Viviane Delghingaro-Augusto - Academia.edu (original) (raw)

Papers by Viviane Delghingaro-Augusto

Research paper thumbnail of Short-chain 3-hydroxyacyl-CoA dehydrogenase is a negative regulator of insulin secretion in response to fuel and non-fuel stimuli in INS832/13 β-cells

Journal of Diabetes, Aug 16, 2010

Background: Hyperinsulinemia associated with non-ketotic hypoglycemia is observed in patients wit... more Background: Hyperinsulinemia associated with non-ketotic hypoglycemia is observed in patients with mutated b-oxidation enzyme short-chain 3-hydroxyacyl-CoA dehydrogenase (HADHSC). In the present study, we investigated the mechanism underlying HADHSC-mediated regulation of insulin secretion. Methods: Knockdown of HADHSC expression by RNA interference in INS832 ⁄ 13 b-cells was achieved using short hairpin RNA and short interference RNA. Results: Knockdown of HADHSC increased both fuel-(glucose or leucine plus glutamine) and non-fuel (high KCl)-induced insulin secretion. Enhanced glucose-stimulated insulin secretion (GSIS) induced by HADHSC knockdown was independent of changes in cytosolic Ca 2+ and also occurred in the presence of fatty acids. l-Carnitine, used in the formation of acyl-carnitine compounds, increased GSIS in control cells, but was unable to further increase the augmented GSIS in HADHSCknockdown cells. The pan transaminase inhibitor amino-oxyacetate reversed HADHSC knockdown-mediated increases in GSIS. Oxidation of [1-14 C]-palmitate and -octanoate was not reduced in HADHSCknockdown cells. l-3-Hydroxybutyryl-carnitine (tested using its precursor l-3-hydroxybutyrate) and l-3-hydroxyglutarate, which accumulate in blood and urine, respectively, of HADHSC-deficient patients, did not change insulin secretion. Conclusions: Insulin secretion promoted by both fuel and non-fuel stimuli is negatively regulated by HADHSC. Enhanced secretion after HADHSC knockdown is not due to inhibition of fatty acid oxidation causing an accumulation of long-chain fatty acids or their CoA derivatives. l-3-Hydroxybutyrate and l-3-hydroxyglutarate do not mediate enhanced secretion caused by reduced HADHSC activity. Transamination reaction(s) and the formation of short-chain acylcarnitines and CoAs may be implicated in the mechanism whereby HADHSC deficiency results in enhanced insulin secretion and hyperinsulinemia.

Research paper thumbnail of Islet Inflammation, Hemosiderosis, and Fibrosis in Intrauterine Growth-Restricted and High Fat-Fed Sprague-Dawley Rats

The American Journal of Pathology, 2014

Prenatal and postnatal factors such as intrauterine growth restriction (IUGR) and high-fat (HF) d... more Prenatal and postnatal factors such as intrauterine growth restriction (IUGR) and high-fat (HF) diet contribute to type 2 diabetes. Our aim was to determine whether IUGR and HF diets interact in type 2 diabetes pathogenesis, with particular attention focused on pancreatic islet morphology including assessment for inflammation. A surgical model of IUGR (bilateral uterine artery ligation) in Sprague-Dawley rats with sham controls was used. Pups were fed either HF or chow diets after weaning. Serial measures of body weight and glucose tolerance were performed. At 25 weeks of age, rat pancreases were harvested for histologic assessment. The birth weight of IUGR pups was 13% lower than that of sham pups. HF diet caused excess weight gain, dyslipidemia, hyperinsulinemia, and mild glucose intolerance, however, this was not aggravated further by IUGR. Markedly abnormal islet morphology was evident in 0 of 6 sham-chow, 5 of 8 sham-HF, 4 of 8 IUGR-chow, and 8 of 9 IUGR-HF rats (chisquare, P Z 0.007). Abnormal islets were characterized by larger size, irregular shape, inflammation with CD68-positive cells, marked fibrosis, and hemosiderosis. b-Cell mass was not altered by IUGR. In conclusion, HF and IUGR independently contribute to islet injury characterized by inflammation, hemosiderosis, and fibrosis. This suggests that both HF and IUGR can induce islet injury via converging pathways. The potential pathogenic or permissive role of iron in this process of islet inflammation warrants further investigation.

Research paper thumbnail of Increased Pancreatic Islet Glucose-Induced Insulin Secretion in the Prevention of Diabetes Following Voluntary Running Exercise in ZDF Rats

Canadian Journal of Diabetes, 2008

Research paper thumbnail of Islet beta cell failure in the 60% pancreatectomised obese hyperlipidaemic Zucker fatty rat: severe dysfunction with altered glycerolipid metabolism without steatosis or a falling beta cell mass

