Historical perspective: beginnings of the beta-cell: current perspectives in beta-cell development

Therapeutic approaches for Type 1 Diabetes: Promising cell-based approaches to achieve ultimate success

Type 1 Diabetes mellitus (T1DM) is a chronic metabolic disorder characterized by pancreatic β-cells destruction. Despite substantial advances in T1DM treatment, lifelong exogenous insulin administration is the mainstay of treatments, and constant control of glucose levels is still a challenge. Endogenous insulin production by replacing insulin-producing cells is an alternative, but the lack of suitable donors is accounted as one of the main obstacles to its widespread application. The research and trials overview demonstrates that endogenous production of insulin has started to go beyond the deceased-derived to stem cells-derived insulin-producing cells. Several protocols have been developed over the past couple of years for generating insulin-producing cells (IPCs) from various stem cell types and reprogramming fully differentiated cells. A straightforward and quick method for achieving this goal is to investigate and apply the β-cell specific transcription factors as a direct strategy for IPCs generation. In this review, we emphasize the significance of transcription factors in IPCs development from different non-beta cell sources, and pertinent research underlies the marked progress in the methods for generating insulin-producing cells and application for Type 1 Diabetes treatment.

Multiple novel functions of circular RNAs in diabetes mellitus

Circular RNAs (circRNAs), as an emerging group of non-coding RNAs (ncRNAs), have received the attention given evidence indicating that these novel ncRNAs are implicated in various biological processes. Due to the absence of 5' and 3' ends in circ-RNAs, their two ends are covalently bonded together, and they are synthesised from pre-mRNAs in a process called back-splicing, which makes them more stable than linear RNAs. There is accumulating evidence showing that circRNAs play a critical role in the pathogenesis of diabetes mellitus (DM). Moreover, it has been indicated that dysregulation of circRNAs has made them promising diagnostic biomarkers for the detection of DM. Recently, increasing attention has been paid to investigate the mechanisms underlying the DM process. It has been demonstrated that there is a strong correlation between the expression of circRNAs and DM. Hence, our aim is to discuss the crosstalk between circRNAs and DM and its complications.

Cell Replacement Therapy for Type 1 Diabetes Patients: Potential Mechanisms Leading to Stem-Cell-Derived Pancreatic β-Cell Loss upon Transplant

Cell replacement therapy using stem-cell-derived insulin-producing β-like cells (sBCs) has been proposed as a practical cure for patients with type one diabetes (T1D). sBCs can correct diabetes in preclinical animal models, demonstrating the promise of this stem cell-based approach. However, in vivo studies have demonstrated that most sBCs, similarly to cadaveric human islets, are lost upon transplantation due to ischemia and other unknown mechanisms. Hence, there is a critical knowledge gap in the current field concerning the fate of sBCs upon engraftment. Here we review, discuss effects, and propose additional potential mechanisms that could contribute toward β-cell loss in vivo. We summarize and highlight some of the literature on phenotypic loss in β-cells under both steady, stressed, and diseased diabetic conditions. Specifically, we focus on β-cell death, dedifferentiation into progenitors, trans-differentiation into other hormone-expressing cells, and/or interconversion into less functional β-cell subtypes as potential mechanisms. While current cell replacement therapy efforts employing sBCs carry great promise as an abundant cell source, addressing the somewhat neglected aspect of β-cell loss in vivo will further accelerate sBC transplantation as a promising therapeutic modality that could significantly enhance the life quality of T1D patients.

On the Origin of Pancreatic Cancer: Molecular Tumor Subtypes in Perspective of Exocrine Cell Plasticity

Pancreatic ductal adenocarcinoma (PDAC) is a devastating type of cancer. While many studies have shed light into the pathobiology of PDAC, the nature of PDAC's cell of origin remains under debate. Studies in adult pancreatic tissue have unveiled a remarkable exocrine cell plasticity including transitional states, mostly exemplified by acinar to ductal cell metaplasia, but also with recent evidence hinting at duct to basal cell transitions. Single-cell RNA sequencing has further revealed intrapopulation heterogeneity among acinar and duct cells. Transcriptomic and epigenomic relationships between these exocrine cell differentiation states and PDAC molecular subtypes have started to emerge, suggesting different ontogenies for different tumor subtypes. This review sheds light on these diverse aspects with particular focus on studies with human cells. Understanding the "masked ball" of exocrine cells at origin of PDAC and leaving behind the binary acinar vs duct cell classification may significantly advance our insights in PDAC biology.

Cell therapy research for Diabetes: Pancreatic β cell differentiation from pluripotent stem cells

Human pluripotent stem cells (PSCs), both embryonic and induced pluripotent stem cells (iPSCs), have been differentiated into pancreatic β isletsin vitrofor more than a decade. The idea is to get enough β cells for cell transplantation for diabetics. Finding a standard cell therapy for diabetes is essential because of the logarithmic increase in the global population of people with diabetes and the insufficient availability of the human cadaveric pancreas. Moreover, with better insights into developmental biology, thein vitroβ cell differentiation protocols have depended on thein vivoβ cell organogenesis. Various protocols for pancreatic β cell differentiation have been developed. Such protocols are based on the modulation of cell signalling pathways with growth factors, small molecules, RNAi approaches, directed differentiation using transcription factors, genome editing. Growth factor free differentiation protocols, epigenetic modulations, 3D differentiation approaches, and encapsulation strategies have also been reported for better glycemic control and endocrine modulations. Here, we have reviewed various aforementionedin vitroβ cell differentiation protocols from human PSCs, their respective comparisons, challenges, past, present, and future. The literature has been reviewed primarily from PubMed from the year 2000 till date using the mentioned keywords.

Beta cell adaptation to pregnancy requires prolactin action on both beta and non-beta cells

Pancreatic islets adapt to insulin resistance of pregnancy by up regulating β-cell mass and increasing insulin secretion. Previously, using a transgenic mouse with global, heterozygous deletion of prolactin receptor (Prlr^+/−), we found Prlr signaling is important for this adaptation. However, since Prlr is expressed in tissues outside of islets as well as within islets and prolactin signaling affects β-cell development, to understand β-cell-specific effect of prolactin signaling in pregnancy, we generated a transgenic mouse with an inducible conditional deletion of Prlr from β-cells. Here, we found that β-cell-specific Prlr reduction in adult mice led to elevated blood glucose, lowed β-cell mass and blunted in vivo glucose-stimulated insulin secretion during pregnancy. When we compared gene expression profile of islets from transgenic mice with global (Prlr^+/−) versus β-cell-specific Prlr reduction (βPrlR^+/−), we found 95 differentially expressed gene, most of them down regulated in the Prlr^+/− mice in comparison to the βPrlR^+/− mice, and many of these genes regulate apoptosis, synaptic vesicle function and neuronal development. Importantly, we found that islets from pregnant Prlr^+/− mice are more vulnerable to glucolipotoxicity-induced apoptosis than islets from pregnant βPrlR^+/− mice. These observations suggest that down regulation of prolactin action during pregnancy in non-β-cells secondarily and negatively affect β-cell gene expression, and increased β-cell susceptibility to external insults.

