Dynamic signaling network for the specification of embryonic pancreas and liver progenitors

β-cell replacement sources for type 1 diabetes: a focus on pancreatic ductal cells

Thorough research on the capacity of human islet transplantation to cure type 1 diabetes led to the achievement of 3- to 5-year-long insulin independence in nearly half of transplanted patients. Yet, translation of this technique to clinical routine is limited by organ shortage and the need for long-term immunosuppression, restricting its use to adults with unstable disease. The production of new bona fide β cells in vitro was thus investigated and finally achieved with human pluripotent stem cells (PSCs). Besides ethical concerns about the use of human embryos, studies are now evaluating the possibility of circumventing the spontaneous tumor formation associated with transplantation of PSCs. These issues fueled the search for cell candidates for β-cell engineering with safe profiles for clinical translation. In vivo studies revealed the regeneration capacity of the exocrine pancreas after injury that depends at least partially on facultative progenitors in the ductal compartment. These stimulated subpopulations of pancreatic ductal cells (PDCs) underwent β-cell transdifferentiation through reactivation of embryonic signaling pathways. In vitro models for expansion and differentiation of purified PDCs toward insulin-producing cells were described using cocktails of growth factors, extracellular-matrix proteins and transcription factor overexpression. In this review, we will describe the latest findings in pancreatic β-cell mass regeneration due to adult ductal progenitor cells. We will further describe recent advances in human PDC transdifferentiation to insulin-producing cells with potential for clinical translational studies.

Iterative use of nuclear receptor Nr5a2 regulates multiple stages of liver and pancreas development

The stepwise progression of common endoderm progenitors into differentiated liver and pancreas organs is regulated by a dynamic array of signals that are not well understood. The nuclear receptor subfamily 5, group A, member 2 gene nr5a2, also known as Liver receptor homolog-1 (Lrh-1) is expressed in several tissues including the developing liver and pancreas. Here, we interrogate the role of Nr5a2 at multiple developmental stages using genetic and chemical approaches and uncover novel pleiotropic requirements during zebrafish liver and pancreas development. Zygotic loss of nr5a2 in a targeted genetic null mutant disrupted the development of the exocrine pancreas and liver, while leaving the endocrine pancreas intact. Loss of nr5a2 abrogated exocrine pancreas markers such as trypsin, while pancreas progenitors marked by ptf1a or pdx1 remained unaffected, suggesting a role for Nr5a2 in regulating pancreatic acinar cell differentiation. In the developing liver, Nr5a2 regulates hepatic progenitor outgrowth and differentiation, as nr5a2 mutants exhibited reduced hepatoblast markers hnf4α and prox1 as well as differentiated hepatocyte marker fabp10a. Through the first in vivo use of Nr5a2 chemical antagonist Cpd3, the iterative requirement for Nr5a2 for exocrine pancreas and liver differentiation was temporally elucidated: chemical inhibition of Nr5a2 function during hepatopancreas progenitor specification was sufficient to disrupt exocrine pancreas formation and enhance the size of the embryonic liver, suggesting that Nr5a2 regulates hepatic vs. pancreatic progenitor fate choice. Chemical inhibition of Nr5a2 at a later time during pancreas and liver differentiation was sufficient to block the formation of mature acinar cells and hepatocytes. These findings define critical iterative and pleiotropic roles for Nr5a2 at distinct stages of pancreas and liver organogenesis, and provide novel perspectives for interpreting the role of Nr5a2 in disease.

Stage-specific regulation of the WNT/β-catenin pathway enhances differentiation of hESCs into hepatocytes

BACKGROUND & AIMS

Hepatocytes differentiated from human embryonic stem cells (hESCs) have the potential to overcome the shortage of primary hepatocytes for clinical use and drug development. Many strategies for this process have been reported, but the functionality of the resulting cells is incomplete. We hypothesize that the functionality of hPSC-derived hepatocytes might be improved by making the differentiation method more similar to normal in vivo hepatic development.

METHODS

We tested combinations of growth factors and small molecules targeting candidate signaling pathways culled from the literature to identify optimal conditions for differentiation of hESCs to hepatocytes, using qRT-PCR for stage-specific markers to identify the best conditions. Immunocytochemistry was then used to validate the selected conditions. Finally, induction of expression of metabolic enzymes in terminally differentiated cells was used to assess the functionality of the hESC-derived hepatocytes.

RESULTS

Optimal differentiation of hESCs was attained using a 5-stage protocol. After initial induction of definitive endoderm (stage 1), we showed that inhibition of the WNT/β-catenin pathway during the 2nd and 3rd stages of differentiation was required to specify first posterior foregut, and then hepatic gut cells. In contrast, during the 4th stage of differentiation, we found that activation of the WNT/β-catenin pathway allowed generation of proliferative bipotent hepatoblasts, which then were efficiently differentiated into hepatocytes in the 5th stage by dual inhibition of TGF-β and NOTCH signaling.

CONCLUSION

Here, we show that stage-specific regulation of the WNT/β-catenin pathway results in improved differentiation of hESCs to functional hepatocytes.

Syndecan4 coordinates Wnt/JNK and BMP signaling to regulate foregut progenitor development

Temporally and spatially dynamic Wnt and BMP signals are essential to pattern foregut endoderm progenitors that give rise to the liver, pancreas and lungs, but how these two signaling pathways are coordinated in the extracellular space is unknown. Here we identify the transmembrane heparan sulphate proteoglycan Syndecan-4 (Sdc4), as a key regulator of both non-canonical Wnt and BMP signaling in the Xenopus foregut. Foregut-specific Sdc4 depletion results in a disrupted Fibronectin (Fn1) matrix, reduced cell adhesion, and failure to maintain foregut gene expression ultimately leading to foregut organ hypoplasia. Sdc4 is required to maintain robust Wnt/JNK and BMP/Smad1 signaling in the hhex+ foregut progenitors. Pathway analysis suggests that Sdc4 functionally interacts with Fzd7 to promote Wnt/JNK signaling, which maintains foregut identity and cell adhesion. In addition, the Sdc4 ectodomain is required to support Fn1 matrix assembly, which is essential for the robust BMP signaling that promotes foregut gene expression. This work sheds lights on how the extracellular matrix can coordinate different signaling pathways during organogenesis.

Extracellular matrix microarrays to study inductive signaling for endoderm specification

During tissue development, stem and progenitor cells are faced with fate decisions coordinated by microenvironmental cues. Although insights have been gained from in vitro and in vivo studies, the role of the microenvironment remains poorly understood due to the inability to systematically explore combinations of stimuli at a large scale. To overcome such restrictions, we implemented an extracellular matrix (ECM) array platform that facilitates the study of 741 distinct combinations of 38 different ECM components in a systematic, unbiased and high-throughput manner. Using embryonic stem cells as a model system, we derived definitive endoderm progenitors and applied them to the array platform to study the influence of ECM, including the interactions of ECM with growth factor signaling, on the specification of definitive endoderm cells towards the liver and pancreas fates. We identified ECM combinations that influence endoderm fate decisions towards these lineages, and demonstrated the utility of this platform for studying ECM-mediated modifications to signal activation during liver specification. In particular, defined combinations of fibronectin and laminin isoforms, as well as combinations of distinct collagen subtypes, were shown to influence SMAD pathway activation and the degree of hepatic differentiation. Overall, our systematic high-throughput approach suggests that ECM components of the microenvironment have modulatory effects on endoderm differentiation, including effects on lineage fate choice and cell adhesion and survival during the differentiation process. This platform represents a robust tool for analyzing effects of ECM composition towards the continued improvement of stem cell differentiation protocols and further elucidation of tissue development processes.

