title: Glutamic acid decarboxylase 65 and 67 isoforms in fetal, neonatal and adult porcine islets: predominant beta cell co-localization by light and confocal microscopy.
abstract: Glutamic acid decarboxylase (GAD) has been shown to exist as two isoforms with molecular weights of 65 kD (GAD65) and 67 kD (GAD67) in the central nervous system as well as in several non-neuronal tissues, including the pancreatic islets. Recently, this enzyme has been proposed as a key beta-cell autoantigen in insulin-dependent diabetes mellitus (IDDM). In the present study, we used double label light and confocal microscopy to examine the expression of the two GAD isoforms in islet cells of fetal, neonatal and adult porcine pancreas. We also aimed to identify the islet cell-type(s) which co-express GAD. In the adult pig, GAD65 was localized exclusively in most of the beta cells, whereas GAD67, in addition to being present in a majority of the beta cells, was also seen in a proportion of glucagon and somatostatin labelled cells. In the 90-day fetus and the 7-day neonate, while GAD65 was also observed in a majority of beta cells, a proportion of glucagon cells also co-expressed this isoform. The cellular expression of GAD67 in the fetal and neonatal stages was similar to that in the adult. Detailed confocal analysis of GAD65 immunoreactive cells showed a granular cytoplasmic staining, with labelled granules often concentrated in specific perinuclear regions, possibly the Golgi apparatus. In contrast, GAD67 positive cells showed more diffuse cytoplasmic staining. The predominant expression of both the isoforms in porcine beta cells suggests that islet cells from this species may act as a suitable cellular model for study of GAD autoreactivity during the early stages of IDDM.
authors.affiliation: Department of Paediatrics, University of Auckland School of Medicine, New Zealand.
authors.forename: S
authors.initials: S
authors.lastname: Reddy
authors.forename: D
authors.initials: D
authors.lastname: Wu
authors.forename: C A
authors.initials: CA
authors.lastname: Poole
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D005968:Glutamate Decarboxylase / Q000737:chemistry*; D007150:Immunohistochemistry; D007515:Islets of Langerhans / Q000166:cytology / Q000196:embryology / Q000201:enzymology*; D007527:Isoenzymes / Q000378:metabolism*; D018613:Microscopy, Confocal; D013552:Swine
chemical_list: D007527:Isoenzymes; D005968:Glutamate Decarboxylase