Insulin production by human embryonic stem cells

Recent advances in stem cell research for the treatment of diabetes

The success achieved over the last decade with islet transplantation has intensified interest in treating diabetes, not only by cell transplantation, but also by stem cells. The formation of insulin-producing cells from pancreatic duct, acinar, and liver cells is an active area of investigation. Protocols for the in vitro differentiation of embryonic stem (ES) cells based on normal developmental processes, have generated insulin-producing cells, though at low efficiency and without full responsiveness to extracellular levels of glucose. Induced pluripotent stem cells, which have been generated from somatic cells by introducing Oct3/4, Sox2, Klf4, and c-Myc, and which are similar to ES cells in morphology, gene expression, epigenetic status and differentiation, can also differentiate into insulin-producing cells. Overexpression of embryonic transcription factors in stem cells could efficiently induce their differentiation into insulin-expressing cells. The purpose of this review is to demonstrate recent progress in the research for new sources of β-cells, and to discuss strategies for the treatment of diabetes.

Are stem cells a cure for diabetes?

With the already heightened demand placed on organ donation, stem cell therapy has become a tantalizing idea to provide glucose-responsive insulin-producing cells to Type 1 diabetic patients as an alternative to islet transplantation. Multiple groups have developed varied approaches to create a population of cells with the appropriate characteristics. Both adult and embryonic stem cells have received an enormous amount of attention as possible sources of insulin-producing cells. Although adult stem cells lack the pluripotent nature of their embryonic counterparts, they appear to avoid the ethical debate that has centred around the latter. This may limit the eventual application of embryonic stem cells, which have already shown promise in early mouse models. One must also consider the potential of stem cells to form teratomas, a complication which would prove devastating in an immunologically compromised transplant recipient. The present review looks at the progress to date in both the adult and embryonic stem cells fields as potential treatments for diabetes. We also consider some of the limitations of stem cell therapy and the potential complications that may develop with their use.

Bioengineering of a functional sheet of islet cells for the treatment of diabetes mellitus

The present study was designed to establish a novel tissue engineering approach for diabetes mellitus (DM) by fabricating a tissue sheet composed of pancreatic islet cells for in vivo transplantation. Pancreatic islet cell suspensions were obtained from Lewis rats, and plated onto temperature-responsive culture dishes coated with extracellular matrix (ECM) proteins. After the cells reached confluency, islet cells cultured on laminin-5 coated dishes were successfully harvested as a uniformly spread tissue sheet by lowering the culture temperature to 20 degrees C for 20 min. The functional activity of the islet cell sheets was confirmed by histological examination and Insulin secretion assay prior to in vivo transplantation. Histological examination revealed that the harvested islet cell sheet was comprised of insulin- (76%) and glucagon- (19%) positive cells, respectively. In vivo functionality of the islet cell sheet was maintained even 7 days after transplantation into the subcutaneous space of Lewis rats. The present study describes an approach to generate a functional sheet of pancreatic islet cells on laminin-5 coated temperature-responsive dishes, which can be subsequently transplanted in vivo. This study serves as the foundation for the creation of a novel cell-based therapy for DM to provide patients an alternative method.

Slow and steady is the key to beta-cell replication

The β-cells of the pancreas are responsible for insulin production and their destruction results in type I diabetes. β-cell maintenance, growth and regenerative repair is thought to occur predominately, if not exclusively, through the replication of existing β-cells, not via an adult stem cell. It was recently found that all β-cells contribute equally to islet growth and maintenance. The fact that all β-cells replicate homogeneously makes it possible to set up straightforward screens for factors that increase β-cell replication either In vitro or in vivo. It is possible that a circulating factor may be capable of increasing β-cell replication or that intrinsic cell cycle regulators may affect β-cell growth. An improved understanding of the in vivo maintenance and growth of β-cells will facilitate efforts to expand β-cells In vitro and may lead to new treatments for diabetes.

Generation of pancreatic islet cells from human embryonic stem cells

Efficiently obtaining functional pancreatic islet cells derived from human embryonic stem (hES) cells not only provides great potential to solve the shortage of islets sources for type I diabetes cell therapy, but also benefits the study of the development of the human pancreas and diabetes pathology. In 2001, hES cells were reported to have the capacity to generate insulin-producing cells by spontaneous differentiation in vitro. Since then, many strategies (such as overexpression of key transcription factors, delivery of key proteins for pancreatic development, co-transplantation of differentiated hES cells along with fetal pancreas, stepwise differentiation by mimicking in vivo pancreatic development) have been employed in order to induce the differentiation of pancreatic islet cells from hES cells. Moreover, patient-specific induced pluripotent stem (iPS) cells can be generated by reprogramming somatic cells. iPS cells have characteristics similar to those of ES cells and offer a new cell source for type I diabetes cell therapy that reduces the risk of immunologic rejection. In this review, we summarize the recent progress made in the differentiation of hES and iPS cells into functional pancreatic islet cells and discuss the challenges for their future study.