STATEMENT OF SIGNIFICANCE

Cellular microarrays can provide the capability to perform high-throughput investigations into the role of microenvironmental signals in a variety of cell functions. This study demonstrates the utility of a high-throughput cellular microarray approach for analyzing the effects of extracellular matrix (ECM) in liver and pancreas differentiation of endoderm progenitor cells. Despite an appreciation that ECM is likely involved in these processes, the influence of ECM, particularly combinations of matrix proteins, had not been systematically explored. In addition to the identification of relevant ECM compositions, this study illustrates the capability of the cellular microarray platform to be integrated with a diverse range of cell fate measurements, which could be broadly applied towards the investigation of cell fate regulation in other tissue development and disease contexts.

Liver-Enriched Gene 1, a Glycosylated Secretory Protein, Binds to FGFR and Mediates an Anti-stress Pathway to Protect Liver Development in Zebrafish

Unlike mammals and birds, teleost fish undergo external embryogenesis, and therefore their embryos are constantly challenged by stresses from their living environment. These stresses, when becoming too harsh, will cause arrest of cell proliferation, abnormal cell death or senescence. Such organisms have to evolve a sophisticated anti-stress mechanism to protect the process of embryogenesis/organogenesis. However, very few signaling molecule(s) mediating such activity have been identified. liver-enriched gene 1 (leg1) is an uncharacterized gene that encodes a novel secretory protein containing a single domain DUF781 (domain of unknown function 781) that is well conserved in vertebrates. In the zebrafish genome, there are two copies of leg1, namely leg1a and leg1b. leg1a and leg1b are closely linked on chromosome 20 and share high homology, but are differentially expressed. In this report, we generated two leg1a mutant alleles using the TALEN technique, then characterized liver development in the mutants. We show that a leg1a mutant exhibits a stress-dependent small liver phenotype that can be prevented by chemicals blocking the production of reactive oxygen species. Further studies reveal that Leg1a binds to FGFR3 and mediates a novel anti-stress pathway to protect liver development through enhancing Erk activity. More importantly, we show that the binding of Leg1a to FGFR relies on the glycosylation at the 70^th asparagine (Asn⁷⁰ or N⁷⁰), and mutating the Asn⁷⁰ to Ala⁷⁰ compromised Leg1’s function in liver development. Therefore, Leg1 plays a unique role in protecting liver development under different stress conditions by serving as a secreted signaling molecule/modulator.

Although being challenged by stresses from their living environment during embryogenesis, teleost fish harbor a robust genetic program dictating liver development as long as any environmental change, including temperature or natural UV irradiation, is not detrimental. It is therefore of interest to explore the mechanism(s) behind this phenomenon. We showed that Liver-enriched gene 1 (Leg1) plays a unique role in protecting liver development under different stress conditions by serving as a secretory signaling molecule/modulator that binds to FGF receptor and activates the Erk signaling pathway. This finding may explain the adaption of teleost fish in coping with environmental changes.

Recent Advances in Disease Modeling and Drug Discovery for Diabetes Mellitus Using Induced Pluripotent Stem Cells

Diabetes mellitus (DM) is a widespread metabolic disease with a progressive incidence of morbidity and mortality worldwide. Despite extensive research, treatment options for diabetic patients remains limited. Although significant challenges remain, induced pluripotent stem cells (iPSCs) have the capacity to differentiate into any cell type, including insulin-secreting pancreatic β cells, highlighting its potential as a treatment option for DM. Several iPSC lines have recently been derived from both diabetic and healthy donors. Using different reprogramming techniques, iPSCs were differentiated into insulin-secreting pancreatic βcells. Furthermore, diabetes patient-derived iPSCs (DiPSCs) are increasingly being used as a platform to perform cell-based drug screening in order to develop DiPSC-based cell therapies against DM. Toxicity and teratogenicity assays based on iPSC-derived cells can also provide additional information on safety before advancing drugs to clinical trials. In this review, we summarize recent advances in the development of techniques for differentiation of iPSCs or DiPSCs into insulin-secreting pancreatic β cells, their applications in drug screening, and their role in complementing and replacing animal testing in clinical use. Advances in iPSC technologies will provide new knowledge needed to develop patient-specific iPSC-based diabetic therapies.

Four and a Half LIM Domains 1b (Fhl1b) Is Essential for Regulating the Liver versus Pancreas Fate Decision and for β-Cell Regeneration

The liver and pancreas originate from overlapping embryonic regions, and single-cell lineage tracing in zebrafish has shown that Bone morphogenetic protein 2b (Bmp2b) signaling is essential for determining the fate of bipotential hepatopancreatic progenitors towards the liver or pancreas. Despite its pivotal role, the gene regulatory networks functioning downstream of Bmp2b signaling in this process are poorly understood. We have identified four and a half LIM domains 1b (fhl1b), which is primarily expressed in the prospective liver anlage, as a novel target of Bmp2b signaling. fhl1b depletion compromised liver specification and enhanced induction of pancreatic cells from endodermal progenitors. Conversely, overexpression of fhl1b favored liver specification and inhibited induction of pancreatic cells. By single-cell lineage tracing, we showed that fhl1b depletion led lateral endodermal cells, destined to become liver cells, to become pancreatic cells. Reversely, when fhl1b was overexpressed, medially located endodermal cells, fated to differentiate into pancreatic and intestinal cells, contributed to the liver by directly or indirectly modulating the discrete levels of pdx1 expression in endodermal progenitors. Moreover, loss of fhl1b increased the regenerative capacity of β-cells by increasing pdx1 and neurod expression in the hepatopancreatic ductal system. Altogether, these data reveal novel and critical functions of Fhl1b in the hepatic versus pancreatic fate decision and in β-cell regeneration.

Lineage-specific multipotent progenitors play crucial roles in embryonic development, regeneration in adult tissues, and diseases such as cancer. Bone morphogenetic protein (Bmp) signaling is critical for regulating the cell fate choice of liver versus pancreas, two essential organs of body metabolism. Through transcriptome profiling of endodermal tissues exposed to increased or decreased Bmp2b signaling, we have discovered the zebrafish gene four and a half LIM domains 1b (fhl1b) as a novel target of Bmp2b signaling. fhl1b is primarily expressed in the prospective liver anlage. Loss- and gain-of-function analyses indicate that Fhl1b suppresses specification of the pancreas and induces the liver. By single-cell lineage tracing, we showed that depletion of fhl1b caused a liver-to-pancreas fate switch, while fhl1b overexpression redirected pancreatic progenitors to become liver cells. At later stages, Fhl1b regulates regeneration of insulin-secreting β-cells by directly or indirectly modulating pdx1 and neurod expression in the hepatopancreatic ductal system. Therefore, our work provides a novel paradigm of how Bmp signaling regulates the hepatic versus pancreatic fate decision and β-cell regeneration through its novel target Fhl1b.

