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Differential effects of chronic pulsatile versus chronic constant maternal hyperglycemia on fetal pancreatic ?-cells.

ABSTRACT: Constant maternal hyperglycemia limits, while pulsatile maternal hyperglycemia may enhance, fetal glucose-stimulated insulin secretion (GSIS) in sheep. However, the impact of such different patterns of hyperglycemia on the development of the fetal ?-cell is unknown. We measured the impact of one week of chronic constant hyperglycemia (CHG, n = 6) versus pulsatile hyperglycemia (PHG, n = 5) versus controls (n = 7) on the percentage of the fetal pancreas staining for insulin (?-cell area), mitotic and apoptotic indices and size of fetal ?-cells, and fetal insulin secretion in sheep. Baseline insulin concentrations were higher in CHG fetuses (P < 0.05) compared to controls and PHG. GSIS was lower in the CHG group (P < 0.005) compared to controls and PHG. PHG ?-cell area was increased 50% (P < 0.05) compared to controls and CHG. CHG ?-cell apoptosis was increased over 400% (P < 0.05) compared to controls and PHG. These results indicate that late gestation constant maternal hyperglycemia leads to significant ?-cell toxicity (increased apoptosis and decreased GSIS). Furthermore, pulsatile maternal hyperglycemia increases pancreatic ?-cell area but did not increase GSIS, indicating decreased ?-cell responsiveness. These findings demonstrate differential effects that the pattern of maternal hyperglycemia has on fetal pancreatic ?-cell development, which might contribute to later life limitation in insulin secretion.

SUBMITTER: Frost MS

PROVIDER: S-EPMC3486011 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Differential effects of chronic pulsatile versus chronic constant maternal hyperglycemia on fetal pancreatic β-cells.

Frost Mackenzie S MS Zehri Aqib H AH Limesand Sean W SW Hay William W WW Rozance Paul J PJ

Journal of pregnancy 20121022

Constant maternal hyperglycemia limits, while pulsatile maternal hyperglycemia may enhance, fetal glucose-stimulated insulin secretion (GSIS) in sheep. However, the impact of such different patterns of hyperglycemia on the development of the fetal β-cell is unknown. We measured the impact of one week of chronic constant hyperglycemia (CHG, n = 6) versus pulsatile hyperglycemia (PHG, n = 5) versus controls (n = 7) on the percentage of the fetal pancreas staining for insulin (β-cell area), mitotic ...[more]

PMID: 23133755

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Project description:ObjectiveInvestigate the DNA damage and its cellular response in blood samples from both mother and the umbilical cord of pregnancies complicated by hyperglycemia.MethodsA total of 144 subjects were divided into 4 groups: normoglycemia (ND; 46 cases), mild gestational hyperglycemia (MGH; 30 cases), gestational diabetes mellitus (GDM; 45 cases) and type-2 diabetes mellitus (DM2; 23 cases). Peripheral blood mononuclear cell (PBMC) isolation and/or leukocytes from whole maternal and umbilical cord blood were obtained from all groups at delivery. Nuclear and mitochondrial DNA damage were measured by gene-specific quantitative PCR, and the expression of mRNA and proteins involved in the base excision repair (BER) pathway were assessed by real-time qPCR and Western blot, respectively. Apoptosis was measured in vitro experiments by caspase 3/7 activity and ATP levels.ResultsGDM and DM2 groups were characterized by an increase in oxidative stress biomarkers, an increase in nuclear and mitochondrial DNA damage, and decreased expression of mRNA (APE1, POL? and FEN1) and proteins (hOGG1, APE1) involved in BER. The levels of hyperglycemia were associated with the in vitro apoptosis pathway. Blood levels of DNA damage in umbilical cord were similar among the groups. Newborns of diabetic mothers had increased expression of BER mRNA (APE1, POL? and FEN1) and proteins (hOGG1, APE1, POL? and FEN1). A diabetes-like environment was unable to induce apoptosis in the umbilical cord blood cells.ConclusionsOur data show relevant asymmetry between maternal and fetal blood cell susceptibility to DNA damage and apoptosis induction. Maternal cells seem to be more predisposed to changes in an adverse glucose environment. This may be due to differential ability in upregulating multiple genes involved in the activation of DNA repair response, especially the BER mechanism. However if this study shows a more effective adaptive response by the fetal organism, it also calls for further studies to determine the limit of this response that definitely changes the fate of a fetus under these conditions of cellular stress.

Project description:Glucagon-like peptide 1 (GLP-1) enhances insulin secretion and protects ?-cell mass. Diabetes therapies targeting the GLP-1 receptor (GLP-1R), expressed in numerous tissues, have diminished dose-response in patients with type 2 diabetes compared with healthy human controls. The aim of this study was to determine the mechanistic causes underlying the reduced efficacy of GLP-1R ligands.Using primary mouse islets and the ?-cell line MIN6, outcomes downstream of the GLP-1R were analyzed: Insulin secretion; phosphorylation of the cAMP-response element binding protein (CREB); cAMP responses. Signaling systems were studied by immunoblotting and qRT-PCR, and PKA activity was assayed. Cell surface localization of the GLP-1R was studied by confocal microscopy using a fluorescein-tagged exendin-4 and GFP-tagged GLP-1R.Rodent ?-cells chronically exposed to high glucose had diminished responses to GLP-1R agonists including: diminished insulin secretory response; reduced phosphorylation of (CREB); impaired cAMP response, attributable to chronically increased cAMP levels. GLP-1R signaling systems were affected by hyperglycemia with increased expression of mRNAs encoding the inducible cAMP early repressor (ICER) and adenylyl cyclase 8, reduced PKA activity due to increased expression of the PKA-RI? subunit, reduced GLP-1R mRNA expression and loss of GLP-1R from the cell surface. To specifically examine the loss of GLP-1R from the plasma membrane a GLP-1R-GFP fusion protein was employed to visualize subcellular localization. Under low glucose conditions or when PKA activity was inhibited, GLP-1R-GFP was found at the plasma membrane. Conversely high glucose, expression of a constitutively active PKA subunit, or exposure to exendin-4 or forskolin led to GLP-1R-GFP internalization. Mutation of serine residue 301 of the GLP-1R abolished the glucose-dependent loss of the receptor from the plasma membrane. This was associated with a loss of an interaction between the receptor and the small ubiquitin-related modifier (SUMO), an interaction that was found to be necessary for internalization of the receptor.These data show that glucose acting, at least in part, via PKA leads to the loss of the GLP-1R from the cell surface and an impairment of GLP-1R signaling, which may underlie the reduced clinical efficacy of GLP-1R based therapies in individuals with poorly controlled hyperglycemia.

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Differential effects of chronic pulsatile versus chronic constant maternal hyperglycemia on fetal pancreatic ?-cells.

Publications

Differential effects of chronic pulsatile versus chronic constant maternal hyperglycemia on fetal pancreatic β-cells.

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