journey from the insulin gene to reprogramming pancreatic tissue

This article was written as a contribution to mark the centenary of the first administration of insulin to a human in 1922. Writing from an Aberdeen perspective, an introductory passage will place emphasis on the role of JJR MacLeod, under whose supervision the discovery of insulin by Banting and Best was made. The major thrust of the article, however, will be on the cloning and sequencing of the human insulin gene, and the impact it had on the scientific career of the author. It initiated a journey to find alternative therapies for diabetes that led sequentially though gene therapy, embryonic stem cell-derived islets, and reprogramming. Our experience in these areas will be described, with emphasis on the strengths and weaknesses of each of these approaches.

Elevated markers of liver function are associated with poorer outcomes in HFREF: an analysis of DAPA-HF

Background

Abnormalities of liver tests in patients with heart failure with reduced ejection fraction (HFrEF) is a well-recognised phenomenon. We examined the prognostic value of measures of liver function in a large contemporary cohort of patients with HFrEF enrolled in the Dapagliflozin and Prevention of Adverse Outcomes in Heart Failure (DAPA-HF) trial

Methods

In this post-hoc analysis of the DAPA-HF trial we studied 4625 patients with liver function tests available at baseline. Cox proportional hazards models were used to assess the association between liver tests (total bilirubin, alkaline phosphatase [ALP], alanine transaminase [ALT], aspartate transaminase [AST]) and the Model for End-stage Liver Disease excluding INR (MELD-XI) score (calculated as 5.11 Ln [total bilirubin as mg/dL] + 11.76 Ln [creatinine as mg/dL] + 9.44), and the risk of the primary composite endpoint (hospitalisation or urgent visit for heart failure or cardiovascular death). Models were adjusted for age, sex, race, region, systolic blood pressure, heart rate, LVEF, eGFR, log-transformed NT-proBNP, NYHA class, history of hypertension, stroke, myocardial infarction, atrial fibrillation, heart failure aetiology and randomized treatment to dapagliflozin and stratified by diabetic status at baseline. An interaction term between each measure and the effect of treatment on the primary composite outcome was tested as a fractional polynomial.

Results

Total bilirubin, ALP, and MELD-XI score were associated with a higher risk of all the primary outcome (Figure 1) but not ALT or AST. These relationships persisted after adjustment: total bilirubin per log unit increase (HR=1.46; 95% CI 1.28 – 1.67, p<0.001), ALP per log unit increase (HR=1.39; 95% CI 1.15 – 1.66, p<0.001), MELD-XI per 1 SD increase (HR 1.27; 95% CI 1.13 – 1.42, p<0.001). The effect of dapagliflozin on the primary outcome was not modified by the baseline levels of either total bilirubin, ALP or MELD-XI score (Figure 2)

Conclusions

Higher total bilirubin, ALP and MELD-XI score were independently associated with a higher risk of cardiovascular death or worsening HF and may be useful routinely available biomarkers to assess prognosis. The efficacy of dapagliflozin was the not modified by baseline levels of any of these markers.

Funding Acknowledgement

Type of funding sources: None. Figure 2

Testicular somatic cell-like cells derived from embryonic stem cells induce differentiation of epiblasts into germ cells

Regeneration of the testis from pluripotent stem cells is a real challenge, reflecting the complexity of the interaction of germ cells and somatic cells. Here we report the generation of testicular somatic cell-like cells (TesLCs) including Sertoli cell-like cells (SCLCs) from mouse embryonic stem cells (ESCs) in xeno-free culture. We find that Nr5a1/SF1 is critical for interaction between SCLCs and PGCLCs. Intriguingly, co-culture of TesLCs with epiblast-like cells (EpiLCs), rather than PGCLCs, results in self-organised aggregates, or testicular organoids. In the organoid, EpiLCs differentiate into PGCLCs or gonocyte-like cells that are enclosed within a seminiferous tubule-like structure composed of SCLCs. Furthermore, conditioned medium prepared from TesLCs has a robust inducible activity to differentiate EpiLCs into PGCLCs. Our results demonstrate conditions for in vitro reconstitution of a testicular environment from ESCs and provide further insights into the generation of sperm entirely in xeno-free culture.

Non-fatal cardiovascular events preceding sudden cardiac death in patients with an acute myocardial infarction complicated by heart failure: insights from the High-Risk-Myocardial-Infarction database

Background

Sudden cardiac death (SCD) is responsible for 20–40% of mortality following acute myocardial infarction (AMI). The risk of SCD is even higher among patients with AMI complicated by heart failure (HF) (either clinically apparent HF or left ventricular dysfunction). The temporal relationship between an AMI complicated by HF and subsequent SCD and the association of non-fatal cardiovascular (CV) events following AMI with SCD has yet to be described.

Purpose

Among patients with AMI complicated by HF, we evaluated the probability and temporal association of subsequent non-fatal cardiovascular (CV) events (HF hospitalization, recurrent MI, or stroke) and SCD.

Methods

The High-Risk Myocardial Infarction (HRMI) database contains 28,771 patients with signs of HF or reduced LV ejection fraction (<40%) after AMI. Among patients with an AMI complicated by HF, we used adjudicated cause of death from the HRMI Database to identify: 1) the temporal distribution of SCD among patients following an index AMI; 2) the probability of having SCD following a non-fatal CV event following the index AMI.

Results

Median follow-up was 1.9 years. Mean age was 65.0±11.5 years and 70% were male. The incidence of CV death was 7.9 per 100 patient-year [py] and for SCD was 3.1 per 100py (40% of CV deaths). SCD rates were highest in the early period (<90 days) after AMI and decreased over time. Recurrent MI preceded 9.6% of SCD after a median time of 145 days; HF hospitalization preceded 17.0% of SCD after a median 144 days; and stroke preceded 2.7% of SCD after a median of 138 days (vs. non-sudden CV death: MI 46.6% at 1 days, HF hospitalization: 30.9% at 67 days, stroke 12.9% at 9 days). The incidence of SCD preceded by HF hospitalization was significantly higher than SCD without preceding HF hospitalization.

Conclusion

Among patients with AMI complicated by HF, SCD predominantly occurred in the early “high-risk” period after AMI; SCD rates decreased afterwards. Patients with non-fatal HF hospitalizations during follow-up may have a higher subsequent SCD risk. Preventing HF onset after MI may help decreasing SCD.

Proportion of sudden cardiac death

Funding Acknowledgement

Type of funding source: Public Institution(s). Main funding source(s): Lucien Award, McGill University

Increased vimentin in human α- and β-cells in type 2 diabetes

Type 2 diabetes (T2DM) is associated with pancreatic islet dysfunction. Loss of β-cell identity has been implicated via dedifferentiation or conversion to other pancreatic endocrine cell types. How these transitions contribute to the onset and progression of T2DM in vivo is unknown. The aims of this study were to determine the degree of epithelial-to-mesenchymal transition occurring in α and β cells in vivo and to relate this to diabetes-associated (patho)physiological conditions. The proportion of islet cells expressing the mesenchymal marker vimentin was determined by immunohistochemistry and quantitative morphometry in specimens of pancreas from human donors with T2DM (n = 28) and without diabetes (ND, n = 38) and in non-human primates at different stages of the diabetic syndrome: normoglycaemic (ND, n = 4), obese, hyperinsulinaemic (HI, n = 4) and hyperglycaemic (DM, n = 8). Vimentin co-localised more frequently with glucagon (α-cells) than with insulin (β-cells) in the human ND group (1.43% total α-cells, 0.98% total β-cells, median; P < 0.05); these proportions were higher in T2DM than ND (median 4.53% α-, 2.53% β-cells; P < 0.05). Vimentin-positive β-cells were not apoptotic, had reduced expression of Nkx6.1 and Pdx1, and were not associated with islet amyloidosis or with bihormonal expression (insulin + glucagon). In non-human primates, vimentin-positive β-cell proportion was larger in the diabetic than the ND group (6.85 vs 0.50%, medians respectively, P < 0.05), but was similar in ND and HI groups. In conclusion, islet cell expression of vimentin indicates a degree of plasticity and dedifferentiation with potential loss of cellular identity in diabetes. This could contribute to α- and β-cell dysfunction in T2DM.

