Glucagon-like peptide-1 differentiation of primate embryonic stem cells into insulin-producing cells

Combined Treatment with Bone Marrow-Derived Mesenchymal Stem Cells and Exendin-4 Promotes Islet Regeneration in Streptozotocin-Induced Diabetic Rats

This study was designed to assess whether the combination of the glucagon-like peptide-1 (GLP-1) analog exendin-4 (Ex4) and bone marrow-derived mesenchymal stem cell (BM-MSC) could enhance β-cell action in streptozotocin (STZ)-induced diabetic rats. Forty male Sprague-Dawley rats were randomly assigned to five groups: the normal control group (Normal), diabetes mellitus (DM) group, MSC-treated group (MSC), Ex4-treated group (Ex4), and MSC plus Ex4-treated group (MSC+Ex4). Body weight, blood glucose level, intraperitoneal glucose tolerance test, and in vitro glucose-stimulated insulin secretion were used to assess the treatment efficacy. The expression level of insulin, glucagon, pancreatic duodenal homeobox-1 (PDX-1), v-maf musculoaponeurotic fibrosarcoma oncogene homolog A (MafA), glucagon-like peptide-1 receptor (GLP-1R), and forkhead transcription factor 1 (FoxO1) was estimated by immunofluorescence analysis. Proliferation was assessed by Ki67 staining, and apoptosis was determined by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining in β-cells. Glucose-induced insulin secretion in the MSC+Ex4 group was significantly increased compared to that in the MSC group in vitro and in vivo. Compared to that of the other groups, the number of insulin-immunopositive cells was increased in both the MSC and MSC+Ex4 groups. However, β-cell proliferation and apoptosis in the MSC group and MSC+Ex4 group were not significantly different. Importantly, the expression level of PDX-1, MafA, FoxO1, and GLP-1R in β-cells in the MSC+Ex4 group was significantly higher than those in the MSC group. The numbers of insulin+ glucagon+ double positive cells and glucagon+ GLP-1+ double positive cells were significantly increased after MSC treatment and MSC+Ex4 combined treatment, suggesting the enhanced function of newly formed islet β-cells. Our findings showed that the combination of MSC and Ex4 enhanced the function of newly formed β-cells in STZ-induced diabetic rats by acting on multiple insulin transcription factors. Thus, combined MSC and Ex4 therapy provides a feasible approach for future diabetes treatments.

Chorionic and amniotic placental membrane-derived stem cells, from gestational diabetic women, have distinct insulin secreting cell differentiation capacities

Women with gestational diabetes mellitus (GDM), and their offspring, are at high risk of developing type 2 diabetes. Chorionic (CMSCs) and amniotic mesenchymal stem cells (AMSCs) derived from placental membranes provide a source of autologous stem cells for potential diabetes therapy. We established an approach for the CMSC/AMSC-based generation of functional insulin-producing cells (IPCs). CMSCs/AMSCs displayed significantly elevated levels of NANOG and OCT4 versus bone marrow-derived MSCs, indicating a potentially broad differentiation capacity. Exposure of Healthy- and GDM-CMSCs/AMSCs to long-term high-glucose culture resulted in significant declines in viability accompanied by elevation, markedly so in GDM-CMSCs/AMSCs, of senescence/stress markers. Short-term high-glucose culture promoted pancreatic transcription factor expression when coupled to a 16-day step-wise differentiation protocol; activin A, retinoic acid, epidermal growth factor, glucagon-like peptide-1 and other chemical components, generated functional IPCs from both Healthy- and GDM-CMSCs. Healthy-/GDM-AMSCs displayed betacellulin-sensitive insulin expression, which was not secreted upon glucose challenge. The pathophysiological state accompanying GDM may cause irreversible impairment to endogenous AMSCs; however, GDM-CMSCs possess comparable therapeutic potential with Healthy-CMSCs and can be effectively reprogrammed into insulin-secreting cells.