Diabetologia, Mar 18, 2009

Aims/hypothesis The Zucker fatty (ZF) rat subjected to 60% pancreatectomy (Px) develops moderate ... more Aims/hypothesis The Zucker fatty (ZF) rat subjected to 60% pancreatectomy (Px) develops moderate diabetes by 3 weeks. We determined whether a progressive fall in beta cell mass and/or beta cell dysfunction contribute to beta cell failure in this type 2 diabetes model. Methods Partial (60%) or sham Px was performed in ZF and Zucker lean (ZL) rats. At 3 weeks post-surgery, beta cell mass and proliferation, proinsulin biosynthesis, pan-creatic insulin content, insulin secretion, and islet glucose and lipid metabolism were measured. Results ZL-Px rats maintained normal glycaemia and glucose-stimulated insulin secretion (GSIS) despite incomplete recovery of beta cell mass possibly due to compensatory enhanced islet glucose metabolism and lipolysis. ZF-Px rats developed moderate hyperglycaemia (14 mmol/l), hypertriacylglycerolaemia and relative hypoinsulinaemia. Despite beta cell mass recovery and normal arginine-induced insulin secretion, GSIS and pancreatic insulin content were profoundly lowered in ZF-Px rats. Proinsulin biosynthesis was not reduced. Compensatory increases in islet glucose metabolism above those observed in ZF-Sham rats were not seen in ZF-Px rats. Triacylglycerol content was not increased in ZF-Px islets, possibly due to lipodetoxification by enhanced lipolysis and fatty acid oxidation. Fatty acid accumulation into monoacylglycerol and diacylglycerol was increased in ZF-Px islets together with a 4.5-fold elevation in stearoyl-CoA desaturase mRNA expression. Conclusions/interpretation Falling beta cell mass, reduced proinsulin biosynthesis and islet steatosis are not implicated in early beta cell failure and glucolipotoxicity in ZF-Px rats. Rather, severe beta cell dysfunction with a specific reduction in GSIS and marked depletion of beta cell insulin stores with altered lipid partitioning underlie beta cell failure in this animal model of type 2 diabetes.

Research paper thumbnail of Estrogen prevents beta-cell failure and diabetes in ZDF male rats: a role for glycerolipid/fatty acid cycling

Canadian Journal of Diabetes, 2008

Research paper thumbnail of Glucose-stimulated insulin secretion is increased and diabetes prevented in ZDF rats following voluntary running exercise training

Canadian Journal of Diabetes, 2009

Research paper thumbnail of Beta-cell dysfunction in the 60% pancreatectomized obese hyperlipidaemic Zucker fatty rat. Altered glycerolipid metabolism without islet cell steatosis

Canadian Journal of Diabetes, 2008

Research paper thumbnail of XBP1 maintains beta cell identity, represses beta-to-alpha cell transdifferentiation and protects against diabetic beta cell failure during metabolic stress in mice

Diabetologia, 2022

Aims/hypothesis Pancreatic beta cell dedifferentiation, transdifferentiation into other islet cel... more Aims/hypothesis Pancreatic beta cell dedifferentiation, transdifferentiation into other islet cells and apoptosis have been implicated in beta cell failure in type 2 diabetes, although the mechanisms are poorly defined. The endoplasmic reticulum stress response factor X-box binding protein 1 (XBP1) is a major regulator of the unfolded protein response. XBP1 expression is reduced in islets of people with type 2 diabetes, but its role in adult differentiated beta cells is unclear. Here, we assessed the effects of Xbp1 deletion in adult beta cells and tested whether XBP1-mediated unfolded protein response makes a necessary contribution to beta cell compensation in insulin resistance states. Methods Mice with inducible beta cell-specific Xbp1 deletion were studied under normal (chow diet) or metabolic stress (high-fat diet or obesity) conditions. Glucose tolerance, insulin secretion, islet gene expression, alpha cell mass, beta cell mass and apoptosis were assessed. Lineage tracing was ...

Research paper thumbnail of The Role of Fatty Acid Signaling in Islet Beta-Cell Adaptation to Normal Pregnancy

Frontiers in Endocrinology, 2022

BackgroundMaintenance of a normal fetal nutrient supply requires major adaptations in maternal me... more BackgroundMaintenance of a normal fetal nutrient supply requires major adaptations in maternal metabolic physiology, including of the islet beta-cell. The role of lipid signaling processes in the mechanisms of islet beta-cell adaptation to pregnancy has been minimally investigated.ObjectiveTo determine the effects of pregnancy on islet fatty acid (FA) metabolic partitioning and FA augmentation of glucose-stimulated insulin secretion (GSIS).MethodsAge matched virgin, early pregnant (gestational day-11, G11) and late pregnant (G19) Sprague-Dawley rats were studied. Fasted and fed state biochemistry, oral glucose tolerance tests (OGTT), and fasted and post-OGTT liver glycogen, were determined to assess in vivo metabolic characteristics. In isolated islets, FA (BSA-bound palmitate 0.25 mmol/l) augmentation of GSIS, FA partitioning into esterification and oxidation processes using metabolic tracer techniques, lipolysis by glycerol release, triacylglycerols (TG) content, and the expressio...

Research paper thumbnail of Decreased Cholinergic Stimulation of Insulin Secretion by Islets from Rats Fed a Low Protein Diet Is Associated with Reduced Protein Kinase Cα Expression

The Journal of Nutrition, 2003

Undernutrition has been shown to affect the autonomic nervous system, leading to permanent altera... more Undernutrition has been shown to affect the autonomic nervous system, leading to permanent alterations in insulin secretion. To understand these interactions better, we investigated the effects of carbamylcholine (CCh) and phorbol 12-myristate 13-acetate (PMA) on insulin secretion in pancreatic islets from rats fed a normal (17%; NP) or low (6%; LP) protein diet for 8 wk. Isolated islets were incubated for 1 h in Krebs-bicarbonate solution containing 8.3 mmol glucose/L, with or without PMA (400 nmol/L) and CCh. Increasing concentrations of CCh (0.1-1000 mol/L) dose dependently increased insulin secretion by islets from both groups of rats. However, insulin secretion by islets from rats fed the NP diet was significantly higher than that of rats fed the LP diet, and the dose-response curve to CCh was shifted to the right in islets from rats fed LP with a 50% effective concentration (EC 50) of 2.15 Ϯ 0.7 and 4.64 Ϯ 0.1 mol CCh/L in islets of rats fed NP and LP diets, respectively (P Ͻ 0.05). PMA-induced insulin secretion was higher in islets of rats fed NP compared with those fed LP. Western blotting revealed that the protein kinase (PK)C␣ and phospholipase (PL)C␤ 1 contents of islets of rats fed LP were 30% lower than those of islets of rats fed NP (P Ͻ 0.05). In addition, PKC␣ mRNA expression was reduced by 50% in islets from rats fed LP. In conclusion, a reduced expression of PKC␣ and PLC␤ 1 may be involved in the decreased insulin secretion by islets from LP rats after stimulation with CCh and PMA.

