Epigenetic programming at the Mogat1 locus may link neonatal overnutrition with long-term hepatic steatosis and insulin resistance.

Postnatal overfeeding increases the risk of chronic diseases later in life, including obesity, insulin resistance, hepatic steatosis, and type 2 diabetes. Epigenetic mechanisms might underlie the long-lasting effects associated with early nutrition. Here we aimed to explore the molecular pathways involved in early development of insulin resistance and hepatic steatosis, and we examined the potential contribution of DNA methylation and histone modifications to long-term programming of metabolic disease. We used a well-characterized mouse model of neonatal overfeeding and early adiposity by litter size reduction. Neonatal overfeeding led to hepatic insulin resistance very early in life that persisted throughout adulthood despite normalizing food intake. Up-regulation of monoacylglycerol O-acyltransferase ( Mogat) 1 conceivably mediates hepatic steatosis and insulin resistance through increasing intracellular diacylglycerol content. Early and sustained deregulation of Mogat1 was associated with a combination of histone modifications that might favor Mogat1 expression. In sum, postnatal overfeeding causes extremely rapid derangements of hepatic insulin sensitivity that remain relatively stable until adulthood. Epigenetic mechanisms, particularly histone modifications, could contribute to such long-lasting effects. Our data suggest that targeting hepatic monoacylglycerol acyltransferase activity during early life might provide a novel strategy to improve hepatic insulin sensitivity and prevent late-onset insulin resistance and fatty liver disease.-Ramon-Krauel, M., Pentinat, T., Bloks, V. W., Cebrià, J., Ribo, S., Pérez-Wienese, R., Vilà, M., Palacios-Marin, I., Fernández-Pérez, A., Vallejo, M., Téllez, N., Rodríguez, M. À., Yanes, O., Lerin, C., Díaz, R., Plosch, T., Tietge, U. J. F., Jimenez-Chillaron, J. C. Epigenetic programming at the Mogat1 locus may link neonatal overnutrition with long-term hepatic steatosis and insulin resistance.

ß-Cell dedifferentiation, reduced duct cell plasticity, and impaired ß-cell mass regeneration in middle-aged rats.

Limitations in ß-cell regeneration potential in middle-aged animals could contribute to the increased risk to develop diabetes associated with aging. We investigated ß-cell regeneration of middle-aged Wistar rats in response to two different regenerative stimuli: partial pancreatectomy (Px + V) and gastrin administration (Px + G). Pancreatic remnants were analyzed 3 and 14 days after surgery. ß-Cell mass increased in young animals after Px and was further increased after gastrin treatment. In contrast, ß-cell mass did not change after Px or after gastrin treatment in middle-aged rats. ß-Cell replication and individual ß-cell size were similarly increased after Px in young and middle-aged animals, and ß-cell apoptosis was not modified. Nuclear immunolocalization of neurog3 or nkx6.1 in regenerative duct cells, markers of duct cell plasticity, was increased in young but not in middle-aged Px rats. The pancreatic progenitor-associated transcription factors neurog3 and sox9 were upregulated in islet ß-cells of middle-aged rats and further increased after Px. The percentage of chromogranin A+/hormone islet cells was significantly increased in the pancreases of middle-aged Px rats. In summary, the potential for compensatory ß-cell hyperplasia and hypertrophy was retained in middle-aged rats, but ß-cell dedifferentiation and impaired duct cell plasticity limited ß-cell regeneration.

Direct reprogramming of human fibroblasts into insulin-producing cells using transcription factors.

Direct lineage reprogramming of one somatic cell into another without transitioning through a progenitor stage has emerged as a strategy to generate clinically relevant cell types. One cell type of interest is the pancreatic insulin-producing ß cell whose loss and/or dysfunction leads to diabetes. To date it has been possible to create ß-like cells from related endodermal cell types by forcing the expression of developmental transcription factors, but not from more distant cell lineages like fibroblasts. In light of the therapeutic benefits of choosing an accessible cell type as the cell of origin, in this study we set out to analyze the feasibility of transforming human skin fibroblasts into ß-like cells. We describe how the timed-introduction of five developmental transcription factors (Neurog3, Pdx1, MafA, Pax4, and Nkx2-2) promotes conversion of fibroblasts toward a ß-cell fate. Reprogrammed cells exhibit ß-cell features including ß-cell gene expression and glucose-responsive intracellular calcium mobilization. Moreover, reprogrammed cells display glucose-induced insulin secretion in vitro and in vivo. This work provides proof-of-concept of the capacity to make insulin-producing cells from human fibroblasts via transcription factor-mediated direct reprogramming.

