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PubMed1989

[The effect of maternal hyperglycemia on insulin secretion by monolayer-cultured B cells of neonatal rats--a perifusion study].

To evaluate the effect of maternal hyperglycemia on insulin secretion by neonatal rat B cells, perifusion was conducted on monolayer cultures of rat neonates from normoglycemic (C) mothers or those made slightly (SH) and highly (HH) hyperglycemic by the injection of streptozotocin. In the C, SH and HH groups, B cells responded to 16.7 mM glucose, 10 mM leucine, 10 mM 2-ketoisocaproate and 10 mM arginine in a biphasic manner, although these nutrients provided stimuli so feeble that insulin secretion in the second phase was slightly raised above basal levels. However, quantitative relationships differed. Compared with the C group, B cells in the SH group showed a significant increase in the secretion of the second phase in response to glucose, 2-ketoisocaproate and arginine but not to leucine, whereas there was no difference in the secretion of the first phase between these two groups. In the HH group, a lower insulin secretion of the first and second phase was observed. These results are compatible with hyperglycemia-hyperinsulinaemia theory concerning the function of B cells in neonates born to slightly hyperglycemic mothers and with a defect in insulin secretion by neonates from highly hyperglycemic females.

Animals↗
PubMed2006

Decreased nutrient-stimulated insulin secretion in chronically hypoglycemic late-gestation fetal sheep is due to an intrinsic islet defect.

We measured in vivo and in vitro nutrient-stimulated insulin secretion in late gestation fetal sheep to determine whether an intrinsic islet defect is responsible for decreased glucose-stimulated insulin secretion (GSIS) in response to chronic hypoglycemia. Control fetuses responded to both leucine and lysine infusions with increased arterial plasma insulin concentrations (average increase: 0.13 +/- 0.05 ng/ml leucine; 0.99 +/- 0.26 ng/ml lysine). In vivo lysine-stimulated insulin secretion was decreased by chronic (0.37 +/- 0.18 ng/ml) and acute (0.27 +/- 0.19 ng/ml) hypoglycemia. Leucine did not stimulate insulin secretion following acute hypoglycemia but was preserved with chronic hypoglycemia (0.12 +/- 0.09 ng/ml). Isolated pancreatic islets from chronically hypoglycemic fetuses had normal insulin and DNA content but decreased fractional insulin release when stimulated with glucose, leucine, arginine, or lysine. Isolated islets from control fetuses responded to all nutrients. Therefore, chronic late gestation hypoglycemia causes defective in vitro nutrient-regulated insulin secretion that is at least partly responsible for diminished in vivo GSIS. Chronic hypoglycemia is a feature of human intrauterine growth restriction (IUGR) and might lead to an islet defect that is responsible for the decreased insulin secretion patterns seen in human IUGR fetuses and low-birth-weight human infants.

Amino Acids, Essential↗
PubMed1975

Persistent testicular delta5-isomerase-3beta-hydroxysteroid dehydrogenase (delta5-3beta-HSD) deficiency in the delta5-3beta-HSD form of congenital adrenal hyperplasia.

A partial testicular defect in testosterone secretion has been documented in a pubertal male with a congenital adrenal hyperplasia due to hereditary deficiency of the delta5-isomerase-3beta-hydroxysteroid dehydrogenase enzyme complex (delta5-3beta-HSD). Diagnosis of the enzymatic defect is based on the clinical picture of ambiguous genitalia and salt-losing crisis in infancy, together with high urinary delta5-pregnenetriol and plasma dehydroepiandrosterone when the patient was taken off replacement corticoid treatment. No hormonal response to ACTH or salt deprivation was demonstrable. In addition, in vivo studies revealed a partial enzymatic defect in the testis. Although plasma testosterone was low-normal (250 ng/100 ml), plasma delta5-androstenediol was markedly elevated and rose to a greater extent than testosterone after human chorionic gonadotropin administration. In vitro testicular incubation studies suggested a testicular delta5-3beta-HSD enzyme defect with less delta4 products formed from delta5 precursors than in a control testis. Histochemical studies of the testis were also consistent with this defect. Testicular biopsy revealed spermatogenic arrest, generally diminished Leydig cells, but with focal areas of Leydig cell hyperplasia as well as benign Leydig cell hyperplasia as well as benign Leudig cell nodules within the spermatic cord. In vivo studies of steroid metabolism suggested intact peripheral or hepatic delta5-3beta-HSD activity. These studies imply that delta5-3beta-HSD activity differs in the gonad, adrenal, and peripheral organs. These findings are compatible with the concept that the enzyme complex consists of subunits and/or that enzymes in these organs are under different genetic control.

