In vitro differentiation of hepatic progenitor cells from mouse embryonic stem cells induced by sodium butyrate

In silico discovery of small molecules for efficient stem cell differentiation into definitive endoderm

Improving methods for human embryonic stem cell differentiation represents a challenge in modern regenerative medicine research. Using drug repurposing approaches, we discover small molecules that regulate the formation of definitive endoderm. Among them are inhibitors of known processes involved in endoderm differentiation (mTOR, PI3K, and JNK pathways) and a new compound, with an unknown mechanism of action, capable of inducing endoderm formation in the absence of growth factors in the media. Optimization of the classical protocol by inclusion of this compound achieves the same differentiation efficiency with a 90% cost reduction. The presented in silico procedure for candidate molecule selection has broad potential for improving stem cell differentiation protocols.

Sodium Butyrate Induces Hepatic Differentiation of Mesenchymal Stem Cells in 3D Collagen Scaffolds

Stem cell-based therapy is considered an attractive tool to overcome the burden of liver diseases. However, efficient hepatic differentiation is still a big challenge for the research community. In this study, we explored a novel method for differentiation of bone marrow-derived mesenchymal stem cells (MSCs) into hepatic-like cells using 3D culture conditions and histone deacetylase inhibitor, sodium butyrate (NaBu). MSCs were characterized by the presence of cell surface markers via immunocytochemistry, flow cytometry, and by their potential for osteogenic, adipogenic, and chondrogenic differentiation. MSCs were treated with 1mM NaBu in 2D and 3D environments for 21 days. The hepatic differentiation was confirmed by qPCR and immunostaining. According to qPCR data, the 3D culture of NaBu-treated MSCs has shown significant upregulation of hepatic gene, CK-18 (P < 0.01), and hepatic proteins, AFP (P < 0.01) and ALB (P < 0.01). In addition, immunocytochemistry analysis showed significant increase (P < 0.05) in the acetylation of histones (H3 and H4) in NaBu-pretreated cells. It can be concluded from the study that NaBu-treated MSCs in 3D culture conditions can induce hepatic differentiation without the use of additional cytokines and growth factors. The method shown in this study represents an improved protocol for hepatic differentiation and could contribute to improvement in future cell-based therapeutics.

Oncological transformation in vitro of hepatic progenitor cell lines isolated from adult mice

Colorectal cancer cells can transfer the oncogene KRAS to distant cells, predisposing them to malignant transformation (Genometastasis Theory). This process could contribute to liver metastasis; besides, hepatic progenitor cells (HPCs) have been found to be involved in liver malignant neoplasms. The objective of this study is to determine if mouse HPCs—Oval cells (OCs)—are susceptible to incorporate Kras GAT (G12D) mutation from mouse colorectal cancer cell line CT26.WT and if OCs with the incorporated mutation behave like malignant cells. To achieve this, three lines of OCs in different conditions were exposed to CT26.WT cells through transwell co-culture for a week. The presence of Kras^G12D and capacity to form tumors were analyzed in treated samples by droplet digital PCR and colony-forming assays, respectively. The results showed that the Kras^G12D mutation was detected in hepatic culture conditions of undifferentiated OCs and these cells were capable of forming tumors in vitro. Therefore, OCs are susceptible to malignant transformation by horizontal transfer of DNA with Kras^G12D mutation in an undifferentiated condition associated with the liver microenvironment. This study contributes to a new step in the understanding of the colorectal metastatic process.

Functional Recellularization of Acellular Rat Liver Scaffold by Induced Pluripotent Stem Cells: Molecular Evidence for Wnt/B-Catenin Upregulation

BACKGROUND

Liver transplantation remains the only viable therapy for liver failure but has a severely restricted utility. Here, we aimed to decellularize rat livers to form acellular 3D bio-scaffolds suitable for seeding with induced pluripotent cells (iPSCs) as a tool to investigate the role of Wnt/β-catenin signaling in liver development and generation.

METHODS

Dissected rat livers were randomly divided into three groups: I (control); II (decellularized scaffolds) and III (recellularized scaffolds). Liver decellularization was established via an adapted perfusion procedure and assessed through the measurement of extracellular matrix (ECM) proteins and DNA content. Liver recellularization was assessed through histological examination and measurement of transcript levels of Wnt/β-catenin pathway, hepatogenesis, liver-specific microRNAs and growth factors essential for liver development. Adult rat liver decellularization was confirmed by the maintenance of ECM proteins and persistence of growth factors essential for liver regeneration.

RESULTS

iPSCs seeded rat decellularized livers displayed upregulated transcript expression of Wnt/β-catenin pathway-related, growth factors, and liver specification genes. Further, recellularized livers displayed restored liver-specific functions including albumin secretion and urea synthesis.

CONCLUSION

This establishes proof-of-principle for the generation of three-dimensional liver organ scaffolds as grafts and functional re-establishment.

