Combined expression of pancreatic duodenal homeobox 1 and islet factor 1 induces immature enterocytes to produce insulin

Biochemical pancreatic β-cell lineage reprogramming: Various cell fate shifts

The incidence of pancreatic diseases has been continuously rising in recent years. Thus, research on pancreatic regeneration is becoming more popular. Chronic hyperglycemia is detrimental to pancreatic β-cells, leading to impairment of insulin secretion which is the main hallmark of pancreatic diseases. Obtaining plenty of functional pancreatic β-cells is the most crucial aspect when studying pancreatic biology and treating diabetes. According to the International Diabetes Federation, diabetes has become a global epidemic, with about 3 million people suffering from diabetes worldwide. Hyperglycemia can lead to many dangerous diseases, including amputation, blindness, neuropathy, stroke, and cardiovascular and kidney diseases. Insulin is widely used in the treatment of diabetes; however, innovative approaches are needed in the academic and preclinical stages. A new approach aims at synthesizing patient-specific functional pancreatic β-cells. The present article focuses on how cells from different tissues can be transformed into pancreatic β-cells.

Direct Reprogramming of Somatic Cells into Induced β-Cells: An Overview

The persistent shortage of insulin-producing islet mass or β-cells for transplantation in the ever-growing diabetic population worldwide is a matter of concern. To date, permanent cure to this medical complication is not available and soon after the establishment of lineage-specific reprogramming, direct β-cell reprogramming became a viable alternative for β-cell regeneration. Direct reprogramming is a straightforward and powerful technique that can provide an unlimited supply of cells by transdifferentiating terminally differentiated cells toward the desired cell type. This approach has been extensively used by multiple groups to reprogram non-β-cells toward insulin-producing β-cells. The β-cell identity has been achieved by various studies via ectopic expression of one or more pancreatic-specific transcription factors in somatic cells, bypassing the pluripotent state. This work highlights the importance of the direct reprogramming approaches (both integrative and non-integrative) in generating autologous β-cells for various applications. An in-depth understanding of the strategies and cell sources could prove beneficial for the efficient generation of integration-free functional insulin-producing β-cells for diabetic patients lacking endogenous β-cells.

Harnessing gut cells for functional insulin production: Strategies and challenges

Reprogrammed glucose-responsive, insulin + cells ("β-like") exhibit the potential to bypass the hurdles of exogenous insulin delivery in treating diabetes mellitus. Current cell-based therapies-transcription factor regulation, biomolecule-mediated enteric signaling, and transgenics - have demonstrated the promise of reprogramming either mature or progenitor gut cells into surrogate "β-like" cells. However, there are predominant challenges impeding the use of gut "β-like" cells as clinical replacements for insulin therapy. Reprogrammed "β-like" gut cells, even those of enteroendocrine origin, mostly do not exhibit glucose - potentiated insulin secretion. Despite the exceptionally low conversion rate of gut cells into surrogate "β-like" cells, the therapeutic quantity of gut "β-like" cells needed for normoglycemia has not even been established. There is also a lingering uncertainty regarding the functionality and bioavailability of gut derived insulin. Herein, we review the strategies, challenges, and opportunities in the generation of functional, reprogrammed "β-like" cells.

Molecular mechanisms of transcription factor mediated cell reprogramming: conversion of liver to pancreas

Transdifferentiation is a type of cellular reprogramming involving the conversion of one differentiated cell type to another. This remarkable phenomenon holds enormous promise for the field of regenerative medicine. Over the last 20 years techniques used to reprogram cells to alternative identities have advanced dramatically. Cellular identity is determined by the transcriptional profile which comprises the subset of mRNAs, and therefore proteins, being expressed by a cell at a given point in time. A better understanding of the levers governing transcription factor activity benefits our ability to generate therapeutic cell types at will. One well-established example of transdifferentiation is the conversion of hepatocytes to pancreatic β-cells. This cell type conversion potentially represents a novel therapy in T1D treatment. The identification of key master regulator transcription factors (which distinguish one body part from another) during embryonic development has been central in developing transdifferentiation protocols. Pdx1 is one such example of a master regulator. Ectopic expression of vector-delivered transcription factors (particularly the triumvirate of Pdx1, Ngn3 and MafA) induces reprogramming through broad transcriptional remodelling. Increasingly, complimentary cell culture techniques, which recapitulate the developmental microenvironment, are employed to coax cells to adopt new identities by indirectly regulating transcription factor activity via intracellular signalling pathways. Both transcription factor-based reprogramming and directed differentiation approaches ultimately exploit transcription factors to influence cellular identity. Here, we explore the evolution of reprogramming and directed differentiation approaches within the context of hepatocyte to β-cell transdifferentiation focussing on how the introduction of new techniques has improved our ability to generate β-cells.

Reprogramming Cells to Make Insulin

Type 1 diabetes is a disease characterized by the destruction of insulin-secreting β-cells in the pancreas. Individuals are treated for this disease with lifelong insulin replacement. However, one attractive treatment possibility is to reprogram an individual’s endogenous cells to acquire the ability to secrete insulin, essentially replacing destroyed β-cells. Herein, we review the literature on the topic of reprogramming endodermal cells to produce insulin.

