Biomedical subjects

Daisy Flamez

Publications and source records attributed to Daisy Flamez.

12 recordsLinked to original sources

PubMed2006

T1DBase: integration and presentation of complex data for type 1 diabetes research.

T1DBase (http://T1DBase.org) [Smink et al. (2005) Nucleic Acids Res., 33, D544-D549; Burren et al. (2004) Hum. Genomics, 1, 98-109] is a public website and database that supports the type 1 diabetes (T1D) research community. T1DBase provides a consolidated T1D-oriented view of the complex data world that now confronts medical researchers and enables scientists to navigate from information they know to information that is new to them. Overview pages for genes and markers summarize information for these elements. The Gene Dossier summarizes information for a list of genes. GBrowse [Stein et al. (2002) Genome Res., 10, 1599-1610] displays genes and other features in their genomic context, and Cytoscape [Shannon et al. (2003) Genome Res., 13, 2498-2504] shows genes in the context of interacting proteins and genes. The Beta Cell Gene Atlas shows gene expression in beta cells, islets, and related cell types and lines, and the Tissue Expression Viewer shows expression across other tissues. The Microarray Viewer shows expression from more than 20 array experiments. The Beta Cell Gene Expression Bank contains manually curated gene and pathway annotations for genes expressed in beta cells. T1DMart is a query tool for markers and genotypes. PosterPages are 'home pages' about specific topics or datasets. The key challenge, now and in the future, is to provide powerful informatics capabilities to T1D scientists in a form they can use to enhance their research.

Animals↗

PubMed2006

Selective inhibition of eukaryotic translation initiation factor 2 alpha dephosphorylation potentiates fatty acid-induced endoplasmic reticulum stress and causes pancreatic beta-cell dysfunction and apoptosis.

Free fatty acids cause pancreatic beta-cell apoptosis and may contribute to beta-cell loss in type 2 diabetes via the induction of endoplasmic reticulum stress. Reductions in eukaryotic translation initiation factor (eIF) 2alpha phosphorylation trigger beta-cell failure and diabetes. Salubrinal selectively inhibits eIF2alpha dephosphorylation, protects other cells against endoplasmic reticulum stress-mediated apoptosis, and has been proposed as a beta-cell protector. Unexpectedly, salubrinal induced apoptosis in primary beta-cells, and it potentiated the deleterious effects of oleate and palmitate. Salubrinal induced a marked eIF2alpha phosphorylation and potentiated the inhibitory effects of free fatty acids on protein synthesis and insulin release. The synergistic activation of the PERK-eIF2alpha branch of the endoplasmic reticulum stress response, but not of the IRE1 and activating transcription factor-6 pathways, led to a marked induction of activating transcription factor-4 and the pro-apoptotic transcription factor CHOP. Our findings demonstrate that excessive eIF2alpha phosphorylation is poorly tolerated by beta-cells and exacerbates free fatty acid-induced apoptosis. This modifies the present paradigm regarding the beneficial role of eIF2alpha phosphorylation in beta-cells and must be taken into consideration when designing therapies to protect beta-cells in type 2 diabetes.

Animals↗

PubMed2005

Control of mRNA translation preserves endoplasmic reticulum function in beta cells and maintains glucose homeostasis.

Type 2 diabetes is a disorder of hyperglycemia resulting from failure of beta cells to produce adequate insulin to accommodate an increased metabolic demand. Here we show that regulation of mRNA translation through phosphorylation of eukaryotic initiation factor 2 (eIF2alpha) is essential to preserve the integrity of the endoplasmic reticulum (ER) and to increase insulin production to meet the demand imposed by a high-fat diet. Accumulation of unfolded proteins in the ER activates phosphorylation of eIF2alpha at Ser51 and inhibits translation. To elucidate the role of this pathway in beta-cell function we studied glucose homeostasis in Eif2s1(tm1Rjk) mutant mice, which have an alanine substitution at Ser51. Heterozygous (Eif2s1(+/tm1Rjk)) mice became obese and diabetic on a high-fat diet. Profound glucose intolerance resulted from reduced insulin secretion accompanied by abnormal distension of the ER lumen, defective trafficking of proinsulin, and a reduced number of insulin granules in beta cells. We propose that translational control couples insulin synthesis with folding capacity to maintain ER integrity and that this signal is essential to prevent diet-induced type 2 diabetes.

