Propagation and maintenance of undifferentiated human embryonic stem cells

Perfluorinated iodine alkanes promote the differentiation of mouse embryonic stem cells by regulating estrogen receptor signaling

Investigating the development toxicity of perfluorinated iodine alkanes (PFIs) is critical, given their estrogenic effects through binding with estrogen receptors (ERs). In the present study, two PFIs, including dodecafluoro-1,6-diiodohexane (PFHxDI) and tridecafluorohexyl iodide (PFHxI), with binding preference to ERα and ERβ, respectively, were selected to evaluate their effects on proliferation and differentiation of the mouse embryonic stem cells (mESCs). The results revealed that, similar to E2, 50 µmol/L PFHxDI accelerated the cell proliferation of the mESCs. The PFI stimulation at the exposure concentrations of 2-50 µmol/L promoted the differentiation of the mESCs as characterized by the upregulation of differentiation-related biomarkers (i.e., Otx2 and Dnmt3β) and downregulation of pluripotency genes (i.e., Oct4, Nanog, Sox2, Prdm14 and Rex1). Comparatively, PFHxDI exhibited higher induction effect on the differentiation of the mESCs than did PFHxI. The tests on ER signaling indicated that both PFI compounds induced exposure concentration-dependent expressions of ER signaling-related biomarkers (i.e., ERα, ERβ and Caveolin-1) in the mESCs, and the downstream ER responsive genes (i.e., c-fos, c-myc and c-jun) well responded to PFHxI stimulation. The role of ER in PFI-induced effects on the mESCs was further validated by the antagonistic experiments using an ER inhibitor (ICI). The findings demonstrated that PFIs triggered ER signaling, and perturbed the differentiation program of the mESCs, causing the potential health risk during early stage of development.

Cellular Therapies for Muscular Dystrophies: Frustrations and Clinical Successes

Cell-based therapy for muscular dystrophies was initiated in humans after promising results obtained in murine models. Early trials failed to show substantial clinical benefit, sending researchers back to the bench, which led to the discovery of many hurdles as well as many new venues to optimize this therapeutic strategy. In this review we summarize progress in preclinical cell therapy approaches, with a special emphasis on human cells potentially attractive for human clinical trials. Future perspectives for cell therapy in skeletal muscle are discussed, including the perspective of combined therapeutic approaches.

Invited review: Stem cells and muscle diseases: advances in cell therapy strategies

Despite considerable progress to increase our understanding of muscle genetics, pathophysiology, molecular and cellular partners involved in muscular dystrophies and muscle ageing, there is still a crucial need for effective treatments to counteract muscle degeneration and muscle wasting in such conditions. This review focuses on cell-based therapy for muscle diseases. We give an overview of the different parameters that have to be taken into account in such a therapeutic strategy, including the influence of muscle ageing, cell proliferation and migration capacities, as well as the translation of preclinical results in rodent into human clinical approaches. We describe recent advances in different types of human myogenic stem cells, with a particular emphasis on myoblasts but also on other candidate cells described so far [CD133+ cells, aldehyde dehydrogenase-positive cells (ALDH+), muscle-derived stem cells (MuStem), embryonic stem cells (ES) and induced pluripotent stem cells (iPS)]. Finally, we provide an update of ongoing clinical trials using cell therapy strategies.

A novel feeder-free culture system for expansion of mouse spermatogonial stem cells

Spermatogonial stem cells (SSCs, also called germline stem cells) are self-renewing unipotent stem cells that produce differentiating germ cells in the testis. SSCs can be isolated from the testis and cultured in vitro for long-term periods in the presence of feeder cells (often mouse embryonic fibroblasts). However, the maintenance of SSC feeder culture systems is tedious because preparation of feeder cells is needed at each subculture. In this study, we developed a Matrigel-based feeder-free culture system for long-term propagation of SSCs. Although several in vitro SSC culture systems without feeder cells have been previously described, our Matrigel-based feeder-free culture system is time- and cost- effective, and preserves self-renewability of SSCs. In addition, the growth rate of SSCs cultured using our newly developed system is equivalent to that in feeder cultures. We confirmed that the feeder-free cultured SSCs expressed germ cell markers both at the mRNA and protein levels. Furthermore, the functionality of feeder-free cultured SSCs was confirmed by their transplantation into germ cell-depleted mice. These results suggest that our newly developed feeder-free culture system provides a simple approach to maintaining SSCs in vitro and studying the basic biology of SSCs, including determination of their fate.

