Expression of neurogenin3 reveals an islet cell precursor population in the pancreas

Estrogen Receptor α Regulates β-Cell Formation During Pancreas Development and Following Injury

Identifying pathways for β-cell generation is essential for cell therapy in diabetes. We investigated the potential of 17β-estradiol (E2) and estrogen receptor (ER) signaling for stimulating β-cell generation during embryonic development and in the severely injured adult pancreas. E2 concentration, ER activity, and number of ERα transcripts were enhanced in the pancreas injured by partial duct ligation (PDL) along with nuclear localization of ERα in β-cells. PDL-induced proliferation of β-cells depended on aromatase activity. The activation of Neurogenin3 (Ngn3) gene expression and β-cell growth in PDL pancreas were impaired when ERα was turned off chemically or genetically (ERα(-/-)), whereas in situ delivery of E2 promoted β-cell formation. In the embryonic pancreas, β-cell replication, number of Ngn3(+) progenitor cells, and expression of key transcription factors of the endocrine lineage were decreased by ERα inactivation. The current study reveals that E2 and ERα signaling can drive β-cell replication and formation in mouse pancreas.

Neurogenin 3 Expressing Cells in the Human Exocrine Pancreas Have the Capacity for Endocrine Cell Fate

Neurogenin 3 (NGN3) is necessary and sufficient for endocrine differentiation during pancreatic development and is expressed by a population of progenitor cells that give rise exclusively to hormone-secreting cells within islets. NGN3 protein can be detected in the adult rodent pancreas only following certain types of injury, when it is transiently expressed by exocrine cells undergoing reprogramming to an endocrine cell fate. Here, NGN3 protein can be detected in 2% of acinar and duct cells in living biopsies of histologically normal adult human pancreata and 10% in cadaveric biopsies of organ donor pancreata. The percentage and total number of NGN3+ cells increase during culture without evidence of proliferation or selective cell death. Isolation of highly purified and viable NGN3+ cell populations can be achieved based on coexpression of the cell surface glycoprotein CD133. Transcriptome and targeted expression analyses of isolated CD133+ / NGN3+ cells indicate that they are distinct from surrounding exocrine tissue with respect to expression phenotype and Notch signaling activity, but retain high level mRNA expression of genes indicative of acinar and duct cell function. NGN3+ cells have an mRNA expression profile that resembles that of mouse early endocrine progenitor cells. During in vitro differentiation, NGN3+ cells express genes in a pattern characteristic of endocrine development and result in cells that resemble beta cells on the basis of coexpression of insulin C-peptide, chromogranin A and pancreatic and duodenal homeobox 1. NGN3 expression in the adult human exocrine pancreas marks a dedifferentiating cell population with the capacity to take on an endocrine cell fate. These cells represent a potential source for the treatment of diabetes either through ex vivo manipulation, or in vivo by targeting mechanisms controlling their population size and endocrine cell fate commitment.

Pancreatic islet cell development and regeneration

PURPOSE OF REVIEW

This review will discuss recent advances in understanding mouse and human pancreatic islet cell development, novel concepts related to β cell dysfunction and improved approaches for replenishing β cells to treat diabetes.

RECENT FINDINGS

Considerable knowledge about pancreatic islet development and function has been gained using model systems with subsequent validation in human tissues. Recently, several rodent studies have revealed that differentiated adult islet cells retain remarkable plasticity and can be converted to other islet cell types by perturbing their transcription factor profiles. Furthermore, significant advances have been made in the generation of β-like cells from stem cell populations. Therefore, the generation of functionally mature β cells by the in-situ conversion of non-β cell populations or by the directed differentiation of human pluripotent stem cells could represent novel mechanisms for replenishing β cells in diabetic patients.

SUMMARY

The overall conservation between mouse and human pancreatic development, islet physiology and etiology of diabetes encourages the translation of novel β cell replacement therapies to humans. Further deciphering the molecular mechanisms that direct islet cell regeneration, plasticity and function could improve and expand the β cell replacement strategies for treating diabetes.

Dissecting Human Gene Functions Regulating Islet Development With Targeted Gene Transduction

During pancreas development, endocrine precursors and their progeny differentiate, migrate, and cluster to form nascent islets. The transcription factor Neurogenin 3 (Neurog3) is required for islet development in mice, but its role in these dynamic morphogenetic steps has been inferred from fixed tissues. Moreover, little is known about the molecular genetic functions of NEUROG3 in human islet development. We developed methods for gene transduction by viral microinjection in the epithelium of cultured Neurog3-null mutant fetal pancreas, permitting genetic complementation in a developmentally relevant context. In addition, we developed methods for quantitative assessment of live-cell phenotypes in single developing islet cells. Delivery of wild-type NEUROG3 rescued islet differentiation, morphogenesis, and live cell deformation, whereas the patient-derived NEUROG3(R107S) allele partially restored indicators of islet development. NEUROG3(P39X), a previously unreported patient allele, failed to restore islet differentiation or morphogenesis and was indistinguishable from negative controls, suggesting that it is a null mutation. Our systems also permitted genetic suppression analysis and revealed that targets of NEUROG3, including NEUROD1 and RFX6, can partially restore islet development in Neurog3-null mutant mouse pancreata. Thus, advances described here permitted unprecedented assessment of gene functions in regulating crucial dynamic aspects of islet development in the fetal pancreas.

Legacy Effect of Foxo1 in Pancreatic Endocrine Progenitors on Adult β-Cell Mass and Function

β-Cell dysfunction in diabetes results from abnormalities of insulin production, secretion, and cell number. These abnormalities may partly arise from altered developmental programming of β-cells. Foxo1 is important to maintain adult β-cells, but little is known about its role in pancreatic progenitor cells as determinants of future β-cell function. We addressed this question by generating an allelic series of somatic Foxo1 knockouts at different stages of pancreatic development in mice. Surprisingly, ablation of Foxo1 in pancreatic progenitors resulted in delayed appearance of Neurogenin3(+) progenitors and their persistence into adulthood as a self-replicating pool, causing a fourfold increase of β-cell mass. Similarly, Foxo1 ablation in endocrine progenitors increased their numbers, extended their survival, and expanded β-cell mass. In contrast, ablation of Foxo1 in terminally differentiated β-cells did not increase β-cell mass nor did it affect Neurogenin3 expression. Despite the increased β-cell mass, islets from mice lacking Foxo1 in pancreatic or endocrine progenitors responded poorly to glucose, resulting in glucose intolerance. We conclude that Foxo1 integrates cues that determine developmental timing, pool size, and functional features of endocrine progenitor cells, resulting in a legacy effect on adult β-cell mass and function. Our results illustrate how developmental programming predisposes to β-cell dysfunction in adults and raise questions on the desirability of increasing β-cell mass for therapeutic purposes in type 2 diabetes.

