scholarly journals Fusion pore regulation by Epac2/cAMP controls cargo release during insulin exocytosis

2018 ◽  
Author(s):  
Alenka Gucek ◽  
Nikhil R Gandasi ◽  
Muhmmad Omar-Hmeadi ◽  
Marit Bakke ◽  
Stein O. Døskeland ◽  
...  
Keyword(s):  
Type 2 Diabetes ◽  
Transmitter Release ◽  
Fusion Pore ◽  
Hormone Release ◽  
Peptide Release ◽  
Insulin Granule ◽  
Insulin Exocytosis ◽  
Camp Elevation ◽  
Pore Expansion

AbstractRegulated exocytosis establishes a narrow fusion pore as the initial aqueous connection to the extracellular space, through which small transmitter molecules such as ATP can exit. Co-release of larger peptides and hormones like insulin requires further expansion of the pore. There is evidence that pore expansion is regulated and can fail in type-2 diabetes and neurodegenerative disease. Here we report that the cAMP-sensor Epac2 (Rap-GEF4) controls fusion pore behavior by acutely recruiting two pore-restricting proteins, amisyn and dynamin-1, to the exocytosis site in insulin-secreting beta-cells. cAMP elevation leads to pore expansion and peptide release, but not when Epac2 is inactivated pharmacologically or in Epac2-/- mice. Conversely, overexpression of Epac2 impedes pore expansion. Widely used antidiabetic drugs (GLP-1 agonists and sulfonylureas) activate this pathway and thereby paradoxically restrict hormone release. We conclude that Epac2/cAMP controls fusion pore expansion and thus the balance of hormone and transmitter release during insulin granule exocytosis.

scholarly journals Fusion pore regulation by cAMP/Epac2 controls cargo release during insulin exocytosis

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Alenka Guček ◽  
Nikhil R Gandasi ◽  
Muhmmad Omar-Hmeadi ◽  
Marit Bakke ◽  
Stein O Døskeland ◽  
...  
Keyword(s):  
Beta Cells ◽  
Transmitter Release ◽  
Extracellular Space ◽  
Fusion Pore ◽  
Hormone Release ◽  
Peptide Release ◽  
Insulin Granule ◽  
Insulin Exocytosis ◽  
Camp Elevation ◽  
Pore Expansion

Regulated exocytosis establishes a narrow fusion pore as initial aqueous connection to the extracellular space, through which small transmitter molecules such as ATP can exit. Co-release of polypeptides and hormones like insulin requires further expansion of the pore. There is evidence that pore expansion is regulated and can fail in diabetes and neurodegenerative disease. Here, we report that the cAMP-sensor Epac2 (Rap-GEF4) controls fusion pore behavior by acutely recruiting two pore-restricting proteins, amisyn and dynamin-1, to the exocytosis site in insulin-secreting beta-cells. cAMP elevation restricts and slows fusion pore expansion and peptide release, but not when Epac2 is inactivated pharmacologically or in Epac2-/- (Rapgef4-/-) mice. Consistently, overexpression of Epac2 impedes pore expansion. Widely used antidiabetic drugs (GLP-1 receptor agonists and sulfonylureas) activate this pathway and thereby paradoxically restrict hormone release. We conclude that Epac2/cAMP controls fusion pore expansion and thus the balance of hormone and transmitter release during insulin granule exocytosis.

scholarly journals Separately Inherited Defects in Insulin Exocytosis and  -Cell Glucose Metabolism Contribute to Type 2 Diabetes

Diabetes ◽  
2006 ◽  
Vol 55 (12) ◽  
pp. 3494-3500 ◽  
Author(s):  
C. Granhall ◽  
A. H. Rosengren ◽  
E. Renstrom ◽  
H. Luthman
Keyword(s):  
Type 2 Diabetes ◽  
Glucose Metabolism ◽  
Insulin Exocytosis ◽  
Cell Glucose

scholarly journals Syndapin 3 modulates fusion pore expansion in mouse neuroendocrine chromaffin cells

2014 ◽  
Vol 306 (9) ◽  
pp. C831-C843 ◽  
Author(s):  
Prattana Samasilp ◽  
Kyle Lopin ◽  
Shyue-An Chan ◽  
Rajesh Ramachandran ◽  
Corey Smith
Keyword(s):  
Chromaffin Cells ◽  
Control Point ◽  
Peripheral Circulation ◽  
Neuroendocrine Cells ◽  
Fusion Pore ◽  
Cell Periphery ◽  
Hormone Release ◽  
Excitatory Synaptic Input ◽  
Activity Dependent ◽  
Pore Expansion

