bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetic markers, humoral autoimmunity, and prediction of type 1 diabetes in siblings of affected children. Childhood Diabetes in Finland Study Group.
Authors: Kulmala P , Savola K , Reijonen H , Veijola R , Vähäsalo P , Karjalainen J , Tuomilehto-Wolf E , Ilonen J , Tuomilehto J , Akerblom H K , Knip M
Published: March 2007

The relationships between genetic markers and disease-associated autoantibodies were studied in an unselected population of 701 siblings of children with type 1 diabetes, and the predictive characteristics of these markers over a period of 9 years were determined. Increased prevalences of all the antibodies were closely associated with HLA identity to the index case, the DR4 and DQB1*0302 alleles, and the DR3/4 phenotype and the DQB1*02/0302 genotype. Antibodies to GAD (GADA) were also associated with the DR3 and DQB1*02 alleles. Siblings carrying the protective DR2 and DQB1*0602-3 alleles were characterized by lower frequencies of islet cell antibodies (ICA), antibodies to IA-2 (IA-2A), and GADA. Higher levels of ICA were related to HLA identity, the DR4 and DQB1*0302 alleles, and the susceptible DQB1 genotypes, while no significant differences were observed in the levels of IA-2A, GADA, or insulin autoantibodies among siblings with different HLA risk markers. The DR2 or DQB1*0602-3 alleles were not related to the levels of any antibody specificity. A combination of the genetic markers and autoantibodies increased the positive predictive values of all autoantibodies substantially, which may have clinical implications when evaluating the risk of developing type 1 diabetes at the individual level or when recruiting high-risk individuals for intervention trials. However, because such combinations also resulted in reduced sensitivity, autoantibodies alone rather than in combination with genetic markers are recommended as the first-line screening in siblings. Finally, not all siblings with a broad humoral autoimmune response or high-risk genetic markers present with type 1 diabetes, while some with a low genetic risk and weak initial signs of humoral autoimmunity may progress to disease.
Portal vein afferents are critical for the sympathoadrenal response to hypoglycemia.
Authors: Hevener A L , Bergman R N , Donovan C M
Published: March 2007

We sought to elucidate the role of the portal vein afferents in the sympathetic response to hypoglycemia. Laparotomy was performed on 27 male Wistar rats. Portal veins were painted with either 90% phenol (denervation group [PDN]) or 0.9% saline solution (sham-operated group [SHAM]). Rats were chronically cannulated in the carotid artery (sampling), jugular vein (infusion), and portal vein (infusion). After a recovery period of 5 days, animals were exposed to a hyperinsulinemic-hypoglycemic clamp, with glucose infused either portally (POR) or peripherally (PER). In all animals, systemic hypoglycemia (2.48+/-0.09 mmol/l) was induced via jugular vein insulin infusion (50 mU x kg(-1) x min(-1)). Arterial plasma catecholamines were assessed at basal (-30 and 0 min) and during sustained hypoglycemia (60, 75, 90, and 105 min). By design, portal vein glucose concentrations were significantly elevated during POR versus PER (4.4+/-0.14 vs. 2.5+/-0.07 mmol/l; P<0.01, respectively) for both PDN and SHAM. There were no significant differences in arterial glucose or insulin concentration between the four experimental conditions at any point in time. When portal glycemia and systemic glycemia fell concomitantly (SHAM-PER), epinephrine increased 12-fold above basal (3.75+/-0.34 and 44.56+/-6.1 nmol/l; P<0.001). However, maintenance of portal normoglycemia (SHAM-POR) caused a 50% suppression of the epinephrine response, despite cerebral hypoglycemia (22.2+/-3.1 nmol/l, P<0.001). Portal denervation resulted in a significant blunting of the sympathoadrenal response to whole-body hypoglycemia (PDN-PER 27.6+/-3.8 nmol/l vs. SHAM-PER; P<0.002). In contrast to the sham experiments, there was no further suppression in arterial epinephrine concentrations observed during PDN-POR versus PDN-PER (P = 0.8). These findings indicate that portal vein afferent innervation is critical for hypoglycemic detection and normal sympathoadrenal counterregulation.
Prevention of albuminuria by aminoguanidine or ramipril in streptozotocin-induced diabetic rats is associated with the normalization of glomerular protein kinase C.
Authors: Osicka T M , Yu Y , Panagiotopoulos S , Clavant S P , Kiriazis Z , Pike R N , Pratt L M , Russo L M , Kemp B E , Comper W D , Jerums G
Published: March 2007

This study examined whether the prevention of diabetes-related albuminuria by aminoguanidine (AG) or ramipril (RAM) may be mediated by a common post-glomerular basement membrane renal intracellular mechanism involving protein kinase C (PKC). The renal handling of albumin was examined over 24 weeks in control and streptozotocin (STZ)-induced diabetic rats. A radioimmunoassay (RIA) that measures intact albumin, and intravenously injected tritium-labeled rat serum albumin, was used to assess the proportion of intact albumin and albumin fragments in urine. Diabetes was induced in male Sprague-Dawley rats by the intravenous administration of STZ at a dose of 50 mg/kg. Age-matched control rats received buffer alone. Diabetes was characterized by an increase in blood glucose (>15 mmol/l), an increase in GHb (means at 24 weeks 29.3+/-1.1%; control 6.1+/-0.1%, P<0.005), an increase in glomerular filtration rate (GFR) (4.13+/-0.15 ml/min; control 3.54+/-0.19 ml/min, P<0.005), an increase in intact albumin excretion rate (expressed as geometric mean 11.64 times/divided by 2.11 mg/24 h; control 0.74 times/divided by 1.57 mg/24 h, P<0.005) as measured by RIA, and an increase in glomerular PKC activity (26.83+/-2.38 pmol x mg(-1) x min(-1); control 14.6+/-2.99 pmol x mg(-1) x min(-1), P<0.005). Treatment of diabetic rats with either AG or RAM prevented the rise in intact albuminuria and glomerular PKC activity. Renal lysosomal cathepsin activity decreased in diabetic rats and this was not prevented by AG or RAM. Neither drug affected glycemic control or GFR, but RAM reduced systolic blood pressure (BP), whereas AG did not. These data indicate that urinary excretion of intact albumin and albumin-derived fragments in diabetes may be modulated independently of glycemic control (AG and RAM) and systolic BP (RAM). While both drugs are known for their different mechanisms of action, the fact that both prevent diabetes-related increases in glomerular PKC activity and albuminuria supports the hypothesis that PKC plays a central role in the development of diabetic nephropathy.
Progression of microalbuminuria to proteinuria in type 1 diabetes: nonlinear relationship with hyperglycemia.
Authors: Warram J H , Scott L J , Hanna L S , Wantman M , Cohen S E , Laffel L M , Ryan L , Krolewski A S
Published: March 2007

