Control of developmental switch of Cyp3a gene expression in mouse liver

描述（由申请人提供）：细胞色素P450 3A亚家族（CYP3A）成员，如CYP3A4、CYP3A5和CYP3A7，是人类肝脏和肠道中表达最丰富的P450酶，负责代谢bb50 %的药物。在肝脏发育过程中发现CYP3A活性和基因表达的显著变化，婴儿和幼儿对许多药物的代谢能力与成人不同。特别是，CYP3A4和CYP3A7在出生后的发育开关中表现出深刻的基因表达互惠模式。然而，在发育过程中调控CYP3A基因的个体表达的机制尚不清楚。我们的长期研究目标是揭示在开发过程中控制药物代谢的机制。本提案的目的是通过小鼠为模型，确定在出生后发育过程中控制肝脏中Cyp3a基因的个体表达的机制。我们的中心假设是，小鼠肝脏中Cyp3a基因的个体表达模式是由转录因子控制的，这些转录因子改变了靶染色质上的表观遗传修饰，并将Cyp3a基因置于不同的核位置，从而允许Cyp3a基因在不同的发育阶段被打开或关闭。为了验证这一假设，我们提出以下具体目标：(1)建立不同年龄肝细胞中Cyp3a基因周围的组蛋白修饰谱；(2)确定不同年龄肝细胞核中Cyp3a基因的染色质凝聚、核位置和相关组蛋白修饰；(3)研究转录因子在肝脏成熟过程中调控Cyp3a基因的致癌性表达中的作用。我们已经组建了一个多学科团队，并为拟议的研究准备了所有的技术和小鼠模型，这将有助于确保拟议研究的成功完成。如果我们证明我们的假设是正确的，我们提出的研究将通过表观遗传机制确定控制Cyp3a基因的个体表达的转录因子。这将大大增加我们对肝脏发育中基因表达的发育调节的基础知识。这一知识对于药物代谢酶来说尤其新颖，因为表观遗传学和基因定位领域在涉及药物生物转化的基因的个体发生方面并没有受到太多关注。这一基础知识的建立对于理解儿童和成人患者之间药物反应的差异至关重要，对于在个性化医疗中建立基于个体间表观基因组差异的药物表观基因组学也很重要。

DESCRIPTION (provided by applicant): The cytochrome P450 3A subfamily (CYP3A) members, such CYP3A4, CYP3A5, and CYP3A7, are the most abundant P450 enzymes expressed in human liver and intestine and are responsible for metabolizing >50% of drugs. Significant variations in CYP3A activity and gene expression have been found in liver during development, with infants and young children having different ability to metabolize many drugs than adults. Particularly, CYP3A4 and CYP3A7 exhibit profound reciprocal patterns of gene expression with a developmental switch after birth. However, the mechanisms governing the ontogenic expression of the CYP3A genes during development are unknown. Our long- term research goal is to unravel the mechanisms that control drug metabolism during development. The objective of this proposal is to identify the mechanisms controlling the ontogenic expression of the Cyp3a genes in livers during postnatal development by using mouse as a model. Our central hypothesis is that the ontogenic expression patterns of the Cyp3a genes in mouse liver are controlled by transcription factors which change epigenetic modifications at the target chromatin, and place the Cyp3a genes in distinct nuclear positions, allowing the Cyp3a genes to be turned on or off at different developmental stages. To test this hypothesis, we propose to pursue the following specific aims: (1) to establish profiles of histone modifications around the Cyp3a genes in liver cells at different ages; (2) to define chromatin condensation, nuclear positions, and associated histone modifications of the Cyp3a genes in hepatocyte nuclei at different ages; and (3) to examine the roles of the transcription factors in controlling ontogenic expression of the Cyp3a genes during liver maturation. We have assembled a multidisciplinary team and have all the techniques and mouse models ready for the proposed studies, which will help to ensure a successful completion of the proposed studies. If we prove our hypothesis is correct, the proposed study will identify transcription factors which control the ontogenic expression of the Cyp3a genes through epigenetic mechanisms. It would add greatly to our fundamental knowledge of developmental regulation of gene expression in liver development. This knowledge is particularly novel for drug metabolizing enzymes, because the areas of epigenetics and gene positioning have not received much attention with respect to the ontogeny of genes involved in drug biotransformation. Establishment of this fundamental knowledge is essential for understanding difference of drug responses between pediatric and adult patients and is important for establishing pharmaco-epigenomics based on inter-individual variation of epigenomes in personalized medicine. PUBLIC HEALTH RELEVANCE: The proposed research is important for establishing the general mechanisms controlling ontogenic gene expression of drug metabolizing enzymes in liver during early postnatal ages. This fundamental knowledge will help us to understand why children have different ability to metabolize drugs than adults.