title: Altered cortical GABAA receptor composition, physiology, and endocytosis in a mouse model of a human genetic absence epilepsy syndrome.
abstract: Patients with generalized epilepsy exhibit cerebral cortical disinhibition. Likewise, mutations in the inhibitory ligand-gated ion channels, GABAA receptors (GABAARs), cause generalized epilepsy syndromes in humans. Recently, we demonstrated that heterozygous knock-out (Hetα1KO) of the human epilepsy gene, the GABAAR α1 subunit, produced absence epilepsy in mice. Here, we determined the effects of Hetα1KO on the expression and physiology of GABAARs in the mouse cortex. We found that Hetα1KO caused modest reductions in the total and surface expression of the β2 subunit but did not alter β1 or β3 subunit expression, results consistent with a small reduction of GABAARs. Cortices partially compensated for Hetα1KO by increasing the fraction of residual α1 subunit on the cell surface and by increasing total and surface expression of α3, but not α2, subunits. Co-immunoprecipitation experiments revealed that Hetα1KO increased the fraction of α1 subunits, and decreased the fraction of α3 subunits, that associated in hybrid α1α3βγ receptors. Patch clamp electrophysiology studies showed that Hetα1KO layer VI cortical neurons exhibited reduced inhibitory postsynaptic current peak amplitudes, prolonged current rise and decay times, and altered responses to benzodiazepine agonists. Finally, application of inhibitors of dynamin-mediated endocytosis revealed that Hetα1KO reduced base-line GABAAR endocytosis, an effect that probably contributes to the observed changes in GABAAR expression. These findings demonstrate that Hetα1KO exerts two principle disinhibitory effects on cortical GABAAR-mediated inhibitory neurotransmission: 1) a modest reduction of GABAAR number and 2) a partial compensation with GABAAR isoforms that possess physiological properties different from those of the otherwise predominant α1βγ GABAARs.
authors.affiliation: From the Department of Neurology, Vanderbilt University, Nashville, Tennessee 37232.
authors.forename: Chengwen
authors.initials: C
authors.lastname: Zhou
authors.affiliation: From the Department of Neurology, Vanderbilt University, Nashville, Tennessee 37232.
authors.forename: Zhiling
authors.initials: Z
authors.lastname: Huang
authors.affiliation: From the Department of Neurology, Vanderbilt University, Nashville, Tennessee 37232.
authors.forename: Li
authors.initials: L
authors.lastname: Ding
authors.affiliation: From the Department of Neurology, Vanderbilt University, Nashville, Tennessee 37232.
authors.forename: M Elizabeth
authors.initials: ME
authors.lastname: Deel
authors.affiliation: From the Department of Neurology, Vanderbilt University, Nashville, Tennessee 37232.
authors.forename: Fazal M
authors.initials: FM
authors.lastname: Arain
authors.affiliation: From the Department of Neurology, Vanderbilt University, Nashville, Tennessee 37232.
authors.forename: Clark R
authors.initials: CR
authors.lastname: Murray
authors.affiliation: From the Department of Neurology, Vanderbilt University, Nashville, Tennessee 37232.
authors.forename: Ronak S
authors.initials: RS
authors.lastname: Patel
authors.affiliation: From the Department of Neurology, Vanderbilt University, Nashville, Tennessee 37232.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Flanagan
authors.affiliation: From the Department of Neurology, Vanderbilt University, Nashville, Tennessee 37232. Electronic address: Martin.Gallagher@Vanderbilt.edu.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Gallagher
mesh_terms: D000483:Alleles; D000818:Animals; D001569:Benzodiazepines / Q000494:pharmacology; D019556:COS Cells; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D002522:Chlorocebus aethiops; D004195:Disease Models, Animal; D034281:Dynamins / Q000378:metabolism; D004705:Endocytosis; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D004832:Epilepsy, Absence / Q000235:genetics* / Q000473:pathology / Q000503:physiopathology*; D058785:GABA-A Receptor Agonists / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D006579:Heterozygote; D006801:Humans; D007700:Kinetics; D051379:Mice; D018345:Mice, Knockout; D008954:Models, Biological; D011485:Protein Binding / Q000187:drug effects; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism; D013569:Synapses / Q000187:drug effects / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D058785:GABA-A Receptor Agonists; D021122:Protein Subunits; D012333:RNA, Messenger; D011963:Receptors, GABA-A; D001569:Benzodiazepines; D005680:gamma-Aminobutyric Acid; D034281:Dynamins
keywords: Brain; Confocal Microscopy; Electrophysiology; Endocytosis; Endoplasmic Reticulum (ER); Epilepsy; GABA Receptors; Glycosylation; Membrane Trafficking; Western Blotting