Nuclear Receptor Control of T Cell Function in Discrete Intestinal Microenvironments

项目摘要 肠道是一个中央免疫器官，宿主-微生物相互作用形成免疫耐受和 局部和全身的炎症。然而，流行的免疫学观点将这两个不同的器官混为一谈。 组成肠道--小肠和大肠(或SI和LI)--这阻碍了对 粘膜免疫调节，错过了为人类开发更安全、更有针对性的治疗方法的机会 炎症性肠病(IBD)。这一应用程序的前提是基于最近从 两个PI(Sundrad，Weaver)之间的协同作用是，粘膜中的CD4+T细胞使用不同的核集合 SI和LI中的受体(NR)与不同类别的宿主和微生物衍生的代谢物相互作用， 分别进行了分析。Sundrad实验室最近的研究证实，Foxp3-T效应器(Tef)亚群-Th1，Th17 细胞-使用一种此前未知的免疫功能的NR，构成雄烷受体 (Car/Nr1i3)，引导一个类似肝细胞的转录反应来对抗潜在的细胞毒性胆汁酸 (Ba)SI中的浓度。在SI(毫摩尔)和Li(微摩尔)之间存在很大的bas梯度 至‘肠-肝’循环--主要在肝脏合成，储存在胆囊中，并在后分泌。 进入十二指肠的肠道被回肠中的特殊肠细胞主动地重新吸收，用于门脉。 再循环到肝脏。因为bas是亲脂性的，所以它们在肝肠道中具有毒性和促炎作用。 组织；许多核受体-包括CAR-已经进化到抑制BA对肝细胞和 肠道细胞。我们的数据表明，肠-肝循环创造了一个独特的恶劣的SI微环境 其中渗透的T细胞必须适应以维持耐受性和组织动态平衡。相比之下，黎族则怀有 细菌比SI多103-107倍，BAs少约1000倍。因此，微生物及其代谢物- 短链脂肪酸(SCFA；例如丁酸)、次级BAs(通过残留的微生物代谢产生) 初级基础)-成为LI中免疫调节的中心。单链脂肪酸抑制组蛋白脱乙酰酶活性 (HDAC)并稳定外周诱导的T调节细胞(ITregs)中Foxp3基因的表达，而 继发性BA通过另一种受体--维生素D受体(VDR)促进LI Treg维持。因此，虽然 肠道菌群中的抗原是启动促炎和抗炎T细胞反应所必需的 在整个肠道中，我们假设细菌和胆汁的丰度存在显著差异 SI和Li建立相应的代谢物梯度，这些梯度由不同的NRs感知以指示 T细胞调节功能的划分。我们通过互补性来检验这一假设，但不是通过内部 依赖，AIMS，利用新的小鼠模型以及基于重组蛋白的NR活性的库 分析，以确定调控转录调节、生化激活和 CAR下游的细胞功能(在SI Tef细胞中)和VDR(在Li iTreg细胞中)。成功完成 这些目标将建立新的生物学范式，并为治疗人类IBD提供更精确的方法。

Project Summary The gut is a central immunological organ, where host-microbe interactions shape immune tolerance and inflammation, both locally and systemically. Yet prevailing immunological views conflate the two distinct organs that comprise the gut—small and large intestine (or SI and LI)—which impedes more robust understanding of mucosal immune regulation, and misses opportunities to develop safer, more targeted therapies for human inflammatory bowel diseases (IBDs). The premise of this application, founded on recent discoveries from, and synergy between, the two PIs (Sundrud, Weaver), is that mucosal CD4+ T cells use distinct sets of nuclear receptors (NRs) in the SI and LI to interface with divergent classes of host- and microbe-derived metabolites, respectively. Recent work from the Sundrud lab establishes that Foxp3- T effector (Teff) subsets—Th1, Th17 cells—use a NR with no previously known immunological function, the constitutive androstane receptor (CAR/Nr1i3), to direct a ‘hepatocyte-like’ transcriptional response to contend with potentially cytotoxic bile acid (BA) concentrations in the SI. A large gradient of BAs exists between the SI (millimolar) and LI (micromolar) due to ‘enterohepatic’ circulation—primary BAs synthesized in the liver, stored in the gallbladder, and secreted post- prandially into the duodenum are actively reabsorbed by specialized enterocytes in the ileum for portal recirculation to the liver. Because BAs are lipophilic, they can be toxic and pro-inflammatory in enterohepatic tissues; a host of nuclear receptors—including CAR—have evolved to suppress BA toxicity in hepatocytes and enterocytes. Our data suggest that enterohepatic circulation creates a uniquely harsh SI microenvironment to which infiltrating T cells must adapt to maintain tolerance and tissue homeostasis. The LI, by contrast, harbors 103-107 times more bacteria than the SI, and ~1000-fold less BAs. Accordingly, microbes and their metabolites— short chain fatty acids (SCFAs; e.g., butyrate), secondary BAs (produced via microbial metabolism of residual primary BAs)—become central to immune regulation in the LI. SCFAs inhibit histone deacetylase enzymes (HDACs) and stabilize Foxp3 gene expression in peripherally-induced T regulatory cells (iTregs), whereas secondary BAs promote LI Treg maintenance through another NR, vitamin D receptor (VDR). Thus, while antigens from the enteric flora are required for priming both pro- and anti-inflammatory T cell responses throughout the intestinal tract, we hypothesize that marked differences in the abundance of bugs and bile in the SI vs. LI establish consequential metabolite gradients that are sensed by different NRs to instruct compartmentalized T cell regulatory functions. We test this hypothesis through complementary, but not inter- dependent, Aims, leveraging new mouse models, as well as a library of recombinant protein-based NR activity assays, to define the mechanisms governing the transcriptional regulation, biochemical activation, and downstream cellular functions of CAR (in SI Teff cells) and VDR (in LI iTreg cells). Successful completion of these Aims will establish new biological paradigms and inform more precise approaches to treat human IBDs.