Functional, persistent, and extended liver to pancreas transdifferentiation

The temporal and hierarchical control of transcription factors-induced liver to pancreas transdifferentiation

Lineage-specific transcription factors (TFs) display instructive roles in directly reprogramming adult cells into alternate developmental fates, in a process known as transdifferentiation. The present study analyses the hypothesis that despite being fast, transdifferentiation does not occur in one step but is rather a consecutive and hierarchical process. Using ectopic expression of Pdx1 in human liver cells, we demonstrate that while glugacon and somatostatin expression initiates within a day, insulin gene expression becomes evident only 2–3 days later. To both increase transdifferentiation efficiency and analyze whether the process indeed display consecutive and hierarchical characteristics, adult human liver cells were treated by three pancreatic transcription factors, Pdx1, Pax4 and Mafa (3pTFs) that control distinct hierarchical stages of pancreatic development in the embryo. Ectopic expression of the 3pTFs in human liver cells, increased the transdifferentiation yield, manifested by 300% increase in the number of insulin positive cells, compared to each of the ectopic factors alone. However, only when the 3pTFs were sequentially supplemented one day apart from each other in a direct hierarchical manner, the transdifferentiated cells displayed increased mature β-cell-like characteristics. Ectopic expression of Pdx1 followed by Pax4 on the 2^nd day and concluded by Mafa on the 3^rd day resulted in increased yield of transdifferentiation that was associated by increased glucose regulated c-peptide secretion. By contrast, concerted or sequential administration of the ectopic 3pTFs in an indirect hierarchical mode resulted in the generation of insulin and somatostatin co-producing cells and diminished glucose regulated processed insulin secretion. In conclusion transcription factors induced liver to pancreas transdifferentiation is a progressive and hierarchical process. It is reasonable to assume that this characteristic is general to wide ranges of tissues. Therefore, our findings could facilitate the development of cell replacement therapy modalities for many degenerative diseases including diabetes.

The temporal and hierarchical control of transcription factors-induced liver to pancreas transdifferentiation

Lineage-specific transcription factors (TFs) display instructive roles in directly reprogramming adult cells into alternate developmental fates, in a process known as transdifferentiation. The present study analyses the hypothesis that despite being fast, transdifferentiation does not occur in one step but is rather a consecutive and hierarchical process. Using ectopic expression of Pdx1 in human liver cells, we demonstrate that while glucagon and somatostatin expression initiates within a day, insulin gene expression becomes evident only 2-3 days later. To both increase transdifferentiation efficiency and analyze whether the process indeed display consecutive and hierarchical characteristics, adult human liver cells were treated by three pancreatic transcription factors, Pdx1, Pax4 and Mafa (3pTFs) that control distinct hierarchical stages of pancreatic development in the embryo. Ectopic expression of the 3pTFs in human liver cells, increased the transdifferentiation yield, manifested by 300% increase in the number of insulin positive cells, compared to each of the ectopic factors alone. However, only when the 3pTFs were sequentially supplemented one day apart from each other in a direct hierarchical manner, the transdifferentiated cells displayed increased mature β-cell-like characteristics. Ectopic expression of Pdx1 followed by Pax4 on the 2(nd) day and concluded by Mafa on the 3(rd) day resulted in increased yield of transdifferentiation that was associated by increased glucose regulated c-peptide secretion. By contrast, concerted or sequential administration of the ectopic 3pTFs in an indirect hierarchical mode resulted in the generation of insulin and somatostatin co-producing cells and diminished glucose regulated processed insulin secretion. In conclusion transcription factors induced liver to pancreas transdifferentiation is a progressive and hierarchical process. It is reasonable to assume that this characteristic is general to wide ranges of tissues. Therefore, our findings could facilitate the development of cell replacement therapy modalities for many degenerative diseases including diabetes.

In vitro quantitative and relative gene expression analysis of pancreatic transcription factors Pdx-1, Ngn-3, Isl-1, Pax-4, Pax-6 and Nkx-6.1 in trans-differentiated human hepatic progenitors

Aims/Introduction

Diabetes is a major health concern throughout the world because of its increasing prevalence in epidemic proportions. β‐Cell deterioration in the pancreas is a crucial factor for the progression of diabetes mellitus. Therefore, the restoration of β‐cell mass and its function is of vital importance for the development of effective therapeutic strategies and most accessible cell sources for the treatment of diabetes mellitus.

Materials and Methods

Human fetuses (12–20 weeks gestation age) were used to isolate human hepatic progenitor cells (hHPCs) from fetal liver using a two‐step collagenase digestion method. Epithelial cell adhesion molecule‐positive (EpCAM+ve)‐enriched hHPCs were cultured in vitro and induced with 5–30 mmol/L concentration of glucose for 0–32 h. Pdx‐1 expression and insulin secretion was analyzed using immunophenotypic and chemifluorescence assays, respectively. Relative gene expression was quantified in induced hHPCs, and compared with uninduced and pancreatic cells to identify the activated transcription factors (Pdx‐1, Ngn‐3, Isl‐1, Pax‐4, Pax‐6 and Nkx‐6.1) involved in β‐cell production.

Results

EpCAM+ve cells derived from human fetal liver showed high in vitro trans‐differentiation potential towards the β‐cell phenotype with 23 mmol/L glucose induction after 24 h. The transcription factors showed eminent expression in induced cells. The expression level of transcription factors was found significantly high in 23 mmol/L‐induced hHPCs as compared with the uninduced cells.

Conclusions

The present study has shown an exciting new insight into β‐cell development from hHPCs trans‐differentiation. Relative quantification of gene expression in trans‐differentiated cells offers vast possibility for the production of a maximum number of functionally active pancreatic β‐cells for a future cure of diabetes.

Beyond islet transplantation in diabetes cell therapy: from embryonic stem cells to transdifferentiation of adult cells

Exogenous insulin is, at the moment, the therapy of choice of diabetes, but does not allow tight regulation of glucose leading to long-term complications. Recently, pancreatic islet transplantation to reconstitute insulin-producing β cells, has emerged as an alternative promising therapeutic approach. Unfortunately, the number of donor islets is too low compared with the high number of patients needing a transplantation leading to a search for renewable sources of high-quality β-cells. This review, summarizes more recent promising approaches to the generation of new β-cells from embryonic stem cells for transdifferentiation of adult cells, particularly a critical examination of the seminal work by Lumelsky et al.

