RESUMEN
Skeletal muscles of old mice demonstrate a profound inability to regenerate fully following damage. Such a failure could be catastrophic to older individuals where muscle loss is already evident. Degeneration and regeneration of muscle fibres following contraction-induced injury in adult and old mice are well characterised, but little is known about the accompanying changes in motor neurons and neuromuscular junctions (NMJs) following this form of injury although defective re-innervation of muscle following contraction-induced damage has been proposed to play a role in sarcopenia. This study visualised and quantified structural changes to motor neurons and NMJs in Extensor digitorum longus (EDL) muscles of adult and old Thy1-YFP transgenic mice during regeneration following contraction-induced muscle damage. Data demonstrated that the damaging contraction protocol resulted in substantial initial disruption to NMJs in muscles of adult mice, which was reversed entirely within 28 days following damage. In contrast, in quiescent muscles of old mice, â¼15 % of muscle fibres were denervated and â¼80 % of NMJs showed disruption. This proportion of denervated and partially denervated fibres remained unchanged following recovery from contraction-induced damage in muscles of old mice although â¼25 % of muscle fibres were completely lost by 28 days post-contractions. Thus, in old mice, the failure to restore full muscle force generation that occurs following damage does not appear to be due to any further deficit in the percentage of disrupted NMJs, but appears to be due, at least in part, to the complete loss of muscle fibres following damage.
Asunto(s)
Neuronas Motoras/ultraestructura , Contracción Muscular , Músculo Esquelético/inervación , Unión Neuromuscular/ultraestructura , Sarcopenia/patología , Animales , Masculino , Ratones , Ratones Transgénicos , Fibras Musculares Esqueléticas/ultraestructura , Proteínas Musculares/genética , Proteínas Musculares/metabolismo , Músculo Esquelético/patología , Imagen Óptica , ARN Mensajero/genética , ARN Mensajero/metabolismo , Proteínas Ligasas SKP Cullina F-box/genética , Proteínas Ligasas SKP Cullina F-box/metabolismo , Proteínas de Motivos Tripartitos/genética , Proteínas de Motivos Tripartitos/metabolismo , Ubiquitina-Proteína Ligasas/genética , Ubiquitina-Proteína Ligasas/metabolismoRESUMEN
With aging, there is a decline in cardiac function accompanying increasing risk of arrhythmias. These effects are likely to be mechanistically associated with age-associated changes in calcium regulation within cardiac myocytes. Previous studies suggest that lifelong exercise can potentially reduce age-associated changes in the heart. Although exercise itself is associated with changes in cardiac function, little is known about the interactions of aging and exercise with respect to myocyte calcium regulation. To investigate this, adult (12 months) and old (24 months) C57/Bl6 mice were trained using moderate-intensity treadmill running. In response to 10 weeks' training, comparable cardiac hypertrophic responses were observed, although aging independently associated with additional cardiac hypertrophy. Old animals also showed increased L- and T-type calcium channels, the sodium-calcium exchange, sarcoendoplasmic reticulum calcium ATPase, and collagen (by 50%, 92%, 66%, 88%, and 113% respectively). Short-term exercise training increased D-type and T-type calcium channels in old animals only, whereas an increase in sodium-calcium exchange was seen only in adult animals. Long-term (12 months) training generally opposed the effects of aging. Significant hypertrophy remained in long-term trained old animals, but levels of sarcoendoplasmic reticulum calcium ATPase, sodium-calcium exchange, and collagen were not significantly different from those found in the adult trained animals.