[Neuroendocrine system of the pancreas and gastrointestinal tract: origin and development]

Gastroenteropancreatic neuroendocrine tumours (GEP NETs) originate from the neuroendocrine cells through the gastrointestinal tract and endocrine pancreas. The embryologic development of the pancreas is a complex process that begins with the "stem cell" that come from the endodermus. These cells go through two phases: in the first transition the "stem cell" differentiates in exocrine and endocrine cells. This process is regulated by transcription factors such as Pdx1 ("insulin promoter factor 1"), Hlxb6 and SOX9. In the second transition the neuroendocrine cell differentiates in the 5 cell types (alpha, beta, delta, PP y epsilon.). This process is regulated through the balance between factors favoring differentiation (mainly neurogenin 3) and inhibitor factors which depend on Notch signals. The existence of a third transition in postnatal pancreas is hypothesized. The "stem cell" from pancreatic ducts would become adult beta cells, through autoduplication and neogenesis. In the small gut of the adult the stem cell are placed in the intestinal crypts and develop to villi in secretor lines (enterocytes, globet and Paneths cells) or neuroendocrine cells from which at least 10 cell types depend. This process is regulated by transcription factors: Math1, neurogenina 3 and NeuroD.

Role of MafA in pancreatic beta-cells

Pancreatic beta-cell-specific insulin gene expression is regulated by a variety of pancreatic transcription factors and the conserved A3, C1 and E1 elements in the insulin gene enhancer region are very important for activation of insulin gene. Indeed, PDX-1 binding to the A3 element and NeuroD binding to the E1 element are crucial for insulin gene transcription. Recently, C1 element-binding transcription factor was identified as MafA, which is a basic-leucine zipper transcription factor and functions as a potent transactivator for the insulin gene. Under diabetic conditions, chronic hyperglycemia gradually deteriorates pancreatic beta-cell function, which is accompanied by decreased expression and/or DNA binding activities of MafA and PDX-1. Furthermore, MafA overexpression, together with PDX-1 and NeuroD, markedly induces insulin biosynthesis in various non-beta-cells and thereby is a useful tool to efficiently induce insulin-producing surrogate beta-cells. These results suggest that MafA plays a crucial role in pancreatic beta-cells and could be a novel therapeutic target for diabetes.

Development of insulin-producing cells from primitive biologic precursors

PURPOSE OF REVIEW

The differentiation of pluripotent and multipotent stem cells into insulin-producing cells has the potential to create a renewable supply of replacement beta cells with tremendous utility in the treatment of diabetes. The purpose of this review is to summarize recent advancements in the field, with emphasis on the limitations of this technology as it relates to the beta cell.

RECENT FINDINGS

Multiple groups have developed successful in-vitro protocols to differentiate human embryonic stem cells and selected tissue specific stem cells into progenitors capable of insulin production and glucose-stimulated insulin secretion. The resulting cells are immature beta cell-like cells that coexpress multiple islet hormones and lack the full complement of genes necessary for normal function. Protocols that include in-vivo maturation in immune-compromised mice produce cells with a more mature phenotype.

SUMMARY

Although tremendous progress has been made in differentiating stem cells into insulin-producing cells, there is still more research needed to produce a fully functional adult beta cell.

Establishment of endoderm progenitors by SOX transcription factor expression in human embryonic stem cells

In this study, we explore endoderm cell fate regulation through the expression of lineage-determining transcription factors. We demonstrate that stable endoderm progenitors can be established from human ES cells by constitutive expression of SOX7 or SOX17, producing extraembryonic endoderm and definitive endoderm progenitors, respectively. In teratoma assays and growth factor-mediated differentiation, SOX7 cells appear restricted to the extraembryonic endoderm, and SOX17 cells demonstrate a mesendodermal phenotype in teratomas and the ability to undergo endoderm maturation in vitro in the absence of cytokine-mediated endoderm induction. These endoderm progenitor cells maintain a stable phenotype through many passages in culture, thereby providing new tools to explore the pathways of endoderm differentiation.

Transdifferentiation of human adipose tissue-derived stromal cells into insulin-producing clusters

Type 1 diabetes mellitus is caused by autoimmune destruction of insulin-producing beta cells. The major obstacle to transplantation of insulin-producing cells to cure the disease is the limited source of these cells. To overcome this problem, we describe here a multistep protocol for generation of insulin-producing islet-like clusters from human adipose tissue-derived stromal cells (ADSCs). Analysis using reverse transcription polymerase chain reaction detected enhanced expression of various pancreatic genes during the differentiation of ADSCs. Immunofluorescence analysis revealed functional similarities between cells derived from ADSCs and pancreatic islet cells, i.e., the presence of insulin- and C-peptide-coexpressing cells in the clusters and glucagon expression on the cell surface. The glucose challenge tests revealed the production of insulin, and such production was regulated via physiological signaling pathways. Our insulin-producing cells derived from ADSCs could be potentially used for cell therapy of type 1 diabetes mellitus.

