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Age‐associated loss of muscle mass and function (sarcopenia) has a profound effect on the quality of life in the elderly. Our previous studies show that CuZnSOD deletion in mice (Sod1−/− mice) recapitulates sarcopenia phenotypes, including elevated oxidative stress and accelerated muscle atrophy, weakness, and disruption of neuromuscular junctions (NMJs). To determine whether deletion of Sod1 initiated in neurons in adult mice is sufficient to induce muscle atrophy, we treated young (2‐ to 4‐month‐old) Sod1flox/SlickHCre mice with tamoxifen to generate i‐mn‐Sod1KO mice. CuZnSOD protein was 40‐50% lower in neuronal tissue in i‐mn‐Sod1KO mice. Motor neuron number in ventral spinal cord was reduced 28% at 10 months and more than 50% in 18‐ to 22‐month‐old i‐mn‐Sod1KO mice. By 24 months, 22% of NMJs in i‐mn‐Sod1KO mice displayed a complete lack of innervation and deficits in specific force that are partially reversed by direct muscle stimulation, supporting the loss of NMJ structure and function. Muscle mass was significantly reduced by 16 months of age and further decreased at 24 months of age. Overall, our findings show that neuronal‐specific deletion of CuZnSOD is sufficient to cause motor neuron loss in young mice, but that NMJ disruption, muscle atrophy, and weakness are not evident until past middle age. These results suggest that loss of innervation is critical but may not be sufficient until the muscle reaches a threshold beyond which it cannot compensate for neuronal loss or rescue additional fibers past the maximum size of the motor unit. [ABSTRACT FROM AUTHOR]

The retinal pigment epithelium (RPE) plays a central role in neuroretinal homoeostasis throughout life. Altered proteolysis and inflammatory processes involving RPE contribute to the pathophysiology of age‐related macular degeneration (AMD), but the link between these remains elusive. We report for the first time the effect of advanced glycation end products (AGE)—known to accumulate on the ageing RPE's underlying Bruch's membrane in situ—on both key lysosomal cathepsins and NF‐κB signalling in RPE. Cathepsin L activity and NF‐κB effector levels decreased significantly following 2‐week AGE exposure. Chemical cathepsin L inhibition also decreased total p65 protein levels, indicating that AGE‐related change of NF‐κB effectors in RPE cells may be modulated by cathepsin L. However, upon TNFα stimulation, AGE‐exposed cells had significantly higher ratio of phospho‐p65(Ser536)/total p65 compared to non‐AGEd controls, with an even higher fold increase than in the presence of cathepsin L inhibition alone. Increased proportion of active p65 indicates an AGE‐related activation of NF‐κB signalling in a higher proportion of cells and/or an enhanced response to TNFα. Thus, NF‐κB signalling modulation in the AGEd environment, partially regulated via cathepsin L, is employed by RPE cells as a protective (para‐inflammatory) mechanism but renders them more responsive to pro‐inflammatory stimuli. [ABSTRACT FROM AUTHOR]

Skeletal muscle ageing is characterised by atrophy, a deficit in specific force generation, increased susceptibility to injury, and incomplete recovery after severe damage. The hypothesis that increased generation of reactive oxygen species (ROS) in vivo plays a key role in the ageing process has been extensively studied, but remains controversial. Skeletal muscle generates ROS at rest and during exercise. ROS can cause oxidative damage particularly to proteins. Indeed, products of oxidative damage accumulate in skeletal muscle during ageing and the ability of muscle cells to respond to increased ROS becomes defective. The aim of this review is to examine the evidence that ROS manipulation in peripheral nerves and/or muscle modifies mechanisms of proteostasis in skeletal muscle and plays a key role in initiating sarcopenia. [ABSTRACT FROM AUTHOR]