While small clinical trials have shown that improved glycemic control reduces the risk of progression of microalbuminuria to proteinuria, two recent clinical trials did not confirm this finding. We sought to reconcile the contradictory evidence by examining the dose-response relationship between hyperglycemia and progression of microalbuminuria to proteinuria in individuals with type 1 diabetes and microalbuminuria (n = 312) who were followed for 4 years with repeated assessments of urinary albumin excretion. Since 33 patients did not participate in follow-up (10.6%), data for 279 patients were analyzed. Urinary albumin excretion level worsened to proteinuria in 40 (4.1 per 100 person-years). To examine the dose-response relationship, baseline HbA1c was divided into four roughly equal groups using the cut points 8, 9, and 10%. The incidence rate varied significantly among the four groups (P = 0.008). Among those with HbA1c <8.0%, the incidence rate of progression was only 1.3 per 100 person-years, while it was 5.1, 4.2, and 6.7 per 100 person-years in the three other groups. We used generalized additive models to examine the dose-response curve using HbA1c as a continuous variable and found that the risk of progression rises steeply between an HbA1c of 7.5-8.5% and then remains approximately constant across higher levels. In conclusion, the results of this study suggest that, in patients with microalbuminuria, the risk of progression to overt proteinuria can be reduced by improved glycemic control only if the HbA1c is maintained below 8.5%. Moreover, below that value, the risk declines as the level of HbA1c decreases.
GAD65-specific autoantibodies enhance the presentation of an immunodominant T-cell epitope from GAD65.
Authors: Reijonen H , Daniels T L , Lernmark A , Nepom G T
Published: March 2007

GAD65 autoantibodies (GAD65Ab) are highly prevalent in type 1 diabetes, but their functional role in the pathogenesis of the disease and their relationship to T-cell reactivity to GAD65 is still unclear. We tested the hypothesis that GAD65Ab modulate presentation of GAD65 to T-cells. T-cell hybridoma T33.1, which recognizes the GAD65 274-286 epitope in the context of HLA-DRB 1*0401, was incubated with antigen-presenting cells exposed to recombinant human GAD65 alone or complexed with GAD65Ab' or GAD65Ab- sera. Stimulation of the T33.1 hybridoma was greatly enhanced by multiple GAD65Ab+ sera. The enhancement effect was most prominent with sera from patients with high GAD65 autoantibody levels. Sera from GAD65Ab- subjects had no effect. The correlation between T-cell stimulation and GAD65Ab levels was not absolute, suggesting that other variables such as autoantibody recognition of different regions of GAD65 and variable effects on processing of the 274-286 epitope may contribute. Uptake of antibody-complexed GAD65 was Fc receptor (FcR)-mediated because the enhancement of presentation was inhibited by monoclonal antibodies against FcR. Our results support the hypothesis that GAD65Ab modulate presentation of GAD65 to T-cells. Increased antigen uptake and heterogeneity in the autoantibody specificity may provide a mechanism for antibody-facilitated T-cell response influencing the progression of type 1 diabetes.
Glucose sensing by the hepatoportal sensor is GLUT2-dependent: in vivo analysis in GLUT2-null mice.
Authors: Burcelin R , Dolci W , Thorens B
Published: March 2007

In the preceding article, we demonstrated that activation of the hepatoportal glucose sensor led to a paradoxical development of hypoglycemia that was associated with increased glucose utilization by a subset of tissues. In this study, we tested whether GLUT2 plays a role in the portal glucose-sensing system that is similar to its involvement in pancreatic beta-cells. Awake RIPGLUT1 x GLUT2-/- and control mice were infused with glucose through the portal (Po-) or the femoral (Fe-) vein for 3 h at a rate equivalent to the endogenous glucose production rate. Blood glucose and plasma insulin concentrations were continuously monitored. Glucose turnover, glycolysis, and glycogen synthesis rates were determined by the 3H-glucose infusion technique. We showed that portal glucose infusion in RIPGLUT1 x GLUT24-/- mice did not induce the hypoglycemia observed in control mice but, in contrast, led to a transient hyperglycemic state followed by a return to normoglycemia; this glycemic pattern was similar to that observed in control Fe-mice and RIPGLUT1 x GLUT2-/- Fe-mice. Plasma insulin profiles during the infusion period were similar in control and RIPGLUT1 x GLUT2-/- Po- and Fe-mice. The lack of hypoglycemia development in RIPGLUT1 x GLUT2-/- mice was not due to the absence of GLUT2 in the liver. Indeed, reexpression by transgenesis of this transporter in hepatocytes did not restore the development of hypoglycemia after initiating portal vein glucose infusion. In the absence of GLUT2, glucose turnover increased in Po-mice to the same extent as that in RIPGLUT1 x GLUT2-/- or control Fe-mice. Finally, co-infusion of somatostatin with glucose prevented development of hypoglycemia in control Po-mice, but it did not affect the glycemia or insulinemia of RIPGLUT1 x GLUT2-/- Po-mice. Together, our data demonstrate that GLUT2 is required for the function of the hepatoportal glucose sensor and that somatostatin could inhibit the glucose signal by interfering with GLUT2-expressing sensing units.
5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) inhibits insulin-stimulated glucose transport in 3T3-L1 adipocytes.
Authors: Salt I P , Connell J M , Gould G W
Published: March 2007

