Seizure control through genetic and pharmacological manipulation of Pumilio: a key component of neuronal homeostasis

Abstract

Epilepsy is a significant disorder for which approximately one-third of patients do not respond to drug treatments. Next-generation drugs, which interact with novel targets, are required to provide a better clinical outcome for these individuals. To identify potential novel targets for antiepileptic drug (AED) design, we used RNA sequencing to identify changes in gene transcription in two seizure models of the fruitfly Drosophila melanogaster. The first model compared gene transcription between wildtype (WT) and the bangsenseless1 (parabss) mutant; a gain-of-function in the sole fly voltage-gated sodium channel (paralytic). The second model compared WT to WT fed the proconvulsant picrotoxin (PTX). We identified 743 genes (FDR≤1%) with significant altered expression levels that are common to both seizure models. Of these, 339 are up-regulated and 397 are down-regulated. We identify dpumilio (dpum) to be down-regulated in both seizure models. Pum is a known homeostatic regulator of action potential firing in both flies and mammals. Pum achieves control of neuronal firing through binding to, and regulating translation of, the mRNA transcripts of voltage-gated sodium channels (Nav). We show that maintaining expression of dpum in the CNS of parabss is potently anticonvulsive, whilst its reduction through RNAi-mediated knockdown is proconvulsive. Using a cell-based luciferase reporter screen, we screened a repurposed chemical library and identified 12 compounds sufficient to increase activity of dPum. Of these compounds, we focus on avobenzone which significantly rescues seizure behaviour in parabss. The mode-of-action of avobenzone includes potentiation of dpum expression and mirrors the ability of this homeostatic regulator to reduce the persistent voltage-gated Na+ current (INaP) in an identified neuron. This study reports a novel approach to suppress seizure and highlights the mechanisms of neuronal homeostasis as potential targets for next-generation AEDs.