RESUMEN
Mucopolysaccharidosis type IIIA (MPS IIIA) is characterized by neurological and skeletal pathologies caused by reduced activity of the lysosomal hydrolase, sulfamidase, and the subsequent primary accumulation of undegraded heparan sulfate (HS). Respiratory pathology is considered secondary in MPS IIIA and the mechanisms are not well understood. Changes in the amount, metabolism, and function of pulmonary surfactant, the substance that regulates alveolar interfacial surface tension and modulates lung compliance and elastance, have been reported in MPS IIIA mice. Here we investigated changes in lung function in 20-wk-old control and MPS IIIA mice with a closed and open thoracic cage, diaphragm contractile properties, and potential parenchymal remodeling. MPS IIIA mice had increased compliance and airway resistance and reduced tissue damping and elastance compared with control mice. The chest wall impacted lung function as observed by an increase in airway resistance and a decrease in peripheral energy dissipation in the open compared with the closed thoracic cage state in MPS IIIA mice. Diaphragm contractile forces showed a decrease in peak twitch force, maximum specific force, and the force-frequency relationship but no change in muscle fiber cross-sectional area in MPS IIIA mice compared with control mice. Design-based stereology did not reveal any parenchymal remodeling or destruction of alveolar septa in the MPS IIIA mouse lung. In conclusion, the increased storage of HS which leads to biochemical and biophysical changes in pulmonary surfactant also affects lung and diaphragm function, but has no impact on lung or diaphragm structure at this stage of the disease.NEW & NOTEWORTHY Heparan sulfate storage in the lungs of mucopolysaccharidosis type IIIA (MPS IIIA) mice leads to changes in lung function consistent with those of an obstructive lung disease and includes an increase in lung compliance and airway resistance and a decrease in tissue elastance. In addition, diaphragm muscle contractile strength is reduced, potentially further contributing to lung function impairment. However, no changes in parenchymal lung structure were observed in mice at 20 wk of age.
Asunto(s)
Resistencia de las Vías Respiratorias , Diafragma , Mucopolisacaridosis III , Alveolos Pulmonares , Animales , Diafragma/fisiopatología , Diafragma/patología , Diafragma/metabolismo , Rendimiento Pulmonar , Ratones , Alveolos Pulmonares/patología , Alveolos Pulmonares/fisiopatología , Alveolos Pulmonares/metabolismo , Mucopolisacaridosis III/patología , Mucopolisacaridosis III/fisiopatología , Mucopolisacaridosis III/metabolismo , Mucopolisacaridosis III/genética , Contracción Muscular/fisiología , Ratones Endogámicos C57BL , Modelos Animales de Enfermedad , Fuerza Muscular , Pulmón/patología , Pulmón/fisiopatología , Pulmón/metabolismo , MasculinoRESUMEN
Duchenne muscular dystrophy (DMD) is a fatal X-linked disease characterised by severe muscle wasting. The mechanisms underlying the DMD pathology likely involve the interaction between inflammation, oxidative stress and impaired Ca2+ signalling. Hypochlorous acid (HOCl) is a highly reactive oxidant produced endogenously via myeloperoxidase; an enzyme secreted by neutrophils that is significantly elevated in dystrophic muscle. Oxidation of Ca2+ -handling proteins by HOCl may impair Ca2+ signalling. This study aimed to determine the effects of HOCl on skeletal muscle function and its potential contribution to the dystrophic pathology. Extensor digitorum longus (EDL), soleus and interosseous muscles were surgically isolated from anaesthetised C57 (wild-type) and mdx (dystrophic) mice for measurement of ex vivo force production and intracellular Ca2+ concentration. In whole EDL muscle, HOCl (200 µM) significantly decreased maximal force and increased resting muscle tension which was only partially reversible by dithiothreitol. The effects of HOCl (200 µM) on maximal force in slow-twitch soleus were lower than found in the fast-twitch EDL muscle. In single interosseous myofibres, HOCl (10 µM) significantly increased resting intracellular Ca2+ concentration and decreased Ca2+ transient amplitude. These effects of HOCl were reduced by the application of tetracaine, Gd3+ or streptomycin, implicating involvement of ryanodine receptors and transient receptor potential channels. These results demonstrate the potent effects of HOCl on skeletal muscle function potentially mediated by HOCl-induced oxidation to Ca2+ signalling proteins. Hence, HOCl may provide a link between chronic inflammation, oxidative stress and impaired Ca2+ handling that is characteristic of DMD and presents a potential therapeutic target for DMD. KEY POINTS: Duchenne muscular dystrophy is a fatal genetic disease with pathological mechanisms which involve the complex interaction of chronic inflammation, increased reactive oxygen species production and increased cytosolic Ca2+ concentrations. Hypochlorous acid can be endogenously produced by neutrophils via the enzyme myeloperoxidase. Both neutrophil and myeloperoxidase activity are increased in dystrophic mice. This study found that hypochlorous acid decreased muscle force production and increased cytosolic Ca2+ concentrations in isolated muscles from wild-type and dystrophic mice at relatively low concentrations of hypochlorous acid. These results indicate that hypochlorous acid may be key in the Duchenne muscular dystrophy disease pathology and may provide a unifying link between the chronic inflammation, increased reactive oxygen species production and increased cytosolic Ca2+ concentrations observed in Duchenne muscular dystrophy. Hypochlorous acid production may be a potential target for therapeutic treatments of Duchenne muscular dystrophy.