Asunto(s)
Envejecimiento , Cardiomegalia/patología , Prueba de Esfuerzo , Ventrículos Cardíacos/patología , Miocitos Cardíacos/patología , Animales , Canales de Calcio Tipo L/metabolismo , Canales de Calcio Tipo T/metabolismo , Señalización del Calcio/genética , Cardiomegalia/metabolismo , Cardiomegalia/fisiopatología , Modelos Animales de Enfermedad , Ventrículos Cardíacos/metabolismo , Ventrículos Cardíacos/fisiopatología , Masculino , Ratones , Ratones Endogámicos C57BL , Contracción Miocárdica , Miocitos Cardíacos/metabolismo , Intercambiador de Sodio-Calcio/metabolismoRESUMEN
We have previously shown that deletion of CuZnSOD in mice (Sod1(-/-) mice) leads to accelerated loss of muscle mass and contractile force during aging. To dissect the relative roles of skeletal muscle and motor neurons in this process, we used a Cre-Lox targeted approach to establish a skeletal muscle-specific Sod1-knockout (mKO) mouse to determine whether muscle-specific CuZnSOD deletion is sufficient to cause muscle atrophy. Surprisingly, mKO mice maintain muscle masses at or above those of wild-type control mice up to 18 mo of age. In contrast, maximum isometric specific force measured in gastrocnemius muscle is significantly reduced in the mKO mice. We found no detectable increases in global measures of oxidative stress or ROS production, no reduction in mitochondrial ATP production, and no induction of adaptive stress responses in muscle from mKO mice. However, Akt-mTOR signaling is elevated and the number of muscle fibers with centrally located nuclei is increased in skeletal muscle from mKO mice, which suggests elevated regenerative pathways. Our data demonstrate that lack of CuZnSOD restricted to skeletal muscle does not lead to muscle atrophy but does cause muscle weakness in adult mice and suggest loss of CuZnSOD may potentiate muscle regenerative pathways.
Asunto(s)
Contracción Muscular/fisiología , Músculo Esquelético/metabolismo , Músculo Esquelético/fisiopatología , Atrofia Muscular/enzimología , Superóxido Dismutasa/metabolismo , Animales , Western Blotting , Peroxidación de Lípido/genética , Peroxidación de Lípido/fisiología , Ratones , Ratones Noqueados , Microscopía Electrónica de Transmisión , Microscopía Fluorescente , Contracción Muscular/genética , Músculo Esquelético/ultraestructura , Atrofia Muscular/genética , Estrés Oxidativo , Superóxido Dismutasa/genética , Superóxido Dismutasa-1 , Tirosina/análogos & derivados , Tirosina/metabolismoRESUMEN
AIMS: The sources of cytosolic superoxide in skeletal muscle have not been defined. This study examined the subcellular sites that contribute to cytosolic superoxide in mature single muscle fibers at rest and during contractile activity. RESULTS: Isolated fibers from mouse flexor digitorum brevis loaded with superoxide and nitric-oxide-sensitive fluorescent probes, specific pathway inhibitors and immunolocalization techniques were used to identify subcellular sites contributing to cytosolic superoxide. Treatment with the electron transport chain complex III inhibitor, antimycin A, but not the complex I inhibitor, rotenone, caused increased cytosolic superoxide through release from the mitochondrial intermembrane space via voltage-dependent anion or Bax channels, but inhibition of these channels did not affect contraction-induced increases in cytosolic superoxide. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitors decreased cytosolic superoxide at rest and following contractions. Protein and mRNA expression of NADPH oxidase subunits was demonstrated in single fibers. NOX2, NOX4, and p22(phox) subunits localized to the sarcolemma and transverse tubules; NOX4 was additionally expressed in mitochondria. Regulatory p40(phox) and p67(phox) proteins were found in the cytoplasm of resting fibers, but following contractions, p40(phox) appeared to translocate to the sarcolemma. INNOVATION: Superoxide and other reactive oxygen species generated by skeletal muscle are important regulators of muscle force production and adaptations to contractions. This study has defined the relative contribution of mitochondrial and cytosolic sources of superoxide within the cytosol of single muscle fibers at rest and during contractions. CONCLUSION: Muscle mitochondria do not modulate cytosolic superoxide in skeletal muscle but NADPH oxidase is a major contributor both at rest and during contractions.