Comparison of enteroendocrine cells and pancreatic β-cells using gene expression profiling and insulin gene methylation

Various subtypes of enteroendocrine cells (EECs) are present in the gut epithelium. EECs and pancreatic β-cells share similar pathways of differentiation during embryonic development and after birth. In this study, similarities between EECs and β-cells were evaluated in detail. To obtain specific subtypes of EECs, cell sorting by flow cytometry was conducted from STC-1 cells (a heterogenous EEC line), and each single cell was cultured and passaged. Five EEC subtypes were established according to hormone expression, measured by quantitative RT-PCR and immunostaining: L, K, I, G and S cells expressing glucagon-like peptide-1, glucose-dependent insulinotropic polypeptide, cholecystokinin, gastrin and secretin, respectively. Each EEC subtype was found to express not only the corresponding gut hormone but also other gut hormones. Global microarray gene expression profiles revealed a higher similarity between each EEC subtype and MIN6 cells (a β-cell line) than between C2C12 cells (a myoblast cell line) and MIN6 cells, and all EEC subtypes were highly similar to each other. Genes for insulin secretion-related proteins were mostly enriched in EECs. However, gene expression of transcription factors crucial in mature β-cells, such as PDX1, MAFA and NKX6.1, were remarkably low in all EEC subtypes. Each EEC subtype showed variable methylation in three cytosine-guanosine dinucleotide sites in the insulin gene (Ins2) promoter, which were fully unmethylated in MIN6 cells. In conclusion, our data confirm that five EEC subtypes are closely related to β-cells, suggesting a potential target for cell-based therapy in type 1 diabetes.

Isl1β Overexpression With Key β Cell Transcription Factors Enhances Glucose-Responsive Hepatic Insulin Production and Secretion

Adenoviral gene transfer of key β cell developmental regulators including Pdx1, Neurod1, and Mafa (PDA) has been reported to generate insulin-producing cells in the liver. However, PDA insulin secretion is transient and glucose unresponsive. Here, we report that an additional β cell developmental regulator, insulin gene enhancer binding protein splicing variant (Isl1β), improved insulin production and glucose-responsive secretion in PDA mice. Microarray gene expression analysis suggested that adenoviral PDA transfer required an additional element for mature β cell generation, such as Isl1 and Elf3 in the liver. In vitro promoter analysis indicated that splicing variant Isl1, or Isl1β, is an important factor for transcriptional activity of the insulin gene. In vivo bioluminescence monitoring using insulin promoter-luciferase transgenic mice verified that adenoviral PDA + Isl1β transfer produced highly intense luminescence from the liver, which peaked at day 7 and persisted for more than 10 days. Using insulin promoter-GFP transgenic mice, we further confirmed that Isl1β supplementation to PDA augmented insulin-producing cells in the liver, insulin production and secretion, and β cell‒related genes. Finally, the PDA + Isl1β combination ameliorated hyperglycemia in diabetic mice for 28 days and enhanced glucose tolerance and responsiveness. Thus, our results suggest that Isl1β is a key additional transcriptional factor for advancing the generation of insulin-producing cells in the liver in combination with PDA.

Cell therapies for pancreatic beta-cell replenishment

The current treatment approach for type 1 diabetes is based on daily insulin injections, combined with blood glucose monitoring. However, administration of exogenous insulin fails to mimic the physiological activity of the islet, therefore diabetes often progresses with the development of serious complications such as kidney failure, retinopathy and vascular disease. Whole pancreas transplantation is associated with risks of major invasive surgery along with side effects of immunosuppressive therapy to avoid organ rejection. Replacement of pancreatic beta-cells would represent an ideal treatment that could overcome the above mentioned therapeutic hurdles. In this context, transplantation of islets of Langerhans is considered a less invasive procedure although long-term outcomes showed that only 10 % of the patients remained insulin independent five years after the transplant. Moreover, due to shortage of organs and the inability of islet to be expanded ex vivo, this therapy can be offered to a very limited number of patients. Over the past decade, cellular therapies have emerged as the new frontier of treatment of several diseases. Furthermore the advent of stem cells as renewable source of cell-substitutes to replenish the beta cell population, has blurred the hype on islet transplantation. Breakthrough cellular approaches aim to generate stem-cell-derived insulin producing cells, which could make diabetes cellular therapy available to millions. However, to date, stem cell therapy for diabetes is still in its early experimental stages. This review describes the most reliable sources of stem cells that have been developed to produce insulin and their most relevant experimental applications for the cure of diabetes.

PDX1 and ISL1 differentially coordinate with epigenetic modifications to regulate insulin gene expression in varied glucose concentrations

The mechanism of insulin gene transcription control in response to glucose concentration is poorly defined. The islet-restricted transcription factors PDX1 and ISL1 interact with BETA2, activating insulin gene expression. However, their contribution and hierarchical organization in insulin expression control based on glucose concentration remain unknown. We investigated PDX1 and ISL1 regulation of insulin gene expression in pancreatic β cells cultured in normal (5 mM/L) and high (25 mM/L) glucose conditions. ISL1 interacted with BETA2 to maintain basic insulin gene transcriptional activity under normal glucose. The ISL1-recruited cofactors SET9 and JMJD3 facilitated insulin gene histone modifications under normal glucose. In high-glucose concentrations, PDX1 formed a complex with BETA2 to enhance insulin gene expression. PDX1 also recruited SET9 and JMJD3 to promote the activation of histone modulation on the insulin promoter. This is the first evidence transcription factors orchestrate epigenetic modifications to control insulin gene expression based on glucose concentration.

Engineering the gut for insulin replacement to treat diabetes

The gut epithelium's large surface area, its direct exposure to ingested nutrients, its vast stem cell population and its immunotolerogenic environment make it an excellent candidate for therapeutic cells to treat diabetes. Thus, several attempts have been made to coax immature gut cells to differentiate into insulin-producing cells by altering the expression patterns of specific transcription factors. Furthermore, because of similarities in enteroendocrine and pancreatic endocrine cell differentiation pathways, other approaches have used genetically engineered enteroendocrine cells to produce insulin in addition to their endogenous secreted hormones. Several studies support the utility of both of these approaches for the treatment of diabetes. Converting a patient's own gut cells into meal-regulated insulin factories in a safe and immunotolerogenic environment is an attractive approach to treat and potentially cure diabetes. Here, we review work on these approaches and indicate where we feel further advancements are required.