Determining Beta Cell Mass, Apoptosis, Proliferation, and Individual Beta Cell Size in Pancreatic Sections.

Pancreatic beta cells have a significant remodeling capacity which plays an essential role in the maintenance of glucose homeostasis. Beta cell apoptosis, replication, size, dedifferentiation, and (neo)generation contribute to the beta cell mass regulation. However, the extent of their respective contribution varies significantly depending on the specific condition, and it is the balance among them that determines the eventual change in beta cell mass. Thus, the study of the pancreatic beta cell mass regulation requires the determination of all these factors. In this chapter, we describe the quantification of beta cell replication based on the incorporation of thymidine analogs into replicated DNA strands and on the expression of Ki67 antigen and phosphorylation of histone H3. Beta cell apoptosis is analyzed by the TUNEL technique, and beta cell mass and cross-sectional area of individual beta cells are determined by computerized image processing methods.

Vitamin D Receptor Overexpression in ß-Cells Ameliorates Diabetes in Mice.

Vitamin D deficiency has been associated with increased incidence of diabetes, both in humans and in animal models. In addition, an association between vitamin D receptor (VDR) gene polymorphisms and diabetes has also been described. However, the involvement of VDR in the development of diabetes, specifically in pancreatic ß-cells, has not been elucidated yet. Here, we aimed to study the role of VDR in ß-cells in the pathophysiology of diabetes. Our results indicate that Vdr expression was modulated by glucose in healthy islets and decreased in islets from both type 1 diabetes and type 2 diabetes mouse models. In addition, transgenic mice overexpressing VDR in ß-cells were protected against streptozotocin-induced diabetes and presented a preserved ß-cell mass and a reduction in islet inflammation. Altogether, these results suggest that sustained VDR levels in ß-cells may preserve ß-cell mass and ß-cell function and protect against diabetes.

Pancreatic ductal cells may have a negative effect on human islet transplantation.

AIM: To evaluate the effect of pancreatic ductal cells on experimental human islet transplantation. MATERIALS AND METHODS: Isolated islets were additionally purified by handpicking. Ductal cells were purified by magnetic cell sorting and then clustered into ductal pancreatospheres (DPS). Islets, DPS, and islets + DPS (100 islets + 75 DPS, or 100 islets + 200 DPS) were cultured and glucose-stimulated insulin secretion, ß-cell apoptosis, and gene expression was determined. Islets and islets + DPS preparations (800 islets + 600 DPS) were transplanted to streptozotocin-treated immunodeficient mice and glycemia, graft morphometry, and gene expression were determined. RESULTS: Insulin stimulation index was higher in islets than in islets co-cultured with DPS (5.59 ± 0.93 vs 4.02 ± 0.46; p<0.05). IL1B and CXCL11 expression was higher in 100 islets + 200 DPS than in islets (p<0.01), and IL-1ß was detected in supernatants collected from DPS and islets + DPS preparations, but not in islets. Hyperglycemia developed in 33% and 67% of mice transplanted with islets or with islets + DPS respectively. ß-cell mass was 26% lower in islets + DPS than in islets grafts (p>0.05), and the ratio ß-/endocrine non-ß-cell mass was lower in islets + DPS grafts (islets: 2.05 ± 0.18, islets + DPS: 1.35 ± 0.15; p<0.01). IL1B and IL1RN expression was significantly higher in islets + DPS grafts. CONCLUSIONS: Islet preparations enriched with ductal cells have a lower insulin stimulation index in vitro and achieved a worse metabolic outcome after transplantation. Inflammation may mediate the deleterious effects of ductal cells on islet cells.

A Model for Human Islet Transplantation to Immunodeficient Streptozotocin-Induced Diabetic Mice.

