Deletion of glutamate dehydrogenase 1 (Glud1) in the central nervous system affects glutamate handling without altering synaptic transmission

• Published in: Journal of neurochemistry Vol. 123; no. 3; pp. 342 - 348
• Main Authors: Frigerio, Francesca, Karaca, Melis, De Roo, Mathias, Mlynárik, Vladimír, Skytt, Dorte M., Carobbio, Stefania, Pajęcka, Kamilla, Waagepetersen, Helle S., Gruetter, Rolf, Muller, Dominique, Maechler, Pierre
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Publishing Ltd 01.11.2012; Wiley-Blackwell
• Subjects: Animals; astrocytes; Biological and medical sciences; Bones, joints and connective tissue. Antiinflammatory agents; Brain - enzymology; Brain - pathology; Brain - physiology; Cells, Cultured; Central nervous system; Central neurotransmission. Neuromudulation. Pathways and receptors; Female; Fundamental and applied biological sciences. Psychology; Gene Deletion; Glud1; glutamate; glutamate dehydrogenase; Glutamic Acid - metabolism; Glutamine - metabolism; Male; Medical research; Medical sciences; Mice; Mice, 129 Strain; Mice, Inbred C57BL; Mice, Knockout; Mice, Transgenic; Neural Pathways - metabolism; Neural Pathways - pathology; Neural Pathways - physiopathology; Neurochemistry; Neurotransmitters; Organ Culture Techniques; Pharmacology. Drug treatments; Receptors, Glutamate - deficiency; Receptors, Glutamate - genetics; Receptors, Glutamate - physiology; Synaptic Transmission - genetics; Synaptic Transmission - physiology; Testing laboratories; Vertebrates: nervous system and sense organs; Neuroglia; Glud1; Rodentia; Central nervous system; Metabolic pathway; Glutamate; Section; Encephalon; Behavioral disorder; Signal transduction; Vertebrata; Mammalia; glutamate dehydrogenase; Enzymatic activity; Mouse; Synaptic transmission; Animal; Excitatory aminoacid; Deletion; Neurotransmitter; Glutamatergic transmission; astrocytes; Pyramidal neuron
• ISSN: 0022-3042; 1471-4159; 1471-4159
• DOI: 10.1111/j.1471-4159.2012.07933.x

Glutamate dehydrogenase (GDH), encoded by GLUD1, participates in the breakdown and synthesis of glutamate, the main excitatory neurotransmitter. In the CNS, besides its primary signaling function, glutamate is also at the crossroad of metabolic and neurotransmitter pathways. Importance of brain GDH was questioned here by generation of CNS‐specific GDH‐null mice (CnsGlud1−/−); which were viable, fertile and without apparent behavioral problems. GDH immunoreactivity as well as enzymatic activity were absent in Cns‐Glud1−/− brains. Immunohistochemical analyses on brain sections revealed that the pyramidal cells of control animals were positive for GDH, whereas the labeling was absent in hippocampal sections of Cns‐Glud1−/− mice. Electrophysiological recordings showed that deletion of GDH within the CNS did not alter synaptic transmission in standard conditions. Cns‐Glud1−/− mice exhibited deficient oxidative catabolism of glutamate in astrocytes, showing that GDH is required for Krebs cycle pathway. As revealed by NMR studies, brain glutamate levels remained unchanged, whereas glutamine levels were increased. This pattern was favored by up‐regulation of astrocyte‐type glutamate and glutamine transporters and of glutamine synthetase. Present data show that the lack of GDH in the CNS modifies the metabolic handling of glutamate without altering synaptic transmission. We investigated the role of GDH in synaptic transmission and in the maintenance of glutamate–glutamine balance. Our data show that the lack of Glud1 in mouse brain inhibits GDH activity, modifies glutamate handling, decreases glutamate catabolism and increases glutamine levels; without affecting synaptic transmission. This study reports the first mouse model with brain‐specific ablation of GDH, named Cns‐Glud1−/−.