Reprogramming of liver cells into insulin-producing cells

Tissue replacement is a promising direction for the treatment of diabetes, which will become widely available only when islets or insulin-producing cells that will not be rejected by the diabetic recipients are available in unlimited amounts. The present review addresses the research in the field of generating functional insulin-producing cells by transdifferentiation of adult liver cells both in vitro and in vivo. It presents recent knowledge of the mechanisms which underlie the process and assesses the challenges which should be addressed for its efficient implementation as a cell based replacement therapy for diabetics.

Role of pancreatic transcription factors in maintenance of mature β-cell function

A variety of pancreatic transcription factors including PDX-1 and MafA play crucial roles in the pancreas and function for the maintenance of mature β-cell function. However, when β-cells are chronically exposed to hyperglycemia, expression and/or activities of such transcription factors are reduced, which leads to deterioration of β-cell function. These phenomena are well known as β-cell glucose toxicity in practical medicine as well as in the islet biology research area. Here we describe the possible mechanism for β-cell glucose toxicity found in type 2 diabetes. It is likely that reduced expression levels of PDX-1 and MafA lead to suppression of insulin biosynthesis and secretion. In addition, expression levels of incretin receptors (GLP-1 and GIP receptors) in β-cells are decreased, which likely contributes to the impaired incretin effects found in diabetes. Taken together, down-regulation of insulin gene transcription factors and incretin receptors explains, at least in part, the molecular mechanism for β-cell glucose toxicity.

Direct Reprogramming for Pancreatic Beta-Cells Using Key Developmental Genes

Direct reprogramming is a promising approach for regenerative medicine whereby one cell type is directly converted into another without going through a multipotent or pluripotent stage. This reprogramming approach has been extensively explored for the generation of functional insulin-secreting cells from non-beta-cells with the aim of developing novel cell therapies for the treatment of people with diabetes lacking sufficient endogenous beta-cells. A common approach for such conversion studies is the introduction of key regulators that are important in controlling beta-cell development and maintenance. In this review, we will summarize the recent advances in the field of beta-cell reprogramming and discuss the challenges of creating functional and long-lasting beta-cells.

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.

A small-molecule inducer of PDX1 expression identified by high-throughput screening

Pancreatic and duodenal homeobox 1 (PDX1), a member of the homeodomain-containing transcription factor family, is a key transcription factor important for both pancreas development and mature β cell function. The ectopic overexpression of Pdx1, Neurog3, and MafA in mice reprograms acinar cells to insulin-producing cells. We developed a quantitative PCR-based gene expression assay to screen more than 60,000 compounds for expression of each of these genes in the human PANC-1 ductal carcinoma cell line. We identified BRD7552, which upregulated PDX1 expression in both primary human islets and ductal cells, and induced epigenetic changes in the PDX1 promoter consistent with transcriptional activation. Prolonged compound treatment induced both insulin mRNA and protein and also enhanced insulin expression induced by the three-gene combination. These results provide a proof of principle for identifying small molecules that induce expression of transcription factors to control cellular reprogramming.

Insulin producing cells established using non-integrated lentiviral vector harboring PDX1 gene

AIM: To investigate reprogramming of human adipose tissue derived stem cells into insulin producing cells using non-integrated lentivirus harboring PDX1 gene.

METHODS: In this study, human adipose tissue derived stem cells (hADSCs) were obtained from abdominal adipose tissues by liposuction, selected by plastic adhesion, and characterized by flow cytometric analysis. Human ADSCs were differentiated into adipocytes and osteocytes using differentiating medium to confirm their multipotency. Non-integrated lentiviruses harboring PDX1 (Non-integrated LV-PDX1) were constructed using specific plasmids (pLV-HELP, pMD2G, LV-105-PDX1-1). Then, hADSCs were transduced with non-integrated LV-PDX1. After transduction, ADSCs^PDX1+ were cultured in high glucose DMEM medium supplement by B27, nicotinamide and βFGF for 21 d. Expressions of PDX1 and insulin were detected at protein level by immunofluorescence analysis. Expressions of PDX1, neurogenin3 (Ngn3), glucagon, glucose transporter2 (Glut2) and somatostatin as specific marker genes were investigated at mRNA level by quantitative RT-PCR. Insulin secretion of hADSCs^PDX1+ in the high-glucose medium was detected by electrochemiluminescence test. Human ADSCs^PDX1+ were implanted into hyperglycemic rats.

RESULTS: Human ADSCs exhibited their fibroblast-like morphology and made colonies after 7-10 d of culture. Determination of hADSCs identified by FACS analysis showed that hADSCs were positive for mesenchymal cell markers and negative for hematopoietic cell markers that guaranteed the lack of hematopoietic contamination. In vitro differentiation of hADSCs into osteocytes and adipocytes were detected by Alizarin red and Oil red O staining and confirmed their multilineage differentiation ability. Transduced hADSCs^+PDX1 became round and clusters in the differentiation medium. The appropriate expression of PDX1 and insulin proteins was confirmed using immunocytochemistry analysis. Significant expressions of PDX1, Ngn3, glucagon, Glut2 and somatostatin were detected by quantitative RT-PCR. hADSCs^PDX1+ revealed the glucose sensing ability by expressing Glut2 when they were cultured in the medium containing high glucose concentration. The insulin secretion of hADSCs^PDX1+ in the high glucose medium was 2.32 μU/mL. hADSCs^PDX1+ implantation into hyperglycemic rats cured it two days after injection by reducing blood glucose levels from 485 mg/dL to the normal level.

CONCLUSION: Human ADSCs can differentiate into IPCs by non-integrated LV-PDX1 transduction and have the potential to be used as a resource in type 1 diabetes cell therapy.