Pancreatic transdifferentiation in porcine liver following lentiviral delivery of human furin-cleavable insulin

Type I diabetes mellitus (TID) results from the autoimmune destruction of the insulin-producing pancreatic β-cells. Gene therapy is one strategy being actively explored to cure TID by affording non-β-cells the ability to secrete insulin in response to physiologic stimuli. In previous studies, we used a novel surgical technique to express furin-cleavable human insulin (INS-FUR) in the livers of streptozotocin (STZ)-diabetic Wistar rats and nonobese diabetic (NOD) mice with the use of the HMD lentiviral vector. Normoglycemia was observed for 500 and 150 days, respectively (experimental end points). Additionally, some endocrine transdifferentiation of the liver, with storage of insulin in granules, and expression of some β-cell transcription factors (eg, Pdx1, Neurod1, Neurog3, Nkx2-2, Pax4) and pancreatic hormones in both studies. The aim of this study was to determine if this novel approach could induce liver to pancreatic transdifferentiation to reverse diabetes in pancreatectomized Westran pigs. Nine pigs were used in the study, however only one pig maintained normal fasting blood glucose levels for the period from 10 to 44 days (experimental end point). This animal was given 2.8 × 10(9) transducing units/kg of the lentiviral vector expressing INS-FUR. A normal intravenous glucose tolerance test was achieved at 30 days. Reverse-transcription polymerase chain reaction analysis of the liver tissue revealed expression of several β-cell transcription factors, including the key factors, Pdx-1 and Neurod1, pancreatic hormones, glucagon, and somatostatin; however, endogenous pig insulin was not expressed. Triple immunofluorescence showed extensive insulin expression, as was previously observed in our studies with rodents. Additionally, a small amount of glucagon and somatostatin protein expression was seen. Collectively, these data indicate that pancreatic transdifferentiation of the liver tissue had occurred. Our data suggest that this regimen may ultimately be used clinically to cure TID, however more work is required to replicate the successful reversal of diabetes in increased numbers of pigs.

Membranes to achieve immunoprotection of transplanted islets

Transplantation of islet or beta cells is seen as the cure for type 1 diabetes since it allows physiological regulation of blood glucose levels without requiring any compliance from the patients. In order to circumvent the use of immunosuppressive drugs (and their side effects), semipermeable membranes have been developed to encapsulate and immunoprotect transplanted cells. This review presents the historical developments of immunoisolation and provides an update on the current research in this field. A particular emphasis is laid on the fabrication, characterization and performance of membranes developed for immunoisolation applications.

Diabetes treatment: A rapid review of the current and future scope of stem cell research

Diabetes mellitus is a major health concern of the developing and developed nations across the globe. This devastating disease accounts for the 5% deaths around the world annually. The current treatment methods do not address the underlying causes of the disease and have severe limitations. Stem cells are unique cells with the potential to differentiate into any type of specialized cells. This feature of both adult and embryonic stem cells was explored in great detail by the scientists around the world and are successful in producing insulin secreting cells. The different type of stem cells (induced pluripotent stem cells (iPSCs), embryonic stem cells (ESCs) and adult stem cells) proves to be potent in treating diabetes with certain limitations. This article precisely reviews the resources and progress made in the field of stem cell research for diabetic treatment.

Reprogramming of enteroendocrine K cells to pancreatic β-cells through the combined expression of Nkx6.1 and Neurogenin3, and reaggregation in suspension culture

Recent studies have demonstrated that adult cells such as pancreatic exocrine cells can be converted to pancreatic β-cells in a process called cell reprogramming. Enteroendocrine cells and β-cells share similar pathways of differentiation during embryonic development. Notably, enteroendocrine K cells express many of the key proteins found in β-cells. Thus, K cells could be reprogrammed to β-cells under certain conditions. However, there is no clear evidence on whether these cells convert to β-cells. K cells were selected from STC-1 cells, an enteroendocrine cell line expressing multiple hormones. K cells were found to express many genes of transcription factors crucial for islet development and differentiation except for Nkx6.1 and Neurogenin3. A K cell clone stably expressing Nkx6.1 (Nkx6.1(+)-K cells) was established. Induction of Neurogenin3 expression in Nkx6.1(+)-K cells, by either treatment with a γ-secretase inhibitor or infection with a recombinant adenovirus expressing Neurogenin3, led to a significant increase in Insulin1 mRNA expression. After infection with the adenovirus expressing Neurogenin3 and reaggregation in suspension culture, about 50% of Nkx6.1(+)-K cells expressed insulin as determined by immunostaining. The intracellular insulin content was increased markedly. Electron microscopy revealed the presence of insulin granules. However, glucose-stimulated insulin secretion was defective, and there was no glucose lowering effect after transplantation of these cells in diabetic mice. In conclusion, we demonstrated that K cells could be reprogrammed partially to β-cells through the combined expression of Nkx6.1 and Neurogenin3, and reaggregation in suspension culture.

Expression of Ins1 and Ins2 genes in mouse fetal liver

A possible cure for diabetes is explored by using non-pancreatic cells such as fetal hepatocytes. The expression of insulin and transcription factors for insulin is investigated in mouse fetal liver. We detected mRNAs for insulin I (Ins1) and insulin II (Ins2) and proinsulin- and mature insulin-positive cells in mouse fetal liver by reverse transcription plus the polymerase chain reaction and immunohistochemistry. Glucagon, somatostatin and pancreatic polypeptide were not expressed throughout development. Mouse Ins2 and Ins1 promoters were transiently activated in mouse fetal hepatocytes of embryonic days 13.5 and 16.5, respectively. Pancreatic and duodenal homeobox 1 (Pdx1) mRNA was not expressed during development of the liver. In contrast, mRNAs and proteins of neurogenic differentiation (NeuroD)/β cell E-box transactivator 2 (Beta2) and v-maf musculoaponeurotic fibrosarcoma oncogene homolog (MafA) were almost simultaneously expressed with insulin genes in the liver. Ins2 and Ins1 promoters were activated in hepatoma cells by the transfection of the expression vector for NeuroD/Beta2 alone and by the combination of NeuroD/Beta2 and MafA, respectively. These results indicate that the expression of NeuroD/Beta2 and MafA is linked temporally with the transcription of Ins2 and Ins1 genes in mouse fetal liver and suggest the potential usage of fetal hepatocytes to make insulin-producing β cells by introducing transcription factors.

Stable insulin-secreting ducts formed by reprogramming of cells in the liver using a three-gene cocktail and a PPAR agonist

With the long-term aim of developing a new type of therapy for diabetes, we have investigated the reprogramming of liver cells in normal mice toward a pancreatic phenotype using the gene combination Pdx1, Ngn3, MafA. CD1 mice were rendered diabetic with streptozotocin and given a single dose of Ad-PNM, an adenoviral vector containing all three genes. Ad-PNM induced hepatocytes of the liver to produce insulin, and the blood glucose became normalized. But over several weeks, the insulin-positive cells were lost and the blood glucose rose back to diabetic levels. Simultaneous administration of a peroxisome-proliferator-activated receptor agonist, WY14643, caused remission of diabetes at a lower dose of Ad-PNM and also caused the appearance of a population of insulin-secreting ductal structures in the liver. The insulin-positive ducts were stable and were able to relieve diabetes in the long term. We show that the effect of WY14643 is associated with the promotion of cell division of the ductal cells, which may increase their susceptibility to being reprogrammed toward a beta cell fate.