An increasingly sophisticated array of approaches are now available for the study of the activities of reactive oxygen species and oxidative modifications in skeletal muscle, but the most up-to-date techniques are not readily available to many researchers in this field due to their requirement for sophisticated mass spectrometry, imaging or other high cost technologies. Most papers published therefore rely on a number of established approaches although the choice of approach is also clearly dependent upon the experimental model and access to skeletal muscle that is available to the investigator, how much detail is required and the overall question to be addressed. Numerous reports have described the problems associated with some of the popular approaches that are widely followed, including measurement of thiobarbituric acid substances and the sole use of fluorescence-based probes such as dichlorodihydrofluorescein. This brief review reports the areas in which methods are improving to allow valid assessments to made in this area and indicates some of the more recent developments that provide alternative ways to assess the activity of individual species and endpoints in the various experimental models that may be examined. [ABSTRACT FROM AUTHOR]

Although it is now clear that reactive oxygen species (ROS) are not the key determinants of longevity, a number of studies have highlighted the key role that these species play in age-related diseases and more generally in determining individual health span. Age-related loss of skeletal muscle mass and function is a key contributor to physical frailty in older individuals and our current understanding of the key areas in which ROS contribute to age-related deficits in muscle is through defective redox signalling and key roles in maintenance of neuromuscular integrity. This topical review will describe how ROS stimulate adaptations to contractile activity in muscle that include up-regulation of short-term stress responses, an increase in mitochondrial biogenesis and an increase in some catabolic processes. These adaptations occur through stimulation of redox-regulated processes that lead to the activation of transcription factors such as NF-κB, AP-1 and HSF1 which mediate changes in gene expression. They are attenuated during ageing and this appears to occur through an age-related increase in mitochondrial hydrogen peroxide production. The potential for redox-mediated cross-talk between motor neurons and muscle is also described to illustrate how ROS released from muscle fibres during exercise may help maintain the integrity of axons and how the degenerative changes in neuromuscular structure that occur with ageing may contribute to mitochondrial ROS generation in skeletal muscle fibres. [ABSTRACT FROM AUTHOR]

Deletion of copper-zinc superoxide dismutase (CuZnSOD) in Sodimice leads to accelerated loss of muscle mass and force during aging, but the losses do not occur with muscle-specific deletion of CuZnSOD. To determine the role of motor neurons in the muscle decline, we generated transgenic Sodl-/- mice in which CuZnSOD was expressed under control of the synapsin 1 promoter ( SynTgSodl-/- mice ) . SynTgSodl-/- mice expressed CuZnSOD in brain, spinal cord, and peripheral nerve, but not in other tissues. Sciatic nerve CuZnSOD content in SynTgSodl-/- mice was ~20% that of control mice, but no reduction in muscle mass or isometric force was observed in SynTg- Sodlmice compared with control animals, whereas muscles of age-matched Sodl-/- mice displayed 30- 40% reductions in mass and force. In addition, increased oxidative damage and adaptations in stress responses observed in muscles of Sodl-/- mice were absent in SynTgSodl-/- mice, and degeneration of neuromuscular junction (NMJ) structure and function occurred in Sodl-/- mice but not in SynTgSodl-/- mice. Our data demonstrate that specific CuZnSOD expression in neurons is sufficient to preserve NMJ and skeletal muscle structure and function in Sodl-/- mice and suggest that redox homeostasis in motor neurons plays a key role in initiating sarcopenia during aging.-- Sakellariou, G. K., Davis, C. S., Shi, Y., Ivannikov, M. V., Zhang, Y., Vasilaki, A., Macleod, G. T., Richardson, A., Van Remmen, H., Jackson, M. J., McArdle, A., Brooks, S. V. Neuron-specific expression of CuZnSOD prevents the loss of muscle mass and function that occurs in homozygous CuZnSOD-knockout mice. [ABSTRACT FROM AUTHOR]

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. Stu-prisingly, 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 demoustrate 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. [ABSTRACT FROM AUTHOR]