17-alpha-Hydroxypregnenolone↗
PubMed2000

Insulin effect during embryogenesis determines fetal growth: a possible molecular link between birth weight and susceptibility to type 2 diabetes.

Low birth weight has been reported to be associated with impaired insulin secretion and insulin resistance. It has been proposed that this association results from fetal programming in response to the intrauterine environment (the thrifty phenotype hypothesis). To elucidate the relationship between birth weight and genetically determined defects in insulin secretion, we measured the birth weights of neonates derived from crosses of male pancreatic beta-cell type glucokinase knockout (Gck+/-) mice and female wild-type (WT) or Gck+/- mice. In 135 offspring, birth weights were lower in the presence of a fetal heterozygous mutation and higher in the presence of a maternal heterozygous mutation. Moreover, Gck-/- neonates had significantly smaller birth weights than WT or Gck+/- neonates (means +/- SE 1.49+/-0.03 [n = 30] vs. 1.63+/-0.03 [n = 30] or 1.63+/-0.02 [n = 50] g, respectively; P<0.01). Thus, Gck mutations in beta-cells may impair insulin response to glucose and alter intrauterine growth as well as glucose metabolism after birth. This study has confirmed the results of a previous report that human subjects carrying mutations in Gck had reduced birth weights and has provided direct evidence for a link between insulin and fetal growth. Moreover, birth weights were reduced in insulin receptor substrate-1 knockout mice despite normal insulin levels. Taken together, these results suggest that a genetically programmed insulin effect during embryogenesis determines fetal growth and provides a possible molecular link between birth weight and susceptibility to type 2 diabetes.

Animals↗
PubMed2001

Defective granule exocytosis in Rab27a-deficient lymphocytes from Ashen mice.

Because mutations in Rab27a have been linked to immune defects in humans, we have examined cytotoxic lymphocyte function in ashen mice, which contain a splicing mutation in Rab27a. Ashen cytotoxic T lymphocytes (CTLs) showed a >90% reduction in lytic activity on Fas-negative target cells compared with control C3H CTLs, and ashen natural killer cell activity was likewise diminished. Although their granule-mediated cytotoxicity pathway is profoundly defective, ashen CTLs displayed a normal FasL-Fas cytotoxicity pathway. The CD4/8 phenotype of ashen T cells and their proliferative responses were similar to controls. Ashen CTLs had normal levels of perforin and granzymes A and B and normal-appearing perforin-positive granules, which polarized upon interaction of the CTLs with anti-CD3-coated beads. However, rapid anti-CD3-induced granule secretion was drastically defective in both CD8(+) and CD4(+) T cells from ashen mice. This defect in exocytosis was not observed in the constitutive pathway, as T cell receptor-stimulated interferon-gamma secretion was normal. Based on these results and our demonstration that Rab27a colocalizes with granzyme B-positive granules and is undetectable in ashen CTLs, we conclude that Rab27a is required for a late step in granule exocytosis, compatible with current models of Rab protein function in vesicle docking and fusion.

Abatacept↗
PubMed1995

Hormonal regulation of albumin gene expression in primary cultures of rat hepatocytes.