Signaling and Gene Regulatory Networks Governing Definitive Endoderm Derivation From Pluripotent Stem Cells

The generation of definitive endoderm (DE) from pluripotent stem cells (PSCs) is a fundamental stage in the formation of highly organized visceral organs, such as the liver and pancreas. Currently, there is a need for a comprehensive study that illustrates the involvement of different signaling pathways and their interactions in the derivation of DE cells from PSCs. This study aimed to identify signaling pathways that have the greatest influence on DE formation using analyses of transcriptional profiles, protein-protein interactions, protein-DNA interactions, and protein localization data. Using this approach, signaling networks involved in DE formation were constructed using systems biology and data mining tools, and the validity of the predicted networks was confirmed experimentally by measuring the mRNA levels of hub genes in several PSCs-derived DE cell lines. Based on our analyses, seven signaling pathways, including the BMP, ERK1-ERK2, FGF, TGF-beta, MAPK, Wnt, and PIP signaling pathways and their interactions, were found to play a role in the derivation of DE cells from PSCs. Lastly, the core gene regulatory network governing this differentiation process was constructed. The results of this study could improve our understanding surrounding the efficient generation of DE cells for the regeneration of visceral organs. J. Cell. Physiol. 231: 1994-2006, 2016. © 2016 Wiley Periodicals, Inc.

From Endoderm to Liver Bud: Paradigms of Cell Type Specification and Tissue Morphogenesis

The early specification, rapid growth and morphogenesis, and conserved functions of the embryonic liver across diverse model organisms have made the system an experimentally facile paradigm for understanding basic regulatory mechanisms that govern cell differentiation and organogenesis. This essay highlights concepts that have emerged from studies of the discrete steps of foregut endoderm development into the liver bud, as well as from modeling the steps via embryonic stem cell differentiation. Such concepts include understanding the chromatin basis for the competence of progenitor cells to develop into specific lineages; the importance of combinatorial signaling from different sources to induce cell fates; the impact of inductive signaling on preexisting chromatin states; the ability of separately specified domains of cells to merge into a common tissue; and the marked cell biological dynamics, including interactions with the developing vasculature, which establish the initial morphogenesis and patterning of a tissue. The principles gleaned from these studies, focusing on the 2 days it takes for the endoderm to develop into a liver bud, should be instructive for many other organogenic systems and for manipulating tissues in regenerative contexts for biomedical purposes.

Human pancreas development

A wealth of data and comprehensive reviews exist on pancreas development in mammals, primarily mice, and other vertebrates. By contrast, human pancreatic development has been less comprehensively reviewed. Here, we draw together those studies conducted directly in human embryonic and fetal tissue to provide an overview of what is known about human pancreatic development. We discuss the relevance of this work to manufacturing insulin-secreting β-cells from pluripotent stem cells and to different aspects of diabetes, especially permanent neonatal diabetes, and its underlying causes.

Bone morphogenetic proteins in inflammation, glucose homeostasis and adipose tissue energy metabolism

Bore morphogenetic proteins (BMPs) are members of the transforming growth factor (TGF)-β superfamily, a group of secreted proteins that regulate embryonic development. This review summarizes the effects of BMPs on physiological processes not exclusively linked to the musculoskeletal system. Specifically, we focus on the involvement of BMPs in inflammatory disorders, e.g. fibrosis, inflammatory bowel disease, anchylosing spondylitis, rheumatoid arthritis. Moreover, we discuss the role of BMPs in the context of vascular disorders, and explore the role of these signalling proteins in iron homeostasis (anaemia, hemochromatosis) and oxidative damage. The second and third parts of this review focus on BMPs in the development of metabolic pathologies such as type-2 diabetes mellitus and obesity. The pancreatic beta cells are the sole source of the hormone insulin and BMPs have recently been implicated in pancreas development as well as control of adult glucose homeostasis. Lastly, we review the recently recognized role of BMPs in brown adipose tissue formation and their consequences for energy expenditure and adiposity. In summary, BMPs play a pivotal role in metabolism beyond their role in skeletal homeostasis. However, increased understanding of these pleiotropic functions also highlights the necessity of tissue-specific strategies when harnessing BMP action as a therapeutic target.

Possible association between hepatitis C virus and malignancies different from hepatocellular carcinoma: A systematic review

AIM

To summarize the current knowledge about the potential relationship between hepatitis C virus (HCV) infection and the risk of several extra-liver cancers.

METHODS

We performed a systematic review of the literature, according to the Preferred Reporting Items for Systematic reviews and Meta-Analysis (PRISMA) Statement. We extracted the pertinent articles, published in MEDLINE and the Cochrane Library, using the following search terms: neoplasm/cancer/malignancy/tumor/carcinoma/adeno-carcinoma and non-Hodgkin lymphomas, kidney/renal-, cholangio-, pancreatic-, thyroid-, breast-,oral-, skin-, prostate-, lung-, colon-, stomach-, haematologic. Case series, case-series with control-group, case-control, cohort-studies as well as meta-analyses, written in English were collected. Some of the main characteristics of retrieved trials, which were designed to investigate the prevalence of HCV infection in each type of the above-mentioned human malignancies were summarised. A main table was defined and included a short description in the text for each of these tumours, whether at least five studies about a specific neoplasm, meeting inclusion criteria, were available in literature. According to these criteria, we created the following sections and the corresponding tables and we indicated the number of included or excluded articles, as well as of meta-analyses and reviews: (1) HCV and haematopoietic malignancies; (2) HCV and cholangiocarcinoma; (3) HCV and pancreatic cancer; (4) HCV and breast cancer; (5) HCV and kidney cancer; (6) HCV and skin or oral cancer; and (7) HCV and thyroid cancer.

RESULTS

According to available data, a clear correlation between regions of HCV prevalence and risk of extra-liver cancers has emerged only for a very small group of types and histological subtypes of malignancies. In particular, HCV infection has been associated with: (1) a higher incidence of some B-cell Non-Hodgkin-Lymphoma types, in countries, where an elevated prevalence of this pathogen is detectable, accounting to a percentage of about 10%; (2) an increased risk of intra-hepatic cholangiocarcinoma; and (3) a correlation between HCV prevalence and pancreatic cancer (PAC) incidence.

CONCLUSION

To date no definitive conclusions may be obtained from the analysis of relationship between HCV and extra-hepatic cancers. Further studies, recruiting an adequate number of patients are required to confirm or deny this association.

BMP-7 Induces Adult Human Pancreatic Exocrine-to-Endocrine Conversion

The exocrine pancreas can give rise to endocrine insulin-producing cells upon ectopic expression of key transcription factors. However, the need for genetic manipulation remains a translational hurdle for diabetes therapy. Here we report the conversion of adult human nonendocrine pancreatic tissue into endocrine cell types by exposure to bone morphogenetic protein 7. The use of this U.S. Food and Drug Administration-approved agent, without any genetic manipulation, results in the neogenesis of clusters that exhibit high insulin content and glucose responsiveness both in vitro and in vivo. In vitro lineage tracing confirmed that BMP-7-induced insulin-expressing cells arise mainly from extrainsular PDX-1(+), carbonic anhydrase II(-) (mature ductal), elastase 3a (acinar)(-) , and insulin(-) subpopulations. The nongenetic conversion of human pancreatic exocrine cells to endocrine cells is novel and represents a safer and simpler alternative to genetic reprogramming.

