Efficient generation of hepatoblasts from human ES cells and iPS cells by transient overexpression of homeobox gene HEX

The Haematopoietically-expressed homeobox transcription factor: roles in development, physiology and disease

The Haematopoietically expressed homeobox transcription factor (Hhex) is a transcriptional repressor that is of fundamental importance across species, as evident by its evolutionary conservation spanning fish, amphibians, birds, mice and humans. Indeed, Hhex maintains its vital functions throughout the lifespan of the organism, beginning in the oocyte, through fundamental stages of embryogenesis in the foregut endoderm. The endodermal development driven by Hhex gives rise to endocrine organs such as the pancreas in a process which is likely linked to its role as a risk factor in diabetes and pancreatic disorders. Hhex is also required for the normal development of the bile duct and liver, the latter also importantly being the initial site of haematopoiesis. These haematopoietic origins are governed by Hhex, leading to its crucial later roles in definitive haematopoietic stem cell (HSC) self-renewal, lymphopoiesis and haematological malignancy. Hhex is also necessary for the developing forebrain and thyroid gland, with this reliance on Hhex evident in its role in endocrine disorders later in life including a potential role in Alzheimer's disease. Thus, the roles of Hhex in embryological development throughout evolution appear to be linked to its later roles in a variety of disease processes.

Integrative network analysis of circular RNAs reveals regulatory mechanisms for hepatic specification of human iPSC-derived endoderm

BACKGROUND

Human-induced pluripotent stem cell (hiPSC)-derived functional hepatic endoderm (HE) is supposed to be an alternative option for replacement therapy for end-stage liver disease. However, the high heterogeneity of HE cell populations is still challenging. Hepatic specification of definitive endoderm (DE) is an essential stage for HE induction in vitro. Recent studies have suggested that circular RNAs (circRNAs) determine the fate of stem cells by acting as competing endogenous RNAs (ceRNAs). To date, the relationships between endogenous circRNAs and hepatic specification remain elusive.

METHODS

The identities of DE and HE derived from hiPSCs were determined by qPCR, cell immunofluorescence, and ELISA. Differentially expressed circRNAs (DEcircRNAs) were analysed using the Arraystar Human circRNA Array. qPCR was performed to validate the candidate DEcircRNAs. Intersecting differentially expressed genes (DEGs) of the GSE128060 and GSE66282 data sets and the DEcircRNA-predicted mRNAs were imported into Cytoscape for ceRNA networks. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were involved in the enrichment analysis. Hepatic markers and Wnt/β-catenin were detected in hsa_circ_004658-overexpressing cells by western blotting. Dual-luciferase reporter assays were used to evaluate the direct binding among hsa_circ_004658, miRNA-1200 and CDX2. DE cells were transfected with miR-1200 mimics, adenovirus containing CDX2, and Wnt/β-catenin was detected by western blotting.

RESULTS

hiPSC-derived DE and HE were obtained at 4 and 9 days after differentiation, as determined by hepatic markers. During hepatic specification, 626 upregulated and 208 downregulated DEcircRNAs were identified. Nine candidate DEcircRNAs were validated by qPCR. In the ceRNA networks, 111 circRNA-miRNA-mRNA pairs were involved, including 90 pairs associated with hsa_circ_004658. In addition, 53 DEGs were identified among the intersecting mRNAs of the GSE128060 and GSE66282 data sets and the hsa_circ_004658-targeted mRNAs. KEGG and GO analyses showed that the DEGs associated with hsa_circ_004658 were mainly enriched in the WNT signalling pathway. Furthermore, hsa_circ_004658 was preliminarily verified to promote hepatic specification, as determined by hepatic markers (AFP, ALB, HNF4A, and CK19) (p < 0.05). This promotive effect may be related to the inhibition of the Wnt/β-catenin signalling pathway (detected by β-catenin, p-β-catenin, and TCF4) when hsa_circ_004658 was overexpressed (p < 0.05). Dual-luciferase reporter assays showed that there were binding sites for miR-1200 in the hsa_circ_004658 sequence, and confirmed the candidate DEG (CDX2) as a miR-1200 target. The level of miR-1200 decreased and the level of CDX2 protein expression increased when hsa_circ_004658 was overexpressed (p < 0.05). In addition, the results showed that CDX2 may suppress the Wnt/β-catenin signalling during hepatic specification (p < 0.05).

CONCLUSIONS

This study analysed the profiles of circRNAs during hepatic specification. We identified the hsa_circ_004658/miR-1200/CDX2 axis and preliminarily verified its effect on the Wnt/β-catenin signalling pathway during hepatic specification. These results provide novel insight into the molecular mechanisms involved in hepatic specification and could improve liver development in the future.

Hepatitis B virus infection modeling using multi-cellular organoids derived from human induced pluripotent stem cells

Chronic infection with hepatitis B virus (HBV) remains a global health concern despite the availability of vaccines. To date, the development of effective treatments has been severely hampered by the lack of reliable, reproducible, and scalable in vitro modeling systems that precisely recapitulate the virus life cycle and represent virus-host interactions. With the progressive understanding of liver organogenesis mechanisms, the development of human induced pluripotent stem cell (iPSC)-derived hepatic sources and stromal cellular compositions provides novel strategies for personalized modeling and treatment of liver disease. Further, advancements in three-dimensional culture of self-organized liver-like organoids considerably promote in vitro modeling of intact human liver tissue, in terms of both hepatic function and other physiological characteristics. Combined with our experiences in the investigation of HBV infections using liver organoids, we have summarized the advances in modeling reported thus far and discussed the limitations and ongoing challenges in the application of liver organoids, particularly those with multi-cellular components derived from human iPSCs. This review provides general guidelines for establishing clinical-grade iPSC-derived multi-cellular organoids in modeling personalized hepatitis virus infection and other liver diseases, as well as drug testing and transplantation therapy.

Rational design and optimization of synthetic gene switches for controlling cell-fate decisions in pluripotent stem cells

Advances in synthetic biology have enabled robust control of cell behavior by using tunable genetic circuits to regulate gene expression in a ligand-dependent manner. Such circuits can be used to direct the differentiation of pluripotent stem cells (PSCs) towards desired cell types, but rational design of synthetic gene circuits in PSCs is challenging due to the variable intracellular environment. Here, we provide a framework for implementing synthetic gene switches in PSCs based on combinations of tunable transcriptional, structural, and posttranslational elements that can be engineered as required, using the vanillic acid-controlled transcriptional activator (VanA) as a model system. We further show that the VanA system can be multiplexed with the well-established reverse tetracycline-controlled transcriptional activator (rtTA) system to enable independent control of the expression of different transcription factors in human induced PSCs in order to enhance lineage specification towards early pancreatic progenitors. This work represents a first step towards standardizing the design and construction of synthetic gene switches for building robust gene-regulatory networks to guide stem cell differentiation towards a desired cell fate.

Current status of hepatocyte-like cell therapy from stem cells

Organ liver transplantation and hepatocyte transplantation are not performed to their full potential because of donor shortage, which could be resolved by identifying new donor sources for the development of hepatocyte-like cells (HLCs). HLCs have been differentiated from some stem cell sources as alternative primary hepatocytes throughout the world; however, the currently available techniques cannot differentiate HLCs to the level of normal adult primary hepatocytes. The outstanding questions are as follows: which stem cells are the best cell sources? which protocol is the best way to differentiate them into HLCs? what is the definition of differentiated HLCs? how can we enforce the function of HLCs? what is the difference between HLCs and primary hepatocytes? what are the problems with HLC transplantation? This review summarizes the current status of HLCs, focusing on stem cell sources, the differentiation protocol for HLCs, the general characterization of HLCs, the generation of more functional HLCs, comparison with primary hepatocytes, and HLCs in cell-transplantation-based liver regeneration.

