Hepatology. Author manuscript; available in PMC 2011 May 1.

Published in final edited form as:

PMCID: PMC2925460

NIHMSID: NIHMS221023

Recent advances in induced pluripotent stem (iPS) cell research significantly changed our perspective on regenerative medicine. Patient specific iPS cells have been derived not only for disease modeling but also as sources for cell replacement therapy. However, there have been insufficient data to prove that iPS cells are functionally equivalent to hES cells or safer than hES cells. There are several important issues which need to be addressed and foremost are the safety and efficacy of human iPS cells from different origins. Human iPS cells have been derived mostly from cells originated from mesoderm, with a few cases from ectoderm. So far there has been no report of endoderm derived human iPS cells, preventing comprehensive comparative investigations on the quality of human iPS cells from different origins.

Here we show for the first time reprogramming of human endoderm derived cells (i.e. primary hepatocytes) to pluripotency. Hepatocyte-derived iPS cells appear indistinguishable from human embryonic stem cells in colony morphology, growth properties, expression of pluripotency-associated transcription factors and surface markers, and differentiation potential in embryoid body formation and teratoma assays. In addition, these cells were able to directly differentiate into definitive endoderm, hepatic progenitors, and mature hepatocytes. The technology to develop endoderm derived human iPS cell lines, together with other established cell lines, will provide a foundation to elucidate the mechanisms of cellular reprogramming and to study the safety and efficacy of differentially originated human iPS cells for cell therapy. For studying liver disease pathogenesis, this technology also provides a potentially more amenable system to generate liver disease specific iPS cells.

Recent advances in induced pluripotent stem (iPS) cell research have provided great potential for these somatic cell-derived stem cells as sources for cell replacement therapy and for establishing disease models.114 Human iPS cells have been shown to be pluripotent in in vitro differentiation and in vivo teratoma assays, similar to human embryonic stem (hES) cells.914 Disease-specific iPS cell lines have been generated from fibroblasts and blood cells and some of the disease features have been recapitulated in tissue culture after directed differentiation of the iPS cells, demonstrating the power of this technology in disease modeling.13,15 However, several key issues have to be addressed in order for the iPS cells to be used for clinical purposes. First, although pluripotency has been demonstrated, it is premature to claim that iPS cells are functionally equivalent to hES cells. In fact, one study has suggested that iPS cells have distinct protein-coding and microRNA gene expression signatures from ES cells.1 These differences can not be completely explained by the reactivation of transgenes used in the reprogramming process since human iPS cells generated without viral or transgene integration also displayed a different transcriptional signature compared to hES cells.2 Secondly it was demonstrated that human iPS cells retained certain gene expression of the parent cells, suggesting that iPS cells from different origins may possess different capacity to differentiate.2 This issue is important not only for the purposes of generating functional cell types for therapy but also for safety implications. A comprehensive study using various mouse iPS cells has demonstrated that the origin of the iPS cells had a profound influence on the tumor-forming propensities in a cell transplantation therapy model.3 Mouse tail-tip fibroblast-iPS cells (mesoderm origin) showed the highest tumorigenic propensity, whereas gastric epithelial cell- and hepatocyte-iPS cells (both are endoderm) showed lower propensities.3 It is therefore extremely important to establish human iPS cell lines from multiple origins and thoroughly examine the source impact on both the safety issues and their differentiation potentials. In addition, the ability to reprogram human hepatocytes is crucial for developing liver disease models using iPS cells, especially for certain liver diseases carrying acquired somatic mutations which occur only in hepatocytes of patients, but not in other cell types.1620

In the mouse, iPS cells have been generated from derivatives of all three embryonic germ layers, including mesodermal fibroblasts,6 epithelial cells of endodermal origin7 and ectodermal keratinocytes,8 whereas human iPS cells have been produced mostly from mesoderm (fibroblasts and blood cells) or from ectoderm (keratinocytes and neural stem cells).913,21,22 Here we show reprogramming of human primary hepatocytes (endoderm) to pluripotency. Hepatocyte-derived iPS cells appear indistinguishable from human embryonic stem cells in colony morphology, growth properties, expression of pluripotency-associated transcription factors and surface markers, and differentiation potential in embryoid body (EB) formation as well as teratoma assays. In addition these cells were able to directly differentiate into definitive endoderm, hepatic progenitors, and mature hepatocytes.

Our study lays the ground work necessary to elucidate the mechanisms of cellular reprogramming and to study the safety and efficacy of differentially originated human iPS cells in cell therapy.

Primary human hepatocytes were obtained from Lonza plated on collagen 1 and matrigel coated dishes, and cultured in serum containing WEM (Willians' Medium E), Gentamicin, Dexamethasone 10 mM, FBS 5%, L-Glutamine, Hepes 15mM, Insulin 4 mg/ml with 50ng/ml of HGF and EGF. Medium for culturing hES cells and iPS cells is Knockout DMEM supplemented with 20% KOSR, NEAA, 2-ME, GlutaMAX, 6 ng/ml basic fibroblast growth factor (all Invitrogen). hESC lines WA09 (H9) and WA01 (H1) (WiCell) were cultured on irradiated MEF feeder layers in ES medium. This study was done in accordance with Johns Hopkins ESCRO regulations and following a protocol approved by the Johns Hopkins IRB.

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Generation of Endoderm derived Human iPS cells from ...