Minireview: Meeting the demand for insulin: molecular mechanisms of adaptive postnatal beta-cell mass expansion

Role of leptin in the pancreatic β-cell: effects and signaling pathways

Leptin plays an important role in the control of food intake, energy expenditure, metabolism, and body weight. This hormone also has a key function in the regulation of glucose homeostasis. Although leptin acts through central and peripheral mechanisms to modulate glucose metabolism, the pancreatic β-cell of the endocrine pancreas is a critical target of leptin actions. Leptin receptors are present in the β-cell, and their activation directly inhibits insulin secretion from these endocrine cells. The effects of leptin on insulin occur also in the long term, since this hormone inhibits insulin gene expression as well. Additionally, β-cell mass can be affected by leptin through changes in proliferation, apoptosis, or cell size. All these different functions in the β-cell are triggered by leptin as a result of the large diversity of signaling pathways that this hormone is able to activate in the endocrine pancreas. Therefore, leptin can participate in glucose homeostasis owing to different levels of modulation of the pancreatic β-cell population. Furthermore, it has been proposed that alterations in this level of regulation could contribute to the impairment of β-cell function in obesity states. In the present review, we will discuss all these issues with special emphasis on the effects and pathways of leptin signaling in the pancreatic β-cell.

Reduced expression of the LRP16 gene in mouse insulinoma (MIN6) cells exerts multiple effects on insulin content, proliferation and apoptosis

This study assessed the effects of leukemia-related protein 16 (LRP16) on the regulation of pancreatic functions in mouse insulinoma (MIN6) cells. Cells with down-regulated expression of LRP16 were obtained by a shRNA interference strategy. Insulin content and glucose-stimulated insulin secretion (GSIS) were examined by radioimmunoassay. Western blotting was applied to detect protein expression. Glucose-stimulated sub-cellular localization of PDX-1 was immunocytochemically determined. Cell proliferation and apoptosis were detected by flow cytometry. Our results showed that LRP16 regulated insulin content in MIN6 cells by controlling expression of insulin and insulin transcription factors. LRP16 gene silence in MIN6 cells led to reduced cell proliferation and increased apoptosis. The observation of phosphorylation of serine-473 Akt and the localization of PDX-1 to the nucleus under glucose-stimulation exhibited that LRP16 was a component mediating Akt signaling in MIN6 cells. These results suggest that LRP16 plays a key role in maintaining pancreatic β-cell functions and may help us to understand the protective effects of estrogen on the functions of pancreatic β-cells.

Optimal elevation of β-cell 11β-hydroxysteroid dehydrogenase type 1 is a compensatory mechanism that prevents high-fat diet-induced β-cell failure

Type 2 diabetes ultimately results from pancreatic β-cell failure. Abnormally elevated intracellular regeneration of glucocorticoids by the enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) in fat or liver may underlie pathophysiological aspects of the metabolic syndrome. Elevated 11β-HSD1 is also found in pancreatic islets of obese/diabetic rodents and is hypothesized to suppress insulin secretion and promote diabetes. To define the direct impact of elevated pancreatic β-cell 11β-HSD1 on insulin secretion, we generated β-cell-specific, 11β-HSD1-overexpressing (MIP-HSD1) mice on a strain background prone to β-cell failure. Unexpectedly, MIP-HSD1(tg/+) mice exhibited a reversal of high fat-induced β-cell failure through augmentation of the number and intrinsic function of small islets in association with induction of heat shock, protein kinase A, and extracellular signal-related kinase and p21 signaling pathways. 11β-HSD1(-/-) mice showed mild β-cell impairment that was offset by improved glucose tolerance. The benefit of higher β-cell 11β-HSD1 exhibited a threshold because homozygous MIP-HSD1(tg/tg) mice and diabetic Lep(db/db) mice with markedly elevated β-cell 11β-HSD1 levels had impaired basal β-cell function. Optimal elevation of β-cell 11β-HSD1 represents a novel biological mechanism supporting compensatory insulin hypersecretion rather than exacerbating metabolic disease. These findings have immediate significance for current therapeutic strategies for type 2 diabetes.