Derivation and characterization of human embryonic stem cell lines from poor quality embryos

Poor quality embryos discarded from in vitro fertilization (IVF) laboratories are good sources for deriving human embryonic stem cell (hESC) lines. In this study, 166 poor quality embryos donated from IVF centers on day 3 were cultured in a blastocyst medium for 2 days, and 32 early blastocysts were further cultured in a blastocyst optimum culture medium for additional 2 days so that the inner cell masses (ICMs) could be identified and isolated easily. The ICMs of 17 blastocysts were isolated by a mechanical method, while those of the other 15 blastocysts were isolated by immunosurgery. All isolated ICMs were inoculated onto a feeder layer for subcultivation. The rates of ICM attachment, primary ICM colony formation and the efficiency of hESC derivation were similar between the ICMs isolated by the two methods (P>0.05). As a result, four new hESC lines were established. Three cell lines had normal karyotypes and one had an unbalanced Robertsonian translocation. All cell lines showed normal hESC characteristics and had the differentiation ability. In conclusion, we established a stable and effective method for hESC isolation and culture, and it was confirmed that the mechanical isolation was an effective method to isolate ICMs from poor embryos. These results further indicate that hESC lines can be derived from poor quality embryos discarded by IVF laboratories.

Human embryos derived by somatic cell nuclear transfer using an alternative enucleation approach

Somatic cell nuclear transfer (SCNT) was used to generate patient-specific embryonic stem cells (ESCs) from blastocysts cloned by nuclear transfer (ntESCs). In this study, a total of 135 oocytes were obtained from 12 healthy donors (30-35 years). Human oocytes, obtained within 2 h following transvaginal aspiration, were enucleated using a Spindle Imaging System to position the spindle and chromosomes that lay on the metaphase plate, and a Zona Infrared Laser Optical System was used to open a single hole in the zona pellucida at the ~ 2 o'clock position. Human fibroblasts and lymphocytes were used to construct SCNT embryos. Nearly half (26 of 58) of the oocytes were fused after electrofusion and embryo development rates were 96.2% (two-cell, 25 of 26), 92.3% (four-cell, 24 of 26), 61.5% (eight-cell, 16 of 26), 34.6% (16-cell, 9 of 26), 26.9% (morula, 7 of 26), and 19.2% (blastocyst, 5 of 26), respectively, following incubation in improved G-series sequential medium. One cloned blastocyst was used for STR-DNA identification and genetic polymorphism analysis of mtDNA, and STR-DNA analysis of all cloned blastocysts indicated they were derived from SCNT. Quantitative analysis showed that mtDNA of cloned embryos reflected the change tendency of those observed in human IVF embryos. Our research provides an alternative enucleation approach for producing human SCNT-derived blastocysts, and may aid in providing a new method for human therapeutic cloning.

Reduced serum concentration is permissive for increased in vitro endocrine differentiation from murine embryonic stem cells

Embryonic stem cells (ESCs) have been shown to be capable of differentiating into pancreatic progenitors and insulin-producing cells in vitro. However, before ESC derivatives can be used in clinical settings, efficient selective differentiation needs to be achieved. Essential to improving ESC differentiation to islet endocrine cells is an understanding of the influences of extrinsic signals and transcription factors on cell specification. Herein, we investigate the influence of serum-supplemented growth conditions on the differentiation of murine ESCs to endocrine lineages in the context of over-expression of two pancreatic transcription factors, Pdx1 and Ngn3. To study the effect of different serum formulations and concentrations on the ability of murine ESCs to differentiate into endocrine cells in vitro, cells were grown into embryoid bodies and then differentiated in various serum replacement (SR), fetal calf serum (FCS) and serum-free conditions. Using immunohistochemistry and quantitative real-time RT-PCR (QPCR), we found that, of the conditions tested, 1% SR differentiation medium resulted in the highest levels of insulin-1 mRNA and significantly increased the total number of insulin-expressing cells. Applying this knowledge to cell lines in which Pdx1 or Ngn3 transgene expression could be induced by exposure to doxycycline we differentiated TetPDX1 and TetNgn3 ESCs under conditions of either 10% FCS or 1% SR medium. In the presence of 10% serum, induced expression of either Pdx1 or Ngn3 in differentiating ESCs resulted in modest increases in hormone transcripts and cell counts. However, changing the serum formulation from 10% FCS to 1% SR significantly enhanced the number of insulin+/C-peptide+ cells in parallel with increased insulin-1 transcript levels in both inducible cell lines. In summary, these data demonstrate that induced expression of key pancreatic transcription factors in combination with low serum/SR concentrations increases endocrine cell differentiation from murine ESCs.

Stem cells to pancreatic beta-cells: new sources for diabetes cell therapy

The number of patients worldwide suffering from the chronic disease diabetes mellitus is growing at an alarming rate. Insulin-secreting beta-cells in the islet of Langerhans are damaged to different extents in diabetic patients, either through an autoimmune reaction present in type 1 diabetic patients or through inherent changes within beta-cells that affect their function in patients suffering from type 2 diabetes. Cell replacement strategies via islet transplantation offer potential therapeutic options for diabetic patients. However, the discrepancy between the limited number of donor islets and the high number of patients who could benefit from such a treatment reflects the dire need for renewable sources of high-quality beta-cells. Human embryonic stem cells (hESCs) are capable of self-renewal and can differentiate into components of all three germ layers, including all pancreatic lineages. The ability to differentiate hESCs into beta-cells highlights a promising strategy to meet the shortage of beta-cells. Here, we review the different approaches that have been used to direct differentiation of hESCs into pancreatic and beta-cells. We will focus on recent progress in the understanding of signaling pathways and transcription factors during embryonic pancreas development and how this knowledge has helped to improve the methodology for high-efficiency beta-cell differentiation in vitro.

