scholarly journals Lactisole inhibits the glucose-sensing receptor T1R3 expressed in mouse pancreatic β-cells

2015 ◽  
Vol 226 (1) ◽  
pp. 57-66 ◽  
Author(s):  
Kunihisa Hamano ◽  
Yuko Nakagawa ◽  
Yoshiaki Ohtsu ◽  
Longfei Li ◽  
Johan Medina ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Glucose Sensing ◽  
Hek293 Cells ◽  
Intracellular Camp ◽  
Dependent Manner ◽  
High Concentration ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Min6 Cells ◽  
Mouse Islets

Glucose activates the glucose-sensing receptor T1R3 and facilitates its own metabolism in pancreatic β-cells. An inhibitor of this receptor would be helpful in elucidating the physiological function of the glucose-sensing receptor. The present study was conducted to examine whether or not lactisole can be used as an inhibitor of the glucose-sensing receptor. In MIN6 cells, in a dose-dependent manner, lactisole inhibited insulin secretion induced by sweeteners, acesulfame-K, sucralose and glycyrrhizin. The IC50 was ∼4 mmol/l. Lactisole attenuated the elevation of cytoplasmic Ca2+ concentration ([Ca2+]c) evoked by sucralose and acesulfame-K but did not affect the elevation of intracellular cAMP concentration ([cAMP]c) induced by these sweeteners. Lactisole also inhibited the action of glucose in MIN6 cells. Thus, lactisole significantly reduced elevations of intracellular [NADH] and intracellular [ATP] induced by glucose, and also inhibited glucose-induced insulin secretion. To further examine the effect of lactisole on T1R3, we prepared HEK293 cells stably expressing mouse T1R3. In these cells, sucralose elevated both [Ca2+]c and [cAMP]c. Lactisole attenuated the sucralose-induced increase in [Ca2+]c but did not affect the elevation of [cAMP]c. Finally, lactisole inhibited insulin secretion induced by a high concentration of glucose in mouse islets. These results indicate that the mouse glucose-sensing receptor was inhibited by lactisole. Lactisole may be useful in assessing the role of the glucose-sensing receptor in mouse pancreatic β-cells.

scholarly journals Fructose-1,6-Bisphosphatase Regulates Glucose-Stimulated Insulin Secretion of Mouse Pancreatic β-Cells

Endocrinology ◽  
2010 ◽  
Vol 151 (10) ◽  
pp. 4688-4695 ◽  
Author(s):  
Ye Zhang ◽  
Zhifang Xie ◽  
Guangdi Zhou ◽  
Hai Zhang ◽  
Jian Lu ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Specific Inhibitor ◽  
Physiological Role ◽  
Glucose Sensing ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Min6 Cells ◽  
Fructose 1,6 Bisphosphatase ◽  
Glucose Stimulated Insulin Secretion

Pancreatic β-cells can precisely sense glucose stimulation and accordingly adjust their insulin secretion. Fructose-1,6-bisphosphatase (FBPase) is a gluconeogenic enzyme, but its physiological significance in β-cells is not established. Here we determined its physiological role in regulating glucose sensing and insulin secretion of β-cells. Considerable FBPase mRNA was detected in normal mouse islets and β-cell lines, although their protein levels appeared to be quite low. Down-regulation of FBP1 in MIN6 cells by small interfering RNA could enhance the glucose-stimulated insulin secretion (GSIS), whereas FBP1-overexpressing MIN6 cells exhibited decreased GSIS. Inhibition of FBPase activity in islet β-cells by its specific inhibitor MB05032 led to significant increase of their glucose utilization and cellular ATP to ADP ratios and consequently enhanced GSIS in vitro. Pretreatment of mice with the MB05032 prodrug MB06322 could potentiate GSIS in vivo and improve their glucose tolerance. Therefore, FBPase plays an important role in regulating glucose sensing and insulin secretion of β-cells and serves a promising target for diabetes treatment.

scholarly journals Somatostatin Inhibits Oxidative Respiration in Pancreatic β-Cells

Endocrinology ◽  
2006 ◽  
Vol 147 (3) ◽  
pp. 1527-1535 ◽  
Author(s):  
Mathew Daunt ◽  
Oliver Dale ◽  
Paul A. Smith
Keyword(s):  
Insulin Secretion ◽  
Glucose Metabolism ◽  
Somatostatin Receptor ◽  
Katp Channels ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
K Channels ◽  
Min6 Cells ◽  
Voltage Gated ◽  
Mouse Islets

