AKT and MAPK signaling pathways in hippocampus reveals the pathogenesis of depression in four stress-induced models

Abstract

Major depressive disorder (MDD) is a highly heterogeneous psychiatric disorder. The pathogenesis of MDD remained unclear, and it may be associated with exposure to different stressors. Most previous studies have focused on molecular changes in a single stress-induced depression model, which limited the identification of the pathogenesis of MDD. The depressive-like behaviors were induced by four well-validated stress models in rats, including chronic unpredictable mild stress, learned helplessness stress, chronic restraint stress and social defeat stress. We applied proteomic and metabolomic to investigate molecular changes in the hippocampus of those four models and revealed 529 proteins and 98 metabolites. Ingenuity Pathways Analysis (IPA) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis identified differentially regulated canonical pathways, and then we presented a schematic model that simulates AKT and MAPK signaling pathways network and their interactions and revealed the cascade reactions. Further, the western blot confirmed that p-AKT, p-ERK12, GluA1, p-MEK1, p-MEK2, p-P38, Syn1, and TrkB, which were changed in at least one depression model. Importantly, p-AKT, p-ERK12, p-MEK1 and p-P38 were identified as common alterations in four depression models. The molecular level changes caused by different stressors may be dramatically different, and even opposite, between four depression models. However, the different molecular alterations converge on a common AKT and MAPK molecular pathway. Further studies of these pathways could contribute to a better understanding of the pathogenesis of depression, with the ultimate goal of helping to develop or select more effective treatment strategies for MDD.

Fig. 1. Procedure for the four depression models protocol.

A The timeline of the stress and control groups regime and behavioral assessments. B The stimulus diagram of the CUMS model. C LH model. D CRS model. E, F SD model. CON, control group.

Fig. 2. Proteomic analysis results of four depression models.

A The volcano plot of the iTRAQ analysis. B The percentage increase or decrease of differentially expressed proteins for each model. Red, increase; green, decrease. C Venn diagram of common and distinct proteins in four depression models, and five commonly expressed proteins and fold change values in four stress-induced models. Red Increase, green, decrease, Pex16 Peroxisomal membrane protein PEX16; Hmgn2, Non-histone chromosomal protein HMG-17, Pjal LOC683077 protein, Smad5 Smad5 protein, Hbb-b1 Hemoglobin subunit beta-1.

Fig. 3. The bioinformatics analysis results of four depression models.

A The IPA and KEGG pathway analysis of differentially expressed proteins in four depression models. B The Gene Ontology (GO) analysis. CUMS Chronic unpredictable mild stress, LH Learned helplessness stress, CRS Chronic restraint stress, SD Social defeat stress, KEGG Kyoto Encyclopedia of Genes and Genomes, IPA Ingenuity Pathway Analysis.

Fig. 4. The results of Western blot of hippocampus in four depression models.

Representative immunoreactive bands and statistical results showing the protein levels of hippocampus (A) AKT and p-AKT, (B) ERK12 and p-ERK12, (C) mTOR and p-mTOR, (D) MEK1 and p-MEK1, (E) MEK2 and p-MEK2, (F) P38 and p-P38, (G) P70S6K and p-P70S6K, (H) GluA1 and PSD95, (I) Syn1 and TRKB in the stress group compare with control group. All results are represented as means ± SEM; *P < 0.05, **P < 0.01, ***P < 0.001.

Fig. 5. The significantly altered proteins and metabolites in each model were poured into Ingenuity Pathways Analysis (IPA) analysis to find typical pathways and validate key proteins.

A schematic model of AKT and MAPK signaling pathways among four depression models in hippocampus. UP Up-regulated, DOWN Down-regulated, NS No significance.