Asunto(s)
Mitocondrias , Contracción Muscular , Fibras Musculares Esqueléticas , NADPH Oxidasas/metabolismo , Animales , Grupo Citocromo b/metabolismo , Citosol , Humanos , Glicoproteínas de Membrana/metabolismo , Ratones , Mitocondrias/metabolismo , Mitocondrias/fisiología , Contracción Muscular/genética , Contracción Muscular/fisiología , Fibras Musculares Esqueléticas/metabolismo , Fibras Musculares Esqueléticas/fisiología , Músculo Esquelético/metabolismo , Músculo Esquelético/fisiología , NADP/metabolismo , NADPH Oxidasa 2 , NADPH Oxidasa 4 , Fosfoproteínas , Especies Reactivas de Oxígeno , Superóxidos/metabolismoRESUMEN
An international workshop was hosted by the University of Liverpool on 15-16 July 2011 to address at a basic level what is known about the fundamental mechanisms by which skeletal muscle mass and function are lost during aging and to examine the nature of interventions that might prevent these mechanistic changes. Of particular importance was to attempt to evaluate how different forms of exercise (or muscle contractile activity) influence these processes and how these effects can be best optimized to prevent or delay age-related loss of muscle function. The program took the form of a two-day meeting, comprising a series of invited talks and breakout sessions designed to identify key gaps in current knowledge and potential future research questions. The aims of this Workshop were two-fold: 1. To identify the current state-of-the-art in the understanding of the mechanisms that contribute to loss of skeletal muscle mass and function that occurs with aging and to address at a mechanistic level how, and to what extent, exercise and/or other interventions might prevent these changes. 2. To identify specific areas of research where information is sparse but which are likely to yield data that will impact on future strategies to manipulate age-related loss of muscle mass and function in older people. The areas discussed in detail were loss of functional motor units, reduced muscle stem cell activity, age-related changes in transcriptional responses of muscle to exercise and nutrition, age-related changes in protein homeostasis, mitochondrial function, altered cross-talk between muscle with immune cells and how the developments in basic science to understand mechanisms underlying age-related loss of muscle mass and function can be translated. Following each session three key areas where further studies are needed were identified.
RESUMEN
Skeletal muscle atrophy and weakness are major contributors to frailty and impact significantly on quality of life of older people. Muscle aging is characterized by a loss of maximum tetanic force (P(o)) generation, primarily due to muscle atrophy, to which mitochondrial dysfunction is hypothesized to contribute. We hypothesized that lifelong overexpression of the mitochondrial heat shock protein (HSP) HSP10 in muscle of mice would protect against development of these deficits. P(o) generation by extensor digitorum longus muscles of adult and old wild-type and HSP10-overexpressing mice was determined in situ. Muscles were subjected to damaging lengthening contractions, and force generation was remeasured at 3 h or 28 days to examine susceptibility to, and recovery from, damage, respectively. Muscles of old wild-type mice had a 23% deficit in P(o) generation and a 10% deficit in muscle cross-sectional area compared with muscles of adult wild-type mice. Overexpression of HSP10 prevented this age-related fall in P(o) generation and reduction in cross-sectional area observed in muscles of old wild-type mice. Additionally, overexpression of HSP10 protected against contraction-induced damage independent of age but did not improve recovery if damage occurred. Preservation of muscle force generation and CSA by HSP10 overexpression was associated with protection against the age-related accumulation of protein carbonyls. Data demonstrate that development of age-related muscle weakness may not be inevitable and show, for the first time, that lifelong overexpression of an HSP prevents the age-related loss of P(o) generation. These findings support the hypothesis that mitochondrial dysfunction is involved in the development of age-related muscle deficits.
