Peripheral SMN restoration is essential for long-term rescue of a severe SMA mouse model

Cold Spring Harbor Laboratory, PO Box 100, Cold Spring Harbor, New York 11724, USA.
Nature (Impact Factor: 41.46). 10/2011; 478(7367):123-6. DOI: 10.1038/nature10485
Source: PubMed


Spinal muscular atrophy (SMA) is a motor neuron disease and the leading genetic cause of infant mortality; it results from loss-of-function mutations in the survival motor neuron 1 (SMN1) gene. Humans have a paralogue, SMN2, whose exon 7 is predominantly skipped, but the limited amount of functional, full-length SMN protein expressed from SMN2 cannot fully compensate for a lack of SMN1. SMN is important for the biogenesis of spliceosomal small nuclear ribonucleoprotein particles, but downstream splicing targets involved in pathogenesis remain elusive. There is no effective SMA treatment, but SMN restoration in spinal cord motor neurons is thought to be necessary and sufficient. Non-central nervous system (CNS) pathologies, including cardiovascular defects, were recently reported in severe SMA mouse models and patients, reflecting autonomic dysfunction or direct effects in cardiac tissues. Here we compared systemic versus CNS restoration of SMN in a severe mouse model. We used an antisense oligonucleotide (ASO), ASO-10-27, that effectively corrects SMN2 splicing and restores SMN expression in motor neurons after intracerebroventricular injection. Systemic administration of ASO-10-27 to neonates robustly rescued severe SMA mice, much more effectively than intracerebroventricular administration; subcutaneous injections extended the median lifespan by 25 fold. Furthermore, neonatal SMA mice had decreased hepatic Igfals expression, leading to a pronounced reduction in circulating insulin-like growth factor 1 (IGF1), and ASO-10-27 treatment restored IGF1 to normal levels. These results suggest that the liver is important in SMA pathogenesis, underscoring the importance of SMN in peripheral tissues, and demonstrate the efficacy of a promising drug candidate.

