Search

Nemaline myopathy (NM) is a genetic muscle disease, primarily caused by mutations in the NEB gene (NEB-NM) and with muscle myosin dysfunction as a major molecular pathogenic mechanism. Recently, we have observed that the myosin biochemical super-relaxed state was significantly impaired in NEB-NM, inducing an aberrant increase in ATP consumption and remodelling of the energy proteome in diseased muscle fibres. Because the small-molecule Mavacamten is known to promote the myosin super-relaxed state and reduce the ATP demand, we tested its potency in the context of NEB-NM. We first conducted in vitro experiments in isolated single myofibres from patients and found that Mavacamten successfully reversed the myosin ATP overconsumption. Following this, we assessed its short-term in vivo effects using the conditional nebulin knockout (cNeb KO) mouse model and subsequently performing global proteomics profiling in dissected soleus myofibres. After a 4 week treatment period, we observed a remodelling of a large number of proteins in both cNeb KO mice and their wild-type siblings. Nevertheless, these changes were not related to the energy proteome, indicating that short-term Mavacamten treatment is not sufficient to properly counterbalance the metabolically dysregulated proteome of cNeb KO mice. Taken together, our findings emphasize Mavacamten potency in vitro but challenge its short-term efficacy in vivo. KEY POINTS: No cure exists for nemaline myopathy, a type of genetic skeletal muscle disease mainly derived from mutations in genes encoding myofilament proteins. Applying Mavacamten, a small molecule directly targeting the myofilaments, to isolated membrane-permeabilized muscle fibres from human patients restored myosin energetic disturbances. Treating a mouse model of nemaline myopathy in vivo with Mavacamten for 4 weeks, remodelled the skeletal muscle fibre proteome without any noticeable effects on energetic proteins. Short-term Mavacamten treatment may not be sufficient to reverse the muscle phenotype in nemaline myopathy., (© 2024 The Author(s). The Journal of Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)

Aims: This study aimed to evaluate the impact of a 12-week calorie-restricted diet and recreational sports training on gene expressions IL-15, ATROGIN-1 and MURF-1 in skeletal muscle of T2D patients., Methods: Older adults with T2D (n = 39, 60 ± 6.0 years, BMI 33.5 ± 0.6 kg/m 2 ) were randomly allocated to Diet+Soccer (DS), Diet+Running (DR) or Diet (D). The training sessions were moderate-to-high-intensity and performed 3 × 40 min/week for 12-weeks. Gene expression from vastus lateralis muscle obtained by qRT-PCR, dual-energy X-ray and fasting blood testing measurements were performed before and after 12-weeks. Statistical analysis adopted were two-way ANOVA and Paired t-test for gene expression, and RM-ANOVA test for the remainder variables., Results: Total body weight was reduced in ~4 kg representing body fat mass in all groups after 12-weeks (P < 0.05). HbA1c values decreased in all groups post-intervention. Lipids profile improved in the training groups (P < 0.05) after 12-weeks. ATROGIN-1 and MURF-1 mRNA reduced in the DS (1.084 ± 0.14 vs. 0.754 ± 1.14 and 1.175 ± 0.34 vs. 0.693 ± 0.12, respectively; P < 0.05), while IL-15 mRNA increased in the DR (1.056 ± 0.12 vs. 1.308 ± 0.13; P < 0.05) after 12-weeks intervention., Conclusion: Recreational training with a moderate calorie-restricted diet can downregulates the expression of atrophy-associated myokines and increases the expression of anti-inflammatory gene IL-15., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The objective of this study was to compare the accuracy of ultrasound (US) with that of magnetic resonance imaging (MRI) in identifying muscle abnormalities in patients with inclusion body myositis (IBM). Twelve patients with IBM underwent muscle US and MRI on the same day. Twelve muscle groups were analyzed per patient. On US, a visual grading system was used to detect whether the muscles were affected. On MRI, muscle atrophy, fat infiltration and edema patterns were analyzed. The inter- and intra-reader reproducibility was similar for US and MRI in the evaluation of muscle abnormalities. All patients with muscle abnormalities identified on US presented with fat infiltration on MRI, which was the most common abnormality identified on MRI. Most importantly, the accuracy of US compared with that of MRI for the detection of muscle abnormalities in patients with IBM was 86.8 (κ coefficient = 0.632), with a sensitivity of 84% and specificity of 100%. In conclusion all patients with muscle abnormalities identified on US presented with fat infiltration on MRI, and the marked increase in echo intensity observed in the muscles of IBM patients was related mostly to fatty replacement. Most importantly, US exhibited significant accuracy compared with MRI., Competing Interests: Conflict of interest disclosure The authors declare no conflicts of interest., (Copyright © 2021 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.)

