Abstract
Seizure can result from increased voltage-gated persistent sodium current expression. Although many clinically-approved antiepileptic drugs target voltage-gated persistent sodium current, none exclusively repress this current without also adversely affecting the transient voltage-gated sodium current. Achieving a more selective block has significant potential for the treatment of epilepsy. Recent studies show that voltage-gated persistent sodium current amplitude is regulated by alternative splicing offering the possibility of a novel route for seizure control. In this study we identify 291 splicing regulators that, on knockdown, alter splicing of the Drosophila voltage-gated sodium channel to favour inclusion of exon K, rather than the mutually exclusive exon L. This change is associated with both a significant reduction in voltage-gated persistent sodium current, without change to transient voltage-gated sodium current, and to rescue of seizure in this model insect. RNA interference mediated knock-down, in two different seizure mutants, shows that 95 of these regulators are sufficient to significantly reduce seizure duration. Moreover, most suppress seizure activity in both mutants, indicative that they are part of well conserved pathways and likely, therefore, to be optimal candidates to take forward to mammalian studies. We provide proof-of-principle for such studies by showing that inhibition of a selection of regulators, using small molecule inhibitors, is similarly effective to reduce seizure. Splicing of the Drosophila sodium channel shows many similarities to its mammalian counterparts, including altering the amplitude of voltage-gated persistent sodium current. Our study provides the impetus to investigate whether manipulation of splicing of mammalian voltage-gated sodium channels may be exploitable to provide effective seizure control.
Highlights
Mutations in more than 60 genes have been linked to epilepsy (Noebels, 2003), a principle commonality underlying seizure generation is neuronal hyperexcitability
Multiple lines of evidence implicate an abnormal increase in neuronal voltage-gated persistent sodium current (INaP) directly contributes to hyperexcitability and, as such, this current component is an attractive target for antiepileptic drug (AED) design (Chen et al, 2001; Stafstrom, 2007)
In K-renilla, a termination codon was introduced in exon L, such that inclusion of exon K leads to expression of a mRNA encoding a renilla-fusion protein, while inclusion of exon L results in a truncated, and nonfunctional, transcript
Summary
Mutations in more than 60 genes have been linked to epilepsy (Noebels, 2003), a principle commonality underlying seizure generation is neuronal hyperexcitability. Multiple lines of evidence implicate an abnormal increase in neuronal voltage-gated persistent sodium current (INaP) directly contributes to hyperexcitability and, as such, this current component is an attractive target for antiepileptic drug (AED) design (Chen et al, 2001; Stafstrom, 2007).
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