Mislocalization of SMN from the I-band and M-band in human skeletal myofibers in spinal muscular atrophy associates with primary structural alterations of the sarcomere

Berciano, Marı́a T.; Castillo-Iglesias, María S.; Val‐Bernal, J. Fernando; Lafarga, Vanesa; Rodríguez‐Rey, José C.; Lafarga, Miguel; Tapia, Olga

doi:10.1007/s00441-020-03236-3

Cited by 10 publications

(6 citation statements)

References 95 publications

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“…In the neuromuscular preparations, an intense Smn signal distributed in axons and axon terminals was observed ( Figure 1 A). Moreover, a weak signal was found outside the NMJ, in accordance with the presence of the Smn protein in muscle fibers [ 33 , 34 ]. When images were acquired with a higher magnification, the Smn signal appeared in the form of granular structures in axons and motor nerve terminals ( Figure 1 B).…”

Section: Resultsmentioning

confidence: 91%

SMN Is Physiologically Downregulated at Wild-Type Motor Nerve Terminals but Aggregates Together with Neurofilaments in SMA Mouse Models

et al. 2022

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Survival motor neuron (SMN) is an essential and ubiquitously expressed protein that participates in several aspects of RNA metabolism. SMN deficiency causes a devastating motor neuron disease called spinal muscular atrophy (SMA). SMN forms the core of a protein complex localized at the cytoplasm and nuclear gems and that catalyzes spliceosomal snRNP particle synthesis. In cultured motor neurons, SMN is also present in dendrites and axons, and forms part of the ribonucleoprotein transport granules implicated in mRNA trafficking and local translation. Nevertheless, the distribution, regulation, and role of SMN at the axons and presynaptic motor terminals in vivo are still unclear. By using conventional confocal microscopy and STED super-resolution nanoscopy, we found that SMN appears in the form of granules distributed along motor axons at nerve terminals. Our fluorescence in situ hybridization and electron microscopy studies also confirmed the presence of β-actin mRNA, ribosomes, and polysomes in the presynaptic motor terminal, key elements of the protein synthesis machinery involved in local translation in this compartment. SMN granules co-localize with the microtubule-associated protein 1B (MAP1B) and neurofilaments, suggesting that the cytoskeleton participates in transporting and positioning the granules. We also found that, while SMN granules are physiologically downregulated at the presynaptic element during the period of postnatal maturation in wild-type (non-transgenic) mice, they accumulate in areas of neurofilament aggregation in SMA mice, suggesting that the high expression of SMN at the NMJ, together with the cytoskeletal defects, contribute to impairing the bi-directional traffic of proteins and organelles between the axon and the presynaptic terminal.

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Section: Resultsmentioning

confidence: 91%

SMN Is Physiologically Downregulated at Wild-Type Motor Nerve Terminals but Aggregates Together with Neurofilaments in SMA Mouse Models

et al. 2022

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“…As low levels of desmin appeared to be associated with sarcomere damage in a rat model of diabetes mellitus ( 95 ) and alpha-actinin staining showed disrupted sarcomere/costamere/ z -disc striations in desmin-null mice ( 96 ), it is coherent that the improved levels of desmin in the AAV9-treated Smn 2B/− mice result in improved sarcomere structure, although higher resolution microscopy is required to confirm this. Interestingly, SMN has been found to be localized to the I- and M-bands of sarcomeres in normal human skeletal fibres ( 97 ) and the Z -disc in mice ( 20 ) which suggests that sarcomeric SMN may directly or indirectly interact with the cytoskeleton and thus be involved in sarcomere structure ( 97 ), or its maintenance ( 20 ). In addition, during heart development, desmin and lamin A are abundant in the cardiac conduction systems; desmin preferentially in the myocardium of the central conduction system and lamin A more localized to the peripheral conduction system, then progressively to the central conduction system ( 98 ).…”

Section: Discussionmentioning

confidence: 99%

AAV9-mediated SMN gene therapy rescues cardiac desmin but not lamin A/C and elastin dysregulation in Smn 2B/− spinal muscular atrophy mice