Amino Acid Substitution↗

PubMed2005

T1DBase, a community web-based resource for type 1 diabetes research.

T1DBase (http://T1DBase.org) is a public website and database that supports the type 1 diabetes (T1D) research community. The site is currently focused on the molecular genetics and biology of T1D susceptibility and pathogenesis. It includes the following datasets: annotated genome sequence for human, rat and mouse; information on genetically identified T1D susceptibility regions in human, rat and mouse, and genetic linkage and association studies pertaining to T1D; descriptions of NOD mouse congenic strains; the Beta Cell Gene Expression Bank, which reports expression levels of genes in beta cells under various conditions, and annotations of gene function in beta cells; data on gene expression in a variety of tissues and organs; and biological pathways from KEGG and BioCarta. Tools on the site include the GBrowse genome browser, site-wide context dependent search, Connect-the-Dots for connecting gene and other identifiers from multiple data sources, Cytoscape for visualizing and analyzing biological networks, and the GESTALT workbench for genome annotation. All data are open access and all software is open source.

Animals↗

PubMed2005

Essential role of chicken ovalbumin upstream promoter-transcription factor II in insulin secretion and insulin sensitivity revealed by conditional gene knockout.

Chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) has been implicated in the control of blood glucose by its potent effect on expression and signaling of various nuclear receptors. To understand the role of COUP-TFII in glucose homeostasis, conditional COUP-TFII-deficient mice were generated and crossed with mice expressing Cre under the control of rat insulin II gene promoter, resulting in deletion of COUP-TFII in pancreatic beta-cells. Homozygous mutants died before birth for yet undetermined reasons. Heterozygous mice appeared healthy at birth and showed normal growth and fertility. When challenged intraperitoneally, the animals had glucose intolerance associated with reduced glucose-stimulated insulin secretion. Moreover, these heterozygous mice presented a mild increase in fasting and random-fed circulating insulin levels. In accordance, islets isolated from these animals exhibited higher insulin secretion in low glucose conditions and markedly decreased glucose-stimulated insulin secretion. Their pancreata presented normal microscopic architecture and insulin content up to 16 weeks of study. Altered insulin secretion was associated with peripheral insulin resistance in whole animals. It can be concluded that COUP-TFII is a new, important regulator of glucose homeostasis and insulin sensitivity.

Animals↗

PubMed2005

Disruption of the gamma-interferon signaling pathway at the level of signal transducer and activator of transcription-1 prevents immune destruction of beta-cells.

beta-cells under immune attack are destroyed by the aberrant activation of key intracellular signaling cascades. The aim of the present study was to evaluate the contribution of the signal transducer and activator of transcription (STAT)-1 pathway for beta-cell apoptosis by studying the sensitivity of beta-cells from STAT-1 knockout (-/-) mice to immune-mediated cell death in vitro and in vivo. Whole islets from STAT-1-/- mice were completely resistant to interferon (IFN)-gamma (studied in combination with interleukin [IL]-1beta)-mediated cell death (92 +/- 4% viable cells in STAT-1-/- mice vs. 56 +/- 3% viable cells in wild-type controls, P < or = 0.001) and had preserved insulin release after exposure to IL-1beta and IFN-gamma. Moreover, analysis of cell death in cytokine-exposed purified beta-cells confirmed that protection was due to absence of STAT-1 in the beta-cells themselves. Deficiency of STAT-1 in islets completely prevented cytokine-induced upregulation of IL-15, interferon inducible protein 10, and inducible nitric oxide synthase transcription but did not interfere with monocyte chemoattractant protein 1 and macrophage inflammatory protein 3alpha expression. In vivo, STAT-1-/- mice were partially resistant to development of diabetes after multiple low-dose streptozotocin injections as reflected by mean blood glucose at 12 days after first injection (159 +/- 28 vs. 283 +/- 81 mg/dl in wild-type controls, P < or = 0.05) and diabetes incidence at the end of the follow-up period (39 vs. 73% in wild-type controls, P < or = 0.05). In conclusion, the present results indicate that STAT-1 is a crucial transcription factor in the process of IFN-gamma-mediated beta-cell death and the subsequent development of immune-mediated diabetes.

Animals↗

PubMed2004

Prior in vitro exposure to GLP-1 with or without GIP can influence the subsequent beta cell responsiveness.