Distinctive Roles of Canonical and Noncanonical Wnt Signaling in Human Embryonic Cardiomyocyte Development

Wnt signaling is a key regulator of vertebrate heart development; however, specific roles for human cardiomyocyte development remain uncertain. Here we use human embryonic stem cells (hESCs) to analyze systematically in human cardiomyocyte development the expression of endogenous Wnt signaling components, monitor pathway activity, and dissect stage-specific requirements for canonical and noncanonical Wnt signaling mechanisms using small-molecule inhibitors. Our analysis suggests that WNT3 and WNT8A, via FZD7 and canonical signaling, regulate BRACHYURY expression and mesoderm induction; that WNT5A/5B, via ROR2 and noncanonical signaling, regulate MESP1 expression and cardiovascular development; and that later in development WNT2, WNT5A/5B, and WNT11, via FZD4 and FZD6, regulate functional cardiomyocyte differentiation via noncanonical Wnt signaling. Our findings confirm in human development previously proposed roles for canonical Wnt signaling in sequential stages of vertebrate cardiomyogenesis, and identify more precise roles for noncanonical signaling and for individual Wnt signal and Wnt receptor genes in human cardiomyocyte development.

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hESCs were used to study Wnt signaling during human cardiomyocyte development

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Previously proposed roles for canonical Wnt signaling were confirmed in human

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Specific roles for noncanonical Wnt signaling were identified in cardiomyogenesis

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Individual Wnt signal and receptor genes were identified in human cardiomyogenesis

Design and fabrication of diffractive atom chips for laser cooling and trapping

It has recently been shown that optical reflection gratings fabricated directly into an atom chip provide a simple and effective way to trap and cool substantial clouds of atoms (Nshii et al. in Nat Nanotechnol 8:321-324, 2013; McGilligan et al. in Opt Express 23(7):8948-8959, 2015). In this article, we describe how the gratings are designed and microfabricated and we characterise their optical properties, which determine their effectiveness as a cold atom source. We use simple scalar diffraction theory to understand how the morphology of the gratings determines the power in the diffracted beams.

Generation of Functional Beta-Like Cells from Human Exocrine Pancreas

Transcription factor mediated lineage reprogramming of human pancreatic exocrine tissue could conceivably provide an unlimited supply of islets for transplantation in the treatment of diabetes. Exocrine tissue can be efficiently reprogrammed to islet-like cells using a cocktail of transcription factors: Pdx1, Ngn3, MafA and Pax4 in combination with growth factors. We show here that overexpression of exogenous Pax4 in combination with suppression of the endogenous transcription factor ARX considerably enhances the production of functional insulin-secreting β-like cells with concomitant suppression of α-cells. The efficiency was further increased by culture on laminin-coated plates in media containing low glucose concentrations. Immunocytochemistry revealed that reprogrammed cultures were composed of ~45% islet-like clusters comprising >80% monohormonal insulin⁺ cells. The resultant β-like cells expressed insulin protein levels at ~15–30% of that in adult human islets, efficiently processed proinsulin and packaged insulin into secretory granules, exhibited glucose responsive insulin secretion, and had an immediate and prolonged effect in normalising blood glucose levels upon transplantation into diabetic mice. We estimate that approximately 3 billion of these cells would have an immediate therapeutic effect following engraftment in type 1 diabetes patients and that one pancreas would provide sufficient tissue for numerous transplants.

Islet transplantation from a nationally funded UK centre reaches socially deprived groups and improves metabolic outcomes

AIMS/HYPOTHESIS

Type 1 diabetes complicated by hypoglycaemia is prevalent in socioeconomically deprived populations. Islet transplantation is of proven efficacy in type 1 diabetes complicated by hypoglycaemia, but it is not known if nationally funded programmes reach the socioeconomically deprived. Our aim was to determine: (1) socioeconomic indices in participants referred to our nationally funded programme; and (2) if metabolic outcomes in our transplant recipients were improved.

METHODS

Participants referred (n = 106) and receiving transplants (n = 18; 32 infusions) were examined with respect to socioeconomic status (deprivation category score) and their ability to work and drive. In participants followed for ≥12 months after transplantation, metabolic and anthropometric measurements (n = 14) were recorded pre- and post-transplant (assessed ~1, ~3, ~6 and ~12 months with mixed-meal tolerance tests and 6 day continuous glucose monitoring assessments). Donor data was also examined.

RESULTS

There was a greater prevalence of socioeconomic deprivation in referred and transplant recipients than the general population (p < 0.05). Of the transplant recipients, 73% were socioeconomically deprived, 88% did not hold a driver's license and 94% had reduced ability to work (all p < 0.01 vs referred participants). Donors were predominantly obese and included circulatory death donors. At 12 months, 93% of participants who had received transplants had graft function, diminished frequency of hypoglycaemia (10 [4-11] vs 0 [0-2] hypoglycaemic episodes/week), improved awareness of hypoglycaemia (Gold score 7 [5-7] vs 1 [1-2]) and glycaemic control (HbA1c: 7.9% [7.2-8.5%]; 63 [55-69] mmol/mol vs 7.2% [6.8-7.5%]; 55 [51-58] mmol/mol), diminished glycaemic lability and decreased central adiposity (all p < 0.05).

CONCLUSIONS/INTERPRETATION

A nationally funded islet transplant programme reaches the socioeconomically deprived and outcomes are significantly improved in this group.

Krüppel-Like Factor 4 Overexpression Initiates a Mesenchymal-to-Epithelial Transition and Redifferentiation of Human Pancreatic Cells following Expansion in Long Term Adherent Culture

A replenishable source of insulin-producing cells has the potential to cure type 1 diabetes. Attempts to culture and expand pancreatic β-cells in vitro have resulted in their transition from insulin-producing epithelial cells to mesenchymal stromal cells (MSCs) with high proliferative capacity but devoid of any hormone production. The aim of this study was to determine whether the transcription factor Krüppel-like factor 4 (KLF4), could induce a mesenchymal-to-epithelial transition (MET) of the cultured cells. Islet-enriched pancreatic cells, allowed to dedifferentiate and expand in adherent cell culture, were transduced with an adenovirus containing KLF4 (Ad-Klf4). Cells were subsequently analysed for changes in cell morphology by light microscopy, and for the presence of epithelial and pancreatic markers by immunocytochemistry and quantitative RT/PCR. Infection with Ad-Klf4 resulted in morphological changes, down-regulation of mesenchymal markers, and re-expression of both epithelial and pancreatic cell markers including insulin and transcription factors specific to β-cells. This effect was further enhanced by culturing cells in suspension. However, the effects of Ad-KLf4 were transient and this was shown to be due to increased apoptosis in Klf4-expressing cells. Klf4 has been recently identified as a pioneer factor with the ability to modulate the structure of chromatin and enhance reprogramming/transdifferentiation. Our results show that Klf4 may have a role in the redifferentiation of expanded pancreatic cells in culture, but before this can be achieved the off-target effects that result in increased apoptosis would need to be overcome.

