Targeted Augmentation of Nuclear Gene Output (TANGO) of Scn1a rescues parvalbumin interneuron excitability and reduces seizures in a mouse model of Dravet Syndrome
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 NaV1.1. 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 GABAA 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 NaV1.1 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 NaV1.1 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 NaV1.1 levels beyond typical levels diminishes high-frequency firing in PV interneurons. These results show that TANGO-mediated augmentation of NaV1.1 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 NaV1.1 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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2022, Advanced Drug Delivery ReviewsCitation Excerpt :However, administration at later time points (P14) showed reduced efficacy in rescue phenotypes, indicating a possible limitation on the developmental time window for the targeted delivery of ASO in mice [158]. A follow-up study by Wengert et al. reported data in support of the results from Han et al. in a mouse model of DS [159]. The ASO approach for treating DS reported by these studies [158,159] is currently undergoing clinical trials in phase 1/2, with the first reports of its safety being encouraging.
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