Stage specific reprogramming of mouse embryo liver cells to a beta cell-like phenotype

We show that cultures of mouse embryo liver generate insulin-positive cells when transduced with an adenoviral vector encoding the three genes: Pdx1, Ngn3 and MafA (Ad-PNM). Only a proportion of transduced cells become insulin-positive and the highest yield occurs in the period E14-16, declining at later stages. Insulin-positive cells do not divide further although they can persist for several weeks. RT-PCR analysis of their gene expression shows the upregulation of a whole battery of genes characteristic of beta cells including upregulation of the endogenous counterparts of the input genes. Other features, including a relatively low insulin content, the expression of genes for other pancreatic hormones, and the fact that insulin secretion is not glucose-sensitive, indicate that the insulin-positive cells remain immature. The origin of the insulin-positive cells is established both by co-immunostaining for α-fetoprotein and albumin, and by lineage tracing for Sox9, which is expressed in the ductal plate cells giving rise to biliary epithelium. This shows that the majority of insulin-positive cells arise from hepatoblasts with a minority from the ductal plate cells.

Long-term reversal of diabetes in non-obese diabetic mice by liver-directed gene therapy

BACKGROUND

Type 1 diabetes (T1D) results from an autoimmune attack against the insulin-producing β-cells of the pancreas. The present study aimed to reverse T1D by gene therapy.

METHODS

We used a novel surgical technique, which involves isolating the liver from the circulation before the delivery of a lentiviral vector carrying furin-cleavable human insulin (INS-FUR) or empty vector to the livers of diabetic non-obese diabetic mice (NOD). This was compared with the direct injection of the vector into the portal circulation. Mice were monitored for body weight and blood glucose. Intravenous glucose tolerance tests were performed. Expression of insulin and pancreatic transcription factors was determined by the reverse transcriptase-polymerase chain reaction and immunohistochemistry and immunoelectron microscopy was used to localise insulin.

RESULTS

Using the novel surgical technique, we achieved long-term transduction (42% efficiency) of hepatocytes, restored normoglycaemia for 150 days (experimental endpoint) and re-established normal glucose tolerance. We showed the expression of β-cell transcription factors, murine insulin, glucagon and somatostatin, and hepatic storage of insulin in granules. The expression of hepatic markers, C/EBP-β, G6PC, AAT and GLUI was down-regulated in INS-FUR-treated livers. Liver function tests remained normal, with no evidence of intrahepatic inflammation or autoimmune destruction of the insulin-secreting liver tissue. By comparison, direct injection of INS-FUR reduced blood glucose levels, and no pancreatic transdifferentiation or normal glucose tolerance was observed.

CONCLUSIONS

This gene therapy protocol has, for the first time, permanently reversed T1D with normal glucose tolerance in NOD mice and, as such, represents a novel therapeutic strategy for the treatment of T1D.

Correction of Diabetic Hyperglycemia and Amelioration of Metabolic Anomalies by Minicircle DNA Mediated Glucose-Dependent Hepatic Insulin Production

Type 1 diabetes mellitus (T1DM) is caused by immune destruction of insulin-producing pancreatic β-cells. Commonly used insulin injection therapy does not provide a dynamic blood glucose control to prevent long-term systemic T1DM-associated damages. Donor shortage and the limited long-term success of islet transplants have stimulated the development of novel therapies for T1DM. Gene therapy-based glucose-regulated hepatic insulin production is a promising strategy to treat T1DM. We have developed gene constructs which cause glucose-concentration-dependent human insulin production in liver cells. A novel set of human insulin expression constructs containing a combination of elements to improve gene transcription, mRNA processing, and translation efficiency were generated as minicircle DNA preparations that lack bacterial and viral DNA. Hepatocytes transduced with the new constructs, ex vivo, produced large amounts of glucose-inducible human insulin. In vivo, insulin minicircle DNA (TA1m) treated streptozotocin (STZ)-diabetic rats demonstrated euglycemia when fasted or fed, ad libitum. Weight loss due to uncontrolled hyperglycemia was reversed in insulin gene treated diabetic rats to normal rate of weight gain, lasting ∼1 month. Intraperitoneal glucose tolerance test (IPGT) demonstrated in vivo glucose-responsive changes in insulin levels to correct hyperglycemia within 45 minutes. A single TA1m treatment raised serum albumin levels in diabetic rats to normal and significantly reduced hypertriglyceridemia and hypercholesterolemia. Elevated serum levels of aspartate transaminase, alanine aminotransferase, and alkaline phosphatase were restored to normal or greatly reduced in treated rats, indicating normalization of liver function. Non-viral insulin minicircle DNA-based TA1m mediated glucose-dependent insulin production in liver may represent a safe and promising approach to treat T1DM.

Artificial induction and disease-related conversion of the hepatic fate

Under normal physiological conditions, the fates of cells that compose various parts of organs are determined during development, and never change to those of other cell types. However, recent advances in induction of cellular reprogramming provide chances to generate a completely different cell type from an original cell source by artificially modulating the microenvironments or gene expressions pattern of cells. Although hepatocytes normally only reside in the liver, the hepatic program can be induced in skin-derived fibroblasts by expressing defined extrinsic transcription factors. These induced hepatocyte-like cells have hepatocyte-specific properties and functionally restore damaged hepatic tissues after transplantation. On the other hand, hepatocytes themselves can be converted into biliary lineage cells as a causative factor of hepatic diseases. Thus, blockade of such disease-related reprogramming of the hepatic fate will become a new therapeutic strategy for refractory diseases in the liver. Moreover, hepatocytes could partially accept the pancreatic program by expressing transcription factors required for pancreas development, suggesting that insulin-producing cells could be generated from hepatocytes and used to treat diabetes. The above-mentioned progress will stimulate studies on the molecular nature of cellular identity and plasticity in hepatocytes, and contribute to the development of potential therapies for liver diseases.

Transcription factors that convert adult cell identity are differentially polycomb repressed

Transcription factors that can convert adult cells of one type to another are usually discovered empirically by testing factors with a known developmental role in the target cell. Here we show that standard genomic methods (RNA-seq and ChIP-seq) can help identify these factors, as most are more strongly Polycomb repressed in the source cell and more highly expressed in the target cell. This criterion is an effective genome-wide screen that significantly enriches for factors that can transdifferentiate several mammalian cell types including neural stem cells, neurons, pancreatic islets, and hepatocytes. These results suggest that barriers between adult cell types, as depicted in Waddington's "epigenetic landscape", consist in part of differentially Polycomb-repressed transcription factors. This genomic model of cell identity helps rationalize a growing number of transdifferentiation protocols and may help facilitate the engineering of cell identity for regenerative medicine.