When primary cultures of rat hepatocytes were placed in a chemically defined serum-free medium containing a combination of insulin, glucagon, and dexamethasone, the synthesis of albumin and total protein and the cellular content of RNA and DNA were maintained at constant values for 8 days. Despite the constant rate of albumin synthesis, secretion of the protein increased more than twofold during the initial 4 days in culture and was then maintained at a value similar to that observed in vivo through day 8. This observation suggested an initial defect in albumin secretion that was corrected with time in culture. Deprivation of insulin between days 2 and 5 resulted in a decline in albumin secretion to approximately 40% of the control value. The decline in albumin secretion was accompanied by proportional decreases in albumin synthesis, albumin mRNA, and albumin gene transcription. Return of insulin-deprived cells to complete medium on day 5 restored albumin synthesis and secretion as well as albumin mRNA to control values by day 8. Deprivation of either glucagon or dexamethasone also resulted in reduced albumin synthesis and secretion accompanied by proportional decreases in albumin mRNA and gene transcription. However, the magnitude of the changes in these parameters was less with glucagon or dexamethasone deprivation compared with insulin deprivation. Return of glucagon- or dexamethasone-deprived cells to complete medium on day 5 restored albumin synthesis and secretion as well as albumin mRNA to control values by day 8.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1978

[Transient diabetes mellitus in a dystrophic newborn infant].

We report a female small for date neonate, who developed transient diabetes mellitus (TDN) five days after birth and required insulin therapy for five weeks. At the onset of the disease, plasma insulin concentration was extremely low. At four weeks of age, after insulin withdrawal, the patient was still hyperglycemic, and basal insulin values assayed over a period of 24 h were mostly inadequate. Glucagon secretion was not suppressed. Growth hormone levels were lower than those of three small for date infants of the same age. At three months of age, the patient was still intolerant to an oral glucose load, insulin secretion remained inadequate while glucagon paradoxically increased 30 min after glucose challenge. The oral glucose tolerance values were in the normal range at six months of age. We conclude that TDN is caused by a transitory defect of insulin secretion, which would also explain the glucagon response as a consequence of insulin deficiency. We found no evidence associating the insulin antagonists observed in our study with the pathogenesis of this illness.

Blood Glucose↗
PubMed1999

Exo84p is an exocyst protein essential for secretion.

The exocyst is a multiprotein complex that plays an important role in secretory vesicle targeting and docking at the plasma membrane. Here we report the identification and characterization of a new component of the exocyst, Exo84p, in the yeast Saccharomyces cerevisiae. Yeast cells depleted of Exo84p cannot survive. These cells are defective in invertase secretion and accumulate vesicles similar to those in the late sec mutants. Exo84p co-immunoprecipitates with the exocyst components, and a portion of the Exo84p co-sediments with the exocyst complex in velocity gradients. The assembly of Exo84p into the exocyst complex requires two other subunits, Sec5p and Sec10p. Exo84p interacts with both Sec5p and Sec10p in a two-hybrid assay. Overexpression of Exo84p selectively suppresses the temperature sensitivity of a sec5 mutant. Exo84p specifically localizes to the bud tip or mother/daughter connection, sites of polarized secretion in the yeast S. cerevisiae. Exo84p is mislocalized in a sec5 mutant. These studies suggest that Exo84p is an essential protein that plays an important role in polarized secretion.

Amino Acid Sequence↗
PubMed2004

Selective deletion of the Hnf1beta (MODY5) gene in beta-cells leads to altered gene expression and defective insulin release.

