title: Wolfram syndrome 1 gene (WFS1) product localizes to secretory granules and determines granule acidification in pancreatic beta-cells.
abstract: Wolfram syndrome is an autosomal recessive disorder characterized by juvenile-onset insulin-dependent diabetes mellitus and optic atrophy. The gene responsible for the syndrome (WFS1) encodes an endoplasmic reticulum (ER) resident transmembrane protein. The Wfs1-null mouse exhibits progressive insulin deficiency causing diabetes. Previous work suggested that the function of the WFS1 protein is connected to unfolded protein response and to intracellular Ca(2+) homeostasis. However, its precise molecular function in pancreatic β-cells remains elusive. In our present study, immunofluorescent and electron-microscopic analyses revealed that WFS1 localizes not only to ER but also to secretory granules in pancreatic β-cells. Intragranular acidification was assessed by measuring intracellular fluorescence intensity raised by the acidotrophic agent, 3-[2,4-dinitroanilino]-3'-amino-N-methyldipropyramine. Compared with wild-type β-cells, there was a 32% reduction in the intensity in WFS1-deficient β-cells, indicating the impairment of granular acidification. This phenotype may, at least partly, account for the evidence that Wfs1-null islets have impaired proinsulin processing, resulting in an increased circulating proinsulin level. Morphometric analysis using electron microscopy evidenced that the density of secretory granules attached to the plasma membrane was significantly reduced in Wfs1-null β-cells relative to that in wild-type β-cells. This may be relevant to the recent finding that granular acidification is required for the priming of secretory granules preceding exocytosis and may partly explain the fact that glucose-induced insulin secretion is profoundly impaired in young prediabetic Wfs1-null mice. These results thus provide new insights into the molecular mechanisms of β-cell dysfunction in patients with Wolfram syndrome.
authors.affiliation: Division of Endocrinology, Department of Bio-Signal Analysis, Yamaguchi University Graduate School of Medicine, Ube, Yamaguchi, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Hatanaka
authors.forename: Katsuya
authors.initials: K
authors.lastname: Tanabe
authors.forename: Akie
authors.initials: A
authors.lastname: Yanai
authors.forename: Yasuharu
authors.initials: Y
authors.lastname: Ohta
authors.forename: Manabu
authors.initials: M
authors.lastname: Kondo
authors.forename: Masaru
authors.initials: M
authors.lastname: Akiyama
authors.forename: Koh
authors.initials: K
authors.lastname: Shinoda
authors.forename: Yoshitomo
authors.initials: Y
authors.lastname: Oka
authors.forename: Yukio
authors.initials: Y
authors.lastname: Tanizawa
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D005947:Glucose / Q000494:pharmacology; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology; D006801:Humans; D050417:Insulin-Secreting Cells / Q000378:metabolism* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000235:genetics / Q000276:immunology*; D051379:Mice; D018345:Mice, Knockout; D011384:Proinsulin / Q000235:genetics / Q000378:metabolism*; D022142:Secretory Vesicles / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D013549:Sweetening Agents / Q000494:pharmacology; D014929:Wolfram Syndrome / Q000235:genetics / Q000378:metabolism / Q000473:pathology
chemical_list: D008565:Membrane Proteins; D013549:Sweetening Agents; C114987:wolframin protein; D011384:Proinsulin; D005947:Glucose; D002118:Calcium