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 cAMP-Mediated and Metabolic Amplification of Insulin Secretion Are Distinct Pathways Sharing Independence of β-Cell Microfilaments

Endocrinology ◽  
2012 ◽  
Vol 153 (10) ◽  
pp. 4644-4654 ◽  
Author(s):  
Nizar I. Mourad ◽  
Myriam Nenquin ◽  
Jean-Claude Henquin
Keyword(s):  
Insulin Secretion ◽  
Actin Polymerization ◽  
Cytosolic Calcium ◽  
Actin Microfilaments ◽  
Insulin Granules ◽  
Adenylate Cyclase Stimulation ◽  
Mouse Islets ◽  
Glucagon Like Peptide ◽  
Glucagon Like Peptide 1 ◽  
Camp Levels

Abstract Insulin secretion is triggered by an increase in the cytosolic calcium concentration ([Ca2+]c) in β-cells. Ca2+-induced exocytosis of insulin granules can be augmented by metabolic amplification (unknown signals generated through glucose metabolism) or neurohormonal amplification (in particular cAMP mediated). Functional actin microfilaments are not required for metabolic amplification, but their possible role in cAMP-mediated amplification is unknown. It is also uncertain whether cAMP (generated in response to glucose) is implicated in metabolic amplification. These questions were addressed using isolated mouse islets. cAMP levels were increased by phosphodiesterase inhibition (with isobutylmethylxanthine) and adenylate-cyclase stimulation (with forskolin or glucagon-like peptide-1, 7-36 amide). Raising cAMP levels had no steady-state impact on actin polymerization in control islets. Neither disruption (depolymerization by latrunculin) nor stabilization (polymerization by jasplakinolide) of actin microfilaments was counteracted by cAMP. Both changes increased both phases of glucose- or tolbutamide-induced insulin secretion but did not prevent further amplification by cAMP. These large changes in secretion were not caused by changes in [Ca2+]c, which was only slightly increased by cAMP. Both phases of insulin secretion were larger in response to glucose than tolbutamide, although [Ca2+]c was lower. This difference in secretion, which reflects metabolic amplification, was independent of microfilaments, was not attributable to differences in cAMP, and persisted in presence of dibutyryl-cAMP or when cAMP levels were variably raised by isobutylmethylxanthine + forskolin or glucagon-like peptide-1, 7-36 amide. We conclude that metabolic and cAMP-mediated amplification of insulin secretion are distinct pathways that accelerate acquisition of release competence by insulin granules that can access exocytotic sites without intervention of microfilaments.

Metabolic amplification of insulin secretion by glucose is independent of β-cell microtubules

2011 ◽  
Vol 300 (3) ◽  
pp. C697-C706 ◽  
Author(s):  
Nizar I. Mourad ◽  
Myriam Nenquin ◽  
Jean-Claude Henquin
Keyword(s):  
Insulin Secretion ◽  
Microtubule Disruption ◽  
Insulin Granules ◽  
Priming Process ◽  
Previous Proposal ◽  
Mouse Islets ◽  
Second Phases ◽  
Channel Dependent ◽  
Amplifying Pathway ◽  
Small Inhibition

Glucose-induced insulin secretion (IS) by β-cells is controlled by two pathways. The triggering pathway involves ATP-sensitive potassium (KATP) channel-dependent depolarization, Ca2+ influx, and 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. After exclusion of the contribution of actin microfilaments, we here tested whether amplification implicates microtubule-dependent granule mobilization. Mouse islets were treated with nocodazole or taxol, which completely depolymerized and polymerized tubulin. 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 [Ca2+]c and IS responses to glucose and tolbutamide. Nocodazole did not alter [Ca2+]c or IS changes induced by the three secretagogues, whereas taxol caused a small inhibition of IS that is partly ascribed to a decrease in [Ca2+]c. When [Ca2+]c was elevated and controlled by KCl or tolbutamide, the amplifying action of glucose was unaffected by microtubule disruption or stabilization. Both phases of IS were larger in response to glucose than tolbutamide, although triggering [Ca2+]c was lower. This difference, due to amplification, persisted in nocodazole- or taxol-treated islets, even when IS was augmented fourfold by microfilament disruption with cytochalasin B or latrunculin B. In conclusion, metabolic amplification rapidly augments first and second phases of IS independently of insulin granule translocation along microtubules. We therefore extend our previous proposal that it does not implicate the cytoskeleton but corresponds to acceleration of the priming process conferring release competence to insulin granules.

scholarly journals Insulin secretion in islets from mice with a double knockout for the dense core vesicle proteins islet antigen-2 (IA-2) and IA-2β

2007 ◽  
Vol 196 (3) ◽  
pp. 573-581 ◽  
Author(s):  
Jean-Claude Henquin ◽  
Myriam Nenquin ◽  
Andras Szollosi ◽  
Atsutaka Kubosaki ◽  
Abner Louis Notkins
Keyword(s):  
Insulin Secretion ◽  
Cell Function ◽  
Dense Core ◽  
Second Phase ◽  
Dense Core Vesicle ◽  
Double Knockout ◽  
Insulin Granules ◽  
Β Cell Function ◽  
Channel Dependent ◽  
Islet Antigen

