The role of activin A in mediating liver repopulation after cell transplantation

描述(由申请人提供)：目前唯一可用的终末期肝病治疗方法是肝移植。由于肝移植名单上的患者数量远远超过可用的捐赠器官数量，替代治疗方法，如肝细胞移植，正在进行深入的研究。然而，迄今为止对成人肝细胞的研究只取得了非常有限的成功，除了那些在高度病理情况下在动物模型系统中进行的研究。几年前，我们的实验室发现，胎肝干/祖细胞可以通过与宿主肝细胞进入细胞竞争而取代正常成年大鼠肝脏中20-25%的肝脏质量。最近，我们观察到，随着大鼠年龄的增长，FLSPC的组织替代水平急剧增加(5倍)。此外，我们还发现，在衰老的大鼠肝脏中，细胞周期停滞的介体激活素A的水平以及细胞凋亡的水平都增加了。我们假设，在老化的肝脏中激活素A的表达增加创造了有利于移植的FLSPC替代肝细胞的宿主组织微环境。我们进一步假设，激活素A通过增加移植的FLSPC和宿主肝细胞之间的细胞竞争来调节老化肝脏中增加的再繁殖。本项目的目的是确定激活素A通过移植的肝星状细胞介导肝脏再充盈的具体机制(S)。将进行1)在老年和年轻细胞移植受者中通过移植FlSPC来确定特定的凋亡、抗凋亡、增殖、细胞周期和衰老相关基因的表达增加或减少；2)体外研究激活素A诱导离体肝细胞生长停滞和凋亡的机制；3)在肝病(即肝纤维化)的实验模型中确定FlSPC的肝再分化是否通过内源性激活素A的分泌而增加。由于终末期肝病患者的数量和年龄在未来20年将继续增加，在终末期之前使用细胞移植治疗这些患者将会有很大的临床益处，特别是在老年人中。因此，确定特定的细胞类型(S)，以有效的细胞移植替代肝实质，恢复老年慢性肝病患者的肝功能，将是一种特别有价值的治疗方法。拟议研究的结果还将提供对基本要求和机制的关键理解，这些基本要求和机制将指导所有年龄段的患者有效地进行肝脏再繁殖。

DESCRIPTION (provided by applicant): The only currently available treatment for end stage liver disease is liver transplantation. Since the number of patients on the liver transplant list far exceeds the number of donor organs available, alternative treatment methods, such as hepatic cell transplantation, are under intensive investigation. However, studies to date with adult hepatocytes have met with only very limited success, except for those performed in animal model systems under highly pathologic circumstances. Several years ago, our laboratory discovered that fetal liver stem/progenitor cells (FLSPC) can replace 20-25% of hepatic mass in the normal adult rat liver by entering into cell competition with host hepatocytes. Recently, we observed that the level of tissue replacement by FLSPC increases dramatically (5-fold) as rats age. In addition, we have discovered that the level of activin A, a mediator of cell cycle arrest, as well as apoptosis, is increased in the aging rat liver. We hypothesize that increased activin A expression in the aging liver creates a host tissue microenvironment favoring replacement of hepatocytes by transplanted FLSPC. We hypothesize further that activin A mediates increased repopulation in the aging liver through increased cell competition between transplanted FLSPC and host hepatocytes. The goal of this project is to determine the specific mechanism(s) by which activin A mediates liver repopulation by transplanted FLSPC. Experiments will be performed 1) to identify specific apoptosis, anti-apoptosis, proliferation, cell cycle and senescence related genes whose expression is increased or decreased during liver repopulation by transplanted FLSPC in older vs younger cell transplant recipients, 2) to study the mechanism in vitro for activin A induced growth arrest and apoptosis in isolated hepatic cells and 3) to determine in an experimental model of liver disease (i.e. hepatic fibrosis) whether liver repopulation by FLSPC is augmented by endogenous secretion of activin A. Since both the number and age of patients with end-stage liver diseases will continue to increase over the next twenty years, the potential use of cell transplantation to treat these patients before the end-stage would be of substantial clinical benefit, especially in the elderly. Therefore, identifying the specific cell type(s) for effective cell transplantation to replace hepatic parenchyma and restore liver function in elderly patients with chronic liver diseases would represent a particularly valuable therapy. Results from the proposed studies will also provide critical understanding of the basic requirements and mechanisms that will serve as a guide for effective liver repopulation in patients of all ages.