Asunto(s)
Distrofia Muscular de Duchenne , Animales , Ratones , Ácido Hipocloroso/farmacología , Ácido Hipocloroso/metabolismo , Ácido Hipocloroso/uso terapéutico , Peroxidasa/metabolismo , Ratones Endogámicos mdx , Ratones Endogámicos C57BL , Músculo Esquelético/metabolismo , Inflamación/metabolismo , Modelos Animales de EnfermedadRESUMEN
Dysferlinopathies are a clinically heterogeneous group of muscular dystrophies caused by a genetic deficiency of the membrane-associated protein dysferlin, which usually manifest post-growth in young adults. The disease is characterized by progressive skeletal muscle wasting in the limb-girdle and limbs, inflammation, accumulation of lipid droplets in slow-twitch myofibers and, in later stages, replacement of muscles by adipose tissue. Previously we reported myofiber-type specific differences in muscle contractile function of 10-month-old dysferlin-deficient BLAJ mice that could not be fully accounted for by altered myofiber-type composition. In order to further investigate these findings, we examined the impact of dysferlin deficiency on the abundance of calcium (Ca2+) handling and glucose/glycogen metabolism-related proteins in predominantly slow-twitch, oxidative soleus and fast-twitch, glycolytic extensor digitorum longus (EDL) muscles of 10-month-old wild-type (WT) C57BL/6J and dysferlin-deficient BLAJ male mice. Additionally, we compared the Ca2+ activation properties of isolated slow- and fast-twitch myofibers from 3-month-old WT and BLAJ male mice. Differences were observed for some Ca2+ handling and glucose/glycogen metabolism-related protein levels between BLAJ soleus and EDL muscles (compared with WT) that may contribute to the previously reported differences in function in these BLAJ muscles. Dysferlin deficiency did not impact glycogen content of whole muscles nor Ca2+ activation of the myofilaments, although soleus muscle from 10-month-old BLAJ mice had more glycogen than EDL muscles. These results demonstrate a further impact of dysferlin deficiency on proteins associated with excitation-contraction coupling and glycogen metabolism in skeletal muscles, potentially contributing to altered contractile function in dysferlinopathy.
Asunto(s)
Calcio , Disferlina , Glucógeno , Animales , Masculino , Ratones , Calcio/metabolismo , Disferlina/deficiencia , Glucosa/metabolismo , Glucógeno/metabolismo , Ratones Endogámicos C57BL , Músculo Esquelético/metabolismoRESUMEN
The preterm diaphragm is functionally immature compared with its term counterpart. In utero inflammation further exacerbates preterm diaphragm dysfunction. We hypothesized that preterm lambs are more vulnerable to in utero inflammation-induced diaphragm dysfunction compared with term lambs. Pregnant ewes received intra-amniotic (IA) injections of saline or 10 mg lipopolysaccharide (LPS) 2 or 7 days before delivery at 121 days (preterm) or â¼145 days (term) of gestation. Diaphragm contractile function was assessed in vitro. Plasma cytokines, diaphragm myosin heavy chain (MHC) isoforms, and oxidative stress were evaluated. Maximum diaphragm force in preterm control lambs was significantly lower (22%) than in term control lambs ( P < 0.001). Despite similar inflammatory cytokine responses to in utero LPS exposure, diaphragm function in preterm and term lambs was affected differentially. In term lambs, maximum force after a 2-day LPS exposure was significantly lower than in controls (by ~20%, P < 0.05). In preterm lambs, maximum forces after 2-day and 7-day LPS exposures were significantly lower than in controls (by ~30%, P < 0.05). Peak twitch force after LPS exposure was significantly lower in preterm than in controls, but not in term lambs. In term lambs, LPS exposure increased the proportion of MHC-I fibers, increased twitch contraction times, and increased fatigue resistance relative to controls. In preterm diaphragm, the cross-sectional area of embryonic MHC fibers was significantly lower after 7-day versus 2-day LPS exposures. We conclude that preterm lambs are more vulnerable to IA LPS-induced diaphragm dysfunction than term lambs. In utero inflammation exacerbates diaphragm dysfunction and may increase susceptibility to postnatal respiratory failure.
