Purpose: Dravet syndrome (DS), a devastating epileptic encephalopathy, is mostly caused by mutations of the SCN1A gene, coding for the voltage-gated Na + channel Na V1.1 α subunit. About 50% of SCN1A DS mutations truncate Na V1.1, possibly causing complete loss of its function. However, it has not been investigated yet if Na V1.1 truncated mutants are dominant negative, if they impair expression or function of wild-type channels, as it has been shown for truncated mutants of other proteins (e.g., Ca V channels). We studied the effect of two DS truncated Na V1.1 mutants, R222* and R1234*, on coexpressed wild-type Na + channels. Methods: We engineered R222* or R1234* in the human cDNA of Na V1.1 (hNa V1.1) and studied their effect on coexpressed wild-type hNa V1.1, hNa V1.2 or hNa V1.3 cotransfecting tsA-201 cells, and on hNa V1.6 transfecting an human embryonic kidney (HEK) cell line stably expressing this channel. We also studied hippocampal neurons dissociated from Na V1.1 knockout (KO) mice, an animal model of DS expressing a truncated Na V1.1 channel. Key Findings: We found no modifications of current amplitude coexpressing the truncated mutants with hNa V1.1, hNa V1.2, or hNa V1.3, but a 30% reduction coexpressing them with hNa V1.6. However, we showed that also coexpression of functional full-length hNa V1.1 caused a similar reduction. Therefore, this effect should not be involved in the pathomechanism of DS. Some gating properties of hNa V1.1, hNa V1.3, and hNa V1.6 were modified, but recordings of hippocampal neurons dissociated from Na V1.1 KO mice did not show any significant modifications of these properties. Therefore, Na V1.1 truncated mutants are not dominant negative, consistent with haploinsufficiency as the cause of DS. Significance: We have better clarified the pathomechanism of DS, pointed out an important difference between pathogenic truncated Ca V2.1 mutants and hNa V1.1 ones, and shown that hNa V1.6 expression can be reduced in physiologic conditions by coexpression of hNa V1.1. Moreover, our data may provide useful information for the development of therapeutic approaches.
- Calcium channel
- Severe myoclonic epilepsy of infancy
ASJC Scopus subject areas
- Clinical Neurology