Temporal and tissue-specific variability of SMN protein levels in mouse models of spinal muscular atrophy

Background: Clinical trials of drugs that increase SMN protein levels in vitro are currently under way in patients with spinal muscular atrophy.Objective: To develop and validate measures of SMN mRNA and protein in peripheral blood and to establish baseline SMN levels in a cohort of controls, carriers, and patients of known genotype, which could be used to follow response to treatment.Methods: SMN1 and SMN2 gene copy numbers were determined in blood samples collected from 86 subjects. Quantitative reverse transcription PCR was used to measure blood levels of SMN mRNA with and without exon 7. A cell immunoassay was used to measure blood levels of SMN protein.Results: Blood levels of SMN mRNA and protein were measured with high reliability. There was little variation in SMN levels in individual subjects over a 5-week period. Levels of exon 7-containing SMN mRNA and SMN protein correlated with SMN1 and SMN2 gene copy number. With the exception of type I SMA, there was no correlation between SMN levels and disease severity.Conclusion: SMN mRNA and protein levels can be reliably measured in the peripheral blood and used during clinical trials in spinal muscular atrophy, but these levels do not necessarily predict disease severity.

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The Survival of Motor Neurons Protein Determines the Capacity for snRNP Assembly: Biochemical Deficiency in Spinal Muscular Atrophy

Molecular and Cellular Biology ◽

10.1128/mcb.25.13.5543-5551.2005 ◽

2005 ◽

Vol 25 (13) ◽

pp. 5543-5551 ◽

Cited By ~ 131

Author(s):

Lili Wan ◽

Daniel J. Battle ◽

Jeongsik Yong ◽

Amelie K. Gubitz ◽

Stephen J. Kolb ◽

...

Keyword(s):

Spinal Muscular Atrophy ◽

Motor Neurons ◽

Muscular Atrophy ◽

Protein Levels ◽

Small Nuclear Ribonucleoprotein ◽

Cell Extracts ◽

Smn Complex ◽

Survival Of Motor Neurons ◽

Smn Protein ◽

Nuclear Ribonucleoprotein

ABSTRACT Reduction of the survival of motor neurons (SMN) protein levels causes the motor neuron degenerative disease spinal muscular atrophy, the severity of which correlates with the extent of reduction in SMN. SMN, together with Gemins 2 to 7, forms a complex that functions in the assembly of small nuclear ribonucleoprotein particles (snRNPs). Complete depletion of the SMN complex from cell extracts abolishes snRNP assembly, the formation of heptameric Sm cores on snRNAs. However, what effect, if any, reduction of SMN protein levels, as occurs in spinal muscular atrophy patients, has on the capacity of cells to produce snRNPs is not known. To address this, we developed a sensitive and quantitative assay for snRNP assembly, the formation of high-salt- and heparin-resistant stable Sm cores, that is strictly dependent on the SMN complex. We show that the extent of Sm core assembly is directly proportional to the amount of SMN protein in cell extracts. Consistent with this, pulse-labeling experiments demonstrate a significant reduction in the rate of snRNP biogenesis in low-SMN cells. Furthermore, extracts of cells from spinal muscular atrophy patients have a lower capacity for snRNP assembly that corresponds directly to the reduced amount of SMN. Thus, SMN determines the capacity for snRNP biogenesis, and our findings provide evidence for a measurable deficiency in a biochemical activity in cells from patients with spinal muscular atrophy.

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Self-oligomerization regulates stability of survival motor neuron protein isoforms by sequestering an SCFSlmb degron

Molecular Biology of the Cell ◽

10.1091/mbc.e17-11-0627 ◽

2018 ◽

Vol 29 (2) ◽

pp. 96-110 ◽

Cited By ~ 15

Author(s):

Kelsey M. Gray ◽

Kevin A. Kaifer ◽

David Baillat ◽

Ying Wen ◽

Thomas R. Bonacci ◽

...

Keyword(s):

Spinal Muscular Atrophy ◽

Motor Neuron ◽

Muscular Atrophy ◽

Survival Motor Neuron ◽

Protein Isoforms ◽

Survival Motor Neuron Protein ◽

Protein Levels ◽

Motor Neuron Protein ◽

Smn Protein ◽

Oligomerization Domain

SMN protein levels inversely correlate with the severity of spinal muscular atrophy. The SCFSlmbE3 ligase complex interacts with a degron embedded within the C-terminal self-oligomerization domain of SMN. The findings elucidate a model whereby accessibility of the SMN degron is regulated by self-multimerization.