From fatty hepatocytes to impaired bile flow: Matching model systems for liver biology and disease

A large variety of model systems are used in hepatobiliary research. In this review, we aim to provide an overview of established and emerging models for specific research questions. We specifically discuss the value and limitations of these models for research on metabolic associated fatty liver disease (MAFLD), (previously named non-alcoholic fatty liver diseases/non-alcoholic steatohepatitis (NAFLD/NASH)) and cholestasis-related diseases such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC). The entire range of models is discussed varying from immortalized cell lines, mature or pluripotent stem cell-based models including organoids/spheroids, to animal models and human ex vivo models such as normothermic machine perfusion of livers and living liver slices. Finally, the pros and cons of each model are discussed as well as the need in the scientific community for continuous innovation in model development to better mimic the human (patho)physiology.

Conversion of mesenchymal stem cells into a canine hepatocyte-like cells by Foxa1 and Hnf4a

Introduction

Hepatocytes, which account for the majority of liver tissue, are derived from the endoderm and become hepatocytes via differentiation of hepatic progenitor cells. Induced hepatocyte-like (iHep) cells and artificial liver tissues are expected to become useful, efficient therapies for severe and refractory liver diseases and to contribute to drug discovery research. The establishment of iHep cell lines are needed to carry out liver transplants and assess liver toxicity in the rising number of dogs affected by liver disease. Recently, direct conversion of non-hepatocyte cells into iHep cells was achieved by transfecting mouse adult fibroblasts with the Forkhead box protein A1 (Foxa1) and hepatocyte nuclear factor 4 homeobox alpha (Hnf4α) genes. Here, we applied this conversion process for the differentiation of canine bone marrow stem cells (cBMSCs) into hepatocyte-like cells.

Methods

Bone marrow specimens were collected from four healthy Beagle dogs and used to culture cBMSCs in Dulbecco's Modified Eagle's Medium (DMEM). The cBMSCs displayed the following characteristic features: plastic adherence; differentiation into adipocytes, osteoblasts and chondrocytes; and a cell surface antigen profile of CD29 (+), CD44 (+), CD90 (+), CD45 (−), CD34 (−) and CD14 (−), or CD11b (−) and CD79a (−), or CD19 (−) and HLA class II(−). The cBMSCs were seeded in a collagen I-coated plate and cultured in DMEM with 10% fetal bovine serum and transfected with retroviruses expressing Foxa1 and Hnf4α the following day. Canine iHep cells were differentiated from cBMSCs in culture on day 10, and were analyzed for morphology, RNA expression, immunocytochemistry, urea production, and low-density lipoprotein (LDL) metabolism.

Results

The cBMSCs expressed CD29 (98.06 ± 1.14%), CD44 (99.59 ± 0.27%) and CD90 (92.78 ± 4.89%), but did not express CD14 (0.47 ± 0.29%), CD19 (0.44 ± 0.39%), CD34 (0.33 ± 0.25%), CD45 (0.46 ± 0.34%) or MHC class II (0.54 ± 0.40%). The iHep cells exhibited morphology that included circular to equilateral circular shapes, and the formation of colonies that adhered to each other 10 days after Foxa1 and Hnf4α transfection. Quantitative RT-PCR analysis showed that the expression levels of the genes encoding albumin (ALB) and cadherin (CDH) in iHep cells on day 10 were increased approximately 100- and 10,000-fold, respectively, compared with cBMSCs. Corresponding protein expression of ALB and epithelial-CDH was confirmed by immunocytochemistry. Important hepatic functions, including LDL metabolic ability and urea production, were increased in iHep cells on day 10.

Conclusion

We successfully induced cBMSCs to differentiate into functional iHep cells. To our knowledge, this is the first report of canine liver tissue differentiation using Foxa1 and Hnf4α gene transfection. Canine iHep cells are expected to provide insights for the construction of liver models for drug discovery research and may serve as potential therapeutics for canine liver disease.

[Pharmaceutical Research on Liver Diseases Using iPS Cell and Genome Editing Technologies]

The liver is a major organ responsible for maintaining the body's homeostasis and xenobiotic metabolism. Liver transplantation is essential for the alleviation of many severe liver diseases. However, there are many patients who cannot receive liver transplants because of donor shortage. Therefore development of effective therapeutic drugs that can replace the need for liver transplantation is desired. To this end, model cells that faithfully reproduce hepatic functions are essential. It is expected that human induced pluripotent stem cell (iPS)-derived hepatocyte-like cells, which faithfully reproduce hepatic functions, would be a valuable tool for drug discovery. Hepatic differentiation from human iPS cells has been performed using growth factors, but the hepatic differentiation efficiency was quite low and liver functions of human iPS cell-derived hepatocyte-like cells were lower than those of primary human hepatocytes. Therefore we tried to improve the hepatic differentiation technology using gene transfer, genome editing, three-dimensional culture, and extracellular matrix technologies. As a result, the purity of human iPS cell-derived hepatocyte-like cells was improved into 90% or more, and the liver functions of human iPS cell-derived hepatocyte-like cells were improved to a level comparable to primary human hepatocytes. In this article, we introduce the research results we have acquired over the last decade.

Generation of human hepatic progenitor cells with regenerative and metabolic capacities from primary hepatocytes

Hepatocytes are regarded as the only effective cell source for cell transplantation to treat liver diseases; however, their availability is limited due to a donor shortage. Thus, a novel cell source must be developed. We recently reported that mature rodent hepatocytes can be reprogrammed into progenitor-like cells with a repopulative capacity using small molecule inhibitors. Here, we demonstrate that hepatic progenitor cells can be obtained from human infant hepatocytes using the same strategy. These cells, named human chemically induced liver progenitors (hCLiPs), had a significant repopulative capacity in injured mouse livers following transplantation. hCLiPs redifferentiated into mature hepatocytes in vitro upon treatment with hepatic maturation-inducing factors. These redifferentiated cells exhibited cytochrome P450 (CYP) enzymatic activities in response to CYP-inducing molecules and these activities were comparable with those in primary human hepatocytes. These findings will facilitate liver cell transplantation therapy and drug discovery studies.

One of the most successful treatments for liver disease is transplanting a donor liver into a patient. But demands for donor livers far outstrips supply. A promising alternative could be, rather than replacing the whole organ, to transplant patients with individual liver cells called hepatocytes. These cells can then move into the liver, replace damaged cells, and help support the organ. However, hepatocytes are also in short supply, as despite the liver’s amazing regenerative abilities, these cells struggle to divide outside of the body. Improving how these cells multiply, could therefore help more people receive hepatocyte transplants.

In 2017, researchers found a way to convert mouse and rat hepatocytes into cells that could divide more rapidly using a cocktail of three small molecules. These 'chemically induced liver progenitors', or CLiPs for short, were able to mature into working hepatocytes and support injured mouse livers. But, discoveries made in rats and mice are not always applicable to humans. Now, Katsuda et al. – including some of the researchers involved in the 2017 work – have set out to investigate whether CLiPs can also be made from human cells, and if so, whether these cells can be used for hepatocyte transplantations.