Progenitor cell niches in the human pancreatic duct system and associated pancreatic duct glands: an anatomical and immunophenotyping study

Pancreatic duct glands (PDGs) are tubule-alveolar glands associated with the pancreatic duct system and can be considered the anatomical counterpart of peribiliary glands (PBGs) found within the biliary tree. Recently, we demonstrated that endodermal precursor niches exist fetally and postnatally and are composed functionally of stem cells and progenitors within PBGs and of committed progenitors within PDGs. Here we have characterized more extensively the anatomy of human PDGs as novel niches containing cells with multiple phenotypes of committed progenitors. Human pancreata (n = 15) were obtained from cadaveric adult donors. Specimens were processed for histology, immunohistochemistry and immunofluorescence. PDGs were found in the walls of larger pancreatic ducts (diameters > 300 μm) and constituted nearly 4% of the duct wall area. All of the cells identified were negative for nuclear expression of Oct4, a pluripotency gene, and so are presumably committed progenitors and not stem cells. In the main pancreatic duct and in large interlobular ducts, Sox9(+) cells represented 5-30% of the cells within PDGs and were located primarily at the bottom of PDGs, whereas rare and scattered Sox9(+) cells were present within the surface epithelium. The expression of PCNA, a marker of cell proliferation, paralleled the distribution of Sox9 expression. Sox9(+) PDG cells proved to be Pdx1(+) /Ngn3(+/-) /Oct4A(-) . Nearly 10% of PDG cells were positive for insulin or glucagon. Intercalated ducts contained Sox9(+) /Pdx1(+) /Ngn3(+) cells, a phenotype that is presumptive of committed endocrine progenitors. Some intercalated ducts appeared in continuity with clusters of insulin-positive cells organized in small pancreatic islet-like structures. In summary, PDGs represent niches of a population of Sox9(+) cells exhibiting a pattern of phenotypic traits implicating a radial axis of maturation from the bottoms of the PDGs to the surface of pancreatic ducts. Our results complete the anatomical background that links biliary and pancreatic tracts and could have important implications for the common patho-physiology of biliary tract and pancreas.

Modeling mouse and human development using organoid cultures

In vitro three-dimensional (3D) cultures are emerging as novel systems with which to study tissue development, organogenesis and stem cell behavior ex vivo. When grown in a 3D environment, embryonic stem cells (ESCs) self-organize into organoids and acquire the right tissue patterning to develop into several endoderm- and ectoderm-derived tissues, mimicking their in vivo counterparts. Tissue-resident adult stem cells (AdSCs) also form organoids when grown in 3D and can be propagated in vitro for long periods of time. In this Review, we discuss recent advances in the generation of pluripotent stem cell- and AdSC-derived organoids, highlighting their potential for enhancing our understanding of human development. We will also explore how this new culture system allows disease modeling and gene repair for a personalized regenerative medicine approach.

Orchestrating liver development

The liver is a central regulator of metabolism, and liver failure thus constitutes a major health burden. Understanding how this complex organ develops during embryogenesis will yield insights into how liver regeneration can be promoted and how functional liver replacement tissue can be engineered. Recent studies of animal models have identified key signaling pathways and complex tissue interactions that progressively generate liver progenitor cells, differentiated lineages and functional tissues. In addition, progress in understanding how these cells interact, and how transcriptional and signaling programs precisely coordinate liver development, has begun to elucidate the molecular mechanisms underlying this complexity. Here, we review the lineage relationships, signaling pathways and transcriptional programs that orchestrate hepatogenesis.

Adult Human Biliary Tree Stem Cells Differentiate to β-Pancreatic Islet Cells by Treatment with a Recombinant Human Pdx1 Peptide

Generation of β-pancreatic cells represents a major goal in research. The aim of this study was to explore a protein-based strategy to induce differentiation of human biliary tree stem cells (hBTSCs) towards β-pancreatic cells. A plasmid containing the sequence of the human pancreatic and duodenal homeobox 1 (PDX1) has been expressed in E. coli. Epithelial-Cell-Adhesion-Molecule positive hBTSCs or mature human hepatocyte cell line, HepG2, were grown in medium to which Pdx1 peptide was added. Differentiation toward pancreatic islet cells were evaluated by the expression of the β-cell transcription factors, Pdx1 and musculoapo-neurotic fibrosarcoma oncogene homolog A, and of the pancreatic hormones, insulin, glucagon, and somatostatin, investigated by real time polymerase chain reaction, western blot, light microscopy and immunofluorescence. C-peptide secretion in response to high glucose was also measured. Results indicated how purified Pdx1 protein corresponding to the primary structure of the human Pdx1 by mass spectroscopy was efficiently produced in bacteria, and transduced into hBTSCs. Pdx1 exposure triggered the expression of both intermediate and mature stage β-cell differentiation markers only in hBTSCs but not in HepG2 cell line. Furthermore, hBTSCs exposed to Pdx1 showed up-regulation of insulin, glucagon and somatostatin genes and formation of 3-dimensional islet-like structures intensely positive for insulin and glucagon. Finally, Pdx1-induced islet-like structures exhibited glucose-regulated C-peptide secretion. In conclusion, the human Pdx1 is highly effective in triggering hBTSC differentiation toward functional β-pancreatic cells.

Cytoskeletal Reorganization Drives Mesenchymal Condensation and Regulates Downstream Molecular Signaling

Skeletal condensation occurs when specified mesenchyme cells self-organize over several days to form a distinctive cartilage template. Here, we determine how and when specified mesenchyme cells integrate mechanical and molecular information from their environment, forming cartilage condensations in the pharyngeal arches of chick embryos. By disrupting cytoskeletal reorganization, we demonstrate that dynamic cell shape changes drive condensation and modulate the response of the condensing cells to Fibroblast Growth Factor (FGF), Bone Morphogenetic Protein (BMP) and Transforming Growth Factor beta (TGF-β) signaling pathways. Rho Kinase (ROCK)-driven actomyosin contractions and Myosin II-generated differential cell cortex tension regulate these cell shape changes. Disruption of the condensation process inhibits the differentiation of the mesenchyme cells into chondrocytes, demonstrating that condensation regulates the fate of the mesenchyme cells. We also find that dorsal and ventral condensations undergo distinct cell shape changes. BMP signaling is instructive for dorsal condensation-specific cell shape changes. Moreover, condensations exhibit ventral characteristics in the absence of BMP signaling, suggesting that in the pharyngeal arches ventral morphology is the ground pattern. Overall, this study characterizes the interplay between cytoskeletal dynamics and molecular signaling in a self-organizing system during tissue morphogenesis.

Efficient generation of NKX6-1+ pancreatic progenitors from multiple human pluripotent stem cell lines

Human pluripotent stem cells (hPSCs) represent a renewable source of pancreatic beta cells for both basic research and therapeutic applications. Given this outstanding potential, significant efforts have been made to identify the signaling pathways that regulate pancreatic development in hPSC differentiation cultures. In this study, we demonstrate that the combination of epidermal growth factor (EGF) and nicotinamide signaling induces the generation of NKX6-1⁺ progenitors from all hPSC lines tested. Furthermore, we show that the size of the NKX6-1⁺ population is regulated by the duration of treatment with retinoic acid, fibroblast growth factor 10 (FGF10), and inhibitors of bone morphogenetic protein (BMP) and hedgehog signaling pathways. When transplanted into NOD scid gamma (NSG) recipients, these progenitors differentiate to give rise to exocrine and endocrine cells, including monohormonal insulin⁺ cells. Together, these findings provide an efficient and reproducible strategy for generating highly enriched populations of hPSC-derived beta cell progenitors for studies aimed at further characterizing their developmental potential in vivo and deciphering the pathways that regulate their maturation in vitro.