Islet Regeneration: Endogenous and Exogenous Approaches

Both type 1 and type 2 diabetes are characterized by a progressive loss of beta cell mass that contributes to impaired glucose homeostasis. Although an optimal treatment option would be to simply replace the lost cells, it is now well established that unlike many other organs, the adult pancreas has limited regenerative potential. For this reason, significant research efforts are focusing on methods to induce beta cell proliferation (replication of existing beta cells), promote beta cell formation from alternative endogenous cell sources (neogenesis), and/or generate beta cells from pluripotent stem cells. In this article, we will review (i) endogenous mechanisms of beta cell regeneration during steady state, stress and disease; (ii) efforts to stimulate endogenous regeneration and transdifferentiation; and (iii) exogenous methods of beta cell generation and transplantation.

Signaling Molecules Regulating Pancreatic Endocrine Development from Pluripotent Stem Cell Differentiation

Diabetes is one of the leading causes of death globally. Currently, the donor pancreas is the only source of human islets, placing extreme constraints on supply. Hence, it is imperative to develop renewable islets for diabetes research and treatment. To date, extensive efforts have been made to derive insulin-secreting cells from human pluripotent stem cells with substantial success. However, the in vitro generation of functional islet organoids remains a challenge due in part to our poor understanding of the signaling molecules indispensable for controlling differentiation pathways towards the self-assembly of functional islets from stem cells. Since this process relies on a variety of signaling molecules to guide the differentiation pathways, as well as the culture microenvironments that mimic in vivo physiological conditions, this review highlights extracellular matrix proteins, growth factors, signaling molecules, and microenvironments facilitating the generation of biologically functional pancreatic endocrine cells from human pluripotent stem cells. Signaling pathways involved in stepwise differentiation that guide the progression of stem cells into the endocrine lineage are also discussed. The development of protocols enabling the generation of islet organoids with hormone release capacities equivalent to native adult islets for clinical applications, disease modeling, and diabetes research are anticipated.

MANF Is Required for the Postnatal Expansion and Maintenance of Pancreatic β-Cell Mass in Mice

Global lack of mesencephalic astrocyte-derived neurotropic factor (MANF) leads to progressive postnatal loss of β-cell mass and insulin-dependent diabetes in mice. Similar to Manf^-/- mice, embryonic ablation of MANF specifically from the pancreas results in diabetes. In this study, we assessed the importance of MANF for the postnatal expansion of pancreatic β-cell mass and for adult β-cell maintenance in mice. Detailed analysis of Pdx-1Cre^+/- ::Manf^fl/fl mice revealed mosaic MANF expression in postnatal pancreata and a significant correlation between the number of MANF-positive β-cells and β-cell mass in individual mice. In vitro, recombinant MANF induced β-cell proliferation in islets from aged mice and protected from hyperglycemia-induced endoplasmic reticulum (ER) stress. Consequently, excision of MANF from β-cells of adult MIP-1Cre^ERT::Manf^fl/fl mice resulted in reduced β-cell mass and diabetes caused largely by β-cell ER stress and apoptosis, possibly accompanied by β-cell dedifferentiation and reduced rates of β-cell proliferation. Thus, MANF expression in adult mouse β-cells is needed for their maintenance in vivo. We also revealed a mechanistic link between ER stress and inflammatory signaling pathways leading to β-cell death in the absence of MANF. Hence, MANF might be a potential target for regenerative therapy in diabetes.

Generation of pancreatic β cells for treatment of diabetes: advances and challenges

Human embryonic stem cells (hESC) and induced pluripotent stem cells (hiPSC) are considered attractive sources of pancreatic β cells and islet organoids. Recently, several reports presented that hESC/iPSC-derived cells enriched with specific transcription factors can form glucose-responsive insulin-secreting cells in vitro and transplantation of these cells ameliorates hyperglycemia in diabetic mice. However, the glucose-stimulated insulin-secreting capacity of these cells is lower than that of endogenous islets, suggesting the need to improve induction procedures. One of the critical problems facing in vivo maturation of hESC/iPSC-derived cells is their low survival rate after transplantation, although this rate increases when the implanted pancreatic cells are encapsulated to avoid the immune response. Several groups have also reported on the generation of hESC/iPSC-derived islet-like organoids, but development of techniques for complete islet structures with the eventual generation of vascularized constructs remains a major challenge to their application in regenerative therapies. Many issues also need to be addressed before the successful clinical application of hESC/iPSC-derived cells or islet organoids. In this review, we summarize advances in the generation of hESC/iPSC-derived pancreatic β cells or islet organoids and discuss the limitations and challenges for their successful therapeutic application in diabetes.

Haploinsufficiency of Insm1 Impairs Postnatal Baseline β-Cell Mass

Baseline β-cell mass is established during the early postnatal period when β-cells expand. In this study, we show that heterozygous ablation of Insm1 decreases baseline β-cell mass and subsequently impairs glucose tolerance. When exposed to a high-fat diet or on an ob/ob background, glucose intolerance was more severe in Insm1^+/lacZ mice compared with Insm1^+/+ mice, although no further decrease in the β-cell mass was detected. In islets of early postnatal Insm1^+/lacZ mice, the cell cycle was prolonged in β-cells due to downregulation of the cell cycle gene Ccnd1 Although Insm1 had a low affinity for the Ccnd1 promoter compared with other binding sites, binding affinity was strongly dependent on Insm1 levels. We observed dramatically decreased binding of Insm1 to the Ccnd1 promoter after downregulation of Insm1 expression. Furthermore, downregulation of Ccnd1 resulted in a prolonged cell cycle, and overexpression of Ccnd1 rescued cell cycle abnormalities observed in Insm1-deficient β-cells. We conclude that decreases in Insm1 interfere with β-cell specification during the early postnatal period and impair glucose homeostasis during metabolic stress in adults. Insm1 levels are therefore a factor that can influence the development of diabetes.

