SMA-miRs (miR-181a-5p, -324-5p, and -451a) are overexpressed in spinal muscular atrophy skeletal muscle and serum samples.

Paola Infante,Emanuela Abiusi,Lorena Travaglini,Maria Carmela Pera,Loredana Le Pera,Francesco Danilo Tiziano,Ludovica Lospinoso Severini,Claudio Bruno,Giorgia Coratti,Eugenio Mercuri,Lucia Di Marcotullio,Cinzia Cagnoli,Francesco Ria,Krizia Pocino,Giovanni Baranello,Isabella Moroni,Maria Barbara Pasanisi,Marika Pane,Marina Mora,Stefania Fiori,Serena Spartano,Denise Locatelli,Agnese Novelli,Enrico Bertini ,Lucia Morandi ,Adele D’amico ,Davide D’amico ,F Diano

doi:10.7554/elife.68054

Abstract

Spinal muscular atrophy (SMA) is a neuromuscular disorder characterized by the degeneration of the second motor neuron. The phenotype ranges from very severe to very mild forms. All patients have the homozygous loss of the SMN1 gene and a variable number of SMN2 (generally 2-4 copies), inversely related to the severity. The amazing results of the available treatments have made compelling the need of prognostic biomarkers to predict the progression trajectories of patients. Besides the SMN2 products, few other biomarkers have been evaluated so far, including some miRs. We performed whole miRNome analysis of muscle samples of patients and controls (14 biopsies and 9 cultures). The levels of muscle differentially expressed miRs were evaluated in serum samples (51 patients and 37 controls) and integrated with SMN2 copies, SMN2 full-length transcript levels in blood and age (SMA-score). Over 100 miRs were differentially expressed in SMA muscle; 3 of them (hsa-miR-181a-5p, -324-5p, -451a; SMA-miRs) were significantly upregulated in the serum of patients. The severity predicted by the SMA-score was related to that of the clinical classification at a correlation coefficient of 0.87 (p<10-5). miRNome analyses suggest the primary involvement of skeletal muscle in SMA pathogenesis. The SMA-miRs are likely actively released in the blood flow; their function and target cells require to be elucidated. The accuracy of the SMA-score needs to be verified in replicative studies: if confirmed, its use could be crucial for the routine prognostic assessment, also in presymptomatic patients. Telethon Italia (grant #GGP12116).

Highlights

Spinal muscular atrophy (SMA) is an autosomal-recessive neuromuscular disorder, characterized by the degeneration of the α-motor neurons of the ventral horns of the spinal cord
We evaluated whether these miRs were differentially expressed in our samples. miR-9, -132, -183, -206, and -431 were not differentially expressed in muscle samples, whereas miR-19a-3 p and -146a were upregulated; miR-2 3a-3p was downregulated. miR-19a-3 p, -146a, and -23a -3p were upregulated in serum samples of patients when evaluated by r-q PCR; these preliminary data were not confirmed by a-qPCR
The usual clinical classification is unsatisfactory for several reasons: (1) the treatment of patients has uncovered novel phenotypes that do not fall in any of the classical forms (Mercuri et al, 2020); (2) the spreading of newborn screening programs is changing the diagnosis of SMA into that of subjects with a genetic defect who might or not develop signs of the condition

Summary

Introduction

Spinal muscular atrophy (SMA) is an autosomal-recessive neuromuscular disorder, characterized by the degeneration of the α-motor neurons of the ventral horns of the spinal cord. Physiological and pathological degeneration of skeletal muscle in SMA has been intensively investigated, focusing on the role of microRNAs (miRs or miRNAs), 20-2 2mers non-c oding RNAs. miRs are involved in most cellular processes: these regulate gene expression through mRNA degradation or translational inhibition, mainly by binding cis-regulatory elements present in the 3′UTR of mRNAs (Bartel, 2009; Vidigal and Ventura, 2015). MiRs have been intensively studied as potential biomarkers in several conditions, including SMA (Kariyawasam et al, 2019) This topic has become even more relevant after the development and registration of the first effective treatments, which have led to a revolutionary change of perspective for patients (Mercuri et al, 2020). We identified three deregulated miRs (miR-1 81a-5 p, miR-3 24-5 p , miR-4 51a: SMA-m iRs) that have been integrated in a composite score (SMA-score), including SMN2 full-length (SMN2-fl) transcript levels, SMN2 copy number and age at sampling, markedly improving the phenotypic predictive value of SMN2 copy number assessment alone

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