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EGF and nicotinamide induce NKX6-1⁺ progenitors from hPSC-derived endoderm

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NKX6-1⁺ progenitor generation can be controlled by the duration of stage 3 treatment

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The generation of polyhormonal cells is dependent on hedgehog signaling inhibition

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NKX6-1⁺ progenitors give rise to ductal, acinar, and endocrine cells in vivo

Toward beta cell replacement for diabetes

The discovery of insulin more than 90 years ago introduced a life-saving treatment for patients with type 1 diabetes, and since then, significant progress has been made in clinical care for all forms of diabetes. However, no method of insulin delivery matches the ability of the human pancreas to reliably and automatically maintain glucose levels within a tight range. Transplantation of human islets or of an intact pancreas can in principle cure diabetes, but this approach is generally reserved for cases with simultaneous transplantation of a kidney, where immunosuppression is already a requirement. Recent advances in cell reprogramming and beta cell differentiation now allow the generation of personalized stem cells, providing an unlimited source of beta cells for research and for developing autologous cell therapies. In this review, we will discuss the utility of stem cell-derived beta cells to investigate the mechanisms of beta cell failure in diabetes, and the challenges to develop beta cell replacement therapies. These challenges include appropriate quality controls of the cells being used, the ability to generate beta cell grafts of stable cellular composition, and in the case of type 1 diabetes, protecting implanted cells from autoimmune destruction without compromising other aspects of the immune system or the functionality of the graft. Such novel treatments will need to match or exceed the relative safety and efficacy of available care for diabetes.

Derivation of Endodermal Progenitors From Pluripotent Stem Cells

Stem and progenitor cells play important roles in organogenesis during development and in tissue homeostasis and response to injury postnatally. As the regenerative capacity of many human tissues is limited, cell replacement therapies hold great promise for human disease management. Pluripotent stem cells such as embryonic stem (ES) cells and induced pluripotent stem (iPS) cells are prime candidates for the derivation of unlimited quantities of clinically relevant cell types through development of directed differentiation protocols, that is, the recapitulation of developmental milestones in in vitro cell culture. Tissue-specific progenitors, including progenitors of endodermal origin, are important intermediates in such protocols since they give rise to all mature parenchymal cells. In this review, we focus on the in vivo biology of embryonic endodermal progenitors in terms of key transcription factors and signaling pathways. We critically review the emerging literature aiming to apply this basic knowledge to achieve the efficient and reproducible in vitro derivation of endodermal progenitors such as pancreas, liver and lung precursor cells.

Advances and challenges in the differentiation of pluripotent stem cells into pancreatic β cells

Pluripotent stem cells (PSCs) are able to differentiate into several cell types, including pancreatic β cells. Differentiation of pancreatic β cells depends on certain transcription factors, which function in a coordinated way during pancreas development. The existing protocols for in vitro differentiation produce pancreatic β cells, which are not highly responsive to glucose stimulation except after their transplantation into immune-compromised mice and allowing several weeks for further differentiation to ensure the maturation of these cells in vivo. Thus, although the substantial improvement that has been made for the differentiation of induced PSCs and embryonic stem cells toward pancreatic β cells, several challenges still hindering their full generation. Here, we summarize recent advances in the differentiation of PSCs into pancreatic β cells and discuss the challenges facing their differentiation as well as the different applications of these potential PSC-derived β cells.

Dominant and context-specific control of endodermal organ allocation by Ptf1a

The timing and gene regulatory logic of organ-fate commitment from within the posterior foregut of the mammalian endoderm is largely unexplored. Transient misexpression of a presumed pancreatic-commitment transcription factor, Ptf1a, in embryonic mouse endoderm (Ptf1a(EDD)) dramatically expanded the pancreatic gene regulatory network within the foregut. Ptf1a(EDD) temporarily suppressed Sox2 broadly over the anterior endoderm. Pancreas-proximal organ territories underwent full tissue conversion. Early-stage Ptf1a(EDD) rapidly expanded the endogenous endodermal Pdx1-positive domain and recruited other pancreas-fate-instructive genes, thereby spatially enlarging the potential for pancreatic multipotency. Early Ptf1a(EDD) converted essentially the entire glandular stomach, rostral duodenum and extrahepatic biliary system to pancreas, with formation of many endocrine cell clusters of the type found in normal islets of Langerhans. Sliding the Ptf1a(EDD) expression window through embryogenesis revealed differential temporal competencies for stomach-pancreas respecification. The response to later-stage Ptf1a(EDD) changed radically towards unipotent, acinar-restricted conversion. We provide strong evidence, beyond previous Ptf1a inactivation or misexpression experiments in frog embryos, for spatiotemporally context-dependent activity of Ptf1a as a potent gain-of-function trigger of pro-pancreatic commitment.

Knowledge Gaps in Rodent Pancreas Biology: Taking Human Pluripotent Stem Cell-Derived Pancreatic Beta Cells into Our Own Hands

In the field of stem cell biology and diabetes, we and others seek to derive mature and functional human pancreatic β cells for disease modeling and cell replacement therapy. Traditionally, knowledge gathered from rodents is extended to human pancreas developmental biology research involving human pluripotent stem cells (hPSCs). While much has been learnt from rodent pancreas biology in the early steps toward Pdx1(+) pancreatic progenitors, much less is known about the transition toward Ngn3(+) pancreatic endocrine progenitors. Essentially, the later steps of pancreatic β cell development and maturation remain elusive to date. As a result, the most recent advances in the stem cell and diabetes field have relied upon combinatorial testing of numerous growth factors and chemical compounds in an arbitrary trial-and-error fashion to derive mature and functional human pancreatic β cells from hPSCs. Although this hit-or-miss approach appears to have made some headway in maturing human pancreatic β cells in vitro, its underlying biology is vaguely understood. Therefore, in this mini-review, we discuss some of these late-stage signaling pathways that are involved in human pancreatic β cell differentiation and highlight our current understanding of their relevance in rodent pancreas biology. Our efforts here unravel several novel signaling pathways that can be further studied to shed light on unexplored aspects of rodent pancreas biology. New investigations into these signaling pathways are expected to advance our knowledge in human pancreas developmental biology and to aid in the translation of stem cell biology in the context of diabetes treatments.

Pluripotent stem cells as a potential tool for disease modelling and cell therapy in diabetes

Diabetes mellitus is the most prevailing disease with progressive incidence worldwide. To date, the pathogenesis of diabetes is far to be understood, and there is no permanent treatment available for diabetes. One of the promising approaches to understand and cure diabetes is to use pluripotent stem cells (PSCs), including embryonic stem cells (ESCs) and induced PCSs (iPSCs). ESCs and iPSCs have a great potential to differentiate into all cell types, and they have a high ability to differentiate into insulin-secreting β cells. Obtaining PSCs genetically identical to the patient presenting with diabetes has been a longstanding dream for the in vitro modeling of disease and ultimately cell therapy. For several years, somatic cell nuclear transfer (SCNT) was the method of choice to generate patient-specific ESC lines. However, this technology faces ethical and practical concerns. Interestingly, the recently established iPSC technology overcomes the major problems of other stem cell types including the lack of ethical concern and no risk of immune rejection. Several iPSC lines have been recently generated from patients with different types of diabetes, and most of these cell lines are able to differentiate into insulin-secreting β cells. In this review, we summarize recent advances in the differentiation of pancreatic β cells from PSCs, and describe the challenges for their clinical use in diabetes cell therapy. Furthermore, we discuss the potential use of patient-specific PSCs as an in vitro model, providing new insights into the pathophysiology of diabetes.

