title: Increased expression of GAD65 and GABA in pancreatic beta-cells impairs first-phase insulin secretion.
abstract: The functional role of glutamate decarboxylase (GAD) and its product GABA in pancreatic islets has remained elusive. Mouse beta-cells express the larger isoform GAD67, whereas human islets express only the smaller isoform GAD65. We have generated two lines of transgenic mice expressing human GAD65 in pancreatic beta-cells (RIP7-hGAD65, Lines 1 and 2) to study the effect that GABA generated by this isoform has on islet cell function. The ascending order of hGAD65 expression and/or activity in beta-cells was Line 1 heterozygotes < Line 2 heterozygotes < Line 1 homozygotes. Line 1 heterozygotes have normal glucose tolerance, whereas Line 1 homozygotes and Line 2 heterozygotes exhibit impaired glucose tolerance and inhibition of insulin secretion in vivo in response to glucose. In addition, fasting levels of blood glucose are elevated and insulin is decreased in Line 1 homozygotes. Pancreas perfusion experiments suggest that GABA generated by GAD65 may function as a negative regulator of first-phase insulin secretion in response to glucose by affecting a step proximal to or at the K(ATP)(+) channel.
authors.affiliation: Departments of Medicine, Microbiology and Immunology, and Hormone Research Institute, School of Medicine, University of California, San Francisco 94143, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Shi
authors.forename: J
authors.initials: J
authors.lastname: Kanaani
authors.forename: V
authors.initials: V
authors.lastname: Menard-Rose
authors.forename: Y H
authors.initials: YH
authors.lastname: Ma
authors.forename: P Y
authors.initials: PY
authors.lastname: Chang
authors.forename: D
authors.initials: D
authors.lastname: Hanahan
authors.forename: A
authors.initials: A
authors.lastname: Tobin
authors.forename: G
authors.initials: G
authors.lastname: Grodsky
authors.forename: S
authors.initials: S
authors.lastname: Baekkeskov
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D005951:Glucose Tolerance Test; D005968:Glutamate Decarboxylase / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D007150:Immunohistochemistry; D007328:Insulin / Q000235:genetics / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism*; D007527:Isoenzymes / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D005680:gamma-Aminobutyric Acid / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D001786:Blood Glucose; D007328:Insulin; D007527:Isoenzymes; D005680:gamma-Aminobutyric Acid; D005968:Glutamate Decarboxylase; C401141:glutamate decarboxylase 2