The Neuroprotective Effect And Mechanism Of Fecal Microbiota Transplantation On CUMS Induced Depressive-like Rats

Background:The main clinical manifestations of depression are low mood accompanied by low self-esteem,sleep and eating disorders,and cognitive changes,and low mood is not consistent with the situation.Although considerable progress has been made in our understanding of the pathophysiology of depression,its pathogenesis remains unknown and there are no reliable biomarkers that can contribute to objective diagnosis and clinical treatment.Different theories and hypotheses have been proposed to explain the etiology of depression,including dysfunction of the neurotransmitter system,neuroinflammation,metabolic abnormalities,and deficiency of neurotrophic factors,but there is no unified understanding.Current classic antidepressants work by increasing levels of monoamine neurotransmitter molecules on the synapses.These antidepressants take several weeks to become clinically effective but often do not respond to patients at high risk of suicide.Research suggests that the gut microbiome may be the direct cause of their disease.Although a potential association has been found between psychosocial disorders and gut microbiota,the mechanism is still unclear.This study used the method of faecal bacteria transplantation to study the behavior and neuroprotective effect of intestinal flora regulation on stress-induced depression-like model rats,and to further explore the inhibitory effect on neuroinflammation,so as to provide a basis for its treatment.Objective:To explore the behavior improvement and neuroprotective effects of fecal microbiota transplantation on depressive-like rats induced by CUMS.Methods:SD rats were randomly divided into normal group,depression group,and fecal microbiota transplantation group.Rats in normal control group were fed normally.Animals in other two groups suffered from CUMS to set up depressive-like rat model,and intervention process by gavage started at the fourth week of modeling.The rats in the FMT group were gavaged with untreated feces and made into bacterial liquid for 2 consecutive weeks,while the rats in the DEP group were gavaged with PBS.Sucrose preference test,open-field test,and forced swim test were carried out to evaluate the changes of behavior.Serotonin(5-HT),the level of proinflammatory cytokines in the prefrontal cortex and hippocampus of rats was measured by ELISA.The colon contents of rat were collected for the gut microbiota compositions analysis by 16S rRNA sequencing and the pathological changes of ileum and colon were observed by HE staining and PAS staining.The distribution and activation of glial cells in the prefrontal cortex and hippocampus of rats were detected by immunofluorescence assay to evaluate neuroinflammation.Western blot and qPCR were used to detect the expression of NLRP3 inflammasome in prefrontal cortex and hippocampus of rats.Results:1.Fecal microbiota transplantation alleviated the depressive-like behaviors,increased the levels of 5-HT in the rat brain and deduced the content of inflammatory cytokines TNF-α and IL-1β.2.Sequencing of 16S rRNA revealed that phylum Bacteroidetes,Desulfobacterota and genus Alloprevotella,Lachnospiraceae,Roseburia,Romboutsia,and Ruminococcus decreased,while phylum Firmicutes,genus Colidextribacter,Muribaculaceae,and Oscillospiraceae increased in fecal samples of DEP rats,remarkably.FMT reduced gut microbial dysbiosis.3.HE staining showed that after CUMS stress,the ileum mucosal layer was thinned,ileum villi were atrophied and loosened,FMT alleviated the damage of ileum mucosal membrane,and PAS staining showed that after CUMS stress,the relative number of intestinal goblet cells and the content of glycoprotein were significantly reduced,while FMT increased the number4.FMT inhibited the activation of glial cell and in the prefrontal cortex and hippocampus,and decreased the expression of NLRP3 inflammasomes signaling pathway molecules in the rat brain.ConclusionThe intervention of fecal microbiota transplantation can improve depression-like behavior,reduce intestinal microbial dysregulation and intestinal histological damage,and inhibit neuroinflammation.This antidepressant effect may be related to the inhibition of the activation of brain microglia and astrocyte cells and NLRP3 inflammasome.