胆汁酸经由肠粘膜肥大细胞 FXR/NGF信号轴诱发结肠内脏高敏感反应的机制研究

The increased level of bile acids in the gastrointestinal lumen is associated with abdominal pain symptoms in functional gastrointestinal disorders such as irritable bowel syndrome (IBS). However, the underlying mechanisms are still unclear. Our preliminary experimental results demonstrate that chronic colonic bile acid insults led to visceral hypersensitivity (VH) and augmented levels of nerve growth factor (NGF), which has been proved to be involved in development of VH. The pronociceptive effect of bile acids was prevented by intestinal mucosal mast cell (IMMC) stabilizer and was accompanied with changes in the nuclear receptor farnesoid X receptor (FXR) expression. The aim of the present study is to test the hypothesis that IMMC FXR/NGF axis contributes to colonic bile acid-induced VH, among which the mechanisms underlying the FXR signaling-initiated NGF expression are intended to be intensively studied. The results will shed new lights on the mechanisms for VH in IBS and may offer novel targets for management of this disease.

胃肠腔内胆汁酸水平升高与FGIDs内脏高敏感反应症状密切相关，但机制不明。我们的预实验结果显示IBS-D患者结肠粘膜内胆汁酸含量高于对照组；结肠腔内慢性胆汁酸刺激引发大鼠内脏高敏感反应，并诱发局部NGF含量升高；胆汁酸促痛效应能够被肠粘膜肥大细胞（IMMC）膜稳定剂阻断，并伴有其核受体FXR表达改变。鉴于NGF/TrkA信号介导内脏高敏感的神经调控作用已被公认，我们推测肠腔内胆汁酸可能经由IMMC FXR启动NGF信号引发内脏高敏感。本项目拟采用神经药理学、分子生物学、免疫荧光和电生理等手段，在整体和细胞水平确定胆汁酸/IMMC FXR/NGF/TrkA致内脏高敏感调控通路的存在，重点阐明胆汁酸通过FXR信号启动IMMC内NGF表达增加的关键机制，填补胆汁酸经由IMMC致NGF神经信号通路改变，引发内脏高敏感的分子机制认知盲点，为减轻胆汁酸诱发的IBS症状探寻可干预的关键分子靶点。

结肠腔内胆汁酸（BA）水平升高是腹泻主导型肠易激综合征（IBS-D）肠道运动、感觉、分泌功能紊乱的常见伴随现象。神经生长因子（NGF）参与内脏高敏感（VH）发病机制。有证据提示，胆汁酸可能引发结肠内脏高敏感反应，但其机制未明。本项目探究了BA通过其核受体FXR及其下游的NGF/TRPV1轴促进粘膜肥大细胞（MMCs）-痛觉感受神经元互作、进而引起VH的分子机制。项目取得了下列原创性研究结果：1）大鼠结肠内灌注CDCA或DCA 促进MMCs分泌NGF，后者通过TrkA受体介导，促进L6-S2脊髓背根神经节（DRG）内TRPV1表达，从而诱发VH；2）结肠组织内BA水平较高的IBS-D患者，其结肠粘膜匀浆上清液促进体外培养的肥大细胞内NGF表达；3）在FXR-/-小鼠中，BA灌肠不再引起VH和结肠组织NGF表达上调；下调体外培养的肥大细胞内FXR表达后，BA不再引起NGF表达及释放；4）整体实验和体外细胞学实验结果显示，FXR介导的NGF表达和分泌中，MKK 3/6/p38MAPK/NF-κB信号轴发挥关键作用。综上，BA通过激活MMCs内FXR/NGF轴，促进脊髓伤害性感觉神经元内TRPV1表达，从而诱发VH。该项目首次揭示了FXR介导的、依赖于MMCs的BA促痛机制；提出在MMCs-伤害性神经元互作促进IBS相关的痛觉信号转导过程中，BA/FXR/NGF/TRPV1轴可能发挥重要作用；确定了MMCs内FXR等为BA诱发VH的关键可干预分子靶标。本研究对于阐明IBS BA相关病理生理机制具有较重要科学意义和理论价值。