Inhibition of beta cell growth and function by bone morphogenetic proteins

AIMS/HYPOTHESIS

Impairment of beta cell mass and function is evident in both type 1 and type 2 diabetes. In healthy physiological conditions pancreatic beta cells adapt to the body's increasing insulin requirements by proliferation and improved function. We hypothesised that during the development of diabetes, there is an increase in the expression of inhibitory factors that prevent the beta cells from adapting to the increased need for insulin. We evaluated the effects of bone morphogenetic protein (BMP) 2 and -4 on beta cells.

METHODS

The effects of BMP2 and -4 on beta cell proliferation, apoptosis, gene expression and insulin release were studied in isolated islets of Langerhans from rats, mice and humans. The expression of BMPs was analysed by immunocytochemistry and real-time PCR. The role of endogenous BMP was investigated using a soluble and neutralising form of the BMP receptor 1A.

RESULTS

BMP2 and -4 were found to inhibit basal as well as growth factor-stimulated proliferation of primary beta cells from rats and mice. Bmp2 and Bmp4 mRNA and protein were expressed in islets and regulated by inflammatory cytokines. Neutralisation of endogenous BMP activity resulted in enhanced proliferation of rodent beta cells. The expression of Id mRNAs was induced by BMP4 in rat and human islets. Finally, glucose-induced insulin secretion was significantly impaired in rodent and human islets pre-treated with BMP4, and inhibition of BMP activity resulted in enhanced insulin release.

CONCLUSIONS/INTERPRETATION

These data show that BMP2 and -4 exert inhibitory actions on beta cells in vitro and suggest that BMPs exert regulatory roles of beta cell growth and function.

FGF signaling is required for anterior but not posterior specification of the murine liver bud

BACKGROUND

The definitive endoderm arises as a naive epithelial sheet that produces the entire gut tube and associated organs including the liver, pancreas and lungs. Murine explant studies demonstrate that fibroblast growth factor (FGF) signaling from adjacent tissues is required to induce hepatic gene expression from isolated foregut endoderm. The requirement of FGF signaling during liver development is examined by means of small molecule inhibition during whole embryo culture.

RESULTS

Loss of FGF signaling before hepatic induction results in morphological defects and gene expression changes that are confined to the anterior liver bud. In contrast the posterior portion of the liver bud remains relatively unaffected. Because FGF is thought to act as a morphogen during endoderm organogenesis, the ventral pancreas was also examined after FGF inhibition. Although the size of the ventral pancreas is not affected, loss of FGF signaling results in a significantly higher density of ventral pancreas cells.

CONCLUSIONS

The requirement for FGF-mediated induction of hepatic gene expression differs across the anterior/posterior axis of the developing liver bud. These results underscore the importance of studying tissue differentiation in the context of the whole embryo.

The fetal liver as cell source for the regenerative medicine of liver and pancreas

Patients affected by liver diseases and diabetes mellitus are in need for sources of new cells to enable a better transition into clinic programs of cell therapy and regenerative medicine. In this setting, fetal liver is becoming the most promising and available source of cells. Fetal liver displays unique characteristics given the possibility to isolate cell populations with a wide spectrum of endodermal differentiation and, the co-existence of endodermal and mesenchymal-derived cells. Thus, the fetal liver is a unique and highly available cell source contemporarily candidate for the regenerative medicine of both liver and pancreas. The purpose of this review is to revise the recent literature on the different stem cells populations isolable from fetal liver and candidate to cell therapy of liver diseases and diabetes and to discuss advantages and limitation with respect to other cell sources.

Dynamics of genomic H3K27me3 domains and role of EZH2 during pancreatic endocrine specification

Endoderm cells undergo sequential fate choices to generate insulin-secreting beta cells. Ezh2 of the PRC2 complex, which generates H3K27me3, modulates the transition from endoderm to pancreas progenitors, but the role of Ezh2 and H3K27me3 in the next transition to endocrine progenitors is unknown. We isolated endoderm cells, pancreas progenitors, and endocrine progenitors from different staged mouse embryos and analyzed H3K27me3 genome-wide. Unlike the decline in H3K27me3 domains reported during embryonic stem cell differentiation in vitro, we find that H3K27me3 domains increase in number during endocrine progenitor development in vivo. Genes that lose the H3K27me3 mark typically encode transcriptional regulators, including those for pro-endocrine fates, whereas genes that acquire the mark typically are involved in cell biology and morphogenesis. Deletion of Ezh2 at the pancreas progenitor stage enhanced the production of endocrine progenitors and beta cells. Inhibition of EZH2 in embryonic pancreas explants and in human embryonic stem cell cultures increased endocrine progenitors in vitro. Our studies reveal distinct dynamics in H3K27me3 targets in vivo and a means to modulate beta cell development from stem cells.

Evidence for multipotent endodermal stem/progenitor cell populations in human gallbladder

BACKGROUND & AIMS

Multipotent stem/progenitor cells are found in peribiliary glands throughout human biliary trees and are able to generate mature cells of hepato-biliary and pancreatic endocrine lineages. The presence of endodermal stem/progenitors in human gallbladder was explored.

METHODS

Gallbladders were obtained from organ donors and laparoscopic surgery for symptomatic cholelithiasis. Tissues or isolated cells were characterized by immunohistochemistry and flow cytometry. EpCAM+ (Epithelial Cell Adhesion Molecule) cells were immunoselected by magnetic microbeads, plated onto plastic in self-replication conditions and subsequently transferred to distinct serum-free, hormonally defined media tailored for differentiation to specific adult fates. In vivo studies were conducted in an experimental model of liver cirrhosis.

RESULTS

The gallbladder does not have peribiliary glands, but it has stem/progenitors organized instead in mucosal crypts. Most of these can be isolated by immune-selection for EpCAM. Approximately 10% of EpCAM+ cells in situ and of immunoselected EpCAM+ cells co-expressed multiple pluripotency genes and various stem cell markers; other EpCAM+ cells qualified as progenitors. Single EpCAM+ cells demonstrated clonogenic expansion ex vivo with maintenance of stemness in self-replication conditions. Freshly isolated or cultured EpCAM+ cells could be differentiated to multiple, distinct adult fates: cords of albumin-secreting hepatocytes, branching ducts of secretin receptor+ cholangiocytes, or glucose-responsive, insulin/glucagon-secreting neoislets. EpCAM+ cells transplanted in vivo in immune-compromised hosts gave rise to human albumin-producing hepatocytes and to human Cytokeratin7+ cholangiocytes occurring in higher numbers when transplanted in cirrhotic mice.

CONCLUSIONS

Human gallbladders contain easily isolatable cells with phenotypic and biological properties of multipotent, endodermal stem cells.

Role of BMP signaling in pancreatic progenitor differentiation from human embryonic stem cells

Transplantation of pancreatic progenitors derived from human embryonic stem cells (hESCs) is a promising way to treat diabetes. Strategies to obtain the required cell mass would rely on the up scaling of current differentiation protocols, or the proliferation of committed progenitors. We aimed at finding conditions that maintain a proliferating pancreatic progenitor pool and we assessed the role of BMP4 signaling in this process. hESCs were differentiated into PDX1 positive pancreatic progenitor stage following our established protocol with few modifications, and then the progenitor cells were passaged in a defined proliferation medium (PM). During passage, the effect of BMP4 signaling on the differentiation and proliferation of pancreatic progenitors was examined by RT-PCR and immunofluorescence analysis. We found that PDX1 positive pancreatic progenitors proliferated and gained NKX6.1 expression in the PM, whereas they failed to express NKX6.1 if BMP signaling was inhibited with Noggin. In this latter condition, part of the progenitors rather generated pro-endocrine cells denoted by NGN3 and synaptophysin expression. On the contrary, addition of BMP4 to the PM promoted the early derivation of PDX1 and NKX6.1 coexpressing pancreatic progenitors. Our findings are in line with mouse pancreas development, and indicate that BMP4 signaling is required for the derivation and maintenance of hESC-derived PDX1+NKX6.1+ pancreatic progenitors. These results are instructive for guiding the development of an efficient pancreas differentiation protocol in view of diabetes cell replacement therapy.