Summary 1. Investment in reproduction is anticipated to be costly and can decrease survival or future reproductive success. For males, substantial reproductive costs may be accrued when competing for mates, particularly when individuals need to invest heavily in the production of sexual signals to attract females. On a proximate level, increased male signalling effort can cause somatic damage because of oxidative stress, although this has been demonstrated only in species with visual sexual signals. 2. We tested whether reproductive effort (comprising reproduction, aggression and scent signalling) is associated with increased oxidative stress in male house mice ( Mus musculus domesticus). Sexual signalling in this species involves the production and deposition of scent signals containing a high concentration of protein around a defended territory. Male reproductive investment was manipulated by housing males alone, with a female or with a female and in the vicinity of competitors. 3. Males breeding in the vicinity of competitors invested the most in olfactory signalling as well as having regular aggressive interactions with other males. These males tended to show greater oxidative damage to lipids in the gastrocnemius muscle but no other indication of increased oxidative stress. Instead, lipid oxidation was lower in the serum and liver of reproductive males compared with those housed alone. 4. Our results highlight that oxidative stress does not always occur simply as a function of increasing reproductive effort. The lack of a consistent increase in oxidative damage could be due to adaptive regulation of antioxidants and/or a consequence of the scent signalling system of house mice, which differs considerably from the visual signalling of birds previously examined in this context. [ABSTRACT FROM AUTHOR]

Summary Mice lacking Cu,Zn superoxide dismutase (SOD1) show accelerated, age-related loss of muscle mass. Lack of SOD1 may lead to increased superoxide, reduced nitric oxide (NO), and increased peroxynitrite, each of which could initiate muscle fiber loss. Single muscle fibers from flexor digitorum brevis of wild-type (WT) and Sod1 −/− mice were loaded with NO-sensitive (4-amino-5-methylamino-2′,7′-difluorofluorescein diacetate, DAF-FM) and superoxide-sensitive (dihydroethidium, DHE) probes. Gastrocnemius muscles were analyzed for SOD enzymes, nitric oxide synthases (NOS), and 3-nitrotyrosine (3-NT) content. A lack of SOD1 did not increase superoxide availability at rest because no increase in ethidium or 2-hydroxyethidium (2-HE) formation from DHE was seen in fibers from Sod1 −/− mice compared with those from WT mice. Fibers from Sod1 −/− mice had decreased NO availability (decreased DAF-FM fluorescence), increased 3-NT in muscle proteins indicating increased peroxynitrite formation and increased content of peroxiredoxin V (a peroxynitrite reductase), compared with WT mice. Muscle fibers from Sod1 −/− mice showed substantially reduced generation of superoxide in response to contractions compared with fibers from WT mice. Inhibition of NOS did not affect DHE oxidation in fibers from WT or Sod1 −/− mice at rest or during contractions, but transgenic mice overexpressing nNOS showed increased DAF-FM fluorescence and reduced DHE oxidation in resting muscle fibers. It is concluded that formation of peroxynitrite in muscle fibers is a major effect of lack of SOD1 in Sod1 −/− mice and may contribute to fiber loss in this model, and that NO regulates superoxide availability and peroxynitrite formation in muscle. [ABSTRACT FROM AUTHOR]

Skeletal muscle generates superoxide and nitric oxide at rest and this generation is increased by contractile activity. In young and adult animals and man, an increase in activities of these species and the secondary products derived from them (reactive oxygen species, ROS) stimulate redox-sensitive signalling pathways to modify the cellular content of cytoprotective regulatory proteins such as the superoxide dismutases, catalase and heat shock proteins that prevent oxidative damage to tissues. The mechanisms underlying these adaptive responses to contraction include activation of redox-sensitive transcription factors such as nuclear factor κB (NFκB), activator protein-1 (AP1) and heat shock factor 1 (HSF1). During ageing all tissues, including skeletal muscle, demonstrate an accumulation of oxidative damage that may contribute to loss of tissue homeostasis. The causes of this increased oxidative damage are uncertain, but substantial data now indicate that the ability of skeletal muscle from aged organisms to respond to an increase in ROS generation by increased expression of cytoprotective proteins through activation of redox-sensitive transcription factors is severely attenuated. This age-related lack of physiological adaptations to the ROS induced by contractile activity appears to contribute to a loss of ROS homeostasis and increased oxidative damage in skeletal muscle. [ABSTRACT FROM AUTHOR]

