An in vitro expansion system for generation of human iPS cell-derived hepatic progenitor-like cells exhibiting a bipotent differentiation potential

Bile acid-FXR signaling facilitates the long-term maintenance of hepatic characteristics in human iPSC-derived organoids

Human induced pluripotent stem cells (iPSCs) can be differentiated into hepatocyte-like cells (iPS-Heps); however, maintaining the long-term proliferation and hepatic characteristics of iPS-Heps remains a challenge. In this study, we aimed to develop a human iPSC-derived hepatic organoid (iHO) culture system that effectively retains hepatic characteristics long term. Our original culture strategy, using bile acids and their receptor (farnesoid X receptor [FXR]) agonists, yielded human iHOs capable of long-term culture with a distinctive "grape-like" structure. Comprehensive analysis showed that these iHOs maintained hepatocyte-like phenotypes, even after multiple passages, whose gene expression profiles were consistent with those of fetal hepatocytes. In addition, the overexpression of small heterodimer partner (SHP), a downstream gene of FXR, in iHOs negatively regulated genes related to the intestine and cholangiocytes. Our data demonstrated that bile acid-FXR signaling promotes both the hepatic characteristics and proliferative potential of iHOs, offering promising potential for future applications in regenerative medicine and as a disease model.

Metabolically purified human stem cell-derived hepatocytes reveal distinct effects of Ebola and Lassa viruses

Ebola and Lassa viruses require biosafety-level-4 (BSL4) containment, infect the liver, and cause deadly hemorrhagic fevers. The cellular effects of these viruses, and whether different families of hemorrhagic-fever viruses elicit similar effects, remain fundamental questions in BSL4 virology. Here, we introduce a new metabolic selection approach to create nearly-pure hepatocytes from human pluripotent stem cells, killing non-liver cells by withholding essential nutrients. Unexpectedly, Ebola and Lassa exerted starkly different effects on human hepatocytes. Ebola infection activated the integrated stress response (ISR) and WNT pathways in hepatocytes in vitro and killed them, whereas Lassa did not. Within non-human primates, Ebola likewise infected hepatocytes and activated ISR signaling in vivo . In summary, we present a single-cell transcriptional and chromatin accessibility roadmap of human hepatocyte differentiation, purification, and viral infection.

Hepatitis B Virus-KMT2B Integration Drives Hepatic Oncogenic Processes in a Human Gene-edited Induced Pluripotent Stem Cells-derived Model

BACKGROUND & AIMS

Hepatitis B virus (HBV)-DNA integration into the host genome contributes to hepatocellular carcinoma (HCC) development. KMT2B is the second most frequent locus of HBV-DNA integration in HCC; however, its role and function remain unclear. We aimed to clarify the impact of HBV-KMT2B integration in HCC development using a human genome-edited induced pluripotent stem cell (iPSCs) model.

METHODS

Based on the genetic information on HBV-KMT2B integration in HCC, we determined its complete DNA sequence and transcript variants. To exclude the effect of other oncogenic mutations, we reproduced HBV integration in healthy donor iPSCs with an intact genome and analyzed its effects using iPSC-derived hepatic progenitor cells (HPCs) and hepatocytes (iPS-Heps).

RESULTS

The reproduced HBV-KMT2B integration significantly upregulated the proliferation of hepatic cells. Comprehensive transcriptional and epigenetic analyses revealed enhanced expression of cell cycle-related genes in hepatic cells with HBV-KMT2B integration based on perturbation of histone 3 lysine 4 tri-methylation (H3K4me3), mimicking that in the original HCC sample. Long-read RNA-sequence detected the common KMT2B transcript variants in the HCC sample and HPCs. Overexpression of the truncated variant significantly enhanced proliferation of hepatic cells, whereas HBV-KMT2B fusion transcripts did not enhance proliferation. HBV-KMT2B-integrated HPCs exhibited replication stress and DNA damage, indicating that our model initiated the process of hepatocarcinogenesis due to abnormally promoted KMT2B function.

CONCLUSIONS

Our disease model using genetically engineered iPSCs provides the first insight into both the KMT2B function in HCC development and the oncogenic processes by HBV-KMT2B integration. We clarified the novel oncogenic mechanism in HBV-related HCC due to aberrant KMT2B function.

Development of a hepatic differentiation method in 2D culture from primary human hepatocyte-derived organoids for pharmaceutical research

Human liver organoids derived from primary human hepatocytes (PHHs) are expected to be a hepatocyte source for preclinical in vitro studies of drug metabolism and disposition. Because hepatic functions of these organoids remain low, it is necessary to enhance the hepatic functions. Here, we develop a novel method for two dimensional (2D)-cultured hepatic differentiation from PHH-derived organoids by screening several compounds, cytokines, and growth factors. Hepatic gene expressions in the hepatocyte-like cells differentiated from PHH-derived organoids (Org-HEPs) were greatly increased, compared to those in PHH-derived organoids. The metabolic activities of cytochrome P450 (CYP) 1A2, CYP2C8, CYP2C19, CYP2E1, and CYP3A4 were at levels comparable to those in PHHs. The cell viability of Org-HEPs treated with hepatotoxic drugs was almost the same as that of PHHs. Thus, PHH-derived organoids could be differentiated into highly functional hepatocytes in 2D culture. Thus, Org-HEPs will be useful for pharmaceutical research, including hepatotoxicity tests.

Drug metabolic activity as a selection factor for pluripotent stem cell-derived hepatic progenitor cells

As a metabolic organ, the liver plays a variety of roles, including detoxification. It has been difficult to obtain stable supplies of hepatocytes for transplantation and for accurate hepatotoxicity determination in drug discovery research. Human pluripotent stem cells, capable of unlimited self-renewal, may be a promising source of hepatocytes. In order to develop a stable supply of embryonic stem cell (ESC)-derived hepatocytes, we have purified human ESC-derived hepatic progenitor cells with exposure to cytocidal puromycin by using their ability to metabolize drugs. Hepatic progenitor cells stably proliferated at least 220-fold over 120 days, maintaining hepatic progenitor cell-like properties. High drug-metabolizing hepatic progenitor cells can be matured into liver cells by suppressing hepatic proliferative signals. The method we developed enables the isolation and proliferation of functional hepatic progenitors from human ESCs, thereby providing a stable supply of high-quality cell resources at high efficiency. Cells produced by this method may facilitate cell therapy for hepatic diseases and reliable drug discovery research.

Dialysis based-culture medium conditioning improved the generation of human induced pluripotent stem cell derived-liver organoid in a high cell density

Human pluripotent stem cell-derived liver organoids (HLOs) have recently become a promising alternative for liver regenerative therapy. To realize this application, a large amount of human-induced pluripotent stem cells (hiPSCs) derived-liver cells are required for partial liver replacement during transplantation. This method requires stepwise induction using costly growth factors to direct the hiPSCs into the hepatic lineage. Therefore, we developed a simple dialysis-based medium conditioning that fully utilized growth factors accumulation to improve hepatic differentiation of hiPSCs at a high cell density. The results demonstrated that the dialysis culture system could accumulate the four essential growth factors required in each differentiation stage: activin A, bone morphogenetic protein 4 (BMP4), hepatocyte growth factor (HGF), and oncostatin M (OSM). As a result, this low lactate culture environment allowed high-density bipotential hepatic differentiation of up to 4.5 × 10⁷ cells/mL of human liver organoids (HLOs), consisting of hiPSC derived-hepatocyte like cells (HLCs) and cholangiocyte like-cells (CLCs). The differentiated HLOs presented a better or comparable hepatic marker and hepatobiliary physiology to the one that differentiated in suspension culture with routine daily medium replacement at a lower cell density. This simple miniaturized dialysis culture system demonstrated the feasibility of cost-effective high-density hepatic differentiation with minimum growth factor usage.

