HNF-6-independent differentiation of mouse embryonic stem cells into insulin-producing cells

Insulin-producing surrogate β-cells from embryonic stem cells: are we there yet?

Embryonic stem cells (ESCs) harbor the potential to generate every cell type of the body by differentiation. The use of hESCs holds great promise for potential cell replacement therapies for degenerative diseases including diabetes mellitus. The recently discovered induced pluripotent stem cells (iPSCs) exhibit immense potential for regenerative medicine as they allow the generation of autologous cells tailored to the patients' immune system. Research for insulin-producing surrogate cells from ESCs has yielded highly controversial results, because many steps and factors in the differentiation process are currently still unknown. Thus, there is no consensus on common standard protocols. The protocols presently used established the differentiation from pluripotent cells toward pancreatic progenitor cells. However, none of the differentiation protocols reported to date have generated by exclusive in vitro differentiation sufficient numbers of insulin-producing cells meeting all essential criteria of a β-cell. The cells often lack the crucial function of regulated insulin secretion upon glucose stimulation. This review focuses on past and current approaches to the generation of insulin-producing cells from pluripotent sources, such as ESCs and iPSCs, and critically discusses the hurdles to be taken before insulin-secreting surrogate cells derived from these stem cells will be of clinical use in humans.

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.

Mesenchymal stem cells: biology and clinical potential in type 1 diabetes therapy

Mesenchymal stem cells (MSCs) can be derived from adult bone marrow, fat and several foetal tissues. In vitro, MSCs have the capacity to differentiate into multiple mesodermal and non-mesodermal cell lineages. Besides, MSCs possess immunosuppressive effects by modulating the immune function of the major cell populations involved in alloantigen recognition and elimination. The intriguing biology of MSCs makes them strong candidates for cell-based therapy against various human diseases. Type 1 diabetes is caused by a cell-mediated autoimmune destruction of pancreatic β-cells. While insulin replacement remains the cornerstone treatment for type 1 diabetes, the transplantation of pancreatic islets of Langerhans provides a cure for this disorder. And yet, islet transplantation is limited by the lack of donor pancreas. Generation of insulin-producing cells (IPCs) from MSCs represents an attractive alternative. On the one hand, MSCs from pancreas, bone marrow, adipose tissue, umbilical cord blood and cord tissue have the potential to differentiate into IPCs by genetic modification and/or defined culture conditions In vitro. On the other hand, MSCs are able to serve as a cellular vehicle for the expression of human insulin gene. Moreover, protein transduction technology could offer a novel approach for generating IPCs from stem cells including MSCs. In this review, we first summarize the current knowledge on the biological characterization of MSCs. Next, we consider MSCs as surrogate β-cell source for islet transplantation, and present some basic requirements for these replacement cells. Finally, MSCs-mediated therapeutic neovascularization in type 1 diabetes is discussed.

Pdx-1-independent differentiation of mouse embryonic stem cells into insulin-expressing cells

To investigate whether insulin-producing cells obtained from ES cells via the nestin-positive cell-mediated method are of the pancreatic lineage, we established a pdx-1 knockout ES cell line and analyzed its differentiation into insulin-producing cells. As a result, pdx-1 knockout ES cell expressed insulin 2 gene at the final differentiated cells. Thus, our study demonstrated that pdx-1 is not essential for insulin gene expression, at least in cells differentiated from this population of nestin-expression enriched ES cells, and suggested that the insulin-producing cells derived from ES cells may be different from the pancreatic beta cells in terms of their lineage.

Hedgehog signals in pancreatic differentiation from embryonic stem cells: revisiting the neglected

Recent demonstrations of insulin expression by progenies of mouse and human embryonic stem (ES) cells have attracted interest in setting up these cells as alternative sources of beta-cells needed in diabetes cell therapy. It is widely acknowledged that information gathered in the field of developmental biology as applied to the pancreas is of relevance for designing in vitro differentiation strategies. However, looking back at the protocols used so far, it appears that the natural route toward the pancreas, which goes via the definitive endoderm, was usually bypassed. As a consequence Hedgehog signaling, the earliest inhibitor of pancreas initiation from the endoderm, was generally not considered. A recall of the status of this pathway during ES cell differentiation appears necessary, especially in the light of findings that Activin A treatment of mouse and human ES cells coax them into definitive endoderm, a lineage showing wide Hedgehog ligands expression with the potential to hinder pancreatic programming.

