Immunomodulatory effects of bilirubin are mediated through aryl hydrocarbon receptor, O2 and purinergic pathways

摘要 炎症性肠病(IBD)可能是免疫系统反应失衡的结果 到改变肠道微生物区系，在遗传易感个体中，其中一些人定义了 免疫反应基因。新的方法很重要，因为IBD是一种严重和常见的疾病，通常 对常规免疫抑制变得难以抵抗。慢性病与大量的 发病率、癌症风险和过早死亡。奇怪的是，黄疸患者的病情可能会自发缓解 免疫疾病，包括IBD。此外，患有吉尔伯特病的人患IBD和胆汁的可能性较小 研究表明，色素可诱导对同种异体胰岛移植物的耐受，并可改善实验性结肠炎。胆绿素- 血红素加氧酶-1(HO-1)分解血红素的最终产物胆红素具有实质性的免疫调节作用 在体外增强FoxP3+调节性T细胞(Tregs)的作用。这些影响可能受到以下因素的影响 多药耐药蛋白1(MDR1)的表达；一种泵送的ATP结合盒转运体 外源物质和宿主内源性介质，如细胞外的未结合胆红素(UCB)。 已知胆红素与芳烃受体(AhR)相互作用，AHR是一种更典型地参与 对外来生物和毒素的反应。AHR与缺氧诱导因子-1-α(HIF-1α)密切相关 调节CD39的表达，CD39是一种由血管和免疫细胞表达的胞外核苷酸酶， 对免疫抑制腺苷的产生负有重要责任。 我们提供了IBD患者Th17细胞AhR表达受损的初步证据。这些 在体外，脐带血暴露后，Th17细胞在上调CD39方面也存在缺陷。我们还注意到Th17 炎症性肠病患者的细胞实质上上调HIF-1α，进而进一步竞争性地抑制AhR-1。 脂溶UCB通过Treg和抑制因子Th17诱导免疫耐受 炎症性肠病中的细胞，通过参与AhR/HIF-1α的通路，并通过嘌呤能信号转导是 效应通路。我们的目的是研究脐带血对Treg-Th17细胞免疫轴的影响，通过 小鼠实验性结肠炎模型中血管紧张素受体、缺氧诱导因子-1α和CD39依赖途径的研究。我们剖析出 脐带血如何影响结肠炎疾病表型和免疫反应。最后，我们将确定是否 旨在通过干扰缺氧诱导因子-1α、增强CD39ectin核苷酸酶活性来增强脐血的干预措施 (如apyrase)，通过UDP-葡萄糖醛酸基转移酶(如indinavir)抑制胆红素结合，或调节 多药耐药基因表达(如利托那韦)可提供毒性有限的有益效果。这些方法将是 使用IBD患者的细胞在体内和体外实验系统中进行实验结肠炎测试。此外 在胆红素、其他环境信号、O2介导的压力和 我们的研究将有助于更好地理解IBD，也将有助于阐明 抑制炎症和阻止疾病进展的潜在治疗方法。

Abstract Inflammatory bowel disease (IBD) may develop as a consequence of imbalanced immune system responses to altered gut microbiota, in genetically predisposed individuals, some of whom have defined mutations in immune response genes. New approaches are important, as IBD is a serious and common illness, which often becomes refractory to conventional immunosuppression. Chronic illness is associated with substantial morbidity, cancer risk and early death. Curiously, jaundiced patients may have spontaneous remissions from immunologic diseases, including IBD. Also, people with Gilbert's disease are less likely to develop IBD and bile pigments have been shown to induce tolerance to islet allografts and ameliorate experimental colitis. Biliverdin- bilirubin, end products of heme catabolism by heme oxygenase-1 (HO-1) have substantive immunomodulatory effects linked to the boosting of regulatory FoxP3+ T-cells (Tregs) in vitro. These effects may be impacted by expression of the multidrug resistance protein 1 (MDR1); an ATP-binding cassette transporter that pumps xenobiotics and host endogenous mediators, e.g. unconjugated bilirubin (UCB), out of cells. Bilirubin is known to interact with the aryl hydrocarbon receptor (AhR), a receptor more typically involved in responses to xenobiotics and toxins. Both the AhR and the hypoxia-inducible-factor-1-alpha (HIF-1α) closely modulate expression of CD39, an ectonucleotidase expressed by the vasculature and immune cells and critically responsible for generation of immune suppressive adenosine. We provide preliminary evidence that expression of AhR is impaired in Th17 cells from IBD patients. These Th17 cells are also defective at upregulating CD39 upon exposure of UCB in vitro. We also note that Th17 cells from IBD patients, substantively upregulate HIF-1α, which in turn further competitively inhibits AhR- mediated boosts to CD39.We propose that lipid soluble UCB induces tolerance via Treg and `suppressor' Th17 cells in IBD, through engagement of pathways involving AhR/HIF-1α and with purinergic signaling being the effector pathway. Our aims study the impact of UCB upon the Treg-Th17 cell immune axis, as modulated by the AhR, HIF-1α and the CD39-dependent pathways in murine models of experimental colitis. We dissect out how UCB impacts colitic disease phenotype and immune responses. Finally we will determine whether interventions aimed to boost UCB either by interfering with HIF-1α, boosting CD39 ectonucleotidase activity (e.g. apyrase), inhibiting bilirubin conjugation by UDP-glucuronosyltransferase (e.g. indinavir), or modulating MDR1 expression (e.g. ritonavir) can provide beneficial effects with limited toxicity. These approaches will be tested in experimental colitis in vivo and in vitro experimental systems using cells from IBD patients. In addition to providing unique connections between bilirubin, other environmental signals, O2-mediated stress and purinergic signaling, our studies will contribute to a better understanding of IBD and will also illuminate potential therapeutic approaches to curb inflammation and halt disease progression.