Pluripotent Stem Cell-derived Strategies to Treat Acute Liver Failure: Current Status and Future Directions

Liver disease has long been a heavy health and economic burden worldwide. Once the disease is out of control and progresses to end-stage or acute organ failure, orthotopic liver transplantation (OLT) is the only therapeutic alternative, and it requires appropriate donors and aggressive administration of immunosuppressive drugs. Therefore, hepatocyte transplantation (HT) and bioartificial livers (BALs) have been proposed as effective treatments for acute liver failure (ALF) in clinics. Although human primary hepatocytes (PHs) are an ideal cell source to support these methods, the large demand and superior viability of PH is needed, which restrains its wide usage. Thus, a finding alternative to meet the quantity and quality of hepatocytes is urgent. In this context, human pluripotent stem cells (PSC), which have unlimited proliferative and differential potential, derived hepatocytes are a promising renewable cell source. Recent studies of the differentiation of PSC into hepatocytes has provided evidence that supports their clinical application. In this review, we discuss the recent status and future directions of the potential use of PSC-derived hepatocytes in treating ALF. We also discuss opportunities and challenges of how to promote such strategies in the common applications in clinical treatments.

Drug metabolic activity is a critical cell-intrinsic determinant for selection of hepatocytes during long-term culture

BACKGROUND

The liver plays an important role in various metabolic processes, including protein synthesis, lipid and drug metabolisms and detoxifications. Primary culture of hepatocytes is used for the understanding of liver physiology as well as for the drug development. Hepatocytes are, however, hardly expandable in vitro making it difficult to secure large numbers of cells from one donor. Alternatively, systems using animal models and hepatocellular carcinoma cells have been established, but interspecies differences, variation between human cell sources and limited hepatic functions are among the challenges faced when using these models. Therefore, there is still a need for a highly stable method to purify human hepatocytes with functional sufficiency. In this study, we aimed to establish an in vitro long-term culture system that enables stable proliferation and maintenance of human hepatocytes to ensure a constant supply.

METHODS

We first established a growth culture system for hepatocytes derived from patients with drug-induced liver injury using fetal mouse fibroblasts and EMUKK-05 medium. We then evaluated the morphology, proliferative capacity, chromosome stability, gene and protein expression profiles, and drug metabolic capacity of hepatocytes in early, middle and late passages with and without puromycin. In addition, hepatic maturation in 3D culture was evaluated from morphological and functional aspects.

RESULTS

In our culture system, the stable proliferation of human hepatocytes was achieved by co-culturing with mouse fetal fibroblasts, resulting in dedifferentiation into hepatic progenitor-like cells. We purified human hepatocytes by selection with cytocidal puromycin and cultured them for more than 60 population doublings over a span of more than 350 days. Hepatocytes with high expression of cytochrome P450 genes survived after exposure to cytocidal antibiotics because of enhanced drug-metabolizing activity.

CONCLUSIONS

These results show that this simple culture system with usage of the cytocidal antibiotics enables efficient hepatocyte proliferation and is an effective method for generating a stable supply of hepatocytes for drug discovery research at a significant cost reduction.

Induced Pluripotent Stem Cells for the Treatment of Liver Diseases: Novel Concepts

Millions of people worldwide with incurable liver disease die because of inadequate treatment options and limited availability of donor organs for liver transplantation. Regenerative medicine as an innovative approach to repairing and replacing cells, tissues, and organs is undergoing a major revolution due to the unprecedented need for organs for patients around the world. Induced pluripotent stem cells (iPSCs) have been widely studied in the field of liver regeneration and are considered to be the most promising candidate therapies. This review will conclude the current state of efforts to derive human iPSCs for potential use in the modeling and treatment of liver disease.

Efficient hepatic differentiation and regeneration potential under xeno-free conditions using mass-producible amnion-derived mesenchymal stem cells

BACKGROUND

Amnion-derived mesenchymal stem cells (AM-MSCs) are an attractive source of stem cell therapy for patients with irreversible liver disease. However, there are obstacles to their use due to low efficiency and xeno-contamination for hepatic differentiation.

METHODS

We established an efficient protocol for differentiating AM-MSCs into hepatic progenitor cells (HPCs) by analyzing transcriptome-sequencing data. Furthermore, to generate the xeno-free conditioned differentiation protocol, we replaced fetal bovine serum (FBS) with polyvinyl alcohol (PVA). We investigated the hepatocyte functions with the expression of mRNA and protein, secretion of albumin, and activity of CYP3A4. Finally, to test the transplantable potential of HPCs, we transferred AM-MSCs along with hepatic progenitors after differentiated days 11, 12, and 13 based on the expression of hepatocyte-related genes and mitochondrial function. Further, we established a mouse model of acute liver failure using a thioacetamide (TAA) and cyclophosphamide monohydrate (CTX) and transplanted AM-HPCs in the mouse model through splenic injection.

RESULTS

We analyzed gene expression from RNA sequencing data in AM-MSCs and detected downregulation of hepatic development-associated genes including GATA6, KIT, AFP, c-MET, FGF2, EGF, and c-JUN, and upregulation of GSK3. Based on this result, we established an efficient hepatic differentiation protocol using the GSK3 inhibitor, CHIR99021. Replacing FBS with PVA resulted in improved differentiation ability, such as upregulation of hepatic maturation markers. The differentiated hepatocyte-like cells (HLCs) not only synthesized and secreted albumin, but also metabolized drugs by the CYP3A4 enzyme. The best time for translation of AM-HPCs was 12 days from the start of differentiation. When the AM-HPCs were transplanted into the liver failure mouse model, they settled in the damaged livers and differentiated into hepatocytes.

CONCLUSION

This study offers an efficient and xeno-free conditioned hepatic differentiation protocol and shows that AM-HPCs could be used as transplantable therapeutic materials. Thus, we suggest that AM-MSC-derived HPCs are promising cells for treating liver disease.

Kruppel-like factor 15 induces the development of mature hepatocyte-like cells from hepatoblasts

The liver is an important metabolic organ that controls homeostasis in the body. Moreover, it functions as a hematopoietic organ, while its metabolic function is low during development. Hepatocytes, which are parenchymal cells of the liver, acquire various metabolic functions by the maturation of hepatic progenitor cells during the fetal period; however, this molecular mechanism is still unclear. In this study, Kruppel-like factor 15 (KLF15) was identified as a new regulator of hepatic maturation through a comprehensive analysis of the expression of transcriptional regulators in mouse fetal and adult hepatocytes. KLF15 is a transcription factor whose expression in the liver increases from the embryonic stage throughout the developmental process. KLF15 induced the overexpression of liver function genes in mouse embryonic hepatocytes. Furthermore, we found that the expression of KLF15 could also induce the expression of liver function genes in hepatoblasts derived from human induced pluripotent stem cells (iPSCs). Moreover, KLF15 increased the promoter activity of tyrosine aminotransferase, a liver function gene. KLF15 also suppressed the proliferation of hepatoblasts. These results suggest that KLF15 induces hepatic maturation through the transcriptional activation of target genes and cell cycle control.