Potential role of stem cell therapy in type 1 diabetes mellitus

Type 1 diabetes mellitus is the result of the autoimmune response against pancreatic beta-cell(s). At the time of clinical diagnosis near 70% of beta-cell mass is been destroyed as a consequence of the auto-destruction that begins months or even years before the clinical diagnosis. Although marked reduction of chronic complications was seen after development and progression of insulin therapy over the years for type 1 diabetic population, associated risks of chronic end-organ damage and hypoglycemia still remain. Besides tight glucose control, beta-cell mass preservation and/or increase are known to be other important targets in management of type 1 diabetes as long as it reduces chronic microvascular complications in the eyes, kidneys and nerves. Moreover, the larger the beta-cell mass, the lower the incidence of hypoglycemic events. In this article, we discuss some insights about beta-cell regeneration, the importance of regulation of the autoimmune process and what is being employed in human type 1 diabetes in regard to stem cell repertoire to promote regeneration and/or preservation of beta-cell mass.

A new experimental protocol for preferential differentiation of mouse embryonic stem cells into insulin-producing cells

Mouse embryonic stem (ES) cells have the potential to differentiate into insulin-producing cells, but efficient protocols for in vitro differentiation have not been established. Here we have developed a new optimized four-stage differentiation protocol and compared this with an established reference protocol. The new protocol minimized differentiation towards neuronal progeny, resulting in a population of insulin-producing cells with beta-cell characteristics but lacking neuronal features. The yield of glucagon and somatostatin cells was negligible. Crucial for this improved yield was the removal of a nestin selection step as well as removal of culture supplements that promote differentiation towards the neuronal lineage. Supplementation of the differentiation medium with insulin and fetal calf serum was beneficial for differentiation towards monohormonal insulin-positive cells. After implantation into diabetic mice these insulin-producing cells produced a time-dependent improvement of the diabetic metabolic state, in contrast to cells differentiated according to the reference protocol. Using a spinner culture instead of an adherent culture of ES cells prevented the differentiation towards insulin-producing cells. Thus, prevention of cell attachment in a spinner culture represents a means to keep ES cells in an undifferentiated state and to inhibit differentiation. In conclusion, this study describes a new optimized four-stage protocol for differentiating ES cells to insulin-producing cells with minimal neuronal cell formation.

Efficient differentiation of insulin-producing cells from skin-derived stem cells

OBJECTIVES

Type 1 diabetes mellitus, characterized by loss of pancreatic beta-cells, can be ameliorated by islet transplantation, but this treatment is restricted by the scarcity of islet tissue and by allograft rejection.

MATERIALS AND METHODS

We isolated and characterized skin-derived precursors (SKPs)--an abundant source of autologous cells--and developed an experimental strategy to convert them into insulin-producing cells (IPCs) in vitro within a short period of time, through extracellular factor modification and analyses of IPCs by reverse transcription-polymerase chain reaction, immunocytochemistry and enzyme-linked immunosorbent assay.

RESULTS

SKPs could self-assemble to form three-dimensional islet cell-like clusters (dithizone-positive) and co-express insulin and C-peptide. In addition, they expressed multiple genes related to pancreatic beta-cell development and function (e.g. insulin 1, insulin 2, islet-1, Pdx-1, NeuroD/beta2, glut-2 and Nkx6.1), but not other pancreas-specific hormones and enzymes (e.g. glucagon, somatostatin and amylase). Moreover, when stimulated with glucose, these cells synthesized and secreted insulin in a glucose-regulated manner.

CONCLUSIONS

The findings of this study indicate that SKPs can differentiate into functional IPCs and can provide an abundant source of autologous cells for transplantation. This study also provides strategies to derive autologous islet-replacement tissues from human skin stem cells.

Stem cell therapy to treat diabetes mellitus

Transplantation of pancreatic islets offers a direct treatment for type 1 diabetes and in some cases, insulin-dependent type 2 diabetes. However, its widespread use is hampered by a shortage of donor organs. Many extant studies have focused on deriving beta-cell progenitors from pancreas and pluripotent stem cells. Efforts to generate beta-cells in vitro will help elucidate the mechanisms of beta-cell formation and thus provide a versatile in vivo system to evaluate the therapeutic potential of these cells to treat diabetes. Various successful experiments using beta-cells in animal models have generated extensive interest in using human embryonic stem cells to restore normoglycemia in diabetic patients. While new techniques are continually unveiled, the success of beta-cell generation rests upon successful manipulation of culture conditions and the induction of key regulatory genes implicated in pancreas development. In this review, we compare successfully conducted protocols, highlight essential steps and identify some of the remarkable shortfalls common to these methods. In addition, we discuss recent advancements in the derivation of patient-specific pluripotent stem cells that may facilitate the use of autologous beta-cells in stem cell therapy.