Asunto(s)
Envejecimiento/fisiología , Proteínas de Choque Térmico/metabolismo , Músculo Esquelético , Atrofia Muscular/fisiopatología , Envejecimiento/metabolismo , Animales , Mecánica , Ratones , Ratones Transgénicos , Contracción Muscular/fisiología , Debilidad Muscular/metabolismo , Debilidad Muscular/patología , Debilidad Muscular/fisiopatología , Músculo Esquelético/metabolismo , Músculo Esquelético/patología , Músculo Esquelético/fisiología , Atrofia Muscular/metabolismo , Atrofia Muscular/patología , Tetania/metabolismo , Tetania/patología , Tetania/fisiopatologíaRESUMEN
Skeletal muscle adapts to the stress of contractile activity via changes in gene expression to yield an increased content of a family of highly conserved cytoprotective proteins known as heat shock proteins (HSPs). These proteins function to maintain homeostasis, facilitate repair from injury and provide protection against future insults. The study of the exercise-induced production of HSPs in skeletal muscle is important for the exercise scientist as it may provide a valuable insight into the molecular mechanisms by which regular exercise can provide increased protection against related and non-related stressors. As molecular chaperones, HSPs are also fundamental in facilitating the cellular remodelling processes inherent to the training response. Whilst the exercise-induced stress response of rodent skeletal muscle is relatively well characterized, data from humans are more infrequent and less insightful. Data indicate that acute endurance- and resistance-type exercise protocols increase the muscle content of ubiquitin, alphaB-crystallin, HSP27, HSP60, HSC70 and HSP70. Although increased HSP transcription occurs during exercise, immediately post-exercise or several hours following exercise, time-course studies using western blotting techniques have typically demonstrated a significant increase in protein content is only detectable within 1-2 days following the exercise stress. However, comparison amongst studies is complicated by variations in exercise protocol (mode, intensity, duration, damaging, non-damaging), muscle group examined, predominant HSP measured and, perhaps most importantly, differences in subject characteristics both within and between studies (training status, recent activity levels, nutritional status, age, sex, etc.). Following 'non-damaging' endurance-type activities (exercise that induces no overt structural and functional damage to the muscle), the stress response is thought to be mediated by redox signalling (transient and reversible oxidation of muscle proteins) as opposed to increases in contracting muscle temperature per se. Following 'damaging' forms of exercise (exercise that induces overt structural and functional damage to the muscle), the stress response is likely initiated by mechanical damage to protein structure and further augmented by the secondary damage associated with inflammatory processes occurring several days following the initial insult. Exercise training induces an increase in baseline HSP levels, which is dependent on a sustained and currently unknown dose of training and also on the individual's initial training status. Furthermore, trained subjects display an attenuated or abolished stress response to customary exercise challenges, likely due to adaptations of baseline HSP levels and the antioxidant system. Whilst further fundamental work is needed to accurately characterize the exercise-induced stress response in specific populations following varying exercise protocols, exercise scientists should also focus their efforts on elucidating the precise biological significance of the exercise-induced induction of HSPs. In addition to their potential cytoprotective properties, the role of HSPs in modulating cell signalling pathways related to both exercise adaptation and health and disease also needs further investigation. As a non-pharmacological intervention, exercise and the associated up-regulation of HSPs and the possible correction of maladapted pathways may therefore prove effective in providing protection against protein misfolding diseases and in preserving muscle function during aging.
Asunto(s)
Adaptación Fisiológica , Ejercicio Físico/fisiología , Músculo Esquelético/fisiología , Estrés Fisiológico , Animales , Proteínas de Choque Térmico/fisiología , Humanos , Estrés Oxidativo , Medicina DeportivaRESUMEN
This study investigates the effects of short-term endurance training on heat shock protein (HSP) adaptations of male and female human skeletal muscle. The data demonstrate that females did not respond to continuous or interval training in terms of increasing HSP content of the vastus lateralis muscle. In contrast, males displayed HSP adaptations to both training interventions. These data provide a platform for future human studies to examine a potential gender-specific stress response to exercise.