Cell therapy for type 1 diabetes

Cell therapy in the form of human islet transplantation has been a successful form of treatment for patients with type 1 diabetes for over 10 years, but is significantly limited by lack of suitable donor material. A replenishable supply of insulin-producing cells has the potential to address this problem; however to date success has been limited to a few preclinical studies. Two of the most promising strategies include differentiation of embryonic stem cells and induced pluripotent stem cells towards insulin-producing cells and transdifferentiation of acinar or other closely related cell types towards β-cells. Here, we discuss recent progress and challenges that need to be overcome in taking cell therapy to the clinic.

Suppression of epithelial-to-mesenchymal transitioning enhances ex vivo reprogramming of human exocrine pancreatic tissue toward functional insulin-producing β-like cells

Because of the lack of tissue available for islet transplantation, new sources of β-cells have been sought for the treatment of type 1 diabetes. The aim of this study was to determine whether the human exocrine-enriched fraction from the islet isolation procedure could be reprogrammed to provide additional islet tissue for transplantation. The exocrine-enriched cells rapidly dedifferentiated in culture and grew as a mesenchymal monolayer. Genetic lineage tracing confirmed that these mesenchymal cells arose, in part, through a process of epithelial-to-mesenchymal transitioning (EMT). A protocol was developed whereby transduction of these mesenchymal cells with adenoviruses containing Pdx1, Ngn3, MafA, and Pax4 generated a population of cells that were enriched in glucagon-secreting α-like cells. Transdifferentiation or reprogramming toward insulin-secreting β-cells was enhanced, however, when using unpassaged cells in combination with inhibition of EMT by inclusion of Rho-associated kinase (ROCK) and transforming growth factor-β1 inhibitors. Resultant cells were able to secrete insulin in response to glucose and on transplantation were able to normalize blood glucose levels in streptozotocin diabetic NOD/SCID mice. In conclusion, reprogramming of human exocrine-enriched tissue can be best achieved using fresh material under conditions whereby EMT is inhibited, rather than allowing the culture to expand as a mesenchymal monolayer.

A comparison of in vitro nucleosome positioning mapped with chicken, frog and a variety of yeast core histones

Using high-throughput sequencing, we have mapped sequence-directed nucleosome positioning in vitro on four plasmid DNAs containing DNA fragments derived from the genomes of sheep, drosophila, human and yeast. Chromatins were prepared by reconstitution using chicken, frog and yeast core histones. We also assembled yeast chromatin in which histone H3 was replaced by the centromere-specific histone variant, Cse4. The positions occupied by recombinant frog and native chicken histones were found to be very similar. In contrast, nucleosomes containing the canonical yeast octamer or, in particular, the Cse4 octamer were assembled at distinct populations of locations, a property that was more apparent on particular genomic DNA fragments. The factors that may contribute to this variation in nucleosome positioning and the implications of the behavior are discussed.

Inhibition of activin/nodal signalling is necessary for pancreatic differentiation of human pluripotent stem cells

AIMS/HYPOTHESIS

Human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hIPSCs) offer unique opportunities for regenerative medicine and for the study of mammalian development. However, developing methods to differentiate hESCs/hIPSCs into specific cell types following a natural pathway of development remains a major challenge.

METHODS

We used defined culture media to identify signalling pathways controlling the differentiation of hESCs/hIPSCs into pancreatic or hepatic progenitors. This approach avoids the use of feeders, stroma cells or serum, all of which can interfere with experimental outcomes and could preclude future clinical applications.

RESULTS

This study reveals, for the first time, that activin/TGF-β signalling blocks pancreatic specification induced by retinoic acid while promoting hepatic specification in combination with bone morphogenetic protein and fibroblast growth factor. Using this knowledge, we developed culture systems to differentiate human pluripotent stem cells into near homogenous population of pancreatic and hepatic progenitors displaying functional characteristics specific to their natural counterparts. Finally, functional experiments showed that activin/TGF-β signalling achieves this essential function by controlling the levels of transcription factors necessary for liver and pancreatic development, such as HEX and HLXB9.

CONCLUSION/INTERPRETATION

Our methods of differentiation provide an advantageous system to model early human endoderm development in vitro, and also represent an important step towards the generation of pancreatic and hepatic cells for clinical applications.

Purification and Characterization of a Population of EGFP-Expressing Cells from the Developing Pancreas of a Neurogenin3/EGFP Transgenic Mouse

Neurogenin 3 (ngn3) is a basic helix loop helix transcription factor that is transiently expressed in the developing mouse pancreas with peak expression around E15. In mice lacking the ngn3 gene the endocrine cells of the pancreas fail to develop suggesting that the ngn3-positive cell may represent a progenitor cell for the endocrine pancreas. In order to purify and characterize this cell in detail we have generated a transgenic mouse, in which the ngn3 promoter drives expression of enhanced green fluorescent protein (EGFP). In the E15.5 embryo EGFP was expressed in the dorsal and ventral pancreas, the duodenum, and lower intestine as well as in the brain. This pattern of expression was in keeping with the known expression profile of the endogenous ngn3 gene. Within the pancreas EGFP was localized in close proximity to cells that stained positive for ngn3, insulin, and glucagon, but was absent from regions of the pancreas that stained positive for amylase. EGFP was also present in the pancreas at E18.5, although there was no detectable expression of ngn3. At this stage EGFP did not colocalize with any of the hormones or exocrine markers. EGFP(+) cells were FACS purified (96%) from the E15 pancreas yielding approximately 10,000 cells or 1.6% of the total pancreatic cells from one litter. RT/PCR analysis confirmed that the purified cells expressed EGFP, ngn3, insulin, glucagon, somatostatin and pancreatic polypeptide. The ability to purify ngn3(+) cells provides an invaluable source of material for charactering in detail their properties.

Palmitate enhances the differentiation of mouse embryonic stem cells towards white adipocyte lineages

The number of adipocyte progenitors is determined early in foetal and neonatal development in a process which may be altered by gender and excess nutrient intake, and which in turn determines fat mass in adulthood and the risk of developing obesity. Here we investigate the hypothesis that excess nutrients, in this case the long chain fatty acid palmitate, can program differentiating stem cells towards white fat lineages. The experiments were performed on mouse embryonic stem cells in chemically defined media (CDM) supplemented with bone morphogenetic protein 4 (BMP4) and all trans-retinoic acid (RA). Subsequent treatment for 21 days with palmitate not only promoted the expression of adipocyte markers and monolocular lipid deposition as observed by RT/QPCR and immunocytochemistry, but also stimulated a considerable enrichment in adipocytes as measured by flow cytometry and a lipolytic response to catecholamines. Palmitate increased protein levels of adiponectin that is preferentially expressed in subcutaneous fat, while inhibiting IGFBP2 and IGFBP3 that are associated with visceral fat. In keeping with this finding, palmitate also increased expression of the subcutaneous markers Shox2 and Twist1 and oestrogenising enzymes. Collectively, these results suggest that palmitate induces differentiation towards subcutaneous fat and that this could occur through its oestrogenising effects on the preadipocyte, suggesting a role for palmitate in programming fat development towards a metabolically favourable profile.