Development of the endocrine pancreas and novel strategies for β-cell mass restoration and diabetes therapy

Diabetes mellitus represents a serious public health problem owing to its global prevalence in the last decade. The causes of this metabolic disease include dysfunction and/or insufficient number of β cells. Existing diabetes mellitus treatments do not reverse or control the disease. Therefore, β-cell mass restoration might be a promising treatment. Several restoration approaches have been developed: inducing the proliferation of remaining insulin-producing cells, de novo islet formation from pancreatic progenitor cells (neogenesis), and converting non-β cells within the pancreas to β cells (transdifferentiation) are the most direct, simple, and least invasive ways to increase β-cell mass. However, their clinical significance is yet to be determined. Hypothetically, β cells or islet transplantation methods might be curative strategies for diabetes mellitus; however, the scarcity of donors limits the clinical application of these approaches. Thus, alternative cell sources for β-cell replacement could include embryonic stem cells, induced pluripotent stem cells, and mesenchymal stem cells. However, most differentiated cells obtained using these techniques are functionally immature and show poor glucose-stimulated insulin secretion compared with native β cells. Currently, their clinical use is still hampered by ethical issues and the risk of tumor development post transplantation. In this review, we briefly summarize the current knowledge of mouse pancreas organogenesis, morphogenesis, and maturation, including the molecular mechanisms involved. We then discuss two possible approaches of β-cell mass restoration for diabetes mellitus therapy: β-cell regeneration and β-cell replacement. We critically analyze each strategy with respect to the accessibility of the cells, potential risk to patients, and possible clinical outcomes.

Using stem cells to produce insulin

INTRODUCTION

Tremendous progress has been made in generating insulin-producing cells from pluripotent stem cells. The best outcome of the refined protocols became apparent in the first clinical trial announced by ViaCyte, based on the implantation of pancreatic progenitors that would further mature into functional insulin-producing cells inside the patient's body.

AREAS COVERED

Several groups, including ours, have contributed to improve strategies to generate insulin-producing cells. Of note, the latest results have gained a substantial amount of interest as a method to create a potentially functional and limitless supply of β-cell to revert diabetes mellitus. This review analyzes the accomplishments that have taken place over the last few decades, summarizes the state-of-art methods for β-cell replacement therapies based on the differentiation of embryonic stem cells into glucose-responsive and insulin-producing cells in a dish and discusses alternative approaches to obtain new sources of insulin-producing cells.

EXPERT OPINION

Undoubtedly, recent events preface the beginning of a new era in diabetes therapy. However, in our opinion, a number of significant hurdles still stand in the way of clinical application. We believe that the combination of the private and public sectors will accelerate the process of obtaining the desired safe and functional β-cell surrogates.

The Basic Helix-Loop-Helix Transcription Factor NEUROG3 Is Required for Development of the Human Endocrine Pancreas

Neurogenin3 (NEUROG3) is a basic helix-loop-helix transcription factor required for development of the endocrine pancreas in mice. In contrast, humans with NEUROG3 mutations are born with endocrine pancreas function, calling into question whether NEUROG3 is required for human endocrine pancreas development. To test this directly, we generated human embryonic stem cell (hESC) lines where both alleles of NEUROG3 were disrupted using CRISPR/Cas9-mediated gene targeting. NEUROG3(-/-) hESC lines efficiently formed pancreatic progenitors but lacked detectible NEUROG3 protein and did not form endocrine cells in vitro. Moreover, NEUROG3(-/-) hESC lines were unable to form mature pancreatic endocrine cells after engraftment of PDX1(+)/NKX6.1(+) pancreatic progenitors into mice. In contrast, a 75-90% knockdown of NEUROG3 caused a reduction, but not a loss, of pancreatic endocrine cell development. We conclude that NEUROG3 is essential for endocrine pancreas development in humans and that as little as 10% NEUROG3 is sufficient for formation of pancreatic endocrine cells.

Transdifferentiation of Bone Marrow Mesenchymal Stem Cells into the Islet-Like Cells: the Role of Extracellular Matrix Proteins

Pancreatic islet implantation has been recently shown to be an efficient method of treatment for type 1 diabetes. However, limited availability of donor islets reduces its use. Bone morrow would provide potentially unlimited source of stem cells for generation of insulin-producing cells. This study was performed to evaluate the influence of extracellular matrix proteins like collagen, laminin, and vitronectin on bone marrow mesenchymal stem cells (BM-MSCs) transdifferentiation into islet-like cells (ILCs) in vitro. To our knowledge, this is the first report evaluating the importance of vitronectin in transdifferentiation of BM-MSCs into ILCs. Rat BM-MSCs were induced to ILCs using four-step protocol on plates coated with collagen type IV, laminin type I and vitronectin type I. Quantitative real-time PCR was performed to detect gene expression related to pancreatic β cell development. The induced cells expressed islet-related genes including: neurogenin 3, neurogenic differentiation 1, paired box 4, NK homeobox factor 6.1, glucagon, insulin 1 and insulin 2. Laminin but not collagen type IV or vitronectin enhanced expression of insulin and promoted formation of islet-like structures in monolayer culture. Laminin triggered transdifferentiation of BM-MSCs into ILCs.

SOX4 cooperates with neurogenin 3 to regulate endocrine pancreas formation in mouse models

AIMS/HYPOTHESIS

The sex-determining region Y (SRY)-related high mobility group (HMG) box (SOX) family of transcription factors is essential for normal organismal development. Despite the longstanding knowledge that many SOX family members are expressed during pancreas development, a role for many of these factors in the establishment of insulin-producing beta cell fate remains to be determined. The aim of this study is to elucidate the role of SOX4 during beta cell development.

METHODS

We used pancreas and endocrine progenitor mouse knockouts of Sox4 to uncover the roles of SOX4 during pancreas development. Lineage tracing and in vitro models were used to determine how SOX4 regulates beta cell formation and understand the fate of Sox4-null endocrine lineage cells.

RESULTS

This study demonstrates a progenitor cell-autonomous role for SOX4 in regulating the genesis of beta cells and shows that it is required at multiple stages of the process. SOX4 deletion in the multipotent pancreatic progenitors resulted in impaired endocrine progenitor cell differentiation. Deletion of SOX4 later in the Neurog3-expressing cells also caused reductions in beta cells. Lineage studies showed loss of Sox4 in endocrine progenitors resulted in a block in terminal islet cell differentiation that was attributed to reduction in the production of key beta cell specification factors.

CONCLUSIONS/INTERPRETATION

These results demonstrate that SOX4 is essential for normal endocrine pancreas development both concomitant with, and downstream of, the endocrine fate decision. In conclusion, these studies position Sox4 temporally in the endocrine differentiation programme and provide a new target for improving in vitro differentiation of glucose-responsive pancreatic beta cells.

