Effects Of Chronic Stress And Estrogen On SOSTDC1 Expression In Mouse MPFC And Hippocampal Brain Regions

Depression is a serious mood disorder.In severe cases,patients have suicidal tendency,which brings huge economic and medical burdens to society.Depression is affected by various genetic,endocrine and environmental risk factors.Current research has not found a single gene that can directly induce depressive symptoms,but long-term stress can make healthy individuals more prone to depressive symptoms.There is a sex difference in depression,and women are twice as likely to suffer from depression as men.This is because the fluctuation of gonadal hormones related to the reproductive cycle makes women more susceptible to depression.Due to sex differences in depression-like behaviors,different chronic stress models are used to induce depression-like behaviors in male and female rodents.Previous studies have found that male animals are more susceptible to long-term chronic stress,while female animals are more susceptible to acute stress.Chronic mild unpredictable stress(CUMS)is a commonly used depression model,male mice are more susceptible to CUMS than female mice.Because the stress conditions are relatively mild,it can more closely simulate various stress events encountered by humans in normal life,and can induce animals to develop depression-like and anxiety-like behaviors.However,subchronic variable stress(SCVS)can only induce depression-like behaviors in female mice.During the modeling period,the mice were alternately exposed to three stressors:foot electric shock,tail suspension,and restraint for one hour a day.After six consecutive days of SCVS,the mice displayed depression-like behaviors.The medial prefrontal cortex(mPFC)is the most evolved area of the brain.It plays a key role in most advanced cognitive and emotional functions,and has significant structural and functional plasticity in response to stress.It receives and sends a large number of nerve projections to the cerebral cortex and the subcortical area related to mood and cognition,which are important brain regions involved in the development of mood disorders.The hippocampus(Hip),as a part of the limbic system,is the most frequently studied brain area related to depression.It establishes brain circuits with other emotionally-related brain areas and has the ability to regulate emotions,learning and memory.These two brain regions are highly vulnerable to stress.Sclerostin domain containing 1(SOSTDC1)is a member of the bone sclerostin family,which encodes a secreted protein with N-glycosylation of a C-terminal cystine knot-like domain and has the effect of antagonizing the Wnt signaling pathway.The abnormal expression of Wnt protein is closely related to the occurrence and development of depression.Overexpression of Wnt2 and Wnt3a has antidepressant effects,and overexpression of Wnt7a increases the number of excitatory synapses.Some studies show that the mRNA level of SOSTDC1 in the hippocampus and prefrontal cortex of rodents is abnormally increased or decreased after stress.These studies raise the questions:Is the antidepressant effect of Wnt protein working through regulating SOSTDC1 protein?Is SOSTDC1 protein involved in the occurrence of depression-like behaviors in animal model of depression?The answers are unknown,and there are no reports available in literature.In addition,the results of previous studies showed that estrogen treatment increases the mRNA content of SOSTDC1 in the hippocampus of the ovariectomized(OVX)rats.However,at the protein level,it is not clear whether the level SOSTDC1 protein is regulated by estrogen.This experiment is the first to explore the expression and localization of SOSTDC1 protein in the mouse brain and its profiles in the brain during postnatal development.The main purpose of the research was to explore the relationship between SOSTDC1 and the depression-like behaviors induced by chronic stress,and to prove whether its protein level is regulated by estrogen.First,the expression and localization of SOSTDC1 protein in the mPFC and hippocampus were evaluated by immunofluorescence staining technique,and Western Blot was used to explore the expression changes of SOSTDC1 protein in the brain during the postnatal development.Second,to establish a mouse depression model(male mouse with CUMS,female mouse with SC VS),and determine the success of the depression model using behavioral tests such as sucrose preference test,forced swim test,open field test,and novelty-suppressed feeding test.Western Blot was used to detect the chronic stress-mediated alterations in the levels of SOSTDC1 protein in the mPFC and hippocampus.Finally,OVX was used to delete the circulating estrogen in mice,and through exogenous supplementation of estrogen,to explore the regulation of SOSTDC1 protein in the hippocampus and mPFC of OVX mice via exogenous estrogen replacement.The results show:1.SOSTDC1 protein is expressed in the mPFC and the pyramidal neurons,granule cells of dentate gyrus and interneuron cells of the hippocampus,and the expression level of SOSTDC1 protein is markedly increased postnatal day 14.2.CUMS-induced depression-like behaviors in male mice were accompanied by a significant increase in SOSTDC1 protein expression in their mPFC and the hippocampus.3.SCVS-induced depression-like behaviors in female mice were also accompanied a significant increase in SOSTDC1 protein level in their mPFC and the hippocampus.4.Exogenous estrogen replacement and SCVS both significantly increased the protein levels of SOSTDC1 in the mPFC and hippocampus of OVX mice,respectively.The above results show that SOSTDC1 protein is mainly expressed in various subregions of the mPFC and the pyramidal neurons,the granule cells of dentate gyrus,and interneurons of the hippocampus.during the critical period of mouse dendritic spines development and formation(14 days after birth)the protein expression level was significantly increased at postnatal day 14,a critical time point of spine formation,suggesting that SOSTDC1 may play a key role in the formation of dendritic spines and synapses.Increased expression of SOSTDC1 protein in the mPFC and the hippocampus of male and female mice accompanied depression-like behaviors induced by CUMS or SCVS.Estrogen regulates the expression of SOSTDC1 protein in the hippocampus.The above results indicate that chronic stress increases the levels of SOSTDC1 protein in the mPFC and hippocampus,SOSTDC1 may play an important role in depression-like behaviors induced by chronic stress.