The Mechanism Of SORL1-Deficiency Resulting In Cognitive Impairment Effected By The Synaptic Plasticity

Objective:By detecting the changes of learning and memory,cognitive behavior and neural electrophysiology,the expression of synapse-related proteins PSD-95 and Homer1 in SORL1-deficient mice.To explore the possible mechanism of SORL1 deficiency leading to cognitive impairment by affecting synaptic plasticity.Methods:（1）Crispr/Cas9 technology was used to construct SORL1knockout mice with a genetic background of C57BL/6J line.WT,SORL1^-/-,SORL1^+/-mice were identified by DNA sequencing and Western blotting.APP/PS1 double transgenic mice of the C57BL/6J line were purchased,which are AD model mice.9-month-old mice were selected as the research objects..（2）Cognitive and behavioral changes such as learning and memory in each group were detected and compared by dark avoidance,shuttle experiment,Y maze and Morris water maze.（3）Quantitative analysis of long-term potentiation（LTP）in hippocampal slices recorded by patch-clamp recordings of WT、AD、SORL1^+/-、SORL1^-/-mice.（4）Molecular biology experiment:HE staining and Nissl staining were used to detect the morphological changes of the mouse hippocampus.Silver-plated staining was used to visualize mouse nerve fibers.（5）The immunohistochemical method was used to detect the expression of Aβ,PSD-95 and Homer1 in mouse brain tissue.The western blot method and q PCR was used to detect the expression of PSD-95 and Homer1 in mouse brain tissue.Results:Behavioral experiment:（1）Dark avoidance and shuttle experiment:Compared with the WT group,the SORL1^-/-group had a shorter latency period,an increase in the number of electric shocks and a significant decrease in the number of active shuttles,P<0.05.（2）Y-maze:Compared with the WT group,the correct rate of spontaneous alternation of the SORL1^-/-group mice was significantly decreased,and the ratio of the exploration time of the new arms to the total time was significantly lower,P<0.05.（3）Morris water maze:Although the time of SORL1^-/-group and AD group was shortened compared with before,the shortened time was much smaller than that of WT group.After analysis of variance,it was concluded that there was a total difference between the groups.The variation was 51.35%,and it’s P<0.05,which was statistically significant.Compared with the WT group,the time of mice in the SORL1^-/-group in the quadrant of the original platform was reduced,P<0.005.Electrophysiological test:Compared with the WT group,the slope of the normalized field potential EPSP in the hippocampal slices of the SORL1^-/-group mice decreased.The EPSP amplitude of the mice in the SORL^-/-group increased instantaneously,and then,with the passage of time,the EPSP amplitude of the two groups of mice showed a downward trend.Indicating that the synaptic plasticity of SORL1 knockout mice was impaired.Molecular biology experiment:（1）Morphological examination:Compared with the WT group,the number of neurons was less,the cell arrangement was sparse,the nucleus stained deeper,and the Nissl bodies were decreased in the CA1 area of the hippocampus of the SORL1^-/-and SORL1^+/-groups.（2）Aβdeposition:Compared with the WT group,Aβdeposition was significantly increased in the cortical of SORL1^-/-and SORL1^+/-groups（P<0.05）.（3）Silver-plated staining:Compared with the WT group:the nerve fibers of the AD group mice and SORL1^-/-group mice were significantly reduced or even disappeared（under a 10x microscope）;Observed under a 60x microscope:The neuronal axons and dendrites of the mice in the SORL1^-/-groups were significantly reduced.（4）PSD-95expression:Immunohisto-chemistry:Compared with the WT group,PSD-95 expression was significantly down-regulated in the hippocampus and cortex of SORL1^-/-and SORL1^+/-groups（P<0.05）.Western blot:Compared with the WT group,the expression of PSD-95was significantly down-regulated in SORL1^-/-and SORL1^+/-groups（P<0.05）.（5）Homer1 expression:Compared with the WT group,the Homer1expression was significantly down-regulated in the cortex and hippocampus of the SORL1^-/-and SORL1^+/-groups（P<0.05）.Conclusion:SORL1 deficiency may affect synaptic plasticity and lead to cognitive impairment by down-regulating the expression of synapse-related proteins.