酸敏感通道对十二指肠黏膜的保护机制及其在溃疡中的作用

Duodenal ulcer (DU) is a common digestive disease with high incidence. Anti-acid treatment and H. pylori eradication have significantly increased short-term curative efficacy of DU, but long-term curative efficacy still needs improving. Although there have a lot of studies on the mucosal injury with much depth, little is known about the gastrointestinal protective factors and cellular and molecular mechanisms of recovery after mucosal injury. Duodenal mucosae can secret mucus and bicarbonate, constituting a major protective mechanism against mucosal injury; therefore,dysregulation of duodenal bicarbonate secretion is invloved in the pathogenesis of DU. Based on our previous studies demonstrating that extracellular Ca2+ entry is critical for the regulation of duodenal bicarbonate secretion, we sought to investigate the expression of novel acid-sensitive Ca2+-permeable channels (TRPV4) in duodenal epithelial cells and their important roles in regulating intracellular Ca2+ concentrations and protecting duodenal mucosae at the levels of molecule, cell, tissue, whole animal and human. We will also elucidate the underlying mechanisms of duodenal mucoasal protection by these calcium channels using cellular and molecular approaches and electrophysiological techniques. In addition, we hope to validate a novel pathway in mucosal epithelial cells regarding gastric acid-induced duodenal bicarbonate secretion and mucosal protection: “acid—TRPV4—Ca2+ signaling—PI3K/Akt pathway —CFTR phophorylation—duodenal bicarbonate secretion— mucosal protection”, which may be more effective action than the currently well-known traditional pathway of duodenal bicarbonate secretion. We will also investigate if the expression and funtion of TRPV4 are alterd in the pathogenesis of DU. We believe this project has scientific and clinical significance because successful execution of the project may find useful mucosal protective factors or potential new targets for drug discovery to prevent/treat gastrointestnal mucosal injury.

十二指肠溃疡（DU）是常见多发病，消除胃酸及根治幽门螺杆菌虽明显提高DU的近期疗效，但远期疗效仍待提高。尽管国内外对肠黏膜屏障损伤的机制有深入的研究，但对保护机制研究则相对较少。十二指肠受胃酸刺激后具有分泌碳酸氢盐的能力，是肠黏膜自我保护的重要机制，而碳酸氢盐分泌的异常参与了DU的发病机制。基于我们前期工作证实外钙内流对碳酸氢盐分泌的重要作用，本课题拟采用细胞及分子生物学和电生理学技术，欲从分子、细胞、组织和整体动物水平，研究新颖的酸敏感通道TRPV4及钙信号在十二指肠黏膜保护中的作用，探讨一条有别于经典理论的胃酸刺激小肠上皮细胞分泌碳酸氢盐，保护肠黏膜的新通路并阐述其作用机制，即“胃酸—TRPV4—Ca2+信号—PI3K/Akt—CFTR磷酸化—碳酸氢盐分泌—黏膜保护”。我们还将研究酸敏感通道TRPV4是否在DU患者发生了改变，从而寻找用于研发重塑肠黏膜屏障及治疗慢性DU新药的研发靶点。

消化性溃疡是消化道的常见多发病，以十二指肠溃疡（DU）在临床上更为多见。已知侵袭因素（如胃酸和幽门螺杆菌定植）增强，以及肠黏膜屏障的减弱在DU的发病中占有重要地位。十二指肠黏膜分泌的HCO3-不仅能够中和胃酸，而且是构建肠黏膜屏障自我保护的重要机制。临床研究已证实在DU病人，十二指肠近侧段分泌HCO3-的能力明显降低，表明HCO3-分泌的异常参与了肠黏膜屏障的障碍及DU的发病机制。国内外既往对cAMP及cGMP等细胞内信使，在调节肠黏膜HCO3-及Cl-分泌中的作用及分子机制的研究已相对清楚。而对细胞内钙离子(Ca2+)信号及钙通道调控HCO3-及Cl-的分泌和机制研究较少，特别是在DU的发病机制中未见报道。本课题从分子、细胞、动物及人体组织水平，阐述了TRPV4离子通道和Ca2+信号，在胃酸刺激十二指肠HCO3-和Cl-分泌及其对肠黏膜保护中的作用和机制。基于我们大量的实验结果得出以下结论：胃酸进入十二指肠后，可对黏膜组织产生损伤和保护两种作用。一方面胃酸可损伤肠黏膜组织，而另一方面可刺激肠黏膜内的神经末梢释放ACh等神经递质。后者作用于肠黏膜上皮细胞基底膜侧的mAChR，激活TRPV4离子通道促进胞外Ca2+内流。细胞内的Ca2+信号通过PI3K/Akt/CFTR磷酸化和激活IKca引起细胞膜超极化这两种主要机制，促进HCO3-的分泌功能从而有效构建肠黏膜屏障，保护十二指肠黏膜免受损伤。而在十二指肠溃疡的发生发展过程中，胃酸经ACh/mAChR刺激TRPV4/Ca2+通路的障碍，可能导致了PI3K/Akt/CFTR磷酸化和IKca通道功能的减弱，抑制了HCO3-的有效分泌及对肠黏膜的保护。上述mAChR/TRPV4/Ca2+新颖通路的发现，不仅具有科学意义，而且有助于寻找肠黏膜保护因子或药物研发靶点，用于重塑肠黏膜屏障及防治消化溃疡的新药研发，具有潜在的应用前景。