Inter-regulatory role of microRNAs in interaction between viruses and stem cells

MicroRNAs (miRNAs) are well known for post-transcriptional regulatory ability over specific mRNA targets. miRNAs exhibit temporal or tissue-specific expression patterns and regulate the cell and tissue developmental pathways. They also have determinative roles in production and differentiation of multiple lineages of stem cells and might have therapeutic advantages. miRNAs are a part of some viruses’ regulatory machinery, not a byproduct. The trace of miRNAs was detected in the genomes of viruses and regulation of cell reprograming and viral pathogenesis. Combination of inter-regulatory systems has been detected for miRNAs during viral infections in stem cells. Contraction between viruses and stem cells may be helpful in therapeutic tactics, pathogenesis, controlling viral infections and defining stem cell developmental strategies that is programmed by miRNAs as a tool. Therefore, in this review we intended to study the inter-regulatory role of miRNAs in the interaction between viruses and stem cells and tried to explain the advantages of miRNA regulatory potentials, which make a new landscape for future studies.

Signaling molecules orchestrating liver regenerative medicine

The liver is in charge of more than 500 functions in the human body, which any damage and failure to the liver can significantly compromise human life. Numerous studies are being carried out in regenerative medicine, as a potential driving force, toward alleviating the need for liver donors and fabrication of a 3D-engineered transplantable hepatic tissue. Liver tissue engineering brings three main factors of cells, extracellular matrix (ECM), and signaling molecules together, while each of these three factors tries to mimic the physiological state of the tissue to direct tissue regeneration. Signaling molecules play a crucial role in directing tissue fabrication in liver tissue engineering. When mimicking the natural in vivo process of regeneration, it is tightly associated with three main phases of differentiation, proliferation (progression), and tissue maturation through vascularization while directing each of these phases is highly regulated by the specific signaling molecules. The understanding of how these signaling molecules guide the dynamic behavior of regeneration would be a tool for further tailoring of bioengineered systems to help the liver regeneration with many cellular, molecular, and tissue-level functions. Hence, the signaling molecules come to aid all these phases for further improvements toward the clinical use of liver tissue engineering as the goal.

Leveraging Population Genomics for Individualized Correction of the Hallmarks of Alpha-1 Antitrypsin Deficiency

Deep medicine is rapidly moving towards a high-definition approach for therapeutic management of the patient as an individual given the rapid progress of genome sequencing technologies and machine learning algorithms. While considered a monogenic disease, alpha-1 antitrypsin (AAT) deficiency (AATD) patients present with complex and variable phenotypes we refer to as the "hallmarks of AATD" that involve distinct molecular mechanisms in the liver, plasma and lung tissues, likely due to both coding and non-coding variation as well as genetic and environmental modifiers in different individuals. Herein, we briefly review the current therapeutic strategies for the management of AATD. To embrace genetic diversity in the management of AATD, we provide an overview of the disease phenotypes of AATD patients harboring different AAT variants. Linking genotypic diversity to phenotypic diversity illustrates the potential for sequence-specific regions of AAT protein fold design to play very different roles during nascent synthesis in the liver and/or function in post-liver plasma and lung environments. We illustrate how to manage diversity with recently developed machine learning (ML) approaches that bridge sequence-to-function-to-structure knowledge gaps based on the principle of spatial covariance (SCV). SCV relationships provide a deep understanding of the genotype to phenotype transformation initiated by AAT variation in the population to address the role of genetic and environmental modifiers in the individual. Embracing the complexity of AATD in the population is critical for risk management and therapeutic intervention to generate a high definition medicine approach for the patient.

Microphysiological systems meet hiPSC technology - New tools for disease modeling of liver infections in basic research and drug development

Complex cell culture models such as microphysiological models (MPS) mimicking human liver functionality in vitro are in the spotlight as alternative to conventional cell culture and animal models. Promising techniques like microfluidic cell culture or micropatterning by 3D bioprinting are gaining increasing importance for the development of MPS to address the needs for more predictivity and cost efficiency. In this context, human induced pluripotent stem cells (hiPSCs) offer new perspectives for the development of advanced liver-on-chip systems by recreating an in vivo like microenvironment that supports the reliable differentiation of hiPSCs to hepatocyte-like cells (HLC). In this review we will summarize current protocols of HLC generation and highlight recently established MPS suitable to resemble physiological hepatocyte function in vitro. In addition, we are discussing potential applications of liver MPS for disease modeling related to systemic or direct liver infections and the use of MPS in testing of new drug candidates.

Alpha-1-antitrypsin deficiency: Genetic variations, clinical manifestations and therapeutic interventions

Alpha-1-antitrypsin (AAT) is an acute phase secretory glycoprotein that inhibits neutrophil proteases like elastase and is considered as the archetype of a family of structurally related serine-protease inhibitors termed serpins. Serum AAT predominantly originates from liver and increases three to five fold during host response to tissue injury and inflammation. The AAT deficiency is unique among the protein-misfolding diseases in that it causes target organ injury by both loss-of-function and gain-of-toxic function mechanisms. Lack of its antiprotease activity is associated with premature development of pulmonary emphysema and loss-of-function due to accumulation of resultant aggregates in chronic obstructive pulmonary disease (COPD). This' in turn' markedly reduces the amount of AAT that is available to protect lungs against proteolytic attack by the enzyme neutrophil elastase. The coalescence of AAT deficiency, its reduced efficacy, and cigarette smoking or poor ventilation conditions have devastating effect on lung function. On the other hand, the accumulation of retained mutant proteins in the endoplasmic reticulum of hepatocytes in a polymerized form rather than secreted into the blood in its monomeric form is associated with chronic liver disease and predisposition to hepatocellular carcinoma (HCC) by gain- of- toxic function. Liver injury resulting from this gain-of-toxic function mechanism in which mutant AAT retained in the ER initiates a series of pathologic events, eventually culminating at liver cirrhosis and HCC. Here in this review, we underline the structural, genetic, polymorphic, biochemical and pathological advances made in the field of AAT deficiency and further comprehensively emphasize on the therapeutic interventions available for the patient.

