Nuclear Receptor Control of T Cell Function in Discrete Intestinal Microenvironments

项目摘要 肠道是一个中心免疫器官，宿主-微生物相互作用在其中形成免疫耐受， 炎症，包括局部和全身。然而，流行的免疫学观点将这两个不同的器官混为一谈 包括肠道-小肠和大肠（或SI和LI）-这阻碍了对 粘膜免疫调节，错过了开发更安全，更有针对性的人类治疗方法的机会。 炎症性肠病（IBD）。该应用程序的前提基于最近的发现，和 两种PI之间的协同作用（Sundrud，Weaver）是粘膜CD 4 + T细胞使用不同的核免疫原性。 受体（NR）与宿主和微生物衍生的代谢物的不同类别的接口， 分别Sundrud实验室的最新工作证实Foxp 3- T效应子（Teff）亚群-Th 1，Th 17 细胞-使用一个NR与以前没有已知的免疫功能，组成雄甾烷受体 (CAR/Nr 1 i3），以指导“肝细胞样”转录反应，以对抗潜在的细胞毒性胆汁酸 (BA)浓度在SI。在SI（毫摩尔）和LI（微摩尔）之间存在大的BA梯度， 到“肠肝”循环-主要的BA在肝脏中合成，储存在胆囊中，并分泌后， 在回肠中被专门的肠上皮细胞主动重吸收， 再循环到肝脏。因为BA是亲脂性的，所以它们在肠肝中可能是有毒的和促炎的。 组织;许多核受体-包括CAR-已经进化为抑制肝细胞中的BA毒性， 肠细胞我们的数据表明，肠肝循环创造了一个独特的苛刻的SI微环境， 浸润性T细胞必须适应以维持耐受性和组织稳态。相比之下， 比SI多103-107倍的细菌，以及少约1000倍的BA。因此，微生物及其代谢产物- 短链脂肪酸（SCFA;例如，丁酸盐）、次级BAs（通过微生物代谢残留的 初级BA）-成为LI中免疫调节的中心。SCFA抑制组蛋白脱乙酰酶 （HDAC）并稳定外周诱导的T调节细胞（iTACs）中的Foxp 3基因表达，而 次级BA通过另一种NR维生素D受体（VDR）促进LI Treg维持。因此，虽然 来自肠道植物群的抗原是引发促炎和抗炎T细胞应答所必需的 在整个肠道中，我们假设细菌和胆汁丰度的显着差异， SI与LI建立由不同NR感测的相应代谢物梯度，以指示 区室化的T细胞调节功能。我们通过互补而不是互- 依赖，目的，利用新的小鼠模型，以及基于重组蛋白的NR活性库 分析，以确定控制转录调控，生化激活， CAR（在SI Teff细胞中）和VDR（在LI iTreg细胞中）的下游细胞功能。成功完成 这些目标将建立新的生物学范例，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.