Islet formation in mice and men: lessons for the generation of functional insulin-producing β-cells from human pluripotent stem cells

The Islets of Langerhans are crucial 'micro-organs' embedded in the glandular exocrine pancreas that regulate nutrient metabolism. They not only synthesize, but also secrete endocrine hormones in a modulated fashion in response to physiologic metabolic demand. These highly sophisticated structures with intricate organization of multiple cell types, namely endocrine, vascular, neuronal and mesenchymal cells, have evolved to perform this task to perfection over time. Not surprisingly, islet architecture and function are dissimilar between humans and typically studied model organisms, such as rodents and zebrafish. Further, recent findings also suggest noteworthy differences in human islet development from that in mouse, including delayed appearance and gradual resolution of key differentiation markers, a single-phase of endocrine differentiation, and prenatal association of developing islets with neurovascular milieu. In light of these findings, it is imperative that a systematic study is undertaken to compare islet development between human and mouse. Illuminating inter-species differences in islet development will likely be critical in furthering our pursuit to generate an unlimited supply of truly functional and fully mature β-cells from human pluripotent stem cell (hPSC) sources for therapeutic purposes.

Diabetes enhances the proliferation of adult pancreatic multipotent progenitor cells and biases their differentiation to more β-cell production

Endogenous pancreatic multipotent progenitors (PMPs) are ideal candidates for regenerative approaches to compensate for β-cell loss since their β-cell-producing capacities as well as strategic location would eliminate unnecessary invasive manipulations. However, little is known about the status and potentials of PMPs under diabetic conditions. Here we show that β-cell metabolic stress and hyperglycemia enhance the proliferation capacities of adult PMP cells and bias their production of progeny toward β-cells in mouse and human. These effects are dynamic and correlate with functional β-cell regeneration when conditions allow.

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.

Gαi/o-coupled receptor signaling restricts pancreatic β-cell expansion

Gi-GPCRs, G protein-coupled receptors that signal via Gα proteins of the i/o class (Gαi/o), acutely regulate cellular behaviors widely in mammalian tissues, but their impact on the development and growth of these tissues is less clear. For example, Gi-GPCRs acutely regulate insulin release from pancreatic β cells, and variants in genes encoding several Gi-GPCRs--including the α-2a adrenergic receptor, ADRA2A--increase the risk of type 2 diabetes mellitus. However, type 2 diabetes also is associated with reduced total β-cell mass, and the role of Gi-GPCRs in establishing β-cell mass is unknown. Therefore, we asked whether Gi-GPCR signaling regulates β-cell mass. Here we show that Gi-GPCRs limit the proliferation of the insulin-producing pancreatic β cells and especially their expansion during the critical perinatal period. Increased Gi-GPCR activity in perinatal β cells decreased β-cell proliferation, reduced adult β-cell mass, and impaired glucose homeostasis. In contrast, Gi-GPCR inhibition enhanced perinatal β-cell proliferation, increased adult β-cell mass, and improved glucose homeostasis. Transcriptome analysis detected the expression of multiple Gi-GPCRs in developing and adult β cells, and gene-deletion experiments identified ADRA2A as a key Gi-GPCR regulator of β-cell replication. These studies link Gi-GPCR signaling to β-cell mass and diabetes risk and identify it as a potential target for therapies to protect and increase β-cell mass in patients with diabetes.

Derivation of Endodermal Progenitors From Pluripotent Stem Cells

Stem and progenitor cells play important roles in organogenesis during development and in tissue homeostasis and response to injury postnatally. As the regenerative capacity of many human tissues is limited, cell replacement therapies hold great promise for human disease management. Pluripotent stem cells such as embryonic stem (ES) cells and induced pluripotent stem (iPS) cells are prime candidates for the derivation of unlimited quantities of clinically relevant cell types through development of directed differentiation protocols, that is, the recapitulation of developmental milestones in in vitro cell culture. Tissue-specific progenitors, including progenitors of endodermal origin, are important intermediates in such protocols since they give rise to all mature parenchymal cells. In this review, we focus on the in vivo biology of embryonic endodermal progenitors in terms of key transcription factors and signaling pathways. We critically review the emerging literature aiming to apply this basic knowledge to achieve the efficient and reproducible in vitro derivation of endodermal progenitors such as pancreas, liver and lung precursor cells.

Impaired proliferation of pancreatic beta cells, by reduced placental growth factor in pre-eclampsia, as a cause for gestational diabetes mellitus

OBJECTIVES

Reduced increase in serum placental growth factor (PLGF) levels frequently occurs in patients with pre-eclampsia (PE) and thus has been used as a predictive factor for developing PE. However, it has remained elusive how shortage of PLGF could affect pancreatic endocrine homoeostasis and function in pregnancy to lead to development of gestational diabetes mellitus (GDM).

MATERIALS AND METHODS

We used l-NAME injection in mice, as a model of human PE, in which PLGF levels were significantly reduced.

RESULTS

We not only confirmed reduced serum PLGF levels in patients with PE but also detected strong correlation of serum PLGF levels and presence of GDM. We found that growth of beta cell mass during pregnancy was significantly impaired by l-NAME injection, as a result of reduced beta cell proliferation. This may explain the higher risk of developing GDM in patients with PE. Moreover, provision of exogenous PLGF in l-NAME-treated pregnant mice significantly rescued beta cell proliferation, with subsequent increase in beta cell mass, suggesting that shortage in PLGF may be responsible for impaired beta cell growth and higher occurrence of GDM in patients with PE.

CONCLUSIONS

Our study highlighted a pivotal role for PLGF in prevention and treatment of GDM in patients with PE.

Conditional deletion of Men1 in the pancreatic β-cell leads to glucagon-expressing tumor development

The tumor suppressor menin is recognized as a key regulator of β-cell proliferation. To induce tumorigenesis within the pancreatic β-cells, floxed alleles of Men1 were selectively ablated using Cre-recombinase driven by the insulin promoter. Despite the β-cell specificity of the RipCre, glucagon-expressing tumors as well as insulinomas developed in old mutant mice. These glucagon-expressing tumor cells were menin deficient and expressed the mature α-cell-specific transcription factors Brain-specific homeobox POU domain protein 4 (Brn4) and v-maf musculoaponeurotic fibrosarcoma oncogene family, protein B (MafB). Moreover, the inactivation of β-cell-specific transcription factors was observed in mutant β-cells. Our work shows that Men1 ablation in the pancreatic β-cells leads to the inactivation of specific transcription factors, resulting in glucagon-expressing tumor development, which sheds light on the mechanisms of islet tumorigenesis.

