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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    • "The ASO does not cross an intact adult blood–brain barrier (BBB). However, the BBB of neonatal mice allows some ASO molecules to penetrate into the CNS after systemic administration, resulting in moderate increases in SMN2 exon 7 inclusion in both the brain and spinal cord (Hua et al. 2011). This raised the questions of whether BBB permeability is essential for the long-term rescue achieved by systemic ASO delivery in neonatal mice and therefore whether increasing SMN in the CNS is necessary—although not sufficient—for efficient rescue of the SMA phenotype. "
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    ABSTRACT: Survival of motor neuron (SMN) deficiency causes spinal muscular atrophy (SMA), but the pathogenesis mechanisms remain elusive. Restoring SMN in motor neurons only partially rescues SMA in mouse models, although it is thought to be therapeutically essential. Here, we address the relative importance of SMN restoration in the central nervous system (CNS) versus peripheral tissues in mouse models using a therapeutic splice-switching antisense oligonucleotide to restore SMN and a complementary decoy oligonucleotide to neutralize its effects in the CNS. Increasing SMN exclusively in peripheral tissues completely rescued necrosis in mild SMA mice and robustly extended survival in severe SMA mice, with significant improvements in vulnerable tissues and motor function. Our data demonstrate a critical role of peripheral pathology in the mortality of SMA mice and indicate that peripheral SMN restoration compensates for its deficiency in the CNS and preserves motor neurons. Thus, SMA is not a cell-autonomous defect of motor neurons in SMA mice. © 2015 Hua et al.; Published by Cold Spring Harbor Laboratory Press.
    Genes & Development 02/2015; 29(3):288-297. DOI:10.1101/gad.256644.114 · 10.80 Impact Factor
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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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