Abstract
ObjectivesSpinal muscular atrophy (SMA) is a devastating motor neuron disorder caused by homozygous loss of the survival motor neuron 1 (SMN1) gene and insufficient functional SMN protein produced by the SMN2 copy gene. Additional genetic protective modifiers such as Plastin 3 (PLS3) can counteract SMA pathology despite insufficient SMN protein. Recently, Spinraza, an SMN antisense oligonucleotide (ASO) that restores full-length SMN2 transcripts, has been FDA- and EMA-approved for SMA therapy. Hence, the availability of biomarkers allowing a reliable monitoring of disease and therapy progression would be of great importance. Our objectives were (i) to analyse the feasibility of SMN and of six SMA biomarkers identified by the BforSMA study in the Taiwanese SMA mouse model, (ii) to analyse the effect of PLS3 overexpression on these biomarkers, and (iii) to assess the impact of low-dose SMN-ASO therapy on the level of SMN and the six biomarkers.MethodsAt P10 and P21, the level of SMN and six putative biomarkers were compared among SMA, heterozygous and wild type mice, with or without PLS3 overexpression, and with or without presymptomatic low-dose SMN-ASO subcutaneous injection. SMN levels were measured in whole blood by ECL immunoassay and of six SMA putative biomarkers, namely Cartilage Oligomeric Matrix Protein (COMP), Dipeptidyl Peptidase 4 (DPP4), Tetranectin (C-type Lectin Family 3 Member B, CLEC3B), Osteopontin (Secreted Phosphoprotein 1, SPP1), Vitronectin (VTN) and Fetuin A (Alpha 2-HS Glycoprotein, AHSG) in plasma.ResultsSMN levels were significantly discernible between SMA, heterozygous and wild type mice. However, no significant differences were measured upon low-dose SMN-ASO treatment compared to untreated animals. Of the six biomarkers, only COMP and DPP4 showed high and SPP1 moderate correlation with the SMA phenotype. PLS3 overexpression neither influenced the SMN level nor the six biomarkers, supporting the hypothesis that PLS3 acts as an independent protective modifier.
Highlights
Spinal muscular atrophy (SMA) is the most common genetic cause of early infant death
No significant differences were measured upon low-dose SMN-antisense oligonucleotide (ASO) treatment compared to untreated animals
There were no differences in the SMN concentration between P10 and P21 observed, neither within the pooled SMA+ASO, nor in the pooled HET+ASO or WT+ASO cohort. These results demonstrate that i) SMN levels in blood are highly significant reduced in pooled SMA mice and still significantly reduced in pooled HET Taiwanese mice compared to WT mice, ii) the fold change reduction of SMN concentrations at P21 is higher than at P10 for pooled SMA and pooled HET groups compared to WT group, iii) low-dose SMN-ASO treatment does not give a measurable elevated SMN level in blood, despite doubling survival of SMA mice, and iv) Plastin 3 (PLS3) overexpression has no influence on SMN levels
Summary
Spinal muscular atrophy (SMA) is the most common genetic cause of early infant death. All patients carry a copy gene, SMN2 [MIM: 601627], which differs from SMN1 in a translationally silent nucleotide exchange that disrupts an exonic splicing enhancer and creates a new splicing silencer This causes the skipping of exon 7 in about 90% of SMN2 transcripts [5,6,7]. 60% of individuals with SMA develop the severe type I form (SMA1 [MIM: 253300]); patients usually carry two SMN2 copies These patients are never able to sit or walk, their life expectancy is below two years, while nutritional and respiratory support is necessary. Individuals with mild type III SMA (SMA3 [MIM: 253400]) usually carry three to four SMN2 copies, disease starts after 18 months of life and patients are able to sit and walk, but often became wheelchair bound with disease progression. Individuals with adult type IV SMA (SMA4 [MIM: 271150]) usually carry four to six SMN2 copies, onset starts after 30 years of life and affected individuals show only very mild motoric dysfunction [10,11,12]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call