title: Increased expression of phosphate-activated glutaminase in hippocampal neurons in human mesial temporal lobe epilepsy.
abstract: Patients with mesial temporal lobe epilepsy (MTLE) have increased basal concentrations of extracellular glutamate in the epileptogenic versus the non-epileptogenic hippocampus. Such elevated glutamate levels have been proposed to underlie the initiation and maintenance of recurrent seizures, and a key question is what causes the elevation of glutamate in MTLE. Here, we explore the possibility that neurons in the hippocampal formation contain higher levels of the glutamate synthesizing enzyme phosphate-activated glutaminase (PAG) in patients with MTLE versus patients with other forms of temporal lobe epilepsy (non-MTLE). Increased PAG immunoreactivity was recorded in subpopulations of surviving neurons in the MTLE hippocampal formation, particularly in CA1 and CA3 and in the polymorphic layer of the dentate gyrus. Immunogold analysis revealed that PAG was concentrated in mitochondria. Double-labeling experiments indicated a positive correlation between the mitochondrial contents of PAG protein and glutamate, as well as between PAG enzyme activity and PAG protein as determined by Western blots. These data suggest that the antibodies recognize an enzymatically active pool of PAG. Western blots and enzyme activity assays of hippocampal homogenates revealed no change in PAG between MTLE and non-MTLE, despite a greatly (>50%) reduced number of neurons in the MTLE hippocampal formation compared to non-MTLE. Thus, the MTLE hippocampal formation contains an increased concentration and activity of PAG per neuron compared to non-MTLE. This increase suggests an enhanced capacity for glutamate synthesis-a finding that might contribute to the disrupted glutamate homeostasis in MTLE.
authors.affiliation: Department of Neurosurgery, Yale University School of Medicine, 333 Cedar Street, P.O. Box 208082, New Haven, CT 06520-8082, USA. tore.eid@yale.edu
authors.forename: Tore
authors.initials: T
authors.lastname: Eid
authors.forename: Janniche
authors.initials: J
authors.lastname: Hammer
authors.forename: Elise
authors.initials: E
authors.lastname: Rundén-Pran
authors.forename: Bjørg
authors.initials: B
authors.lastname: Roberg
authors.forename: Marion J
authors.initials: MJ
authors.lastname: Thomas
authors.forename: Kirsten
authors.initials: K
authors.lastname: Osen
authors.forename: Svend
authors.initials: S
authors.lastname: Davanger
authors.forename: Petter
authors.initials: P
authors.lastname: Laake
authors.forename: Ingeborg A
authors.initials: IA
authors.lastname: Torgner
authors.forename: Tih-Shih W
authors.initials: TS
authors.lastname: Lee
authors.forename: Jung H
authors.initials: JH
authors.lastname: Kim
authors.forename: Dennis D
authors.initials: DD
authors.lastname: Spencer
authors.forename: Ole Petter
authors.initials: OP
authors.lastname: Ottersen
authors.forename: Nihal C
authors.initials: NC
authors.lastname: de Lanerolle
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D004833:Epilepsy, Temporal Lobe / Q000201:enzymology / Q000473:pathology*; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D005972:Glutaminase / Q000378:metabolism*; D006624:Hippocampus / Q000473:pathology*; D006801:Humans; D008297:Male; D016253:Microscopy, Immunoelectron / Q000379:methods; D008875:Middle Aged; D009474:Neurons / Q000201:enzymology* / Q000648:ultrastructure; D018709:Statistics, Nonparametric
chemical_list: D005972:Glutaminase