Glucose-regulated Insulin Secretion Research Articles

The Adrenal Gland and Pancreatic Islets - A Beneficial Endocrine Alliance.

Intraportal islet transplantation in patients with type 1 diabetes enables restoration of glucose-regulated insulin secretion. However, several factors hamper a widespread application and long-term success: chronic hypoxia, an inappropriate microenvironment and suppression of regenerative and proliferative potential by high local levels of immunosuppressive agents. Therefore, the identification of alternative and superior transplant sites is of major scientific and clinical interest. Here, we aim to evaluate the adrenal as an alternative transplantation site. The adrenal features a particular microenvironment with extensive vascularization, anti-apoptotic and pro-proliferative, anti-inflammatory and immunosuppressive effects. To validate this novel transplantation site, an in vitro co-culture system of adrenal cells and pancreatic islets was established and viability, islet survival, functional potency and antioxidative defense capacity were evaluated. For in vivo validation, an immune-deficient diabetic mouse model for intra-adrenal islet transplantation was applied. The functional capacity of intra-adrenally grafted islets to reverse diabetes was compared to a standard islet transplant model and measures of engraftment such as vascular integration were evaluated. The presence of adrenal cells positively impacted on cell metabolism and oxidative stress. Following transplantation, we could demonstrate enhanced islet function in comparison to standard models with improved engraftment and superior re-vascularization. This experimental approach allows for novel insights into the interaction of endocrine systems and may open up novel strategies for islet transplantation augmented through the bystander effect of other endocrine cells or the active factors secreted by adrenal cells modulating the microenvironment.

Ildr1 gene deletion protects against diet-induced obesity and hyperglycemia

ObjectiveImmunoglobulin-like Domain-Containing Receptor 1 (ILDR1) is expressed on nutrient sensing cholecystokinin-positive enteroendocrine cells of the gastrointestinal tract and it has the unique ability to induce fat-mediated CCK secretion. However, the role of ILDR1 in CCK-mediated regulation of satiety is unknown. In this study, we examined the effects of ILDR1 on food intake and metabolic activity using mice with genetically-deleted Ildr1.MethodsThe expression of ILDR1 in murine tissues and the measurement of adipocyte cell size were evaluated by light and fluorescence confocal microscopy. The effects of Ildr1 deletion on mouse metabolism were quantitated using CLAMS chambers and by targeted metabolomics assays of multiple tissues. Hormone levels were measured by ELISA. The effects of Ildr1 gene deletion on glucose and insulin levels were determined using in vivo oral glucose tolerance, meal tolerance, and insulin tolerance tests, as well as ex vivo islet perifusion.ResultsILDR1 is expressed in a wide range of tissues. Analysis of metabolic data revealed that although Ildr1-/- mice consumed more food than wild-type littermates, they gained less weight on a high fat diet and exhibited increased metabolic activity. Adipocytes in Ildr1-/- mice were significantly smaller than in wild-type mice fed either low or high fat diets. ILDR1 was expressed in both alpha and beta cells of pancreatic islets. Based on oral glucose and mixed meal tolerance tests, Ildr1-/- mice were more effective at lowering post-prandial glucose levels, had improved insulin sensitivity, and glucose-regulated insulin secretion was enhanced in mice lacking ILDR1.ConclusionIldr1 loss significantly modified metabolic activity in these mutant mice. While Ildr1 gene deletion increased high fat food intake, it reduced weight gain and improved glucose tolerance. These findings indicate that ILDR1 modulates metabolic responses to feeding in mice.

Gs/Gq signaling switch in β cells defines incretin effectiveness in diabetes.