Asunto(s)
Corioamnionitis/fisiopatología , Diafragma/fisiopatología , Lipopolisacáridos , Contracción Muscular , Fuerza Muscular , Debilidad Muscular/inducido químicamente , Efectos Tardíos de la Exposición Prenatal , Animales , Animales Recién Nacidos , Corioamnionitis/sangre , Corioamnionitis/inducido químicamente , Citocinas/sangre , Diafragma/metabolismo , Modelos Animales de Enfermedad , Femenino , Edad Gestacional , Mediadores de Inflamación/sangre , Debilidad Muscular/sangre , Debilidad Muscular/fisiopatología , Cadenas Pesadas de Miosina/metabolismo , Estrés Oxidativo , Embarazo , Nacimiento Prematuro , Índice de Severidad de la Enfermedad , Oveja DomésticaRESUMEN
KEY POINTS: Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease associated with increased inflammation and oxidative stress. The antioxidant N-acetylcysteine (NAC) has been proposed as a therapeutic intervention for DMD boys, but potential adverse effects of NAC have not been widely investigated. We used young (6 weeks old) growing mdx mice to investigate the capacity of NAC supplementation (2% in drinking water for 6 weeks) to improve dystrophic muscle function and to explore broader systemic effects of NAC treatment. NAC treatment improved normalised measures of muscle function, and decreased inflammation and oxidative stress, but significantly reduced body weight gain, muscle weight and liver weight. Unexpected significant adverse effects of NAC on body and muscle weights indicate that interpretation of muscle function based on normalised force measures should be made with caution and careful consideration is needed when proposing the use of NAC as a therapeutic treatment for young DMD boys. ABSTRACT: Duchenne muscular dystrophy (DMD) is a fatal X-linked muscle wasting disease characterised by severe muscle weakness, necrosis, inflammation and oxidative stress. The antioxidant N-acetylcysteine (NAC) has been proposed as a potential therapeutic intervention for DMD boys. We investigated the capacity of NAC to improve dystrophic muscle function in the mdx mouse model of DMD. Young (6 weeks old) mdx and non-dystrophic C57 mice receiving 2% NAC in drinking water for 6 weeks were compared with untreated mice. Grip strength and body weight were measured weekly, before the 12 week old mice were anaesthetised and extensor digitorum longus (EDL) muscles were excised for functional analysis and tissues were sampled for biochemical analyses. Compared to untreated mice, the mean (SD) normalised grip strength was significantly greater in NAC-treated mdx [3.13 (0.58) vs 4.87 (0.78) g body weight (bw)-1 ; P < 0.001] and C57 mice [3.90 (0.32) vs 5.32 (0.60) g bw-1 ; P < 0.001]. Maximum specific force was significantly greater in NAC-treated mdx muscles [9.80 (2.27) vs 13.07 (3.37) N cm-2 ; P = 0.038]. Increased force in mdx mice was associated with reduced thiol oxidation and inflammation in fast muscles, and increased citrate synthase activity in slow muscle. Importantly, NAC significantly impaired body weight gain in both strains of young growing mice, and reduced liver weight in C57 mice and muscle weight in mdx mice. These potentially adverse effects of NAC emphasise the need for caution when interpreting improvements in muscle function based on normalised force measures, and that careful consideration be given to these effects when proposing NAC as a potential treatment for young DMD boys.
Asunto(s)
Acetilcisteína/efectos adversos , Depuradores de Radicales Libres/efectos adversos , Distrofia Muscular de Duchenne/tratamiento farmacológico , Acetilcisteína/administración & dosificación , Acetilcisteína/uso terapéutico , Animales , Peso Corporal/efectos de los fármacos , Evaluación Preclínica de Medicamentos , Depuradores de Radicales Libres/administración & dosificación , Depuradores de Radicales Libres/uso terapéutico , Hígado/efectos de los fármacos , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Endogámicos mdx , Fuerza Muscular , Músculo Esquelético/efectos de los fármacos , Músculo Esquelético/metabolismo , Músculo Esquelético/fisiopatología , Distrofia Muscular de Duchenne/genética , Estrés OxidativoRESUMEN
BackgroundPregnant women at a high risk of preterm delivery receive glucocorticoids to accelerate fetal lung maturation and surfactant synthesis. However, the effect of antenatal steroids on the developing diaphragm remains unclear. We hypothesized that maternal betamethasone impairs the fetal diaphragm, and the magnitude of the detrimental effect increases with longer duration of exposure. We aimed to determine how different durations of fetal exposure to maternal betamethasone treatment influence the fetal diaphragm at the functional and molecular levels.MethodsDate-mated merino ewes received intramuscular injections of saline (control) or two doses of betamethasone (5.7 mg) at an interval of 24 h commencing either 2 or 14 days before delivery. Preterm lambs were killed after cesarean delivery at 121-day gestational age. In vitro contractile measurements were performed on the right hemidiaphragm, whereas molecular/cellular analyses used the left costal diaphragm.ResultsDifferent durations of fetal exposure to maternal betamethasone had no consistent effect on the protein metabolic pathway, expression of glucocorticoid receptor and its target genes, cellular oxidative status, or contractile properties of the fetal lamb diaphragm.ConclusionThese data suggest that the potential benefits of betamethasone exposure on preterm respiratory function are not compromised by impaired diaphragm function after low-dose maternal intramuscular glucocorticoid exposure.