Using a similar cocktail of molecules, Katsuda et al. managed to convert infant human hepatocytes into CLiPs. As with the rodent cells, these human CLiPs were able to turn back into mature, working liver cells. When transplanted into mice with genetic liver diseases, the human CLiPs moved into the liver and became part of the organ. These transplanted cells were able to reconstruct the liver tissue of diseased mice, and in some cases, replaced more than 90% of the liver’s damaged cells.

Developing human CLiP technology could provide a new way to support people on the waiting list for liver transplantation. But there are some obstacles still to overcome. At present the technique only works with hepatocytes from infant donors. The next step is to improve the method so that it works with liver cells donated by adults.

Generation of functional human hepatocytes in vitro: current status and future prospects

Liver and hepatocyte transplantation are the only effective therapies for late-stage liver diseases, in which the liver loses its regenerative capacity. However, there is a shortage of donors. As a potential alternative approach, functional hepatocytes were recently generated from various cell sources. Analysis of drug metabolism in the human liver is important for drug development. Consequently, cells that metabolize drugs similar to human primary hepatocytes are required. This review discusses the current challenges and future perspectives concerning hepatocytes and hepatic progenitor cells that have been reprogrammed from various cell types, focusing on their functions in transplantation models and their ability to metabolize drugs.

Technological advancements for the development of stem cell-based models for hepatotoxicity testing

Stem cells are characterized by their self-renewal capacity and their ability to differentiate into multiple cell types of the human body. Using directed differentiation strategies, stem cells can now be converted into hepatocyte-like cells (HLCs) and therefore, represent a unique cell source for toxicological applications in vitro. However, the acquired hepatic functionality of stem cell-derived HLCs is still significantly inferior to primary human hepatocytes. One of the main reasons for this is that most in vitro models use traditional two-dimensional (2D) setups where the flat substrata cannot properly mimic the physiology of the human liver. Therefore, 2D-setups are progressively being replaced by more advanced culture systems, which attempt to replicate the natural liver microenvironment, in which stem cells can better differentiate towards HLCs. This review highlights the most recent cell culture systems, including scaffold-free and scaffold-based three-dimensional (3D) technologies and microfluidics that can be employed for culture and hepatic differentiation of stem cells intended for hepatotoxicity testing. These methodologies have shown to improve in vitro liver cell functionality according to the in vivo liver physiology and allow to establish stem cell-based hepatic in vitro platforms for the accurate evaluation of xenobiotics.

Directed Differentiation of Pluripotent Stem Cells by Transcription Factors

Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have been used as promising tools for regenerative medicine, disease modeling, and drug screening. Traditional and common strategies for pluripotent stem cell (PSC) differentiation toward disease-relevant cell types depend on sequential treatment of signaling molecules identified based on knowledge of developmental biology. However, these strategies suffer from low purity, inefficiency, and time-consuming culture conditions. A growing body of recent research has shown efficient cell fate reprogramming by forced expression of single or multiple transcription factors. Here, we review transcription factor-directed differentiation methods of PSCs toward neural, muscle, liver, and pancreatic endocrine cells. Potential applications and limitations are also discussed in order to establish future directions of this technique for therapeutic purposes.

Fine Tuning of Hepatocyte Differentiation from Human Embryonic Stem Cells: Growth Factor vs. Small Molecule-Based Approaches

Human embryonic stem cells (hESCs) are being utilized in diverse areas of studies such as development and disease modeling, cell replacement therapy, or drug toxicity testing because of their potential to be differentiated into any cell type in the body. The directed differentiation of hESCs into hepatocytes could provide an invaluable source of liver cells for various liver-based applications. Therefore, several protocols have been established in the past for hESC-hepatocyte differentiation based on the knowledge of signaling pathways and growth factors involved in different stages of embryonic hepatogenesis. Although successful derivation of hepatocytes has been achieved through these protocols, the efficiency is not always ideal. Herein, we have tested several combinations of published protocols, for example, growth factor vs. small molecule and different time durations of treatment for definitive endoderm (DE) induction and further hepatocyte differentiation to develop an efficient DE induction and hepatocyte differentiation in a highly reproducible manner based on the stage-specific marker expression and functional analysis.

Analysis of differentially expressed genes among human hair follicle-derived iPSCs, induced hepatocyte-like cells, and primary hepatocytes

Background

Differentiation of human induced pluripotent stem cells (hiPSCs) into hepatocytes has important clinical significance in providing a new stem cell source for cell therapy of terminal liver disease. The differential gene expression analysis of hiPSCs, induced hepatocyte-like cells (HLCs), and primary human hepatocytes (PHHs) provides valuable information for optimization of an induction scheme and exploration of differentiation mechanisms.

Methods

Human hair follicle-derived iPSCs (hHF-iPSCs) were induced in vitro by mimicking the environment of a developing liver for 19 days. Expression of specific proteins was determined by immunofluorescence staining; the function of HLCs in storage and metabolism was identified by detecting periodic acid–Schiff, indocyanine green, and low-density lipoprotein. Based on the transcriptomics data, the differential gene expression profiles of hHF-iPSCs, HLCs, and PHHs were analyzed by Gene Ontology, Kyoto Encyclopedia of Genes and Genomes pathway, FunRich, and network analysis methods.

Results

HLCs were able to express albumin (ALB), alpha-fetoprotein, CYP3A4, and CYP7A1, and exhibited matured liver cell functions such as glycogen synthesis and storage. Complement and coagulation cascades and metabolic pathways ranked top in the downregulated list of HLCs/PHHs, while the cell cycle ranked top in the upregulated list of HLCs/PHHs. In the protein–protein interaction network, according to the degree rankings, TOP2A, CDK1, etc. were the important upregulated differentially expressed genes (DEGs), while ALB, ACACB, etc. were the major downregulated DEGs in HLCs/PHHs; the module analysis indicated that CDCA8, AURKB, and AURKA were the top upregulated DEGs in HLCs/PHHs.

Conclusions

We presented the differences in gene expression among hHF-iPSCs, HLCs, and PHHs through transcriptome array data and provided new ideas for the optimization of induction.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0940-z) contains supplementary material, which is available to authorized users.

[Effect of bone morphogenetic protein-4 overexpression on the biological activity of mouse induced pluripotent stem cells]

OBJECTIVE

This study aimed to construct the expression of bone morphogenetic protein-4 (BMP4) lentiviral vector gene and explore its influence on the biological activity of mouse induced pluripotent stem (iPS) cells.

METHODS

iPS cell lines stably overexpressing BMP4 were constructed by lentivirus transfection (BMP4-overexpressing group). Cells without transfection served as the blank group, and cells with only vector transfection served as the empty-vector group. Cell proliferation was detected by CCK8, and the expression levels of ameloblastin (AMBN), cytokeratin (CK) 14, dentin sialophospho-protein (DSPP), bone sialoprotein (BSP), and Runx2 mRNA were detected by quantitative polymerase chain reaction. Alkaline phosphatase (ALP) activity was used to detect the degree of cell differentiation.

RESULTS

Compared with blank and empty-vector groups, proliferation activity and ALP activity of BMP4-overexpressing group obvious increased (P<0.05), BMP4, AMBN, CK14, DSPP, BSP, Runx2 mRNA expression also increased (P<0.05).

CONCLUSIONS

BMP4 can significantly promote the odontogenic differentiation of iPS.

H. MH, Yaghmaei P, Mobarra N, Geramizadeh B. Efficient Production of Hepatocyte-like Cells from Human-induced Pluripotent Stem Cells by Optimizing Growth Factors

BACKGROUND

Generating hepatocytes with complete liver functions is still a challenge and developing more functional hepatocytes is needed.

