GABAergic inhibitory neurons are responsible for maintaining a correct balance between excitation and inhibition in the brain. Mutations in genes essential for the function of these cells cause a variety of encephalopathies, including Dravet syndrome.

We have evaluated different approaches to obtain preferential expression of transgenes in GABAergic neurons, using adenoviral vectors.

In order to favor infection of these cells, we considered ErbB4 as a surface target. Incorporation of the EGF-like domain from neuregulin 1 alpha (NRG1α) in the fiber of adenovirus capsid allowed preferential infection in cells lines expressing ErbB4. However, it had no impact on the infectivity of the vector in primary cultures or in vivo. 

For transcriptional control of transgene expression, we evaluated different regulatory sequences based on genes preferentially expressed on inhibitory neurons. We paid special attention to the SCN1A gene, which is mutated in most Dravet syndrome cases. We selected a 3.6 Kb-long hybrid promoter (DP3V) based on the Distal-less homolog enhancer (Dlx), the vesicular GABA transporter (VGAT) promoter and a portion of the SCN1A 5’UTR. DP3V allowed preferential expression of transgenes in GABAergic neurons both in vitro and in vivo, although it had low potency compared with ubiquitous promoters.

Our results suggest that the DP3V promoter can be suitable for adenoviral vectors if (i) the gene product is therapeutic at moderate levels in inhibitory neurons, and (ii) it is beneficial to limit expression in other brain cells such as excitatory neurons and astrocytes.