Leticia P Roma

University of Campinas, Conceição de Campinas, São Paulo, Brazil

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Publications (15)53.52 Total impact

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    ABSTRACT: The glucose stimulation of insulin secretion by pancreatic β-cells depends on increased production of metabolic coupling factors, among which changes in NADPH and reactive oxygen species (ROS) may alter the glutathione redox state (EGSH) and signal through changes in thiol oxidation. However, whether nutrients affect EGSH in β-cell subcellular compartments is unknown. Using redox-sensitive GFP2 fused to glutaredoxin 1 and its mitochondria-targeted form, we studied the acute nutrient regulation of EGSH in the cytosol/nucleus or the mitochondrial matrix of rat islet cells. These probes were mainly expressed in β-cells and reacted to low concentrations of exogenous H2O2 and menadione. Under control conditions, cytosolic/nuclear EGSH was close to -300 mV and unaffected by glucose (from 0 to 30 mM). In comparison, mitochondrial EGSH was less negative and rapidly regulated by glucose and other nutrients, ranging from -280 mV in the absence of glucose to -299 mV in 30 mM glucose. These changes were largely independent from changes in intracellular Ca2+ concentration and in mitochondrial pH. They were unaffected by overexpression of SOD2 and mitochondria-targeted catalase, but were inversely correlated with changes in NAD(P)H autofluorescence, suggesting that they indirectly resulted from increased NADPH availability rather than from changes in ROS concentration. Interestingly, the opposite regulation of mitochondrial EGSH and NAD(P)H autofluorescence by glucose was also observed in human islets isolated from two donors. In conclusion, this study demonstrates that glucose and other nutrients acutely reduce mitochondrial but not cytosolic/nuclear EGSH in pancreatic β-cells under control conditions.
    Biochemical Journal 03/2014; · 4.65 Impact Factor
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    ABSTRACT: Progesterone has been associated with gestational diabetes (GD) development due to the enhancement of insulin resistance. Since β-cell apoptosis participates in type 1 and type 2 diabetes pathophysiology, we hypothesized that progesterone might contribute to the development of GD through a mechanism that also involves β-cell death. To address this question, RINm5F insulin-producing cells were incubated with progesterone (25 to 100 μM), in the presence or absence of α-tocopherol (40 μM). After 24 or 48 h, membrane integrity and DNA fragmentation were analyzed by flow cytometry. Caspase activity was used to identify the mode of cell death. The involvement of endoplasmic reticulum stress in the action of progesterone was investigated by Western blotting. Oxidative stress was measured by DCFDA oxidation. Isolated rat islets were used in similar experiments in order to confirm the effect of progesterone in primary β-cells. Incubation of RINm5F cells with progesterone increased the number of cells with membrane integrity loss and DNA fragmentation. Progesterone induced reactive species generation. Pre-incubation with α-tocopherol attenuated progesterone-induced apoptosis. Western blot analyses revealed an increased expression of CREB-2 and CHOP in progesterone-treated cells. Progesterone caused apoptotic death of rat islet cells and enhanced reactive species generation. Our results show that progesterone can be toxic to pancreatic β-cells through an oxidative stress-dependent mechanism inducing apoptosis. This effect may contribute to the development of GD during pregnancy, particularly under conditions that require administration of pharmacological doses of this hormone.
