scholarly journals Aged insulin granules display reduced microtubule-dependent mobility and are disposed within actin-positive multigranular bodies

2015 ◽  
Vol 112 (7) ◽  
pp. E667-E676 ◽  
Author(s):  
Peter Hoboth ◽  
Andreas Müller ◽  
Anna Ivanova ◽  
Hassan Mziaut ◽  
Jaber Dehghany ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Glucose Homeostasis ◽  
Secretory Granules ◽  
Glucose Stimulation ◽  
Actin Depolymerization ◽  
Insulin Granules ◽  
Dependent Transport ◽  
Over Time ◽  
Dynamic Microtubule ◽  
Three Components

Insulin secretion is key for glucose homeostasis. Insulin secretory granules (SGs) exist in different functional pools, with young SGs being more mobile and preferentially secreted. However, the principles governing the mobility of age-distinct SGs remain undefined. Using the time-reporter insulin-SNAP to track age-distinct SGs we now show that their dynamics can be classified into three components: highly dynamic, restricted, and nearly immobile. Young SGs display all three components, whereas old SGs are either restricted or nearly immobile. Both glucose stimulation and F-actin depolymerization recruit a fraction of nearly immobile young, but not old, SGs for highly dynamic, microtubule-dependent transport. Moreover, F-actin marks multigranular bodies/lysosomes containing aged SGs. These data demonstrate that SGs lose their responsiveness to glucose stimulation and competence for microtubule-mediated transport over time while changing their relationship with F-actin.

Metabolic amplifying pathway increases both phases of insulin secretion independently of β-cell actin microfilaments

2010 ◽  
Vol 299 (2) ◽  
pp. C389-C398 ◽  
Author(s):  
Nizar I. Mourad ◽  
Myriam Nenquin ◽  
Jean-Claude Henquin
Keyword(s):  
Insulin Secretion ◽  
Actin Polymerization ◽  
Second Phase ◽  
Actin Microfilaments ◽  
Actin Depolymerization ◽  
Inhibitory Function ◽  
Insulin Granules ◽  
Priming Process ◽  
Underlying Mechanisms ◽  
Amplifying Pathway

Two pathways control glucose-induced insulin secretion (IS) by β-cells. The triggering pathway involves ATP-sensitive potassium (KATP) channel-dependent depolarization, Ca2+ influx, and a rise in the cytosolic Ca2+ concentration ([Ca2+]c), which triggers exocytosis of insulin granules. The metabolic amplifying pathway augments IS without further increasing [Ca2+]c. The underlying mechanisms are unknown. Here, we tested the hypothesis that amplification implicates actin microfilaments. Mouse islets were treated with latrunculin B and cytochalasin B to depolymerize actin or jasplakinolide to polymerize actin. They were then perifused to measure [Ca2+]c and IS. Metabolic amplification was studied during imposed steady elevation of [Ca2+]c by tolbutamide or KCl or by comparing the magnitude of [Ca2+]c and IS changes produced by glucose and tolbutamide. Both actin polymerization and depolymerization augmented IS triggered by all stimuli without increasing (sometimes decreasing) [Ca2+]c, which indicates a predominantly inhibitory function of microfilaments in exocytosis at a step distal to [Ca2+]c increase. When [Ca2+]c was elevated and controlled by KCl or tolbutamide, the amplifying action of glucose was facilitated by actin depolymerization and unaffected by polymerization. Both phases of IS were larger in response to high-glucose than to tolbutamide in low-glucose, although triggering [Ca2+]c was lower. This difference in IS, due to amplification, persisted when the IS rate was doubled by actin depolymerization or polymerization. In conclusion, metabolic amplification is rapid and influences the first as well as the second phase of IS. It is a late step of stimulus-secretion coupling, which does not require functional actin microfilaments and could correspond to acceleration of the priming process conferring release competence to insulin granules.

scholarly journals Pancreatic β-cell specific deletion of VPS41 causes diabetes due to defects in insulin secretion

2020 ◽  
Author(s):  
Ada Admin ◽  
Christian H. Burns ◽  
Belinda Yau ◽  
Anjelica Rodriguez ◽  
Jenna Triplett ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Glucose Homeostasis ◽  
Transmembrane Protein ◽  
Secretory Granules ◽  
Protein Composition ◽  
Regulated Exocytosis ◽  
Specific Proteins ◽  
Pancreatic B Cells ◽  
Cytosolic Factor ◽  
Hops Complex