Incubation of skeletal muscle with 5-aminoimidazole-4carboxamide ribonucleoside (AICAR), a compound that activates 5'-AMP-activated protein kinase (AMPK), has been demonstrated to stimulate glucose transport and GLUT4 translocation to the plasma membrane. In this study, we characterized the AMPK cascade in 3T3-L1 adipocytes and the response of glucose transport to incubation with AICAR. Both isoforms of the catalytic alpha-subunit of AMPK are expressed in 3T3-L1 adipocytes, in which AICAR stimulated AMPK activity in a time- and dose-dependent fashion. AICAR stimulated 2-deoxy-D-glucose transport twofold and reduced insulin-stimulated uptake to 62% of the control transport rate dose-dependently, closely correlating with the activation of AMPK. AICAR also inhibited insulin-stimulated GLUT4 translocation, assessed using the plasma membrane lawn assay. The effects of AICAR on insulin-stimulated glucose transport are not mediated by either adenosine receptors or nitric oxide synthase and are mediated downstream of phosphatidylinositol 3'-kinase stimulation. We propose that in contrast to skeletal muscle, in which AMPK stimulation promotes glucose transport to provide ATP as a fuel, AMPK stimulation inhibits insulin-stimulated glucose transport in adipocytes, inhibiting triacylglycerol synthesis, to conserve ATP under conditions of cellular stress. Investigation of the mode of action of AICAR and AMPK may, therefore, give insight into the mechanism of insulin action.
Anti-CD154 (CD40L) prevents recurrence of diabetes in islet isografts in the DR-BB rat.
Authors: Kover K L , Geng Z , Hess D M , Benjamin C D , Moore W V
Published: March 2007

Islet transplantation for the treatment of autoimmune diabetes is more difficult because of the additional barrier presented by the autoimmunity. We tested the ability of hamster anti-rat CD154 to prevent recurrence of diabetes in renal subcapsular islet isografts in DR-BB (RT1uu) rats with established autoimmune diabetes. Experimental animals with established diabetes received intravenous injections of 15 mg/kg anti-CD154 on a specified schedule starting 2 days before renal subcapsular transplantation of an islet isograft. Control animals received either saline or hamster IgG. Plasma glucose levels >250 mg/dl over 3 days were used to indicate the recurrence of diabetes. Rats that received saline (n = 5) or control antibody (n = 3) had a recurrence of diabetes 6-11 days after transplantation. Histological examination of islet isografts from these rats showed complete destruction of the insulin-producing portion of the isograft with residual cells positive for glucagon. Recipient rats that received anti-CD154 at the 15-mg/kg dosage (n = 6) did not have a recurrence of diabetes for 308-461 days after transplantation. Islet isografts removed from the rats showed low levels of insulin immunoreactivity, high levels of insulin mRNA, and focal infiltration with lymphocytes but no evidence of islet destruction. Mean peak antibody concentration was 266 microg/ml and returned to undetectable levels by 67-88 days after transplantation. Rats that received anti-CD154 starting at 4-7 days after transplantation had a recurrence of diabetes within 11 days of the isotransplantation. Therefore, anti-CD154 as the sole immunomodulator prevented the recurrence of diabetes in islet isografts in rats with established autoimmune diabetes. This suggests that CD40/CD154 blockade is effective in preventing the insulitis or the effector phase of autoimmune diabetes.
NOD Idd5 locus controls insulitis and diabetes and overlaps the orthologous CTLA4/IDDM12 and NRAMP1 loci in humans.
Authors: Hill N J , Lyons P A , Armitage N , Todd J A , Wicker L S , Peterson L B
Published: March 2007

A genome scan for B10-derived loci that reduce the frequency of diabetes and insulitis in NOD mice demonstrated a large region (34 cM) of linkage on the proximal end of chromosome 1. This locus was designated Idd5 and encompassed candidate genes including Il1r1, Il1r2, Stat1, Stat4, Nramp1, and Bcl2. In the current study, we have confirmed the existence of Idd5 by developing a series of congenic mouse strains that are resistant to diabetes and determined that Idd5 is actually two genes located within a 9.4-cM interval. Idd5.1 is in the proximal 1.5-cM portion of the interval and contains the candidates Casp8, Cflar (FLIP), Cd28, and Cd152 (CTLA4). Idd5.1 overlaps the orthologous CTLA4/IDDM12 locus in humans. Idd5.2 is in the distal 5.1-cM portion of the 9.4-cM interval and contains the candidates Nramp1, which has a functional polymorphism between NOD and B10, and Cmkar2 (CXCR2, interleukin [IL]-8 receptor alpha). Candidate genes eliminated by this analysis include Il1r1, Ilr2, Zap70, Orch5, Stat1, Stat4, Bcl2, Cmkar4 (CXCR4), and Il10. On its own, the Idd5 locus provides a significant amount of protection from diabetes (50% reduction from parental frequency) and when combined with another resistance locus (Idd3 on chromosome 3), provides nearly complete protection from diabetes and insulitis.
Triggering and amplifying pathways of regulation of insulin secretion by glucose.
Authors: Henquin J C
Published: March 2007