Somatostatin potently inhibits insulin secretion from pancreatic β-cells. It does so via activation of ATP-sensitive K+-channels (KATP) and G protein-regulated inwardly rectifying K+-channels, which act to decrease voltage-gated Ca2+-influx, a process central to exocytosis. Because KATP channels, and indeed insulin secretion, is controlled by glucose oxidation, we investigated whether somatostatin inhibits insulin secretion by direct effects on glucose metabolism. Oxidative metabolism in β-cells was monitored by measuring changes in the O2 consumption (ΔO2) of isolated mouse islets and MIN6 cells, a murine-derived β-cell line. In both models, glucose-stimulated ΔO2, an effect closely associated with inhibition of KATP channel activity and induction of electrical activity (r > 0.98). At 100 nm, somatostatin abolished glucose-stimulated ΔO2 in mouse islets (n = 5, P < 0.05) and inhibited it by 80 ± 28% (n = 17, P < 0.01) in MIN6 cells. Removal of extracellular Ca2+, 5 mm Co2+, or 20 μm nifedipine, conditions that inhibit voltage-gated Ca2+ influx, did not mimic but either blocked or reduced the effect of the peptide on ΔO2. The nutrient secretagogues, methylpyruvate (10 mm) and α-ketoisocaproate (20 mm), also stimulated ΔO2, but this was unaffected by somatostatin. Somatostatin also reversed glucose-induced hyperpolarization of the mitochondrial membrane potential monitored using rhodamine-123. Application of somatostatin receptor selective agonists demonstrated that the peptide worked through activation of the type 5 somatostatin receptor. In conclusion, somatostatin inhibits glucose metabolism in murine β-cells by an unidentified Ca2+-dependent mechanism. This represents a new signaling pathway by which somatostatin can inhibit cellular functions regulated by glucose metabolism.

scholarly journals Peroxisome Proliferator-Activated Receptor α (PPARα) Potentiates, whereas PPARγ Attenuates, Glucose-Stimulated Insulin Secretion in Pancreatic β-Cells

Endocrinology ◽  
2005 ◽  
Vol 146 (8) ◽  
pp. 3266-3276 ◽  
Author(s):  
Kim Ravnskjaer ◽  
Michael Boergesen ◽  
Blanca Rubi ◽  
Jan K. Larsen ◽  
Tina Nielsen ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Mitochondrial Membrane ◽  
Uncoupling Protein ◽  
Peroxisome Proliferator ◽  
Dependent Manner ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Peroxisome Proliferator Activated Receptor ◽  
Glucose Stimulated Insulin Secretion

Abstract Fatty acids (FAs) are known to be important regulators of insulin secretion from pancreatic β-cells. FA-coenzyme A esters have been shown to directly stimulate the secretion process, whereas long-term exposure of β-cells to FAs compromises glucose-stimulated insulin secretion (GSIS) by mechanisms unknown to date. It has been speculated that some of these long-term effects are mediated by members of the peroxisome proliferator-activated receptor (PPAR) family via an induction of uncoupling protein-2 (UCP2). In this study we show that adenoviral coexpression of PPARα and retinoid X receptor α (RXRα) in INS-1E β-cells synergistically and in a dose- and ligand-dependent manner increases the expression of known PPARα target genes and enhances FA uptake and β-oxidation. In contrast, ectopic expression of PPARγ/RXRα increases FA uptake and deposition as triacylglycerides. Although the expression of PPARα/RXRα leads to the induction of UCP2 mRNA and protein, this is not accompanied by reduced hyperpolarization of the mitochondrial membrane, indicating that under these conditions, increased UCP2 expression is insufficient for dissipation of the mitochondrial proton gradient. Importantly, whereas expression of PPARγ/RXRα attenuates GSIS, the expression of PPARα/RXRα potentiates GSIS in rat islets and INS-1E cells without affecting the mitochondrial membrane potential. These results show a strong subtype specificity of the two PPAR subtypes α and γ on lipid partitioning and insulin secretion when systematically compared in a β-cell context.

scholarly journals The adaptor protein APPL2 controls glucose-stimulated insulin secretion via F-actin remodeling in pancreatic β-cells