OBJECTIVE

To compare various differentiation factors and protocols and introducing a preferable protocol to differentiate human-induced pluripotent stem cells (hiPSCs) into hepatocyte-like cells (HLCs).

METHODS

After 3 days of the endoderm differentiation of hiPSCs, the cells were incubated with 5 hepatocyte differentiation culture media, protocols (P), for 14 days-P1: hepatocyte growth factor and fibroblast growth factor-4 (FGF-4) for the first week and oncostatin-M and dexamethasone for the second week; P2: similar to P1 but FGF4 was used in both the first and second weeks; P3: similar to P1 but FGF-4 was not used; P4: similar to P1 but FGF-4 and dexamethasone were not used; and P5: similar to P1 but FGF-4 and oncostatin-M were not used. After 17 days, characterization was done by qRT-PCR, immunofluorescence and ELISA.

RESULTS

The mRNA expression levels of hepatocyte markers (albumin, cytokeratin-18, tyrosine aminotransferase, hepatocyte nuclear factor-4α, cytochrome-P450 7A1) increased significantly (p<0.05) in the differentiated cells by 5 different protocols. Furthermore, significant protein expression and secretion of albumin were detected in the differentiated cells by 5 different protocols. In P3, the differentiated cells had the highest exhibit of hepatocyte characteristics and in P4 they had the lowest. Moreover, in P1 and P2 similar results were observed.

CONCLUSION

Since P3 gave us the best results among all protocols, we recommend it as an efficient protocol to differentiate the functional HLCs from hiPSCs, which can improve cell therapies.

Development of hepatoma-derived, bidirectional oval-like cells as a model to study host interactions with hepatitis C virus during differentiation

Directed differentiation of human stem cells including induced pluripotent stem cells into hepatic cells potentially leads to acquired susceptibility to hepatitis C virus (HCV) infection. However, cellular determinants that change their expression during cell reprogramming or hepatic differentiation and are pivotal for supporting the HCV life cycle remain unclear. In this study, by introducing a set of reprogramming factors, we established HuH-7-derived oval-like cell lines, Hdo-17 and -23, which possess features of bipotential liver precursors. Upon induction of hepatocyte differentiation, expression of mature hepatocyte markers and hepatoblast markers in cells increased and decreased, respectively. In contrast, in response to cholangiocytic differentiation induction, gene expression of epithelium markers increased and cells formed round cysts with a central luminal space. Hdo cells lost their susceptibility to HCV infection and viral RNA replication. Hepatic differentiation of Hdo cells potentially led to recovery of permissiveness to HCV RNA replication. Gene expression profiling showed that most host-cell factors known to be involved in the HCV life cycle, except CD81, are expressed in Hdo cells comparable to HuH-7 cells. HCV pseudoparticle infectivity was significantly but partially recovered by ectopic expression of CD81, suggesting possible involvement of additional unidentified factors in HCV entry. In addition, we identified miR200a-3p, which is highly expressed in Hdo cells and stem cells but poorly expressed in differentiated cells and mature hepatocytes, as a novel negative regulator of HCV replication. In conclusion, our results showed that epigenetic reprogramming of human hepatoma cells potentially changes their permissivity to HCV.

Neural differentiation of human embryonic stem cells induced by the transgene-mediated overexpression of single transcription factors

Pluripotent human embryonic stem cells (hESCs) can differentiate into multiple cell lineages, thus, providing one of the best platforms to study molecular mechanisms during cell differentiation. Recently, we have reported rapid and efficient differentiation of hESCs into functional neurons by introducing a cocktail of synthetic mRNAs encoding five transcription factors (TFs): NEUROG1, NEUROG2, NEUROG3, NEUROD1, and NEUROD2. Here we further tested a possibility that even single transcription factors, when expressed ectopically, can differentiate hESCs into neurons. To this end, we established hESC lines in which each of these TFs can be overexpressed by the doxycycline-inducible piggyBac vector. The overexpression of any of these five TFs indeed caused a rapid and rather uniform differentiation of hESCs, which were identified as neurons based on their morphologies, qRT-PCR, and immunohistochemistry. Furthermore, calcium-imaging analyses and patch clamp recordings demonstrated that these differentiated cells are electrophysiologically functional. Interestingly, neural differentiations occurred despite the cell culture conditions that rather promote the maintenance of the undifferentiated state. These results indicate that over-expression of each of these five TFs can override the pluripotency-specific gene network and force hESCs to differentiate into neurons.

Human induced-pluripotent stem cell-derived hepatocyte-like cells as an in vitro model of human hepatitis B virus infection

In order to understand the life cycle of hepatitis B virus (HBV) and to develop efficient anti-HBV drugs, a useful in vitro cell culture system which allows HBV infection and recapitulates virus-host interactions is essential; however, pre-existing in vitro HBV infection models are often problematic. Here, we examined the potential of human induced-pluripotent stem (iPS) cell-derived hepatocyte-like cells (iPS-HLCs) as an in vitro HBV infection model. Expression levels of several genes involved in HBV infection, including the sodium taurocholate cotransporting polypeptide (NTCP) gene, were gradually elevated as the differentiation status of human iPS cells proceeded to iPS-HLCs. The mRNA levels of these genes were comparable between primary human hepatocytes (PHHs) and iPS-HLCs. Following inoculation with HBV, we found significant production of HBV proteins and viral RNAs in iPS-HLCs. The three major forms of the HBV genome were detected in iPS-HLCs by Southern blotting analysis. Anti-HBV agents entecavir and Myrcludex-B, which are a nucleoside analogue reverse transcriptase inhibitor and a synthetic pre-S1 peptide, respectively, significantly inhibited HBV infection in iPS-HLCs. These data demonstrate that iPS-HLCs can be used as a promising in vitro HBV infection model.

Oncostatin M in William's E medium is suitable for initiation of hepatocyte differentiation in human induced pluripotent stem cells

William's E (WE) is a suitable medium for the differentiation of human induced pluripotent stem (iPS) cells to the hepatocyte lineage. The aim of the present study was to investigate various growth factors in their ability to promote hepatocyte differentiation of iPS cells in WE medium. Human iPS 201B7 cells were cultured in WE medium supplemented with growth factors, and mRNA expression levels and promoter activities of α‑fetoprotein (AFP) and albumin were examined by reverse transcription‑quantitative polymerase chain reaction and luciferase assay, respectively. In addition, time course analysis of AFP mRNA expression was performed in 201B7 cells cultured in WE medium supplemented with oncostatin M. The results demonstrated that mRNA expression levels of AFP were significantly elevated by most growth factors tested as supplements in WE medium, except all‑trans retinoic acid, compared with cells cultured in ReproFF (a medium that maintains pluripotency). The highest increase in AFP mRNA expression levels was observed by oncostatin M stimulation. Albumin mRNA expression levels were increased by all‑trans retinoic acid and insulin‑transferrin‑selenium supplementation in WE medium compared with cells cultured in ReproFF. Oncostatin M supplementation significantly stimulated the promoter activity of the AFP gene, but no growth factor tested significantly stimulated the promoter activity of the albumin gene. By time course analysis, significant increase of AFP mRNA expression was observed on the sixth day post‑stimulation, compared with cells cultured in WE medium alone. In conclusion, the present study demonstrated that oncostatin M supplementation in WE medium was sufficient to initiate hepatocyte differentiation in iPS cells.