Liver-derived human mesenchymal stem cells: a novel therapeutic source for liver diseases

Mesenchymal stem cells (MSCs) represent an attractive cell type for research and therapy due to their ability to proliferate, differentiate, modulate immune reactions, and secrete trophic factors. MSCs exist in a multitude of tissues, including bone marrow, umbilical cord, and adipose tissues. Moreover, MSCs have recently been isolated from the liver. Compared with other MSC types, liver-derived human MSCs (LHMSCs) possess general morphologies, immune functions, and differentiation capacities. Interestingly, LHMCSs produce higher levels of pro-angiogenic, anti-inflammatory, and anti-apoptotic cytokines than those of bone marrow-derived MSCs. Thus, these cells may be a promising therapeutic source for liver diseases. This paper summarizes the biological characteristics of LHMSCs and their potential benefits and risks for the treatment of liver diseases.

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.

Signalling pathways involved in the process of mesenchymal stem cells differentiating into hepatocytes

End‐stage liver disease can be the termination of acute or chronic liver diseases, with manifestations of liver failure; transplantation is currently an effective treatment for these. However, transplantation is severely limited due to the serious lack of donors, expense, graft rejection and requirement of long‐term immunosuppression. Mesenchymal stem cells (MSCs) have attracted considerable attention as therapeutic tools as they can be obtained with relative ease and expanded in culture, along with features of self‐renewal and multidirectional differentiation. Many scientific groups have sought to use MSCs differentiating into functional hepatocytes to be used in cell transplantation with liver tissue engineering to repair diseased organs. In most of the literature, hepatocyte differentiation refers to use of various additional growth factors and cytokines, such as hepatocyte growth factor (HGF), fibroblast growth factor (FGF), epidermal growth factor (EGF), oncostatin M (OSM) and more, and most are involved in signalling pathway regulation and cell–cell/cell–matrix interactions. Signalling pathways have been shown to play critical roles in embryonic development, tumourigenesis, tumour progression, apoptosis and cell‐fate determination. However, mechanisms of MSCs differentiating into hepatocytes, particularly signalling pathways involved, have not as yet been completely illustrated. In this review, we have focused on progress of signalling pathways associated with mesenchymal stem cells differentiating into hepatocytes along with the stepwise differentiation procedure.

Sodium butyrate promotes the differentiation of rat bone marrow mesenchymal stem cells to smooth muscle cells through histone acetylation

Establishing an effective method to improve stem cell differentiation is crucial in stem cell transplantation. Here we aimed to explore whether and how sodium butyrate (NaB) induces rat bone marrow mesenchymal stem cells (MSCs) to differentiate into bladder smooth muscle cells (SMCs). We found that NaB significantly suppressed MSC proliferation and promoted MSCs differentiation into SMCs, as evidenced by the enhanced expression of SMC specific genes in the MSCs. Co-culturing the MSCs with SMCs in a transwell system promoted the differentiation of MSCs into SMCs. NaB again promoted MSC differentiation in this system. Furthermore, NaB enhanced the acetylation of SMC gene-associated H3K9 and H4, and decreased the expression of HDAC2 and down-regulated the recruitment of HDAC2 to the promoter regions of SMC specific genes. Finally, we found that NaB significantly promoted MSC depolarization and increased the intracellular calcium level of MSCs upon carbachol stimulation. These results demonstrated that NaB effectively promotes MSC differentiation into SMCs, possibly by the marked inhibition of HDAC2 expression and disassociation of HDAC2 recruitment to SMC specific genes in MSCs, which further induces high levels of H3K9ace and H4ace and the enhanced expression of target genes, and this strategy could potentially be applied in clinical tissue engineering and cell transplantation.

Propitious role of bone marrow-derived mononuclear cells in an experimental bile duct ligation model: potential clinical implications in obstructive cholangiopathy

PURPOSE

To evaluate the role of bone marrow-derived mononuclear cells (BMC) in rat bile duct ligation (BDL) model.

METHODS

Wistar rats were categorized into four Groups A-D. Normal liver biopsy was taken from Group A. BDL model was created in Groups B and C (15 each). Normal saline and BMC were injected through portal vein (PV) in Groups B and C, respectively. In Group D (healthy rat), only BMC were infused through PV. Groups B and C were compared for body weight, liver functions, survival, and histopathological changes.

RESULTS

Serum bilirubin was lower in Group C at day 6 (p = 0.0010). Median survival time was 5 (4, 6) and 13 (9, 17) days in Groups B and C (p = 0.0147), respectively. Portal edema (p = 0.013) and portal inflammation (p = 0.025) were less in Group C vs Group B. On post hoc subgroup analysis of rats surviving 8-26 days, portal inflammation (p = 0.004), bile duct proliferation (p = 0.016) and portal fibrosis (p = 0.038) were less in Group C vs Group B. Hepatocyte regeneration was found in four rats in Group C. CD34-positive cells were prominent in sinusoids and portal tracts in the BDL rat model.

CONCLUSIONS

BMC have shown to delay fibrosis, facilitate hepatocyte regeneration and improve survival in an experimental BDL model, with potential clinical implication in obstructive cholangiopathy.

