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 5

Mitochondrial electron transport chain (ETC) complex expression and mtDNA copy number are altered in type II SMA muscle.

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Mitochondrial electron transport chain (ETC) complex expression and mtDN...
(A) Schematic of how the mito-score was calculated for each sample, using the expression (in TPM) of the highlighted oxidative phosphorylation (OXPHOS) genes. (B) The mito-score for each sample represented on a number line. (C) Western blots of control (n = 6) and SMA (n = 6) muscle samples incubated with the anti-OXPHOS antibody cocktail and vinculin as the housekeeping gene. The dotted line represents the 2 individual Western blots, imaged at the same time. Each band represents an ETC complex, which is labeled. Complex IV was not detected in either blot. Complex I was not detected in the blot on the right. The proteins designating each complex are as follows: complex I, NDUFB8; complex II, SDHB; complex III, UQCRC2; complex IV, MTCO1; and complex V, ATP5A. (D–G) Quantification of the blots in C. Each data point represents the normalized complex/vinculin value for each sample (n = 6 controls, n = 8 SMA samples). (D) Complex I, where n = 3 control and n = 4 SMA samples. (E) Complex II. (F) Complex III. (G) Complex V. The means of each group were compared with a 2-sided Student’s t test. *P < 0.05. NS, not significant (P > 0.05). (H) Relative quantification (qPCR) of the mtDNA copy number normalized to the numbers of gDNA copies using the β2-microglobulin gene in control (n = 5) and SMA (n = 8) paravertebral muscle gDNA samples. Each data point represents 1 sample. The means of the groups were compared with a 2-sided Student’s t test. *P < 0.01. (I) Same as in H, but from gDNA derived from the PBMCs of type III SMA patients. Each data point represents 1 sample (n = 22 controls, n = 14 SMA). Groups were compared with a 2-sided Student’s t test. ***P < 0.001.