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The E3 ubiquitin ligase mind bomb 1 ubiquitinates and promotes the degradation of survival of motor neuron protein

Molecular Biology of the Cell ◽

10.1091/mbc.e13-01-0042 ◽

2013 ◽

Vol 24 (12) ◽

pp. 1863-1871 ◽

Cited By ~ 32

Author(s):

Deborah Y. Kwon ◽

Maria Dimitriadi ◽

Barbara Terzic ◽

Casey Cable ◽

Anne C. Hart ◽

...

Keyword(s):

Spinal Muscular Atrophy ◽

Motor Neuron ◽

Ubiquitin Ligase ◽

Cultured Cells ◽

Muscular Atrophy ◽

E3 Ubiquitin Ligase ◽

Proteasome Inhibition ◽

Protein Levels ◽

Smn Protein ◽

Survival Of Motor Neuron

Spinal muscular atrophy is an inherited motor neuron disease that results from a deficiency of the survival of motor neuron (SMN) protein. SMN is ubiquitinated and degraded through the ubiquitin proteasome system (UPS). We have previously shown that proteasome inhibition increases SMN protein levels, improves motor function, and reduces spinal cord, muscle, and neuromuscular junction pathology of spinal muscular atrophy (SMA) mice. Specific targets in the UPS may be more efficacious and less toxic. In this study, we show that the E3 ubiquitin ligase, mind bomb 1 (Mib1), interacts with and ubiquitinates SMN and facilitates its degradation. Knocking down Mib1 levels increases SMN protein levels in cultured cells. Also, knocking down the Mib1 orthologue improves neuromuscular function in Caenorhabditis elegans deficient in SMN. These findings demonstrate that Mib1 ubiquitinates and catalyzes the degradation of SMN, and thus represents a novel therapeutic target for SMA.

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N.P.2 04 Patients with spinal muscular atrophy (SMA) and healthy siblings sharing homozygous deletions of the SMN1 gene reveal an identical number of SMN2 gene copies but different SMN protein levels

Neuromuscular Disorders ◽

10.1016/j.nmd.2006.05.042 ◽

2006 ◽

Vol 16 (9-10) ◽

pp. 652

Author(s):

H.H. Lemmink ◽

Y.J. Vos ◽

I. Plaza de Menacho ◽

J. Dijkhuis ◽

N.V.A.M. Knoers ◽

...

Keyword(s):

Spinal Muscular Atrophy ◽

Muscular Atrophy ◽

Smn1 Gene ◽

Protein Levels ◽

Gene Copies ◽

Smn2 Gene ◽

Healthy Siblings ◽

Identical Number ◽

Smn Protein ◽

Homozygous Deletions

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Treatment strategies for spinal muscular atrophy

Translational Neuroscience ◽

10.2478/v10134-010-0045-4 ◽

2010 ◽

Vol 1 (4) ◽

Cited By ~ 4

Author(s):

Heidi Fuller ◽

Marija Barišić ◽

Đurđica Šešo-Šimić ◽

Tea Špeljko ◽

Glenn Morris ◽

...

Keyword(s):

Spinal Muscular Atrophy ◽

Muscular Atrophy ◽

Treatment Strategies ◽

Transcript Level ◽

Survival Motor Neuron ◽

Current Status ◽

Protein Levels ◽

Smn2 Gene ◽

Smn Protein ◽

Cell And Gene Therapy

AbstractProgress in understanding the genetic basis and pathophysiology of spinal muscular atrophy (SMA), along with continuous efforts in finding a way to increase survival motor neuron (SMN) protein levels have resulted in several strategies that have been proposed as potential directions for efficient drug development. Here we provide an overview on the current status of the following approaches: 1) activation of SMN2 gene and increasing full length SMN2 transcript level, 2) modulating SMN2 splicing, 3) stabilizing SMN mRNA and SMN protein, 4) development of neurotrophic, neuroprotective and anabolic compounds and 5) stem cell and gene therapy. The new preclinical advances warrant a cautious optimism for emergence of an effective treatment in the very near future.

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Effect of Discontinuation of Nusinersen Treatment in Long-Standing SMA3

Journal of Neuromuscular Diseases ◽

10.3233/jnd-210644 ◽

2021 ◽

pp. 1-6

Author(s):

Miriam Hiebeler ◽

Angela Abicht ◽

Peter Reilich ◽

Maggie C. Walter

Keyword(s):