Glucose stimulates insulin secretion by generating triggering and amplifying signals in beta-cells. The triggering pathway is well characterized. It involves the following sequence of events: entry of glucose by facilitated diffusion, metabolism of glucose by oxidative glycolysis, rise in the ATP-to-ADP ratio, closure of ATP-sensitive K+ (KATP) channels, membrane depolarization, opening of voltage-operated Ca2+ channels, Ca2+ influx, rise in cytoplasmic free Ca2+ concentration ([Ca2+]i), and activation of the exocytotic machinery. The amplifying pathway can be studied when beta-cell [Ca2+]i is elevated and clamped by a depolarization with either a high concentration of sulfonylurea or a high concentration of K+ in the presence of diazoxide (K(ATP) channels are then respectively blocked or held open). Under these conditions, glucose still increases insulin secretion in a concentration-dependent manner. This increase in secretion is highly sensitive to glucose (produced by as little as 1-6 mmol/l glucose), requires glucose metabolism, is independent of activation of protein kinases A and C, and does not seem to implicate long-chain acyl-CoAs. Changes in adenine nucleotides may be involved. The amplification consists of an increase in efficacy of Ca2+ on exocytosis of insulin granules. There exists a clear hierarchy between both pathways. The triggering pathway predominates over the amplifying pathway, which remains functionally silent as long as [Ca2+]i has not been raised by the first pathway; i.e., as long as glucose has not reached its threshold concentration. The alteration of this hierarchy by long-acting sulfonylureas or genetic inactivation of K(ATP) channels may lead to inappropriate insulin secretion at low glucose. The amplifying pathway serves to optimize the secretory response not only to glucose but also to nonglucose stimuli. It is impaired in beta-cells of animal models of type 2 diabetes, and indirect evidence suggests that it is altered in beta-cells of type 2 diabetic patients. Besides the available drugs that act on K(ATP) channels and increase the triggering signal, novel drugs that correct a deficient amplifying pathway would be useful to restore adequate insulin secretion in type 2 diabetic patients.
Cytokine- or chemically derived nitric oxide alters the expression of proteins detected by two-dimensional gel electrophoresis in neonatal rat islets of Langerhans.
Authors: John N E , Andersen H U , Fey S J , Larsen P M , Roepstorff P , Larsen M R , Pociot F , Karlsen A E , Nerup J , Green I C , Mandrup-Poulsen T
Published: March 2007

Interleukin-1beta (IL-1beta) treatment of neonatal rat islets for 24 h induces changes in the expression of 105 of 2,200 proteins, as determined previously by two-dimensional (2D) gel electrophoresis. Nitric oxide (NO) has been implicated as one of the mediators of IL-1beta effects in insulin-containing cell lines and rat islets. The aims of this study were 1) to determine the involvement of NO in IL-1beta-induced alterations in protein expression and 2) to investigate the effects of chemically generated NO on protein expression by 2D gel electrophoresis of neonatal rat islet samples. IL-1beta-induced NO production was prevented by incubation of islets in arginine-free medium supplemented with the arginine analog NG-nitro-L-arginine. [35S]methionine-labeled islet proteins were separated using 2D gel electrophoresis and analyzed using the BioImage computer program. Analysis revealed that the expression levels of 23 protein spots of the 105 protein spots, altered by prior treatment with IL-1beta (60 U/ml) alone, were significantly affected (P < 0.01 [n = 4] and P < 0.05 [n = 19]) when NO production was prevented. The effects of chemically generated NO were investigated by exposing islets to the NO donor GSNO (100 micromol/l) for 24 h before labeling with [35S]methionine and 2D gel electrophoresis. Computer-based analysis identified alterations in the expression of 19 of a total of 1,600 detectable proteins in GSNO-treated islets (P < 0.01). We conclude 1) that the expression of up to 42 proteins is altered by cytokine-induced or chemically generated NO in the precise experimental conditions chosen and 2) that the majority of proteins altered by prior treatment with IL-1beta may be the result of NO-independent IL-1beta-mediated regulation of gene expression. This study demonstrates that the combination of 2D gel electrophoresis and mass spectrometry is a powerful tool in the identification of beta-cell proteins involved in the response to toxic mediators.
PIP2 and ATP cooperatively prevent cytosolic Ca2+-induced modification of ATP-sensitive K+ channels in rat pancreatic beta-cells.
Authors: Koriyama N , Kakei M , Nakazaki M , Yaekura K , Ichinari K , Gong Q , Morimitsu S , Yada T , Tei C
Published: March 2007

