Chronic social stress alters dexamethasone sensitivity of glucocorticoid receptor target genes

Abstract

Glucocorticoids are well-known for their role in adapting to physical and psycho-emotional stress. The prefrontal cortex (PFC) is a crucial target-tissue for glucocorticoid receptors (GR) that coordinates the stress response. Transcriptome sequencing was conducted on the prefrontal cortex of male C57Bl/6 mice subjected to 30 days of chronic social defeat stress (CSDS). Prior to tissue extraction, the mice were injected with either 2 µg/g dexamethasone or saline, resulting in four groups: CSDS+sal, CSDS+dex, control+sal, and control+dex. The study sought to identify genes regulated by GR within the differentially expressed genes (DEG) by analyzing five public GR ChIPseq experiments performed on rodent brain tissue. This endeavor aimed to elucidate the role of GR in the PFC stress response. GR binding sites that were situated –5k to +1k bp from tss were categorized as regulatory regions. The closest genes were then identified. For further analysis, 3023 genes recognized as GR-regulated by at least two studies were selected. Of these, 320 genes were demonstrated to be expressed in the PFC based on our RNAseq data. We found a significant increase in GR sites among PFC DEGs that responded to DEX treatment in both the control group (control+sal vs control+dex: OR=2.17, p 0.001) and CSDS (CSDS+sal vs CSDS+dex: OR=1.86, p 0.001). However, chronic stress alone did not result in enrichment of genes regulated by GR. Notably, genes that responded differently to DEX treatment in CSDS and control showed a higher OR value (dex*CSDS: OR=2.32, p 0.01). Common GR-target genes between DEX-con and DEX-csds exhibited the same expression change direction, except for the Sft2d2 gene, which encodes a vesicle transport protein. These genes are involved in PDZ domain binding (Fzd2, Mpp3), serine/threonine kinase activity (Rps6ka5, Akt2, Camkk1), and oxidoreductase activity (Prodh, Smox). GR-regulated genes specific to the CSDS group participate in cytokine production (e.g., Ltbp1, P2rx7, Dhx33, Hdac9, Bcl6, Lgr4, etc.) and modulate chemical synaptic transmission (e.g., Arc, Syt12, Cacng3, etc.), including components of the glutamatergic synapse (e.g., Magi2, Erc2, Dnm1, Clstn2, and Itgb1). Changes in expression of structural component genes, including those involved in membrane raft (Cavin1, Smpd2, and Slc2a1) and anchoring junction (B4galt1, Gjb6, Fzd4, and Limk1) genes, indicate the control group’s response to DEX treatment. A total of 14 genes showed differential regulation by GR in both CSDS and control groups. Among these genes are those involved in axon elongation (Link1, Rasgrf1), synaptic morphology (Clstn2), and vesicle endocytosis (Dnm1). Additionally, vital genes for axonal regeneration (Tubb3), neuroprotection (Hspb8), regulation of apoptosis (Bugalt1), and microglia activation (Cavin1) are included. In conclusion, we aimed to decipher the pathways of GR regulation triggered by social stress and DEX treatment in the PFC. Chronic stress resulted in alterations in GR regulatory networks in the PFC that impacted processes related to synapse function and the inflammatory response.