Spinal Muscular Atrophy ◽

Motor Function ◽

Rna Splicing ◽

Rating Scale ◽

Muscular Atrophy ◽

Spinal Muscular Atrophy Type ◽

Protein Levels ◽

Discontinuation Of Treatment ◽

Smn Protein ◽

Treatment Onset

Background: Spinal muscular atrophy is an autosomal recessive neuromuscular disease leading to ongoing degeneration of anterior horn cells in the spinal cord. Nusinersen is the first approved treatment for the condition, an intrathecally administered antisense oligonucleotide. It modulates pre-RNA splicing of the SMN2 gene and increases full-length SMN protein expression, thereby increasing SMN protein levels. The benefit of Nusinersen for patients with spinal muscular atrophy type 3 (SMA3) has recently been shown in several real-world cohorts. Objective: We aim to elucidate not only the effect of therapy with Nusinersen, but the development of the disease course after discontinuation of treatment. To our knowledge, there are so far no reports on the effects of Nusinersen discontinuation. Methods: We report on a 45-year-old female patient with genetically confirmed SMA3 and a disease duration of 40 years prior to treatment onset. Results: The patient was non-ambulantory, best motor function at treatment onset was holding arms with support, reflected in MRC of 3/5 in upper limbs. After having received Nusinersen for 11 months without complications, the patient showed improvement in motor functions, as measured by hand grip measurement (HGS), Hammersmith Functional Rating Scale Expanded (HFMSE), and Revised Upper Limb Module (RULM). Due to worsening of a pre-existing anxiety disorder, treatment was discontinued after six injections. Sixteen months later, progression of the disease became evident with worsening of HFMSE and RULM scores, while hand strength remained stable. Conclusion: Treatment with Nusinersen in SMA3 improves motor function in longstanding disease even in clinically advanced stages; however, after discontinuation of treatment, further progression mirroring the natural history of the disease is anticipated.

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Assessment of motor neuron pathology and potential compensatory mechanisms in phenotypically normal mice with reduced Survival Motor Neuron levels.

Journal of Student Science and Technology ◽

10.13034/jsst.v8i1.42 ◽

2015 ◽

Vol 8 (1) ◽

Author(s):

Rebecca Xu Xu ◽

Lyndsay M. Murray M. Murray Murray ◽

Yves De Repentigny De Repentigny ◽

Rashmi Kothary Kothary

Keyword(s):

Motor Neuron ◽

Mouse Models ◽

Motor Neurons ◽

Neuromuscular Junctions ◽

Muscular Atrophy ◽

Neuromuscular Disorder ◽

Survival Motor Neuron ◽

Compensatory Mechanisms ◽

Protein Levels ◽

Smn Protein

Spinal muscular atrophy (SMA) is a destructive pediatric neuromuscular disorder caused by low survival motor neuron (Smn) protein levels due to mutations and deletions within the survival motor neuron 1 (SMN1) gene. Motor neurons are the main pathological targets, and along with neuromuscular junctions (NMJs), they play an early significant role in the pathogenesis of SMA. Previous studies demonstrate that a pathological reduction in Smn levels can lead to significant remodeling defects in both the outgrowth of axonal sprouts and in the nerve-directed clustering of AChRs in mouse models. However, whether this pathological reduction in Smn leads to ubclinical features has not been investigated. Here, we have employed the Smn2B/2B and Smn+/- mouse models to study whether similar SMA pathology is present sub-clinically, and if so whether there is any compensation present. We show a decrease in the motor neuron number in the mouse models, no change in myelin thickness and modest NMJ pathology in both mouse models. Additionally, compensation through the expansion of the motor unit size is suggested.L’amyotrophie spinale (AMS) est un trouble neuromusculaire pédiatrique destructif causé par le niveau bas de protéine du neurone de moteur de survie (NMS) en raison des mutations et des effacements dans le neurone de moteur de survie 1 gène (NMS1). Des neurones du moteur sont les cibles pathologiques principales, et ce, avec des jonctions neuromusculaires (JNMs), ils jouent, en avance, un rôle significatif dans la pathogénie de AMS. Des études précédentes démontrent qu’une réduction pathologique de niveaux de NMS peut mener aux défauts importants de réorganisation tant dans l’excroissance axonale que dans l’agrégation du récepteur de l’acétylcholine (AChR) sous la terminaison nerveuse dans des modèles de souris. Cependant, si cette reduction pathologique de NMS mène aux caractéristiques infracliniques n’a pas été à l’étude. Ici, nous avons employé le NMS2B/2B et NMS +/- des modèles de souris afin de déterminer si une pathologie semblable à l’AMS est présente infracliniquement, ainsi s’il y a présence de quelconque compensation. Nous montrons une diminution dans le nombre des neurones du moteur dans les modèles de souris, aucun changement de l’épaisseur du myelin et une pathologie modeste de JNM dans les deux modèles de souris. De plus, une compensation par l’expansion de la taille d’unité du moteur est suggérée.

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