Nemaline myopathy (NM) is a skeletal muscle disorder caused by mutations in genes that are generally involved in muscle contraction, in particular those related to the structure and/or regulation of the thin filament. Many pathogenic aspects of this disease remain largely unclear. Here, we report novel pathological defects in skeletal muscle fibres of mouse models and patients with NM: irregular spacing and morphology of nuclei; disrupted nuclear envelope; altered chromatin arrangement; and disorganisation of the cortical cytoskeleton. Impairments in contractility are the primary cause of these nuclear defects. We also establish the role of microtubule organisation in determining nuclear morphology, a phenomenon which is likely to contribute to nuclear alterations in this disease. Our results overlap with findings in diseases caused directly by mutations in nuclear envelope or cytoskeletal proteins. Given the important role of nuclear shape and envelope in regulating gene expression, and the cytoskeleton in maintaining muscle fibre integrity, our findings are likely to explain some of the hallmarks of NM, including contractile filament disarray, altered mechanical properties and broad transcriptional alterations.

Glucocorticoids represent some of the most prescribed drugs that are widely used in the treatment of neuromuscular diseases, but their usage leads to side effects such as muscle atrophy. However, different synthetic glucocorticoids can lead to different muscle effects, depending upon its chemical formulation. Here, we intended to demonstrate the muscle histologic and molecular effects of administering different glucocorticoids in equivalency and different dosages. Methods : Seventy male Wistar rats distributed into seven groups received different glucocorticoids in equivalency for ten days or saline solution. The study groups were: Control group (CT) saline solution; dexamethasone (DX) 1.25 or 2.5 mg/kg/day; methylprednisolone (MP) 6.7 or 13.3mg/kg/day; and deflazacort (DC) 10 or 20 mg/kg/day. At the end of the study, the animals were euthanized, and the tibialis anterior and gastrocnemius muscles were collected for metachromatic ATPase (Cross-sectional area (CSA) measurement), Western blotting (protein expression of IGF-1 and Ras/Raf/MEK/ERK pathways) and RT-PCR ( MYOSTATIN, MuRF-1 , Atrogin-1, REDD-1, REDD-2, MYOD, MYOG and IRS1/2 genes expression) experiments. Results : Muscle atrophy occurred preferentially in type 2B fibers in all glucocorticoid treated groups. DC on 10 mg/kg/day was less harmful to type 2B fibers CSA than other doses and types of synthetic glucocorticoids. In type 1 fibers CSA, lower doses of DC and DX were more harmful than high doses. DX had a greater effect on the IGF-1 pathway than other glucocorticoids. MP more significantly affected P-ERK1/2 expression, muscle fiber switching (fast-to-slow), and expression of REDD1 and MyoD genes than other glucocorticoids. Compared to DX and MP, DC had less of an effect on the expression of atrogenes ( MURF-1 and Atrogin-1 ) despite increased MYOSTATIN and decreased IRS-2 genes expression. Conclusions : Different glucocorticoids appears to cause muscle atrophy affecting secondarily different signaling mechanisms. MP is more likely to affect body/muscles mass, MEK/ERK pathway and fiber type transition, DX the IGF-1 pathway and IRS1/2 expression. DC had the smallest effect on muscle atrophic response possibly due a delayed timing on atrogenes response.