Streptozotocin (STZ) is a cytotoxic glucose analogue that causes beta cell death and is widely used to induce experimental diabetes in rodents. The sensitivity of beta cells to STZ is species-specific and human beta cells are resistant to STZ. In experimental islet transplantation to rodents, STZ-diabetes must be induced before transplantation to avoid destruction of grafted islets by STZ. In human islet transplantation, injection of STZ before transplantation is inconvenient and costly, since human islet availability depends on organ donation and frail STZ-diabetic mice must be kept for unpredictable lapses of time until a human islet preparation is available. Based on the high resistance of human beta cells to STZ, we have tested a new model for STZ-diabetes induction in which STZ is injected after human islet transplantation. Human and mouse islets were transplanted under the kidney capsule of athymic nude mice, and 10-14 days after transplantation mice were intraperitoneally injected with five consecutive daily doses of STZ or vehicle. Beta-cell death increased and beta-cell mass was reduced in mouse islet grafts after STZ injection. In contrast, in human islet grafts beta cell death and mass did not change after STZ injection. Mice transplanted with rodent islets developed hyperglycemia after STZ-injection. Mice transplanted with human islets remained normoglycemic and developed hyperglycemia when the graft was harvested. STZ had no detectable toxic effects on beta cell death, mass and function of human transplanted islets. We provide a new, more convenient and cost-saving model for human islet transplantation to STZ-diabetic recipients in which STZ is injected after islet transplantation.

Publisher Correction: Purification of replicating pancreatic ß-cells for gene expression studies.

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Epithelial to mesenchymal transition in human endocrine islet cells.

BACKGROUND: ß-cells undergo an epithelial to mesenchymal transition (EMT) when expanded in monolayer culture and give rise to highly proliferative mesenchymal cells that retain the potential to re-differentiate into insulin-producing cells. OBJECTIVE: To investigate whether EMT takes place in the endocrine non-ß cells of human islets. METHODOLOGY: Human islets isolated from 12 multiorgan donors were dissociated into single cells, purified by magnetic cell sorting, and cultured in monolayer. RESULTS: Co-expression of insulin and the mesenchymal marker vimentin was identified within the first passage (p1) and increased subsequently (insulin+vimentin+ 7.2±6% at p1; 43±15% at p4). The endocrine non-ß-cells did also co-express vimentin (glucagon+vimentin+ 59±1.5% and 93±6%, somatostatin+vimentin+ 16±9.4% and 90±10% at p1 and p4 respectively; PP+vimentin+ 74±14% at p1; 88±12% at p2). The percentage of cells expressing only endocrine markers was progressively reduced (0.6±0.2% insulin+, 0.2±0.1% glucagon+, and 0.3±0.2% somatostatin+ cells at p4, and 0.7±0.3% PP+ cells at p2. Changes in gene expression were also indicated of EMT, with reduced expression of endocrine markers and the epithelial marker CDH-1 (p<0.01), and increased expression of mesenchymal markers (CDH-2, SNAI2, ZEB1, ZEB2, VIM, NT5E and ACTA2; p<0.05). Treatment with the EMT inhibitor A83-01 significantly reduced the percentage of co-expressing cells and preserved the expression of endocrine markers. CONCLUSIONS: In adult human islets, all four endocrine islet cell types undergo EMT when islet cells are expanded in monolayer conditions. The presence of EMT in all islet endocrine cells could be relevant to design of strategies aiming to re-differentiate the expanded islet cells towards a ß-cell phenotype.

Interleukin-1beta and inducible form of nitric oxide synthase expression in early syngeneic islet transplantation.

Islets are particularly vulnerable in the initial days after transplantation when cell death results in the loss of more than half of the transplanted islet tissue. To determine whether a non-specific inflammation at the grafted site mediated by the local expression of inflammatory cytokines could play a role on the initial damage to transplanted islets, we studied the expressions of interleukin-1beta (IL-1beta) and inducible form of nitric oxide synthase (iNOS) after syngeneic islet transplantation. Insulin-treated streptozotocin-diabetic Lewis rats were syngeneically transplanted with 500 islets. Grafts were harvested 1, 3, or 7 days after transplantation, and the expressions of IL-1beta and iNOS genes were determined by RT-PCR. IL-1beta and iNOS mRNAs were detected in islets immediately after isolation, and were upregulated after transplantation. IL-1beta mRNA was ninefold increased on day 1, was still sevenfold increased on day 3 after transplantation, and declined towards pretransplantation levels on day 7. iNOS mRNA showed a similar pattern of expression to that of IL-1beta: on days 1 and 3 after transplantation it was 14-and 4-fold higher respectively than in freshly isolated islets. In addition, IL-1beta and iNOS were identified in islet grafts and found to be produced mainly by CD68-positive macrophages. A low number of IL-1beta- and iNOS-positive but CD68-negative cells were also identified suggesting that other cell types, in addition to macrophages, were involved in the expression of IL-1beta and NO production in islet grafts. The finding of increased IL-1beta and iNOS gene expressions in the initial days after islet transplantation and the presence of IL-beta and iNOS proteins in the graft confirmed the presence of an early non-specific inflammatory response after islet transplantation. Overall, the data suggest that IL-1beta plays a role in the extensive beta-cell death found in the initial days after islet transplantation.