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

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

Mechanisms of β-cell dedifferentiation in diabetes: recent findings and future research directions

Like all the cells of an organism, pancreatic β-cells originate from embryonic stem cells through a complex cellular process termed differentiation. Differentiation involves the coordinated and tightly controlled activation/repression of specific effectors and gene clusters in a time-dependent fashion thereby giving rise to particular morphological and functional cellular features. Interestingly, cellular differentiation is not a unidirectional process. Indeed, growing evidence suggests that under certain conditions, mature β-cells can lose, to various degrees, their differentiated phenotype and cellular identity and regress to a less differentiated or a precursor-like state. This concept is termed dedifferentiation and has been proposed, besides cell death, as a contributing factor to the loss of functional β-cell mass in diabetes. β-cell dedifferentiation involves: (1) the downregulation of β-cell-enriched genes, including key transcription factors, insulin, glucose metabolism genes, protein processing and secretory pathway genes; (2) the concomitant upregulation of genes suppressed or expressed at very low levels in normal β-cells, the β-cell forbidden genes; and (3) the likely upregulation of progenitor cell genes. These alterations lead to phenotypic reconfiguration of β-cells and ultimately defective insulin secretion. While the major role of glucotoxicity in β-cell dedifferentiation is well established, the precise mechanisms involved are still under investigation. This review highlights the identified molecular mechanisms implicated in β-cell dedifferentiation including oxidative stress, endoplasmic reticulum (ER) stress, inflammation and hypoxia. It discusses the role of Foxo1, Myc and inhibitor of differentiation proteins and underscores the emerging role of non-coding RNAs. Finally, it proposes a novel hypothesis of β-cell dedifferentiation as a potential adaptive mechanism to escape cell death under stress conditions.

Islet-like organoids derived from human pluripotent stem cells efficiently function in the glucose responsiveness in vitro and in vivo

Insulin secretion is elaborately modulated in pancreatic ß cells within islets of three-dimensional (3D) structures. Using human pluripotent stem cells (hPSCs) to develop islet-like structures with insulin-producing ß cells for the treatment of diabetes is challenging. Here, we report that pancreatic islet-like clusters derived from hESCs are functionally capable of glucose-responsive insulin secretion as well as therapeutic effects. Pancreatic hormone-expressing endocrine cells (ECs) were differentiated from hESCs using a step-wise protocol. The hESC-derived ECs expressed pancreatic endocrine hormones, such as insulin, somatostatin, and pancreatic polypeptide. Notably, dissociated ECs autonomously aggregated to form islet-like, 3D structures of consistent sizes (100–150 μm in diameter). These EC clusters (ECCs) enhanced insulin secretion in response to glucose stimulus and potassium channel inhibition in vitro. Furthermore, ß cell-deficient mice transplanted with ECCs survived for more than 40 d while retaining a normal blood glucose level to some extent. The expression of pancreatic endocrine hormones was observed in tissues transplanted with ECCs. In addition, ECCs could be generated from human induced pluripotent stem cells. These results suggest that hPSC-derived, islet-like clusters may be alternative therapeutic cell sources for treating diabetes.

Sox9b is a mediator of retinoic acid signaling restricting endocrine progenitor differentiation

Centroacinar cells (CACs) are ductal Notch-responsive progenitors that in the larval zebrafish pancreas differentiate to form new islets and ultimately contribute to the majority of the adult endocrine mass. Uncovering the mechanisms regulating CAC differentiation will facilitate understanding how insulin-producing β cells are formed. Previously we reported retinoic acid (RA) signaling and Notch signaling both regulate larval CAC differentiation, suggesting a shared downstream intermediate. Sox9b is a transcription factor important for islet formation whose expression is upregulated by Notch signaling in larval CACs. Here we report that sox9b expression in larval CACs is also regulated by RA signaling. Therefore, we hypothesized that Sox9b is an intermediate between both RA- and Notch-signaling pathways. In order to study the role of Sox9b in larval CACs, we generated two cre/lox based transgenic tools, which allowed us to express full-length or truncated Sox9b in larval CACs. In this way we were able to perform spatiotemporal-controlled Sox9b gain- and loss-of-function studies and observe the subsequent effect on progenitor differentiation. Our results are consistent with Sox9b regulating CAC differentiation by being a downstream intermediate of both RA- and Notch-signaling pathways. We also demonstrate that adult zebrafish with only one functional allele of sox9b undergo accelerated β-cell regeneration, an observation consistent with sox9b regulating CAC differentiation in adults.

The Spatiotemporal Pattern of Glis3 Expression Indicates a Regulatory Function in Bipotent and Endocrine Progenitors during Early Pancreatic Development and in Beta, PP and Ductal Cells

The transcription factor Glis-similar 3 (Glis3) has been implicated in the development of neonatal, type 1 and type 2 diabetes. In this study, we examined the spatiotemporal expression of Glis3 protein during embryonic and neonatal pancreas development as well as its function in PP cells. To obtain greater insights into the functions of Glis3 in pancreas development, we examined the spatiotemporal expression of Glis3 protein in a knockin mouse strain expressing a Glis3-EGFP fusion protein. Immunohistochemistry showed that Glis3-EGFP was not detectable during early pancreatic development (E11.5 and E12.5) and at E13.5 and 15.5 was not expressed in Ptf1a⁺ cells in the tip domains indicating that Glis3 is not expressed in multipotent pancreatic progenitors. Glis3 was first detectable at E13.5 in the nucleus of bipotent progenitors in the trunk domains, where it co-localized with Sox9, Hnf6, and Pdx1. It remained expressed in preductal and Ngn3⁺ endocrine progenitors and at later stages becomes restricted to the nucleus of pancreatic beta and PP cells as well as ductal cells. Glis3-deficiency greatly reduced, whereas exogenous Glis3, induced Ppy expression, as reported for insulin. Collectively, our study demonstrates that Glis3 protein exhibits a temporal and cell type-specific pattern of expression during embryonic and neonatal pancreas development that is consistent with a regulatory role for Glis3 in promoting endocrine progenitor generation, regulating insulin and Ppy expression in beta and PP cells, respectively, and duct morphogenesis.

Insulin-secreting β cells require a post-genomic concept

Pancreatic insulin-secreting β cells are essential in maintaining normal glucose homeostasis accomplished by highly specialized transcription of insulin gene, of which occupies up to 40% their transcriptome. Deficiency of these cells causes diabetes mellitus, a global public health problem. Although tremendous endeavors have been made to generate insulin-secreting cells from human pluripotent stem cells (i.e., primitive cells capable of giving rise to all cell types in the body), a regenerative therapy to diabetes has not yet been established. Furthermore, the nomenclature of β cells has become inconsistent, confusing and controversial due to the lack of standardized positive controls of developmental stage-matched in vivo cells. In order to minimize this negative impact and facilitate critical research in this field, a post-genomic concept of pancreatic β cells might be helpful. In this review article, we will briefly describe how β cells were discovered and islet lineage is developed that may help understand the cause of nomenclatural controversy, suggest a post-genomic definition and finally provide a conclusive remark on future research of this pivotal cell.

