Study On The Role And Mechanism Of DAAO In Learning And Memory Impairment Of Offspring Mice Induced By Arsenic Exposure

Objective Children exposed to environmental arsenic may suffer from intellectual development disorders.However,the mechanism of arsenic damaging learning and memory ability is not clear at present.D-serine is an endogenous agonist of N-methyl-D-aspartate receptor(NMDAR)in learning and memory,and D-amino acid oxidase(DAAO)is its degrading enzyme.In this study,the arsenic exposure model of offspring mice was established,and the DAAO inhibitor 6-chlorobenzo[d]isoxazol-3-ol(CBIO)was given to intervene,so as to explore the mechanism of DAAO’s influence on learning and memory impairment of offspring mice induced by arsenic exposure,provide experimental data and important intervention targets for further elucidating the neurotoxicity mechanism of arsenic,and guide the prevention and treatment of arsenic poisoning.Methods On the first day of gestation,24 pregnant mice were randomly divided into distilled water drinking group(12 mice)and arsenic exposure group(12 mice),which were exposed to arsenic by free drinking water.The offspring mice exposed to arsenic from latex and drinking water,brain stereotactic locator was used to place cannulae in the brain of offspring mice on the 21 th day after birth,and CBIO was administered to the lateral ventricle of offspring mice on the 28 th day after birth for 1 week according to the following groups.The offspring mice from group drunk distilled water were divided into the control and 1 mg/m L CBIO group.Litters from the arsenic exposure group were randomly divided into 60 mg/LNa As O2 group and 60 mg/L Na As O2+1 mg/m L CBIO group.Six litters from each group were selected for each experiment.Y-maze was used to detect learning and memory abilities of offspring mice,and HE staining was used for the observation of the morphology of the nerve cells in the hippocampus.The D-serine and L-serine levels were determined by UHPLC-MSMS,and m RNA and protein levels of synaptophysin(SYP),postsynaptic density 95(PSD95),DAAO,serine racemase(SR),NMDAR subunits NR1,NR2 A and NR2 B were detected by Real-time RT-PCR and Western blot,respectively.Results There were no significant differences in body weight,brain weight and hippocampal weight among all groups(P>0.05).The results of Y maze experiment showed that the alternation reaction rate of the offspring mice exposed to Na As O2 was obviously lower than that in control group,and the alternation reaction rate of pups in Na As O2+CBIO group was significantly higher than that in Na As O2 group(P<0.05).Otherwise,there was no difference in the total number of pups entering the arms among all groups.HE staining was used to observe the CA1 and CA3 regions of the hippocampus,and it was found that neurocytes in the hippocampus of offspring mice exposed to Na As O2 were swollen,the number of nerve cells in the hippocampus of the Na As O2+CBIO group increased,and the cell morphology was improved.UHPLC-MSMS results showed that compared with the control group,the concentrations of D-serine and L-serine in the hippocampus of offspring mice exposed Na As O2 decreased obviously(P<0.05).Compared to the Na As O2 group,the level of D-serine in the Na As O2+CBIO offspring was significantly higher.The difference was statistically significant(P<0.05),but the L-serine level had no significant change(P>0.05).In the experiment results of Real-time RT-PCR,compared to control,the expressions of SR and NR1 m RNA in mice exposed to Na As O2 decreased obviously(P<0.05),level of DAAO m RNA were obviously higher(P<0.05).The m RNA levels of SYP,PSD95,NR2 A and NR2 B showed no difference(P>0.05).Compared with Na As O2 group,NR1 m RNA level in the hippocampus in Na As O2+CBIO group increased significantly(P<0.05),moreover,the level of DAAO m RNA was obviously lower(P<0.05).In the results of Western blot,compared to control,the protein levels of SYP,PSD95,SR,NR1 and NR2 A in the hippocampus of pups exposed to Na As O2 were obviously lower(P<0.05),and DAAO protein level increased obviously(P<0.05).There was no obvious difference in the protein level of NR2B(P>0.05).Compared with Na As O2 group,protein levels of SYP and NR1 in hippocampus of pups in Na As O2+CBIO group increased significantly(P<0.05),while DAAO protein level reduced significantly(P<0.05).There were no significant differences in levels of PSD95,SR,NR2 A and NR2 B proteins in hippocampus(P>0.05).Conclusions1.Arsenic exposure can reduce the levels of D-serine and L-serine in the hippocampus of offspring mice;2.Arsenic exposure can increase the level of DAAO and decrease the expressions of SR and NMDAR subunits in the hippocampus of offspring mice,which may influence the ability of learning and memory of offspring mice by affecting D-serine metabolism;3.Inhibition of DAAO might increase the levels of D-serine and NMDAR subunit NR1 in the hippocampus of offspring mice,DAAO might play a role in learning and memory impairment of offspring mice induced by arsenic exposure by affecting D-serine metabolism.