Characterization of SMA type II skeletal muscle from treated patients shows OXPHOS deficiency and denervation
Fiorella Carla Grandi, Stéphanie Astord, Sonia Pezet, Elèna Gidaja, Sabrina Mazzucchi, Maud Chapart, Stéphane Vasseur, Kamel Mamchaoui, Piera Smeriglio
Fiorella Carla Grandi, Stéphanie Astord, Sonia Pezet, Elèna Gidaja, Sabrina Mazzucchi, Maud Chapart, Stéphane Vasseur, Kamel Mamchaoui, Piera Smeriglio
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Research Article Genetics Muscle biology

Characterization of SMA type II skeletal muscle from treated patients shows OXPHOS deficiency and denervation

Abstract

Spinal muscular atrophy (SMA) is a recessive developmental disorder caused by the genetic loss or mutation of the gene SMN1 (survival of motor neuron 1). SMA is characterized by neuromuscular symptoms and muscle weakness. Several years ago, SMA treatment underwent a radical transformation, with the approval of 3 different SMN-dependent disease-modifying therapies. This includes 2 SMN2 splicing therapies — risdiplam and nusinersen. One main challenge for type II SMA patients treated with these drugs is ongoing muscle fatigue, limited mobility, and other skeletal problems. To date, few molecular studies have been conducted on SMA patient–derived tissues after treatment, limiting our understanding of what targets remain unchanged after the spinal cord–targeted therapies are applied. Therefore, we collected paravertebral muscle from 8 type II patients undergoing spinal surgery for scoliosis and 7 controls. We used RNA-seq to characterize their transcriptional profiles and correlate these molecular changes with muscle histology. Despite the limited cohort size and heterogeneity, we observed a consistent loss of oxidative phosphorylation (OXPHOS) machinery of the mitochondria, a decrease in mitochondrial DNA copy number, and a correlation between signals of cellular stress, denervation, and increased fibrosis. This work provides new putative targets for combination therapies for type II SMA.

Authors

Fiorella Carla Grandi, Stéphanie Astord, Sonia Pezet, Elèna Gidaja, Sabrina Mazzucchi, Maud Chapart, Stéphane Vasseur, Kamel Mamchaoui, Piera Smeriglio

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Figure 1

SMN RNA and protein levels are comparable between SMA type II and control paravertebral muscle.

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SMN RNA and protein levels are comparable between SMA type II and contro...
(A) Diagram of the cohort with the sex balance for each group. (B) Age, in years, for the SMA (n = 8) and control (n = 7) groups. Each data point represents 1 patient. Groups were compared with a 2-sided Student’s t test. **P < 0.001. (C and D) Relative quantification (qPCR) of the copy number of SMN1 (C) or SMN2 (D) in gDNA (n = 5 controls, n = 8 SMA). Relative quantification was calculated with RPPH1 as a loading control. Each data point represents the average of 2 technical replicates of the measurement per patient. (E and F) Reads, represented as transcripts per million (TPM) mapping to the SMN full-length transcript (E), and the SMNΔ7 transcript missing exon 7 (F). The origin of the full-length transcript, either the SMN1 or SMN2 locus, is designated below each pair of violin plots. Each data point represents 1 sample: n = 7 for controls, n = 8 for SMA. Adjusted P values are derived from an ordinary 1-way ANOVA with Dunnett’s multiple-hypothesis testing. **Padj < 0.001, ***Padj < 0.0001, ****Padj < 0.00001. (G) Western blot for the approximately 37 kDa SMN protein and approximately 117 kDa vinculin protein. Each patient is labeled on the top. (H) Quantification of the blot in G. Each data point represents the normalized SMN/vinculin value for each sample (n = 6 controls, n = 6 SMA samples). The mean of the group was compared with a 2-sided Student’s t test. NS, not significant (P = 0.8). (I) Correlation between the TPM values of the full-length (FL) SMN transcripts in each sample in E and F compared to the normalized protein quantification in H (n = 6 controls in black, n = 6 SMA in pink). Pearson’s R2 value and it’s associated P value are reported. The solid line represents the simple linear regression and the dashed lines represent the 95% confidence internal.