In vitro reconstitution of pancreatic islets

The lack of transplantable pancreatic islets is a serious problem that affects the treatment of patients with type 1 diabetes mellitus. Beta cells can be induced from various sources of stem or progenitor cells, including induced pluripotent stem cells in the near future; however, the reconstitution of islets from β cells in culture dishes is challenging. The generation of highly functional islets may require three-dimensional spherical cultures that resemble intact islets. This review discusses recent advances in the reconstitution of islets. Several factors affect the reconstitution of pseudoislets with higher functions, such as architectural similarity, cell-to-cell contact, and the production method. The actual transplantation of naked or encapsulated pseudoislets and islet-like cell clusters from various stem cell sources is also discussed. Advancing our understanding of the methods used to reconstitute pseudoislets should expand the range of potential strategies available for developing de novo islets for therapeutic applications.

Activin A, exendin-4, and glucose stimulate differentiation of human pancreatic ductal cells

Islet transplantation is one treatment option for diabetes mellitus. However, novel sources of pancreatic islets or insulin-producing cells are required because the amount of donor tissue available is severely limited. Pancreatic ductal cells are an alternative source of β-cells because they have the potential to differentiate into insulin-producing cells. We investigated whether treatment of human pancreatic ductal cells with activin A (ActA) and exendin-4 (EX-4) stimulated transdifferentiation of the cells, both in vitro and in vivo. We treated human pancreatic ductal cells with ActA and EX-4 in high-glucose media to induce differentiation into insulin-producing cells and transplanted the cells into streptozotocin-induced diabetic nude mice. Co-treatment of mice with ActA and EX-4 promoted cell proliferation, induced expression of pancreatic β-cell-specific markers, and caused glucose-induced insulin secretion compared with the ActA or EX-4 mono-treatment groups respectively. When pancreatic ductal cells treated with ActA and EX-4 in high-glucose media were transplanted into diabetic nude mice, their blood glucose levels normalized and insulin was detected in the graft. These findings suggest that pancreatic ductal cells have a potential to replace pancreatic islets for the treatment of diabetes mellitus when the ductal cells are co-treated with ActA, EX-4, and glucose to promote their differentiation into functional insulin-producing cells.

GLP-1 could improve the similarity of IPCs and pancreatic beta cells in cellular ultrastructure and function

Transplantation of functional insulin-producing cells (IPCs) provides a novel mode for insulin replacement, but is often accompanied by many undesirable side effects. Our previous studies suggested that IPCs could not mimic the physiological regulation of insulin secretion performed by pancreatic beta cells. To obtain a better method through which to acquire more similar IPCs, we compared the difference between IPCs of the GLP-1 group and IPCs of the non-GLP-1 group in the morphological features in cellular level and physiological function. The levels of insulin secretion were measured by ELISA. The insulin and glucagon-like peptide-1 (GLP-1) mRNA gene expression was determined by real-time quantitative PCR. The morphological features were detected by atomic force microscopy (AFM) and laser confocal scanning microscopy (LCSM). Intracellular Ca(2+) levels and Glucagon-like peptide-1 receptor (GLP-1R) levels were determined by flow cytometer (FCM). We found that IPCs of the GLP-1 group had bigger membrane particle size and average roughness (Ra ) than IPCs of the non-GLP-1 group but still smaller than normal human pancreatic beta cells. The physiology function of IPCs of the GLP-1 group were much closer to normal human pancreatic beta cells than IPCs of the non-GLP-1 group. GLP-1 could improve the similarity of IPCs from human adipose tissue-derived mesenchymal stem cells and pancreatic beta cells in cellular ultrastructure and function.

