Desmin and dystrophin abnormalities in upper airway muscles of snorers and patients with sleep apnea

Histological and Molecular Manifestations of Cleft Myopathy

OBJECTIVE

Apart from rupture and displacement of muscle fibers, structural defects exist in cleft muscles but have not been adequately investigated. This study aimed to examine the histological and molecular features of the cleft muscles.

DESIGN

Orbicularis oris (OO) and tensor fasciae latae (TFL) muscle samples were obtained from patients with cleft lip and alveolar. The non-cleft OO muscles were obtained from patients with facial trauma. Myofiber histology, stem cell composition, and molecular signatures were compared among the cleft OO muscle, non-cleft OO muscle, and TFL muscle.

MAIN OUTCOME MEASURES

Histological analysis of the fibrotic area, myofiber size, fiber type composition, and dystrophin expression pattern was performed to characterize the pathological manifestations in cleft muscles. Immunofluorescent staining of Pax7+ muscle satellite cells (MuSCs) and PDGFRα+ fibro-adipogenic progenitors (FAPs) and transcriptional profiling of MuSCs were carried out to explore the stem cell number and behavior in the cleft muscle.

RESULTS

Cleft muscles had an increased fibrotic area, variation in fiber size, and proportion of human fast myofiber. The defect in dystrophin expression was considerable in the non-cleft OO muscle and was even higher in the cleft OO muscle. MuSCs from cleft muscles showed a trend of increased Dux4 signature gene expression and repressed Pax7 target gene expression.

CONCLUSION

Cleft myopathy resembles facial muscle-specific muscular dystrophy. The characterization of structural deformity inherited in cleft muscles could pave the way for a deeper understanding of orofacial cleft pathology.

Desmin gene expression is not ubiquitous in all upper airway myofibers and the pattern differs between healthy and sleep apnea subjects

BACKGROUND

Desmin is a major cytoskeletal protein considered ubiquitous in mature muscle fibers. However, we earlier reported that a subgroup of muscle fibers in the soft palate of healthy subjects and obstructive sleep apnea patients (OSA) lacked immunoexpression for desmin. This raised the question of whether these fibers also lack messenger ribonucleic acid (mRNA) for desmin and can be considered a novel fiber phenotype. Moreover, some fibers in the OSA patients had an abnormal distribution and aggregates of desmin. Thus, the aim of the study was to investigate if these desmin protein abnormalities are also reflected in the expression of desmin mRNA in an upper airway muscle of healthy subjects and OSA patients.

METHODS

Muscle biopsies from the musculus uvulae in the soft palate were obtained from ten healthy male subjects and six male patients with OSA. Overnight sleep apnea registrations were done for all participants. Immunohistochemistry, in-situ hybridization, and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) techniques were used to evaluate the presence of desmin protein and its mRNA.

RESULTS

Our findings demonstrated that a group of muscle fibers lacked expression for desmin mRNA and desmin protein in healthy individuals and OSA patients (12.0 ± 5.6% vs. 23.1 ± 10.8%, p = 0.03). A subpopulation of these fibers displayed a weak subsarcolemmal rim of desmin accompanied by a few scattered mRNA dots in the cytoplasm. The muscles of OSA patients also differed from healthy subjects by exhibiting muscle fibers with reorganized or accumulated aggregates of desmin protein (14.5 ± 6.5%). In these abnormal fibers, the density of mRNA was generally low or concentrated in specific regions. The overall quantification of desmin mRNA by RT-qPCR was significantly upregulated in OSA patients compared to healthy subjects (p = 0.01).

CONCLUSIONS

Our study shows evidence that muscle fibers in the human soft palate lack both mRNA and protein for desmin. This indicates a novel cytoskeletal structure and challenges the ubiquity of desmin in muscle fibers. Moreover, the observation of reorganized or accumulated aggregates of desmin mRNA and desmin protein in OSA patients suggests a disturbance in the transcription and translation process in the fibers of the patients.

Desmin and its molecular chaperone, the αB-crystallin: How post-translational modifications modulate their functions in heart and skeletal muscles?