Direct differentiation of hepatic stem-like WB cells into insulin-producing cells using small molecules

Recent evidence suggests that experimental induction of hepatocytes into pancreatic cells provides new cell transplantation therapy prospects for type 1 diabetes mellitus. Stepwise differentiation from rat liver epithelial stem-like WB-F344 cells (WB cells) into functional insulin-secreting cells will identify key steps in β-cell development and may yet prove useful for transplantation therapy for diabetic patients. An essential step in this protocol was the generation of pancreatic precursor cell that express Pdx1 based on induction by a combination of 5-aza-2′-deoxycytidine, trichostatin A, retinoic acid, and a mix of insulin, transferrin and selenite. The Pdx1-expressing cells express other pancreatic markers and contribute to endocrine cells in vitro and in vivo. This study indicates an efficient chemical protocol for differentiating WB cells into functional insulin-producing cells using small molecules, and represents a promising hepatocyte-based treatment for diabetes mellitus.

Diabetes Mellitus: New Challenges and Innovative Therapies

Diabetes is a common chronic disease affecting an estimated 285 million adults worldwide. The rising incidence of diabetes, metabolic syndrome, and subsequent vascular diseases is a major public health problem in industrialized countries. This chapter summarizes current pharmacological approaches to treat diabetes mellitus and focuses on novel therapies for diabetes mellitus that are under development.

There is great potential for developing a new generation of therapeutics that offer better control of diabetes, its co-morbidities and its complications. Preclinical results are discussed for new approaches including AMPK activation, the FGF21 target, cell therapy approaches, adiponectin mimetics and novel insulin formulations. Gene-based therapies are among the most promising emerging alternatives to conventional treatments. Therapies based on gene silencing using vector systems to deliver interference RNA to cells (i.e. against VEGF in diabetic retinopathy) are also a promising therapeutic option for the treatment of several diabetic complications.

In conclusion, treatment of diabetes faces now a new era that is characterized by a variety of innovative therapeutic approaches that will improve quality of life in the near future.

Genetic modification of primate amniotic fluid-derived stem cells produces pancreatic progenitor cells in vitro

Insulin therapy for type 1 diabetes does not prevent serious long-term complications including vascular disease, neuropathy, retinopathy and renal failure. Stem cells, including amniotic fluid-derived stem (AFS) cells - highly expansive, multipotent and nontumorigenic cells - could serve as an appropriate stem cell source for β-cell differentiation. In the current study we tested whether nonhuman primate (nhp)AFS cells ectopically expressing key pancreatic transcription factors were capable of differentiating into a β-cell-like cell phenotype in vitro. nhpAFS cells were obtained from Cynomolgus monkey amniotic fluid by immunomagnetic selection for a CD117 (c-kit)-positive population. RT-PCR for endodermal and pancreatic lineage-specific markers was performed on AFS cells after adenovirally transduced expression of PDX1, NGN3 and MAFA. Expression of MAFA was sufficient to induce insulin mRNA expression in nhpAFS cell lines, whereas a combination of MAFA, PDX1 and NGN3 further induced insulin expression, and also induced the expression of other important endocrine cell genes such as glucagon, NEUROD1, NKX2.2, ISL1 and PCSK2. Higher induction of these and other important pancreatic genes was achieved by growing the triply infected AFS cells in media supplemented with a combination of B27, betacellulin and nicotinamide, as well as culturing the cells on extracellular matrix-coated plates. The expression of pancreatic genes such as NEUROD1, glucagon and insulin progressively decreased with the decline of adenovirally expressed PDX1, NGN3 and MAFA. Together, these experiments suggest that forced expression of pancreatic transcription factors in primate AFS cells induces them towards the pancreatic lineage.

Present and future cell therapies for pancreatic beta cell replenishment

If only at a small scale, islet transplantation has successfully addressed what ought to be the primary endpoint of any cell therapy: the functional replenishment of damaged tissue in patients. After years of less-than-optimal approaches to immunosuppression, recent advances consistently yield long-term graft survival rates comparable to those of whole pancreas transplantation. Limited organ availability is the main hurdle that stands in the way of the widespread clinical utilization of this pioneering intervention. Progress in stem cell research over the past decade, coupled with our decades-long experience with islet transplantation, is shaping the future of cell therapies for the treatment of diabetes. Here we review the most promising avenues of research aimed at generating an inexhaustible supply of insulin-producing cells for islet regeneration, including the differentiation of pluripotent and multipotent stem cells of embryonic and adult origin along the beta cell lineage and the direct reprogramming of non-endocrine tissues into insulin-producing cells.

Restoring insulin production for type 1 diabetes

Current therapies for the treatment of type 1 diabetes include daily administration of exogenous insulin and, less frequently, whole-pancreas or islet transplantation. Insulin injections often result in inaccurate insulin doses, exposing the patient to hypo- and/or hyperglycemic episodes that lead to long-term complications. Islet transplantation is also limited by lack of high-quality islet donors, early graft failure, and chronic post-transplant immunosuppressive treatment. These barriers could be circumvented by designing a safe and efficient strategy to restore insulin production within the patient's body. Porcine islets have been considered as a possible alternative source of transplantable insulin-producing cells to replace human cadaveric islets. More recently, embryonic or induced pluripotent stem cells have also been examined for their ability to differentiate in vitro into pancreatic endocrine cells. Alternatively, it may be feasible to generate new β-cells by ectopic expression of key transcription factors in endogenous non-β-cells. Finally, engineering surrogate β-cells by in vivo delivery of the insulin gene to specific tissues is also being studied as a possible therapy for type 1 diabetes. In the present review, we discuss these different approaches to restore insulin production.

From cellular therapies to tissue reprogramming and regenerative strategies in the treatment of diabetes

Diabetes mellitus represents a global epidemic affecting over 350 million patients worldwide and projected by the WHO to surpass the 500 million patient mark within the next two decades. Besides Type 1 and Type 2 diabetes mellitus, the study of the endocrine compartment of the pancreas is of great translational interest, as strategies aimed at restoring its mass could become therapies for glycemic dysregulation, drug-related diabetes following diabetogenic therapies, or hyperglycemic disturbances following the treatment of cancer and nesidioblastosis. Such strategies generally fall under one of the ‘three Rs’: replacement (islet transplantation and stem cell differentiation); reprogramming (e.g., from the exocrine compartment of the pancreas); and regeneration (replication and induction of endogenous stem cells). As the latter has been extensively reviewed in recent months by us and others, this article focuses on emerging reprogramming and replacement approaches.

