Effects of apoptotic epithelial cell engulfment on mucosal inflammation

描述(申请人提供)：上皮将大量的管腔抗原与胃肠道组织分开，在这个位置，它是第一个遇到许多病原体的地方。上皮细胞来自腺体更深层的干细胞，当它们向管腔迁移时，干细胞会分化。在到达腺体或绒毛的顶端后，上皮细胞死亡，要么滑入管腔，要么被固有层内的吞噬细胞吞噬。抗原提呈细胞(APC)，包括巨噬细胞和树突状细胞，可以通过吞噬或自噬来清除细菌、细胞碎片和死亡细胞。吞噬凋亡细胞通常是抗炎的，因为它刺激转化生长因子-β的释放。缺乏凋亡细胞受体的小鼠发生结肠炎的事实支持了适当的吞噬作用在控制胃肠道炎症中的重要性。相反，在携带伤寒沙门氏菌的细胞内感染时发生凋亡的细胞可能扮演着微生物“特洛伊木马”的角色，将内化的细菌输送到APC中，从而刺激炎症反应。因此，我假设凋亡的上皮细胞被抗原提呈细胞识别和吞噬，这一过程调节局部炎症反应。具体地说，我建议确定，在没有细胞内感染的情况下，吞噬呈现凋亡的人类上皮细胞是否具有积极的抗炎作用，而摄取受感染的身体则有利于诱导炎症。这项建议的目的是确定调控整个人类胃肠道内凋亡细胞识别和吞噬的分子基础，以及这一过程对免疫调节的影响。这些目标将在以下具体目标中实现：目标1：确定哪些结构识别肠道中的凋亡上皮细胞。目的2：研究调节上皮细胞身体吞噬的信号事件。目的3：研究细菌蛋白在调节rac1活性和粘膜炎症中的作用。虽然先天免疫的许多方面已经被研究，但对人类消化道内的细胞凋亡和吞噬上皮细胞的机制及其对宿主局部反应的影响知之甚少。我们知识中的这一差距使拟议中的研究成为一个令人兴奋的新前沿，与人类粘膜免疫具有广泛的相关性。这项建议将研究吞噬细胞介导凋亡的上皮细胞吞噬的机制，以及这一过程如何影响粘膜炎症。建立吞噬作用和参与这一过程的受体的新角色将导致未来的翻译研究，在人类消化道中模拟这一过程。这一新信息可能在预防或治疗由感染引发的消化系统疾病方面具有治疗应用，包括炎症性肠病和感染性腹泻。

DESCRIPTION (provided by applicant): The epithelium separates the vast array of luminal antigens from the underlying gastrointestinal tissue and in this position, it serves as the first site to encounter many pathogens. Epithelial cells emerge from stem cells from the deeper layers of the glands which differentiate as they migrate towards the lumen. After reaching the top of the gland or villous, epithelial cells die and either slough into the lumen or get engulfed by phagocytes within the lamina propria. Antigen presenting cells (APC), including macrophages and dendritic cells, can remove bacteria, cellular debris and dead cells through phagocytosis or autophagy. Engulfment of apoptotic cells is generally anti- inflammatory since it stimulates the release of TGF-¿. The importance of proper phagocytosis in the control of gastrointestinal inflammation is supported by the fact that mice deficient in a receptor for apoptotic cells develop colitis. In contrast, cells that undergo apoptosis when they carry an intracellular infection with Salmonella enterica serovar Typhimurium may act as a microbial "Trojan horse" that transports internalized bacteria into the APC thereby stimulating inflammatory responses. Thus, I hypothesize that apoptotic epithelial cells are recognized and engulfed by antigen presenting cells and this process modulates local inflammatory responses. Specifically, I propose to determine if engulfment of human epithelial cells rendered apoptotic in the absence of intracellular infections are actively anti-inflammatory while uptake of infected corpses favors the induction of inflammation. The objective of this proposal is to define the molecular basis governing the recognition and engulfment of apoptotic cells throughout the human gastrointestinal tract and the impact of this process on immune regulation. These objectives will be achieved in the following Specific Aims: Aim 1: Define which structures recognize apoptotic epithelial cells in the gut. Aim 2: Examine the signaling events that regulate the engulfment of epithelial cell corpses. Aim 3: Examine the role of bacterial proteins in regulating Rac1 activation and mucosal inflammation. Although many aspects of innate immunity have been studied, little is known about the mechanisms of apoptotic, epithelial cell engulfment in the human digestive tract and their impact on local host responses. This gap in our knowledge makes the proposed studies an exciting new frontier with broad relevance for mucosal immunity in humans. This proposal will examine the mechanisms by which phagocytes mediate the engulfment of apoptotic epithelial cells and how this process impacts mucosal inflammation. Establishing a novel role for engulfment and the receptors involved in this process will lead to future translational studies that model this process in the human digestive tract. This new information may have therapeutic applications for the prevention or treatment of digestive diseases triggered by infection including inflammatory bowel diseases and infectious diarrhea.