AUTHOR=Layer Nikolas , Sonnenberg Lukas , Pardo González Emilio , Benda Jan , Hedrich Ulrike B. S. , Lerche Holger , Koch Henner , Wuttke Thomas V. 

TITLE=Dravet Variant SCN1AA1783V Impairs Interneuron Firing Predominantly by Altered Channel Activation

JOURNAL=Frontiers in Cellular Neuroscience

VOLUME=15

YEAR=2021

URL=https://www.frontiersin.org/journals/cellular-neuroscience/articles/10.3389/fncel.2021.754530

DOI=10.3389/fncel.2021.754530

ISSN=1662-5102

ABSTRACT=<p>Dravet syndrome (DS) is a developmental epileptic encephalopathy mainly caused by functional Na<sub>V</sub>1.1 haploinsufficiency in inhibitory interneurons. Recently, a new conditional mouse model expressing the recurrent human p.(Ala1783Val) missense variant has become available. In this study, we provided an electrophysiological characterization of this variant in tsA201 cells, revealing both altered voltage-dependence of activation and slow inactivation without reduced sodium peak current density. Based on these data, simulated interneuron (IN) firing properties in a conductance-based single-compartment model suggested surprisingly similar firing deficits for Na<sub>V</sub>1.1<sup>A1783V</sup> and full haploinsufficiency as caused by heterozygous truncation variants. Impaired Na<sub>V</sub>1.1<sup>A1783V</sup> channel activation was predicted to have a significantly larger impact on channel function than altered slow inactivation and is therefore proposed as the main mechanism underlying IN dysfunction. The computational model was validated in cortical organotypic slice cultures derived from conditional <italic>Scn1a</italic><sup><italic>A</italic>1783<italic>V</italic></sup> mice. Pan-neuronal activation of the p.Ala1783V <italic>in vitro</italic> confirmed a predicted IN firing deficit and revealed an accompanying reduction of interneuronal input resistance while demonstrating normal excitability of pyramidal neurons. Altered input resistance was fed back into the model for further refinement. Taken together these data demonstrate that primary loss of function (LOF) gating properties accompanied by altered membrane characteristics may match effects of full haploinsufficiency on the neuronal level despite maintaining physiological peak current density, thereby causing DS.</p>