Induced pluripotency and oncogenic transformation are related processes

Induced pluripotent stem cells (iPSCs) have the potential for creating patient-specific regenerative medicine therapies, but the links between pluripotency and tumorigenicity raise important safety concerns. More specifically, the methods employed for the production of iPSCs and oncogenic foci (OF), a form of in vitro produced tumor cells, are surprisingly similar, raising potential concerns about iPSCs. To test the hypotheses that iPSCs and OF are related cell types and, more broadly, that the induction of pluripotency and tumorigenicity are related processes, we produced iPSCs and OF in parallel from common parental fibroblasts. When we compared the transcriptomes of these iPSCs and OF to their parental fibroblasts, similar transcriptional changes were observed in both iPSCs and OF. A significant number of genes repressed during the iPSC formation were also repressed in OF, including a large cohort of differentiation-associated genes. iPSCs and OF shared a limited number of genes that were upregulated relative to parental fibroblasts, but gene ontology analysis pointed toward monosaccharide metabolism as upregulated in both iPSCs and OF. iPSCs and OF were distinct in that only iPSCs activated a host of pluripotency-related genes, while OF activated cellular damage and specific metabolic pathways. We reprogrammed oncogenic foci (ROF) to produce iPSC-like cells, a process dependent on Nanog. However, the ROF had reduced differentiation potential compared to iPSC, suggesting that oncogenic transformation leads to cellular changes that impair complete reprogramming. Taken together, these findings support a model in which OF and iPSCs are related, yet distinct cell types, and in which induced pluripotency and induced tumorigenesis are similar processes.

Epigenetic landscape of pluripotent stem cells

SIGNIFICANCE

Derived from the inner cell mass of the preimplantation embryo, embryonic stem cells are prototype pluripotent stem (PS) cells that have the ability of self-renewal and differentiation into almost all cell types. Exploration of the mechanisms governing this pluripotency is important for understanding reprogramming mechanisms and stem cell behavior of PS cells and can lead to enhancing reprogramming efficiency and other applications.

RECENT ADVANCES

Induced pluripotent stem cells are recently discovered PS cells that can be derived from somatic cells by overexpression of pluripotency-related transcription factors. Recent studies have shown that transcription factors and their epigenetic regulation play important roles in the generating, maintaining, and differentiating these PS cells. Recent advances in sequencing technologies allow detailed analysis of target epigenomes and microRNAs (miRs), and have revealed unique epigenetic marks and miRs for PS cells.

CRITICAL ISSUES

Epigenetic modifications of genes include histone modifications, DNA methylation, and chromatin remodeling. Working closely with epigenetic modifiers, miRs play an important role in inducing and maintaining pluripotency.

FUTURE DIRECTIONS

The dynamic changes in epigenetic marks during reprogramming and their role in cell fate changes are being uncovered. This review focuses on these new advances in the epigenetics of PS cells.

Widespread RNA 3'-end oligouridylation in mammals

Nontemplated 3'-end oligouridylation of RNA occurs in many species, including humans. Unlike the familiar phenomenon of polyadenylation, nontemplated addition of uridines to RNA is poorly characterized in higher eukaryotes. Recent studies have reported nontemplated 3'-end oligouridylation of small RNAs and mRNAs. Oligouridylation is involved in many aspects of microRNA biology from biogenesis to turnover of the mature species, and it may also mark long mRNAs for degradation by promoting decapping of the protective 5'-cap structure. To determine the prevalence of oligouridylation in higher eukaryotes, we used next-generation sequencing technology to deeply examine the population of small RNAs in human cells. Our data revealed widespread nontemplated nucleotide addition to the 3' ends of many classes of RNA, with short stretches of uridine being the most frequently added nucleotide.

Human fetal liver stromal cells expressing erythropoietin promote hematopoietic development from human embryonic stem cells

Blood cells transfusion and hematopoietic stem cells (HSCs) transplantation are important methods for cell therapy. They are widely used in the treatment of incurable hematological disorder, infectious diseases, genetic diseases, and immunologic deficiency. However, their availability is limited by quantity, capacity of proliferation and the risk of blood transfusion complications. Recently, human embryonic stem cells (hESCs) have been shown to be an alternative resource for the generation of hematopoietic cells. In the current study, we describe a novel method for the efficient production of hematopoietic cells from hESCs. The stable human fetal liver stromal cell lines (hFLSCs) expressing erythropoietin (EPO) were established using the lentiviral system. We observed that the supernatant from the EPO transfected hFLSCs could induce the hESCs differentiation into hematopoietic cells, especially erythroid cells. They not only expressed fetal and embryonic globins but also expressed the adult-globin chain on further maturation. In addition, these hESCs-derived erythroid cells possess oxygen-transporting capacity, which indicated hESCs could generate terminally mature progenies. This should be useful for ultimately developing an animal-free culture system to generate large numbers of erythroid cells from hESCs and provide an experimental model to study early human erythropoiesis.

In vitro characterization of trophic factor expression in neural precursor cells

In cellular transplantation strategies for repairing the injured central nervous system, interactions between transplanted neural precursor cells (NPCs) and host tissue remain incompletely understood. Although trophins may contribute to the benefits observed, little research has explored this possibility. Candidate trophic factors were identified, and primers were designed for these genes. Template RNA was isolated from 3 NPC sources, and also from bone marrow stromal cells (BMSCs) and embryonic fibroblasts as comparative controls. Quantitative polymerase chain reaction was performed to determine the effect of cell source, passaging, cellular differentiation, and environmental changes on trophin factor expression in NPCs. Results were analyzed with multivariate statistical analyses. NPCs, BMSCs, and fibroblasts each expressed trophic factors in unique patterns. Trophic factor expression was similar among NPCs whether harvested from rat or mouse, brain or spinal cord, or their time in culture. The expression of neurotrophin NT-3, NT-4/5, glial-derived neurotrophic factor, and insulin-like growth factor-1 decreased with time in culture. Induced differentiation of NPCs led to a marked and statistically significant increase in the expression of trophic factors. Culture conditions and environmental changes were also associated with significant changes in trophin expression. These results suggest that trophins could contribute to the benefits associated with transplantation of NPCs as well as BMSCs. Trophic factor expression changes with NPC differentiation and environmental conditions, which could have important implications with regard to their behavior after in vivo transplantation.

