Prostaglandin D2 and its receptor CRTH2 regulate intestinal inflammation and homeostasis

肠上皮细胞（IECs）是肠道内稳态和机体健康的中心调节因子。作为对感染或损伤的反应，肠上皮干细胞（ISCs）改变其分化以促进上皮内的宿主保护性炎症。然而，肠上皮炎症必须严格调控以防止病理发生。2型肠道炎症发生在食物过敏和寄生虫感染期间，它们共同导致世界范围内的大量发病率。在这种情况下，生物活性脂质被局部释放，脂质受体的表达被动态调节，完美地定位脂质来微调IEC活动。然而，脂质如何调节2型上皮炎症尚不清楚，这表明我们对过敏或蠕虫感染后肠道稳态如何恢复的理解存在空白。在肠道2型炎症中，IECs感知刺激并释放警报，激活免疫细胞分泌细胞因子IL-13， IL-13作用于ISCs，促进其分化为分泌杯状细胞和簇状细胞。我们实验室最近的研究表明，生物活性脂质前列腺素D2 （PGD2）的受体CRTH2在小鼠和人IECs中表达，并在ISCs中富集。缺乏crth2的ISCs在体外更容易分化为杯状细胞。在体外和体内实验中，依赖于CRTH2的PGD2可抵消IL-13对小鼠小肠内皮细胞的影响，抑制寄生蠕虫感染期间杯状细胞的分化。最后，在解决2型免疫激活后，crth2缺陷小鼠保留了杯状细胞增生和屏障通透性增加。基于这些数据，我们假设PGD2作用于CRTH2+ ISCs，使肠道在2型炎症事件后恢复稳态，并形成IEC对新刺激的反应。为了验证这个想法，我们提出了两个目标。目的1包括机制研究，将测试PGD2是否抑制ISC分化为分泌谱系，以响应2型细胞因子。Aim 1将使用一种新的crth2报告小鼠来鉴定pgd2应答的iec，并将测试PGD2-CRTH2途径如何影响小鼠和人类ISC生物学。目的2包括评估pgd2 - crth2介导的IEC反应抑制的生物学意义的研究。目的2将测试PGD2和CRTH2如何影响2型炎症后的屏障功能和稳态以及表观遗传程序ISCs，以及2型炎症期间IEC CRTH2缺乏如何影响随后急性或慢性炎症事件中的肠道修复和病理。这些研究对于了解PGD2和CRTH2如何在2型炎症后帮助恢复肠道稳态至关重要，并将为使用现有的CRTH2调节剂和其他靶向脂质药物治疗肠道炎症性疾病提供信息。

Intestinal epithelial cells (IECs) are central regulators of intestinal homeostasis and organismal well-being. In response to infection or injury, intestinal epithelial stem cells (ISCs) alter their differentiation to promote host-protective inflammation in the epithelium. However, intestinal epithelial inflammation must be tightly regulated to prevent pathology. Type 2 intestinal inflammation occurs during food allergy and parasitic helminth infection that together cause substantial morbidity worldwide. In this context, bioactive lipids are released locally and lipid receptor expression is dynamically regulated, perfectly positioning lipids to fine tune IEC activities. However, how lipids regulate Type 2 epithelial inflammation is poorly defined, representing a gap in our understanding of how intestinal homeostasis is restored following allergy or worm infection. In intestinal Type 2 inflammation, IECs sense stimuli and release alarmins that activate immune cells to secrete the cytokine IL-13, which acts on ISCs to promote their differentiation to secretory goblet and tuft cells. Studies from our laboratory have recently shown that CRTH2, a receptor for the bioactive lipid prostaglandin D2 (PGD2), is expressed in murine and human IECs and enriched in ISCs. CRTH2-deficient ISCs were more likely to differentiate into goblet cells in vitro. PGD2, dependent on CRTH2, counteracted effects of IL-13 on murine small intestine IECs in vitro and in vivo, suppressing goblet cell differentiation during infection with a parasitic helminth. Finally, CRTH2-deficient mice retained goblet cell hyperplasia and increased barrier permeability after the resolution of Type 2 immune activation. Based on these data, we hypothesize that PGD2 acts on CRTH2+ ISCs to return the intestine to homeostasis after a Type 2 inflammatory event and to shape the IEC response to new stimuli. To test this idea, we propose 2 Aims. Aim 1 includes mechanistic studies that will test if PGD2 suppresses ISC differentiation to secretory lineages in response to Type 2 cytokines. Aim 1 will use a novel CRTH2-reporter mouse to identify PGD2-responsive IECs and will test how the PGD2-CRTH2 pathway affects murine and human ISC biology. Aim 2 includes studies that assess the biological significance of PGD2-CRTH2-mediated suppression of IEC responses. Aim 2 will test how PGD2 and CRTH2 affect barrier function and homeostasis and epigenetically program ISCs after Type 2 inflammation and how IEC CRTH2 deficiency during Type 2 inflammation impacts intestinal repair and pathology during a subsequent, acute or chronic inflammatory event. These studies are essential for understanding how PGD2 and CRTH2 aid in restoring gut homeostasis after Type 2 inflammation and will inform the use of existing CRTH2 modulators and other drugs that target lipids in the treatment of intestinal inflammatory disorders.