Expression profiling of nuclear receptors in human and mouse embryonic stem cells

Nuclear receptors (NRs) regulate gene expression in essential biological processes including differentiation and development. Here we report the systematic profiling of NRs in human and mouse embryonic stem cell (ESC) lines and during their early differentiation into embryoid bodies. Expression of the 48 human and mouse NRs was assessed by quantitative real-time PCR. In general, expression of NRs between the two human cell lines was highly concordant, whereas in contrast, expression of NRs between human and mouse ESCs differed significantly. In particular, a number of NRs that have been implicated previously as crucial regulators of mouse ESC biology, including ERRbeta, DAX-1, and LRH-1, exhibited diametric patterns of expression, suggesting they may have distinct species-specific functions. Taken together, these results highlight the complexity of the transcriptional hierarchy that exists between species and governs early development. These data should provide a unique resource for further exploration of the species-specific roles of NRs in ESC self-renewal and differentiation.

Comparative transcriptional analysis of embryoid body versus two-dimensional differentiation of murine embryonic stem cells

Understanding the process of ex vivo embryonic stem (ES) cell differentiation is important for generating higher yields of desirable cell types or lineages and for understanding fundamental aspects of ES differentiation. We used DNA microarray analysis to investigate the differentiation of mouse ES cells cultured under three differentiation conditions. Embryoid body (EB) formation was compared to differentiation on surfaces coated with either gelatin (GEL) or matrigel (MAT). Based on the transcriptional patterns of a list of literature-based "stemness" genes, ES cell differentiation on the two coated surfaces appeared similar but not identical to EB differentiation. A notable difference was the GEL and MAT upregulation but EB downregulation of nine such stemness genes, which are related to cell adhesion and epithelial differentiation. Further, GEL and MAT differentiation showed higher expression of bone formation-related genes (Spp1, Csf1, Gsn, Bmp8b, Crlf1). Gene ontology analysis shows an increase in the expression of genes related to migration and cell structure in all three conditions. Overall, GEL and MAT conditions resulted in a more similar to each other transcriptional profile than to the EB condition, and such differences are apparently related to higher nutrient and metabolite gradients and limitations in the EB versus the GEL or MAT cultures.

Effect of extracellular matrix and 3D morphogenesis on islet hormone gene expression by Ngn3-infected mouse pancreatic ductal epithelial cells

We verified the proendocrine effects of Matrigel overlay in an adult mouse pancreatic ductal epithelial cells (PDEC) model and then decomposed the environment to delineate the specific factors responsible for this effect. Following overlay with Matrigel, supplementation of Matrigel to the culture medium, or suspension within Matrigel, neurogenin3-infected mouse PDEC underwent dramatic morphogenesis, transitioning from a two-dimensional monolayer to three-dimensional (3D) cysts. Along with these morphogenic changes, the cells displayed up to approximately sixfold increase in mRNA for the islet hormones somatostatin and ghrelin. Following overlay with collagen or suspension within collagen, PDEC also displayed similar morphogenic changes, but a much smaller increase in expression was observed (1.5- to 3-fold), suggesting that while 3D morphogenesis is capable of independently enhancing islet differentiation, biochemical factors present within Matrigel also have proendocrine effects. Following suspension within laminin gels, PDEC formed 3D cysts and also displayed an increase in islet hormone expression, similar to those cultured within Matrigel. However, medium supplemented with laminin failed to promote 3D morphogenesis of PDEC or enhance islet hormone expression, suggesting that while laminin is capable of enhancing islet hormone expression, 3D morphogenesis is required for this effect. Cell clustering appeared to maximize differentiation, as PDEC cultured on Matrigel formed aggregates and stimulated the highest expression of somatostatin and ghrelin (up to approximately 200-fold).

Stem cell sources for regenerative medicine

Tissue-resident stem cells or primitive progenitors play an integral role in homeostasis of most organ systems. Recent developments in methodologies to isolate and culture embryonic and somatic stem cells have many new applications poised for clinical and preclinical trials, which will enable the potential of regenerative medicine to be realized. Here, we overview the current progress in therapeutic applications of various stem cells and discuss technical and social hurdles that must be overcome for their potential to be realized.

In vivo characterization of transplanted human embryonic stem cell-derived pancreatic endocrine islet cells

OBJECTIVES

Islet-like clusters (ILCs), differentiated from human embryonic stem cells (hESCs), were characterized both before and after transplantation under the kidney capsule of streptozotocin-induced diabetic immuno-incompetent mice.

MATERIALS AND METHODS

Multiple independent ILC preparations (n = 8) were characterized by immunohistochemistry, flow cytometry and cell insulin content, with six preparations transplanted into diabetic mice (n = 42), compared to controls, which were transplanted with either a human fibroblast cell line or undifferentiated hESCs (n = 28).

RESULTS

Prior to transplantation, ILCs were immunoreactive for the islet hormones insulin, C-peptide and glucagon, and for the ductal epithelial marker cytokeratin-19. ILCs also had cellular insulin contents similar to or higher than human foetal islets. Expression of islet and pancreas-specific cell markers was maintained for 70 days post-transplantation. The mean survival of recipients was increased by transplanted ILCs as compared to transplanted human fibroblast cells (P < 0.0001), or undifferentiated hESCs (P < 0.042). Graft function was confirmed by secretion of human C-peptide in response to an oral bolus of glucose.

CONCLUSIONS

hESC-derived ILC grafts continued to contain cells that were positive for islet endocrine hormones and were shown to be functional by their ability to secrete human C-peptide. Further enrichment and maturation of ILCs could lead to generation of a sufficient source of insulin-producing cells for transplantation into patients with type 1 diabetes.