The promise of human embryonic stem cells in aging-associated diseases

Aging-associated diseases are often caused by progressive loss or dysfunction of cells that ultimately affect the overall function of tissues and organs. Successful treatment of these diseases could benefit from cell-based therapy that would regenerate lost cells or otherwise restore tissue function. Human embryonic stem cells (hESCs) promise to be an important therapeutic candidate in treating aging-associated diseases due to their unique capacity for self-renewal and pluripotency. To date, there are numerous hESC lines that have been developed and characterized. We will discuss how hESC lines are derived, their molecular and cellular properties, and how their ability to differentiate into all three embryonic germ layers is determined. We will also outline the methods currently employed to direct their differentiation into populations of tissue-specific, functional cells. Finally, we will highlight the general challenges that must be overcome and the strategies being developed to generate highly-purified hESC-derived cell populations that can safely be used for clinical applications.

Derivation and characterization of human embryonic stem cell lines from the Chinese population

Human embryonic stem cells (hESCs) can self-renew indefinitely and differentiate into all cell types in the human body. Therefore, they are valuable in regenerative medicine, human developmental biology and drug discovery. A number of hESC lines have been derived from the Chinese population, but limited of them are available for research purposes. Here we report the derivation and characterization of two hESC lines derived from human blastocysts of Chinese origin. These hESCs express alkaline phosphatase and hESC-specific markers, including Oct4, Nanog, SSEA-3, SSEA-4, TRA-1-60 and TRA-1-81. They also have high levels of telomerase activity and normal karyotypes. These cells can form embryoid body in vitro and can be differentiated into all three germ layers in vivo by teratoma formation. The newly established hESCs will be distributed for research purposes. The availability of hESC lines from the Chinese population will facilitate studies on the differences in hESCs from different ethnic groups.

Epithelial to mesenchymal transition (EMT) induced by bleomycin or TFG(b1)/EGF in murine induced pluripotent stem cell-derived alveolar Type II-like cells

Induced pluripotent stem (iPS) cells are derived from reprogrammed somatic cells and are similar to embryonic stem (ES) cells in morphology, gene/protein expression, and pluripotency. In this study, we explored the potential of iPS cells to differentiate into alveolar Type II (ATII)-like epithelial cells. Analysis using quantitative real time polymerase chain reaction and immunofluorescence staining showed that pulmonary surfactant proteins commonly expressed by ATII cells such as surfactant protein A (SPA), surfactant protein B (SPB), and surfactant protein C (SPC) were upregulated in the differentiated cells. Microphilopodia characteristics and lamellar bodies were observed by transmission electron microscopy and lipid deposits were verified by Nile Red and Periodic Acid Schiff staining. C3 complement protein, a specific feature of ATII cells, was present at high levels in culture supernatants demonstrating functionality of these cells in culture. These data show that the differentiated cells generated from iPS cells using a culture method developed previously (Rippon et al., 2006) are ATII-like cells. To further characterize these ATII-like cells, we tested whether they could undergo epithelial to mesenchymal transition (EMT) by exposure to drugs that induce lung fibrosis in mice, such as bleomycin, and the combination of transforming growth factor beta1 (TGF(b1)) and epidermal growth factor (EGF). When the ATII-like cells were exposed to either bleomycin or a TGF(b1)-EGF cocktail, they underwent phenotypic changes including acquisition of a mesenchymal/fibroblastic morphology, upregulation of mesenchymal markers (Col1, Vim, a-Sma, and S100A4), and downregulation of surfactant proteins and E-cadherin. We have shown that ATII-like cells can be derived from skin fibroblasts and that they respond to fibrotic stimuli. These cells provide a valuable tool for screening of agents that can potentially ameliorate or prevent diseases involving lung fibrosis.

Current advances in cell therapy strategies for muscular dystrophies

INTRODUCTION

Muscular dystrophies are a heterogeneous group of genetic diseases characterized by muscle weakness, wasting and degeneration. Cell therapy consists of delivering myogenic precursor cells to damaged tissue for the complementation of missing proteins and/or the regeneration of new muscle fibres.

AREAS COVERED

We focus on human candidate cells described so far (myoblasts, mesoangioblasts, pericytes, myoendothelial cells, CD133(+) cells, aldehyde-dehydrogenase-positive cells, mesenchymal stem cells, embryonic stem cells, induced pluripotent stem cells), gene-based strategies developed to modify cells prior to injection, animal models (dystrophic and/or immunodeficient) used for pre-clinical studies, and clinical trials that have been performed using cell therapy strategies. The approaches are reviewed in terms of feasibility, hurdles, potential solutions and/or research areas from where the solution may come and potential application in terms of types of dystrophies and targets.

EXPERT OPINION

Cell therapy for muscular dystrophies should be put in the context of which dystrophy or muscle group is targeted, what tools are available at hand, but even more importantly what can cell therapy bring as compared with and/or in combination with other therapeutic strategies. The solution will probably be the right dosage of these combinations adapted to each dystrophy, or even to each type of mutation within a dystrophy.

