Transcription Factor Control of Liver Development and Function

项目摘要 该提案的目标是确定FoxO 1转录因子如何促进人类肝脏 在分化的肝细胞中作为基因表达和代谢的介导物的发育。这 知识将有助于更全面地了解肝细胞的机制 分化和功能所必需的解决普遍的人类代谢紊乱，以及改善 从多能干细胞衍生肝细胞。FoxO 1被归类为“先锋”或初始染色质结合 由于其独特的能力，打开沉默的致密染色质和扰动潜在的转录因子， 组蛋白：DNA接触，以促进招募额外的调节因子。我们用了一个新的人类 诱导多能干细胞（hiPSC）肝细胞分化系统首次显示， FoxO 1染色质结合的特异性破坏阻止了肝祖细胞在肝内的建立。 定形内胚层和严重削减肝规格，前两个阶段的肝脏发展。这 这项发现提出了一种令人兴奋的可能性，即FoxO 1强制性地调节所需的基因网络 以确定人类胚胎中肝脏的命运。此外，我们已经证明，在人类肝细胞中， FoxO 1和另一种肝脏富集的先驱因子FoxA相互依赖的染色质结合， 在维持活跃的染色质环境以及转录因子的结合中起重要作用， 诱导胰岛素调节基因。最近的一项研究表明，FoxO 1和FoxA共同靶向 与葡萄糖、脂质、胆固醇和胆汁酸代谢途径相关的多个基因，这一发现指出， 相互依赖的FoxO 1/FoxA结合作为一种通用的调节机制， 维持活跃的染色质状态以响应细胞外信号，用于广泛的肝代谢 流程.基于这一证据，我们假设FoxO 1利用其多样的染色质结合， 重塑能力在人类肝脏发育中发挥两种不同的作用：（1）参与关键的 发育途径作为肝细胞所需靶基因的转录调节因子 特化和分化，然后（2）与FoxA因子合作以激活和调节 成熟肝细胞所必需的代谢基因的表达。我们建议对此进行调查 通过识别FoxO 1诱导的重要基因调控网络， 用于人肝命运的规范和确定FoxO 1/FoxA结合和 转录调节因子的募集影响其激活肝脏的基本代谢 功能协调发展的相应基因调控事件的破坏可能是代谢性疾病的一个贡献者。 紊乱和肝脏疾病，这使得我们发现关键机制和参与者至关重要。

Project Summary The goal of this proposal is to determine how the FoxO1 transcription factor contributes to human liver development as a mediator of gene expression and metabolism in the differentiating hepatocyte. This knowledge will contribute to a more complete understanding of the mechanisms underlying hepatocyte differentiation and function necessary for tackling pervasive human metabolic disorders, as well as improving hepatocyte derivation from pluripotent stem cells. FoxO1 is classified as a “pioneer” or initial chromatin binding transcription factor due to its unique ability to open silent compacted chromatin and perturb underlying histone:DNA contacts to promote recruitment of additional regulatory factors. We have used a novel human induced pluripotent stem cell (hiPSC) hepatocyte differentiation system to show, for the first time, that stage- specific disruption of FoxO1 chromatin binding prevents the establishment of hepatic progenitors within the definitive endoderm and severely curtails hepatic specification, the first two stages of liver development. This discovery raises the exciting possibility that FoxO1 obligatorily regulates the network of genes that is required to specify hepatic fate in the human embryo. Additionally, we've show that, in human hepatocytes, interdependent chromatin binding by FoxO1 and another liver-enriched pioneer factor, FoxA, plays an essential role in maintaining an active chromatin environment as well as the binding of transcription factors that induce insulin-regulated genes. Taken together with a recent study showing that FoxO1 and FoxA co-target multiple genes linked to metabolic pathways for glucose, lipids, cholesterol, and bile acids, this finding points to interdependent FoxO1/FoxA binding as a general regulatory mechanism enabling the creation and maintenance of active chromatin states in response to extracellular cues for a broad array of hepatic metabolic processes. Based on this evidence, we hypothesize that FoxO1 uses its diverse chromatin binding and remodeling capabilities to play two distinct roles in human liver development: (1) participation in key developmental pathways as a transcriptional regulator of target genes required for hepatocyte specification and differentiation followed by (2) cooperation with FoxA factors to activate and modulate expression of metabolic genes essential for the mature hepatocyte. We propose to investigate this hypothesis by identifying the essential gene regulatory networks induced by FoxO1 that are responsible for specification of human hepatic fate and determining how interdependent FoxO1/FoxA binding and transcription regulatory factor recruitment impacts their activation of essential hepatic metabolic functions. Subversion of the corresponding gene regulatory events is a likely contributor to metabolic derangements and hepatic disease, making it vital that we uncover the key mechanisms and players.