Insulin secretory granules (SGs) mediate the regulated secretion of insulin, which is essential for glucose homeostasis. The basic machinery responsible for this regulated exocytosis consists of specific proteins present both at the plasma membrane and on insulin SGs. The protein composition of insulin SGs thus dictates their release properties, yet the mechanisms controlling insulin SG formation, which determines this molecular composition, remain poorly understood. VPS41, a component of the endo-lysosomal tethering HOPS complex, was recently identified as a cytosolic factor involved in the formation of neuroendocrine and neuronal granules. We now find that VPS41 is required for insulin SG biogenesis and regulated insulin secretion. Loss of VPS41 in pancreatic b-cells leads to a reduction in insulin SG number, changes in their transmembrane protein composition, and defects in granule regulated exocytosis. Exploring a human point mutation, identified in patients with neurological but no endocrine defects, we show that the effect on SG formation is independent of HOPS complex formation. Finally, we report that mice with a deletion of VPS41 specifically in β-cells develop diabetes due to severe depletion of insulin SG content and a defect in insulin secretion. In sum, our data demonstrate that VPS41 contributes to glucose homeostasis and metabolism.

scholarly journals Granuphilin Modulates the Exocytosis of Secretory Granules through Interaction with Syntaxin 1a

2002 ◽  
Vol 22 (15) ◽  
pp. 5518-5526 ◽  
Author(s):  
Seiji Torii ◽  
Shengli Zhao ◽  
Zhaohong Yi ◽  
Toshiyuki Takeuchi ◽  
Tetsuro Izumi
Keyword(s):  
Insulin Secretion ◽  
Pancreatic Beta Cells ◽  
Endocrine Cells ◽  
Secretory Granules ◽  
Syntaxin 1A ◽  
Open Conformation ◽  
High K ◽  
Insulin Granules ◽  
Basal Insulin Secretion ◽  
Dense Core Granules

ABSTRACT The molecular mechanism for the regulated exocytosis of dense-core granules in endocrine cells remains relatively uncharacterized compared to that of synaptic vesicles in neurons. A novel set of Rab and its effector, Rab27a/granuphilin, which is localized on insulin granules in pancreatic beta cells, was recently identified. Here we demonstrate that granuphilin directly binds to syntaxin 1a on the plasma membrane, and this interaction is regulated by Rab27a. Granuphilin shows affinity to syntaxin 1a with a closed conformation but not to mutant syntaxin 1a, which adopts an open conformation constitutively. Overexpression of granuphilin significantly enhances basal insulin secretion but profoundly inhibits high K+-induced insulin secretion. The effect of granuphilin on insulin secretion was impaired by its mutation that disrupts the binding to either Rab27a or syntaxin 1a. Thus, granuphilin is the first regulator in the exocytotic pathway that functions by directly connecting two critical vesicle transport proteins, Rab and SNARE.

scholarly journals α-Synuclein binds the KATP channel at insulin-secretory granules and inhibits insulin secretion

2011 ◽  
Vol 300 (2) ◽  
pp. E276-E286 ◽  
Author(s):  
Xuehui Geng ◽  
Haiyan Lou ◽  
Jian Wang ◽  
Lehong Li ◽  
Alexandra L. Swanson ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Secretory Granules ◽  
Cell Types ◽  
Β Cells ◽  
Glucose Stimulation ◽  
Transmission Electron ◽  
Parkinson’S Diseases ◽  
Granule Density ◽  
Numerous Cell ◽  
Glucose Stimulated Insulin Secretion

α-Synuclein has been studied in numerous cell types often associated with secretory processes. In pancreatic β-cells, α-synuclein might therefore play a similar role by interacting with organelles involved in insulin secretion. We tested for α-synuclein localizing to insulin-secretory granules and characterized its role in glucose-stimulated insulin secretion. Immunohistochemistry and fluorescent sulfonylureas were used to test for α-synuclein localization to insulin granules in β-cells, immunoprecipitation with Western blot analysis for interaction between α-synuclein and KATP channels, and ELISA assays for the effect of altering α-synuclein expression up or down on insulin secretion in INS1 cells or mouse islets, respectively. Differences in cellular phenotype between α-synuclein knockout and wild-type β-cells were found by using confocal microscopy to image the fluorescent insulin biosensor Ins-C-emGFP and by using transmission electron microscopy. The results show that anti-α-synuclein antibodies labeled secretory organelles within β-cells. Anti-α-synuclein antibodies colocalized with KATP channel, anti-insulin, and anti-C-peptide antibodies. α-Synuclein coimmunoprecipitated in complexes with KATP channels. Expression of α-synuclein downregulated insulin secretion at 2.8 mM glucose with little effect following 16.7 mM glucose stimulation. α-Synuclein knockout islets upregulated insulin secretion at 2.8 and 8.4 mM but not 16.7 mM glucose, consistent with the depleted insulin granule density at the β-cell surface membranes observed in these islets. These findings demonstrate that α-synuclein interacts with KATP channels and insulin-secretory granules and functionally acts as a brake on secretion that glucose stimulation can override. α-Synuclein might play similar roles in diabetes as it does in other degenerative diseases, including Alzheimer's and Parkinson's diseases.