Asunto(s)
Betametasona/administración & dosificación , Diafragma/efectos de los fármacos , Edad Gestacional , Glucocorticoides/administración & dosificación , Exposición Materna , Ovinos/embriología , Animales , Western Blotting , Cesárea , Diafragma/metabolismo , Diafragma/fisiología , Relación Dosis-Respuesta a Droga , Femenino , Regulación de la Expresión Génica , Complejo Mayor de Histocompatibilidad/genética , Contracción Muscular/efectos de los fármacos , Proteolisis , ARN/aislamiento & purificación , Receptores de Glucocorticoides/genética , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Transducción de SeñalRESUMEN
KEY POINTS: Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease associated with increased inflammation, oxidative stress and myofibre necrosis. Cysteine precursor antioxidants such as N-acetyl cysteine (NAC) and l-2-oxothiazolidine-4-carboxylate (OTC) reduce dystropathology in the mdx mouse model for DMD, and we propose this is via increased synthesis of the amino acid taurine. We compared the capacity of OTC and taurine treatment to increase taurine content of mdx muscle, as well as effects on in vivo and ex vivo muscle function, inflammation and oxidative stress. Both treatments increased taurine in muscles, and improved many aspects of muscle function and reduced inflammation. Taurine treatment also reduced protein thiol oxidation and was overall more effective, as OTC treatment reduced body and muscle weight, suggesting some adverse effects of this drug. These data suggest that increasing dietary taurine is a better candidate for a therapeutic intervention for DMD. ABSTRACT: Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease for which there is no widely available cure. Whilst the mechanism of loss of muscle function in DMD and the mdx mouse model are not fully understood, disruptions in intracellular calcium homeostasis, inflammation and oxidative stress are implicated. We have shown that protein thiol oxidation is increased in mdx muscle, and that the indirect thiol antioxidant l-2-oxothiazolidine-4-carboxylate (OTC), which increases cysteine availability, decreases pathology and increases in vivo strength. We propose that the protective effects of OTC are a consequence of conversion of cysteine to taurine, which has itself been shown to be beneficial to mdx pathology. This study compares the efficacy of taurine with OTC in decreasing dystropathology in mdx mice by measuring in vivo and ex vivo contractile function and measurements of inflammation and protein thiol oxidation. Increasing the taurine content of mdx muscle improved both in vivo and ex vivo muscle strength and function, potentially via anti-inflammatory and antioxidant effects of taurine. OTC treatment increased taurine synthesis in the liver and taurine content of mdx muscle, improved muscle function and decreased inflammation. However, OTC was less effective than taurine treatment, with OTC also decreasing body and EDL muscle weights, suggesting that OTC had some detrimental effects. These data support continued research into the use of taurine as a therapeutic intervention for DMD, and suggest that increasing dietary taurine is the better strategy for increasing taurine content and decreasing severity of dystropathology.
Asunto(s)
Músculo Esquelético/efectos de los fármacos , Músculo Esquelético/fisiología , Distrofia Muscular de Duchenne/dietoterapia , Distrofia Muscular de Duchenne/metabolismo , Taurina/administración & dosificación , Taurina/biosíntesis , Animales , Modelos Animales de Enfermedad , Femenino , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Endogámicos mdx , Contracción Muscular/efectos de los fármacos , Contracción Muscular/fisiología , Distrofia Muscular de Duchenne/genética , Ácido Pirrolidona Carboxílico/administración & dosificación , Tiazolidinas/administración & dosificaciónRESUMEN
INTRODUCTION: Protease-activated receptors (PARs) may play a role in skeletal muscle development. We compared the contractile properties of slow-twitch soleus muscles and fast-twitch extensor digitorum longus (EDL) muscles from PAR-1 null and littermate control mice. METHODS: Contractile function was measured using a force transducer system. Fiber type proportions were determined using immunohistochemistry. RESULTS: Soleus muscles from PAR-1 null mice exhibited longer contraction times, a leftward shift in the force-stimulation frequency relationship, and decreased fatiguability compared with controls. PAR-1 null soleus muscles also had increased type 1 and decreased type IIb/x fiber numbers compared with controls. In PAR-1 null EDL muscles, no differences were found, except for a slower rate of fatigue compared with controls. CONCLUSIONS: The absence of PAR-1 results in a slower skeletal muscle contractile phenotype, likely due to an increase in type I and a decrease in type IIb/x fiber numbers. Muscle Nerve 50: 991-998, 2014.
