Expression Of PCNA And Caspase-3 In Rats After Cerebral Ischemic Preconditioning

Objective:To observe the dynamic changes of PCNA and Caspase-3 protein expression in rats after cerebral ischemic preconditioning.To further explore the possible mechanism of cerebral ischemic preconditioning.Methods:100 Adult Male Wistar rats(weight 230-250g)were divided randomly into 4 groups:sham group(S)(n=10),cerebral ischemic group (PMCAO)(n=30),preconditioning control group(IPC)(n=30),and ischemic preconditioning(IP+PMCAO)group(n=30).Each group were divided into 6h,12h,24h,48h and 72h subgroups respectively,and each subgroup had five rats. (Another five rats from each group were prepared for 24h TTC).Sham group: only separated internal carotid artery and external carotid artery not put thread in. The permanent occlusion of middle cerebral artery(PMCAO)model of rats was made by using a thread to occlude the left middle cerebral artery.In ischemic preconditioning group rats were treated by the method of both carotid artery occlusions,while injected with saline water into left internal carotid artery. These procedures were repeated three times,3 min every time in an interval of 7 min.The ischemia preconditioning group were subjected the middle cerebral artery occlusion after 72h of preconditioning.The following indexes in 4 groups were observed respectively:neurologic deficits,infarcts averaging by TTC, tissue pathological changes by Hematoxylin-Eosin(H.E)staining,and the expression of PCNA and Caspase-3(immunohistochemistry method). Results:(1)Neurological function:The mean scores of neurological function were 0 in sham group and preconditioning group.The neurological deficits score is lower at the same time in cerebral ischemic group than that in ischemic preconditioning group(p＜0.05).(2)TTC stain and HE stain:Sham group and preconditioning group had no infarction areas.The ratio of cerebral infarction volume in preconditioning ischemic group reduced significantly compared with ischemia group(P＜0.05). HE stain showed that the pictures under substantial microscope showed that control group of imitational operation and control group of preconditioning focal cerebral ischemia had no evident pathological changes.Infarction center of preconditioning ischemic group decreased distinctively compared with cerebral ischemic group,structure integrated neural cells around infarction areas increased cleared.(3)Immunohistochemistry:there were similar expression on PCNA in both sham group and preconditioning group in basal ganglia(p＞0.05)。PCNA decreased after ischemia at 6h,and kept the low expression till 72h.There was a significantly higher expression of PCNA in ischemic preconditioning group at each time than that of in ischemic group(P＜0.05).There was no significant changes between sham group and preconditioning group of Caspase-3 in ischemic basal ganglia(P＞0.05).The expression of Caspase-3 in both ischemic group and ischemic preconditioning group were increase at 6h,and to the maximum at 24h.but the expression of Caspase-3 in ischemic preconditioning group were significantly lower than that of in ischemic group(P＜0.05). Conclusion:1.Our study shows that ischemic preconditioning could increase the tolerance obviously to severe ischemia injury.2.The impairment of DNA repair system and the activation of the apoptosis gene may lead to the death of neuron after ischemia.Ischemia preconditioning could promote DNA repair and decrease apoptosis to lessen the cerebral ischemia by downing regulation of the expression of apoptosis gene Caspase-3 and increasing the expression of DNA repair protein PCNA.