Survival motor neuron gene 2 silencing by DNA methylation correlates with spinal muscular atrophy disease severity and can be bypassed by histone deacetylase inhibition

Spinal muscular atrophy (SMA), a common neuromuscular disorder, is caused by homozygous absence of the survival motor neuron gene 1 (SMN1), while the disease severity is mainly influenced by the number of SMN2 gene copies. This correlation is not absolute, suggesting the existence of yet unknown factors modulating disease progression. We demonstrate that the SMN2 gene is subject to gene silencing by DNA methylation. SMN2 contains four CpG islands which present highly conserved methylation patterns and little interindividual variations in SMN1-deleted SMA patients. The comprehensive analysis of SMN2 methylation in patients suffering from severe versus mild SMA carrying identical SMN2 copy numbers revealed a correlation of CpG methylation at the positions −290 and −296 with the disease severity and the activity of the first transcriptional start site of SMN2 at position −296. These results provide first evidence that SMN2 alleles are functionally not equivalent due to differences in DNA methylation. We demonstrate that the methyl-CpG-binding protein 2, a transcriptional repressor, binds to the critical SMN2 promoter region in a methylation-dependent manner. However, inhibition of SMN2 gene silencing conferred by DNA methylation might represent a promising strategy for pharmacologic SMA therapy. We identified histone deacetylase (HDAC) inhibitors including vorinostat and romidepsin which are able to bypass SMN2 gene silencing by DNA methylation, while others such as valproic acid and phenylbutyrate do not, due to HDAC isoenzyme specificities. These findings indicate that DNA methylation is functionally important regarding SMA disease progression and pharmacological SMN2 gene activation which might have implications for future SMA therapy regimens

Dysregulation of ubiquitin homeostasis and β-catenin signaling promote spinal muscular atrophy

Acknowledgements The authors are grateful to Nils Lindstrom and members of the Gillingwater laboratory for advice and assistance with this study and helpful comments on the manuscript; Neil Cashman for the NSC-34 cell line; and Ji-Long Liu for the DrosophilasmnA and smnB lines. This work was supported by grants from the SMA Trust (to T.H. Gillingwater, P.J. Young, and R. Morse), BDF Newlife (to T.H. Gillingwater and S.H. Parson), the Anatomical Society (to T.H. Gillingwater and S.H. Parson), the Muscular Dystrophy Campaign (to T.H. Gillingwater), the Jennifer Trust for Spinal Muscular Atrophy (to H.R. Fuller), the Muscular Dystrophy Association (to G.E. Morris), the Vandervell Foundation (to P.J. Young), the Medical Research Council (GO82208 to I.M. Robinson), Roslin Institute Strategic Grant funding from the BBSRC (to T.M. Wishart), the BBSRC (to C.G. Becker), the Deutsche Forschungsgemeinschaft and EU FP7/2007-2013 (grant no. 2012-305121, NeurOmics, to B. Wirth), the Center for Molecular Medicine Cologne (to B. Wirth and M. Hammerschmidt), and SMA Europe (to M.M. Reissland). We would also like to acknowledge financial support to the Gillingwater lab generated through donations to the SMASHSMA campaign.Peer reviewedPublisher PD

Neurocalcin Delta Suppression Protects against Spinal Muscular Atrophy in Humans and across Species by Restoring Impaired Endocytosis

This document is the Accepted Manuscript version of the following article: Riessland et al., 'Neurocalcin Delta Suppression Protects against Spinal Muscular Atrophy in Humans and across Species by Restoring Impaired Endocytosis', The American Journal of Human Genetics, Vol. 100 (2): 297-315, first published online 26 January 2017. The final, published version is available online at doi: http://dx.doi.org/10.1016/j.ajhg.2017.01.005 © 2017 American Society of Human Genetics.Homozygous SMN1 loss causes spinal muscular atrophy (SMA), the most common lethal genetic childhood motor neuron disease. SMN1 encodes SMN, a ubiquitous housekeeping protein, which makes the primarily motor neuron-specific phenotype rather unexpected. SMA-affected individuals harbor low SMN expression from one to six SMN2 copies, which is insufficient to functionally compensate for SMN1 loss. However, rarely individuals with homozygous absence of SMN1 and only three to four SMN2 copies are fully asymptomatic, suggesting protection through genetic modifier(s). Previously, we identified plastin 3 (PLS3) overexpression as an SMA protective modifier in humans and showed that SMN deficit impairs endocytosis, which is rescued by elevated PLS3 levels. Here, we identify reduction of the neuronal calcium sensor Neurocalcin delta (NCALD) as a protective SMA modifier in five asymptomatic SMN1-deleted individuals carrying only four SMN2 copies. We demonstrate that NCALD is a Ca(2+)-dependent negative regulator of endocytosis, as NCALD knockdown improves endocytosis in SMA models and ameliorates pharmacologically induced endocytosis defects in zebrafish. Importantly, NCALD knockdown effectively ameliorates SMA-associated pathological defects across species, including worm, zebrafish, and mouse. In conclusion, our study identifies a previously unknown protective SMA modifier in humans, demonstrates modifier impact in three different SMA animal models, and suggests a potential combinatorial therapeutic strategy to efficiently treat SMA. Since both protective modifiers restore endocytosis, our results confirm that endocytosis is a major cellular mechanism perturbed in SMA and emphasize the power of protective modifiers for understanding disease mechanism and developing therapies.Peer reviewedFinal Accepted Versio

