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，超过四分之一的列出的患者在接受器官之前就已经过期。开发一种在组织培养条件下刺激肝脏再生或培养肝细胞的方法，可能会消除移植的需要。虽然有几个小组试图在实验室培养肝脏干细胞，但能够满足当前移植需求的强大条件尚未开发出来。我们的实验室最近发现了两项可能有助于肝脏干细胞扩增的发现。首先，我们发现河马信号的改变可以将成熟的肝细胞重新编程为显示双潜能肝祖细胞特征的细胞。河马信号此前曾被描述为一种强有力的生长调节器，但这一发现表明，这一途径也赋予分化细胞更高的可塑性。其次，我们开发了培养条件，在这种条件下，操纵河马信号允许肝脏祖细胞和重新编程的肝细胞长期生长和巨大扩张。我们建议从三个方面研究这些发现的性质：1)利用一个新的河马报告小鼠系来确定内源性河马活性是否可以原位标记难以捉摸的肝祖细胞。2)阐明重编程肝细胞是否含有经体外和体内功能测试的真正干细胞；3)研究YAP重编程肝细胞的下游机制。该项目的完成将阐明肝脏祖细胞/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的一种策略。

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.