The Application of Induced Pluripotent Stem Cells Against Liver Diseases: An Update and a Review

Liver diseases are a major health concern globally, and are associated with poor survival and prognosis of patients. This creates the need for patients to accept the main alternative treatment of liver transplantation to prevent progression to end-stage liver disease. Investigation of the molecular mechanisms underpinning complex liver diseases and their pathology is an emerging goal of stem cell scope. Human induced pluripotent stem cells (hiPSCs) derived from somatic cells are a promising alternative approach to the treatment of liver disease, and a prospective model for studying complex liver diseases. Here, we review hiPSC technology of cell reprogramming and differentiation, and discuss the potential application of hiPSC-derived liver cells, such as hepatocytes and cholangiocytes, in refractory liver-disease modeling and treatment, and drug screening and toxicity testing. We also consider hiPSC safety in clinical applications, based on genomic and epigenetic alterations, tumorigenicity, and immunogenicity.

Liver bioengineering: Recent trends/advances in decellularization and cell sheet technologies towards translation into the clinic

Development of novel technologies provides the best tissue constructs engineering and maximizes their therapeutic effects in regenerative therapy, especially for liver dysfunctions. Among the currently investigated approaches of tissue engineering, scaffold-based and scaffold-free tissues are widely suggested for liver regeneration. Analogs of liver acellular extracellular matrix (ECM) are utilized in native scaffolds to increase the self-repair and healing ability of organs. Native ECM analog could improve liver repairing through providing the supportive framework for cells and signaling molecules, exerting normal biomechanical, biochemical, and physiological signal complexes. Recently, innovative cell sheet technology is introduced as an alternative for conventional tissue engineering with the advantage of fewer scaffold restrictions and cell culture on a Thermo-Responsive Polymer Surface. These sheets release the layered cells through a temperature-controlled procedure without enzymatic digestion, while preserving the cell-ECM contacts and adhesive molecules on cell-cell junctions. In addition, several novelties have been introduced into the cell sheet and decellularization technologies to aid cell growth, instruct differentiation/angiogenesis, and promote cell migration. In this review, recent trends, advancements, and issues linked to translation into clinical practice are dissected and compared regarding the decellularization and cell sheet technologies for liver tissue engineering.

Tissue-Engineered Bile Ducts for Disease Modeling and Therapy

Recent biotechnical advances in the in vitro culture of cholangiocytes and generation of bioengineered biliary tissue have a high potential for creating biliary tissue to be used for disease modeling, drug screening, and transplantation. For the past few decades, scientists have searched for a source of cholangiocytes, focused on primary cholangiocytes or cholangiocytes derived from hepatocytes or stem cells. At the same time, the development of scaffolds for biliary tissue engineering for transplantation and modeling of cholangiopathies has been explored. In this review, we provide an overview on the current understanding of cholangiocytes sources, the effect of signaling molecules, and transcription factors on cell differentiation, along with the effects of extracellular matrix molecules and scaffolds on bioengineered biliary tissues, and their application in disease modeling and drug screening. Impact statement Over the past few decades, biliary tissue engineering has acquired significant attention, but currently a number of factors hinder this field to eventually generate bioengineered bile ducts that mimic in vivo physiology and are suitable for transplantation. In this review, we present the latest advances with respect to cell source selection, influence of growth factors and scaffolds, and functional characterization, as well as applications in cholangiopathy modeling and drug screening. This review is suited for a broad spectrum of readers, including fundamental liver researchers and clinicians with interest in the current state and application of bile duct engineering and disease modeling.

Current Perspective: 3D Spheroid Models Utilizing Human-Based Cells for Investigating Metabolism-Dependent Drug-Induced Liver Injury

Drug-induced liver injury (DILI) remains a leading cause for the withdrawal of approved drugs. This has significant financial implications for pharmaceutical companies, places increasing strain on global health services, and causes harm to patients. For these reasons, it is essential that in-vitro liver models are capable of detecting DILI-positive compounds and their underlying mechanisms, prior to their approval and administration to patients or volunteers in clinical trials. Metabolism-dependent DILI is an important mechanism of drug-induced toxicity, which often involves the CYP450 family of enzymes, and is associated with the production of a chemically reactive metabolite and/or inefficient removal and accumulation of potentially toxic compounds. Unfortunately, many of the traditional in-vitro liver models fall short of their in-vivo counterparts, failing to recapitulate the mature hepatocyte phenotype, becoming metabolically incompetent, and lacking the longevity to investigate and detect metabolism-dependent DILI and those associated with chronic and repeat dosing regimens. Nevertheless, evidence is gathering to indicate that growing cells in 3D formats can increase the complexity of these models, promoting a more mature-hepatocyte phenotype and increasing their longevity, in vitro. This review will discuss the use of 3D in vitro models, namely spheroids, organoids, and perfusion-based systems to establish suitable liver models to investigate metabolism-dependent DILI.

Scaffold-Free Bio-3D Printing Using Spheroids as "Bio-Inks" for Tissue (Re-)Construction and Drug Response Tests

In recent years, scaffold-free bio-3D printing using cell aggregates (spheroids) as "bio-inks" has attracted increasing attention as a method for 3D cell construction. Bio-3D printing uses a technique called the Kenzan method, wherein spheroids are placed one-by-one in a microneedle array (the "Kenzan") using a bio-3D printer. The bio-3D printer is a machine that was developed to perform bio-3D printing automatically. Recently, it has been reported that cell constructs can be produced by a bio-3D printer using spheroids composed of many types of cells and that this can contribute to tissue (re-)construction. This progress report summarizes the production and effectiveness of various cell constructs prepared using bio-3D printers. It also considers the future issues and prospects of various cell constructs obtained by using this method for further development of scaffold-free 3D cell constructions.

Synergistic modulation of signaling pathways to expand and maintain the bipotency of human hepatoblasts

Background

The limited proliferative ability of hepatocytes is a major limitation to meet their demand for cell-based therapy, bio-artificial liver device, and drug tests. One strategy is to amplify cells at the hepatoblast (HB) stage. However, expansion of HBs with their bipotency preserved is challenging. Most HB expansion methods hardly maintain the bipotency and also lack functional confirmation.

Methods

On the basis of analyzing and manipulating related signaling pathways during HB (derived from human induced pluripotent stem cells, iPSCs) differentiation and proliferation, we established a specific chemically defined cocktails to synergistically regulate the related signaling pathways that optimize the balance of HB proliferation ability and stemness maintenance, to expand the HBs and investigate their capacity for injured liver repopulation in immune-deficient mice.

Results

We found that the proliferative ability progressively declines during HB differentiation process. Small molecule activation of Wnt or inhibition of TGF-β pathways promoted HB proliferation but diminished their bipotency, whereas activation of hedgehog (HH) signaling stimulated proliferation and sustained HB phenotypes. A cocktail synergistically regulating the BMP/WNT/TGF-β/HH pathways created a fine balance for expansion and maintenance of the bipotency of HBs. After purification, colony formation, and expansion for 20 passages, HBs retained their RNA profile integrity, normal karyotype, and ability to differentiate into mature hepatocytes and cholangiocytes. Moreover, upon transplantation into liver injured mice, the expanded HBs could engraft and differentiate into mature human hepatocytes and repopulate liver tissue with restoring hepatocyte mass.

Conclusion

Our data contribute to the understanding of some signaling pathways for human HB proliferation in vitro. Simultaneous BMP/HGF induction, activation of Wnt and HH, and inhibition of TGF-β pathways created a reliable method for long-term stable large-scale expansion of HBs to obtain mature hepatocytes that may have substantial clinical applications.