Adrenal neuroendocrine chromaffin cells receive excitatory synaptic input from the sympathetic nervous system and secrete hormones into the peripheral circulation. Under basal sympathetic tone, modest amounts of freely soluble catecholamine are selectively released through a restricted fusion pore formed between the secretory granule and the plasma membrane. Upon activation of the sympathoadrenal stress reflex, elevated stimulation drives fusion pore expansion, resulting in increased catecholamine secretion and facilitating release of copackaged peptide hormones. Thus regulated expansion of the secretory fusion pore is a control point for differential hormone release of the sympathoadrenal stress response. Previous work has shown that syndapin 1 deletion alters transmitter release and that the dynamin 1-syndapin 1 interaction is necessary for coupled endocytosis in neurons. Dynamin has also been shown to be involved in regulation of fusion pore expansion in neuroendocrine chromaffin cells through an activity-dependent association with syndapin. However, it is not known which syndapin isoform(s) contributes to pore dynamics in neuroendocrine cells. Nor is it known at what stage of the secretion process dynamin and syndapin associate to modulate pore expansion. Here we investigate the expression and localization of syndapin isoforms and determine which are involved in mediating fusion pore expansion. We show that all syndapin isoforms are expressed in the adrenal medulla. Mutation of the SH3 dynamin-binding domain of all syndapin isoforms shows that fusion pore expansion and catecholamine release are limited specifically by mutation of syndapin 3. The mutation also disrupts targeting of syndapin 3 to the cell periphery. Syndapin 3 exists in a persistent colocalized state with dynamin 1.

scholarly journals A glucose-dependent spatial patterning of exocytosis in human β-cells is disrupted in type 2 diabetes

2019 ◽  
Author(s):  
Jianyang Fu ◽  
John Maringa Githaka ◽  
Xiaoqing Dai ◽  
Gregory Plummer ◽  
Kunimasa Suzuki ◽  
...  
Keyword(s):  
Type 2 Diabetes ◽  
Hot Spots ◽  
Secretory Granules ◽  
Relative Proportion ◽  
List Type ◽  
Spatial Patterning ◽  
Β Cells ◽  
C Terminus ◽  
Insulin Exocytosis

SUMMARYImpaired insulin secretion in type 2 diabetes (T2D) is linked to reduced insulin granule docking, disorganization of the exocytotic site, and an impaired glucose-dependent facilitation of insulin exocytosis. We show in β-cells from 80 human donors that the glucose-dependent amplification of exocytosis is disrupted in T2D. Spatial analyses of granule fusion events, visualized by total internal reflection fluorescence (TIRF) microscopy, demonstrate that these are non-random across the surface of β-cells from donors with no diabetes (ND). The compartmentalization of events occurs within regions defined by concurrent or recent membrane-resident secretory granules. This organization, and the number of membrane-associated granules, is glucose-dependent and notably impaired in T2D β-cells. Mechanistically, multi-channel Kv2.1 clusters contribute to maintaining the density of membrane-resident granules and the number of fusion ‘hot spots’, while SUMOylation sites at the channel N-(K145) and C-terminus (K470) determine the relative proportion of fusion events occurring within these regions. Thus, a glucose-dependent compartmentalization of fusion, regulated in part by a structural role for Kv2.1, is disrupted in β-cells from donors with type 2 diabetes.HIGHLIGHTSExocytosis of secretory granules is non-random across the surface of human β-cells, and this organization is disrupted in type 2 diabetes.Increasing glucose facilitates the spatial compartmentalization of fusion, independent of an overall increase in event frequency.Compartmentalized ‘hot spots’ occur at sites marked by membrane-associated granules, the density of which is regulated in part by a clustered K+ channel (Kv2.1).SUMOylation status of the channel controls the proportion of events that occur within these local regions.

scholarly journals The type 2 diabetes gene product STARD10 is a phosphoinositide binding protein that controls insulin secretory granule biogenesis

2020 ◽  
Author(s):  
Gaelle R. Carrat ◽  
Elizabeth Haythorne ◽  
Alejandra Tomas ◽  
Leena Haataja ◽  
Andreas Müller ◽  
...  
Keyword(s):  
Type 2 Diabetes ◽  
Cell Function ◽  
Phosphatidyl Inositol ◽  
Binding Pocket ◽  
Membrane Lipid ◽  
Lipid Transfer ◽  
Β Cell ◽  
Lipid Kinase ◽  
Insulin Granule