Islet antigen-2 (IA-2 or ICA 512) and IA-2β (or phogrin) are major autoantigens in type 1 diabetes. They are located in dense core secretory vesicles including insulin granules, but their role in β-cell function is unclear. Targeted disruption of either IA-2 or IA-2β, or both, impaired glucose tolerance, an effect attributed to diminution of insulin secretion. In this study, we therefore characterized the dynamic changes in cytosolic Ca2+([Ca2+]c) and insulin secretion in islets from IA-2/IA-2β double knockout (KO) mice. High glucose (15 mM) induced biphasic insulin secretion in IA-2/IA-2β KO islets, with a similar first phase and smaller second phase compared with controls. Since the insulin content of IA-2/IA-2β KO islets was ∼45% less than that of controls, fractional insulin secretion (relative to content) was thus increased during first phase and unaffected during second phase. This peculiar response occurred in spite of a slightly smaller rise in [Ca2+]c, could not be attributed to an alteration of glucose metabolism (NADPH fluorescence) and also was observed with tolbutamide. The dual control of insulin secretion via the KATP channel-dependent triggering pathway and KATP channel-independent amplifying pathway was unaltered in IA-2/IA-2β KO islets, and so were the potentiations by acetylcholine or cAMP (forskolin). Intriguingly, amino acids, in particular the cationic arginine and lysine, induced larger fractional insulin secretion in IA-2/IA-2β KO than control islets. In conclusion, IA-2 and IA-2β are dispensable for exocytosis of insulin granules, but are probably more important for cargo loading and/or stability of dense core vesicles.

Amino acid metabolism, insulin secretion and diabetes

2007 ◽  
Vol 35 (5) ◽  
pp. 1180-1186 ◽  
Author(s):  
P. Newsholme ◽  
K. Bender ◽  
A. Kiely ◽  
L. Brennan
Keyword(s):  
Amino Acids ◽  
Insulin Secretion ◽  
Insulin Granules ◽  
Chain Acyl ◽  
Mitochondrial Origin ◽  
Cellular Integrity ◽  
Amplifying Pathway ◽  
Influence Gene Expression

In addition to the primary stimulus of glucose, specific amino acids may acutely and chronically regulate insulin secretion from pancreatic β-cells in vivo and in vitro. Mitochondrial metabolism is crucial for the coupling of glucose, alanine, glutamine and glutamate recognition with exocytosis of insulin granules. This is illustrated by in vitro and in vivo observations discussed in the present review. Mitochondria generate ATP (the main coupling messenger in insulin secretion) and other factors that serve as sensors for the control of the exocytotic process. The main factors that mediate the key amplifying pathway over the Ca2+ signal in nutrient-stimulated insulin secretion are nucleotides (ATP, GTP, cAMP and NADPH), although metabolites have also been proposed, such as long-chain acyl-CoA derivatives and glutamate. In addition, after chronic exposure, specific amino acids may influence gene expression in the β-cell, which have an impact on insulin secretion and cellular integrity. Therefore amino acids may play a direct or indirect (via generation of putative messengers of mitochondrial origin) role in insulin secretion.

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.

Relative importance of first- and second-phase insulin secretion in glucose homeostasis in conscious dog. II. Effects on gluconeogenesis

Diabetes ◽  
1986 ◽  
Vol 35 (7) ◽  
pp. 776-784 ◽  
Author(s):  
K. E. Steiner ◽  
S. M. Mouton ◽  
P. E. Williams ◽  
W. W. Lacy ◽  
A. D. Cherrington
Keyword(s):  
Insulin Secretion ◽  
Glucose Homeostasis ◽  
Second Phase ◽  
Relative Importance ◽  
Conscious Dog

scholarly journals The Capacity to Secrete Insulin Is Dose-Dependent to Extremely High Glucose Concentrations: A Key Role for Adenylyl Cyclase

Metabolites ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 401
Author(s):  
Katherine M. Gerber ◽  
Nicholas B. Whitticar ◽  
Daniel R. Rochester ◽  
Kathryn L. Corbin ◽  
William J. Koch ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Adenylyl Cyclase ◽  
Human Islets ◽  
Adenylyl Cyclase Activity ◽  
World Record ◽  
Glucokinase Activator ◽  
Amplifying Pathway ◽  
Dose Dependent ◽  
Adenylyl Cyclase Inhibitor ◽  
Cyclase Activator