Asunto(s)
Contracción Muscular/fisiología , Fibras Musculares de Contracción Rápida/fisiología , Fibras Musculares de Contracción Lenta/fisiología , Músculo Esquelético/fisiología , Receptor PAR-1/deficiencia , Animales , Estimulación Eléctrica , Femenino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Fatiga Muscular/fisiología , Fuerza Muscular/fisiología , Fenotipo , Receptor PAR-1/genética , Receptor PAR-1/fisiologíaRESUMEN
BACKGROUND: Dysferlinopathies are a clinically heterogeneous group of muscular dystrophies caused by gene mutations resulting in deficiency of the membrane-associated protein dysferlin. They manifest post-growth and are characterised by muscle wasting (primarily in the limb and limb-gridle muscles), inflammation, and replacement of myofibres with adipose tissue. The precise pathomechanism for dysferlinopathy is currently unclear; as such there are no treatments currently available. Glucocorticoids (GCs) are widely used to reduce inflammation and treat muscular dystrophies, but when administered to patients with dysferlinopathy, they have unexpected adverse effects, with accelerated loss of muscle strength. METHODS: To investigate the mechanistic basis for the adverse effects of GCs in dysferlinopathy, the potent GC dexamethasone (Dex) was administered for 4-5 weeks (0.5-0.75 µg/mL in drinking water) to dysferlin-deficient BLA/J and normal wild-type (WT) male mice, sampled at 5 (Study 1) or 10 months (Study 2) of age. A wide range of analyses were conducted. Metabolism- and immune-related gene expression was assessed in psoas muscles at both ages and in quadriceps at 10 months of age. For the 10-month-old mice, quadriceps and psoas muscle histology was assessed. Additionally, we investigated the impact of Dex on the predominantly slow and fast-twitch soleus and extensor digitorum longus (EDL) muscles (respectively) in terms of contractile function, myofibre-type composition, and levels of proteins related to contractile function and metabolism, plus glycogen. RESULTS: At both ages, many complement-related genes were highly expressed in BLA/J muscles, and WT mice were generally more responsive to Dex than BLA/J. The effects of Dex on BLA/J mice included (i) increased expression of inflammasome-related genes in muscles (at 5 months) and (ii) exacerbated histopathology of quadriceps and psoas muscles at 10 months. A novel observation was pronounced staining for glycogen in many myofibres of the damaged quadriceps muscles, with large pale vacuolated myofibres, suggesting possible myofibre death by oncosis. CONCLUSION: These pilot studies provide a new focus for further investigation into the adverse effects of GCs on dysferlinopathic muscles.
Asunto(s)
Dexametasona , Disferlina , Glucocorticoides , Músculo Esquelético , Distrofia Muscular de Cinturas , Animales , Disferlina/genética , Disferlina/metabolismo , Dexametasona/efectos adversos , Dexametasona/farmacología , Masculino , Distrofia Muscular de Cinturas/genética , Distrofia Muscular de Cinturas/metabolismo , Distrofia Muscular de Cinturas/patología , Glucocorticoides/efectos adversos , Proyectos Piloto , Ratones , Músculo Esquelético/metabolismo , Músculo Esquelético/patología , Músculo Esquelético/efectos de los fármacos , Proteínas de la Membrana/genética , Proteínas de la Membrana/metabolismo , Modelos Animales de Enfermedad , Fuerza Muscular/efectos de los fármacosRESUMEN
Preterm birth is associated with inflammation of the fetal membranes (chorioamnionitis). We aimed to establish how chorioamnionitis affects the contractile function and phenotype of the preterm diaphragm. Pregnant ewes received intra-amniotic injections of saline or 10 mg LPS, 2 days or 7 days before delivery at 121 days of gestation (term = 150 d). Diaphragm strips were dissected for the assessment of contractile function after terminal anesthesia. The inflammatory cytokine response, myosin heavy chain (MHC) fibers, proteolytic pathways, and intracellular molecular signaling were analyzed using quantitative PCR, ELISA, immunofluorescence staining, biochemical assays, and Western blotting. Diaphragm peak twitch force and maximal tetanic force were approximately 30% lower than control values in the 2-day and 7-day LPS groups. Activation of the NF-κB pathway, an inflammatory response, and increased proteasome activity were observed in the 2-day LPS group relative to the control or 7-day LPS group. No inflammatory response was evident after a 7-day LPS exposure. Seven-day LPS exposure markedly decreased p70S6K phosphorylation, but no effect on other signaling pathways was evident. The proportion of MHC IIa fibers was lower than that for control samples in the 7-day LPS group. MHC I fiber proportions did not differ between groups. These results demonstrate that intrauterine LPS impairs preterm diaphragmatic contractility after 2-day and 7-day exposures. Diaphragm dysfunction, resulting from 2-day LPS exposure, was associated with a transient activation of proinflammatory signaling, with subsequent increased atrophic gene expression and enhanced proteasome activity. Persistently impaired contractility for the 7-day LPS exposure was associated with the down-regulation of a key component of the protein synthetic signaling pathway and a reduction in the proportions of MHC IIa fibers.
