Role of Epithelial Cell Death for Re-Establishment of the Gut Barrier During Resolution of Intestinal Inflammation

慢性肠道炎症是由上皮细胞死亡导致屏障功能障碍、微生物易位和过度免疫细胞激活引发更多上皮细胞死亡的恶性循环驱动的。相反，肠道炎症的解决与上皮的恢复和强大屏障功能的恢复有关，试图打破这种恶性循环。在IBD炎症发作期间存在细胞毒性炎症环境时上皮屏障恢复的机制目前尚不清楚。我们之前已经表明，失调的坏死性下垂是慢性肠道炎症的驱动因素。最近，我们发现脂质介质前列腺素E2 （PGE2）通过与IEC上的EP4受体结合，能够在炎症环境中通过抑制ripk3 - mlkl诱导的IEC坏死性坏死来诱导肠道炎症的消退。引人注目的是，我们在临床前模型中引入了一种具有治疗效果的新型EP4激动剂，并证明了炎症性肠病患者中EP4高表达的有益结果。在拟议的项目中，我们将继续这一思路，重点是揭示EP4介导的炎症消退的分子机制，以及开发和评估基于EP4激动剂的新型治疗方法。因此，我们的目标是利用可诱导的ep4 - iec特异性条件敲除小鼠，通过解读IECs中前列腺素信号通路与坏死体形成之间的联系，以及促炎性和抗炎性通路对该信号中枢的影响，在分子水平上描述ep4依赖性屏障保护。由于EP4受体信号传导可诱导肠道炎症的消退，我们的目标是开发一种肠促性EP4受体激动剂。为了实现这一目标，我们将评估候选分子在体内的功效和肠道特异性。此外，我们未发表的数据显示，除了PGE2外，PGJ2还能阻断IECs中坏死下垂的诱导。因此，我们将研究PGJ2在促进炎症消退方面是否与PGE2相似或甚至互补，并阐明这些分子在炎症背景下介导对病理性细胞死亡的保护作用中的细胞来源、受体使用和下游信号传导。总之，我们的项目旨在建立特异性前列腺素作为打破肠道慢性炎症、上皮细胞死亡和屏障功能障碍恶性循环的关键分子。我们相信，拟议的项目将为IBD的解决带来新的见解，并为受影响的患者提供有效治疗的新策略。

Chronic intestinal inflammation is driven by a vicious cycle of epithelial cell death leading to barrier dysfunction, microbial translocation and excessive immune cell activation triggering more epithelial cell death. Conversely, resolution of intestinal inflammation is associated with epithelial restitution and restoration of robust barrier function in an attempt to break this vicious cycle. The mechanisms by which the epithelial barrier is restored in the presence of a cytotoxic inflammatory environment during an inflammatory flare of IBD are currently unknown. We have previously shown that dysregulated necroptosis is a driver of chronic intestinal inflammation. More recently, we have shown that the lipid mediator prostaglandin E2 (PGE2), via binding to the EP4 receptor on IEC, is able to induce resolution of intestinal inflammation by suppressing RIPK3-MLKL-induced IEC necroptosis in an inflammatory environment. Strikingly, we have introduced a novel EP4 agonist with therapeutic efficacy in preclinical models and demonstrated a beneficial outcome of high EP4 expression in inflammatory bowel disease patients. In the proposed project, we will continue in this vein, with a focus on unravelling the molecular mechanisms of EP4-mediated resolution of inflammation and the development and evaluation of novel EP4 agonism-based therapeutic approaches. Accordingly, we aim to delineate EP4-dependent barrier protection at the molecular level by deciphering the link between the prostanoid signalling pathway in IECs and necrosome formation and the influence of pro- and anti-inflammatory pathways on this signalling hub, taking advantage of inducible EP4-IEC-specific conditional knockout mice. Since EP4 receptor signalling induces resolution of intestinal inflammation, we aim to develop a gut-tropic EP4 receptor agonist. To achieve this, we will evaluate candidate molecules for efficacy and gut specificity in vivo. In addition, our unpublished data show that PGJ2 blocks necroptosis induction in IECs in addition to PGE2. We will therefore investigate whether PGJ2 is similarly efficient or even complementary to PGE2 in promoting resolution of inflammation, and we will elucidate the cellular source, receptor usage and downstream signalling of these molecules in mediating the protective effects against pathological cell death in an inflammatory context. In summary, our project aims to establish specific prostanoids as key molecules in breaking the vicious cycle of chronic inflammation, epithelial cell death and barrier dysfunction in the gut. We are confident that the proposed project will lead to new insights into the resolution of IBD and new strategies for effective therapies for affected patients.