Isolation and expansion of human pluripotent stem cell-derived hepatic progenitor cells by growth factor defined serum-free culture conditions

Limited growth potential, narrow ranges of sources, and difference in variability and functions from batch to batch of primary hepatocytes cause a problem for predicting drug-induced hepatotoxicity during drug development. Human pluripotent stem cell (hPSC)-derived hepatocyte-like cells in vitro are expected as a tool for predicting drug-induced hepatotoxicity. Several studies have already reported efficient methods for differentiating hPSCs into hepatocyte-like cells, however its differentiation process is time-consuming, labor-intensive, cost-intensive, and unstable. In order to solve this problem, expansion culture for hPSC-derived hepatic progenitor cells, including hepatic stem cells and hepatoblasts which can self-renewal and differentiate into hepatocytes should be valuable as a source of hepatocytes. However, the mechanisms of the expansion of hPSC-derived hepatic progenitor cells are not yet fully understood. In this study, to isolate hPSC-derived hepatic progenitor cells, we tried to develop serum-free growth factor defined culture conditions using defined components. Our culture conditions were able to isolate and grow hPSC-derived hepatic progenitor cells which could differentiate into hepatocyte-like cells through hepatoblast-like cells. We have confirmed that the hepatocyte-like cells prepared by our methods were able to increase gene expression of cytochrome P450 enzymes upon encountering rifampicin, phenobarbital, or omeprazole. The isolation and expansion of hPSC-derived hepatic progenitor cells in defined culture conditions should have advantages in terms of detecting accurate effects of exogenous factors on hepatic lineage differentiation, understanding mechanisms underlying self-renewal ability of hepatic progenitor cells, and stably supplying functional hepatic cells.

Prediction of Differentiation Tendency Toward Hepatocytes from Gene Expression in Undifferentiated Human Pluripotent Stem Cells

Functional hepatocytes derived from human pluripotent stem cells (hPSCs) have potential as tools for predicting drug-induced hepatotoxicity in the early phases of drug development. However, the propensity of hPSC lines to differentiate into specific lineages is reported to differ. The ability to predict low propensity of hPSCs to differentiate into hepatocytes would facilitate the selection of useful hPSC clones and substantially accelerate development of hPSC-derived hepatocytes for pharmaceutical research. In this study, we compared the expression of genes associated with hepatic differentiation in five hPSC lines including human ES cell line, H9, which is known to differentiate into hepatocytes, and an hPSC line reported with a poor propensity for hepatic differentiation. Genes distinguishing between undifferentiated hPSCs, hPSC-derived hepatoblast-like differentiated cells, and primary human hepatocytes were drawn by two-way cluster analysis. The order of expression levels of genes in undifferentiated hPSCs was compared with that in hPSC-derived hepatoblast-like cells. Three genes were selected as predictors of low propensity for hepatic differentiation. Expression of these genes was investigated in 23 hPSC clones. Review of representative cells by induction of hepatic differentiation suggested that low prediction scores were linked with low hepatic differentiation. Thus, our model using gene expression ranking and bioinformatic analysis could reasonably predict poor differentiation propensity of hPSC lines.

Generation of human pluripotent stem cell-derived hepatocyte-like cells for drug toxicity screening

Because drug-induced liver injury is one of the main reasons for drug development failures, it is important to perform drug toxicity screening in the early phase of pharmaceutical development. Currently, primary human hepatocytes are most widely used for the prediction of drug-induced liver injury. However, the sources of primary human hepatocytes are limited, making it difficult to supply the abundant quantities required for large-scale drug toxicity screening. Therefore, there is an urgent need for a novel unlimited, efficient, inexpensive, and predictive model which can be applied for large-scale drug toxicity screening. Human embryonic stem (ES) cells and induced pluripotent stem (iPS) cells are able to replicate indefinitely and differentiate into most of the body's cell types, including hepatocytes. It is expected that hepatocyte-like cells generated from human ES/iPS cells (human ES/iPS-HLCs) will be a useful tool for drug toxicity screening. To apply human ES/iPS-HLCs to various applications including drug toxicity screening, homogenous and functional HLCs must be differentiated from human ES/iPS cells. In this review, we will introduce the current status of hepatocyte differentiation technology from human ES/iPS cells and a novel method to predict drug-induced liver injury using human ES/iPS-HLCs.

Determination of Functional Activity of Human iPSC-Derived Hepatocytes by Measurement of CYP Metabolism

The advent of induced pluripotent stem cell (iPSC) technology has enabled the modeling of an array of specific human disease phenotypes, aiding in the increasingly important and indispensable understanding of disease progression and pathogenesis. Pluripotent stem cell-derived hepatocytes present a new avenue for drug screening and personalized drug testing toward precision medicine. CYP450 microsomal enzymes play a critical role in drug metabolism. Hence, CYP activity measurement of iPSC-derived hepatocytes is a vital prerequisite, to ensure metabolic functionality before proceeding to drug testing. Herein, we describe the protocol for measurement of different CYP450 enzyme activities in human iPSC-derived hepatocytes.

Parametric analysis of colony morphology of non-labelled live human pluripotent stem cells for cell quality control

Given the difficulties inherent in maintaining human pluripotent stem cells (hPSCs) in a healthy state, hPSCs should be routinely characterized using several established standard criteria during expansion for research or therapeutic purposes. hPSC colony morphology is typically considered an important criterion, but it is not evaluated quantitatively. Thus, we designed an unbiased method to evaluate hPSC colony morphology. This method involves a combination of automated non-labelled live-cell imaging and the implementation of morphological colony analysis algorithms with multiple parameters. To validate the utility of the quantitative evaluation method, a parent cell line exhibiting typical embryonic stem cell (ESC)-like morphology and an aberrant hPSC subclone demonstrating unusual colony morphology were used as models. According to statistical colony classification based on morphological parameters, colonies containing readily discernible areas of differentiation constituted a major classification cluster and were distinguishable from typical ESC-like colonies; similar results were obtained via classification based on global gene expression profiles. Thus, the morphological features of hPSC colonies are closely associated with cellular characteristics. Our quantitative evaluation method provides a biological definition of ‘hPSC colony morphology’, permits the non-invasive monitoring of hPSC conditions and is particularly useful for detecting variations in hPSC heterogeneity.

Hepatocyte-like cells derived from induced pluripotent stem cells

The discovery that coordinated expression of a limited number of genes can reprogram differentiated somatic cells to induced pluripotent stem cells (iPSC) has opened novel possibilities for developing cell-based models of diseases and regenerative medicine utilizing cell reprogramming or cell transplantation. Directed differentiation of iPSCs can potentially generate differentiated cells belonging to any germ layer, including cells with hepatocyte-like morphology and function. Such cells, termed iHeps, can be derived by sequential cell signaling using available information on embryological development or by forced expression of hepatocyte-enriched transcription factors. In addition to the translational aspects of iHeps, the experimental findings have provided insights into the mechanisms of cell plasticity that permit one cell type to transition to another. However, iHeps generated by current methods do not fully exhibit all characteristics of mature hepatocytes, highlighting the need for additional research in this area. Here we summarize the current approaches and achievements in this field and discuss some existing hurdles and emerging approaches for improving iPSC differentiation, as well as maintaining such cells in culture for increasing their utility in disease modeling and drug development.

