Investigation of the homeostasis regulation in the intestine1) Role of NO-sensitive guanylyl cyclase in the intestinal ecosystem 2) Characterization of PD-1 expression on intestinal innate lymphoid cells group 2 (ILC2)

粘膜部位会遇到大量的抗原，包括共生菌、食物环境抗原和病原体。NO/cGMP信号通路在胃肠道(GI)中起着至关重要的作用，因为其关键酶一氧化氮合酶(NO)敏感的鸟苷酸环化酶(GC)缺失的基因敲除小鼠(GCKO)具有严重的GI表型。它们因结肠和盲肠破裂和出血而过早死亡，因此，一种特殊的减少纤维的饮食对生存至关重要。在胃肠道，NO-GC表达在肌层细胞和固有层的不明细胞中。根据GI表型，NO-GC在这些细胞中的表达可能在维持GI自我稳定方面发挥显著作用。为了验证，GCKO小鼠将被保存在无菌(GF)和无特定病原体(SPF)的条件下。通过对GCKO小鼠和对照组小鼠的细菌组成和免疫细胞分布的分析，可以确定NO-GC缺乏对微生物区系的影响。此外，粘液层和上皮屏障将被评估，以评估粘膜屏障的完整性，从而确定炎症的早期阶段。为了弥合GCKO建立的时间差距，应该在一个独立的项目中分析肠道固有淋巴细胞组2(ILC2)上PD-1/PD-L1表达的功能。最近研究发现，负性调节因子PD-1及其配体PD-L1表达于肺和小肠的ILC2。然而，目前还没有确定受体和配体在相似细胞类型上的表达，也没有确定PD-1/PD-L1在结肠ILC2上的表达和功能。PD-1/PD-L1的表达将通过流式细胞仪进行分析，并在GF和SPF小鼠之间、抗生素治疗后以及肠道炎症和癌症的疾病模型中进行比较。最终，这两个项目将提供对GI稳态调节的更好了解，并可能有助于改进GI炎症和癌症等高流行疾病的治疗。

Mucosal sites encounter vast antigens including commensal bacteria, food environmental antigens and pathogens. To maintain homeostasis, unique mechanisms evolved to regulate mucosal immune response.The NO/cGMP signaling pathway plays a crucial role in the gastrointestinal (GI) tract as knockout mice (GCKO), deficient for its key enzyme nitric oxide (NO)-sensitive guanylyl cyclase (GC), suffer from a severe GI phenotype. They die a premature death due to ruptures and hemorrhages in colon and caecum, thus, a special fibre-reduced diet is crucial for survival.In the GI tract NO-GC expression has been shown in cells of the muscle layer and in unidentified cells of the lamina propria. Based on the GI phenotype, NO-GC expression in these cells potentially play a notable role in the maintenance of GI homeostasis.For verification, GCKO mice will be kept under germ-free (GF) and specific-pathogen-free (SPF) conditions. Analysis of bacterial composition and immune cell distribution of GCKO and control mice will identify the effect of NO-GC deficiency on the microbiota. Moreover, the mucus layer and the epithelial barrier will be evaluated to assess mucosal barrier integrity and thus identify early stages of inflammation.To bridge the time gap of GCKO establishment, function of PD-1/PD-L1 expression on intestinal innate lymphoid cells group 2 (ILC2) should be analyzed in an independent project. The negative regulator PD-1 and its ligand PD-L1 have been recently shown to be expressed on ILC2 of lung and small intestine. However, neither the expression of either both, receptor and ligand on a similar cell type, nor expression and function of PD-1/PD-L1 on colonic ILC2 has been determined yet. PD-1/PD-L1 expression will be analyzed by FACS and compared between GF and SPF mice, after antibiotics treatment and in disease models for intestinal inflammation and cancer.Finally, both projects will provide a better understanding of GI homeostasis regulation and may contribute to the improvement of therapies of highly prevalent diseases like GI inflammation and cancer.