In vitro transdifferentiation of adult pancreatic acinar cells into insulin-expressing cells

Exploring the mechanism of pancreatic cell fate decisions via cell-cell communication

The endocrine and exocrine cells in pancreas originate initially from a group of apparently identical endoderm cells in the early gut. The endocrine and exocrine tissues are composed of islet/acinar and duct cells respectively. To explore the mechanism of pancreas cell fate decisions, we first construct a minimal mathematical model related to pancreatic regulations. The regulatory mechanism of acinar-to-islet cell conversion is revealed by bifurcation analysis of the model. In addition, Notch signaling is critical in determining the fate of endocrine and exocrine in the developing pancreas and it is a typical mediator of lateral inhibition which instructs adjacent cells to make different fate decisions. Next, we construct a multicellular model of cell-cell communication mediated by Notch signaling with trans-activation and cis-inhibition. The roles of Notch signaling in regulating fate decisions of endocrine and exocrine cells during the differentiation of pancreatic cells are explored. The results indicate that high (or low) level of Notch signaling drive cells to select the fate of exocrine (or endocrine) progenitor cells. The networks and the models presented here might be good candidates for providing qualitative mechanisms of pancreatic cell fate decisions. These results can also provide some insight on choosing perturbation strategies for further experimental analysis.

Transdifferentiation of both intra- and extra-islet cells into beta cells in nicotinamide treated neonatal diabetic rats: An in situ hybridization and double immunohistochemical study

We aimed to study the effect of nicotinamide (NA) on beta (β)-cell regeneration and apoptosis in streptozotocin induced neonatal rats (n-STZ). Three groups were performed: Control group, n2-STZ group (100 mg/kg STZ on the second day-after birth), n2-STZ + NA group (STZ;100 mg/kg + NA;500 mg/kg/day for 5 days). The pancreatic tissue sections were immunostained with insulin, glucagon, somatostatin, Pdx1, Notch1 and active caspase-3 antibodies, and double immunostained with insulin/PCNA, insulin/glucagon and insulin/somatostatin antibodies. In situ hybridization carried out with insulin probe. Apoptotic β-cell were shown by TUNEL assay, followed by immunostaining. The number of insulin/PCNA, insulin/glucagon and insulin/somatostatin double-positive cells significantly increased in n2-STZ + NA group compared with the other groups (p < 0.001). n2- STZ group had lower number of insulin and Pdx1 positive cells in islets, compared to NA treated diabetics. The insulin and Pdx1 immun positive cells were located in the small clusters or scattered through the exocrine tissue and around to ducts in n2-STZ + NA group. Notch1 positive cell numbers were increased, whereas caspase-3 and TUNEL positive β-cell numbers were decreased in n2-STZ + NA group. NA treatment induces the neogenic insulin positive islets orginated from the differentiation of ductal progenitor cells, transdifferentiation of acinar cells into β cells, and transformation of potent precursor cells and centroacinar cells via the activated Notch expression into β-cells in n-STZ rats.

Mixed ductal-acinar cell carcinoma of the pancreas: A case report

Mixed carcinoma of the pancreas is defined as the concurrent existence of pancreatic ductal carcinoma, acinar cell carcinoma, and/or islet cell carcinoma within the same neoplasm. We herein report a rare case of mixed ductal-acinar cell carcinoma in a 74-year-old man who was undergoing treatment for hypertension and diabetes at another hospital. After an abrupt worsening of his blood glucose control, the patient was referred to our hospital for further evaluation. Abdominal contrast-enhanced computed tomography and magnetic resonance imaging revealed a tumor with a multilocular cystic lesion in the head of the pancreas. Endoscopic retrograde cholangiopancreatography revealed obstruction of the main pancreatic duct and dilation of the dorsal pancreatic duct; in addition, adenocarcinoma was detected in the pancreatic juice cytology. Based on the abovementioned findings, the patient was diagnosed with carcinoma of the pancreatic head and underwent subtotal stomach-preserving pancreaticoduodenectomy. Based on the histopathological and immunohistochemical findings, the patient was diagnosed with mixed ductal-acinar cell carcinoma. The patient was prescribed TS-1 as postoperative adjuvant chemotherapy upon discharge. However, treatment was discontinued 2 months later due to marked general malaise, and the patient succumbed to tumor recurrence in the residual pancreas 12 months after the surgery.