Graphical abstract

Prenatal liver stromal cells: Favorable feeder cells for long-term culture of hepatic progenitor cells

Clinical and pharmaceutical applications of primary hepatocytes (PHs) are limited due to inadequate number of donated livers and potential challenges in successful maintenance of PHs in culture. Freshly isolated hepatocytes lose their specific features and rapidly de-differentiate in culture. Bipotent hepatoblasts, as liver precursor cells that can differentiate into both hepatocytes and cholangiocytes (Alb- and Ck19-positive cells, respectively), could be used as an alternative and reliable cell source to produce enough PHs for drug discovery or possible clinical applications. In this study, growth factor-free coculture systems of prenatal or postnatal murine liver stromal cells (pre-LSCs or post-LSCs, respectively) were used as feeder cells to support freshly isolated mice hepatoblasts. DLK1-positive hepatoblasts were isolated from mouse fetuses (E14.5) and cocultured with feeder cells under adherent conditions. The hepatoblasts' bipotent features, proliferation rate, and colony formation capacity were assessed on day 5 and 7 post-seeding. Immunofluorescence staining showed that the hepatoblasts remained double positive for Alb and Ck19 on both Pre- and Post-LSCs, after 5 and 7 days of coculture. Moreover, application of pre-LSCs as feeder cells significantly increased the number of DLK1-positive cells and their proliferation rate (ie, increased the number of Ki-67 positive cells) on day 7, compared to Post-LSCs group. Finally, to address our ultimate goal, which was an extension of hepatoblasts ex vivo maintenance, 3D spheres of isolated hepatoblasts were, cultured in conditioned medium (CM) derived from pre-LSCs until day 30. It was observed that the CM derived from Pre-LSCs could successfully prolong the maintenance of hepatic progenitor cells (HPCs) in 3D suspension culture.

Analysis of the mechanism underlying liver diseases using human induced pluripotent stem cells

Results of recent studies have shown that disease models using human induced pluripotent stem (iPS) cells have recapitulated the pathophysiology of genetic liver diseases, viral hepatitis and hepatic fibrosis. The utilization of human iPS cells as a model of liver diseases has several substantial advantages compared with primary hepatocytes and cancer cell lines, such as the potential for unlimited expansion and similarity of biological characteristics to normal liver cells. In this review, we have focused on modeling liver diseases using human iPS cells and discussed the experimental evidence that supports the utility of such disease models, including that in our recent studies. Genetically modified or patient-derived human iPS cells can mimic congenital liver disease phenotypes. Human iPS-derived hepatic cells can be infected with the hepatitis viruses. The co-culture of human iPS-derived hepatocytes and mesenchyme partially mimics the process of liver fibrosis. Human iPS cell-derived hepatic cells and the co-culture system of such cells will contribute to the progress of studies on the pathophysiology of genetic and non-genetic liver diseases and development of novel therapeutic strategies for treating liver diseases.

Loss of fibrocystin promotes interleukin-8-dependent proliferation and CTGF production of biliary epithelium

BACKGROUND & AIMS

Congenital hepatic fibrosis (CHF) is a genetic liver disease resulting in abnormal proliferation of cholangiocytes and progressive hepatic fibrosis. CHF is caused by mutations in the PKHD1 gene and the subsequent dysfunction of the protein it encodes, fibrocystin. However, the underlying molecular mechanism of CHF, which is quite different from liver cirrhosis, remains unclear. This study investigated the molecular mechanism of CHF pathophysiology using a genetically engineered human induced pluripotent stem (iPS) cell model to aid the discovery of novel therapeutic agents for CHF.

METHODS

PKHD1-knockout (PKHD1-KO) and heterozygously mutated PKHD1 iPS clones were established by RNA-guided genome editing using the CRISPR/Cas9 system. The iPS clones were differentiated into cholangiocyte-like cells in cysts (cholangiocytic cysts [CCs]) in a 3D-culture system.

RESULTS

The CCs were composed of a monolayer of cholangiocyte-like cells. The proliferation of PKHD1-KO CCs was significantly increased by interleukin-8 (IL-8) secreted in an autocrine manner. IL-8 production was significantly elevated in PKHD1-KO CCs due to mitogen-activated protein kinase pathway activation caused by fibrocystin deficiency. The production of connective tissue growth factor (CTGF) was also increased in PKHD1-KO CCs in an IL-8-dependent manner. Furthermore, validation analysis demonstrated that both the serum IL-8 level and the expression of IL-8 and CTGF in the liver samples were significantly increased in patients with CHF, consistent with our in vitro human iPS-disease model of CHF.

CONCLUSIONS

Loss of fibrocystin function promotes IL-8-dependent proliferation of, and CTGF production by, human cholangiocytes, suggesting that IL-8 and CTGF are essential for the pathogenesis of CHF. IL-8 and CTGF are candidate molecular targets for the treatment of CHF.

LAY SUMMARY

Congenital hepatic fibrosis (CHF) is a genetic liver disease caused by mutations of the PKHD1 gene. Dysfunction of the protein it encodes, fibrocystin, is closely associated with CHF pathogenesis. Using an in vitro human induced pluripotent stem cell model and patient samples, we showed that the loss of fibrocystin function promotes proliferation of cholangiocytes and the production of connective tissue growth factor (CTGF) in an interleukin 8 (IL-8)-dependent manner. These results suggest that IL-8 and CTGF are essential for the pathogenesis of CHF.

Size-dependent hepatic differentiation of human induced pluripotent stem cells spheroid in suspension culture

Suspension culture of three-dimensional (3D) spheroid of human induced pluripotent stem cells (hiPSCs) has been known as a potential method to enhance the scalability of hepatic differentiation of hiPSCs. However, the impact of size-related factor of initial formed spheroid were not largely considered. To address this problem, we evaluate the impact of different specific spheroid size of hiPSCs by forming the individual spheroid from different number of hiPSCs and differentiated into hiPSCs-derived hepatocytes (iHeps). The results showed that larger spheroid exhibit enhanced capability to differentiated into hepatic lineage by increasing the expression marker albumin, CYP3A4 and lower expression of fetal hepatic marker AFP. Several factor such as the tendency of cystic like structure forming, the necrotic area of the large dense spheroid, and interference of WNT/β-catenin signaling was significantly affecting the resulted iHeps. In this study, we suggest that the optimal spheroid size for hepatic differentiation can be attained from 500 to 600 μm diameter spheroid formed from 12,500–25,000 hiPSCs. This size can be potentially applied for various practical use of hepatic differentiation in scalable suspension culture.

LIM homeobox 2 promotes interaction between human iPS-derived hepatic progenitors and iPS-derived hepatic stellate-like cells

Human induced pluripotent stem (iPS) cells can differentiate into hepatocyte lineages, although the phenotype of the differentiated cells is immature compared to adult hepatocytes. Improvement of cell-cell interactions between epithelium and mesenchyme is a potential approach to address this phenotype issue. In this study, we developed a model system for improving interactions between human iPS-derived hepatic progenitor cells (iPS-HPCs) and human iPS-derived hepatic stellate cell-like cells (iPS-HSCs). The phenotype of iPS-HSCs, including gene and protein expression profiles and vitamin A storage, resembled that of hepatic stellate cells. Direct co-culture of iPS-HSCs with iPS-HPCs significantly improved hepatocytic maturation in iPS-HPCs, such as their capacity for albumin production. Next, we generated iPS cell lines overexpressing LIM homeobox 2 (LHX2), which suppresses myofibroblastic changes in HSCs in mice. Hepatocytic maturation in iPS-HPCs was significantly increased in direct co-culture with iPS-HSCs overexpressing LHX2, but not in co-culture with a human hepatic stellate cell line (LX-2) overexpressing LHX2. LHX2 regulated the expression of extracellular matrices, such as laminin and collagen, in iPS-HSCs. In conclusion, this study provides an evidence that LHX2 upregulation in iPS-HSCs promotes hepatocytic maturation of iPS-HPCs, and indicates that genetically modified iPS-HSCs will be of value for research into cell-cell interactions.

