Loss Of Muscle Cells Research Articles

A case of congenital insensitivity to pain with anhidrosis.

A case of congenital insensitivity to pain with anhidrosis.

Nitric Oxide Controls Fat Deposition in Dystrophic Skeletal Muscle by Regulating Fibro-Adipogenic Precursor Differentiation

Duchenne muscular dystrophy (DMD) is an hereditary disease characterized by loss of muscle fibers and their progressive substitution by fat and fibrous tissue. Mesenchymal fibro-adipogenic progenitors (FAPs) expressing the platelet-derived growth factor receptor alpha (PDGFRα) are an important source of fibrosis and adipogenesis in dystrophic skeletal muscle. Among the therapies suggested for dystrophy are those based on nitric oxide (NO) donating drugs, the administration of which slows disease progression. NO has been shown to act by enhancing the regenerative potential of the diseased muscle. Whether it acts also by inhibiting fibrosis and adipogenesis was not known. Here, we show in vitro that NO regulates FAP fate through inhibition of their differentiation into adipocytes. In mdx mice, an animal model of DMD, treatment with the NO donating drug molsidomine reduced the number of PDGFRα(+) cells as well as the deposition of both skeletal muscle fat and connective tissues. Inhibition of adipogenesis was due to NO-induced increased expression of miR-27b leading to downregulation of peroxisome proliferator-activated receptors gamma (Pparγ1) expression in a pathway independent of cGMP generation. These findings reveal an additional effect of NO in dystrophic muscle that conceivably synergizes with its known effects on regeneration improvement and explain why NO-based therapies appear effective in the treatment of muscular dystrophy.

Gene Expression Profiling in Tibial Muscular Dystrophy Reveals Unfolded Protein Response and Altered Autophagy

Tibial muscular dystrophy (TMD) is a late onset, autosomal dominant distal myopathy that results from mutations in the two last domains of titin. The cascade of molecular events leading from the causative Titin mutations to the preterm death of muscle cells in TMD is largely unknown. In this study we examined the mRNA and protein changes associated with the myopathology of TMD. To identify these components we performed gene expression profiling using muscle biopsies from TMD patients and healthy controls. The profiling results were confirmed through quantitative real-time PCR and protein level analysis. One of the pathways identified was activation of endoplasmic reticulum (ER) stress response. ER stress activates the unfolded protein response (UPR) pathway. UPR activation was supported by elevation of the marker genes HSPA5, ERN1 and the UPR specific XBP1 splice form. However, UPR activation appears to be insufficient to correct the protein abnormalities causing its activation because degenerative TMD muscle fibres show an increase in ubiquitinated protein inclusions. Abnormalities of VCP-associated degradation pathways are also suggested by the presence of proteolytic VCP fragments in western blotting, and VCP's accumulation within rimmed vacuoles in TMD muscle fibres together with p62 and LC3B positive autophagosomes. Thus, pathways controlling turnover and degradation, including autophagy, are distorted and lead to degeneration and loss of muscle fibres.

Towards a Treatment of Stress Urinary Incontinence: Application of Mesenchymal Stromal Cells for Regeneration of the Sphincter Muscle.

Stress urinary incontinence is a significant social, medical, and economic problem. It is caused, at least in part, by degeneration of the sphincter muscle controlling the tightness of the urinary bladder. This muscular degeneration is characterized by a loss of muscle cells and a surplus of a fibrous connective tissue. In Western countries approximately 15% of all females and 10% of males are affected. The incidence is significantly higher among senior citizens, and more than 25% of the elderly suffer from incontinence. When other therapies, such as physical exercise, pharmacological intervention, or electrophysiological stimulation of the sphincter fail to improve the patient’s conditions, a cell-based therapy may improve the function of the sphincter muscle. Here, we briefly summarize current knowledge on stem cells suitable for therapy of urinary incontinence: mesenchymal stromal cells, urine-derived stem cells, and muscle-derived satellite cells. In addition, we report on ways to improve techniques for surgical navigation, injection of cells in the sphincter muscle, sensors for evaluation of post-treatment therapeutic outcome, and perspectives derived from recent pre-clinical studies.

Predicting Birth-Related Levator Ani Tear Severity in Primiparous Women: Evaluating Maternal Recovery from Labor and Delivery (EMRLD Study).