scholarly journals Pancreatic beta-cell specific deletion of VPS41 causes diabetes due to defects in insulin secretion

2020 ◽  
Author(s):  
Christian H. Burns ◽  
Belinda Yau ◽  
Anjelica Rodriguez ◽  
Jenna Triplett ◽  
Drew Maslar ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Glucose Homeostasis ◽  
Transmembrane Protein ◽  
Secretory Granules ◽  
Pancreatic Beta Cell ◽  
Protein Composition ◽  
Β Cells ◽  
Regulated Exocytosis ◽  
Specific Proteins ◽  
Hops Complex

AbstractInsulin secretory granules (SGs) mediate the regulated secretion of insulin, which is essential for glucose homeostasis. The basic machinery responsible for this regulated exocytosis consists of specific proteins present both at the plasma membrane and on insulin SGs. The protein composition of insulin SGs thus dictates their release properties, yet the mechanisms controlling insulin SG formation, which determines this molecular composition, remain poorly understood. VPS41, a component of the endo-lysosomal tethering HOPS complex, was recently identified as a cytosolic factor involved in the formation of neuroendocrine and neuronal granules. We now find that VPS41 is required for insulin SG biogenesis and regulated insulin secretion. Loss of VPS41 in pancreatic β-cells leads to a reduction in insulin SG number, changes in their transmembrane protein composition, and defects in granule regulated exocytosis. Exploring a human point mutation, identified in patients with neurological but no endocrine defects, we show that the effect on SG formation is independent of HOPS complex formation. Finally, we report that mice with a deletion of VPS41 specifically in β-cells develop diabetes due to severe depletion of insulin SG content and a defect in insulin secretion. In sum, our data demonstrate that VPS41 contributes to glucose homeostasis and metabolism.

Pancreatic β-cell specific deletion of VPS41 causes diabetes due to defects in insulin secretion

2020 ◽  
Author(s):  
Ada Admin ◽  
Christian H. Burns ◽  
Belinda Yau ◽  
Anjelica Rodriguez ◽  
Jenna Triplett ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Glucose Homeostasis ◽  
Transmembrane Protein ◽  
Secretory Granules ◽  
Protein Composition ◽  
Regulated Exocytosis ◽  
Specific Proteins ◽  
Pancreatic B Cells ◽  
Cytosolic Factor ◽  
Hops Complex

Insulin secretory granules (SGs) mediate the regulated secretion of insulin, which is essential for glucose homeostasis. The basic machinery responsible for this regulated exocytosis consists of specific proteins present both at the plasma membrane and on insulin SGs. The protein composition of insulin SGs thus dictates their release properties, yet the mechanisms controlling insulin SG formation, which determines this molecular composition, remain poorly understood. VPS41, a component of the endo-lysosomal tethering HOPS complex, was recently identified as a cytosolic factor involved in the formation of neuroendocrine and neuronal granules. We now find that VPS41 is required for insulin SG biogenesis and regulated insulin secretion. Loss of VPS41 in pancreatic b-cells leads to a reduction in insulin SG number, changes in their transmembrane protein composition, and defects in granule regulated exocytosis. Exploring a human point mutation, identified in patients with neurological but no endocrine defects, we show that the effect on SG formation is independent of HOPS complex formation. Finally, we report that mice with a deletion of VPS41 specifically in β-cells develop diabetes due to severe depletion of insulin SG content and a defect in insulin secretion. In sum, our data demonstrate that VPS41 contributes to glucose homeostasis and metabolism.

scholarly journals Purification of age-distinct insulin secretory granules through antigen restriction using the CLIP-tag

2020 ◽  
Author(s):  
Martin Neukam ◽  
Katharina Ganß ◽  
Jovana Vasiljević ◽  
Johannes Broichhagen ◽  
Kai Johnsson ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Insulin Secretion ◽  
Beta Cells ◽  
Solid Phase ◽  
Secretory Granules ◽  
Islet Beta Cells ◽  
Temporal Variables ◽  
Pancreatic Islet Beta Cells ◽  
Insulin Granules ◽  
Insulin Granule

