GAPDH-mediated posttranscriptional regulations of sodium channel Scn1a and Scn3a genes under seizure and ketogenic diet conditions.

Abnormal expressions of sodium channel SCN1A and SCN3A genes alter neural excitability that are believed to contribute to the pathogenesis of epilepsy, a long-term risk of recurrent seizures. Ketogenic diet (KD), a high-fat and low-carbohydrate treatment for difficult-to-control (refractory) epilepsy in children, has been suggested to reverse gene expression patterns. Here, we reveal a novel role of GAPDH on the posttranscriptional regulation of mouse Scn1a and Scn3a expressions under seizure and KD conditions. We show that GAPDH binds to a conserved region in the 3' UTRs of human and mouse SCN1A and SCN3A genes, which decreases and increases genes' expressions by affecting mRNA stability through SCN1A 3' UTR and SCN3A 3' UTR, respectively. In seizure mice, the upregulation and phosphorylation of GAPDH enhance its binding to the 3' UTR, which lead to downregulation of Scn1a and upregulation of Scn3a. Furthermore, administration of KD generates ß-hydroxybutyric acid which rescues the abnormal expressions of Scn1a and Scn3a by weakening the GAPDH's binding to the element. Taken together, these data suggest that GAPDH-mediated expression regulation of sodium channel genes may be associated with epilepsy and the anticonvulsant action of KD.

Nontruncating SCN1A mutations associated with severe myoclonic epilepsy of infancy impair cell surface expression.

Mutations in SCN1A, encoding the voltage-gated sodium channel Na(V)1.1, are the most common cause of severe myoclonic epilepsy of infancy (SMEI) or Dravet syndrome. SMEI is most often associated with premature truncations of Na(V)1.1 that cause loss of function, but nontruncating mutations also occur. We hypothesized that some nontruncating mutations might impair trafficking of Na(V)1.1 to the plasma membrane. Here we demonstrated that seven nontruncating missense or in-frame deletion mutations (L986F, delF1289, R1648C, F1661S, G1674R, and G1979E) exhibited reduced cell surface expression relative to wild type (WT) Na(V)1.1 consistent with impaired trafficking. We tested whether two commonly prescribed antiepileptic drugs (phenytoin, lamotrigine), as well as the cystic fibrosis transmembrane conductance regulator (CFTR) trafficking corrector VRT-325, could rescue cell surface and functional expression of two representative Na(V)1.1 mutants (R1648C, G1674R). Treatment of cells with phenytoin increased cell surface expression of WT-Na(V)1.1 and both mutant channels, whereas lamotrigine only increased surface expression of R1648C. VRT-325 did not alter surface expression of WT-Na(V)1.1 or mutant channels. Although phenytoin increased surface expression of G1674R, channel function was not restored, suggesting that this mutation also causes an intrinsic loss of function. Both phenytoin and lamotrigine increased functional expression of R1648C, but lamotrigine also increased persistent sodium current evoked by this mutation. Our findings indicate that certain nontruncating SCN1A mutations associated with SMEI have impaired cell surface expression and that some alleles may be amenable to pharmacological rescue of this defect. However, rescue of dysfunctional Na(V)1.1 channels to the plasma membrane could contribute to exacerbating rather than ameliorating the disease.