Reprogramming of human pancreatic exocrine cells to β-like cells

Rodent acinar cells exhibit a remarkable plasticity as they can transdifferentiate to duct-, hepatocyte- and islet β-like cells. We evaluated whether exocrine cells from adult human pancreas can similarly respond to proendocrine stimuli. Exocrine cells from adult human pancreas were transduced directly with lentiviruses expressing activated MAPK (mitogen-activated protein kinase) and STAT3 (signal transducer and activator of transcription 3) and cultured as monolayers or as 3D structures. Expression of STAT3 and MAPK in human exocrine cells activated expression of the proendocrine factor neurogenin 3 in 50% to 80% of transduced exocrine cells. However, the number of insulin-positive cells increased only in the exocrine cells grown initially in suspension before 3D culture. Lineage tracing identified human acinar cells as the source of Ngn3- and insulin-expressing cells. Long-term engraftment into immunocompromised mice increased the efficiency of reprogramming to insulin-positive cells. Our data demonstrate that exocrine cells from human pancreas can be reprogrammed to transplantable insulin-producing cells that acquire functionality. Given the large number of exocrine cells in a donor pancreas, this approach presents a novel strategy to expand cell therapy in type 1 diabetes.

RNA-Seq accurately identifies cancer biomarker signatures to distinguish tissue of origin

Metastatic cancer of unknown primary (CUP) accounts for up to 5% of all new cancer cases, with a 5-year survival rate of only 10%. Accurate identification of tissue of origin would allow for directed, personalized therapies to improve clinical outcomes. Our objective was to use transcriptome sequencing (RNA-Seq) to identify lineage-specific biomarker signatures for the cancer types that most commonly metastasize as CUP (colorectum, kidney, liver, lung, ovary, pancreas, prostate, and stomach). RNA-Seq data of 17,471 transcripts from a total of 3,244 cancer samples across 26 different tissue types were compiled from in-house sequencing data and publically available International Cancer Genome Consortium and The Cancer Genome Atlas datasets. Robust cancer biomarker signatures were extracted using a 10-fold cross-validation method of log transformation, quantile normalization, transcript ranking by area under the receiver operating characteristic curve, and stepwise logistic regression. The entire algorithm was then repeated with a new set of randomly generated training and test sets, yielding highly concordant biomarker signatures. External validation of the cancer-specific signatures yielded high sensitivity (92.0% ± 3.15%; mean ± standard deviation) and specificity (97.7% ± 2.99%) for each cancer biomarker signature. The overall performance of this RNA-Seq biomarker-generating algorithm yielded an accuracy of 90.5%. In conclusion, we demonstrate a computational model for producing highly sensitive and specific cancer biomarker signatures from RNA-Seq data, generating signatures for the top eight cancer types responsible for CUP to accurately identify tumor origin.

Pancreatic stem cells remain unresolved

Diabetes mellitus is caused by absolute (type 1) or relative (type 2) deficiency of insulin-secreting islet β cells. An ideal treatment of diabetes would, therefore, be to replace the lost or deficient β cells, by transplantation of donated islets or differentiated endocrine cells or by regeneration of endogenous islet cells. Due to their ability of unlimited proliferation and differentiation into all functional lineages in our body, including β cells, embryonic stem cells and induced pluripotent stem cells are ideally placed as cell sources for a diabetic transplantation therapy. Unfortunately, the inability to generate functional differentiated islet cells from pluripotent stem cells and the poor availability of donor islets have severely restricted the broad clinical use of the replacement therapy. Therefore, endogenous sources that can be directed to becoming insulin-secreting cells are actively sought after. In particular, any cell types in the developing or adult pancreas that may act as pancreatic stem cells (PSC) would provide an alternative renewable source for endogenous regeneration. In this review, we will summarize the latest progress and knowledge of such PSC, and discuss ways that facilitate the future development of this often controversial, but crucial research.

Gastrin induces ductal cell dedifferentiation and β-cell neogenesis after 90% pancreatectomy

Induction of β-cell mass regeneration is a potentially curative treatment for diabetes. We have recently found that long-term gastrin treatment results in improved metabolic control and β-cell mass expansion in 95% pancreatectomised (Px) rats. In this study, we investigated the underlying mechanisms of gastrin-induced β-cell mass expansion after Px. After 90%-Px, rats were treated with gastrin (Px+G) or vehicle (Px+V), pancreatic remnants were harvested on days 1, 3, 5, 7, and 14 and used for gene expression, protein immunolocalisation and morphometric analyses. Gastrin- and vehicle-treated Px rats showed similar blood glucose levels throughout the study. Initially, after Px, focal areas of regeneration, showing mesenchymal cells surrounding ductal structures that expressed the cholecystokinin B receptor, were identified. These focal areas of regeneration were similar in size and cell composition in the Px+G and Px+V groups. However, in the Px+G group, the ductal structures showed lower levels of keratin 20 and β-catenin (indicative of duct dedifferentiation) and higher levels of expression of neurogenin 3 and NKX6-1 (indicative of endocrine progenitor phenotype), as compared with Px+V rats. In Px+G rats, β-cell mass and the number of scattered β-cells were significantly increased compared with Px+V rats, whereas β-cell replication and apoptosis were similar in the two groups. These results indicate that gastrin treatment-enhanced dedifferentiation and reprogramming of regenerative ductal cells in Px rats, increased β-cell neogenesis and fostered β-cell mass expansion.

Insm1 promotes endocrine cell differentiation by modulating the expression of a network of genes that includes Neurog3 and Ripply3

Insulinoma associated 1 (Insm1) plays an important role in regulating the development of cells in the central and peripheral nervous systems, olfactory epithelium and endocrine pancreas. To better define the role of Insm1 in pancreatic endocrine cell development we generated mice with an Insm1^GFPCre reporter allele and used them to study Insm1-expressing and null populations. Endocrine progenitor cells lacking Insm1 were less differentiated and exhibited broad defects in hormone production, cell proliferation and cell migration. Embryos lacking Insm1 contained greater amounts of a non-coding Neurog3 mRNA splice variant and had fewer Neurog3/Insm1 co-expressing progenitor cells, suggesting that Insm1 positively regulates Neurog3. Moreover, endocrine progenitor cells that express either high or low levels of Pdx1, and thus may be biased towards the formation of specific cell lineages, exhibited cell type-specific differences in the genes regulated by Insm1. Analysis of the function of Ripply3, an Insm1-regulated gene enriched in the Pdx1-high cell population, revealed that it negatively regulates the proliferation of early endocrine cells. Taken together, these findings indicate that in developing pancreatic endocrine cells Insm1 promotes the transition from a ductal progenitor to a committed endocrine cell by repressing a progenitor cell program and activating genes essential for RNA splicing, cell migration, controlled cellular proliferation, vasculogenesis, extracellular matrix and hormone secretion.

