The differentiation capacity of human embryonic stem cells (hESCs) holds great promise for therapeutic applications. We report a novel three-stage method to efficiently direct the differentiation of human embryonic stem cells into hepatic cells in serum-free medium. Human ESCs were first differentiated into definitive endoderm cells by 3 days of Activin A treatment. Next, the presence of fibroblast growth factor-4 and bone morphogenetic protein-2 in the culture medium for 5 days induced efficient hepatic differentiation from definitive endoderm cells. Approximately 70% of the cells expressed the hepatic marker albumin. After 10 days of further in vitro maturation, these cells expressed the adult liver cell markers tyrosine aminotransferase, tryptophan oxygenase 2, phosphoenolpyruvate carboxykinase (PEPCK), Cyp7A1, Cyp3A4 and Cyp2B6. Furthermore, these cells exhibited functions associated with mature hepatocytes including albumin secretion, glycogen storage, indocyanine green, and low-density lipoprotein uptake, and inducible cytochrome P450 activity. When transplanted into CCl 4 injured severe combined immunodeficiency mice, these cells integrated into the mouse liver and expressed human alpha-1 antitrypsin for at least 2 months. In addition, we found that the hESC-derived hepatic cells were readily infected by human immunodeficiency virus-hepatitis C virus pseudotype viruses. Conclusion: We have developed an efficient way to direct the differentiation of human embryonic stem cells into cells that exhibit characteristics of mature hepatocytes. Our studies should facilitate searching the molecular mechanisms underlying human liver development, and form the basis for hepatocyte transplantation and drug tests. (HEPATOLOGY 2007;45: 1229-1239.)
The derivation of hepatic progenitor cells from human embryonic stem (hES) cells is of value both in the study of early human liver organogenesis and in the creation of an unlimited source of donor cells for hepatocyte transplantation therapy. Here, we report for the first time the generation of hepatic progenitor cells derived from hES cells. Hepatic endoderm cells were generated by activating FGF and BMP pathways and were then purified by fluorescence activated cell sorting using a newly identified surface marker, N-cadherin. After co-culture with STO feeder cells, these purified hepatic endoderm cells yielded hepatic progenitor colonies, which possessed the proliferation potential to be cultured for an extended period of more than 100 days. With extensive expansion, they co-expressed the hepatic marker AFP and the biliary lineage marker KRT7 and maintained bipotential differentiation capacity. They were able to differentiate into hepatocyte-like cells, which expressed ALB and AAT, and into cholangiocyte-like cells, which formed duct-like cyst structures, expressed KRT19 and KRT7, and acquired epithelial polarity. In conclusion, this is the first report of the generation of proliferative and bipotential hepatic progenitor cells from hES cells. These hES cell–derived hepatic progenitor cells could be effectively used as an in vitro model for studying the mechanisms of hepatic stem/progenitor cell origin, self-renewal and differentiation.
Gain and phase uncertainties would destroy the invariance property of both the transmit array and the receive array in bistatic MIMO radar, so the computationally efficient ESPRIT algorithm cannot be applied directly. Proposed is a novel ESPRIT-like algorithm, which uses the instrumental sensors method (ISM), to estimate the direction of departures and direction of arrivals. The ESPRIT-like algorithm is able to achieve favourable and unambiguous angle estimation without any information of the gain and phase uncertainties. The effectiveness of the proposed algorithm is verified by simulation results.Introduction: Multiple-input multiple-output (MIMO) radar is characterised by using multiple antennas to simultaneously transmit orthogonal waveforms and multiple antennas to receive the reflected signals [1]. Direction of departure (DOD) and direction of arrival (DOA) have been recently investigated in [2][3][4]. All of them are based on the assumption that the transmit array and receive array steering vector are exactly known corresponding to the array geometry. But the transmit array and receive array steering vector cannot be obtained precisely when there exist gain and phase uncertainties. Therefore, the performance of the algorithms proposed in [2 -4] will seriously degrade. To deal with the problem of gain and phase uncertainties of the transmit array and the receive array, a novel ESPRIT-like angle estimation algorithm is proposed in this Letter. As there is not requirement of space searching or iterative procedure, the computational complexity is low.
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