Insulin gene therapy from design to beta cell generation

Despite the fact that insulin injection can protect diabetic patients from developing diabetes-related complications, recent meta-analyses indicate that rapid and long-acting insulin analogues only provide a limited benefit compared with conventional insulin regarding glycemic control. As insulin deficiency is the main sequel of type-1 diabetes (T1D), transfer of the insulin gene-by-gene therapy is becoming an attractive treatment modality even though T1D is not caused by a single genetic defect. In contrast to human insulin and insulin analogues, insulin gene therapy targets to supplement patients not only with insulin but also with C-peptide. So far, insulin gene therapy has had limited success because of delayed and/or transient gene expression. Sustained insulin gene expression is now feasible using current gene-therapy vectors providing patients with basal insulin coverage, but management of postprandial hyperglycaemia is still difficult to accomplish because of the inability to properly control insulin secretion. Enteroendocrine cells of the gastrointestinal track (K cells and L cells) may be ideal targets for insulin gene therapy, but cell-targeting difficulties have limited practical implementation of insulin gene therapy for diabetes treatment. Therefore, recent gene transfer technologies developed to generate authentic beta cells through transdifferentiation are also highlighted in this review.

In vivo reprogramming of Sox9+ cells in the liver to insulin-secreting ducts

In embryonic development, the pancreas and liver share developmental history up to the stage of bud formation. Therefore, we postulated that direct reprogramming of liver to pancreatic cells can occur when suitable transcription factors are overexpressed. Using a polycistronic vector we misexpress Pdx1, Ngn3, and MafA in the livers of NOD-SCID mice rendered diabetic by treatment with streptozotocin (STZ). The diabetes is relieved long term. Many ectopic duct-like structures appear that express a variety of β-cell markers, including dense core granules visible by electron microscopy (EM). Use of a vector also expressing GFP shows that the ducts persist long after the viral gene expression has ceased, indicating that this is a true irreversible cell reprogramming event. We have recovered the insulin(+) cells by cell sorting and shown that they display glucose-sensitive insulin secretion. The early formed insulin(+) cells can be seen to coexpress SOX9 and are also labeled in mice lineage labeled for Sox9 expression. SOX9(+) cells are normally found associated with small bile ducts in the periportal region, indicating that the duct-like structures arise from this source. This work confirms that developmentally related cells can be reprogrammed by suitable transcription factors and also suggests a unique therapy for diabetes.

Forgotten and novel aspects in pancreas development

Diseases related to the pancreas are of highest importance in public health. It is anticipated that a detailed understanding of the molecular events that govern the embryonic development of this organ will have an immediate impact on clinical research relating to this issue. One major aim is the reconstruction of embryonic development in vitro with appropriate precursor cells, a second strategy is aimed at understanding the transdifferentiation of non-pancreatic into pancreatic tissue, and a third avenue is defined by the stimulation of the intrinsic ability of the pancreas to regenerate. Recent progress in developmental biology with respect to these different topics is reviewed in the present article. In addition, we also address evolutionary aspects of pancreas development, emphasizing the role of the South African clawed frog, Xenopus laevis, as an additional useful model system to study the molecular control of pancreas development.

Stem cell-based treatments for Type 1 diabetes mellitus: bone marrow, embryonic, hepatic, pancreatic and induced pluripotent stem cells

Type 1 diabetes mellitus--characterized by the permanent destruction of insulin-secreting β-cells--is responsive to cell-based treatments that replace lost β-cell populations. The current gold standard of pancreas transplantation provides only temporary independence from exogenous insulin and is fraught with complications, including increased mortality. Stem cells offer a number of theoretical advantages over current therapies. Our review will focus on the development of treatments involving tissue stem cells from bone marrow, liver and pancreatic cells, as well as the potential use of embryonic and induced pluripotent stem cells for Type 1 diabetes therapy. While the body of research involving stem cells is at once promising and inconsistent, bone marrow-derived mesenchymal stem cell transplantation seems to offer the most compelling evidence of efficacy. These cells have been demonstrated to increase endogenous insulin production, while partially mitigating the autoimmune destruction of newly formed β-cells. However, recently successful experiments involving induced pluripotent stem cells could quickly move them into the foreground of therapeutic research. We address the limitations encountered by present research and look toward the future of stem cell treatments for Type 1 diabetes.

In vitro transdifferentiation of HepG2 cells to pancreatic-like cells by CCl₄, D-galactosamine, and ZnCl₂

OBJECTIVE

The objective of the study was to induce transdifferentiation of human hepatoma HepG2 cells into pancreatic-like cells without direct genetic intervention.

METHODS

HepG2 cells were transfected with plasmids for the hepatocyte marker protein green fluorescent protein (albumin-GFP) and the pancreatic cell marker Discosoma spp red fluorescent protein (elastase-DsRed) to create FAE-HepG2 cells. Fluorescent marker expression was used to monitor in vitro transdifferentiation stimulated 100 mM CCl₄, 2 mM D-galactosamine, or 200 μM ZnCl₂. Concentrations were selected for optimal cell survival rate. Transdifferentiation was also characterized by immunohistochemical detection of amylase, glucagon, and insulin and by polymerase change reaction analysis of amylase and insulin mRNA production.

RESULTS

Control cells expressed albumin-GFP but no elastase-DsRed. By 30 days of culture, all 3 agents induced expression of pancreatic-like cell marker elastase-DsRed. ZnCl₂ was the most effective as most cells expressed elastase-DsRed in the absence of simultaneous expression of albumin-GFP. For CCl₄ and D-galactosamine, elastase-DsRed was expressed in the same cells as albumin-GFP. Cells treated by each agent also expressed amylase, insulin, and glucagon proteins and mRNAs.

CONCLUSIONS

Without direct genetic intervention, select low small molecules can induce in vitro transformation of hepatoma cells into pancreatic-like cells.

Ectopic PDX-1 expression directly reprograms human keratinocytes along pancreatic insulin-producing cells fate

BACKGROUND

Cellular differentiation and lineage commitment have previously been considered irreversible processes. However, recent studies have indicated that differentiated adult cells can be reprogrammed to pluripotency and, in some cases, directly into alternate committed lineages. However, although pluripotent cells can be induced in numerous somatic cell sources, it was thought that inducing alternate committed lineages is primarily only possible in cells of developmentally related tissues. Here, we challenge this view and analyze whether direct adult cell reprogramming to alternate committed lineages can cross the boundaries of distinct developmental germ layers.

METHODOLOGY/PRINCIPAL FINDINGS

We ectopically expressed non-integrating pancreatic differentiation factors in ectoderm-derived human keratinocytes to determine whether these factors could directly induce endoderm-derived pancreatic lineage and β-cell-like function. We found that PDX-1 and to a lesser extent other pancreatic transcription factors, could rapidly and specifically activate pancreatic lineage and β-cell-like functional characteristics in ectoderm-derived human keratinocytes. Human keratinocytes transdifferentiated along the β cell lineage produced processed and secreted insulin in response to elevated glucose concentrations. Using irreversible lineage tracing for KRT-5 promoter activity, we present supporting evidence that insulin-positive cells induced by ectopic PDX-1 expression are generated in ectoderm derived keratinocytes.