Efficient differentiation of AR42J cells towards insulin-producing cells using pancreatic transcription factors in combination with growth factors

The AR42J-B13 rat pancreatic acinar cell line was used to identify pancreatic transcription factors and exogenous growth factors (GFs) that might facilitate the reprogramming of exocrine cells into islets. Adenoviruses were used to induce exogenous expression of the pancreatic transcription factors (TFs) Pdx1, MafA, Ngn3 and Pax4. Individually Pdx1, MafA and Pax4 had no effect on the expression of endocrine markers, whilst adeno-Ngn3 on its own increased the expression of Pax4, Ngn3 and NeuroD. In combination the four TFs had a significant effect on the expression of insulin 1 and 2 that was associated with a change in cell morphology from a rounded to a spindle-like shape. Amongst a range of growth factors, Betacellulin and Nicotinamide were shown to enhance the effects of the four TFs. The presence of adeno-Pax4 in the differentiation cocktail was important in limiting the expression of glucagon and in generating glucose sensitive insulin secretion. Further experiments asked whether the adenoviral TFs could be replaced by protein transduction domain (PTD)-containing TFs. The results showed that the PTD-TFs could mimic in part the effects of the adeno-TFs, but the resultant cells did not undergo the important morphological change associated with differentiation to endocrine lineages and levels of endogenous markers were very much lower. In summary, the results describe a cocktail of four TFs and two GFs that can be used to induce formation of glucose sensitive insulin secreting cells from ARJ42 cells, and demonstrate that it would be difficult to replace adenoviral transduction with PTD-TFS.

Pancreatic transcription factors containing protein transduction domains drive mouse embryonic stem cells towards endocrine pancreas

Protein transduction domains (PTDs), such as the HIV1-TAT peptide, have been previously used to promote the uptake of proteins into a range of cell types, including stem cells. Here we generated pancreatic transcription factors containing PTD sequences and administered these to endoderm enriched mouse embryonic stem (ES) cells under conditions that were designed to mimic the pattern of expression of these factors in the developing pancreas. The ES cells were first cultured as embryoid bodies and treated with Activin A and Bone morphogenetic protein 4 (BMP4) to promote formation of definitive endoderm. Cells were subsequently plated as a monolayer and treated with different combinations of the modified recombinant transcription factors Pdx1 and MafA. The results demonstrate that each transcription factor was efficiently taken up by the cells, where they were localized in the nuclei. RT-qPCR was used to measure the expression levels of pancreatic markers. After the addition of Pdx1 alone for a period of five days, followed by the combination of Pdx1 and TAT-MafA in a second phase, up-regulation of insulin 1, insulin 2, Pdx1, Glut2, Pax4 and Nkx6.1 was observed. As assessed by immunocytochemistry, double positive insulin and Pdx1 cells were detected in the differentiated cultures. Although the pattern of pancreatic markers expression in these cultures was comparable to that of a mouse transformed β-cell line (MIN-6) and human islets, the expression levels of insulin observed in the differentiated ES cell cultures were several orders of magnitude lower. This suggests that, although PTD-TFs may prove useful in studying the role of exogenous TFs in the differentiation of ES cells towards islets and other pancreatic lineages, the amount of insulin generated is well below that required for therapeutically useful cells.

A factor(s) secreted from MIN-6 beta-cells stimulates differentiation of definitive endoderm enriched embryonic stem cells towards a pancreatic lineage

In the mouse the developing pancreas is controlled by contact with, and signalling molecules secreted from, surrounding cells. These factors are best studied using explant cultures of embryonic tissue. The present study was undertaken to determine whether embryonic stem (ES) cells could be used as an alternative model in vitro system to investigate the role of cell-cell interactions in the developing pancreas. Transwell culture experiments showed that MIN-6 beta-cells secreted a factor or factors that promoted differentiation of ES cell derived definitive endoderm enriched cells towards a pancreatic fate. Further studies using MIN-6 condition medium showed that the factor(s) involved was restricted to MIN-6 cells, could be concentrated with ammonium sulphate, and was sensitive to heat treatment, suggesting that it was a protein or peptide. Further analyses showed that insulin or proinsulin failed to mimic the effects of the conditioned media. Collectively, these results suggest that beta-cells secrete a factor(s) capable of controlling their own differentiation and maturation. The culture system described here presents unique advantages in the identification and characterisation of these factors.

An engineered zinc finger protein reveals a role for the insulin VNTR in the regulation of the insulin and adjacent IGF2 genes

An engineered zinc finger protein (eZFP) was isolated from a library based on its ability to activate expression of the endogenous insulin gene in HEK-293 cells. Using a panel of insulin promoter constructs, the eZFP was shown to act through the variable number of tandem repeat (VNTR) region located 365 base pairs upstream of the transcription start site. The eZFP also activated expression of the IGF2 gene that lies close to INS on chromosome 11p15. These results demonstrate that the INSVNTR controls expression of the insulin and IGF2 genes and provide a mechanistic explanation for previous studies that demonstrated an association between INSVNTR genotypes and placental levels of IGF2.

Biphasic induction of Pdx1 in mouse and human embryonic stem cells can mimic development of pancreatic beta-cells

Embryonic stem (ES) cells represent a possible source of islet tissue for the treatment of diabetes. Achieving this goal will require a detailed understanding of how the transcription factor cascade initiated by the homeodomain transcription factor Pdx1 culminates in pancreatic beta-cell development. Here we describe a genetic approach that enables fine control of Pdx1 transcriptional activity during endoderm differentiation of mouse and human ES cell. By activating an exogenous Pdx1VP16 protein in populations of cells enriched in definitive endoderm we show a distinct lineage-dependent requirement for this transcription factor's activity. Mimicking the natural biphasic pattern of Pdx1 expression was necessary to induce an endocrine pancreas-like cell phenotype, in which 30% of the cells were beta-cell-like. Cell markers consistent with the different beta-cell differentiation stages appeared in a sequential order following the natural pattern of pancreatic development. Furthermore, in mouse ES-derived cultures the differentiated beta-like cells secreted C-peptide (insulin) in response to KCl and 3-isobutyl-1-methylxanthine, suggesting that following a natural path of development in vitro represents the best approach to generate functional pancreatic cells. Together these results reveal for the first time a significant effect of the timed expression of Pdx1 on the non-beta-cells in the developing endocrine pancreas. Collectively, we show that this method of in vitro differentiation provides a template for inducing and studying ES cell differentiation into insulin-secreting cells.

Combinatorial transcription factor regulation of the cyclic AMP-response element on the Pgc-1alpha promoter in white 3T3-L1 and brown HIB-1B preadipocytes

Cold stress in rodents increases the expression of UCP1 and PGC-1alpha in brown and white adipose tissue. We have previously reported that C/EBPbeta specifically binds to the CRE on the proximal Pgc-1alpha promoter and increases forskolin-sensitive Pgc-1alpha and Ucp1 expression in white 3T3-L1 preadipocytes. Here we show that in mice exposed to a cold environment for 24 h, Pgc-1alpha, Ucp1, and C/ebpbeta but not C/ebpalpha or C/ebpdelta expression were increased in BAT. Conversely, expression of the C/EBP dominant negative Chop10 was increased in WAT but not BAT during cold exposure. Reacclimatization of cold-exposed mice to a warm environment for 24 h completely reversed these changes in gene expression. In HIB-1B, brown preadipocytes, forskolin increased expression of Pgc-1alpha, Ucp1, and C/ebpbeta early in differentiation and inhibited Chop10 expression. Employing chromatin immunoprecipitation, we demonstrate that C/EBPbeta, CREB, ATF-2, and CHOP10 are bound to the Pgc-1alpha proximal CRE, but CHOP10 does not bind in HIB-1B cell lysates. Forskolin stimulation and C/EBPbeta overexpression in 3T3-L1 cells increased C/EBPbeta and CREB but displaced ATF-2 and CHOP10 binding to the Pgc-1alpha proximal CRE. Overexpression of ATF-2 and CHOP10 in 3T3-L1 cells decreased Pgc-1alpha transcription. Knockdown of Chop10 in 3T3-L1 cells using siRNA increased Pgc-1alpha transcription, whereas siRNA against C/ebpbeta in HIB-1B cells decreased Pgc-1alpha and Ucp1 expression. We conclude that the increased cAMP stimulation of Pgc-1alpha expression is regulated by the combinatorial effect of transcription factors acting at the CRE on the proximal Pgc-1alpha promoter.

