Minireview: transcriptional regulation in pancreatic development

Dynamic regulation of Pdx1 enhancers by Foxa1 and Foxa2 is essential for pancreas development

The onset of pancreas development in the foregut endoderm is marked by activation of the homeobox gene Pdx1 (IPF1). Pdx1 is essential for the expansion of the pancreatic primordium and the development of endocrine islets. The control of Pdx1 expression has been only partially elucidated. We demonstrate here that the winged-helix transcription factors Foxa1 and Foxa2 co-occupy multiple regulatory domains in the Pdx1 gene. Compound conditional ablation of both Foxa1 and Foxa2 in the pancreatic primordium results in complete loss of Pdx1 expression and severe pancreatic hypoplasia. Mutant mice exhibit hyperglycemia with severely disrupted acinar and islet development, and die shortly after birth. Assessment of developmental markers in the mutant pancreas revealed a failure in the expansion of the pancreatic anlage, a blockage of exocrine and endocrine cell differentiation, and an arrest at the primitive duct stage. Comparing their relative developmental activity, we find that Foxa2 is the major regulator in promoting pancreas development and cell differentiation. Using chromatin immunoprecipitations (ChIP) and ChIP sequencing (ChIPSeq) of fetal pancreas and islet chromatin, we demonstrate that Foxa1 and Foxa2 predominantly occupy a distal enhancer at -6.4 kb relative to the transcriptional start site in the Pdx1 gene. In addition, occupancy of the well-characterized proximal Pdx1 enhancer by Foxa1 and Foxa2 is developmental stage-dependent. Thus, the regulation of Pdx1 expression by Foxa1 and Foxa2 is a key early event controlling the expansion and differentiation of the pancreatic primordia.

Menin promotes the Wnt signaling pathway in pancreatic endocrine cells

Menin is a tumor suppressor protein mutated in patients with multiple endocrine neoplasia type 1. We show that menin is essential for canonical Wnt/beta-catenin signaling in cultured rodent islet tumor cells. In these cells, overexpression of menin significantly enhances TCF gene assay reporter activity in response to beta-catenin activation. Contrastingly, inhibition of menin expression with Men1 siRNA decreases TCF reporter gene activity. Likewise, multiple endocrine neoplasia type 1 disease associated missense mutations of menin abrogate the ability to increase TCF reporter gene activity. We show that menin physically interacts with proteins involved in the canonical Wnt signaling pathway, including beta-catenin, TCF3 (TCFL1), and weakly with TCF4 (TCFL2). Menin overexpression increases expression of the Wnt/beta-catenin downstream target gene Axin2, which is associated with increased H3K4 trimethylation of the Axin2 gene promoter. Moreover, inhibition of menin expression by siRNA abrogates H3K4 trimethylation and Axin2 gene expression. Based on these studies, we hypothesized that Wnt signaling could inhibit islet cell proliferation because loss of menin function is thought to increase endocrine tumor cell proliferation. TGP61 rodent islet tumor cells treated with a glycogen synthase kinase 3beta inhibitor that increases Wnt pathway signaling had decreased cell proliferation compared with vehicle-treated cells. Collectively, these data suggest that menin has an essential role in Wnt/beta-catenin signaling through a mechanism that eventually affects histone trimethylation of the downstream target gene Axin2, and activation of Wnt/beta-catenin signaling inhibits islet tumor cell proliferation.

Dicer is required for maintaining adult pancreas

Dicer1, an essential component of RNA interference and the microRNA pathway, has many important roles in the morphogenesis of developing tissues. Dicer1 null mice have been reported to die at E7.5; therefore it is impossible to study its function in adult tissues. We previously reported that Dicer1-hypomorphic mice, whose Dicer1 expression was reduced to 20% in all tissues, were unexpectedly viable. Here we analyzed these mice to ascertain whether the down-regulation of Dicer1 expression has any influence on adult tissues. Interestingly, all tissues of adult (8–10 week old) Dicer1-hypomorphic mice were histologically normal except for the pancreas, whose development was normal at the fetal and neonatal stages; however, morphologic abnormalities in Dicer1-hypomorphic mice were detected after 4 weeks of age. This suggested that Dicer1 is important for maintaining the adult pancreas.

Gene expression analysis in diabetes research

Global gene expression profiling through the use of microarray technology is among the most powerful molecular biological techniques available to diabetes researchers today. In this chapter, we outline how to appropriately perform a microarray experiment using pancreatic islets or total pancreas, based upon over a decade of experience in our laboratory. Through the utilization of careful experimental designs, large numbers of biological replicates, production of high-quality starting material, optimized protocols for hybridization, and sophisticated tools for data processing and statistical analysis, the full potential of high-quality expression profiling can be realized.

Hydrodynamics-based transfection of pancreatic duodenal homeobox 1 DNA improves hyperglycemia and is associated with limited complications in diabetic mice

The biohazards caused by the viral delivery of pancreatic duodenal homeobox gene 1 (Pdx1) to the murine liver limits its application. We aimed to evaluate the feasibility of hydrodynamics-based transfection (HBT) with Pdx1 in improving hyperglycemia. Murine hepatocellular carcinoma (Hepa1-6) cells were transfected with the Pdx1-expressing plasmid, pcDNA3.1/V5-His A (pcDNA)-Pdx1. Hepatic delivery of pcDNA-Pdx1 or pcDNA in streptozocin- induced diabetic mice was achieved by HBT. The sequential serum glucose and alanine aminotransferase (ALT) levels were assessed. On the 3(rd) day after transfection, the transfection efficiency in the Hepa1-6 cells and the mice livers was 5% and 0.35 %, respectively. At 1 wk after HBT, asides from hepatic expression of insulin, the diabetic mice transfected with pcDNA-Pdx1 had a significantly lower sugar (211 +/- 61.6 vs. 413 +/- 62 mg/dL; p = 0.002) level than those transfected with pcDNA; however, the difference diminished afterward. No significant difference in the ALT levels was observed between the 2 groups. No mortality was noted in the mice transfected with pcDNA-Pdx1. The hypoglycemic effect of Pdx1 delivered by HBT was transient and associated with negligible complications. In studies on the short-term biological effects of Pdx1 in vivo, HBT is a potential alternative to viral delivery of Pdx1 to the murine liver.

MIN6 is not a pure beta cell line but a mixed cell line with other pancreatic endocrine hormones

MIN6 cells retains glucose-stimulated insulin secretion (GSIS) as isolated islets. We comprehensively evaluated the gene expression and production of other islet hormones in MIN6 cells. Islet hormones were demonstrated by immunohistochemical staining and measured by ELISA. The gene expression profiles of MIN6 cells were compared with those in the mouse islets obtained by the laser capture micro-dissection (LCM). MIN6 cells excreted insulin, glucagon, somatostatin and ghrelin. They expressed mRNAs of insulin I and II, proglucagon, somatostatin, pancreatic polypeptide (PP) and ghrelin which were shown in the mouse pancreatic islet core and periphery obtained by LCM. A variety of genes closely related to the islet hormone producing cells were expressed in MIN6. Confocal laser scanning microscopy revealed that MIN6 cells included not only insulin positive cells but also insulin and glucagon or somatostin double positive cells. Glucagon, somatostatin and ghrelin were detectable in the culture medium. The present study clearly demonstrated that MIN6 produce pancreatic endocrine cells. It would be possible to use this cell line as a model to research the development, cell differentiation and function of pancreatic islets.