To determine which maternal characteristics or birth events independently predict severity of levator ani muscle (LA) tears at first vaginal birth in a longitudinal/observational investigation in a tertiary care hospital. Ninety primiparas with at least one at risk for LA tear inclusion factor at vaginal birth: maternal age ≥ 33 years, second stage ≥ 150 minutes, macrosomia, instrumented delivery, and/or anal sphincter laceration were studied. Magnetic Resonance Imaging (MRI) was obtained early postpartum (mean ± sd 48.9 ± 21.6 days) to identify LA tear. Severity of LA muscle fiber loss was graded on an ordinal scale of: "0" as no loss, "1" as <50% unilateral loss, "2" as ≥50% unilateral or <50% bilateral loss, and "3" as ≥50% bilateral loss. Data were analyzed using proportional odds modeling. Inclusion factors were explored as predictors of LA tear severity and at analysis episiotomy, time spent actively pushing, epidural, and oxytocin were also considered. The main outcome measures of interest included grading of severity of LA muscle fiber loss on an ordinal scale. Respective counts/percentages of women within each 0 thru 3 ordered category of LA tear severity were: "0" = 58(64%), "1" = 9(10%), "2" = 15(17%), and "3" = 8(9%). Estimates and 95% CI for significant demographic or obstetric univariate predictors of LA tear severity level were age, OR 1.093 (CI 1.012 - 1.180), p = 0.023; and time spent in active pushing, OR 1.089 (CI 1.005 - 1.180), p = 0.038. The other factors considered were not significant. There were too few women with forceps deliveries to analyze. CONCLUSION: In our enriched sample of primiparous women, 26% showed a significant LA tear. Maternal age and time spent actively pushing independently predict LA tear severity.

Intestine of dystrophic mice presents enhanced contractile resistance to stretching despite morphological impairment

Protein dystrophin is a component of the dystrophin-associated protein complex, which links the contractile machinery to the plasma membrane and to the extracellular matrix. Its absence leads to a condition known as Duchenne muscular dystrophy (DMD), a disease characterized by progressive skeletal muscle degeneration, motor disability, and early death. In mdx mice, the most common DMD animal model, loss of muscle cells is observed, but the overall disease alterations are less intense than in DMD patients. Alterations in gastrointestinal tissues from DMD patients and mdx mice are not yet completely understood. Thus, we investigated the possible relationships between morphological (light and electron microscopy) and contractile function (by recording the isometric contractile response) with alterations in Ca²⁺ handling in the ileum of mdx mice. We evidenced a 27% reduction in the ileal muscular layer thickness, a partial damage to the mucosal layer, and a partial damage to mitochondria of the intestinal myocytes. Functionally, the ileum from mdx presented an enhanced responsiveness during stretch, a mild impairment in both the electromechanical and pharmacomechanical signaling associated with altered calcium influx-induced contraction, with no alterations in the sarcoplasmic reticulum Ca²⁺ storage (maintenance of the caffeine and thapsigargin-induced contraction) compared with control animals. Thus, it is evidenced that the protein dystrophin plays an important role in the preservation of both the microstructure and ultrastructure of mice intestine, while exerting a minor but important role concerning the intestinal contractile responsiveness and calcium handling.

Reducing CTGF/CCN2 slows down mdx muscle dystrophy and improves cell therapy

In Duchenne muscular dystrophy (DMD) and the mdx mouse model, the absence of the cytoskeletal protein dystrophin causes defective anchoring of myofibres to the basal lamina. The resultant myofibre degeneration and necrosis lead to a progressive loss of muscle mass, increased fibrosis and ultimately fatal weakness. Connective tissue growth factor (CTGF/CCN-2) is critically involved in several chronic fibro-degenerative diseases. In DMD, the role of CTGF might extend well beyond replacement fibrosis secondary to loss of muscle fibres, since its overexpression in skeletal muscle could by itself induce a dystrophic phenotype. Using two independent approaches, we here show that mdx mice with reduced CTGF availability do indeed have less severe muscular dystrophy. Mdx mice with hemizygous CTGF deletion (mdx-Ctgf+/-), and mdx mice treated with a neutralizing anti-CTGF monoclonal antibody (FG-3019), performed better in an exercise endurance test, had better muscle strength in isolated muscles and reduced skeletal muscle impairment, apoptotic damage and fibrosis. Transforming growth factor type-β (TGF-β), pERK1/2 and p38 signalling remained unaffected during CTGF suppression. Moreover, both mdx-Ctgf+/- and FG-3019 treated mdx mice had improved grafting upon intramuscular injection of dystrophin-positive satellite cells. These findings reveal the potential of targeting CTGF to reduce disease progression and to improve cell therapy in DMD.