The factors that influence functional coupling between the sulfonylurea receptor (SUR1) and Kir6.2 subunits of ATP-sensitive K+ (K+(ATP)) channels were studied in rat pancreatic beta-cells using patch clamp and microfluorometric techniques. Tolbutamide at 10 micromol/l inhibited K+(ATP) channels in association with occurrence of action currents, but further exposure of beta-cells to the drug for 30 min or longer resulted in reappearance of K+(ATP) channel events. Half-maximal inhibition concentration (IC50) for tolbutamide was 1.5 microl/mol in 2.8 mmol/l glucose, and it was increased to 13.3 micromol/l when the cellular metabolism was inhibited by 0.5 mmol/l 2,4-dinitrophenol (DNP) for 5 min. Tolbutamide at 10 micromol/l induced an increase in cytosolic Ca2+ concentration ([Ca2+]i), and its amplitude was markedly reduced following exposure to 0.5 mmol/l DNP or long-term (30 min) exposure to 10 micromol/l tolbutamide. This tolbutamide insensitivity, as assessed by the [Ca2+]i response, was not observed when the external Ca2+ was omitted during the long-term exposure to tolbutamide. In cell-attached membrane patches, the tolbutamide insensitivity was also produced by treatment of cells with 150 micromol/l diazoxide and 25 mmol/l KCl in the presence, but not absence, of 2 mmol/l Ca2+ in the external solution. When the cytoplasmic face of inside-out membrane patches was treated with higher Ca2+ concentrations (2 micromol/l), both ADP-evoked activation and tolbutamide-induced inhibition of K+ ATP channels were attenuated with retaining ATP-induced inhibition, indicating the modification of K+(ATP) channels. The Ca2+-induced channel modification was prevented partially by phosphatidylinositol 4,5-bisphosphate (PIP2) and completely by ATP and PIP2 together, but not by ATP alone. Treatment of the channel with cytochalasin D, a disrupter of F-actin, evoked channel modification similar to that induced by Ca2+. The modification was prevented completely by phalloidin, a stabilizer of F-actin. In conclusion, long-term exposure to tolbutamide or metabolic inhibition causes modification of K+ ATP channels via mechanisms involving Ca2+-dependent reaction. The modification, which may reflect functional disconnection between SUR1 and Kir6.2, is prevented by ATP and PIP2, which may act cooperatively to stabilize membrane cytoskeletons (F-actin structures).
Glucose-induced [Ca2+]i abnormalities in human pancreatic islets: important role of overstimulation.
Authors: Björklund A , Lansner A , Grill V E
Published: March 2007

Chronic hyperglycemia desensitizes beta-cells to glucose. To further define the mechanisms behind desensitization and the role of overstimulation, we tested human pancreatic islets for the effects of long-term elevated glucose levels on cytoplasmic free Ca2+ concentration ([Ca2+]i) and its relationship to overstimulation. Islets were cultured for 48 h with 5.5 or 27 mmol/l glucose. Culture with 27 mmol/l glucose obliterated postculture insulin responses to 27 mmol/l glucose. This desensitization was specific for glucose versus arginine. Desensitization was accompanied by three major [Ca2+]i abnormalities: 1) elevated basal [Ca2+]i, 2) loss of a glucose-induced rise in [Ca2+]i, and 3) perturbations of oscillatory activity with a decrease in glucose-induced slow oscillations (0.2-0.5 min(-1)). Coculture with 0.3 mmol/l diazoxide was performed to probe the role of overstimulation. Neither glucose nor diazoxide affected islet glucose utilization or oxidation. Coculture with diazoxide and 27 mmol/l glucose significantly (P < 0.05) restored postculture insulin responses to glucose and lowered basal [Ca2+]i and normalized glucose-induced oscillatory activity. However, diazoxide completely failed to revive an increase in [Ca2+]i during postculture glucose stimulation. In conclusion, desensitization of glucose-induced insulin secretion in human pancreatic islets is induced in parallel with major glucose-specific [Ca2+]i abnormalities. Overstimulation is an important but not exclusive factor behind [Ca2+]i abnormalities.
Impaired insulin secretion and increased insulin sensitivity in familial maturity-onset diabetes of the young 4 (insulin promoter factor 1 gene).
Authors: Clocquet A R , Egan J M , Stoffers D A , Muller D C , Wideman L , Chin G A , Clarke W L , Hanks J B , Habener J F , Elahi D
Published: March 2007

Diabetes resulting from heterozygosity for an inactivating mutation of the homeodomain transcription factor insulin promoter factor 1 (IPF-1) is due to a genetic defect of beta-cell function referred to as maturity-onset diabetes of the young 4. IPF-1 is required for the development of the pancreas and mediates glucose-responsive stimulation of insulin gene transcription. To quantitate islet cell responses in a family harboring a Pro63fsdelC mutation in IPF-1, we performed a five-step (1-h intervals) hyperglycemic clamp on seven heterozygous members (NM) and eight normal genotype members (NN). During the last 30 min of the fifth glucose step, glucagon-like peptide 1 (GLP-1) was also infused (1.5 pmol x kg(-1) x min(-1)). Fasting plasma glucose levels were greater in the NM group than in the NN group (9.2 vs. 5.9 mmol/l, respectively; P < 0.05). Fasting insulin levels were similar in both groups (72 vs. 105 pmol/l for NN vs. NM, respectively). First-phase insulin and C-peptide responses were absent in individuals in the NM group, who had markedly attenuated insulin responses to glucose alone compared with the NN group. At a glucose level of 16.8 mmol/l above fasting level, GLP-1 augmented insulin secretion equivalently (fold increase) in both groups, but the insulin and C-peptide responses to GLP-1 were sevenfold less in the NM subjects than in the NN subjects. In both groups, glucagon levels fell during each glycemic plateau, and a further reduction occurred during the GLP-1 infusion. Sigmoidal dose-response curves of glucose clearance versus insulin levels during the hyperglycemic clamp in the two small groups showed both a left shift and a lower maximal response in the NM group compared with the NN group, which is consistent with an increased insulin sensitivity in the NM subjects. A sharp decline occurred in the dose-response curve for suppression of nonesterified fatty acids versus insulin levels in the NM group. We conclude that the Pro63fsdelC IPF-1 mutation is associated with a severe impairment of beta-cell sensitivity to glucose and an apparent increase in peripheral tissue sensitivity to insulin and is a genetically determined cause of beta-cell dysfunction.
Repeated 2-deoxy-D-glucose-induced glucoprivation attenuates Fos expression and glucoregulatory responses during subsequent glucoprivation.
Authors: Sanders N M , Ritter S
Published: March 2007