Asunto(s)
Proteínas de Choque Térmico/metabolismo , Músculo Esquelético/metabolismo , Esfuerzo Físico/fisiología , Caracteres Sexuales , Estudios Transversales , Femenino , Respuesta al Choque Térmico/fisiología , Humanos , Masculino , Resistencia Física , Adulto JovenRESUMEN
Unlike muscles of young mice, skeletal muscles of old mice fail to recover completely following contraction-induced damage. The mechanisms by which this occurs are not fully understood. The ability of muscles of old mice to adapt following exercise by the increased production of heat shock proteins (HSPs) is blunted. Studies using transgenic mice have shown that this inability to produce HSPs has a major effect on muscle regeneration. Overexpression of HSP70 facilitated complete recovery of maximum tetanic force generation in muscles of old transgenic mice following contraction induced-damage in comparison with a deficit in muscles of old wild-type (WT) mice. We hypothesized that pharmacological induction of HSP70 in muscles of old WT mice would result in enhanced recovery from contraction-induced damage. A single dose of 40 mg/kg of 17-(allylamino)-17-demethoxygeldanamycin (17AAG) resulted in a significant increase in the HSP70 content of extensor digitorum longus muscles of adult C57BL6/J mice 3 days following treatment compared with vehicle-treated mice. Four weekly treatments of adult and old mice resulted in a two- to four-fold increase in muscle HSP70 content. Treatment of old mice with 17AAG at 3 days prior to and weekly for 4 weeks following a severely damaging contraction protocol resulted in enhanced recovery of force generation at 28 days postdamage compared with muscles of vehicle-treated mice. Data suggest that 17AAG overcomes the mechanism by which activation of the stress response fails in muscles of old mice and may have therapeutic benefit in the recovery following damage in muscles of older individuals.
Asunto(s)
Benzoquinonas/farmacología , Proteínas de Choque Térmico/metabolismo , Lactamas Macrocíclicas/farmacología , Contracción Muscular/fisiología , Músculo Esquelético/efectos de los fármacos , Animales , Células Cultivadas , Femenino , Proteínas HSP70 de Choque Térmico/antagonistas & inhibidores , Proteínas HSP70 de Choque Térmico/metabolismo , Proteínas HSP90 de Choque Térmico/antagonistas & inhibidores , Proteínas HSP90 de Choque Térmico/metabolismo , Proteínas de Choque Térmico/antagonistas & inhibidores , Ratones , Ratones Endogámicos C57BL , Músculo Esquelético/metabolismoRESUMEN
Mammalian adult skeletal muscle adapts to the stress of contractile activity with increased gene expression by yielding a family of highly conserved cytoprotective proteins known as heat shock proteins (HSPs). Although the exercise-induced stress response of both animal and human skeletal muscle is now well documented, the precise mechanisms underlying this adaptation remain unclear. The induction of HSPs after exercise is severely blunted in the muscle of older individuals. This review focuses on the effects of different forms of exercise and training on the induction of HSPs in the muscles of adult individuals, and examines the proposed mechanisms underlying this adaptation. Furthermore, the functional effect of the inability of the muscles of older individuals to adapt in this way is discussed, together with the proposed mechanisms underlying this maladaptation.