In muscle, aging is associated with a failure of adaptive responses to contractile activity, and this is hypothesized to play an important role in age-related loss of muscle mass and function. Mice lacking the Cu,Zn superoxide dismutase (Cu,ZnSOD, SOD1) show an accelerated, age-related loss of muscle mass and function. This work determined whether adult mice lacking Cu,ZnSOD ( Sod1 mice) show a premature failure of adaptive responses to contractions in a similar manner to old wild-type (WT) mice. Adult Sod1 mice (6-8 months of age) had a ∼ 30% reduction in gastrocnemius muscle mass compared with age-matched WT mice. This lower muscle mass was associated with an activation of DNA binding by NFκB and AP-1 at rest. Measurements of the activity of reactive oxygen species (ROS) in single fibres from the muscles of Sod1 mice at rest indicated an elevation in activity compared with fibres from WT mice. Following 15 min of isometric contractions, muscle fibres from WT mice showed an increase in the intracellular ROS activities and activation of NFκB and AP-1, but no changes in either ROS activity or NFκB and AP-1 activation were seen in the muscles of Sod1 mice following contractions. This pattern of changes mimics that seen in the muscles of old WT mice, suggesting that the attenuated responses to contractile activity seen in old mice result from chronic exposure to increased oxidant activity. Data support the use of the Sod1 mouse model to evaluate potential mechanisms that contribute to the loss of muscle mass and function in the elderly. [ABSTRACT FROM AUTHOR]

Chronic exercise improves endurance and skeletal muscle oxidative capacity. Despite the potential importance of reactive oxygen species (ROS) generated during exercise as regulators of these adaptations, the effect of repeated bouts of aerobic exercise on ROS generation by skeletal muscles during contractions has not been examined. Our aim was to establish the impact of repeated treadmill running exercise on muscle ROS generation and activation of redox-sensitive transcription factors. Following 8 weeks of treadmill running, mice displayed an improvement in running speed that was associated with an enhanced ability of gastrocnemius (GTN) muscles to maintain force during a protocol of isometric contractions. In contrast to GTN muscles of cage-sedentary (Sed) mice, muscles from exercised (Exer) mice did not release superoxide or nitric oxide during the isometric contractions. For male mice, basal levels of nuclear factor κB (NFκB) and activator protein-1 (AP-1) DNA binding were increased by treadmill running, and the contraction-induced activation of NFκB and AP-1 observed in muscles of Sed mice was absent in Exer muscles. Also in contrast to Sed muscles, Exer muscles displayed no reductions in glutathione or protein thiol levels in response to contraction. Our observations of decreases for Exer compared with Sed muscles in contraction-induced (i) ROS generation, (ii) activation of redox-sensitive signalling pathways, and (iii) ROS stress suggest that exercise conditioning enhances the ability of skeletal muscle to readily and rapidly detoxify ROS and/or reduces ROS generation, providing protection from ROS-induced damage and reducing signals that might act to mediate further unnecessary adaptations. [ABSTRACT FROM AUTHOR]