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Available from: Guy Horev, Sep 29, 2015
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    • "Martinez et al. [66] also show that conditional expression of SMN in SMA skeletal muscle may help grow and maintain muscle independent of MNs. Increasing SMN expression outside of the nervous system with either splice-switching oligonucleotides [69] or adeno-associated virus (AAV) vectors [70], [71] markedly improves the phenotype and survival of SMA mice. These studies suggest that comparative analysis of SMA MN transcriptomes from these models may provide limited insight into the pathobiology of SMA; however, it is appropriate to examine the transcript profiles of isolated SMA MNs since they are affected in a cell autonomous fashion [26], [65]–[67]. "
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    ABSTRACT: Proximal spinal muscular atrophy (SMA) is an early onset, autosomal recessive motor neuron disease caused by loss of or mutation in SMN1 (survival motor neuron 1). Despite understanding the genetic basis underlying this disease, it is still not known why motor neurons (MNs) are selectively affected by the loss of the ubiquitously expressed SMN protein. Using a mouse embryonic stem cell (mESC) model for severe SMA, the RNA transcript profiles (transcriptomes) between control and severe SMA (SMN2+/+;mSmn-/-) mESC-derived MNs were compared in this study using massively parallel RNA sequencing (RNA-Seq). The MN differentiation efficiencies between control and severe SMA mESCs were similar. RNA-Seq analysis identified 3,094 upregulated and 6,964 downregulated transcripts in SMA mESC-derived MNs when compared against control cells. Pathway and network analysis of the differentially expressed RNA transcripts showed that pluripotency and cell proliferation transcripts were significantly increased in SMA MNs while transcripts related to neuronal development and activity were reduced. The differential expression of selected transcripts such as Crabp1, Crabp2 and Nkx2.2 was validated in a second mESC model for SMA as well as in the spinal cords of low copy SMN2 severe SMA mice. Furthermore, the levels of these selected transcripts were restored in high copy SMN2 rescue mouse spinal cords when compared against low copy SMN2 severe SMA mice. These findings suggest that SMN deficiency affects processes critical for normal development and maintenance of MNs.
    PLoS ONE 09/2014; 9(9):e106818. DOI:10.1371/journal.pone.0106818 · 3.23 Impact Factor
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    • "Animals were kept in a controlled environment at 25 °C and 50% humidity, with a 12 hours light/dark photoperiod, and were monitored daily for health. Three SMA mouse models were utilized in this study (see Supplementary Table S1): 5058-homozygous mice (SMN2tg/o;SMN2tg/o;Smntm1Hung/tm1Hung) were generated as described;28,29 5058-Hemi FVB/N SMA mice (SMN2tg/o;Smntm1Hung/tm1Hung) were generated as described;18,27 5058-Hemi hybrid SMA mice (SMN2tg/o; Smntm1Hung/tm1.1Jme) were generated by crossing 5058-homozygous FVB/N mice (SMN2tg/o;SMN2tg/o;Smntm1Hung/tm1Hung) with the heterozygous mice harboring the ▵7Smn Melki allele (Smntm1.1Jme/Wt; "
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    ABSTRACT: Recent reports underscore the unparalleled potential of antisense-oligonucleotide (ASO)-based approaches to ameliorate various pathological conditions. However, in vivo studies validating the effectiveness of a short ASO (<10-mer) in the context of a human disease have not been performed. One disease with proven amenability to ASO-based therapy is spinal muscular atrophy (SMA). SMA is a neuromuscular disease caused by loss-of-function mutations in the survival motor neuron 1 (SMN1) gene. Correction of aberrant splicing of the remaining paralog, SMN2, can rescue mouse models of SMA. Here, we report the therapeutic efficacy of an 8-mer ASO (3UP8i) in two severe models of SMA. While 3UP8i modestly improved survival and function in the more severe Taiwanese SMA model, it dramatically increased survival, improved neuromuscular junction pathology, and tempered cardiac deficits in a new, less severe model of SMA. Our results expand the repertoire of ASO-based compounds for SMA therapy, and for the first time, demonstrate the in vivo efficacy of a short ASO in the context of a human disease.
    Molecular Therapy - Nucleic Acids 07/2014; 3(7):e174. DOI:10.1038/mtna.2014.23 · 4.51 Impact Factor
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    • "It fails to completely compensate for the loss of SMN1 due to aberrant splicing of exon 7 which leads to the production of predominantly truncated transcripts and a corresponding decrease in the amounts of functional protein [12]–[14]. As SMN2 is present in all SMA patients it has been extensively studied and serves as a drug target for drugs that specifically correct splicing of exon 7 and thereby increases amounts of functional SMN protein [15]–[17]. As such, large animal models where broader effects of both early and late treatment can be carefully examined are becoming increasingly relevant. "
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    ABSTRACT: Spinal Muscular Atrophy is caused by homozygous loss of SMN1. All patients retain at least one copy of SMN2 which produces an identical protein but at lower levels due to a silent mutation in exon 7 which results in predominant exclusion of the exon. Therapies targeting the splicing of SMN2 exon 7 have been in development for several years, and their efficacy has been measured using either in vitro cellular assays or in vivo small animal models such as mice. In this study we evaluated the potential for constructing a mini-pig animal model by introducing minimal changes in the endogenous porcine Smn1 gene to maintain the native genomic structure and regulation. We found that while a Smn2-like mutation can be introduced in the porcine Smn1 gene and can diminish the function of the ESE, it would not recapitulate the splicing pattern seen in human SMN2 due to absence of a functional ISS immediately downstream of exon 7. We investigated the ISS region and show here that the porcine ISS is inactive due to disruption of a proximal hnRNP A1 binding site, while a distal hnRNP A1 binding site remains functional but is unable to maintain the functionality of the ISS as a whole.
    PLoS ONE 06/2014; 9(6):e98841. DOI:10.1371/journal.pone.0098841 · 3.23 Impact Factor
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