The physiology of rodent beta-cells in pancreas slices

Beta-cells in pancreatic islets form complex syncytia. Sufficient cell-to-cell electrical coupling seems to ensure coordinated depolarization pattern and insulin release that can be further modulated by rich innervation. The complex structure and coordinated action develop after birth during fast proliferation of the endocrine tissue. These emergent properties can be lost due to various reasons later in life and can lead to glucose intolerance and diabetes mellitus. Pancreas slice is a novel method of choice to study the physiology of beta-cells still embedded in their normal cellulo-social context. I present major advantages, list drawbacks and provide an overview on recent advances in our understanding of the physiology of beta-cells using the pancreas slice approach.

The Caenorhabditis elegans vulva: a post-embryonic gene regulatory network controlling organogenesis

The Caenorhabditis elegans vulva is an elegant model for dissecting a gene regulatory network (GRN) that directs postembryonic organogenesis. The mature vulva comprises seven cell types (vulA, vulB1, vulB2, vulC, vulD, vulE, and vulF), each with its own unique pattern of spatial and temporal gene expression. The mechanisms that specify these cell types in a precise spatial pattern are not well understood. Using reverse genetic screens, we identified novel components of the vulval GRN, including nhr-113 in vulA. Several transcription factors (lin-11, lin-29, cog-1, egl-38, and nhr-67) interact with each other and act in concert to regulate target gene expression in the diverse vulval cell types. For example, egl-38 (Pax2/5/8) stabilizes the vulF fate by positively regulating vulF characteristics and by inhibiting characteristics associated with the neighboring vulE cells. nhr-67 and egl-38 regulate cog-1, helping restrict its expression to vulE. Computational approaches have been successfully used to identify functional cis-regulatory motifs in the zmp-1 (zinc metalloproteinase) promoter. These results provide an overview of the regulatory network architecture for each vulval cell type.

The role of incretins in glucose homeostasis and diabetes treatment

Incretins are gut hormones that are secreted from enteroendocrine cells into the blood within minutes after eating. One of their many physiological roles is to regulate the amount of insulin that is secreted after eating. In this manner, as well as others to be described in this review, their final common raison d'être is to aid in disposal of the products of digestion. There are two incretins, known as glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide-1 (GLP-1), that share many common actions in the pancreas but have distinct actions outside of the pancreas. Both incretins are rapidly deactivated by an enzyme called dipeptidyl peptidase 4 (DPP4). A lack of secretion of incretins or an increase in their clearance are not pathogenic factors in diabetes. However, in type 2 diabetes (T2DM), GIP no longer modulates glucose-dependent insulin secretion, even at supraphysiological (pharmacological) plasma levels, and therefore GIP incompetence is detrimental to beta-cell function, especially after eating. GLP-1, on the other hand, is still insulinotropic in T2DM, and this has led to the development of compounds that activate the GLP-1 receptor with a view to improving insulin secretion. Since 2005, two new classes of drugs based on incretin action have been approved for lowering blood glucose levels in T2DM: an incretin mimetic (exenatide, which is a potent long-acting agonist of the GLP-1 receptor) and an incretin enhancer (sitagliptin, which is a DPP4 inhibitor). Exenatide is injected subcutaneously twice daily and its use leads to lower blood glucose and higher insulin levels, especially in the fed state. There is glucose-dependency to its insulin secretory capacity, making it unlikely to cause low blood sugars (hypoglycemia). DPP4 inhibitors are orally active and they increase endogenous blood levels of active incretins, thus leading to prolonged incretin action. The elevated levels of GLP-1 are thought to be the mechanism underlying their blood glucose-lowering effects.

The stability and transactivation potential of the mammalian MafA transcription factor are regulated by serine 65 phosphorylation

The level of the MafA transcription factor is regulated by a variety of effectors of beta cell function, including glucose, fatty acids, and insulin. Here, we show that phosphorylation at Ser(65) of mammalian MafA influences both protein stability and transactivation potential. Replacement of Ser(65) with Glu to mimic phosphorylation produced a protein that was as unstable as the wild type, whereas Asp or Ala mutation blocked degradation. Analysis of MafA chimeric and deletion constructs suggests that protein phosphorylation at Ser(65) alone represents the initial degradation signal, with ubiquitinylation occurring within the C terminus (amino acids 234-359). Although only wild type MafA and S65E were polyubiquitinylated, both S65D and S65E potently stimulated transactivation compared with S65A. Phosphorylation at Ser(14) also enhanced activation, although it had no impact on protein turnover. The mobility of MafA S65A was profoundly affected upon SDS-PAGE, with the S65E and S65D mutants influenced less due to their ability to serve as substrates for glycogen synthase kinase 3, which acts at neighboring N-terminal residues after Ser(65) phosphorylation. Our observations not only illustrate the sensitivity of the cellular transcriptional and degradation machinery to phosphomimetic mutants at Ser(65), but also demonstrate the singular importance of phosphorylation at this amino acid in regulating MafA activity.

Pancreatic transcription factors and their role in the birth, life and survival of the pancreatic beta cell

In recent years major progress has been made in understanding the role of transcription factors in the development of the endocrine pancreas in the mouse. Here we describe how a number of these transcription factors play a role in maintaining the differentiated phenotype of the beta cell, and in the mechanisms that allow the beta cell to adapt to changing metabolic demands that occur throughout life. Amongst these factors, Pdx1 plays a critical role in defining the region of the primitive gut that will form the pancreas, Ngn3 expression drives cells towards an endocrine lineage, and a number of additional proteins including Pdx1, in a second wave of expression, Pax4, NeuroD1/beta2, and MafA act as beta cell differentiation factors. In the mature beta cell Pdx1, MafA, beta2, and Nkx2.2 play important roles in regulating expression of insulin and to some extent other genes responsible for maintaining beta cell function. We emphasise here that data from gene expression studies in rodents seldom map on to the known structure of the corresponding human promoters. In the adult the beta cell is particularly susceptible to autoimmune-mediated attack and to the toxic metabolic milieu associated with over-eating, and utilises a number of these transcription factors in its defence. Pdx1 has anti-apoptotic and proliferative activities that help facilitate the maintenance of beta cell mass, while Ngn3 may be involved in the recruitment of progenitor cells, and Pax4 (and possibly HNF1alpha and Hnf4alpha) in the proliferation of beta cells in the adult pancreas. Other transcription factors with a more widespread pattern of expression that play a role in beta cell survival or proliferation include Foxo1, CREB family members, NFAT, FoxM1, Snail and Asc-2.

Mist1 regulates pancreatic acinar cell proliferation through p21 CIP1/WAF1

BACKGROUND & AIMS

Mist1 is a basic helix-loop-helix (bHLH) transcription factor that is important to the proper development of the exocrine pancreas. The aim of this study was to investigate the role of Mist1 in modulating acinar cell proliferation.

METHODS

Ductal and acinar pancreatic cell lines were engineered to express an inducible Mist1 complementary DNA or to express a short hairpin RNA that targeted endogenous Mist1. Alterations in RNA and protein levels were detected by real-time reverse-transcription polymerase chain reaction and immunoblots. Chromatin immunoprecipitation and reporter gene assays were performed to map Mist1-responsive elements on target genes; the overall proliferation index of acinar cells from Mist1 null pancreata was evaluated by immunohistochemistry.