De novo formation and ultra-structural characterization of a fiber-producing human hair follicle equivalent in vitro

Across many tissues and organs, the ability to create an organoid, the smallest functional unit of an organ, in vitro is the key both to tissue engineering and preclinical testing regimes. The hair follicle is an organoid that has been much studied based on its ability to grow quickly and to regenerate after trauma. But hair follicle formation in vitro has been elusive. Replacing hair lost due to pattern baldness or more severe alopecia, including that induced by chemotherapy, remains a significant unmet medical need. By carefully analyzing and recapitulating the growth conditions of hair follicle formation, we recreated human hair follicles in tissue culture that were capable of producing hair. Our microfollicles contained all relevant cell types and their structure and orientation resembled in some ways excised hair follicle specimens from human skin. This finding offers a new window onto hair follicle development. Having a robust culture system for hair follicles is an important step towards improved hair regeneration as well as to an understanding of how marketed drugs or drug candidates, including cancer chemotherapy, will affect this important organ.

miRNA in pluripotent stem cells

Embryonic stem cells and induced pluripotent stem cells are characterized by their ability to self-renew and differentiate into any cell type. The molecular mechanism behind this process is a complex interplay between the transcriptional factors with epigenetic regulators and signaling pathways. miRNAs are an integral part of this regulatory network, with essential roles in pluripotent maintenance, proliferation and differentiation. miRNAs are a class of small noncoding RNAs that target protein-encoding mRNA to inhibit translation and protein synthesis. Discovered close to 20 years ago, miRNAs have rapidly emerged as key regulatory molecules in several critical cellular processes across species. Recent studies have begun to clarify the specific role of miRNA in regulatory circuitries that control self-renewal and pluripotency of both embryonic stem cells and induced pluripotent stem cells. These advances suggest a critical role for miRNAs in the process of reprogramming somatic cells to pluripotent cells.

Evaluation of 28 Human Embryonic Stem Cell Lines for Use as Unrelated Donors in Stem Cell Therapy: Implications of HLA and ABO Genotypes

For human embryonic stem cells (hESCs) to be used clinically, it is imperative that immune responses evoked by hESCs and their derivates after transplantation should be prevented. Human leukocyte antigens (HLA) and ABO blood group antigens are important histocompatibility factors in graft rejection. HLA matching between recipient and unrelated donors, in particular, is important in improving outcomes in hematopoietic cell transplantation (HCT). We have established and successfully maintained 29 hESC lines and analyzed the HLA and ABO genotypes of these lines. HLA-A, -B, -C and -DR (DRB1) genotyping was performed by polymerase chain reaction (PCR) sequence-based typing and ABO genotyping was carried out by PCR restriction fragment length polymorphism methods. To determine what proportion of the Korean population would be covered by these cell lines in organ transplantation, 27 cell lines with HLA-A, -B, and -DR data were evaluated for HCT (cord blood) donors and 28 cell lines with HLA-DR and ABO data were evaluated for solid organ (kidney) transplantation donors, and then compared the data with those from 6,740 donated cord bloods. When 2 HLA mismatches are allowed for HCT, as currently accepted for cord blood transplantation, it was estimated that about 16% and 25% of the possible recipients can find one or more donor cell lines with ≤2 mismatches at A, B, DRB1 allele level and at A, B antigen/DRB1 allele level, respectively. When HLA-DR antigen level matching and ABO compatibility was considered for solid organ (kidney) transplantation, it was estimated that about 29% and 96% of the possible recipients can find one or more ABO-compatible donor cell lines with 0 and 1 DR mismatches, respectively. We provided the first report on the HLA and ABO genotypes of hESC lines, and estimated the degree of HLA and ABO matching in organ transplantation for the Korean population.

Alu sequences in undifferentiated human embryonic stem cells display high levels of A-to-I RNA editing

Adenosine to Inosine (A-to-I) RNA editing is a site-specific modification of RNA transcripts, catalyzed by members of the ADAR (Adenosine Deaminase Acting on RNA) protein family. RNA editing occurs in human RNA in thousands of different sites. Some of the sites are located in protein-coding regions but the majority is found in non-coding regions, such as 3′UTRs, 5′UTRs and introns - mainly in Alu elements. While editing is found in all tissues, the highest levels of editing are found in the brain. It was shown that editing levels within protein-coding regions are increased during embryogenesis and after birth and that RNA editing is crucial for organism viability as well as for normal development. In this study we characterized the A-to-I RNA editing phenomenon during neuronal and spontaneous differentiation of human embryonic stem cells (hESCs). We identified high editing levels of Alu repetitive elements in hESCs and demonstrated a global decrease in editing levels of non-coding Alu sites when hESCs are differentiating, particularly into the neural lineage. Using RNA interference, we showed that the elevated editing levels of Alu elements in undifferentiated hESCs are highly dependent on ADAR1. DNA microarray analysis showed that ADAR1 knockdown has a global effect on gene expression in hESCs and leads to a significant increase in RNA expression levels of genes involved in differentiation and development processes, including neurogenesis. Taken together, we speculate that A-to-I editing of Alu sequences plays a role in the regulation of hESC early differentiation decisions.