Free fatty acids block glucose-induced β-cell proliferation in mice by inducing cell cycle inhibitors p16 and p18

Pancreatic β-cell proliferation is infrequent in adult humans and is not increased in type 2 diabetes despite obesity and insulin resistance, suggesting the existence of inhibitory factors. Free fatty acids (FFAs) may influence proliferation. In order to test whether FFAs restrict β-cell proliferation in vivo, mice were intravenously infused with saline, Liposyn II, glucose, or both, continuously for 4 days. Lipid infusion did not alter basal β-cell proliferation, but blocked glucose-stimulated proliferation, without inducing excess β-cell death. In vitro exposure to FFAs inhibited proliferation in both primary mouse β-cells and in rat insulinoma (INS-1) cells, indicating a direct effect on β-cells. Two of the fatty acids present in Liposyn II, linoleic acid and palmitic acid, both reduced proliferation. FFAs did not interfere with cyclin D2 induction or nuclear localization by glucose, but increased expression of inhibitor of cyclin dependent kinase 4 (INK4) family cell cycle inhibitors p16 and p18. Knockdown of either p16 or p18 rescued the antiproliferative effect of FFAs. These data provide evidence for a novel antiproliferative form of β-cell glucolipotoxicity: FFAs restrain glucose-stimulated β-cell proliferation in vivo and in vitro through cell cycle inhibitors p16 and p18. If FFAs reduce proliferation induced by obesity and insulin resistance, targeting this pathway may lead to new treatment approaches to prevent diabetes.

Interleukin-1 receptor antagonist: a new therapy for type 2 diabetes mellitus

Various complex mechanisms and their multifactorial pathways decisively provoke low-grade local and systemic inflammation in β-cells of pancreatic islets and peripheral tissues to induce β-cells' dysfunction and apoptosis, insulin resistance, and ultimately, overt type 2 diabetes mellitus (T2DM). Conventional antidiabetic agents are being less popular, as they have some potential adverse effects. Currently, many anti-inflammatory therapeutic modalities are being investigated to abate the infuriating effects of inducers of T2DM and among them, interleukin-1 receptor antagonist (IL-1Ra) is the only one that has been approved by US Food and Drug Administration. We have compared IL-1Ra with other anti-inflammatory agents and conventional antidiabetic agents. Although, IL-1Ra has broad-spectrum anti-inflammatory activities, it also has some limitations due to its short half-life. To overcome the problem of short half-life of IL-1Ra, recently, we fused IL-1Ra in recombinant human serum albumin and expressed it in Pichia pastoris. Its bioactivity was also checked by IL-1-induced A375.S2 apoptotic cells. Furthermore, we have also formulated IL-1Ra with Pluronic F-127-based thermosensitive gel and investigated its in vitro characteristics to prolong its therapeutic effects. Further studies are required to investigate its therapeutic effects against diabetes and diabetes-associated complications.

Central prolactin modulates insulin sensitivity and insulin secretion in diabetic rats

BACKGROUND

Prolactin secretion is self-regulating as it acts upon hypothalamic dopaminergic systems which inhibit prolactin release from the anterior pituitary. Circulating prolactin improves glucose homeostasis by increasing insulin action and secretion, but central prolactin effects on glucose homeostasis have not been examined. Here, we determined that chronic central infusion of prolactin modulates insulin resistance and β-cell function and mass in 90% of pancreatectomized diabetic male rats.

METHODS

Diabetic rats were divided into three groups according to the dose of intracerebroventricular infusion of prolactin during 4 weeks: (1) low-dose prolactin (Low-PRL; 0.1 µg/h), (2) high-dose prolactin (High-PRL; 1 µg/h) and (3) vehicle only (cerebrospinal fluid). Nondiabetic rats were centrally infused with the vehicle.

RESULTS

Chronic intracerebroventricular infusion of Low-PRL lowered body weight and epididymal fat pads by increasing hypothalamic dopamine levels that reduced serum prolactin levels and potentiated leptin signaling. However, High-PRL slightly exacerbated energy dysregulation, decreased hypothalamic dopamine levels, and elevated serum prolactin levels. Both dosages promoted β-cell mass but in a different manner: Low-PRL decreased β-cell apoptosis, whereas High-PRL increased its proliferation. However, only Low-PRL enhanced first-phase insulin secretion and improved insulin sensitivity at a hyperglycemic state in comparison to the control. Low-PRL also increased glucose infusion rates and decreased hepatic glucose output in hyperinsulinemic states, signifying an improvement in hepatic insulin sensitivity. However, High-PRL exacerbated hepatic insulin resistance compared with the control diabetic rats.

