Based On DTI And MRS Technology To Explore The Effect Of ApoE Gene On Cognitive Function After Cerebral Ischemic Injury In Mice

Objective:Diffusion tensor imaging(DTI)and magnetic resonance spectroscopy(MRS)were used to detect changes in white matter,neurometabolic substances,neurovascular unit main components and cognitive function after wild-type and ApoE-/-mice cerebral ischemic injury,To explore the effect of ApoE gene on cognitive function after cerebral ischemic injury in mice Methods:Healthy male SPF ApoE-/-mice and wild-type mice(Wild type,WT)mice of 8-10 weeks old were divided into 6 groups at random:(1)WT sham operation group(WT-sham,n = 8),(2)WT 7 days postoperation group(WT-7d,n = 12),(3)WT 30 days postoperation group(WT-30 d,n = 12),(4)ApoE sham operation group(ApoE-sham,n = 8),(5)ApoE 7 days postoperation group(ApoE-7d,n = 12),(5)ApoE 30 days postoperation group(ApoE-7d,n = 12).In the operation group,bilateral common carotid arteries were ligated for 15 minutes and then reperfusion.The sham operation group only isolated blood vessels without ligating.One day after the operation,the nerve damage was observed by the modified nerve severity score.Morris water maze was performed on ApoE-/-mice and WT mice on the 7th or 30 th day after surgery to test the learning and memory abilities of each group of mice.Changes in FA values were calculated;changes in choline(Choline)and N-acetylaspatate(NAA)contents in the hippocampal neurometabol were detected by magnetic resonance spectroscopy(MRS);Western blot detected Hippocampal tight junction proteins Occludin,Claudin-5,ZO-1 protein expression;Nissl staining to observe the neural arrangement and morphology of hippocampal CA1 region;immunohistochemical detecte of hippocampal CA1 region glial fibrillary acidic protein(GFAP).Results:(1)Results of modified nerve severity score: In the operation group,the score on the first day after operation showed that the mice were moderately injured;at 7 and 30 days after surgery,the ApoE-/-modified nerve severity score was higher than that of WT mice(P<0.05).(2)Changes in learning and memory abilities of mice in each group: There was no significant difference between the escape latency and the number of platforms crossing between the ApoE-sham group and the WT-sham group(P>0.05);ApoE-7d group and WT-7d had longer escape latency(P<0.05)and the number of crossing platforms decreased(P<0.05),and the learning and memory ability of the ApoE-7d group was the worst(P<0.05);Compare of WT-30 d group,the escape latency was prolonged(P<0.01)and the number of crossing platforms was decreased in the ApoE-30 d group(P<0.05).(3)Changes of FA value in hippocampus of each group of mice: There was no significant difference in FA value in bilateral hippocampus of ApoE-sham group and WT-sham group(P>0.05);The FA value of bilateral hippocampal area of ApoE-7d group and WT-7d group decreased(P<0.05),and the FA value of bilateral hippocampal area of ApoE-7d group decreased significantly compared with WT-7d group(P<0.05);FA values in the bilateral hippocampal area of the ApoE-30 d group were lower than WT-30 d group decreased significantly(P<0.05).(4)Changes of neurometabolic substances in hippocampus of mice in each group: There was no significant difference in NAA content in hippocampus of ApoE-sham group and WTsham group(P>0.05),but Cho content in hippocampus of ApoE-sham group was higher than that of WT-sham Group(P<0.05);Cho and NAA contents in hippocampus area of ApoE-7d group and WT-7d group decreased significantly(P<0.01),and Cho and NAA contents in hippocampal area of ApoE-7d group decreased significantly compared with WT-7d group(P<0.01);Cho and NAA contents in hippocampus of ApoE-30 d group were significantly lower than those in WT-30 d group(P<0.05).(5)Changes in hippocampal tight junction protein expression in each group of mice: There was no statistical difference in the expressions of Occludin,Claudin-5 and ZO-1 in the hippocampus of the ApoE-sham group and the WT-sham group(P>0.05);the ApoE-7d group The expressions of Occludin,Claudin-5 and ZO-1 in the hippocampal region of the WT-7d group were significantly decreased(P<0.01),and the expressions of the ApoE-7d group were significantly decreased(P<0.01);the Occludin,The expressions of Claudin-5 and ZO-1 were also significantly lower than those in WT-30 d group(P<0.01).(6)Results of hippocampal nissl staining of mice in each group: The neuron arrangement and structure of hippocampus in the ApoE-sham and WT-sham groups were normal,but the neurons in the WT-7d and ApoE-7d groups were disorderly arranged and cell wrinkled.The neurons of ApoE-30 d groups was disordered than WT-30 d groups,and the shrunken neurons were more obvious.(7)Expression of GFAP in hippocampal CA1 region of each group of mice: The expression of GFAP in hippocampal CA1 region of ApoE-sham group and WT-sham group was not significantly different(P>0.05);GFAP expression in hippocampal CA1 region of ApoE-7d group and WT-7d group were increased(P<0.01),and the expression of GFAP in the ApoE-7d group was significantly higher than that in the WT-7d group(P<0.01);the GFAP in the hippocampal CA1 region of the ApoE-30 d group was significantly higher than that in the WT-30 d group(P<0.01).Conclusion:ApoE knockout mice are more susceptible to cerebral ischemic injury than wild-type mice,showing obvious learning and memory impairments,the mechanism of which is related to the damage of white matter fibers and abnormal neurometabolism in the hippocampus,and the main components of neurovascular units(Cerebrovascular endothelial cell tight junction protein,nerve cell morphology,astrocytes)destruction is closely related,suggesting that the ApoE gene plays an important role in the maintenance of brain tissue function.