    Journal of Endocrinology 03/2014; · 4.06 Impact Factor
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    ABSTRACT: Monosodium glutamate-obese rats are glucose intolerant and insulin resistant. Their pancreatic islets secrete more insulin at increasing glucose concentrations, despite the possible imbalance in the autonomic nervous system of these rats. Here, we investigate the involvement of the cholinergic/protein kinase (PK)-C and PKA pathways in MSG β-cell function. Male newborn Wistar rats received a subcutaneous injection of MSG (4 g/kg body weight (BW)) or hyperosmotic saline solution during the first 5 days of life. At 90 days of life, plasma parameters, islet static insulin secretion and protein expression were analyzed. Monosodium glutamate rats presented lower body weight and decreased nasoanal length, but had higher body fat depots, glucose intolerance, hyperinsulinemia and hypertrigliceridemia. Their pancreatic islets secreted more insulin in the presence of increasing glucose concentrations with no modifications in the islet-protein content of the glucose-sensing proteins: the glucose transporter (GLUT)-2 and glycokinase. However, MSG islets presented a lower secretory capacity at 40 mM K(+) (P < 0.05). The MSG group also released less insulin in response to 100 μM carbachol, 10 μM forskolin and 1 mM 3-isobutyl-1-methyl-xantine (P < 0.05, P < 0.0001 and P < 0.01). These effects may be associated with a the decrease of 46 % in the acetylcholine muscarinic type 3 (M3) receptor, and a reduction of 64 % in PKCα and 36 % in PKAα protein expressions in MSG islets. Our data suggest that MSG islets, whilst showing a compensatory increase in glucose-induced insulin release, demonstrate decreased islet M3/PKC and adenylate cyclase/PKA activation, possibly predisposing these prediabetic rodents to the early development of β-cell dysfunction.
    Molecular Biology Reports 05/2013; · 2.51 Impact Factor
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    ABSTRACT: BACKGROUND: Loss of β-cell function hastens deterioration of metabolic control in type 2 diabetes patients. Besides amyloid deposit and lipo- and glucotoxicity, AGEs seem to contribute to this process by promoting islet apoptosis. In order to investigate the role of AGEs in β-cell deterioration, we evaluated the temporal and dose effects of AGE compounds on apoptosis rate, ROS generation and expression of pro- and anti-apoptotic genes in cultured islets. METHODS: Rat pancreatic islets were exposed or not for 24, 48, 72 and 96 h to albumin modified by glycoaldehyde (AlbGAD). Apoptosis, ROS and superoxide content and NADPH oxidase activity were evaluated as well as RNA expression of the genes Ager (codes for RAGE), Bax, Bcl2 and Nfkb1. RESULTS: In 24 and 48 h, AlbGAD elicited a decrease in apoptosis rate in comparison to the control condition concomitantly with a reduction in Bax/Bcl2 RNA ratio and in Nfkb1 RNA expression. In contrast, after 72 and 96 h, AlbGAD promoted an increase in apoptosis rate concomitantly with an increase in Bax/Bcl2 RNA ratio and in Nfkb1 RNA expression. In 24 h, AlbGAD elicited a decrease in the islet content of ROS while after 48 and 72 h, it promoted an opposite effect, increasing superoxide generation. The NADPH oxidase inhibitor VAS2870 attenuated superoxide production, implicating NADPH oxidase as an important source of ROS in islets exposed to AGEs. CONCLUSIONS: AlbGAD exerted a dual effect in cultured pancreatic islets, being protective against apoptosis after short exposure but pro-apoptotic after prolonged exposure. Copyright © 2013 John Wiley & Sons, Ltd.
    Diabetes/Metabolism Research and Reviews 01/2013; · 2.97 Impact Factor
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    ABSTRACT: Pancreatic beta cells chronically exposed to low glucose concentrations show signs of oxidative stress, loss of glucose-stimulated insulin secretion (GSIS) and increased apoptosis. Our aim was to confirm the role of mitochondrial oxidative stress in rat islet cell apoptosis under these culture conditions and to evaluate whether its reduction similarly improves survival and GSIS. Apoptosis, oxidative stress-response gene mRNA expression and glucose-induced stimulation of mitochondrial metabolism, intracellular Ca(2+) concentration and insulin secretion were measured in male Wistar rat islets cultured for 1 week in RPMI medium containing 5-10 mmol/l glucose with or without manganese(III)tetrakis(4-benzoic acid)porphyrin (MnTBAP) or N-acetyl-L-: cysteine (NAC). Oxidative stress was measured in islet cell clusters cultured under similar conditions using cytosolic and mitochondrial redox-sensitive green fluorescent protein (roGFP1/mt-roGFP1). Prolonged culture in 5 vs 10 mmol/l glucose increased mt-roGFP1 (but not roGFP1) oxidation followed by beta cell apoptosis and loss of GSIS resulting from reduced insulin content, mitochondrial metabolism, Ca(2+) influx and Ca(2+)-induced secretion. Tolbutamide-induced, but not high K(+)-induced, Ca(2+) influx was also suppressed. Under these conditions, MnTBAP, but not NAC, triggered parallel ~50-70% reductions in mt-roGFP1 oxidation and beta cell apoptosis, but failed to protect against the loss of GSIS despite significant improvement in glucose-induced and tolbutamide-induced Ca(2+) influx. Mitochondrial oxidative stress contributes differently to rat pancreatic islet cell apoptosis and insulin secretory defects during culture in a low glucose concentration. Thus, targeting beta cell survival may not be sufficient to restore insulin secretion when beta cells suffer from prolonged mitochondrial oxidative stress, e.g. in the context of reduced glucose metabolism.