Lack of Prox1 Downregulation Disrupts the Expansion and Maturation of Postnatal Murine β-Cells

Transcription factor expression fluctuates during β-cell ontogeny, and disruptions in this pattern can affect the development or function of those cells. Here we uncovered that murine endocrine pancreatic progenitors express high levels of the homeodomain transcription factor Prox1, whereas both immature and mature β-cells scarcely express this protein. We also investigated if sustained Prox1 expression is incompatible with β-cell development or maintenance using transgenic mouse approaches. We discovered that Prox1 upregulation in mature β-cells has no functional consequences; in contrast, Prox1 overexpression in immature β-cells promotes acute fasting hyperglycemia. Using a combination of immunostaining and quantitative and comparative gene expression analyses, we determined that Prox1 upregulation reduces proliferation, impairs maturation, and enables apoptosis in postnatal β-cells. Also, we uncovered substantial deficiency in β-cells that overexpress Prox1 of the key regulator of β-cell maturation MafA, several MafA downstream targets required for glucose-stimulated insulin secretion, and genes encoding important components of FGF signaling. Moreover, knocking down PROX1 in human EndoC-βH1 β-cells caused increased expression of many of these same gene products. These and other results in our study indicate that reducing the expression of Prox1 is beneficial for the expansion and maturation of postnatal β-cells.

Endocrine Pancreas Development and Regeneration: Noncanonical Ideas From Neural Stem Cell Biology

Loss of insulin-producing pancreatic islet β-cells is a hallmark of type 1 diabetes. Several experimental paradigms demonstrate that these cells can, in principle, be regenerated from multiple endogenous sources using signaling pathways that are also used during pancreas development. A thorough understanding of these pathways will provide improved opportunities for therapeutic intervention. It is now appreciated that signaling pathways should not be seen as "on" or "off" but that the degree of activity may result in wildly different cellular outcomes. In addition to the degree of operation of a signaling pathway, noncanonical branches also play important roles. Thus, a pathway, once considered as "off" or "low" may actually be highly operational but may be using noncanonical branches. Such branches are only now revealing themselves as new tools to assay them are being generated. A formidable source of noncanonical signal transduction concepts is neural stem cells because these cells appear to have acquired unusual signaling interpretations to allow them to maintain their unique dual properties (self-renewal and multipotency). We discuss how such findings from the neural field can provide a blueprint for the identification of new molecular mechanisms regulating pancreatic biology, with a focus on Notch, Hes/Hey, and hedgehog pathways.

Human pancreatic beta-like cells converted from fibroblasts

Pancreatic beta cells are of great interest for biomedical research and regenerative medicine. Here we show the conversion of human fibroblasts towards an endodermal cell fate by employing non-integrative episomal reprogramming factors in combination with specific growth factors and chemical compounds. On initial culture, converted definitive endodermal progenitor cells (cDE cells) are specified into posterior foregut-like progenitor cells (cPF cells). The cPF cells and their derivatives, pancreatic endodermal progenitor cells (cPE cells), can be greatly expanded. A screening approach identified chemical compounds that promote the differentiation and maturation of cPE cells into functional pancreatic beta-like cells (cPB cells) in vitro. Transplanted cPB cells exhibit glucose-stimulated insulin secretion in vivo and protect mice from chemically induced diabetes. In summary, our study has important implications for future strategies aimed at generating high numbers of functional beta cells, which may help restoring normoglycemia in patients suffering from diabetes.

Pdx1 regulates pancreas tubulogenesis and E-cadherin expression

Current efforts in developing treatments for diabetes focus on in vitro generation of functional β-cells for cell replacement therapies; however, these attempts have only been partly successful because factors involved in islet formation remain incompletely understood. The embryonic pancreas, which gives rise to β-cells, undergoes early epithelial rearrangements, including transient stratification of an initially monolayered epithelium, followed by microlumen formation and later resolution into branches. Within the epithelium, a multipotent progenitor cell (MPC) population is specified, giving rise to three important lineages: acinar, ductal and endocrine. Pdx1 is a transcription factor required for pancreas development and lineage specification; however, few Pdx1 targets that regulate pancreatogenesis have been identified. We find that pancreatic defects in Pdx1(-/-) embryos initiate at the time when the progenitor pool is specified and the epithelium should resolve into branches. Pdx1(-/-) microlumen diameters expand aberrantly, resulting in failure of epithelial tubulogenesis and ductal plexus formation. Pdx1(-/-) epithelial cell proliferation is decreased and the MPC pool is rapidly lost. We identify two conserved Pdx1 binding sites in the epithelial cadherin (E-cad, Cdh1) promoter, and show that Pdx1 directly binds and activates E-cad transcription. In addition, Pdx1 is required in vivo for maintenance of E-cad expression, actomyosin complex activity and cell shape. These findings demonstrate a novel link between regulators of epithelial architecture, specification of pancreatic cell fate and organogenesis.

A Gene Regulatory Network Cooperatively Controlled by Pdx1 and Sox9 Governs Lineage Allocation of Foregut Progenitor Cells

The generation of pancreas, liver, and intestine from a common pool of progenitors in the foregut endoderm requires the establishment of organ boundaries. How dorsal foregut progenitors activate pancreatic genes and evade the intestinal lineage choice remains unclear. Here, we identify Pdx1 and Sox9 as cooperative inducers of a gene regulatory network that distinguishes the pancreatic from the intestinal lineage. Genetic studies demonstrate dual and cooperative functions for Pdx1 and Sox9 in pancreatic lineage induction and repression of the intestinal lineage choice. Pdx1 and Sox9 bind to regulatory sequences near pancreatic and intestinal differentiation genes and jointly regulate their expression, revealing direct cooperative roles for Pdx1 and Sox9 in gene activation and repression. Our study identifies Pdx1 and Sox9 as important regulators of a transcription factor network that initiates pancreatic fate and sheds light on the gene regulatory circuitry that governs the development of distinct organs from multi-lineage-competent foregut progenitors.

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.

The basic helix-loop-helix transcription factor E47 reprograms human pancreatic cancer cells to a quiescent acinar state with reduced tumorigenic potential

OBJECTIVES

Pancreatic ductal adenocarcinoma (PDA) initiates from quiescent acinar cells that attain a Kras mutation, lose signaling from basic helix-loop-helix (bHLH) transcription factors, undergo acinar-ductal metaplasia, and rapidly acquire increased growth potential. We queried whether PDA cells can be reprogrammed to revert to their original quiescent acinar cell state by shifting key transcription programs.

METHODS

Human PDA cell lines were engineered to express an inducible form of the bHLH protein E47. Gene expression, growth, and functional studies were investigated using microarray, quantitative polymerase chain reaction, immunoblots, immunohistochemistry, small interfering RNA, chromatin immunoprecipitation analyses, and cell transplantation into mice.

RESULTS

In human PDA cells, E47 activity triggers stable G0/G1 arrest, which requires the cyclin-dependent kinase inhibitor p21 and the stress response protein TP53INP1. Concurrently, E47 induces high level expression of acinar digestive enzymes and feed forward activation of the acinar maturation network regulated by the bHLH factor MIST1. Moreover, induction of E47 in human PDA cells in vitro is sufficient to inhibit tumorigenesis.