Purpose of Review: The purpose of this review article is to highlight the current role of diagnostic imaging in the assessment of inflammatory myopathies., Recent Findings: Recent research demonstrates that imaging plays an important role in evaluating patients with symptoms of an inflammatory myopathy. In general, MRI is the pivotal imaging modality for assessing inflammatory myopathies, revealing precise anatomic details because of changes in the signal intensity of the muscles. Whole-body MR imaging has become increasingly important over the last several years. US is also a valuable imaging modality for scanning muscles. Together with the clinical history, familiarity with the imaging features of inflammatory myopathies is essential for formulating an accurate diagnosis.

Objectives: Inherited myopathies are major causes of muscle atrophy and are often characterized by rigid spine syndrome, a clinical feature designating patients with early spinal contractures. We aim to present a decision algorithm based on muscular whole body magnetic resonance imaging (mWB-MRI) as a unique tool to orientate the diagnosis of each inherited myopathy long before the genetically confirmed diagnosis., Methods: This multicentre retrospective study enrolled 79 patients from referral centres in France, Brazil and Chile. The patients underwent 1.5-T or 3-T mWB-MRI. The protocol comprised STIR and T1 sequences in axial and coronal planes, from head to toe. All images were analyzed manually by multiple raters. Fatty muscle replacement was evaluated on mWB-MRI using both the Mercuri scale and statistical comparison based on the percentage of affected muscle., Results: Between February 2005 and December 2015, 76 patients with genetically confirmed inherited myopathy were included. They were affected by Pompe disease or harbored mutations in RYR1, Collagen VI, LMNA, SEPN1, LAMA2 and MYH7 genes. Each myopathy had a specific pattern of affected muscles recognizable on mWB-MRI. This allowed us to create a novel decision algorithm for patients with rigid spine syndrome by segregating these signs. This algorithm was validated by five external evaluators on a cohort of seven patients with a diagnostic accuracy of 94.3% compared with the genetic diagnosis., Conclusion: We provide a novel decision algorithm based on muscle fat replacement graded on mWB-MRI that allows diagnosis and differentiation of inherited myopathies presenting with spinal rigidity., Key Points: • Inherited myopathies are rare, diagnosis is challenging and genetic tests require specialized centres and often take years. • Inherited myopathies are often characterized by spinal rigidity. • Whole body magnetic resonance imaging is a unique tool to orientate the diagnosis of each inherited myopathy presenting with spinal rigidity. • Each inherited myopathy in this study has a specific pattern of affected muscles that orientate diagnosis. • A novel MRI-based algorithm, usable by every radiologist, can help the early diagnosis of these myopathies.

Aims: To identify the urethral migration of muscle derived stem cells (MDSCs) after intravenous (IV) injection in rats that underwent vaginal distension (VD) and to analyze the effects of MDSC in the urethra of rats after trauma in regards to: (1) mRNA expression of collagens, Vegf, Ngf, Ki67, Myh11, and Myh2; (2) expression of smooth and striated muscle proteins., Methods: MDSCs expressing green fluorescent protein (GFP) were injected into the tail vein of rats 3 days after VD. The location of GFP cells was verified at 2 h and at 7 days following IV injection. Urethras of three groups were analyzed: Control, Trauma 7D, and MDSC 7D. Real-time RT-qPCR and immunohistochemistry were performed., Results: MDSCs were identified only after 2 h of the procedure in the urethra. Myh11 gene was overexpressed in the Trauma group in relation to Control. Ki67 gene expression was increased in the MDSC group relative to Trauma and Control. Col1a1 and Col3a1 genes expression were increased in the MDSC group relative to Control. Ngf mRNA level was decreased in the MDSC group in relation to Trauma. Protein expression of Mhy11, Myh2, and Desmin were increased in the MDSC group in relation to Trauma and decreased in the Trauma in relation to Control., Conclusion: MDSCs migrated early to the traumatized urethra, but did not integrate into the tissue. MDSC alters the expression of genes related to cell proliferation, neural growth factor and extracellular matrix and the expression of smooth and striated muscle proteins in the traumatized rat urethra., (© 2018 Wiley Periodicals, Inc.)

