Lei Shan, Cheng Tianming, Guo Yandong, Li Chen, Zhang Wendi, Zhi Fachao
Guangdong Provincial Key Laboratory of Gastroenterology, Department of Gastroenterology, Nanfang Hospital, Southern Medical University, Guangzhou, China.
Guangdong Provincial Key Laboratory of Gastroenterology, Department of Gastroenterology, Nanfang Hospital, Southern Medical University, Guangzhou, China.
Eur J Cell Biol. 2014 Jul;93(7):299-307. doi: 10.1016/j.ejcb.2014.05.003. Epub 2014 Jun 2.
Dysfunction of the epithelial barrier is an important pathogenic factor of inflammatory bowel disease and other inflammatory conditions of the gut. Somatostatin (SST) has been demonstrated to reduce local and systemic inflammation reactions and maintain the integrity of the blood-brain barrier (BBB). To determine the beneficial effect of SST on lipopolysaccharide (LPS)-induced damage of the tight junction (TJ) and its mechanisms, Caco2 cells pretreated with SST (1nM) or MEK inhibitor U0126 (10μM) were exposed to LPS. LPS significantly reduced the expression of TJ proteins in a dose-dependent way. LPS (100μg/ml) greatly induced Caco2 monolayer barrier dysfunction by decreasing transepithelial resistance and increasing epithelial permeability. Pretreatment with SST effectively improved the barrier dysfunction of Caco2 cells. SST significantly increased the expression of TJ proteins occludin and ZO-1 and inhibited the redistribution of TJ proteins due to LPS stimulation. Furthermore, SST decreased the LPS-induced phosphorylation of ERK1/2, and a selective MEK inhibitor markedly protected the barrier function against LPS disturbance by blocking the activation of the ERK-MAPK pathway in Caco2 cells. Besides, LPS significantly increased the mRNA level of SSTR5, which was partly inhibited by pretreatment with SST. In conclusion, the present study indicates that SST protects the Caco2 monolayer barrier against LPS-induced tight junction breakdown by down-regulating the activation of the ERK-MAPK pathway and suppression the activation of SSTR5.
上皮屏障功能障碍是炎症性肠病和肠道其他炎症性疾病的重要致病因素。已证明生长抑素（SST）可减轻局部和全身炎症反应，并维持血脑屏障（BBB）的完整性。为了确定SST对脂多糖（LPS）诱导的紧密连接（TJ）损伤的有益作用及其机制，将用SST（1nM）或MEK抑制剂U0126（10μM）预处理的Caco2细胞暴露于LPS。LPS以剂量依赖性方式显著降低TJ蛋白的表达。LPS（100μg/ml）通过降低跨上皮电阻和增加上皮通透性，极大地诱导了Caco2单层屏障功能障碍。用SST预处理可有效改善Caco2细胞的屏障功能障碍。SST显著增加TJ蛋白occludin和ZO-1的表达，并抑制由于LPS刺激导致的TJ蛋白重新分布。此外，SST降低了LPS诱导的ERK1/2磷酸化，并且选择性MEK抑制剂通过阻断Caco2细胞中ERK-MAPK途径的激活，显著保护屏障功能免受LPS干扰。此外，LPS显著增加SSTR5的mRNA水平，而SST预处理可部分抑制该水平。总之，本研究表明，SST通过下调ERK-MAPK途径的激活和抑制SSTR5的激活，保护Caco2单层屏障免受LPS诱导的紧密连接破坏。
