CRISPRa restores a haploinsufficient neuronal sodium channel
Haploinsufficiency – in which a single copy of a gene cannot produce enough proteins for normal function – is one of the most common causes of neurodevelopmental disorders. Gene replacement therapy could perhaps compensate for the missing copy, but this approach relies on delivery vehicles with a payload capacity that many genes associated with haploinsufficiency exceed. Write in NatureTamura et al. demonstrate that packaging a delivery vehicle with a CRISPR activation system (CRISPRa) can stimulate expression of the functional allele, thereby providing a strategy for treating haploinsufficiency in neurodevelopmental disorders.
The authors used dead Cas9 fused to a transcriptional activator to upregulate sodium channel alpha 2 subunit (voltage-gated) gene expression.SCN2A). SCN2A encodes a voltage-gated neuronal sodium channel that is widely expressed in the brain, and its haploinsufficiency is one of the most common causes of neuronal developmental disorders, including autism, intellectual disability, and epilepsy. An in vitro screen identified a single guide RNA targeting the Scn2a promoter who upregulated Scn2a double expression with minimal off-target effects. Scn2a haploinsufficiency is known to impair dendritic excitability and excitatory synapse function, and the authors showed that local injection of an adeno-associated virus carrying CRISPRa and single guide RNA in adolescents Scn2a heterozygous mice could rescue these defects. Systemic injections also rescued electrophysiological defects and reduced potassium channel antagonist-induced seizures. In SCN2A+/− neurons derived from human embryonic stem cells, SCN2A activation of the promoter restored action potential production to levels observed in healthy neurons.