Background: Nemaline myopathy is a rare congenital disease of skeletal muscle characterized by muscle weakness and hypotonia, as well as the diagnostic presence of nemaline rods in skeletal muscle fibers. Nemaline myopathy is genetically and phenotypically heterogeneous and, so far, mutations in 11 different genes have been associated with this disease. Dominant mutations in ACTA1 are the second most frequent genetic cause of nemaline myopathy and can lead to a variety of clinical and histologic phenotypes., Patients and Methods: We present a series of ACTA1-related cases from a Brazilian cohort of 23 patients with nemaline myopathy, diagnosed after Sanger sequencing the entire coding region of ACTA1, and review the literature on ACTA1-related nemaline myopathy., Results: The study confirmed ACTA1 mutations in four patients, including one with intranuclear rods, one with large intracytoplasmic aggregates, and two with nemaline intracytoplasmic rods. A repeat muscle biopsy in one patient did not show histological progression., Conclusion: Despite the recognized phenotypic variability in ACTA1-related nemaline myopathy, clinical and histological presentations appear to correlate with the position of the mutation, which confirms emerging genotype/phenotype correlations and better predict the prognosis of affected patients., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Background: Myotubular myopathy is a rare X-linked congenital myopathy characterized by marked neonatal hypotonia and respiratory insufficiency, facial and ocular involvement, and muscle biopsy with prominent central nuclei in the majority of muscle fibers. It is caused by mutations in MTM1, which codes for the phosphoinositides phosphatase myotubularin. In this work, we established and detailed a new cohort of six patients at the clinical, histologic, and genetic levels., Patients and Methods: Patients were recruited after screening 3065 muscle biopsy reports from two large biopsy banks in Sao Paulo, Brazil from the years 2008 to 2013, and from referrals to a neuromuscular outpatient clinic between 2011 and 2013. We reviewed biopsy slides, evaluated patients, and Sanger sequenced MTM1 in the families., Results: All patients but one had classic phenotypes with a stable course after a severe onset. Two patients died suddenly from hypovolemic shock. Muscle biopsies had been performed in five patients, all of whom showed a classic pattern with a predominance of centrally located nuclei and increased oxidative activity in the center of the fibers. Two patients showed necklace fibers, and two families had novel truncating mutations in MTM1., Conclusions: X-linked myotubular myopathy is rare in the Brazilian population. Necklace fibers might be more prevalent in this condition than previously reported. Direct Sanger sequencing of MTM1 on clinical suspicion avoids the need of a muscle biopsy., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by loss of motor neurons. Familial ALS is strongly associated to dominant mutations in the gene for Cu/Zn superoxide dismutase (SOD1). Recent evidences point to skeletal muscle as a primary target in the ALS mouse model. Wnt/PI3 K signaling pathways and epithelial-mesenchymal transition (EMT) have important roles in maintenance and repair of skeletal muscle. Wnt/PI3 K pathways and EMT gene expression profile were investigated in gastrocnemius muscle from SOD1(G93A) mouse model and age-paired wild-type control in the presymptomatic ages of 40 and 80 days aiming the early neuromuscular abnormalities that precede motor neuron death in ALS. A customized cDNA microarray platform containing 326 genes of Wnt/PI3 K and EMT was used and results revealed eight up-regulated (Loxl2, Pik4ca, Fzd9, Cul1, Ctnnd1, Snf1lk, Prkx, Dner) and nine down-regulated (Pik3c2a, Ripk4, Id2, C1qdc1, Eif2ak2, Rac3, Cds1, Inppl1, Tbl1x) genes at 40 days, and also one up-regulated (Pik3ca) and five down-regulated (Cd44, Eef2 k, Fzd2, Crebbp, Piki3r1) genes at 80 days. Also, protein-protein interaction networks grown from the differentially expressed genes of 40 and 80 days old mice have identified Grb2 and Src genes in both presymptomatic ages, thus playing a potential central role in the disease mechanisms. mRNA and protein levels for Grb2 and Src were found to be increased in 80 days old ALS mice. Gene expression changes in the skeletal muscle of transgenic ALS mice at presymptomatic periods of disease gave further evidence of early neuromuscular abnormalities that precede motor neuron death. The results were discussed in terms of initial triggering for neuronal degeneration and muscle adaptation to keep function before the onset of symptoms.