By restoring glucose-regulated insulin secretion, glucagon-like peptide-1-based (GLP-1-based) therapies are becoming increasingly important in diabetes care. Normally, the incretins GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) jointly maintain normal blood glucose levels by stimulation of insulin secretion in pancreatic β cells. However, the reason why only GLP-1-based drugs are effective in improving insulin secretion after presentation of diabetes has not been resolved. ATP-sensitive K+ (KATP) channels play a crucial role in coupling the systemic metabolic status to β cell electrical activity for insulin secretion. Here, we have shown that persistent membrane depolarization of β cells due to genetic (β cell-specific Kcnj11-/- mice) or pharmacological (long-term exposure to sulfonylureas) inhibition of the KATP channel led to a switch from Gs to Gq in a major amplifying pathway of insulin secretion. The switch determined the relative insulinotropic effectiveness of GLP-1 and GIP, as GLP-1 can activate both Gq and Gs, while GIP only activates Gs. The findings were corroborated in other models of persistent depolarization: a spontaneous diabetic KK-Ay mouse and nondiabetic human and mouse β cells of pancreatic islets chronically treated with high glucose. Thus, a Gs/Gq signaling switch in β cells exposed to chronic hyperglycemia underlies the differential insulinotropic potential of incretins in diabetes.

Control by Ca2+ of mitochondrial structure and function in pancreatic β-cells

Mitochondria play a central role in glucose metabolism and the stimulation of insulin secretion from pancreatic β-cells. In this review, we discuss firstly the regulation and roles of mitochondrial Ca2+ transport in glucose-regulated insulin secretion, and the molecular machinery involved. Next, we discuss the evidence that mitochondrial dysfunction in β-cells is associated with type 2 diabetes, from a genetic, functional and structural point of view, and then the possibility that these changes may in part be mediated by dysregulation of cytosolic Ca2+. Finally, we review the importance of preserved mitochondrial structure and dynamics for mitochondrial gene expression and their possible relevance to the pathogenesis of type 2 diabetes.

PACAP stimulates insulin secretion by PAC1 receptor and ion channels in β-cells

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) plays a crucial role in the endocrine system. The present study aimed to investigate the effect of PACAP38 on insulin secretion and the underlying mechanism in rat pancreatic β-cells. The insulin secretion results showed that PACAP38 stimulated insulin secretion in a glucose- and dose-dependent manner. The insulinotropic effect was mediated by PAC1 receptor, but not by VPAC1 and VPAC2 receptors. Inhibition of adenylyl cyclase and protein kinase A suppressed PACAP38-augmented insulin secretion. Glucose-regulated insulin secretion is dependent on a series of electrophysiological activities. Current-clamp technology suggested that PACAP38 prolonged action potential duration. Voltage-clamp recordings revealed that PACAP38 blocked voltage-dependent potassium currents, and this effect was reversed by inhibition of PAC1 receptor, adenylyl cyclase, or protein kinase A. Activation of Ca2+ channels by PACAP38 was also observed, which could be antagonized by the PAC1 receptor antagonist. In addition, calcium-imaging analysis indicated that PACAP38 increased intracellular Ca2+ concentration, which was decreased by PAC1 receptor antagonist. These findings demonstrate that PACAP38 stimulates glucose-induced insulin secretion mainly by acting on PAC1 receptor, inhibiting voltage-dependent potassium channels, activating Ca2+ channels and increasing intracellular Ca2+ concentration. Further, PACAP blocks voltage-dependent potassium currents via the adenylyl cyclase/protein kinase A signaling pathway.

The role of the vasculature niche on insulin-producing cells generated by transdifferentiation of adult human liver cells

