Cell-wide analysis of secretory granule dynamics in three dimensions in living pancreatic β-cells: evidence against a role for AMPK-dependent phosphorylation of KLC1 at Ser517/Ser520 in glucose-stimulated insulin granule movement

2010 ◽  
Vol 38 (1) ◽  
pp. 205-208 ◽  
Author(s):  
Angela McDonald ◽  
Sarah Fogarty ◽  
Isabelle Leclerc ◽  
Elaine V. Hill ◽  
D. Grahame Hardie ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Glutathione Transferase ◽  
Three Dimensions ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Glucose Levels ◽  
Insulin Granules ◽  
Elevated Glucose ◽  
Glucose Stimulated Insulin Secretion

Glucose-stimulated insulin secretion from pancreatic β-cells requires the kinesin-1/Kif5B-mediated transport of insulin granules along microtubules. 5′-AMPK (5′-AMP-activated protein kinase) is a heterotrimeric serine/threonine kinase which is activated in β-cells at low glucose concentrations, but inhibited as glucose levels increase. Active AMPK blocks glucose-stimulated insulin secretion and the recruitment of insulin granules to the cell surface, suggesting motor proteins may be targets for this kinase. While both kinesin-1/Kif5B and KLC1 (kinesin light chain-1) contain consensus AMPK phosphorylation sites (Thr693 and Ser520, respectively) only recombinant GST (glutathione transferase)–KLC1 was phosphorylated by purified AMPK in vitro. To test the hypothesis that phosphorylation at this site may modulate kinesin-1-mediated granule movement, we developed an approach to study the dynamics of all the resolvable granules within a cell in three dimensions. This cell-wide approach revealed that the number of longer excursions (>10 μm) increased significantly in response to elevated glucose concentration (30 versus 3 mM) in control MIN6 β-cells. However, similar changes were seen in cells overexpressing wild-type KLC1, phosphomimetic (S517D/S520D) or non-phosphorylatable (S517A/S520A) mutants of KLC1. Thus, changes in the phosphorylation state of KLC1 at Ser517/Ser520 seem unlikely to affect motor function.

scholarly journals Teucrium polium: Potential Drug Source for Type 2 Diabetes Mellitus

Biology ◽  
2022 ◽  
Vol 11 (1) ◽  
pp. 128
Author(s):  
Yaser Albadr ◽  
Andrew Crowe ◽  
Rima Caccetta
Keyword(s):  
Diabetes Mellitus ◽  
Type 2 Diabetes ◽  
Type 2 Diabetes Mellitus ◽  
Insulin Secretion ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Glucose Levels ◽  
Teucrium Polium

The prevalence of type 2 diabetes mellitus is rising globally and this disease is proposed to be the next pandemic after COVID-19. Although the cause of type 2 diabetes mellitus is unknown, it is believed to involve a complex array of genetic defects that affect metabolic pathways which eventually lead to hyperglycaemia. This hyperglycaemia arises from an inability of the insulin-sensitive cells to sufficiently respond to the secreted insulin, which eventually results in the inadequate secretion of insulin from pancreatic β-cells. Several treatments, utilising a variety of mechanisms, are available for type 2 diabetes mellitus. However, more medications are needed to assist with the optimal management of the different stages of the disease in patients of varying ages with the diverse combinations of other medications co-administered. Throughout modern history, some lead constituents from ancient medicinal plants have been investigated extensively and helped in developing synthetic antidiabetic drugs, such as metformin. Teucrium polium L. (Tp) is a herb that has a folk reputation for its antidiabetic potential. Previous studies indicate that Tp extracts significantly decrease blood glucose levels r and induce insulin secretion from pancreatic β-cells in vitro. Nonetheless, the constituent/s responsible for this action have not yet been elucidated. The effects appear to be, at least in part, attributable to the presence of selected flavonoids (apigenin, quercetin, and rutin). This review aims to examine the reported glucose-lowering effect of the herb, with a keen focus on insulin secretion, specifically related to type 2 diabetes mellitus. An analysis of the contribution of the key constituent flavonoids of Tp extracts will also be discussed.

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 Increased Slc12a1 expression in β-cells and improved glucose disposal in Slc12a2 heterozygous mice

2015 ◽  
Vol 227 (3) ◽  
pp. 153-165 ◽  
Author(s):  
Saeed Alshahrani ◽  
Mohammed Mashari Almutairi ◽  
Shams Kursan ◽  
Eduardo Dias-Junior ◽  
Mohamed Mahmoud Almiahuob ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Insulin Response ◽  
Chloride Concentration ◽  
Glucose Disposal ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Glucose Levels ◽  
Fasting Glycemia ◽  
Blood Glucose Levels ◽  
Glucose Stimulated Insulin Secretion

