Downregulation of CRTC1 Is Involved in CUMS-Induced Depression-Like Behavior in the Hippocampus and Its RNA Sequencing Analysis.

Chronic stress is an important risk factor for mood disorders including depression. The decreased level of CREB (cAMP-responsive element binding)-regulated transcription coactivator 1 (CRTC1) expression in hippocampus may be involved in depression-like behavior in some stress-induced depression models. But the mechanism of CRTC1 in mediating depression-like behavior remains unknown. In this study, chronic unpredictable mild stress (CUMS)-treated mice showed depression-like behavior accompanied by the downregulation of CRTC1 in the hippocampus. Adeno-associated virus (AAV)-CRTC1-mediated overexpression of CRTC1 in the hippocampus by stereotactic brain injection could significantly prevent depression-like behavior in CUMS-treated mice. The above data reveal that the downregulation of hippocampal CRTC1 expression participates in CUMS-induced depression-like behavior. In order to explore the key targets regulated by CRTC1, AAV-mediated CRTC1 short hairpin (shRNA) was constructed to achieve knockdown of CRTC1 in the hippocampus, and then the hippocampi were collected for RNA-sequencing (RNA-seq). The RNA-seq data show that upregulated genes were enriched in stress and immune system-associated GO terms and pathways such as response to stress and external stimulus and regulation of immune response and that downregulated genes were enriched in neural activity such as synaptic transmission and cognitive behavior. We further provided RT-qPCR data that the inflammation-related factors including Gpr84, Tlr2, Lyz2, and Icam1 were significantly upregulated in the hippocampus of both CUMS- and CRTC1 shRNA-induced models, some of them were also validated in protein levels by Western blotting. We propose a hypothesis that CUMS induces downregulation of CRTC1, which might lead to depression-like behavior via neuroinflammation pathway. This study provides new explanation for the inflammatory hypothesis of depression and some clues for exploring the molecular mechanism of CRTC1 regulation.