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Functional differences between aggregated and dispersed insulin-producing cells
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Cell Biology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Cell Biology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Cell Biology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Cell Biology.
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2013 (English)In: Diabetologia, ISSN 0012-186X, E-ISSN 1432-0428, Vol. 56, no 7, 1557-1568 p.Article in journal (Refereed) Published
Abstract [en]

Beta cells situated in the islet of Langerhans respond more vigorously to glucose than do dissociated beta cells. Mechanisms for this discrepancy were studied by comparing insulin-producing MIN6 cells aggregated into pseudoislets with MIN6 monolayer cells and mouse and human islets. MIN6 monolayers, pseudoislets and mouse and human islets were exposed to glucose, alpha-ketoisocaproic acid (KIC), pyruvate, KIC plus glutamine and the phosphatidylinositol 3-kinase (PI3K) inhibitors LY294002 or wortmannin. Insulin secretion (ELISA), cytoplasmic Ca2+ concentration ([Ca2+](c); microfluorometry), glucose oxidation (radiolabelling), the expression of genes involved in mitochondrial metabolism (PCR) and the phosphorylation of insulin receptor signalling proteins (western blotting) were measured. Insulin secretory responses to glucose, pyruvate, KIC and glutamine were higher in pseudoislets than monolayers and comparable to those of human islets. Glucose oxidation and genes for mitochondrial metabolism were upregulated in pseudoislets compared with single cells and monolayers, respectively. Phosphorylation at the inhibitory S636/639 site of IRS-1 was significantly higher in monolayers and dispersed human and mouse cells than pseudoislets and intact human and mouse islets. PI3K inhibition only slightly attenuated glucose-stimulated insulin secretion from monolayers, but substantially reduced that from pseudoislets and human and mouse islets without suppressing the glucose-induced [Ca2+](c) response. We propose that islet architecture is critical for proper beta cell mitochondrial metabolism and IRS-1 signalling, and that PI3K regulates insulin secretion at a step distal to the elevation of [Ca2+](c).

Place, publisher, year, edition, pages
2013. Vol. 56, no 7, 1557-1568 p.
Keyword [en]
Beta cell, Ca2+, Insulin secretion, IRS-1, Islets, Mitochondrial metabolism, PI3-kinase
National Category
Medical and Health Sciences
URN: urn:nbn:se:uu:diva-203520DOI: 10.1007/s00125-013-2903-3ISI: 000319881300013OAI: diva2:637175
Available from: 2013-07-16 Created: 2013-07-15 Last updated: 2015-01-23Bibliographically approved
In thesis
1. Role of Cell-cell Interactions and Palmitate on β-cells Function
Open this publication in new window or tab >>Role of Cell-cell Interactions and Palmitate on β-cells Function
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The islets of Langerhans secrets insulin in response to fluctuations of blood glucose level and efficient secretion requires extensive intra-islet communication. Secretory failure from islets is one of the hallmark in progression of type 2 diabetes.  Changes in islet structure and high levels of saturated free fatty acids may contribute to this failure. The aim of this thesis is to study the role of cell-cell interactions and palmitate on β-cells functions.

To address the role of cell-cell interactions on β-cells functions MIN6 cells were cultured as monolayers and as pseudoislets. Glucose stimulated insulin secretion was higher in pseudoislets compared to monolayers. Transcript levels of mitochondrial metabolism as well glucose oxidation rate was higher in pseudoislets. Insulin receptor substrate-1 (IRS-1) phosphorylation was altered when cells were grown as pseudoislets. Proteins expression levels related to glycolysis, cellular connections and translational regulations were up-regulated in pseudoislets. We propose the superior capacity of pseudoislets compared to monolayers depend on metabolism, cell coupling, gene translation, protein turnover and differential IRS-1 phosphorylation.

To address the role of palmitate on β-cells human islets were cultured in palmitate. Long term palmitate treatment decreased insulin secretion which is associated with up-regulation of suppressor of cytokine signaling-2 (SOCS2) and protein inhibitor of activated STAT-1 (PIAS1). Up-regulation of SOCS2 decreased phosphorylation of Akt at site T308, whereas PIAS1 decreased protein level of ATP- citrate lyase (ACLY) and ATP synthase subunit B (ATP5B). We propose long term palmitate treatment reduces phosphatidylinositol 3-kinase (PI3K) activity, attenuates formation of acetyl-CoA and decreases ATP synthesis which may aggravate β-cells dysfunction.  

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 42 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1025
Metabolism, PI3K, Pseudoislets, Human islets, SOCS, PIAS
National Category
Cell and Molecular Biology
Research subject
Biology with specialization in Molecular Biology
urn:nbn:se:uu:diva-230841 (URN)978-91-554-9021-8 (ISBN)
Public defence
2014-10-17, B41, BMC, Husargatan 3, Uppsala, 09:15 (English)
Available from: 2014-09-25 Created: 2014-08-30 Last updated: 2015-01-23

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