2020 ◽  
Vol 117 (45) ◽  
pp. 28307-28315
Author(s):  
Baile Wang ◽  
Huige Lin ◽  
Xiaomu Li ◽  
Wenqi Lu ◽  
Jae Bum Kim ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Pancreatic Islets ◽  
Adaptor Protein ◽  
Hek293 Cells ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells ◽  
Actin Remodeling ◽  
Actin Depolymerization ◽  
Glucose Stimulated Insulin Secretion

Filamentous actin (F-actin) cytoskeletal remodeling is critical for glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells, and its dysregulation causes type 2 diabetes. The adaptor protein APPL1 promotes first-phase GSIS by up-regulating solubleN-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein expression. However, whether APPL2 (a close homology of APPL1 with the same domain organization) plays a role in β-cell functions is unknown. Here, we show that APPL2 enhances GSIS by promoting F-actin remodeling via the small GTPase Rac1 in pancreatic β-cells. β-cell specific abrogation of APPL2 impaired GSIS, leading to glucose intolerance in mice. APPL2 deficiency largely abolished glucose-induced first- and second-phase insulin secretion in pancreatic islets. Real-time live-cell imaging and phalloidin staining revealed that APPL2 deficiency abolished glucose-induced F-actin depolymerization in pancreatic islets. Likewise, knockdown of APPL2 expression impaired glucose-stimulated F-actin depolymerization and subsequent insulin secretion in INS-1E cells, which were attributable to the impairment of Ras-related C3 botulinum toxin substrate 1 (Rac1) activation. Treatment with the F-actin depolymerization chemical compounds or overexpression of gelsolin (a F-actin remodeling protein) rescued APPL2 deficiency-induced defective GSIS. In addition, APPL2 interacted with Rac GTPase activating protein 1 (RacGAP1) in a glucose-dependent manner via the bin/amphiphysin/rvs-pleckstrin homology (BAR-PH) domain of APPL2 in INS-1E cells and HEK293 cells. Concomitant knockdown of RacGAP1 expression reverted APPL2 deficiency-induced defective GSIS, F-actin remodeling, and Rac1 activation in INS-1E cells. Our data indicate that APPL2 interacts with RacGAP1 and suppresses its negative action on Rac1 activity and F-actin depolymerization thereby enhancing GSIS in pancreatic β-cells.

scholarly journals Secretagogin affects insulin secretion in pancreatic β-cells by regulating actin dynamics and focal adhesion

2016 ◽  
Vol 473 (12) ◽  
pp. 1791-1803 ◽  
Author(s):  
Seo-Yun Yang ◽  
Jae-Jin Lee ◽  
Jin-Hee Lee ◽  
Kyungeun Lee ◽  
Seung Hoon Oh ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Focal Adhesion ◽  
Underlying Mechanism ◽  
Neuroendocrine Cells ◽  
Actin Dynamics ◽  
Second Phase ◽  
Dependent Manner ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Insulinoma Cells

Secretagogin (SCGN), a Ca2+-binding protein having six EF-hands, is selectively expressed in pancreatic β-cells and neuroendocrine cells. Previous studies suggested that SCGN enhances insulin secretion by functioning as a Ca2+-sensor protein, but the underlying mechanism has not been elucidated. The present study explored the mechanism by which SCGN enhances glucose-induced insulin secretion in NIT-1 insulinoma cells. To determine whether SCGN influences the first or second phase of insulin secretion, we examined how SCGN affects the kinetics of insulin secretion in NIT-1 cells. We found that silencing SCGN suppressed the second phase of insulin secretion induced by glucose and H2O2, but not the first phase induced by KCl stimulation. Recruitment of insulin granules in the second phase of insulin secretion was significantly impaired by knocking down SCGN in NIT-1 cells. In addition, we found that SCGN interacts with the actin cytoskeleton in the plasma membrane and regulates actin remodelling in a glucose-dependent manner. Since actin dynamics are known to regulate focal adhesion, a critical step in the second phase of insulin secretion, we examined the effect of silencing SCGN on focal adhesion molecules, including FAK (focal adhesion kinase) and paxillin, and the cell survival molecules ERK1/2 (extracellular-signal-regulated kinase 1/2) and Akt. We found that glucose- and H2O2-induced activation of FAK, paxillin, ERK1/2 and Akt was significantly blocked by silencing SCGN. We conclude that SCGN controls glucose-stimulated insulin secretion and thus may be useful in the therapy of Type 2 diabetes.