Asunto(s)
Envejecimiento/fisiología , Ejercicio Físico/fisiología , Proteínas HSP70 de Choque Térmico/fisiología , Debilidad Muscular/fisiopatología , Músculo Esquelético/fisiología , Estrés Fisiológico/fisiología , Envejecimiento/patología , Animales , Proteínas HSP70 de Choque Térmico/metabolismo , Humanos , Debilidad Muscular/metabolismo , Músculo Esquelético/metabolismoRESUMEN
PURPOSE: 1) To compare the baseline levels of heat shock and antioxidant protein content in the skeletal muscle of trained and untrained humans and 2) to characterize the exercise-induced stress response of aerobically trained human skeletal muscle to an acute exercise challenge. METHODS: Resting muscle biopsies were obtained from the vastus lateralis muscle of six untrained and six aerobically trained young males. To characterize the stress response of a trained population, the trained subjects also performed a 45-min nondamaging running exercise protocol at an intensity corresponding to 75% of V O2max. Muscle biopsies were obtained from the vastus lateralis muscle at 48 h and 7 d after exercise. RESULTS: Trained subjects displayed significantly higher (P<0.05) resting levels of heat shock protein 60 (HSP60, 25%), alphaB-crystallin (43%), and manganese superoxide (MnSOD, 45%) protein content compared with untrained subjects. Trained subjects also exhibited no significant change (P > 0.05) in resting levels of HSP70 (16%), HSC70 (13%), and total superoxide dismutase (SOD) activity (46%) compared with untrained subjects. Resting HSP27 levels were unaffected by exercise training (P > 0.05). In the trained subjects, exercise failed to induce significant increases (P>0.05)in muscle content of HSP70, HSC70, HSP60, HSP27, alphaB-crystallin, and MnSOD protein content or in the activity of SOD at any time point after exercise. CONCLUSION: This study demonstrates for the first time that trained men display a selective up-regulation of basal heat shock and antioxidant protein content and do not exhibit a stress response to customary running exercise. It is suggested that an increase in these protective systems functions to maintain homeostasis during the stress of exercise by protecting against disruptions to the cytoskeleton/contractile machinery, by maintaining redox balance, and by facilitating mitochondrial biogenesis.
Asunto(s)
Adaptación Fisiológica/fisiología , Antioxidantes/metabolismo , Proteínas de Choque Térmico/metabolismo , Músculo Esquelético/metabolismo , Carrera/fisiología , Adulto , Antioxidantes/análisis , Biopsia , Regulación de la Temperatura Corporal , Proteínas de Choque Térmico/análisis , Humanos , Masculino , Músculo Esquelético/química , Músculo Esquelético/fisiología , Estrés Fisiológico/fisiologíaRESUMEN
Skeletal muscle atrophy and weakness are major causes of frailty in the elderly. Functional deficits in muscles of old humans and rodents are associated with attenuated production of heat shock proteins (HSPs) after exercise, and transgenic overexpression of HSP70 reverses this functional decline. We hypothesized that training would increase HSP70 content of muscle in adult and old wild-type mice and that this would protect against the development of age-related functional deficits. A 10-wk treadmill training protocol at 15 m/min, for 15 min, 3 days/wk resulted in a significant increase in HSP70 content of muscles of adult mice. Muscles of old untrained mice demonstrated a significant increase in HSP70 protein content and a reduction in HSP70 mRNA content compared with adult untrained mice. Training for 12 mo starting at age 12-14 mo old or for 10 wk starting from age 24 mo old resulted in modification of HSP70 protein and mRNA content to levels of adult mice. Training did not change force generation of extensor digitorum longus muscles of old mice or improve recovery after damaging contractions. The twofold increase in HSP70 content in muscles of adult mice after training may have not been sufficient to provide protection in this instance.
Asunto(s)
Envejecimiento/fisiología , Proteínas HSP70 de Choque Térmico/genética , Proteínas HSP70 de Choque Térmico/metabolismo , Músculo Esquelético/fisiología , Condicionamiento Físico Animal/fisiología , Animales , Peso Corporal/fisiología , Ratones , Ratones Endogámicos C57BL , Contracción Muscular/fisiología , ARN Mensajero/metabolismo , Succinato Deshidrogenasa/metabolismoRESUMEN
Increased extracellular generation of reactive oxygen species (ROS) as a result of increasing reliance on glycolytic metabolism by old mitochondria-rich tissues has been claimed to contribute to the propagation of oxidative damage during aging (the reductive hotspot hypothesis), but the process has not been examined experimentally in old animals. Superoxide activity in the extracellular fluid of gastrocnemius muscle and markers of oxidation in blood and the liver were examined in adult and old mice at rest and following a period of demanding isometric contractions. The activity of superoxide in muscle microdialysates did not differ between adult and old mice at rest, but during contractile activity, there was a significant increase in the superoxide activity in microdialysates from adult muscle but no increase in microdialysates from old muscle. At rest, the liver of old mice contained an increased malonaldehyde content and a decreased protein thiol content in comparison with adult mice, but following the contraction protocol, only the adult mice showed significant, transient increases in the serum and liver malonaldehyde content and a decrease in liver glutathione and protein thiol content. Further studies revealed that the lack of superoxide release from contracting muscle of old mice was not due to reduced force generation by these muscles. These data provide no evidence for an increased extracellular superoxide in resting or contracting skeletal muscle of old mice, or that release of superoxide from muscle contributes to oxidation of blood components in the liver in old mice as is predicted from the reductive hotspot hypothesis.