CONCLUSIONS/SIGNIFICANCE

These findings constitute the first demonstration of human ectoderm cells to endoderm derived pancreatic cells transdifferentiation. The study represents a proof of concept which suggests that transcription factors induced reprogramming is wider and more general developmental process than initially considered. These results expanded the arsenal of adult cells that can be used as a cell source for generating functional endocrine pancreatic cells. Directly reprogramming somatic cells into alternate desired tissues has important implications in developing patient-specific, regenerative medicine approaches.

Human liver cells expressing albumin and mesenchymal characteristics give rise to insulin-producing cells

Activation of the pancreatic lineage in the liver has been suggested as a potential autologous cell replacement therapy for diabetic patients. Transcription factors-induced liver-to-pancreas reprogramming has been demonstrated in numerous species both in vivo and in vitro. However, human-derived liver cells capable of acquiring the alternate pancreatic repertoire have never been characterized. It is yet unknown whether hepatic-like stem cells or rather adult liver cells give rise to insulin-producing cells. Using an in vitro experimental system, we demonstrate that proliferating adherent human liver cells acquire mesenchymal-like characteristics and a considerable level of cellular plasticity. However, using a lineage-tracing approach, we demonstrate that insulin-producing cells are primarily generated in cells enriched for adult hepatic markers that coexpress both albumin and mesenchymal markers. Taken together, our data suggest that adult human hepatic tissue retains a substantial level of developmental plasticity, which could be exploited in regenerative medicine approaches.

Isolation of genes involved in pancreas regeneration by subtractive hybridization

The deterioration of β cells in the pancreas is a crucial factor in the progression of diabetes mellitus; therefore, the recovery of β cells is of vital importance for effective diabetic therapeutic strategies. Partially pancreatectomized rats have been used for the investigation of pancreatic regeneration. Because it was determined that tissue extract from the partially-dissected pancreas induces pancreatic differentiation in embryonic stem cells, paracrine factors were thought to be involved in the regeneration. In this study, we screened for genes that had higher mRNA levels 2 days after 60%-pancreatectomy. The genes were isolated using subtractive hybridization and DNA sequencing. Twelve genes (adipsin, Aplp2, Clu, Col1a2, Glul, Krt8, Lgmn, LOC299907, LOC502894, Pla2g1b, Reg3α and Xbp1) were identified, and RT-PCR and real-time PCR analyses were performed to validate their expression levels. Among the genes identified, three genes (Glul, Lgmn and Reg3a) were selected for further analyses. Assays revealed that Glul and Reg3α enhance cell growth. Glul, Lgmn and Reg3α change the expression level of islet marker genes, where NEUROD, NKX2.2, PAX4 and PAX6 are up-regulated and somatostatin is down-regulated. Thus, we believe that Glul, Lgmn and Reg3a can serve as novel targets in diabetes mellitus genetic therapy.

Hydrodynamics-based transfection of the combination of betacellulin and neurogenic differentiation 1 DNA ameliorates hyperglycemia in mice with streptozotocin-induced diabetes

BACKGROUND

The biohazards caused by the viral delivery of pancreatic transcription factors, including neurogenic differentiation 1 (Neurod1) and Betacellulin (Btc), to the murine liver limit application of this procedure in reversing diabetes. We aimed to evaluate the feasibility of hydrodynamics-based transfection (HBT) with Neurod1 and Btc in improving hyperglycemia.

METHODS

Murine hepatocellular carcinoma (Hepa1-6) cells were transfected with the combination of Neurod1-expressing plasmid, pcDNA3.1/V5-His A (pcDNA)-Neurod1, and Btc-expressing plasmid, pcDNA3.1/V5-His A (pcDNA)-Btc. Hepatic delivery of a combination of pcDNA-Neurod1 and pcDNA-Btc (experimental group) or pcDNA (control group) to mice with streptozocin-induced diabetes was achieved by HBT. The sequential serum glucose and alanine aminotransferase (ALT) levels were assessed.

RESULTS

On day 3 after transfection, the transfection efficiencies of pcDNA-Btc and pcDNA-Neurod1 in the Hepa1-6 cells were 20% and 8%, respectively; respective values in the mouse livers were 30% and 10%. At 1 week after HBT, aside from hepatic expression of insulin, the experimental mice had a significantly lower sugar level (8-14 days after HBT, P values ranged from 0.034 to <0.001) than the control mice; the difference remained for 1 week but diminished afterward. The ALT levels and the body weight change were not different between the two groups. No mortality was noted in both groups.

CONCLUSIONS

The hypoglycemic effect of Neurod1 and Btc delivered by HBT was transient and associated with negligible complications. In studies on the short-term hypoglycemic effects of Neurod1 and Btc in vivo, HBT is a potential alternative to viral delivery of Neurod1 and Btc to the murine liver.

NKX6.1 promotes PDX-1-induced liver to pancreatic β-cells reprogramming

Reprogramming adult mammalian cells is an attractive approach for generating cell-based therapies for degenerative diseases, such as diabetes. Adult human liver cells exhibit a high level of developmental plasticity and have been suggested as a potential source of pancreatic progenitor tissue. An instructive role for dominant pancreatic transcription factors in altering the hepatic developmental fate along the pancreatic lineage and function has been demonstrated. Here we analyze whether transcription factors expressed in mature pancreatic β-cells preferentially activate β-cell lineage differentiation in liver. NKX6.1 is a transcription factor uniquely expressed in β-cells of the adult pancreas, its potential role in reprogramming liver cells to pancreatic lineages has never been analyzed. Our results suggest that NKX6.1 activates immature pancreatic markers such as NGN-3 and ISL-1 but not pancreatic hormones gene expression in human liver cells. We hypothesized that its restricted capacity to activate a wide pancreatic repertoire in liver could be related to its incapacity to activate endogenous PDX-1 expression in liver cells. Indeed, the complementation of NKX6.1 by ectopic PDX-1 expression substantially and specifically promoted insulin expression and glucose regulated processed hormone secretion to a higher extent than that of PDX-1 alone, without increasing the reprogrammed cells. This may suggest a potential role for NKX6.1 in promoting PDX-1 reprogrammed cells maturation along the β-cell-like lineage. By contrast, NKX6.1 repressed PDX-1 induced proglucagon gene expression. The individual and concerted effects of pancreatic transcription factors in adult extra-pancreatic cells, is expected to facilitate developing regenerative medicine approaches for cell replacement therapy in diabetics.

Induction of a mature hepatocyte phenotype in adult liver derived progenitor cells by ectopic expression of transcription factors

BACKGROUND/AIMS

By ectopic expression of a distinct combination of transcription factors we aimed to induce a mature hepatocyte phenotype in an adult liver derived progenitor cell population (ALDPC).