The potential deleterious roles of “oxidative stress” have been studied in skeletal muscle for over 30 years, but recent studies have identified that reactive oxygen species and nitric oxide generated by skeletal muscle can exert regulatory roles in cell signalling processes. This “redox regulation” appears to depend upon the reversible oxidation of cysteine residues within key proteins with reversible gluathionylation and formation of protein disulphides potentially leading to changes in the activities of proteins such as enzymes, transcription factors or transporters. Control of this process is dependent upon the local redox environment pertaining at a subcellular level. This short review provides examples of redox-regulated physiological processes in skeletal muscle that include some activation of transcription factors and changes in gene expression that result from contractile activity and the modulation of force generation during sustained contractions. There is also increasing evidence that dysregulation of redox-sensitive processes plays a role in the loss of muscle mass and function that occurs during normal ageing and in the gross muscle degeneration in disorders such as the muscular dystrophies. © 2008 IUBMB IUBMB Life, 60(8): 497–501, 2008 [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) is thought to play multiple roles in skeletal muscle including regulation of some adaptations to contractile activity, but appropriate methods for the analysis of intracellular NO activity are lacking. In this study we have examined the intracellular generation of NO in isolated single mature mouse skeletal muscle fibres at rest and following a period of contractile activity. Muscle fibres were isolated from the flexor digitorum brevis muscle of mice and intracellular NO production was visualized in real-time using the fluorescent NO probe 4-amino-5-methylamino-2′,7′-difluorofluorescein diacetate (DAF-FM DA). Some leakage of DAF-FM was apparent from fibres loaded with the probe, but they retained sufficient probe to respond to changes in intracellular NO following addition of the NO donor 3-(2-hydroxy-1-methyl-2-nitrosohydrazino)- N-methyl-1-propanamine (NOC-7) up to 30 min after loading. Electrically stimulated contractions in isolated fibres increased the rate of change in DAF-FM fluorescence by ∼48% compared to non-stimulated fibres ( P < 0.05) and the rate of change in DAF-FM fluorescence in the stimulated fibres returned to control values by 5 min after contractions. Treatment of isolated fibres with the NO synthase inhibitors NG-nitro-l-arginine methyl ester hydrochloride (l-NAME) or NG-monomethyl-l-arginine (l-NMMA) reduced the increase in DAF-FM fluorescence observed in response to contractions of untreated fibres. Treatment of fibres with the cell-permeable superoxide scavenger 4,5-dihydroxy-1,3-benzenedisulphonic acid (Tiron) also reduced the increase in fluorescence observed during contractions suggesting that superoxide, or more probably peroxynitrite, contributes to the fluorescence observed. Thus this technique can be used to examine NO generation in quiescent and contracting skeletal muscle fibres in real time, although peroxynitrite and other reactive nitrogen species may potentially contribute to the fluorescence values observed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study was performed to test the hypothesis that expression of heat shock proteins (HSPs) exhibits a spatially selective response within intact human skin following in vivo exposure to thermal stress. This response is believed to protect cells and tissues from further damage. Using Western blotting and immunohistochemistry, we studied the expression of a range of HSPs in normal human skin of 5 subjects prior to and following heating in vivo. The skin was heated to 41±0.5°C for 1 h and biopsies were taken at 4, 8 and 24 h and from control, untreated skin. HSPs 27, 60, 72i, 90, 110 and heat shock constitutive (HSC)70 were expressed in normal skin, but the extent and distribution of these HSPs showed considerable variation. HSP27, 60 and 72i were found predominantly in the epidermis, whereas HSC70 showed weak epidermal staining but strong dermal expression. Heating the skin in vivo resulted in an increased skin content of HSP27, 60, 72i and 90, with maximal increase at 24 h following hyperthermia, while the skin content of HSC70 and HSP110 were unchanged. Significant increases in the content of HSP72i and HSP90 had occurred by 4 h following hyperthermia, with a mean ±SEM of 206±50% and 197±38% of the control, untreated values, respectively (p<0.05). These findings indicate the complexity of HSP dynamics in human skin, and suggest that heating within the experimental range may protect the skin from further stresses for at least 24 h. [ABSTRACT FROM AUTHOR]

Examines muscles of quiescent adult and old wild-type and heat shock protein 70 (HSP70) overexpressor mice for markers of oxidative damage. Ability of the muscles to activate nuclear factor-κB in response to nondamaging contractile activity; Characterization of muscle aging; Age-related changes in muscles from the HSP70 transgenic mice.

Presents a study on the effect of overexpression of heat-shock proteins70 (HSP70) in mouse skeletal muscle on muscle damage and age-related muscle dysfunction. Protection against lengthening contraction-induced damage by transgenic overexpression of HSP70 in skeletal muscle; Recovery of muscles of adult and old HSP70 transgenic mice compared to muscles of age-matched wild-type mice; Conclusion of the study.

Presents a study which examined the mechanisms by which skeletal muscle adapts to the oxidative stress component of contraction. Background on the oxygen uptake by skeletal muscle; Methodology; Attenuation of the ability of skeletal muscle to adapt to oxidative stress during aging.