Generation of Insulin-Expressing Cells in Mouse Small Intestine by Pdx1, MafA, and BETA2/NeuroD

BACKGROUND

To develop surrogate insulin-producing cells for diabetes therapy, adult stem cells have been identified in various tissues and studied for their conversion into β-cells. Pancreatic progenitor cells are derived from the endodermal epithelium and formed in a manner similar to gut progenitor cells. Here, we generated insulin-producing cells from the intestinal epithelial cells that induced many of the specific pancreatic transcription factors using adenoviral vectors carrying three genes: PMB (pancreatic and duodenal homeobox 1 [Pdx1], V-maf musculoaponeurotic fibrosarcoma oncogene homolog A [MafA], and BETA2/NeuroD).

METHODS

By direct injection into the intestine through the cranial mesenteric artery, adenoviruses (Ad) were successfully delivered to the entire intestine. After virus injection, we could confirm that the small intestine of the mouse was appropriately infected with the Ad-Pdx1 and triple Ad-PMB.

RESULTS

Four weeks after the injection, insulin mRNA was expressed in the small intestine, and the insulin gene expression was induced in Ad-Pdx1 and Ad-PMB compared to control Ad-green fluorescent protein. In addition, the conversion of intestinal cells into insulin-expressing cells was detected in parts of the crypts and villi located in the small intestine.

CONCLUSION

These data indicated that PMB facilitate the differentiation of mouse intestinal cells into insulin-expressing cells. In conclusion, the small intestine is an accessible and abundant source of surrogate insulin-producing cells.

β-Cell replacement as a treatment for type 1 diabetes: an overview of possible cell sources and current axes of research

To efficiently treat type 1 diabetes, exogenous insulin injections currently represent the main approach to counter chronic hyperglycaemia. Unfortunately, such a therapeutic approach does not allow for perfectly maintained glucose homeostasis and, in time, cardiovascular complications may arise. Therefore, seeking alternative/improved treatments has become a major health concern as an increasing proportion of type 2 diabetes patients also require insulin supplementation. Towards this goal, numerous laboratories have focused their research on β-cell replacement therapies. Herein, we will review the current state of this research area and describe the cell sources that could potentially be used to replenish the depleted β-cell mass in diabetic patients.

Pancreatic β Cell Mass Death

Type two diabetes (T2D) is a challenging metabolic disorder for which a cure has not yet been found. Its etiology is associated with several phenomena, including significant loss of insulin-producing, beta cell (β cell) mass via progressive programmed cell death and disrupted cellular autophagy. In diabetes, the etiology of β cell death and the role of mitochondria are complex and involve several layers of mechanisms. Understanding the dynamics of those mechanisms could permit researchers to develop an intervention for the progressive loss of β cells. Currently, diabetes research has shifted toward rejuvenation and plasticity technology and away from the simplified approach of hormonal compensation. Diabetes research is currently challenged by questions such as how to enhance cell survival, decrease apoptosis and replenish β cell mass in diabetic patients. In this review, we discuss evidence that β cell development and mass formation are guided by specific signaling systems, particularly hormones, transcription factors, and growth factors, all of which could be manipulated to enhance mass growth. There is also strong evidence that β cells are dynamically active cells, which, under specific conditions such as obesity, can increase in size and subsequently increase insulin secretion. In certain cases of aggressive or advanced forms of T2D, β cells become markedly impaired, and the only alternatives for maintaining glucose homeostasis are through partial or complete cell grafting (the Edmonton protocol). In these cases, the harvesting of an enriched population of viable β cells is required for transplantation. This task necessitates a deep understanding of the pharmacological agents that affect β cell survival, mass, and function. The aim of this review is to initiate discussion about the important signals in pancreatic β cell development and mass formation and to highlight the process by which cell death occurs in diabetes. This review also examines the attempts that have been made to recover or increase cell mass in diabetic patients by using various pharmacological agents.

Current status of regeneration of pancreatic β-cells

Newly generated insulin‐secreting cells for use in cell therapy for insulin‐deficient diabetes mellitus require properties similar to those of native pancreatic β‐cells. Pancreatic β‐cells are highly specialized cells that produce a large amount of insulin, and secrete insulin in a regulated manner in response to glucose and other stimuli. It is not yet explained how the β‐cells acquire this complex function during normal differentiation. So far, in vitro generation of insulin‐secreting cells from embryonic stem cells, induced‐pluripotent stem cells and adult stem/progenitor‐like cells has been reported. However, most of these cells are functionally immature and show poor glucose‐responsive insulin secretion compared to that of native pancreatic β‐cells (or islets). Strategies to generate functional β‐cells or a whole organ in vivo have also recently been proposed. Establishing a protocol to generate fully functional insulin‐secreting cells that closely resemble native β‐cells is a critical matter in regenerative medicine for diabetes. Understanding the physiological processes of differentiation, proliferation and regeneration of pancreatic β‐cells might open the path to cell therapy to cure patients with absolute insulin deficiency.

