Glucagon receptor inactivation leads to α-cell hyperplasia in zebrafish.

Glucagon antagonism is a potential treatment for diabetes. One potential side effect is α-cell hyperplasia, which has been noted in several approaches to antagonize glucagon action. To investigate the molecular mechanism of the α-cell hyperplasia and to identify the responsible factor, we created a zebrafish model in which glucagon receptor (gcgr) signaling has been interrupted.

Human islet preparations distributed for research exhibit a variety of insulin-secretory profiles.

Human islet research is providing new insights into human islet biology and diabetes, using islets isolated at multiple US centers from donors with varying characteristics. This creates challenges for understanding, interpreting, and integrating research findings from the many laboratories that use these islets. In what is, to our knowledge, the first standardized assessment of human islet preparations from multiple isolation centers, we measured insulin secretion from 202 preparations isolated at 15 centers over 11 years and noted five distinct patterns of insulin secretion.

Comparison of the physiological relevance of systemic vs. portal insulin delivery to evaluate whole body glucose flux during an insulin clamp.

To understand the underlying pathology of metabolic diseases, such as diabetes, an accurate determination of whole body glucose flux needs to be made by a method that maintains key physiological features. One such feature is a positive differential in insulin concentration between the portal venous and systemic arterial circulation (P/S-IG). P/S-IG during the determination of the relative contribution of liver and extra-liver tissues/organs to whole body glucose flux during an insulin clamp with either systemic (SID) or portal (PID) insulin delivery was examined with insulin infusion rates of 1, 2, and 5 mU·kg(-1)·min(-1) under either euglycemic or hyperglycemic conditions in 6-h-fasted conscious normal rats.

Dose-response effects of insulin glargine in type 2 diabetes.

Objective: To determine the pharmacokinetic and pharmacodynamic dose-response effects of insulin glargine administered subcutaneously in individuals with type 2 diabetes.

Research Design And Methods: Twenty obese type 2 diabetic individuals (10 male and 10 female, aged 50 +/- 3 years, with BMI 36 +/- 2 kg/m(2) and A1C 8.3 +/- 0.

Pancreatic islet production of vascular endothelial growth factor--a is essential for islet vascularization, revascularization, and function.

To investigate molecular mechanisms controlling islet vascularization and revascularization after transplantation, we examined pancreatic expression of three families of angiogenic factors and their receptors in differentiating endocrine cells and adult islets. Using intravital lectin labeling, we demonstrated that development of islet microvasculature and establishment of islet blood flow occur concomitantly with islet morphogenesis. Our genetic data indicate that vascular endothelial growth factor (VEGF)-A is a major regulator of islet vascularization and revascularization of transplanted islets.

Proteomic exploration of pancreatic islets in mice null for the alpha2A adrenergic receptor.

The present studies extend recent findings that mice null for the alpha(2A) adrenergic receptor (alpha(2A) AR KO mice) lack suppression of exogenous secretagogue-stimulated insulin secretion in response to alpha(2) AR agonists by evaluating the endogenous secretagogue, glucose, ex vivo, and providing in vivo data that baseline insulin levels are elevated and baseline glucose levels are decreased in alpha(2A) AR KO mice. These latter findings reveal that the alpha(2A) AR subtype regulates glucose-stimulated insulin release in response to endogenous catecholamines in vivo. The changes in alpha(2A) AR responsiveness and resultant changes in insulin/glucose homeostasis encouraged us to utilize proteomics strategies to identify possible alpha(2A) AR downstream signaling molecules or other resultant changes due to perturbation of alpha(2A) AR expression.

Assessment of human pancreatic islet architecture and composition by laser scanning confocal microscopy.

The recent success of pancreatic islet transplantation has generated considerable enthusiasm. To better understand the quality and characteristics of human islets used for transplantation, we performed detailed analysis of islet architecture and composition using confocal laser scanning microscopy. Human islets from six separate isolations provided by three different islet isolation centers were compared with isolated mouse and non-human primate islets.

Assessment of pancreatic islet mass after islet transplantation using in vivo bioluminescence imaging.

Background: Pancreatic islet transplantation is an emerging therapy for type 1 diabetes, but it is difficult to assess islets after transplantation and thus to design interventions to improve islet survival.

Methods: To image and quantify islets, the authors transplanted luciferase-expressing murine or human islets (by adenovirus-mediated gene transfer) into the liver or beneath the renal capsule of immunodeficient mice and quantified the in vivo bioluminescence imaging (BLI) of mice using a cooled charge-coupled device camera and digital photon-counting image analysis. To account for variables that are independent of islet mass such as transplant site, animal positioning, and wound healing, the BLI of transplanted islets was calibrated against measurement of luminescence of an implanted bead emitting a constant light intensity.

Reduced PDX-1 expression impairs islet response to insulin resistance and worsens glucose homeostasis.