Generating insulin-producing cells for diabetic therapy: existing strategies and new development

Type 1 and 2 diabetes are characterized by a deficiency in β-cell mass, which cannot be reversed with existing therapeutic strategies. Therefore, restoration of the endogenous insulin-producing cell mass holds great promise for curing diabetes in the future. Since the initial induction of insulin-producing cells (IPCs) from embryonic stem (ES) cells in 1999, several strategies and alternative cell sources have been developed to generate β-like cells, including direct differentiation from ES cells or induced pluripotent stem (iPS) cells, proliferation of existing adult β-cells, and reprogramming of non-pancreatic adult stem/mature cells or pancreatic non-β-cells to β-like-cells. However, several barriers persist in the translation of the aforementioned strategies into clinically applicable methods for IPC induction. We briefly review the most relevant studies for each strategy, and discuss the comparative merits and drawbacks. We propose that ex vivo patient-specific IPCs generated from iPS cells may be practical for cell transplantation in the near future, and in situ regeneration of IPCs from cells within the pancreas may be preferable for diabetes therapy.

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.

Differentiation of human adipose tissue-derived stem cells into aggregates of insulin-producing cells through the overexpression of pancreatic and duodenal homeobox gene-1

The pancreatic and duodenal homeobox gene 1 (Pdx-1) plays a key role in normal pancreas development and is required for maintaining the normal function of islets. In this study, we examined whether human adipose tissue-derived stem cells (hASCs) could differentiate into insulin-producing cells by exogenously expressed Pdx-1. hASCs were infected with recombinant adenovirus encoding the mouse Pdx-1 gene and differentiated under high-glucose conditions. Insulin transcript levels and the expression of key transcription factors required for pancreatic development including FoxA2, Nkx2.2, and NeuroD were significantly increased by exogenous Pdx-1 overexpression. The expression of Nkx6.1 was found only in Pdx-1-induced hASCs. In addition to transcripts for transcription factors involved in pancreatic development, transcripts for the GLP-1 receptor, glucokinase, and glucose transporter, which are required for maintaining the function of pancreatic β-cells, were observed only in Pdx-1-induced hASCs. Pdx-1-induced hASCs exhibited insulin secretion in response to glucose challenge in vitro. When Pdx-1-induced hASCs were transplanted into streptozotocin (STZ)-induced diabetic mice, they reduced blood glucose levels, although they did not restore normoglycemia. These results demonstrate that the expression of exogenous Pdx-1 is sufficient to induce pancreatic differentiation in vitro but does not induce the fully functional, mature insulin-producing cells that are required for restoring normoglycemia in vivo.

Rapid protein kinase D1 signaling promotes migration of intestinal epithelial cells

We have examined the role of protein kinase D1 (PKD1) signaling in intestinal epithelial cell migration. Wounding monolayer cultures of intestinal epithelial cell line IEC-18 or IEC-6 induced rapid PKD1 activation in the cells immediately adjacent to the wound edge, as judged by immunofluorescence microscopy with an antibody that detects the phosphorylated state of PKD1 at Ser(916), an autophosphorylation site. An increase in PKD1 phosphorylation at Ser(916) was evident as early as 45 s after wounding, reached a maximum after 3 min, and persisted for ≥15 min. PKD1 autophosphorylation at Ser(916) was prevented by the PKD family inhibitors kb NB 142-70 and CRT0066101. A kb NB 142-70-sensitive increase in PKD autophosphorylation was also elicited by wounding IEC-6 cells. Using in vitro kinase assays after PKD1 immunoprecipitation, we corroborated that wounding IEC-18 cells induced rapid PKD1 catalytic activation. Further results indicate that PKD1 signaling is required to promote migration of intestinal epithelial cells into the denuded area of the wound. Specifically, treatment with kb NB 142-70 or small interfering RNAs targeting PKD1 markedly reduced wound-induced migration in IEC-18 cells. To test whether PKD1 promotes migration of intestinal epithelial cells in vivo, we used transgenic mice that express elevated PKD1 protein in the small intestinal epithelium. Enterocyte migration was markedly increased in the PKD1 transgenic mice. These results demonstrate that PKD1 activation is one of the early events initiated by wounding a monolayer of intestinal epithelial cells and indicate that PKD1 signaling promotes the migration of these cells in vitro and in vivo.

Reprogramming gut and pancreas endocrine cells to treat diabetes

Multiple approaches have been investigated with the ultimate goal of providing insulin independence to patients with either type 1 or type 2 diabetes. Approaches to produce insulin-secreting cells in culture, convert non-β-cells into functional β-cells or engineer autologous cells to express and secrete insulin in a meal-responsive manner have all been described. This research has been facilitated by significant improvements in both viral and non-viral gene delivery approaches that have enabled new experimental strategies. Many studies have examined possible avenues to confer islet cytoprotection against immune rejection, inflammation and apoptosis by genetic manipulation of islet cells prior to islet transplantation. Here we review several reports based on the reprogramming of pancreas and gut endocrine cells to treat diabetes.

Regenerative medicine for insulin deficiency: creation of pancreatic islets and bioartificial pancreas

Recent advances in pancreas organogenesis have greatly improved the understanding of cell lineage from inner cell mass to fully differentiated β-cells. Based upon such knowledge, insulin-producing cells similar to β-cells to a certain extent have been generated from various cell sources including embryonic stem cells (ESCs) and induced pluripotent stem (iPS) cells, although fully differentiated cells comparable to β-cells are not yet available. The bioartificial pancreas is a therapeutic approach to enable allo- and xenotransplantation of islets without immune suppression. Among several types of bioartificial pancreases (BAPs), micro-encapsulated porcine islets are already in use in clinical trials and may, perhaps, replace islet transplantation in the near future. Some types of bioartificial pancreas such as macro-encapsulation are also useful for keeping transplanted cells enclosed in case retrieval is necessary. Therefore, early clinical applications of artificially generated β-like cells, especially those from ESCs or iPS cells, will be considered in combination with retrievable BAPs.