In vitro generation of insulin-secreting cells from human pancreatic exocrine cells

Transplantation of surrogate β‐cells is a promising option for the treatment of insulin‐deficient diabetes mellitus in the future. Although pancreatic exocrine cells of rodents have been shown to transdifferentiate into insulin‐secreting cells, no studies are reported on human exocrine cells. Here, we report the generation of insulin‐secreting cells from exocrine cells of the human pancreas. When cultured in suspension with epidermal growth factor, human pancreatic exocrine cells readily formed spherical cell clusters. Expression of Pdx1 was induced in all 19 cases in which we successfully isolated exocrine cells, and insulin expression was induced in 11 cases. In addition, insulin secretion was evaluated in four cases, and the newly‐made cells were found to secrete insulin in response to various stimuli. Although further studies are required to improve both the quality and quantity of such insulin‐secreting cells, our data suggest that pancreatic exocrine cells represent a potential source of insulin‐secreting cells for treatment of type 1 diabetes. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00095.x, 2011)

Tissue engineering approaches to cell-based type 1 diabetes therapy

Type 1 diabetes mellitus is an autoimmune disease resulting from the destruction of insulin-producing pancreatic β-cells. Cell-based therapies, involving the transplantation of functional β-cells into diabetic patients, have been explored as a potential long-term treatment for this condition; however, success is limited. A tissue engineering approach of culturing insulin-producing cells with extracellular matrix (ECM) molecules in three-dimensional (3D) constructs has the potential to enhance the efficacy of cell-based therapies for diabetes. When cultured in 3D environments, insulin-producing cells are often more viable and secrete more insulin than those in two dimensions. The addition of ECM molecules to the culture environments, depending on the specific type of molecule, can further enhance the viability and insulin secretion. This review addresses the different cell sources that can be utilized as β-cell replacements, the essential ECM molecules for the survival of these cells, and the 3D culture techniques that have been used to benefit cell function.

Generation of functional insulin-producing cells from neonatal porcine liver-derived cells by PDX1/VP16, BETA2/NeuroD and MafA

Surrogate β-cells derived from stem cells are needed to cure type 1 diabetes, and neonatal liver cells may be an attractive alternative to stem cells for the generation of β-cells. In this study, we attempted to generate insulin-producing cells from neonatal porcine liver-derived cells using adenoviruses carrying three genes: pancreatic and duodenal homeobox factor1 (PDX1)/VP16, BETA2/NeuroD and v-maf musculo aponeurotic fibrosarcoma oncogene homolog A (MafA), which are all known to play critical roles in pancreatic development. Isolated neonatal porcine liver-derived cells were sequentially transduced with triple adenoviruses and grown in induction medium containing a high concentration of glucose, epidermal growth factors, nicotinamide and a low concentration of serum following the induction of aggregation for further maturation. We noted that the cells displayed a number of molecular characteristics of pancreatic β-cells, including expressing several transcription factors necessary for β-cell development and function. In addition, these cells synthesized and physiologically secreted insulin. Transplanting these differentiated cells into streptozotocin-induced immunodeficient diabetic mice led to the reversal of hyperglycemia, and more than 18% of the cells in the grafts expressed insulin at 6 weeks after transplantation. These data suggested that neonatal porcine liver-derived cells can be differentiated into functional insulin-producing cells under the culture conditions presented in this report and indicated that neonatal porcine liver-derived cells (NPLCs) might be useful as a potential source of cells for β-cell replacement therapy in efforts to cure type I diabetes.

Transdifferentiation of pancreatic cells by loss of contact-mediated signaling

Background

Replacement of dysfunctional β-cells in the islets of Langerhans by transdifferentiation of pancreatic acinar cells has been proposed as a regenerative therapy for diabetes. Adult acinar cells spontaneously revert to a multipotent state upon tissue dissociation in vitro and can be stimulated to redifferentiate into β-cells. Despite accumulating evidence that contact-mediated signals are involved, the mechanisms regulating acinar-to-islet cell transdifferentiation remain poorly understood.

Results

In this study, we propose that the crosstalk between two contact-mediated signaling mechanisms, lateral inhibition and lateral stabilization, controls cell fate stability and transdifferentiation of pancreatic cells. Analysis of a mathematical model combining gene regulation with contact-mediated signaling reveals the multistability of acinar and islet cell fates. Inhibition of one or both modes of signaling results in transdifferentiation from the acinar to the islet cell fate, either by dedifferentiation to a multipotent state or by direct lineage switching.

Conclusions

This study provides a theoretical framework to understand the role of contact-mediated signaling in pancreatic cell fate control that may help to improve acinar-to-islet cell transdifferentiation strategies for β-cell neogenesis.