scholarly journals SPARC promotes insulin secretion through down-regulation of RGS4 protein in pancreatic β cells

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Li Hu ◽  
Fengli He ◽  
Meifeng Huang ◽  
Qian Zhao ◽  
Lamei Cheng ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Underlying Mechanism ◽  
Negative Regulator ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Promoting Effect ◽  
Down Regulation ◽  
Mouse Islets ◽  
Glucose Stimulated Insulin Secretion ◽  
Phosphoinositide 3 Kinase

Abstract SPARC-deficient mice have been shown to exhibit impaired glucose tolerance and insulin secretion, but the underlying mechanism remains unknown. Here, we showed that SPARC enhanced the promoting effect of Muscarinic receptor agonist oxotremorine-M on insulin secretion in cultured mouse islets. Overexpression of SPARC down-regulated RGS4, a negative regulator of β-cell M3 muscarinic receptors. Conversely, knockdown of SPARC up-regulated RGS4 in Min6 cells. RGS4 was up-regulated in islets from sparc −/− mice, which correlated with decreased glucose-stimulated insulin secretion (GSIS). Furthermore, inhibition of RGS4 restored GSIS in the islets from sparc −/− mice, and knockdown of RGS4 partially decreased the promoting effect of SPARC on oxotremorine-M-stimulated insulin secretion. Phosphoinositide 3-kinase (PI3K) inhibitor LY-294002 abolished SPARC-induced down-regulation of RGS4. Taken together, our data revealed that SPARC promoted GSIS by inhibiting RGS4 in pancreatic β cells.

scholarly journals The Orphan Nuclear Receptor NR4A1 Protects Pancreatic β-Cells from Endoplasmic Reticulum (ER) Stress-mediated Apoptosis

2015 ◽  
Vol 290 (34) ◽  
pp. 20687-20699 ◽  
Author(s):  
Cong Yu ◽  
Shang Cui ◽  
Chen Zong ◽  
Weina Gao ◽  
Tongfu Xu ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells ◽  
Survivin Promoter ◽  
Min6 Cells ◽  
Chop Expression ◽  
Mouse Islets

The role of NR4A1 in apoptosis is controversial. Pancreatic β-cells often face endoplasmic reticulum (ER) stress under adverse conditions such as high free fatty acid (FFA) concentrations and sustained hyperglycemia. Severe ER stress results in β-cell apoptosis. The aim of this study was to analyze the role of NR4A1 in ER stress-mediated β-cell apoptosis and to characterize the related mechanisms. We confirmed that upon treatment with the ER stress inducers thapsigargin (TG) or palmitic acid (PA), the mRNA and protein levels of NR4A1 rapidly increased in both MIN6 cells and mouse islets. NR4A1 overexpression in MIN6 cells conferred resistance to cell loss induced by TG or PA, as assessed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, and TUNEL assays indicated that NR4A1 overexpression also protected against ER stress-induced apoptosis. This conclusion was further confirmed by experiments exploiting siRNA to knockdown NR4A1 expression in MIN6 cells or exploiting NR4A1 knock-out mice. NR4A1 overexpression in MIN6 cells reduced C/EBP homologous protein (CHOP) expression and Caspase3 activation induced by TG or PA. NR4A1 overexpression in MIN6 cells or mouse islets resulted in Survivin up-regulation. A critical regulatory element was identified in Survivin promoter (−1872 bp to −1866 bp) with a putative NR4A1 binding site; ChIP assays demonstrated that NR4A1 physically associates with the Survivin promoter. In conclusion, NR4A1 protects pancreatic β-cells against ER stress-mediated apoptosis by up-regulating Survivin expression and down-regulating CHOP expression, which we termed as “positive and negative regulation.”

scholarly journals VAMP7 Regulates Autophagosome Formation by Supporting Atg9a Functions in Pancreatic β-Cells From Male Mice