Gene Editing in Human Pluripotent Stem Cells: Recent Advances for Clinical Therapies

The identification of human embryonic stem cells and reprogramming technology to obtain induced pluripotent stem cells from adult somatic cells have provided unique opportunity to create human disease models, gene editing strategies and cell therapy options.Development of pluripotent stem cells from somatic cells and genomic manipulation tools enabled to use site specific nucleases in the cell therapy research. Identification of efficient gene manipulation, safe differentiation and use will provide a novel strategy to treat many diseases in the near future. Current available registered clinical trials clearly indicate the need for pluripotent stem cell and gene therapy treatment options. Although gene editing based pluripotent stem cell research is a popular field for research worldwide, improvement of clinical approaches for treatment still remains to be investigated. In this review, we summarized the current situation of gene editing based pluripotent cell therapy developments and applications in clinics.

Treatment of AECHB and Severe Hepatitis (Liver Failure)

This chapter describes the general treatment and immune principles and internal management for AECHB and HBV ACLF, including ICU monitoring, general supportive medications/nutrition/nursing, immune therapy, artificial liver supportive systems, hepatocyte/stem cell, and liver transplant, management for special populations, frequently clinical complications and the utilization of Chinese traditional medicines.

Early clinical indicators of severe hepatitis B include acratia, gastrointestinal symptoms, a daily increase in serum bilirubin >1 mg/dL, toxic intestinal paralysis, bleeding tendency and mild mind anomaly or character change, and the presence of other diseases inducing severe hepatitis. Laboratory indicators include T-Bil, PTA, cholinesterase, pre-albumin and albumin. The roles of immune indicators (such as IL-6, TNF-α, and fgl2), gene polymorphisms, HBV genotypes, and gene mutations as early clinical indicators.

Intensive Care Unit monitor patients with severe hepatitis include intracranial pressure, infection, blood dynamics, respiratory function, renal function, blood coagulation function, nutritional status and blood purification process. Nursing care should not only include routine care, but psychological and special care (complications).

Nutrition support and nursing care should be maintained throughout treatment for severe hepatitis. Common methods of evaluating nutritional status include direct human body measurement, creatinine height index (CHI) and subject global assessment of nutrition (SGA). Malnourished patients should receive enteral or parenteral nutrition support.

Immune therapies for severe hepatitis include promoting hepatocyte regeneration (e.g. with glucagon, hepatocyte growth factor and prostaglandin E1), glucocorticoid suppressive therapy, and targeting molecular blocking. Corticosteroid treatment should be early and sufficient, and adverse drug reactions monitored. Treatments currently being investigated are those targeting Toll-like receptors, NK cell/NK cell receptors, macrophage/immune coagulation system, CTLA-4/PD-1 and stem cell transplantation.

In addition to conventional drugs and radioiodine, corticosteroids and artificial liver treatment can also be considered for severe hepatitis patients with hyperthyreosis. Patients with gestational severe hepatitis require preventive therapy for fetal growth restriction, and it is necessary to choose the timing and method of fetal delivery. For patients with both diabetes and severe hepatitis, insulin is preferred to oral antidiabetic agents to control blood glucose concentration. Liver toxicity of corticosteroids and immune suppressors should be monitored during treatment for severe hepatitis in patients with connective tissue diseases including SLE, RA and sicca syndrome. Patient with connective tissue diseases should preferably be started after the antiviral treatment with nucleos(t)ide analogues.

An artificial liver can improve patients’ liver function; remove endotoxins, blood ammonia and other toxins; correct amino acid metabolism and coagulation disorders; and reverse internal environment imbalances. Non-bioartificial livers are suitable for patients with early and middle stage severe hepatitis; for late-stage patients waiting for liver transplantation; and for transplanted patients with rejection reaction or transplant failure. The type of artificial liver should be determined by each patient’s condition and previous treatment purpose, and patients should be closely monitored for adverse reactions and complications. Bio- and hybrid artificial livers are still under development.

MELD score is the international standard for choosing liver transplantation. Surgical methods mainly include the in situ classic type and the piggyback type; transplantation includes no liver prophase, no liver phase or new liver phase. Preoperative preparation, management of intraoperative and postoperative complications and postoperative long-term treatment are keys to success.

Severe hepatitis belongs to the categories of “acute jaundice”, “scourge jaundice”, and “hot liver” in traditional Chinese medicine. Treatment methods include Chinese traditional medicines, acupuncture and acupoint injection, external application of drugs, umbilical compress therapy, drip, blow nose therapy, earpins, and clysis. Dietary care is also an important part of traditional Chinese medicine treatment.

Culture System of Bile Duct-Like Cystic Structures Derived from Human-Inducible Pluripotent Stem Cells

Inducible pluripotent stem (iPS) cells are multipotent stem cells that are produced by gene transfer of reprogramming factors to somatic cells. They are thought to be an important source of regenerative medicine because of their pluripotency and self-renewal ability. Although the liver has high regeneration ability, continuous death of hepatocytes due to chronic inflammation leads to liver cirrhosis and liver carcinoma. With regard to such serious liver diseases, liver transplantation is used as a complete cure, but there is a problem of donor shortage. Therefore, transplantation therapy using liver tissue generated from stem cells in vitro is expected.We are developing a system to induce the differentiation of cholangiocytes, one of important non-parenchymal cells in living liver tissue, from human iPS cells. Bile duct-like cystic structures can be induced by purifying human iPS cell-derived hepatoblasts expressing hepatic progenitor cell surface markers and inducing differentiation under appropriate culture conditions. These cells are considered to be useful in constructing a hepatic organoid that reproduces the liver structure of the living body.

An in vitro model of polycystic liver disease using genome-edited human inducible pluripotent stem cells

In the developing liver, bile duct structure is formed through differentiation of hepatic progenitor cells (HPC) into cholangiocytes. A subtype of polycystic liver diseases characterized by uncontrolled expansion of bile ductal cells is caused by genetic abnormalities such as in that of protein kinase C substrate 80 K-H (PRKCSH). In this study, we aimed to mimic the disease process in vitro by genome editing of the PRKCSH locus in human inducible pluripotent stem (iPS) cells. A proportion of cultured human iPS cell-derived CD13+CD133+ HPC differentiated into CD13- cells. During the subsequent gel embedding culture, CD13- cells formed bile ductal marker-positive cystic structures with the polarity of epithelial cells. A deletion of PRKCSH gene increased expression of cholangiocytic transcription factors in CD13- cells and the number of cholangiocytic cyst structure. These results suggest that PRKCSH deficiency promotes the differentiation of HPC-derived cholangiocytes, providing a good in vitro model to analyze the molecular mechanisms underlying polycystic diseases.