Why short stature is beneficial in duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is caused by a genetic defect resulting in absent dystrophin, yet children are able to walk when small and young but lose this ability as they grow. The mdx mouse has absent dystrophin yet does not exhibit significant disability. Allometric modeling of linearly increasing load per muscle fiber and stress on the sarcolemma with growth and exponential decline associated with loss of muscle fibers correlated with case studies and animal models of DMD. Smaller species or breeds are predictably less affected than large as follows: mdx mice < small golden retriever muscular dystrophy (GRMD) dogs < large GRMD dogs < humans. Case reports of combined growth hormone and dystrophin deficiency show a relatively benign course of disease. Future therapeutic trials in DMD might include specific growth inhibitors in combination with standard of care treatments to delay the clinical onset and reduce the severity of disease and disability.

Long-term wheel running compromises diaphragm function but improves cardiac and plantarflexor function in the mdx mouse

Dystrophin-deficient muscles suffer from free radical injury, mitochondrial dysfunction, apoptosis, and inflammation, among other pathologies that contribute to muscle fiber injury and loss, leading to wheelchair confinement and death in the patient. For some time, it has been appreciated that endurance training has the potential to counter many of these contributing factors. Correspondingly, numerous investigations have shown improvements in limb muscle function following endurance training in mdx mice. However, the effect of long-term volitional wheel running on diaphragm and cardiac function is largely unknown. Our purpose was to determine the extent to which long-term endurance exercise affected dystrophic limb, diaphragm, and cardiac function. Diaphragm specific tension was reduced by 60% (P < 0.05) in mice that performed 1 yr of volitional wheel running compared with sedentary mdx mice. Dorsiflexor mass (extensor digitorum longus and tibialis anterior) and function (extensor digitorum longus) were not altered by endurance training. In mice that performed 1 yr of volitional wheel running, plantarflexor mass (soleus and gastrocnemius) was increased and soleus tetanic force was increased 36%, while specific tension was similar in wheel-running and sedentary groups. Cardiac mass was increased 15%, left ventricle chamber size was increased 20% (diastole) and 18% (systole), and stroke volume was increased twofold in wheel-running compared with sedentary mdx mice. These data suggest that the dystrophic heart may undergo positive exercise-induced remodeling and that limb muscle function is largely unaffected. Most importantly, however, as the diaphragm most closely recapitulates the human disease, these data raise the possibility of exercise-mediated injury in dystrophic skeletal muscle.

Skeletal muscle evaluation by MRI in a rabbit model of acute ischaemia

To assess rhabdomyolysis-associated skeletal muscle changes induced by complete ischaemia in rabbits using MRI. Acute ischaemia was induced in the right hind limb of 34 New Zealand white rabbits by arterial ligation. MRI of vastus lateralis was carried out pre-operatively and every hour post-operatively up to 7 h. T1 weighted images, T2 weighted images with fat suppression, T2 maps and diffusion tensor scans were obtained. The correlation of MRI findings with histopathological changes in biopsies of vastus lateralis was examined. Histopathology demonstrated early cellular oedema 1 h post ischaemia and irreversible injuries by 7 h, including loss of striation and broken muscle fibres. T2 weighted images with fat suppression showed inhomogeneous high signal intensity of vastus lateralis, which progressively increased from 2 h following ischaemia. The T2 relaxation rate of ischaemic vastus lateralis was significantly greater than normal muscle (p<0.001) and demonstrated a linear increase with time following ischaemia. A similar linear increase was also found in the ischaemic vastus lateralis apparent diffusion coefficient (ADC) 1-5 h post ischaemia (p=0.006). Both the T2 ADC and fractional anisotropy (FA) were significantly higher on the ischaemic side 7 h post ischaemia (for T2, p=0.02; for ADC, p=0.004). Muscle oedema is detectable on MR images and is reflected well by T2, ADC and FA values. MRI may have value in clinical evaluation of rhabdomyolysis. Ischaemic changes detected by MRI may have value in the diagnosis of rhabdomyolysis.