BackgroundInsulin-dependent diabetes is a multifactorial disorder that could be theoretically cured by functional pancreatic islets and insulin-producing cell (IPC) implantation. Regenerative medicine approaches include the potential for growing tissues and organs in the laboratory and transplanting them when the body cannot heal itself. However, several obstacles remain to be overcome in order to bring regenerative medicine approach for diabetes closer to its clinical implementation; the cells generated in vitro are typically of heterogenic and immature nature and the site of implantation should be readily vascularized for the implanted cells to survive in vivo. The present study addresses these two limitations by analyzing the effect of co-implanting IPCs with vasculature promoting cells in an accessible site such as subcutaneous. Secondly, it analyzes the effects of reconstituting the in vivo environment in vitro on the maturation and function of insulin-producing cells.MethodsIPCs that are generated by the transdifferentiation of human liver cells are exposed to the paracrine effects of endothelial colony-forming cells (ECFCs) and human bone marrow mesenchymal stem cells (MSCs), which are the “building blocks” of the blood vessels. The role of the vasculature on IPC function is analyzed upon subcutaneous implantation in vivo in immune-deficient rodents. The paracrine effects of vasculature on IPC maturation are analyzed in culture.ResultsCo-implantation of MSCs and ECFCs with IPCs led to doubling the survival rates and a threefold increase in insulin production, in vivo. ECFC and MSC co-culture as well as conditioned media of co-cultures resulted in a significant increased expression of pancreatic-specific genes and an increase in glucose-regulated insulin secretion, compared with IPCs alone. Mechanistically, we demonstrate that ECFC and MSC co-culture increases the expression of CTGF and ACTIVINβα, which play a key role in pancreatic differentiation.ConclusionsVasculature is an important player in generating regenerative medicine approaches for diabetes. Vasculature displays a paracrine effect on the maturation of insulin-producing cells and their survival upon implantation. The reconstitution of the in vivo niche is expected to promote the liver-to-pancreas transdifferentiation and bringing this cell therapy approach closer to its clinical implementation.

Whole-exome sequencing for mutation detection in pediatric disorders of insulin secretion: Maturity onset diabetes of the young and congenital hyperinsulinism.

To assess the utility of whole-exome sequencing (WES) for mutation detection in maturity-onset diabetes of the young (MODY) and congenital hyperinsulinism (CHI). MODY and CHI are the two commonest monogenic disorders of glucose-regulated insulin secretion in childhood, with 13 causative genes known for MODY and 10 causative genes identified for CHI. The large number of potential genes makes comprehensive screening using traditional methods expensive and time-consuming. Ten subjects with MODY and five with CHI with known mutations underwent WES using two different exome capture kits (Nimblegen SeqCap EZ Human v3.0 Exome Enrichment Kit, Nextera Rapid Capture Exome Kit). Analysis was blinded to previously identified mutations, and included assessment for large deletions. The target capture of five exome capture technologies was also analyzed using sequencing data from >2800 unrelated samples. Four of five MODY mutations were identified using Nimblegen (including a large deletion in HNF1B). Although targeted, one mutation (in INS) had insufficient coverage for detection. Eleven of eleven mutations (six MODY, five CHI) were identified using Nextera Rapid (including the previously missed mutation). On reconciliation, all mutations concorded with previous data and no additional variants in MODY genes were detected. There were marked differences in the performance of the capture technologies. WES can be useful for screening for MODY/CHI mutations, detecting both point mutations and large deletions. However, capture technologies require careful selection.

The Generation of Insulin Producing Cells from Human Mesenchymal Stem Cells by MiR-375 and Anti-MiR-9

BackgroundMicroRNAs (miRNAs) are a group of endogenous small non-coding RNAs that regulate gene expression at the post-transcriptional level. A number of studies have led to the notion that some miRNAs have key roles in control of pancreatic islet development and insulin secretion. Based on some studies on miRNAs pattern, the researchers in this paper investigated the pancreatic differentiation of human bone marrow mesenchymal stem cells (hBM-MSCs) by up-regulation of miR-375 and down-regulation of miR-9 by lentiviruses containing miR-375 and anti-miR-9.MethodologyAfter 21 days of induction, islet-like clusters containing insulin producing cells (IPCs) were confirmed by dithizone (DTZ) staining. The IPCs and β cell specific related genes and proteins were detected using qRT-PCR and immunofluorescence on days 7, 14 and 21 of differentiation. Glucose challenge test was performed at different concentrations of glucose so extracellular and intracellular insulin and C-peptide were assayed using ELISA kit. Although derived IPCs by miR-375 alone were capable to express insulin and other endocrine specific transcription factors, the cells lacked the machinery to respond to glucose.ConclusionIt was found that over-expression of miR-375 led to a reduction in levels of Mtpn protein in derived IPCs, while treatment with anti-miR-9 following miR-375 over-expression had synergistic effects on MSCs differentiation and insulin secretion in a glucose-regulated manner. The researchers reported that silencing of miR-9 increased OC-2 protein in IPCs that may contribute to the observed glucose-regulated insulin secretion. Although the roles of miR-375 and miR-9 are well known in pancreatic development and insulin secretion, the use of these miRNAs in transdifferentiation was never demonstrated. These findings highlight miRNAs functions in stem cells differentiation and suggest that they could be used as therapeutic tools for gene-based therapy in diabetes mellitus.