Systematically labeling developmental stage-specific genes for the study of pancreatic β-cell differentiation from human embryonic stem cells

The applications of human pluripotent stem cell (hPSC)-derived cells in regenerative medicine has encountered a long-standing challenge: how can we efficiently obtain mature cell types from hPSCs? Attempts to address this problem are hindered by the complexity of controlling cell fate commitment and the lack of sufficient developmental knowledge for guiding hPSC differentiation. Here, we developed a systematic strategy to study hPSC differentiation by labeling sequential developmental genes to encompass the major developmental stages, using the directed differentiation of pancreatic β cells from hPSCs as a model. We therefore generated a large panel of pancreas-specific mono- and dual-reporter cell lines. With this unique platform, we visualized the kinetics of the entire differentiation process in real time for the first time by monitoring the expression dynamics of the reporter genes, identified desired cell populations at each differentiation stage and demonstrated the ability to isolate these cell populations for further characterization. We further revealed the expression profiles of isolated NGN3-eGFP(+) cells by RNA sequencing and identified sushi domain-containing 2 (SUSD2) as a novel surface protein that enriches for pancreatic endocrine progenitors and early endocrine cells both in human embryonic stem cells (hESC)-derived pancreatic cells and in the developing human pancreas. Moreover, we captured a series of cell fate transition events in real time, identified multiple cell subpopulations and unveiled their distinct gene expression profiles, among heterogeneous progenitors for the first time using our dual reporter hESC lines. The exploration of this platform and our new findings will pave the way to obtain mature β cells in vitro.

Menin determines K-RAS proliferative outputs in endocrine cells

Endocrine cell proliferation fluctuates dramatically in response to signals that communicate hormone demand. The genetic alterations that override these controls in endocrine tumors often are not associated with oncogenes common to other tumor types, suggesting that unique pathways govern endocrine proliferation. Within the pancreas, for example, activating mutations of the prototypical oncogene KRAS drive proliferation in all pancreatic ductal adenocarcimomas but are never found in pancreatic endocrine tumors. Therefore, we asked how cellular context impacts K-RAS signaling. We found that K-RAS paradoxically suppressed, rather than promoted, growth in pancreatic endocrine cells. Inhibition of proliferation by K-RAS depended on antiproliferative RAS effector RASSF1A and blockade of the RAS-activated proproliferative RAF/MAPK pathway by tumor suppressor menin. Consistent with this model, a glucagon-like peptide 1 (GLP1) agonist, which stimulates ERK1/2 phosphorylation, did not affect endocrine cell proliferation by itself, but synergistically enhanced proliferation when combined with a menin inhibitor. In contrast, inhibition of MAPK signaling created a synthetic lethal interaction in the setting of menin loss. These insights suggest potential strategies both for regenerating pancreatic β cells for people with diabetes and for targeting menin-sensitive endocrine tumors.

Loss of Fbw7 reprograms adult pancreatic ductal cells into α, δ, and β cells

The adult pancreas is capable of limited regeneration after injury but has no defined stem cell population. The cell types and molecular signals that govern the production of new pancreatic tissue are not well understood. Here, we show that inactivation of the SCF-type E3 ubiquitin ligase substrate recognition component Fbw7 induces pancreatic ductal cells to reprogram into α, δ, and β cells. Loss of Fbw7 stabilized the transcription factor Ngn3, a key regulator of endocrine cell differentiation. The induced β cells resemble islet β cells in morphology and histology, express genes essential for β cell function, and release insulin after glucose challenge. Thus, loss of Fbw7 appears to reawaken an endocrine developmental differentiation program in adult pancreatic ductal cells. Our study highlights the plasticity of seemingly differentiated adult cells, identifies Fbw7 as a master regulator of cell fate decisions in the pancreas, and reveals adult pancreatic duct cells as a latent multipotent cell type.

From pancreas morphogenesis to β-cell regeneration

Type 1 diabetes is a metabolic disease resulting in the selective loss of pancreatic insulin-producing β-cells and affecting millions of people worldwide. The side effects of diabetes are varied and include cardiovascular, neuropathologic, and kidney diseases. Despite the most recent advances in diabetes care, patients suffering from type 1 diabetes still display a shortened life expectancy compared to their healthy counterparts. In an effort to improve β-cell-replacement therapies, numerous approaches are currently being pursued, most of these aiming at finding ways to differentiate stem/progenitor cells into β-like cells by mimicking embryonic development. Unfortunately, these efforts have hitherto not allowed the generation of fully functional β-cells. This chapter summarizes recent findings, allowing a better insight into the molecular mechanisms underlying the genesis of β-cells during the course of pancreatic morphogenesis. Furthermore, a focus is made on new research avenues concerning the conversion of pre-existing pancreatic cells into β-like cells, such approaches holding great promise for the development of type 1 diabetes therapies.

Aberrant innate immune activation following tissue injury impairs pancreatic regeneration

Normal tissue architecture is disrupted following injury, as resident tissue cells become damaged and immune cells are recruited to the site of injury. While injury and inflammation are critical to tissue remodeling, the inability to resolve this response can lead to the destructive complications of chronic inflammation. In the pancreas, acinar cells of the exocrine compartment respond to injury by transiently adopting characteristics of progenitor cells present during embryonic development. This process of de-differentiation creates a window where a mature and stable cell gains flexibility and is potentially permissive to changes in cellular fate. How de-differentiation can turn an acinar cell into another cell type (such as a pancreatic β-cell), or a cell with cancerous potential (as in cases of deregulated Kras activity) is of interest to both the regenerative medicine and cancer communities. While it is known that inflammation and acinar de-differentiation increase following pancreatic injury, it remains unclear which immune cells are involved in this process. We used a combination of genetically modified mice, immunological blockade and cellular characterization to identify the immune cells that impact pancreatic regeneration in an in vivo model of pancreatitis. We identified the innate inflammatory response of macrophages and neutrophils as regulators of pancreatic regeneration. Under normal conditions, mild innate inflammation prompts a transient de-differentiation of acinar cells that readily dissipates to allow normal regeneration. However, non-resolving inflammation developed when elevated pancreatic levels of neutrophils producing interferon-γ increased iNOS levels and the pro-inflammatory response of macrophages. Pancreatic injury improved following in vivo macrophage depletion, iNOS inhibition as well as suppression of iNOS levels in macrophages via interferon-γ blockade, supporting the impairment in regeneration and the development of chronic inflammation arises from aberrant activation of the innate inflammatory response. Collectively these studies identify targetable inflammatory factors that can be used to influence the development of non-resolving inflammation and pancreatic regeneration following injury.

Pancreatic differentiation of human dental pulp CD117⁺ stem cells

AIM

Adult stem cells cannot proliferate to produce enough cells for human transplantation with keeping stem cell characteristics shown in the primary culture. We established a novel culture protocol using human dental pulp stem cells (DPSCs) that can produce quantities sufficient for human transplantation. The present study assessed differentiation of DPSCs toward a pancreatic lineage in serum-free conditions, which is essential for safe transplantation.

MATERIALS & METHODS

CD117⁺ stem cells were separated from human exfoliated deciduous teeth (stem cells from human exfoliated deciduous teeth; SHED) and adult DPSCs. The cells were characterized with real-time reverse-transcription PCR for a panel of embryonal lineage markers.