    Diabetologia 05/2012; 55(8):2226-37. · 6.49 Impact Factor
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    ABSTRACT: Chronic administration of glucocorticoids (GC) leads to characteristic features of type 2 diabetes in mammals. The main action of dexamethasone in target cells occurs through modulation of gene expression, although the exact mechanisms are still unknown. We therefore investigated the gene expression profile of pancreatic islets from rats treated with dexamethasone using a cDNA array screening analysis. The expression of selected genes and proteins involved in mitochondrial apoptosis was further analyzed by PCR and immunoblotting. Insulin, triglyceride and free fatty acid plasma levels, as well as glucose-induced insulin secretion, were significantly higher in dexamethasone-treated rats compared with controls. Out of 1176 genes, 60 were up-regulated and 28 were down-regulated by dexamethasone treatment. Some of the modulated genes are involved in apoptosis, stress response, and proliferation pathways. RT-PCR confirmed the cDNA array results for 6 selected genes. Bax α protein expression was increased, while Bcl-2 was decreased. In vivo dexamethasone treatment decreased the mitochondrial production of NAD(P)H, and increased ROS production. Concluding, our data indicate that dexamethasone modulates the expression of genes and proteins involved in several pathways of pancreatic-islet cells, and mitochondria dysfunction might be involved in the deleterious effects after long-term GC treatment.
    General Physiology and Biophysics 03/2012; 31(1):65-76. · 0.85 Impact Factor
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    ABSTRACT: Anti-oxidation and exocytosis are important for maintaining exocrine tissue homeostasis. During aging, functional and structural alterations occur in the lacrimal gland (LG), including oxidative damage to proteins, lipids, and DNA. The aims of the present study were to determine in the aging LG: a) the effects of aging on LG structure and secretory activity and b) changes in the expression of oxidative stress markers. To address these goals, tear secretion composition and corneal impression cytology were compared between male Wistar rats of 2 (control) and 24 (aged) months. LG morphology and the expression levels of vitamin E and malonaldehyde (MDA) were evaluated to determine the anti-oxidant activity and lipid peroxidation, respectively. RT-PCR and western blot analysis were used for the analysis of Ras related in brain GTPase protein (Rab) and soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins of the secretory machinery (i.e.; Rab 3d, Rab 27, vesicle-associated membrane protein-2 (Vamp-2), and syntaxin). Histological analysis of aged rats revealed a higher frequency of corneal epithelia metaplasia. In the acinar cells, organelles underwent degeneration, and lipofucsin-like material accumulated in the cytoplasm along with declines in the anti-oxidant marker vitamin E. Rab3d and Rab27b mRNA levels fell along with Rab3d protein expression, whereas syntaxin levels increased. These findings indicate that exocytotic and anti-oxidant mechanisms become impaired with age in the rat LG. In parallel with these structural alterations, functional declines may contribute to the pathophysiology caused by tear film modification in dry eye disease.
