title: Characterization of phospholipids in insulin secretory granules and mitochondria in pancreatic beta cells and their changes with glucose stimulation.
abstract: The lipid composition of insulin secretory granules (ISG) has never previously been thoroughly characterized. We characterized the phospholipid composition of ISG and mitochondria in pancreatic beta cells without and with glucose stimulation. The phospholipid/protein ratios of most phospholipids containing unsaturated fatty acids were higher in ISG than in whole cells and in mitochondria. The concentrations of negatively charged phospholipids, phosphatidylserine, and phosphatidylinositol in ISG were 5-fold higher than in the whole cell. In ISG phosphatidylserine, phosphatidylinositol, phosphatidylethanolamine, and sphingomyelin, fatty acids 12:0 and 14:0 were high, as were phosphatidylserine and phosphatidylinositol containing 18-carbon unsaturated FA. With glucose stimulation, the concentration of many ISG phosphatidylserines and phosphatidylinositols increased; unsaturated fatty acids in phosphatidylserine increased; and most phosphatidylethanolamines, phosphatidylcholines, sphingomyelins, and lysophosphatidylcholines were unchanged. Unsaturation and shorter fatty acid length in phospholipids facilitate curvature and fluidity of membranes, which favors fusion of membranes. Recent evidence suggests that negatively charged phospholipids, such as phosphatidylserine, act as coupling factors enhancing the interaction of positively charged regions in SNARE proteins in synaptic or secretory vesicle membrane lipid bilayers with positively charged regions in SNARE proteins in the plasma membrane lipid bilayer to facilitate docking of vesicles to the plasma membrane during exocytosis. The results indicate that ISG phospholipids are in a dynamic state and are consistent with the idea that changes in ISG phospholipids facilitate fusion of ISG with the plasma membrane-enhancing glucose-stimulated insulin exocytosis.
authors.affiliation: From the Children's Diabetes Center, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706 and mjmacdon@wisc.edu.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: MacDonald
authors.affiliation: the Departments of Biochemistry and.
authors.forename: Lacmbouh
authors.initials: L
authors.lastname: Ade
authors.affiliation: the Departments of Biochemistry and Nutritional Sciences, University of Wisconsin, Madison, Wisconsin 53706.
authors.forename: James M
authors.initials: JM
authors.lastname: Ntambi
authors.affiliation: From the Children's Diabetes Center, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706 and.
authors.forename: Israr-Ul H
authors.initials: IU
authors.lastname: Ansari
authors.affiliation: From the Children's Diabetes Center, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706 and.
authors.forename: Scott W
authors.initials: SW
authors.lastname: Stoker
mesh_terms: D000818:Animals; D002460:Cell Line; D005089:Exocytosis / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*; D022142:Secretory Vesicles / Q000378:metabolism*; D013549:Sweetening Agents / Q000494:pharmacology*
chemical_list: D007328:Insulin; D010743:Phospholipids; D013549:Sweetening Agents; D005947:Glucose
keywords: Human Pancreatic Islets; Insulin Secretion; Membrane Fusion; Mitochondrial Biosynthesis; Pancreatic Beta Cells; Phosphatidylinositol; Phosphatidylserine; Phospholipid Metabolism; Unsaturated Fatty Acids; Vesicles