Enhancement of glucagon secretion in mouse and human pancreatic alpha cells by protein kinase C (PKC) involves intracellular trafficking of PKCα and PKCδ

Marinis, Yang Z. De; Zhang, Enming; Amisten, Stefan; Taneera, Jalal; Renström, Erik; Rorsman, Patrik; Eliasson, Lena

doi:10.1007/s00125-009-1635-x

Cited by 19 publications

(19 citation statements)

References 49 publications

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“…Another study [18] and we, here, have reported GLP-1 values in the picomolar range, suggesting intrinsic islet biological variability and/or differences in experimental conditions. In addition, in our study, glucagon release from isolated islets was similar to that reported by some other authors [36,37], but several fold lower than that observed during perifusion experiments [38]. All this led, in our hands, to a glucagon/GLP-1 molar secretion ratio (basal condition) of approximately 5.7, similar to findings previously reported for αTC1-6 cells [16].…”

Section: Discussionsupporting

confidence: 92%

A local glucagon-like peptide 1 (GLP-1) system in human pancreatic islets

et al. 2012

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Aims/hypothesis Glucagon-like peptide 1 (GLP-1) is a major incretin, mainly produced by the intestinal L cells, with beneficial actions on pancreatic beta cells. However, while in vivo only very small amounts of GLP-1 reach the pancreas in bioactive form, some observations indicate that GLP-1 may also be produced in the islets. We performed comprehensive morphological, functional and molecular studies to evaluate the presence and various features of a local GLP-1 system in human pancreatic islet cells, including those from type 2 diabetic patients. MethodsThe presence of insulin, glucagon, GLP-1, proconvertase (PC) 1/3 and PC2 was determined in human pancreas by immunohistochemistry with confocal microscopy. Islets were isolated from non-diabetic and type 2 diabetic donors. GLP-1 protein abundance was evaluated by immunoblotting and matrix-assisted laser desorption-ionisation-time of flight (MALDI-TOF) mass spectrometry. Single alpha and beta cell suspensions were obtained by enzymatic dissociation and FACS sorting. Glucagon and GLP-1 release were measured in response to nutrients. Diabetologia (2012) 55:3262-3272 DOI 10.1007/s00125-012-2716 Electronic supplementary material The online version of this article (doi:10.1007/s00125-012-2716-9) contains peer-reviewed but unedited supplementary material, which is available to authorised users. Results Confocal microscopy showed the presence of GLP-1-like and PC1/3 immunoreactivity in subsets of alpha cells, whereas GLP-1 was not observed in beta cells. The presence of GLP-1 in isolated islets was confirmed by immunoblotting, followed by mass spectrometry. Isolated islets and alpha (but not beta) cell fractions released GLP-1, which was regulated by glucose and arginine. PC1/3 (also known as PCSK1) gene expression was shown in alpha cells. GLP-1 release was significantly higher from type 2 diabetic than from nondiabetic isolated islets. Conclusions/interpretation We have shown the presence of a functionally competent GLP-1 system in human pancreatic islets, which resides in alpha cells and might be modulated by type 2 diabetes.

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Section: Discussionsupporting

confidence: 92%

A local glucagon-like peptide 1 (GLP-1) system in human pancreatic islets

et al. 2012

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“…However, recent accumulating evidence suggests that dysregulation of glucagon secretion can also induce hyperglycemia, which is ameliorated by inhibition of glucagon function (6 -9). Moreover, it was reported that treatment with high glucose increased glucagon secretion from isolated islets and PKC is involved in this event, although the responsible PKC isozyme was not identified (12)(13)(14). Our data demonstrate that PKCδ signaling is responsible for the PMA-induced augmentation of glucagon secretion in the isolated islets.…”