    Molecular vision 01/2012; 18:194-202. · 1.99 Impact Factor
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    ABSTRACT: Rat pancreatic islet cell apoptosis is minimal after prolonged culture in 10 mmol/l glucose (G10), largely increased in 5 mmol/l glucose (G5) and moderately increased in 30 mmol/l glucose (G30). This glucose-dependent asymmetric V-shaped profile is preceded by parallel changes in the mRNA levels of oxidative stress-response genes like Metallothionein 1a (Mt1a). In this study, we tested the effect of ZnCl(2), a potent inducer of Mt1a, on apoptosis, mitochondrial oxidative stress and alterations of glucose-induced insulin secretion (GSIS) induced by prolonged exposure to low and high vs. intermediate glucose concentrations. Male Wistar rat islets were cultured in RPMI medium. Islet gene mRNA levels were measured by RTq-PCR. Apoptosis was quantified by measuring islet cytosolic histone-associated DNA fragments and the percentage of TUNEL-positive β-cells. Mitochondrial thiol oxidation was measured in rat islet cell clusters expressing "redox sensitive GFP" targeted to the mitochondria (mt-roGFP1). Insulin secretion was measured by RIA. As observed for Mt1a mRNA levels, β-cell apoptosis and loss of GSIS, culture in either G5 or G30 vs. G10 significantly increased mt-roGFP1 oxidation. While TPEN decreased Mt1a/2a mRNA induction by G5, addition of 50-100 µM ZnCl(2) to the culture medium strongly increased Mt1a/2a mRNA and protein levels, reduced early mt-roGFP oxidation and significantly decreased late β-cell apoptosis after prolonged culture in G5 or G30 vs. G10. It did not, however, prevent the loss of GSIS under these culture conditions. ZnCl(2) reduces mitochondrial oxidative stress and improves rat β-cell survival during culture in the presence of low and high vs. intermediate glucose concentrations without improving their acute GSIS.
    PLoS ONE 01/2012; 7(10):e46831. · 3.53 Impact Factor
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    ABSTRACT: Using the ROS (reactive oxygen species)-sensitive fluorescent dyes dichlorodihydrofluorescein and dihydroethidine, previous studies yielded opposite results about the glucose regulation of oxidative stress in insulin-secreting pancreatic β-cells. In the present paper, we used the ratiometric fluorescent proteins HyPer and roGFP1 (redox-sensitive green fluorescent protein 1) targeted to mitochondria [mt-HyPer (mitochondrial HyPer)/mt-roGFP1 (mitochondrial roGFP1)] to monitor glucose-induced changes in mitochondrial hydrogen peroxide concentration and glutathione redox state in adenovirus-infected rat islet cell clusters. Because of the reported pH sensitivity of HyPer, the results were compared with those obtained with the mitochondrial pH sensors mt-AlpHi and mt-SypHer. The fluorescence ratio of the mitochondrial probes slowly decreased (mt-HyPer) or increased (mt-roGFP1) in the presence of 10 mmol/l glucose. Besides its expected sensitivity to H2O2, mt-HyPer was also highly pH sensitive. In agreement, changes in mitochondrial metabolism similarly affected mt-HyPer, mt-AlpHi and mt-SypHer fluorescence signals. In contrast, the mt-roGFP1 fluorescence ratio was only slightly affected by pH and reversibly increased when glucose was lowered from 10 to 2 mmol/l. This increase was abrogated by the catalytic antioxidant Mn(III) tetrakis (4-benzoic acid) porphyrin but not by N-acetyl-L-cysteine. In conclusion, due to its pH sensitivity, mt-HyPer is not a reliable indicator of mitochondrial H2O2 in β-cells. In contrast, the mt-roGFP1 fluorescence ratio monitors changes in β-cell mitochondrial glutathione redox state with little interference from pH changes. Our results also show that glucose acutely decreases rather than increases mitochondrial thiol oxidation in rat β-cells.