Generation of Glucose-Responsive, Insulin-Producing Cells from Human Umbilical Cord Blood-Derived Mesenchymal Stem Cells

We sought to assess the potential of human cord blood-derived mesenchymal stem cells (CB-MSCs) to derive insulin-producing, glucose-responsive cells. We show here that differentiation protocols based on stepwise culture conditions initially described for human embryonic stem cells (hESCs) lead to differentiation of cord blood-derived precursors towards a pancreatic endocrine phenotype, as assessed by marker expression and in vitro glucose-regulated insulin secretion. Transplantation of these cells in immune-deficient animals shows human C-peptide production in response to a glucose challenge. These data suggest that human cord blood may be a promising source for regenerative medicine approaches for the treatment of diabetes mellitus.

Islet-enriched gene expression and glucose-induced insulin secretion in human and mouse islets

Aims/hypothesisOur understanding of the transcription factors that control the development and function of rodent islet beta cells is advancing rapidly, yet less is known of the role they play in similar processes in human islets.MethodsTo characterise the abundance and regulation of key proteins involved in glucose-regulated insulin secretion in human islets, we examined the expression of MAFA, MAFB, GLUT2 (also known as SLC2A2), βGK (also known as GCK) and PDX1 in isolated, highly purified human islets with an intact insulin secretory pattern. We also assessed these features in islets from two different mouse strains (C57BL/6J and FVB).ResultsCompared with mouse islets, human islets secreted more insulin at baseline glucose (5.6 mmol/l), but less upon stimulation with high glucose (16.7 mmol/l) or high glucose plus 3-isobutyl-1-methyl-xanthine. Human islets had relatively more MAFB than PDX1 mRNA, while mouse islets had relatively more Pdx1 than Mafb mRNA. However, v-maf musculoaponeurotic fibrosarcoma oncogene homologue (MAF) B protein was found in human islet alpha and beta cells. This is unusual as this regulator is only produced in islet alpha cells in adult mice. The expression of insulin, MAFA, βGK and PDX1 was not glucose-regulated in human islets with an intact insulin secretory pattern.Conclusions/interpretationOur results suggest that human islets have a distinctive distribution and function of key regulators of the glucose-stimulated insulin secretion pathway, emphasising the urgent need to understand the processes that regulate human islet beta cell function.Electronic supplementary materialThe online version of this article (doi:10.1007/s00125-011-2369-0) contains peer-reviewed but unedited supplementary material, which is available to authorised users.

Analysis of functional and pathway association of differential co-expressed genes: A case study in drug addiction

Drug addiction has been considered as a kind of chronic relapsing brain disease influenced by both genetic and environmental factors. At present, many causative genes and pathways related to diverse kinds of drug addiction have been discovered, while less attention has been paid to common mechanisms shared by different drugs underlying addiction. By applying a co-expression meta-analysis method to mRNA expression profiles of alcohol, cocaine, heroin addicted and normal samples, we identified significant gene co-expression pairs. As co-expression networks of drug group and control group constructed, associated function term pairs and pathway pairs reflected by co-expression pattern changes were discovered by integrating functional and pathway information respectively. The results indicated that respiratory electron transport chain, synaptic transmission, mitochondrial electron transport, signal transduction, locomotory behavior, response to amphetamine, negative regulation of cell migration, glucose regulation of insulin secretion, signaling by NGF, diabetes pathways, integration of energy metabolism, dopamine receptors may play an important role in drug addiction. In addition, the results can provide theory support for studies of addiction mechanisms.