Reversible molecular pathology of skeletal muscle in spinal muscular atrophy

Low levels of full-length survival motor neuron (SMN) protein cause the motor neuron disease, spinal muscular atrophy (SMA). Although motor neurons undoubtedly contribute directly to SMA pathogenesis, the role of muscle is less clear. We demonstrate significant disruption to the molecular composition of skeletal muscle in pre-symptomatic severe SMA mice, in the absence of any detectable degenerative changes in lower motor neurons and with a molecular profile distinct from that of denervated muscle. Functional cluster analysis of proteomic data and phospho-histone H2AX labelling of DNA damage revealed increased activity of cell death pathways in SMA muscle. Robust upregulation of voltage-dependent anion-selective channel protein 2 (Vdac2) and downregulation of parvalbumin in severe SMA mice was confirmed in a milder SMA mouse model and in human patient muscle biopsies. Molecular pathology of skeletal muscle was ameliorated in mice treated with the FDA-approved histone deacetylase inhibitor, suberoylanilide hydroxamic acid. We conclude that intrinsic pathology of skeletal muscle is an important and reversible event in SMA and also suggest that muscle proteins have the potential to act as novel biomarkers in SMA

Analysis of the Fibroblast Growth Factor System Reveals Alterations in a Mouse Model of Spinal Muscular Atrophy

The monogenetic disease Spinal Muscular Atrophy (SMA) is characterized by a progressive loss of motoneurons leading to muscle weakness and atrophy due to severe reduction of the Survival of Motoneuron (SMN) protein. Several models of SMA show deficits in neurite outgrowth and maintenance of neuromuscular junction (NMJ) structure. Survival of motoneurons, axonal outgrowth and formation of NMJ is controlled by neurotrophic factors such as the Fibroblast Growth Factor (FGF) system. Besides their classical role as extracellular ligands, some FGFs exert also intracellular functions controlling neuronal differentiation. We have previously shown that intracellular FGF-2 binds to SMN and regulates the number of a subtype of nuclear bodies which are reduced in SMA patients. In the light of these findings, we systematically analyzed the FGF-system comprising five canonical receptors and 22 ligands in a severe mouse model of SMA. In this study, we demonstrate widespread alterations of the FGF-system in both muscle and spinal cord. Importantly, FGF-receptor 1 is upregulated in spinal cord at a pre-symptomatic stage as well as in a mouse motoneuron-like cell-line NSC34 based model of SMA. Consistent with that, phosphorylations of FGFR-downstream targets Akt and ERK are increased. Moreover, ERK hyper-phosphorylation is functionally linked to FGFR-1 as revealed by receptor inhibition experiments. Our study shows that the FGF system is dysregulated at an early stage in SMA and may contribute to the SMA pathogenesis

RNA-seq differential expression of N2A cells treated with DMSO (ctrl) or Glucocerebrosides (40 uM) for 7days.

RNA-seq differential expression of N2A cells treated with DMSO (ctrl) or Glucocerebrosides (40 uM) for 7days. GC treatment induced a senescence-like phenotype.</p

Investigational therapies for the treatment of spinal muscular atrophy

Introduction: Currently, there is no cure available for the hereditary neurodegenerative disease proximal spinal muscular atrophy (SMA), which is the number one genetic killer in early childhood. However, growing knowledge of SMA pathophysiology has opened new avenues for potential therapeutic interventions. Areas covered: This review summarizes a variety of investigational therapeutic approaches for SMA. Focusing on the current state-of-the-art applications, the authors discuss the outcome of the first clinical interventions and compare the first results from the newest strategies. The achievements of the investigational drugs highlighted in this article were deduced from original articles, pharmaceutical company press releases and clinical trial results. Expert opinion: Nearly two decades after the discovery of the disease causing gene survival motor neuron 1, many therapeutic options for SMA have been developed, some of which made it to clinical trials but could not prove their promising experimental results. Recently, big research efforts from academia, government and the pharmaceutical industry have led to the development of highly promising compounds that are currently in clinical trials, and which could lead to feasible treatment options in the future