Characterization of distal airway stem-like cells expressing N-terminally truncated p63 and thyroid transcription factor-1 in the human lung

Distal airway stem cells (DASCs) in the mouse lung can differentiate into bronchioles and alveoli. However, it remains unclear whether the same stem cells exist in the human lung. Here, we found that human lung epithelial (HuL) cells, derived from normal, peripheral lung tissue, in monolayer, mostly express both the N-terminally truncated isoform of p63 (∆Np63), a marker for airway basal cells, and thyroid transcription factor-1 (TTF-1), a marker for alveolar epithelial cells, even though these two molecules are usually expressed in a mutually exclusive way. Three-dimensionally cultured HuL cells differentiated to form bronchiole-like and alveolus-like organoids. We also uncovered a few bronchiolar epithelial cells expressing both ∆Np63 and TTF-1 in the human lung, suggesting that these cells are the cells of origin for HuL cells. Taken together, ΔNp63⁺ TTF-1⁺ peripheral airway epithelial cells are possibly the human counterpart of mouse DASCs and may offer potential for future regenerative medicine.

Differentiation of human-induced pluripotent stem cell under flow conditions to mature hepatocytes for liver tissue engineering

Hepatic differentiation of human-induced pluripotent stem cells (hiPSCs) under flow conditions in a 3D scaffold is expected to be a major step forward for construction of bioartificial livers. The aims of this study were to induce hepatic differentiation of hiPSCs under perfusion conditions and to perform functional comparisons with fresh human precision-cut liver slices (hPCLS), an excellent benchmark for the human liver in vivo. The majority of the mRNA expression of CYP isoenzymes and transporters and the tested CYP activities, Phase II metabolism, and albumin, urea, and bile acid synthesis in the hiPSC-derived cells reached values that overlap those of hPCLS, which indicates a higher degree of hepatic differentiation than observed until now. Differentiation under flow compared with static conditions had a strong inducing effect on Phase II metabolism and suppressed AFP expression but resulted in slightly lower activity of some of the Phase I metabolism enzymes. Gene expression data indicate that hiPSCs differentiated into both hepatic and biliary directions. In conclusion, the hiPSC differentiated under flow conditions towards hepatocytes express a wide spectrum of liver functions at levels comparable with hPCLS indicating excellent future perspectives for the development of a bioartificial liver system for toxicity testing or as liver support device for patients.

Hepatic stem cells with self-renewal and liver repopulation potential are harbored in CDCP1-positive subpopulations of human fetal liver cells

BACKGROUND

Mature human hepatocytes are critical in preclinical research and therapy for liver disease, but are difficult to manipulate and expand in vitro. Hepatic stem cells (HpSCs) may be an alternative source of functional hepatocytes for cell therapy and disease modeling. Since these cells play an import role in regenerative medicine, the precise characterization that determines specific markers used to isolate these cells as well as whether they contribute to liver regeneration still remain to be shown.

METHOD

In this study, human HpSCs were isolated from human primary fetal liver cells (FLCs) by flow cytometry using CDCP1, CD90, and CD66 antibodies. The isolated CDCP1+CD90+CD66- HpSCs were cultured on dishes coated with type IV collagen in DMEM nutrient mixture F-12 Ham supplemented with FBS, human γ-insulin, nicotinamide, dexamethasone, and L-glutamine for at least 2 weeks, and were characterized by transcriptomic profiling, quantitative real-time PCR, immunocytochemistry, and in-vivo transplantation.

RESULTS

The purified CDCP1+CD90+CD66- subpopulation exhibited clonal expansion and self-renewal capability, and bipotential capacity was further identified in single cell-derived colonies containing distinct hepatocytes and cholangiocytes. Moreover, in-vivo liver repopulation assays demonstrated that human CDCP1+CD90+CD66- HpSCs repopulated over 90% of the mouse liver and differentiated into functional hepatocytes with drug metabolism activity.

CONCLUSIONS

We identified a human hepatic stem/progenitor population in the CDCP1+CD90+CD66- subpopulation in human FLCs, indicating CDCP1 marker could potentially be utilized to identify and isolate HpSCs for further cytotherapy of liver disease.

In vivo and ex vivo methods of growing a liver bud through tissue connection

Cell-based therapy has been proposed as an alternative to orthotopic liver transplantation. The novel transplantation of an in vitro-generated liver bud might have therapeutic potential. In vivo and ex vivo methods for growing a liver bud are essential for paving the way for the clinical translation of liver bud transplantation. We herein report a novel transplantation method for liver buds that are grown in vivo involving orthotopic transplantation on the transected parenchyma of the liver, which showed long engraftment and marked growth in comparison to heterotopic transplantation. Furthermore, this study demonstrates a method for rapidly fabricating scalable liver-like tissue by fusing hundreds of liver bud-like spheroids using a 3D bioprinter. Its system to fix the shape of the 3D tissue with the needle-array system enabled the fabrication of elaborate geometry and the immediate execution of culture circulation after 3D printing—thereby avoiding an ischemic environment ex vivo. The ex vivo-fabricated human liver-like tissue exhibited self-tissue organization ex vivo and engraftment on the liver of nude rats. These achievements conclusively show both in vivo and ex vivo methods for growing in vitro-generated liver buds. These methods provide a new approach for in vitro-generated liver organoids transplantation.

Fail-Safe System against Potential Tumorigenicity after Transplantation of iPSC Derivatives

Human induced pluripotent stem cells (iPSCs) are promising in regenerative medicine. However, the risks of teratoma formation and the overgrowth of the transplanted cells continue to be major hurdles that must be overcome. Here, we examined the efficacy of the inducible caspase-9 (iCaspase9) gene as a fail-safe against undesired tumorigenic transformation of iPSC-derived somatic cells. We used a lentiviral vector to transduce iCaspase9 into two iPSC lines and assessed its efficacy in vitro and in vivo. In vitro, the iCaspase9 system induced apoptosis in approximately 95% of both iPSCs and iPSC-derived neural stem/progenitor cells (iPSC-NS/PCs). To determine in vivo function, we transplanted iPSC-NS/PCs into the injured spinal cord of NOD/SCID mice. All transplanted cells whose mass effect was hindering motor function recovery were ablated upon transduction of iCaspase9. Our results suggest that the iCaspase9 system may serve as an important countermeasure against post-transplantation adverse events in stem cell transplant therapies.

Concise Review: Liver Regenerative Medicine: From Hepatocyte Transplantation to Bioartificial Livers and Bioengineered Grafts

Donor organ shortage is the main limitation to liver transplantation as a treatment for end-stage liver disease and acute liver failure. Liver regenerative medicine may in the future offer an alternative form of therapy for these diseases, be it through cell transplantation, bioartificial liver (BAL) devices, or bioengineered whole organ liver transplantation. All three strategies have shown promising results in the past decade. However, before they are incorporated into widespread clinical practice, the ideal cell type for each treatment modality must be found, and an adequate amount of metabolically active, functional cells must be able to be produced. Research is ongoing in hepatocyte expansion techniques, use of xenogeneic cells, and differentiation of stem cell-derived hepatocyte-like cells (HLCs). HLCs are a few steps away from clinical application, but may be very useful in individualized drug development and toxicity testing, as well as disease modeling. Finally, safety concerns including tumorigenicity and xenozoonosis must also be addressed before cell transplantation, BAL devices, and bioengineered livers occupy their clinical niche. This review aims to highlight the most recent advances and provide an updated view of the current state of affairs in the field of liver regenerative medicine. Stem Cells 2017;35:42-50.