RESULTS

Expression of Mist1 resulted in a significant decrease in the proliferative potential of cells that was associated with induced expression of p21(CIP1/WAF1). Short hairpin RNA-directed knockdown of p21(CIP1/WAF1) generated cells that were refractory to Mist1 expression, whereas knockdown of Mist1 transcripts or deletion of Mist1 from the mouse genome led to increased cell proliferation and a concomitant decrease in p21(CIP1/WAF1) protein levels. Surprisingly, Mist1-dependent activation of the p21(CIP1/WAF1) promoter was independent of classic basic helix-loop-helix protein binding sites. Instead, Sp1 binding sites were essential for Mist1-dependent transcription, suggesting that Mist1 activates p21(CIP1/WAF1) expression through a unique Sp1 pathway. Indeed, coimmunoprecipitation studies demonstrated that Mist1 and Sp1 were found within the same transcription complex.

CONCLUSIONS

Our results show that Mist1 has a dual role in the development of the exocrine pancreas: controlling cell proliferation and promoting terminal differentiation.

Tissue-specific transcription factors in progression of epithelial tumors

Dedifferentiation and epithelial-mesenchymal transition are important steps in epithelial tumor progression. A central role in the control of functional and morphological properties of different cell types is attributed to tissue-specific transcription factors which form regulatory cascades that define specification and differentiation of epithelial cells during embryonic development. The main principles of the action of such regulatory systems are reviewed on an example of a network of hepatocyte nuclear factors (HNFs) which play a key role in establishment and maintenance of hepatocytes--the major functional type of liver cells. HNFs, described as proteins binding to promoters of most hepatospecific genes, not only control expression of functional liver genes, but are also involved in regulation of proliferation, morphogenesis, and detoxification processes. One of the central components of the hepatospecific regulatory network is nuclear receptor HNF4alpha. Derangement of the expression of this gene is associated with progression of rodent and human hepatocellular carcinomas (HCCs) and contributes to increase of proliferation, loss of epithelial morphology, and dedifferentiation. Dysfunction of HNF4alpha during HCC progression can be either caused by structural changes of this gene or occurs due to modification of up-stream regulatory signaling pathways. Investigations preformed on a model system of the mouse one-step HCC progression have shown that the restoration of HNF4alpha function in dedifferentiated cells causes partial reversion of malignant phenotype both in vitro and in vivo. Derangement of HNFs function was also described in other tumors of epithelial origin. We suppose that tissue-specific factors that underlie the key steps in differentiation programs of certain tissues and are able to receive or modulate signals from the cell environment might be considered as promising candidates for the role of tumor suppressors in the tissue types where they normally play the most significant role.

Insulin protein and proliferation in ductal cells in the transplanted pancreas of patients with type 1 diabetes and recurrence of autoimmunity

AIM/HYPOTHESIS

We investigated whether beta cell neoformation occurs in the transplanted pancreas in patients with type 1 diabetes who had received a simultaneous pancreas-kidney transplant (SPK) and later developed recurrence of autoimmunity.

METHODS

We examined pancreas transplant biopsies from nine SPK patients with or without recurrent autoimmunity or recurrent diabetes and from 16 non-diabetic organ donors. Tissues were analysed by immunohistochemistry and immunofluorescence.

RESULTS

Numerous cytokeratin-19 (CK-19)(+) pancreatic ductal cells stained for insulin in six SPK recipients with recurrent autoimmunity, in five of whom diabetes requiring insulin therapy recurred. These cells also stained for the transcription factor pancreatic-duodenal homeobox-1 (Pdx-1), which is implicated in pancreatic development and beta cell differentiation. The number of insulin(+) ductal cells varied, being highest in the patient with the most severe beta cell loss and lowest in the normoglycaemic patient. In the patient with the most severe beta cell loss, we detected insulin(+)CK-19(+)Pdx-1(+) cells staining for the proliferation-related Ki-67 antigen (Ki-67), indicating proliferation. We were unable to detect Ki-67(+) beta cells within the islets in any SPK patient. Some insulin(+)CK-19(-) ductal cells contained chromogranin A, suggesting further endocrine differentiation. Insulin(+) cells were rarely noted in the pancreas transplant ducts in three SPK patients without islet autoimmunity and in six of 16 non-diabetic organ donors; these insulin(+) cells were never CK-19(+).

CONCLUSIONS/INTERPRETATION

Insulin(+) pancreatic ductal cells, some apparently proliferating, were found in the transplanted pancreas with recurrent islet autoimmunity/diabetes. Replicating beta cells were not detected within islets. The observed changes may represent attempts at tissue remodelling and beta cell regeneration involving ductal cells in the human transplanted pancreas, possibly stimulated by hyperglycaemia and chronic inflammation.

A seriation approach for visualization-driven discovery of co-expression patterns in Serial Analysis of Gene Expression (SAGE) data

Background

Serial Analysis of Gene Expression (SAGE) is a DNA sequencing-based method for large-scale gene expression profiling that provides an alternative to microarray analysis. Most analyses of SAGE data aimed at identifying co-expressed genes have been accomplished using various versions of clustering approaches that often result in a number of false positives.

Principal Findings

Here we explore the use of seriation, a statistical approach for ordering sets of objects based on their similarity, for large-scale expression pattern discovery in SAGE data. For this specific task we implement a seriation heuristic we term ‘progressive construction of contigs’ that constructs local chains of related elements by sequentially rearranging margins of the correlation matrix. We apply the heuristic to the analysis of simulated and experimental SAGE data and compare our results to those obtained with a clustering algorithm developed specifically for SAGE data. We show using simulations that the performance of seriation compares favorably to that of the clustering algorithm on noisy SAGE data.

Conclusions

We explore the use of a seriation approach for visualization-based pattern discovery in SAGE data. Using both simulations and experimental data, we demonstrate that seriation is able to identify groups of co-expressed genes more accurately than a clustering algorithm developed specifically for SAGE data. Our results suggest that seriation is a useful method for the analysis of gene expression data whose applicability should be further pursued.

Isosteviol increases insulin sensitivity and changes gene expression of key insulin regulatory genes and transcription factors in islets of the diabetic KKAy mouse

AIMS

Isosteviol (ISV), a diterpene molecule, is an isomer of the backbone structure of a group of substances with recently proven antidiabetic capabilities in both man and rodents. The aim of this study was to investigate if ISV possesses beneficial effects on the metabolism in the diabetic KKAy mouse and to establish the long-term in vivo effects of ISV on the gene expression profile of key insulin regulatory genes in islets.

METHODS

Twenty KKAy mice, aged 5 weeks, were divided into two groups and treated for 9 weeks with either (i) standard chow diet (control) or (ii) chow + 20 mg/kg body weight of ISV. Blood samples were collected before and after intervention and were subsequently analysed. As a non-diabetic control group, 10 normal C57BL mice were fed with standard chow diet. Gene expression was determined in islets by quantitative real-time RT-PCR and Affymetrix microarray.

RESULTS

We demonstrated that long-term treatment with ISV improves glucose homeostasis, increases insulin sensitivity, lowers plasma triglycerides and lowers weight in the diabetic KKAy mice. Furthermore, ISV markedly changes the gene expression profile of key insulin regulatory genes GLUT2, Ins1, Ins2, Pdx1/Ipf1, Beta2/Neurod1, Pax6 and 11-beta-HSD-1 and beta-cell transcription factors Nkx2-2, Nkx6-1, C/EBPalpha and FoxA2 in isolated islets of the KKAy mice.