Human embryonic stem cells are pre-mitotically committed to self-renewal and acquire a lengthened G1 phase upon lineage programming

Self-renewal of human embryonic stem (hES) cells proceeds by a unique abbreviated cell cycle with a shortened G1 phase and distinctions in molecular cell cycle regulatory parameters. In this study, we show that early lineage-commitment of pluripotent hES cells modifies cell cycle kinetics. Human ES cells acquire a lengthened G1 within 72 h after lineage-programming is initiated, as reflected by loss of the pluripotency factor Oct4 and alterations in nuclear morphology. In hES cells that maintain the pristine pluripotent state, we find that autocrine mechanisms contribute to sustaining the abbreviated cell cycle. Our data show that naïve and mitotically synchronized pluripotent hES cells are competent to initiate two consecutive S phases in the absence of external growth factors. We conclude that short-term self-renewal of pluripotent hES cells occurs autonomously, in part due to secreted factors, and that pluripotency is functionally linked to the abbreviated hES cell cycle.

Renal ontogeny in the rhesus monkey (Macaca mulatta) and directed differentiation of human embryonic stem cells towards kidney precursors

The development of the metanephric kidney was studied immunohistochemically across gestation in monkeys to identify markers of cell specification, and to aid in developing experimental paradigms for renal precursor differentiation from human embryonic stem cells (hESC). PAX2, an important kidney developmental marker, was expressed at the tips of the ureteric bud, in the surrounding condensing mesenchyme, and in the renal vesicle. Vimentin, a mesenchymal and renal marker, was strongly expressed in the metanephric blastema then found to be limited to the glomerulus and interstitial cells of the medulla and cortex. A model of gene expression based on human and nonhuman primate renal ontogeny was developed and incorporated into studies of hESC differentiation. Spontaneous hESC differentiation revealed markers of metanephric mesenchyme (OSR1, PAX2, SIX2, WT1) that increased over time, followed by upregulation of kidney precursor markers (EYA1, LIM1, CD24). Directed hESC differentiation was also evaluated with the addition of retinoic acid, Activin-A, and BMP-4 or BMP-7, and using different culture substrate conditions. Of the culture substrates studied, gelatin most closely recapitulated the anticipated directed developmental pattern of renal gene expression. No differences were found when BMP-4 and BMP-7 were compared with baseline conditions. PAX2 and Vimentin immunoreactivity in differentiating hESC was also similar to the renal precursor patterns reported for human fetal kidneys and findings described in rhesus monkeys. The results of these studies are as follows: (1) provide additional data to support that rhesus monkey kidney development parallels that of humans, and (2) provide a useful model for hESC directed differentiation towards renal precursors.

Embryonic stem cells as a source of pulmonary epithelium in vitro and in vivo

Embryonic stem cells (ESCs) derived from the preimplantation blastocyst are pluripotent and capable of indefinite expansion in vitro. As such, they present a cell source to derive a potentially inexhaustible supply of pulmonary cells and tissue. ESC-derived pulmonary epithelium could be used for in vitro cell or tissue models or, in the future, implanted into the damaged or diseased lung to effect repair. Efforts to date have largely focused on obtaining distal lung epithelial phenotypes from ESCs, notably alveolar epithelium. Several disparate methods have been developed to enhance differentiation of ESCs into pulmonary epithelial lineages; these are broadly based on recapitulating developmental signaling events, mimicking the physical environment, or forcibly reprogramming the ESC nucleus. Early findings of our preclinical experiments implanting differentiated ESCs into the injured lung are also described here. Future efforts will focus on maximizing ESC differentiation efficiency and yield of the target phenotype, as well as characterizing the function of derived cells in vivo and in vitro.

The road to pluripotence: the research response to the embryonic stem cell debate

The controversies surrounding embryonic stem cell research have prompted scientists to invent beyond restrictive national policy and moral concerns. The impetus behind these reports comes from different sources, including individually held moral beliefs, societal pressures and resource constraints, both biological and financial. Along with other contributions to public policy such as advocacy or public testimony, experimentation and scientific curiosity are perhaps more natural responses scientists use to surmount impediments to research. In a research context, we review the history of the first stem cell discoveries, and describe scientific efforts leading up to recent reports of pluripotent lines made without the use of human embryos and eggs. We argue that despite the promise of these new lines, we must not lose sight of fundamental questions remaining at the frontiers of embryology and early human development. The answers to these questions will impact studies of genetics, cell biology and diseases such as cancer, autoimmunity and disorders of development. Human embryonic stem cell research is barely a decade old. The recent pace of discovery--in spite of federal restrictions--is testament to the potential of these cells to uncover some of biology's most intractable mysteries.

