The liver is a promising target for cell therapy since it supports and functionally integrates transplanted cells. Human liver contains more than 50 billion cells and more than 10% replacement will be required for most liver diseases. Hence, embryonic stem cells (ESC), which have unlimited growth capacities, represent one of the few cell types with potential for liver cell therapy. However, to be functionally effective and safe, ESC have to be differentiated into hepatocytes, the cells of the liver that provide its typical functions, before transplantation. Unfortunately, current ESC differentiation protocols generate cells that are not fully differentiated or functional. To achieve levels of differentiation that would be therapeutic we propose to identify the mechanisms that establish hepatocyte function in progenitor cells in the adult liver. Adult liver progenitors are typically absent from the normal liver but become apparent in liver disease when hepatocytes are damaged. Remarkably, adult liver progenitors can differentiate into fully functional hepatocytes within a few days. We hope to identify the genes that enable this rapid maturation process in order to apply it to immature cells derived from ESC. If maturation can be induced and these hepatocyte-like cells function to correct a mouse model of a human liver disease we will have provided proof-of-principle for the potential of ESC for liver cell therapy.
Liver transplantation is the only curative option for patients with severe liver diseases. As donor livers are rare, many Californians are currently waiting to receive a transplant. In fact, many patients on the waiting list die before a donor organ becomes available. If successful, the proposed project would help to alleviate the need for donor organs by establishing embryonic stem cells as a source of hepatocytes for transplantation. As hepatocyte transplantation would be less invasive and expensive than orthotopic liver transplantation, funds might become available that could be used to benefit the citizens of California in other areas.
This application is concerned with liver regeneration and the differentiation of hepatocytes. In particular, the proposal is focused on the function of microRNAs in hepatocyte differentiation and on the role of oval cells, a population of adult liver progenitors. The premise is that although hepatic progenitors can be derived from embryonic stem cells (ESCs), these are typically immature and have not been shown to be therapeutically effective in animal models, and that knowledge from adult regeneration models might instruct full differentiation and maturation of ESC-derived hepatocytes. The first specific aim is to identify and characterize microRNAs that function in hepatocytes and oval cells in both in vitro and in vivo models. The second objective is to isolate and analyze oval cells in a mouse model of hepatocyte differentiation and identify regulators of this process. The third aim is to use information from aims 1 and 2 to promote the differentiation of ESC-derived hepatocyte-like cells into functional hepatocytes.
This proposal is focused on the important problem of liver regeneration. Moreover, in concentrates on a largely uncharacterized, final phase in the differentiation of liver cells and has high significance for the development of hepatocytes for therapeutic use. Reviewers’ enthusiasm was somewhat dampened by an overly ambitious proposal that lacked sufficient detail in some of the experimental design. This added to uncertainty about the feasibility of some of the proposed experiments. However, reviewers felt that the study is likely to open exciting, new avenues of investigation and contribute to the development of approaches for the generation of mature hepatocytes which could lead to novel therapies for patients with liver disease.
The applicant, a physician-scientist and newly appointed assistant professor, is a clear strength of the application. S/he has published highly significant papers in stem cell biology and liver regeneration and trained with one of the international leaders in the field. The proposal includes well designed career development and mentoring plans. Reviewers were particularly enthusiastic about the applicant’s strong connections to both clinical and basic science, suggesting a strong and continued therapeutic focus to the developing research program.
The institutional commitment was viewed as excellent. The research environment is extremely strong and supportive. Outstanding collaborators, facilities, and resources are readily available. The applicant received substantial start-up funds to establish a robust research program. The institution has an excellent reputation and strong commitment to support stem cell research.
Overall this is a good proposal with two outstanding components: the applicant and the institutional commitment. Although reviewers harbored concerns about the research plan, the potential benefit of these studies was recognized as highly significant. Furthermore, the proposed study is likely to advance the field and make important contributions to therapeutic development.