Self-inducible secretion of glucagon-like peptide-1 (GLP-1) that allows MIN6 cells to maintain insulin secretion and insure cell survival

Based on the hypothesis that MIN6 cells could produce glucagon-like peptide-1 (GLP-1) to maintain cell survival, we analyzed the effects of GLP-1 receptor agonist, exendin-4 (Ex4), and antagonist, exendin-(9-39) (Ex9) on cell function and cell differentiation. MIN6 cells expressed proglucagon mRNAs and produced GLP-1, which was accelerated by Ex4 and suppressed by Ex9. Moreover, Ex4 further enhanced glucose-stimulated GLP-1 secretion, suggesting autocrine loop-contributed amplification of the GLP-1 signal. Ex4 up-regulated cell differentiation- and cell function-related CREBBP, Pdx-1, Pax6, proglucagon, and PC1/3 gene expressions. The confocal laser scanning images revealed that GLP-1 positive cells were dominant in the early stage of cells, but positive for insulin were more prominent in the mature stage of cells. Ex4 accelerated cell viability, while Ex9 and anti-GLP-1 receptor antibody enhanced cell apoptosis. MIN6 cells possess a mechanism of GLP-1 signal amplification in an autocrine fashion, by which the cells maintained insulin production and cell survival.

Improved outcome of islet transplantation in partially pancreatectomized diabetic mice by inhibition of dipeptidyl peptidase-4 with sitagliptin

OBJECTIVE

Glucagon-like peptide-1 (GLP-1) is known to promote beta cell proliferation, and dipeptidyl peptidase-4 (DPP-4) inhibitor increases GLP-1 levels by preventing its degradation. This study was designed to evaluate the effects of sitagliptin (sita), a DPP-4 inhibitor, on the outcome of islet transplantation (ITx) in diabetic mice after partial pancreatectomy (Px).

METHODS

A diabetic mouse model was prepared by performing 70% Px in C57BL/6 mice. The diabetic mice were treated with sita, subjected to ITx, or both treated with sita and subjected to ITx. After 12 days of sita treatment, the pancreatic remnants and transplanted islets were histologically examined.

RESULTS

Dipeptidyl peptidase-4 inhibitor increased the concentration of plasma active GLP-1 regardless of ITx and improved glycemic control in the ITx group. The beta cell mass of the pancreatic remnants increased in the ITx group, and mice that received combined treatment with ITx and sita showed a greater increase in the beta cell mass. Dipeptidyl peptidase-4 inhibitor seems to induce proliferation and inhibit apoptosis of beta cells in pancreatic remnants.

CONCLUSIONS

The DPP-4 inhibitor favorably affects ITx in partially pancreatectomized diabetic mice by increasing the beta cell mass through cell proliferation and inhibition of beta cell apoptosis.

Gastrointestinal hormones and the regulation of β-cell mass

Type 2 diabetes occurs due to a relative deficit in β-cell mass or function. Glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), cholecystokinin (CCK), and gastrin are gastrointestinal hormones that are secreted in response to nutrient intake, regulating digestion, insulin secretion, satiety, and β-cell mass. In this review, we focus upon β-cell mass regulation. β-cell mass expands through β-cell proliferation and islet neogenesis; β-cell mass is lost via apoptosis. GLP-1 and GIP are well-studied gastrointestinal hormones and influence β-cell proliferation, apoptosis, and islet neogenesis. CCK regulates β-cell apoptosis and mitogenesis, and gastrin stimulates islet neogenesis. GLP-1 and GIP bind to G protein-coupled receptors and regulate β-cell mass via multiple signaling pathways. The protein kinase A pathway is central to this process because it directly regulates proliferative and anti-apoptotic genes and transactivates several signaling cascades, including Akt and mitogen-activated protein kinases. However, the signaling pathways downstream of G protein-coupled CCK receptors that influence β-cell mass remain unidentified. Gastrointestinal hormones integrate nutrient signals from the gut to the β-cell, regulating insulin secretion and β-cell mass adaptation.