Pancreatic β-cells are generated by neogenesis from non-β-cells after birth

The mass of pancreatic β-cells is maintained throughout lifetime to control blood glucose levels. Although the major mechanism of the maintenance of β-cell mass after birth is thought to be selfreplication of pre-existing β-cells, it is possible that pancreatic β-cells are also generated from non-β-cells. Here, we address this issue by using the inducible Cre/loxP system to trace β-cells. We generated Ins2-CreERT2/R26R-YFP double knock-in mice, in which pancreatic β-cells can be labeled specifically and permanently upon injection of the synthetic estrogen analog tamoxifien, and then traced the β-cells by pulse and chase experiment in several different conditions. When β-cells were labeled in adults under physiological and untreated conditions, the frequency of the labeling (labeling index) was not altered significantly throughout the 12-month experimental period. In addition, the labeling index was not changed after ablation of β-cells by streptozotocin treatment. However, when tamoxifen was injected to pregnant mothers just before they gave birth, the labeling index in the neonates was decreased significantly around weaning, suggesting that β-cells are generated from non-β-cells. These results indicate that various mechanisms are involved in the maintenance of β-cells after birth, and that the present system using knock-in mice is useful for investigation of β-cell fate.

A novel explant outgrowth culture model for mouse pancreatic acinar cells with long-term maintenance of secretory phenotype

The development of in vitro models able to support the long-term viability and function of acinar cells is critical for exploring pancreatic pathophysiology. Despite considerable efforts, no long-term culture models for non-transformed pancreatic acini exist. Our aim was to develop and validate culture conditions for this purpose. An explant outgrowth culture design was established in which mouse pancreatic explants were cultured at the gas-liquid interphase. An enriched culture medium, pH 7.8, was employed to promote the selective outgrowth of acinar cells and to support their differentiated phenotype. After 7 days, the outgrown primary acinar cells were subcultured and maintained up to an additional 7 days as secondary monolayers on tissue culture plastic. Measurements of basal and caerulein-induced amylase secretion, phase-contrast microscopy and immunohistochemical analyses were used to characterize the cultures. Explants retained their pancreatic cytoarchitecture for 2 days in vitro. A triphasic dose response to caerulein was detected in 7-day primary cultures. The maximal rate of secretion was 1.2-fold versus basal (p=0.009) and 1.7-fold versus 1 pM caerulein (p=0.014). In secondary cultures the response was biphasic with maximal rates of secretion being 1.9-fold in 3- to 4-day cultures at 0.01 nM (p=0.049) and 2-fold in 6- to 7-day cultures at 0.1 nM (p=0.003). The present culture model provides a means to obtain functionally competent normal mouse acinar cells for long-term in vitro experimentation.

Visualization of mouse pancreas architecture using MR microscopy

Pancreatic diseases, which include diabetes, pancreatitis, and pancreatic cancer, are often difficult to detect and/or stage, contributing to a reduced quality of life and lifespan for patients. Thus, there is need for a technology that can visualize tissue changes in the pancreas, improve understanding of disease progression, and facilitate earlier detection in the human population. Because of low spatial resolution, current clinical magnetic resonance imaging (MRI) at low field strength has yet to fully visualize the exocrine, endocrine, vascular, and stromal components of the pancreas. We used high field strength magnetic resonance microscopy (μMRI) to image mouse pancreas ex vivo without contrast agents at high spatial resolution. We analyzed the resulting high-resolution images using volume rendering to resolve components in the pancreas, including acini, islets, blood vessels, and extracellular matrix. Locations and dimensions of pancreatic components as seen in three-dimensional μMRI were compared with histological images, and good correspondence was found. Future longitudinal studies could expand on the use of in vivo μMRI in mouse models of pancreatic diseases. Capturing three-dimensional structural changes through μMRI could help to identify early cellular and tissue changes associated with pancreatic disease, serving as a mode of improved detection in the clinic for endocrine and exocrine pathologies.

Evidence for epithelial-mesenchymal transition in adult human pancreatic exocrine cells

It has been shown that adult pancreatic ductal cells can dedifferentiate and act as pancreatic progenitors. Dedifferentiation of epithelial cells is often associated with the epithelial-mesenchymal transition (EMT). In this study, we investigated the occurrence of EMT in adult human exocrine pancreatic cells both in vitro and in vivo. Cells of exocrine fraction isolated from the pancreas of brain-dead donors were first cultured in suspension for eight days. This led to the formation of spheroids, composed of a principal population of cells with duct-like phenotype. When cultivated in tissue culture-treated flasks, spheroid cells exhibited a proliferative capacity and coexpressed epithelial (cytokeratin7 and cytokeratin19) and mesenchymal (vimentin and alpha-smooth muscle actin) markers as well as marker of progenitor pancreatic cells (pancreatic duodenal homeobox factor-1) and surface markers of mesenchymal stem cells. The switch from E-cadherin to N-cadherin associated with Snail1 expression suggested that these cells underwent EMT. In addition, we showed coexpression of epithelial and mesenchymal markers in ductal cells of one normal adult pancreas and three type 2 diabetic pancreases. Some of the vimentin-positive cells were found to coexpress glucagon or amylase. These results point to the occurrence of EMT, which may take place on dedifferentiation of ductal cells during the regeneration or renewal of human pancreatic tissues.

