The Perinatal Pharmacology of the Nuclear Receptor

说明(申请人提供)：这是R01 HD073070的重新提交，它是根据PAR-11-057提交的。我们的目标是了解核受体法尼醇X受体(FXR)对围产期肝脏功能的影响，特别是FXR在围产期发育过程中激活对肝脏的影响。最近的研究表明，FXR激活具有多种治疗益处，因此，FXR已被广泛用作治疗靶点。以往关于FXR功能的结论大多依赖于成年动物的使用，而对FXR在围产期发育中的作用知之甚少。FXR的激活通过抑制CYP7A1的转录抑制胆汁酸的合成。据认为，围产期肝脏对胆酸池大小减小特别敏感，这是因为CYP7A1的基础表达较低，以及出生后早期肝内胆汁酸再循环不足。胆汁酸是一种临床药物，已用于治疗肝胆疾病，包括某些儿科疾病。由于母亲使用胆汁酸药物和其他非胆汁酸FXR激活剂，围产期激活FXR的机会也很多。因此，了解FXR的围产期药理作用是非常必要的。我们的初步结果表明：1)围产期激活FXR转基因小鼠导致肝脏毒性、部分致死性和炎症征象；2)FXR转基因围产期毒性与胆汁酸分泌减少有关，可能是由于Cyp7a1的抑制；3)围产期补充胆汁酸和/或维生素缓解了转基因幼鼠的肝脏毒性和部分致死性；4)对转基因小鼠的存活有实质性影响，转基因小鼠的存活率比对照小鼠差；5)FXR的围产期毒性与成纤维细胞生长因子诱导的即刻早期反应蛋白14(Fn14)的激活有关，Fn14基因在新生儿肝脏中高表达，参与炎症反应。在Fn14基因启动子中发现了一个可能的FXR反应元件，提示Fn14是FXR的转录靶点；6)我们成功地合成了具有良好生物利用度的高效FXR激动剂6？-ECDCA。根据我们的初步数据，我们假设FXR在围产期发育过程中具有以前未被认识到的作用。具体地说，我们假设FXR的激活在围产期发育过程中可能对肝脏有毒性，原因是1)抑制 这可能与以下因素有关：1)胆汁酸合成不足；2)肠道维生素吸收不足；3)围产期对胆酸池大小过小敏感；4)母体FXR激活导致的“有毒牛奶”。此外，FXR的围产期毒性可能是通过激活FXR的一个新的转录靶点Fn14来实现的。我们提出了四个具体的目标来检验我们的假设：(1)确定FXR在围产期发育期间的基因激活是否对肝脏有毒性，以及是否可以通过饮食补充胆汁酸和/或维生素来缓解围产期毒性；(2)确定在围产期发育期间FXR的药理激活是否对肝脏有毒性，以及药理效应是否依赖FXR；(3)确定FXR激活对围产期毒性的母体效应；以及(4)确定Fn14是否是FXR的转录靶点，以及Fn14是否是FXR围产期毒性所必需的。据我们所知，这项研究是系统评价FXR围产期药理学的第一次尝试。本研究结果将加深我们对FXR围产期功能的了解，为更好地发挥FXR的治疗效益提供指导。*此申请者同意并已申请资金，以参加由NIH赞助的为期两天的年度会议，重点是在马里兰州贝塞斯达举行的发展药理学会议。此申请者还同意与其他调查人员合作。

DESCRIPTION (provided by applicant): This is the resubmission of R01 HD073070, which was submitted in response to PAR-11-057. Our goal is to understand the perinatal liver function of the nuclear receptor farnesoid X receptor (FXR), especially the hepatic consequence of FXR activation during perinatal development. Recent studies have suggested multiple therapeutic benefits of FXR activation and as a result, FXR has been intensively pursued as a therapeutic target. The majority of the previous conclusions on the function of FXR have relied on the use of adult animals, whereas little is known about the function of FXR during the perinatal development. Activation of FXR suppresses bile acid synthesis through the transcriptional suppression of CYP7A1. It is believed that the perinatal livers are particularly sensitive to a decreased bile acid pool size because of a lower basal expression of CYP7A1, as well as the insufficient enterohepatic bile acid recirculation in the early postnatal period. Bile acids are clinical drugs that have been used to treat hepatobiliary diseases including certain pediatric disorders. There are also ample opportunities for perinatal activation of FXR as a result of maternal use of bile acid drugs and other non-bile acid FXR-activating agents. As such, it is imperative to understand the perinatal pharmacology of FXR. Our preliminary results show that: 1) Perinatal activation of FXR in transgenic mice resulted in hepatotoxicity, partial lethality, an signs of inflammation; 2) The perinatal toxicity of the FXR transgene was associated with a decreased biliary secretion of bile acids, likely due to the suppression of Cyp7a1; 3) Perinatal dietary supplement of bile acids and/or vitamins relived the hepatotoxicity and partial lethality o the transgenic pups; 4) There was a material effect on the survival of the transgenic mice, in which the transgenic pups nursed by transgenic dams had a worse survival than those nursed by control dams; 5) The perinatal toxicity of FXR was associated with the activation of the fibroblast growth factor-inducible immediate-early response protein 14 (Fn14), a gene highly expressed in the neonatal liver and implicated in inflammation. A putative FXR response element has been identified in the Fn14 gene promoter, suggesting Fn14 as a transcriptional target of FXR; and 6) we have successfully synthesized 6?-ECDCA, a potent FXR agonist with a favorable bioavailability. Based on our preliminary data, we hypothesize that FXR has a previously unrecognized role during perinatal development. Specifically, we hypothesize that activation of FXR might be toxic to the liver during perinatal development due to 1) the inhibition of bile acid synthesis; 2) a deficiency in intestinal vitamin absorption; 3) a perinatal hypersensitivity to decreased bile acid pool size; and 4) the "toxic milk" as a result of maternal FXR activation. Moreover, the perinatal toxicity of FXR might have been contributed to by the activation of Fn14, a novel transcriptional target of FXR. We propose four specific aims to test our hypotheses: (1) To determine whether a genetic activation of FXR during perinatal development is toxic to the liver, and whether the perinatal toxicity will be relieved by the dietay supplement of bile acids and/or vitamins; (2) To determine whether a pharmacological activation of FXR during perinatal development is toxic to the liver, and whether the pharmacological effect is FXR- dependent; (3) To determine the maternal effect of FXR activation on perinatal toxicity; and (4) To determine whether Fn14 is a transcriptional target of FXR and whether Fn14 is necessary for the perinatal toxicity of FXR. To our knowledge, this study represents the first attempt to systematically evaluate the perinatal pharmacology of FXR. Results from this study will increase our understanding of the perinatal function of FXR, which will offer better guidance in harnessing the therapeutic benefit of FXR. *This applicant agrees and has requested funds to participate in the annual NIH-sponsored two-day meetings focusing on Developmental Pharmacology in Bethesda, MD. This applicant also agrees to cooperate with other investigators.