[Establishment of a Method of Hepatocyte Differentiation from Human Pluripotent Stem Cells for Innovative Drug Development]

Hepatocyte-like cells differentiated from human pluripotent stem cells (such as human embryonic stem (ES) cells and induced pluripotent stem (iPS) cells) are expected to be utilized in drug screening. However, the hepatocyte differentiation efficiency and hepatic functions of hepatocyte-like cells were not sufficient to perform ES/iPS cell-based drug discovery. Therefore, we decided to improve the method of hepatocyte differentiation from human ES/iPS cells. To enhance this hepatocyte differentiation efficiency, hepatocyte-related transcription factors, such as forkhead box protein A2 (FOXA2) and hepatocyte nuclear factor 1 alpha (HNF1α), were overexpressed during the hepatocyte differentiation process. In addition, to enhance the functions of hepatocyte-like cells, these cells were cultured in three dimensional (3D) conditions using a Nanopillar plate. By FOXA2 and HNF1α overexpression, human ES/iPS cells could efficiently (more than 80%) differentiate into albumin-positive hepatocyte-like cells. Various hepatic functions, including albumin secretion and drug metabolism capacities, of the hepatocyte-like cells were significantly enhanced by performing 3D cell culture. These results suggest that the method of hepatocyte differentiation could be improved by using gene transfer and 3D cell culture technologies. We believe that these new hepatocyte-like cells would be useful tools in drug development.

Screening of Human cDNA Library Reveals Two differentiation-Related Genes, HHEX and HLX, as Promoters of Early Phase Reprogramming toward Pluripotency

Gene screenings have identified a number of reprogramming factors that induce pluripotency from somatic cells. However, the screening methods have mostly considered only factors that maintain pluripotency in embryonic stem cells, ignoring a potentially long list of other contributing factors involved. To expand the search, we developed a new screening method that examined 2,008 human genes in the generation of human induced pluripotent stem cells (iPSCs), including not only pluripotent genes but also differentiation-related genes that suppress pluripotency. We found the top 100 genes that increased reprogramming efficiency and discovered they contained many differentiation-related genes and homeobox genes. We selected two, HHEX and HLX, for further analysis. These genes enhanced the appearance of premature reprograming cells in the early phase of human iPSC induction, but had inhibitory effect on the late phase. In addition, when expressed in human iPSCs, HHEX and HLX interfered with the pluripotent state, indicating inverse effects on somatic reprograming and pluripotent maintenance. These results demonstrate that our screening is useful for identifying differentiation-related genes in somatic reprograming. Stem Cells 2016;34:2661-2669.

Improved Survival and Initiation of Differentiation of Human Induced Pluripotent Stem Cells to Hepatocyte-Like Cells upon Culture in William's E Medium followed by Hepatocyte Differentiation Inducer Treatment

BACKGROUND

Hepatocyte differentiation inducer (HDI) lacks both glucose and arginine, but is supplemented with galactose and ornithine, and is added together with other reagents such as apoptosis inhibitor and oncostatin M. Although human induced pluripotent stem (iPS) cells initiate hepatocyte differentiation, most die within 7 days. In this study, we investigated both HDI and conventional media for their potential to improve cell survival.

MATERIALS AND METHODS

201B7 iPS cells were cultured in conventional media. This consisted of three cycles of 5-day culture in William's E (WE) medium, followed by a 2-day culture in HDI.

RESULTS

Expression levels of α-feto protein (AFP) were higher in cells cultured in WE and in Dulbecco's Modified Eagle's Medium/Nutrient F-12 Ham (DF12). 201B7 cells expressed the highest AFP and albumin (ALB) when cultured in HDI for 2 days following 7-day culture in WE. After three cycles of 5-day culture in WE followed by 2 days in HDI, 201B7 cells expressed AFP and ALB 54 ± 2.3 (average ± standard deviation) and 73 ± 15.1 times higher, respectively, than those cultured in ReproFF (feeder-free condition).

CONCLUSION

201B7 cells survived culture in WE for 7 days followed HDI for 2 days. After three cycles of culture under these conditions, hepatocyte differentiation was enhanced, as evidenced by increased AFP and ALB expression.

An Optimal Medium Supplementation Regimen for Initiation of Hepatocyte Differentiation in Human Induced Pluripotent Stem Cells

Human induced pluripotent stem (hiPS) cells are an ideal source for hepatocytes. Glucose and arginine are necessary for cells to survive. Hepatocytes have galactokinase (GALK), which metabolizes galactose for gluconeogenesis, and ornithine transcarbamylase (OTC), which converts ornithine to arginine in the urea cycle. Hepatocyte selection medium (HSM) lacks both glucose and arginine, but contains galactose and ornithine. Although human primary hepatocytes survive in HSM, all the hiPS cells die in 3 days. The aim of this study was to modify HSM so as to initiate hepatocyte differentiation in hiPS cells within 2 days. Hepatocyte differentiation initiating medium (HDI) was prepared by adding oncostatin M (10 ng/ml), hepatocyte functional proliferation inducer (10 nM), 2,2'-methylenebis (1,3-cyclohexanedione) (M50054) (100 μg/ml), 1× non-essential amino acid, 1× sodium pyruvate, nicotinamide (1.2 mg/ml), L-proline (30 ng/ml), and L-glutamine (0.3 mg/ml) to HSM. HiPS cells (201B7 cells) were cultured in HDI for 2 days. RNA was isolated, used as template for cDNA, and subjected to real-time quantitative polymerase chain reaction. Alpha-fetoprotein, γ-glutamyl transpeptidase, and delta-like 1 were upregulated. Expression of albumin was not observed. Expression of transcription factors specific to hepatocytes was upregulated. The expression of GALK2, OTC, and CYP3A4 were increased. In conclusion, differentiation of 201B7 cells to hepatoblast-like cells was initiated in HDI. Limitations were small number of cells were obtained, and the cells with HDI were not mature hepatocytes.

Hepatic differentiation of human pluripotent stem cells in miniaturized format suitable for high-throughput screen

The establishment of protocols to differentiate human pluripotent stem cells (hPSCs) including embryonic (ESC) and induced pluripotent (iPSC) stem cells into functional hepatocyte-like cells (HLCs) creates new opportunities to study liver metabolism, genetic diseases and infection of hepatotropic viruses (hepatitis B and C viruses) in the context of specific genetic background. While supporting efficient differentiation to HLCs, the published protocols are limited in terms of differentiation into fully mature hepatocytes and in a smaller-well format. This limitation handicaps the application of these cells to high-throughput assays. Here we describe a protocol allowing efficient and consistent hepatic differentiation of hPSCs in 384-well plates into functional hepatocyte-like cells, which remain differentiated for more than 3weeks. This protocol affords the unique opportunity to miniaturize the hPSC-based differentiation technology and facilitates screening for molecules in modulating liver differentiation, metabolism, genetic network, and response to infection or other external stimuli.

