Rescue of a Dystrophin-like Protein by Exon Skipping In Vivo Restores GABAA-receptor Clustering in the Hippocampus of the mdx Mouse

Dystrophin, the cytoskeletal protein whose defect is responsible for Duchenne muscular dystrophy (DMD), is normally expressed in both muscles and brain. Genetic loss of brain dystrophin in the mdx mouse model of DMD reduces the capacity for type A.-aminobutyric acid (GABA(A))-receptor clustering in central inhibitory synapses, which is thought to be a main molecular defect leading to brain and cognitive alterations in this syndrome. U7 small nuclear RNAs modified to encode antisense sequences and expressed from recombinant adeno-associated viral (rAAV) vectors have proven efficient after intramuscular injection to induce skipping of the mutated exon 23 and rescue expression of a functional dystrophin-like product in muscle tissues of mdx mice in vivo. Here, we report that intrahippocampal injection of a single dose of rAAV2/1-U7 can rescue substantial levels of brain dystrophin expression (15-25%) in mdx mice for months. This is sufficient to completely restore GABA(A) -receptor clustering in pyramidal and dendritic layers of CA1 hippo-campus, suggesting exon-skipping strategies offer the prospect to investigate and correct both brain and muscle alterations in DMD. This provides new evidence that in the adult brain dystrophin is critical for the control of GABA(A)-receptor clustering, which may have an important role in activity-dependent synaptic plasticity in hippocampal circuits.