Glial cell line-derived neurotrophic factor enhances neurogenin3 gene expression and beta-cell proliferation in the developing mouse pancreas

Glial cell line-derived neurotrophic factor (GDNF) is a factor produced by glial cells that is required for the development of the enteric nervous system. In transgenic mice that overexpress GDNF in the pancreas, GDNF has been shown to enhance beta-cell mass and improve glucose control, but the transcriptional and cellular processes involved are not known. In this study we examined the influence of GDNF on the expression of neurogenin3 (Ngn3) and other transcription factors implicated in early beta-cell development, as well as on beta-cell proliferation during embryonic and early postnatal mouse pancreas development. Embryonic day 15.5 (E15.5) mouse pancreatic tissue when exposed to GDNF for 24 h showed higher Ngn3, pancreatic and duodenal homeobox gene 1 (Pdx1), neuroD1/beta(2), paired homeobox gene 4 (Pax4), and insulin mRNA expression than tissue exposed to vehicle only. Transgenic expression of GDNF in mouse pancreata was associated with increased numbers of Ngn3-expressing pancreatic cells and higher beta-cell mass at embryonic day 18 (E18), as well as higher beta-cell proliferation and Pdx1 expression in beta-cells at E18 and postnatal day 1. In the HIT-T15 beta-cell line, GDNF enhanced the expression of Pax6. This response was, however, blocked in the presence of Pdx1 small interfering RNA (siRNA). Chromatin immunoprecipitation studies using the HIT-T15 beta-cell line demonstrated that GDNF can influence Pdx1 gene expression by enhancing the binding of Sox9 and neuroD1/beta(2) to the Pdx1 promoter. Our data provide evidence of a mechanism by which GDNF influences beta-cell development. GDNF could be a potential therapeutic target for the treatment and prevention 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.

Exendin-4 promotes liver cell proliferation and enhances the PDX-1-induced liver to pancreas transdifferentiation process

Over the last few years, evidence has accumulated revealing the unexpected potential of committed mammalian cells to convert to a different phenotype via a process called transdifferentiation or adult cell reprogramming. These findings may have major practical implications because this process may facilitate the generation of functional autologous tissues that can be used for replacing malfunctioning organs. An instructive role for transcription factors in diverting the developmental fate of cells in adult tissues has been demonstrated when adult human liver cells were induced to transdifferentiate to the pancreatic endocrine lineage upon ectopic expression of the pancreatic master regulator PDX-1 (pancreatic and duodenal homeobox gene 1). Since organogenesis and lineage commitment are affected also by developmental signals generated in response to environmental triggers, we have now analyzed whether the hormone GLP-1 (glucogen-like peptide-1) documented to play a role in pancreatic beta cell differentiation, maturation, and survival, can also increase the efficiency of liver to pancreas transdifferentiation. We demonstrate that the GLP-1R agonist, exendin-4, significantly improves the efficiency of PDX-1-mediated transdifferentiation. Exendin-4 affects the transdifferentiation process at two distinct steps; it increases the proliferation of liver cells predisposed to transdifferentiated in response to PDX-1 and promotes the maturation of transdifferentiated cells along the pancreatic lineage. Liver cell reprogramming toward the pancreatic beta cell lineage has been suggested as a strategy for functional replacement of the ablated insulin-producing cells in diabetics. Understanding the cellular and molecular basis of the transdifferentiation process will allow us to increase the efficiency of the reprogramming process and optimize its therapeutic merit.

Identification of a pancreatic stellate cell population with properties of progenitor cells: new role for stellate cells in the pancreas