AbstractPancreatic islet beta cells employ secretory granules for the storage and glucose-stimulated release of the hormone insulin. The competence of an insulin granule for exocytosis depends on spatial and temporal variables such as its proximity to the plasma membrane as well as its age, with newly-generated granules being preferentially released. The molecular underpinnings for the control of these variables remain largely unknown and their uncovering is of high relevance for the study of diabetes, which results from deficient insulin secretion. However, we still lack a comprehensive view about the molecular composition of the insulin granules and how this may change over their lifetime. Here we report a strategy for the background-free purification of insulin secretory granules of distinct age from insulinoma INS-1 cells. We show that utilization of an immuno-based affinity approach for pulse-chase labeled insulin secretory granules, produces a highly enriched granular fraction. Our approach precludes typical contaminants from the solid phase and may be designed to purify secretory granules of a distinct age.

scholarly journals Pancreatic β-cell specific deletion of VPS41 causes diabetes due to defects in insulin secretion

2020 ◽  
Author(s):  
Ada Admin ◽  
Christian H. Burns ◽  
Belinda Yau ◽  
Anjelica Rodriguez ◽  
Jenna Triplett ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Glucose Homeostasis ◽  
Transmembrane Protein ◽  
Secretory Granules ◽  
Protein Composition ◽  
Regulated Exocytosis ◽  
Specific Proteins ◽  
Pancreatic B Cells ◽  
Cytosolic Factor ◽  
Hops Complex

Insulin secretory granules (SGs) mediate the regulated secretion of insulin, which is essential for glucose homeostasis. The basic machinery responsible for this regulated exocytosis consists of specific proteins present both at the plasma membrane and on insulin SGs. The protein composition of insulin SGs thus dictates their release properties, yet the mechanisms controlling insulin SG formation, which determines this molecular composition, remain poorly understood. VPS41, a component of the endo-lysosomal tethering HOPS complex, was recently identified as a cytosolic factor involved in the formation of neuroendocrine and neuronal granules. We now find that VPS41 is required for insulin SG biogenesis and regulated insulin secretion. Loss of VPS41 in pancreatic b-cells leads to a reduction in insulin SG number, changes in their transmembrane protein composition, and defects in granule regulated exocytosis. Exploring a human point mutation, identified in patients with neurological but no endocrine defects, we show that the effect on SG formation is independent of HOPS complex formation. Finally, we report that mice with a deletion of VPS41 specifically in β-cells develop diabetes due to severe depletion of insulin SG content and a defect in insulin secretion. In sum, our data demonstrate that VPS41 contributes to glucose homeostasis and metabolism.

scholarly journals Pancreatic β-cell specific deletion of VPS41 causes diabetes due to defects in insulin secretion

2020 ◽  
Author(s):  
Ada Admin ◽  
Christian H. Burns ◽  
Belinda Yau ◽  
Anjelica Rodriguez ◽  
Jenna Triplett ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Glucose Homeostasis ◽  
Transmembrane Protein ◽  
Secretory Granules ◽  
Protein Composition ◽  
Regulated Exocytosis ◽  
Specific Proteins ◽  
Pancreatic B Cells ◽  
Cytosolic Factor ◽  
Hops Complex

Insulin secretory granules (SGs) mediate the regulated secretion of insulin, which is essential for glucose homeostasis. The basic machinery responsible for this regulated exocytosis consists of specific proteins present both at the plasma membrane and on insulin SGs. The protein composition of insulin SGs thus dictates their release properties, yet the mechanisms controlling insulin SG formation, which determines this molecular composition, remain poorly understood. VPS41, a component of the endo-lysosomal tethering HOPS complex, was recently identified as a cytosolic factor involved in the formation of neuroendocrine and neuronal granules. We now find that VPS41 is required for insulin SG biogenesis and regulated insulin secretion. Loss of VPS41 in pancreatic b-cells leads to a reduction in insulin SG number, changes in their transmembrane protein composition, and defects in granule regulated exocytosis. Exploring a human point mutation, identified in patients with neurological but no endocrine defects, we show that the effect on SG formation is independent of HOPS complex formation. Finally, we report that mice with a deletion of VPS41 specifically in β-cells develop diabetes due to severe depletion of insulin SG content and a defect in insulin secretion. In sum, our data demonstrate that VPS41 contributes to glucose homeostasis and metabolism.

Sign in / Sign up

Export Citation Format

Share Document