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抗原，包括共生细菌、食物环境抗原和病原体。为了维持体内平衡，形成了独特的机制来调节粘膜免疫反应。NO/cGMP信号通路在胃肠道（GI）中起着至关重要的作用，因为基因敲除小鼠（GCKO）缺乏其关键酶一氧化氮（NO）敏感的鸟酰环化酶（GC），患有严重的GI表型。它们会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。在胃肠道中，NO-GC在肌层细胞和固有层细胞中表达。基于GI表型，NO-GC在这些细胞中的表达可能在维持GI稳态中发挥重要作用。为了验证，GCKO小鼠将在无菌（GF）和无特定病原体（SPF）条件下饲养。通过分析GCKO小鼠和对照小鼠的细菌组成和免疫细胞分布，确定NO-GC缺乏对微生物群的影响。此外，将对黏液层和上皮屏障进行评估，以评估粘膜屏障的完整性，从而识别炎症的早期阶段。为了弥补GCKO建立的时间缺口，PD-1/PD-L1表达对肠道先天淋巴样细胞2组（ILC2）的作用需要在独立项目中进行分析。负调节因子PD-1及其配体PD-L1最近被证实在肺和小肠的ILC2上表达。然而，受体和配体在相似细胞类型上的表达，以及PD-1/PD-L1在结肠ILC2上的表达和功能尚未确定。通过FACS分析PD-1/PD-L1的表达，并比较GF和SPF小鼠、抗生素治疗后以及肠道炎症和癌症疾病模型中PD-1/PD-L1的表达。最后，这两个项目将提供对胃肠道稳态调节的更好理解，并可能有助于改善胃肠道炎症和癌症等高发疾病的治疗。

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.