Hepatocyte nuclear factor 1alpha (HNF1alpha) and HNF1beta (or vHNF1) are closely related transcription factors expressed in liver, kidney, gut, and pancreatic beta-cells. Many HNF1 target genes are involved in carbohydrate metabolism. Human mutations in HNF1alpha or HNF1beta lead to maturity-onset diabetes of the young (MODY3 and MODY5, respectively), and patients present with impaired glucose-stimulated insulin secretion. The underlying defect in MODY5 is not known. Analysis of HNF1beta deficiency in mice has not been possible because HNF1beta null mice die in utero. To examine the role of HNF1beta in glucose homeostasis, viable mice deleted for HNF1beta selectively in beta-cells (beta/H1beta-KO mice) were generated using a Cre-LoxP strategy. beta/H1beta-KO mice had normal growth, fertility, fed or fasted plasma glucose and insulin levels, pancreatic insulin content, and insulin sensitivity. However, beta/H1beta-KO mice exhibited impaired glucose tolerance with reduced insulin secretion compared with wild-type mice but preserved a normal insulin secretory response to arginine. Moreover, beta/H1beta-KO islets had increased HNF1alpha and Pdx-1, decreased HNF4 mRNA levels, and reduced glucose-stimulated insulin release. These results indicate that HNF1beta is involved in regulating the beta-cell transcription factor network and is necessary for glucose sensing or glycolytic signaling.

Animals↗
PubMed1998

YscO of Yersinia pestis is a mobile core component of the Yop secretion system.

The Yersinia pestis low-Ca2+ response stimulon is responsible for the temperature- and Ca2+-regulated expression and secretion of plasmid pCD1-encoded antihost proteins (V antigen and Yops). We have previously shown that lcrD, yscC, yscD, yscG, and yscR encode proteins that are essential for high-level expression and secretion of V antigen and Yops at 37 degreesC in the absence of Ca2+. In this study, we characterized yscO of the Yop secretion (ysc) operon that contains yscN through yscU by determining the localization of its gene product and the phenotype of an in-frame deletion. The yscO mutant grew and expressed the same levels of Yops as the parent at 37 degreesC in the presence of Ca2+. In the absence of Ca2+, the mutant grew independently of Ca2+, expressed only basal levels of V antigen and Yops, and failed to secrete these. These defects could be partially complemented by providing yscO in trans in the yscO mutant. Overexpression of YopM and V antigen in the mutant failed to restore the export of either protein, showing that the mutation had a direct effect on secretion. These results indicated that the yscO gene product is required for high-level expression and secretion of V antigen and Yops. YscO was found by immunoblot analysis in the soluble and membrane fractions of bacteria growing at 37 degreesC irrespective of the presence of Ca2+ and in the culture medium in the absence of Ca2+. YscO is the only mobile protein identified so far in the Yersinia species that is required for secretion of V antigen and Yops.

Bacterial Proteins↗
PubMed2000

Pulsatile insulin secretion.

Insulin is secreted in a pulsatile manner. Recently it has been shown that almost all (approximately 70-100%) of insulin is secreted in discrete insulin secretory bursts occurring approximately every 6 min. Furthermore, it has been revealed that regulation of the rate of insulin secretion is achieved primarily through modulation of the mass of these discrete insulin bursts. Thus meal ingestion increases insulin secretion by enhancing insulin burst mass by approximately 50% but also increases pulse frequency by approximately 50%. Interestingly, the hepatic clearance of insulin is also apparently closely related to the pattern of insulin delivery to the liver. It has been known for many years that the pattern of insulin delivery is abnormal in patients with type 2 diabetes. Recently, with new more sensitive insulin assays (ELISA) and validated methods for pulse detection, it has been possible to examine more precisely the abnormalities of pulsatile insulin in patients with type 2 diabetes. These recent studies suggest that the principal defect of insulin secretion is a deficient pulse mass of insulin with no changes in pulse frequency, and that this defect can be overcome by a period of beta cell rest.

Diabetes Mellitus↗
PubMed2001

CFTR may play a role in regulated secretion by lymphocytes: a new hypothesis for the pathophysiology of cystic fibrosis.