Interleukin‐6 induces ErbBs receptor phosphorylation and utrophin expression in dystrophic myotubes.

Duchenne muscular dystrophy (DMD) is a neuromuscular disease originated by mutations in the dystrophin gene, leading to skeletal muscle fiber loss. A promising pharmacological treatment aims to increase the level of utrophin, a functional dystrophin homolog that could compensate dystrophin absence in DMD muscle fibers. It has been described that interleukin‐6 (IL‐6) and neuregulin‐1 (NRG‐1) induce utrophin expression in skeletal muscle.We investigated a possible functional link among IL‐6, NRG‐1 and utrophin, in normal (C57) and dystrophic (mdx) skeletal muscle cells.Using Western Blot and semiquantitative PCR, we demonstrated that IL‐6 (100 ng/ml) induces NRG‐1 receptor phosphorylation (ErbB2/ErbB3) in both cellular types, and a transient increase on utrophin mRNA levels in dystrophic myotubes. We observed that BAPTA‐AM (an intracellular Ca2+ chelator), GM6001 (a general metalloproteinase inhibitor), genistein (a general protein tyrosine kinase inhibitor) and PD‐158780 (an ErbB receptor tyrosine kinase inhibitor) treatment abolished utrophin mRNA induction.Our results suggest that IL‐6 induces utrophin expression in dystrophic myotubes, through NRG‐1/ErbBs signaling activation, elicited by proteolytic processing of NRG‐1 and ErbBs phosphorylation. Understanding the mechanism involved on utrophin up regulation could help to the development of DMD new therapies.FONDECYT 11100267

The decline in skeletal muscle mass with aging is mainly attributed to a reduction in type II muscle fiber size

BackgroundThe loss of skeletal muscle mass with aging has been attributed to a decline in muscle fiber number and muscle fiber size. ObjectiveTo define to what extent differences in leg muscle cross-sectional area (CSA) between young and elderly men are attributed to differences in muscle fiber size. MethodsQuadriceps muscle CSA and type I and type II muscle fiber size were measured in healthy young (n=25; 23±1y) and older (n=26; 71±1y) men. Subsequently, the older subjects performed 6months of resistance type exercise training, after which measurements were repeated. Differences in quadriceps muscle CSA were compared with differences in type I and type II muscle fiber size. ResultsQuadriceps CSA was substantially smaller in older versus young men (68±2 vs 80±2cm2, respectively; P<0.001). Type II muscle fiber size was substantially smaller in the elderly vs the young (29%; P<0.001), with a tendency of smaller type I muscle fibers (P=0.052). Differences in type II muscle fiber size fully explained differences in quadriceps CSA between groups. Prolonged resistance type exercise training in the elderly increased type II muscle fiber size by 24±8% (P<0.01), explaining 100±3% of the increase in quadriceps muscle CSA (from 68±2 to 74±2cm2). ConclusionReduced muscle mass with aging is mainly attributed to smaller type II muscle fiber size and, as such, is unlikely accompanied by substantial muscle fiber loss. In line, the increase in muscle mass following prolonged resistance type exercise training can be attributed entirely to specific type II muscle fiber hypertrophy.

Grafting of a Single Donor Myofibre Promotes Hypertrophy in Dystrophic Mouse Muscle

Skeletal muscle has a remarkable capability of regeneration following injury. Satellite cells, the principal muscle stem cells, are responsible for this process. However, this regenerative capacity is reduced in muscular dystrophies or in old age: in both these situations, there is a net loss of muscle fibres. Promoting skeletal muscle muscle hypertrophy could therefore have potential applications for treating muscular dystrophies or sarcopenia. Here, we observed that muscles of dystrophic mdx nude host mice that had been acutely injured by myotoxin and grafted with a single myofibre derived from a normal donor mouse exhibited increased muscle area. Transplantation experiments revealed that the hypertrophic effect is mediated by the grafted fibre and does not require either an imposed injury to the host muscle, or the contribution of donor cells to the host muscle. These results suggest the presence of a crucial cross-talk between the donor fibre and the host muscle environment.

