GSE171191
Temporally controlled Scn1a gene reconstitution rescues seizures, behavioral deficits and altered gene expression after symptom onset in Dravet syndrome mice
Dravet Syndrome (DS) is a severe epileptic encephalopathy caused primarily by haploinsufficiency of the SCN1A gene. While different therapeutic strategies based on the upregulation of the healthy gene copy are being developed, repetitive seizures might lead to endurable and hardly treatable neural deficits. In fact, whether and to which extent this severe pathology is reversible after symptom onset remains unknown and the lack of this knowledge prevents the development of more effective therapies. We generated a novel Scn1a conditional knock-in mouse model (Scn1aStop) where Scn1a expression could be re-activated on-demand during the mouse lifetime. Scn1a gene disruption leads to the development of seizures, often associated with SUDEP and behavioral alterations including hyperactivity, social interaction deficits and cognitive impairment starting from the second/third week of age. However, we showed that Scn1a gene reconstitution when symptoms were already manifested (P30) led to a complete rescue of both spontaneous and thermic inducible seizures and marked amelioration of behavioral abnormalities. Normalization of firing of hippocampal parvalbumin interneurons was observed after reactivation of the Scn1a mutant allele. We also identified dramatic gene expression alterations associated with astrogliosis in DS mice, rescued by Scn1a gene expression normalization at P30. Interestingly, regaining of Nav1.1 physiological levels rescued epileptic seizures also in adult DS mice (P90) after months of repetitive seizure events. These results uncover the principles governing the reversibility of a severe epileptic encephalopathy as DS and they are central for accelerating therapeutic translation, providing key insights on the timing of delivery of the disease modifying therapies in DS. Overall design: n=4 Scn1a wt Cortex, n=4 Scn1a wt  Hippocampus, n=4 Scn1a het Cortex, n=4 Scn1a het  Hippocampus, n=4 Scn1a rec Cortex, n=4 Scn1a rec Hippocampus