CONCLUSIONS

Human PDA cells retain a high degree of plasticity, which can be exploited to induce a quiescent acinar cell state with reduced tumorigenic potential. Moreover, bHLH activity is a critical node coordinately regulating human PDA cell growth versus cell fate.

Controlled induction of human pancreatic progenitors produces functional beta-like cells in vitro

Directed differentiation of human pluripotent stem cells into functional insulin-producing beta-like cells holds great promise for cell replacement therapy for patients suffering from diabetes. This approach also offers the unique opportunity to study otherwise inaccessible aspects of human beta cell development and function in vitro. Here, we show that current pancreatic progenitor differentiation protocols promote precocious endocrine commitment, ultimately resulting in the generation of non-functional polyhormonal cells. Omission of commonly used BMP inhibitors during pancreatic specification prevents precocious endocrine formation while treatment with retinoic acid followed by combined EGF/KGF efficiently generates both PDX1(+) and subsequent PDX1(+)/NKX6.1(+) pancreatic progenitor populations, respectively. Precise temporal activation of endocrine differentiation in PDX1(+)/NKX6.1(+) progenitors produces glucose-responsive beta-like cells in vitro that exhibit key features of bona fide human beta cells, remain functional after short-term transplantation, and reduce blood glucose levels in diabetic mice. Thus, our simplified and scalable system accurately recapitulates key steps of human pancreas development and provides a fast and reproducible supply of functional human beta-like cells.

Hnf1b controls pancreas morphogenesis and the generation of Ngn3+ endocrine progenitors

Heterozygous mutations in the human HNF1B gene are associated with maturity-onset diabetes of the young type 5 (MODY5) and pancreas hypoplasia. In mouse, Hnf1b heterozygous mutants do not exhibit any phenotype, whereas the homozygous deletion in the entire epiblast leads to pancreas agenesis associated with abnormal gut regionalization. Here, we examine the specific role of Hnf1b during pancreas development, using constitutive and inducible conditional inactivation approaches at key developmental stages. Hnf1b early deletion leads to a reduced pool of pancreatic multipotent progenitor cells (MPCs) due to decreased proliferation and increased apoptosis. Lack of Hnf1b either during the first or the secondary transitions is associated with cystic ducts. Ductal cells exhibit aberrant polarity and decreased expression of several cystic disease genes, some of which we identified as novel Hnf1b targets. Notably, we show that Glis3, a transcription factor involved in duct morphogenesis and endocrine cell development, is downstream Hnf1b. In addition, a loss and abnormal differentiation of acinar cells are observed. Strikingly, inactivation of Hnf1b at different time points results in the absence of Ngn3(+) endocrine precursors throughout embryogenesis. We further show that Hnf1b occupies novel Ngn3 putative regulatory sequences in vivo. Thus, Hnf1b plays a crucial role in the regulatory networks that control pancreatic MPC expansion, acinar cell identity, duct morphogenesis and generation of endocrine precursors. Our results uncover an unappreciated requirement of Hnf1b in endocrine cell specification and suggest a mechanistic explanation of diabetes onset in individuals with MODY5.

An integrated cell purification and genomics strategy reveals multiple regulators of pancreas development

The regulatory logic underlying global transcriptional programs controlling development of visceral organs like the pancreas remains undiscovered. Here, we profiled gene expression in 12 purified populations of fetal and adult pancreatic epithelial cells representing crucial progenitor cell subsets, and their endocrine or exocrine progeny. Using probabilistic models to decode the general programs organizing gene expression, we identified co-expressed gene sets in cell subsets that revealed patterns and processes governing progenitor cell development, lineage specification, and endocrine cell maturation. Purification of Neurog3 mutant cells and module network analysis linked established regulators such as Neurog3 to unrecognized gene targets and roles in pancreas development. Iterative module network analysis nominated and prioritized transcriptional regulators, including diabetes risk genes. Functional validation of a subset of candidate regulators with corresponding mutant mice revealed that the transcription factors Etv1, Prdm16, Runx1t1 and Bcl11a are essential for pancreas development. Our integrated approach provides a unique framework for identifying regulatory genes and functional gene sets underlying pancreas development and associated diseases such as diabetes mellitus.

Discovery of specific pancreas developmental regulators has accelerated in recent years. In contrast, the global regulatory programs controlling pancreas development are poorly understood compared to other organs or tissues like heart or blood. Decoding this regulatory logic may accelerate development of replacement organs from renewable sources like stem cells, but this goal requires identification of regulators and assessment of their functions on a global scale. To address this important challenge for pancreas biology, we combined purification of normal and mutant cells with genome-scale methods to generate and analyze expression profiles from developing pancreas cells. Our work revealed regulatory gene sets governing development of pancreas progenitor cells and their progeny. Our integrative approach nominated multiple pancreas developmental regulators, including suspected risk genes for human diabetes, which we validated by phenotyping mutant mice on a scale not previously reported. Selection of these candidate regulators was unbiased; thus it is remarkable that all were essential for pancreatic islet development. Thus, our studies provide a new heuristic resource for identifying genetic functions underlying pancreas development and diseases like diabetes mellitus.

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.

In vitro differentiation and expansion of human pluripotent stem cell-derived pancreatic progenitors

Recent progress in understanding stem cell biology has been remarkable, especially in deciphering signals that support differentiation towards tissue-specific lineages. This achievement positions us firmly at the beginning of an era of patient-specific regenerative medicine and human disease modeling. It will be necessary to equip the progress in this era with a reliable source of self-renewing progenitor cells that differentiate into functional target cells. The generation of pancreatic progenitors that mature in vivo into functional beta-cells has raised the hope for new therapeutic options in diabetes, but key challenges still remain including the production of sufficient numbers of cells for research and transplantation. Recent approaches to this problem have shown that the presence of organ- and stage-specific mesenchyme improves the generation of progenitors, from endoderm to endocrine cells. Alternatively, utilization of three-dimensional culture may improve the efficiency and yield of directed differentiation. Here, we review the current knowledge of pancreatic directed differentiation and ex vivo expansion of pancreatic progenitors, including recent advances in differentiation strategies for the generation of pancreatic progenitors, and we discuss persistent challenges which will need to be overcome before personalized cell-based therapy becomes a practical strategy.

Cdc42/N-WASP signaling links actin dynamics to pancreatic β cell delamination and differentiation

Delamination plays a pivotal role during normal development and cancer. Previous work has demonstrated that delamination and epithelial cell movement within the plane of an epithelium are associated with a change in cellular phenotype. However, how this positional change is linked to differentiation remains unknown. Using the developing mouse pancreas as a model system, we show that β cell delamination and differentiation are two independent events, which are controlled by Cdc42/N-WASP signaling. Specifically, we show that expression of constitutively active Cdc42 in β cells inhibits β cell delamination and differentiation. These processes are normally associated with junctional actin and cell-cell junction disassembly and the expression of fate-determining transcription factors, such as Isl1 and MafA. Mechanistically, we demonstrate that genetic ablation of N-WASP in β cells expressing constitutively active Cdc42 partially restores both delamination and β cell differentiation. These findings elucidate how junctional actin dynamics via Cdc42/N-WASP signaling cell-autonomously control not only epithelial delamination but also cell differentiation during mammalian organogenesis.