Research paper thumbnail of Reversibility of Defects in Proinsulin Processing and Islet β-Cell Failure in Obesity-Related Type 2 Diabetes

Research paper thumbnail of Genetic predisposition for beta cell fragility underlies type 1 and type 2 diabetes

Nature genetics, May 21, 2016

Type 1 (T1D) and type 2 (T2D) diabetes share pathophysiological characteristics, yet mechanistic ... more Type 1 (T1D) and type 2 (T2D) diabetes share pathophysiological characteristics, yet mechanistic links have remained elusive. T1D results from autoimmune destruction of pancreatic beta cells, whereas beta cell failure in T2D is delayed and progressive. Here we find a new genetic component of diabetes susceptibility in T1D non-obese diabetic (NOD) mice, identifying immune-independent beta cell fragility. Genetic variation in Xrcc4 and Glis3 alters the response of NOD beta cells to unfolded protein stress, enhancing the apoptotic and senescent fates. The same transcriptional relationships were observed in human islets, demonstrating the role of beta cell fragility in genetic predisposition to diabetes.

Research paper thumbnail of A low protein diet alters gene expression in rat pancreatic islets

The Journal of nutrition, 2004

Insulin secretion is regulated mainly by circulating nutrients, particularly glucose, and is also... more Insulin secretion is regulated mainly by circulating nutrients, particularly glucose, and is also modulated by hormonal and neuronal inputs. Nutritional alterations during fetal and early postnatal periods, induced by either low protein or energy-restricted diets, produce beta-cell dysfunction. As a consequence, insulin secretion in response to different secretagogues is reduced, as is the number of beta-cells and the size and vascularization of islets. In this study, we used a cDNA macroarray technique and RT-PCR to assess the pattern of gene expression in pancreatic islets from rats fed isocaloric low (6 g/100 g, LP) and normal (17 g/100 g, NP) protein diets, after weaning. Thirty-two genes related to metabolism, neurotransmitter receptors, protein trafficking and targeting, intracellular kinase network members and hormones had altered expression (up- or down-regulated). RT-PCR confirmed the macroarray results for five selected genes, i.e., clusterin, secretogranin II precursor, e...

Research paper thumbnail of Decreased insulin secretion in islets from rats fed a low protein diet is associated with a reduced PKAalpha expression

The Journal of nutrition, 2004

A low protein diet has been shown to affect the amount and activity of several enzymes and to dec... more A low protein diet has been shown to affect the amount and activity of several enzymes and to decrease insulin secretion by islets isolated from rats fed such a diet. To understand the mechanisms involved in this phenomenon, we investigated the effects of forskolin, a stimulator of adenylyl cyclase, on insulin secretion by pancreatic islets from rats fed a normal (17%; NP) or low (6%; LP) protein diet for 8 wk. Isolated islets were incubated for 1 h in Krebs-bicarbonate solution containing 8.3 mmol glucose/L, with or without 10 micromol forskolin/L. The forskolin-induced insulin secretion was higher in islets from NP rats than in those from LP rats (P<0.05). Western blotting revealed that the amount of the alpha catalytic subunit of protein kinase A (PKAalpha) was 35% lower in islets from LP rats than in islets from NP rats (P<0.05). Moreover, PKAalpha mRNA expression was reduced by 30% in islets from LP rats (P<0.05). Our results indicated a possible relationship between a...

Research paper thumbnail of RNA sequencing of all transcripts and how islet β-cells fail

Research paper thumbnail of α/β-Hydrolase Domain-6-Accessible Monoacylglycerol Controls Glucose-Stimulated Insulin Secretion

Cell Metabolism, 2014

Glucose metabolism in pancreatic b cells stimulates insulin granule exocytosis, and this process ... more Glucose metabolism in pancreatic b cells stimulates insulin granule exocytosis, and this process requires generation of a lipid signal. However, the signals involved in lipid amplification of glucose-stimulated insulin secretion (GSIS) are unknown. Here we show that in b cells, glucose stimulates production of lipolysis-derived long-chain saturated monoacylglycerols, which further increase upon inhibition of the membrane-bound monoacylglycerol lipase a/b-Hydrolase Domain-6 (ABHD6). ABHD6 expression in b cells is inversely proportional to GSIS. Exogenous monoacylglycerols stimulate b cell insulin secretion and restore GSIS suppressed by the panlipase inhibitor orlistat. Whole-body and b-cellspecific ABHD6-KO mice exhibit enhanced GSIS, and their islets show elevated monoacylglycerol production and insulin secretion in response to glucose. Inhibition of ABHD6 in diabetic mice restores GSIS and improves glucose tolerance. Monoacylglycerol binds and activates the vesicle priming protein Munc13-1, thereby inducing insulin exocytosis. We propose saturated monoacylglycerol as a signal for GSIS and ABHD6 as a negative modulator of insulin secretion.