Identification of adjacent binding sites for the YY1 and E4BP4 transcription factors in the ovine PrP (Prion) gene promoter

The PrP gene encodes the cellular isoform of the prion protein (PrP(c)) which has been shown to be crucial to the development of transmissible spongiform encephalopathies (TSEs). PrP knock-out mice, which do not express endogenous PrP(c), exhibit resistance to TSE disease. The regulation of PrP gene expression represents, therefore, a crucial factor in the development of TSEs. Two sequence motifs in the PrP promoter (positions -287 to -263 from transcriptional start) were previously reported as being highly conserved, and it was suggested that they represent binding sites for as yet unidentified transcription factors. To test this hypothesis, binding of nuclear proteins was analyzed by electrophoretic mobility shift assays using ovine or murine cells and tissues with radiolabeled DNA probes containing the conserved motif sequences. Specific binding was observed to both motifs, and polymorphic variants of these motifs exhibited differential binding. Two proteins bound to these motifs were identified as the Yin Yang 1 (YY1) (motif 1) and E4BP4 (motif 2) transcription factors. Functional promoter analysis of four different promoter variants revealed that motif 1 (YY1) was associated with inhibitory activity in the context of the PrP promoter, whereas motif 2 (E4BP4) was linked to a slight enhancing activity. This represents the first demonstration of binding of nuclear factors to two highly conserved DNA sequence motifs within mammalian PrP promoters. The action of these factors on the PrP promoter is haplotype-specific, leading us to propose that the prion protein expression pattern and, with it, the distribution of TSE infectivity may be associated with PrP promoter genotype.

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.

C/EBPβ Reprograms White 3T3-L1 Preadipocytes to a Brown Adipocyte Pattern of Gene Expression

cAMP-dependent protein kinase induction of PPARgamma coactivator-1alpha (PGC-1alpha) and uncoupling protein 1 (UCP1) expression is an essential step in the commitment of preadipocytes to the brown adipose tissue (BAT) lineage. We studied the molecular mechanisms responsible for differential expression of PGC-1alpha in HIB1B (BAT) and 3T3-L1 white adipose tissue (WAT) precursor cell lines. In HIB1B cells PGC-1alpha and UCP1 expression is cAMP-inducible, but in 3T3-L1 cells, expression is reduced and is cAMP-insensitive. A proximal 264-bp PGC-1alpha reporter construct was cAMP-inducible only in HIB1B cells and was suppressed by site-directed mutagenesis of the proximal cAMP response element (CRE). In electrophoretic mobility shift assays, the transcription factors CREB and C/EBPbeta, but not C/EBPalpha and C/EBPdelta, bound to the CRE on the PGC-1alpha promoter region in HIB1B and 3T3-L1 cells. Chromatin immunoprecipitation studies demonstrated that C/EBPbeta and CREB bound to the CRE region in HIB1B and 3T3-L1 cell lysates. C/EBPbeta expression was induced by cAMP only in HIB1B cells, and overexpression of C/EBPbeta rescued cAMP-inducible PGC-1alpha and UCP1 expression in 3T3-L1 cells. These data demonstrate that differentiation of preadipocytes toward the BAT rather than the WAT phenotype is controlled in part by the action of C/EBPbeta on the CRE in PGC-1alpha proximal promoter.

ATF-2 stimulates the human insulin promoter through the conserved CRE2 sequence

The insulin promoter contains a number of dissimilar cis-acting regulatory elements that bind a range of tissue specific and ubiquitous transcription factors. Of the regulatory elements within the insulin promoter, the cyclic AMP responsive element (CRE) binds by far the most diverse array of transcription factors. Rodent insulin promoters have a single CRE site, whereas there are four CREs within the human insulin gene, of which CRE2 is the only one conserved between species. The aim of this study was to characterise the human CRE2 site and to investigate the effects of the two principal CRE-associated transcription factors; CREB-1 and ATF-2. Co-transfection of INS-1 pancreatic beta-cells with promoter constructs containing the human insulin gene promoter placed upstream of the firefly luciferase reporter gene and expression plasmids for ATF-2 or CREB-1 showed that ATF-2 stimulated transcriptional activity while CREB-1 elicited an inhibitory effect. Mutagenesis of CRE2 diminished the effect of ATF-2 but not that of CREB-1. ATF-2 was shown to bind to the CRE2 site by electrophoretic mobility shift assay and by chromatin immunoprecipitation, while siRNA mediated knockdown of ATF-2 diminished the stimulatory effects of cAMP related signalling on promoter activity. These results suggest that ATF-2 may be a key regulator of the human insulin promoter possibly stimulating activity in response to extracellular signals.

Comparative analysis of insulin gene promoters: implications for diabetes research

DNA sequences that regulate expression of the insulin gene are located within a region spanning approximately 400 bp that flank the transcription start site. This region, the insulin promoter, contains a number of cis-acting elements that bind transcription factors, some of which are expressed only in the beta-cell and a few other endocrine or neural cell types, while others have a widespread tissue distribution. The sequencing of the genome of a number of species has allowed us to examine the manner in which the insulin promoter has evolved over a 450 million-year period. The major findings are that the A-box sites that bind PDX-1 are among the most highly conserved regulatory sequences, and that the conservation of the C1, E1, and CRE sequences emphasize the importance of MafA, E47/beta2, and cAMP-associated regulation. The review also reveals that of all the insulin gene promoters studied, the rodent insulin promoters are considerably dissimilar to the human, leading to the conclusion that extreme care should be taken when extrapolating rodent-based data on the insulin gene to humans.

Presence of endocrine and exocrine markers in EGFP-positive cells from the developing pancreas of a nestin/EGFP mouse

In order to purify and characterize nestin-positive cells in the developing pancreas a transgenic mouse was generated, in which the enhanced green fluorescent protein (EGFP) was driven by the nestin second intronic enhancer and upstream promoter. In keeping with previous studies on the distribution of nestin, EGFP was expressed in the developing embryo in neurones in the brain, eye, spinal cord, tail bud and glial cells in the small intestine. In the pancreas there was no detectable EGFP at embryonic day 11.5 (E11.5). EGFP expression appeared at E12.5 and increased in intensity through E14.5, E18.5 and post-natal day 1. Flow cytometry was used to quantify and purify the EGFP positive population in the E15.5 pancreas. The purified (96%) EGFP-expressing cells, which represent 20% of the total cell population, were shown by RT/PCR to express exocrine cell markers (amylase and P48) and endocrine cell markers (insulin 1, insulin 2, and Ngn3). They also expressed, at a lower level, PDX-1, Isl-1, and the islet hormones pancreatic polypeptide, glucagon and somatostatin as well as GLUT2, the stem cell marker ABCG2 and PECAM, a marker of endothelial cells. It was further shown by immunocytochemistry of the E15.5 pancreas that EGFP colocalised in separate subpopulations of cells that expressed nestin, insulin and amylase. These results support the conclusion that nestin expressing cells can give rise to both endocrine and exocrine cells. The ability to purify these putative progenitor cells may provide further insights into their properties and function.

Transcription factor cycling on the insulin promoter

Using MIN6 beta-cells and chromatin immunoprecipitation (ChIP) assays, the chronological sequence of binding of MafA, E47/beta2 and PDX-1 to the insulin promoter in living beta-cells were investigated. All four factors were shown to bind to the mouse insulin 2 promoter in a cyclical manner with a periodicity of approximately 10-15 min. The cyclical binding of MafA, E47 and beta2 was largely unaffected by the glucose or insulin concentration in the media. However, the binding and cycling of PDX-1 was markedly abolished in low glucose (1 mM), and this was reversed in the presence of low concentrations of insulin.