Role of blood glucose in cytokine gene expression in early syngeneic islet transplantation.

In islet transplantation, local production of cytokines at the grafted site may contribute to the initial nonspecific inflammation response. We have determined whether the metabolic condition of the recipient modulates the cytokine expression in islet grafts in the initial days after transplantation. Normoglycemic and hyperglycemic streptozotocin-diabetic Lewis rats were transplanted with 500 syngeneic islets, an insufficient beta cell mass to restore normoglycemia in hyperglycemic recipients. The expression of IL-1beta, TNF-alpha, IFN-gamma, IL-6, IL-10, and IL-4 genes was determined by real-time PCR in freshly isolated islets, in 24-h cultured islets and in islet grafts on days 1, 3, and 7 after transplantation. IL-1beta mRNA was strongly and similarly increased in normoglycemic and hyperglycemic groups on days 1, 3, and 7 after transplantation compared with freshly isolated and cultured islets. TNF-alpha mRNA was also strongly increased on day 1, and it remained increased on days 3 and 7. IL-6 and IL-10 were not detected in freshly isolated islets, but their expression was clearly enhanced in 24-h cultured islets and islet grafts. IL-6 was further increased in hyperglycemic grafts. IL-10 expression was increased in both normoglycemic and hyperglycemic grafts on day 1 after transplantation, and remained increased in hyperglycemic grafts compared to 24-h cultured islets. IFN-gamma mRNA was barely detected in a few grafts, and IL-4 mRNA was never detected. Thus, the inflammatory response in islet grafts was maximal on day 1 after transplantation, it was sustained, although at lower levels, on days 3 and 7, and it was partly enhanced by hyperglycemia.

Purification of replicating pancreatic ß-cells for gene expression studies.

ß-cell proliferation is a rare event in adult pancreatic islets. To study the replication-related ß-cell biology we designed a replicating ß-cells sorting system for gene expression experiments. Replicating ß-cells were identified by EdU incorporation and purified by flow cytometry. For ß-cell separation islet cells were sorted by size, granularity and Newport Green fluorescence emission that was combined with emitted fluorescence for EdU-labelled replicating cells sorting. The purity of the resulting sorted populations was evaluated by insulin staining and EdU for ß-cell identification and for replicating cells, respectively. Total RNA was isolated from purified cell-sorted populations for gene expression analysis. Cell sorting of dispersed islet cells resulted in 96.2% purity for insulin positivity in the collected ß-cell fraction and 100% efficiency of the EdU-based cell separation. RNA integrity was similar between FACS-sorted replicating and quiescent ß-cells. Global transcriptome analysis of replicating vs quiescent ß-cells showed the expected enrichment of categories related to cell division and DNA replication. Indeed, key genes in the spindle check-point were the most upregulated genes in replicating ß-cells. This work provides a method that allows for the isolation of replicating ß-cells, a very scarce population in adult pancreatic islets.

Short-term culture with the caspase inhibitor z-VAD.fmk reduces beta cell apoptosis in transplanted islets and improves the metabolic outcome of the graft.

In the initial days after transplantation islets are particularly vulnerable and show increased apoptosis and necrosis. We have studied the effects of caspase inhibition on this early beta cell death in syngeneically transplanted islets. Streptozotocin-diabetic C57BL/6 mice were transplanted with 150 syngeneic islets, an insufficient mass to restore normoglycemia, preincubated with or without the pan-caspase inhibitor z-VAD. fmk 2 h before transplantation. Beta cell apoptosis was increased in control islets on day 3 after transplantation (0.28 +/- 0.02%) compared with freshly isolated islets (0.08 +/- 0.02%, p < 0.001), and was partially reduced in transplanted islets preincubated with z-VAD.fmk 200 microM (0.14 +/- 0.02%, p = 0.003) or with z-VAD.fmk 500 microM (0.17 +/- 0.01%, p = 0.012), but not with a lower z-VAD.fmk (100 microM) concentration. Diabetic mice transplanted with islets preincubated with z-VAD.fmk 500 microM showed an improved metabolic evolution compared with control and z-VAD.fmk 200 microM groups. The z-VAD.fmk 500 microM group showed an overall lower blood glucose after transplantation (p = 0.02), and at the end of the study blood glucose values were reduced compared with transplantation day (15.7 +/- 3.6 vs. 32.5 +/- 0.5 mmol/L, p = 0.001). In contrast, blood glucose was not significantly changed in control and z-VAD.fmk 200 microM groups. Four weeks after transplantation beta cell mass was higher in z-VAD.fmk 500 microM group (0.15 +/- 0.02 mg) than in the control group (0.10 +/- 0.02 mg) (p = 0.043). In summary, the treatment of freshly isolated islets with the caspase inhibitor z-VAD.fmk reduced the subsequent apoptosis of the islets once they were transplanted and improved the outcome of the graft.