METHODS

The open reading frames encoding murine Foxa2, Hnf4α and C/ebpα were cloned into lentivirus vectors and sequentially expressed in target cells. After seven days of culture, cells were analysed for expression of liver specific genes, and functional assays were performed. Fresh primary hepatocytes, twenty four hours in culture, served as positive controls.

RESULTS

Untransduced ALDPC under established differentiation conditions exhibited moderate signs of maturation, in particular in comparison with fresh hepatocyte controls. In transcription factor transduced cells, fifteen mRNA´s coding for secreted proteins, cytochrome p450 isoenzymes, liver metabolic enzymes were detected by RT-qPCR at levels close to controls. Albumin secretion increased incrementally in single (Foxa2), double (Foxa2, Hnf4α) and triple-transduced cells (Foxa2, Hnf4α, C/ebpα) and reached levels observed in primary hepatocytes. Glycogen storage as determined by PAS staining was detectable in double and triple transduced cells, comparable to controls. Ureagenesis was also induced in triple transduced cells, but at lower levels compared to primary hepatocytes.

CONCLUSIONS

Sequential expression of Foxa2, Hnf4α and C/ebpα induces a mature hepatocyte phenotype in an expandable liver derived progenitor cell line.

Defining the cancer master switch

BACKGROUND

Recent research has focused on signaling cascades and their interactions yielding considerable insight into which genetic pathways are targeted and how they tend to be altered in tumors. Therapeutic interventions now can be designed based on the knowledge of pathways vital to tumor growth and survival. These critical targets for intervention, master switches for cancer, are termed so because the tumor attempts to "flip the switch" in a way that promotes its survival, whereas molecular therapy aims to "switch off" signals important for tumor-related processes.

METHODS

Literature review.

CONCLUSIONS

Defining useful targets for therapy depends on identifying pathways that are crucial for tumor growth, survival, and metastasis. Because not all signaling cascades are created equal, selecting master switches or targets for intervention needs to be done in a systematic fashion. This discussion proposes a set of criteria to define what it means to be a cancer master switch and provides examples to illustrate their application.

Stem cell-derived islet cells for transplantation

PURPOSE OF REVIEW

The promise of islet transplantation for type 1 diabetes has been hampered by the lack of a renewable source of insulin-producing cells. However, steadfast advances in the field have set the stage for stem cell-based approaches to take over in the near future. This review focuses on the most intriguing findings reported in recent years, which include not only progress in adult and embryonic stem cell differentiation, but also the direct reprogramming of nonendocrine tissues into insulin-producing beta cells.

RECENT FINDINGS

In spite of their potential for tumorigenesis, human embryonic stem (hES) cells are poised to be in clinical trials within the next decade. This situation is mainly due to the preclinical success of a differentiation method that recapitulates beta cell development. In contrast, adult stem cells still need one such gold standard of differentiation, and progress is somewhat impeded by the lack of consensus on the best source. A concerted effort is necessary to bring their potential to clinical fruition. In the meantime, reported success in reprogramming might offer a 'third way' towards the rescue of pancreatic endocrine function.

SUMMARY

Here we discuss the important strategic decisions that need to be made in order to maximize the therapeutic chances of each of the presented approaches.

Reprogramming into pancreatic endocrine cells based on developmental cues

Due to the increasing prevalence of type 1 diabetes and the complications arising from actual therapies, alternative treatments need to be established. In order to compensate the beta-cell deficiency associated with type 1 diabetes, current researches focus on new strategies to generate insulin-producing beta cells for transplantation purpose, including the differentiation of stem or progenitor cells, as well as the transdifferentiation of dispensable mature cell types. However, to successfully force any cell to adopt a functional beta-cell fate or phenotype, a better understanding of the molecular mechanisms underlying the genesis of these in vivo is required. The present short review summarizes the hitherto known functions and interplays of several key factors involved in the differentiation of the endocrine cell lineages during pancreas morphogenesis, as well as there potential in generating beta cells. Furthermore, an emphasize is made on beta-cell regeneration and the determinants implicated.

Adult cell fate reprogramming: converting liver to pancreas

Regenerative medicine aims at producing new cells for repair or replacement of diseased and damaged tissues. Embryonic and adult stem cells have been suggested as attractive sources of cells for generating the new cells needed. The leading dogma was that adult cells in mammals, once committed to a specific lineage, become "terminally differentiated" and can no longer change their fate. However, in recent years increasing evidence has accumulated demonstrating the remarkable ability of some differentiated cells to be converted into a different cell type via a process termed developmental redirection or adult cells reprogramming. For example, abundant human cell types, such as dermal fibroblasts and adipocytes, could potentially be harvested and converted into other, medically important cell types, such as neurons, cardiomyocytes, or pancreatic beta cells. In this chapter, we describe a method of activating the pancreatic lineage and beta-cells function in adult human liver cells by ectopic expression of pancreatic transcription factors. This approach aims to generate custom-made autologous surrogate beta cells for treatment of diabetes, and possibly bypass both the shortage of cadaveric human donor tissues and the need for life-long immune-suppression.

Novel monoclonal antibodies against Pdx1 reveal feedback regulation of Pdx1 protein levels

The aim of this study was to characterize two monoclonal antibodies (F6A11 and F109-D12) generated against Pdx1 (pancreatic and duodenal homeobox-1), a homeodomain transcription factor, which is critical for pancreas formation as well as for normal pancreatic beta cell function. For production of monoclonal antibodies, we immunized Robertsonian POSF (RBF)mice with a GST-Pdx1 fusion protein containing a 68-amino acid C-terminal fragment of rat Pdx1. These monoclonal antibodies detect Pdx1 by western blotting and allow immunohistochemical detection of Pdx1 in both mouse and rat tissue. F6A11 and F109-D12 produce IHC staining patterns indistinguishable from that obtained with highly specific polyclonal Pdx1 antisera raised in rabbits and goats, when applied to embryonic or adult mouse pancreatic tissue. In contrast to previously generated polyclonal anti-Pdx1 antisera, we also demonstrate that F6A11 works for intracellular fluorescence activated cell sorting (FACS) staining of Pdx1. By using F6A11, we characterize the induction of Pdx1 in the Doxycycline (DOX) inducible insulinoma cell line INSrαβ-Pdx1 and follow the reduction of Pdx1 after removing Dox. Finally, we show that induction of exogenous Pdx1 leads to a reduction in endogenous Pdx1 levels, which suggests that a negative feedback loop is involved in maintaining correct levels of Pdx1 in the cell.

Cellular plasticity within the pancreas--lessons learned from development

The pancreas has been the subject of intense research due to the debilitating diseases that result from its dysfunction. In this review, we summarize current understanding of the critical tissue interactions and intracellular regulatory events that take place during formation of the pancreas from a small cluster of cells in the foregut domain of the mouse embryo. Importantly, an understanding of principles that govern the development of this organ has equipped us with the means to manipulate both embryonic and differentiated adult cells in the context of regenerative medicine. The emerging area of lineage modulation within the adult pancreas is of particular interest, and this review summarizes recent findings that exemplify how lessons learned from development are being applied to reveal the potential of fully differentiated cells to change fate.

