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供体器官数量，替代治疗方法，如肝细胞移植，正在进行深入研究。然而，迄今为止，除了在高度病理情况下在动物模型系统中进行的研究外，成年肝细胞的研究仅取得了非常有限的成功。几年前，我们实验室发现胎肝干/祖细胞（FLSPC）可以通过与宿主肝细胞的细胞竞争来替代正常成年大鼠肝脏中20-25%的肝脏质量。最近，我们观察到FLSPC的组织替代水平随着大鼠年龄的增长而急剧增加（5倍）。此外，我们还发现，激活素A的水平，细胞周期停滞的介质，以及细胞凋亡，在老龄大鼠肝脏增加。我们推测，激活素A在衰老肝脏中的表达增加，产生了有利于移植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FLSPC和宿主肝细胞之间的细胞竞争介导衰老肝脏中再增殖的增加。本项目的目标是确定激活素A通过移植FLSPC介导肝脏再增殖的具体机制。将进行实验1）鉴定特定的细胞凋亡、抗细胞凋亡、增殖、细胞周期和衰老相关基因，其表达在老年与年轻细胞移植受者中通过移植的FLSPC的肝脏再增殖期间增加或减少，2）研究激活素A诱导离体肝细胞生长停滞和凋亡的体外机制;在肝病（即肝纤维化）的实验模型中确定通过FLSPC的肝再增殖是否通过激活素A的内源性分泌而增强。由于终末期肝病患者的数量和年龄在未来20年内将继续增加，因此在终末期之前使用细胞移植治疗这些患者将具有实质性的临床益处，特别是在老年人中。因此，鉴定用于有效细胞移植的特定细胞类型以替代患有慢性肝病的老年患者的肝实质并恢复肝功能将代表特别有价值的疗法。拟议研究的结果还将提供对基本要求和机制的关键理解，这些要求和机制将作为所有年龄段患者有效肝脏重建的指南。

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.