Asunto(s)
Músculo Esquelético/metabolismo , Superóxidos/metabolismo , Animales , Glutatión/metabolismo , Hígado/metabolismo , Masculino , Malondialdehído/sangre , Malondialdehído/metabolismo , Ratones , Ratones Endogámicos C57BL , Contracción Muscular/fisiología , Músculo Esquelético/enzimología , Oxidación-Reducción , Especies Reactivas de Oxígeno/sangre , Especies Reactivas de Oxígeno/metabolismo , Superóxido Dismutasa , Factores de TiempoRESUMEN
Skeletal muscle aging is characterized by atrophy, a deficit in specific force generation, increased susceptibility to injury, and incomplete recovery after severe injury. The ability of muscles of old mice to produce heat shock proteins (HSPs) in response to stress is severely diminished. Studies in our laboratory using HSP70 overexpressor mice demonstrated that lifelong overexpression of HSP70 in skeletal muscle provided protection against damage and facilitated successful recovery after damage in muscles of old mice. The mechanisms by which HSP70 provides this protection are unclear. Aging is associated with the accumulation of oxidation products, and it has been proposed that this may play a major role in age-related muscle dysfunction. Muscles of old wild-type (WT) mice demonstrated increased lipid peroxidation, decreased glutathione content, increased catalase and superoxide dismutase (SOD) activities, and an inability to activate nuclear factor (NF)-kappaB after contractions in comparison with adult WT mice. In contrast, levels of lipid peroxidation, glutathione content, and the activities of catalase and SOD in muscles of old HSP70 overexpressor mice were similar to adult mice and these muscles also maintained the ability to activate NF-kappaB after contractions. These data provide an explanation for the preservation of muscle function in old HSP70 overexpressor mice.
Asunto(s)
Envejecimiento/fisiología , Proteínas HSP70 de Choque Térmico/genética , Contracción Muscular/fisiología , Músculo Esquelético/fisiología , Estrés Oxidativo/fisiología , Actinas/genética , Animales , Catalasa/metabolismo , Femenino , Glutatión/metabolismo , Masculino , Ratones , Ratones Transgénicos , Modelos Animales , Músculo Esquelético/crecimiento & desarrollo , FN-kappa B/metabolismo , Regiones Promotoras Genéticas , Ratas , Superóxido Dismutasa/metabolismoRESUMEN
The ability of muscles of old mice to recover force generation following substantial damage is severely impaired, particularly during the late phase of regeneration. This inability to recover successfully may be associated with the attenuated ability of muscles of old mice to produce heat shock proteins (HSPs) in response to stress since muscles of old mice overexpressing HSP70 recover successfully following damage. The capacity of mature mammalian skeletal muscle to regenerate following damage is due to the presence of undifferentiated mononuclear myogenic precursor cells (satellite cells) at the periphery of mature skeletal muscle fibres. HSP expression is under the primary transcriptional control of heat shock factors 1 and 2 (HSF1 and HSF2). The aim of this study was to examine the expression of heat shock factors 1 and 2 by western blotting in mouse-derived C2C12 myoblasts as an experimental model system for investigating skeletal muscle regeneration. Data demonstrated that the HSF2 content of myotubes was significantly increased during the early stages of regeneration. In contrast, the HSF1 content of myotubes remained relatively low until late during regeneration. Thus, abnormal activation of HSF1 may play a role in the defective regeneration seen in muscles of old mice.