RESULTS

82 out of 84 markers were expressed in different levels in SHED or DPSCs. After pancreatic differentiation in vitro, we found expression of pancreatic-specific endocrine markers insulin, glucagon, somatostatin and pancreatic polypeptide, and exocrine marker amylase-2a in both cultures. We also found reprogramming in both cell cultures mimicking the embryonal stages of development of the pancreas. Transcription factors PDX1, HHEX, MNX1, NEUROG3, PAX4, PAX6 and NKX6-1, crucial markers for the pancreatic development, were all activated. Expression of these factors strongly implies that the cells differentiated toward a distinguished pancreatic lineage.

CONCLUSION

Our results show that CD117⁺ SHED and DPSCs are capable of differentiation toward all functional endocrine and exocrine subsets of pancreatic cells in serum-free conditions. SHED and DPSCs may therefore have great potential for future cell therapy of pancreatic disorders.

Transcriptional control of mammalian pancreas organogenesis

The field of pancreas development has markedly expanded over the last decade, significantly advancing our understanding of the molecular mechanisms that control pancreas organogenesis. This growth has been fueled, in part, by the need to generate new therapeutic approaches for the treatment of diabetes. The creation of sophisticated genetic tools in mice has been instrumental in this progress. Genetic manipulation involving activation or inactivation of genes within specific cell types has allowed the identification of many transcription factors (TFs) that play critical roles in the organogenesis of the pancreas. Interestingly, many of these TFs act at multiple stages of pancreatic development, and adult organ function or repair. Interaction with other TFs, extrinsic signals, and epigenetic regulation are among the mechanisms by which TFs may play context-dependent roles during pancreas organogenesis. Many of the pancreatic TFs directly regulate each other and their own expression. These combinatorial interactions generate very specific gene regulatory networks that can define the different cell lineages and types in the developing pancreas. Here, we review recent progress made in understanding the role of pancreatic TFs in mouse pancreas formation. We also summarize our current knowledge of human pancreas development and discuss developmental pancreatic TFs that have been associated with human pancreatic diseases.

FOXO1 inhibition yields functional insulin-producing cells in human gut organoid cultures

Generation of surrogate sources of insulin-producing β-cells remains a goal of diabetes therapy. While most efforts have been directed at differentiating embryonic or induced pluripotent stem (iPS) cells into β-like-cells through endodermal progenitors, we have shown that gut endocrine progenitor cells of mice can be differentiated into glucose-responsive, insulin-producing cells by ablation of transcription factor Foxo1. Here we show that FOXO1 is present in human gut endocrine progenitor and serotonin-producing cells. Using gut organoids derived from human iPS cells, we show that FOXO1 inhibition using a dominant-negative mutant or lentivirus-encoded shRNA promotes generation of insulin-positive cells that express all markers of mature pancreatic β-cells, release C-peptide in response to secretagogues, and survive in vivo following transplantation into mice. The findings raise the possibility of using gut-targeted FOXO1 inhibition or gut organoids as a source of insulin-producing cells to treat human diabetes.

Generation of insulin-producing β-like cells from human iPS cells in a defined and completely xeno-free culture system

Human induced pluripotent stem (hiPS) cells are considered a potential source for the generation of insulin-producing pancreatic β-cells because of their differentiation capacity. In this study, we have developed a five-step xeno-free culture system to efficiently differentiate hiPS cells into insulin-producing cells in vitro. We found that a high NOGGIN concentration is crucial for specifically inducing the differentiation first into pancreatic and duodenal homeobox-1 (PDX1)-positive pancreatic progenitors and then into neurogenin 3 (NGN3)-expressing pancreatic endocrine progenitors, while suppressing the differentiation into hepatic or intestinal cells. We also found that a combination of 3-isobutyl-1-methylxanthine (IBMX), exendin-4, and nicotinamide was important for the differentiation into insulin single-positive cells that expressed various pancreatic β-cell markers. Most notably, the differentiated cells contained endogenous C-peptide pools that were released in response to various insulin secretagogues and high levels of glucose. Therefore, our results demonstrate the feasibility of generating hiPS-derived pancreatic β-cells under xeno-free conditions and highlight their potential to treat patients with type 1 diabetes.

Transplantation of mesenchymal stem cells recruits trophic macrophages to induce pancreatic beta cell regeneration in diabetic mice

Alleviation of hyperglycemia in chemical-induced diabetic mice has been reported after bone marrow transplantation. Nevertheless, the underlying mechanism remains elusive. In the present study, we transplanted genetically labeled primary mouse mesenchymal stem cells into the pancreas of the streptozotocin-treated hyperglycemic isogeneic mice, resulting in a decrease in blood glucose due to a recovery in beta cell mass. Further analysis revealed that the increase in beta cell mass was predominantly attributable to beta cell replication. The grafted mesenchymal stem cells did not transdifferentiate into beta cells themselves but recruited and polarized macrophages in a Stromal cell-derived factor 1-dependent manner, which in turn promoted beta cell replication. Our finding thus suggests that transplantation of autogenic mesenchymal stem cells may increase functional beta cell mass by boosting beta cell replication in diabetes.

Pax4 and Arx Represent Crucial Regulators of the Development of the Endocrine Pancreas

The development of the endocrine pancreas is under the control of highly orchestrated, cross-interacting transcription factors. Pancreas genesis is initiated by the emergence of a Pdx1/Ptf1a marked territory at the foregut/midgut junction. A small fraction of pancreatic fated cells activates the expression of the bHLH transcription factor Ngn3 triggering the endocrine cell program, thus giving rise to beta-, alpha-, delta-, PP-, and epsilon-cells, producing insulin, glucagon, somatostatin, pancreatic polypeptide, and ghrelin, respectively. Two transcription factors, Pax4 and Arx, play a crucial role in differential endocrine cell subtype specification. They were shown to be necessary and sufficient to endow endocrine progenitors with either a beta- or alpha-cell destiny. Interestingly, whereas the forced expression of Arx in beta-cells converts these into cells exhibiting alpha- and PP-cell characteristics, the sole expression of Pax4 in alpha-cells promotes alpha-cell-neogenesis and the acquisition of beta-cell features, the resulting beta-like cells being capable of counteracting chemically induced diabetes. Gaining new insights into the molecular mechanisms controlling Pax4 and Arx expression in the endocrine pancreas may therefore pave new avenues for the therapy of diabetes.

