Effects Of AQP4 On Depression-like Behavior In Mice By Regulating The Function Of NMDA Receptors In The Nucleus Accumbens

Objective:Major depression is a common,recurrent and serious mental illness that affects millions of people worldwide.Aquaporins(AQPs)are a family of membrane channels that play a significant role in regulating water homeostasis.Our preliminary experiments have found that AQP4 knockout(KO)mice displayed significantly decreased social interaction,compared with control normal mice.We also demonstrated that Aquaporin-4(AQP4)deficiency selectively impaired long-term depression(LTD)in the cortico-accumbal glutamatergic synapse,which may underlie the behavioral effects of AQP4 deficiency.Our team has identified NMDA receptors in the prefrontal cortex-nucleus accumbens circuit as a key regulator in the modulation of persistent psychomotor plasticity in major depression animal model.However,the mechanisms underlying this effect of NMDA receptors have not been investigated.Therefore,we proposed that decreased brain AQP4 might contribute to the hypofunction of NMDARs and the onset of behavioral disorders in depression,and regulating brain AQP4 would improve the behavioral performances via enhancing NMDARs function.Chronic social defeat stress(CSDS)and Subthreshold social defeat stress(SSDS)models will be used to evaluate the relation between AQP4 in the nucleus accumbens and major depression.Based on these evidences,we are going to use various methods,including behavioral,electrophysiological,biochemical and molecular biological techniques and adeno-associated viral gene interference.We hope to reveal the role of AQP4 in the pathogenesis of major depression,providing new information for the pathophysiology of depression and proposing a new strategy for the treatment of depression.Methods:Using the CSDS model to distinguish susceptible and unsusceptible mice by a series of behavioral experiments;AQP4 protein level in the susceptible and unsusceptible mice was examined by western blot in the hippocampus,prefrontal cortex,nucleus accumbens,and amygdala;AQP4 knockdown and AQP4 overexpression adeno-associated virus were stereotactic injection to study depressivelike behavior of mice;the changes in glutamate NMDA receptor associated subunits were detected by western blot;Electrophysiological technique was used to study the NMDA receptor-dependent synaptic functional plasticity and basal synaptic transmission efficiency in mice after AQP4 knockdown or overexpression;Golgi-Cox staining was performed to study synaptic structural plasticity of dendritic spine density changes.Results:(1)Brain regions screening revealed that the expression of AQP4 protein in the NAc was decreased in susceptible mice.(2)Knockdown of AQP4 in na?ve mice NAc does not directly cause depressive-like behaviors.(3)Knockdown of NAc AQP4 combining with subthreshold stress increase mice susceptibility to depression and reduces the expression of NMDARs subunits of NR2 B.(4)Overexpression of NAc AQP4 prevents chronic stress induced depressivelike behaviors and downregulation effect on NR2 B.(5)Altered NAc glutamatergic synaptic plasticity in stressed mice were strongly and particularly regulated by AQP4.(6)Overexpression of NAc AQP4 prevented chronic stress induced abnormal of spine density.Conclusion:We demonstrated the relationship between AQP4 protein expression and the depressive-like behavior induced by chronic defeat stress.The decrease in AQP4 expression promotes vulnerability of depression.On the contrary,the increase in the expression of AQP4 may exhibit resistance to stress-induced development of depressive-like behaviors.Knockdown of AQP4 expression in NAc results in dysfunction of NMDARs subunits of NR2 B,thus further impair the NMDA receptor-dependent synaptic functional and structural plasticity,and increase in stress vulnerability in mice.Therefore,based on all the above results,we speculate when the expression level of AQP4 is decreased,the regulatory effect on NR2 B is weakened,resulting in impaired glutamate receptor function,in turn,increase mice vulnerability to stress-induced depression.