Recognition, Prevention, and Proactive Management of Hypoglycemia in Patients with Type 1 Diabetes Mellitus

Hypoglycemia is the key barrier that prevents patients from optimizing glycemic control with the use of pharmacotherapeutic interventions. Optimal glycemic control for patients with type 1 diabetes (T1DM) includes methods that provide glucose-regulated physiologic insulin replacement or secretion in association with glucose monitoring methods designed to predict and prevent acute extreme changes in glycemic variability. Patients with T1DM experience an average of 2 episodes of symptomatic hypoglycemia each week and at least 1 episode of severe, disabling hypoglycemia annually. Asymptomatic hypoglycemia is common, as shown in studies using continuous glucose monitoring (CGM). Episodes of hypoglycemia (symptomatic and asymptomatic) impair counterregulatory defenses against subsequent events, resulting in the inability to respond to and recover from serious hypoglycemia. This defective counterregulation is known as hypoglycemic-associated autonomic failure. When patients are prescribed a more intensive medication regimen or reinforcing lifestyle interventions, such as medical nutrition therapy and exercise therapy, providers should also assess their ability to proactively identify and manage hypoglycemia. Although self-monitoring of blood glucose regimens, such as pre- and post-meal and periodic middle-of-the-night glucose testing, can help predict the risk of developing hypoglycemia, CGM technology allows patients to receive real-time notification of impending events either through preset alarms or simply by looking at the device display. This review explores the utility of initiating CGM within the primary care setting for patients at high risk for developing hypoglycemia.

The endoplasmic reticulum stress response in the pancreatic β‐cell

Eukaryotic cells respond to stress in the endoplasmic reticulum (ER) resulting from insufficient protein folding capacity or altered ER homeostasis by activating the unfolded protein response (UPR). In mammalian cells the UPR is mediated by at least three ER-localized sensors/transducers, and the cellular response and susceptibility to ER stress is likely to be cell-type specific to some degree. Here, we review the response of pancreatic β-cells or islets to ER stress induced by pharmacological agents, misfolded insulin expression, excessive nutrient exposure and in animal models of type 2 diabetes. This review highlights the particular importance of PERK-mediated translational control and the transcriptional response in pancreatic β-cells and how these relate to the highly specialized function of β-cells, namely glucose-regulated insulin secretion and production. We examine how chronic ER stress may prematurely 'age' the β-cell or cause its genetic reprogramming to either reduce its ability to mount a cell survival response to ER stress, or impair normal function. Both could contribute to β-cell failure in diabetes. We also explore the therapeutic potential of targeting the UPR to preserve β-cell function.

Tight Coupling between Glucose and Mitochondrial Metabolism in Clonal β-Cells Is Required for Robust Insulin Secretion

The biochemical mechanisms underlying glucose-stimulated insulin secretion from pancreatic beta-cells are not completely understood. To identify metabolic disturbances in beta-cells that impair glucose-stimulated insulin secretion, we compared two INS-1-derived clonal beta-cell lines, which are glucose-responsive (832/13 cells) or glucose-unresponsive (832/2 cells). To this end, we analyzed a number of parameters in glycolytic and mitochondrial metabolism, including mRNA expression of genes involved in cellular energy metabolism. We found that despite a marked impairment of glucose-stimulated insulin secretion, 832/2 cells exhibited a higher rate of glycolysis. Still, no glucose-induced increases in respiratory rate, ATP production, or respiratory chain complex I, III, and IV activities were seen in the 832/2 cells. Instead, 832/2 cells, which expressed lactate dehydrogenase A, released lactate regardless of ambient glucose concentrations. In contrast, the glucose-responsive 832/13 line lacked lactate dehydrogenase and did not produce lactate. Accordingly, in 832/2 cells mRNA expression of genes for glycolytic enzymes were up-regulated, whereas mitochondria-related genes were down-regulated. This could account for a Warburg-like effect in the 832/2 cell clone, lacking in 832/13 cells as well as primary beta-cells. In human islets, mRNA expression of genes such as lactate dehydrogenase A and hexokinase I correlated positively with HbA(1c) levels, reflecting perturbed long term glucose homeostasis, whereas that of Slc2a2 (glucose transporter 2) correlated negatively with HbA(1c) and thus better metabolic control. We conclude that tight metabolic regulation enhancing mitochondrial metabolism and restricting glycolysis in 832/13 cells is required for clonal beta-cells to secrete insulin robustly in response to glucose. Moreover, a similar expression pattern of genes controlling glycolytic and mitochondrial metabolism in clonal beta-cells and human islets was observed, suggesting that a similar prioritization of mitochondrial metabolism is required in healthy human beta-cells. The 832 beta-cell lines may be helpful tools to resolve metabolic perturbations occurring in Type 2 diabetes.