CONCLUSIONS

The results indicate that ISV improves glucose and insulin sensitivity as well as improving the lipid profile and upregulates the gene expression of key beta-cell genes, including insulin regulatory transcription factors.

PDX-1 interaction and regulation of the Pancreatic Derived Factor (PANDER, FAM3B) promoter

Pancreatic Derived Factor (PANDER) is a novel cytokine-like protein dominantly expressed within the endocrine pancreas. Our previous study demonstrated that the PANDER promoter was both tissue-specific and glucose-responsive. Surrounding the PANDER transcriptional start site are several putative A- and E-Box elements that may bind to the various pancreatic transcriptional factors of MafA, BETA2/NeuroD, and Pancreatic Duodenal Homeobox-1 (PDX-1). To characterize the transcriptional regulatory factors involved in PANDER gene expression, we performed co-transfection reporter gene analysis and demonstrated upregulation by all three transcription factors, with the greatest individual increase stemming from PDX-1. Potential binding of PDX-1 to A box (TAAT) regions of the PANDER promoter was demonstrated by chromatin immunoprecipitation (ChIP) and further corroborated by electrophoretic mobility shift assay (EMSA). Binding of PDX-1 to the A box regions was inhibited by mutagenized (TAGT) oligonucleotides. Site-directed mutagenesis of the three PDX-1 A box binding motifs revealed that A box sites 2 and 3 in combination were critical for maximal gene expression and deletion resulted in a 82% reduction in promoter activity. Furthermore, deletion of A box sites 2 and 3 completely diminished the glucose-responsiveness of the PANDER promoter. Our findings demonstrate that PANDER is a potential PDX-1 target gene and the A box sites within the promoter region are critical for basal and glucose-stimulated PANDER expression.

Conversion of immortal liver progenitor cells into pancreatic endocrine progenitor cells by persistent expression of Pdx-1

The conversion of expandable liver progenitor cells into pancreatic beta cells would provide a renewable cell source for diabetes cell therapy. Previously, we reported the establishment of liver epithelial progenitor cells (LEPCs). In this work, LEPCs were modified into EGFP/Pdx-1 LEPCs, cells with stable expression of both Pdx-1 and EGFP. Unlike previous work, with persistent expression of Pdx-1, EGFP/Pdx-1 LEPCs acquired the phenotype of pancreatic endocrine progenitor cells rather than giving rise to insulin-producing cells directly. EGFP/Pdx-1 LEPCs proliferated vigorously and expressed the crucial transcription factors involved in beta cell development, including Ngn3, NeuroD, Nkx2.2, Nkx6.1, Pax4, Pax6, Isl1, MafA and endogenous Pdx-1, but did not secrete insulin. When cultured in high glucose/low serum medium supplemented with cytokines, EGFP/Pdx-1 LEPCs stopped proliferating and gave rise to functional beta cells without any evidence of exocrine or other islet cell lineage differentiation. When transplanted into diabetic SCID mice, EGFP/Pdx-1 LEPCs ameliorated hyperglycemia by secreting insulin in a glucose regulated manner. Considering the limited availability of beta cells, we propose that our experiments will provide a framework for utilizing the immortal liver progenitor cells as a renewable cell source for the generation of functional pancreatic beta cells.

Transcription factor expression in the developing human fetal endocrine pancreas

AIMS/HYPOTHESIS

Morphological changes that occur during pancreatic endocrine cell differentiation have been shown in rodent systems to be dependent on sequential alterations in transcription factor expression. However, similar data for humans have been limited. The aim of the present study was to provide a connection between pancreatic morphology, transcription factor gene expression and protein localisation during human fetal development.

METHODS

Human fetal pancreases were examined at early (8-12 weeks of fetal age), middle (14-16 weeks) and late (19-21 weeks) stages, using immunohistological, microarray and qRT-PCR analyses.

RESULTS

We observed a significant decrease in pancreatic duodenal homeobox 1 (PDX-1)(+)/cytokeratin 19(+) cells (p < 0.001), with a simultaneous increase in PDX-1(+)/insulin(+) cells from 8 to 21 weeks (p < 0.05). Increased PDX-1/insulin co-localisation within islet clusters was noted, while no co-expression of PDX-1 with glucagon was found, suggesting that loss of PDX-1 is essential for alpha cell formation. Given that neurogenin 3 (NGN3) expression is critical for establishing the endocrine cell programme in the rodent pancreas, we examined its expression pattern and co-localisation in PDX-1(+), insulin(+) and glucagon(+) cells. Co-localisation of NGN3 with PDX-1, insulin and glucagon was noted during early development, with significant decreases in middle and late stages (p < 0.001). Our microarray and co-localisation analyses of transcription factors linked to NGN3 demonstrated that ISL1 transcription factor (ISL1), neurogenic differentiation 1 (NEUROD1), NK2 related transcription factor related, locus 2 (NKX2-2) and paired box gene 6 (PAX6) were upregulated during development and present in all four endocrine cell types, while NK6 related transcription factor related, locus 1 (NKX6-1) was expressed exclusively in beta cells.

CONCLUSIONS/INTERPRETATION

This study is an important step towards identifying key molecular factors involved in development of the human fetal endocrine pancreas.

Increased insulin sensitivity and changes in the expression profile of key insulin regulatory genes and beta cell transcription factors in diabetic KKAy-mice after feeding with a soy bean protein rich diet high in isoflavone content

High content isoflavone soy protein (SBP) (Abalon) has been found in animal studies to possess beneficial effects on a number of the characteristic features of the insulin resistance syndrome. The aim of this study was to investigate whether SBP exerts beneficial effects on metabolism in the diabetic KKAy-mouse. Furthermore, we investigated the long-term in vivo effect of SBP on the expression profile in islets of key insulin regulatory genes. Twenty KKAy-mice, aged 5 weeks, were divided into 2 groups and treated for 9 weeks with either (A) standard chow diet (control) or (B) chow + 50% SBP. Twenty normal C57BL-mice fed with standard chow diet served as nondiabetic controls (C). Blood samples were collected and analyzed before and after intervention. Gene expression was determined in islets by quantitative real-time RT-PCR and Affymetrix microarray. It was demonstrated that long-term treatment with SBP improves glucose homeostasis, increases insulin sensitivity, and lowers plasma triglycerides in diabetic KKAy-mice. SBP reduces fasting plasma glucose, insulin, triglycerides, and total cholesterol. Furthermore, SBP markedly changes the gene expression profile of key insulin regulatory genes GLUT2, GLUT3, Ins1, Ins2, IGF1, Beta2/Neurod1, cholecystokinin, and LDLr, and proliferative genes in islets isolated from KKAy-mice. After 9 weeks of treatment with SBP, plasma glucose and insulin homeostasis was normalized compared to start levels. The results indicate that SBP improves glucose and insulin sensitivity and up-regulates the expression of key insulin regulatory genes.

