Sub-chronic Exposure To Aluminum Affects Cognitive Function And Abnormal Phosphorylation Of Tau Protein On Transgenic ApoE4 Mice

Objective:To explore the combined effects of aluminum and ApoE4 gene on cognitive function and abnormal phosphorylation of tau protein in mice,and to clarify the mechanism of environmental factors aluminum-induced Alzheimer’s disease.Methods:There are two types mouse.The first group consists of 16 ApoE4 transgenic mice,and the second group consists of 16 wild type（unmodified C57BL/6）mice.Each type of mice were randomly divided into aluminum exposure group（40μmol/kg Al（mal）₃）and control group（normal saline）with 8 mice in each group.The mode of exposure was intraperitoneal injection,which was performed successively for 5 days,and paused for 2days,and the wholeexposure duration lasted for 60 days.The content of aluminum in hippocampus of mice was detected by ICP-MS,the genotypes of transgenic ApoE4 mice were determined by ligase method,the learning and memory ability of mice was detected by Morris water maze,the synaptic plasticity of hippocampal CA1 region was detected by Golgi staining,and the protein expressions of tau-5,pThr181,pThr231,pSer262 and pSer396 in hippocampus were detected by Western blotting.Results:1.Effects of aluminum exposure combined with ApoE4 gene on learning and memory in mice:The results of Morris water maze showed that the escape latencies of C57BL/6 control group,C57BL/6 aluminum exposure group,ApoE4 control group and ApoE4 aluminum exposed group on the first day were（48.56±18.31）s,（46.77±19.91）s,（45.13±19.07）s,（46.81±18.04）s,respectively.On the 5th day,it decreased to（18.80±13.46）s,（27.03±17.47）s,（21.27±20.17）s,（30.37±20.07）s,respectively.The analysis of variance showed that there were significant differences for escape lantency among the four groups on the 4th and 5th day（P<0.05）,in which the control group of the same type mice was lower than that of aluminum exposed group,and the C57BL/6 type was lower than that of ApoE4 type under the same conditions,However,the interaction between ApoE4 gene transfer and aluminum exposed on the 4th and 5th day was analyzed,and there was no significant difference between the two days.（P>0.05）.The times of crossing the platform in C57BL/6 control group,C57BL/6aluminum staining group,ApoE4 control group and ApoE4 aluminum staining group were 2.86±0.99,1.88±0.64,2.63±0.77 and 0.50±0.53,respectively.The interaction between ApoE4 gene and aluminum exposed was statistically significant in the number of times of crossing the platform（P<0.05）.The new object recognition test showed that there was no significant difference in the search time between the two same objects in T₁stage（P>0.05）.In T₂ stage,the searching time of new objects in C57BL/6 control group,C57BL/6 aluminum group and ApoE4 control group was higher than that in old objects,and the difference was statistically significant（P<0.05）.There was no significant difference in the search time for new objects in ApoE4 aluminum group.T₂ time discrimination index and discrimination ratio had statistical significance in the interaction between animal type（ApoE4）and aluminum exposure[Al（mal）₃]（P<0.05）.2.The results of ICP-MS showed that the average concentration of aluminum in hippocampus of C57BL/6 mice was 5.75μg/g in control group and 33.62μg/g in aluminum exposed group.The average concentration of aluminum in hippocampus of ApoE4 transgenic mice was 5.79μg/g in control group and 33.56μg/g in aluminum exposed group.The concentration of aluminum in hippocampus of aluminum exposed group was higher than that of control group,and the difference was statistically significant（P<0.05）.Under the same exposure,the concentration of aluminum in hippocampus both of C57BL/6 mice and ApoE4 transgenic mice was basically the same,the difference was not statistically significant（P<0.05）.3.Effects of aluminum exposure combined with ApoE4 gene on synaptic plasticity of mouse neurons:under 100x microscope,a large number of neurons in the CA1 area were fractured in the ApoE4 aluminum group,and the neurons in other groups were more intact.Under a 1000x microscope,a large number of neuronal ruptures were clearly seen in the aluminum-exposed group of ApoE4,and nodular changes were observed in the ApoE4 control group and C57BL/6 aluminum-exposed group.The analysis of neuronal complexity showed that the neuronal complexity of C57BL/6 mice was higher than that of ApoE4 mice,and it decreased in the same kind of mice exposed to aluminum.The interaction between ApoE4 gene and aluminum in neuronal complexity analysis was statistically significant at 20μm.（P<0.05）.The density of dendritic spines in C57BL/6mice was higher than that in ApoE4 mice,and the density of dendritic spines decreased in the same kind of mice exposed to aluminum.The interaction between ApoE4 gene and aluminum exposed on the density of dendritic spines was statistically significant.（P<0.05）.4.Effects of aluminum exposure combined with ApoE4 gene on the contents of total tau protein and phosphorylated tau protein:western blot results showed that aluminum exposure could increase the protein expression of tau-5,pThr181,pThr231 and pSer396（P<0.05）.Under the same measures,the protein expression of tau-5,pThr181,pThr231,pSer262 and pSer396 in ApoE4 type was higher than that in C57BL/6 type.The results of interaction showed that the interaction between ApoE4 gene and aluminum exposed on the protein expression of tau-5,pThr181,pThr231 and pSer396 was statistically significant.（P<0.05）.Conclusion:1.Aluminum exposure can damage the learning and memory ability of mice,and transgenic ApoE4 gene transfer may also lead to the decline of learning and memory function in mice.The combined effect of aluminum exposure and ApoE4 may aggravate the impairment of learning and memory function in mice.2.Aluminum exposure could lead to neuronal damage,and ApoE4 transgenic mice showed neuronal damage.Aluminum and ApoE4 genes may have an interactive effect on synaptic plasticity in hippocampal CA1 region,indicating that the combined action of aluminum and ApoE4 genes may affect neuronal damage.3.Both aluminum exposure and transgenic ApoE4 can increase the protein expression of tau-5 and pThr181,pThr231 and pSer396 in mice,and the combined action of aluminum and ApoE4 genes can further up-regulate the expression of tau-5 and pThr181,pThr231 and pSer396.