Production of beta-cells from human embryonic stem cells

The making of functional pancreatic islets in renewable numbers has been a goal of stem cell biologists since early 2000. Since that time, many studies have reported successful creation of glucose-responsive pancreatic beta-cells. Not until the more recent systematic application of developmental principles to stem cell biology systems were breakthroughs achieved on directed specification of the required early developmental intermediates. The most important first step is the formation of the definitive endoderm (DE) lineage which is compulsory for production of the epithelium of the pancreas and the other important endoderm-derived organs such as the liver, intestine and lung. The formation of DE from embryonic stem cells made possible additional experimentation aimed at directing the endoderm to further specified foregut and pancreatic endoderm lineages. With these discoveries came the first production of immature pancreatic endocrine cells. Most recently, the production in vivo of glucose-responsive insulin-producing cells with the capacity to correct Steptozotocin-induced hyperglycaemia in mice has been achieved. The work leading up to this achievement, in relation to the other principle human stem cell studies conducted in this area, will be briefly described. The necessary steps and ideal characteristics of embryonic stem cell-based differentiation to pancreatic beta-cells capable of glucose stimulated insulin secretion will be underscored.

Derivation of cranial neural crest-like cells from human embryonic stem cells

The neural crest is a transient population of multipotent progenitors contributing to a diverse array of tissues throughout the vertebrate embryo. Embryonic stem (ES) cells are able to form embryoid body and spontaneously differentiate to various lineages, following a reproducible temporal pattern of development that recapitulates early embryogenesis. Embryoid bodies were triturated and the dissociated cells were processed for fluorescence-activated cell sorting (FACS), and more than 1% of cells were identified as frizzled-3(+)/cadherin-11(+). Expression of marker genes associated with various terminal fates was detected for chondrocytes, glia, neurons, osteoblasts and smooth muscles, indicating that the FACS-sorted frizzled-3(+)/cadherin-11(+) cells were multipotent progenitor cells capable of differentiating to fates associated with cranial neural crest. Moreover, the sorted cells were able to self-renew and maintain multipotent differentiation potential. The derivation of cranial neural crest-like multipotent progenitor cells from ES cells provides a new tool for cell lineage analysis of neural crest in vitro.

Parthenogenesis-derived multipotent stem cells adapted for tissue engineering applications

Embryonic stem cells are envisioned as a viable source of pluripotent cells for use in regenerative medicine applications when donor tissue is not available. However, most current harvest techniques for embryonic stem cells require the destruction of embryos, which has led to significant political and ethical limitations on their usage. Parthenogenesis, the process by which an egg can develop into an embryo in the absence of sperm, may be a potential source of embryonic stem cells that may avoid some of the political and ethical concerns surrounding embryonic stem cells. Here we provide the technical aspects of embryonic stem cell isolation and expansion from the parthenogenetic activation of oocytes. These cells were characterized for their stem-cell properties. In addition, these cells were induced to differentiate to the myogenic, osteogenic, adipogenic, and endothelial lineages, and were able to form muscle-like and bony-like tissue in vivo. Furthermore, parthenogenetic stem cells were able to integrate into injured muscle tissue. Together, these results demonstrate that parthenogenetic stem cells can be successfully isolated and utilized for various tissue engineering applications.

In vitro differentiation of human adipose tissue-derived stem cells into cells with pancreatic phenotype by regenerating pancreas extract

Pancreas extract from regenerating pancreas after partial pancreatectomy is known to contain factors that induce islet neogenesis in animals with streptozotocin (STZ)-induced diabetes [A.A. Hardikar, R.R. Bhonde, Modulating experimental diabetes by treatment with cytosolic extract from the regenerating pancreas, Diabetes Res. Clin. Pract. 46 (1999) 203-211]. In this study, we evaluate the effects of regenerating pancreas extract (RPE) from 90% partially pancreatectomized rats on induction of pancreatic differentiation of human adipose tissue-derived stem cells (hASCs). We found that undifferentiated hASCs expressed OCT-3/4, Nanog, and REX-1, markers of embryonic stem cells (ESCs). Genes involved in early pancreas development showed increased expression in RPE-treated culture. Sox17 and IPF-1 were expressed only in RPE-treated culture. Immunocytochemical analysis showed C-peptide-positive cells in RPE-treated culture but not in undifferentiated hASCs. In conclusion, hASCs have the characteristics of ESCs and the potential to differentiate into pancreas cell lineages phenotypically in response to RPE.

Similar biological characteristics of human embryonic stem cell lines with normal and abnormal karyotypes

BACKGROUND

Human embryonic stem cell (hESC) lines derived from poor quality embryos usually have either normal or abnormal karyotypes. However, it is still unclear whether their biological characteristics are similar.

METHODS

Seven new hESC lines were established using discarded embryos. Five cell lines had normal karyotype, one was with an unbalanced Robertsonian translocation and one had a triploid karyotype. Their biological characteristics, short tandem repeat loci, HLA typing, differentiation capability and imprinted gene, DNA methylation and X chromosome inactivation status were compared between different cell lines.

