| Abstrakt: |
Summary Purpose: Dravet syndrome (DS), a devastating epileptic encephalopathy, is mostly caused by mutations of the SCN1A gene, coding for the voltage-gated Na+ channel NaV1.1 α subunit. About 50% of SCN1A DS mutations truncate NaV1.1, possibly causing complete loss of its function. However, it has not been investigated yet if NaV1.1 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., CaV channels). We studied the effect of two DS truncated NaV1.1 mutants, R222* and R1234*, on coexpressed wild-type Na+ channels. Methods: We engineered R222* or R1234* in the human cDNA of NaV1.1 (hNaV1.1) and studied their effect on coexpressed wild-type hNaV1.1, hNaV1.2 or hNaV1.3 cotransfecting tsA-201 cells, and on hNaV1.6 transfecting an human embryonic kidney (HEK) cell line stably expressing this channel. We also studied hippocampal neurons dissociated from NaV1.1 knockout (KO) mice, an animal model of DS expressing a truncated NaV1.1 channel. Key Findings: We found no modifications of current amplitude coexpressing the truncated mutants with hNaV1.1, hNaV1.2, or hNaV1.3, but a 30% reduction coexpressing them with hNaV1.6. However, we showed that also coexpression of functional full-length hNaV1.1 caused a similar reduction. Therefore, this effect should not be involved in the pathomechanism of DS. Some gating properties of hNaV1.1, hNaV1.3, and hNaV1.6 were modified, but recordings of hippocampal neurons dissociated from NaV1.1 KO mice did not show any significant modifications of these properties. Therefore, NaV1.1 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 CaV2.1 mutants and hNaV1.1 ones, and shown that hNaV1.6 expression can be reduced in physiologic conditions by coexpression of hNaV1.1. Moreover, our data may provide useful information for the development of therapeutic approaches. [ABSTRACT FROM AUTHOR] |
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