Inhibition of AKT/GSK3β/CREB Pathway Improves the Responsiveness to AMPA Receptor Antagonists by Regulating GRIA1 Surface Expression in Chronic Epilepsy Rats.

Ji-Eun Kim,Duk-Shin Lee,Tae-Hyun Kim,Hana Park,Tae-Cheon Kang

doi:10.3390/biomedicines9040425

Abstract

α-Amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR) has been reported as one of the targets for treatment of epilepsy. Although maladaptive regulation of surface expression of glutamate ionotropic receptor AMPA type subunit 1 (GRIA1) subunit is relevant to the responsiveness to AMPAR antagonists (perampanel and GYKI 52466) in LiCl-pilocarpine-induced chronic epilepsy rats, the underlying mechanisms of refractory seizures to AMPAR antagonists have yet been unclear. In the present study, we found that both AMPAR antagonists restored the up-regulations of GRIA1 surface expression and Src family-mediated glycogen synthase kinase 3β (GSK3β)-Ca2+/cAMP response element-binding protein (CREB) phosphorylations to control levels in responders (whose seizure activities were responsive to AMPAR) but not non-responders (whose seizure activities were uncontrolled by AMPAR antagonists). In addition, 3-chloroacetyl indole (3CAI, an AKT inhibitor) co-treatment attenuated spontaneous seizure activities in non-responders, accompanied by reductions in AKT/GSK3β/CREB phosphorylations and GRIA1 surface expression. Although AMPAR antagonists reduced GRIA2 tyrosine (Y) phosphorylations in responders, they did not affect GRIA2 surface expression and protein interacting with C kinase 1 (PICK1) protein level in both responders and non-responders. Therefore, our findings suggest that dysregulation of AKT/GSK3β/CREB-mediated GRIA1 surface expression may be responsible for refractory seizures in non-responders, and that this pathway may be a potential target to improve the responsiveness to AMPAR antagonists.

Highlights

Epilepsy is a common clinical neurological disease characterized by spontaneous seizures due to abnormal neuronal discharges
We have reported that membrane glutamate ionotropic receptor AMPA type subunit 1 (GRIA1)/GRIA2 ratio is significantly higher in chronic epilepsy rats than that in control animals, indicating the existing preponderance of Ca2+ -permeable Amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR), both GRIA1 and GRIA2 levels are lower in the hippocampus
S133 phosphorylation ratio to control level in non-responders to perampanel (t(8) = 5.4, p < 0.001, Student t-test) and GYKI 52466 (t(8) = 4.9, p = 0.001, Student t-test), respectively (Figure 9A,G). 3CAI co-treatment did not alter protein interacting with C kinase 1 (PICK1) protein level in non-responders to perampanel and GYKI 52466 (Figure 9A,H). These findings indicate that the glycogen synthase kinase 3β (GSK3β) activation may improve anti-convulsive effects of AMPAR antagonists in non-responders by regulating cAMP response element-binding protein (CREB) activity rather than PICK1 expression

Summary

Introduction

Epilepsy is a common clinical neurological disease characterized by spontaneous seizures due to abnormal neuronal discharges. About 30% temporal lobe epilepsy (TLE) patients show refractory seizures that are uncontrolled by standard medications with antiepileptic drugs (AEDs). Patients with intractable seizures have a high mortality rate [1,2]. Given the inefficacy of AEDs and the unrelenting nature of intractable epilepsy, the necessity to explore the underlying mechanisms of generation of refractory seizures is undoubted. The pathogenesis of epilepsy remains to be fully elucidated, hyper-activation of the glutamate receptor is one of the important causes of epilepsy. A massive release of glutamate and the subsequent over-activation of glutamate receptors cause aberrant neuronal hyper-excitability, followed by delayed neuronal death and secondary injury [3,4]

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Conclusion