Identification of miRNAs Involved in Reprogramming Acinar Cells into Insulin Producing Cells.

Reprogramming acinar cells into insulin producing cells using adenoviral (Ad)-mediated delivery of Pdx1, Ngn3 and MafA (PNM) is an innovative approach for the treatment of diabetes. Here, we aimed to investigate the molecular mechanisms involved in this process and in particular, the role of microRNAs. To this end, we performed a comparative study of acinar-to-ß cell reprogramming efficiency in the rat acinar cell line AR42J and its subclone B13 after transduction with Ad-PNM. B13 cells were more efficiently reprogrammed than AR42J cells, which was demonstrated by a strong activation of ß cell markers (Ins1, Ins2, IAPP, NeuroD1 and Pax4). miRNome panels were used to analyze differentially expressed miRNAs in acinar cells under four experimental conditions (i) non-transduced AR42J cells, (ii) non-transduced B13 cells, (iii) B13 cells transduced with Ad-GFP vectors and (iv) B13 cells transduced with Ad-PNM vectors. A total of 59 miRNAs were found to be differentially expressed between non-transduced AR42J and B13 cells. Specifically, the miR-200 family was completely repressed in B13 cells, suggesting that these cells exist in a less differentiated state than AR42J cells and as a consequence they present a greater plasticity. Adenoviral transduction per se induced dedifferentiation of acinar cells and 11 miRNAs were putatively involved in this process, whereas 8 miRNAs were found to be associated with PNM expression. Of note, Ad-PNM reprogrammed B13 cells presented the same levels of miR-137-3p, miR-135a-5p, miR-204-5p and miR-210-3p of those detected in islets, highlighting their role in the process. In conclusion, this study led to the identification of miRNAs that might be of compelling importance to improve acinar-to-ß cell conversion for the future treatment of diabetes.

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

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

Increased ß-cell replication and ß-cell mass regeneration in syngeneically transplanted rat islets overexpressing insulin-like growth factor II.

Insulin-like growth factor II (IGF2) is a growth-promoting peptide that increases ß-cell proliferation and survival. The aim of the study was to determine the effect of IGF2 overexpression on ß-cell mass in transplanted islets. Islets infected with adenovirus encoding for IGF2 (Ad-IGF2 group), for luciferase (Ad-Luc control group), or with uninfected islets (control group) were syngeneically transplanted to streptozotocin-diabetic Lewis rats. Eight hundred islets, a minimal mass model to restore normoglycemia, or 500 islets, a clearly insufficient mass, were transplanted. Rats transplanted with 800 Ad-IGF2 islets showed a better metabolic evolution than control groups. As expected, rats transplanted with 500 Ad-IGF2 or control islets maintained similar hyperglycemia throughout the study, ensuring comparable metabolic conditions among both groups. ß-Cell replication was higher in Ad-IGF2 group than in control group on days 3 [1.45% (IQR: 0.26) vs. 0.58% (IQR: 0.18), p = 0.006], 10 [1.58% (IQR: 1.40) vs. 0.90% (IQR: 0.61), p = 0.035], and 28 [1.35% (IQR: 0.35) vs. 0.64% (IQR: 0.28), p = 0.004] after transplantation. ß-Cell mass was similarly reduced on day 3 after transplantation in Ad-IGF2 and control group [0.36 mg (IQR: 0.26) vs. 0.38 mg (IQR: 0.19)], it increased on day 10, and on day 28 it was higher in Ad-IGF2 than in control group [0.63 mg (IQR: 0.38) vs. 0.42 mg (IQR: 0.31), p = 0.008]. Apoptosis was similarly increased in Ad-IGF2 and control islets after transplantation. No differences in insulin secretion were found between Ad-IGF2 and uninfected control islets. In summary, IGF2 overexpression in transplanted islets increased ß-cell replication, induced the regeneration of the transplanted ß-cell mass, and had a beneficial effect on the metabolic outcome reducing the ß-cell mass needed to achieve normoglycemia.

Gastrin treatment stimulates ß-cell regeneration and improves glucose tolerance in 95% pancreatectomized rats.