The products of theSlc12a1andSlc12a2genes, commonly known as Na+-dependent K+2Cl−co-transporters NKCC2 and NKCC1, respectively, are the targets for the diuretic bumetanide. NKCCs are implicated in the regulation of intracellular chloride concentration ([Cl−]i) in pancreatic β-cells, and as such, they may play a role in glucose-stimulated plasma membrane depolarization and insulin secretion. Unexpectedly, permanent elimination of NKCC1 does not preclude insulin secretion, an event potentially linked to the homeostatic regulation of additional Cl−transporters expressed in β-cells. In this report we provide evidence for such a mechanism. Mice lacking a single allele ofSlc12a2exhibit lower fasting glycemia, increased acute insulin response (AIR) and lower blood glucose levels 15–30 min after a glucose load when compared to mice harboring both alleles of the gene. Furthermore, heterozygous expression or complete absence ofSlc12a2associates with increased NKCC2 protein expression in rodent pancreatic β-cells. This has been confirmed by using chronic pharmacological down-regulation of NKCC1 with bumetanide in the mouse MIN6 β-cell line or permanent molecular silencing of NKCC1 in COS7 cells, which results in increased NKCC2 expression. Furthermore, MIN6 cells chronically pretreated with bumetanide exhibit increased initial rates of Cl−uptake while preserving glucose-stimulated insulin secretion. Together, our results suggest that NKCCs are involved in insulin secretion and that a singleSlc12a2allele may protect β-cells from failure due to increased homeostatic expression ofSlc12a1.

scholarly journals In pancreatic β-cells myosin 1b regulates glucose-stimulated insulin secretion by modulating an early step in insulin granule trafficking from the Golgi

2021 ◽  
pp. mbc.E21-03-0094
Author(s):  
Hiroshi Tokuo ◽  
Shigeru Komaba ◽  
Lynne M. Coluccio
Keyword(s):  
Insulin Secretion ◽  
Islet Cells ◽  
Early Stage ◽  
Secretory Granules ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Glucose Levels ◽  
Insulin Granule ◽  
Glucose Stimulated Insulin Secretion ◽  
Insulinoma Cells

Pancreatic β-cells secrete insulin, which controls blood glucose levels, and defects in insulin secretion are responsible for diabetes mellitus. The actin cytoskeleton and some myosins support insulin granule trafficking and release, although a role for the class I myosin Myo1b, an actin- and membrane-associated load-sensitive motor, in insulin biology is unknown. We found by immunohistochemistry that Myo1b is expressed in islet cells of rat pancreas. In cultured rat insulinoma 832/13 cells Myo1b localized near actin patches, the trans-Golgi network (TGN) marker TGN38, and insulin granules in the perinuclear region. Myo1b depletion by siRNA in 832/13 cells reduced intracellular proinsulin and insulin content and glucose-stimulated insulin secretion (GSIS), and led to the accumulation of (pro)insulin SGs at the TGN. Using an in situ fluorescent pulse-chase strategy to track nascent proinsulin (Bearrows et al., 2019), Myo1b depletion in insulinoma cells reduced the number of (pro)insulin-containing secretory granules budding from the TGN. The studies indicate for the first time that in pancreatic β-cells Myo1b controls GSIS at least in part by mediating an early stage in insulin granule trafficking from the TGN.

scholarly journals Redox Signaling is Essential for Insulin Secretion

2021 ◽  
Author(s):  
Petr Ježek ◽  
Blanka Holendová ◽  
Martin Jabůrek ◽  
Jan Tauber ◽  
Andrea Dlasková ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Insulin Secretion ◽  
Redox Signaling ◽  
H2o2 Production ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Nadph Oxidase 4 ◽  
Elevated Glucose ◽  
Branched Chain ◽  
Glucose Stimulated Insulin Secretion

In this review, we place redox signaling in pancreatic β-cells to the context with signaling pathways leading to insulin secretion, acting for example upon the action of incretins (GLP-1, GIP) and the metabotropic receptor GPR40. Besides a brief description of ion channel participation in depolarization/repolarization of the plasma membrane, we emphasize a prominent role of the elevated glucose level in pancreatic β-cells during glucose-stimulated insulin secretion (GSIS). We focus on our recent findings, which revealed that for GSIS, not only elevated ATP synthesis is required, but also fundamental redox signaling originating from the NADPH oxidase 4- (NOX4-) mediated H2O2 production. We hypothesized that the closing of the ATP-sensitive K+ channel (KATP) is only possible when both ATP plus H2O2 are elevated in INS-1E cells. KATP alone or with synergic channels provides an element of logical sum, integrating both metabolic plus redox homeostasis. This is also valid for other secretagogues, such as branched chain ketoacids (BCKAs); and partly for fatty acids (FAs). Branched chain aminoacids, leucine, valine and isoleucine, after being converted to BCKAs are metabolized by a series of reactions resembling β-oxidation of FAs. This increases superoxide formation in mitochondria, including its portion elevated due to the function of electron transfer flavoprotein ubiquinone oxidoreductase (ETF:QOR). After superoxide conversion to H2O2 the oxidation of BCKAs provides the mitochondrial redox signaling extending up to the plasma membrane to induce its depolarization together with the elevated ATP. In contrast, experimental FA-stimulated insulin secretion in the presence of non-stimulating glucose concentrations is predominantly mediated by GPR40, for which intramitochondrial redox signaling activates phospholipase iPLA2γ, cleaving free FAs from mitochondrial membranes, which diffuse to the plasma membrane and largely amplify the GPR40 response. These events are concomitant to the insulin release due to the metabolic component. Hypothetically, redox signaling may proceed by simple H2O2 diffusion or via an SH-relay enabled by peroxiredoxins to target proteins. However, these aspects have yet to be elucidated.

