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- Wendt, Anna, et al.
(författare)
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Synapsins I and II Are Not Required for Insulin Secretion from Mouse Pancreatic beta-cells
- 2012
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Ingår i: Endocrinology. - : The Endocrine Society. - 0013-7227 .- 1945-7170. ; 153:5, s. 2112-2119
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Tidskriftsartikel (refereegranskat)abstract
- Synapsins are a family of phosphoproteins that modulate the release of neurotransmitters from synaptic vesicles. The release of insulin from pancreatic beta-cells has also been suggested to be regulated by synapsins. In this study, we have utilized a knock out mouse model with general disruptions of the synapsin I and II genes [synapsin double knockout (DKO)]. Stimulation with 20 mM glucose increased insulin secretion 9-fold in both wild-type (WT) and synapsin DKO islets, whereas secretion in the presence of 70 mM K+ and 1mM glucose was significantly enhanced in the synapsin DKO mice compared to WT. Exocytosis in single beta-cells was investigated using patch clamp. The exocytotic response, measured by capacitance measurements and elicited by a depolarization protocol designed to visualize exocytosis of vesicles from the readily releasable pool and from the reserve pool, was of the same size in synapsin DKO and WT beta-cells. The increase in membrane capacitance corresponding to readily releasable pool was approximately 50fF in both genotypes. We next investigated the voltage-dependent Ca2+ influx. In both WT and synapsin DKO beta-cells the Ca2+ current peaked at 0 mV and measured peak current (I-p) and net charge (Q) were of similar magnitude. Finally, ultrastructural data showed no variation in total number of granules (N-v) or number of docked granules (N-s) between the beta-cells from synapsin DKO mice and WT control. We conclude that neither synapsin I nor synapsin II are directly involved in the regulation of glucose-stimulated insulin secretion and Ca-2-dependent exocytosis in mouse pancreatic beta-cells. (Endocrinology 153: 2112-2119, 2012)
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- Andersson, Sofia A, et al.
(författare)
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Reduced insulin secretion correlates with decreased expression of exocytotic genes in pancreatic islets from patients with type 2 diabetes.
- 2012
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Ingår i: Molecular and Cellular Endocrinology. - : Elsevier BV. - 1872-8057 .- 0303-7207. ; 364:1-2, s. 36-45
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Tidskriftsartikel (refereegranskat)abstract
- Reduced insulin release has been linked to defect exocytosis in β-cells. However, whether expression of genes suggested to be involved in the exocytotic process (exocytotic genes) is altered in pancreatic islets from patients with type 2 diabetes (T2D), and correlate to insulin secretion, needs to be further investigated. Analysing expression levels of 23 exocytotic genes using microarray revealed reduced expression of five genes in human T2D islets (χ(2)=13.25; p<0.001). Gene expression of STX1A, SYT4, SYT7, SYT11, SYT13, SNAP25 and STXBP1 correlated negatively to in vivo measurements of HbA1c levels and positively to glucose stimulated insulin secretion (GSIS) in vitro in human islets. STX1A, SYT4 and SYT11 protein levels correspondingly decreased in human T2D islets. Moreover, silencing of SYT4 and SYT13 reduced GSIS in INS1-832/13 cells. Our data support that reduced expression of exocytotic genes contributes to impaired insulin secretion, and suggest decreased expression of these genes as part of T2D pathogenesis.
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