A condition of reduced responsiveness to hypoglycemia, known as hypoglycemia-associated autonomic failure (HAAF), occurs in diabetic patients in the wake of a prior hypoglycemic episode. This condition suggests that hypoglycemia alters central glucose-sensing mechanisms. This experiment examined the effects of repeated 2-deoxy-D-glucose (2DG)-induced glucoprivation on subsequent 2DG-induced feeding and hyperglycemic responses in rats. Fos immunoreactivity (ir) in adrenal medulla and brain sites involved in these responses was also examined. Rats were injected daily for 10 days with 2DG (200 mg/kg) or saline (0.9%) or were handled. On day 11, rats were injected with 2DG (200 mg/kg). After injection, food intake was measured in one group. In another group, food was withheld, and multiple blood samples were collected for glucose determination. In a third group, food was withheld, and rats were killed after 2 h for evaluation of Fos-ir. Prior repeated glucoprivation reduced subsequent feeding and hyperglycemia responses to 2DG to baseline levels. Double-label immunohistochemistry showed that Fos-ir was reduced or abolished in catecholamine cell groups A1, A1/C1, C1, C3, and A6 and in the paraventricular nucleus of the hypothalamus and adrenal medulla. In other brain sites, 2DG-induced Fos-ir was diminished or unaffected by prior glucoprivation. Sites in which Fos-ir was abolished have been implicated previously in glucoprivic control of feeding and adrenal medullary secretion. Therefore, the present findings may identify crucial neuroanatomical sites that are altered by prior glucoprivation and that mediate some of the physiological deficits observed in HAAF.
Unlike leptin, ciliary neurotrophic factor does not reverse the starvation-induced changes of serum corticosterone and hypothalamic neuropeptide levels but induces expression of hypothalamic inhibitors of leptin signaling.
Authors: Ziotopoulou M , Erani D M , Hileman S M , Bjørbaek C , Mantzoros C S
Published: March 2007

Leptin mediates neuroendocrine responses to fasting and restores the starvation-induced changes of several hypothalamic neuropeptides. Ciliary neurotrophic factor (CNTF), a cytokine closely related to leptin, reduces food intake and reverses obesity, but its role in restoring the starvation-induced changes of hormones or hypothalamic neuropeptides remains largely unknown. To comparatively assess the roles of CNTF and leptin in reversing the starvation-induced changes of hypothalamic neuropeptides and endocrine function and in inducing expression of hypothalamic inhibitors of leptin and CNTF signaling (suppressor of cytokine signaling 3 [SOCS-3]) and mediators of energy expenditure (cyclo-oxygenase 2 [COX-2]), we studied the effect of CNTF and leptin administered by intraperitoneal injections (1 microg/g twice daily) in C57Bl/6J mice fasted for 48 h. Serum corticosterone levels increased with fasting, and leptin administration partially normalized them, whereas CNTF administration had no effect. Hypothalamic neuropeptide Y (NPY) and agouti-related protein (AgRP) mRNA expression increased and pro-opiomelanocortin (POMC) decreased in response to fasting. Leptin administration decreased NPY and AgRP and increased POMC mRNA levels toward baseline, but CNTF administration in fasted mice had no effect of comparable significance. Both leptin and CNTF administration in fasted mice resulted in an induction of SOCS-3 mRNA expression. CNTF also induced hypothalamic SOCS-2 mRNA expression. Finally, neither leptin nor CNTF administration in mice fasted for 48 h alters hypothalamic COX-2 expression. Our data suggest that only falling leptin levels mediate the starvation-induced alterations in corticosterone levels and expression of hypothalamic neuropeptides, but inhibitors of leptin signaling are induced by both leptin and CNTF. This may be of clinical importance because both agents are now being evaluated for the treatment of obesity in humans.
Adrenalectomy reverses obese phenotype and restores hypothalamic melanocortin tone in leptin-deficient ob/ob mice.
Authors: Makimura H , Mizuno T M , Roberts J , Silverstein J , Beasley J , Mobbs C V
Published: March 2007

In genetically obese leptin-deficient ob/ob mice, adrenalectomy reverses or attenuates the obese phenotype. Relative to lean controls, ob/ob mice also exhibit decreased hypothalamic proopiomelanocortin (POMC) mRNA and increased hypothalamic agouti-related peptide (AGRP) mRNA and neuropeptide Y (NPY) mRNA. It has been hypothesized that this profile of hypothalamic gene expression contributes to the obese phenotype caused by leptin deficiency. To assess if reversal of obese phenotype by adrenalectomy entails normalization of hypothalamic gene expression, male wild-type and ob/ob mice were adrenalectomized (with saline supplementation) or sham adrenalectomized at 2 months of age. Mice were sacrificed 2 weeks after adrenalectomy, during which time food intake and body weight were monitored daily. After sacrifice, hypothalamic gene expression was assessed by Northern blot analysis as well as in situ hybridization. In wild-type mice, adrenalectomy significantly decreased AGRP mRNA but did not significantly influence POMC or NPY mRNA. In ob/ob mice, adrenalectomy reduced the levels of plasma glucose, serum insulin and corticosterone, and food intake toward or below wild-type levels, and it restored hypothalamic POMC and AGRP mRNA but not NPY mRNA to wild-type levels. These studies suggest that adrenalectomy reverses or attenuates the obese phenotype in ob/ob mice, in part by restoring hypothalamic melanocortin tone toward wild-type levels. These studies also demonstrate that factors other than leptin may play a major role in regulating hypothalamic melanocortin function.
High glucose level and free fatty acid stimulate reactive oxygen species production through protein kinase C--dependent activation of NAD(P)H oxidase in cultured vascular cells.
Authors: Inoguchi T , Li P , Umeda F , Yu H Y , Kakimoto M , Imamura M , Aoki T , Etoh T , Hashimoto T , Naruse M , Sano H , Utsumi H , Nawata H
Published: March 2007