Relative contribution of PDX-1, MafA and E47/beta2 to the regulation of the human insulin promoter

The insulin promoter binds a number of tissue-specific and ubiquitous transcription factors. Of these, the homoeodomain protein PDX-1 (pancreatic duodenal homeobox factor-1), the basic leucine zipper protein MafA and the basic helix-loop-helix heterodimer E47/BETA2 (beta-cell E box transactivator 2; referred to here as beta2) bind to important regulatory sites. Previous studies have shown that PDX-1 can interact synergistically with E47 and beta2 to activate the rat insulin 1 promoter. The aim of the present study was to determine the relative contribution of PDX-1, MafA and E47/beta2 in regulating the human insulin promoter, and whether these factors could interact synergistically in the context of the human promoter. Mutagenesis of the PDX-1, MafA and E47/beta2 binding sites reduced promoter activity by 60, 74 and 94% respectively, in INS-1 beta-cells. In the islet glucagonoma cell line alphaTC1.6, overexpression of PDX-1 and MafA separately increased promoter activity approx. 2.5-3-fold, and in combination approx. 6-fold, indicating that their overall effect was additive. Overexpression of E47 and beta2 had no effect. In HeLa cells, PDX-1 stimulated the basal promoter by approx. 40-fold, whereas MafA, E47 and beta2 each increased activity by less than 2-fold. There was no indication of any synergistic effects on the human insulin promoter. On the other hand, the rat insulin 1 promoter and a mutated version of the human insulin promoter, in which the relevant regulatory elements were separated by the same distances as in the rat insulin 1 promoter, did exhibit synergy. PDX-1 was shown further to activate the endogenous insulin 1 gene in alphaTC1.6 cells, whereas MafA activated the insulin 2 gene. In combination, PDX-1 and MafA activated both insulin genes. Chromatin immunoprecipitation assays confirmed that PDX-1 increased the association of acetylated histones H3 and H4 with the insulin 1 gene and MafA increased the association of acetylated histone H3 with the insulin 2 gene.

Glucagon-like peptide-1 stimulates human insulin promoter activity in part through cAMP-responsive elements that lie upstream and downstream of the transcription start site

Glucagon-like peptide-1 (GLP-1) is a peptide hormone secreted from the enteroendocrine L-cells of the gut and which acts primarily to potentiate the effects of glucose on insulin secretion from pancreatic beta-cells. It also stimulates insulin gene expression, proinsulin biosynthesis and affects the growth and differentiation of the islets of Langerhans. Previous studies on the mechanisms whereby GLP-1 regulates insulin gene transcription have focused on the rat insulin promoter. The aim of this study was to determine whether the human insulin promoter was also responsive to GLP-1, and if so to investigate the possible role of cAMP-responsive elements (CREs) that lie upstream (CRE1 and CRE2) and downstream (CRE3 and CRE4) of the transcription start site. INS-1 pancreatic beta-cells were transfected with promoter constructs containing fragments of the insulin gene promoter placed upstream of the firefly luciferase reporter gene. GLP-1 was found to stimulate the human insulin promoter, albeit to a lesser degree than the rat insulin promoter. Mutagenesis of CRE2, CRE3 and CRE4 blocked the stimulatory effect of GLP-1 while mutagenesis of CRE1 had no effect. Analysis of nuclear protein binding to the four CREs showed that, while they share some proteins, each CRE site is unique. Stimulation of transcription by GLP-1 through CRE2, CRE3 and CRE4 resulted in altered protein binding that was different for each of the CRE sites involved. Collectively, these data show that the four human CREs are not simply multiple copies of the rat CRE site and further emphasise that the human insulin promoter is distinct from the rodent promoter.

Insulin promoter factor-1 mutations and diabetes in Trinidad: identification of a novel diabetes-associated mutation (E224K) in an Indo-Trinidadian family

This study investigated the prevalence of insulin promoter factor-1(IPF-1) mutations in familial early-onset diabetes mellitus in Trinidad. We screened 264 unrelated subjects with type 2 diabetes diagnosed before 40 yr of age and a family history of diabetes for mutations in the minimal promoter and coding region of the IPF-1 gene (IPF1). This study population included 169 patients of East Indian descent (Indo-Trinidadians), 66 of African descent (Afro-Trinidadians), and 29 of mixed ancestry. We identified five IPF1 variants, including one new missense mutation E224K, the previously described diabetes-associated duplication P242 P243dupP, two silent mutations in the codons for Leu54 (c.162G>A) and Ala256 (c.768C>A), and a substitution in the 5'-untranslated region (c.-18C>T). The E224K mutation was found in two unrelated diabetic Indo-Trinidadians and 0 of 60 controls. It was present on the same haplotype in both patients suggesting a founder effect. The E224K mutation cosegregated with early-onset diabetes or impaired glucose tolerance in a large family, suggestive of the type 4 form of maturity-onset diabetes of the young rather than type 2 diabetes. Functional studies of E224K showed reduced transactivation activity. IPF1 mutations leading to synthesis of a mutant protein may contribute to the development of familial early-onset diabetes/maturity-onset diabetes of the young in Indo-Trinidadians.

Enhanced expression of a furin-cleavable proinsulin

Cell engineering or gene therapy may represent an alternative to current methods of treating diabetes mellitus. Cells could be engineered to secrete insulin ex vivo for transplantation or the insulin gene could be administered directly by injection into muscle. A problem has been that non-neuroendocrine cells lack the endoproteases (PC3/1 and PC2) that are responsible for the processing of proinsulin to insulin. This can be surmounted by engineering the paired basic amino acid processing sites within proinsulin to sites that would be recognized by the ubiquitously expressed protease, furin. However, in every study to date, the expression of the furin-cleavable construct was greatly reduced relative to that of the unmodified proinsulin construct. We investigated possible causes for this, including mRNA stability, the presence of additional CpG islands, and the amino acid substitutions within furin-cleavable proinsulin. Several furin-cleavable rat proinsulin I cDNAs were engineered and used to transfect human HEK293, rat L6 and mouse C(2)C(12) cell lines. The stability of wild-type and furin-cleavable proinsulin mRNA in transfected C(2)C(12) cells was measured by RT-PCR. Comparison of the decay rates in the presence of actinomycin D showed no significant difference between the two species of mRNA. A furin-cleavable proinsulin cDNA was created to contain the same distribution of CpG islands as wild-type proinsulin. Comparison of insulin-like immunoreactivity in all three cell lines transfected with either this construct or a widely used furin-cleavable proinsulin containing additional CpG islands showed that the presence of the extra CpG islands had no effect. Studies to examine amino acid substitutions used to create furin consensus sequences showed that the addition of basic residues at the C-peptide/A-chain junction was responsible for the reduced production of furin-cleavable proinsulin. Using this information, we engineered a cDNA for furin-cleavable rat proinsulin I that was efficiently processed to mature insulin and expressed at the same level as wild-type proinsulin.