Betacellulin overexpression in mesenchymal stem cells induces insulin secretion in vitro and ameliorates streptozotocin-induced hyperglycemia in rats

Betacellulin (BTC), a ligand of the epidermal growth factor receptor, has been shown to promote growth and differentiation of pancreatic β-cells and to improve glucose metabolism in experimental diabetic rodent models. Mesenchymal stem cells (MSCs) have been already proved to be multipotent. Recent work has attributed to rat and human MSCs the potential to differentiate into insulin-secreting cells. Our goal was to transfect rat MSCs with a plasmid containing BTC cDNA to guide MSC differentiation into insulin-producing cells. Prior to induction of cell MSC transfection, MSCs were characterized by flow cytometry and the ability to in vitro differentiate into mesoderm cell types was evaluated. After rat MSC characterization, these cells were electroporated with a plasmid containing BTC cDNA. Transfected cells were cultivated in Dulbecco's modified Eagle medium high glucose (H-DMEM) with 10 mM nicotinamide. Then, the capability of MSC-BTC to produce insulin in vitro and in vivo was evaluated. It was possible to demonstrate by radioimmunoassay analysis that 10(4) MSC-BTC cells produced up to 0.4 ng/mL of insulin, whereas MSCs transfected with the empty vector (negative control) produced no detectable insulin levels. Moreover, MSC-BTC were positive for insulin in immunohistochemistry assay. In parallel, the expression of pancreatic marker genes was demonstrated by molecular analysis of MSC-BTC. Further, when MSC-BTC were transplanted to streptozotocin diabetic rats, BTC-transfected cells ameliorated hyperglycemia from over 500 to about 200 mg/dL at 35 days post-cell transplantation. In this way, our results clearly demonstrate that BTC overabundance enhances glucose-induced insulin secretion in MSCs in vitro as well as in vivo.

High-fat feeding stimulates endocrine, glucose-dependent insulinotropic polypeptide (GIP)-expressing cell hyperplasia in the duodenum of Wistar rats

AIMS/HYPOTHESIS

Incretins are hormones released by enteroendocrine cells in response to meals, depending upon absorption of nutrients. The present study aimed to elucidate the mechanisms through which a high-fat diet (HFD) induces insulin resistance and insulin hypersecretion by focusing on the effects on enteroendocrine cells, especially those secreting glucose-dependent insulinotropic polypeptide (GIP).

METHODS

Forty male Wistar rats, 4 months old, were randomised into two groups; one group received a chow diet and the other one received a purified tripalmitin-based HFD ad libitum. An OGTT was performed every 10 days and histological and immunofluorescence evaluations of the duodenum were obtained at 60 days from the beginning of the diets. Plasma glucose, insulin, GIP and glucagon-like peptide-1 (GLP-1) levels were measured. Immunofluorescence analysis of duodenal sections for pancreatic duodenal homeobox-1 (PDX-1), KI67, GLP-1, GIP and insulin were performed.

RESULTS

Compared with chow diet, HFD induced a progressive significant increase of the glucose, insulin and GIP responses to OGTT, whereas GLP-1 circulating levels were reduced over time. After 60 days of HFD, cellular agglomerates of KI67 and PDX-1 positive cells, negative for insulin and GLP-1 but positive for GIP staining, were found inside the duodenal mucosa, and apoptosis was significantly increased.

CONCLUSIONS/INTERPRETATION

With the limitation that we could not establish a causal relationship between events, our study shows that HFD stimulates duodenal proliferation of endocrine cells differentiating towards K cells and oversecreting GIP. The progressive increment of GIP levels might represent the stimulus for insulin hypersecretion and insulin resistance.

Pancreatic stem/progenitor cells for the treatment of diabetes

Patients with type 1 diabetes, and most patients with type 2 diabetes, have associated hyperglycemia due to the absence or reduction of insulin production by pancreatic β-cells. Surgical resection of the pancreas may also cause insulin-dependent diabetes depending on the size of the remaining pancreas. Insulin therapy has greatly improved the quality of life of diabetic patients, but this method is inaccurate and requires lifelong treatment that only mitigates the symptoms. The successes achieved over the last few decades by the transplantation of whole pancreas and isolated islets suggest that diabetes can be cured by the replenishment of deficient β-cells. These observations are proof-of-principle and have intensified interest in treating diabetes by cell transplantation, and by the use of stem cells. Pancreatic stem/progenitor cells could be one of the sources for the treatment of diabetes. Islet neogenesis, the budding of new islets from pancreatic stem/progenitor cells located in or near pancreatic ducts, has long been assumed to be an active process in the postnatal pancreas. Several in vitro studies have shown that insulin-producing cells can be generated from adult pancreatic ductal tissues. Acinar cells may also be a potential source for differentiation into insulin-producing cells. This review describes recent progress on pancreatic stem/progenitor cell research for the treatment of diabetes.

Glucagon like peptide-1-directed human embryonic stem cells differentiation into insulin-producing cells via hedgehog, cAMP, and PI3K pathways

OBJECTIVES

That glucagonlike peptide-1 (GLP-1) induces differentiation of primate embryonic stem (ES) cells into insulin-producing cells has been reported by several groups and also confirmed with our observations.

METHODS

To further elucidate the process in detail and the signaling pathways involved in this differentiation, we induced human ES cells HUES1 differentiated into insulin secretion cells by GLP-1 treatment.

RESULTS

A time-dependent pattern of down expression of the stem cell markers (human telomerase reverse transcriptase and octamer-4), and the appearance of multiple beta-cell-specific proteins (insulin, glucokinase, glucose transporter, type 2, and islet duodenal homeobox 1) and hedgehog signal molecules (Indian hedgehog, sonic hedgehog, and hedgehog receptor, patched) have been identified. Cotreatment with hedgehog signal inhibitor cytopamine was able to block this differentiation, providing evidence of the involvement of the hedgehog signaling pathway in GLP-1-induced differentiation. We also observed increased transcripts of the transcription factors of activator protein 1, serum response element-1, DNA-binding transcription factors, and cAMP response element in GLP-1-induced ES cell differentiation. Inhibition profile by its specific inhibitors indicated that the cyclic adenosine monophosphate and phosphatidylinositol-3-kinase pathways, but not the mitogen-activated protein kinase pathway, were required for the induced differentiation of ES cells.

