Liver MAPs

Project Summary

The major outcome of this project is to produce functionally mature embryonic stem cell (ESC)/ induced pluripotent stem cell (iPSC) derived hepatocytes in 3D organotypic cultures. We also anticipate that the epigenetic analysis in this project will yield basic principles for understanding maturation relevant to other tissues, and thus should facilitate even wider use of human ESC/iPSC-derivatives in toxicological studies. In vitro liver models for toxicity testing and drug discovery are overly reliant on primary cells which lose their mature phenotype over time in vitro or on animal derived cells which do represent all the features of a human liver cell.

This Project is aimed at understanding the genetic and epigenetic controls of liver differentiation and maturation, with the goal of achieving functional maturation of human ES cell-derived liver cells in 3D organotypic cultures. The derivation of human ES cells by the Thomson lab in 1981, and the derivation of human iPS cells by the Thomson and Yamanaka laboratories in 2007 created a potentially unlimited, scalable source for human hepatocytes suitable for toxicological studies. However, although there are already good protocols published for the differentiation human pluripotent stem cells down the hepatic lineage, the metabolic function of the resulting cells has been immature and inadequate for routine toxicological studies. A better understanding of the genetic and epigenetic control mechanisms of liver cell maturation with the Pathway Analysis Core is expected to lead to improved methods for culturing and differentiating human ES/iPS cells to mature hepatocytes for toxicological studies.

In this project, we will focus on the hepatocyte lineage, but a basic understanding of the genetic and epigenetic control of developmental timing and tissue maturation should be germane to other lineages and broadly important across the entire human ES/iPS cell field. A key challenge for both in vitro modeling and therapeutics is that the in vitro timing of human ES/iPS cell differentiation very closely recapitulates a human developmental program of nine months. What controls this species-specific timing, and what controls final maturation is currently unknown for any lineage. There is therefore a pressing need to understand the control of species-specific developmental timing and tissue maturation across different tissues so that fully functional cells can be derived from human ES/iPS cells. Given that the timing of tissue growth and maturation scales fairly uniformly across lineages between species, we anticipate that at least some of the underlying mechanisms controlling maturation are conserved through vertebrate evolution and shared across lineages. Thus a fundamental understanding of liver maturation will likely lead to insights critical to understanding the maturation of other lineages and ultimately lead to a more representative liver model.