| BackgroundDepression is a common mental disorder that is thought to be caused by genetic,psychological and environmental factors,and characterized by significant and persistent low mood,anhedonia,loss of interest and so on.As stated by World Health Organization(WHO),depression could become the leading cause of disability worldwide within the next two years.At present,numerous studies have been conducted to investigate and hypothesize the pathogenesis of depression,but the specific mechanism is still unclear.Recent studies have proposed that "microbiota-gut-brain axis" may play an important role in the pathogenesis of depression.The intestinal tract,as the largest and most direct external environment of the organism,is an important media for the interaction between microbiota and the host.Previous studies have found that brain function and behaviors of the host were affected by microbiota through altered tryptophan metabolism,immune regulation,and HPA axis.These studies were mostly concentrated in the alterations of microbiota and brain areas.However,few studies on the intestine were conducted.Therefore,in this study,we use high-throughput detection technologies to explore the changes of intestine and gut microbial metabolic signature,which might shed light on the role of “microbiota-gut-brain axis” in depression and provide new perspective for the study of depression.Objectives1.Based on the chronic unpredictable mild stress(CUMS)model,proteomics method was used to investigate the changes of intestinal protein phenotype after stress.Bioinformatic analysis and further validation were used to depict the molecular and functional alterations in the pathogenetic process.2.Based on the chronic social defeated stress(CSDS)model,microbial diversity detection,untargeted metabonomics and lipidomics methods were used to compare the alterations of gut microbiota composition and host colon tissues between the control and depressed groups,in order to find the key nodes in the pathogenesis of depression and provide new clues for the study of “microbiota-gut-brain axis”.Methods1.The model of CUMS in rats was established and assessed by depression-related behavioral indicators;iTRAQ technique was used to analyze and identify the differential proteins in the small intestine between rats assigned into CUMS group and non-stressed control group.GO functional annotation and KEGG pathway enrichment analysis were carried out.RT-qPCR and WB were used to verify the intestinal differential proteins screened by bioinformatics analysis.The levels of cytokines in the small intestine,serum and hypothalamus were detected by ELISA.2.The model of CSDS in mice was established.16 S rRNA sequencing and untargeted GC-MS metabolomics were combined to describe the microbiota composition and metabolic signature of feces.LC-MS lipidomics was used to compare the changes of colonic lipids between mice in the depressed group and non-stressed group.The correlation analysis of differential microbiota,fecal metabolites and lipids was carried out to identify the key molecules influencing the interaction between microbiota and hosts,and to explore the potential relationship between microbiota and hosts.Results1.(i)Rats in CUMS group exhibited typical depression-like and anxiety-like behaviors: decreased body weight gain and sucrose preference,increased immobility time in forced swimming test(FST),and decreased travelled distance and percentage in the center zone of open field test(OFT),indicating the CUMS model was successfully established.(ii)Based on iTRAQ,349 differential proteins were identified in the small intestine between CUMS group and non-stressed control group,of which209 were down-regulated and 140 were up-regulated.(iii)Based on GO analysis,differential proteins were mainly involved in the biological process of protein complexes assembly,especially the assembly of SNARE complex,the members of SNAP23,VAMP3 and VAMP8 involved;Based on KEGG pathway analysis,protein digestion and absorption ranked the top and was related to amino acid metabolism.(iv)Compared with rats in non-stressed control group,intestinal Snap23,Vamp3 and Vamp8 in CUMS group were increased in the gene level,but only VAMP3 and VAMP8 were increased in the protein level;(v)the levels of TNF?,IL6 and IL1? in the small intestine of CUMS rats were significantly up-regulated,TNF? was significantly down-regulated in the hypothalamus and serum,and IL1? was down-regulated in the serum.2.(i)Compared with non-stressed control group,mice subjected to CSDS showed typical depression-like and anxiety-like behaviors:decreased social interaction(SI,CSDS mice were assigned to depressed and resilient group based on SI ratio),increased immobility time in FST,decreased travelled distance and percentage in the central zone,decreased travelled time and entry frequency in the central zone in OFT.However,no significance was observed in sucrose preference,elevated plus maze and tail suspended test;(ii)16S rRNA sequencing indicated that Actinobacteria was down-regulated while Bacteroidetes was up-regulated in the depressed group.The functional prediction analysis of PICRUSt indicated metabolic dysfunction in the gut microbiota.(iii)A total of twenty differential metabolites were identified in feces,and pathway analysis suggested that perturbation of lipid metabolism was the top.(iv)Thirty-six differential lipids were identified in colon tissues,belonging to glycerophospholipids,glycerolipids and sphingolipids,respectively.(v)Spearman correlation analysis demonstrated that differential gut microbiota,fecal metabolites and colonic lipids were significantly correlated with depression-like and anxiety-like behaviors in depressed mice.ConclusionA systematic study of the intestinal tract in this study found that CUMS might affect the immune response mediated by the small intestinal SNARE complex and regulate central and peripheral cytokines simultaneously.In the CSDS model,we found that differential gut microbiota,fecal metabolites and colonic lipids were strongly associated with depression-and anxiety-like behaviors in depressed mice,indicating that microbiota might influence host behaviors through its metabolites and host lipids,which might be a potential mechanism for bidirectional communication between microbiota and host.This study provided new clues for further study in the role of “microbiota-gut-brain axis” in the pathogenesis of depression. |
PDF Full Text Request