CONCLUSIONS

In contrast to the exacerbation of insulin resistance caused by High-PRL, Low-PRL may improve energy and glucose metabolism by increasing hypothalamic dopamine levels in diabetic rats.

Early peroxisome proliferator-activated receptor gamma regulated genes involved in expansion of pancreatic beta cell mass

BACKGROUND

The progression towards type 2 diabetes depends on the allostatic response of pancreatic beta cells to synthesise and secrete enough insulin to compensate for insulin resistance. The endocrine pancreas is a plastic tissue able to expand or regress in response to the requirements imposed by physiological and pathophysiological states associated to insulin resistance such as pregnancy, obesity or ageing, but the mechanisms mediating beta cell mass expansion in these scenarios are not well defined. We have recently shown that ob/ob mice with genetic ablation of PPARγ2, a mouse model known as the POKO mouse failed to expand its beta cell mass. This phenotype contrasted with the appropriate expansion of the beta cell mass observed in their obese littermate ob/ob mice. Thus, comparison of these models islets particularly at early ages could provide some new insights on early PPARγ dependent transcriptional responses involved in the process of beta cell mass expansion

RESULTS

Here we have investigated PPARγ dependent transcriptional responses occurring during the early stages of beta cell adaptation to insulin resistance in wild type, ob/ob, PPARγ2 KO and POKO mice. We have identified genes known to regulate both the rate of proliferation and the survival signals of beta cells. Moreover we have also identified new pathways induced in ob/ob islets that remained unchanged in POKO islets, suggesting an important role for PPARγ in maintenance/activation of mechanisms essential for the continued function of the beta cell.

CONCLUSIONS

Our data suggest that the expansion of beta cell mass observed in ob/ob islets is associated with the activation of an immune response that fails to occur in POKO islets. We have also indentified other PPARγ dependent differentially regulated pathways including cholesterol biosynthesis, apoptosis through TGF-β signaling and decreased oxidative phosphorylation.

[Gestational diabetes]

Gestational diabetes is one of the most common complications during pregnancy. Its incidence has increased in recent decades. This is partly due to improved screening strategies and more stringent diagnostic criteria. Using the updated diagnostic thresholds, it is expected that 5-10% at least of all pregnant women will be diagnosed with diabetes mellitus. The rationale for the novel blood glucose criteria are data from prospective studies reporting an increase of fetal and maternal complications even when the blood glucose is only slightly increased. For the first time, solid evidence now exists for the diagnosis and treatment of gestational diabetes.

Serum prolactin concentrations determine whether they improve or impair β-cell function and insulin sensitivity in diabetic rats

BACKGROUND

Prolactin improves glucose homeostasis by increasing β-cell mass under certain conditions such as pregnancy, whereas hyperprolactinaemia due to a pituitary gland adenoma tumour exacerbates insulin resistance. However, previous studies have not evaluated how prolactin modulates β-cell function and insulin sensitivity at different dosages. Here, we determined that chronic intraperitoneal injections of different dosages of prolactin have opposite effects on insulin resistance and β-cell function and mass in 90% pancreatectomized diabetic male rats, and the mechanisms were explored.

METHODS

Diabetic rats were divided into three groups according to the dose of intraperitoneally injected prolactin for 4 weeks: (1) low dose of prolactin (25 µg/kg bw/12 h), (2) high dose of prolactin (250 µg/kg bw/12 h), and (3) vehicle. As a non-diabetic control group, sham-operated rats were injected with vehicle.

RESULTS

Chronic high- and low-dose prolactin injections elevated serum prolactin levels by 2.5- and 11.8-fold, respectively. Both dosages promoted β-cell mass by increasing β-cell proliferation and neogenesis through the potentiation of phosphorylation of signal transducer and activator of transcription 5 and decreased menin expression in diabetic rats. However, only the low-dose prolactin injection potentiated glucose-stimulated insulin secretion though glucokinase and glucose transporter 2 induction in the diabetic rats. In addition, low-dose prolactin decreased hepatic glucose output in hyperinsulinaemic states, indicating an improvement in hepatic insulin resistance. However, the high-dose prolactin injection exacerbated whole-body and hepatic insulin resistance in diabetic rats.

CONCLUSIONS

In contrast to the normal adaptive increases in glucose-stimulated insulin secretion through expanded β-cell mass and insulin sensitivity realized with moderately increased prolactin levels, high levels of prolactin exacerbate insulin resistance and impair the insulin-secretory capacity in diabetic mice.