Development of a rapid screen for the endodermal differentiation potential of human pluripotent stem cell lines

A challenge facing the human pluripotent stem cell (hPSC) field is the variability observed in differentiation potential of hPSCs. Variability can lead to time consuming and costly optimisation to yield the cell type of interest. This is especially relevant for the differentiation of hPSCs towards the endodermal lineages. Endodermal cells have the potential to yield promising new knowledge and therapies for diseases affecting multiple organ systems, including lung, thymus, intestine, pancreas and liver, as well as applications in regenerative medicine and toxicology. Providing a means to rapidly, cheaply and efficiently assess the differentiation potential of multiple hPSCs is of great interest. To this end, we have developed a rapid small molecule based screen to assess the endodermal potential (EP) of hPSCs, based solely on definitive endoderm (DE) morphology. This drastically reduces the cost and time to identify lines suitable for use in deriving endodermal lineages. We demonstrate the efficacy of this screen using 10 different hPSCs, including 4 human embryonic stem cell lines (hESCs) and 6 human induced pluripotent stem cell lines (hiPSCs). The screen clearly revealed lines amenable to endodermal differentiation, and only lines that passed our morphological assessment were capable of further differentiation to hepatocyte like cells (HLCs).

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.

Generation and In Vitro Expansion of Hepatic Progenitor Cells from Human iPS Cells

Stem cells have the unique properties of self-renewal and multipotency (producing progeny belonging to two or more lineages). Induced pluripotent stem (iPS) cells can be generated from somatic cells by simultaneous expression of pluripotent factors (Oct3/4, Klf4, Sox2, and c-Myc). They share the same properties as embryonic stem (ES) cells and can differentiate into several tissue cells, i.e., neurons, hematopoietic cells, and liver cells. Therefore, iPS cells are suitable candidate cells for regenerative medicine and analyses of disease mechanisms.The liver is the major organ that regulates a multitude of metabolic functions. Hepatocytes are the major cell type populating the liver parenchyma and express several metabolic enzymes that are necessary for liver functions. Although hepatocytes are essential for maintaining homeostasis, it is difficult to alter artificial and transplanted cells because of their multifunctionality, donor shortage, and immunorejection risk. During liver development, hepatic progenitor cells in the fetal liver differentiate into both mature hepatocytes and cholangiocytes. As hepatic progenitor cells have bipotency and high proliferation ability, they could present a potential source for generating transplantable cells or as a liver study model. Here we describe the induction and purification of hepatic progenitor cells derived from human iPS cells. These cells can proliferate for a long term under suitable culture conditions.

Double primary hepatic cancer (hepatocellular carcinoma and intrahepatic cholangiocarcinoma) originating from hepatic progenitor cell: a case report and review of the literature

BACKGROUND

Synchronous development of primary hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC) in different sites of the liver have rarely been reported before. The purpose of this study is to investigate the clinicopathological characteristics of synchronous double cancer of HCC and ICC.

CASE PRESENTATION

A 56-year-old Chinese man without obvious liver cirrhosis was preoperation diagnosed with multiple HCC in segments VI (SVI) and VII (SVII) by the abdominal computed tomography (CT) and contrast-enhanced ultrasonography (CEUS). We performed hepatic resection of both segments. The tumors in SVI and SVII were pathologically diagnosed as ICC and HCC, respectively. Immunohistochemically, the HCC in SVII was positive for HepPar-1 and negative for CK19, while the ICC in SVI tumor was positive for CK19 and negative for HepPar-1. Interestingly, the immunohistochemical results also showed that the classic hepatic progenitor cell (HPCs) markers CD34 and CD117 were both positive of the two tumors. The patient still survived and at a 1-year follow-up did not show evidence of metastasis or new recurrent lesions. We speculate that the two masses may have originated from HPCs based on the findings of this patient.

CONCLUSIONS

Synchronous development of HCC and ICC is very rare with unique clinical and pathological features. The correct preoperative diagnosis of double hepatic cancer of HCC and ICC is difficult. Hepatitis B virus (HBV) and hepatitis C virus (HCV) infection were both the independent risk factor to the development of double liver cancer. Hepatic resection is the preferred and most effective treatment choice. The prognosis of synchronous occurrence of double hepatic cancer was poorer than for either HCC or ICC, and the origin of it needs further study.

Human induced pluripotent stem cell-derived hepatic cell lines as a new model for host interaction with hepatitis B virus

Hepatitis B virus (HBV) is not eradicated by current antiviral therapies due to persistence of HBV covalently closed circular DNA (cccDNA) in host cells, and thus development of novel culture models for productive HBV infection is urgently needed, which will allow the study of HBV cccDNA eradication. To meet this need, we developed culture models of HBV infection using human induced pluripotent stem cell-derived hepatocyte lineages, including immature proliferating hepatic progenitor-like cell lines (iPS-HPCs) and differentiated hepatocyte-like cells (iPS-Heps). These cells were susceptible to HBV infection, produced HBV particles, and maintained innate immune responses. The infection efficiency of HBV in iPS-HPCs predominantly depended on the expression levels of sodium taurocholate cotransporting polypeptide (NTCP), and was low relative to iPS-Heps: however, long-term culture of iPS-Heps was difficult. To provide a model for HBV persistence, iPS-HPCs overexpressing NTCP were established. The long-term persistence of HBV cccDNA was detected in iPS-HPCs overexpressing NTCP, and depended on the inhibition of the Janus-kinase signaling pathway. In conclusion, this study provides evidence that iPS-derived hepatic cell lines can be utilized for novel HBV culture models with genetic variation to investigate the interactions between HBV and host cells and the development of anti-HBV strategies.

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.

Personalized medicine for cystic fibrosis: establishing human model systems

With over 1,500 identifiable mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene that result in distinct functional and phenotypical abnormalities, it is virtually impossible to perform randomized clinical trials to identify the best therapeutics for all patients. Therefore, a personalized medicine approach is essential. The only way to realistically accomplish this is through the development of improved in vitro human model systems. The lack of a readily available and infinite supply of human CFTR-expressing airway epithelial cells is a key bottleneck. We propose that a concerted two-pronged approach is necessary for patient-specific cystic fibrosis research to continue to prosper and realize its potential: (1) more effective culture and differentiation conditions for growing primary human airway and nasal epithelial cells and (2) the development of collective protocols for efficiently differentiating disease- and patient-specific induced pluripotent stem cells (iPSC) into pure populations of adult epithelial cells. Ultimately, we need a personalized human model system for cystic fibrosis with the capacity for uncomplicated bankability, widespread availability, and universal applicability for patient-specific disease modeling, novel pharmacotherapy investigation and screening, and readily executable genetic modification.

Generation of Self-Renewing Hepatoblasts From Human Embryonic Stem Cells by Chemical Approaches

Somatic stem cells play crucial roles in organogenesis and tissue homeostasis and regeneration and may ultimately prove useful for cell therapy for a variety of degenerative diseases and injuries; however, isolation and expansion of most types of somatic stem cells from tissues are technically challenging. Human pluripotent stem cells are a renewable source for any adult cell types, including somatic stem cells. Generation of somatic stem cells from human pluripotent stem cells is a promising strategy to get these therapeutically valuable cells. Previously, we developed a chemically defined condition for mouse hepatoblast self-renewal through a reiterative screening strategy. In the present study, we efficiently generated hepatoblasts from human embryonic stem cells by a stepwise induction strategy. Importantly, these human embryonic stem cell-derived hepatoblasts can be captured and stably maintained using conditions previously established for mouse hepatoblast self-renewal, which includes basal media supplemented with insulin, transferrin, sodium selenite, epidermal growth factor, glycogen synthase kinase 3 inhibitor, transforming growth factor β receptor inhibitor, lysophosphatidic acid, and sphingosine 1-phosphate. The cells can stably retain hepatoblast phenotypes during prolonged culture and can differentiate into mature hepatocytes through in vitro provision of hepatocyte lineage developmental cues. After being embedded into three-dimensional Matrigel, these cells efficiently formed bile duct-like structures resembling native bile duct tissues. These human embryonic stem cell-derived hepatoblasts would be useful as a renewable source for cell therapy of liver diseases.