Human embryonic stem cells are prone to generate primitive, undifferentiated tumors in engrafted human fetal tissues in severe combined immunodeficient mice

Embryonic stem (ES) cells are uniquely endowed with the capacity of self-renewal and the potential to give rise to all possible cell types. Their differentiation potential has raised hope that these cells could be used as a renewable source for cell transplantation in severe degenerative diseases. However, progress in this direction is still limited. Using two human embryonic stem (ES) cell lines, H1 and HSF-6, and three types of human fetal tissues--thymus, lung and pancreas-we investigated whether engrafted human fetal tissues in severe combined immunodeficient mice (SCID) mice could provide a physiologically-relevant microenvironment for human ES cells to differentiate into mature cells of corresponding tissues. Surprisingly, we observed an aggressive growth of tumors when human ES cells were injected into engrafted human fetal tissues in SCID mice. These tumors displayed histological characteristics of primitive, undifferentiated tumors rather than differentiated teratomas. Additionally, these tumors exhibited a normal karyotype and did not express the characteristic antigens of embryonic carcinomas. We also found differences among human fetal tissue types in their abilities to support the growth of these primitive tumors. Our study supports and validates a previously reported phenomenon in mouse that tumorigenesis of ES cells is host dependent. Our study is also the first report to demonstrate that human ES cells are prone to generate primitive, undifferentiated tumors in human fetal tissue grafts in SCID mice and raises a potential safety concern for using human ES cell-derived cell products in humans.

Human placenta-derived feeders support prolonged undifferentiated propagation of a human embryonic stem cell line, SNUhES3: comparison with human bone marrow-derived feeders

Co-culture of human embryonic stem (ES) cells on mouse fibroblast feeders is the commonly used method for in vitro expansion of human ES cells in an undifferentiated state. However, it has potential risks of pathogen transmission from animals; thus, human cell-derived feeders have been employed to minimize this problem. In this study, we compared human placenta-derived feeders with bone marrow to demonstrate its effectiveness as feeders for in vitro long-term culture of human ES cells. We cultured a human ES cell line, SNUhES3, on human placenta-derived mesenchymal stem cell feeders and compared their culture efficiency with human bone marrow-derived feeders and control group (mouse fibroblast feeders, STO). The mean number of human ES cell colonies was 166 +/- 35 in the placenta feeders; this was significantly higher than bone marrow-derived feeders (87 +/- 16, p < 0.05). We could propagate the culture of SNUhES3 on the placenta feeders past the 50th week similar to control group. During the culture, the maintenance of undifferentiated state of SNUhES3 was demonstrated by the expression of SSEA-4, TRA-1-81, TRA-1-60, and Oct-4. However, we failed to propagate the culture of human ES cells on the human bone marrow-derived feeders past the 5th week. The efficiency of embryoid body formation was similar between placenta and control group, indicating the preservation of differentiation ability. Thus, placenta-derived feeders are more efficient for the long-term in vitro culture of human ES cells than bone marrow-derived feeders suggesting the possible role of placenta as a source for human cell-derived feeders.

Differentiation and enrichment of hepatocyte-like cells from human embryonic stem cells in vitro and in vivo

Human embryonic stem cells (hESC) may provide a cell source for functional hepatocytes. The aim of this study is to establish a viable human hepatocyte-like cell line from hESC that can be used for cell-based therapies. The differentiated hESC were enriched by transducing with a lentivirus vector containing the green fluorescent protein (GFP) gene driven by the alpha1-antitrypsin promoter; the GFP gene is expressed in committed hepatocyte progenitors and hepatocytes. GFP+ hESC were purified by laser microdissection and pressure catapulting. In addition, differentiated hESC that were transduced with a lentivirus triple-fusion vector were transplanted into NOD-SCID mice, and the luciferase-induced bioluminescence in the livers was evaluated by a charge-coupled device camera. GFP+ hESC expressed a large series of liver-specific genes, and expression levels of these genes were significantly improved by purifying GFP+ hESC; our results demonstrated that purified differentiated hESC express nearly physiological levels of liver-specific genes and have liver-specific functions that are comparable to those of primary human hepatocytes. The differentiated hESC survived and engrafted in mouse livers, and human liver-specific mRNA and protein species were detected in the transplanted mouse liver and serum at 3 weeks after transplantation. This is the first time that human albumin generated by hESC-derived hepatocytes was detected in the serum of an animal model. This also represents the first successful transplantation of differentiated hESC in an animal liver and the first bioluminescence imaging of hESC in the liver. This study is an initial step in establishing a viable hepatocyte-like cell line from hESC. Disclosure of potential conflicts of interest is found at the end of this article.

A panel of tests to standardize the characterization of human embryonic stem cells

Human embryonic stem cells offer a renewable source of a wide range of cell types for use in research and cell-based therapies. Characterizing these cells provides important information about their current state and affords relevant details for subsequent downstream manipulation. Prior to considering therapeutic applications, it is crucial that the cells are surveyed at a genetic and proteomic level during the extensive propagation, expansion and differentiation. Hence, a set of characterization tests to measure stem cell stability and identity--genomic, epigenomic and mitochondrial markers, as well as functional measures of utility, need to be developed. Thus, we outline a plan of standard assays that can be afforded by multiple laboratories to unambiguously test the quality of human embryonic stem cells. In this manuscript, we describe a comprehensive characterization of ReliCell hES1, the only human embryonic stem cell line reported from the Indian subcontinent. Our study employs gene expression analysis using quantitative reverse transcription-polymerase chain reaction and microarray, mitochondrial DNA sequencing, microRNA analysis, immunophenotyping and teratoma formation, in addition to demonstrating its capacity to propagate under feeder-free conditions.

