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- Gucek, Alenka, et al.
(författare)
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Fusion pore regulation by cAMP/Epac2 controls cargo release during insulin exocytosis
- 2019
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Ingår i: eLIFE. - : ELIFE SCIENCES PUBLICATIONS LTD. - 2050-084X. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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- Omar-Hmeadi, Muhmmad, et al.
(författare)
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Local PI(4,5)P2 signaling inhibits fusion pore expansion during exocytosis
- 2023
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Ingår i: Cell Reports. - : Elsevier. - 2211-1247. ; 42:2
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Tidskriftsartikel (refereegranskat)abstract
- Phosphatidylinositol(4,5)bisphosphate (PI(4,5)P2) is an important signaling phospholipid that is required for regulated exocytosis and some forms of endocytosis. The two processes share a topologically similar pore structure that connects the vesicle lumen with the outside. Widening of the fusion pore during exocytosis leads to cargo release, while its closure initiates kiss&run or cavicapture endocytosis. We show here, using live-cell total internal reflection fluorescence (TIRF) microscopy of insulin granule exocytosis, that transient accumulation of PI(4,5)P2 at the release site recruits components of the endocytic fission machinery and stalls the late fusion pore expansion that is required for peptide release. The absence of clathrin differentiates this mechanism from clathrin-mediated endocytosis. Knockdown of phosphatidylinositol-phosphate-5-kinase-1c or optogenetic recruitment of 5-phosphatase reduces PI(4,5)P2 transients and accelerates fusion pore expansion, suggesting that acute PI(4,5)P2 synthesis is involved. Thus, local phospholipid signaling inhibits fusion pore expansion and peptide release through an unconventional endocytic mechanism.
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- Wang, Ye, et al.
(författare)
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Studies on Alpha-synuclein and Islet Amyloid Polypeptide Interaction in Islets
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Both Parkinson's diseases and type 2 diabetes are protein-misfolding diseases. In Parkinson'sdisease, alpha-synuclein (aSyn) forms insoluble Lewy bodies and Lewy neurites in brain neurons,and in type 2 diabetes, islet amyloid polypeptide (IAPP) comprises the amyloid in the islets ofLangerhans. In this study, we demonstrate the expression of aSyn in secretory granules of β cells,and in part in α cells in human islets and the human β cell line EndoC-βH1. In the Bimolecularfluorescence complementation (BiFC) assay, co-expression of aSyn and IAPP generates afluorescent signal indicative of molecular interaction. However, in co-localization studies, aSynco-localizes with IAPP intracellularly, while aSyn is absent in the extracellular amyloid deposits.Preformed aSyn fibrils seed IAPP fibril formation in vitro, but the addition of preformed IAPPseeds to aSyn do not change aSyn fibrillation. In addition, monomeric aSyn does not affect IAPPfibril formation. Knockdown of endogenous aSyn does not affect β cell function or viability, nordoes overexpression of aSyn affect β cell viability. Therefore, despite the proximity of aSyn andIAPP in β cells and the detected capacity of preformed aSyn fibrils to seed IAPP in vitro, it is stillan open question if this occurs in real life.
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- Xie, Beichen, et al.
(författare)
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Plasma Membrane Phosphatidylinositol 4,5-Bisphosphate Regulates Ca2+-Influx and Insulin Secretion from Pancreatic beta Cells
- 2016
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Ingår i: CELL CHEMICAL BIOLOGY. - : Elsevier BV. - 2451-9448 .- 2451-9456. ; 23:7, s. 816-826
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Tidskriftsartikel (refereegranskat)abstract
- Insulin secretion from pancreatic beta cells is regulated by the blood glucose concentration and occurs through Ca2+-triggered exocytosis. The activities of multiple ion channels in the beta cell plasma membrane are required to fine-tune insulin secretion in order to maintain normoglycemia. Phosphoinositide lipids in the plasma membrane often gate ion channels, and variations in the concentration of these lipids affect ion-channel open probability and conductance. Using light-regulated synthesis or depletion of plasma membrane phosphatidylinositol 4,5-bisphosphate (PI[4,5]P-2), we found that this lipid positively regulated both depolarization- and glucose-triggered Ca2+ influx in a dose-dependent manner. Small reductions of PI(4,5)P-2 caused by brief illumination resulted in partial suppression of Ca2+ influx that followed the kinetics of the lipid, whereas depletion resulted in marked inhibition of both Ca2+ influx and insulin secretion.
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