Foxi3 is necessary for the induction of the chick otic placode in response to FGF signaling

Vertebrate cranial sensory organs are derived from region at the border of the anterior neural plate called the pre-placodal region (PPR). The otic placode, the anlagen of the inner ear, is induced from PPR ectoderm by FGF signaling. We have previously shown that competence of embryonic ectoderm to respond to FGF signaling during otic placode induction correlates with the expression of PPR genes, but the molecular basis of this competence is poorly understood. Here, we characterize the function of a transcription factor, Foxi3 that is expressed at very early stages in the non-neural ectoderm and later in the PPR of chick embryos. Ablation experiments showed that the underlying hypoblast is necessary for the initiation of Foxi3 expression. Mis-expression of Foxi3 was sufficient to induce markers of non-neural ectoderm such as Dlx5, and the PPR such as Six1 and Eya2. Electroporation of Dlx5, or Six1 together with Eya1 also induced Foxi3, suggesting direct or indirect positive regulation between non-neural ectoderm genes and PPR genes. Knockdown of Foxi3 in chick embryos prevented the induction of otic placode markers, and was able to prevent competent cranial ectoderm from expressing otic markers in response to FGF2. In contrast, Foxi3 expression alone was not sufficient to confer competence to respond to FGF on embryonic ectoderm. Our analysis of PPR and FGF-responsive genes after Foxi3 knockdown at gastrula stages suggests it is not necessary for the expression of PPR genes at these stages, nor for the transduction of FGF signals. The early expression but late requirement for Foxi3 in ear induction suggests it may have some of the properties associated with pioneer transcription factors.

Differentiation of trophoblast cells from human embryonic stem cells: to be or not to be?

It is imperative to unveil the full range of differentiated cell types into which human pluripotent stem cells (hPSCs) can develop. The need is twofold: it will delimit the therapeutic utility of these stem cells and is necessary to place their position accurately in the developmental hierarchy of lineage potential. Accumulated evidence suggested that hPSC could develop in vitro into an extraembryonic lineage (trophoblast (TB)) that is typically inaccessible to pluripotent embryonic cells during embryogenesis. However, whether these differentiated cells are truly authentic TB has been challenged. In this debate, we present a case for and a case against TB differentiation from hPSCs. By analogy to other differentiation systems, our debate is broadly applicable, as it articulates higher and more challenging standards for judging whether a given cell type has been genuinely produced from hPSC differentiation.

Prostaglandin E2 regulates liver versus pancreas cell-fate decisions and endodermal outgrowth

The liver and pancreas arise from common endodermal progenitors. How these distinct cell fates are specified is poorly understood. Here we describe prostaglandin E2 (PGE2) as a regulator of endodermal fate specification during development. Modulating PGE2 activity has opposing effects on liver versus pancreas specification in zebrafish embryos as well as mouse endodermal progenitors. The PGE2 synthetic enzyme cox2a and receptor ep2a are patterned such that cells closest to PGE2 synthesis acquire a liver fate, whereas more distant cells acquire a pancreas fate. PGE2 interacts with the bmp2b pathway to regulate fate specification. At later stages of development, PGE2 acting via the ep4a receptor promotes outgrowth of both the liver and pancreas. PGE2 remains important for adult organ growth, as it modulates liver regeneration. This work provides in vivo evidence that PGE2 may act as a morphogen to regulate cell-fate decisions and outgrowth of the embryonic endodermal anlagen.

Pluripotent stem cell-derived hepatocyte-like cells

Liver disease is an important clinical problem, impacting over 30 million Americans and over 600 million people worldwide. It is the 12th leading cause of death in the United States and the 16th worldwide. Due to a paucity of donor organs, several thousand Americans die yearly while waiting for liver transplantation. Unfortunately, alternative tissue sources such as fetal hepatocytes and hepatic cell lines are unreliable, difficult to reproduce, and do not fully recapitulate hepatocyte phenotype and functions. As a consequence, alternative cell sources that do not have these limitations have been sought. Human embryonic stem (hES) cell- and induced pluripotent stem (iPS) cell-derived hepatocyte-like cells may enable cell based therapeutics, the study of the mechanisms of human disease and human development, and provide a platform for screening the efficacy and toxicity of pharmaceuticals. iPS cells can be differentiated in a step-wise fashion with high efficiency and reproducibility into hepatocyte-like cells that exhibit morphologic and phenotypic characteristics of hepatocytes. In addition, iPS-derived hepatocyte-like cells (iHLCs) possess some functional hepatic activity as they secrete urea, alpha-1-antitrypsin, and albumin. However, the combined phenotypic and functional traits exhibited by iHLCs resemble a relatively immature hepatic phenotype that more closely resembles that of fetal hepatocytes rather than adult hepatocytes. Specifically, iHLCs express fetal markers such as alpha-fetoprotein and lack key mature hepatocyte functions, as reflected by drastically reduced activity (~0.1%) of important detoxification enzymes (i.e. CYP2A6, CYP3A4). These key differences between iHLCs and primary adult human hepatocytes have limited the use of stem cells as a renewable source of functional adult hepatocytes for in vitro and in vivo applications. Unfortunately, the developmental pathways that control hepatocyte maturation from a fetal into an adult hepatocyte are poorly understood, which has hampered the field in its efforts to induce further maturation of iPS-derived hepatic lineage cells. This review analyzes recent developments in the derivation of hepatocyte-like cells, and proposes important points to consider and assays to perform during their characterization. In the future, we envision that iHLCs will be used as in vitro models of human disease, and in the longer term, provide an alternative cell source for drug testing and clinical therapy.

Efficient endoderm induction from human pluripotent stem cells by logically directing signals controlling lineage bifurcations

Human pluripotent stem cell (hPSC) differentiation typically yields heterogeneous populations. Knowledge of signals controlling embryonic lineage bifurcations could efficiently yield desired cell types through exclusion of alternate fates. Therefore, we revisited signals driving induction and anterior-posterior patterning of definitive endoderm to generate a coherent roadmap for endoderm differentiation. With striking temporal dynamics, BMP and Wnt initially specified anterior primitive streak (progenitor to endoderm), yet, 24 hr later, suppressed endoderm and induced mesoderm. At lineage bifurcations, cross-repressive signals separated mutually exclusive fates; TGF-β and BMP/MAPK respectively induced pancreas versus liver from endoderm by suppressing the alternate lineage. We systematically blockaded alternate fates throughout multiple consecutive bifurcations, thereby efficiently differentiating multiple hPSC lines exclusively into endoderm and its derivatives. Comprehensive transcriptional and chromatin mapping of highly pure endodermal populations revealed that endodermal enhancers existed in a surprising diversity of "pre-enhancer" states before activation, reflecting the establishment of a permissive chromatin landscape as a prelude to differentiation.

