A Preliminary Study Of Hippocampal Excitatory Amino Acid Transporter 2 Regulating Depressive-like Behavior

BackgroundMajor depression disorder(MDD)is a serious neuropsychiatric disease affecting physical and mental health of human which symptoms include anhedonia,insomnia,hopelessness and suicide.MDD not only affects the health of individuals,but also brings huge life pressure to the whole family,and even increases the economic burden of the whole society.MDD is a complex disease.Although there have been many hypotheses so far,none of them can fully explain the pathogenesis of MDD.The complexity of the pathogenesis of MDD determines its difficulty in treatment.Therefore,the exploration of therapeutic targets is beneficial to provide new ideas for the treatment of MDD.Almost all depressed patients are accompanied by varying degrees of neurotransmitter disorders.Glutamate is an important neurotransmitter in brain,which is mainly responsible for the transmission of excitatory signals.Excitatory amino acid transporter(EAAT),as an important transporter of glutamate,plays a vital role in glutamate metabolic pathway.The lack or abnormality of EAAT can result in the inability of glutamate to be transported and metabolized,further causing the accumulation of glutamate in the synaptic cleft,leading to neurotoxicity and,therefore,severe neurological dysfunction.Objectives1.Through the construction of different depression models,glutamaterelated molecules were validated in hippocampus of multiple models to determine whether there were differences in glutamate pathways in depression models.2.Intervention with differential molecules in hippocampus was used to observe whether the behaviors of rats or mice changed.3.Related pathways were detected in hippocampus after DHK intervention to find downstream effector pathways or molecules of EAAT2.Methods1.The chronic unpredictable mild stress(CUMS)rat model and the chronic social defeated stress(CSDS)mouse model were constructed.Then western blot was used to validated the glutamate-related molecules in hippocampus of the depression models including: Excitatory amino acid transporter 1/2(EAAT1/2),vesicular glutamate transporter 1/2(VGLUT1/2),AMPA receptor 1/2(Glu R1/2),N-methyl-D-aspartate receptor 2A/2B(NMDAR2A/B).2.Injection of lenti-EAAT2 into dorsal hippocampus of SD rats was conducted to observe whether the behavior of rats was changed.The behaviors of C57 wild type mice was observed after infusing dihydrokainate(DHK),the antagonist of EAAT2 into dorsal hippocampus.3.The phosphorylated antibody microarray assay was performed in hippocampal tissues of mice treated with DHK.The Kyoto Encyclopedia of Genes and Genomes(KEGG)was used to analyze the differentially expressed pathways and molecules.Results1.Depressive-like behaviors were assessed by weight change,sucrose preference test,and forced swimming test after SD rats were exposed with 6 weeks of chronic unpredictable mild stress.The results indicated that susceptible group showed depressive-like behaviors,compared to control and resistance groups.After mice were exposed with 10 days of chronic social defeated stress,depressive behaviors were evaluated by social interaction test,open field test,tail suspending test,and forced swimming test.The results demonstrated that susceptible mice showed significantly depressive-like behaviors compared to control and resistance groups.2.Through the validation of glutamate-related molecules in hippocampus of depression model,we found that in CUMS rat model,the protein levels of EAAT2,vGlut1 and GluR1 in susceptible group were significantly lower than those in control group.In CSDS mice model,the protein level of EAAT2 in susceptible group was significantly lower than that in control group,while the protein level of EAAT1 in resistant group was significantly higher than that in control and susceptible groups.3.We observed a protective behavior against depression in the overexpression group after injection of lenti-EAAT2 into hippocampus of rats.After infusion with DHK to hippocampus of mice,we observed a significant depressive-like behavior in DHK-treated group.4.After the phosphorylated antibody microarray assay on hippocampal tissues of mice infused with DHK,then a KEGG pathway analysis was conducted,we found that the PI3K-Akt signaling pathway and MAPK signaling pathway ranked the top two.ConclusionOur experimental results revealed that EAAT2 may be involved in the occurrence and development of MDD,so EAAT2 may become a new drug target and provide a new idea for the treatment of MDD.