Functional differences between aggregated and dispersed insulin-producing cells

• Published in: Diabetologia Vol. 56; no. 7; pp. 1557 - 1568
• Main Authors: Chowdhury, A., Dyachok, O., Tengholm, A., Sandler, S., Bergsten, P.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.07.2013; Springer; Springer Nature B.V
• Subjects: Animals; Beta cell; Biological and medical sciences; Blotting, Western; Ca2; Calcium - metabolism; Cell Line, Tumor; Cells; Diabetes. Impaired glucose tolerance; Endocrine pancreas. Apud cells (diseases); Endocrinopathies; Etiopathogenesis. Screening. Investigations. Target tissue resistance; Glucose; Human Physiology; Insulin; Insulin - metabolism; Insulin secretion; Internal Medicine; IRS-1; Islets; Islets of Langerhans - metabolism; Kinases; Medical sciences; Medicine; Medicine & Public Health; Metabolic Diseases; Metabolism; Mice; Mitochondrial metabolism; Oxidation; Penicillin; Phosphatidylinositol 3-Kinases - metabolism; Phosphorylation; PI3-kinase; Real-Time Polymerase Chain Reaction; Mitochondrial metabolism; IRS-1; Beta cell; Islets; PI3-kinase; Ca; Insulin secretion; Endocrinopathy; Pancreatic hormone; Calcium; Secretion; Diabetes mellitus; Langerhans islet; Metabolism; Inorganic element; Insulin; Insulin receptor substrate protein; Mitochondria; β Cell; Endocrine pancreas
• ISSN: 0012-186X; 1432-0428; 1432-0428
• DOI: 10.1007/s00125-013-2903-3

Aims/hypothesis 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. Methods MIN6 monolayers, pseudoislets and mouse and human islets were exposed to glucose, α-ketoisocaproic acid (KIC), pyruvate, KIC plus glutamine and the phosphatidylinositol 3-kinase (PI3K) inhibitors LY294002 or wortmannin. Insulin secretion (ELISA), cytoplasmic Ca 2+ concentration ([Ca 2+ ] 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. Results 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 [Ca 2+ ] c response. Conclusions/interpretation 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 [Ca 2+ ] c .