Control of developmental switch of Cyp3a gene expression in mouse liver

说明(申请人提供)：细胞色素P450 3A亚家族成员，如细胞色素P450 3A4、细胞色素P450 3A5和细胞色素P450 3A7，是人体肝脏和肠道中表达最丰富的P450酶，负责代谢50%的药物。在发育过程中，肝脏中的CYP3A活性和基因表达存在显著差异，婴幼儿对许多药物的代谢能力与成年人不同。尤其是，细胞色素P3A4和细胞色素P3A7在出生后表现出深刻的基因表达模式的相互作用和发育开关。然而，调控细胞色素P3A基因在发育过程中的个体表达的机制尚不清楚。我们的长期研究目标是解开在发育过程中控制药物代谢的机制。本研究的目的是以小鼠为模型，研究肝细胞色素P3A基因在出生后发育过程中的表达调控机制。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目标染色质的表观遗传修饰，并将CYP3A基因置于不同的核位置，允许CYP3A基因在不同的发育阶段被打开或关闭。为了验证这一假说，我们建议追求以下特定目标：(1)建立不同年龄的肝细胞中CYP3A基因周围的组蛋白修饰的图谱；(2)确定不同年龄肝细胞核中CYP3A基因的染色质凝集、核位置和相关的组蛋白修饰；以及(3)研究转录因子在肝脏成熟过程中控制CYP3A基因个体表达的作用。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老鼠模型，这将有助于确保拟议的研究成功完成。如果我们证明我们的假设是正确的，这项拟议的研究将确定通过表观遗传机制控制CYP3A基因个体表达的转录因子。这将极大地增加我们对肝脏发育过程中基因表达的发育调控的基础知识。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个体发育方面没有受到太多关注。这一基础知识的建立对于了解儿童和成人患者的药物反应差异是必不可少的，对于在个性化医学中建立基于表观基因组个体差异的药物表观基因组学也是重要的。 公共卫生相关性：拟议的研究对于建立在出生后早期肝脏中控制药物代谢酶个体基因表达的一般机制很重要。这些基础知识将帮助我们理解为什么儿童的药物代谢能力与成年人不同。

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.