Asunto(s)
Corioamnionitis/fisiopatología , Diafragma/fisiopatología , Lipopolisacáridos , Contracción Miocárdica , Animales , Corioamnionitis/sangre , Corioamnionitis/inducido químicamente , Corioamnionitis/inmunología , Citocinas/metabolismo , Diafragma/inmunología , Diafragma/metabolismo , Modelos Animales de Enfermedad , Femenino , Edad Gestacional , Mediadores de Inflamación/sangre , Fibras Musculares Esqueléticas/inmunología , Fibras Musculares Esqueléticas/metabolismo , Fuerza Muscular , Atrofia Muscular/sangre , Atrofia Muscular/inmunología , Atrofia Muscular/fisiopatología , Cadenas Pesadas de Miosina/sangre , FN-kappa B/metabolismo , Embarazo , Complejo de la Endopetidasa Proteasomal/metabolismo , Ovinos , Transducción de Señal , Factores de TiempoRESUMEN
Many neuromuscular disorders can have a differential impact on a specific myofibre type, forming the central premise of this review. The many different skeletal muscles in mammals contain a spectrum of slow- to fast-twitch myofibres with varying levels of protein isoforms that determine their distinctive contractile, metabolic, and other properties. The variations in functional properties across the range of classic 'slow' to 'fast' myofibres are outlined, combined with exemplars of the predominantly slow-twitch soleus and fast-twitch extensor digitorum longus muscles, species comparisons, and techniques used to study these properties. Other intrinsic and extrinsic differences are discussed in the context of slow and fast myofibres. These include inherent susceptibility to damage, myonecrosis, and regeneration, plus extrinsic nerves, extracellular matrix, and vasculature, examined in the context of growth, ageing, metabolic syndrome, and sexual dimorphism. These many differences emphasise the importance of carefully considering the influence of myofibre-type composition on manifestation of various neuromuscular disorders across the lifespan for both sexes. Equally, understanding the different responses of slow and fast myofibres due to intrinsic and extrinsic factors can provide deep insight into the precise molecular mechanisms that initiate and exacerbate various neuromuscular disorders. This focus on the influence of different myofibre types is of fundamental importance to enhance translation for clinical management and therapies for many skeletal muscle disorders.
Asunto(s)
Fibras Musculares de Contracción Rápida , Fibras Musculares de Contracción Lenta , Masculino , Animales , Femenino , Músculo Esquelético/fisiología , Contracción Muscular/fisiología , Envejecimiento , MamíferosRESUMEN
[This corrects the article DOI: 10.1371/journal.pone.0214908.].
RESUMEN
INTRODUCTION: The skeletal muscle weakness associated with many chronic diseases has been attributed to the catabolic effect of pro-inflammatory cytokines. We aimed to determine if local muscle inflammation has direct affects on contractile function and contributes to muscle weakness independent of muscle atrophy or mechanical injury. METHODS: Local muscle inflammation was induced by injecting an algal-derived polysaccharide, carrageenan (10 mg/kg), into the right tibialis anterior muscle in healthy ARC mice. The contralateral muscle was injected with sterile isotonic saline, and the muscles were removed after 24 h for measurement of contractile function and cytokine concentration. RESULTS: Carrageenan significantly reduced maximum specific force, decreased the maximum rate of force development, altered the force-frequency relationship, and increased intramuscular levels of pro-inflammatory cytokines and chemokines. CONCLUSIONS: These results indicate that carrageenan directly affects contractile function and causes skeletal muscle weakness. Local muscle inflammation may contribute to the weakness observed in inflammatory related disorders.
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Carragenina , Inflamación/inducido químicamente , Debilidad Muscular/inducido químicamente , Músculo Esquelético/efectos de los fármacos , Animales , Citocinas/metabolismo , Inflamación/metabolismo , Inflamación/fisiopatología , Ratones , Contracción Muscular/efectos de los fármacos , Contracción Muscular/fisiología , Debilidad Muscular/metabolismo , Debilidad Muscular/fisiopatología , Músculo Esquelético/metabolismo , Músculo Esquelético/fisiopatologíaRESUMEN
The region over which skeletal muscles operate on their force-length (F-L) relationship is fundamental to the mechanics, control and economy of movement. Yet surprisingly little experimental data exist on normalized length operating ranges of muscle during human gait, or how they are modulated when mechanical demands (such as force output) change. Here we explored the soleus muscle (SOL) operating lengths experimentally in a group of healthy young adults by combining subject-specific F-L relationships with in vivo muscle imaging during gait. We tested whether modulation of operating lengths occurred between walking and running, two gaits that require different levels of force production and different muscle-tendon mechanics, and examined the relationship between optimal fascicle lengths (L(0)) and normalized operating lengths during these gaits. We found that the mean active muscle lengths reside predominantly on the ascending limbs of the F-L relationship in both gaits (walk, 0.70-0.94 L(0); run, 0.65-0.99 L(0)). Furthermore, the mean normalized muscle length at the time of the peak activation of the muscle was the same between the two gaits (0.88 L(0)). The active operating lengths were conserved, despite a fundamentally different fascicle strain pattern between walking (stretch-shorten cycle) and running (near continuous shortening). Taken together, these findings indicate that the SOL operating length is highly conserved, despite gait-dependent differences in muscle-tendon dynamics, and appear to be preferentially selected for stable force production compared with optimal force output (although length-dependent force capacity is high when maximal forces are expected to occur). Individuals with shorter L(0) undergo smaller absolute muscle excursions (P<0.05) so that the normalized length changes during walking and running remain independent of L(0). The correlation between L(0) and absolute length change was not explained on the basis of muscle moment arms or joint excursion, suggesting that regulation of muscle strain may occur via tendon stretch.
