Rabbit Anti-Human GLUD1 Polyclonal antibody

Glucose homeostasis is determined by insulin secretion from the beta-cells in pancreatic islets and by glucose uptake in skeletal muscle and other insulin target tissues. While glutamate dehydrogenase (GDH) senses mitochondrial energy supply and regulates insulin secretion, its role in the muscle has not been elucidated. Here we investigated the possible interplay between GDH and the cytosolic energy sensing enzyme 5'-AMP kinase (AMPK), in both isolated islets and myotubes from mice and humans. The green tea polyphenol epigallocatechin-3-gallate (EGCG) was used to inhibit GDH. Insulin secretion was reduced by EGCG upon glucose stimulation and blocked in response to glutamine combined with the allosteric GDH activator BCH (2-aminobicyclo-[2,2,1] heptane-2-carboxylic acid). Insulin secretion was similarly decreased in islets of mice with beta-cell-targeted deletion of GDH (beta Gludl(-/-)). EGCG did not further reduce insulin secretion in the mutant islets, validating its specificity. In human islets, EGCG attenuated both basal and nutrient-stimulated insulin secretion. Glutamine/BCH-induced lowering of AMPK phosphorylation did not operate in beta Glud1(-/-) islets and was similarly prevented by EGCG in control islets, while high glucose systematically inactivated AMPK. In mouse C2C12 myotubes, like in islets, the inhibition of AMPK following GDH activation with glutamine/BCH was reversed by EGCG. Stimulation of GDH in primary human myotubes caused lowering of insulin-induced 2-deoxy-glucose uptake, partially counteracted by EGCG. Thus, mitochondrial energy provision through anaplerotic input via GDH influences the activity of the cytosolic energy sensor AMPK. EGCG may be useful in obesity by resensitizing insulin-resistant muscle while blunting hypersecretion of insulin in hypermetabolic states. (C) 2017 Elsevier Ltd. All rights reserved.

In pancreatic beta-cells, glutamate dehydrogenase (GDH) modulates insulin secretion, although its function regarding specific secretagogues is unclear. This study investigated the role of GDH using a beta-cell-specific GDH knockout mouse model, called bGlud1(-/-). The absence of GDH in islets isolated from beta Glud1(-/-) mice resulted in abrogation of insulin release evoked by glutamine combined with 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid or l-leucine. Reintroduction of GDH in beta Glud(1-/-) islets fully restored the secretory response. Regarding glucose stimulation, insulin secretion in islets isolated from beta Glud1(-/-) mice exhibited half of the response measured in control islets. The amplifying pathway, tested at stimulatory glucose concentrations in the presence of KCl and diazoxide, was markedly inhibited in beta Glud1(-/-) islets. On glucose stimulation, net synthesis of glutamate from a-ketoglutarate was impaired in GDH-deficient islets. Accordingly, glucose-induced elevation of glutamate levels observed in control islets was absent in beta Glud1(-/-) islets. Parallel biochemical pathways, namely alanine and aspartate aminotransferases, could not compensate for the lack of GDH. However, the secretory response to glucose was fully restored by the provision of cellular glutamate when beta Glud1(-/-) islets were exposed to dimethyl glutamate. This shows that permissive levels of glutamate are required for the full development of glucose-stimulated insulin secretion and that GDH plays an indispensable role in this process.