Epidermal growth factor (EGF)-receptor signalling is needed for murine beta cell mass expansion in response to high-fat diet and pregnancy but not after pancreatic duct ligation

AIMS/HYPOTHESIS

Epidermal growth factor receptor (EGFR) signalling is essential for the proper fetal development of pancreatic islets and in the postnatal formation of an adequate beta cell mass. In this study we investigated the role of EGFR signalling in the physiological states of beta cell mass expansion in adults during metabolic syndrome and pregnancy, as well as in regeneration after pancreatic duct ligation.

METHODS

Heterozygous Pdx1-EGFR-dominant-negative (E1-DN) mice, which have a kinase-negative EGFR under the Pdx1 promoter, and wild-type mice were both subjected to a high-fat diet, pregnancy and pancreatic duct ligation.

RESULTS

The beta cell mass of wild-type mice fed the high-fat diet increased by 70% and the mice remained normoglycaemic; the E1-DN mice became diabetic and failed to show any compensatory beta cell mass expansion. Similarly, pregnant wild-type mice had four times more proliferating beta cells and a 75% increase in beta cell mass at mid-gestation, in contrast to the pregnant E1-DN mice, which did not show any significant beta cell compensation and were hyperglycaemic in an intraperitoneal glucose tolerance test. However, after pancreatic duct ligation, both the wild-type and E1-DN mice showed similar expression of Ngn3 (also known as Neurog3) and beta cell proliferation increased to a similar level in the ligated part of pancreas.

CONCLUSIONS/INTERPRETATIONS

EGFR signalling is essential in beta cell mass expansion during a high-fat diet and pregnancy where replication is the primary mechanism for compensatory beta cell mass expansion. In contrast, EGFR signalling appears not to be crucial to increased beta cell proliferation after pancreatic duct ligation.

Control of pancreatic β cell regeneration by glucose metabolism

Recent studies revealed a surprising regenerative capacity of insulin-producing β cells in mice, suggesting that regenerative therapy for human diabetes could in principle be achieved. Physiologic β cell regeneration under stressed conditions relies on accelerated proliferation of surviving β cells, but the factors that trigger and control this response remain unclear. Using islet transplantation experiments, we show that β cell mass is controlled systemically rather than by local factors such as tissue damage. Chronic changes in β cell glucose metabolism, rather than blood glucose levels per se, are the main positive regulator of basal and compensatory β cell proliferation in vivo. Intracellularly, genetic and pharmacologic manipulations reveal that glucose induces β cell replication via metabolism by glucokinase, the first step of glycolysis, followed by closure of K(ATP) channels and membrane depolarization. Our data provide a molecular mechanism for homeostatic control of β cell mass by metabolic demand.

Glucose stimulates human beta cell replication in vivo in islets transplanted into NOD-severe combined immunodeficiency (SCID) mice

AIMS/HYPOTHESIS

We determined whether hyperglycaemia stimulates human beta cell replication in vivo in an islet transplant model

METHODS

Human islets were transplanted into streptozotocin-induced diabetic NOD-severe combined immunodeficiency mice. Blood glucose was measured serially during a 2 week graft revascularisation period. Engrafted mice were then catheterised in the femoral artery and vein, and infused intravenously with BrdU for 4 days to label replicating beta cells. Mice with restored normoglycaemia were co-infused with either 0.9% (wt/vol.) saline or 50% (wt/vol.) glucose to generate glycaemic differences among grafts from the same donors. During infusions, blood glucose was measured daily. After infusion, human beta cell replication and apoptosis were measured in graft sections using immunofluorescence for insulin, and BrdU or TUNEL.

RESULTS

Human islet grafts corrected diabetes in the majority of cases. Among grafts from the same donor, human beta cell proliferation doubled in those exposed to higher glucose relative to lower glucose. Across the entire cohort of grafts, higher blood glucose was strongly correlated with increased beta cell replication. Beta cell replication rates were unrelated to circulating human insulin levels or donor age, but tended to correlate with donor BMI. Beta cell TUNEL reactivity was not measurably increased in grafts exposed to elevated blood glucose.

CONCLUSIONS/INTERPRETATION

Glucose is a mitogenic stimulus for transplanted human beta cells in vivo. Investigating the underlying pathways may point to mechanisms capable of expanding human beta cell mass in vivo.

