SAHA (Vorinostat) Corrects Inhibitory Synaptic Deficits Caused by Missense Epilepsy Mutations to the GABAA Receptor γ2 Subunit

• Published in: Frontiers in molecular neuroscience 2018-03, Vol.11, p.89-89
• Main Authors: Durisic, Nela, Keramidas, Angelo, Dixon, Christine L., Lynch, Joseph W.
• Format: Article
• Language: English
• Subjects: Acids; Cancer; Channel gating; Contamination; Convulsions & seizures; Epilepsy; febrile seizures; GABA receptors; Immunohistochemistry; Inhibitory postsynaptic potentials; Investigations; Mutation; Neurons; Neuroscience; Neurosciences; Peptides; proteostasis; Seizures; suberanilohydroxamic acid; Subunit structure; synaptic inhibition; Transfection; γ-Aminobutyric acid A receptors
• ISSN: 1662-5099; 1662-5099
• DOI: 10.3389/fnmol.2018.00089

The GABAA receptor (GABAAR) α1 subunit A295D epilepsy mutation reduces the surface expression of 1A295D22 GABAARs via ER-associated protein degradation. Suberanilohydroxamic acid (SAHA, also known as Vorinostat) was recently shown to correct the misfolding of 1A295D subunits and thereby enhance the functional surface expression of 1A295D22 GABAARs. Here we investigated whether SAHA can also restore the surface expression of 2 GABAAR subunits that incorporate epilepsy mutations (N40S, R43Q, P44S, R138G) known to reduce surface expression via ER-associated protein degradation. As a control, we also investigated the 2K289M epilepsy mutation that impairs gating without reducing surface expression. Effects of mutations were evaluated on inhibitory postsynaptic currents (IPSCs) mediated by the major synaptic 122 GABAAR isoform. Recordings were performed in neuron-HEK293 cell artificial synapses to minimise contamination by GABAARs of undefined subunit composition. Transfection with α1β2γ2N40S, α1β2γ2R43Q, α1β2γ2P44S and α1β2γ2R138G subunits produced IPSCs with decay times slower than those of unmutated α1β2γ2 GABAARs due to the low expression of mutant γ2 subunits and the correspondingly high expression of slow-decaying α1β2 GABAARs. SAHA pre-treatment significantly accelerated the decay time constants of IPSCs consistent with the upregulation of mutant 2 subunit expression. This increase in surface expression was confirmed by immunohistochemistry. SAHA had no effect on either the IPSC kinetics or surface expression levels of 122K289M GABAARs, confirming its specificity for ER-retained mutant 2 subunits. We also found that 122K289M GABAARs and SAHA-treated α1β2γ2R43Q, α1β2γ2P44S and α1β2γ2R138G GABAARs all mediated IPSCs that decayed at significantly faster rates than wild type receptors as temperature was increased from 22 to 40 oC. This may help explain why these mutations cause febrile seizures. Given that SAHA is approved by therapeutic regulatory agencies for human use, we propose that it may be worth investigating as a treatment for epilepsies caused the N40S, R43Q, P44S and R138G mutations. Although SAHA has already been proposed as a therapeutic for patients harbouring the α1A295D epilepsy mutation, the present study extends its potential utility to a new subunit and four new mutations.