SIGNIFICANCE

Somatic stem cells have been proposed as promising candidates for cell-based therapy; however, isolation of somatic stem cells from adult tissues is usually invasive and technically challenging. In the present study, hepatoblasts from human embryonic stem cells were efficiently generated. These human hepatoblasts were then stably captured and maintained by a growth factor and small molecule cocktail, which included epidermal growth factor, glycogen synthase kinase 3 inhibitor, transforming growth factor β receptor inhibitor, lysophosphatidic acid, and sphingosine 1-phosphate. These human embryonic stem cell-derived hepatoblasts would be useful as a renewable source for cell therapy of liver diseases.

CPM Is a Useful Cell Surface Marker to Isolate Expandable Bi-Potential Liver Progenitor Cells Derived from Human iPS Cells

To develop a culture system for large-scale production of mature hepatocytes, liver progenitor cells (LPCs) with a high proliferation potential would be advantageous. We have found that carboxypeptidase M (CPM) is highly expressed in embryonic LPCs, hepatoblasts, while its expression is decreased along with hepatic maturation. Consistently, CPM expression was transiently induced during hepatic specification from human-induced pluripotent stem cells (hiPSCs). CPM⁺ cells isolated from differentiated hiPSCs at the immature hepatocyte stage proliferated extensively in vitro and expressed a set of genes that were typical of hepatoblasts. Moreover, the CPM⁺ cells exhibited a mature hepatocyte phenotype after induction of hepatic maturation and also underwent cholangiocytic differentiation in a three-dimensional culture system. These results indicated that hiPSC-derived CPM⁺ cells share the characteristics of LPCs, with the potential to proliferate and differentiate bi-directionally. Thus, CPM is a useful marker for isolating hiPSC-derived LPCs, which allows development of a large-scale culture system for producing hepatocytes and cholangiocytes.

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CPM is a novel marker for hepatoblasts during liver development

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Self-renewing hiPSC-derived CPM⁺ LPCs exhibit bi-potency in vitro

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An efficient and convenient protocol for the generation of hiPSC-derived LPCs

Directed differentiation of cholangiocytes from human pluripotent stem cells

Although bile duct disorders are well-recognized causes of liver disease, the molecular and cellular events leading to biliary dysfunction are poorly understood. To enable modeling and drug discovery for biliary disease, we describe a protocol that achieves efficient differentiation of biliary epithelial cells (cholangiocytes) from human pluripotent stem cells (hPSCs) through delivery of developmentally relevant cues, including NOTCH signaling. Using three-dimensional culture, the protocol yields cystic and/or ductal structures that express mature biliary markers, including apical sodium-dependent bile acid transporter, secretin receptor, cilia and cystic fibrosis transmembrane conductance regulator (CFTR). We demonstrate that hPSC-derived cholangiocytes possess epithelial functions, including rhodamine efflux and CFTR-mediated fluid secretion. Furthermore, we show that functionally impaired hPSC-derived cholangiocytes from cystic fibrosis patients are rescued by CFTR correctors. These findings demonstrate that mature cholangiocytes can be differentiated from hPSCs and used for studies of biliary development and disease.

A Paracrine Mechanism Accelerating Expansion of Human Induced Pluripotent Stem Cell-Derived Hepatic Progenitor-Like Cells

Hepatic stem/progenitor cells in liver development have a high proliferative potential and the ability to differentiate into both hepatocytes and cholangiocytes. In this study, we focused on the cell surface molecules of human induced pluripotent stem (iPS) cell-derived hepatic progenitor-like cells (HPCs) and analyzed how these molecules modulate expansion of these cells. Human iPS cells were differentiated into immature hepatic lineage cells by cytokines. In addition to hepatic progenitor markers (CD13 and CD133), the cells were coimmunostained for various cell surface markers (116 types). The cells were analyzed by flow cytometry and in vitro colony formation culture with feeder cells. Twenty types of cell surface molecules were highly expressed in CD13(+)CD133(+) cells derived from human iPS cells. Of these molecules, CD221 (insulin-like growth factor receptor), which was expressed in CD13(+)CD133(+) cells, was quickly downregulated after in vitro expansion. The proliferative ability was suppressed by a neutralizing antibody and specific inhibitor of CD221. Overexpression of CD221 increased colony-forming ability. We also found that inhibition of CD340 (erbB2) and CD266 (fibroblast growth factor-inducible 14) signals suppressed proliferation. In addition, both insulin-like growth factor (a ligand of CD221) and tumor necrosis factor-like weak inducer of apoptosis (a ligand of CD266) were provided by feeder cells in our culture system. This study revealed the expression profiles of cell surface molecules in human iPS cell-derived HPCs and that the paracrine interactions between HPCs and other cells through specific receptors are important for proliferation.

Liver maturation deficiency in p57(Kip2)-/- mice occurs in a hepatocytic p57(Kip2) expression-independent manner

Fetal hepatic stem/progenitor cells, hepatoblasts, are highly proliferative cells and the source of both hepatocytes and cholangiocytes. In contrast, mature hepatocytes have a low proliferative potency and high metabolic functions. Cell proliferation is regulated by cell cycle-related molecules. However, the correlation between cell cycle regulation and hepatic maturation are still unknown. To address this issue, we revealed that the cell cycle inhibitor p57(Kip2) was expressed in the hepatoblasts and mesenchymal cells of fetal liver in a spatiotemporal manner. In addition, we found that hepatoblasts in p57(Kip2)-/- mice were highly proliferative and had deficient maturation compared with those in wild-type (WT) mice. However, there were no remarkable differences in the expression levels of cell cycle- and bipotency-related genes except for Ccnd2. Furthermore, p57(Kip2)-/- hepatoblasts could differentiate into mature hepatocytes in p57(Kip2)-/- and WT chimeric mice, suggesting that the intrinsic activity of p57(Kip2) does not simply regulate hepatoblast maturation.

Engineered in vitro disease models

The ultimate goal of most biomedical research is to gain greater insight into mechanisms of human disease or to develop new and improved therapies or diagnostics. Although great advances have been made in terms of developing disease models in animals, such as transgenic mice, many of these models fail to faithfully recapitulate the human condition. In addition, it is difficult to identify critical cellular and molecular contributors to disease or to vary them independently in whole-animal models. This challenge has attracted the interest of engineers, who have begun to collaborate with biologists to leverage recent advances in tissue engineering and microfabrication to develop novel in vitro models of disease. As these models are synthetic systems, specific molecular factors and individual cell types, including parenchymal cells, vascular cells, and immune cells, can be varied independently while simultaneously measuring system-level responses in real time. In this article, we provide some examples of these efforts, including engineered models of diseases of the heart, lung, intestine, liver, kidney, cartilage, skin and vascular, endocrine, musculoskeletal, and nervous systems, as well as models of infectious diseases and cancer. We also describe how engineered in vitro models can be combined with human inducible pluripotent stem cells to enable new insights into a broad variety of disease mechanisms, as well as provide a test bed for screening new therapies.