Gut-liver crosstalk in bile-acid induced diarrhea

 描述（由申请人提供）：胆汁酸过度产生与几种GI疾病（如炎症性肠病（IBD）和肠易激综合征（IBS））相关的腹泻有关。回肠中的胆汁酸刺激回肠成纤维细胞生长因子19（小鼠中的FGF 15）的表达和分泌，其循环至肝脏以抑制介导胆汁酸合成的限速步骤的CYP 7A 1酶。最近的研究表明，在肠道炎症小鼠模型和IBD患者中，FGF 15/19的水平降低沿着肝胆汁酸合成速率增加。这些观察结果为FGF 15/19在肠道炎症期间腹泻发病机制中的关键作用提供了证据，尽管这种减少的机制尚未完全了解。我们的初步数据提供的证据表明，TNF降低了FGF 15/19的表达和启动子活性，表明促炎细胞因子对FGF 15/19表达的直接影响。在这方面，可以利用增加回肠FGF 15/19表达的膳食化合物来减少胆汁酸的过量产生。我们的新的初步研究结果表明，溶血磷脂酸（LPA），通常发现在食品，如大豆和蛋黄，诱导FGF 15/19的表达，提供了一个新的线索，新的治疗干预措施，以治疗胆汁酸诱导的腹泻。基于这些数据，我们假设回肠FGF 15/19表达通过转录机制被促炎细胞因子降低，导致随后肝CYP 7A 1增加并加重与肠道炎症相关的腹泻。我们进一步假设，肠上皮细胞中LPA受体的激活， 细胞触发特定的信号通路，导致FGF 15/19表达增加，并可用作胆汁酸诱导的腹泻的治疗。拟议的研究将利用先进的体外模型，包括在三维基质胶中培养的肠类器官和人上皮Caco 2细胞。将使用FGF 15敲除小鼠和肝脏过表达CYP 7A 1并过量产生胆汁酸的转基因小鼠来研究破坏FGF 15/19-CYP 7A 1轴对腹泻和肠道炎症的影响。目的1中的研究将确定参与细胞因子抑制FGF 15/19的分子机制。目的2中提出的研究将调查LPA上调FGF 15/19表达和分泌的潜在机制，并利用LPA受体敲除小鼠确定所涉及的LPA受体亚型。目的3研究LPA对胆汁酸稳态的影响，并检查在肠道炎症（DSS和TNBS诱导的肠道炎症）小鼠模型中破坏回肠FGF 15-肝CYP 7A 1对腹泻和肠道离子转运失调的贡献。揭示控制肠道和肝脏之间串扰的分子机制将为未来的临床研究提供基础，以设计胆汁酸诱导的腹泻的新疗法。

 DESCRIPTION (provided by applicant): Bile acid overproduction is implicated in diarrhea associated with several GI disorders such as inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS). Bile acids in the ileum stimulate the expression and secretion of ileal Fibroblast Growth Factor 19 (FGF15 in mice), which circulates to the liver to suppress CYP7A1 enzyme that mediates the rate-limiting step of bile acid synthesis. Recent studies showed that the levels of FGF15/19 are decreased in mouse model of intestinal inflammation and in patients with IBD along with an increase in the rate of hepatic bile acid synthesis. These observations provided evidence for the key role of FGF15/19 in the pathogenesis of diarrhea during intestinal inflammation, albeit the mechanisms underlying this decrease are not fully understood. Our preliminary data provided evidence demonstrating a decrease in FGF15/19 expression and promoter activity by TNF suggesting a direct effect of proinflammatory cytokines on FGF15/19 expression. In this regards, dietary compounds that increase ileal FGF15/19 expression could be exploited to reduce the excessive production of bile acids. Our novel preliminary findings showed that lysophosphatidic acid (LPA), normally found in foods such as soy and egg yolk, induced the expression of FGF15/19 providing a new lead to novel therapeutic interventions to treat bile acid-induced diarrhea. Based on these data, we hypothesized that ileal FGF15/19 expression is decreased by pro-inflammatory cytokines via transcriptional mechanisms leading to subsequent increase in hepatic CYP7A1 and exacerbating diarrhea associated with intestinal inflammation. We further hypothesized that the activation of LPA-receptors in intestinal epithelial cells triggers specific signaling pathways that lead to an increase in FGF15/19 expression and could be exploited as a therapy for bile acid-induced diarrhea. The proposed studies will utilize advanced in vitro models including intestinal organoids and human epithelial Caco2 cells cultured in 3 dimensional matrigel. FGF15 knockout mice and transgenic mice with hepatic overexpression of CYP7A1 with overproduction of bile acids will be used to investigate the impact of disrupting FGF15/19-CYP7A1 axis on diarrhea and intestinal inflammation. Studies in Aim 1 will determine the molecular mechanisms involved in the inhibition of FGF15/19 by cytokines. Proposed studies in Aim 2 will investigate the mechanisms underlying the upregulation of FGF15/19 expression and secretion by LPA and determine the LPA receptor subtype involved utilizing LPA receptor knockout mice. Aim 3 is designed to investigate the effects of LPA on bile acid homeostasis and examine the contribution of disrupting ileal FGF15-hepatic CYP7A1 to diarrhea and deregulation of intestinal ion transport in mouse models of intestinal inflammation (DSS and TNBS-induced intestinal inflammation). Unraveling the molecular mechanisms controlling crosstalk between the gut and liver will provide the basis for future clinical studies to design novel therapy for bile acid-induced diarrhea.