Glucose Regulation of Insulin Secretion

Glucose Regulation of Insulin Secretion

Glucose Regulation of Insulin Secretion

Glucose Regulation of Insulin Secretion

Relationship between vitamin D receptor BsmI and FokI polymorphisms and anthropometric and biochemical parameters describing metabolic syndrome

Introduction. It was found that vitamin D may have a direct effect on adipocyte differentiation and metabolism and might be involved in the glucose regulation of insulin secretion, as suggested from the discovery of a nuclear localization of 1,25-(OH)2D3 in pancreatic islets. In recent years, several polymorphisms in the VDR gene which are able to alter the activity of VDR protein have been described. The BsmI and FokI polymorphisms were described in relation to obesity and type 2 diabetes.The aim of the study was to find whether there are associations between BsmI and FokI polymorphisms and anthropometric (BMI, WHR, BP) and biochemical parameters describing metabolic syndrome.Materials and methods. Studied were 176 randomly selected men aged 25–65 years (mean: 51.99 years) with a mean BMI of 28.06 kg/m2. Two polymorphisms of the VDR gene (FokI and BsmI) were explored using the PCR-RFLP method. Serum glucose, insulin, total cholesterol, LDL, HDL, and TG were measured using commercially available kits.Results. It was found that BB carriers tend to have higher BMI (29.00 ± 3.74 versus 26.81 ± 3.76, p = 0.024) and waist circumference (101.79 ± 10.59 versus 96.23 ± 10.35, p = 0.014) compared with the bb genotypes. Similarly, FF and Ff carriers had higher fasting insulin levels than the ff genotypes (12.30 ± 10.26 versus 9.76 ± 5.88, p = 0.001 and 9.76 ± 5.88 vs. 6.35 ± 2.64, p = 0.008), and lover cHDL levels in comparison to ff genotypes (52.28 ± 10.02 versus 60.63 ± 16.58, p = 0.015 and 53.70 ± 12.03 versus 60.63 ± 16.58, p = 0.032. Besides these, no significant differences were found.Conclusions. The BsmI VDR polymorphism seems to influence BMI, while the FokI VDR polymorphism appears to affect insulin sensitivity and serum cHDL level.

The vitamin D receptor gene BsmI polymorphism is not associated with anthropometric and biochemical parameters describing metabolic syndrome in postmenopausal women

Aim. Vitamin D could have a direct effect on adipocyte differentiation and metabolism and might be involved in glucose regulation of insulin secretion. In recent years several polymorphisms in the gene encoding the vitamin D receptor (VDR), which are potent to alter the activity of VDR protein, have been described. The present study aimed to investigate the prevalence of the VDR BsmI polymorphism and its association with anthropometric and biochemical features of metabolic syndrome in postmenopausal women.Materials and methods. We studied 351 randomly selected healthy postmenopausal women, with mean age of 55.43 ± 2.75 years and mean body mass index (BMI) of 27.5 ± 4.78 kg/m2, to evaluate the frequency of BsmI polymorphism (by restriction fragment length polymorphism–polymerase chain reaction) in the VDR gene and to find out whether there is an association between this polymorphism and BMI, total fat volume and visceral fat (as determined by total body dual-energy X-ray absorptiometry), blood pressure, lipid profile (total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol, triglycerides) glucose and fasting insulin in the whole group, as well as subgroups of obese and non-obese women.Results. The prevalence of BsmI genotypes in the study group was 51.0% Bb, 37.3% bb and 11.7% BB. Genotype distribution did not differ from that expected under Hardy–Weinberg equilibrium conditions (χ2 = 2.95, p = 0.22). Apart from LDL-C levels (F = 3.46, p = 0.032), there were no significant differences in anthropometric or metabolic parameters between genotypes.Conclusions. The BsmI polymorphism in the VDR gene does not seem to predispose to obesity and insulin resistance, but the BB genotype is connected with an unfavorable lipid profile.

