The Fetal Hepatocyte Phenotype and Cell-Based Therapy for Liver Disease

肝脏的生长和功能分化对妊娠晚期胎儿的新陈代谢、围产儿的 新生儿的过渡和代谢适应。胎儿肝脏发育的生物学也有 胎儿体细胞生长调控、肝癌发生和肝细胞治疗的意义 疾病。我们的实验室长期以来一直专注于啮齿类动物妊娠晚期肝脏的发育。为了做到这一点，我们 已经确定了一种胎儿肝细胞表型，它是由调节胎儿肝细胞的信号通路定义的 肝细胞生长、增殖和基因表达。最近，我们展示了后来的能力 具有关键肝细胞标记物亮氨酸氨基肽酶(LAP)的妊娠大鼠胎肝细胞 重新填充受损的成人肝脏。这是成年大鼠肝细胞所不具备的能力。目前的建议是 基于组蛋白变体和组蛋白翻译后修饰(PTM)的中心假设， 通过对染色质结构的影响解释妊娠晚期胎鼠的信号表型 肝细胞和这种表型在成人肝脏移植后的持久性 微环境。该项目的长期目标是确定遗传和表观遗传机制 解释了胎肝细胞的新特征，从而应用了对胎肝的理解 发展以细胞为基础的肝病治疗。这一目标将通过 三个具体目标。具体目标1是通过检测胎儿肝细胞的表观遗传学特征 胎儿和成人晚期肝脏的染色质结构、组蛋白变体和组蛋白PTM。特定目标 2刻画了组蛋白变异体、组蛋白PTMS、染色质结构与组蛋白结构之间的功能关系 胎儿向成人转变过程中肝脏关键生长调节基因的调控。这一目标将考验 特异组蛋白变体和PTM与关键疾病的发育变化相关的假说 生长调节基因。在具体目标3中，我们将评估在 目标1和目标2在定义和维持妊娠晚期胎鼠肝细胞修复损伤的能力中的作用 成年大鼠肝脏。这一目标将检验这样的假设，即胎儿肝脏表观遗传特征是一种 同时拥有肝细胞和胆管标记物的胎儿肝细胞亚群，这 表观遗传特征在移植前和植入后都存在。完成这些目标将 洞察决定发育中的肝脏细胞行为的分子机制 以细胞为基础的肝病治疗进展。该项目在多个方面具有创新性。我们 将产生关于肝脏发育过程中基因表达的表观遗传调控的新信息。 在这样做的过程中，我们将描述胎儿肝脏中一个以前未被鉴定的多潜能细胞群，它可以 重新填充受损的成人肝脏。最后，我们将在整个研究过程中使用创新的方法，因此 提高在哺乳动物发育生理学背景下研究表观遗传调控的能力。

Growth and functional differentiation of the liver are critical to late gestation fetal metabolism, the perinatal transition and metabolic adaptation by the newborn. The biology of fetal liver development also has implications for regulation of fetal somatic growth, hepatic carcinogenesis, and cell-based therapy for liver disease. Our laboratory has long focused on late gestation liver development in the rodent. In doing so, we have identified a fetal hepatocyte phenotype that is defined by the signaling pathways that regulate fetal hepatocyte growth, proliferation and gene expression. More recently, we demonstrated the ability of late gestation fetal rat liver cells possessing a key hepatocyte marker, leucine amino peptidase (LAP), to repopulate an injured adult liver. This is a capacity not shared by adult rat hepatocytes. The present proposal is based on the central hypothesis that histone variants and histone posttranslational modifications (PTMs), acting through effects on chromatin structure, account for the signaling phenotype of late gestation fetal rat hepatocytes and the persistence of this phenotype following transplantation into the adult liver microenvironment. The long term goal of the project is to identify genetic and epigenetic mechanisms that account for the novel characteristics of fetal liver cells, thereby applying an understanding of fetal liver development to the development of cell-based therapy for liver disease. This goal will be pursued through three Specific Aims. Specific Aim 1 is to identify a fetal hepatocyte epigenetic signature by examining chromatin structure, histone variants and histone PTMs in liver during late fetal versus adult life. Specific Aim 2 is to characterize the functional relationship between histone variants, histone PTMs, chromatin structure and regulation of key growth-regulating genes in liver during the fetal to adult transition. This aim will test the hypothesis that specific histone variants and PTMs are associated with developmental changes in critical growth-regulating genes. In Specific Aim 3, we will assess the role of the epigenetic signature identified in Aims 1 and 2 in defining and maintaining the ability of late gestation fetal rat liver cells to repopulate an injured adult rat liver. This aim will test the hypothesis that a fetal hepatic epigenetic signature is characteristic of a subpopulation of fetal hepatocytes that possess both hepatocyte and bile ductular markers, and that this epigenetic signature is present both before transplantation and after engraftment. Completion of these aims will provide insight into molecular mechanisms that determine cell behavior in the developing liver while advancing the development of cell-based therapy for liver disease. The project is innovative in a number of aspects. We will generate new information regarding the epigenetic regulation of gene expression during liver development. In doing so, we will characterize a previously unidentified, multipotent cell population in fetal liver that can repopulate an injured adult liver. Finally, we will use innovative methods throughout these studies, thus advancing the ability to study epigenetic regulation in the context of mammalian developmental physiology.