Glucagon-like peptide-1 (7-36) amide (GLP-1) and glucose-dependent insulinotropic peptide (GIP) potentiate glucose-induced insulin release when present at the time of nutrient stimulation. This study examines whether they can also influence rat beta cell responsiveness to subsequent stimulations. When rat beta cells were cultured for 24 h with 1 nM GLP-1, they progressively desensitized to subsequent GLP-1 stimuli, as evidenced by cellular cAMP production. This GLP-1-induced desensitization did not occur when the incretin was only present during three periods of 1 h at 10 mM glucose that alternated with 6-9 h culture at 3 mM glucose. After these 24h, the beta cells exhibited the same secretory response to glucose (10 mM) and GLP-1 (10 nM at 10 mM glucose), whether GLP-1 was present during the pulses or not. Similarly the presence of 1 nM GIP during these one hour pulses did not influence subsequent secretory responses to glucose and GLP-1. However, when both GLP-1 and GIP, each at 0.5 nM, were added to the one hour pulses, they not only amplified insulin release during the pulses, as was the case with their single addition, but also increased the secretory response to a subsequent stimulation by glucose and GLP-1. These data distinguish between a desensitization effect of a prolonged exposure to GLP-1 and a positive priming effect of a discontinuous exposure to a combination of GLP-1 plus GIP. They may have to be taken into account in drug treatment strategies aiming the mimicking of physiologic patterns in the regulation of insulin release.

Animals↗

PubMed2003

A globin in the nucleus!

Cytoglobin and neuroglobin are recently discovered members of the globin family. In situ hybridization localized neuroglobin mainly in brain and retina, while cytoglobin was expressed ubiquitously in all analyzed tissues. In the present study, polyclonal antibodies were raised against both proteins and the distribution of them was studied by immunocytochemistry at tissue and subcellular level. Cytoglobin immunoreactivity was uniformly distributed and found in all tissues studied. At the subcellular level, cytoglobin immunoreactivity was exclusively detected in the cell nucleus. In contrast, neuroglobin immunoreactivity was detected in specific brain regions with varying intensities and in the islet of Langerhans in the pancreas. The immunoreactivity was restricted to the cytoplasm of neurons and endocrine beta cells. The nuclear localization of cytoglobin opens new perspectives for possible function(s) of globin-folded proteins as transcriptional regulators.

Animals↗

PubMed2003

Hypoglycemia, defective islet glucagon secretion, but normal islet mass in mice with a disruption of the gastrin gene.

BACKGROUND AND AIMS: Both cholecystokinin (CCK)-A and CCK-B receptors are expressed in the pancreas, and exogenous gastrin administration stimulates glucagon secretion from human islets. Although gastrin action has been linked to islet neogenesis, transdifferentiation, and beta-cell regeneration, an essential physiologic role(s) for gastrin in the pancreas has not been established. METHODS: We examined glucose homeostasis, glucagon gene expression, glucagon secretion, and islet mass in mice with a targeted gastrin gene disruption. RESULTS: Gastrin -/- mice exhibit fasting hypoglycemia and significantly reduced glycemic excursion following glucose challenge. Insulin sensitivity was normal and levels of circulating insulin and insulin messenger RNA transcripts were appropriately reduced in gastrin -/- mice. In contrast, levels of circulating glucagon and pancreatic glucagon messenger RNA transcripts were not up-regulated in hypoglycemic gastrin -/- mice. Furthermore, the glucagon response to epinephrine in isolated perifused islets was moderately impaired in gastrin -/- versus gastrin +/+ islets (40% reduction; P < 0.01, gastrin +/+ vs. gastrin -/- mice). Moreover, the glucagon response but not the epinephrine response to hypoglycemia was significantly attenuated in gastrin -/- compared with gastrin +/+ mice (P < 0.05). Despite gastrin expression in the developing fetal pancreas, beta-cell area, islet topography, and the islet proliferative response to experimental injury were normal in gastrin -/- mice. CONCLUSIONS: These findings show an essential physiologic role for gastrin in glucose homeostasis; however, the gastrin gene is not essential for murine islet development or the adaptive islet proliferative response to beta-cell injury.

Animals↗

PubMed2003

The AMP-activated protein kinase alpha2 catalytic subunit controls whole-body insulin sensitivity.