Analysis of transcription factors key for mouse pancreatic development establishes NKX2-2 and MNX1 mutations as causes of neonatal diabetes in man

Understanding transcriptional regulation of pancreatic development is required to advance current efforts in developing beta cell replacement therapies for patients with diabetes. Current knowledge of key transcriptional regulators has predominantly come from mouse studies, with rare, naturally occurring mutations establishing their relevance in man. This study used a combination of homozygosity analysis and Sanger sequencing in 37 consanguineous patients with permanent neonatal diabetes to search for homozygous mutations in 29 transcription factor genes important for murine pancreatic development. We identified homozygous mutations in 7 different genes in 11 unrelated patients and show that NKX2-2 and MNX1 are etiological genes for neonatal diabetes, thus confirming their key role in development of the human pancreas. The similar phenotype of the patients with recessive mutations and mice with inactivation of a transcription factor gene support there being common steps critical for pancreatic development and validate the use of rodent models for beta cell development.

Pak3 promotes cell cycle exit and differentiation of β-cells in the embryonic pancreas and is necessary to maintain glucose homeostasis in adult mice

The transcription factor neurogenin3 (Ngn3) triggers islet cell differentiation in the developing pancreas. However, little is known about the molecular mechanisms coupling cell cycle exit and differentiation in Ngn3(+) islet progenitors. We identified a novel effector of Ngn3 endocrinogenic function, the p21 protein-activated kinase Pak3, known to control neuronal differentiation and implicated in X-linked intellectual disability in humans. We show that Pak3 expression is initiated in Ngn3(+) endocrine progenitor cells and next maintained in maturing hormone-expressing cells during pancreas development as well as in adult islet cells. In Pak3-deficient embryos, the proliferation of Ngn3(+) progenitors and β-cells is transiently increased concomitantly with an upregulation of Ccnd1. β-Cell differentiation is impaired at E15.5 but resumes at later stages. Pak3-deficient mice do not develop overt diabetes but are glucose intolerant under high-fat diet (HFD). In the intestine, Pak3 is expressed in enteroendocrine cells but is not necessary for their differentiation. Our results indicate that Pak3 is a novel regulator of β-cell differentiation and function. Pak3 acts downstream of Ngn3 to promote cell cycle exit and differentiation in the embryo by a mechanism that might involve repression of Ccnd1. In the adult, Pak3 is required for the proper control of glucose homeostasis under challenging HFD.

Functions and roles of proteins: diabetes as a paradigm

Molecular and cellular biology has moved towards complete and accurate knowledge of how molecules behave in space and time. Protein is considered as the primary group of molecules responsible for mediating most physiological processes. Changes in the levels of proteins may lead to the altered function and are responsible for many diseases. This review provides a partial molecular explanation of biological force-ratio generation that may act to split protein into branches, and shows molecular functional divergence. Developing a non-reductionist theory of the cellular function in medicine is clearly not sufficient. Finding effective parameters of the models by characterizing molecular interactions becomes necessary. Protein interactivity and stability provides a basis for an integrated understanding of pathologies such diabetes. One example of how a mechanistic analysis of such physiological processes can be of value is the time-delay between mRNA and translation that can act as a fork allowing a slowdown in gene expression.

Aldh1-expressing endocrine progenitor cells regulate secondary islet formation in larval zebrafish pancreas

Aldh1 expression is known to mark candidate progenitor populations in adult and embryonic mouse pancreas, and Aldh1 enzymatic activity has been identified as a potent regulator of pancreatic endocrine differentiation in zebrafish. However, the location and identity of Aldh1-expressing cells in zebrafish pancreas remain unknown. In this study we demonstrate that Aldh1-expressing cells are located immediately adjacent to 2F11-positive pancreatic ductal epithelial cells, and that their abundance dramatically increases during zebrafish secondary islet formation. These cells also express neurod, a marker of endocrine progenitor cells, but do not express markers of more mature endocrine cells such as pax6b or insulin. Using formal cre/lox-based lineage tracing, we further show that Aldh1-expressing pancreatic epithelial cells are the direct progeny of pancreatic notch-responsive progenitor cells, identifying them as a critical intermediate between multi-lineage progenitors and mature endocrine cells. Pharmacologic manipulation of Aldh1 enzymatic activity accelerates cell entry into the Aldh1-expressing endocrine progenitor pool, and also leads to the premature maturation of these cells, as evidenced by accelerated pax6b expression. Together, these findings suggest that Aldh1-expressing cells act as both participants and regulators of endocrine differentiation during zebrafish secondary islet formation.

Cooperation by fibroblasts and bone marrow-mesenchymal stem cells to improve pancreatic rat-to-mouse islet xenotransplantation

Experimental and clinical experiences highlight the need to review some aspects of islet transplantation, especially with regard to site of grafting and control of the immune response. The subcutaneous space could be a good alternative to liver but its sparse vasculature is its main limitation. Induction of graft tolerance by using cells with immunoregulatory properties is a promising approach to avoid graft rejection. Both Fibroblasts and Mesenchymal Stem Cells (MSCs) have shown pro-angiogenic and immunomodulatory properties. Transplantation of islets into the subcutaneous space using plasma as scaffold and supplemented with fibroblasts and/or Bone Marrow-MSCs could be a promising strategy to achieve a functional extra-hepatic islet graft, without using immunosuppressive drugs. Xenogenic rat islets, autologous fibroblasts and/or allogenic BM-MSCs, were mixed with plasma, and coagulation was induced to constitute a Plasma-based Scaffold containing Islets (PSI), which was transplanted subcutaneously both in immunodeficient and immunocompetent diabetic mice. In immunodeficient diabetic mice, PSI itself allowed hyperglycemia reversion temporarily, but the presence of pro-angiogenic cells (fibroblasts or BM-MSCs) within PSI was necessary to improve graft re-vascularization and, thus, consistently maintain normoglycemia. In immunocompetent diabetic mice, only PSI containing BM-MSCs, but not those containing fibroblasts, normalized glycemia lasting up to one week after transplantation. Interestingly, when PSI contained both fibroblasts and BM-MSCs, the normoglycemia period showed an increase of 4-times with a physiological-like response in functional tests. Histology of immunocompetent mice showed an attenuation of the immune response in those grafts with BM-MSCs, which was improved by co-transplantation with fibroblasts, since they increased BM-MSC survival. In summary, fibroblasts and BM-MSCs showed similar pro-angiogenic properties in this model of islet xenotransplantation, whereas only BM-MSCs exerted an immunomodulatory effect, which was improved by the presence of fibroblasts. These results suggest that cooperation of different cell types with islets will be required to achieve a long-term functional graft.

