The Role Of Hippocampal CNTN1 In Cognitive Behavior

Objective: To investigate the expression of adhesion molecule CNTN1(Contactin-1)in hippocampus of Alzheimer’s disease dementia patients and its role and mechanism in mouse cognitive behaviorMethods: The expression of CNTN1 in hippocampus of Alzheimer’s disease dementia patients and normal brains was observed by immunohistochemical staining.Eight-week-old male healthy mice(C57BL/6)were randomly divided into Normal group(Normal),virus control group(AAV-Con)and CNTN1 overexpression group(AAV-CNTN1).An adeno-associated virus(AAV)-based approach to directly overexpress CNTN1 via stereotactic the bilateral hippocampus of the mice.After 21 days of virus expression,cognitive behavior of mice was detected by Novel object recognition test,Novel place recognition test and Social cognition test.To investigate CNTN1 overexpression in hippocampus on neurons and microglia,Immunohistochemistry(IHC),real-time fluorescence quantitative PCR(RT-q PCR)and Western blot(WB)are used to determine the expressions of Neu N and Iba1 in the hippocampus of each group.In this study,adult male mice(C57BL/6)aged 8 weeks were randomly divided into Normal+NS group,Normal+minocycline group,AAV-Con+NS group,AAV-CNTN1+NS group and AAV-CNTN1+ minocycline group.Four days before the behavioral test,Minocycline(Mino,ip,50mg/kg)and normal saline(NS,ip,10ml/kg)were intraperitoneally injected for four consecutive days.The expression of Neu N and Iba1 in the hippocampus of mice was detected by IHC,RT-q PCR,WB and other methods after the behavioral experiment,to observe whether the overexpression of CNTN1 in the hippocampus plays a role in cognitive behavior by affecting microglia.Results:(1)Expression of CNTN1 in hippocampus of normal subjects and Alzheimer’s disease dementia patients: Compared with normal subjects,the expression of CNTN1 in hippocampus of dementia patients was significantly increased.(2)The effect of overexpression of CNTN1 on the cognitive behavior of mice:(1)Open field experiment:there was no significant difference in the total movement distance of the three groups in the open field for 5 minutes(p>0.05);(2)Novel object recognition test and Novel place recognition test: The recognition index of AAV-CNTN1 group decreased significantly compared with the other two groups(p<0.05);(3)Social cognition test: In the detection phase,compared with Normal and AAV-Con groups,AAV-CNTN1 groups exploration time for strange mice was significantly reduced and the discrimination ratio was significantly decreased(p<0.05);(3)Effects of overexpression of CNTN1 on microglia and neurons of the mouse hippocampus: Compared with Normal group and AAV-control group,the number of Iba1-positive cells and cell branches in the hippocampus of mice overexpressed in CNTN1 group were significantly increased,and the m RNA expression of microglial markers(CD11B,CD68)was up-regulated,with significant difference(p<0.05);The number of Neu N positive cells and Nissl bodies in the hippocampus of CNTN1 overexpressed mice decreased significantly(p<0.05),there was no significant difference in HE staining results among the three groups.(4)Effects of intraperitoneal injection of minocycline on the cognitive behavior of mice in the overexpression group of CNTN1: Compared with the overexpression group of CNTN1,the recognition index of mice in the AAV-CNTN1+Mino group was significantly increased in the Novel object recognition test and Novel place recognition test,as well as the discrimination ratio of Social cognition test(p<0.05);The number of Iba1 positive cells in the hippocampus of AAV-CNTN1+Mino group was significantly decreased,and the m RNA expression of CD11 B,CD68,IL-1α and IL-6 were significantly down-regulated(p<0.05);In the AAV-CNTN1 +Mino group,the number of Nissl bodies and Neu N positive cells significantly increased(p<0.05).Conclusion: The expression of CNTN1 is increased in hippocampus of Alzheimer’s disease dementia patients.By adeno-associated virus(AAV)-mediated overexpression of CNTN1 in the hippocampus of mice and found that CNTN1 overexpression in the hippocampus triggered a battery of cognitive deficits in addition to microglia activated in the hippocampus,the expression of neuron marker Neu N decreased,and the expression of pro-inflammatory cytokines increased.Intraperitoneal injection of minocycline inhibited the activation of microglia in overexpressed CNTN1 mice,up-regulated the expression of Neu N,and improved the cognitive deficits of overexpressed CNTN1 mice.