. 3 HE staining method was used to observe the pathological changes of neuron in cerebral ischemia rats at different time points after reperfusion in frontal cortex, Immunohistochemistry and Western blot was used to observe the expression of HIF-1αand VEGF in cortical area surrounding infarct locus and hippocampus CA1 region.Results 1 Brain tissue pathomorphological changes were not observed in SO group. Compared with MCAO group, rats of BIP group had milder brain tissue pathological changes. 2 In MCAO group, the expression of HIF-1α positive cells in cortical area surrounding infarct locus and hippocampus CA1 region both increased at 2h after I/R and reached maximum level at 24 h, then gradually decreased, the level at 72 h is still higher than so group. In the BIP group, we have found out the number of HIF-1α positive cells at each time point is more than the number of MCAO group except the time point of 2h, 6hof reperfusion, there was statistical significance( P<0.05).In BIP group, the expression trend of HIF-1α positive cells in cortical area surrounding infarct locus and HIF-1α protein in cortical area consistent with MCAO group. We have compared the BIP group with MCAO group, the number of HIF-1α positive cells were higher than that in MCAO group at each time point, the difference was statistically significant(P<0.05). 3 In MCAO group, the expression of VEGF positive cells in cortical area surrounding infarct locus and hippocampus CA1 region both increased at 2h after I/R and reached maximum level at 24 h, then gradually decreased, the level at 72 h is still higher than so group. In the BIP group, we have found out the number of VEGF positive cells at each time point is more than the number of MCAO group, there was statistical significance(P<0.05). 4 In SO group, the expression of HIF-1α protein appeared faint band of protein. In MCAO group, the expression of HIF-1α protein increased at 2h after I/R and reached maximum level at 24 h, then gradually decreased, the level at 72 h is still higher than so group. In the BIP group, we have found out the expression of HIF-1α protein at each time point is more than the number of MCAO group, there was statistical significance(P<0.05). 5 In SO group, the expression of VEGF protein appeared faint band of protein. In MCAO group, the expression of VEGF protein increased at 2h after I/R and reached maximum level at 24 h, then gradually decreased, the level at 72 h is still higher than so group. In the BIP group, we have found out the expression of VEGF protein at each time point is more than the number of MCAO group, there was statistical significance(P<0.05).Conclusions 1 Focal cerebral ischemic reperfusion after ischemic preconditioning exhibited milder brain tissue histopathological changes, which effectively reduced cerebral ischemic reperfusion injury. 2 Ischemic preconditioning can promote the expression of HIF-1α and VEGF in cortical area surrounding infarct locus and hippocampus CA1 region after I /R in rats. 3 Ischemic preconditioning may induce ischemic tolerance through upregulating the expression of HIF-1α and VEGF, which play a protective role in brain.