Human lymphocytes and pancreatic acinar cells have a common function: both cell types secrete specific proteins in response to extracellular signals. Acinar cells secrete digestive enzymes, while lymphocytes secrete antibodies and cytokines. Both cell types utilize similar receptor-mediated activation systems, similar signal transduction pathways (i.e., alpha adrenergic receptors, and cAMP), and express the cystic fibrosis transmembrane conductance regulator (CFTR). Preliminary tests of the hypothesis that B lymphocytes are capable of regulated secretion were carried out using transformed lymphocytes. lambda light chain secretion rates were measured in response to treatment with 8-CPT-cAMP. A rapid transient increase in secretion was observed in non-CF lymphocytes. This effect was absent in CF lymphocytes. A failure of regulated secretion could cause a reduced response to antigen presentation, and an inability to completely clear pathogens such as Pseudomonas aeruginosa. Another piece of circumstantial evidence is that lung-transplanted CF patients remain chronically ill. While immunosuppressive therapy may contribute to the chronic illness, the phenomenon is more acute in CF lung-transplant patients than non-CF lung-transplant recipients receiving the same immunosuppressive therapy. A defect in regulated secretion of antibodies and cytokines in response to antigens may be the source of a long suspected, but as yet unproved CFTR-mediated immunological defect underlying the pulmonary morbidity and mortality in cystic fibrosis (CF).

Cells, Cultured↗
PubMed1997

Characterization of a novel yeast SNARE protein implicated in Golgi retrograde traffic.

The protein trafficking machinery of eukaryotic cells is employed for protein secretion and for the localization of resident proteins of the exocytic and endocytic pathways. Protein transit between organelles is mediated by transport vesicles that bear integral membrane proteins (v-SNAREs) which selectively interact with similar proteins on the target membrane (t-SNAREs), resulting in a docked vesicle. A novel Saccharomyces cerevisiae SNARE protein, which has been termed Vti1p, was identified by its sequence similarity to known SNAREs. Vti1p is a predominantly Golgi-localized 25-kDa type II integral membrane protein that is essential for yeast viability. Vti1p can bind Sec17p (yeast SNAP) and enter into a Sec18p (NSF)-sensitive complex with the cis-Golgi t-SNARE Sed5p. This Sed5p/Vti1p complex is distinct from the previously described Sed5p/Sec22p anterograde vesicle docking complex. Depletion of Vti1p in vivo causes a defect in the transport of the vacuolar protein carboxypeptidase Y through the Golgi. Temperature-sensitive mutants of Vti1p show a similar carboxypeptidase Y trafficking defect, but the secretion of invertase and gp400/hsp150 is not significantly affected. The temperature-sensitive vti1 growth defect can be rescued by the overexpression of the v-SNARE, Ykt6p, which physically interacts with Vti1p. We propose that Vti1p, along with Ykt6p and perhaps Sft1p, acts as a retrograde v-SNARE capable of interacting with the cis-Golgi t-SNARE Sed5p.

Adenosine Triphosphatases↗
PubMed2006

The Noggin null mouse phenotype is strain dependent and haploinsufficiency leads to skeletal defects.

Noggin is a secreted peptide that binds and inactivates Bone Morphogenetic Proteins, members of the transforming growth factor beta superfamily of secreted signaling molecules. In vertebrate limbs, Noggin is expressed in condensing cartilage and immature chondrocytes. Inactivation of the Noggin gene has been reported in an inbred 129X1/SvJ mouse genetic background. The null allele was lethal at 18.5 dpc and resulted in severe hyperplasia of the cartilage together with multiple joint fusions. In order to investigate the effect of the genetic background on the phenotypic manifestation of Noggin inactivation, we crossed the Noggin null allele into the outbred CD1 and inbred DBA1 and C57BL/6 mouse strains. We describe here skeletal phenotypes of Noggin null mice, such as accelerated or delayed mineralization of different bones suggestive of a complex tissue response to the perturbations in BMP balances. Additionally, we found that in the absence of Noggin, early specification of myogenic differentiation was unaffected, whereas terminal stages of myogenesis were delayed. Furthermore, we have discovered Noggin haploinsufficiency leading to carpal and tarsal fusions reminiscent of some phenotypes reported for NOGGIN haploinsufficiency in humans.