Liver bioengineering: Current status and future perspectives

The present review aims to illustrate the strategies that are being implemented to regenerate or bioengineer livers for clinical purposes. There are two general pathways to liver bioengineering and regeneration. The first consists of creating a supporting scaffold, either synthetically or by decellularization of human or animal organs, and seeding cells on the scaffold, where they will mature either in bioreactors or in vivo. This strategy seems to offer the quickest route to clinical translation, as demonstrated by the development of liver organoids from rodent livers which were repopulated with organ specific cells of animal and/or human origin. Liver bioengineering has potential for transplantation and for toxicity testing during preclinical drug development. The second possibility is to induce liver regeneration of dead or resected tissue by manipulating cell pathways. In fact, it is well known that the liver has peculiar regenerative potential which allows hepatocyte hyperplasia after amputation of liver volume. Infusion of autologous bone marrow cells, which aids in liver regeneration, into patients was shown to be safe and to improve their clinical condition, but the specific cells responsible for liver regeneration have not yet been determined and the underlying mechanisms remain largely unknown. A complete understanding of the cell pathways and dynamics and of the functioning of liver stem cell niche is necessary for the clinical translation of regenerative medicine strategies. As well, it will be crucial to elucidate the mechanisms through which cells interact with the extracellular matrix, and how this latter supports and drives cell fate.

Expression of epithelial cell adhesion molecule and proliferating cell nuclear antigen in diethylnitrosamine-induced hepatocarcinogenesis in mice

To clarify the role of stem cells in hepatocarcinogenesis, the expression of epithelial cell adhesion molecule (EpCAM) and proliferating cell nuclear antigen (PCNA) was investigated in mouse hepatic tumors and embryonic cell lineages. Ten ICR mice were treated with diethylnitrosamine (DEN) at 14 days of age and sacrificed at 36 weeks subsequent to DEN treatment to obtain the hepatic tumors. Mouse embryonic stem cells, hepatic progenitor cells and hepatocyte-like cells, representing 0, 22 and 40 days of differentiation, respectively, were treated in vitro with DEN at four doses (0, 1, 5 and 15 mM; G1, G2, G3 and G4, respectively) for 24 h and RNA was isolated. A total of 71 hepatic tumors were obtained from the DEN-treated mice. EpCAM expression was increased mainly in hepatic tumor cells, although it was also detected in the surrounding visually normal cells. Double staining showed that EpCAM and PCNA were co-expressed in numerous tumor cells. In vitro, EpCAM expression was significantly different for G4 at day 0 (P<0.01) and for G2, G3 and G4 at day 40 (P<0.01) compared with the control (G1) at the corresponding time-point. PCNA expression was significantly different for G3 and G4 at day 0 (P<0.01), for G2, G3 and G4 at day 22 (P<0.01) and for G2 at day 40 (P<0.01) compared with G1 at the corresponding time-point. In summary, the expression of EpCAM and PCNA was increased in DEN-induced tumors and the expression of EpCAM and PCNA was altered by DEN treatment in cultured cells. This suggests that EpCAM expression may be modulated in the progeny of adult liver stem cells during their differentiation toward hepatocytes and may be increased during DEN-induced hepatocarcinogenesis.

Histone deacetylase inhibitors in cell pluripotency, differentiation, and reprogramming

Histone deacetylase inhibitors (HDACi) are small molecules that have important and pleiotropic effects on cell homeostasis. Under distinct developmental conditions, they can promote either self-renewal or differentiation of embryonic stem cells. In addition, they can promote directed differentiation of embryonic and tissue-specific stem cells along the neuronal, cardiomyocytic, and hepatic lineages. They have been used to facilitate embryo development following somatic cell nuclear transfer and induced pluripotent stem cell derivation by ectopic expression of pluripotency factors. In the latter method, these molecules not only increase effectiveness, but can also render the induction independent of the oncogenes c-Myc and Klf4. Here we review the molecular pathways that are involved in the functions of HDAC inhibitors on stem cell differentiation and reprogramming of somatic cells into pluripotency. Deciphering the mechanisms of HDAC inhibitor actions is very important to enable their exploitation for efficient and simple tissue regeneration therapies.

Generation of functional hepatic cells from pluripotent stem cells

Liver diseases affect millions of people worldwide, especially in developing country. According to the American Liver Foundation, nearly 1 in every 10 Americans suffers from some form of liver disease. Even though, the liver has great ability to self-repair, in end-stage liver diseases including fibrosis, cirrhosis, and liver cancer induced by viral hepatitis and drugs, the liver regenerative capacity is exhausted. The only successful treatment for chronic liver failure is the whole liver transplantation. More recently, some clinical trials using hepatocyte transplantation have shown some clinical improvement for metabolic liver diseases and acute liver failure. However, the shortage of donor livers remains a life-threatening challenge in liver disease patients. To overcome the scarcity of donor livers, hepatocytes generated from embryonic stem cell or induced pluripotent stem cell differentiation cultures could provide an unlimited supply of such cells for transplantation. This review provides an updated summary of hepatic differentiation protocols published so far, with a characterization of the hepatic cells generated in vitro and their ability to regenerate damaged livers in vivo following transplantation in pre-clinical liver deficient mouse models.

