Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI, USA.
Department of Gastroenterology, Beijing Friendship Hospital, Capital Medical University, Beijing, China.
Neurogastroenterol Motil. 2020 Dec;32(12):e13941. doi: 10.1111/nmo.13941. Epub 2020 Aug 2.
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.
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.
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.
慢性应激与 HPA 轴的激活、促炎细胞因子水平的升高、肠道上皮细胞紧密连接（TJ）蛋白的减少以及内脏痛觉的增强有关。目前尚不清楚表观遗传调控途径是否在慢性应激诱导的肠道屏障功能障碍和内脏痛觉过敏中发挥作用。
将年轻成年雄性大鼠置于避水应激条件下，并给予 H3K9 甲基化抑制剂或 siRNA。评估内脏痛觉反应。用皮质醇或 IL-6 处理分化的 Caco-2/BBE 细胞和人结肠类器官，并加入相应的拮抗剂。测量 TJ、IL-6 和基因启动子处 H3K9 甲基化状态的表达。评估跨上皮电阻和 FITC-葡聚糖通透性。
慢性应激诱导大鼠结肠中 IL-6 的上调，随后 TJ 蛋白减少。IL-6 水平与紧密连接蛋白 occludin 的表达呈负相关。IL-6 的处理降低了 occludin 的表达并诱导了内脏痛觉过敏。慢性应激和 IL-6 增加了 H3K9 甲基化，并减少了转录因子 GR 对 occludin 基因启动子的结合，导致蛋白表达下调和细胞旁通透性增加。直肠内给予 H3K9 甲基化拮抗剂可预防大鼠慢性应激诱导的内脏痛觉过敏。在人类结肠类器官模型中，皮质醇降低了 occludin 的表达，GR 拮抗剂 RU486 可阻止这种作用，而 IL-6 增加了 H3K9 甲基化并降低了 TJ 蛋白水平，这两种作用都可以被 H3K9 甲基化抑制剂所阻止。
我们的研究结果支持一种新的观点，即抑制性组蛋白 H3K9 的甲基化在调节慢性应激、促炎细胞因子介导的结肠 TJ 蛋白水平降低、细胞旁通透性增加和内脏痛觉过敏中起作用。
