Transcription Factor Control of Liver Development and Function

项目摘要 这项提议的目标是确定FoxO1转录因子如何对人类肝脏起作用 发育作为分化肝细胞基因表达和新陈代谢的中介。这 知识将有助于更全面地了解肝细胞的潜在机制。 应对普遍存在的人类代谢紊乱所需的分化和功能，以及改善 多能干细胞来源的肝细胞。Foxo1被归类为“先驱者”或初始染色质结合 转录因子由于其独特的能力打开沉默的紧密的染色质和扰动的潜在 组蛋白：DNA接触促进招募额外的调节因子。我们用了一个新奇的人类 诱导多能干细胞(HiPSC)肝细胞分化系统首次显示出该阶段- FoxO1染色质结合的特异性破坏阻止了肝祖细胞在 明确的内胚层和严重限制肝脏规格，这是肝脏发育的前两个阶段。这 这一发现提出了一种令人兴奋的可能性，即FoxO1必须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， FoxO1和另一种富含肝脏的先驱因子FoxA相互依赖的染色质结合在一起 在维持活跃的染色质环境以及与转录因子的结合中发挥重要作用 诱导胰岛素调节基因。再加上最近的一项研究表明，FoxO1和FoxA共同作用于 多个基因与葡萄糖、脂类、胆固醇和胆汁酸的代谢途径有关，这一发现指出 相互依赖的FoxO1/FoxA结合作为一种通用的调节机制，使创建和 广泛肝脏代谢的细胞外信号对染色质活性状态的维持 流程。根据这一证据，我们假设FoxO1使用其不同的染色质结合和 重塑能力在人类肝脏发育中扮演两个不同的角色：(1)参与关键的 作为肝细胞所需靶基因转录调节因子的发育途径 规范和分化后(2)与FoxA因子协同激活和调节 成熟肝细胞必需代谢基因的表达。我们建议对此进行调查 通过确定FoxO1诱导的负责的必要基因调控网络的假说 关于人类肝脏命运的规范和确定相互依赖的FoxO1/FoxA结合和 转录调节因子招募影响其对必要的肝脏代谢的激活 功能。相应基因调控事件的颠覆可能是代谢的贡献者 错乱和肝病，使我们发现关键的机制和参与者是至关重要的。

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.