The γ-aminobutyric acid (GABA) type A receptor (GABA A R) is the major inhibitory neurotransmitter receptor in the brain. Its multiple subunits show regional, developmental, and disease-related plasticity of expression; however, the regulatory networks controlling GABA A R subunit expression remain poorly understood. We report that the seizure-induced decrease in GABA A R α1 subunit expression associated with epilepsy is mediated by the Janus kinase (JAK)/ signal transducer and activator of transcription (STAT) pathway regulated by brain-derived neurotrophic factor (BDNF). BDNF-and seizure-dependent phosphorylation of STAT3 cause the adenosine 3′,5′-monophosphate (cAMP) response element-binding protein (CREB) family member ICER (inducible cAMP early repressor) to bind with phosphorylated CREB at the Gabra1:CRE site. JAK/STAT pathway inhibition prevents the seizure-induced decrease in GABA A R α1 abundance in vivo and, given that BDNF is known to increase the abundance of GABA A R α4 in a JAK/STATindependent manner, indicates that BDNF acts through at least two distinct pathways to influence GABA A R-dependent synaptic inhibition.

Differential expression of GABA A receptor (GABR) subunits has been demonstrated in hippocampus from patients and animals with temporal lobe epilepsy (TLE), but whether these changes are important for epileptogenesis remains unknown. Previous studies in the adult rat pilocarpine model of TLE found reduced expression of GABR ␣1 subunits and increased expression of ␣4 subunits in dentate gyrus (DG) of epileptic rats compared with controls. To investigate whether this altered subunit expression is a critical determinant of spontaneous seizure development, we used adeno-associated virus type 2 containing the ␣4 subunit gene (GABRA4) promoter to drive transgene expression in DG after status epilepticus (SE). This novel use of a condition-dependent promoter upregulated after SE successfully increased expression of GABR ␣1 subunit mRNA and protein in DG at 1-2 weeks after SE. Enhanced ␣1 expression in DG resulted in a threefold increase in mean seizure-free time after SE and a 60% decrease in the number of rats developing epilepsy (recurrent spontaneous seizures) in the first 4 weeks after SE. These findings provide the first direct evidence that altering GABR subunit expression can affect the development of epilepsy and suggest that ␣1 subunit levels are important determinants of inhibitory function in hippocampus.

Fig. 1. Protein-protein interactions between gp32 and gp59 on fDNA. (A) The fluorescence from individual molecules of fDNA with the proteins bound in the order as indicated at the side of each row. The gp32 protein is labeled with A488 (gp32 D ) and the gp59 protein is labeled with A555 (gp59 A ). The filter sets are described in Experimental Methods: F1 is for A488 emission, F2 for FRET between A488 and A555, and F3 for A555 emission. (B) Ensemble FRET studies of Oregon-green-488-maleimide-labeled gp59 titrated into a solution of 400 nM CPM-labeled gp32 and 100 nM fDNA. The fluorescence spectra of 400 nM CPM-gp32 alone (black line), the endpoint of the titration at 1 M Oregon-green-488-maleimide-gp59 (dark gray line), and several intermediate spectra (light gray lines) are shown. (C) Analysis of the donor quenching and acceptor sensitization plotted against the gp59 concentration determines the stoichiometry among gp32, gp59, and fDNA to be 1:1:1 with a calculated binding constant of Ϸ40 nM.