Clinical presentation and autoimmune characteristics of very young children at the onset of type 1 diabetes mellitus

The aim of our study was to identify factors that are related to a more aggressive beta-cell destruction in children at presentation of type 1 diabetes mellitus (T1D). We analyzed age, HbAlc, pH, bicarbonate, IAA, IA2, GADA, C peptide of 290 consecutive patients with T1D at onset. Seventy-three (25.2%) were younger than 4 years; 217 (74.8%) were aged 4-18 years. Younger patients had lower C peptide, pH and bicarbonate than older ones. Age at T1D onset was negatively related to IAA titers (r: -0.3404, p < 0.001), positively related to IA2 titers (r: 0.1249, p: 0.03) and to C peptide (r: 0.42, p: < 0.001). Multivariable linear regression showed that C peptide was negatively related to HbA1c and positively related to age, pH at admission and IAA titers. T1D in very young children is characterized by a more extensive beta-cell destruction, and younger age at onset is related to a more severe decompensation.

Reciprocal modulation of adult beta cell maturity by activin A and follistatin

AIMS/HYPOTHESIS

The functional maturity of pancreatic beta cells is impaired in diabetes mellitus. We sought to define factors that can influence adult beta cell maturation status and function.

METHODS

MIN6 cells labelled with a Pdx1 monomeric red fluorescent protein-Ins1 enhanced green fluorescent protein dual reporter lentivirus were used to screen candidate growth and/or differentiation factors using image-based approaches with confirmation by real-time RT-PCR and assays of beta cell function using primary mouse islets.

RESULTS

Activin A strikingly decreased the number of mature beta cells and increased the number of immature beta cells. While activins are critical for pancreatic morphogenesis, their role in adult beta cells remains controversial. In primary islets and MIN6 cells, activin A significantly decreased the expression of insulin and several genes associated with beta cell maturity (e.g. Pdx1, Mafa, Glut2 [also known as Slc2a2]). Genes found in immature beta cells (e.g. Mafb) tended to be upregulated by activin A. Insulin secretion was also reduced by activin A. In addition, activin A-treated MIN6 cells proliferated faster than non-treated cells. The effects of endogenous activin A on beta cells were completely reversed by exogenous follistatin.

CONCLUSIONS/INTERPRETATION

These results suggest that autocrine and/or paracrine activin A signalling exerts a suppressive effect on adult beta cell maturation and function. Thus, the maturation state of adult beta cells can be modulated by external factors in culture. Interventions inhibiting activin or its signalling pathways may improve beta cell function. Understanding of maturation and plasticity of adult pancreatic tissue has significant implications for islet regeneration and for in vitro generation of functional beta cells.

'Giving and taking': endothelial and beta-cells in the islets of Langerhans

The beta-cells of the islets of Langerhans are embedded in a dense capillary network. The blood vessels supply the islet cells with nutrients and oxygen, and in turn take up the secreted islet hormones to deliver them to target tissues. In addition, vessels provide a basement membrane, which optimizes islet function. In this review we focus on the dynamic interactions between blood vessels and beta-cells, which are pivotal for enhancing insulin expression and beta-cell proliferation in response to increased insulin demand during body growth, pregnancy, and virtually all conditions associated with insulin resistance. Importantly, a failure in this adaptive response might contribute to the onset of type 2 diabetes mellitus.

Autophagy in health and disease. 4. The role of pancreatic β-cell autophagy in health and diabetes

Autophagy is an evolutionarily conserved machinery for degradation and recycling of various cytoplasmic components such as long-lived proteins and organelles. In pancreatic β-cells, as in most other cells, autophagy is also important for the low basal turnover of ubiquitinated proteins and damaged organelles under normal conditions. Insulin resistance results in upregulation of autophagic activity in β-cells. Induced autophagy in β-cells plays a pivotal role in the adaptive expansion of β-cell mass. Nevertheless, it is not clear whether autophagy is protective or detrimental in response to cellular stresses in β-cells. In this review, we describe the crucial roles of autophagy in normal function of β-cells and discuss how dysfunction of the autophagic machinery could lead to the development of diabetes mellitus.

Current status of islet cell replacement and regeneration therapy

CONTEXT

Beta cell mass and function are decreased to varying degrees in both type 1 and type 2 diabetes. In the future, islet cell replacement or regeneration therapy may thus offer therapeutic benefit to people with diabetes, but there are major challenges to be overcome.