RESULTS

All seven hESC lines had similar biological characteristics regardless of karyotype (five normal and two abnormal), such as expression of stage-specific embryonic antigen (SSEA)-4, tumor-rejection antigen (TRA)-1-81 and TRA-1-60 proteins, transcription factor octamer binding protein 4 mRNA, no detectable expression of SSEA-1 protein and high levels of alkaline phosphatase activity. All cell lines were able to undergo differentiation. Imprinted gene expression and DNA methylation were also similar among these cell lines. Non-random X chromosome inactivation patterns were found in XX cell lines.

CONCLUSIONS

The present results suggest that hESC lines with abnormal karyotype are also useful experimental materials for cell therapy, developmental biology and genetic research.

Embryonic stem cells to beta-cells by understanding pancreas development

Insulin injections treat but do not cure Type 1 diabetes (T1DM). The success of islet transplantation suggests cell replacement therapies may offer a curative strategy. However, cadaver islets are of insufficient number for this to become a widespread treatment. To address this deficiency, the production of beta-cells from pluripotent stem cells offers an ambitious far-sighted opportunity. Recent progress in generating insulin-producing cells from embryonic stem cells has shown promise, highlighting the potential of trying to mimic normal developmental pathways. Here, we provide an overview of the current methodology that has been used to differentiate stem cells toward a beta-cell fate. Parallels are drawn with what is known about normal development, especially regarding the human pancreas.

Stem cell-based therapy in gastroenterology and hepatology

Protagonists of a new scientific era, stem cells are promising tools on which regenerative medicine relies for the treatment of human pathologies. Stem cells can be obtained from various sources, including embryos, fetal tissues, umbilical cord blood, and also terminally differentiated organs. Once forced to expand and differentiate into functional progenies, stem cells may become suitable for cell replacement and tissue engineering. The manipulation and/or stimulation of adult stem cells seems to be particularly promising, as it could improve the endogenous regenerative potential without risks of rejection and overcome the ethical and political issues related to embryonic stem cell research. Stem cells are already leaving the bench and reaching the bedside, despite an incomplete knowledge of the genetic control program driving their fate and plasticity. In gastroenterology and hepatology, the first attempts to translate stem cell basic research into novel therapeutic strategies have been made for the treatment of several disorders, such as inflammatory bowel diseases, diabetes mellitus, celiachy and acute or chronic hepatopaties. Nonetheless, critical aspects need to be further addressed, including the long-term safety, tolerability and efficacy of cell-based treatments, as well as their carcinogenic potential. Aim of this review is to summarize the state-of-the-arts on gastrointestinal and hepatic stem cells and on stem cell-based therapies in gastroenterology and hepatology, highlighting both the benefits and the potential risks of these new tools for the treatment and prevention of human diseases.

Embryonic stem cells: from markers to market

ABSTRACT Embryonic stem cells are considered the mother of all kinds of tissues and cells and it is envisioned as the holy grail of regenerative medicine. However, their use in cell replacement therapies (CRT) has so far been limited and their potentials are yet to be fully realized. The use of human embryonic stem cells (hESC) involves many safety issues pertaining to culture conditions and epigenetic changes. The role and importance of an epigenomic signature in derivation and maintenance of hESC are discussed. We provide a list of important epigenetic markers, which should be studied for evaluation of safety in hESC-based cell replacement therapies. These genes also need to be screened to determine an epigenetic signature for pluripotency in the hESCs. Finally a comprehensive list of all known stemness signature genes and the marker genes for different germ line lineages are presented. This review aims at summing up most of the intriguing molecules that can play a role in the maintenance of pluripotency and can help in determining hESC differentiation to various lineages. Extensive understanding of these markers will eventually help the researchers to transform the hESC research from bench to the bedside. The use of hESCs in CRTs is still in its infancy; much effort is warranted to turn them into the much dreamed about magic wand of regenerative medicine.

Stem cells: promises versus limitations

Stem cells are the self-renewing progenitors of several body tissues and are classified according to their origin and their ability to differentiate. Current research focuses on the potential uses of stem cells in medicine and how they can provide effective treatment for a range of diseases. This approach has resulted in the field of medical practice called regenerative medicine. To attain the promises of regenerative medicine, it is necessary to fully understand the biology and properties of stem cells, achieve their successful differentiation into functional tissues, overcome the barriers related to immune responses after administration, and assess any oncogenic properties that limit their use. The availability of human stem cells not only raises hope for cell replacement therapies, but also provides a system for understanding the mechanisms of embryonic development and disease progression. Nevertheless, it raises ethical concerns that need to be addressed before the use of stem cells in clinical practice.

PDX-1 and MafA play a crucial role in pancreatic beta-cell differentiation and maintenance of mature beta-cell function

Pancreatic and duodenal homeobox factor-1 (PDX-1) plays a crucial role in pancreas development, beta-cell differentiation, and maintenance of mature beta-cell function. PDX-1 expression is maintained in pancreatic precursor cells during pancreas development but becomes restricted to beta-cells in mature pancreas. In mature beta-cells, PDX-1 transactivates the insulin and other genes involved in glucose sensing and metabolism such as GLUT2 and glucokinase. MafA is a recently isolated beta-cell-specific transcription factor which functions as a potent activator of insulin gene transcription. Furthermore, these transcription factors play an important role in induction of insulin-producing cells in various non-beta-cells and thus could be therapeutic targets for diabetes. On the other hand, under diabetic conditions, expression and/or activities of PDX-1 and MafA in beta-cells are reduced, which leads to suppression of insulin biosynthesis and secretion. It is likely that alteration of such transcription factors explains, at least in part, the molecular mechanism for beta-cell glucose toxicity found in diabetes.

