Altered Cortical GABA(A) Receptor Composition, Physiology, and Endocytosis in a Mouse Model of a Human Genetic Absence Epilepsy Syndrome

作者：Zhou Chengwen; Huang Zhiling; Ding Li; Deel M Elizabeth; Arain Fazal M; Murray Clark R; Patel Ronak S; Flanagan Christopher D; Gallagher Martin J^*

来源：JOURNAL OF BIOLOGICAL CHEMISTRY, 2013, 288(29): 21458-21472.

DOI：10.1074/jbc.M112.444372

Patients with generalized epilepsy exhibit cerebral cortical disinhibition. Likewise, mutations in the inhibitory ligand-gated ion channels, GABA(A) receptors (GABA(A)Rs), cause generalized epilepsy syndromes in humans. Recently, we demonstrated that heterozygous knock-out (Het(alpha 1)KO) of the human epilepsy gene, the GABA(A)R alpha 1 subunit, produced absence epilepsy in mice. Here, we determined the effects of Het(alpha 1)KO on the expression and physiology of GABA(A)Rs in the mouse cortex. We found that Het(alpha 1)KO caused modest reductions in the total and surface expression of the beta 2 subunit but did not alter beta 1 or beta 3 subunit expression, results consistent with a small reduction of GABAARs. Cortices partially compensated for Het(alpha 1)KO by increasing the fraction of residual alpha 1 subunit on the cell surface and by increasing total and surface expression of alpha 3, but not alpha 2, subunits. Co-immunoprecipitation experiments revealed that Het(alpha 1)KO increased the fraction of alpha 1 subunits, and decreased the fraction of alpha 3 subunits, that associated in hybrid alpha 1 alpha 3 beta gamma receptors. Patch clamp electrophysiology studies showed that Het(alpha 1)KO 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 Het(alpha 1)KO reduced base-line GABA(A)R endocytosis, an effect that probably contributes to the observed changes in GABA(A)R expression. These findings demonstrate that Het(alpha 1)KO exerts two principle disinhibitory effects on cortical GABA(A)R-mediated inhibitory neurotransmission: 1) a modest reduction of GABA(A)R number and 2) a partial compensation with GABA(A)R isoforms that possess physiological properties different from those of the otherwise predominant alpha 1 beta gamma GABA(A)Rs.

• 出版日期2013-7-19