Transfer of SCN1A to the brain of adolescent mouse model of Dravet syndrome improves epileptic, motor, and behavioral manifestations

Abstract

Dravet syndrome is a genetic encephalopathy characterized by severe epilepsy combined with motor, cognitive, and behavioral abnormalities. Current antiepileptic drugs achieve only partial control of seizures and provide little benefit on the patient’s neurological development. In >80% of cases, the disease is caused by haploinsufficiency of the SCN1A gene, which encodes the alpha subunit of the Nav1.1 voltage-gated sodium channel. Novel therapies aim to restore SCN1A expression in order to address all disease manifestations. We provide evidence that a high-capacity adenoviral vector harboring the 6-kb SCN1A cDNA is feasible and able to express functional Nav1.1 in neurons. In vivo , the best biodistribution was observed after intracerebral injection in basal ganglia, cerebellum, and prefrontal cortex. SCN1A A1783V knockin mice received the vector at 5 weeks of age, when most neurological alterations were present. Animals were protected from sudden death, and the epileptic phenotype was attenuated. Improvement of motor performance and interaction with the environment was observed. In contrast, hyperactivity persisted, and the impact on cognitive tests was variable (success in novel object recognition and failure in Morris water maze tests). These results provide proof of concept for gene supplementation in Dravet syndrome and indicate new directions for improvement.

Exogenous NaV1.1 activity in excitatory and inhibitory neurons reverts Dravet syndrome comorbidities when delivered post-symptom onset in mice with Dravet

“…3-7 ). This is in contrast to previous attempts to provide gene-specific treatments for DS, which demonstrated a therapeutic effect when administered during the asymptomatic, pre-epileptic stage (5, 7, 8), or during the chronic phase (6, 29). When administered during the severe stage of the disease, CAV-SCN1A improved the survival, reduced the occurrence of spontaneous seizures, the frequency of epileptic spikes and protected from thermally-induced seizures ( Figs.…”

“…In addition to the size of the SCN1A cDNA, the sequence is prone to rearrangement when subcloned into a plasmid and propagated in E. coli (19). However, codon modification can enhance the stability and thereby facilitate the creation of vectors (29). To be able to readily subclone the SCN1A cDNA, we generated a codon-modified open reading frame and then manually screened for and eliminated short (10-15 bp) repeat sequences found primarily in the regions encoding the transmembrane domains of Na V 1.1.…”

“…Similarly, epileptic spikes and spontaneous seizures were still detected following neonate dCas9-based Scn1a activation (5), and SUDEP (despite improved survival) was still evident following vector-mediated overexpression of Na V β1 (8). Likewise, in most cases abnormal epileptic activity still persists when the treatments were administered during the chronic stage of the disease (6, 29).…”

“…All CAV-2 vectors used in this work were generated using a seamless ligation cloning extract (SLiCE) strategy (63). The following promoters were obtained from Addgene: the NSE promoter (plasmid # 50958 James Bamburg, (64)); the CAG promoter (plasmid # 51274, Pawel Pelczar, (65)) ;hSyn promoter (plasmid # 22909, Edward Callaway, (66)); the Dlx5/6 enhancer (plasmid # 83900, Gordon Fishell, (28)), mCitrine, SCN1A cDNA (29) and the bovine growth hormone polyA sequence. Fragments were subcloned into the E1 region of E1/E3-deleted pCAV-2.…”

Genetic therapeutic advancements for Dravet Syndrome

“…Traditional gene supplementation therapies have proven challenging for DS due to the large and unstable nature of SCN1A cDNA, yet a recent study overcame this through codon optimization and packaging into a high-capacity adenoviral vector [78]. Administration of high capacity adenoviral SCN1A gene therapy to adolescent heterozygous DS mice by stereotaxic injections into multiple brain regions resulted in increases in SCN1A mRNA, Nav1.1 protein, survival, reduction of thermal-induced seizure, and several behavioral readouts [78]. This study provided crucial evidence into the treatment of older DS mice, improving translatability of treatments to those patients who have had a diagnosis of DS for some time.…”