Glucose responsive insulin production from human embryonic germ (EG) cell derivatives

Type 1 diabetes mellitus subjects millions to a daily burden of disease management, life threatening hypoglycemia and long-term complications such as retinopathy, nephropathy, heart disease, and stroke. Cell transplantation therapies providing a glucose-regulated supply of insulin have been implemented clinically, but are limited by safety, efficacy and supply considerations. Stem cells promise a plentiful and flexible source of cells for transplantation therapies. Here, we show that cells derived from human embryonic germ (EG) cells express markers of definitive endoderm, pancreatic and beta-cell development, glucose sensing, and production of mature insulin. These cells integrate functions necessary for glucose responsive regulation of preproinsulin mRNA and expression of insulin C-peptide in vitro. Following transplantation into mice, cells become insulin and C-peptide immunoreactive and produce plasma C-peptide in response to glucose. These findings suggest that EG cell derivatives may eventually serve as a source of insulin producing cells for the treatment of diabetes.

Deriving and identifying hepatocytes from embryonic stem cells

The generation of hepatocytes from embryonic stem cells (ESCs) holds considerable promise for basic and applied research. However, the unequivocal identification of hepatocytes in ESC differentiation strategies has been hampered by a lack of hepatocyte-specific markers. Recent studies are beginning to address this issue with the identification of hepatocyte-specific genes and the production of hepatocytes from intermediate cell types like definitive endoderm. Assuming the successful identification of ESC-derived hepatocytes, the next challenge will be in balancing the proliferation and differentiation of these cells in order to generate usable numbers of functional hepatocytes in vitro.

Committing embryonic stem cells to early endocrine pancreas in vitro

A panel of genetic markers was used to assess the in vitro commitment of murine embryonic stem (ES) cells toward the endoderm-derived pancreas and to distinguish insulin-expressing cells of this lineage from other lineages such as neuron, liver, and yolk sac. There are two nonallelic insulin genes in mice. Neuronal cells express only insulin II, whereas the pancreas expresses both insulin I and II. Yolk sac and fetal liver express predominately insulin II, small amounts of insulin I, and no glucagon. We found that ES-derived embryoid bodies cultured in the presence of stage-specific concentrations of monothio-glycerol and 15% fetal calf serum, followed by serum-free conditions, give rise to a population that expresses insulin I, insulin II, pdx-1 (a pancreas marker), and Sox17 (an endoderm marker). Immunohistochemical staining shows intracellular insulin particles, and its de novo production was confirmed by staining for C-peptide. Most, but not all, of the insulin+ or C-peptide+ cells coexpress glucagon, demonstrating a differentiation pathway to pancreas rather than yolk sac or fetal liver. Addition of beta-cell specification and differentiation factors activin beta B, nicotinamide, and exendin-4 to later-stage culture increased insulin-positive cells to 2.73% of the total population, compared with the control culture, which gave rise to less than 1% insulin-staining cells. These findings suggest that stepwise culture manipulations can direct ES cells to become early endocrine pancreas.

Embryonic stem cells and islet replacement in diabetes mellitus

Transplantation of functional islets of Langerhans may emerge as a useful therapy for some patients with type 1 diabetes mellitus (DM), but donor islet shortages motivate the search for new sources of transplantable islets. Pluripotent embryonic stem (ES) cells are expandable in culture and have the potential to give rise to all cell types in the body. The recent isolation of pluripotent ES cells from humans has generated excitement over the possibility of engineering glucose-responsive islet replacement tissue from these cells in large quantities. In this study, we review the recent advances in generating insulin-producing cells (IPC) from mouse and human ES (hES) cells.

Generation of insulin-expressing cells from mouse embryonic stem cells

The therapeutic potential of transplantation of insulin-secreting pancreatic beta-cells has stimulated interest in using pluripotent embryonic stem (ES) cells as a starting material from which to generate insulin secreting cells in vitro. Mature beta-cells are endodermal in origin so most reported differentiation protocols rely on the identification of endoderm-specific markers. However, endoderm development is an early event in embryogenesis that produces cells destined for the gut and associated organs in the embryo, and for the development of extra-embryonic structures such as the yolk sac. We have demonstrated that mouse ES cells readily differentiate into extra-embryonic endoderm in vitro, and that these cell populations express the insulin gene and other functional elements associated with beta-cells. We suggest that the insulin-expressing cells generated in this and other studies are not authentic pancreatic beta-cells, but may be of extra-embryonic endodermal origin.