Insulin Therapy and Hypoglycemia in Type 2 Diabetes Mellitus

Background: Iatrogenic hypoglycemia, the limiting factor in the glycemic management of diabetes mellitus (DM), is the result of therapeutic insulin excess and compromised physiological and behavioral defenses against falling plasma glucose concentrations. Objective: The goal of this article was to review the available evidence on insulin therapy and hypoglycemia, with a focus on type 2 DM. Methods: This review was based on the author's clinical experience, his >3 decades of translational research in the area of hypoglycemia, and his knowledge of the relevant preclinical and clinical literature. Results: Glycemic defenses become compromised rapidly in type 1 DM but slowly in type 2 DM. As a result, the frequency of hypoglycemia increases progressively as patients approach the insulin-deficient end of the spectrum of type 2 DM. Indeed, it appears that most episodes of hypoglycemia, including those of severe hypoglycemia, occur in individuals with type 2 DM. The conventional risk factors for hypoglycemia are based on relative or absolute insulin excess. It is clear that the pathogenesis of hypoglycemia-associated autonomic failure, and thus an increased risk for iatrogenic hypoglycemia, stems fundamentally from insulin deficiency. Relevant additional risk factors include the degree of insulin deficiency, a history of severe hypoglycemia, hypoglycemia unawareness, or both, as well as recent antecedent hypoglycemia, prior exercise and sleep, and aggressive glycemic therapy per se in advanced type 2 DM, just as in type 1 DM. The prevention of hypoglycemia involves the practice of hypoglycemia risk reductionȔdiscussion of the issue, application of the principles of aggressive therapy, and consideration of both the conventional risk factors and those relevant to compromised glycemic defensesȔin advanced type 2 DM, just as in type 1 DM. With this approach, it is possible to improve glycemic control and reduce the frequency of hypoglycemia in many people with DM. Conclusions: Pending the prevention and cure of DM, people with this disease need safe and effective therapies. Ultimately, that will require glucose-regulated insulin replacement or secretion. In the meantime, insight into the mechanisms of hypoglycemia-associated autonomic failure may lead to interventions that will further improve the lives of people affected by DM by reducing the frequency of hypoglycemia without compromising glycemic control.( Insulin. 2007;2:127-133)

Regulation of glucagon secretion by glucose transporter type 2 (glut2) and astrocyte-dependent glucose sensors

Ripglut1;glut2-/- mice have no endogenous glucose transporter type 2 (glut2) gene expression but rescue glucose-regulated insulin secretion. Control of glucagon plasma levels is, however, abnormal, with fed hyperglucagonemia and insensitivity to physiological hypo- or hyperglycemia, indicating that GLUT2-dependent sensors control glucagon secretion. Here, we evaluated whether these sensors were located centrally and whether GLUT2 was expressed in glial cells or in neurons. We showed that ripglut1;glut2-/- mice failed to increase plasma glucagon levels following glucoprivation induced either by i.p. or intracerebroventricular 2-deoxy-D-glucose injections. This was accompanied by failure of 2-deoxy-D-glucose injections to activate c-Fos-like immunoreactivity in the nucleus of the tractus solitarius and the dorsal motor nucleus of the vagus. When glut2 was expressed by transgenesis in glial cells but not in neurons of ripglut1;glut2-/- mice, stimulated glucagon secretion was restored as was c-Fos-like immunoreactive labeling in the brainstem. When ripglut1;glut2-/- mice were backcrossed into the C57BL/6 genetic background, fed plasma glucagon levels were also elevated due to abnormal autonomic input to the alpha cells; glucagon secretion was, however, stimulated by hypoglycemic stimuli to levels similar to those in control mice. These studies identify the existence of central glucose sensors requiring glut2 expression in glial cells and therefore functional coupling between glial cells and neurons. These sensors may be activated at different glycemic levels depending on the genetic background.