Hippocampal Metabolic Differences In Four Rat Models Of Depression And Integrated Analysis For Metabolomics-proteomics Data In CUMS Rat Model

BACKGROUNDMajor depressive disorder(MDD)is a common and serious mental disorder with high rates of disability and suicidality.MDD can be long-lasting or recurrent,substantially impairing quality of life and functioning.MDD is a multifactorial disorder with substantial molecular alterations and pathway dysregulations involved,which makes the pathophysiology of MDD complicated and largely unknown.Stress event play a crucial role in the development of MDD.Different stressors were associated with heterogeneous and even opposed stress responses.Therefore,examining brain molecular changes among different stress models of depression is a promising way to investigate the pathogenetic processes of depression.Omics technologies are useful tools for molecular profiling,biomarkers identification,and pathophysiological processes examination.In recent years,large numbers of single-omics studies for depression have accumulated.However,a number of contradictory results exist in these studies,which make them difficult to interpret.Therefore,the integrated analysis of multiple types of omics data,which allows mutual verification of changes at different levels of biochemical regulation,has become a promising and hot topic.In this study,we focused on hippocampus,a critical brain region for memory and mood regulation,to examine the metabolic differences between four rat models of depression.Furthermore,we applied an integrated analysis of metabolomic and proteomic data in chronic unpredictable mild stress(CUMS)rat model,which will help to gain further insights into the pathogenesis of MDD.OBJECTIVE1.To identify differential metabolites in hippocampus between the four stress models of depression,which include CUMS,learned helplessness(LH),chronic restraint stress(CRS),and social defeat(SD),and the corresponding control groups.2.By analyzing the differences of hippocampal metabolic profiling among the four stress groups,we aim to investigate the molecular mechanism of heterogeneous stress response in depression.3.By applying integrated analysis of metabolomic and proteomic data in CUMS rat model,we aim to further investigate the pathogenesis of depression and provide potential targets for antidepressant drugs.METHODS1.Four rat models(CUMS,LH,CRS and SD)and their corresponding control groups were established.Sucrose preference test(SPT)was used to screen stress-susceptible rats for subsequent experiments.SPT and forced swim test(FST)were conducted to assess depressive-like behavior,and open field test(OFT)and elevated plus-maze(EPM)were performed to evaluate anxiety-like behavior.2.We conducted gas chromatography-mass spectrometry(GC-MS)-based metabolomic approach to examine the metabolomic profiling among the four stress models of depression and their control groups.Matlab software was used to conduct heat maps and unsupervised hierarchical clustering analysis,and Ingenuity Pathway Analysis(IPA)was applied to perform pathways and networks analysis.3.We conducted isobaric tags for relative and absolute quantitation(iTRAQ)-based proteomic examination with the hippocampus of CUMS and control rats to identify differential expressed proteins.IPA and IMPaLA tools were used for further integrated metabolomic and proteomic analysis.RESULTS1.Body weight gain was significantly decreased in CUMS,CRS and SD rats compared with their control groups.All four stressed groups showed a significant decrease of sucrose preference in SPT and a significant increase of immobility time in SFT.Only CUMS rats showed a decrease of total distance and rearing frequency in OFT.In addition,CUMS rats spent less time in the open arms in EPM compared with the control group.2.A total of 30,24,19,and 25 differential metabolites were identified by metabolomic profiling in the CUMS,LH,CRS,and SD model,respectively.The hierarchical clustering analysis revealed two patterns of metabolic changes,which were in accordance with the type of stress.Cluster 1 included CUMS and LH model,which may represent physical stress.Cluster 2 included CRS and SD model,and it may represent psychological stress.3.IPA analysis showed that physical stress was mainly associated with lipid and glutamate metabolism changes,while psychological stress was linked to cell signaling,cellular proliferation,and neurodevelopment alterations.Nine common differential metabolites,which mainly involved in the functions of cellular proliferation and neurodevelopment,were opposite in the directions of change between physical and psychological models.4.A total of 170 proteins were identified by iTRAQ-based proteomic analysis.The integrated analysis revealed four major changes in the hippocampus of CUMS rats:(1)impairment in amino acid metabolism and protein synthesis/degradation;(2)dysregulation of glutamate and glycine metabolism and their transport/catabolism related proteins;(3)disturbances in fatty acid and glycerophospholipid metabolism accompanied by alterations in the corresponding metabolic enzymes;(4)abnormal expression of synapse-associated proteins.CONCLUSION1.All the four stress models can induce significant depressive-like behaviors in rats,whereas only CUMS model can induce anxiety-like behaviors.2.Physical and psychological stress can lead to different metabolic changes.Physical stress is associated with lipid and glutamate metabolism changes,while psychological stress is linked to cell signaling,cellular proliferation,and neurodevelopment alterations.3.The common pathway to depression,which is mainly associated with the functions of cellular proliferation and neurodevelopment,is different in the response to physical and psychological stress.4.The integrated analysis found a set of consistent alterations among metabolomics and proteomics in CUMS rats,including the dysregulated amino acid metabolism,lipid metabolism,and synaptic transmission.These findings provide important further insights into the pathogenesis of depression and may help identify potential targets for antidepressant drugs.