Pancreatic beta-cell signaling: toward better understanding of diabetes and its treatment

Pancreatic beta-cells play a central role in the maintenance glucose homeostasis by secreting insulin, a key hormone that regulates blood glucose levels. Dysfunction of the beta-cells and/or a decrease in the beta-cell mass are associated closely with the pathogenesis and pathophysiology of diabetes mellitus, a major metabolic disease that is rapidly increasing worldwide. Clarification of the mechanisms of insulin secretion and beta-cell fate provides a basis for the understanding of diabetes and its better treatment. In this review, we discuss cell signaling critical for the insulin secretory function based on our recent studies.

Investigation and characterization of the duct cell-enriching process during serum-free suspension and monolayer culture using the human exocrine pancreas fraction

OBJECTIVES

We aimed to characterize a serum-free culture system resulting in highly enriched duct cells from human exocrine pancreas. In addition, we tested the effect of vascular endothelial growth factor (VEGF) on endothelial cell proliferation and endocrine differentiation of the duct cells.

METHODS

The exocrine pellet fraction was cultivated in suspension followed by monolayer culture. Time course analysis of multiple acinar and duct cell markers was performed using reverse transcription-polymerase chain reaction and immunocytochemistry. The effects of VEGF and placental growth factor on the quantities of endothelial, duct, and endocrine cells and fibroblasts were investigated using computerized imaging analysis.

RESULTS

Suspension culture of the exocrine material efficiently enriched the cultures for duct cells. Frequent acinar cell death as well as cell selective adherence of acinar cells to the culture dish was the underlying cause of the enrichment. Confocal microscopy demonstrated the virtual absence of cells coexpressing duct cell- and acinar cell-specific markers. The endothelial immunoreactivity of the suspension culture system could be increased 2-fold by VEGF treatment, yet no effect was observed on endocrine cell numbers.

CONCLUSIONS

We have characterized a serum-free in vitro culture system to enrich human duct cells and further show that the contribution of acinoductal transdifferentiation to the enrichment of duct cells is negligible.

Identification and characterization of a novel expandable adult stem/progenitor cell population in the human exocrine pancreas

It is a general opinion that tissue-specific stem cells are present in adult tissues but their specific properties remain elusive. They are rare in tissues and heterogeneous; in addition, their identification and the characterization of their progeny has encountered technical difficulties. In particular, the existence of pancreatic stem cells remains elusive because specific markers for their identification are not available. We established a method for the isolation of a population of stem/progenitor cells from the human exocrine pancreas, and propose it as a model for other human compact organs. We also used markers that identified and finally characterized these cells. Spheroids with self-replicative potential were obtained from all specimens. The isolated population contained a subset of CD34+ CD45- cells and was able to generate, in appropriate conditions, colonies that produce insulin. We obtained evidence that most freshly isolated spheroids, when co-cultured with the c-kit positive neuroblastoma cell line LAN 5, produced a c-kit positive progeny of cells larger in their cytoplasmic content than the original spheroid population, with elongated morphology resembling the neuronal phenotype. We identified a novel predominant functional type of stem/progenitor cell within the human exocrine pancreas, able to generate insulin-producing cells and potentially non-pancreatic cells.

Beta-cell replacement and regeneration: Strategies of cell-based therapy for type 1 diabetes mellitus

Pancreatic islet transplantation has demonstrated that long-term insulin independence may be achieved in patients suffering from diabetes mellitus type 1. However, because of limited availability of islet tissue, new sources of insulin producing cells that are responsive to glucose are required. Development of pancreatic beta-cell lines from rodent or human origin has progressed slowly in recent years. Current experiments for ex vivo expansion of beta cells and in vitro differentiation of embryonic and adult stem cells into insulin producing beta-cell phenotypes led to promising results. Nevertheless, the cells generated to date lack important characteristics of mature beta cells and generally display reduced insulin secretion and loss of proliferative capacity. Therefore, much better understanding of the mechanisms that regulate expansion and differentiation of stem/progenitor cells is necessary. Here, we review recent advances in the identification of potential cellular sources, and the development of strategies to regenerate or fabricate insulin producing and glucose sensing cells that might enable future cell-based therapies of diabetes mellitus type 1.