Remodeling the exocrine pancreas at metamorphosis in Xenopus laevis

At metamorphosis the Xenopus laevis tadpole exocrine pancreas remodels in two stages. At the climax of metamorphosis thyroid hormone (TH) induces dedifferentiation of the entire exocrine pancreas to a progenitor state. The organ shrinks to 20% of its size, and approximately 40% of its cells die. The acinar cells lose their zymogen granules and approximately 75% of their RNA. The mRNAs that encode exocrine-specific proteins (including the transcription factor Ptf1a) undergo almost complete extinction at climax, whereas PDX-1, Notch-1, and Hes-1, genes implicated in differentiation of the progenitor cells, are activated. At the end of spontaneous metamorphosis when the endogenous TH has reached a low level, the pancreas begins to redifferentiate. Exogenous TH induces the dedifferentiation phase but not the redifferentation phase. The tadpole pancreas lacks the mature ductal system that is found in adult vertebrate pancreases, including the frog. Exocrine pancreases of transgenic tadpoles expressing a dominant negative form of the TH receptor controlled by the elastase promoter are resistant to TH. They do not shrink when subjected to TH. Their acinar cells do not dedifferentiate at climax, nor do they down-regulate exocrine-specific genes or activate Notch-1 and Hes-1. Even 2 months after metamorphosis these frogs have not developed a mature ductal system and the acinar cells are abnormally arranged. The TH-dependent dedifferentiation of the tadpole acinar cells at climax is a necessary step in the formation of a mature frog pancreas.

Identification of transcripts with enriched expression in the developing and adult pancreas

BACKGROUND

Despite recent advances, the transcriptional hierarchy driving pancreas organogenesis remains largely unknown, in part due to the paucity of comprehensive analyses. To address this deficit we generated ten SAGE libraries from the developing murine pancreas spanning Theiler stages 17-26, making use of available Pdx1 enhanced green fluorescent protein (EGFP) and Neurog3 EGFP reporter strains, as well as tissue from adult islets and ducts.

RESULTS

We used a specificity metric to identify 2,536 tags with pancreas-enriched expression compared to 195 other mouse SAGE libraries. We subsequently grouped co-expressed transcripts with differential expression during pancreas development using K-means clustering. We validated the clusters first using quantitative real time PCR and then by analyzing the Theiler stage 22 pancreas in situ hybridization staining patterns of over 600 of the identified genes using the GenePaint database. These were then categorized into one of the five expression domains within the developing pancreas. Based on these results we identified a cascade of transcriptional regulators expressed in the endocrine pancreas lineage and, from this, we developed a predictive regulatory network describing beta-cell development.

CONCLUSION

Taken together, this work provides evidence that the SAGE libraries generated here are a valuable resource for continuing to elucidate the molecular mechanisms regulating pancreas development. Furthermore, our studies provide a comprehensive analysis of pancreas development, and insights into the regulatory networks driving this process are revealed.

Neonatal and late-onset diabetes mellitus caused by failure of pancreatic development: report of 4 more cases and a review of the literature

OBJECTIVE

Permanent neonatal diabetes mellitus caused by developmental failure of the pancreas is rare. Thus far, only a few genetic causes have been reported. We now report the clinical and genetic aspects of 4 more cases of permanent neonatal diabetes mellitus caused by pancreatic agenesis or hypoplasia.

PATIENTS AND METHODS

All 4 of the patients were from consanguineous kinships, and all presented with diabetes mellitus and pancreatic exocrine insufficiency. Three patients had pancreatic agenesis, and 1 had pancreatic hypoplasia on computed tomography scan. DNA was extracted from blood samples of patients and unaffected family members. Specific genes were amplified by polymerase chain reaction and characterized by DNA sequencing.

RESULTS

Several genes that encode transcription factors that have known roles in pancreas development were characterized in the affected children and unaffected family members. These genes include Pdx1, the master regulator of pancreas development and beta-cell differentiation, and other transcription factors that are expressed early in pancreas development, namely, Ptf1a, Sox9, Sox17, Hnf6, and HlxB9. Several novel polymorphisms were found in our patients. However, these were also present in unaffected individuals. No disease-causing mutations were found in any of these genes.

CONCLUSIONS

These findings add to the 4 cases already in the literature in which the Pdx1 structural gene has been found to be normal in patients with pancreatic agenesis or hypoplasia. The analysis here has been extended to include the screening of 4 other candidate genes in addition to promoter elements upstream of the Pdx1. Two of the cases occurred in a sibling pair, and 2 were isolated, so there may be more than 1 etiology in the cases reported here.

Neonatal diabetes mellitus

An explosion of work over the last decade has produced insight into the multiple hereditary causes of a nonimmunological form of diabetes diagnosed most frequently within the first 6 months of life. These studies are providing increased understanding of genes involved in the entire chain of steps that control glucose homeostasis. Neonatal diabetes is now understood to arise from mutations in genes that play critical roles in the development of the pancreas, of beta-cell apoptosis and insulin processing, as well as the regulation of insulin release. For the basic researcher, this work is providing novel tools to explore fundamental molecular and cellular processes. For the clinician, these studies underscore the need to identify the genetic cause underlying each case. It is increasingly clear that the prognosis, therapeutic approach, and genetic counseling a physician provides must be tailored to a specific gene in order to provide the best medical care.

The 45-kDa form of Pdx-1 does not result from post-translational modifications

Pdx-1 is a key regulator of glucose-stimulated insulin gene transcription in beta-cells. The regulation of Pdx-1 in response to glucose has previously been associated with a remarkable shift in electrophoretic mobility on SDS-PAGE from 31 to 45kDa. This has been attributed to different post-translational modifications including phosphorylation, sumoylation or glycosylation. However, and in contrast with previous studies, we describe in this paper that Pdx-1 produced in Escherichia coli, by in vitro transcription/translation or exogenously expressed in eukaryotic cells, migrates with an apparent molecular mass of 45kDa despite a calculated mass of 31kDa. Moreover, we show that the migration of endogenous Pdx-1 obtained from a mouse beta-cell line as well as from human primary islets is not dependent on glucose concentration. Taken together, these data, validated by mass spectrometry techniques, establish that anomalous migration of Pdx-1 on SDS-PAGE does not result from post-translational modifications.

Stimulation of human and rat islet beta-cell proliferation with retention of function by the homeodomain transcription factor Nkx6.1

The homeodomain transcription factor Nkx6.1 plays an important role in pancreatic islet beta-cell development, but its effects on adult beta-cell function, survival, and proliferation are not well understood. In the present study, we demonstrated that treatment of primary rat pancreatic islets with a cytomegalovirus promoter-driven recombinant adenovirus containing the Nkx6.1 cDNA (AdCMV-Nkx6.1) causes dramatic increases in [methyl-(3)H] thymidine and 5-bromo-2'-deoxyuridine (BrdU) incorporation and in the number of cells per islet relative to islets treated with a control adenovirus (AdCMV-betaGAL), whereas suppression of Nkx6.1 expression reduces thymidine incorporation. Immunocytochemical studies reveal that >80% of BrdU-positive cells in AdCMV-Nkx6.1-treated islets are beta cells. Microarray, real-time PCR, and immunoblot analyses reveal that overexpression of Nkx6.1 in rat islets causes concerted upregulation of a cadre of cell cycle control genes, including those encoding cyclins A, B, and E, and several regulatory kinases. Cyclin E is upregulated earlier than the other cyclins, and adenovirus-mediated overexpression of cyclin E is shown to be sufficient to activate islet cell proliferation. Moreover, chromatin immunoprecipitation assays demonstrate direct interaction of Nkx6.1 with the cyclin A2 and B1 genes. Overexpression of Nkx6.1 in rat islets caused a clear enhancement of glucose-stimulated insulin secretion (GSIS), whereas overexpression of Nkx6.1 in human islets caused an increase in the level of [(3)H]thymidine incorporation that was twice the control level, along with complete retention of GSIS. We conclude that Nkx6.1 is among the very rare factors capable of stimulating beta-cell replication with retention or enhancement of function, properties that may be exploitable for expansion of beta-cell mass in treatment of both major forms of diabetes.