Insulin secretion is widely thought to be maximally stimulated in glucose concentrations of 16.7-to-30 mM (300-to-540 mg/dL). However, insulin secretion is seldom tested in hyperglycemia exceeding these levels despite the Guinness World Record being 147.6 mM (2656 mg/dL). We investigated how islets respond to 1-h exposure to glucose approaching this record. Insulin secretion from human islets at 12 mM glucose intervals dose-dependently increased until at least 72 mM glucose. Murine islets in 84 mM glucose secreted nearly double the insulin as in 24 mM (p < 0.001). Intracellular calcium was maximally stimulated in 24 mM glucose despite a further doubling of insulin secretion in higher glucose, implying that insulin secretion above 24 mM occurs through amplifying pathway(s). Increased osmolarity of 425-mOsm had no effect on insulin secretion (1-h exposure) or viability (48-h exposure) in murine islets. Murine islets in 24 mM glucose treated with a glucokinase activator secreted as much insulin as islets in 84 mM glucose, indicating that glycolytic capacity exists above 24 mM. Using an incretin mimetic and an adenylyl cyclase activator in 24 mM glucose enhanced insulin secretion above that observed in 84 mM glucose while adenylyl cyclase inhibitor reduced stimulatory effects. These results highlight the underestimated ability of islets to secrete insulin proportionally to extreme hyperglycemia through adenylyl cyclase activity.

scholarly journals What Is the Metabolic Amplification of Insulin Secretion and Is It (Still) Relevant?

Metabolites ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 355
Author(s):  
Ingo Rustenbeck ◽  
Torben Schulze ◽  
Mai Morsi ◽  
Mohammed Alshafei ◽  
Uwe Panten
Keyword(s):  
Insulin Secretion ◽  
Beta Cell ◽  
Adenine Nucleotides ◽  
Pancreatic Beta Cell ◽  
Secretory Response ◽  
Mitochondrial Activity ◽  
Insulin Synthesis ◽  
Sequence Of Events ◽  
Insulin Granules

The pancreatic beta-cell transduces the availability of nutrients into the secretion of insulin. While this process is extensively modified by hormones and neurotransmitters, it is the availability of nutrients, above all glucose, which sets the process of insulin synthesis and secretion in motion. The central role of the mitochondria in this process was identified decades ago, but how changes in mitochondrial activity are coupled to the exocytosis of insulin granules is still incompletely understood. The identification of ATP-sensitive K+-channels provided the link between the level of adenine nucleotides and the electrical activity of the beta cell, but the depolarization-induced Ca2+-influx into the beta cells, although necessary for stimulated secretion, is not sufficient to generate the secretion pattern as produced by glucose and other nutrient secretagogues. The metabolic amplification of insulin secretion is thus the sequence of events that enables the secretory response to a nutrient secretagogue to exceed the secretory response to a purely depolarizing stimulus and is thus of prime importance. Since the cataplerotic export of mitochondrial metabolites is involved in this signaling, an orienting overview on the topic of nutrient secretagogues beyond glucose is included. Their judicious use may help to define better the nature of the signals and their mechanism of action.

scholarly journals PWD/PhJ and WSB/EiJ Mice Are Resistant to Diet-Induced Obesity But Have Abnormal Insulin Secretion

Endocrinology ◽  
2011 ◽  
Vol 152 (8) ◽  
pp. 3005-3017 ◽  
Author(s):  
Katie T. Y. Lee ◽  
Subashini Karunakaran ◽  
Maggie M. Ho ◽  
Susanne M. Clee
Keyword(s):  
Insulin Secretion ◽  
Insulin Sensitivity ◽  
Large Scale ◽  
Mouse Strains ◽  
Second Phase ◽  
Fasting Insulin ◽  
High Fat ◽  
Diet Induced Obesity ◽  
Obesity And Diabetes

Recently, novel inbred mouse strains that are genetically distinct from the commonly used models have been developed from wild-caught mice. These wild-derived inbred strains have been included in many of the large-scale genomic projects, but their potential as models of altered obesity and diabetes susceptibility has not been assessed. We examined obesity and diabetes-related traits in response to high-fat feeding in two of these strains, PWD/PhJ (PWD) and WSB/EiJ (WSB), in comparison with C57BL/6J (B6). Young PWD mice displayed high fasting insulin levels, although they had normal insulin sensitivity. PWD mice subsequently developed a much milder and delayed-onset obesity compared with B6 mice but became as insulin resistant. PWD mice had a robust first-phase and increased second-phase glucose-stimulated insulin secretion in vivo, rendering them more glucose tolerant. WSB mice were remarkably resistant to diet-induced obesity and maintained very low fasting insulin throughout the study. WSB mice exhibited more rapid glucose clearance in response to an insulin challenge compared with B6 mice, consistent with their low percent body fat. Interestingly, in the absence of a measurable in vivo insulin secretion, glucose tolerance of WSB mice was better than B6 mice, likely due to their enhanced insulin sensitivity. Thus PWD and WSB are two obesity-resistant strains with unique insulin secretion phenotypes. PWD mice are an interesting model that dissociates hyperinsulinemia from obesity and insulin resistance, whereas WSB mice are a model of extraordinary resistance to a high-fat diet.

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