Objectives: Our aim was to demonstrate the benefit of whole-body magnetic resonance imaging (WBMRI) as a diagnostic modality in the detection of muscle activity in juvenile dermatomyositis (JDM)/polymyositis (JPM) patients and to correlate these findings with clinical evaluation, laboratory examinations, nailfold capillaroscopy (NFC), and muscle biopsy., Method: Thirty-four patients aged 5.5 to 18.9 years with a diagnosis of JDM/JPM were prospectively evaluated using clinical examination, muscle enzyme determination, the Childhood Myositis Assessment Scale (CMAS), Disease Activity Score (DAS), Manual Muscle Testing (MMT), NFC, and WBMRI. An open muscle biopsy was performed if muscle disease activity was detected on WBMRI., Results: Disease activity was detected in WBMRI in four (11.7%) patients and confirmed by muscle biopsy. All four patients had elevation of at least one muscle enzyme and NFC showed scleroderma patterns in these patients., Conclusions: WBMRI allows us to evaluate the extent and symmetry of muscle disease and inflammatory activity. NFC is an important additional examination to assess disease activity.

X-linked myotubular myopathy due to mutations in the MTM1 gene is classically characterized by a severe neonatal phenotype and a typical muscle biopsy presenting globular and centrally located nuclei in muscle myofibers. Recently, four patients with mild late-onset form have been described, a male with a hemizygous mutation and three females with heterozygous mutations in the MTM1 gene. The muscle biopsies were performed at 13-35 years of age and a new histological marker, the necklace fibers, was described. Here, we report two siblings with the pathogenic c.664 C>T mutation in the MTM1 gene, presenting a severe muscle weakness and respiratory impairment requiring ventilatory support since the first months of life until death, at the age of 36 months and 5 months. In the older brother the muscle biopsy, performed at the age of 30 months, showed almost 100% of necklace fibers, which were not present in the younger one submitted to muscle biopsy at 5 months of age. Our findings confirm the necklace fibers can be a histopathological finding of MTM1 myopathies, even in the severe neonatal form, and suggest that the necklace fibers appear or increase in number over time., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Objective: To compare muscle strength (MS) and motor function in patients with Duchenne muscular dystrophy (DMD) receiving steroids for different times against the natural evolution of DMD described by Scott et al., Method: 90 patients with DMD (aged 5- 12 years), receiving steroids for one to seven years, were evaluated by Medical Research Council Scale (MRC) and Hammersmith motor ability score. The relation between MS and motor abilities measurement from our data and Scott's ones were ascertained statistically., Results: The relation between patient's age and Hammersmith scores revealed decrease of 0.76 point per year for age against decrease of 2.23 points on Scott's study. The relation between MRC scale and patient's age showed decrease of 0.80 point per year of age against decrease of 3.65 points on Scott's study., Conclusion: In patients with DMD aged five to 12 years the progression of the disease is delayed by steroids and the motor function is less reduced than muscular strength.

Congenital muscular dystrophies (CMD) are characterized by neonatal hypotonia and/or artrogriposis associated with a dystrophic muscle biopsy. The CMD1A form is caused by a deficiency of the alpha2 chain of laminin 2 (LAMA2 gene at 6q2), a protein present in the basal lamina of muscle fibers, in Schwann cells, epidermis, and in fetal trophoblastic tissue. This allows its study for prenatal diagnosis in the chorionic villous (CV), which was performed in a family with one deceased affected CMD1A child. Immunohistochemical analysis of the CV using antibodies against the C- and N-terminal domains of the alpha2-laminin protein showed a normal positive labeling for both antibodies in the "at-risk" CV, which did not differ from the normal control CV. The integrity of the CV membrane was confirmed through the analysis with antibodies against alpha1, beta1, and gamma1 laminins. DNA study using markers flanking the 6q2 region showed that the affected patient and the "at-risk" fetus did not share the same haplotype. Therefore, the fetus was considered normal through both methodologies, which was confirmed after the birth of a clinically normal male baby. As the LAMA2 gene is very large and the spectrum of mutations causing disease is wide, the analysis of the protein in muscle biopsy has been largely used for the diagnosis. Besides, the possibility to detect it in the chorionic villous, mainly using positive markers, also offers a powerful tool for prenatal diagnosis.