Pluripotency-related, valproic acid (VPA)-induced genome-wide histone H3 lysine 9 (H3K9) acetylation patterns in embryonic stem cells

Embryonic stem cell (ESC) chromatin is characterized by a unique set of histone modifications, including enrichment for H3 lysine 9 acetylation (H3K9ac). Recent studies suggest that histone deacetylase (HDAC) inhibitors promote pluripotency. Here, using H3K9ac ChIP followed by high throughput sequencing analyses and gene expression in E14 mouse ESCs before and after treatment with a low level of the HDAC inhibitor valproic acid, we show that H3K9ac is enriched at gene promoters and is highly correlated with gene expression and with various genomic features, including different active histone marks and pluripotency-related transcription factors. Curiously, it predicts the cellular location of gene products. Treatment of ESCs with valproic acid leads to a pervasive genome-wide and time-dependent increase in H3K9ac, but this increase is selectively suppressed after 4 h in H3K4me3/H3K27me3 bivalent genes. H3K9ac increase is dependent on the promoter's chromatin state and is affected by the binding of P300, various transcription factors, and active histone marks. This study provides insights into the genomic response of ESCs to a low level of HDAC inhibitor, which leads to increased pluripotency. The results suggest that a mild (averaging less than 40%) but global change in the chromatin state is involved in increased pluripotency and that specific mechanisms operate selectively in bivalent genes to maintain constant H3K9ac levels. Our data support the notion that H3K9ac has an important role in ESC biology.

Prospects for Induced Phiripotent Stem Cell-Derived Hepatocytes in Cell Therapy

Induced pluripotent stem (iPS) cells, first established in 2006, have the same characteristics of self-renew-ability and pluripotency as embryonic stem (ES) cells. iPS cells are inducible from patient-specific somatic cells; therefore, they hold significant advantages for overcoming immunological rejection as well as the ethical issues associated with the derivation of ES cells from embryos. Generation of patient-derived hepatocytes by iPS technology and their use in cell transplantation therapy for patients with liver disease is quite attractive. Here, we discuss recent advances and challenges in hepatocyte differentiation from iPS cells and their utility in cell therapy.

Directed hepatic differentiation from embryonic stem cells

The liver is the largest internal organ in mammals, and is important for the maintenance of normal physiological functions of other tissues and organs. Hepatitis, cirrhosis, liver cancer and other chronic liver diseases are serious threats to human health, and these problems are compounded by a scarcity of liver donors for transplantation therapies. Directed differentiation of embryonic stem cells to liver cells is a promising strategy for obtaining hepatocytes that can be used for cell transplantation. In vitro hepatocyte differentiation of embryonic stem cells requires a profound understanding of normal development during embryonic hepatogenesis. Here we provide a simple description of hepatogenesis in vivo and discuss directed differentiation of embryonic stem cells into hepatocytes in vitro.

Musashi 1-positive cells derived from mouse embryonic stem cells can differentiate into neural and intestinal epithelial-like cells in vivo

Msi1 (Musashi 1) is regarded as a marker for neural and intestinal epithelial stem cells. However, it is still unclear whether Msi1-positive cells derived from mouse embryonic stem cells have the ability to differentiate into neural or intestinal epithelial cells. A pMsi1-GFP (green fluorescent protein) reporter plasmid was constructed in order to sort Msi1-positive cells out of the differentiated cell population. The GFP-positive cells (i.e. Msi1-positive cells) were sorted by FACS and were hypodermically engrafted into the backs of NOD/SCID (non-obese diabetic/severe combined immunodeficient) mice. The presence of neural and intestinal epithelial cells in the grafts was detected. Msi1 was highly expressed in the GFP-positive cells, but not in the GFP-negative cells. The markers for neural cells (Nestin and Tubulin β III) and intestinal epithelial cells [FABP2 (fatty acid binding protein 2), Lyz (lysozyme) and ChA (chromogranin A)] were more highly expressed in the grafts from Msi1-positive cells than those from Msi1-negative cells (P<0.05). The grafts from the Msi1-negative cells contained more mesodermal-like tissues than those from the Msi1-positive cells. The pMsi1-GFP vector can be used to sort Msi1-positive cells from a cell population derived from mouse embryonic stem cells. The Msi1-positive cells can differentiate into neural and intestinal epithelial-like cells in vivo.

Differentiation of embryonic stem cells into hepatocytes that coexpress coagulation factors VIII and IX

AIM

To establish an efficient culture system to support embryonic stem (ES) cell differentiation into hepatocytes that coexpress F-VIII and F-IX.

METHODS

Mouse E14 ES cells were cultured in differentiation medium containing sodium butyrate (SB), basic fibroblast growth factor (bFGF), and/or bone morphogenetic protein 4 (BMP4) to induce the differentiation of endoderm cells and hepatic progenitor cells. Hepatocyte growth factor, oncostatin M, and dexamethasone were then used to induce the maturation of ES cell-derived hepatocytes. The mRNA expression levels of endoderm-specific genes and hepatocyte-specific genes, including the levels of F-VIII and F-IX, were detected by RT-PCR and real-time PCR during various stages of differentiation. Protein expression was examined by immunofluorescence and Western blot. At the final stage of differentiation, flow cytometry was performed to determine the percentage of cells coexpressing F-VIII and F-IX, and ELISA was used to detect the levels of F-VIII and F-IX protein secreted into the culture medium.