Recent studies have revealed that vascular cells can produce reactive oxygen species (ROS) through NAD(P)H oxidase, which may be involved in vascular injury. However, the pathological role of vascular NAD(P)H oxidase in diabetes or in the insulin-resistant state remains unknown. In this study, we examined the effect of high glucose level and free fatty acid (FFA) (palmitate) on ROS production in cultured aortic smooth muscle cells (SMCs) and endothelial cells (ECs) using electron spin resonance spectroscopy. Exposure of cultured SMCs or ECs to a high glucose level (400 mg/dl) for 72 h significantly increased the free radical production compared with low glucose level exposure (100 mg/dl). Treatment of the cells for 3 h with phorbol myristic acid (PMA), a protein kinase C (PKC) activator, also increased free radical production. This increase was restored to the control value by diphenylene iodonium, a NAD(P)H oxidase inhibitor, suggesting ROS production through PKC-dependent activation of NAD(P)H oxidase. The increase in free radical production by high glucose level exposure was completely restored by both diphenylene iodonium and GF109203X, a PKC-specific inhibitor. Exposure to palmitate (200 micromol/l) also increased free radical production, which was concomitant with increases in diacylglycerol level and PKC activity. Again, this increase was restored to the control value by both diphenylene iodonium and GF109203X. The present results suggest that both high glucose level and palmitate may stimulate ROS production through PKC-dependent activation of NAD(P)H oxidase in both vascular SMCs and ECs. This finding may be involved in the excessive acceleration of atherosclerosis in patients with diabetes and insulin resistance syndrome.
beta-cell transcription factors and diabetes: no evidence for diabetes-associated mutations in the gene encoding the basic helix-loop-helix transcription factor neurogenic differentiation 4 (NEUROD4) in Japanese patients with MODY.
Authors: Horikawa Y , Horikawa Y , Cox N J , Iwasaki N , Ogata M , Iwamoto Y , Schwitzgebel V , German M S , Bell G I
Published: March 2007

The basic helix-loop-helix (bHLH) family of transcription factors plays an important role in the normal development and function of the endocrine pancreas. Heterozygous mutations in the gene encoding one member of this family, NeuroD1/BETA2, are associated with a monogenic form of diabetes that resembles maturity-onset diabetes of the young (MODY) in many respects. This result prompted us to screen the genes encoding related bHLH transcription factors that are also expressed in pancreatic islets for diabetes-associated mutations. We have screened 57 unrelated Japanese subjects with a clinical diagnosis of MODY for mutations in the NeuroD4/Math-3/ATH-3 gene (NEUROD4). This analysis revealed seven frequent polymorphisms that were not associated with MODY, including five in the 5'-untranslated region (UTR) (-477G/A, -436delA, -324delT, -107insTTTT, and -104T/C [cDNA sequences]) and two in the 3'-UTR (1027C/T and 1076C/A). A missense mutation, K68T (203A/C), was found in a heterozygous state in one MODY subject and two nondiabetic subjects. The results of our study suggest that genetic variation in NEUROD4 is not a common cause of MODY in Japanese.
Organizing glucose disposal: emerging roles of the glycogen targeting subunits of protein phosphatase-1.
Authors: Newgard C B , Brady M J , O'Doherty R M , Saltiel A R
Published: March 2007

Glucose is stored in mammalian tissues in the form of glycogen. Glycogen levels are markedly reduced in liver or muscle cells of patients with insulin-resistant or insulin-deficient forms of diabetes, suggesting that impaired glycogen synthesis may contribute to development of hyperglycemia. Recently, interest in this area has been further stimulated by new insights into the spatial organization of metabolic enzymes within cells and the importance of such organization in regulation of glycogen metabolism. It is now clear that a four-member family of glycogen targeting subunits of protein phosphatase-1 (PP1) plays a major role in coordinating these events. These proteins target PP1 to the glycogen particle and also bind differentially to glycogen synthase, glycogen phosphorylase, and phosphorylase kinase, thereby serving as molecular scaffolds. Moreover, the various glycogen-targeting subunits have distinct tissue expression patterns and can influence regulation of glycogen metabolism in response to glycogenic and glycogenolytic signals. The purpose of this article is to summarize new insights into the structure, function, regulation, and metabolic effects of the glycogen-targeting subunits of PP1 and to evaluate the possibility that these molecules could serve as therapeutic targets for lowering of blood glucose in diabetes.
Activation of glucose transport by AMP-activated protein kinase via stimulation of nitric oxide synthase.
Authors: Fryer L G , Hajduch E , Rencurel F , Salt I P , Hundal H S , Hardie D G , Carling D
Published: March 2007

Glucose transport in skeletal muscle is stimulated by two distinct stimuli, insulin and exercise. The mechanism by which exercise stimulates glucose transport is not known, although it is distinct from the insulin-mediated pathway. Recently, it has been shown that AMP-activated protein kinase (AMPK) is activated by exercise in skeletal muscle, whereas pharmacological activation of AMPK by 5-amino-4-imidazolecarboxamide riboside (AICAR) leads to increased glucose transport. It has been postulated, therefore, that AMPK may be the link between exercise and glucose transport. To address this, we have examined the signaling pathway involved in the stimulation of glucose uptake after activation of AMPK. Here we show that activation of AMPK by AICAR in rat muscle and mouse H-2Kb muscle cells activates glucose transport approximately twofold. AMPK in H-2Kb cells is also activated by hyperosmotic stress and the mitochondrial uncoupling agent, dinitrophenol, both of which lead to increased glucose transport. In contrast, insulin, which activates glucose transport two- to-threefold in both rat muscle and H-2Kb cells, has no effect on AMPK activity. A previous study has shown that AMPK phosphorylates and activates endothelial nitric oxide synthase (NOS). We show here that NOS activity in H-2Kb cells is activated after stimulation of AMPK by AICAR. Treatment of H-2Kb cells or rat muscle with NOS inhibitors completely blocks the increase in glucose transport after activation of AMPK. In addition, an inhibitor of guanylate cyclase also blocks activation of glucose transport by AICAR in H-2Kb cells. These results indicate that activation of AMPK in muscle cells stimulates glucose transport by activation of NOS coupled to downstream signaling components, including cyclic GMP.
Dehydroepiandrosterone sulfate and beta-cell function: enhanced glucose-induced insulin secretion and altered gene expression in rodent pancreatic beta-cells.
Authors: Dillon J S , Yaney G C , Zhou Y , Voilley N , Bowen S , Chipkin S , Bliss C R , Schultz V , Schuit F C , Prentki M , Waxman D J , Corkey B E
Published: March 2007