Research paper thumbnail of High Passage MIN6 Cells Have Impaired Insulin Secretion with Impaired Glucose and Lipid Oxidation

PLoS ONE, 2012

Type 2 diabetes is a metabolic disorder characterized by the inability of beta-cells to secrete e... more Type 2 diabetes is a metabolic disorder characterized by the inability of beta-cells to secrete enough insulin to maintain glucose homeostasis. MIN6 cells secrete insulin in response to glucose and other secretagogues, but high passage (HP) MIN6 cells lose their ability to secrete insulin in response to glucose. We hypothesized that metabolism of glucose and lipids were defective in HP MIN6 cells causing impaired glucose stimulated insulin secretion (GSIS). HP MIN6 cells had no first phase and impaired second phase GSIS indicative of global functional impairment. This was coupled with a markedly reduced ATP content at basal and glucose stimulated states. Glucose uptake and oxidation were higher at basal glucose but ATP content failed to increase with glucose. HP MIN6 cells had decreased basal lipid oxidation. This was accompanied by reduced expressions of Glut1, Gck, Pfk, Srebp1c, Ucp2, Sirt3, Nampt. MIN6 cells represent an important model of beta cells which, as passage numbers increased lost first phase but retained partial second phase GSIS, similar to patients early in type 2 diabetes onset. We believe a number of gene expression changes occurred to produce this defect, with emphasis on Sirt3 and Nampt, two genes that have been implicated in maintenance of glucose homeostasis.

Research paper thumbnail of Fatty acids alter glycerolipid metabolism and induce lipid droplet formation, syncytialisation and cytokine production in human trophoblasts with minimal glucose effect or interaction

Placenta, 2010

The diabetic pregnancy is characterized by maternal hyperglycaemia and dyslipidaemia, such that p... more The diabetic pregnancy is characterized by maternal hyperglycaemia and dyslipidaemia, such that placental trophoblast cells are exposed to both. The objective was to determine the effects of hyperglycaemia, elevated non-esterified fatty acids (NEFA) and their interactions on trophoblast cell metabolism and function. Trophoblasts were isolated from normal term human placentas and established in culture for 16 h prior to experiments. Glucose utilisation, fatty acid oxidation and fatty acid esterification were determined using radiolabelled metabolic tracer methodology at various glucose and NEFA concentrations. Trophoblast lipid droplet formation including adipophilin mRNA expression, viability, apoptosis, syncytialisation, secretion of hormones and pro-inflammatory cytokines were also assessed. Glucose utilisation via glycolysis was near maximal at the low physiological glucose concentration of 4 mM; whereas NEFA esterification into triacylglycerol and diacylglycerol increased linearly with increasing NEFA concentrations without evidence of plateau. Culture of trophoblasts in 0.25 mM NEFA for 24 h upregulated fatty acid esterification processes, inhibited fatty acid oxidation, inhibited glycerol release (a marker of lipolysis) and promoted adipophilin and lipid droplet formation, all consistent with upregulation of fatty acid storage and buffering capacity. NEFA also promoted trophoblast syncytialisation and TNFa, IL-1b, IL-6 and IL-10 production without effects on cell viability, apoptosis or hormone secretion. Hyperglycaemia caused intracellular glycogen accumulation and reduced lipid droplet formation, but had no other effects on trophoblast metabolism or function. NEFA have effects on trophoblast metabolism and function, mostly independent of glucose, that may have protective as well as pathophysiological roles in pregnancies complicated by diabetes and/or obesity.

Research paper thumbnail of Restoration of insulin secretion in pancreatic islets of protein-deficient rats by reduced expression of insulin receptor substrate (IRS)-1 and IRS-2

Journal of Endocrinology, 2004

Autocrine and paracrine insulin signaling may participate in the fine control of insulin secretio... more Autocrine and paracrine insulin signaling may participate in the fine control of insulin secretion. In the present study, tissue distribution and protein amounts of the insulin receptor and its major substrates, insulin receptor substrate (IRS)-1 and IRS-2, were evaluated in a model of impaired glucose-induced insulin secretion, the protein-deficient rat. Immunoblot and RT-PCR studies showed that the insulin receptor and IRS-2 expression are increased, whilst IRS-1 protein and mRNA contents are decreased in pancreatic islets of protein-deficient rats. Immunohistochemical studies revealed that the insulin receptor and IRS-1 and -2 are present in the great majority of islet cells; however, the greatest staining was localized at the periphery, suggesting a co-localization with non-insulin-secreting cells. Exogenous insulin stimulation of isolated islets promoted higher insulin receptor and IRS-1 and -2 tyrosine phosphorylation in islets from protein-deficient rats, as compared with con...

Research paper thumbnail of Estrogen receptor activation reduces lipid synthesis in pancreatic islets and prevents β cell failure in rodent models of type 2 diabetes

Journal of Clinical Investigation, 2011

The failure of pancreatic β cells to adapt to an increasing demand for insulin is the major mecha... more The failure of pancreatic β cells to adapt to an increasing demand for insulin is the major mechanism by which patients progress from insulin resistance to type 2 diabetes (T2D) and is thought to be related to dysfunctional lipid homeostasis within those cells. In multiple animal models of diabetes, females demonstrate relative protection from β cell failure. We previously found that the hormone 17β-estradiol (E2) in part mediates this benefit. Here, we show that treating male Zucker diabetic fatty (ZDF) rats with E2 suppressed synthesis and accumulation of fatty acids and glycerolipids in islets and protected against β cell failure. The antilipogenic actions of E2 were recapitulated by pharmacological activation of estrogen receptor α (ERα) or ERβ in a rat β cell line and in cultured ZDF rat, mouse, and human islets. Pancreas-specific null deletion of ERα in mice (PERα-/-) prevented reduction of lipid synthesis by E2 via a direct action in islets, and PERα-/mice were predisposed to islet lipid accumulation and β cell dysfunction in response to feeding with a high-fat diet. ER activation inhibited β cell lipid synthesis by suppressing the expression (and activity) of fatty acid synthase via a nonclassical pathway dependent on activated Stat3. Accordingly, pancreas-specific deletion of Stat3 in mice curtailed ER-mediated suppression of lipid synthesis. These data suggest that extranuclear ERs may be promising therapeutic targets to prevent β cell failure in T2D. Conflict of interest: The authors have declared that no conflict of interest exists.