ß-Cell mass reduction is a central aspect in the development of type 1 and type 2 diabetes, and substitution or regeneration of the lost ß-cells is a potentially curative treatment of diabetes. To study the effects of gastrin on ß-cell mass in rats with 95% pancreatectomy (95%-Px), a model of pancreatic regeneration, rats underwent 95% Px or sham Px and were treated with [15 leu] gastrin-17 (Px+G and S+G) or vehicle (Px+V and S+V) for 15 d. In 95% Px rats, gastrin treatment reduced hyperglycemia (280 ± 52 mg vs. 436 ± 51 mg/dl, P < 0.05), and increased ß-cell mass (1.15 ± 0.15 mg)) compared with vehicle-treated rats (0.67 ± 0.15 mg, P < 0.05). Gastrin treatment induced ß-cell regeneration by enhancing ß-cell neogenesis (increased number of extraislet ß-cells in Px+G: 0.42 ± 0.05 cells/mm(2) vs. Px+V: 0.27 ± 0.07 cells/mm(2), P < 0.05, and pancreatic and duodenal homeobox 1 expression in ductal cells of Px+G: 1.21 ± 0.38% vs. Px+V: 0.23 ± 0.10%, P < 0.05) and replication (Px+G: 1.65 ± 0.26% vs. S+V: 0.64 ± 0.14%; P < 0.05). In addition, reduced ß-cell apoptosis contributed to the increased ß-cell mass in gastrin-treated rats (Px+G: 0.07 ± 0.02%, Px+V: 0.23 ± 0.05%; P < 0.05). Gastrin action on ß-cell regeneration and survival increased ß-cell mass and improved glucose tolerance in 95% Px rats, supporting a potential role of gastrin in the treatment of diabetes.

The atrial natriuretic peptide and guanylyl cyclase-A system modulates pancreatic beta-cell function.

Atrial natriuretic peptide (ANP) and its guanylyl cyclase-A (GC-A) receptor are being involved in metabolism, although their role in the endocrine pancreas is still greatly unknown. The aim of this work is to study a possible role for the ANP/GC-A system in modulating pancreatic beta-cell function. The results presented here show a direct effect of the GC-A receptor in regulating glucose-stimulated insulin secretion (GSIS) and beta-cell mass. GC-A activation by its natural ligand, ANP, rapidly blocked ATP-dependent potassium (K(ATP)) channel activity, increased glucose-elicited Ca(2+) signals, and enhanced GSIS in islets of Langerhans. The effect in GSIS was inhibited in islets from GC-A knockout (KO) mice. Pancreatic islets from GC-A KO mice responded to increasing glucose concentrations with enhanced insulin secretion compared with wild type (WT). Remarkably, islets from GC-A KO mice were smaller, presented lower beta-cell mass and decreased insulin content. However, glucose-induced Ca(2+) response was more vigorous in GC-A KO islets, and basal K(ATP) channel activity in GC-A KO beta-cells was greatly diminished compared with WT. When protein levels of the two K(ATP) channel constitutive subunits sulfonylurea receptor 1 and Inward rectifier potassium channel 6.2 were measured, both were diminished in GC-A KO islets. These alterations on beta-cell function were not associated with disruption of glucose tolerance or insulin sensitivity in vivo. Glucose and insulin tolerance tests were similar in WT and GC-A KO mice. Our data suggest that the ANP/GC-A system may have a modulating effect on beta-cell function.

Pancreatic remodeling: beta-cell apoptosis, proliferation and neogenesis, and the measurement of beta-cell mass and of individual beta-cell size.

The endocrine pancreas has a significant remodeling capacity that plays a crucial role in the maintenance of glucose homeostasis. Changes in beta-cell apoptosis, replication and size, and islet neogenesis contribute to the remodeling of the endocrine pancreas. The extent of their respective contribution varies significantly depending on the specific condition under consideration, and it is the balance among them that determines the eventual change in beta-cell mass. Thus, the study of pancreatic remodeling requires the determination of all these factors. In this chapter, we describe the quantification of beta-cell replication based on 3-bromo-2-deoxyuridine incorporation into DNA and on the expression of Ki67 antigen, of beta-cell apoptosis by the TUNEL technique and islet neogenesis by quantification of number of islets budding from pancreatic ducts, by confocal assessment of the expression of islet cell hormones in ductal cells, and by identification of small group of extra-islet beta-cells. Point counting morphometry is used to estimate beta-cell mass and planimetry to determine the cross-sectional area of individual beta-cells, a measure of beta-cell size.