RESULTS

The expression of endoderm-specific and hepatocyte-specific markers was upregulated to highest level in response to the combination of SB, bFGF, and BMP4. Treatment with the three inducers during hepatic progenitor differentiation significantly enhanced the mRNA and protein levels of F-VIII and F-IX in ES cell-derived hepatocytes. More importantly, F-VIII and F-IX were coexpressed with high efficiency at the final stage of differentiation, and they were also secreted into the culture medium.

CONCLUSION

We have established a novel in vitro differentiation protocol for ES-derived hepatocytes that coexpress F-VIII and F-IX that may provide a foundation for stem cell replacement therapy for hemophilia.

Generating hepatic cell lineages from pluripotent stem cells for drug toxicity screening

Hepatotoxicity is an enormous and increasing problem for the pharmaceutical industry. Early detection of problems during the drug discovery pathway is advantageous to minimize costs and improve patient safety. However, current cellular models are sub-optimal. This review addresses the potential use of pluripotent stem cells in the generation of hepatic cell lineages. It begins by highlighting the scale of the problem faced by the pharmaceutical industry, the precise nature of drug-induced liver injury and where in the drug discovery pathway the need for additional cell models arises. Current research is discussed, mainly for generating hepatocyte-like cells rather than other liver cell-types. In addition, an effort is made to identify where some of the major barriers remain in translating what is currently hypothesis-driven laboratory research into meaningful platform technologies for the pharmaceutical industry.

Progress in stem cell-derived technologies for hepatocellular carcinoma

Primary hepatocellular carcinoma (HCC) is a common malignancy that has a poor prognosis because it is often diagnosed at an advanced stage. HCC normally develops as a consequence of underlying liver disease and is most often associated with cirrhosis. Surgical resection and liver transplantation are the current best options to treat liver cancer. However, problems associated with liver transplantation, such as shortage of donors, risk of immune rejection, and tissue damage following surgery provided the impetus for development of alternative therapies. The emerging field of stem cell therapy has raised hopes for finding curative options for liver cancer. Stem cells have the ability not only to proliferate after transplantation but also to differentiate into most mammalian cell types in vivo. In this review, progress on stem cell-derived technologies for the treatment of liver cancer is discussed.

Effects of sodium butyrate on the differentiation of pancreatic and hepatic progenitor cells from mouse embryonic stem cells

Recently significant progress has been made in differentiating embryonic stem (ES) cells toward pancreatic cells. However, little is known about the generation and identification of pancreatic progenitor cells from ES cells. Here we explored the influence of sodium butyrate on pancreatic progenitor differentiation, and investigated the different effects of sodium butyrate on pancreatic and hepatic progenitor formation. Our results indicated that different concentration and exposure time of sodium butyrate led to different differentiating trends of ES cells. A relatively lower concentration of sodium butyrate with shorter exposure time induced more pancreatic progenitor cell formation. When stimulated by a higher concentration and longer exposure time of sodium butyrate, ES cells differentiated toward hepatic progenitor cells rather than pancreatic progenitor cells. These progenitor cells could further mature into pancreatic and hepatic cells with the supplement of exogenous inducing factors. The resulting pancreatic cells expressed specific markers such as insulin and C-peptide, and were capable of insulin secretion in response to glucose stimulation. The differentiated hepatocytes were characterized by the expression of a number of liver-associated genes and proteins, and had the capability of glycogen storage. Thus, the current study demonstrated that sodium butyrate played different roles in inducing ES cells toward pancreatic or hepatic progenitor cells. These progenitor cells could be further induced into mature pancreatic cells and hepatocytes. This finding may facilitate the understanding of pancreatic and hepatic cell differentiation from ES cells, and provide a potential source of transplantable cells for cell-replacement therapies.

Generation of functional hepatocytes from mouse induced pluripotent stem cells

Induced pluripotent stem cells are derived from somatic cells by forced expression of several transcriptional factors. Induced pluripotent stem cells resemble embryonic stem cells in many aspects, such as the expression of certain stem cell markers, chromatin methylation patterns, embryoid body formation and teratoma formation. Therefore, induced pluripotent stem cells provide a powerful tool for study of developmental biology and unlimited resources for transplantation therapy. Here we reported the successful induction of mouse induced pluripotent stem cells and a simple and efficient process for generation of functional hepatocytes from mouse induced pluripotent stem cells by sequential addition of inducing factors. These induced pluripotent stem cell-derived hepatocytes, just as mouse embryonic stem cell-derived hepatocytes, expressed hepatic lineage markers including CK7, CK8, CK18, CK19, alpha-fetoprotein, albumin, Cyp7a1, and exhibited functional hepatic characteristics, including glycogen storage, indocyanine green (ICG) uptake and release, low-density lipoprotein (LDL) uptake and urea secretion. Although we observed some variations in the efficiency of hepatic differentiation between induced pluripotent stem cells and common mouse embryonic stem cell lines, our results indicate that mouse induced pluripotent stem cells can efficiently differentiate into functional hepatocytes in vitro, which may be helpful for the study of liver development and regenerative medicine.

