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

Grimaldi, Mariagrazia; Karaca Emre, Melis; Latini, Livia; Brioudes, Estelle; Schalch, Thomas; Maechler, Pierre

doi:10.1093/hmg/ddx213

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Title		Identification of the molecular dysfunction caused by glutamate dehydrogenase S445L mutation responsible for hyperinsulinism/hyperammonemia
Authors		Grimaldi, Mariagrazia Karaca Emre, Melis Latini, Livia Brioudes, Estelle Schalch, Thomas Maechler, Pierre
Published in		Human Molecular Genetics. 2017, vol. 26, no. 18, p. 3453-3465
Abstract		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.
Identifiers		DOI: 10.1093/hmg/ddx213 PMID: 28911206
Full text		Article (Published version) (778 Kb) - Limited access to UNIGE
Structures		Faculté de médecine / Section de médecine fondamentale / Département de physiologie cellulaire et métabolisme Faculté des sciences / Section de biologie / Département de biologie moléculaire
Research group		Mitochondries et sécrétion d'insuline (671)
Project		FNS: 166625
Citation (ISO format)		GRIMALDI, Mariagrazia et al. Identification of the molecular dysfunction caused by glutamate dehydrogenase S445L mutation responsible for hyperinsulinism/hyperammonemia. In: Human Molecular Genetics, 2017, vol. 26, n° 18, p. 3453-3465. doi: 10.1093/hmg/ddx213 https://archive-ouverte.unige.ch/unige:96833