Microglia-specific transcriptional repression of interferon-regulated genes after prolonged stress in mice.

Stress-induced neuroinflammation is considered an important mechanism in the pathogenesis of depression. As immune effector cells in the brain, microglia play an essential role in neuroinflammation under stress, but the underlying mechanism remains controversial. Here, we performed RNA-seq and ATAC-seq to study microglia-specific epigenomic changes in mice after 12 weeks of exposure to mild stress. Our study revealed that chronic stress induced pronounced anxiety and depressive-like behavioral changes. However, microglia did not manifest a state of neuroinflammatory activation; instead, they displayed morphological changes characterized by hyper-ramification. Furthermore, we revealed large-scale transcriptional repression in microglia isolated from the stressed brain, including many interferon (IFN)-regulated genes (IRGs) and some encompassing DNA repeats. GSEA showed that the down-regulated genes were enriched in the IFN-mediated neuroimmune signaling pathways. In addition, integrative analysis with a published scRNA-seq dataset revealed that these down-regulated genes were enriched in a distinct subpopulation of "Interferon microglia". ATAC-seq analysis further showed that differential gene expression was positively correlated with the changes in chromatin accessibility, and the IFN-stimulated response element (ISRE) was enriched in the down-regulated ATAC-seq loci. Interestingly, this phenotype was not associated with the production of IFNs. Instead, the gene encoding Activating Transcription Factor 3 (ATF3) was significantly increased in the stressed microglia, which might contribute to the transcriptional repression of IRGs. Our study reported microglia-specific transcriptional repression of IRGs independent of the production of IFNs, providing some new insights into neuroimmune dysregulation under prolonged stress.