GSK3β Activity Alleviates Epileptogenesis and Limits GluA1 Phosphorylation

Abstract

Background: Glycogen synthase kinase-3β (GSK3β) is a key regulator of cellular homeostasis. In neurons, GSK3β contributes to the control of neuronal transmission and plasticity, but its role in epilepsy remains to be defined. Methods: Biochemical and electrophysiological methods were used to assess the role of GSK3β in regulating neuronal transmission and epileptogenesis. GSK3β activity was increased genetically in GSK3β[S9A] mice. Its effects on neuronal transmission and epileptogenesis induced by kainic acid were assessed by field potential recordings in mice brain slices and video electroencephalography in vivo. The ion channel expression was measured in brain samples from mice and followed by analysis in samples from patients with temporal lobe epilepsy or focal cortical dysplasia in correlation to GSK3β phosphorylation. Findings: Higher GSK3β activity decreased the susceptibility to kainic acid-induced epileptiform discharges and the progression of epileptogenesis. At the biochemical level, higher GSK3β activity increased the expression of hyperpolarization-activated cyclic nucleotide-gated (HCN) channel 4 and decreased phosphorylation of the glutamate α±-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit GluA1. The phosphorylation of GluA1 at Serine 831 and Serine 845 was lower in GSK3β[S9A] mice than in wildtype controls, under basal conditions and in the epileptic mouse brain, respectively. Moreover, we found a significant correlation between higher inhibitory GSK3β phosphorylation at Serine 9 and higher activating GluA1 phosphorylation at Serine 845 in brain samples from epileptic patients. Interpretation: Our data imply GSK3β activity in the protection of neuronal networks from hyper-activation and indicate that the anti-epileptogenic function of GSK3I² involves decreasing the synaptic AMPA receptors pool. Funding: Research was supported by the Polish National Science Centre (no. 2011/01/N/NZ3/05409 to MU; no. 2017/26/D/NZ4/00159 to PK-G) and FP7 European Union grants (no. 223276, “NeuroGSK3” to FvL and JJ; no. 229676, “HealthProt” to JJ; no. 602102, “Epitarget” to EV and EA.). This study was also co-financed by European Union funds from the European Social Fund (MU). The work of MU was partially financed by IUVENTUS IP2012 037872. The work of MU, KKotulska, SJ, EA and JJ was partly supported by 7FP grant “EPISTOP” (grant agreement no. 602391), and the Polish Ministerial funds for science (years 2014-2019) for the implementation of international co-financed projects. The work of AG was financed by the Polish National Science Centre (grant no. 2011/01/B/NZ3/05397). KKotulska, SJ and JJ were partly financed by the Polish National Center for Research and Development (grant EPIMARKER, no. STRATEGMED3/306306/4/2017). MU was a recipient of a L’OrealUNESCO for Women and Science Fellowship in Poland and EMBO Short Term Fellowship. JJ and MU were also recipients of a Foundation for Polish Science Mistrz Professorial Subsidy and Fellowship, respectively. Declaration of Interest: SJ received Advisory Board honoraria from Novartis Oncology. The other authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Ethical Approval: The study was approved by the local Ethics Board in Warsaw (approval no. 223/KBE/2015).