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.

New sources of pancreatic beta cells

In both type 1 and type 2 diabetes, insufficient numbers of insulin-producing beta cells are a major cause of defective control of blood glucose and its complications. Accordingly, therapies that increase functional beta-cell mass may offer a cure for diabetes. Efforts to achieve this goal explore several directions. Based on the realization that beta cells are capable of significant proliferation throughout adult life, the enhanced proliferation of beta cells in vivo or in vitro is pursued as a strategy for regenerative medicine for diabetes. Alternatively, the conversion of differentiated cells such as hepatocytes into beta cells is being attempted using molecular insights into the transcriptional makeup of beta cells. Advances were also made in directing the differentiation of embryonic stem cells into beta cells. Although progress is encouraging, major gaps in our understanding of developmental biology of the pancreas and adult beta-cell dynamics remain to be closed before a therapeutic application is made possible.

Generation of insulin-secreting cells from pancreatic acinar cells of animal models of type 1 diabetes

We recently found that pancreatic acinar cells isolated from normal adult mouse can transdifferentiate into insulin-secreting cells in vitro. Using two different animal models of type 1 diabetes, we show here that insulin-secreting cells can also be generated from pancreatic acinar cells of rodents in the diabetic state with absolute insulin deficiency. When pancreatic acinar cells of streptozotocin-treated mice were cultured in suspension in the presence of epidermal growth factor and nicotinamide under low-serum condition, expressions of insulin genes gradually increased. In addition, expressions of other pancreatic hormones, including glucagon, somatostatin, and pancreatic polypeptide, were also induced. Analysis by the Cre/loxP-based direct cell lineage tracing system revealed that these newly made cells originated from amylase-expressing pancreatic acinar cells. Insulin secretion from the newly made cells was significantly stimulated by high glucose and other secretagogues. In addition, insulin-secreting cells were generated from pancreatic acinar cells of Komeda diabetes-prone rats, another animal model of type 1 diabetes. The present study demonstrates that insulin-secreting cells can be generated by transdifferentiation from pancreatic acinar cells of rodents in the diabetic state and further suggests that pancreatic acinar cells represent a potential source of autologous transplantable insulin-secreting cells for treatment of type 1 diabetes.

Downregulation of EGF receptor signaling in pancreatic islets causes diabetes due to impaired postnatal beta-cell growth

Epidermal growth factor receptor (EGF-R) signaling is essential for proper fetal development and growth of pancreatic islets, and there is also evidence for its involvement in beta-cell signal transduction in the adult. To study the functional roles of EGF-R in beta-cell physiology in postnatal life, we have generated transgenic mice that carry a mutated EGF-R under the pancreatic duodenal homeobox-1 promoter (E1-DN mice). The transgene was expressed in islet beta- and delta-cells but not in alpha-cells, as expected, and it resulted in an approximately 40% reduction in pancreatic EGF-R, extracellular signal-related kinase, and Akt phosphorylation. Homozygous E1-DN mice were overtly diabetic after the age of 2 weeks. The hyperglycemia was more pronounced in male than in female mice. The relative beta-cell surface area of E1-DN mice was highly reduced at the age of 2 months, while alpha-cell surface area was not changed. This defect was essentially postnatal, since the differences in beta-cell area of newborn mice were much smaller. An apparent explanation for this is impaired postnatal beta-cell proliferation; the normal surge of beta-cell proliferation during 2 weeks after birth was totally abolished in the transgenic mice. Heterozygous E1-DN mice were glucose intolerant in intraperitoneal glucose tests. This was associated with a reduced insulin response. However, downregulation of EGF-R signaling had no influence on the insulinotropic effect of glucagon-like peptide-1 analog exendin-4. In summary, our results show that even a modest attenuation of EGF-R signaling leads to a severe defect in postnatal growth of the beta-cells, which leads to the development of diabetes.

Regenerative medicine of the pancreatic beta cells

Diabetes mellitus is a metabolic disorder that affects millions of people. The number of patients suffering from diabetes continues to increase all over the world. Both type 1 and type 2 diabetes result from an inadequate mass of functioning beta cells. To achieve the ultimate goal of curing diabetes in the future, the mechanism of the regenerative process of the adult human pancreas must be elucidated. In this review, we first summarize the regenerative processes of the pancreas observed in animal models in vivo, and approaches to promote the regeneration of the pancreas in vivo. Next we consider other new approaches, such as stem cell research and cell-based therapy, for the cure of diabetes in the future. Based on the innovative success of the Edmonton protocol, islet transplantation has been considered to be a new therapeutic option for the treatment of diabetes. However, a serious shortage of donor pancreata is a critical problem. We suggest that the following issues should be solved in order to realize cell-based therapy. The first is to establish a source of stem/progenitor cells that will multiply easily in vitro and maintain their property as progenitor cells. The probable use of adult stem cells will circumvent potential ethical problems, and autotransplantation will become possible. The most difficult and as yet unsolved issue is how to differentiate these cells and acquire fully functional islets. Further investigations to understand the regenerative process of the adult pancreas and the appropriate induction of stem cell differentiation will help to establish cell-based therapy in diabetes.