    Biochemical Journal 11/2011; 441(3):971-8. · 4.65 Impact Factor
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    ABSTRACT: Sarco-endoplasmic reticulum Ca(2+)-ATPase 2b (SERCA2b) and SERCA3 pump Ca(2+) in the endoplasmic reticulum (ER) of pancreatic β-cells. We studied their role in the control of the free ER Ca(2+) concentration ([Ca(2+)](ER)) and the role of SERCA3 in the control of insulin secretion and ER stress. β-Cell [Ca(2+)](ER) of SERCA3(+/+) and SERCA3(-/-) mice was monitored with an adenovirus encoding the low Ca(2+)-affinity sensor D4 addressed to the ER (D4ER) under the control of the insulin promoter. Free cytosolic Ca(2+) concentration ([Ca(2+)](c)) and [Ca(2+)](ER) were simultaneously recorded. Insulin secretion and mRNA levels of ER stress genes were studied. Glucose elicited synchronized [Ca(2+)](ER) and [Ca(2+)](c) oscillations. [Ca(2+)](ER) oscillations were smaller in SERCA3(-/-) than in SERCA3(+/+) β-cells. Stimulating cell metabolism with various [glucose] in the presence of diazoxide induced a similar dose-dependent [Ca(2+)](ER) rise in SERCA3(+/+) and SERCA3(-/-) β-cells. In a Ca(2+)-free medium, glucose moderately raised [Ca(2+)](ER) from a highly buffered cytosolic Ca(2+) pool. Increasing [Ca(2+)](c) with high [K] elicited a [Ca(2+)](ER) rise that was larger but more transient in SERCA3(+/+) than SERCA3(-/-) β-cells because of the activation of a Ca(2+) release from the ER in SERCA3(+/+) β-cells. Glucose-induced insulin release was larger in SERCA3(-/-) than SERCA3(+/+) islets. SERCA3 ablation did not induce ER stress. [Ca(2+)](c) and [Ca(2+)](ER) oscillate in phase in response to glucose. Upon [Ca(2+)](c) increase, Ca(2+) is taken up by SERCA2b and SERCA3. Strong Ca(2+) influx triggers a Ca(2+) release from the ER that depends on SERCA3. SERCA3 deficiency neither impairs Ca(2+) uptake by the ER upon cell metabolism acceleration and insulin release nor induces ER stress.
    Diabetes 09/2011; 60(10):2533-45. · 7.90 Impact Factor
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    ABSTRACT: Reactive oxygen species (ROS) are involved in many physiological and pathological processes. In the present study, we analysed whether the synthetic glucocorticoid dexamethasone induces oxidative stress in cultured pancreatic islets and whether the effects of dexamethasone on insulin secretion, gene expression, and viability can be counteracted by concomitant incubation with N-acetylcysteine (NAC). ROS production was measured by dichlorofluorescein (DCFH-DA) assay, insulin secretion by radioimmunoassay, intracellular calcium dynamics by fura-2-based fluorescence, gene expression by real-time polymerase chain reaction analyses and cell viability by the MTS assay. Dexamethasone (Dexa) increased ROS production and decreased glucose-stimulated insulin secretion after 72 hours incubation. Intracellular ROS levels were decreased and the insulin secretion capacity was recovered by concomitant treatment with Dexa+NAC. The total insulin content and intracellular Ca2+ levels were not modulated in either Dexa or Dexa+NAC groups. There was a decrease in the NAD(P)H production, used as an indicator of viability, after dexamethasone treatment. Concomitant incubation with NAC returned viability to control levels. Dexa also decreased synaptotagmin VII (SYT VII) gene expression. In contrast, the Dexa+NAC group demonstrated an increased expression of SYT VII compared to controls. Surprisingly, treatment with NAC decreased the gene expression of the antioxidant enzyme copper zinc superoxide dismutase soluble. Our results indicate that dexamethasone increases ROS production, decreases viability, and impairs insulin secretion in pancreatic rat islets. These effects can be counteracted by NAC, which not only decreases ROS levels but also modulates the expression of genes involved in the secretory pathway and those coding for antioxidant enzymes.