AbstractObjectiveRisk alleles for type 2 diabetes at the STARD10 locus are associated with lowered STARD10 expression in the β-cell, impaired glucose-induced insulin secretion and decreased circulating proinsulin:insulin ratios. Although likely to serve as a mediator of intracellular lipid transfer, the identity of the transported lipids, and thus the pathways through which STARD10 regulates β-cell function, are not understood. The aim of this study was to identify the lipids transported and affected by STARD10 in the β-cell and its effect on proinsulin processing and insulin granule biogenesis and maturation.MethodsWe used isolated islets from mice deleted selectively in the β-cell for Stard10 (βStarD10KO) and performed electron microscopy, pulse-chase, RNA sequencing and lipidomic analyses. Proteomic analysis of STARD10 binding partners was executed in INS1 (832/13) cell line. X-ray crystallography followed by molecular docking and lipid overlay assay were performed on purified STARD10 protein.ResultsβStarD10KO islets had a sharply altered dense core granule appearance, with a dramatic increase in the number of “rod-like” dense cores. Correspondingly, basal secretion of proinsulin was increased. Amongst the differentially expressed genes in βStarD10KO islets, expression of the phosphoinositide binding proteins Pirt and Synaptotagmin 1 were decreased while lipidomic analysis demonstrated changes in phosphatidyl inositol levels. The inositol lipid kinase PIP4K2C was also identified as a STARD10 binding partner. STARD10 bound to inositides phosphorylated at the 3’ position and solution of the crystal structure of STARD10 to 2.3 Å resolution revealed a binding pocket capable of accommodating polyphosphoinositides.ConclusionOur data indicate that STARD10 binds to, and may transport, phosphatidylinositides, influencing membrane lipid composition, insulin granule biosynthesis and insulin processing.

scholarly journals Type-2 Diabetes - A Fusion Pore Disease?

2018 ◽  
Vol 114 (3) ◽  
pp. 10a
Author(s):  
Patrik Rorsman ◽  
Stephan C. Collins ◽  
Benoit Hastoy
Keyword(s):  
Type 2 Diabetes ◽  
Fusion Pore

scholarly journals Reduced Insulin Exocytosis in Human Pancreatic  -Cells With Gene Variants Linked to Type 2 Diabetes

Diabetes ◽  
2012 ◽  
Vol 61 (7) ◽  
pp. 1726-1733 ◽  
Author(s):  
A. H. Rosengren ◽  
M. Braun ◽  
T. Mahdi ◽  
S. A. Andersson ◽  
M. E. Travers ◽  
...  
Keyword(s):  
Type 2 Diabetes ◽  
Gene Variants ◽  
Pancreatic Cells ◽  
Insulin Exocytosis

scholarly journals A randomised trial of enteric-coated nutrient pellets to stimulate gastrointestinal peptide release and lower glycaemia in type 2 diabetes

Diabetologia ◽  
2013 ◽  
Vol 56 (6) ◽  
pp. 1236-1242 ◽  
Author(s):  
J. Ma ◽  
H. L. Checklin ◽  
J. M. Wishart ◽  
J. E. Stevens ◽  
K. L. Jones ◽  
...  
Keyword(s):  
Type 2 Diabetes ◽  
Randomised Trial ◽  
Peptide Release ◽  
Enteric Coated

scholarly journals The PI(4)P phosphatase Sac2 controls insulin granule docking and release

2019 ◽  
Vol 218 (11) ◽  
pp. 3714-3729 ◽  
Author(s):  
Phuoc My Nguyen ◽  
Nikhil R. Gandasi ◽  
Beichen Xie ◽  
Sari Sugahara ◽  
Yingke Xu ◽  
...  
Keyword(s):  
Type 2 Diabetes ◽  
Plasma Membrane ◽  
Insulin Secretion ◽  
Dependent Manner ◽  
Impaired Insulin Secretion ◽  
Insulin Granules ◽  
Impaired Insulin ◽  
Insulin Granule ◽  
Phosphatidylinositol 4

Insulin granule biogenesis involves transport to, and stable docking at, the plasma membrane before priming and fusion. Defects in this pathway result in impaired insulin secretion and are a hallmark of type 2 diabetes. We now show that the phosphatidylinositol 4-phosphate phosphatase Sac2 localizes to insulin granules in a substrate-dependent manner and that loss of Sac2 results in impaired insulin secretion. Sac2 operates upstream of granule docking, since loss of Sac2 prevented granule tethering to the plasma membrane and resulted in both reduced granule density and number of exocytic events. Sac2 levels correlated positively with the number of docked granules and exocytic events in clonal β cells and with insulin secretion in human pancreatic islets, and Sac2 expression was reduced in islets from type 2 diabetic subjects. Taken together, we identified a phosphoinositide switch on the surface on insulin granules that is required for stable granule docking at the plasma membrane and impaired in human type 2 diabetes.

Sign in / Sign up

Export Citation Format

Share Document