IQGAP1 modulates activation of B-Raf

IQGAP1 modulates several cellular functions, including cell-cell adhesion, transcription, cytoskeletal architecture, and selected signaling pathways. We previously documented that IQGAP1 binds ERK and MAPK kinase (MEK) and regulates EGF-stimulated MEK and ERK activity. Here we characterize the interaction between IQGAP1 and B-Raf, the molecule immediately upstream of MEK in the Ras/MAPK signaling cascade. B-Raf binds directly to IQGAP1 in vitro and coimmunoprecipitates with IQGAP1 from cell lysates. Importantly, IQGAP1 modulates B-Raf function. EGF is unable to stimulate B-Raf activity in IQGAP1-null cells and in cells transfected with an IQGAP1 mutant construct that is unable to bind B-Raf. Interestingly, binding to IQGAP1 significantly enhances B-Raf activity in vitro. Our data identify a previously unrecognized interaction between IQGAP1 and B-Raf and suggest that IQGAP1 is a scaffold necessary for activation of B-Raf by EGF.

A Method for Single-Cell Sorting and Expansion of Genetically Modified Human Embryonic Stem Cells

Genetic modification of human embryonic stem (hES) cells is essential for studies of gene function and differentiation. The expression of transgenes may direct tissue-specific differentiation and aid in the identification of various differentiated cell types. Stable genomic integration of transgenes is optimal because hES cell differentiation can span several days to weeks and include numerous cell divisions, and establishing homogeneous modified cell lines will facilitate research studies. Herein we provide a method for producing and expanding hES cell lines from single cells that have been isolated by fluorescence-activated cell sorting (FACS) following genetic modification by lentivirus vectors. Using this method, we have established enhanced green fluorescent protein (eGFP)-expressing hES cell lines that are pluripotent, contain a diploid chromosomal content, and stably express eGFP following more than 2 months of routine culture and in vivo differentiation.

Derivation of oocyte-like cells from a clonal pancreatic stem cell line

Adult pancreatic stem cells (PSCs) are able to differentiate spontaneously in vitro into various somatic cell types. Stem cells isolated from rat pancreas show extensive self-renewal ability and grow in highly viable long-term cultures. Additionally, these cells express typical stem cell markers such as Oct-4, nestin and SSEA-1. Although differentiation potential is slightly decreasing in long-term cultures, it is possible to keep cell lines up to passage 140. Clonal cell lines could be established from different passages and showed similar characteristics. Remarkably, one clonal cell line, generated from passage 75, showed deviant properties during further culture. Clonal cells formed aggregates, which built tissue-like structures in suspension culture. These generated 3D aggregates produced permanently new cells at the outside margin. Released cells had remarkable size, and closer examination by light microscopy analysis revealed oocyte-like morphology. A comparison of the gene expression patterns between primary cultures of passages 8 and 75, the clonal cell line and the produced oocyte-like cells (OLCs) from tissue-like structures demonstrated some differences. Expression of various germ cell markers, such as Vasa, growth differentiation marker 9 and SSEA-1, increased in the clonal cell line, and OLCs showed additionally expression of meiosis-specific markers SCP3 and DMC1. We here present a first pilot study investigating the putative germ line potential of adult PSCs.

Hydrogels as artificial matrices for human embryonic stem cell self-renewal

Human embryonic stem cells (hESCs) have the potential to differentiate into all cell types in the body and hold great promise for regenerative medicine; however, large-scale expansion of undifferentiated hESCs remains a major challenge. Self-renewal of hESCs requires culturing these cells on either mouse or human fibroblast cells (i.e., a feeder layer of cells), or on artificial extracellular matrices (ECMs) while supplementing the media with soluble growth factors. Here we report a completely synthetic ECM system composed of a semi-interpenetrating polymer network (sIPN), a polymer hydrogel, which was designed to allow the independent manipulation of cell adhesion ligand presentation and matrix stiffness. In the short term, hESCs that were cultured on the sIPN adhered to the surface, remained viable, maintained the morphology, and expressed the markers of undifferentiated hESCs. This was the first demonstration that a completely synthetic ECM can support short-term self-renewal of hESCs.

Human embryonic stem cells have a unique epigenetic signature

Human embryonic stem (hES) cells originate during an embryonic period of active epigenetic remodeling. DNA methylation patterns are likely to be critical for their self-renewal and pluripotence. We compared the DNA methylation status of 1536 CpG sites (from 371 genes) in 14 independently isolated hES cell lines with five other cell types: 24 cancer cell lines, four adult stem cell populations, four lymphoblastoid cell lines, five normal human tissues, and an embryonal carcinoma cell line. We found that the DNA methylation profile clearly distinguished the hES cells from all of the other cell types. A subset of 49 CpG sites from 40 genes contributed most to the differences among cell types. Another set of 25 sites from 23 genes distinguished hES cells from normal differentiated cells and can be used as biomarkers to monitor differentiation. Our results indicate that hES cells have a unique epigenetic signature that may contribute to their developmental potential.