    Redox report: communications in free radical research 01/2011; 16(4):173-80. · 1.51 Impact Factor
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    ABSTRACT: Pancreatic beta cells are very sensitive to reactive oxygen species (ROS) and this might play an important role in beta cell death in diabetes. Dexamethasone is a synthetic diabetogenic glucocorticoid, which impairs pancreatic beta cell function. Therefore we investigated the toxicity of dexamethasone in RINm5F insulin-producing cells and its dependence on the expression level of the antioxidant enzyme catalase, which inactivates hydrogen peroxide. This was correlated with oxidative stress and cell death. An increased generation of ROS was observed in dexamethasone-treated cells together with an increase in caspase-3 activity and apoptosis rate. Interestingly, exposure to dexamethasone increased the cytosolic superoxide dismutase Cu/ZnSOD protein expression and activity, whereas the mitochondrial MnSOD isoform was not affected by the glucocorticoid. Catalase overexpression in insulin-producing cells prevented all the cytotoxic effects of dexamethasone. In conclusion, dexamethasone-induced cell death in insulin-producing cells is ROS mediated. Increased levels of expression and activity of the Cu/ZnSOD might favor the generation of hydrogen peroxide in dexamethasone-treated cells. Increased ROS scavenging capacity in insulin-producing cells, through overexpression of catalase, prevents a deleterious increase in hydrogen peroxide generation and thus prevents dexamethasone-induced apoptosis.
    Free Radical Biology and Medicine 09/2009; 47(10):1386-93. · 5.27 Impact Factor
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    ABSTRACT: Prolactin induces maturation of insulin secretion in cultured neonatal rat islets. In this study, we investigated whether the improved secretory response to glucose caused by prolactin involves alteration in the expression, association and phosphorylation of several proteins that participate in these processes. Messenger RNA was extracted from neonatal rat islets cultured for 5 days in the presence of prolactin and reverse transcribed. Gene expression was analyzed by semi-quantitative RT-PCR and by Western blotting for proteins. The gene transcription and protein expression of kinesin and MAP-2 were increased in prolactin-treated islets compared to the controls. The association and phosphorylation of proteins was analyzed by immunoprecipitation followed by Western blotting, after acute exposure to prolactin. Prolactin increased the association between SNARE proteins and kinesin/MAP-2 while the association of munc-18/syntaxin 1A was decreased. Serine phosphorylation of SNAP-25, syntaxin 1A, munc-18, MAP-2 was significantly higher whereas kinesin phosphorylation was decreased in prolactin-treated islets. There was an increase in SNARE complex formation in islets stimulated with prolactin, 22 mM glucose, 40 mM K(+), 200 microM carbachol and 1 microM PMA. The prolactin-induced increase in the formation of SNARE complex and syntaxin 1A phosphorylation was inhibited by PD098059 and U0126, inhibitors of the MAPK pathway. These findings indicate that prolactin primes pancreatic beta-cells to release insulin by increasing the expression and phosphorylation/association of proteins implicated in the secretory machinery and the MAPK/PKC pathway is important for this effect.
    Molecular and Cellular Endocrinology 08/2007; 273(1-2):32-41. · 4.04 Impact Factor
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    ABSTRACT: Augmented glucose-stimulated insulin secretion (GSIS) is an adaptive mechanism exhibited by pancreatic islets from insulin-resistant animal models. Gap junction proteins have been proposed to contribute to islet function. As such, we investigated the expression of connexin 36 (Cx36), connexin 43 (Cx43), and the glucose transporter Glut2 at mRNA and protein levels in pancreatic islets of dexamethasone (DEX)-induced insulin-resistant rats. Study rats received daily injections of DEX (1 mg/kg body mass, i.p.) for 5 days, whereas control rats (CTL) received saline solution. DEX rats exhibited peripheral insulin resistance, as indicated by the significant postabsorptive insulin levels and by the constant rate for glucose disappearance (KITT). GSIS was significantly higher in DEX islets (1.8-fold in 16.7 mmol/L glucose vs. CTL, p < 0.05). A significant increase of 2.25-fold in islet area was observed in DEX vs. CTL islets (p < 0.05). Cx36 mRNA expression was significantly augmented, Cx43 diminished, and Glut2 mRNA was unaltered in islets of DEX vs. CTL (p < 0.05). Cx36 protein expression was 1.6-fold higher than that of CTL islets (p < 0.05). Glut2 protein expression was unaltered and Cx43 was not detected at the protein level. We conclude that DEX-induced insulin resistance is accompanied by increased GSIS and this may be associated with increase of Cx36 protein expression.