Stem cell sources and therapeutic approaches for central nervous system and neural retinal disorders

In the past decades, stem cell biology has made a profound impact on our views of mammalian development as well as opened new avenues in regenerative medicine. The potential of stem cells to differentiate into various cell types of the body is the principal reason they are being explored in treatments for diseases in which there may be dysfunctional cells and/or loss of healthy cells due to disease. In addition, other properties are unique to stem cells; their endogenous trophic support, ability to home to sites of pathological entities, and stability in culture, which allows genetic manipulation, are also being utilized to formulate stem cell-based therapy for central nervous system (CNS) disorders. In this review, the authors will review key characteristics of embryonic and somatic (adult) stem cells, consider therapeutic strategies employed in stem cell therapy, and discuss the recent advances made in stem cell-based therapy for a number of progressive neurodegenerative diseases in the CNS as well as neuronal degeneration secondary to other abnormalities and injuries. Although a great deal of progress has been made in our knowledge of stem cells and their utility in treating CNS disorders, much still needs to be elucidated regarding the biology of the stem cells and the pathogenesis of targeted CNS diseases to maximize therapeutic benefits. Nonetheless, stem cells present tremendous promise in the treatment of a variety of neurodegenerative diseases.

Viral-mediated coexpression of Pdx1 and p48 regulates exocrine pancreatic differentiation in mouse ES cells

Embryonic stem cells (ES) can spontaneously activate a pancreatic differentiation program in vitro, although with low efficiency. The aim was to improve such process by using viral mediated gene transduction. In this study, we have examined the suitability of using viral vectors to express key transcriptional factors involved in pancreatic development. ES cell lines that constitutively express Pdx1, a homeodomain protein involved in both exocrine and endocrine pancreatic development and differentiation, were established using a lentiviral vector. These cells were additionally infected with an adenovirus expressing p48, a bHLH factor that is also crucial for pancreatic development and acinar differentiation. Quantitative RT-PCR analysis demonstrated an increase in the expression of exocrine genes, including those coding for both digestive enzymes and transcription factors. Immunocytochemical staining also revealed an increase in the number of amylase-expressing cell clusters. However, other important genes involved in acinar cell maturation (i.e., Mist1) were not modulated under these conditions, suggesting that the cells display features of immature exocrine cells or because of an uncoupled gene expression of the exocrine differentiation program. Importantly, this effect was selective for the acinar lineage as the expression of a large set of endocrine markers remained unchanged. Therefore, combined expression of key genes involved in pancreatic development may be a promising approach to generate mature pancreatic exocrine cells.

Engineering tissues, organs and cells

Patients suffering from diseased and injured organs may be treated with transplanted organs; however, there is a severe shortage of donor organs that is worsening yearly, given the ageing population. In the field of regenerative medicine and tissue engineering, scientists apply the principles of cell transplantation, materials science and bioengineering to construct biological substitutes that will restore and maintain normal function in diseased and injured tissues. Therapeutic cloning, where the nucleus from a donor cell is transferred into an enucleated oocyte in order to extract pluripotent embryonic stem cells, offers a potentially limitless source of cells for tissue engineering applications. The stem cell field is also advancing rapidly, opening new options for therapy, including the use of amniotic and placental fetal stem cells. This review covers recent advances that have occurred in regenerative medicine and describes applications of these technologies using chemical compounds that may offer novel therapies for patients with end-stage organ failure.

PAX4 enhances beta-cell differentiation of human embryonic stem cells

Background

Human embryonic stem cells (HESC) readily differentiate into an apparently haphazard array of cell types, corresponding to all three germ layers, when their culture conditions are altered, for example by growth in suspension as aggregates known as embryoid bodies (EBs). However, this diversity of differentiation means that the efficiency of producing any one particular cell type is inevitably low. Although pancreatic differentiation has been reported from HESC, practicable applications for the use of β-cells derived from HESC to treat diabetes will only be possible once techniques are developed to promote efficient differentiation along the pancreatic lineages.

Methods and Findings

Here, we have tested whether the transcription factor, Pax4 can be used to drive the differentiation of HESC to a β-cell fate in vitro. We constitutively over-expressed Pax4 in HESCs by stable transfection, and used Q-PCR analysis, immunocytochemistry, ELISA, Ca²⁺ microfluorimetry and cell imaging to assess the role of Pax4 in the differentiation and intracellular Ca²⁺ homeostasis of β-cells developing in embryoid bodies produced from such HESC. Cells expressing key β-cell markers were isolated by fluorescence-activated cell sorting after staining for high zinc content using the vital dye, Newport Green.

Conclusion

Constitutive expression of Pax4 in HESC substantially enhances their propensity to form putative β-cells. Our findings provide a novel foundation to study the mechanism of pancreatic β-cells differentiation during early human development and to help evaluate strategies for the generation of purified β-cells for future clinical applications.