Numerous studies conducted in a diversity of adult tissues have shown that certain stem cells are characterized by the expression of a protein known as the ABCG2 transporter (where ABC is ATP- binding cassette). In the adult pancreas, although various multipotent progenitors have been proposed, the ABCG2 marker has only been detected in the so-called 'side population' (a primitive haematopoietic cell population with a multipotential capacity). In the present study we sought to identify new ABCG2+ pancreatic cell populations and to explore whether they exhibit the properties of progenitor cells. We isolated and expanded mitoxantrone-resistant cells from pancreata of lactating rats by drug selection. These cells were characterized and maintained in different stages of differentiation using several media 'cocktails' plus Matrigel (BD Biosciences). Differentiation was assessed by RT-PCR (reverse transcription-PCR), immunocytochemistry, electron microscopy and ELISA. The expanded cell population demonstrated a phenotype of PaSCs (pancreatic stellate cells). Spontaneous cell clusters occurred during cell expansion and they showed weak expression of the transcription factor Pdx1 (pancreatic and duodenal homeobox 1). Moreover, the presence of inductive factors in the Matrigel plus exendin-4 led to an increase in Pdx1 and endocrine genes, such as insulin, islet amyloid polypeptide, glucagon, the glucose transporter GLUT2, chromogranin A and the convertases PC1/3 and PC2 were also detected. Immunocytochemical analysis showed co-localization of insulin and C-peptide, whereas ultrastructural studies revealed the presence of granules. Insulin secretion from cell clusters was detected in the cell culture medium. We identified a population of PaSCs that express the ABCG2+ transporter and have the capacity to transdifferentiate into insulin-producing cells. Although the potential therapeutic application remains to be tested, PaSCs could represent a future option for insulin replacement in diabetes research.

A feat of metabolic proportions: Pdx1 orchestrates islet development and function in the maintenance of glucose homeostasis

Emerging evidence over the past decade indicates a central role for transcription factors in the embryonic development of pancreatic islets and the consequent maintenance of normal glucose homeostasis. Pancreatic and duodenal homeobox 1 (Pdx1) is the best studied and perhaps most important of these factors. Whereas deletion or inactivating mutations of the Pdx1 gene causes whole pancreas agenesis in both mice and humans, even haploinsufficiency of the gene or alterations in its expression in mature islet cells causes substantial impairments in glucose tolerance and the development of a late-onset form of diabetes known as maturity onset diabetes of the young. The study of Pdx1 has revealed crucial phenotypic interrelationships of the varied cell types within the pancreas, particularly as these impinge upon cellular differentiation in the embryo and neogenesis and regeneration in the adult. In this review, we describe the actions of Pdx1 in the developing and mature pancreas and attempt to unify these actions with its known roles in modulating transcriptional complex formation and chromatin structure at the molecular genetic level.

Mechanisms of action of glucagon-like peptide 1 in the pancreas

Glucagon-like peptide 1 (GLP-1) is a hormone that is encoded in the proglucagon gene. It is mainly produced in enteroendocrine L cells of the gut and is secreted into the blood stream when food containing fat, protein hydrolysate, and/or glucose enters the duodenum. Its particular effects on insulin and glucagon secretion have generated a flurry of research activity over the past 20 years culminating in a naturally occurring GLP-1 receptor (GLP-1R) agonist, exendin 4 (Ex-4), now being used to treat type 2 diabetes mellitus (T2DM). GLP-1 engages a specific guanine nucleotide-binding protein (G-protein) coupled receptor (GPCR) that is present in tissues other than the pancreas (brain, kidney, lung, heart, and major blood vessels). The most widely studied cell activated by GLP-1 is the insulin-secreting beta cell where its defining action is augmentation of glucose-induced insulin secretion. Upon GLP-1R activation, adenylyl cyclase (AC) is activated and cAMP is generated, leading, in turn, to cAMP-dependent activation of second messenger pathways, such as the protein kinase A (PKA) and Epac pathways. As well as short-term effects of enhancing glucose-induced insulin secretion, continuous GLP-1R activation also increases insulin synthesis, beta cell proliferation, and neogenesis. Although these latter effects cannot be currently monitored in humans, there are substantial improvements in glucose tolerance and increases in both first phase and plateau phase insulin secretory responses in T2DM patients treated with Ex-4. This review will focus on the effects resulting from GLP-1R activation in the pancreas.