Section: Discussionmentioning

confidence: 55%

Protein kinase C-δ signaling regulates glucagon secretion from pancreatic islets

et al. 2017

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: Accumulating evidence supports the "glucagonocentric hypothesis", in which antecedent α-cell failure and inhibition of glucagon secretion are responsible for diabetes progression. Protein kinase C (PKC) is involved in glucagon secretion from α-cells, although which PKC isozyme is involved and the mechanism underlying this PKC-regulated glucagon secretion remains unknown. Here, the involvement of PKCδ in the onset and progression of diabetes was elucidated. Immunofluorescence studies revealed that PKCδ was expressed and activated in α-cells of STZ-induced diabetic model mice. Phorbol 12-myristate 13-acetate (PMA) stimulation significantly augmented glucagon secretion from isolated islets. Pre-treatment with quercetin and rottlerin, PKCδ signaling inhibitors, significantly suppressed the PMA-induced elevation of glucagon secretion. While Go6976, a Ca 2+ -dependent PKC selective inhibitor did not suppress glucagon secretion. Quercetin suppressed PMA-induced phosphorylation of Tyr 311 of PKCδ in isolated islets. However, quercetin itself had no effect on either glucagon secretion or glucagon mRNA expression. Our data suggest that PKCδ signaling inhibitors suppressed glucagon secretion. Elucidation of detailed signaling pathways causing PKCδ activation in the onset and progression of diabetes followed by the augmentation of glucagon secretion could lead to the identification of novel therapeutic target molecules and the development of novel therapeutic drugs for diabetes.

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“…Munc-18 has been implicated in transport of syntaxin 1A [32] and demonstrated to be phosphorylated by PKC [10]. More detailed studies are indeed needed in the future to be able to fully answer the question regarding syntaxin 1A trafficking in the alpha-cells but we have earlier shown that PKC plays an important role in the regulation of the pancreatic alpha-cell exocytosis [7].…”

Section: Discussionmentioning

confidence: 98%

“…In these experiments exocytosis was elicited by a train of ten 500 msdepolarisations from -70 mV to 0 mV (Fig 2a-b). It has earlier been suggested that the capacitance increase evoked by the two first and latter eight depolarisations of a train represent the maximum size of the RRP and the refilling from RP, respectively [7]. We used this approach and applied an antibody against SNAP-25 intracellularly by inclusion in the pipette solution.…”

Section: Antibodies Against Snap-25 Reduce Exocytosis Of Glucagon-conmentioning

confidence: 99%

Glucose-dependent docking and SNARE protein-mediated exocytosis in mouse pancreatic alpha-cell

Andersson

Pedersen

Vikman

et al. 2011

Pflugers Arch - Eur J Physiol

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The function of alpha-cells in patients with type 2 diabetes (T2D) is often disturbed; glucagon secretion is increased at hyperglycaemia, yet fails to respond to hypoglycaemia. A crucial mechanism behind the fine-tuned release of glucagon relies in the exocytotic machinery including SNARE proteins. Here we aimed to investigate the temporal role of syntaxin 1A and SNAP-25 in mouse alpha-cell exocytosis. First, we used confocal imaging to investigate glucosedependency in the localisation of SNAP-25 and syntaxin 1A. SNAP-25 was mainly distributed in the plasma membrane at 2.8 mM glucose whereas the syntaxin 1A distribution in the plasma membrane, as compared to the cytosolic fraction, was highest at 8.3 mM glucose. Further, following inclusion of an antibody against SNAP-25 or syntaxin 1A, exocytosis evoked by a train of ten depolarisations and measured as an increase in membrane capacitance was reduced by ~50%. Closer inspection revealed a reduction in the refilling of granules from the reserve pool (RP), but also showed a decreased size of the readily releasable pool (RRP) by ~45%. Disparate from the situation in pancreatic beta-cells, the voltage-dependent Ca 2+ -current was not reduced, but the Ca 2+ -sensitivity of exocytosis decreased by the antibody against syntaxin 1A. Finally, ultrastructural analysis revealed that the number of docked granules was >2-fold higher at 16.7 mM than at 1 mM glucose. We conclude that syntaxin 1A and SNAP-25 are necessary for alphacell exocytosis and regulate fusion of granules belonging to both the RRP and RP without affecting the Ca 2+ -current.3

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Enhancement of glucagon secretion in mouse and human pancreatic alpha cells by protein kinase C (PKC) involves intracellular trafficking of PKCα and PKCδ

Cited by 19 publications

References 49 publications

A local glucagon-like peptide 1 (GLP-1) system in human pancreatic islets

A local glucagon-like peptide 1 (GLP-1) system in human pancreatic islets

Protein kinase C-δ signaling regulates glucagon secretion from pancreatic islets

Glucose-dependent docking and SNARE protein-mediated exocytosis in mouse pancreatic alpha-cell

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