Pancreas organogenesis: from lineage determination to morphogenesis

The pancreas is an essential organ for proper nutrient metabolism and has both endocrine and exocrine function. In the past two decades, knowledge of how the pancreas develops during embryogenesis has significantly increased, largely from developmental studies in model organisms. Specifically, the molecular basis of pancreatic lineage decisions and cell differentiation is well studied. Still not well understood are the mechanisms governing three-dimensional morphogenesis of the organ. Strategies to derive transplantable β-cells in vitro for diabetes treatment have benefited from the accumulated knowledge of pancreas development. In this review, we provide an overview of the current understanding of pancreatic lineage determination and organogenesis, and we examine future implications of these findings for treatment of diabetes mellitus through cell replacement.

Conversion of mature human β-cells into glucagon-producing α-cells

Conversion of one terminally differentiated cell type into another (or transdifferentiation) usually requires the forced expression of key transcription factors. We examined the plasticity of human insulin-producing β-cells in a model of islet cell aggregate formation. Here, we show that primary human β-cells can undergo a conversion into glucagon-producing α-cells without introduction of any genetic modification. The process occurs within days as revealed by lentivirus-mediated β-cell lineage tracing. Converted cells are indistinguishable from native α-cells based on ultrastructural morphology and maintain their α-cell phenotype after transplantation in vivo. Transition of β-cells into α-cells occurs after β-cell degranulation and is characterized by the presence of β-cell-specific transcription factors Pdx1 and Nkx6.1 in glucagon(+) cells. Finally, we show that lentivirus-mediated knockdown of Arx, a determinant of the α-cell lineage, inhibits the conversion. Our findings reveal an unknown plasticity of human adult endocrine cells that can be modulated. This endocrine cell plasticity could have implications for islet development, (patho)physiology, and regeneration.

Gene regulatory networks governing pancreas development

Elucidation of cellular and gene regulatory networks (GRNs) governing organ development will accelerate progress toward tissue replacement. Here, we have compiled reference GRNs underlying pancreas development from data mining that integrates multiple approaches, including mutant analysis, lineage tracing, cell purification, gene expression and enhancer analysis, and biochemical studies of gene regulation. Using established computational tools, we integrated and represented these networks in frameworks that should enhance understanding of the surging output of genomic-scale genetic and epigenetic studies of pancreas development and diseases such as diabetes and pancreatic cancer. We envision similar approaches would be useful for understanding the development of other organs.

Liver-specific disruption of the murine glucagon receptor produces α-cell hyperplasia: evidence for a circulating α-cell growth factor

Glucagon is a critical regulator of glucose homeostasis; however, mechanisms regulating glucagon action and α-cell function and number are incompletely understood. To elucidate the role of the hepatic glucagon receptor (Gcgr) in glucagon action, we generated mice with hepatocyte-specific deletion of the glucagon receptor. Gcgr(Hep)(-/-) mice exhibited reductions in fasting blood glucose and improvements in insulin sensitivity and glucose tolerance compared with wild-type controls, similar in magnitude to changes observed in Gcgr(-/-) mice. Despite preservation of islet Gcgr signaling, Gcgr(Hep)(-/-) mice developed hyperglucagonemia and α-cell hyperplasia. To investigate mechanisms by which signaling through the Gcgr regulates α-cell mass, wild-type islets were transplanted into Gcgr(-/-) or Gcgr(Hep)(-/-) mice. Wild-type islets beneath the renal capsule of Gcgr(-/-) or Gcgr(Hep)(-/-) mice exhibited an increased rate of α-cell proliferation and expansion of α-cell area, consistent with changes exhibited by endogenous α-cells in Gcgr(-/-) and Gcgr(Hep)(-/-) pancreata. These results suggest that a circulating factor generated after disruption of hepatic Gcgr signaling can increase α-cell proliferation independent of direct pancreatic input. Identification of novel factors regulating α-cell proliferation and mass may facilitate the generation and expansion of α-cells for transdifferentiation into β-cells and the treatment of diabetes.

Alpha cells come of age

The alpha cells that coinhabit the islets with the insulin-producing beta cells have recently captured the attention of diabetes researchers because of new breakthrough findings highlighting the importance of these cells in the maintenance of beta cell health and functions. In normal physiological conditions alpha cells produce glucagon but in conditions of beta cell injury they also produce glucagon-like peptide-1 (GLP-1), a growth and survival factor for beta cells. In this review we consider these new findings on the functions of alpha cells. Alpha cells remain somewhat enigmatic inasmuch as they now appear to be important in the maintenance of the health of beta cells, but their production of glucagon promotes diabetes. This circumstance prompts an examination of approaches to coax alpha cells to produce GLP-1 instead of glucagon.

GATA6 mutations cause a broad phenotypic spectrum of diabetes from pancreatic agenesis to adult-onset diabetes without exocrine insufficiency

We recently reported de novo GATA6 mutations as the most common cause of pancreatic agenesis, accounting for 15 of 27 (56%) patients with insulin-treated neonatal diabetes and exocrine pancreatic insufficiency requiring enzyme replacement therapy. We investigated the role of GATA6 mutations in 171 subjects with neonatal diabetes of unknown genetic etiology from a cohort of 795 patients with neonatal diabetes. Mutations in known genes had been confirmed in 624 patients (including 15 GATA6 mutations). Sequencing of the remaining 171 patients identified nine new case subjects (24 of 795, 3%). Pancreatic agenesis was present in 21 case subjects (six new); two patients had permanent neonatal diabetes with no enzyme supplementation and one had transient neonatal diabetes. Four parents with heterozygous GATA6 mutations were diagnosed with diabetes outside the neonatal period (12-46 years). Subclinical exocrine insufficiency was demonstrated by low fecal elastase in three of four diabetic patients who did not receive enzyme supplementation. One parent with a mosaic mutation was not diabetic but had a heart malformation. Extrapancreatic features were observed in all 24 probands and three parents, with congenital heart defects most frequent (83%). Heterozygous GATA6 mutations cause a wide spectrum of diabetes manifestations, ranging from pancreatic agenesis to adult-onset diabetes with subclinical or no exocrine insufficiency.