Silymarin induces expression of pancreatic Nkx6.1 transcription factor and β-cells neogenesis in a pancreatectomy model

A physio-pathological feature of diabetes mellitus is a significant reduction of β-pancreatic cells. The growth, differentiation and function maintenance of these cells is directed by transcription factors. Nkx6.1 is a key transcription factor for the differentiation, neogenesis and maintenance of β-pancreatic cells. We reported that silymarin restores normal morphology and endocrine function of damaged pancreatic tissue after alloxan-induced diabetes mellitus in rats. The aim of this study was to analyze the effect of silymarin on Nkx6.1 transcription factor expression and its consequence in β cells neogenesis. Sixty male Wistar rats were partially pancreatectomized and divided into twelve groups. Six groups were treated with silymarin (200 mg/Kg p.o) for periods of 3, 7, 14, 21, 42 and 63 days. Additionally, an unpancreatectomized control group was used. Nkx6.1 and insulin gene expression were assessed by RT-PCR assay in total pancreatic RNA. β-Cell neogenesis was determined by immunoperoxidase assay. Silymarin treated group showed an increase of Nkx6.1 and insulin genic expression. In this group, there was an increment of β-cell neogenesis in comparison to pancreatectomized untreated group. Silymarin treatment produced a rise in serum insulin and serum glucose normalization. These results suggest that silymarin may improve the reduction of β pancreatic cells observed in diabetes mellitus.

Adult tissue sources for new β cells

The diabetes pandemic incurs extraordinary public health and financial costs that are projected to expand for the foreseeable future. Consequently, the development of definitive therapies for diabetes is a priority. Currently, a wide spectrum of therapeutic strategies-from implantable insulin delivery devices to transplantation-based cell replacement therapy, to β-cell regeneration-focus on replacing the lost insulin-producing capacity of individuals with diabetes. Among these, β-cell regeneration remains promising but heretofore unproved. Indeed, recent experimental work has uncovered surprising biology that underscores the potential therapeutic benefit of β-cell regeneration. These studies have elucidated a variety of sources for the endogenous production of new β cells from existing cells. First, β cells, long thought to be postmitotic, have demonstrated the potential for regenerative capacity. Second, the presence of pancreatic facultative endocrine progenitor cells has been established. Third, the malleability of cellular identity has availed the possibility of generating β cells from other differentiated cell types. Here, we review the exciting developments surrounding endogenous sources of β-cell production and consider the potential of realizing a regenerative therapy for diabetes from adult tissues.

Transplantation of human menstrual blood progenitor cells improves hyperglycemia by promoting endogenous progenitor differentiation in type 1 diabetic mice

Recently, a unique population of progenitor cells was isolated from human menstrual blood. The human menstrual blood progenitor cells (MBPCs) possess many advantages, such as the noninvasive acquisition procedure, broad multipotency, a higher proliferative rate, and low immunogenicity, and have attracted extensive attention in regenerative medicine. Preclinical studies to test the safety and efficacy of MBPCs have been underway in several animal models. However, relevant studies in type 1 diabetes mellitus (T1DM) have not yet been proceeded. Herein, we studied the therapeutic effect of MBPCs and the mechanism of β-cell regeneration after MBPC transplantation in the T1DM model. Intravenous injection of MBPCs can reverse hyperglycemia and weight loss, prolong lifespan, and increase insulin production in diabetic mice. Histological and immunohistochemistry analyses indicated that T1DM mice with MBPC transplantation recovered islet structures and increased the β-cell number. We further analyzed in vivo distribution of MBPCs and discovered that a majority of MBPCs migrated into damaged pancreas and located at the islet, duct, and exocrine tissue. MBPCs did not differentiate into insulin-producing cells, but enhanced neurogenin3 (ngn3) expression, which represented endocrine progenitors that were activated. Ngn3(+) cells were not only in the ductal epithelium, but also in the islet and exocrine tissue. We analyzed a series of genes associated with the embryonic mode of β-cell development by real-time polymerase chain reaction and the results showed that the levels of those gene expressions all increased after cell transplantation. According to the results, we concluded that MBPCs stimulated β-cell regeneration through promoting differentiation of endogenous progenitor cells.

Sequential introduction and dosage balance of defined transcription factors affect reprogramming efficiency from pancreatic duct cells into insulin-producing cells

While the exogenous expression of a combination of transcription factors have been shown to induce the conversion of non-β cells into insulin-producing cells, the reprogramming efficiency remains still low. In order to develop an in vitro screening system for an optimized reprogramming protocol, we generated the reporter cell line mPac-MIP-RFP in which the reprogramming efficiency can be quantified with red fluorescent protein expressed under the control of the insulin promoter. Analysis with mPac-MIP-RFP cells sequentially infected with adenoviruses expressing Pdx1, Neurog3, and Mafa revealed that expression of Pdx1 prior to Neurog3 or Mafa augments the reprogramming efficiency. Next, infection with a polycistronic adenoviral vector expressing Pdx1, Neurog3 and Mafa significantly increased the expression level of insulin compared with the simultaneous infection of three adenoviruses carrying each transcription factor, although excessive expression of Mafa together with the polycistronic vector dramatically inhibited the reprogramming into insulin-producing cells. Thus, in vitro screening with the mPac-MIP-RFP reporter cell line demonstrated that the timing and dosage of gene delivery with defined transcription factors influence the reprogramming efficiency. Further investigation should optimize the reprogramming conditions for the future cell therapy of diabetes.

Extra-nuclear activity of INSM1 transcription factor enhances insulin receptor signaling pathway and Nkx6.1 expression through RACK1 interaction

INSM1 is an islet transcription factor essential for pancreas development. INSM1 functions as a transcriptional repressor of NeuroD/β2 and insulin gene in the pancreas. INSM1 also possesses extra-nuclear activities through binding to multiple cellular regulators such as cyclin D1 and RACK1. In this study, we report that the interaction of INSM1 and RACK1 is essential to enhance the insulin receptor (InR)-mediated signaling pathway. A proline-rich region in the N-terminus of INSM1 is required for RACK1 binding, which interrupts RACK1-InR interaction and enhances InR signal activation. Binding of INSM1 to RACK1 increases AKT phosphorylation. The INSM1-enhanced AKT phosphorylation can be inhibited by the PI3K inhibitor, LY294002. When INSM1 induces AR42J cell trans-differentiation, the Nkx6.1 gene is activated through the InR-mediated signaling pathway and an elevation of the acetyl-H4 modification on the Nkx6.1 gene promoter/enhancer is observed. The PI3K inhibitor interrupts Nkx6.1 and insulin gene expression. Therefore, we conclude that the extra-nuclear activity of INSM1 by enhancing the PI3K/AKT signaling pathway is important for pancreatic cell differentiation.

Increase of beta cell mass by beta cell replication, but not neogenesis, in the maternal pancreas in mice

Strategies for increasing functional beta cell mass are effective for diabetes therapy. Although controversy remains on the existence of facultative beta cell progenitors in the adult pancreas, most evidence does not support such a possibility. One of the greatest physiological increases in beta cells has been detected in the maternal pancreas during pregnancy, following neonatal period and in the setting of insulin resistance. However, no systematical analysis on the beta cell growth in this period has been ever performed. Here we analyzed beta cell replication by quantifying BrdU incorporated beta cells at different time points in the pregnant mice. Similarly, we evaluated the possible involvement of beta cell neogenesis (differentiation from progenitor cells) by analyzing expression of Neurog3, a key determinant of pancreatic endocrine cell neogenesis during embryogenesis, in the exocrine pancreas. We found a dynamic increase in beta cell replication, but failed to detect beta cell neogenesis, demonstrating that beta cell growth in the maternal pancreas during pregnancy is predominantly attributable to beta cell replication, rather than beta cell neogenesis.