Minireview: beta-cell replacement therapy for diabetes in the 21st century: manipulation of cell fate by directed differentiation

Pancreatic beta-cell failure underlies type 1 diabetes; it also contributes in an essential way to type 2 diabetes. beta-Cell replacement is an important component of any cure for diabetes. The current options of islet and pancreas transplantation are not satisfactory as definitive forms of therapy. Here, we review strategies for induced de novo pancreatic beta-cell formation, which depend on the targeted differentiation of cells into pancreatic beta-cells. With this objective in mind, one can manipulate the fate of three different types of cells: 1) from terminally differentiated cells, e.g. exocrine pancreatic cells, into beta-cells; 2) from multipotent adult stem cells, e.g. hepatic oval cells, into pancreatic islets; and 3) from pluripotent stem cells, e.g. embryonic stem cells and induced pluripotent stem cells, into beta-cells. We will examine the pros and cons of each strategy as well as the hurdles that must be overcome before these approaches to generate new beta-cells will be ready for clinical application.

Inhibition of Hes1 activity in gall bladder epithelial cells promotes insulin expression and glucose responsiveness

The biliary system has a close developmental relationship with the pancreas, evidenced by the natural occurrence of small numbers of biliary-derived beta-cells in the biliary system and by the replacement of biliary epithelium with pancreatic tissue in mice lacking the transcription factor Hes1. In normal pancreatic development, Hes1 is known to repress endocrine cell formation. Here we show that glucose-responsive insulin secretion can be induced in biliary epithelial cells when activity of the transcription factor Hes1 is antagonised. We describe a new culture system for adult murine gall bladder epithelial cells (GBECs), free from fibroblast contamination. We show that Hes1 is expressed both in adult murine gall bladder and in cultured GBECs. We have created a new dominant negative Hes1 (DeltaHes1) by removal of the DNA-binding domain, and show that it antagonises Hes1 function in vivo. When DeltaHes1 is introduced into the GBEC it causes expression of insulin RNA and protein. Furthermore, it confers upon the cells the ability to secrete insulin following exposure to increased external glucose. GBEC cultures are induced to express a wider range of mature beta cell markers when co-transduced with DeltaHes1 and the pancreatic transcription factor Pdx1. Introduction of DeltaHes1 and Pdx1 can therefore initiate a partial respecification of phenotype from biliary epithelial cell towards the pancreatic beta cell.

Diabetes mellitus: new challenges and innovative therapies

Diabetes mellitus is a widespread disease prevalence and incidence of which increases worldwide. The introduction of insulin therapy represented a major breakthrough in type 1 diabetes; however, frequent hyper- and hypoglycemia seriously affects the quality of life of these patients. New therapeutic approaches, such as whole pancreas transplant or pancreatic islet transplant, stem cell, gene therapy and islets encapsulation are discussed in this review. Regarding type 2 diabetes, therapy has been based on drugs that stimulate insulin secretion (sulphonylureas and rapid-acting secretagogues), reduce hepatic glucose production (biguanides), delay digestion and absorption of intestinal carbohydrate (alpha-glucosidase inhibitors) or improve insulin action (thiazolidinediones). This review is also focused on the newer therapeutically approaches such as incretin-based therapies, bariatric surgery, stem cells and other emerging therapies that promise to further extend the options available. Gene-based therapies are among the most promising emerging alternatives to conventional treatments. Some of these therapies rely on genetic modification of non-differentiated cells to express pancreatic endocrine developmental factors, promoting differentiation of non-endocrine cells into β-cells, enabling synthesis and secretion of insulin in a glucose-regulated manner. Alternative therapies based on gene silencing using vector systems to deliver interference RNA to cells (i.e. against VEGF in diabetic retinopathy) are also a promising therapeutic option for the treatment of several diabetic complications. In conclusion, treatment of diabetes faces now a new era that is characterized by a variety of innovative therapeutic approaches that will improve quality-life and allow personalized therapy-planning in the near future.

Stem cell therapy for type 1 diabetes mellitus

The use of stem cells in regenerative medicine holds great promise for the cure of many diseases, including type 1 diabetes mellitus (T1DM). Any potential stem-cell-based cure for T1DM should address the need for beta-cell replacement, as well as control of the autoimmune response to cells which express insulin. The ex vivo generation of beta cells suitable for transplantation to reconstitute a functional beta-cell mass has used pluripotent cells from diverse sources, as well as organ-specific facultative progenitor cells from the liver and the pancreas. The most effective protocols to date have produced cells that express insulin and have molecular characteristics that closely resemble bona fide insulin-secreting cells; however, these cells are often unresponsive to glucose, a characteristic that should be addressed in future protocols. The use of mesenchymal stromal cells or umbilical cord blood to modulate the immune response is already in clinical trials; however, definitive results are still pending. This Review focuses on current strategies to obtain cells which express insulin from different progenitor sources and highlights the main pathways and genes involved, as well as the different approaches for the modulation of the immune response in patients with T1DM.

Stem cell and gene therapies for diabetes mellitus

In this Perspectives article, we comment on the progress in experimental stem cell and gene therapies that might one day become a clinical reality for the treatment of patients with diabetes mellitus. Research on the ability of human embryonic stem cells to differentiate into islet cells has defined the developmental stages and transcription factors involved in this process. However, the clinical applications of human embryonic stem cells are limited by ethical concerns, as well as the potential for teratoma formation. As a consequence, alternative forms of stem cell therapies, such as induced pluripotent stem cells and bone marrow-derived mesenchymal stem cells, have become an area of intense study. Finally, gene therapy shows some promise for the generation of insulin-producing cells. Here, we discuss two of the most frequently used approaches: in vitro gene delivery into cells which are then transplanted into the recipient and direct delivery of genes in vivo.

Reprogramming into pancreatic endocrine cells based on developmental cues

Due to the increasing prevalence of type 1 diabetes and the complications arising from actual therapies, alternative treatments need to be established. In order to compensate the beta-cell deficiency associated with type 1 diabetes, current research focuses on new strategies to generate insulin-producing beta-cells for transplantation purpose, including the differentiation of stem or progenitor cells, as well as the transdifferentiation of dispensable mature cell types. However, to successfully force specific cells to adopt a functional beta-cell fate or phenotype, a better understanding of the molecular mechanisms underlying beta-cell genesis is required. The present short review summarizes the hitherto known functions and interplays of several key factors involved in the development of the different endocrine cell lineages during pancreas morphogenesis, as well as their potential to direct the generation of beta-cells. Furthermore, an emphasis is made on beta-cell regeneration and the determinants implicated.