Histone H3K9 methylation regulates chronic stress and IL‐6–induced colon epithelial permeability and visceral pain

Abstract

Background: Chronic stress is associated with activation of the HPA axis, elevation in pro-inflammatory cytokines, decrease in intestinal epithelial cell tight junction (TJ) proteins, and enhanced visceral pain. It is unknown whether epigenetic regulatory pathways play a role in chronic stress-induced intestinal barrier dysfunction and visceral hyperalgesia. Methods: Young adult male rats were subjected to water avoidance stress ± H3K9 methylation inhibitors or siRNAs. Visceral pain response was assessed. Differentiated Caco-2/BBE cells and human colonoids were treated with cortisol or IL-6 ± antagonists. Expression of TJ, IL-6, and H3K9 methylation status at gene promoters was measured. Transepithelial electrical resistance and FITC-dextran permeability were evaluated. Key Results: Chronic stress induced IL-6 up-regulation prior to a decrease in TJ proteins in the rat colon. The IL-6 level inversely correlated with occludin expression. Treatment with IL-6 decreased occludin and induced visceral hyperalgesia. Chronic stress and IL-6 increased H3K9 methylation and decreased transcriptional GR binding to the occludin gene promoter, leading to down-regulation of protein expression and increase in paracellular permeability. Intrarectal administration of a H3K9 methylation antagonist prevented chronic stress-induced visceral hyperalgesia in the rat. In a human colonoid model, cortisol decreased occludin expression, which was prevented by the GR antagonist RU486, and IL-6 increased H3K9 methylation and decreased TJ protein levels, which were prevented by inhibitors of H3K9 methylation. Conclusions & Inferences: Our findings support a novel role for methylation of the repressive histone H3K9 to regulate chronic stress, pro-inflammatory cytokine-mediated reduction in colon TJ protein levels, and increase in paracellular permeability and visceral hyperalgesia.

Chronic psychological stress alters gene expression in rat colon epithelial cells promoting chromatin remodeling, barrier dysfunction and inflammation

“…The loss of these paracellular junction proteins leads to the increase in paracellular permeability, sensitizes nerve terminals of afferent neurons and enhances visceral pain sensation. Our recent study supports the role of pro-inflammatory cytokines such as IL6 in down-regulation of tight junction proteins and increase in visceral hypersensitivity ( Wiley et al, 2020 ).…”

“…In the WAS rats, Ehmt2 and Suv39h2 significantly increased and concurrently H3K9 demethylases such as Kdm3b, Kdm4a and Kdm4b decreased in the rat colon epithelial cells. Differential alterations of these enzymes can increase the H3K9 methylation status at epithelial tight junction gene promoters, culminating in suppression of gene transcription and increase in paracellular permeability ( Wiley et al, 2020 ).…”

Stress-induced visceral pain in female rats is associated with epigenetic remodeling in the central nucleus of the amygdala

“…The sexual dimorphism in pain perception may also be explained by stress-induced epigenetic changes that occur outside of the CeA. For instance, chronic WAS causes epigenetic remodeling at the promoter regions of genes encoding tight junction proteins in the colonic epithelial cells leading to increased colonic permeability ( Wiley et al, 2020 ). In addition, chronic WAS also increased CpG methylation at the GR and CNR1 promoters in the L6-S2 DRG, which ultimately lead to the increase of pro-nociceptive TRPV1 ( Hong et al, 2015 ).…”

Differential Activation of Colonic Afferents and Dorsal Horn Neurons Underlie Stress-Induced and Comorbid Visceral Hypersensitivity in Female Rats

“…Likewise, neonatal stress or chronic stress in adults increases the magnitude of the VMR to visceral stimulation 15,16,31,32,47,57,60 . Stress activates the HPA axis and sympathomedullary axis increasing release of inflammatory mediators in the colon and altering corticotrophin releasing factor (CRF)/CRF receptor signaling, degranulation of mast cells and release of serotonin suggesting stress sensitizes colonic afferents and dorsal horn neurons contributing to visceral hypersensitivity 4,31,55,66 . However, the duration of stressinduced visceral hypersensitivity (SIH) is limited, generally resolving within weeks to a month.…”