Maintenance of the highly organized striated muscle tissue requires a cell-wide dynamic network through protein-protein interactions providing an effective mechanochemical integrator of morphology and function. Through a continuous and complex trans-cytoplasmic network, desmin intermediate filaments ensure this essential role in heart and in skeletal muscle. Besides their role in the maintenance of cell shape and architecture (permitting contractile activity efficiency and conferring resistance towards mechanical stress), desmin intermediate filaments are also key actors of cell and tissue homeostasis. Desmin participates to several cellular processes such as differentiation, apoptosis, intracellular signalisation, mechanotransduction, vesicle trafficking, organelle biogenesis and/or positioning, calcium homeostasis, protein homeostasis, cell adhesion, metabolism and gene expression. Desmin intermediate filaments assembly requires αB-crystallin, a small heat shock protein. Over its chaperone activity, αB-crystallin is involved in several cellular functions such as cell integrity, cytoskeleton stabilization, apoptosis, autophagy, differentiation, mitochondria function or aggresome formation. Importantly, both proteins are known to be strongly associated to the aetiology of several cardiac and skeletal muscles pathologies related to desmin filaments disorganization and a strong disturbance of desmin interactome. Note that these key proteins of cytoskeleton architecture are extensively modified by post-translational modifications that could affect their functional properties. Therefore, we reviewed in the herein paper the impact of post-translational modifications on the modulation of cellular functions of desmin and its molecular chaperone, the αB-crystallin.

Recent advances in establishing a cure for GNE myopathy

PURPOSE OF REVIEW

GNE myopathy is a rare autosomal recessive disease caused by biallelic variants in the GNE gene, which encodes an enzyme involved in sialic acid biosynthesis. No drugs are approved for the treatment of GNE myopathy. Following proof-of-concept of sialic acid supplementation efficacy in mouse models, multiple clinical trials have been conducted. Here, we review clinical trials of sialic acid supplementation therapies and provide new insights into the additional clinical features of GNE myopathy.

RECENT FINDINGS

Clinical trials of sialic acid supplementation have been conducted in Europe, the USA, Japan, and South Korea. Some clinical trials of NeuAc-extended release tablets demonstrated amelioration of decline in upper extremity muscle strength; however, no significant improvement was observed in phase 3 trials in Europe and USA. A phase 2 trial of ManNAc showed slowed decline of both upper and lower extremity strength. GNE myopathy patient registries have been established in Europe and Japan, and have provided information on extramuscular manifestations such as thrombocytopenia, respiratory dysfunction, and sleep apnea syndrome. Sensitive and reliable biomarkers, and a disease-specific functional activity scale, have also been investigated.

SUMMARY

We discuss recent advances in establishing a GNE myopathy cure, and discuss other prospective therapeutic options, including gene therapy.

Obstructive Sleep Apnea and Role of the Diaphragm

Obstructive sleep apnea (OSA) causes multiple local and systemic pathophysiological consequences, which lead to an increase in morbidity and mortality in patients suffering from this disorder. OSA presents with various nocturnal events of apnoeas or hypopneas and with sub-clinical airflow limitations during wakefulness. OSA involves a large percentage of the population, particularly men, but the estimate of OSA patients could be much broader than data from the literature. Most of the research carried out in the muscle field is to understand the causes of the presence of chronic nocturnal desaturation and focus on the genioglossus muscle and other muscles related to dilating the upper airways. Sparse research has been published regarding the diaphragm muscle, which is the main muscle structure to insufflate air into the airways. The article reviews the functional anatomy of the muscles used to open the upper respiratory tract and the non-physiological adaptation that follows in the presence of OSA, as well as the functional anatomy and pathological adaptive aspects of the diaphragm muscle. The intent of the text is to highlight the disparity of clinical interest between the dilator muscles and the diaphragm, trying to stimulate a broader approach to patient evaluation.

