Effects Of Triphenyl Phosphate Exposure On Alzheimer’s Disease And Its Mechanism

Objective: To investigate the effects of exposure to TPHP on the neurobehavior of AD model mice and its possible mechanism.Methods:A total of 30 AD double transgenic male mice(APP/PS1)and 10 wild type male mice were randomly divided into WT control group,APP/PS1 control group,AD model mice exposed to low dose(5 mg/kg)and high dose(50 mg/kg)of TPHP by gavage for 90 days.After the end of exposure,the novel feeding inhibition test,open field test,forced swimming test,tail suspension test,novel object recognition test and Morris water maze test were performed to evaluate the effects of TPHP exposure on neurobehavior of AD model mice.Glycine silver staining was used to detect neurofibrillary tangles and Tau protein,the hallmark markers of AD,and immunofluorescence was used to detect the characteristic marker proteins of astrocyte activation(GFAP)and microglia activation(Iba-1).Oil red O staining,total cholesterol kit and Western blot were used to detect the expression of Aβ protein,Tau protein,IBA-1 protein,LXRα,cholesterol transport related proteins and inflammation-related pathway proteins.Results:1.The results of novel feeding inhibition test,open field test,forced swimming test and tail suspension test all showed that the depression of APP/PS1-vehicle group was more obvious than that of WT-vehicle group.In contrast to the APP/PS1-vehicle group,the feeding latency was prolonged,the food consumption within 10 min was decreased,the total distance to move in the open field device and the distance to explore the central area were decreased,the defecation frequency during the open field test and the immobility time in FST/TST were increased with the increase of TPHP dose(P<0.05).Morris water maze test results showed that the escape latency of all mice in each group decreased gradually during the 5-day navigation test.After the fifth day of training,it was found that compared with the APP/PS1-vehicle group,the escape latency of the APP/PS1-5mg/kg group was decreased,while the escape latency of the APP/PS1-50mg/kg group was increased,but the difference was not statistically significant(P>0.05);Compared with the WT-vehicle group,the total distance of mice in the water maze after removal of the platform and the number of crossing the original platform position in the AD model group decreased significantly,and the difference between the APP/PS1-vehicle group and the WT-vehicle group was statistically significant(P<0.05);Compared with the APP/PS1-vehicle group,the number of platform crossings in each TPHP exposure group decreased in a dose-dependent manner,but there was no statistical difference(P>0.05).Similarly,the results of novel object recognition test showed that the total distance and discrimination index of each exposure group of AD model mice decreased with the increase of TPHP dose,but the difference was not statistically significant(P>0.05).2.The results of glycine silver staining showed that there was no neurofibrillary tangles formation in the cerebral cortex and hippocampus of the WT-vehicle group.Compared with the APP/PS1-vehicle group,the NFTS in the brain of APP/PS1-5 mg/kg group and APP/PS1-50 mg/kg group increased with the increase of TPHP dose(P<0.05).The results of Western blot showed that the expression of Aβ and Tau protein in the APP/PS1-50mg/kg group was higher than that in the control group and the low-dose AD model group(P<0.05).3.The results of oil red O staining showed that the liver lipid deposition in the AD model mice in each exposure group was more obvious comparing with the WT-vehicle group,and with the increase of TPHP exposure dose,the liver lipid deposition was more obvious.The results of total cholesterol kit showed that the total cholesterol content in serum and brain tissue homogenate of mice increased significantly with the increase of TPHP dose(P<0.05);The results of GFAP immunofluorescence assay showed that the GFAP fluorescence intensity in the cerebral cortex and hippocampus of AD model mice in each exposure group increased,and astrocytes were activated.In addition,Western blot results showed that,Compared with the control group and the TPHP low-dose group,the expression of LXRα,ABCA1 and CYP46A1 in the high dose TPHP group was decreased,while the expression of ATAD3 A was increased(P<0.05).4.The results of IBA-1 immunofluorescence showed that compared with the WT-vehicle group,the microglia in the cerebral cortex and hippocampus of the AD model mice in each exposure group were activated,and the fluorescence intensity of the fluorescent marker gene IBA-1 increased(P<0.05);Western blot results also showed that the expression of IBA-1 protein in the cerebral cortex and hippocampus of the AD model mice in the high dose group of TPHP also increased(P<0.05).In addition,the expression of NF-κB inflammatory pathway-related proteins was also increased,including NF-κB,IL-6,and TNFα protein expression compared with the WT-vehicle group;compared with the APP/PS1-vehicle group,the TPHP treatment groups also showed a dose-dependent increase(P<0.05).Conclusions:1.TPHP exposure can induce neuropsychiatric symptoms such as depression and anxiety in AD mice,and increase the formation of Aβ and Tau protein,the hallmark pathological features of AD.2.TPHP exposure can inhibit the expression of LXRα and activate astrocytes to disrupt cholesterol metabolism in the whole body and brain of AD model mice.3.TPHP can inhibit LXRα and activate the inflammatory response in microglia,which further accelerates the development of AD.