Secretion of bioactive human insulin following plasmid-mediated gene transfer to non-neuroendocrine cell lines, primary cultures and rat skeletal muscle in vivo

The objective of these studies was to evaluate human insulin gene expression following intramuscular plasmid injection in non-diabetic rats as a potential approach to gene therapy for diabetes mellitus avoiding the need for immunosuppression. A wild-type human preproinsulin construct and a mutant construct in which PC2/PC3 sites were engineered to form furin consensus sites were evaluated in in vitro transfections of hepatocyte (HepG2) and myoblast (C2C12/L6) cell lines, primary rat myoblasts, and dermal fibroblasts. In vivo gene transfer by percutaneous plasmid injection of soleus muscle +/- prior notexin-induced myolysis was assessed in rats. In vitro transfection of non-neuroendocrine cell lines and primary cultures with wild-type human preproinsulin resulted in secretion of predominantly unprocessed proinsulin. Employing the mutant construct, there was significant processing to mature insulin (HepG2, 95%; C2C12, 75%; L6, 65%; primary myoblasts, 48%; neonatal fibroblasts, 56%; adult fibroblasts, 87%). In rats aged 5 weeks, circulating human (pro)insulin was detected from 1 to 37 days following plasmid injection and the potential of augmenting transfection efficiency by prior notexin injection was demonstrated (wild-type processing, 87%; mutant, 90%). Relative hypoglycaemia was confirmed by HbA1C (saline, 5.5%; wild type, 5.1%; mutant, 5.1% (P<0.05)). Human (pro)insulin levels and processing (wild-type, 8%; mutant, 53%) were lower in rats aged 9 months but relative hypoglycaemia was confirmed by serum glucose at 10 days (saline, 6.4 mmol/l; wild-type, 6.0 mmol/l; mutant, 5.4 mmol/l). In conclusion, prolonged constitutive systemic secretion of bioactive human (pro)insulin has been attained in non-neuroendocrine cells in vitro and in growing and mature rats following intramuscular plasmid injection.

The effect of water temperature on the GABAergic and reproductive systems in female and male goldfish (Carassius auratus)

This study investigated the effect of water temperature on the synthesis of the amino acid neurotransmitter gamma-aminobutyric acid (GABA). In goldfish, GABA stimulates the release of pituitary gonadotropin-II (GTH-II), which regulates gonadal function. Fish were maintained in water of 11, 18, or 24 degrees. In the female and male goldfish, GABA synthesis rates estimated following inhibition of GABA catabolism by gamma-vinyl GABA (GVG) in both the telencephalon (TEL) and the hypothalamus (HYP) were increased in fish held at 24 degrees compared to those at either 11 or 18 degrees (P < 0.05). Additionally, GABA synthesis rates in the pituitary increased in a temperature-dependent manner. Glutamate is the precursor for GABA synthesis; however, no consistent pattern was seen between glutamate and GABA synthesis rates, indicating that glutamate is not a limiting factor in GABA synthesis. Both water temperature and GVG administration increased serum GTH-II levels in female goldfish. However, in male goldfish water temperature had no significant effect on serum GTH-II levels, and GVG injection increased serum GTH-II levels only in fish maintained at 24 degrees. The effects of temperature on the levels of mRNA expression of the GABA-synthesizing enzymes glutamate decarboxylase 65 (GAD(65)) and GAD(67) were measured by semiquantitative PCR. In the TEL and HYP of female goldfish, GAD(65) was not affected, whereas temperature change from 11 to 18 degrees increased (P < 0.05) GAD(67) mRNA levels. These results demonstrate that central GABAergic systems in the goldfish are temperature sensitive.

Growth and development of the islets of Langerhans: implications for the treatment of diabetes mellitus

In the past couple of years a number of major breakthroughs have been made in understanding the developmental biology of the islets of Langerhans. These include the involvement of the hedgehog signalling pathway in defining the region of the gut endoderm that will develop into the pancreas; the discovery that the transcription factor neurogenin3 and the Delta/Notch signalling pathway control endocrine cell differentiation through a lateral inhibition mechanism; and that alpha and beta cells are derived from an islet progenitor cell and follow independent lineage pathways rather than arising from a common mutihormonal progenitor cell as previously thought. This knowledge had been used in strategies to provide a replenishable supply of insulin-secreting cells for the treatment of diabetes mellitus. Thus, islet progenitor cells in adult pancreatic ducts or in isolated islets of Langerhans have been induced to grow in culture and their endocrine-like properties have been characterised. A proliferating beta-like cell line has been derived from tissue removed from a child with persistent hyperinsulinaemic hypoglycaemia of infancy and been engineered in culture to secrete insulin in response to glucose. And finally, embryonic stem cells have been shown to adopt islet-like characteristics under defined culture conditions.

Pancreatic duodenal homeobox-1, PDX-1, a major regulator of beta cell identity and function

Pancreatic duodenal homeobox -1 is a transcription factor that is expressed in beta and delta cells of the islets of Langerhans and in dispersed endocrine cells of the duodenum. It is involved in regulating the expression of a number of key beta-cell genes as well as somatostatin. It also plays a pivotal part in the development of the pancreas and islet cell ontogeny. Thus homozygous disruption of the gene in mice and humans results in pancreatic agenesis. Heterozygous mutations in the gene result in impaired glucose tolerance and symptoms of diabetes as seen in MODY4 and late-onset Type II (non-insulin-dependent) diabetes mellitus. In adults pancreatic duodenal homeobox-1 expression is increased in duct cells of the pancreas that have been induced to proliferate and differentiate to form new islets. Defects in pancreatic duodenal homeobox-1 could therefore contribute to Type II diabetes by affecting compensatory mechanisms that increase the rate of beta-cell neogenesis to meet the increased insulin secretory demand. It could also be a pharmacological target for beta-cell defects in Type II diabetes, while its role as a regulator of islet stem cell activity is being exploited to produce a replenishable source of islet tissue for transplantation in Type I (insulin-dependent) diabetes mellitus.

Phosphorylation-dependent nucleocytoplasmic shuttling of pancreatic duodenal homeobox-1

Pancreatic duodenal homeobox-1 (PDX-1) is a homeodomain protein that plays an important role in the development of the pancreas and in maintaining the identity and function of the islets of Langerhans. It also regulates the expression of the insulin gene in response to changes in glucose and insulin concentrations. Glucose and insulin regulate PDX-1 by way of a signaling pathway involving phosphatidylinositol 3-kinase (PI 3-kinase) and SAPK2/p38. Activation of this pathway leads to phosphorylation of PDX-1 and its movement into the nucleus. To investigate the intracellular trafficking of PDX-1, immunocytochemistry was used to localize PDX-1 in the human beta-cell line NesPDX-1, in which PDX-1 is overexpressed, and in MIN6 beta-cells. In low-glucose conditions, PDX-1 localized predominantly to the nuclear periphery, with some staining in the cytoplasm. After stimulation with glucose, PDX-1 was present in the nucleoplasm. The translocation of PDX-1 to the nucleoplasm was complete within 15 min and occurred in 5-10 mmol/l glucose. Insulin and sodium arsenite, an activator of the stress-activated pathway, also stimulated PDX-1 movement from the nuclear periphery to the nucleoplasm. When cells were transferred between high glucose- and low glucose-containing medium, PDX-1 rapidly shuttled between the nuclear periphery and the nucleoplasm. Glucose- and insulin-stimulated translocation of PDX-1 to the nucleoplasm was inhibited by wortmannin and SB 203580, indicating that a pathway involving PI 3-kinase and SAPK2/p38 was involved; translocation was unaffected by PD 098959 and rapamycin, suggesting that neither mitogen-activated protein kinase nor p70(s6k) were involved. Arsenite-stimulated import of PDX-1 into the nucleus was inhibited by SB 203580 but not by wortmannin. Export from the nucleoplasm to the nuclear periphery was inhibited by calyculin A and okadaic acid, suggesting that dephosphorylation of PDX-1 was involved. These results demonstrated that PDX-1 shuttles between the nuclear periphery and nucleoplasm in response to changes in glucose and insulin concentrations and that these events are dependent on PI 3-kinase, SAPK2/p38, and a nuclear phosphatase(s).