Dynamic chromatin remodeling mediated by polycomb proteins orchestrates pancreatic differentiation of human embryonic stem cells

Embryonic development is characterized by dynamic changes in gene expression, yet the role of chromatin remodeling in these cellular transitions remains elusive. To address this question, we profiled the transcriptome and select chromatin modifications at defined stages during pancreatic endocrine differentiation of human embryonic stem cells. We identify removal of Polycomb group (PcG)-mediated repression on stage-specific genes as a key mechanism for the induction of developmental regulators. Furthermore, we discover that silencing of transitory genes during lineage progression associates with reinstatement of PcG-dependent repression. Significantly, in vivo- but not in vitro-differentiated endocrine cells exhibit close similarity to primary human islets in regard to transcriptome and chromatin structure. We further demonstrate that endocrine cells produced in vitro do not fully eliminate PcG-mediated repression on endocrine-specific genes, probably contributing to their malfunction. These studies reveal dynamic chromatin remodeling during developmental lineage progression and identify possible strategies for improving cell differentiation in culture.

Pancreatic stem cells: from possible to probable

Type 1 and some forms of type 2 diabetes mellitus are caused by deficiency of insulin-secretory islet β cells. An ideal treatment for these diseases would therefore be to replace β cells, either by transplanting donated islets or via endogenous regeneration (and controlling the autoimmunity in type 1 diabetes). Unfortunately, the poor availability of donor islets has severely restricted the broad clinical use of islet transplantation. The ability to differentiate embryonic stem cells into insulin-expressing cells initially showed great promise, but the generation of functional β cells has proven extremely difficult and far slower than originally hoped. Pancreatic stem cells (PSC) or transdifferentiation of other cell types in the pancreas may hence provide an alternative renewable source of surrogate β cells. However, the existence of PSC has been hotly debated for many years. In this review, we will discuss the latest development and future perspectives of PSC research, giving readers an overview of this controversial but important area.

Neonatal β cell development in mice and humans is regulated by calcineurin/NFAT

Little is known about the mechanisms governing neonatal growth and maturation of organs. Here we demonstrate that calcineurin/Nuclear Factor of Activated T cells (Cn/NFAT) signaling regulates neonatal pancreatic development in mouse and human islets. Inactivation of calcineurin b1 (Cnb1) in mouse islets impaired dense core granule biogenesis, decreased insulin secretion, and reduced cell proliferation and mass, culminating in lethal diabetes. Pancreatic β cells lacking Cnb1 failed to express genes revealed to be direct NFAT targets required for replication, insulin storage, and secretion. In contrast, glucokinase activation stimulated Cn-dependent expression of these genes. Calcineurin inhibitors, such as tacrolimus, used for human immunosuppression, induce diabetes. Tacrolimus exposure reduced Cn/NFAT-dependent expression of factors essential for insulin dense core granule formation and secretion and neonatal β cell proliferation, consistent with our genetic studies. Discovery of conserved pathways regulating β cell maturation and proliferation suggests new strategies for controlling β cell growth or replacement in human islet diseases.

Formation of a human β-cell population within pancreatic islets is set early in life

CONTEXT

Insulin resistance can be compensated by increased functional pancreatic β-cell mass; otherwise, diabetes ensues. Such compensation depends not only on environmental and genetic factors but also on the baseline β-cell mass from which the expansion originates.

OBJECTIVE

Little is known about assembly of a baseline β-cell mass in humans. Here, we examined formation of β-cell populations relative to other pancreatic islet cell types and associated neurons throughout the normal human lifespan.

DESIGN AND METHODS

Human pancreatic sections derived from normal cadavers aged 24 wk premature to 72 yr were examined by immunofluorescence. Insulin, glucagon, and somatostatin were used as markers for β-, α-, and δ-cells, respectively. Cytokeratin-19 marked ductal cells, Ki67 cell proliferation, and Tuj1 (neuronal class III β-tubulin) marked neurons.

RESULTS

Most β-cell neogenesis was observed preterm with a burst of β-cell proliferation peaking within the first 2 yr of life. Thereafter, little indication of β-cell growth was observed. Postnatal proliferation of α- and δ-cells was rarely seen, but a wave of ductal cell proliferation was found mostly associated with exocrine cell expansion. The β-cell to α-cell ratio doubled neonatally, reflecting increased growth of β-cells, but during childhood, there was a 7-fold change in the β-cell to δ-cell ratio, reflecting an additional loss of δ-cells. A close association of neurons to pancreatic islets was noted developmentally and retained throughout adulthood. Negligible neuronal association to exocrine pancreas was observed.

CONCLUSION

Human baseline β-cell population and appropriate association with other islet cell types is established before 5 yr of age.

Surrogate insulin-producing cells

Diabetes, a large and growing worldwide health concern, affects the functional mass of the pancreatic beta cell, which in turn affects the glucose regulation of the body. Successful transplantation of cadaveric islets and pancreata for patients with uncontrolled type 1 diabetes has provided proof-of-concept for the development of commercial cell therapy approaches to treat diabetes. Three broad issues must be addressed before surrogate insulin-producing cells can become a reality: the development of a surrogate beta-cell source, immunoprotection, and translation. Cell therapy for diabetes is a real possibility, but many questions remain; through the collaborative efforts of multiple stakeholders this may become a reality.

Synergizing genomic analysis with biological knowledge to identify and validate novel genes in pancreatic development

OBJECTIVE

This study investigated the utility of advanced computational techniques to large-scale genome-based data to identify novel genes that govern murine pancreatic development.

METHODS

An expression data set for mouse pancreatic development was complemented with high-throughput data analyzer to identify and prioritize novel genes. Quantitative real-time polymerase chain reaction, in situ hybridization, and immunohistochemistry were used to validate selected genes.

RESULTS

Four new genes whose roles in the development of murine pancreas have not previously been established were identified: cystathionine β-synthase (Cbs), Meis homeobox 1, growth factor independent 1, and aldehyde dehydrogenase 18 family, member A1. Their temporal expression during development was documented. Cbs was localized in the cytoplasm of the tip cells of the epithelial chords of the undifferentiated progenitor cells at E12.5 and was coexpressed with the pancreatic and duodenal homeobox 1 and pancreas-specific transcription factor, 1a-positive cells. In the adult pancreas, Cbs was localized primarily within the acinar compartment.

CONCLUSIONS

In silico analysis of high-throughput microarray data in combination with background knowledge about genes provides an additional reliable method of identifying novel genes. To our knowledge, the expression and localization of Cbs have not been previously documented during mouse pancreatic development.

Exocrine ontogenies: on the development of pancreatic acinar, ductal and centroacinar cells

This review summarizes our current understanding of exocrine pancreas development, including the formation of acinar, ductal and centroacinar cells. We discuss the transcription factors associated with various stages of exocrine differentiation, from multipotent progenitor cells to fully differentiated acinar and ductal cells. Within the branching epithelial tree of the embryonic pancreas, this involves the progressive restriction of multipotent pancreatic progenitor cells to either a central "trunk" domain giving rise to the islet and ductal lineages, or a peripheral "tip" domain giving rise to acinar cells. This review also discusses the soluble morphogens and other signaling pathways that influence these events. Finally, we examine centroacinar cells as an enigmatic pancreatic cell type whose lineage remains uncertain, and whose possible progenitor capacities continue to be explored.