Molecular and functional characterization of glutamate dehydrogenase (GDH) enzyme in irats islets submitted to protein restriction and supplemented with leucine

Author(s)

Priscilla Muniz Ribeiro da Silva

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2011-03-15

Examining board members

Everardo Magalhães Carneiro; Gabriel Forato Anhê; Eliana Pereira de Araujo; Eduardo Rebelato Lopes de Oliveira; Fernando Abdulkader

• Advisor: Everardo Magalhães Carneiro

Abstract

Glutamate dehydrogenase (GDH) is a mitochondrial matrix enzyme that catalyzes the reversible reaction of glutamate to ?-ketoglutarate. In the pancreatic islets, this enzyme is associated with insulin secretion by augmenting ATP levels. Protein malnourished rats displayed reduced insulin secretion. Leucine (LEU) supplementation augments the insulin secretion response to insulinotropic agents. The present study investigated the influence of LEU supplementation on GDH expression and its involvement with insulin secretion in malnourished rats supplemented with LEU. Male rats were fed normal- (17%, NP) or low-protein diet (6%, LP) for eight weeks. Half of rats of each group were supplemented with LEU (1.5%) in drinking water for the following four weeks (NPL and LPL groups). GDH protein content in brain, liver, kidney and skeletal muscles was not different in any group. GDH RNAm and protein content was reduced in LP islets and LEU supplementation augmented RNAm expression restoring protein content similar to NP. Insulin secretion was reduced in LP islets compared with NP when stimulated by insulinotropics agents or inhybitors, combinaned or not. LEU supplementation augmented insulin secretion to similar values as NP, an effect that was blunted when LPL islets were incubated with EGCG. LP islets showed lower [Ca2+]i when exposed to GLN+BCH. LEU supplementation augmented these patterns similar to NP. Taken together, we may conclude that diminution in GDH expression induced by LP diet was central to endocrine pancreas and was associated with reduced insulin secretion observed in LP rats. LEU supplementation was able to restore GDH expression and it was capable to restore insulin secretion via GDH restoration. Yet, GDH may contribute to insulin secretion via Ca2+ regulation stimulus/secretion coupling (AU)