Induction of Hepatocyte Differentiation in Human Pluripotent Stem Cells

Abstract

Culturing of hepatocytes is used in both experimental and clinical procedures. Human induced pluripotent stem (hiPS) cells can be established from the somatic cells of individual patients. The In vitro production of hepatocytes from these hiPS cells would be advantageous in that it could resolve the ethical problems associated with stem cell research and could eliminate the need for administration of immunosuppresants in hepatocyte transplantation. To establish a method for the production of hepatocytes from hiPS cells, it is necessary to understand both the mechanism of hepatocyte differentiation as well as the current techniques for culturing of primary hepatocytes. Meanwhile, hepatocytes can also be differentiated from endodermal cells upon stimulation with growth factors that induce expression of specific transcriptional regulators. Current protocols for the generation of hepatocytes from hiPS cells include the sequential application of growth factors to mimic the environment of fetal liver. Initially, cells are treated with activin and bone morphogenetic proteins, followed by the application of hepatocyte growth factor and, at the final differentiation stage, Oncostatin M. Expression of transcription factors is necessary for hepatocyte differentiation. However, because the efficiency at which vectors expressing these factors can be transfected into hiPS cells is disappointingly low, adenoviral vectors have been used, which have a transduction efficiency of 100%. This method is used to sequentially introduce sex-determining region Y (Sry) HMG box (Sox) 17, hematopoietically expressed homeobox, and hepatocyte nuclear factor-4α into hiPS cells. These factors, in concert with the stimulation with growth factors, promote differentiation of these cells to hepatocytes. Despite the development of these procedures, however, the resulting cells remain immature and only perform certain hepatocyte functions. In this review, we describe each of the above points, and then discuss novel approaches and future directions for the In vitro production of hepatocytes.