Defining pancreatic endocrine precursors and their descendants

OBJECTIVE

The global incidence of diabetes continues to increase. Cell replacement therapy and islet transplantation offer hope, especially for severely affected patients. Efforts to differentiate insulin-producing beta-cells from progenitor or stem cells require knowledge of the transcriptional programs that regulate the development of the endocrine pancreas.

RESEARCH DESIGN AND METHODS

Differentiation toward the endocrine lineage is dependent on the transcription factor Neurogenin 3 (Neurog3, Ngn3). We utilize a Neurog3-enhanced green fluorescent protein knock-in mouse model to isolate endocrine progenitor cells from embryonic pancreata (embryonic day [E]13.5 through E17.5). Using advanced genomic approaches, we generate a comprehensive gene expression profile of these progenitors and their immediate descendants.

RESULTS

A total of 1,029 genes were identified as being temporally regulated in the endocrine lineage during fetal development, 237 of which are transcriptional regulators. Through pathway analysis, we have modeled regulatory networks involving these proteins that highlight the complex transcriptional hierarchy governing endocrine differentiation.

CONCLUSIONS

We have been able to accurately capture the gene expression profile of the pancreatic endocrine progenitors and their descendants. The list of temporally regulated genes identified in fetal endocrine precursors and their immediate descendants provides a novel and important resource for developmental biologists and diabetes researchers alike.

Pdx-1-independent differentiation of mouse embryonic stem cells into insulin-expressing cells

To investigate whether insulin-producing cells obtained from ES cells via the nestin-positive cell-mediated method are of the pancreatic lineage, we established a pdx-1 knockout ES cell line and analyzed its differentiation into insulin-producing cells. As a result, pdx-1 knockout ES cell expressed insulin 2 gene at the final differentiated cells. Thus, our study demonstrated that pdx-1 is not essential for insulin gene expression, at least in cells differentiated from this population of nestin-expression enriched ES cells, and suggested that the insulin-producing cells derived from ES cells may be different from the pancreatic beta cells in terms of their lineage.

siRNA specific to Pdx-1 disturbed the formation of the islet in early zebrafish embryos

Pdx-1, an important transcription factor highlighting in the early pancreatic development, islet functions and pancreatic disorders, needs to be more investigated in zebrafish, and siRNA is still seldom applied in zebrafish embryo-related research. Our aim was to explore the role of pdx-1 in pancreatic development of zebrafish embryos by using siRNA approach. Microinjection, reverse transcriptase-PCR (RT-PCR), in situ hybridization and immunofluorescent staining were used in this research, and the morphology of the islet in normal zebrafish embryos, and in those treated with the siRNA specific to pdx-1 (siPDX-1) or siGFP was observed and compared. The expression of pdx-1 was detected in the stages of 1-cell, 2-cell, 4-cell, 8-cell, 16-cell, 16-hour by RT-PCT. The in situ hybridization and immunofluorescent staining results showed that siPDX-1 disturbed the formation of the islet in zebrafish embryos. Pdx-1 played multiple roles in maintaining the phenotype of the islet during embryogenesis in zebrafish.

Genomewide expression analysis in zebrafish mind bomb alleles with pancreas defects of different severity identifies putative Notch responsive genes

Background

Notch signaling is an evolutionarily conserved developmental pathway. Zebrafish mind bomb (mib) mutants carry mutations on mib gene, which encodes a RING E3 ligase required for Notch activation via Delta/Jagged ubiquitylation and internalization.

Methodology/Principal Findings

We examined the mib mutants for defects in pancreas development using in situ hybridization and GFP expression analysis of pancreas-specific GFP lines, carried out the global gene expression profile analysis of three different mib mutant alleles and validated the microarray data using real-time PCR and fluorescent double in situ hybridization. Our study showed that the mib mutants have diminished exocrine pancreas and this defect was most severe in mib^ta52b followed by mib^m132 and then mib^tfi91, which is consistent with the compromised Notch activity found in corresponding mib mutant alleles. Global expression profile analysis of mib mutants showed that there is a significant difference in gene expression profile of wt and three mib mutant alleles. There are 91 differentially expressed genes that are common to all three mib alleles. Through detailed analysis of microarray data, we have identified several previously characterized genes and some putative Notch-responsive genes involved in pancreas development. Moreover, results from real-time PCR and fluorescent double in situ hybridization were largely consistent with microarray data.

Conclusions/Significance

This study provides, for the first time, a global gene expression profile in mib mutants generating useful genomic resources and providing an opportunity to identify the function of novel genes involved in Notch signaling and Notch-regulated developmental processes.

Alpha-fetoprotein is dynamically expressed in rat pancreas during development

To identify proteins involved in pancreatic development, we used a differential proteomics approach by comparing pancreatic extracts from four biologically significant stages of development: embryonic day (E) 15.5, E18.5, postnatal (P) days 0 and adult. By two-dimensional gel electrophoresis (2D-E) and MALDI-TOF MS (Matrix Assisted Laser Desorption/Ionization Time-Of-Flight Mass Spectrometry) following database searching and protein annotation, 15 proteins were identified as being differently expressed in the pancreas between the four phases. The expression pattern and the localization of alpha-fetoprotein (AFP), one of significant changed proteins observed, were further determined. Four isoforms of AFP (72 kDa, 60 kDa, 48 kDa and 37 kDa) were found by Western blotting in the pancreas tested, most of them showed a stronger signal in E18.5 followed by a steady decrease and only a 60-kDa isoform was detected in the adult pancreas. Immunolocalization for AFP revealed that a positive reactivity was detectable at E15.5 pancreas, became stronger in the cytoplasm of mesenchyme cells at E18.5, and declined after birth to a nearly undetectable level in adults. The dynamic expression of AFP in rat pancreas from different stages indicates that AFP might be involved in some aspects of pancreatic development.

Strategies for differentiating embryonic stem cells (ESC) into insulin-producing cells and development of non-invasive imaging techniques using bioluminescence

Diabetes is a chronic autoimmune disease that affects 4-5% of the world's population. If the present trends continue, diabetes would soon become a major/leading health problem worldwide. Hence there is an urgent need to develop novel approaches for the treatment of diabetes. While transplantation of the pancreas or that of isolated pancreatic islets can lead to the cure of the disease in some patients, immunological complications and the chronic shortage of donors makes it impossible to adequately treat all patients. Interestingly, embryonic stem cells (ESC) have emerged as a possible source of pluripotent cells that can be coaxed into insulin-producing cells (IPCs) that can be used to treat diabetes. However, until appropriate protocols have been established, this new technology will be difficult to tap into. Our laboratory is interested in developing new strategies for harnessing the pluripotency of ESC and differentiating them into IPCs that are stable and will continue to produce insulin in vivo. A second aspect is the non-availability of non-invasive imaging protocols. We show here that transcriptionally targeted luciferase expression can be used successfully to non-invasively monitor the transplanted cells in vivo.

