Key Laboratory of Animal Physiology & Biochemistry, Nanjing Agricultural University, Nanjing, 210095, PR China.
Free Radic Biol Med. 2021 Jan;162:478-489. doi: 10.1016/j.freeradbiomed.2020.11.003. Epub 2020 Nov 12.
The immunoinhibitory effect of glucocorticoid and immunoenhancing attributes of melatonin (MEL) are well known, however, the involvement of glucocorticoid receptor (GR) in melatonin modulation of bacterial toxins caused-inflammation has not been studied in colon. Pyocyanin (PCN), a toxin released by Pseudomonas aeruginosa, can destroy cells through generating superoxide products and inflammatory response. Here we report that PCN treatment elevated the generation of reactive oxygen species (ROS), which further lead to mitochondrial swelling and caspase cascades activation both in vivo and in vitro. However, MEL treatment alleviated the oxidative stress caused by PCN on cells through scavenging ROS and restoring the expression of antioxidant enzyme so that to effectively alleviate the apoptosis. Large amounts of ROS can activate the NLRP3 signaling pathway, so MEL inhibited PCN induced NLRP3 inflammasome activation and inflammatory cytokines (IL-1β, IL-8, and TNF-α) secretion. In order to further investigate the molecular mechanism, goblet cells were exposed to MEL and PCN in the presence of luzindole and RU486, inhibitors of MEL receptors and GR respectively. It was found that PCN significantly inhibited the expression level of GR, and MEL effectively alleviated the inhibition phenomenon. Moreover, we found that MEL mainly upregulated the expression of GR to achieve its anti-inflammatory and anti-apoptotic functions rather than through its own receptor (MT2) in colon goblet cells. Therefore, MEL can reverse the inhibitory effects of PCN on GR/p-GR expression to present its anti-oxidative and anti-apoptotic function.
糖皮质激素的免疫抑制作用和褪黑素（MEL）的免疫增强特性是众所周知的，然而，糖皮质激素受体（GR）在褪黑素调节细菌毒素引起的炎症中的作用在结肠中尚未得到研究。绿脓杆菌释放的绿脓菌素（PCN）可以通过产生超氧化物产物和炎症反应来破坏细胞。在这里，我们报告 PCN 处理会增加活性氧（ROS）的产生，这会导致体内和体外的线粒体肿胀和半胱天冬酶级联激活。然而，MEL 通过清除 ROS 和恢复抗氧化酶的表达来减轻 PCN 对细胞造成的氧化应激，从而有效地减轻细胞凋亡。大量的 ROS 可以激活 NLRP3 信号通路，因此 MEL 抑制了 PCN 诱导的 NLRP3 炎性小体激活和炎性细胞因子（IL-1β、IL-8 和 TNF-α）的分泌。为了进一步研究分子机制，在 presence of luzindole 和 RU486（分别是 MEL 受体和 GR 的抑制剂）的情况下，将杯状细胞暴露于 MEL 和 PCN 中。结果发现，PCN 显著抑制了 GR 的表达水平，而 MEL 有效地缓解了这种抑制现象。此外，我们发现 MEL 主要通过上调 GR 的表达来实现其抗炎和抗凋亡功能，而不是通过其自身受体（MT2）在结肠杯状细胞中实现。因此，MEL 可以逆转 PCN 对 GR/p-GR 表达的抑制作用，从而发挥其抗氧化和抗凋亡作用。
