Novel aminoglycosides increase SMN levels in spinal muscular atrophy fibroblasts

Abstract

Spinal muscular atrophy (SMA) is the leading genetic cause of infant mortality. SMA is caused by the homozygous absence of survival motor neuron-1 (SMN1). SMN2, a nearly identical copy gene, is retained in all SMA patients and encodes an identical protein as SMN1; however, SMN1 and SMN2 differ by a silent C to T transition which results in the production of an alternatively spliced isoform (SMNDelta7), which encodes a defective protein, demonstrating that the absence of the short peptide encoded by SMN exon 7 is critical in SMA development. Previously, we have shown that for some functions heterologous sequences can compensate for the exon 7 peptide, suggesting that the SMN C-terminus functions non-specifically. Consistent with this hypothesis, we now identify novel aminoglycosides that can induce SMN protein levels in patient fibroblasts. This hypothesis was supported, in part, by a novel fluorescent SMN read-through assay. Interestingly, however, through the development of a SMN exon 7-specific antibody, results suggested that levels of normal full-length SMN might also be elevated by aminoglycoside treatment. These results demonstrate that the compounds that promote read-through may provide an alternative platform for the discovery of compounds that induce SMN protein levels.

A SMNΔ7 read-through product confers functionality to the SMNΔ7 protein

“…Some compounds, including the aminoglycoside class, are thought to stabilize the existing SMNΔ7 protein by a process known as 'read-through'. While it has been shown previously that this class of compounds can elevate gem numbers as well as total SMN protein [15,22], the read-through protein product has not been thoroughly examined. This work demonstrates SMN 'read-through' isoform's functionality in a variety of cellular assays.…”

“…Recent reports demonstrate that certain compounds increase SMN protein levels by inducing a read-through event of the SMNΔ7 protein or through unknown mechanisms [14,15,22]. Unlike the HDAC inhibitors [21] that induce expression of native SMN, the read-through inducing compounds likely induce a novel SMN species: the SMNΔ7 read-through product.…”

Repair of pre-mRNA splicing

“…In addition to such efforts to increase SMN2 transcription, a forced translational read-through of the premature termination codon of SMN∆7 transcripts by aminoglycoside compounds was also shown to increase functional SMN protein levels in fibroblasts derived from SMA patients. 108 Finally, it should be mentioned that a gene replacement therapy is also a valid option, despite the size of the SMN gene. Two recent reports have demonstrated that different adeno-associated virus (AAV) vectors expressing SMN cDNA can reach motoneurons and partly rescue newborn mice that would otherwise show a severe SMA phenotype.…”

Thérapie spécifique d’allèle

“…Plusieurs approches sont actuellement envisagées afin de contrer ces effets secondaires, telles que l'administration d'antioxydants, qui permettent de réduire le niveau de radicaux libres [24], ou de polyanions, comme le poly-L-aspartate, qui semblent réduire les effets toxiques de la gentamicine [25]. [26] et les composés NB54, NB74 et NB84 [27,28]. Des molécules non apparentées aux aminoglycosides peuvent également être efficaces sur la translecture, c'est le cas de la négamycine (Figure 3), un antibiotique dipeptide issu d'une souche de Streptomyces.…”