Animals↗
PubMed1998

The MUC2 gene product: a human intestinal mucin.

The MUC2 gene product is the first human secretory mucin protein core to be fully sequenced. Like the other eight human MUC genes identified to date, MUC2 is characterised by tandem and irregular repeat sequences rich in threonine and serine, the potential sites of attachment of the oligosaccharide chains. The MUC2 gene product is more than 5100 amino acids in its commonest allelic form and accounts for one fifth by weight of the mucin glycoprotein molecule (80% oligosaccharide side chains). The MUC2 product is polymerised end to end through disulphide bridges to form large secreted polymeric gel-forming mucins (Mr approximately 10(7)). The primary function of the MUC2 gene product is to provide a protective barrier between the epithelial surfaces and the gut lumen. There is decreased expression of MUC2 in colonic cancer and defective polymerisation of secreted mucin in ulcerative colitis. Elucidation of the MUC2 and other mucin gene sequences has opened the way for a full structural characterisation and an improved understanding of the structure and function of these complex mucus gel secretions.

Amino Acid Sequence↗
PubMed2002

Treating dual defects in diabetes: insulin resistance and insulin secretion.

The therapeutic goals in patients with type 2 diabetes mellitus and the mechanisms of insulin resistance and secretion are discussed. Sulfonylureas improve glycemic control, restore the acute insulin response, and help improve beta-cell function in the short term. Meglitinides and phenylalanine derivatives and alpha-glucosidase inhibitors may be useful for elderly patients and others with normal fasting blood glucose levels and postprandial hyperglycemia, but they are less effective in achieving goal HbA1c levels in patients with marked fasting hyperglycemia. Metformin and thiazolidinediones act on hepatic, muscle, and adipose tissue through different mechanisms to improve glycemic control, beta-cell function, and the lipid profile. Thiazolidinediones have a greater impact on free fatty acids than metformin. They may have an additive effect with sulfonylureas, metformin, or insulin in improving glycemic control and the lipid profile. Many patients require combination therapy with one or more insulin sensitizers and an insulin secretagogue to achieve therapeutic goals. Insulin therapy should be initiated in patients in whom an HbA1c level less than 7.0% cannot be maintained with other therapies. This is vital in preventing diabetes complications. Insulin sensitizers should be continued during insulin therapy to reduce insulin resistance and treat the insulin resistance syndrome. Therapeutic goals for patients with type 2 diabetes mellitus include improvement in glycemic control and prevention of diabetes complications. Elevated levels of fasting blood glucose should be addressed before postprandial levels to reduce HbA1c levels and glucotoxicity to the beta cell. Dyslipidemia, hypertension, and hypercoagulability should be treated to minimize the increased cardiovascular risk seen in people with diabetes, which is responsible for the majority of deaths.

Animals↗
PubMed2002

Aspergillus nidulans sod(VI)C1 mutation causes defects in cell wall biogenesis and protein secretion.

Growth at the restrictive temperature (42 degrees C) of Aspergillus nidulans B120, carrying the conditional-lethal mutation sod(VI)C1, was partially improved by the addition of 1.0 M sorbitol to the medium. The mutant grown at 42 degrees C, with osmotic stabilizer, showed abnormal hyphal morphology, a decrease in beta-1,3-glucan synthase activity as well as cell wall sugar content, but an increase in chitin synthase activity and N-acetyl-glucosamine content. The mutation also affected the secretion of extracellular protease. The temperature-dependent osmo-sensitive phenotype of a Saccharomyces cerevisiae alpha-COP mutation can be rescued by the A. nidulans sod(VI)C(+) gene. These results indicate that the sod(VI)C1 mutation affects proper processing of secretory proteins destined for the surface of cells or beyond.

Aspergillus nidulans↗