CONCLUSIONS

These data support that GLP-1 directs human ES cell differentiation into insulin-producing cells via hedgehog, cyclic adenosine monophosphate, and phosphatidylinositol-3-kinase pathways.

Regenerating pancreatic beta-cells: plasticity of adult pancreatic cells and the feasibility of in-vivo neogenesis

PURPOSE OF REVIEW

Diabetes results from inadequate functional mass of pancreatic beta-cells and therefore replenishing with new glucose-responsive beta-cells is an important therapeutic option. In addition to replication of pre-existing beta-cells, new beta-cells can be produced from differentiated adult cells using in-vitro or in-vivo approaches. This review will summarize recent advances in in-vivo generation of beta-cells from cells that are not beta-cells (neogenesis) and discuss ways to overcome the limitations of this process.

RECENT FINDINGS

Multiple groups have shown that adult pancreatic ducts, acinar and even endocrine cells exhibit cellular plasticity and can differentiate into beta-cells in vivo. Several different approaches, including misexpression of transcription factors and tissue injury, have induced neogenesis of insulin-expressing cells in vivo and ameliorated diabetes.

SUMMARY

Recent breakthroughs demonstrating cellular plasticity of adult pancreatic cells to form new beta-cells are a positive first step towards developing in-vivo regeneration-based therapy for diabetes. Currently, neogenesis processes are inefficient and do not generate sufficient amounts of beta-cells required to normalize hyperglycemia. However, an improved understanding of mechanisms regulating neogenesis of beta-cells from adult pancreatic cells and of their maturation into functional glucose-responsive beta-cells can make therapies based on in-vivo regeneration a reality.

Islet cell development

Over the last years, there has been great success in driving stem cells toward insulin-expressing cells. However, the protocols developed to date have some limitations, such as low reliability and low insulin production. The most successful protocols used for generation of insulin-producing cells from stem cells mimic in vitro pancreatic organogenesis by directing the stem cells through stages that resemble several pancreatic developmental stages. Islet cell fate is coordinated by a complex network of inductive signals and regulatory transcription factors that, in a combinatorial way, determine pancreatic organ specification, differentiation, growth, and lineage. Together, these signals and factors direct the progression from multipotent progenitor cells to mature pancreatic cells. Later in development and adult life, several of these factors also contribute to maintain the differentiated phenotype of islet cells. A detailed understanding of the processes that operate in the pancreas during embryogenesis will help us to develop a suitable source of cells for diabetes therapy. In this chapter, we will discuss the main transcription factors involved in pancreas specification and beta-cell formation.

Amelioration of hyperglycemia by intestinal overexpression of glucagon-like peptide-1 in mice

To investigate whether the local production of glucagon-like peptide-1 (GLP-1) in the intestine can differentiate intestinal stem/progenitor cells into insulin-producing cells, we intra-intestinally injected a recombinant adenovirus expressing GLP-1 (rAd-GLP-1) into diabetic mice. There were no significant differences in body weight or food intake between rAd-GLP-1- and rAd-betaGAL-treated control mice. rAd-GLP-1-treated mice showed intestinal insulin mRNA expression, insulin- and glucagon-positive cells in the intestine, and significantly increased serum insulin, but not glucagon. rAd-GLP-1 injection significantly reduced blood glucose levels and improved glucose tolerance compared with controls. Expression of transcription factors related to beta cell differentiation, neurogenin 3 (ngn3) and neurogenin differentiation factor (NeuroD), was detected in the intestine at 2 weeks after rAd-GLP-1 injection. We suggest that expression of GLP-1 in the intestine by intra-intestinal delivery of rAd-GLP-1 may induce differentiation of intestinal stem/progenitor cells into insulin-producing cells, mediated by ngn3 and NeuroD expression, contributing to lowered blood glucose levels in diabetic mice.

Multi-organ expression profiling uncovers a gene module in coronary artery disease involving transendothelial migration of leukocytes and LIM domain binding 2: the Stockholm Atherosclerosis Gene Expression (STAGE) study

Environmental exposures filtered through the genetic make-up of each individual alter the transcriptional repertoire in organs central to metabolic homeostasis, thereby affecting arterial lipid accumulation, inflammation, and the development of coronary artery disease (CAD). The primary aim of the Stockholm Atherosclerosis Gene Expression (STAGE) study was to determine whether there are functionally associated genes (rather than individual genes) important for CAD development. To this end, two-way clustering was used on 278 transcriptional profiles of liver, skeletal muscle, and visceral fat (n = 66/tissue) and atherosclerotic and unaffected arterial wall (n = 40/tissue) isolated from CAD patients during coronary artery bypass surgery. The first step, across all mRNA signals (n = 15,042/12,621 RefSeqs/genes) in each tissue, resulted in a total of 60 tissue clusters (n = 3958 genes). In the second step (performed within tissue clusters), one atherosclerotic lesion (n = 49/48) and one visceral fat (n = 59) cluster segregated the patients into two groups that differed in the extent of coronary stenosis (P = 0.008 and P = 0.00015). The associations of these clusters with coronary atherosclerosis were validated by analyzing carotid atherosclerosis expression profiles. Remarkably, in one cluster (n = 55/54) relating to carotid stenosis (P = 0.04), 27 genes in the two clusters relating to coronary stenosis were confirmed (n = 16/17, P<10(-27 and-30)). Genes in the transendothelial migration of leukocytes (TEML) pathway were overrepresented in all three clusters, referred to as the atherosclerosis module (A-module). In a second validation step, using three independent cohorts, the A-module was found to be genetically enriched with CAD risk by 1.8-fold (P<0.004). The transcription co-factor LIM domain binding 2 (LDB2) was identified as a potential high-hierarchy regulator of the A-module, a notion supported by subnetwork analysis, by cellular and lesion expression of LDB2, and by the expression of 13 TEML genes in Ldb2-deficient arterial wall. Thus, the A-module appears to be important for atherosclerosis development and, together with LDB2, merits further attention in CAD research.

