Hedgehog Signaling and Adult Liver Regeneration

摘要 肝再生使活体肝移植成为可能，是肝损伤后修复的基础。 然而，异常的修复过程，如在由于肝炎或肥胖引起的慢性损伤的情况下，可导致 肝硬化和肝癌。相当多的研究工作，包括我们自己的，试图澄清命运关系 在参与肝再生的细胞类型中，包括肝细胞、胆管细胞和星状细胞。 然而，关于控制这些细胞可塑性的机制，关键的知识差距仍然存在。此外，本发明还 尽管一系列信号通路与肝修复有关，但这些通路如何整合到 具体说明和维持肝脏内的祖细胞命运仍然是未知的。我们的最终目标是 控制肝脏再生的机制，因此这些知识可以应用于预防和治疗关键 误修的后果。迄今为止，我们的工作表明：（1）Hedgehog（Hh）通路指导成年人的 通过控制肝祖细胞和肌成纤维细胞（MF）群体的大小来进行肝修复;（2）激活 Hh-应答细胞中的通路驱使它们变得更原始（即，分化程度较低，糖酵解程度较高， 增殖、迁移和纤维化），而沉默Hh信号具有相反的作用;（3）肝星状细胞 细胞（HSC）是Hh-反应性血管周围细胞网络的肝脏驻留成员（即，周细胞）， 似乎保留了间充质干细胞的特征（也被其他人报道）;和（4）在广泛的数据支持下， 我们目前的建议是，Hh信号与Hippo/雅普通路相互作用，这是一种独特的发育通路 已知有助于控制间充质干细胞的命运决定，并通过调节 肝祖细胞群体大小。然而，目前尚不清楚Hh-YAP合作如何导致HSC 重编程或为什么这对肝脏修复是必要的。基于我们和其他人的工作，我们的假设是 Hedgehog激活HSC中的雅普以优化MF-HSC的积累，其增强细胞的生长， 肝再生能力，这一过程需要Hh/YAP依赖性的HSC重编程， 新陈代谢的变化。我们的目标是阐明Hh-YAP串扰对肝脏修复的功能后果 并将阐明协调这种串扰的能量相关机制。每个目标都涉及一个关键问题： 重编程的HSC如何在肝修复过程中控制肝细胞的可塑性？Hh如何重编程HSC 在肝脏修复过程中Hh如何与雅普相互作用以将HSC重编程为增殖性MF？成功 这些目标的完成将加深对共同调节Hedgehog的机制的理解， 雅普/Hippo实现有效的肝脏修复。这些知识将阐明这个复杂的过程是如何出错的 在人类肝脏疾病期间，并能够开发干预措施以增强适当的再生。 我们强大的初步数据和经验丰富、富有成效的研究团队为我们的成功奠定了基础。

ABSTRACT Liver regeneration enables living donor liver transplantation and is fundamental to repair after liver injury. However, aberrant repair processes, as in the setting of chronic injury due to hepatitis or obesity, can lead to cirrhosis and liver cancer. Considerable research effort, including our own, seeks to clarify fate relationships among cell types involved in liver regeneration, including hepatocytes, cholangiocytes, and stellate cells. However, key knowledge gaps persist regarding mechanisms controlling these cells' plasticity. Further, although an array of signaling pathways have been implicated in liver repair, how these are integrated to specify and maintain progenitor fate within the liver remains unknown. Our ultimate goal is to delineate the mechanisms that control liver regeneration so this knowledge can be applied to prevent and treat key consequences of mis-repair. Our work to date has shown that (1) the Hedgehog (Hh) pathway directs adult liver repair by controlling the size of liver progenitor and myofibroblast (MF) populations; (2) activating the pathway in Hh-responsive cells drives them to become more primitive (i.e., less differentiated, more glycolytic, proliferative, migratory, and fibrogenic), and silencing Hh signaling has the opposite effects; (3) hepatic stellate cells (HSC) are liver-resident members of a network of Hh-responsive perivascular cells (i.e., pericytes) that appear to retain mesenchymal stem cell traits (also reported by others); and (4) in extensive data underpinning our current proposal, Hh signaling interacts with the Hippo/YAP pathway, a distinct developmental pathway known to help control fate decisions in mesenchymal stem cells and to control adult liver growth by regulating liver progenitor population size. However, it is unknown how the Hh-YAP collaboration causes HSC reprogramming or why this is necessary for liver repair. Based on work by us and others, our hypothesis is that Hedgehog activates YAP in HSC to optimize accumulation of MF-HSC that enhance growth of cells with liver repopulating capacity, and this process requires Hh/YAP-dependent reprogramming of HSC through metabolism changes. Our aims will elucidate the functional consequences of Hh-YAP cross-talk on liver repair and will clarify energy-related mechanisms that coordinate this cross-talk. Each Aim addresses a key question: How do reprogrammed HSC control hepatocyte plasticity during liver repair? How does Hh reprogram HSC during liver repair? How does Hh interact with YAP to reprogram HSC into proliferative MF? Successful completion of these aims will deepen understanding of mechanisms that co-regulate Hedgehog and YAP/Hippo to achieve effective liver repair. This knowledge will clarify how this intricate process goes awry during human liver disease, and enable development of interventions to enhance appropriate regeneration. Our strong preliminary data and experienced and productive research team position us for success.