Global O-GlcNAcylation changes impact desmin phosphorylation and its partition toward cytoskeleton in C2C12 skeletal muscle cells differentiated into myotubes

Desmin is the guardian of striated muscle integrity, permitting the maintenance of muscle shape and the efficiency of contractile activity. It is also a key mediator of cell homeostasis and survival. To ensure the fine regulation of skeletal muscle processes, desmin is regulated by post-translational modifications (PTMs). It is more precisely phosphorylated by several kinases connecting desmin to intracellular processes. Desmin is also modified by O-GlcNAcylation, an atypical glycosylation. However, the functional consequence of O-GlcNAcylation on desmin is still unknown, nor its impact on desmin phosphorylation. In a model of C2C12 myotubes, we modulated the global O-GlcNAcylation level, and we determined whether the expression, the PTMs and the partition of desmin toward insoluble material or cytoskeleton were impacted or not. We have demonstrated in the herein paper that O-GlcNAcylation variations led to changes in desmin behaviour. In particular, our data clearly showed that O-GlcNAcylation increase led to a decrease of phosphorylation level on desmin that seems to involve CamKII correlated to a decrease of its partition toward cytoskeleton. Our data showed that phosphorylation/O-GlcNAcylation interplay is highly complex on desmin, supporting that a PTMs signature could occur on desmin to finely regulate its partition (i.e. distribution) with a spatio-temporal regulation.

Myopathy of the upper airway in snoring and obstructive sleep apnea

Objective

Previous reports of muscle changes in the upper airways of obstructive sleep apnea (OSA) patients have primarily been attributed to acquired nerve lesions due to snoring vibrations. The aim of this study was to investigate whether alterations reflecting muscle fiber injuries also occur in the upper respiratory tract of snoring and OSA patients and if these changes relate to upper airway dysfunction.

Methods

Muscle changes in biopsies from the soft palate of 20 patients suffering from snoring and OSA were investigated with enzyme, immunohistochemical, and morphometric techniques. Biopsies from eight healthy non‐snoring subjects were used as controls. Swallowing dysfunction was assessed with videoradiography.

Results

Fourteen patients had various degrees of swallowing dysfunction. The muscle samples from all the patients showed changes typical for both motor‐nerve lesions and muscle fiber injuries. The most common alterations reflecting myopathy were fibers having aggregates and disorganization of cytoskeletal proteins (15.5 ± 10.7%). Other changes were fibers with vacuole‐like structures (5.0 ± 4.4%), centrally positioned myonuclei (7.9 ± 4.8%), subsarcolemmal accumulations of nuclei, and various forms and sizes of ring fibers, that is, fibers where the myofilaments were disorganized peripherally (2.8 ± 2.8%).

Conclusion

The results show that muscle changes mirroring both myopathy and neuropathy co‐exist in the upper airway of snoring OSA patients. These findings suggest muscle weakness as a contributing factor to the upper airway dysfunction in OSA patients.

Fiberoptic endoscopic evaluation of swallowing and the Brazilian version of the Eating Assessment Tool-10 in resistant hypertensive patients with obstructive sleep apnea

OBJECTIVE

The aim of this study was to describe the prevalence and characteristics of OD through Fiberoptic Endoscopic Evaluation of Swallowing (FEES) and the Eating Assessment Tool-10 (EAT-10) in hypertensive patients with OSA, as well as to describe the sensitivity of EAT-10 for the detection of OD in this population.

METHODS

This study included a convenience sample in which 85 resistant hypertensive patients diagnosed with OSA in an university hospital participated. Participants were subjected to the EAT-10 (index test) and FEES (reference standard).

RESULTS

The median EAT-10 score was 2 (0-5.5). According to the FEES, 27 participants did not have dysphagia, 42 had mild dysphagia and 16 had mild to moderate dysphagia. The sensitivity of the EAT-10 was 70.7% (95% CI: 57.3-81.9) at a cutoff score ≥1, with a discriminatory power of 67.4% (p = 0.005). The most prevalent symptom in this population was "food stuck in the throat", while the most prevalent signs were delayed initiation of the pharyngeal phase of swallowing, premature bolus spillage and pharyngeal residue.

CONCLUSION

In our study, the cutoff score for the EAT-10 for screening for OD in this population was ≥ 1. In conclusion, this population presented a high prevalence of dysphagia detected in FEES and its severity is associated with higher EAT-10 scores.