Nemaline myopathy is a structural congenital myopathy associated with the presence of rodlike structures inside the muscle fibers and type I predominance. It may be caused by mutations in at least five genes: slow alpha-tropomyosin 3 (chromosome 1q22-23), nebulin (chromosome 2q21.1-q22), actin (chromosome 1q42), tropomyosin 2 (chromosome 9p13), and troponin T1 (chromosome 19q13.4). The effect of these mutations in the expression of the protein and the mechanism of rod formation is still under investigation. We analyzed the possibility of progressive alterations with time and/or disease evolution, such as transformation of type I to type II fiber and rod pattern and distribution in muscle fibers from patients with nemaline myopathy, through a morphometric and immunohistochemical analysis of different muscle protein isoforms. A tendency of diffuse rods to be organized in the subsarcolemmal region was observed in two patients who were submitted to subsequent biopsies after 10 and 13 years. Additionally, we observed the expression of type II protein isoforms in type I fibers and a higher proportion of type II fibers in the younger patient of a pair of affected sibs, giving further support to the hypothesis of progressive conversion of type II to type I fibers in nemaline myopathy.

Long-distance runners generally have a remarkably high proportion of slow type I fibers in their lower muscle groups. However, the transformation of type II fast fibers to slow type I fibers as a result of exercise has not been demonstrated clearly. We report the analysis of muscle type composition on m. vastus lateralis from six endurance athletes through the expression of fast, slow, and developmental myosin isoforms, and alpha-actinin-3 (ACTN3) protein. Only one among the marathon runners presented evident type I fiber predominance, and surprisingly, a second athlete showed a deficiency of ACTN3. The deficiency of ACTN3 in the muscle tissue of endurance athletes confirmed the redundancy of this protein for muscle function, even in muscles that are highly required.

Nemaline myopathy is a structural congenital myopathy which may show both autosomal dominant and autosomal recessive inheritance patterns. Mutations in three different genes have been identified as the cause of nemaline myopathy: the gene for slow alpha-tropomyosin 3 (TPM3) at 1q22-23, the nebulin gene (NEB) at 2q21.1-q22, and the actin gene (ACTA1) at 1q42. The typical autosomal recessive form appears to be the most common one and is caused by mutations in the nebulin gene. We have studied the pattern of nebulin labeling, in patients with the typical congenital form (ten patients), the severe congenital form (two patients) or the mild, childhood-onset form (one patient), using antibodies against three different domains of nebulin. A qualitative and quantitative nebulin analysis in muscle tissue showed the presence of nebulin in myofibers from all patients. Some differences relating to the rod structure were observed. The majority of the largest subsarcolemmal rods were not labeled with the N2 nebulin antibody (I-band epitope) and showed an indistinct pattern with the two antibodies directed to the Z-band portion of nebulin (epitopes M176-181 and serine-rich domain). Diffuse rods were not revealed using the three antibodies. A discordant pattern of nebulin N2 epitope labeling was found in two affected sisters with a mutation in the nebulin gene, suggesting that modifications in nebulin distribution inside the rods might occur with the progression of the disease. Western blot analysis showed no direct correlation with immunofluorescence data. In nine patients, the band had a molecular weight comparable to the normal control, while in one patient, it was detected with a higher molecular weight. Our results suggest that presence/absence of specific nebulin Z-band epitopes in rod structures is variable and could depend on the degree of rod organization.