Identification of the molecular dysfunction caused by glutamate dehydrogenase S445L mutation responsible for hyperinsulinism/hyperammonemia

Article Article scientifique Article Identification of the molecular dysfunction caused by glutamate dehydrogenase S445L mutation responsible for hyperinsulinism/hyperammonemia eng 2017 author Grimaldi Mariagrazia 791675 author Karaca Emre Melis 718062 author Latini Livia 825977 author Brioudes Estelle 743625 author Schalch Thomas 787942 author Maechler Pierre 0000-0002-2005-1433 76515 3453-3465 10.1093/hmg/ddx213 28911206 0964-6906 Congenital hyperinsulinism/hyperammonemia (HI/HA) syndrome gives rise to unregulated protein-induced insulin secretion from pancreatic beta-cells, fasting hypoglycemia and elevated plasma ammonia levels. Mutations associated with HI/HA were identified in the Glud1 gene, encoding for glutamate dehydrogenase (GDH). We aimed at identifying the molecular causes of dysregulation in insulin secretion and ammonia production conferred by the most frequent HI/HA mutation Ser445Leu. Following transduction with adenoviruses carrying the human GDH-wild type or GDH-S445L-mutant gene, immunoblotting showed efficient expression of the transgenes in all the investigated cell types. Enzymatic activity tested in INS-1E beta-cells revealed that the mutant was much more sensitive to the allosteric activator ADP, rendering it highly responsive to substrates. INS-1E cells expressing either the wild type or mutant GDH responded similarly to glucose stimulation regarding mitochondrial activation and insulin secretion. However, at basal glucose glutamine stimulation increased mitochondrial activity and insulin release only in the mutant cells. In mouse and human islets, expression of mutant GDH resulted in robust elevation of insulin secretion upon glutamine stimulation, not observed in control islets. Hepatocytes expressing either the wild type or mutant GDH produced similar levels of ammonia when exposed to glutamine, although alanine response was strongly elevated with the mutant form. In conclusion, the GDH-S445L mutation confers hyperactivity to this enzyme due to higher sensitivity to ADP allosteric activation. This renders beta-cells responsive to amino acid stimulation, explaining protein-induced hypoglycemia secondary to non-physiological insulin release. Hepatocytes carrying mutant GDH produced more ammonia upon alanine exposure, which underscores hyperammonemia developed by the patients. Dewey 570 Dewey 612 Swiss National Science Foundation 166625 CH 43 Département de biologie moléculaire 161 134 Département de physiologie cellulaire et métabolisme 21C false 402 Mitochondries et métabolisme énergétique 671 Human Molecular Genetics 26 18 35eb6849-7691-4b5f-a693-204ba9f0c318 Article (Published version) Restricted 2017-Grimaldi-HMG-mutGDH.pdf 796671 application/pdf restrictedAccess Faculté des sciences / Section de biologie / Département de biologie moléculaire Faculté de médecine / Section de médecine fondamentale / Département de physiologie cellulaire et métabolisme

Title	Published in	Access level	OA Policy	Year	Views	Downloads

Identification of the molecular dysfunction caused by glutamate dehydrogenase S445L mutation responsible for hyperinsulinism/hyperammonemia	Human Molecular Genetics			2017	572	10

Archive ouverte UNIGE

Latini, Livia