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Músculo Esquelético/fisiología , Carrera/fisiología , Estrés Mecánico , Tendones/fisiología , Caminata/fisiología , Adulto , Fenómenos Biomecánicos , Marcha/fisiología , Humanos , Masculino , Contracción Muscular , Torque , Torsión MecánicaRESUMEN
When an active muscle is stretched, the force increases due to strain of contractile and noncontractile proteins. We examined this force enhancement in rat extensor digitorum longus (EDL) and soleus muscles, which differ in their composition of these proteins, and their susceptibility to damage. Small stretches were applied at different velocities during isometric contractions from which we quantified the velocity-dependent contractile and velocity-independent noncontractile contributions to force enhancement. Whereas the contractile contribution was significantly greater in soleus than EDL, the noncontractile force enhancement was significantly greater in EDL than soleus, and increased ≈6-fold after damaging eccentric contractions. The increased contractile stiffness may be functionally beneficial in slow muscle, as resistance to lengthening is fundamental to maintaining posture. Following stretch-induced muscle damage this capacity is compromised, leading to increased strain of noncontractile proteins that may facilitate the activation of signaling pathways involved in muscle adaptation to injury.
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Fibras Musculares Esqueléticas/fisiología , Músculo Esquelético/fisiología , Algoritmos , Animales , Técnicas In Vitro , Contracción Isométrica/fisiología , Contracción Muscular/fisiología , Fibras Musculares de Contracción Rápida/fisiología , Fibras Musculares de Contracción Lenta/fisiología , Músculo Esquelético/citología , Ratas , Ratas Wistar , Estrés MecánicoRESUMEN
BACKGROUND: In utero diaphragm development is critically important for postnatal respiratory function and any disturbance to fetal development may lead to diaphragm dysfunction and respiratory complications in the postnatal period. Intrauterine growth restriction (IUGR) has been shown to affect respiratory function in a sex-dependent manner; however, the effect of IUGR on diaphragm function is unknown. AIM: This study used a maternal hypoxia-induced mouse model of IUGR to investigate the impact of IUGR on diaphragm function and structure in male and female adult offspring. MATERIALS AND METHODS: Pregnant BALB/c mice were housed under hypoxic conditions (10.5% O2 ) from gestational days 11 to 17.5 and then returned to normoxic conditions. Control mice were housed under normoxic conditions throughout pregnancy. At 8 weeks of age, offspring were euthanized and diaphragms isolated for functional assessment in organ bath experiments and for histological analysis. RESULTS: IUGR offspring were lighter at birth and remained lighter at 8 weeks of age compared to Controls. While diaphragm force (maximal or twitch) was not affected by treatment or sex, the IUGR group exhibited a longer half-relaxation time after twitch contractions compared to Control. Female offspring had a lower maximum rate of force development and higher fatigue resistance compared to males, independent of IUGR. There was no difference in the diaphragm myofibre cross-sectional area between groups or sexes. CONCLUSION: Sex and IUGR independently affect diaphragm contraction in adult mice without changes in structure. This study demonstrates that IUGR affects diaphragm contractile function in later life and could impair respiratory function if exacerbated under conditions of increased respiratory load.
Asunto(s)
Diafragma/fisiopatología , Retardo del Crecimiento Fetal/fisiopatología , Animales , Modelos Animales de Enfermedad , Femenino , Retardo del Crecimiento Fetal/etiología , Hipoxia/complicaciones , Hipoxia/fisiopatología , Masculino , Ratones , Ratones Endogámicos BALB C , EmbarazoRESUMEN
Duchenne muscular dystrophy (DMD) is a genetic disorder in which muscle weakness and fragility contribute to ongoing muscle degeneration. Although exercise-induced muscle damage is associated with adaptation that protects normal muscle from further damage, exploiting this process to protect dystrophic muscle has been avoided for fear of inducing excessive muscle degeneration. However, muscle-specific over-expression of the class 1:Ea isoform of insulin-like growth factor-1 (IGF-1) reduces myofibre necrosis in dystrophic mdx mice (a model for DMD) and, therefore, may enhance the adaptation process in response to eccentric exercise. To test this hypothesis, we evaluated the effect of transgenic class 1:Ea IGF-1 over-expression on the susceptibility to muscle damage and subsequent adaptation in 12-week-old dystrophic mdx and non-dystrophic control mice. Experiments were conducted in vivo using a custom-built isokinetic mouse dynamometer to measure the deficit in joint torque (indicating muscle damage) after 20 maximal lengthening (eccentric) contractions. Adaptation to this damaging exercise was evaluated by repeating the protocol 7 days after the initial exercise. The over-expression of IGF-1 significantly increased the normalised joint torque in non-dystrophic mice and appeared to ameliorate the muscle weakness in dystrophic mice. All mice displayed a marked reduction in the susceptibility to muscle damage on day 7; however, this adaptation was unaffected by IGF-1, showing that IGF-1 does not protect the dystrophic muscles of adult mdx mice against damage resulting from maximal lengthening contractions.