Stem cells in the treatment of diabetes

Clinical islet transplantation trials based on cadaveric allogenic islets have demonstrated that it is indeed possible to restore near-physiological insulin secretion capacity in a type 1 diabetic patient through transplantation of insulin-producing cells. In order to develop this form of therapy to become available for the vast majority of patients with diabetes, new sources of transplantable insulin-producing cells need to be identified. Stem cells provide the best potential to achieve this goal. Controversial results have been presented concerning the existence and nature of pancreatic islet stem or precursor cells. An increasing body of evidence suggests that the pancreatic and hepatic cell types (hepatocytes, islet, acinar and ductal cells) have remarkable plasticity and can de- and trans-differentiate into each other under appropriate conditions. Elucidation of the molecular mechanisms regulating these processes could lead to clinically applicable ways of either inducing pancreatic islet regeneration in situ or to expanding the insulin-producing cells in vitro for transplantation. The emergence of human embryonic stem cells has led to an active area of research aiming to achieve targeted differentiation of these cells into a safely transplantable beta-like cell. After initial excitement, it appears that much basic research is still required before this goal could be achieved.

Stem cell-based approaches to solving the problem of tissue supply for islet transplantation in type 1 diabetes

Type 1 diabetes is a debilitating condition, affecting millions worldwide, that is characterized by the autoimmune destruction of insulin-producing pancreatic islets of Langerhans. Although exogenous insulin administration has traditionally been the mode of treatment for this disease, recent advancements in the transplantation of donor-derived insulin-producing cells have provided new hope for a cure. However, in order for islet transplantation to become a widely used technique, an alternative source of cells must be identified to supplement the limited supply currently available from cadaveric donor organs. Stem cells represent a promising solution to this problem, and current research is being aimed at the creation of islet-endocrine tissue from these undifferentiated cells. This review presents a summary of the research to date involving stem cells and cell replacement therapy for type 1 diabetes. The potential for the differentiation of embryonic stem (ES) cells to islet phenotype is discussed, as well as the possibility of identifying and exploiting a pancreatic progenitor/stem cell from the adult pancreas. The possibility of creating new islets from adult stem cells derived from other tissues, or directly form other terminally differentiated cell types is also addressed. Finally, a model for the isolation and maturation of islets from the neonatal porcine pancreas is discussed as evidence for the existence of an islet precursor cell in the pancreas.

Stem cells: a promising source of pancreatic islets for transplantation in type 1 diabetes

Diabetes is a disease that affects millions and causes a major burden on the health care system. Type 1 diabetes has traditionally been managed with exogenous insulin therapy, however factors such as cost, lifestyle restriction, and life threatening complications necessitate the development of a more efficient treatment alternative. Pancreas transplantation, and more recently transplant of purified pancreatic islets, has offered the potential for independence from insulin injections. Islet transplantation is gaining acceptance as it has been shown to be effective for certain patients with type 1 diabetes. One obstacle, however, is the fact that there is an inadequate supply of cadaveric human islets to implement this procedure on a widespread clinical basis. A promising source of transplantable islets in the future will come through the use of adult or embryonic stem cells. This chapter presents an overview of the advancements made in the development of a stem cell based application to islet transplantation. Advantages and limitations are discussed regarding the use of embryonic stem cells, adult pancreatic stem/progenitor cells, and the use of nonpancreatic tissues based on current experimental models in the literature. It is concluded that stem cells offer the greatest potential for the development of an abundant source of pancreatic islets, although specific obstacles must be overcome before this can become a reality.

Stem cells today: A. Origin and potential of embryo stem cells

The study of embryo stem cells began in 1963, initially using disaggregates of cleaving rabbit and mouse embryos. Their differentiation in vitro was modest, and usually curtailed at best to the formation of trophectoderm cells, which attached to plastic. Rabbit morulae and blastocysts adhered more readily, trophectoderm forming a sheet of cells which was overgrown by stem cells from inner cell mass. Whole-blastocyst cultures on collagen-coated surfaces produced a pile of cells, and its outgrowths included neural, blood, neuronal, phagocytic and many other types of cell. When inner cell mass was freed and cultured intact or as cell disaggregates, lines of embryo stem cells (ES) were established which possessed good rates of cleavage, and immense stability in their secretion of enzymes, morphology and chromosomal complement. Developmental capacities of single mouse embryo stem cells were measured by injecting one or more into a recipient blastocyst, and extent of colonization in resulting chimaeras measured their pluripotency. In mouse, cell clumps were termed embryoid bodies, which produced similar outgrowths as in rabbit. Component cells again differentiated widely, depending to a limited extent on their exposure to various cytokines or substrates. Markers for differentiation or pluripotency were established, which revealed how neural, cardiac, haematological and other ES lines could be established in vitro. These have proved useful to study early differentiation and their use in grafting to sick recipients. Displaying similar properties, human ES cells emerged in the late 1990s. Models for the clinical use of ES cells showed how they colonized rapidly, travelled to target tissues via fetal pathways, differentiated and colonized target organs. No signs of inflammation or tissue damage were noted; injured tissues could be repaired including remyelination, and no cancers were formed. ES cells offer wide therapeutic potentials for humans, although extensive clinical trials are still awaited.