Research paper thumbnail of Short-chain 3-hydroxyacyl-CoA dehydrogenase is a negative regulator of insulin secretion in response to fuel and non-fuel stimuli in INS832/13 β-cells

Journal of Diabetes, Aug 16, 2010

Background: Hyperinsulinemia associated with non-ketotic hypoglycemia is observed in patients wit... more Background: Hyperinsulinemia associated with non-ketotic hypoglycemia is observed in patients with mutated b-oxidation enzyme short-chain 3-hydroxyacyl-CoA dehydrogenase (HADHSC). In the present study, we investigated the mechanism underlying HADHSC-mediated regulation of insulin secretion. Methods: Knockdown of HADHSC expression by RNA interference in INS832 ⁄ 13 b-cells was achieved using short hairpin RNA and short interference RNA. Results: Knockdown of HADHSC increased both fuel-(glucose or leucine plus glutamine) and non-fuel (high KCl)-induced insulin secretion. Enhanced glucose-stimulated insulin secretion (GSIS) induced by HADHSC knockdown was independent of changes in cytosolic Ca 2+ and also occurred in the presence of fatty acids. l-Carnitine, used in the formation of acyl-carnitine compounds, increased GSIS in control cells, but was unable to further increase the augmented GSIS in HADHSCknockdown cells. The pan transaminase inhibitor amino-oxyacetate reversed HADHSC knockdown-mediated increases in GSIS. Oxidation of [1-14 C]-palmitate and -octanoate was not reduced in HADHSCknockdown cells. l-3-Hydroxybutyryl-carnitine (tested using its precursor l-3-hydroxybutyrate) and l-3-hydroxyglutarate, which accumulate in blood and urine, respectively, of HADHSC-deficient patients, did not change insulin secretion. Conclusions: Insulin secretion promoted by both fuel and non-fuel stimuli is negatively regulated by HADHSC. Enhanced secretion after HADHSC knockdown is not due to inhibition of fatty acid oxidation causing an accumulation of long-chain fatty acids or their CoA derivatives. l-3-Hydroxybutyrate and l-3-hydroxyglutarate do not mediate enhanced secretion caused by reduced HADHSC activity. Transamination reaction(s) and the formation of short-chain acylcarnitines and CoAs may be implicated in the mechanism whereby HADHSC deficiency results in enhanced insulin secretion and hyperinsulinemia.

Research paper thumbnail of Islet Inflammation, Hemosiderosis, and Fibrosis in Intrauterine Growth-Restricted and High Fat-Fed Sprague-Dawley Rats

The American Journal of Pathology, 2014

Prenatal and postnatal factors such as intrauterine growth restriction (IUGR) and high-fat (HF) d... more Prenatal and postnatal factors such as intrauterine growth restriction (IUGR) and high-fat (HF) diet contribute to type 2 diabetes. Our aim was to determine whether IUGR and HF diets interact in type 2 diabetes pathogenesis, with particular attention focused on pancreatic islet morphology including assessment for inflammation. A surgical model of IUGR (bilateral uterine artery ligation) in Sprague-Dawley rats with sham controls was used. Pups were fed either HF or chow diets after weaning. Serial measures of body weight and glucose tolerance were performed. At 25 weeks of age, rat pancreases were harvested for histologic assessment. The birth weight of IUGR pups was 13% lower than that of sham pups. HF diet caused excess weight gain, dyslipidemia, hyperinsulinemia, and mild glucose intolerance, however, this was not aggravated further by IUGR. Markedly abnormal islet morphology was evident in 0 of 6 sham-chow, 5 of 8 sham-HF, 4 of 8 IUGR-chow, and 8 of 9 IUGR-HF rats (chisquare, P Z 0.007). Abnormal islets were characterized by larger size, irregular shape, inflammation with CD68-positive cells, marked fibrosis, and hemosiderosis. b-Cell mass was not altered by IUGR. In conclusion, HF and IUGR independently contribute to islet injury characterized by inflammation, hemosiderosis, and fibrosis. This suggests that both HF and IUGR can induce islet injury via converging pathways. The potential pathogenic or permissive role of iron in this process of islet inflammation warrants further investigation.

Research paper thumbnail of Increased Pancreatic Islet Glucose-Induced Insulin Secretion in the Prevention of Diabetes Following Voluntary Running Exercise in ZDF Rats

Canadian Journal of Diabetes, 2008

Research paper thumbnail of Islet beta cell failure in the 60% pancreatectomised obese hyperlipidaemic Zucker fatty rat: severe dysfunction with altered glycerolipid metabolism without steatosis or a falling beta cell mass

Diabetologia, Mar 18, 2009

Aims/hypothesis The Zucker fatty (ZF) rat subjected to 60% pancreatectomy (Px) develops moderate ... more Aims/hypothesis The Zucker fatty (ZF) rat subjected to 60% pancreatectomy (Px) develops moderate diabetes by 3 weeks. We determined whether a progressive fall in beta cell mass and/or beta cell dysfunction contribute to beta cell failure in this type 2 diabetes model. Methods Partial (60%) or sham Px was performed in ZF and Zucker lean (ZL) rats. At 3 weeks post-surgery, beta cell mass and proliferation, proinsulin biosynthesis, pan-creatic insulin content, insulin secretion, and islet glucose and lipid metabolism were measured. Results ZL-Px rats maintained normal glycaemia and glucose-stimulated insulin secretion (GSIS) despite incomplete recovery of beta cell mass possibly due to compensatory enhanced islet glucose metabolism and lipolysis. ZF-Px rats developed moderate hyperglycaemia (14 mmol/l), hypertriacylglycerolaemia and relative hypoinsulinaemia. Despite beta cell mass recovery and normal arginine-induced insulin secretion, GSIS and pancreatic insulin content were profoundly lowered in ZF-Px rats. Proinsulin biosynthesis was not reduced. Compensatory increases in islet glucose metabolism above those observed in ZF-Sham rats were not seen in ZF-Px rats. Triacylglycerol content was not increased in ZF-Px islets, possibly due to lipodetoxification by enhanced lipolysis and fatty acid oxidation. Fatty acid accumulation into monoacylglycerol and diacylglycerol was increased in ZF-Px islets together with a 4.5-fold elevation in stearoyl-CoA desaturase mRNA expression. Conclusions/interpretation Falling beta cell mass, reduced proinsulin biosynthesis and islet steatosis are not implicated in early beta cell failure and glucolipotoxicity in ZF-Px rats. Rather, severe beta cell dysfunction with a specific reduction in GSIS and marked depletion of beta cell insulin stores with altered lipid partitioning underlie beta cell failure in this animal model of type 2 diabetes.

