Reprogramming of liver cell fate by Hippo signaling

描述（由申请人提供）：肝移植是第二种最常见的实体器官移植形式，超过四分之一的上市患者在接受器官之前死亡。开发一种刺激肝再生或在组织培养条件下培养肝细胞的方法可能会消除对移植的需求。虽然有几个研究小组试图在实验室中培养肝干细胞，但尚未开发出能够满足当前移植需求的强大条件。我们的实验室最近发现了两个可能对肝脏干细胞的扩增有用的发现。首先，我们发现Hippo信号的变化可以将成熟肝细胞重编程为显示双能肝祖细胞特征的细胞。Hippo信号传导以前被描述为一种有效的生长调节剂，但这一发现表明，这种途径也赋予分化细胞增加的可塑性。其次，我们已经开发了培养条件，其中Hippo信号传导的操纵允许肝祖细胞和重编程肝细胞的长期生长和巨大扩增。我们建议从三个方面研究这些发现的本质：1）利用一种新的Hippo报告小鼠系来确定内源性Hippo活性是否可以原位标记难以捉摸的肝祖细胞。2)阐明重编程的肝细胞是否含有真正的干细胞，如在体外和体内功能测试;和3）研究雅普重编程肝细胞的下游机制。该项目的完成将阐明肝祖细胞/干细胞室的性质;并探索肝细胞命运的可塑性作为开发可移植细胞用于移植的策略。

DESCRIPTION (provided by applicant): Liver transplantation is the second most common form of solid organ transplant with more than a quarter of listed patients expiring prior to receiving an organ. Developing a means to either stimulate liver regeneration or cultivate liver cells under tissue culture conditions could potentially abrogate the need for transplantation. While several groups have attempted to cultivate liver stem cells in the laboratory, robust conditions that could fulfill the current transplantation needs have yet to be developed. Our laboratory has made two recent discoveries that may be useful for the expansion of liver stem cells. First, we have found that changes in Hippo signaling can reprogram mature hepatocytes into cells displaying characteristics of bipotential liver progenitor cells. Hippo signaling has ben previously described as a potent growth regulator, but this finding suggests this pathway also confers increased plasticity upon differentiated cells. Secondly, we have developed culture conditions in which manipulation of Hippo signaling allows for long-term growth and enormous expansion of liver progenitors and reprogrammed hepatocytes. We propose to investigate the nature of these findings in three parts: 1) Utilize a novel Hippo reporter mouse line to determine whether endogenous Hippo activity can mark the elusive liver progenitor cell in situ. 2) Elucidate whether reprogrammed-hepatocytes contain bona fide stem cells as tested functionally in vitro and in vivo; and 3) Investigate the downstream mechanisms by which YAP reprograms hepatocytes. Completion of this project would elucidate the nature of the liver progenitor/stem cell compartment; and explore the plasticity of liver cell fate as a strategy to develop transplantable cells for transplantation.