Trans-Splicing-Mediated Improvement in a Severe Mouse Model of Spinal Muscular Atrophy

Abstract

Spinal muscular atrophy is a leading genetic cause of infantile death and occurs in ϳ1/6000 live births. SMA is caused by the loss of Survival Motor Neuron-1 (SMN1), however, all patients retain at least one copy of a nearly identical gene called SMN2. While SMN2 and SMN1 are comprised of identical coding sequences, the majority of SMN2 transcripts are alternatively spliced, encoding a truncated protein that is unstable and nonfunctional. Considerable effort has focused upon modulating the SMN2 alternative splicing event since this would produce more wild-type protein. Recently we reported the development of an optimized trans-splicing system that involved the coexpression of a SMN2 trans-splicing RNA and an antisense RNA that blocks a downstream splice site in SMN2 pre-mRNA. Here, we demonstrate that in vivo delivery of the optimized trans-splicing vector increases an important SMN-dependent activity, snRNP assembly, in disease-relevant tissue in the SMA mouse model. A single injection of the vector into the intracerebral-ventricular space in SMA neonates also lessens the severity of the SMA phenotype in a severe SMA mouse model, extending survival ϳ70%. Collectively, these results provide the first in vivo demonstration that SMN2 trans-splicing leads to a lessening of the severity of the SMA phenotype and provide evidence for the power of this strategy for reprogramming genetic diseases at the pre-mRNA level.

Targeting RNA-Splicing for SMA Treatment

“…This promising perspective seems to be greatly boosted by recent developments in SMN/SMA studies in which technologies such as trans-splicing, bifunctional oligonucleotides, and anti-sense oligonucleotides very specifically increase the inclusion of exon 7 into SMN2 mRNA (Fig. 2) (Baughan et al, 2006;Coady and Lorson, 2010;Coady et al, 2007;Dickson et al, 2008;Hua et al, 2010;Lorson et al, 2010;Osman et al, 2012;Shababi and Lorson, 2011;Shababi et al, 2011;Skordis et al, 2003). In particular, the effectiveness of anti-sense oligos in animals with SMA has excited the scientific community so that SMA may be treatable in the near future.…”

“…This strategy has been comprehensively explored by Lorson's group during the last few years to correct SMN2 splicing. They optimized trans-splicing strategies and demonstrated that transsplicing increases exon 7 insertion into SMN2 mRNA and extend the life of animals with SMA (Coady and Lorson, 2010;Coady et al, 2007;Shababi and Lorson, 2011;Shababi et al, 2011).…”

Modeling Spinal Muscular Atrophy in Mouse: A Disease of Splicing, Stability, and Timing

“…Accordingly, the inability to rescue survival at later timepoints may be a result of limited access to the CNS by the maturation of the blood brain barrier. The use of RNA molecules that mediate splicing correction can extend survival when administered early postnatally as well (Baughan et al 2009;Coady et al 2010;Passini et al 2010). The ability of each of these therapeutic modalities requires access to the CNS and motor neurons for effective therapeutic benefit in SMA mouse models.…”

“…Drug correction of SMN2 splicing underscores the importance of targeting the correction of SMN2 splicing as a mode for increased SMN expression. The use of RNA based therapies aimed at increasing exon 7 inclusion can be achieved by sequestering a negatively acting www.intechopen.com sequence in the pre-mRNA and preventing it negative function (Singh et al 2006;Hua et al 2007;Williams et al 2009;Passini et al 2010), recruiting positively acting splicing factors to exon 7 (Baughan et al 2009;Meyer et al 2009;Voigt et al 2010), blocking exon 8 inclusion (Dickson et al 2008), or providing an RNA substrate used in the splicing reaction (trans-splicing) (Coady et al 2010). These techniques have successfully increased exon 7 inclusion and SMN levels, and have improved survival and phenotype in SMA mouse models.…”

Chimeric RNAs as potential biomarkers for tumor diagnosis

“…Further studies have indicated that many other RNA chimeras are generated from mechanisms such as transcription read-through and splicing, transcription of short homologous sequence slippage or from so called trans-splicing (Table 1) (1). In the aid of high-throughput sequencing technology and bioinformatics analysis, a growing number of chimeric RNAs have been identified and validated during the last two years (2)(3)(4)(5)(6)(7)(8) …”