Research paper thumbnail of Estrogen prevents beta-cell failure and diabetes in ZDF male rats: a role for glycerolipid/fatty acid cycling

Canadian Journal of Diabetes, 2008

Research paper thumbnail of Glucose-stimulated insulin secretion is increased and diabetes prevented in ZDF rats following voluntary running exercise training

Canadian Journal of Diabetes, 2009

Research paper thumbnail of Beta-cell dysfunction in the 60% pancreatectomized obese hyperlipidaemic Zucker fatty rat. Altered glycerolipid metabolism without islet cell steatosis

Canadian Journal of Diabetes, 2008

Research paper thumbnail of XBP1 maintains beta cell identity, represses beta-to-alpha cell transdifferentiation and protects against diabetic beta cell failure during metabolic stress in mice

Diabetologia, 2022

Aims/hypothesis Pancreatic beta cell dedifferentiation, transdifferentiation into other islet cel... more Aims/hypothesis Pancreatic beta cell dedifferentiation, transdifferentiation into other islet cells and apoptosis have been implicated in beta cell failure in type 2 diabetes, although the mechanisms are poorly defined. The endoplasmic reticulum stress response factor X-box binding protein 1 (XBP1) is a major regulator of the unfolded protein response. XBP1 expression is reduced in islets of people with type 2 diabetes, but its role in adult differentiated beta cells is unclear. Here, we assessed the effects of Xbp1 deletion in adult beta cells and tested whether XBP1-mediated unfolded protein response makes a necessary contribution to beta cell compensation in insulin resistance states. Methods Mice with inducible beta cell-specific Xbp1 deletion were studied under normal (chow diet) or metabolic stress (high-fat diet or obesity) conditions. Glucose tolerance, insulin secretion, islet gene expression, alpha cell mass, beta cell mass and apoptosis were assessed. Lineage tracing was ...

Research paper thumbnail of The Role of Fatty Acid Signaling in Islet Beta-Cell Adaptation to Normal Pregnancy

Frontiers in Endocrinology, 2022

BackgroundMaintenance of a normal fetal nutrient supply requires major adaptations in maternal me... more BackgroundMaintenance of a normal fetal nutrient supply requires major adaptations in maternal metabolic physiology, including of the islet beta-cell. The role of lipid signaling processes in the mechanisms of islet beta-cell adaptation to pregnancy has been minimally investigated.ObjectiveTo determine the effects of pregnancy on islet fatty acid (FA) metabolic partitioning and FA augmentation of glucose-stimulated insulin secretion (GSIS).MethodsAge matched virgin, early pregnant (gestational day-11, G11) and late pregnant (G19) Sprague-Dawley rats were studied. Fasted and fed state biochemistry, oral glucose tolerance tests (OGTT), and fasted and post-OGTT liver glycogen, were determined to assess in vivo metabolic characteristics. In isolated islets, FA (BSA-bound palmitate 0.25 mmol/l) augmentation of GSIS, FA partitioning into esterification and oxidation processes using metabolic tracer techniques, lipolysis by glycerol release, triacylglycerols (TG) content, and the expressio...

Research paper thumbnail of Decreased Cholinergic Stimulation of Insulin Secretion by Islets from Rats Fed a Low Protein Diet Is Associated with Reduced Protein Kinase Cα Expression

The Journal of Nutrition, 2003

Undernutrition has been shown to affect the autonomic nervous system, leading to permanent altera... more Undernutrition has been shown to affect the autonomic nervous system, leading to permanent alterations in insulin secretion. To understand these interactions better, we investigated the effects of carbamylcholine (CCh) and phorbol 12-myristate 13-acetate (PMA) on insulin secretion in pancreatic islets from rats fed a normal (17%; NP) or low (6%; LP) protein diet for 8 wk. Isolated islets were incubated for 1 h in Krebs-bicarbonate solution containing 8.3 mmol glucose/L, with or without PMA (400 nmol/L) and CCh. Increasing concentrations of CCh (0.1-1000 mol/L) dose dependently increased insulin secretion by islets from both groups of rats. However, insulin secretion by islets from rats fed the NP diet was significantly higher than that of rats fed the LP diet, and the dose-response curve to CCh was shifted to the right in islets from rats fed LP with a 50% effective concentration (EC 50) of 2.15 Ϯ 0.7 and 4.64 Ϯ 0.1 mol CCh/L in islets of rats fed NP and LP diets, respectively (P Ͻ 0.05). PMA-induced insulin secretion was higher in islets of rats fed NP compared with those fed LP. Western blotting revealed that the protein kinase (PK)C␣ and phospholipase (PL)C␤ 1 contents of islets of rats fed LP were 30% lower than those of islets of rats fed NP (P Ͻ 0.05). In addition, PKC␣ mRNA expression was reduced by 50% in islets from rats fed LP. In conclusion, a reduced expression of PKC␣ and PLC␤ 1 may be involved in the decreased insulin secretion by islets from LP rats after stimulation with CCh and PMA.