AMP-activated protein kinase (AMPK) is viewed as a fuel sensor for glucose and lipid metabolism. To better understand the physiological role of AMPK, we generated a knockout mouse model in which the AMPKalpha2 catalytic subunit gene was inactivated. AMPKalpha2(-/-) mice presented high glucose levels in the fed period and during an oral glucose challenge associated with low insulin plasma levels. However, in isolated AMPKalpha2(-/-) pancreatic islets, glucose- and L-arginine-stimulated insulin secretion were not affected. AMPKalpha2(-/-) mice have reduced insulin-stimulated whole-body glucose utilization and muscle glycogen synthesis rates assessed in vivo by the hyperinsulinemic euglycemic clamp technique. Surprisingly, both parameters were not altered in mice expressing a dominant-negative mutant of AMPK in skeletal muscle. Furthermore, glucose transport was normal in incubated isolated AMPKalpha2(-/-) muscles. These data indicate that AMPKalpha2 in tissues other than skeletal muscles regulates insulin action. Concordantly, we found an increased daily urinary catecholamine excretion in AMPKalpha2(-/-) mice, suggesting altered function of the autonomic nervous system that could explain both the impaired insulin secretion and insulin sensitivity observed in vivo. Therefore, extramuscular AMPKalpha2 catalytic subunit is important for whole-body insulin action in vivo, probably through modulation of sympathetic nervous activity.

AMP-Activated Protein Kinases↗

PubMed2002

Glucose-regulated gene expression maintaining the glucose-responsive state of beta-cells.

The mammalian beta-cell has particular properties that synthesize, store, and secrete insulin in quantities that are matched to the physiological demands of the organism. To achieve this task, beta-cells are regulated both acutely and chronically by the extracellular glucose concentration. Several in vivo and in vitro studies indicate that preservation of the glucose-responsive state of beta-cells is lost when the extracellular glucose concentration chronically deviates from the normal physiological condition. Experiments with the protein synthesis inhibitor cycloheximide suggest that the maintenance of the functional state of beta-cells depends on protein(s) with rapid turnover. Analysis of newly synthesized proteins via two-dimensional gel electrophoresis and high-density gene expression microarrays demonstrates that the glucose-dependent preservation of beta-cell function is correlated with glucose regulation of a large number of beta-cell genes. Two different microarray analyses of glucose regulation of the mRNA profile in beta-cells show that the sugar influences expression of multiple genes involved in energy metabolism, the regulated insulin biosynthetic/secretory pathway, membrane transport, intracellular signaling, gene transcription, and protein synthesis/degradation. Functional analysis of some of these regulated gene clusters has provided new evidence for the concept that cataplerosis, the conversion of mitochondrial metabolites into lipid intermediates, is a major metabolic pathway that allows beta-cell activation independently of closure of ATP-sensitive potassium channels.

Animals↗

PubMed2002

Critical role for cataplerosis via citrate in glucose-regulated insulin release.

The molecular mechanisms mediating acute regulation of insulin release by glucose are partially known. The process involves at least two pathways that can be discriminated on basis of their (in)dependence of closure of ATP-sensitive potassium (K+(ATP)) channels. The mechanism of the K+(ATP) channel-independent pathway was proposed to involve cataplerosis, the export of mitochondrial intermediates into the cytosol and in the induction of fatty acid-derived signaling molecules. In the present article, we have explored in fluorescence-activated cell sorter (FACS)-purified rat beta-cells the molecular steps involved in chronic glucose regulation of the insulin secretory response. When compared with culture in 10 mmol/l glucose, 24 h culture in 3 mmol/l glucose shifts the phenotype of the cells into a state with low further secretory responsiveness to glucose, lower rates of glucose oxidation, and lower rates of cataplerosis. Microarray mRNA analysis indicates that this shift can be attributed to differences in expression of genes involved in the K+(ATP) channel-dependent pathway, in cataplerosis and in fatty acid/cholesterol biosynthesis. This response was paralleled by glucose upregulation of the transcription factor sterol regulatory element binding protein 1c (SREBP1c) (ADD1) and downregulation of peroxisome proliferator-activated receptor (PPAR)-alpha and PPAR-beta (PPARdelta). The functional importance of cataplerosis via citrate for glucose-induced insulin release was further supported by the observation that two ATP-citrate lyase inhibitors, radicicol and (-)-hydroxycitrate, block part of glucose-stimulated release in beta-cells. In conclusion, chronic glucose regulation of the glucose-responsive secretory phenotype is associated with coordinated changes in gene expression involved in the K+(ATP) channel-dependent pathway, in cataplerosis via citrate and in acyl CoA/cholesterol biosynthesis.

Animals↗