Endocrinology ◽  
2018 ◽  
Vol 159 (11) ◽  
pp. 3674-3688 ◽  
Author(s):  
Kyota Aoyagi ◽  
Makoto Itakura ◽  
Toshiyuki Fukutomi ◽  
Chiyono Nishiwaki ◽  
Yoko Nakamichi ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Molecular Mechanism ◽  
Snare Complex ◽  
Diabetic Patients ◽  
Dependent Manner ◽  
Β Cells ◽  
Autophagosome Formation ◽  
Pancreatic Β Cells ◽  
Recycling Endosomes ◽  
Glucose Stimulated Insulin Secretion

Abstract Dysfunctional mitochondria are observed in β-cells of diabetic patients, which are eventually removed by autophagy. Vesicle-associated membrane protein (VAMP)7, a vesicular SNARE protein, regulates autophagosome formation to maintain mitochondrial homeostasis and control insulin secretion in pancreatic β-cells. However, its molecular mechanism is largely unknown. In this study, we investigated the molecular mechanism of VAMP7-dependent autophagosome formation using VAMP7-deficient β-cells and β-cell–derived Min6 cells. VAMP7 localized in autophagy-related (Atg)9a–resident vesicles of recycling endosomes (REs), which contributed to autophagosome formation, and it interacted with Hrb, Syntaxin16, and SNAP-47. Hrb recruited VAMP7 and Atg9a from the plasma membrane to REs. Syntaxin16 and SNAP-47 mediated autophagosome formation at a step later than the proper localization of VAMP7 to Atg9a-resident vesicles. Knockdown of Hrb, Syntaxin16, and SNAP-47 resulted in defective autophagosome formation, accumulation of dysfunctional mitochondria, and impairment of glucose-stimulated insulin secretion. Our data indicate that VAMP7 and Atg9a are initially recruited to REs to organize VAMP7 and Atg9a-resident vesicles in an Hrb-dependent manner. Additionally, VAMP7 forms a SNARE complex with Syntaxin16 and SNAP-47, which may cause fusions of Atg9a-resident vesicles during autophagosome formation. Thus, VAMP7 participates in autophagosome formation by supporting Atg9a functions that contribute to maintenance of mitochondrial quality.

CFTR silencing in pancreatic β-cells reveals a functional impact on glucose-stimulated insulin secretion and oxidative stress response

2016 ◽  
Vol 310 (3) ◽  
pp. E200-E212 ◽  
Author(s):  
Thierry Ntimbane ◽  
Geneviève Mailhot ◽  
Schohraya Spahis ◽  
Remi Rabasa-Lhoret ◽  
Marie-Laure Kleme ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Cystic Fibrosis ◽  
Insulin Secretion ◽  
Inflammatory Responses ◽  
Lipid Peroxides ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Min6 Cells ◽  
Atp Production

Cystic fibrosis (CF)-related diabetes (CFRD) has become a critical complication that seriously affects the clinical outcomes of CF patients. Although CFRD has emerged as the most common nonpulmonary complication of CF, little is known about its etiopathogenesis. Additionally, whether oxidative stress (OxS), a common feature of CF and diabetes, influences CFRD pathophysiology requires clarification. The main objective of this study was to shed light on the role of the cystic fibrosis transmembrane conductance regulator (CFTR) in combination with OxS in insulin secretion from pancreatic β-cells. CFTR silencing was accomplished in MIN6 cells by stable expression of small hairpin RNAs (shRNA), and glucose-induced insulin secretion was evaluated in the presence and absence of the valuable prooxidant system iron/ascorbate (Fe/Asc; 0.075/0.75 mM) along with or without the antioxidant Trolox (1 mM). Insulin output from CFTR-silenced MIN6 cells was significantly reduced (∼70%) at basal and at different glucose concentrations compared with control Mock cells. Furthermore, CFTR silencing rendered MIN6 cells more sensitive to OxS as evidenced by both increased lipid peroxides and weakened antioxidant defense, especially following incubation with Fe/Asc. The decreased insulin secretion in CFTR-silenced MIN6 cells was associated with high levels of NF-κB (the major participant in inflammatory responses), raised apoptosis, and diminished ATP production in response to the Fe/Asc challenge. However, these defects were alleviated by the addition of Trolox, thereby pointing out the role of OxS in aggravating the effects of CFTR deficiency. Our findings indicate that CFTR deficiency in combination with OxS may contribute to endocrine cell dysfunction and insulin secretion, which at least in part may explain the development of CFRD.

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