Islet- and stem-cell-based tissue engineering in diabetes

New sources of insulin-producing cells are needed to overcome the limited availability of islet tissue for transplantation to diabetic patients. The engineering of murine or human transformed beta-cell lines and of non beta-cells has progressed slowly in recent years, while significant achievements have been claimed in the differentiation of insulin-producing cells from embryonic and adult stem cells. Some of the results have been questioned, however, and the generated cells lack many characteristics of differentiated beta-cells. A much better understanding of the processes that govern the expansion and differentiation of stem cells is needed.

Conophylline: a novel differentiation inducer for pancreatic beta cells

Reduction of the beta cell mass is critical in the pathogenesis of diabetes mellitus. The discovery of agents, which induce differentiation of pancreatic progenitors to beta cells, would be useful to develop a new therapeutic approach to treat diabetes. To identify a new agent to stimulate differentiation of pancreatic progenitor cells to beta cells, we screened various compounds using pancreatic AR42J cells, a model of pancreatic progenitor cells. Among various compounds and extracts tested, we found that conophylline, a vinca alkaloid extracted from leaves of a tropical plant Ervatamia microphylla, was effective in converting AR42J into endocrine cells. Conophylline reproduces the differentiation-inducing activity of activin A. Unlike activin A, however, conophylline does not induce apoptosis. To induce differentiation of AR42J cells, conophylline increases the expression of neurogenin-3 by activating p38 mitogen-activated protein kinase. Conophylline also induces differentiation in cultured pancreatic progenitor cells obtained from fetal and neonatal rats. More importantly, conophylline is effective in reversing hyperglycemia in neonatal streptozotocin-treated rats, and both the insulin content and the beta cell mass are increased by conophylline. Histologically, conophylline increases the numbers of ductal cells positive for pancreatic-duodenal-homeobox protein-1 and islet-like cell clusters. Conophylline and related compounds are useful in inducing differentiation of pancreatic beta cells both in vivo and in vitro.

Lineage tracing and characterization of insulin-secreting cells generated from adult pancreatic acinar cells

Although several studies have suggested that insulin-secreting cells can be generated in vitro from cells residing in adult exocrine pancreas, neither the origin of these cells nor their precise insulin secretory properties was obtained. We show here that insulin-secreting cells can be derived from adult mouse pancreatic exocrine cells by suspension culture in the presence of EGF and nicotinamide. The frequency of insulin-positive cells was only 0.01% in the initial preparation and increased to approximately 5% in the culture conditions. Analysis by the Cre/loxP-based direct cell lineage tracing system indicates that these newly made cells originate from amylase/elastase-expressing pancreatic acinar cells. Insulin secretion is stimulated by glucose, sulfonylurea, and carbachol, and potentiation by glucagon-like peptide-1 also occurs. Insulin-containing secretory granules are present in these cells. In addition, we found that the enzymatic dissociation of pancreatic acini itself leads to activation of EGF signaling, and that inhibition of EGF receptor kinase blocks the transdifferentiation. These data demonstrate that pancreatic acinar cells can transdifferentiate into insulin-secreting cells with secretory properties similar to those of native pancreatic beta cells, and that activation of EGF signaling is required in such transdifferentiation.

Mechanisms of compensatory beta-cell growth in insulin-resistant rats: roles of Akt kinase

