Glucocorticoids and Tumor Necrosis Factor-α Synergize to Induce Absorption by the Epithelial Sodium Channel in the Colon
Glucocorticoids and Tumor Necrosis Factor-α Synergize to Induce Absorption by the Epithelial Sodium Channel in the Colon
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DOI：
10.1053/j.gastro.2008.12.008
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发表时间：
2009-03-01
期刊：
影响因子：
29.4
通讯作者：
Schulzke, Joerg-Dieter
中科院分区：
文献类型：
--
作者：
Bergann, Theresa;Zeissig, Sebastian;Schulzke, Joerg-Dieter
背景和目的：上皮钠通道 (ENaC) 介导远端结肠的电钠吸收。在炎症性肠病 (IBD) 患者中，ENaC 的诱导受到损害，主要是通过肿瘤坏死因子 (TNF)-α 等促炎细胞因子的转录抑制所致。糖皮质激素治疗迅速增加钠吸收；我们研究了 TNF-α、糖皮质激素和 ENaC 诱导之间相互作用的分子机制。方法：在合成糖皮质激素地塞米松和 TNF-α 的影响下，在 Ussing 室中对表达糖皮质激素受体 (GR) 的 HT-29/B6 细胞和大鼠远端结肠中 ENaC 介导的钠转运进行定量。通过实时聚合酶链式反应监测 ENaC 信使 RNA (mRNA) 水平。通过基因报告、免疫印迹和共聚焦免疫荧光显微镜分析研究 GR 反式激活和表达。测定GR mRNA半衰期。使用丝裂原激活蛋白激酶抑制剂来表征信号通路。结果：地塞米松不仅阻止 TNF-α 介导的 ENaC 抑制，而且在 HT-29/136-GR 细胞和大鼠远端结肠中协同诱导 ENaC 依赖性钠吸收。这种协同作用是由于 GR mRNA 稳定和随后地塞米松的 GR 反式激活而导致 TNF-α 介导的 GR 蛋白水平增加。结果，ENaC β 和 γ 亚基的转录上调，增加了 ENaC 依赖性钠吸收。这种协同效应需要 p38 丝裂原激活蛋白激酶：p38 抑制可阻止 GR 蛋白表达和 ENaC 依赖性钠吸收的增加。结论：TNF-α 和地塞米松可诱导 ENaC，解释了糖皮质激素治疗快速而强烈的促吸收作用。
Background & Aims: The epithelial sodium channel (ENaC) mediates electrogenic sodium absorption in distal colon. In patients with inflammatory bowel disease (IBD), ENaC induction is impaired, mainly through transcriptional suppression by proinflammatory cytokines such as tumor necrosis factor (TNF)-alpha. Glucocorticoid therapy rapidly increases sodium absorption; we investigated the molecular mechanisms underlying the interaction among TNF-alpha, glucocorticoids, and ENaC induction. Methods: ENaC-mediated sodium transport in glucocorticoid receptor (GR)-expressing HT-29/B6 cells and rat distal colon, under the influence of the synthetic glucocorticoid dexamethasone and TNF-alpha, was quantified in Ussing chambers. ENaC messenger RNA (mRNA) levels were monitored by real-time polymerase chain reaction. GR transactivation and expression were investigated by gene reporter, immunoblot, and confocal immunofluorescence microscopy analyses. The GR mRNA half-life was determined. Signaling pathways were characterized using mitogen-activated protein kinase inhibitors. Results: Dexamethasone not only prevented TNF-alpha-mediated ENaC suppression but caused synergistic induction of ENaC-dependent sodium absorption in HT-29/136-GR cells and rat distal colon. This synergy resulted from TNF-alpha-mediated increases in GR protein levels because of GR mRNA stabilization and subsequent GR transactivation by dexamethasone. As a consequence, transcription of the ENaC beta- and gamma-subunits was up-regulated, increasing ENaC-dependent sodium absorption. p38 Mitogen-activated protein kinase is required for this synergistic effect: p38 inhibition blocked the increase in GR protein expression and ENaC-dependent sodium absorption. Conclusions: TNF-alpha and dexamethasone induce ENaC, explaining the rapid and intense proabsorptive effect of glucocorticoid therapies.