415. Stimulating Full-Length SMN2 Expression by Delivering Bi-Functional RNAs Via a Viral Vector

Abstract

Spinal Muscular Atrophy is an autosomal recessive neuromuscular disorder that is the leading genetic cause of infant mortality. SMA is caused by the homozygous absence of Survival Motor Neuron-1 (SMN1). In humans, a nearly identical copy gene is present called SMN2. SMN2 is retained in all SMA patients and encodes an identical protein compared to SMN1, however, SMN1 and SMN2 differ by a silent C to T transition at the 5' end of exon 7. This single nucleotide difference results in the production of an alternatively spliced isoform called SMN-delta7 that encodes an unstable and non-functional protein. Even though the majority of SMN2-derived transcripts lack exon 7, the presence of SMN2 represents a unique therapeutic target because SMN2 has the capacity to encode a fully functional protein. Here we describe an in vivo delivery system for short bi-functional RNAs that modulate SMN2 splicing. Bi-functional RNAs derive their name due to the presence of two functional domains: an RNA sequence that is complimentary to a specific cellular RNA (e.g. SMN exon 7); and an untethered RNA segment that serves as a sequence-specific binding platform for cellular splicing factors, such as SR proteins. Plasmid-based and recombinant adeno-associated virus vectors were developed that expressed bi-functional RNAs that stimulated SMN2 exon 7 inclusion and full-length SMN protein in patient fibroblasts. These experiments provide a mechanism to modulate splicing from a variety of genetic contexts and directly demonstrate a novel therapeutic approach for SMA.