The physiological mechanisms underlying the compensatory growth of beta-cell mass in insulin-resistant states are poorly understood. Using the insulin-resistant Zucker fatty (fa/fa) (ZF) rat and the corresponding Zucker lean control (ZLC) rat, we investigated the factors contributing to the age-/obesity-related enhancement of beta-cell mass. A 3.8-fold beta-cell mass increase was observed in ZF rats as early as 5 weeks of age, an age that precedes severe insulin resistance by several weeks. Closer investigation showed that ZF rat pups were not born with heightened beta-cell mass but developed a modest increase over ZLC rats by 20 days that preceded weight gain or hyperinsulinemia that first developed at 24 days of age. In these ZF pups, an augmented survival potential of beta-cells of ZF pups was observed by enhanced activated (phospho-) Akt, phospho-BAD, and Bcl-2 immunoreactivity in the postweaning period. However, increased beta-cell proliferation in the ZF rats was only detected at 31 days of age, a period preceding massive beta-cell growth. During this phase, we also detected an increase in the numbers of small beta-cell clusters among ducts and acini, increased duct pancreatic/duodenal homeobox-1 (PDX-1) immunoreactivity, and an increase in islet number in the ZF rats suggesting duct- and acini-mediated heightened beta-cell neogenesis. Interestingly, in young ZF rats, specific cells associated with ducts, acini, and islets exhibited an increased frequency of PDX-1+/phospho-Akt+ staining, indicating a potential role for Akt in beta-cell differentiation. Thus, several adaptive mechanisms account for the compensatory growth of beta-cells in ZF rats, a combination of enhanced survival and neogenesis with a transient rise in proliferation before 5 weeks of age, with Akt serving as a potential mediator in these processes.

Morphogenetic plasticity of adult human pancreatic islets of Langerhans

The aim of this study was to investigate the phenotypic plasticity of pancreatic islets of Langerhans. Quiescent adult human islets were induced to undergo a phenotypic switch to highly proliferative duct-like structures in a process characterized by a loss of expression of islet-specific hormones and transcription factors as well as a temporally related rise in the expression of markers of both duct epithelial and progenitor cells. Short-term treatment of these primitive duct-like structures with the neogenic factor islet neogenesis-associated protein (INGAP104-118) induced their reconversion back to islet-like structures in a PI3-kinase-dependent manner. These neoislets resembled freshly isolated human islets with respect to the presence and topological arrangement of the four endocrine cell types, islet gene expression and hormone production, insulin content and glucose-responsive insulin secretion. Our results suggest that adult human islets possess a remarkable degree of morphogenetic plasticity. This novel observation may have important implications for understanding pancreatic carcinogenesis and islet neogenesis.

Tolerance induction and endogenous regeneration of pancreatic beta-cells in established autoimmune diabetes

Studies aimed at the understanding of the multifactorial development of autoimmune diabetes have made substantial contributions toward elucidating the molecular mechanisms that open the road to an effective prevention of defective immune responses. Immunomodulatory regimens capable of inducing tolerance are shown to be effective even in the reversal of established autoimmune diabetes in animal models. Experimental trials including the reeducation of autoreactive T cells, depletion of macrophages, dendritic cells, and T cells, as well as the use of monoclonal antibodies, have yielded encouraging results, but have not yet been translated into beneficial clinical outcomes. In addition, we are now seeing an emergence of promising new directions aimed at the induction of islet regeneration by endogenous factors, suggesting that the repair of pancreatic tissue is possible without the need for an engraftment of donor tissue. These recent waves of technological progress have injected new hope for a combined therapy to offer diabetic patients long-term benefits of insulin independence. This article reviews the latest findings on diabetic pathogenesis and discusses promising avenues to tolerance induction and islet regeneration.

In vitro generation of insulin-producing beta cells from adult exocrine pancreatic cells

AIMS/HYPOTHESIS

Transplantation of insulin-producing beta cells from donors can cure diabetes, but they are available in insufficient quantities. In this study, we investigated the possibility of generating insulin-producing cells from adult rat exocrine cells cultured in the presence of growth factors.

METHODS

Rat exocrine pancreatic cells were isolated and treated in vitro with epidermal growth factor (EGF) and leukaemia inhibitory factor (LIF). Analysis was performed by immunocytochemistry, DNA measurement and radioimmunoassay. Cells were transplanted to alloxan-treated (70 mg/kg) nude mice and glycaemia was monitored for 21 days. Nephrectomy was performed on day 15.

RESULTS

In a 3-day culture period, addition of LIF plus EGF to the medium resulted in an 11-fold increase of the beta cell mass. This could not be attributed to the very low mitotic activity of contaminating beta cells. Furthermore, when contaminating beta cells were initially destroyed with alloxan, this effect was even more pronounced. The newly formed cells secreted insulin in response to glucose and were immunoreactive for C-peptide-I, Pdx-1 and GLUT-2, which are characteristics of mature beta cells. Electron microscopy showed that they also contained insulin-immunoreactive secretory granules. Some insulin-positive cells were immunoreactive for amylase and cytokeratin-20, or were binucleated, which are characteristics of exocrine cells. The cells were able to restore normoglycaemia when transplanted to alloxan-diabetic mice, and hyperglycaemia recurred upon removal of the graft.

CONCLUSIONS/INTERPRETATION

Our study shows that functional beta cells can be generated from exocrine tissue by transdifferentiation and thereby may offer a new perspective for beta cell therapy.