EVIDENCE ACQUISITION

A review of published peer-reviewed medical literature on beta-cell development and regeneration was performed. Only publications considered most relevant were selected for citation, with particular attention to the period 2000-2009 and the inclusion of earlier landmark studies.

EVIDENCE SYNTHESIS

Islet cell regenerative therapy could be achieved by in situ regeneration or implantation of cells previously derived in vitro. Both approaches are being explored, and their ultimate success will depend on the ability to recapitulate key events in the normal development of the endocrine pancreas to derive fully differentiated islet cells that are functionally normal. There is also debate as to whether beta-cells alone will assure adequate metabolic control or whether it will be necessary to regenerate islets with their various cell types and unique integrated function. Any approach must account for the potential dangers of regenerative therapy.

CONCLUSIONS

Islet cell regenerative therapy may one day offer an improved treatment of diabetes and potentially a cure. However, the various approaches are at an early stage of preclinical development and should not be offered to patients until shown to be safe as well as more efficacious than existing therapy.

High Fat Diet Regulation of β-Cell Proliferation and β-Cell Mass

Type 2 Diabetes (T2D) is characterized by relative insulin insufficiency, caused when peripheral tissues such as liver, muscle, and adipocytes have a decreased response to insulin. One factor that elevates the risk for insulin resistance and T2D is obesity. In obese patients without T2D and initially in people who develop T2D, pancreatic β-cells are able to compensate for insulin resistance by increasing β-cell mass, effected by increased proliferation and hypertrophy, as well as increased insulin secretion per β-cell. In patients that go on to develop T2D, however, this initial period of compensation is followed by β-cell failure due to decreased proliferation and increased apoptosis. The forkhead box transcription factor FoxM1 is required for β-cell replication in mice after four weeks of age, during pregnancy, and after partial pancreatectomy. We investigated whether it is also required for β-cell proliferation due to diet-induced obesity.

Comparative study of regenerative potential of beta cells from young and aged donor mice using a novel islet transplantation model

BACKGROUND

The effect of ageing on beta-cell regeneration under hyperglycemia has not been defined and may best be addressed using a unique islet-transplantation model.

METHODS

Streptozotocin-induced diabetic FVB/NJ mice were rendered normoglycemic with a therapeutic mass of syngeneic islets implanted in the epididymal fat pad, followed by a subrenal capsular implantation of a subtherapeutic mass of 25 islets from young (3 months) or old (24 months) mice. Three weeks after the second transplant, the islet containing fat pad was removed to reintroduce hyperglycemia. Bromodeoxyuridine (BrdU) was provided to mice continuously in drinking water. Islet grafts under the kidney capsule were harvested at different time points and examined for markers of beta-cell regeneration by immunohistochemistry.

RESULTS

After a 7-day labeling, BrdU was detected in 54.2% or 53.0% beta cells of the young or old islet grafts, respectively, under hyperglycemia when compared with 3.3% in grafts under normoglycemia. Ki67-positive beta cells were enhanced from a baseline level of 0.5% to 5.2% (young islets) or 4.0% (old islets) on day 7 of hyperglycemia, then decreased to 2.4% on day 21, at which time point an accumulative 75.3% or 66.8% BrdU-positive beta cells was detected in the young or old grafts, respectively. No statistic difference in the percent BrdU- or Ki67-positive beta cells was detected between the young and aged grafts at any time point studied.

CONCLUSIONS

These data reveal that islet beta cells from aged mice can replicate in response to hyperglycemia after transplantation at a capacity and frequencies not significantly different than that of the young adult ones.

The pancreatic beta-cell in the islet and organ community

The endocrine pancreas consists of highly vascularized and innervated endocrine mini-organs--the islets of Langerhans. These contain multiple types of hormone-producing cells, including the insulin-secreting beta-cell. The major task of the fully differentiated beta-cell is the tight regulation of blood glucose levels by secreting insulin into the blood stream. This requires molecular features to measure glucose and produce, process, and release insulin by exocytosis. Now multiple interactions with endocrine and nonendocrine islet cells as well as with other organs have been shown to affect the developing as well as the mature beta-cell. Therefore, failure of any of these interactions can inhibit beta-cell differentiation and glucohomeostasis. Here we review recent reports on intrapancreatic cell-cell interactions as well as signals derived from extrapancreatic organs that affect the pancreatic beta-cell.