Sodium Valproate Ameliorates Neuronal Apoptosis in a Kainic Acid Model of Epilepsy via Enhancing PKC-Dependent GABA(A)R gamma 2 Serine 327 Phosphorylation

GABA is a dominant inhibitory neurotransmitter in the brain and A type GABA receptor (GABA(A)R) phosphorylation is critical for GABA-mediated inhibitory effect. However, its role in the neuroprotective effect of sodium valproate (VPA), a prevalent drug for treating patients with epilepsy, remains elusive. The present study was conducted to explore the role of GABA(A)R phosphorylation in the neuroprotection of VPA against a kainic acid-induced epileptic rat model and the potential molecular mechanisms. Neuronal apoptosis was evaluated by TUNEL assay, PI/Annexin V double staining, caspase-3 activity detection and Bax and Bcl-2 proteins expression via Western blot analysis. The primary rat hippocampal neurons were cultivated and cell viability was measured by CCK8 detection following KA- or free Mg2+-induced neuronal impairment. Our results found that VPA treatment significantly reduced neuronal apoptosis in the KA-induced rat model (including reductions of TUNEL-positive cells, caspase-3 activity and Bax protein expression, and increase of Bcl-2 protein level). In the in vitro experiments, VPA at the concentration of 1mM for 24h also increased cell survival and suppressed cell apoptosis in KA- or no Mg2+-induced models via CCK8 assay and PI/Annexin V double staining, respectively. What is more important, the phosphorylation of 2 subunit at serine 327 residue for GABA(A)R was found to be robustly enhanced both in the KA-induced epileptic rat model and neuronal cultures following KA exposure after VPA treatment, while no evident alteration was found in terms of GABA(A)R 3 phosphorylation (408 or 409 serine residue). Additionally, pharmacological inhibition of protein kinase C (PKC) clearly abrogated the neuroprotective potential of VPA against KA- or free Mg2+-associated neuronal injury, indicating a critical role of PKC in the effect of GABA(A)R 2 serine 327 phosphorylation in VPA's protection. In summary, our work reveals that VPA mitigates neuronal apoptosis in KA-triggered epileptic seizures, at least, via augmenting PKC-dependent GABA(A)R 2 phosphorylation at serine 327 residue.