Transcription Factors and Medium Suitable for Initiating the Differentiation of Human-Induced Pluripotent Stem Cells to the Hepatocyte Lineage

Transcription factors and culture media were investigated to determine the condition to initiate the differentiation of human-induced pluripotent stem (iPS) cells most efficiently. The expression of genes in human adult liver was compared with that in 201B7 cells (iPS cells) using cDNA microarray analysis. Episomal plasmids expressing transcription factors were constructed. 201B7 cells were transfected with the episomal plasmids and cultured in ReproFF (feeder-free media maintaining pluripotency), Leibovitz-15 (L15), William's E (WE), or Dulbecco's modified Eagle medium/Nutrient F-12 Ham (DF12) for 7 days. RNA was isolated and subjected to real-time quantitative PCR to analyze the expression of alpha-feto protein (AFP) and albumin. cDNA microarray analysis revealed 16 transcription factors that were upregulated in human adult liver relative to that in 201B7 cells. Episomal plasmids expressing these 16 genes were transfected into 201B7 cells. CCAAT/enhancer-binding protein alpha (CEBPA), CCAAT/enhancer-binding protein beta (CEBPB), forkhead box A1 (FOXA1), and forkhead box A3 (FOXA3) up-regulated AFP and down-regulated Nanog. These four genes were further analyzed. The expression of AFP and albumin was the highest in 201B7 cells transfected with the combination of CEBPA, CEBPB, FOXA1, and FOXA3 and cultured in WE. The combination of CEBPA, CEBPB, FOXA1, and FOXA3 was suitable for 201B7 cells to initiate differentiation to the hepatocyte lineage and WE was the most suitable medium for culture after transfection. J. Cell. Biochem. 117: 2001-2009, 2016. © 2016 Wiley Periodicals, Inc.

Hepatic maturation of human iPS cell-derived hepatocyte-like cells by ATF5, c/EBPα, and PROX1 transduction

Hepatocyte-like cells differentiated from human iPS cells (human iPS-HLCs) are expected to be utilized in drug development and research. However, recent hepatic characterization of human iPS-HLCs showed that these cells resemble fetal hepatocytes rather than adult hepatocytes. Therefore, in this study, we aimed to develop a method to enhance the hepatic function of human iPS-HLCs. Because the gene expression levels of the hepatic transcription factors (activating transcription factor 5 (ATF5), CCAAT/enhancer-binding protein alpha (c/EBPα), and prospero homeobox protein 1 (PROX1)) in adult liver were significantly higher than those in human iPS-HLCs and fetal liver, we expected that the hepatic functions of human iPS-HLCs could be enhanced by adenovirus (Ad) vector-mediated ATF5, c/EBPα, and PROX1 transduction. The gene expression levels of cytochrome P450 (CYP) 2C9, 2E1, alpha-1 antitrypsin, transthyretin, Na+/taurocholate cotransporting polypeptide, and uridine diphosphate glucuronosyl transferase 1A1 and protein expression levels of CYP2C9 and CYP2E1 were upregulated by ATF5, c/EBPα, and PROX1 transduction. These results suggest that the hepatic functions of the human iPS-HLCs could be enhanced by ATF5, c/EBPα, and PROX1 transduction. Our findings would be useful for the hepatic maturation of human iPS-HLCs.

The basic helix-loop-helix transcription factor, Mist1, induces maturation of mouse fetal hepatoblasts

Hepatic stem/progenitor cells, hepatoblasts, have a high proliferative ability and can differentiate into mature hepatocytes and cholangiocytes. Therefore, these cells are considered to be useful for regenerative medicine and drug screening for liver diseases. However, it is problem that in vitro maturation of hepatoblasts is insufficient in the present culture system. In this study, a novel regulator to induce hepatic differentiation was identified and the molecular function of this factor was examined in embryonic day 13 hepatoblast culture with maturation factor, oncostatin M and extracellular matrices. Overexpression of the basic helix-loop-helix type transcription factor, Mist1, induced expression of mature hepatocytic markers such as carbamoyl-phosphate synthetase1 and several cytochrome P450 (CYP) genes in this culture system. In contrast, Mist1 suppressed expression of cholangiocytic markers such as Sox9, Sox17, Ck19, and Grhl2. CYP3A metabolic activity was significantly induced by Mist1 in this hepatoblast culture. In addition, Mist1 induced liver-enriched transcription factors, CCAAT/enhancer-binding protein α and Hepatocyte nuclear factor 1α, which are known to be involved in liver functions. These results suggest that Mist1 partially induces mature hepatocytic expression and function accompanied by the down-regulation of cholangiocytic markers.

Hepatocyte selection medium eliminating induced pluripotent stem cells among primary human hepatocytes

Hepatic insufficiency is a fatal liver disease with a significant decrease in functioning hepatocytes. If hepatocytes could be generated from human induced pluripotent stem (hiPS) cells and transplanted into patients with hepatic insufficiency, the disease may become curable. However, a major limitation to this therapeutic strategy is due to the tumorigenicity of hiPS cells and their ability to form cancer. Current methods for eliminating unwanted hiPS cells use genetic manipulation or reagents that are potentially hazardous for hepatocytes; therefore, revised methods are necessary and anticipated. Glucose and arginine are essential cell culture medium ingredients for the survival of most cells, including hiPS cells. However, hepatocytes can produce its own glucose and arginine through galactokinase and ornithine transcarbamylase, respectively. Therefore, it was hypothesized that unwanted hiPS cells could be eliminated in a medium without glucose and arginine, and supplemented with galactose and ornithine instead. This modified medium has been established as hepatocyte selection medium (HSM). So far, attempts to generate a pure colony of mature hepatocytes from hiPS cells have not been successful. After establishment of co-culture in HSM, primary human hepatocytes survive while hiPS cells die within three days. Our latest results regarding a modification of HSM will be introduced in this manuscript.

Two Effective Routes for Removing Lineage Restriction Roadblocks: From Somatic Cells to Hepatocytes

The conversion of somatic cells to hepatocytes has fundamentally re-shaped traditional concepts regarding the limited resources for hepatocyte therapy. With the various induced pluripotent stem cell (iPSC) generation routes, most somatic cells can be effectively directed to functional stem cells, and this strategy will supply enough pluripotent material to generate promising functional hepatocytes. However, the major challenges and potential applications of reprogrammed hepatocytes remain under investigation. In this review, we provide a summary of two effective routes including direct reprogramming and indirect reprogramming from somatic cells to hepatocytes and the general potential applications of the resulting hepatocytes. Through these approaches, we are striving toward the goal of achieving a robust, mature source of clinically relevant lineages.

A Cytotoxic Antibody Recognizing Lacto-N-fucopentaose I (LNFP I) on Human Induced Pluripotent Stem (hiPS) Cells

We have generated a mouse monoclonal antibody (R-17F, IgG1 subtype) specific to human induced pluripotent stem (hiPS)/embryonic stem (ES) cells by using a hiPS cell line as an antigen. Triple-color confocal immunostaining images of hiPS cells with R-17F indicated that the R-17F epitope was expressed exclusively and intensively on the cell membranes of hiPS cells and co-localized partially with those of SSEA-4 and SSEA-3. Lines of evidence suggested that the predominant part of the R-17F epitope was a glycolipid. Upon TLC blot of total lipid extracts from hiPS cells with R-17F, one major R-17F-positive band was observed at a slow migration position close to that of anti-blood group H1(O) antigen. MALDI-TOF-MS and MS(n) analyses of the purified antigen indicated that the presumptive structure of the R-17F antigen was Fuc-Hex-HexNAc-Hex-Hex-Cer. Glycan microarray analysis involving 13 different synthetic oligosaccharides indicated that R-17F bound selectively to LNFP I (Fucα1-2Galβ1-3GlcNAcβ1-3Galβ1-4Glc). A critical role of the terminal Fucα1-2 residue was confirmed by the selective disappearance of R-17F binding to the purified antigen upon α1-2 fucosidase digestion. Most interestingly, R-17F, when added to hiPS/ES cell suspensions, exhibited potent dose-dependent cytotoxicity. The cytotoxic effect was augmented markedly upon the addition of the secondary antibody (goat anti-mouse IgG1 antibody). R-17F may be beneficial for safer regenerative medicine by eliminating residual undifferentiated hiPS cells in hiPS-derived regenerative tissues, which are considered to be a strong risk factor for carcinogenesis.