scholarly journals Kisspeptin-Activated Autophagy Independently Suppresses Non-Glucose-Stimulated Insulin Secretion from Pancreatic β-Cells

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Chien Huang ◽  
Hao-Yi Wang ◽  
Mu-En Wang ◽  
Meng-Chieh Hsu ◽  
Yi-Hsieng Samuel Wu ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Insulin Granules ◽  
Autophagic Degradation ◽  
Basal Insulin Secretion ◽  
Glucose Stimulated Insulin Secretion

AbstractPrevious studies have demonstrated the important role of kisspeptin in impaired glucose-stimulated insulin secretion (GSIS). In addition, it was reported that the activation of autophagy in pancreatic β-cells decreases insulin secretion by selectively degrading insulin granules. However, it is currently unknown whether kisspeptin suppresses GSIS in β-cells by activating autophagy. To investigate the involvement of autophagy in kisspeptin–regulated insulin secretion, we overexpressed Kiss1 in NIT-1 cells to mimic the long-term exposure of pancreatic β-cells to kisspeptin during type 2 diabetes (T2D). Interestingly, our data showed that although kisspeptin potently decreases the intracellular proinsulin and insulin ((pro)insulin) content and insulin secretion of NIT-1 cells, autophagy inhibition using bafilomycin A1 and Atg5 siRNAs only rescues basal insulin secretion, not kisspeptin-impaired GSIS. We also generated a novel in vivo model to investigate the long-term exposure of kisspeptin by osmotic pump. The in vivo data demonstrated that kisspeptin lowers GSIS and (pro)insulin levels and also activated pancreatic autophagy in mice. Collectively, our data demonstrated that kisspeptin suppresses both GSIS and non-glucose-stimulated insulin secretion of pancreatic β-cells, but only non-glucose-stimulated insulin secretion depends on activated autophagic degradation of (pro)insulin. Our study provides novel insights for the development of impaired insulin secretion during T2D progression.

scholarly journals Brain-selective Kinase 2 (BRSK2) Phosphorylation on PCTAIRE1 Negatively Regulates Glucose-stimulated Insulin Secretion in Pancreatic β-Cells

2012 ◽  
Vol 287 (36) ◽  
pp. 30368-30375 ◽  
Author(s):  
Xin-Ya Chen ◽  
Xiu-Ting Gu ◽  
Hexige Saiyin ◽  
Bo Wan ◽  
Yu-Jing Zhang ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Glucose Stimulated Insulin Secretion

scholarly journals Regulation of glucokinase in pancreatic islets by prolactin: a mechanism for increasing glucose-stimulated insulin secretion during pregnancy

2007 ◽  
Vol 193 (3) ◽  
pp. 367-381 ◽  
Author(s):  
Anthony J Weinhaus ◽  
Laurence E Stout ◽  
Nicholas V Bhagroo ◽  
T Clark Brelje ◽  
Robert L Sorenson
Keyword(s):  
Insulin Secretion ◽  
Glucose Metabolism ◽  
Pancreatic Islets ◽  
Glucose Transporter ◽  
Β Cells ◽  
Glucose Transporter 2 ◽  
Underlying Mechanisms ◽  
Glucose Stimulated Insulin Secretion ◽  
Induced Changes

Glucokinase activity is increased in pancreatic islets during pregnancy and in vitro by prolactin (PRL). The underlying mechanisms that lead to increased glucokinase have not been resolved. Since glucose itself regulates glucokinase activity in β-cells, it was unclear whether the lactogen effects are direct or occur through changes in glucose metabolism. To clarify the roles of glucose metabolism in this process, we examined the interactions between glucose and PRL on glucose metabolism, insulin secretion, and glucokinase expression in insulin 1 (INS-1) cells and rat islets. Although the PRL-induced changes were more pronounced after culture at higher glucose concentrations, an increase in glucose metabolism, insulin secretion, and glucokinase expression occurred even in the absence of glucose. The presence of comparable levels of insulin secretion at similar rates of glucose metabolism from both control and PRL-treated INS-1 cells suggests the PRL-induced increase in glucose metabolism is responsible for the increase in insulin secretion. Similarly, increases in other known PRL responsive genes (e.g. the PRL receptor, glucose transporter-2, and insulin) were also detected after culture without glucose. We show that the upstream glucokinase promoter contains multiple STAT5 binding sequences with increased binding in response to PRL. Corresponding increases in glucokinase mRNA and protein synthesis were also detected. This suggests the PRL-induced increase in glucokinase mRNA and its translation are sufficient to account for the elevated glucokinase activity in β-cells with lactogens. Importantly, the increase in islet glucokinase observed with PRL is in line with that observed in islets during pregnancy.

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.

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