Setting appropriate boundaries: fate, patterning and competence at the neural plate border

The neural crest and craniofacial placodes are two distinct progenitor populations that arise at the border of the vertebrate neural plate. This border region develops through a series of inductive interactions that begins before gastrulation and progressively divide embryonic ectoderm into neural and non-neural regions, followed by the emergence of neural crest and placodal progenitors. In this review, we describe how a limited repertoire of inductive signals-principally FGFs, Wnts and BMPs-set up domains of transcription factors in the border region which establish these progenitor territories by both cross-inhibitory and cross-autoregulatory interactions. The gradual assembly of different cohorts of transcription factors that results from these interactions is one mechanism to provide the competence to respond to inductive signals in different ways, ultimately generating the neural crest and cranial placodes.

Mutually exclusive signaling signatures define the hepatic and pancreatic progenitor cell lineage divergence

A key question in stem cell biology is how distinct cell types arise from common multipotent progenitor cells. It is unknown how liver and pancreas cells diverge from a common endoderm progenitor population and adopt specific fates. Using RNA-seq, Spagnoli and colleagues define the gene expression programs of liver and pancreas progenitors and identify the noncanonical Wnt pathway as a potential developmental regulator of this fate decision. Furthermore, this study provides a framework for lineage-reprogramming strategies to convert adult hepatic cells into pancreatic cells.

Understanding how distinct cell types arise from multipotent progenitor cells is a major quest in stem cell biology. The liver and pancreas share many aspects of their early development and possibly originate from a common progenitor. However, how liver and pancreas cells diverge from a common endoderm progenitor population and adopt specific fates remains elusive. Using RNA sequencing (RNA-seq), we defined the molecular identity of liver and pancreas progenitors that were isolated from the mouse embryo at two time points, spanning the period when the lineage decision is made. The integration of temporal and spatial gene expression profiles unveiled mutually exclusive signaling signatures in hepatic and pancreatic progenitors. Importantly, we identified the noncanonical Wnt pathway as a potential developmental regulator of this fate decision and capable of inducing the pancreas program in endoderm and liver cells. Our study offers an unprecedented view of gene expression programs in liver and pancreas progenitors and forms the basis for formulating lineage-reprogramming strategies to convert adult hepatic cells into pancreatic cells.

The biological implication of cancer stem cells in hepatocellular carcinoma: a possible target for future therapy

Recent studies indicated the importance of stem cells in cancer, including in hepatocellular carcinoma. The presence of the stem cells and cancer stem cells in liver diseases is associated with the initiation, maintenance, metastasis and chemoresistance. Since hepatocellular carcinoma is a heterogeneous disease with a wide variety of prognostic types, which may limit the efficiency of standardized therapy, the understanding of the source of the cancer, alteration in important molecular signaling pathways and interaction between cancer cells and other cells types will be important in defining future, tailored treatment strategies.

The status of HBV infection influences metastatic pattern and survival in Chinese patients with pancreatic cancer

Background

It has been proved that hepatitis B virus (HBV) infection alters the metastatic pattern and affects survival in colorectal cancer (CRC) and hepatocellular carcinoma (HCC), while the influence of HBV infection on metastatic pattern and survival in patients with pancreatic cancer (PC) has not been investigated yet.

Methods

We conducted an investigation to evaluate the impact of HBV infection on metastatic pattern and overall survival in PC. We collected the data of 460 PC patients treated in our hospital from 1999 to 2010. Serum HBV markers were tested with enzyme-linked immunosorbent assay. The impact of HBV infection on metastatic pattern and overall survival was analyzed.

Results

We found that the incidence of synchronous liver metastasis was significantly higher in patients with HBsAg positive than those with HBsAg negative (46.0% vs 32.0%, P < 0.05), and higher in chronic HBV infection (CHB) group than both non HBV infection and resolved HBV infection group (61.1% vs 33.9%, P < 0.05, and 61.1% vs 28.7%, P < 0.05, respectively). What’s more, Kaplan-Meier analysis showed that CHB, resolved HBV infection and non HBV infection group had significant longer overall survival (OS) compared with inactive HBsAg carriers (IC) group (P=0.037, P=0.009, and P=0.019 respectively). But, in the multivariate analysis, only the CHB and non HBV infection group had significant better overall survival compared with IC group (P=0.010 and P=0.018 respectively).

Conclusions

Our study found that HBV infection increased synchronous liver metastasis rate, and HBV infection status was an independent prognostic factor in PC patients.

Concise review: clinical programs of stem cell therapies for liver and pancreas

Regenerative medicine is transitioning into clinical programs using stem/progenitor cell therapies for repair of damaged organs. We summarize those for liver and pancreas, organs that share endodermal stem cell populations, biliary tree stem cells (hBTSCs), located in peribiliary glands. They are precursors to hepatic stem/progenitors in canals of Hering and to committed progenitors in pancreatic duct glands. They give rise to maturational lineages along a radial axis within bile duct walls and a proximal-to-distal axis starting at the duodenum and ending with mature cells in the liver or pancreas. Clinical trials have been ongoing for years assessing effects of determined stem cells (fetal-liver-derived hepatic stem/progenitors) transplanted into the hepatic artery of patients with various liver diseases. Immunosuppression was not required. Control subjects, those given standard of care for a given condition, all died within a year or deteriorated in their liver functions. Subjects transplanted with 100-150 million hepatic stem/progenitor cells had improved liver functions and survival extending for several years. Full evaluations of safety and efficacy of transplants are still in progress. Determined stem cell therapies for diabetes using hBTSCs remain to be explored but are likely to occur following ongoing preclinical studies. In addition, mesenchymal stem cells (MSCs) and hematopoietic stem cells (HSCs) are being used for patients with chronic liver conditions or with diabetes. MSCs have demonstrated significant effects through paracrine signaling of trophic and immunomodulatory factors, and there is limited evidence for inefficient lineage restriction into mature parenchymal or islet cells. HSCs' effects are primarily via modulation of immune mechanisms.

Recent advances in the morphological and functional heterogeneity of the biliary epithelium

This review focuses on the recent advances related to the heterogeneity of different-sized bile ducts with regard to the morphological and phenotypical characteristics, and the differential secretory, apoptotic and proliferative responses of small and large cholangiocytes to gastrointestinal hormones/peptides, neuropeptides and toxins. We describe several in vivo and in vitro models used for evaluating biliary heterogeneity. Subsequently, we discuss the heterogeneous proliferative and apoptotic responses of small and large cholangiocytes to liver injury and the mechanisms regulating the differentiation of small into large (more differentiated) cholangiocytes. Following a discussion on the heterogeneity of stem/progenitor cells in the biliary epithelium, we outline the heterogeneity of bile ducts in human cholangiopathies. After a summary section, we discuss the future perspectives that will further advance the field of the functional heterogeneity of the biliary epithelium.

How to make a functional β-cell

Insulin-secreting pancreatic β-cells are essential regulators of mammalian metabolism. The absence of functional β-cells leads to hyperglycemia and diabetes, making patients dependent on exogenously supplied insulin. Recent insights into β-cell development, combined with the discovery of pluripotent stem cells, have led to an unprecedented opportunity to generate new β-cells for transplantation therapy and drug screening. Progress has also been made in converting terminally differentiated cell types into β-cells using transcriptional regulators identified as key players in normal development, and in identifying conditions that induce β-cell replication in vivo and in vitro. Here, we summarize what is currently known about how these strategies could be utilized to generate new β-cells and highlight how further study into the mechanisms governing later stages of differentiation and the acquisition of functional capabilities could inform this effort.