H.pylori—microRNA-495—TLR4正反馈轴的表观调控机制在胃炎恶变致癌过程中作用的研究

Helicobacter pylori (H. pylori) infection is a major cause of gastritis and often leads to gastric cancer, but molecular mechanisms of H. pylori pathogenesis are elusive. Recently, malignancies resulted from infection-caused chronic inflammation attracted increasing attention. Our preliminary studies showed a reduced expression of miR-495 in gastritis and gastric cancer tissues and an increased methylation of miR-495 gene in H. pylori infected tissues, suggesting that H. pylori infection might regulate miR-495 expression through a mechanism involving epigenetic silence: miR-495 is capable of targeting a key molecule in inflammation, TLR4. Thus miR-495 may play a role in inflammatory signaling that induces gastritis and gastric cancer by regulating TLR4 expression. Therefore, by using an entry point of the regulation of miR-495 upon H. pylori infection, the present project aims to: address the consequence of deregulation of miR-495 in gastric malignancy arising from gastritis; investigate the function and relevant mechanism of Hp~miR-495~TLR4 signaling in tumorigenesis and development; elucidate the role of epigenetics in H. pylori induced inflammation and subsequent tumorigenesis. Together, all these research outcomes will allow us to further illustrate the pathogenesis of gastric cancer and develop new strategy for early detection and intervention.

幽门螺杆菌（Hp）感染是胃炎和胃癌发生的重要原因，但其致病的分子机制尚不甚清楚。我们在前期工作中发现miR-495在胃炎和胃癌组织中低表达，且在Hp感染组织中的甲基化水平升高；同时初步确定了TLR4是miR-495的靶基因，TLR4在炎症反应中是公认的关键分子，能够能够识别结合Hp，启动下游炎症信号，据此推测Hp可能表观沉默miR-495，进而间接促进TLR4的表达，激活下游的炎症信号；表达上调的TLR4又可以进一步结合识别Hp，形成正反馈的信号轴，推动了炎症恶变的进程。本项目将以Hp感染对miR-495的表观调控为切入点，阐释miR-495表达失调在胃炎恶变致癌过程中的作用，探讨Hp—miR-495—TLR4信号轴在炎症恶变过程中的功能及机制；初步阐述Hp诱发炎症，促进肿瘤发生过程中的表观调控作用。为进一步阐释胃癌发生机制以及临床早期诊断或干预提供新的策略。

胃癌是最常见的恶性肿瘤之一，严重影响人类健康。幽门螺杆菌感染是诱发胃癌的I类风险因子，然而幽门螺杆菌感染在促炎和致癌过程中的具体作用机制尚不明确。microRNA(miRNA)是一类能够在转录后调控中发挥重要功能的非编码小分子RNA。本项目发现miR-495在胃癌组织中低表达，通过体外和裸鼠成瘤实验证明miR-495可抑制胃癌细胞的增殖、迁移和侵袭。通过TargetScan网站进一步发现miR-495与TLR4之间存在靶向关系。双荧光素酶报告基因检测结果证实了TLR4与miR-495存在相互结合。同时，相比于非胃癌组织，在胃癌组织中，TLR4的表达升高，提示miR-495可能通过靶向TLR4抑制胃癌的发生发展。有研究指出肿瘤细胞中miRNA启动子区高甲基化会抑制其转录，进而导致miRNA靶基因的异常表达，促进肿瘤的发生发展。将H.pylori与胃癌细胞系共培养后，发现胃癌细胞系中miR-495的甲基化水平升高，miR-495表达下降，TLR4、IL-6表达升高。综上所述，在慢性胃炎的进展过程中，H.pylori 引起miR-495启动子区DNA甲基化水平升高，使得miR-495表达降低，对TLR4的抑制作用减弱，机体炎症失衡，促进胃癌发生发展。本项目解析了H.pylori-miR-495-TLR4轴在胃炎恶变致癌过程中的表观遗传学机制，为胃癌的治疗和诊断提供新的分子靶标和理论依据。