Transient cytokine treatment induces acinar cell reprogramming and regenerates functional beta cell mass in diabetic mice

Reprogramming of pancreatic exocrine cells into cells resembling beta cells may provide a strategy for treating diabetes. Here we show that transient administration of epidermal growth factor and ciliary neurotrophic factor to adult mice with chronic hyperglycemia efficiently stimulates the conversion of terminally differentiated acinar cells to beta-like cells. Newly generated beta-like cells are epigenetically reprogrammed, functional and glucose responsive, and they reinstate normal glycemic control for up to 248 d. The regenerative process depends on Stat3 signaling and requires a threshold number of Neurogenin 3 (Ngn3)-expressing acinar cells. In contrast to previous work demonstrating in vivo conversion of acinar cells to beta-like cells by viral delivery of exogenous transcription factors, our approach achieves acinar-to-beta-cell reprogramming through transient cytokine exposure rather than genetic modification.

The window period of NEUROGENIN3 during human gestation

The basic helix-loop-helix transcription factor, NEUROG3, is critical in causing endocrine commitment from a progenitor cell population in the developing pancreas. In human, NEUROG3 has been detected from 8 weeks post-conception (wpc). However, the profile of its production and when it ceases to be detected is unknown. In this study we have defined the profile of NEUROG3 detection in the developing pancreas to give insight into when NEUROG3-dependent endocrine commitment is possible in the human fetus. Immunohistochemistry allowed counting of cells with positively stained nuclei from 7 wpc through to term. mRNA was also isolated from sections of human fetal pancreas and NEUROG3 transcription analyzed by quantitative reverse transcription and polymerase chain reaction. NEUROG3 was detected as expected at 8 wpc. The number of NEUROG3-positive cells increased to peak levels between 10 wpc and 14 wpc. It declined at and after 18 wpc such that it was not detected in human fetal pancreas at 35-41 wpc. Analysis of NEUROG3 transcription corroborated this profile by demonstrating very low levels of transcript at 35-41 wpc, more than 10-fold lower than levels at 12-16 wpc. These data define the appearance, peak and subsequent disappearance of the critical transcription factor, NEUROG3, in human fetal pancreas for the first time. By inference, the window for pancreatic endocrine differentiation via NEUROG3 action opens at 8 wpc and closes between 21 and 35 wpc.

Overexpression of PAX4 reduces glucagon expression in differentiating hESCs

Human embryonic stem cells (hESCs) are pluripotent and capable of generating new β-cells, but current in vitro differentiation protocols generally fail to produce mature, glucose-responsive, unihormonal β-cells. Instead, these methods tend to produce immature polyhormonal endocrine cells which mature in vivo into glucagon-positive α-cells. PAX4 is an established transcription factor in β-cell development and function, and is capable of converting glucagon-positive cells to insulin-positive cells in mice. Work in human and mouse ESCs has shown that constitutive PAX4 expression promotes the development of insulin-positive cells, but whether acute PAX4 expression is sufficient to guide specific endocrine cell fates has not been addressed in hESCs. In this study, we applied recombinant adenovirus to ectopically express human PAX4 in hESC-derived pancreatic progenitors, with the aim of influencing the endocrine developmental cascade away from polyhormonal cells toward unihormonal insulin-positive cells. Gene delivery to pancreatic progenitors was efficient and dose-dependent. By the end of in vitro differentiation, PAX4 reduced ARX expression, but only the high dose tested significantly reduced glucagon release. Single cell analysis revealed that while PAX4 did not alter the proportion of endocrine cells, it did reduce the number of glucagon-positive cells and increased the number of unihormonal insulin-positive cells. These data suggest that acute PAX4 overexpression can reduce expression of ARX and glucagon resulting in improved numbers of unihormonal insulin-positive cells.

Conditional deletion of p53 and Rb in the renin-expressing compartment of the pancreas leads to a highly penetrant metastatic pancreatic neuroendocrine carcinoma

Efforts to model human pancreatic neuroendocrine tumors (PanNETs) in animals have been moderately successful, with minimal evidence for glucagonomas or metastatic spread. The renin gene, although classically associated with expression in the kidney, is also expressed in many other extrarenal tissues including the pancreas. To induce tumorigenesis within rennin-specific tissues, floxed alleles of p53 and Rb were selectively abrogated using Cre-recombinase driven by the renin promoter. The primary neoplasm generated is a highly metastatic islet cell carcinoma of the pancreas. Lineage tracing identifies descendants of renin-expressing cells as pancreatic alpha cells despite a lack of active renin expression in the mature pancreas. Both primary and metastatic tumors express high levels of glucagon; furthermore, an increased level of glucagon is found in the serum, identifying the pancreatic cancer as a functional glucagonoma. This new model is highly penetrant and exhibits robust frequency of metastases to the lymph nodes and the liver, mimicking human disease, and provides a useful platform for better understanding pancreatic endocrine differentiation and development, as well as islet cell carcinogenesis. The use of fluorescent reporters for lineage tracing of the cells contributing to disease initiation and progression provides an unique opportunity to dissect the timeline of disease, examining mechanisms of the metastatic process, as well as recovering primary and metastatic cells for identifying cooperating mutations that are necessary for progression of disease.

Generation of functional insulin-producing cells from mouse embryonic stem cells through 804G cell-derived extracellular matrix and protein transduction of transcription factors

Embryonic stem (ES) and induced pluripotent stem (iPS) cells have potential applications to regenerative medicine for diabetes; however, a useful and safe way to generate pancreatic β cells has not been developed. In this study, we tried to establish an effective method of differentiation through the protein transduction of three transcription factors (Pdx1, NeuroD, and MafA) important to pancreatic β cell development. The method poses no risk of unexpected genetic modifications in target cells. Transduction of the three proteins induced the differentiation of mouse ES and mouse iPS cells into insulin-producing cells. Furthermore, a laminin-5-rich extracellular matrix efficiently induced differentiation under feeder-free conditions. Cell differentiation was confirmed with the expression of the insulin 1 gene in addition to marker genes in pancreatic β cells, the differentiated cells secreted glucose-responsive C-peptide, and their transplantation restored normoglycemia in diabetic mice. Moreover, Pdx1 protein transduction had facilitative effects on differentiation into pancreatic endocrine progenitors from human iPS cells. These results suggest the direct delivery of recombinant proteins and treatment with laminin-5-rich extracellular matrix to be useful for the generation of insulin-producing cells.

WITHDRAWN: Transplantation of mesenchymal stem cells recruits trophic macrophages to induce pancreatic beta cell regeneration in diabetic mice

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