What does desmin do: A bibliometric assessment of the functions of the muscle intermediate filament

Intermediate filaments were first described in muscle in 1968, and desmin was biochemically identified about 10 years afterwards. Its importance grew after the identification of desminopathies and desmin mutations that cause mostly cardiopathies. Since its characterization until recently, different functions have been attributed to desmin. Here, we use bibliometric tools to evaluate the articles published about desmin and to assess its several putative functions. We identified the most productive authors and the relationships between research groups. We studied the more frequent words among 9734 articles (September 2021) containing "desmin" on the title and abstract, to identify the major research focus. We generated an interactive spreadsheet with the 934 papers that contain "desmin" only on the title that can be used to search and quantify terms in the abstract. We further selected the articles that contained the terms "function" or "role" from the spreadsheet, which we then classified according to type of function, organelle, or tissue involved. Based on the bibliographic analysis, we assess comparatively the putative functions, and we propose an alternative explanation for the desmin function.

Fiberoptic Endoscopic Evaluation of Swallowing in Resistant Hypertensive Patients With and Without Sleep Obstructive Apnea

Resistant arterial hypertension (RAH) is strongly associated with obstructive sleep apnea (OSA). Individuals with OSA may have subclinical swallow impairment, diagnosed by instrumental assessments, such as videofluoroscopy and fiberoptic endoscopic evaluation of swallowing (FEES). However, few studies have evaluated this population and included a control group of individuals without OSA. To evaluate, through FEES, the swallowing characteristics of resistant hypertensive patients with and without OSA and to investigate the association between the signs of swallow impairment and OSA. This was an observational study in which individuals with RAH underwent baseline polysomnography and were diagnosed with and without OSA. All participants underwent an initial assessment with the collection of demographic characteristics and FEES. Individuals were divided into 2 groups based on the presence or absence of OSA. Seventy-nine resistant hypertensive patients were evaluated: 60 with OSA (19 with mild OSA, 21 with moderate OSA, and 20 with severe OSA) and 19 without OSA. The most prevalent swallowing differences between groups with and without OSA were piecemeal deglutition, in 61.7% and 31.6%, respectively (p = 0.022); spillage, in 58.3% and 21.1% (p = 0.005); penetration/aspiration, in 55% and 47.4% (p = 0.561); and pharyngeal residue, in 51.5% and 26.3% (p = 0.053). The prevalence of swallow impairment among the participants in this study was 58.3% and 47.4% in the groups with OSA and without OSA, respectively (p = 0.402). This study shows a high prevalence of swallow impairment both in hypertensive patients with OSA and without OSA. The characteristics of swallowing associated with hypertensive patients with OSA are spillage, piecemeal deglutition, and the onset of the pharyngeal phase in the hypopharynx.

Absence of Desmin in Myofibers of the Zebrafish Extraocular Muscles

Purpose

To study the medial rectus (MR) muscle of zebrafish (Daniorerio) with respect to the pattern of distribution of desmin and its correlation to distinct types of myofibers and motor endplates.

Methods

The MRs of zebrafish were examined using confocal microscopy in whole-mount longitudinal specimens and in cross sections processed for immunohistochemistry with antibodies against desmin, myosin heavy chain isoforms, and innervation markers. Desmin patterns were correlated to major myofiber type and type of innervation. A total of 1382 myofibers in nine MR muscles were analyzed.

Results

Four distinct desmin immunolabeling patterns were found in the zebrafish MRs. Approximately a third of all slow myofibers lacked desmin, representing 8.5% of the total myofiber population. The adult zebrafish MR muscle displayed en grappe, en plaque, and multiterminal en plaque neuromuscular junctions (NMJs) with intricate patterns of desmin immunolabeling.

Conclusions

The MRs of zebrafish showed important similarities with the human extraocular muscles with regard to the pattern of desmin distribution and presence of the major types of NMJs and can be regarded as an adequate model to further study the role of desmin and the implications of heterogeneity in cytoskeletal protein composition.

Translational Relevance

The establishment of a zebrafish model to study the cytoskeleton in muscles that are particularly resistant to muscle disease opens new avenues to understand human myopathies and muscle dystrophies and may provide clues to new therapies.