肠上皮细胞NR2B介导的神经信号通路在肠易激综合征内脏高敏感中作用的研究

Irritable bowel syndrome (IBS) is a functional bowel disorder characterized by abdominal pain/discomfort and altered bowel habits. Visceral hypersensitivity has been proved to be an important characteristic of patients with IBS. The sensation threshold decreased and even some physiological stimulation could result in the symptoms of abdominal pain/discomfort in these patients. However, the exact pathogenetic mechanisms of visceral hypersensitivity are unknown. Previous studies focused on the functions of afferent neurons and fibers of nervous system. But the roles of colonic epithelial cells which are adjacent to the nerve fibers and contact directly with the luminal environment have not been explored. Recently, we found the expression of a specific sensory receptor, NR2B in human colonic epithelial cells and a significant increase of NR2B expression in IBS patients. These findings indicated that the epithelial cells may involve in visceral hypersensitivity in patients with IBS. In this study, we focus on the role of colonic epithelial NR2B mediated neural signaling pathway in visceral hypersensitivity in IBS: (i) To examine the colonic epithelial NR2B expression and the relation with abnormal visceral sensitivity in IBS patients; (ii) To establish the animal model with visceral hypersensitivity and explore the effects of luminal administration of NR2B agonists/antagonists on the visceral sensitivity; (iii) To culture the NR2B gene knockdown epithelial cells in vitro and investigate the function of NR2B-ERK-CREB-BDNF signaling pathway in visceral hypersensitivity. In this study, we will illustrate the role of colonic epithelial NR2B mediated neural signaling pathway in peripheral sensitization in IBS and to find a sound way to prevent visceral hypersensitivity by blockading the luminal epithelial NR2B. It is meaningful to provide new insights into the mechanism of visceral hypersensitivity, and find new peripheral therapeutic targets and safe drugs for IBS patients.

肠易激综合征（IBS）的内脏高敏感表现在感觉传入通路对各种刺激的敏感性异常增高。既往感觉传入通路研究的下游终点为肠壁内感觉神经元及神经纤维，而与神经纤维毗邻，同时与肠腔环境直接接触的肠上皮细胞在感觉通路中的作用未得到重视。我们前期研究发现，肠上皮细胞表达一种内脏高敏感特异性受体NR2B，且IBS患者表达增高，提示肠上皮细胞可能作为将肠道刺激传递至感觉神经的环节之一参与内脏高敏感发生。本项目将阐明肠上皮细胞NR2B-ERK-CREB-BDNF神经信号通路在IBS内脏高敏感中的作用：明确IBS患者肠上皮细胞NR2B表达改变与内脏高敏感的关系；检测内脏高敏感动物肠腔内应用NR2B激动及拮抗剂后内脏敏感性变化；体外培养NR2B基因沉默的肠上皮细胞，验证NR2B活化后通过ERK-CREB通路合成释放BDNF，参与肠神经重构及内脏高敏感。本研究将为探索IBS内脏高敏感安全有效的外周治疗靶点提供新思路。

我们前期研究发现，内脏高敏感特异性受体NMDA受体及其NR2B亚基在IBS患者的结肠表达增高，提示结肠细胞可能通过此受体将肠道刺激传递至感觉神经进而参与内脏高敏感的发生。本课题通过利用临床标本、动物实验及细胞实验，探讨结肠NMDA受体及其NR2B亚基在IBS内脏高敏感中的作用及可能机制。主要发现有：（1）人及小鼠的结肠黏膜广泛表达NMDA受体，IBS患者及内脏高敏感模型小鼠结肠NMDA受体表达显著高于正常对照，并且表达量与内脏高敏感相关症状评分呈显著关联性；（2）结肠黏膜NMDA受体活化可引起结肠BDNF合成和释放增加，进而导致内脏高敏感的发生，而结肠黏膜NMDA受体活化后BDNF合成和释放的增加是通过活化细胞内ERK信号通路实现的；（3）NR2的四个亚基中，只有NR2B亚基在IBS-D患者的结肠黏膜中的表达升高，并且与结肠BDNF表达量及患者的腹部症状评分呈显著相关性。而NMDA受体拮抗剂和NR2B亚基的拮抗剂，均可以抑制NMDA受体活化引起的BDNF合成增加。我们的研究结果证实，对NMDA受体、NR2B亚基及其信号通路的调控有望改善IBS内脏高敏感症状，为深入探讨IBS内脏高敏感的发生机制及针对相关分子机制制定治疗策略，提供了理论依据。