Expression Analysis of cPLA2 Alpha Interacting TIP60 in Diabetic KKAy and Non-Diabetic C57BL Wild-Type Mice: No Impact of Transient and Stable TIP60 Overexpression on Glucose-Stimulated Insulin Secretion in Pancreatic Beta-Cells

In the present study we investigate the expression levels of cytosolic phospholipase A2 alpha (cPLA2alpha) interacting histone acetyl transferase proteins TIP60alpha and TIP60beta in non-diabetic C57BL wild-type mice and obese type 2 diabetic KKAy model mice. The aim was to test our hypothesis that TIP60 plays a regulatory role in glucose-stimulated insulin secretion from pancreatic beta-cells.

MATERIAL AND METHODS

Ten obese diabetic KKAy mice and ten non-diabetic C57BL mice were fed a standard chow diet. After nine weeks, islet RNA was purified and used to measure TIP60 expression. We investigated the effect of TIP60alpha and TIP60beta on glucose-stimulated insulin secretion by transient and stable overexpression in the pancreatic mouse beta-cell line MIN6 and the rat beta-cell line INS-1E.

RESULTS

We found that non-diabetic C57BL mice and diabetic KKAy mice have the same level of both the alpha and beta splice forms of TIP60. Furthermore, we demonstrated that transient and stable expression of TIP60 in INS-1E cells affects neither glucose-stimulated insulin secretion, insulin output nor cell insulin content. Also susceptibility to developing gluco-toxicity was unaffected.

CONCLUSION

TIP60 over-expression does not affect glucose stimulated insulin secretion, insulin content or abnormal beta-cell function during glucotoxicity.

Notch signalling suppresses apoptosis in adult human and mouse pancreatic islet cells

AIMS/HYPOTHESIS

The pathogenesis of diabetes and the success of islet transplantation depend on the control of pancreatic beta cell fate. The Notch signalling pathway is essential for normal prenatal pancreatic development, but the presence and function of this gene network in adult islets has received much less attention.

METHODS

The presence of Notch signalling components was assessed in vitro using RT-PCR, western blotting and immunofluorescence. The functional consequences of altering Notch signalling on insulin secretion and programmed cell death were examined.

RESULTS

Adult mouse islets, human islets and mouse insulinoma MIN6 cells possess key components of the Notch pathway. RT-PCR, western blotting and immunofluorescence indicated that the Notch target gene, neurogenin3 (Ngn3, also known as Neurog3), is also present in adult islet cells. Inhibiting Notch signalling with N-[N-(3,5-difluorophenacetyl-L-alanyl)]-S-phenylglycine t-butyl ester (DAPT) increased Ngn3 mRNA expression and protein levels in adult islets. The activated notch homologue 1 (NOTCH1) protein level was decreased upon serum withdrawal, as well as after treatment with a phosphatidylinositol 3-kinase inhibitor, or hydroxy-2-naphthalenylmethylphosphonic acid, an insulin receptor inhibitor. While islets cultured in DAPT did not exhibit defects in insulin secretion, indicating that differentiation is unaltered, inhibiting gamma-secretase-dependent Notch activation led to a dose-dependent increase in caspase-3-dependent apoptosis in both MIN6 cells and human islets. Conversely, gamma-secretase overactivity resulted in an accumulation of cleaved NOTCH1 and protection from apoptosis.

CONCLUSIONS/INTERPRETATION

Together these results show that the Notch/Ngn3 signalling network is intact and functional in adult islets. This pathway represents an attractive target for modulating beta cell fate in diabetes, islet transplantation and efforts to derive beta cell surrogates in vitro.

New pancreas from old: microregulators of pancreas regeneration

MicroRNAs (miRNAs) are 18-22 nucleotide RNA molecules that mediate post-transcriptional gene silencing, primarily by binding to the 3' untranslated region of their target mRNA. Several studies have demonstrated the role of miRNAs in mouse pancreas development (miR-124a, miR-503, miR-541, miR-214) as well as in insulin secretion (miR-375, miR-9). Pancreatic transcription factors that are temporally expressed during early pancreas development are re-expressed during pancreas regeneration following pancreatectomy in mice. The only exception to this is Neurogenin3 (NGN3). Here, we discuss recent evidence for miRNA-mediated silencing of ngn3, which inhibits endocrine cell development via the classical 'stem cell pathway' during mouse pancreatic regeneration, thereby favoring beta-cell regeneration.

Intrauterine programming of the endocrine pancreas

Epidemiological studies have revealed strong relationships between poor foetal growth and subsequent development of the metabolic syndrome. Persisting effects of early malnutrition become translated into pathology, thereby determine chronic risk for developing glucose intolerance and diabetes. These epidemiological observations identify the phenomena of foetal programming without explaining the underlying mechanisms that establish the causal link. Animal models have been established and studies have demonstrated that reduction in the availability of nutrients during foetal development programs the endocrine pancreas and insulin-sensitive tissues. Whatever the type of foetal malnutrition, whether there are not enough calories or protein in food or after placental deficiency, malnourished pups are born with a defect in their beta-cell population that will never completely recover, and insulin-sensitive tissues will be definitively altered. Despite the similar endpoint, different cellular and physiological mechanisms are proposed. Hormones operative during foetal life like insulin itself, insulin-like growth factors and glucocorticoids, as well as specific molecules like taurine, or islet vascularization were implicated as possible factors amplifying the defect. The molecular mechanisms responsible for intrauterine programming of the beta cells are still elusive, but two hypotheses recently emerged: the first one implies programming of mitochondria and the second, epigenetic regulation.

Low-density lipoprotein receptor-related protein-5 C/T polymorphism in exon 18 is associated with C peptide and proinsulin levels in control women and patients with polycystic ovary syndrome

OBJECTIVE

To assess the previously unstudied potential role of C/T (A1330V) polymorphism of the low-density lipoprotein receptor-related protein-5 gene in insulin sensitivity and secretion in polycystic ovary syndrome. The low-density lipoprotein receptor-related protein-5 gene has been found to play a role in determining insulin secretion in animal models.

DESIGN

Case-control study.

SETTING

Tertiary outpatient clinic.

PATIENT(S)

Women with polycystic ovary syndrome (n = 299; age, 27.5 +/- 7.1 y [mean +/- SD]), according to the European Society of Human Reproduction and Embryology criteria, as well as healthy control women (n = 187, age, 28.9 +/- 9.8 y).

INTERVENTION(S)

Oral glucose tolerance test, blood sampling.

MAIN OUTCOME MEASURE(S)

Glucose, insulin, C peptide, proinsulin during oral glucose tolerance tests, and lipids. Genotyping of C/T (A1330V) polymorphism by polymerase chain reaction-restriction fragment length polymorphism.

RESULT(S)

There was no difference in the frequency of genotypes between women with polycystic ovary syndrome (CC/CT/TT: 80.3%, 18.4%, 1.3%) and the control women (79.1%, 19.8%, and 1.1%). Carriers of the T allele had statistically significantly higher basal and stimulated C peptide and proinsulin levels than CC homozygotes, both basally and at the 180th minute. Regarding insulin sensitivity, there was no difference between T carriers and CC homozygotes.

CONCLUSION(S)

Polymorphism of C/T in the low-density lipoprotein receptor-related protein-5 gene is associated with C-peptide and proinsulin secretion but does not influence insulin sensitivity in either healthy women or women with polycystic ovary syndrome.