Asunto(s)
Factor I del Crecimiento Similar a la Insulina/fisiología , Distrofia Muscular Animal/terapia , Distrofia Muscular de Duchenne/terapia , Transgenes , Animales , Modelos Animales de Enfermedad , Expresión Génica , Terapia Genética , Factor I del Crecimiento Similar a la Insulina/genética , Factor I del Crecimiento Similar a la Insulina/uso terapéutico , Masculino , Ratones , Ratones Endogámicos mdx , Ratones Transgénicos , Contracción Muscular , Fatiga Muscular , Músculo Esquelético/patología , Músculo Esquelético/fisiopatología , Esfuerzo Físico/fisiologíaRESUMEN
Dysferlinopathies are a form of muscular dystrophy caused by gene mutations resulting in deficiency of the protein dysferlin. Symptoms manifest later in life in a muscle specific manner, although the pathomechanism is not well understood. This study compared the impact of dysferlin-deficiency on in vivo and ex vivo muscle function, and myofibre type composition in slow (soleus) and fast type (extensor digitorum longus; EDL) muscles using male dysferlin-deficient (dysf-/-) BLAJ mice aged 10 months, compared with wild type (WT) C57Bl/6J mice. There was a striking increase in muscle mass of BLAJ soleus (+25%) (p<0.001), with no strain differences in EDL mass, compared with WT. In vivo measures of forelimb grip strength and wheel running capacity showed no strain differences. Ex vivo measures showed the BLAJ soleus had faster twitch contraction (-21%) and relaxation (-20%) times, and delayed post fatigue recovery (ps<0.05); whereas the BLAJ EDL had a slower relaxation time (+11%) and higher maximum rate of force production (+25%) (ps<0.05). Similar proportions of MHC isoforms were evident in the soleus muscles of both strains (ps>0.05); however, for the BLAJ EDL, there was an increased proportion of type IIx MHC isoform (+5.5%) and decreased type IIb isoform (-5.5%) (ps<0.01). This identification of novel differences in the impact of dysferlin-deficiency on slow and fast twitch muscles emphasises the importance of evaluating myofibre type specific effects to provide crucial insight into the mechanisms responsible for loss of function in dysferlinopathies; this is critical for the development of targeted future clinical therapies.
Asunto(s)
Disferlina/deficiencia , Animales , Disferlina/genética , Disferlina/fisiología , Humanos , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Actividad Motora/genética , Actividad Motora/fisiología , Contracción Muscular/genética , Contracción Muscular/fisiología , Fibras Musculares de Contracción Rápida/fisiología , Fibras Musculares de Contracción Lenta/fisiología , Fuerza Muscular/genética , Fuerza Muscular/fisiología , Músculo Esquelético/patología , Músculo Esquelético/fisiopatología , Distrofia Muscular de Cinturas/genética , Distrofia Muscular de Cinturas/fisiopatología , Distrofia Muscular Animal/genética , Distrofia Muscular Animal/patología , Distrofia Muscular Animal/fisiopatología , MutaciónRESUMEN
Stretch of an activated muscle causes a transient increase in force during the stretch and a sustained, residual force enhancement (RFE) after the stretch. The purpose of this study was to determine whether RFE is present in human muscles under physiologically relevant conditions (i.e., when stretches were applied within the working range of large postural leg muscles and under submaximal voluntary activation). Submaximal voluntary plantar flexion (PF(v)) and dorsiflexion (DF(v)) activation was maintained by providing direct visual feedback of the EMG from soleus or tibialis anterior, respectively. RFE was also examined during electrical stimulation of the plantar flexion muscles (PF(s)). Constant-velocity stretches (15 degrees /s) were applied through a range of motion of 15 degrees using a custom-built ankle torque motor. The muscles remained active throughout the stretch and for at least 10 s after the stretch. In all three activation conditions, the stable joint torque measured 9-10 s after the stretch was greater than the isometric joint torque at the final joint angle. When expressed as a percentage of the isometric torque, RFE values were 7, 13, and 12% for PF(v), PF(s), DF(v), respectively. These findings indicate that RFE is a characteristic of human skeletal muscle and can be observed during submaximal (25%) voluntary activation when stretches are applied on the ascending limb of the force-length curve. Although the underlying mechanisms are unclear, it appears that sarcomere popping and passive force enhancement are insufficient to explain the presence of RFE in these experiments.