Association of prohormone convertase 3 with membrane lipid rafts

Prohormone convertase 3 (PC3) is a neuroendocrine-specific member of the subtilisin-kexin family, involved in the intracellular processing and maturation of prohormones and proneuropeptides. PC3 is synthesised as a proprotein that undergoes two different cleavages resulting in the mature PC3 and the enzymatically active PC3DeltaC. In vitro translated proPC3 and proPC3DeltaC bind to trans-Golgi network (TGN)/granule-enriched membranes from the AtT20 neuroendocrine cell line in a pH-dependent manner suggesting both a dominant role for the pro-region in membrane association and that the C-terminal region is not essential. However, while PC3 bound to membranes the majority of PC3DeltaC did not, suggesting that either the pro-region or the C-terminal region of PC3 is required for membrane association. Removal of peripheral membrane proteins did not affect the binding properties of any of the in vitro translated proteins. Chromaffin granule membranes (CGMs) were used to study the binding characteristics of endogenous PC3 and its active C-terminal truncated counterpart (PC3DeltaC). Incubation of CGMs with Triton X-100 did not completely solubilise either of these forms of PC3. Moreover, both PC3 and PC3DeltaC remained associated with detergent-resistant membrane microdomains, termed lipid rafts, purified from CGMs. The data raise the possibility that PC3 and PC3DeltaC are sorted to the regulated secretory pathway via their association with membrane lipid rafts.

Sex steroid regulation of glutamate decarboxylase mRNA expression in goldfish brain is sexually dimorphic

Testosterone and oestradiol can modulate GABA synthesis in sexually regressed goldfish. Here we investigated their effects on the mRNA expression of two isoforms of the GABA synthesizing enzyme glutamate decarboxylase (GAD(65) and GAD(67), EC 4.1.1.15). Full-length GAD clones were isolated from a goldfish cDNA library and sequenced. Goldfish GAD(65) encodes a polypeptide of 583 amino acid residues, which is 77% identical to human GAD(65). Goldfish GAD(67) encodes a polypeptide of 587 amino acid residues and is 82% identical to human GAD(67). Goldfish GAD(65) and GAD(67) are 63% identical. Sexually regressed male and female goldfish were implanted with solid silastic pellets containing testosterone, oestradiol or no steroid. Semiquantitative PCR analysis showed that oestradiol significantly increased GAD(65) mRNA expression in female hypothalamus and telencephalon, while testosterone resulted in a significant increase only in telencephalon. GAD(67) mRNA levels were not affected by steroids in females. In contrast, both steroids induced significant decreases of GAD(65) and GAD(67) mRNA levels in male hypothalamus, but had no effect on GAD mRNA expression in male telencephalon. Our results indicate that modulation of GAD mRNA expression is a possible mechanism for steroid action on GABA synthesis, which may have opposite effects in males and females.

Sexually dimorphic expression of glutamate decarboxylase mRNA in the hypothalamus of the deep sea armed grenadier, Coryphaenoides (Nematonurus) armatus

Glutamate decarboxylase (GAD), is a key enzyme in the central nervous system (CNS) that synthesizes the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) from glutamate. Our previous phylogenetic studies on the evolution of this enzyme indicates that there are at least two distinct forms: GAD65 and GAD67. They are the products of separate genes and probably derive from a common ancestral GAD gene following gene duplication prior to the emergence of the teleosts more than 200 Myr ago. Furthermore, a third GAD-like molecule, GAD3, discovered in the armed grenadier, Coryphaenoides (Nematonurus) armatus, is equally divergent from both GAD65 and GAD67. Specimens of C. (N.) armatus were collected by trawl at a depth of 4,000 m in the Porcupine Seabight (Northeastern Atlantic), and brains dissected and frozen for RNA extraction. All three GAD forms are found in the cerebellum, telencephalon and hypothalamus. Semiquantitative PCR analysis showed that males and females have similar levels of expression of GAD67 and GAD3 in the tissues studied. Independent of the sex examined, the levels of expression of GAD65 and GAD67 in the cerebellum were approximately half that in the telencephalon. GAD3 levels were approximately 30% higher in the cerebellum than in either the telencephalon or hypothalamus. In contrast to GAD67 and GAD3, hypothalamic expression of GAD65 mRNA is 1.8 times higher (p < 0.05) in males than in females. These data indicate that the expression of GAD65, a key enzyme for the synthesis of GABA is sexually dimorphic in females and males of C. (N.) armatus.

Processing of synthetic pro-islet amyloid polypeptide (proIAPP) 'amylin' by recombinant prohormone convertase enzymes, PC2 and PC3, in vitro

Islet amyloid polypeptide (IAPP), amylin, is the constituent peptide of pancreatic islet amyloid deposits which form in islets of Type 2 diabetic subjects. Human IAPP is synthesized as a 67-residue propeptide in islet beta-cells and colocalized with insulin in beta-cell granules. The mature 37-amino acid peptide is produced by proteolysis at pairs of basic residues at the C- and N-termini of the mature peptide. To determine the enzymes responsible for proteolysis and their activity at the potential cleavage sites, synthetic human proIAPP was incubated (0.5-16 h) with recombinant prohormone convertases, PC2 or PC3 at appropriate conditions of calcium and pH. The products were analysed by MS and HPLC. Proinsulin was used as a control and was cleaved by both recombinant enzymes resulting in intermediates. PC3 was active initially at the N-terminal-IAPP junction and later at the C-terminus, whereas initial PC2 activity was at the IAPP-C-terminal junction. Processing at the basic residues within the C-terminal flanking peptide rarely occurred. There was no evidence for substantial competition for the processing enzymes when the combined substrates proinsulin and proIAPP were incubated with both PC2 and PC3. As proinsulin cleavage is sequential in vivo (PC3 active at the B-chain-C-peptide junction, followed by PC2 at A chain-C-peptide junction), these data suggest that proteolysis of proIAPP and proinsulin is coincident in secretory granules and increased proinsulin secretion in diabetes could be accompanied by increased production of proIAPP.

Involvement of the membrane lipid bilayer in sorting prohormone convertase 2 into the regulated secretory pathway

Prohormone convertase 2 (PC2) is a neuroendocrine-specific protease involved in the intracellular maturation of prohormones and proneuropeptides. PC2 is synthesised as a proprotein (proPC2) that undergoes proteolysis, aggregation and membrane association during its transit through the regulated secretory pathway. We have previously shown that the pro region of proPC2 plays a key role in its aggregation and membrane association. To investigate this further, we determined the binding properties of a peptide containing amino acids 45-84 of proPC2 (proPC2(45-84)) to trans-Golgi network/granule-enriched membranes from the AtT20 cell line. Removal of peripheral membrane proteins or hydrolysis of integral membrane proteins did not affect the binding properties of proPC2(45-84). Rather, proPC2(45-84) was shown to bind to protein-free liposomes in a pH- and Ca(2+)-dependent manner. To identify the component of the lipid bilayer involved in this membrane association, we used chromaffin-granule membranes and studied the binding properties of the endogenous PC2. Treatment of the membranes with saponin, a cholesterol-depleting detergent, failed to extract PC2 from the membranes, whereas chromogranin A (CgA) was removed. Treatment of the membranes with Triton X-100 yielded a low-density detergent-insoluble fraction enriched in PC2, but not CgA. The detergent-insoluble fraction also contained glycoprotein III, known to be part of the lipid rafts (membrane microdomains rich in sphingolipids). Finally, sphingolipid depletion of AtT20 cells resulted in the mis-sorting of PC2, suggestive of a link between the association of PC2 with lipid rafts in the membrane and its sorting into the regulated secretory pathway.