Myotubularin family phosphatase ceMTM3 is required for muscle maintenance by preventing excessive autophagy in Caenorhabditis elegans

BackgroundAutophagy is a ubiquitous cellular process responsible for the bulk degradation of cytoplasmic components through the autophagosomal-lysosomal pathway. In skeletal muscle, autophagy has been regarded as a key regulator for muscle mass maintenance, and its imbalance leads to sarcopenia. However, the underlying mechanism is poorly understood.ResultsIn this study, we demonstrate that ceMTM3, a FYVE-domain containing myotubalarin family phosphatase, is required for the maintenance of muscle fibers by preventing excessive autophagy in Caenorhabditis elegans. Knockdown of ceMTM3 by using feeding-based RNA interference caused loss of muscle fibers accompanied by shortening of muscle cell and body size in aged C. elegans worms. This was preceded by the occurrence of excessive autophagy in the muscle and other tissues, which subsequently resulted in increased lysosomal activity and necrotic cell death. However, knockdown of ceMTM3 did not aggravate the abnormalities of muscle wasting in autophagy-deficient atg-18 mutant worms.ConclusionsOur data suggest an important role of ceMTM3 in regulating autophagy and maintaining muscle fibers. This study may have clinical implications for prevention and treatment of sarcopenia.

The CMAP scan as a tool to monitor disease progression in ALS and PMA

Amyotrophic lateral sclerosis (ALS) and progressive muscular atrophy (PMA) are characterized by a loss of motor units (MUs), reinnervation and, eventually, muscle fibre loss. These three aspects are all reflected in the compound muscle action potential scan (CMAP scan, a high-detail stimulus response curve), which visualizes large MU potentials as ‘steps’. We explored changes in the CMAP scan over time, combined the information on steps and CMAP amplitude into a CMAP scan-based progression score (CSPS), and correlated this score with motor unit number estimates (MUNE). Ten patients (three PMA, seven ALS; age 37−77 years) were included. CMAP scan and MUNE measurements were performed five times during a three-month period. Nine patients had additional measurements. The follow-up period was 3−24 months. Results demonstrated that abnormalities in steps preceded a decline in maximum CMAP amplitude during follow-up. Usually, both steps and maximum CMAP amplitude changed between recordings. The correlation between the CSPS and MUNE was −0.80 (p < 0.01). In conclusion, the CMAP scan can be used to visualize and quantify disease progression in a muscle affected by MND. The CSPS is a measure of MU loss that is quick and easy to obtain and that, in contrast to MUNE, has no sample bias.

Muscle Fiber Atrophy and Regeneration Coexist in Collagen VI-Deficient Human Muscle: Role of Calpain-3 and Nuclear Factor-κB Signaling

Ullrich congenital muscular dystrophy (UCMD) is a common form of muscular dystrophy associated with defects in collagen VI. It is characterized by loss of individual muscle fibers and muscle mass and proliferation of connective and adipose tissues. We sought to investigate the mechanisms by which collagen VI regulates muscle cell survival, size, and regeneration and, in particular, the potential role of the ubiquitin-proteasome and calpain-proteolytic systems. We studied muscle biopsies of UCMD (n = 6), other myopathy (n = 12), and control patients (n = 10) and found reduced expression of atrogin-1, MURF1, and calpain-3 mRNAs in UCMD cases. Downregulation of calpain-3 was associated with changes in the nuclear immunolocalization of nuclear factor-κB. We also observed increased expression versus controls of regeneration markers at the protein and RNA levels. Satellite cell numbers did not differ in collagen VI-deficient muscle versus normal nonregenerating muscle, indicating that collagen VI does not play a key role in the maintenance of the satellite cell pool. Our results indicate that alterations in calpain-3 and nuclear factor-κB signaling pathways may contribute to muscle mass loss in UCMD muscle, whereas atrogin-1 and MURF1 are not likely to play a major role.