Generation of a monoclonal antibody specifically reacting with undifferentiated liver progenitor cells

An adult rat liver progenitor cell line Lig-8 was established. In the induction by sodium butyrate, these cells were shown to be able to differentiate into both hepatocytes and bile duct cells expressing albumin and cytokeratin-19, the markers of respective cell types. In order to generate Lig-8 specific antibody for further studies, we produced a monoclonal antibody using the whole Lig-8 cells as immunogen. The yielded monoclonal antibody, named Ligab, belongs to IgG subclass G1 and kappa light chain. It specifically stained on Lig-8 cells in the cytoplasm but not on a rat hepatoma cell line H4IIE. Its immunoreaction against Lig-8 cell lysate on dot blots diminished as the concentration of sodium dodecyl sulfate (SDS) in the lysate increased to 2%, a level in the sample buffer of standard SDS-polyacrylamide gel electrophoresis (PAGE). Not surprisingly, Ligab failed to detect its reacting antigen in Lig-8 cell lysate by standard SDS-PAGE-based immunoblotting. It could detect this antigen only by native PAGE-based immunoblotting. These characteristics suggested that the antigenic epitope for Ligab is likely a molecular structure instead of a peptide sequence. More interestingly, expression of Ligab-reacting antigen in Lig-8 cells declined as the cells were induced to differentiate by sodium butyrate. This antigen is very likely a differentiation-related marker for these cells, and this monoclonal antibody may help study the molecular mechanisms of liver progenitor cell differentiation.

Sodium butyrate and dexamethasone promote exocrine pancreatic gene expression in mouse embryonic stem cells

AIM

The feasibility of inducing endocrine pancreatic differentiation of embryonic stem (ES) cells has been well documented. However, whether ES cells possess the potential for exocrine pancreatic differentiation requires further exploration. Here, we investigated whether sodium butyrate and glucocorticoids were conducive to the exocrine pancreatic differentiation of ES cells.

METHODS

E14 mouse ES cells were cultured in suspension to form embryoid bodies (EBs). These EBs were cultured in differentiating medium containing varying concentrations of sodium butyrate. The effects of activinA and dexamethasone (Dex) on exocrine differentiation were also explored. Finally, the combination of sodium butyrate, activinA, and Dex was used to promote the differentiation of exocrine pancreatic cells. Specific exocrine pancreatic gene expression was detected by reverse transcription polymerase chain reaction (RT-PCR) and amylase expression was examined by immunofluorescence staining. Flow cytometry analysis was also performed to determine the percentage of amylase-positive cells after the treatment with activinA, sodium butyrate, and Dex.

RESULTS

Exposure of ES cells to 1 mmol/L sodium butyrate for 5 days promoted exocrine pancreatic gene expression. Further combination with Dex and other pancreatic-inducing factors, such as activinA, significantly enhanced the mRNA and protein levels of exocrine pancreatic markers. Additionally, flow cytometry revealed that approximately 17% of the final differentiated cells were amylase-positive.

CONCLUSION

These data indicate that the exocrine pancreatic differentiation of ES cells can be induced by activinA, sodium butyrate, and Dex, providing a potential tool for studying pancreatic differentiation and pancreas-related diseases.

In vitro differentiation of embryonic and adult stem cells into hepatocytes: state of the art

Stem cells are a unique source of self-renewing cells within the human body. Before the end of the last millennium, adult stem cells, in contrast to their embryonic counterparts, were considered to be lineage-restricted cells or incapable of crossing lineage boundaries. However, the unique breakthrough of muscle and liver regeneration by adult bone marrow stem cells at the end of the 1990s ended this long-standing paradigm. Since then, the number of articles reporting the existence of multipotent stem cells in skin, neuronal tissue, adipose tissue, and bone marrow has escalated, giving rise, both in vivo and in vitro, to cell types other than their tissue of origin. The phenomenon of fate reprogrammation and phenotypic diversification remains, though, an enigmatic and rare process. Understanding how to control both proliferation and differentiation of stem cells and their progeny is a challenge in many fields, going from preclinical drug discovery and development to clinical therapy. In this review, we focus on current strategies to differentiate embryonic, mesenchymal(-like), and liver stem/progenitor cells into hepatocytes in vitro. Special attention is paid to intracellular and extracellular signaling, genetic modification, and cell-cell and cell-matrix interactions. In addition, some recommendations are proposed to standardize, optimize, and enrich the in vitro production of hepatocyte-like cells out of stem/progenitor cells.

Role of epigenetics in liver-specific gene transcription, hepatocyte differentiation and stem cell reprogrammation

Controlling both growth and differentiation of stem cells and their differentiated somatic progeny is a challenge in numerous fields, from preclinical drug development to clinical therapy. Recently, new insights into the underlying molecular mechanisms have unveiled key regulatory roles of epigenetic marks driving cellular pluripotency, differentiation and self-renewal/proliferation. Indeed, the transcription of genes, governing cell-fate decisions during development and maintenance of a cell's differentiated status in adult life, critically depends on the chromatin accessibility of transcription factors to genomic regulatory and coding regions. In this review, we discuss the epigenetic control of (liver-specific) gene-transcription and the intricate interplay between chromatin modulation, including histone (de)acetylation and DNA (de)methylation, and liver-enriched transcription factors. Special attention is paid to their role in directing hepatic differentiation of primary hepatocytes and stem cells in vitro.