Administration of dehydroepiandrosterone (DHEA), or its sulfated form (DHEAS), controls hyperglycemia in diabetic rodents without directly altering insulin sensitivity. We show that DHEAS enhanced glucose-stimulated insulin secretion when administered in vivo to rats or in vitro to beta-cell lines, without changing cellular insulin content. Insulin secretion increased from 3 days of steroid exposure in vitro, suggesting that DHEAS did not directly activate the secretory processes. DHEAS selectively increased the beta-cell mRNA expression of acyl CoA synthetase-2 and peroxisomal acyl CoA oxidase in a time-dependent manner. Although DHEAS is a peroxisomal proliferator, it did not alter the mRNA expression of peroxisomal proliferator-activated receptor (PPAR) alpha or beta, or enhance the activity of transfected PPAR alpha, beta, or gamma in vitro. Thus, DHEAS directly affected the beta-cell to enhance glucose-stimulated insulin secretion and increased the mRNA expression of specific beta-cell mitochondrial and peroxisomal lipid metabolic enzymes. This effect of DHEAS on insulin secretion may contribute to the amelioration of hyperglycemia seen in various rodent models of diabetes.
Differential patterns of glucose-induced electrical activity and intracellular calcium responses in single mouse and rat pancreatic islets.
Authors: Antunes C M , Salgado A P , Rosário L M , Santos R M
Published: March 2007

Although isolated rat islets are widely used to study in vitro insulin secretion and the underlying metabolic and ionic processes, knowledge on the properties of glucose-induced electrical activity (GIEA), a key step in glucose-response coupling, has been gathered almost exclusively from microdissected mouse islets. Using a modified intracellular recording technique, we have now compared the patterns of GIEA in collagenase-isolated rat and mouse islets. Resting membrane potentials of rat and mouse beta-cells were approximately -50 and -60 mV, respectively. Both rat and mouse beta-cells displayed prompt membrane depolarizations in response to glucose. However, whereas the latter exhibited a bursting pattern consisting of alternating hyperpolarized and depolarized active phases, rat beta-cells fired action potentials from a nonoscillating membrane potential at all glucose concentrations (8.4-22.0 mmol/l). This was mirrored by changes in the intracellular Ca2+ concentration ([Ca2+]i), which was oscillatory in mouse and nonoscillatory in rat islets. Stimulated rat beta-cells were strongly hyperpolarized by diazoxide, an activator of ATP-dependent K+ channels. Glucose evoked dose-dependent depolarizations and [Ca2+]i increases in both rat (EC50 5.9-6.9 mmol/l) and mouse islets (EC50 8.3-9.5 mmol/l), although it did not affect the burst plateau potential in the latter case. We conclude that there are important differences between beta-cells from both species with respect to early steps in the stimulus-secretion coupling cascade based on the following findings: 1) mouse beta-cells have a larger resting K+ conductance in 2 mmol/l glucose, 2) rat beta-cells lack the compensatory mechanism responsible for generating membrane potential oscillations and holding the depolarized plateau potential in mouse beta-cells, and 3) the electrical and [Ca2+]i dose-response curves in rat beta-cells are shifted toward lower glucose concentrations. Exploring the molecular basis of these differences may clarify several a priori assumptions on the electrophysiological properties of rat beta-cells, which could foster the development of new working models of pancreatic beta-cell function.
Hedgehog signaling regulation of insulin production by pancreatic beta-cells.
Authors: Thomas M K , Rastalsky N , Lee J H , Habener J F
Published: March 2007

Hedgehogs (Hhs) are intercellular signaling molecules that regulate tissue patterning in mammalian development. Mammalian Hhs include Sonic hedgehog (Shh), Indian hedgehog (Ihh), and Desert hedgehog (Dhh). The absence of Shh expression is required for the early development of the endocrine and exocrine pancreas, but whether Hh signaling functions in the fully developed adult endocrine pancreas is unknown. Here we report that Hhs Ihh and Dhh and their receptors patched (Ptc) and smoothened are expressed in the endocrine islets of Langerhans of the fully developed rat pancreas and in the clonal gamma-cell line INS-1. We demonstrate the coexpression of Ptc with insulin in beta-cells of mouse pancreatic islets, indicating that beta-cells are targets of active Hh signaling. The administration of cyclopamine, a Hh signaling inhibitor, decreases both insulin secretion from and insulin content of INS-1 cells. The effects of Hh signaling on insulin production occur at the transcriptional level because activation of Hh signal transduction by ectopic expression of Shh increases rat insulin I promoter activation in a dose-dependent manner in transient transfections of INS-1 and MIN6 beta-cell lines. In contrast, inhibition of Hh signaling with increasing concentrations of cyclopamine progressively reduces insulin promoter activity. Furthermore, the treatment of INS-1 cells with cyclopamine diminishes endogenous insulin mRNA expression. We propose that Hh signaling is not restricted to patterning in early pancreas development but also continues to signal in differentiated beta-cells of the endocrine pancreas in regulating insulin production. Thus, defective Hh signaling in the pancreas should be considered as a potential factor in the pathogenesis of type 2 diabetes.