Weakness of whole muscles in mice deficient in Cu, Zn superoxide dismutase is not explained by defects at the level of the contractile apparatus

Mice deficient in Cu,Zn superoxide dismutase (Sod1 (-/-) mice) demonstrate elevated oxidative stress associated with rapid age-related declines in muscle mass and force. The decline in mass for muscles of Sod1 (-/-) mice is explained by a loss of muscle fibers, but the mechanism underlying the weakness is not clear. We hypothesized that the reduced maximum isometric force (F o) normalized by cross-sectional area (specific F o) for whole muscles of Sod1 (-/-) compared with wild-type (WT) mice is due to decreased specific F o of individual fibers. Force generation was measured for permeabilized fibers from muscles of Sod1 (-/-) and WT mice at 8 and 20 months of age. WT mice were also studied at 28 months to determine whether any deficits observed for fibers from Sod1 (-/-) mice were similar to those observed in old WT mice. No effects of genotype were observed for F o or specific F o at either 8 or 20 months, and no age-associated decrease in specific F o was observed for fibers from Sod1 (-/-) mice, whereas specific F o for fibers of WT mice decreased by 20 % by 28 months. Oxidative stress has also been associated with decreased maximum velocity of shortening (V max), and we found a 10 % lower V max for fibers from Sod1 (-/-) compared with WT mice at 20 months. We conclude that the low specific F o of muscles of Sod1 (-/-) mice is not explained by damage to contractile proteins. Moreover, the properties of fibers of Sod1 (-/-) mice do not recapitulate those observed with aging in WT animals.

Endurance and resistance training modifies the transcriptional profile of the vastus lateralis skeletal muscle in healthy elderly subjects

Ageing in humans is associated with physiological loss of strength and skeletal muscle fibres, known as sarcopenia. This results in loss of mobility and independence in the elderly, and is a major socioeconomic and public health issue. Progression of sarcopenia can be influenced by a range of concomitant factors. In our ongoing investigations into the effects on skeletal muscle of specific and intensity-graduated endurance and resistance training, we investigated the associated muscle adaptation at the molecular level through transcription profile analysis. Although the 12-week training programmes appeared to have little benefit, with increases in muscle strength of 1–2%, the transcriptional profiles obtained from tiny percutaneous needle biopsies of the vastus lateralis muscle demonstrated that the training was specific and efficient. This classification of the transcriptome in terms of the functional groupings of the gene expression profiles associated with the endurance and resistance training programmes provides a signature of the muscle responsiveness to the specific training. Therefore, such analyses could provide a useful tool to personalize specific skeletal muscle training, and they indicate that both endurance and resistance training should indeed be incorporated into weekly scheduled exercise in elderly subjects.

Clinical, pathological, and genetic mutation analysis of sporadic inclusion body myositis in Japanese people

Previous studies have identified several genetic loci associated with the development of familial inclusion body myopathy. However, there have been few genetic analyses of sporadic inclusion body myositis (sIBM). In order to explore the molecular basis of sIBM and to investigate genotype-phenotype correlations, we performed a clinicopathological analysis of 21 sIBM patients and screened for mutations in the Desmin, GNE, MYHC2A, VCP, and ZASP genes. All coding exons of the five genes were sequenced directly. Definite IBM was confirmed in 14 cases, probable IBM in three cases, and possible IBM in four cases. No cases showed missense mutations in the Desmin, GNE, or VCP genes. Three patients carried the missense mutation c.2542T>C (p.V805A) in the MYHC2A gene; immunohistochemical staining for MYHC isoforms in these three cases showed atrophy or loss of muscle fibers expressing MYHC IIa or IIx. One patient harbored the missense mutation c.1719G>A (p.V566M) in the ZASP gene; immunohistochemical studies of Z-band-associated proteins revealed Z-band abnormalities. Both of the novel heterogeneous mutations were located in highly evolutionarily conserved domains of their respective genes. Cumulatively, these findings have expanded our understanding of the molecular background of sIBM. However, we advocate further clinicopathology and investigation of additional candidate genes in a larger cohort.

Cellular and Molecular Mechanisms of Apoptosis in Age-Related Muscle Atrophy

Age-related muscle atrophy is due to loss of muscle fibers as well as atrophy of the remaining fibers. Evidence shows that loss of myofibers may be, in part, due to apoptosis. Two major apoptotic pathways have been extensively studied which are the mitochondrion-mediated and receptor-mediated pathways. However, other pathways exist, such as the p53 pathway. To date, it is not completely clear what pathways are responsible for loss of fibers in age-related muscle atrophy. Evidence suggests that multiple pathways may play a role. In this review article the effects of aging on the mitochondrion-, receptor-, and p53-mediated apoptotic pathways in skeletal muscle are discussed.