Genetic identification of a novel NeuroD1 function in the early differentiation of islet alpha, PP and epsilon cells

Nkx2.2 and NeuroD1 are vital for proper differentiation of pancreatic islet cell types. Nkx2.2-null mice fail to form beta cells, have reduced numbers of alpha and PP cells and display an increase in ghrelin-producing epsilon cells. NeuroD1-null mice display a reduction of alpha and beta cells after embryonic day (e) 17.5. To begin to determine the relative contributions of Nkx2.2 and NeuroD1 in islet development, we generated Nkx2.2-/-;NeuroD1-/- double knockout (DKO) mice. As expected, the DKO mice fail to form beta cells, similar to the Nkx2.2-null mice, suggesting that the Nkx2.2 phenotype may be dominant over the NeuroD1 phenotype in the beta cells. Surprisingly, however, the alpha, PP and epsilon phenotypes of the Nkx2.2-null mice are partially rescued by the simultaneous elimination of NeuroD1, even at early developmental time points when NeuroD1 null mice alone do not display a phenotype. Our results indicate that Nkx2.2 and NeuroD1 interact to regulate pancreatic islet cell fates, and this epistatic relationship is cell-type dependent. Furthermore, this study reveals a previously unappreciated early function of NeuroD1 in regulating the specification of alpha, PP and epsilon cells.

Differentiation of mouse embryonic stem cells to insulin-producing cells

Here, we describe a basic protocol for the in vitro differentiation of mouse embryonic stem (ES) cells into insulin-producing cells. The three-step protocol comprises (i) the formation of embryoid bodies, (ii) the spontaneous differentiation of embryoid bodies into progenitor cells of ecto-, meso- and endodermal lineages, and (iii) the induction of differentiation of early progenitors into the pancreatic lineage. Differentiated cells can be obtained within approximately 33 d. Differentiation induction by growth and extracellular-matrix factors, including laminin, nicotinamide and insulin, leads to the formation of ES-derived progeny that resembles cells committed to the pancreatic lineage. During differentiation, transcript levels of genes expressed in early pancreatic cells are upregulated. Continued differentiation results in the development of C-peptide/insulin-positive islet-like clusters that release insulin upon glucose stimulation. Differentiated ES cells that overexpress the pancreatic developmental control gene Pax4 develop insulin-secretory granules and reveal functional properties with respect to the pancreas-specific ATP-modulated K+ channel and the normalization of glycemia of streptozotocin-treated diabetic mice.

Nkx2.2 regulates beta-cell function in the mature islet

Nkx2.2 is a homeodomain transcription factor that is critical for pancreatic endocrine cell specification and differentiation in the developing mouse embryo. The purpose of this study was to determine whether Nkx2.2 is also required for the maintenance and function of the mature beta-cell in the postnatal islet. We have demonstrated previously that a repressor derivative of Nkx2.2 can functionally substitute for endogenous Nkx2.2 to fully restore alpha- and immature beta-cells in the embryonic islet; however, Nkx2.2 activator functions appear to be required to form a functional beta-cell. In this study, we have created transgenic mouse lines to express the Nkx2.2-repressor derivative in the mature beta-cell in the presence of endogenous Nkx2.2. The transgenic mice were assessed for beta-cell function, overall islet structure, and expression of beta-cell-specific markers. Using this transgenic approach, we have determined that the Nkx2.2-repressor derivative disrupts endogenous Nkx2.2 expression in adult mice and causes downregulation of the mature beta-cell factors, MafA and Glut2. Consistently, the Nkx2.2-repressor mice display reduced insulin gene expression and pancreatic insulin content and impaired insulin secretion. At weaning, the male Nkx2.2-repressor mice are overtly diabetic and all Nkx2.2-repressor transgenic mice exhibit glucose intolerance. Furthermore, the loss of beta-cell function in the Nkx2.2-repressor transgenic mice is associated with disrupted islet architecture. These studies indicate a previously undiscovered role for Nkx2.2 in the maintenance of mature beta-cell function and the formation of normal islet structure.

Noninsulinoma pancreatogenous hypoglycemia syndrome: quantitative and immunohistochemical analyses of islet cells for insulin, glucagon, somatostatin, and pancreatic and duodenal homeobox protein

OBJECTIVE

To present a case of an elderly man with noninsulinoma pancreatogenous hypoglycemia syndrome (NIPHS) and to determine the pathogenesis of this syndrome.

METHODS

The pancreas of our patient with NIPHS was immunocytochemically stained for insulin-, glucagon-, and somatostatin-secreting cells and pancreatic and duodenal homeobox protein (PDX-1). The clinical findings and morphologic and immunocytochemical analyses of the islets of our patient are described, along with a review of related published reports.

RESULTS

A 78-year-old man presented with hyperinsulinemic hypoglycemia, with episodes unrelated to meals or fasting. An insulinoma could not be localized by preoperative imaging or by intraoperative ultrasonography or palpation. He underwent a 70% distal pancreatectomy. For assessment of the possibility that a nuclear transcription factor regulating islet beta-cell growth and development is overexpressed in this disease and is responsible for diffuse islet hyperfunction and proliferation of beta-cells, pancreatic sections from our patient were stained immunocytochemically for PDX-1, insulin, glucagon, and somatostatin. Morphologic findings were compared with pancreatic sections from normal control patients and normative data reported in the literature. Clinical findings and morphologic analyses were consistent with NIPHS. Islets were arranged in long clusters, both in the pancreatic tissue and in peripancreatic adipose tissue. Islets were small but increased in number, and insulin, glucagon, and somatostatin were present in the islets. The relative intensity of insulin staining was increased in our patient in comparison with that in the control patients, and PDX-1 was not overexpressed.

CONCLUSION

The etiopathogenesis of NIPHS in this patient involved (1) an increased number of islets with development of ectopic islets in the peripancreatic adipose tissue; (2) alpha- and delta- as well as beta-cell proliferation; and (3) an early step in the development of the islet not involving overexpression of PDX-1.

Generation of insulin-producing islet-like clusters from human embryonic stem cells

Recent success in pancreatic islet transplantation has energized the field to discover an alternative source of stem cells with differentiation potential to beta cells. Generation of glucose-responsive, insulin-producing beta cells from self-renewing, pluripotent human ESCs (hESCs) has immense potential for diabetes treatment. We report here the development of a novel serum-free protocol to generate insulin-producing islet-like clusters (ILCs) from hESCs grown under feeder-free conditions. In this 36-day protocol, hESCs were treated with sodium butyrate and activin A to generate definitive endoderm coexpressing CXCR4 and Sox17, and CXCR4 and Foxa2. The endoderm population was then converted into cellular aggregates and further differentiated to Pdx1-expressing pancreatic endoderm in the presence of epidermal growth factor, basic fibroblast growth factor, and noggin. Soon thereafter, expression of Ptf1a and Ngn3 was detected, indicative of further pancreatic differentiation. The aggregates were finally matured in the presence of insulin-like growth factor II and nicotinamide. The temporal pattern of pancreas-specific gene expression in the hESC-derived ILCs showed considerable similarity to in vivo pancreas development, and the final population contained representatives of the ductal, exocrine, and endocrine pancreas. The hESC-derived ILCs contained 2%-8% human C-peptide-positive cells, as well as glucagon- and somatostatin-positive cells. Insulin content as high as 70 ng of insulin/mug of DNA was measured in the ILCs, representing levels higher than that of human fetal islets. In addition, the hESC-derived ILCs contained numerous secretory granules, as determined by electron microscopy, and secreted human C-peptide in a glucose-dependent manner. Disclosure of potential conflicts of interest is found at the end of this article.