The Perinatal Pharmacology of the Nuclear Receptor

描述（由申报人提供）：这是R01 HD073070的重新提交，是针对PAR-11-057提交的。我们的目的是了解核受体法氏体X受体（FXR）的围产期肝功能，特别是FXR在围产期发育过程中的激活对肝脏的影响。最近的研究表明，激活FXR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功能的结论大多基于成年动物，而FXR在围产期发育中的功能了解甚少。FXR的激活通过抑制CYP7A1转录抑制胆汁酸合成。据认为，围产期肝脏对胆汁酸池大小的减少特别敏感，因为CYP7A1的基础表达较低，以及出生后早期肠肝胆汁酸再循环不足。胆汁酸是一种临床药物，已被用于治疗肝胆疾病，包括某些儿科疾病。由于母亲使用胆汁酸类药物和其他非胆汁酸类FXR活化剂，围产期FXR也有充分的激活机会。因此，有必要了解FXR的围产期药理学。我们的初步结果表明：1)FXR在转基因小鼠的围产期激活导致肝毒性、部分致死和炎症迹象；2) FXR转基因的围产期毒性与胆汁酸分泌减少有关，可能是由于抑制了Cyp7a1；3)围产期饲粮中添加胆汁酸和/或维生素可减轻转基因幼鼠的肝毒性和部分致死率；4)对转基因小鼠的成活率有实质性影响，转基因坝喂养的转基因幼鼠成活率低于对照坝喂养的转基因幼鼠；5) FXR的围产期毒性与成纤维细胞生长因子诱导的即时早期反应蛋白14 （Fn14）的激活有关，Fn14是一种在新生儿肝脏中高表达的基因，与炎症有关。在Fn14基因启动子中发现了一个推测的FXR应答元件，表明Fn14是FXR的转录靶点；我们已经成功地合成了6？-ECDCA，一种有效的FXR激动剂，具有良好的生物利用度。根据我们的初步数据，我们假设FXR在围产期发育中具有以前未被认识到的作用。具体来说，我们假设FXR的激活可能在围产期发育期间对肝脏有毒性，原因如下：1)抑制

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.