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.

The LIM-homeodomain protein ISL1 activates insulin gene promoter directly through synergy with BETA2

The LIM-homeodomain transcription factor ISL1 (islet factor 1) is essential for pancreatic islet cell and dorsal mesenchyme development. Mutations in ISL1 are associated with maturity-onset diabetes of the young and type 2 diabetes. Whether ISL1 plays a role in the insulin gene expression has not been fully elucidated. In the present study, we show that ISL1 can synergistically activate insulin gene transcription with BETA2 in pancreatic beta cells. The protein-protein interactions of ISL1 and BETA2 are directly mediated by the LIM domains of ISL1 and the basic helix-loop-helix domain of BETA2. Deletion of the two LIM domains of ISL1 enhances the transcriptional activation of the insulin gene, indicating a key role for the homeodomain in activating the insulin promoter. Furthermore, ISL1 can bind with the A3/4 box in the rat insulin gene capital I, Ukrainian promoter through its homeodomain. ISL1 expression is up-regulated at the mRNA level in type 2 diabetes (db/db mouse model) but down-regulated by dexamethasone in rat insulinoma cells. These results suggest that ISL1 is a transcriptional activator for insulin gene expression, and the interactions of ISL1 with BETA2 are required for the transcriptional activity of the insulin gene. Reduction in Isl1 gene expression appears to be involved in the impairment of insulin expression mediated by dexamethasone.

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.

Two ParaHox genes, SpLox and SpCdx, interact to partition the posterior endoderm in the formation of a functional gut

We report the characterization of the ortholog of the Xenopus XlHbox8 ParaHox gene from the sea urchin Strongylocentrotus purpuratus, SpLox. It is expressed during embryogenesis, first appearing at late gastrulation in the posterior-most region of the endodermal tube, becoming progressively restricted to the constriction between the mid- and hindgut. The physiological effects of the absence of the activity of this gene have been analyzed through knockdown experiments using gene-specific morpholino antisense oligonucleotides. We show that blocking the translation of the SpLox mRNA reduces the capacity of the digestive tract to process food, as well as eliminating the morphological constriction normally present between the mid- and hindgut. Genetic interactions of the SpLox gene are revealed by the analysis of the expression of a set of genes involved in endoderm specification. Two such interactions have been analyzed in more detail: one involving the midgut marker gene Endo16, and another involving the other endodermally expressed ParaHox gene, SpCdx. We find that SpLox is able to bind Endo16 cis-regulatory DNA, suggesting direct repression of Endo16 expression in presumptive hindgut territories. More significantly, we provide the first evidence of interaction between ParaHox genes in establishing hindgut identity, and present a model of gene regulation involving a negative-feedback loop.

Transcription factors as therapeutic targets for diabetes

BACKGROUND

Islet cell implantation and pancreas transplantation have been used as treatments for diabetes but are limited by the shortage of donors and the requirement for lifelong immunosuppression. As an alternative, the generation of surrogate insulin-producing cells has been an area of interest for many researchers. Understanding how pancreatic beta-cells are generated during pancreas development will provide information that can be applied to generating surrogate beta-cells.

OBJECTIVE

To outline the current knowledge of pancreas development and differentiation, with a focus on the regulatory network of pancreas-enriched transcription factors and their targets.

METHODS

A review of relevant literature.

CONCLUSIONS

Pancreatic and duodenal homeobox 1 (Pdx1), Neurogenin 3 (Ngn3), and musculoaponeurotic fibrosarcoma oncogene homolog A (MafA) have been shown to play essential roles in pancreas development and beta-cell differentiation, and gain-of-function approaches indicate the potency of these factors for inducing differentiation of non-beta-cells into insulin-producing cells, which could lead to a novel therapy to cure diabetes.

A simple method to induce differentiation of murine bone marrow mesenchymal cells to insulin-producing cells using conophylline and betacellulin-delta4

The present study was conducted to establish a method to induce differentiation of bone marrow (MB)-derived mesenchymal cells into insulin-producing cells. When mouse BM-derived mesenchymal cells were cultured for 60 days in medium containing 10% fetal calf serum and 25 mM glucose, they expressed insulin. Addition of activin A and betacellulin (BTC) accelerated differentiation, and immunoreactive insulin was detected 14 days after the treatment. Insulin-containing secretory granules were observed in differentiated cells by electron microscopy. Treatment of BM-derived mesenchymal cells with conophylline (CnP) and BTC-delta4 further accelerated differentiation, and mRNA for insulin was detected 5 to 7 days after the treatment. Mesencymal cells treated with CnP and BTC-delta4 responded to a high concentration of glucose and secreted mature insulin. When these cells were transplanted into streptozotocin-treated mice, they markedly reduced the plasma glucose concentration, and the effect continued for at least 4 weeks. These results indicate an efficacy of the combination of CnP and BTC-delta4 in inducing differentiation of BM-derived mesenchymal cells into insulin-producing cells.