In type 2 diabetes mellitus, insulin resistance and an inadequate pancreatic beta-cell response to the demands of insulin resistance lead to impaired insulin secretion and hyperglycemia. Pancreatic duodenal homeodomain-1 (PDX-1), a transcription factor required for normal pancreatic development, also plays a key role in normal insulin secretion by islets. To investigate the role of PDX-1 in islet compensation for insulin resistance, we examined glucose disposal, insulin secretion, and islet cell mass in mice of four different genotypes: wild-type mice, mice with one PDX-1 allele inactivated (PDX-1+/-, resulting in impaired insulin secretion), mice with one GLUT4 allele inactivated (GLUT4+/-, resulting in insulin resistance), and mice heterozygous for both PDX-1 and GLUT4 (GLUT4+/-;PDX-1+/-).

Gene expression phenotyping of an ACTH-producing small cell lung cancer line.

DNA microarray techniques were used to compare gene expression in an adrenocorticotropin (ACTH)-producing human small cell lung carcinoma line (DMS-79) with six other small cell lung cancer (SCLC) lines that do not produce ACTH. Twelve genes were expressed at more than five-fold higher levels in DMS-79 cells. Two transcription factors were the genes that exhibited the most remarkable over-expression: T-box 3 mRNA was detected at levels 19.

A novel mutation in the preprovasopressin gene identified in a kindred with autosomal dominant neurohypophyseal diabetes insipidus.

Autosomal dominant neurohypophyseal diabetes insipidus (ADNDI) is a defect in free water conservation caused by mutations in the single gene that encodes both vasopressin (VP) and its binding protein, neurophysin II (NP II). Most of the human mutations in this gene have been in the portion encoding the NP molecule; the resultant abnormal gene products are believed to cause cellular toxicity as improperly folded precursor molecules accumulate in the endoplasmic reticulum. We identified a new American kindred with ADNDI and found a novel mutation in the VP molecule.

Oxidative stress is a mediator of glucose toxicity in insulin-secreting pancreatic islet cell lines.

Pancreatic beta cells secrete insulin in response to changes in the extracellular glucose. However, prolonged exposure to elevated glucose exerts toxic effects on beta cells and results in beta cell dysfunction and ultimately beta cell death (glucose toxicity). To investigate the mechanism of how increased extracellular glucose is toxic to beta cells, we used two model systems where glucose metabolism was increased in beta cell lines by enhancing glucokinase (GK) activity and exposing cells to physiologically relevant increases in extracellular glucose (3.

Epidermal growth factor increases cortisol production and type II 3 beta-hydroxysteroid dehydrogenase/Delta(5)-Delta(4)-isomerase expression in human adrenocortical carcinoma cells: evidence for a Stat5-dependent mechanism.

We tested the ability of epidermal growth factor (EGF) to regulate a key enzyme in the adrenal synthesis of glucocorticoids: human type II 3beta-hydroxysteroid dehydrogenase/Delta(5)-Delta(4)-isomerase (3 beta HSD). EGF treatment (25 ng/ml) of human adrenocortical carcinoma cells (H295R) resulted in a 5-fold increase in cortisol production and a corresponding 2-fold increase in 3 beta HSD mRNA. Experiments were performed to determine whether EGF is acting through a previously identified signal transducer and activator of transcription 5 (Stat5)-responsive element located from -110 to -118 in the human type II 3 beta HSD promoter.

Glucocorticoids enhance activation of the human type II 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase gene.

Glucocorticoids indirectly alter adrenocortical steroid output through the inhibition of ACTH secretion by the anterior pituitary. However, previous studies suggest that glucocorticoids can directly affect adrenocortical steroid production. Therefore, we have investigated the ability of glucocorticoids to affect transcription of adrenocortical steroid biosynthetic enzymes.

Pancreatic islet beta-cells transiently metabolize pyruvate.

Pancreatic beta-cell metabolism was followed during glucose and pyruvate stimulation of pancreatic islets using quantitative two-photon NAD(P)H imaging. The observed redox changes, spatially separated between the cytoplasm and mitochondria, were compared with whole islet insulin secretion. As expected, both NAD(P)H and insulin secretion showed sustained increases in response to glucose stimulation.

Reduction in pancreatic transcription factor PDX-1 impairs glucose-stimulated insulin secretion.

Complete lack of transcription factor PDX-1 leads to pancreatic agenesis, whereas heterozygosity for PDX-1 mutations has been recently noted in some individuals with maturity-onset diabetes of the young (MODY) and in some individuals with type 2 diabetes. To determine how alterations in PDX-1 affect islet function, we examined insulin secretion and islet physiology in mice with one PDX-1 allele inactivated. PDX-1(+/-) mice had a normal fasting blood glucose and pancreatic insulin content but had impaired glucose tolerance and secreted less insulin during glucose tolerance testing.