title: Seizure-induced reduction in PIP3 levels contributes to seizure-activity and is rescued by valproic acid.
abstract: Phosphatidylinositol (3-5) trisphosphate (PIP3) is a central regulator of diverse neuronal functions that are critical for seizure progression, however its role in seizures is unclear. We have recently hypothesised that valproic acid (VPA), one of the most commonly used drugs for the treatment of epilepsy, may target PIP3 signalling as a therapeutic mode of action. Here, we show that seizure induction using kainic acid in a rat in vivo epilepsy model resulted in a decrease in hippocampal PIP3 levels and reduced protein kinase B (PKB/AKT) phosphorylation, measured using ELISA mass assays and Western blot analysis, and both changes were restored following VPA treatment. These finding were reproduced in cultured rat hippocampal primary neurons and entorhinal cortex-hippocampal slices during exposure to the GABA(A) receptor antagonist pentylenetetrazol (PTZ), which is widely used to generate seizures and seizure-like (paroxysmal) activity. Moreover, VPA's effect on paroxysmal activity in the PTZ slice model is blocked by phosphatidylinositol 3-kinase (PI3K) inhibition or PIP2 sequestration by neomycin, indicating that VPA's efficacy is dependent upon PIP3 signalling. PIP3 depletion following PTZ treatment may also provide a positive feedback loop, since enhancing PIP3 depletion increases, and conversely, reducing PIP3 dephosphorylation reduces paroxysmal activity and this effect is dependent upon AMPA receptor activation. Our results therefore indicate that PIP3 depletion occurs with seizure activity, and that VPA functions to reverse these effects, providing a novel mechanism for VPA in epilepsy treatment.
authors.affiliation: Centre for Biomedical Sciences, School of Biological Sciences, Royal Holloway University of London, Egham TW20 0EX, UK.
authors.forename: Pishan
authors.initials: P
authors.lastname: Chang
authors.affiliation: Department of Clinical and Experimental Epilepsy, Institute of Neurology, University College London, WC1N 3BG, UK. Electronic address: m.walker@ucl.ac.uk.
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Walker
authors.affiliation: Centre for Biomedical Sciences, School of Biological Sciences, Royal Holloway University of London, Egham TW20 0EX, UK. Electronic address: robin.williams@rhul.ac.uk.
authors.forename: Robin S B
authors.initials: RS
authors.lastname: Williams
mesh_terms: D000818:Animals; D000927:Anticonvulsants / Q000627:therapeutic use*; D002478:Cells, Cultured; D018756:GABA Antagonists / Q000494:pharmacology; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism / Q000503:physiopathology; D007608:Kainic Acid / Q000633:toxicity; D008297:Male; D009474:Neurons / Q000378:metabolism*; D010433:Pentylenetetrazole / Q000494:pharmacology; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000378:metabolism; D013226:Status Epilepticus / Q000139:chemically induced / Q000188:drug therapy* / Q000378:metabolism*; D014635:Valproic Acid / Q000627:therapeutic use*
chemical_list: D000927:Anticonvulsants; D018756:GABA Antagonists; D018129:Phosphatidylinositol Phosphates; D018091:Receptors, AMPA; C060974:phosphatidylinositol 3,4,5-triphosphate; D014635:Valproic Acid; D051057:Proto-Oncogene Proteins c-akt; D007608:Kainic Acid; D010433:Pentylenetetrazole
keywords: Kainic acid; PIP(3); PKB/AKT; Pentylenetetrazol; Seizure control; Valproic acid (VPA); mTOR2