Asunto(s)
Envejecimiento/metabolismo , Proteínas de Choque Térmico/metabolismo , Desarrollo de Músculos/fisiología , Músculo Esquelético/metabolismo , Regeneración/fisiología , Envejecimiento/fisiología , Animales , Diferenciación Celular , Células Cultivadas , Proteínas de Unión al ADN/metabolismo , Factores de Transcripción del Choque Térmico , Ratones , Fibras Musculares Esqueléticas/metabolismo , Músculo Esquelético/citología , Músculo Esquelético/fisiología , Mioblastos/citología , Mioblastos/metabolismo , Factores de Transcripción/metabolismoRESUMEN
The exercise-induced expression of heat shock proteins (HSPs) in rodent models is relatively well defined. In contrast, comparable data from human studies are limited and the exercise-induced stress response of human skeletal muscle is far from understood. This study has characterized the time course and magnitude of the HSP response in the skeletal muscles of a healthy active, but untrained, young male population following a running exercise protocol. Eight subjects performed 45 min of treadmill running at a speed corresponding to their lactate threshold (11.7 +/- 0.5 km/h; 69.8 +/- 4.8% maximum O2 uptake). Muscle biopsies were obtained from the vastus lateralis muscle immediately before and at 24 h, 48 h, 72 h, and 7 days postexercise. Exercise induced a significant (P < 0.05) but variable increase in HSP70, heat shock cognate (HSC) 70, and HSP60 expression with peak increases (typically occurring at 48 h postexercise) to 210, 170, and 139% of preexercise levels, respectively. In contrast, exercise did not induce a significant increase in either HSP27, alphaB-crystallin, SOD 2 (MnSOD) protein content, or the activity of SOD and catalase. When examining baseline protein levels, HSC70, HSP27, and alphaB-crystallin appeared consistently expressed between subjects, whereas HSP70 and MnSOD displayed marked individual variation of up to 3- and 1.5-fold, respectively. These data are the first to define the time course and extent of HSP production in human skeletal muscle following a moderately demanding and nondamaging running exercise protocol. Data demonstrate a differential effect of aerobic exercise on specific HSPs.
Asunto(s)
Ejercicio Físico/fisiología , Proteínas de Choque Térmico/metabolismo , Músculo Esquelético/metabolismo , Adulto , Biopsia , Catalasa/metabolismo , Chaperonina 60/metabolismo , Prueba de Esfuerzo , Regulación de la Expresión Génica , Proteínas del Choque Térmico HSC70/metabolismo , Proteínas de Choque Térmico HSP27 , Proteínas HSP70 de Choque Térmico/metabolismo , Humanos , Masculino , Chaperonas Moleculares , Músculo Esquelético/patología , Proteínas de Neoplasias/metabolismo , Superóxido Dismutasa/metabolismo , Superóxido Dismutasa-1 , Factores de Tiempo , Cadena B de alfa-Cristalina/metabolismoRESUMEN
Skeletal muscle comprises the largest organ system in the human body and is essential for force generation and movement. Skeletal muscle is subjected to considerable stresses during everyday use. However, muscle has the unique ability to adapt and remodel to provide protection against such stresses. This adaptation occurs at the structural through to the cellular level, which includes changes in transcription of a range of protective proteins. Failure in such processes can be catastrophic. This failure in adaptation is particularly notable in older individuals. Our skeletal muscles become smaller and weaker as we age. This loss of muscle bulk results in a reduced capacity to generate force and results in a loss of the ability to undertake everyday tasks. This article describes the normal adaptive responses of muscle in younger individuals to the stress of various forms of exercise and the implications of a failure of these adaptive responses in the elderly.