The potential of stem cell therapies for neurological diseases

As a novel neurotherapeutic strategy, stem cell transplantation has received considerable attention, yet little of this attention has been devoted to the probabilities of success of stem cell therapies for specific neurological disorders. Given the complexities of the cellular organization of the nervous system and the manner in which it is assembled during development, it is unlikely that a cellular replacement strategy will succeed for any but the simplest of neurological disorders in the near future. A general strategy for stem cell transplantation to prevent or minimize neurological disorders is much more likely to succeed. Two broad categories of neurological disease, inherited metabolic disorders and invasive brain tumors, are among the most likely candidates.

Mammalian stem cells

Stem cells are quickly coming into focus of much biomedical research eventually aiming at the therapeutic applications for various disorders and trauma. It is important, however, to keep in mind the difference between the embryonic stem cells, somatic stem cells and somatic precursor cells when considering potential clinical applications. Here we provide the review of the current status of stem cell field and discuss the potential of therapeutic applications for blood and Immune system disorders, multiple sclerosis, hypoxic-ischemic brain injury and brain tumors. For the complimentary information about various stem cells and their properties we recommend consulting the National Institutes of Health stem cell resources (http://stemcells.nih.gov/info/basics).

Megakaryocytes derived from human embryonic stem cells: a genetically tractable system to study megakaryocytopoiesis and integrin function

BACKGROUND

The platelet fibrinogen receptor, a heterodimer consisting of integrin subunits alpha(IIb) and beta(3), is required for platelet aggregation, spreading, and hemostasis. Platelet agonists such as thrombin and adenosine diphosphate (ADP) lead to the activation of alpha(IIb)beta(3), thereby enhancing its affinity and avidity for binding fibrinogen (inside-out signaling). Furthermore, fibrinogen binding to alpha(IIb)beta(3) triggers cytoskeletal changes and granule release (outside-in signaling).

AIM

Genetic approaches to characterize the molecular pathways involved in alpha(IIb)beta(3) signaling are not possible with anucleate blood platelets. Therefore, we have established an OP9 stromal cell co-culture system to generate megakaryocytes from human embryonic stem cells (hESCs).

RESULTS

alpha(IIb)beta(3) activation, measured by soluble fibrinogen binding to hESC-derived megakaryocytes, /GPIbalpha(+) cells, is readily detectable following stimulation with known platelet agonists. Dose-response curves for peptide agonists specific for the two platelet thrombin receptors, protease-activated receptor 1 (PAR1) and PAR4, show a relative responsiveness that mirrors that of human platelets, and sub-maximal ADP responses are augmented by epinephrine. Moreover, hESC-derived megakaryocytes undergo lamellipodia formation, actin filament assembly, and vinculin localization at focal adhesions when plated on a fibrinogen-coated surface, characteristic of alpha(IIb)beta(3) outside-in signaling. Undifferentiated hESCs genetically modified by lentiviral infection can be cloned and maintained in an undifferentiated state and then differentiated into megakaryocytes capable of alpha(IIb)beta(3) activation.

CONCLUSION

Using hESCs, we have developed a renewable source of human megakaryocytes, and a genetically tractable system for studying megakaryocytopoiesis and alpha(IIb)beta(3) signaling in the native cellular environment.

Derivation of Three Clones from Human Embryonic Stem Cell Lines by FACS Sorting and Their Characterization

Here we describe the first report of three human embryonic stem cell (hESC) clones, hES 3.1, 3.2, and 3.3, derived from the parent line hES3 by sorting of single-cell preparations by flow cytometry. The viability of single-cell preparations before and after cell sorting remained >98%. The hESC were selected by size gating and forward-angle light scatter and were dispersed directly as single cell/ well into 96-well plates containing human fetal fibroblasts as feeder layers. Single stem cell dispersion into 96-well plates was confirmed by using cells from a hES3 line that constitutively expressed green fluorescence protein (eGFP) under similar conditions of flow cytometry. Three clones were obtained from the parent line hES3 -- hES3.1, 3.2, and 3.3 -- and they have been in continuous culture for more than 1 year. The cloning efficiency was less than <0.5%. These hESC clones show normal stem cell characteristics, such as undifferentiated growth, high nucleocytoplasmic ratio, the same karyotype as that of the parent line (46 XX), stem cell surface markers (i.e., SSEA3, SSEA4, OCT4, TRA-1-60, and TRA-1-81), and gene expression for pluripotency (Oct-4 and nanog). They all formed embryoid bodies in suspension cultures, and after seeding in culture plates they showed pluripotency in vitro by forming cell lineages derived from all three germ layers as indicated by expression of the ectodermal marker nestin, the mesodermal marker renin, and the endodermal markers alpha-fetoprotein and GATA6. All clones showed normal expression of alkaline phosphatase activity, a marker of in vitro pluripotency. When hESC clones (1-2 x 10(6) total) were injected into nonobese diabetic-severe combined immunodeficiency (NOD-SCID) mice under the kidney capsule, all formed teratomas within 6-8 weeks. Analysis of the stem cell surface marker TRA-1-160 by flow cytometry showed nonsignificant (p < 0.05) differences between the clones and the parent line. The clones also differed in their expression of genes, with only one, hES 3.2, expressing the endodermal markers, i.e., alpha-fetoprotein and GATA6. The ability to produce clones from a parent hESC line rapidly by FACS sorting will help provide a homogeneous population of cells for achieving uniformed lineage specifications for future transplantation therapies and biomedical research.