Proteomic analysis identifies proteins that continue to grow hepatic stem-like cells without differentiation

To understand the molecular mechanism underlying vigorous proliferative activity of hepatic stem-like (HSL) cells, we performed two-dimensional electrophoresis to identify the proteins statistically more abundant in rapidly growing undifferentiated HSL cells than in sodium butyrate-treated differentiated HSL cells. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry and Mascot search identified 6 proteins including prohibitin, vimentin, ezrin, annexin A3, acidic ribosomal phosphoprotein P0 and Grp75. Prohibitin and vimentin control the mitogen-activated protein (MAP) kinase pathway. Ezrin is phosphorylated by various protein-tyrosine kinases and modulates interactions between cytoskeletal and membrane proteins. Annexin A3 has a role in DNA synthesis. Acidic ribosomal phosphoprotein P0 and Grp75 play in protein synthesis. These results suggest that the proteins related to the MAP kinase cascade had some role in continuous proliferation of HSL cells without differentiation.

Nuclear proteomics and directed differentiation of embryonic stem cells

During the past decade, regenerative medicine has been the subject of intense interest due, in large part, to our growing knowledge of embryonic stem (ES) cell biology. ES cells give rise to cell lineages from the three primordial germ layers--endoderm, mesoderm, and ectoderm. This process needs to be channeled if these cells are to be differentiated efficiently and used subsequently for therapeutic purposes. Indeed, an important area of investigation involves directed differentiation to influence the lineage commitment of these pluripotent cells in vitro. Various strategies involving timely growth factor supplementation, cell co-cultures, and gene transfection are used to drive lineage specific emergence. The underlying goal is to control directly the center of gene expression and cellular programming--the nucleus. Gene expression is enabled, managed, and sustained by the collective actions and interactions of proteins found in the nucleus--the nuclear proteome--in response to extracellular signaling. Nuclear proteomics can inventory these nuclear proteins in differentiating cells and decipher their dynamics during cellular phenotypic commitment. This review details what is currently known about nuclear effectors of stem cell differentiation and describes emerging techniques in the discovery of nuclear proteomics that will illuminate new transcription factors and modulators of gene expression.

Selective enrichment of hepatocytes from mouse embryonic stem cells with a culture system containing cholestatic serum

AIM

There is increasing evidence indicating that embryonic stem (ES) cells are capable of differentiating into hepatocyte-like cells in vitro. However, it is necessary to improve the differentiation efficiency so as to promote the clinical application. Here, we report an efficient culture system to support hepatocyte differentiation from ES cells by utilizing cholestatic serum.

METHODS

One week after the induction of E14 mouse ES cells into hepatocytes with sodium butyrate, cholestatic serum was added into the culture system at various concentrations and hepatocyte-like cells were induced to proliferate. The morphological and phenotypic markers of hepatocytes were characterized using light microscopy, immunocytochemistry, and RT-PCR, respectively. The function of glycogen storage of the differentiated cells was detected by Periodic acid-Schiff (PAS) reaction, and the ratio of hepatic differentiation was determined by counting the albumin and PAS-positive cells.

RESULTS

In the presence of conditional selective medium containing cholestatic serum, numerous epithelial cells resembling hepatocytes were observed. The RT-PCR analysis showed that undifferentiated ES cells did not express any hepatic-specific markers; however, in the presence of sodium butyrate and conditional selective medium containing cholestatic serum, hepatic differentiation markers were detected. Immunofluorescence staining showed that those ES-derived hepatocytes were alpha-fetoprotein, albumin, and cytokeratin 18 positive, with the ability of storing glycogen. Further determination of the hepatic differentiation ratio showed that the application of cholestatic serum efficiently enriched ES-derived hepatocyte-like cells by inducing lineage differentiation and enhancing lineage proliferation.

CONCLUSION

The conditional selective medium containing cholestatic serum is optimal to selectively enrich hepatocyte-like cells from mixed differentiated ES cells, which may provide a novel method to improve the hepatic differentiation ratio of ES cells.

Pluripotency of embryonic stem cells

Embryonic stem (ES) cells derived from pre-implantation embryos have the potential to differentiate into any cell type derived from the three germ layers of ectoderm (epidermal tissues and nerves), mesoderm (muscle, bone, blood), and endoderm (liver, pancreas, gastrointestinal tract, lungs), including fetal and adult cells. Alone, these cells do not develop into a viable fetus or adult animal because they do not retain the potential to contribute to extraembryonic tissue, and in vitro, they lack spatial and temporal signaling cues essential to normal in vivo development. The basis of pluripotentiality resides in conserved regulatory networks composed of numerous transcription factors and multiple signaling cascades. Together, these regulatory networks maintain ES cells in a pluripotent and undifferentiated form; however, alterations in the stoichiometry of these signals promote differentiation. By taking advantage of this differentiation capacity in vitro, ES cells have clearly been shown to possess the potential to generate multipotent stem and progenitor cells capable of differentiating into a limited number of cell fates. These latter types of cells may prove to be therapeutically viable, but perhaps more importantly, the studies of these cells have led to a greater understanding of mammalian development.

Alpha one antitrypsin deficiency: from gene to treatment

Alpha1-antitrypsin deficiency is a genetic disorder which contributes to the development of chronic obstructive pulmonary disease, bronchiectasis, liver cirrhosis and panniculitis. The discovery of alpha1-antitrypsin and its function as an antiprotease led to the protease-antiprotease hypothesis, which goes some way to explaining the pathogenesis of emphysema. This article will review the clinical features of alpha1-antitrypsin deficiency, the genetic mutations known to cause it, and how they do so at a molecular level. Specific treatments for the disorder based on this knowledge will be reviewed, including alpha1-antitrypsin replacement, gene therapy and possible future therapies, such as those based on stem cells.