Targeted Augmentation of Nuclear Gene Output (TANGO) of Scn1a rescues parvalbumin interneuron excitability and reduces seizures in a mouse model of Dravet Syndrome

doi:10.1016/j.brainres.2021.147743

Brain Research

Volume 1775, 15 January 2022, 147743

https://doi.org/10.1016/j.brainres.2021.147743 Get rights and content

Highlights

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STK-001 treatment reduces seizures in a mouse model of Dravet Syndrome.
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STK-001 prolongs survival in a mouse model of Dravet Syndrome.
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Parvalbumin-positive interneuron hypoexcitability is rescued by STK-001.

Abstract

Dravet Syndrome (DS) is a severe developmental and epileptic encephalopathy typically caused by loss-of-function de novo mutations in the SCN1A gene which encodes the voltage-gated sodium channel isoform Na_V1.1. Decreased Na_V1.1 expression results in impaired excitability of inhibitory interneurons and seizure onset. To date, there are no clinically available treatments for DS that directly address the core mechanism of disease; reduced Na_V1.1 expression levels in interneurons. Recently, Targeted Augmentation of Nuclear Gene Output (TANGO) of SCN1A by the antisense oligonucleotide (ASO) STK-001, was shown to increase Scn1a mRNA levels, increase Na_V1.1 protein expression, reduce seizures, and improve survival in the Scn1a^+/− mouse model of DS. However, it remains unknown whether STK-001 treatment rescues the reduced intrinsic excitability of parvalbumin-positive (PV) inhibitory interneurons associated with DS. In this study, we demonstrate that STK-001 treatment reduces seizures, prolongs survival, and rescues PV interneuron excitability in Scn1a^+/− mice to levels observed in WT littermates. Together, these results support the notion that TANGO-mediated augmentation of Na_V1.1 levels directly targets and rescues one of the core disease mechanisms of DS.

Graphical abstract

Introduction

Dravet syndrome (DS) is a devastating neurodevelopmental and epileptic encephalopathy with seizure onset in the first few years of life (Dravet, 2011). Patients additionally exhibit other cognitive and motor impairments and have a substantial risk for sudden unexpected death in epilepsy (SUDEP) (Dravet, 2011, Scheffer, 2012). Most patients with DS have de novo mutations in the SCN1A gene which encodes the voltage-gated sodium channel (VGSC) isoform Na_V1.1. Characterization of DS patient mutations has revealed that variants are typically loss-of-function leading to reduced intrinsic neuronal excitability of fast-spiking parvalbumin-positive (PV) inhibitory interneurons (Catterall, 2018, Favero et al., 2018, Tai et al., 2014). Because PV interneurons serve to constrain network excitability, selective impairment in their excitability ultimately renders the network hyperexcitable and seizure-prone (Catterall, 2018).

Although VGSC inhibitors are frequently used to treat epilepsy in general, clinical studies have demonstrated that reducing VGSC function can exacerbate seizures in patients with DS and DS mouse models (Guerrini et al., 1998, Hawkins et al., 2017). Circumventing this issue, current treatment approaches seek to augment GABAergic inhibitory neurotransmission primarily through GABA_A receptor agonists such as stiripentol, clobazam, and others (Cross et al., 2019). Additionally, fenfluramine, presumably acting through augmentation of serotonergic signaling, and cannabidiol, acting through endocannabinoid pathways, are newer therapies for treating seizures in DS (Cross et al., 2019). However, current approaches do not fully control seizures in the majority of patients and are not disease modifying, indicating the pressing demand for novel therapeutic strategies (Cross et al., 2019).

In theory, restoration of Na_V1.1 expression to normal physiological levels would restore proper inhibitory interneuron function and directly address the core mechanism of DS pathology. Targeted Augmentation of Nuclear Gene Output (TANGO) is a novel approach which utilizes antisense oligonucleotides (ASOs) to specifically increase levels of productive mRNA transcripts to boost functional protein levels (Lim et al., 2020). A recent report demonstrated that treatment with STK-001, a TANGO-based ASO, on postnatal day 2 (P2) increased Scn1a mRNA and Na_V1.1 expression in the brain, reduced seizure frequency, and prolonged survival of Scn1a^+/− in a DS mouse model (Han et al., 2020). However, it remains unknown how STK-001 treatment specifically affects PV interneuron physiological function. In this study, we demonstrate the in vivo efficacy of STK-001 in the Scn1a^+/− mouse model of DS. Additionally, using patch-clamp electrophysiological recordings of PV interneurons from wild-type (WT) and Scn1a^+/− mice treated either with vehicle or STK-001 we provide evidence that STK-001 rescues Scn1a^+/− PV intrinsic excitability to WT levels but slightly reduces excitability in WT mice suggesting that elevating Na_V1.1 levels beyond typical levels diminishes high-frequency firing in PV interneurons. These results show that TANGO-mediated augmentation of Na_V1.1 function by STK-001 represents a novel, disease-modifying method for treating DS.

Section snippets

Results

We collected video-electrocorticogram (ECoG) recordings from WT and Scn1a^+/− mice treated with either vehicle or STK-001 and allocated to either Group 1 (preweaning; monitored for 8 hours/day) or Group 2 (postweaning; monitored continuously) to examine spontaneous seizure frequency and survival (Fig. 1A). As expected, vehicle-treated WT mice did not experience seizures at any timepoint examined (Fig. 1B) whereas vehicle-treated Scn1a^+/− mice experienced seizures as early as P16 and sudden death

Discussion

Dravet Syndrome is a devastating and complex developmental and epileptic encephalopathy which is commonly refractory to therapeutic intervention (Cross et al., 2019). Currently available treatments of DS, which include pharmacological approaches, in addition to the non-pharmacological approaches (ketogenic diet and vagal nerve stimulation) are symptomatic and do not address the underlying cause of the disease. The TANGO-based treatment STK-001 boosts Scn1a mRNA levels and Na_V1.1 expression,

Experimental procedures

All procedures were approved by the University of Virginia Animal Care and Use Committee.

Declaration of Competing Interest

Ian C. Wenker and Manoj K. Patel own stock in Stoke Therapeutics. Anne Christiansen and Gene Liau are employees and own stock in Stoke Therapeutics. Other authors have nothing to disclose.

Acknowledgement

This work was funded by a grant from Stoke Therapeutics Inc.

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View full text

Targeted Augmentation of Nuclear Gene Output (TANGO) of Scn1a rescues parvalbumin interneuron excitability and reduces seizures in a mouse model of Dravet Syndrome

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Results

Discussion

Experimental procedures

Declaration of Competing Interest

Acknowledgement

Prominent role of forebrain excitatory neurons in SCN8A encephalopathy

Brain

Specific deletion of NaV1.1 sodium channels in inhibitory interneurons causes seizures and premature death in a mouse model of Dravet syndrome

Proc. Natl. Acad. Sci. U. S. A.

dCas9-Based Scn1a gene activation restores inhibitory interneuron excitability and attenuates seizures in dravet syndrome mice

Mol. Ther.

Dravet syndrome: treatment options and management of prolonged seizures

Epilepsia

The core Dravet syndrome phenotype

Epilepsia

Preferential inactivation of Scn1a in parvalbumin interneurons increases seizure susceptibility

Neurobiol. Dis.

A transient developmental window of fast-spiking interneuron dysfunction in a mouse model of Dravet Syndrome

J. Neurosci.

Treatment of infantile-onset spinal muscular atrophy with nusinersen: a phase 2, open-label, dose-escalation study

Lancet