    Canadian Journal of Physiology and Pharmacology 06/2007; 85(5):536-45. · 1.56 Impact Factor
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    ABSTRACT: Augmented glucose-stimulated insulin secretion (GSIS) is an adaptive mechanism exhibited by pancreatic islets from insulin-resistant animal models. Gap junction proteins have been proposed to contribute to islet function. As such, we investigated the expression of connexin 36 (Cx36), connexin 43 (Cx43), and the glucose transporter Glut2 at mRNA and protein levels in pancreatic islets of dexamethasone (DEX)-induced insulin-resistant rats. Study rats received daily in-jections of DEX (1 mg/kg body mass, i.p.) for 5 days, whereas control rats (CTL) received saline solution. DEX rats ex-hibited peripheral insulin resistance, as indicated by the significant postabsorptive insulin levels and by the constant rate for glucose disappearance (K ITT). GSIS was significantly higher in DEX islets (1.8-fold in 16.7 mmol/L glucose vs. CTL, p < 0.05). A significant increase of 2.25-fold in islet area was observed in DEX vs. CTL islets (p < 0.05). Cx36 mRNA expression was significantly augmented, Cx43 diminished, and Glut2 mRNA was unaltered in islets of DEX vs. CTL (p < 0.05). Cx36 protein expression was 1.6-fold higher than that of CTL islets (p < 0.05). Glut2 protein expression was unal-tered and Cx43 was not detected at the protein level. We conclude that DEX-induced insulin resistance is accompanied by increased GSIS and this may be associated with increase of Cx36 protein expression. Résumé : L'augmentation de la sécrétion d'insuline stimulée par le glucose (SISG) est un mécanisme adaptatif montré par les lots pancréatiques de modèles animaux insulinorésistants. On croit que les protéines des jonctions lacunaires partici-pent à la fonction des lots. Pour vérifier cette hypothèse, nous avons examiné l'expression de la connexine 36 (Cx36), de la connexine 43 (Cx43) et de Glut2 au niveau de l'ARNm et au niveau protéique dans les lots pancréatiques de rats ren-dus insulinorésistants par dexaméthasone. Nous avons soumis des rats (DEX) à des injections quotidiennes de dexamétha-sone (1 mg/kg, p.c., i.p.) pendant 5 jours, alors que les rats témoins (CTL) ont reçu une solution saline. Les rats DEX ont montré une insulinorésistance périphérique, comme indiqué par les taux élevés d'insuline en phase postabsorptive et par le test de tolérance à l'insuline (valeur K TTI). La SISG a été beaucoup plus élevée dans les lots DEX (facteur 1,8 dans 16,7 mmol/L de glucose vs CTL; p < 0,05). Une augmentation significative d'un facteur 2,25 de la surface des lots a été obser-vée dans les lots DEX vs CTL (p < 0,05). L'expression de l'ARNm Cx36 a augmenté de manière significative, Cx43 a di-minué et l'ARNm Glut2 est demeuré stable dans les lots DEX vs CTL (p < 0,05). L'expression de la protéine Cx36 a été d'un facteur 1,6 plus élevée que dans les lots CTL (p < 0,05). L'expression protéique de Glut2 n'a pas été modifiée, et Cx43 n'a pas été détectée à ce niveau. Nous concluons que l'insulinorésistance induite par le dexaméthasone est accompa-gnée d'une augmentation de la SISG et que cette association pourrait être liée à une augmentation de l'expression pro-téique de Cx36. Mots-clés : connexines, glucocorticodes, insulinorésistance, sécrétion d'insuline stimulée par le glucose, lots pancréati-ques. [Traduit par la Rédaction]
    Canadian Journal of Physiology and Pharmacology 01/2007; 85:536-545. · 1.56 Impact Factor

Publication Stats

78 Citations
53.52 Total Impact Points

Institutions

  • 2009–2013
    • University of Campinas
      • • Departamento de Biologia Estrutural e Funcional
      • • Instituto de Biologia (IB)
      Conceição de Campinas, São Paulo, Brazil
  • 2012
    • Catholic University of Louvain
      • Institute of Experimental and Clinical Research (IREC)
      Louvain-la-Neuve, WAL, Belgium