title: High extracellular glucose inhibits exocytosis through disruption of syntaxin 1A-containing lipid rafts.
abstract: Diabetes is characterized by high blood glucose which eventually impairs the secretion of insulin. Glucose directly affects cholesterol biosynthesis and may in turn affect cellular structures that depend on the sterol, including lipid rafts that help organize the secretory apparatus. Here, we investigated the long-term effects of glucose upon lipid rafts and secretory granule dynamics in pancreatic beta-cells. Raft fractions, identified by the presence of GM1 and flotillin, contained characteristically high levels of cholesterol and syntaxin 1A, the t-SNARE which tethers granules to the plasma membrane. Seventy-two hours exposure to 28mM glucose resulted in approximately 30% reduction in membrane cholesterol, with consequent redistribution of raft markers and syntaxin 1A throughout the plasma membrane. Live cell imaging indicated loss of syntaxin 1A from granule docking sites, and fewer docked granules. In conclusion, glucose-mediated inhibition of cholesterol biosynthesis perturbs lipid raft stability, resulting in a loss of syntaxin 1A from granule docking sites and inhibition of insulin secretion.
authors.affiliation: Centre for Diabetes, Blizard Institute of Cell and Molecular Science, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, Whitechapel, London E1 2AT, UK.
authors.forename: Sangeeta
authors.initials: S
authors.lastname: Somanath
authors.forename: Sebastian
authors.initials: S
authors.lastname: Barg
authors.forename: Catriona
authors.initials: C
authors.lastname: Marshall
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Silwood
authors.forename: Mark D
authors.initials: MD
authors.lastname: Turner
mesh_terms: D000818:Animals; D002460:Cell Line; D002784:Cholesterol / Q000096:biosynthesis; D003924:Diabetes Mellitus, Type 2 / Q000209:etiology / Q000378:metabolism*; D005089:Exocytosis; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology; D006943:Hyperglycemia / Q000150:complications / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism; D021962:Membrane Microdomains / Q000378:metabolism*; D051381:Rats; D050827:Syntaxin 1 / Q000378:metabolism*
chemical_list: D007328:Insulin; D050827:Syntaxin 1; D002784:Cholesterol; D005947:Glucose