Research paper thumbnail of Reversibility of Defects in Proinsulin Processing and Islet β-Cell Failure in Obesity-Related Type 2 Diabetes

Research paper thumbnail of Genetic predisposition for beta cell fragility underlies type 1 and type 2 diabetes

Nature genetics, May 21, 2016

Type 1 (T1D) and type 2 (T2D) diabetes share pathophysiological characteristics, yet mechanistic ... more Type 1 (T1D) and type 2 (T2D) diabetes share pathophysiological characteristics, yet mechanistic links have remained elusive. T1D results from autoimmune destruction of pancreatic beta cells, whereas beta cell failure in T2D is delayed and progressive. Here we find a new genetic component of diabetes susceptibility in T1D non-obese diabetic (NOD) mice, identifying immune-independent beta cell fragility. Genetic variation in Xrcc4 and Glis3 alters the response of NOD beta cells to unfolded protein stress, enhancing the apoptotic and senescent fates. The same transcriptional relationships were observed in human islets, demonstrating the role of beta cell fragility in genetic predisposition to diabetes.

Research paper thumbnail of A low protein diet alters gene expression in rat pancreatic islets

The Journal of nutrition, 2004

Insulin secretion is regulated mainly by circulating nutrients, particularly glucose, and is also... more Insulin secretion is regulated mainly by circulating nutrients, particularly glucose, and is also modulated by hormonal and neuronal inputs. Nutritional alterations during fetal and early postnatal periods, induced by either low protein or energy-restricted diets, produce beta-cell dysfunction. As a consequence, insulin secretion in response to different secretagogues is reduced, as is the number of beta-cells and the size and vascularization of islets. In this study, we used a cDNA macroarray technique and RT-PCR to assess the pattern of gene expression in pancreatic islets from rats fed isocaloric low (6 g/100 g, LP) and normal (17 g/100 g, NP) protein diets, after weaning. Thirty-two genes related to metabolism, neurotransmitter receptors, protein trafficking and targeting, intracellular kinase network members and hormones had altered expression (up- or down-regulated). RT-PCR confirmed the macroarray results for five selected genes, i.e., clusterin, secretogranin II precursor, e...

Research paper thumbnail of Decreased insulin secretion in islets from rats fed a low protein diet is associated with a reduced PKAalpha expression

The Journal of nutrition, 2004

A low protein diet has been shown to affect the amount and activity of several enzymes and to dec... more A low protein diet has been shown to affect the amount and activity of several enzymes and to decrease insulin secretion by islets isolated from rats fed such a diet. To understand the mechanisms involved in this phenomenon, we investigated the effects of forskolin, a stimulator of adenylyl cyclase, on insulin secretion by pancreatic islets from rats fed a normal (17%; NP) or low (6%; LP) protein diet for 8 wk. Isolated islets were incubated for 1 h in Krebs-bicarbonate solution containing 8.3 mmol glucose/L, with or without 10 micromol forskolin/L. The forskolin-induced insulin secretion was higher in islets from NP rats than in those from LP rats (P<0.05). Western blotting revealed that the amount of the alpha catalytic subunit of protein kinase A (PKAalpha) was 35% lower in islets from LP rats than in islets from NP rats (P<0.05). Moreover, PKAalpha mRNA expression was reduced by 30% in islets from LP rats (P<0.05). Our results indicated a possible relationship between a...

Research paper thumbnail of RNA sequencing of all transcripts and how islet β-cells fail

Research paper thumbnail of α/β-Hydrolase Domain-6-Accessible Monoacylglycerol Controls Glucose-Stimulated Insulin Secretion

Cell Metabolism, 2014

Glucose metabolism in pancreatic b cells stimulates insulin granule exocytosis, and this process ... more Glucose metabolism in pancreatic b cells stimulates insulin granule exocytosis, and this process requires generation of a lipid signal. However, the signals involved in lipid amplification of glucose-stimulated insulin secretion (GSIS) are unknown. Here we show that in b cells, glucose stimulates production of lipolysis-derived long-chain saturated monoacylglycerols, which further increase upon inhibition of the membrane-bound monoacylglycerol lipase a/b-Hydrolase Domain-6 (ABHD6). ABHD6 expression in b cells is inversely proportional to GSIS. Exogenous monoacylglycerols stimulate b cell insulin secretion and restore GSIS suppressed by the panlipase inhibitor orlistat. Whole-body and b-cellspecific ABHD6-KO mice exhibit enhanced GSIS, and their islets show elevated monoacylglycerol production and insulin secretion in response to glucose. Inhibition of ABHD6 in diabetic mice restores GSIS and improves glucose tolerance. Monoacylglycerol binds and activates the vesicle priming protein Munc13-1, thereby inducing insulin exocytosis. We propose saturated monoacylglycerol as a signal for GSIS and ABHD6 as a negative modulator of insulin secretion.