Insulin - producing cells derived from stem cells: recent progress and future directions

Type 1 diabetes is characterized by the selective destruction of pancreatic β-cells caused by an autoimmune attack. Type 2 diabetes is a more complex pathology which, in addition to β-cell loss caused by apoptotic programs, includes β-cell dedifferentiation and peripheric insulin resistance. β-Cells are responsible for insulin production, storage and secretion in accordance to the demanding concentrations of glucose and fatty acids. The absence of insulin results in death and therefore diabetic patients require daily injections of the hormone for survival. However, they cannot avoid the appearance of secondary complications affecting the peripheral nerves as well as the eyes, kidneys and cardiovascular system. These afflictions are caused by the fact that external insulin injection does not mimic the tight control that pancreaticderived insulin secretion exerts on the body’s glycemia. Restoration of damaged β-cells by transplantation from exogenous sources or by endocrine pancreas regeneration would be ideal therapeutic options. In this context, stem cells of both embryonic and adult origin (including β-cell/islet progenitors) offer some interesting alternatives, taking into account the recent data indicating that these cells could be the building blocks from which insulin secreting cells could be generated in vitro under appropriate culture conditions. Although in many cases insulin-producing cells derived from stem cells have been shown to reverse experimentally induced diabetes in animal models, several concerns need to be solved before finding a definite medical application. These refer mainly to the obtainment of a cell population as similar as possible to pancreatic β-cells, and to the problems related with the immune compatibility and tumor formation. This review will summarize the different approaches that have been used to obtain insulin-producing cells from embryonic and adult stem cells, and the main problems that hamper the clinical applications of this technology.

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.

Pleiotropic Roles of PDX-1 in the Pancreas

It is well known that pancreatic and duodenal homeobox factor-1 (PDX-1) plays a pleiotropic role in the pancreas. In the developing pancreas, PDX-1 is involved in both pancreas formation and beta-cell differentiation. In mature beta-cells, PDX-1 transactivates insulin and other beta-cell-related genes such as GLUT2 and glucokinase. Furthermore, PDX-1 plays an important role in the induction of insulin-producing cells in various non-beta-cells and is thereby a possible therapeutic target for diabetes. On the other hand, under diabetic conditions, expression and/or activity of PDX-1 in beta-cells is reduced, which leads to suppression of insulin biosynthesis and secretion. It is likely that PDX-1 inactivation explains, at least in part, the molecular mechanism for beta-cell glucose toxicity found in diabetes.

Beta-cell replacement for insulin-dependent diabetes mellitus

Beta-cell replacement is considered the optimal treatment for type 1 diabetes, however, it is hindered by a shortage of human organ donors. Given the difficulty of expanding adult beta cells in vitro, stem/progenitor cells, which can be expanded in tissue culture and induced to differentiate into multiple cell types, represent an attractive source for generation of cells with beta-cell properties. In the absence of well-characterized human pancreas progenitor cells, investigators are exploring the use of embryonic stem cells and stem/progenitor cells from other tissues. Once abundant surrogate beta cells are available, the challenge will be to protect them from recurring autoimmunity.

In vitro cultivation and differentiation of fetal liver stem cells from mice

During embryonic development, pluripotent endoderm tissue in the developing foregut may adopt pancreatic fate or hepatic fate depending on the activation of key developmental regulators. Transdifferentiation occurs between hepatocytes and pancreatic cells under specific conditions. Hepatocytes and pancreatic cells have the common endodermal progenitor cells. In this study we isolated hepatic stem/progenitor cells from embryonic day (ED) 12-14 Kun-Ming mice with fluorescence-activated cell sorting (FACS). The cells were cultured under specific conditions. The cultured cells deploy dithizone staining and immunocytochemical staining at the 15th, 30th and 40th day after isolation. The results indicated the presence of insulin-producing cells. When the insulin-producing cells were transplanted into alloxan-induced diabetic mice, the nonfasting blood glucose level was reduced. These results suggested that fetal liver stem/progenitor cells could be converted into insulin-producing cells under specific culture conditions. Fetal liver stem/progenitor cells could become the potential source of insulin-producing cells for successful cell transplantation therapy strategies of diabetes.

Role of PDX-1 and MafA as a potential therapeutic target for diabetes

Pancreatic and duodenal homeobox factor-1 (PDX-1) plays a crucial role in pancreas development, beta-cell differentiation, and maintaining mature beta-cell function. During pancreas development, PDX-1 expression is maintained in precursor cells, and later it becomes restricted to beta-cells. In mature beta-cells, PDX-1 regulates gene expression of various beta-cell-related factors including insulin. Also, PDX-1 has potency to induce insulin-producing cells from non-beta-cells in various tissues, and PDX-1-VP16 fusion protein more efficiently induces insulin-producing cells, especially in the presence of NeuroD or Ngn3. MafA is a recently isolated beta-cell-specific transcription factor which functions as a potent activator of insulin gene transcription. During pancreas development, MafA expression is first detected at the beginning of the principal phase of insulin-producing cell production. Furthermore, MafA markedly enhances insulin gene promoter activity and ameliorates glucose tolerance in diabetic mice, especially in the presence of PDX-1 and NeuroD. Taken together, PDX-1 and MafA play a crucial role in inducing surrogate beta-cells and could be a therapeutic target for diabetes.

Extra-pancreatic insulin production in RAt lachrymal gland after streptozotocin-induced islet β-cells destruction

Previous work has revealed that insulin is secreted in the tear film; its mRNA is expressed in the lachrymal gland (LG) and its receptor in tissues of the ocular surface. To test the hypothesis of insulin production in the LG, we compared normal and diabetic rats for: (1) the presence of insulin and C-peptide, (2) glucose- and carbachol-induced insulin secretion ex-vivo, and (3) biochemical and histological characteristics of diabetic LG that would support this possibility. Four weeks after streptozotocin injection, blood and tears were collected from streptozotocin-diabetic male Wistar rats. Insulin levels in the tear film rose after glucose stimulation in diabetic rats, but remained unchanged in the blood. Ex vivo static secretion assays demonstrated that higher glucose and 200 microM carbachol significantly increased mean insulin levels from LG samples of both groups. Insulin and C-peptide were expressed in LG of diabetic rats as determined by RIA. Comparable synaptophysin immune staining and peroxidase activity in the LG of both groups suggest that the structure and function of these tissues were maintained. These findings provide evidence of insulin production by LG. Higher expression of reactive oxygen species scavengers may prevent oxidative damage to LG compared to pancreatic beta-cells.