Brown

Šoltić

Synowsky

et al. 2023

Human Molecular Genetics

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Structural, functional and molecular cardiac defects have been reported in spinal muscular atrophy (SMA) patients and mouse models. Previous quantitative proteomics analyses demonstrated widespread molecular defects in the severe Taiwanese SMA mouse model. Whether such changes are conserved across different mouse models, including less severe forms of the disease, has yet to be established. Here, using the same high-resolution proteomics approach in the less-severe Smn2B/− SMA mouse model, 277 proteins were found to be differentially abundant at a symptomatic timepoint (post-natal day (P) 18), 50 of which were similarly dysregulated in severe Taiwanese SMA mice. Bioinformatics analysis linked many of the differentially abundant proteins to cardiovascular development and function, with intermediate filaments highlighted as an enriched cellular compartment in both datasets. Lamin A/C was increased in cardiac tissue whilst another intermediate filament protein, desmin, was reduced. The extracellular matrix (ECM) protein, elastin, was also robustly decreased in the heart of Smn2B/− mice. AAV9-SMN1-mediated gene therapy rectified low levels of survival motor neuron (SMN) protein and restored desmin levels in heart tissues of Smn2B/− mice. In contrast AAV9-SMN1 therapy failed to correct lamin A/C or elastin levels. Intermediate filament proteins and the ECM have key roles in cardiac function and their dysregulation may explain cardiac impairment in SMA, especially since mutations in genes encoding these proteins cause other diseases with cardiac aberration. Cardiac pathology may need to be considered in the long-term care of SMA patients, as it is unclear whether currently available treatments can fully rescue peripheral pathology in SMA.

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“…In particular, patterned surfaces had a profound effect on sarcomere orientation in iPSC-derived CMs. Beside this optimization of cardiac and skeletal muscle cell differentiation protocols, our method can also be valuable tool in disease modeling as some cardiac dysfunctions and myopathies have been shown to be related to an impaired sarcomere integrity [ 63 – 67 ].…”

Section: Discussionmentioning

confidence: 99%

Monitoring the maturation of the sarcomere network: a super-resolution microscopy-based approach

Skorska

Johann

Chabanovska

et al. 2022

Cell. Mol. Life Sci.

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The in vitro generation of human cardiomyocytes derived from induced pluripotent stem cells (iPSC) is of great importance for cardiac disease modeling, drug-testing applications and for regenerative medicine. Despite the development of various cultivation strategies, a sufficiently high degree of maturation is still a decisive limiting factor for the successful application of these cardiac cells. The maturation process includes, among others, the proper formation of sarcomere structures, mediating the contraction of cardiomyocytes. To precisely monitor the maturation of the contractile machinery, we have established an imaging-based strategy that allows quantitative evaluation of important parameters, defining the quality of the sarcomere network. iPSC-derived cardiomyocytes were subjected to different culture conditions to improve sarcomere formation, including prolonged cultivation time and micro patterned surfaces. Fluorescent images of α-actinin were acquired using super-resolution microscopy. Subsequently, we determined cell morphology, sarcomere density, filament alignment, z-Disc thickness and sarcomere length of iPSC-derived cardiomyocytes. Cells from adult and neonatal heart tissue served as control. Our image analysis revealed a profound effect on sarcomere content and filament orientation when iPSC-derived cardiomyocytes were cultured on structured, line-shaped surfaces. Similarly, prolonged cultivation time had a beneficial effect on the structural maturation, leading to a more adult-like phenotype. Automatic evaluation of the sarcomere filaments by machine learning validated our data. Moreover, we successfully transferred this approach to skeletal muscle cells, showing an improved sarcomere formation cells over different differentiation periods. Overall, our image-based workflow can be used as a straight-forward tool to quantitatively estimate the structural maturation of contractile cells. As such, it can support the establishment of novel differentiation protocols to enhance sarcomere formation and maturity.

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Mislocalization of SMN from the I-band and M-band in human skeletal myofibers in spinal muscular atrophy associates with primary structural alterations of the sarcomere

Cited by 10 publications

References 95 publications

SMN Is Physiologically Downregulated at Wild-Type Motor Nerve Terminals but Aggregates Together with Neurofilaments in SMA Mouse Models

SMN Is Physiologically Downregulated at Wild-Type Motor Nerve Terminals but Aggregates Together with Neurofilaments in SMA Mouse Models

AAV9-mediated SMN gene therapy rescues cardiac desmin but not lamin A/C and elastin dysregulation in Smn 2B/− spinal muscular atrophy mice

Monitoring the maturation of the sarcomere network: a super-resolution microscopy-based approach

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