Synergistic effects of FGF-2 and Activin A on early neural differentiation of human pluripotent stem cells

Neural differentiation is an important target of human embryonic stem cells, which provide a source for cell-based therapy, developmental biology, and pharmaceutical research. Previous studies revealed that inhibition of the bone morphogenetic protein is required for neural induction from human embryonic stem cells. On the contrary, the functions of fibroblast growth factors and Activin/Nodal signaling are controversial. Fibroblast growth factor-2 and Activin/Nodal pathways exert divergent influences on human embryonic stem cell concerning the maintenance of both pluripotency and cellular differentiation. We hypothesized that the combination of fibroblast growth factor-2 and Activin A at various concentrations synergistically exerts diverse effects on cell differentiation. To determine the effects of fibroblast growth factor-2 and Activin A on cellular differentiation into neural lineages, we examined the expression of neural differentiation markers in human embryonic stem cells treated with fibroblast growth factor-2 and/or Activin A at various concentrations in a growth factor-defined serum-free medium in short-term culture. In this study, we provide evidence that fibroblast growth factor-2 and Activin A synergistically regulated the initiation of human embryonic stem cell differentiation into neural cell lineages even though human embryonic stem cells autonomously differentiate into neural cell lineages.

Three-dimensional cell culture technique and pathophysiology

Three-dimensional (3D) tissue constructs consisting of human cells have opened a new avenue for tissue engineering, pharmaceutical and pathophysiological applications, and have great potential to estimate the dynamic pharmacological effects of drug candidates, metastasis processes of cancer cells, and toxicity expression of nano-materials, as a 3D-human tissue model instead of in vivo animal experiments. However, most 3D-cellular constructs are a cell spheroid, which is a heterogeneous aggregation, and thus the reconstruction of the delicate and precise 3D-location of multiple types of cells is almost impossible. In recent years, various novel technologies to develop complex 3D-human tissues including blood and lymph capillary networks have demonstrated that physiological human tissue responses can be replicated in the nano/micro-meter ranges. Here, we provide a brief overview on current 3D-tissue fabrication technologies and their biomedical applications. 3D-human tissue models will be a powerful technique for pathophysiological applications.

Efficient Engraftment of Human Induced Pluripotent Stem Cell-Derived Hepatocyte-Like Cells in uPA/SCID Mice by Overexpression of FNK, a Bcl-xL Mutant Gene

Human liver chimeric mice are expected to be applied for drug toxicity tests and human hepatitis virus research. Human induced pluripotent stem cell-derived hepatocyte-like cells (iPSC-HLCs) are a highly attractive donor source for the generation of human liver chimeric mice because they can be produced on a large scale and established from an individual. Although these cells have been successfully used to generate human liver chimeric mice, there is still room for improvement in the repopulation efficiency. To enhance the repopulation efficacy, the human iPSC-HLCs were transduced with an adenovirus vector (Ad-FNK) expressing FNK, a hyperactive mutant gene from Bcl-xL, which was expected to inhibit apoptosis in the process of integration into liver parenchyma. We then transplanted Ad-FNK-transduced human iPSC-HLCs into urokinase-type plasminogen activator-transgenic severe combined immunodeficiency (uPA/SCID) mice (FNK mice) and evaluated the repopulation efficacy. The antiapoptotic effects of the human iPSC-HLCs were enhanced by FNK overexpression in vitro. Human albumin levels in the transplanted mice were significantly increased by transplantation of Ad-FNK-transduced human iPSC-HLCs (about 24,000 ng/ml). Immunohistochemical analysis with an anti-human αAT antibody revealed greater repopulation efficacy in the livers of FNK mice than control mice. Interestingly, the expression levels of human hepatocyte-related genes in the human iPSC-HLCs of FNK mice were much higher than those in the human iPSC-HLCs before transplantation. We succeeded in improving the repopulation efficacy of human liver chimeric mice generated by transplanting the Ad-FNK-transduced human iPSC-HLCs into uPA/SCID mice. Our method using ectopic expression of FNK was useful for generating human chimeric mice with high chimerism.

Stem cells in liver regeneration and their potential clinical applications

Stem cells constitute a population of "primitive cells" with the ability to divide indefinitely and give rise to specialized cells under special conditions. Because of these two characteristics they have received particular attention in recent decades. These cells are the primarily responsible factors for the regeneration of tissues and organs and for the healing of lesions, a feature that makes them a central key in the development of cell-based medicine, called Regenerative Medicine. The idea of wound and organ repair and body regeneration is as old as the mankind, reflecting the human desire for inhibiting aging and immortality and it is first described in the ancient Greek myth of Prometheus. It is of interest that the myth refers to liver, an organ with remarkable regenerative ability after loss of mass and function caused by liver injury or surgical resection. Over the last decade there has been an important progress in understanding liver physiology and the mechanisms underlying hepatic development and regeneration. As liver transplantation, despite its difficulties, remains the only effective therapy for advanced liver disease so far, scientific interest has nowadays been orientated towards Regenerative Medicine and the use of stem cells to repair damaged liver. This review is focused on the available literature concerning the role of stem cells in liver regeneration. It summarizes the results of studies concerning endogenous liver regeneration and stem cell experimental protocols. Moreover, this review discusses the clinical studies that have been conducted in humans so far.

HHEX promotes hepatic-lineage specification through the negative regulation of eomesodermin

Human embryonic stem cells (hESCs) could provide a major window into human developmental biology, because the differentiation methods from hESCs mimic human embryogenesis. We previously reported that the overexpression of hematopoietically expressed homeobox (HHEX) in the hESC-derived definitive endoderm (DE) cells markedly promotes hepatic specification. However, it remains unclear how HHEX functions in this process. To reveal the molecular mechanisms of hepatic specification by HHEX, we tried to identify the genes directly targeted by HHEX. We found that HHEX knockdown considerably enhanced the expression level of eomesodermin (EOMES). In addition, HHEX bound to the HHEX response element located in the first intron of EOMES. Loss-of-function assays of EOMES showed that the gene expression levels of hepatoblast markers were significantly upregulated, suggesting that EOMES has a negative role in hepatic specification from the DE cells. Furthermore, EOMES exerts its effects downstream of HHEX in hepatic specification from the DE cells. In conclusion, the present results suggest that HHEX promotes hepatic specification by repressing EOMES expression.

iPS cells: a game changer for future medicine

The induced pluripotent stem cell (iPSC) technology is instrumental in advancing the fields of disease modeling and cell transplantation. We herein discuss the various issues regarding disease modeling and cell transplantation presented in previous reports, and also describe new iPSC-based medicine including iPSC clinical trials. In such trials, iPSCs from patients can be used to predict drug responders/non-responders by analyzing the efficacy of the drug on iPSC-derived cells. They could also be used to stratify patients after actual clinical trials, including those with sporadic diseases, based on the drug responsiveness of each patient in the clinical trials. iPSC-derived cells can be used for the identification of response markers, leading to increased success rates in such trials. Since iPSCs can be used in micromedicine for drug discovery, and in macromedicine for actual clinical trials, their use would tightly connect both micro- and macromedicine. The use of iPSCs in disease modeling, cell transplantation, and clinical trials could therefore lead to significant changes in the future of medicine.