Research paper thumbnail of High Passage MIN6 Cells Have Impaired Insulin Secretion with Impaired Glucose and Lipid Oxidation

PLoS ONE, 2012

Type 2 diabetes is a metabolic disorder characterized by the inability of beta-cells to secrete e... more Type 2 diabetes is a metabolic disorder characterized by the inability of beta-cells to secrete enough insulin to maintain glucose homeostasis. MIN6 cells secrete insulin in response to glucose and other secretagogues, but high passage (HP) MIN6 cells lose their ability to secrete insulin in response to glucose. We hypothesized that metabolism of glucose and lipids were defective in HP MIN6 cells causing impaired glucose stimulated insulin secretion (GSIS). HP MIN6 cells had no first phase and impaired second phase GSIS indicative of global functional impairment. This was coupled with a markedly reduced ATP content at basal and glucose stimulated states. Glucose uptake and oxidation were higher at basal glucose but ATP content failed to increase with glucose. HP MIN6 cells had decreased basal lipid oxidation. This was accompanied by reduced expressions of Glut1, Gck, Pfk, Srebp1c, Ucp2, Sirt3, Nampt. MIN6 cells represent an important model of beta cells which, as passage numbers increased lost first phase but retained partial second phase GSIS, similar to patients early in type 2 diabetes onset. We believe a number of gene expression changes occurred to produce this defect, with emphasis on Sirt3 and Nampt, two genes that have been implicated in maintenance of glucose homeostasis.

Research paper thumbnail of Fatty acids alter glycerolipid metabolism and induce lipid droplet formation, syncytialisation and cytokine production in human trophoblasts with minimal glucose effect or interaction

Placenta, 2010

The diabetic pregnancy is characterized by maternal hyperglycaemia and dyslipidaemia, such that p... more The diabetic pregnancy is characterized by maternal hyperglycaemia and dyslipidaemia, such that placental trophoblast cells are exposed to both. The objective was to determine the effects of hyperglycaemia, elevated non-esterified fatty acids (NEFA) and their interactions on trophoblast cell metabolism and function. Trophoblasts were isolated from normal term human placentas and established in culture for 16 h prior to experiments. Glucose utilisation, fatty acid oxidation and fatty acid esterification were determined using radiolabelled metabolic tracer methodology at various glucose and NEFA concentrations. Trophoblast lipid droplet formation including adipophilin mRNA expression, viability, apoptosis, syncytialisation, secretion of hormones and pro-inflammatory cytokines were also assessed. Glucose utilisation via glycolysis was near maximal at the low physiological glucose concentration of 4 mM; whereas NEFA esterification into triacylglycerol and diacylglycerol increased linearly with increasing NEFA concentrations without evidence of plateau. Culture of trophoblasts in 0.25 mM NEFA for 24 h upregulated fatty acid esterification processes, inhibited fatty acid oxidation, inhibited glycerol release (a marker of lipolysis) and promoted adipophilin and lipid droplet formation, all consistent with upregulation of fatty acid storage and buffering capacity. NEFA also promoted trophoblast syncytialisation and TNFa, IL-1b, IL-6 and IL-10 production without effects on cell viability, apoptosis or hormone secretion. Hyperglycaemia caused intracellular glycogen accumulation and reduced lipid droplet formation, but had no other effects on trophoblast metabolism or function. NEFA have effects on trophoblast metabolism and function, mostly independent of glucose, that may have protective as well as pathophysiological roles in pregnancies complicated by diabetes and/or obesity.

Research paper thumbnail of Restoration of insulin secretion in pancreatic islets of protein-deficient rats by reduced expression of insulin receptor substrate (IRS)-1 and IRS-2

Journal of Endocrinology, 2004

Autocrine and paracrine insulin signaling may participate in the fine control of insulin secretio... more Autocrine and paracrine insulin signaling may participate in the fine control of insulin secretion. In the present study, tissue distribution and protein amounts of the insulin receptor and its major substrates, insulin receptor substrate (IRS)-1 and IRS-2, were evaluated in a model of impaired glucose-induced insulin secretion, the protein-deficient rat. Immunoblot and RT-PCR studies showed that the insulin receptor and IRS-2 expression are increased, whilst IRS-1 protein and mRNA contents are decreased in pancreatic islets of protein-deficient rats. Immunohistochemical studies revealed that the insulin receptor and IRS-1 and -2 are present in the great majority of islet cells; however, the greatest staining was localized at the periphery, suggesting a co-localization with non-insulin-secreting cells. Exogenous insulin stimulation of isolated islets promoted higher insulin receptor and IRS-1 and -2 tyrosine phosphorylation in islets from protein-deficient rats, as compared with con...

Research paper thumbnail of Estrogen receptor activation reduces lipid synthesis in pancreatic islets and prevents β cell failure in rodent models of type 2 diabetes

Journal of Clinical Investigation, 2011

The failure of pancreatic β cells to adapt to an increasing demand for insulin is the major mecha... more The failure of pancreatic β cells to adapt to an increasing demand for insulin is the major mechanism by which patients progress from insulin resistance to type 2 diabetes (T2D) and is thought to be related to dysfunctional lipid homeostasis within those cells. In multiple animal models of diabetes, females demonstrate relative protection from β cell failure. We previously found that the hormone 17β-estradiol (E2) in part mediates this benefit. Here, we show that treating male Zucker diabetic fatty (ZDF) rats with E2 suppressed synthesis and accumulation of fatty acids and glycerolipids in islets and protected against β cell failure. The antilipogenic actions of E2 were recapitulated by pharmacological activation of estrogen receptor α (ERα) or ERβ in a rat β cell line and in cultured ZDF rat, mouse, and human islets. Pancreas-specific null deletion of ERα in mice (PERα-/-) prevented reduction of lipid synthesis by E2 via a direct action in islets, and PERα-/mice were predisposed to islet lipid accumulation and β cell dysfunction in response to feeding with a high-fat diet. ER activation inhibited β cell lipid synthesis by suppressing the expression (and activity) of fatty acid synthase via a nonclassical pathway dependent on activated Stat3. Accordingly, pancreas-specific deletion of Stat3 in mice curtailed ER-mediated suppression of lipid synthesis. These data suggest that extranuclear ERs may be promising therapeutic targets to prevent β cell failure in T2D. Conflict of interest: The authors have declared that no conflict of interest exists.