Redox homeostasis and age-related deficits in neuromuscular integrity and function

Peroxiredoxin 2 regulates DAF-16/FOXO mediated mitochondrial remodelling in response to exercise that is disrupted in ageing

OBJECTIVES

A decline in mitochondrial function and increased susceptibility to oxidative stress is a hallmark of ageing. Exercise endogenously generates reactive oxygen species (ROS) in skeletal muscle and promotes mitochondrial remodelling resulting in improved mitochondrial function. It is unclear how exercise induced redox signalling results in alterations in mitochondrial dynamics and morphology.

METHODS

In this study, a Caenorhabditis elegans model of exercise and ageing was used to determine the mechanistic role of Peroxiredoxin 2 (PRDX-2) in regulating mitochondrial morphology. Mitochondrial morphology was analysed using transgenic reporter strains and transmission electron microscopy, complimented with the analysis of the effects of ageing and exercise on physiological activity.

RESULTS

The redox state of PRDX-2 was altered with exercise and ageing, hyperoxidised peroxiredoxins were detected in old worms along with basally elevated intracellular ROS. Exercise generated intracellular ROS and rapid mitochondrial remodelling, which was disrupted with age. The exercise intervention promoted mitochondrial ER contact sites (MERCS) assembly and increased DAF-16/FOXO nuclear localisation. The prdx-2 mutant strain had a disrupted mitochondrial network as evidenced by increased mitochondrial fragmentation. In the prdx-2 mutant strain, exercise did not activate DAF-16/FOXO, mitophagy or increase MERCS assembly. The results demonstrate that exercise generated ROS increased DAF-16/FOXO transcription factor nuclear localisation required for activation of mitochondrial fusion events that were blunted with age.

CONCLUSIONS

The data demonstrate the critical role of PRDX-2 in orchestrating mitochondrial remodelling in response to a physiological stress by regulating redox dependent DAF-16/FOXO nuclear localisation.

Association between oxidative balance score and skeletal muscle mass and strength: NHANES from 2011 to 2018

Objective

Oxidative stress is a risk factor for sarcopenia. The Oxidative Balance Score (OBS) is a widely employed tool for evaluating the oxidative stress-related exposures from dietary and lifestyle factors. In this study, we aimed to conducted to explore the relationship between OBS and skeletal muscle mass and strength.

Methods

6,438 subjects from 2011 to 2018 and 5,414 from 2011 to 2014 from the National Health and Nutrition Examination Survey (NHANES) were selected for analysis. The correlations between OBS and skeletal muscle mass and handgrip strength were investigated using multivariate logistic regression and linear regression analysis.

Results

Compared with lowest OBS, participants with OBS in the highest quartile had lower risk of low skeletal muscle mass (OR = 0.173 (0.120 ~ 0.248), p < 0.0001) and low handgrip strength (β = 0.173 (0.120 ~ 0.248), p = 0.011). The negative association also were found between dietary/lifestyle OBS and skeletal muscle mass (OR = 0.268 (0.178 ~ 0.404), p < 0.0001; OR = 0.231 (0.130 ~ 0.410), p < 0.0001) and handgrip strength (β = 1.812 (0.555 ~ 3.071), p = 0.008; β = -2.255 (-3.430 ~ -1.079), p < 0.001) independently. The positive association remains significant, especially among men and those with higher education levels by subgroup analysis.

Conclusion

All of these results indicated a negative association between OBS and low skeletal muscle mass and handgrip strength. An antioxidant-rich diet and healthy lifestyle are crucial for enhancing skeletal muscle mass and strength.

Mitochondrial targeted catalase improves muscle strength following arteriovenous fistula creation in mice with chronic kidney disease

Hand dysfunction is a common observation after arteriovenous fistula (AVF) creation for hemodialysis access and has a variable clinical phenotype; however, the underlying mechanism responsible is unclear. Grip strength changes are a common metric used to assess AVF-associated hand disability but has previously been found to poorly correlate with the hemodynamic perturbations post-AVF placement implicating other tissue-level factors as drivers of hand outcomes. In this study, we sought to test if expression of a mitochondrial targeted catalase (mCAT) in skeletal muscle could reduce AVF-related limb dysfunction in mice with chronic kidney disease (CKD). Male and female C57BL/6J mice were fed an adenine-supplemented diet to induce CKD prior to placement of an AVF in the iliac vascular bundle. Adeno-associated virus was used to drive expression of either a green fluorescent protein (control) or mCAT using the muscle-specific human skeletal actin (HSA) gene promoter prior to AVF creation. As expected, the muscle-specific AAV-HSA-mCAT treatment did not impact blood urea nitrogen levels (P = 0.72), body weight (P = 0.84), or central hemodynamics including infrarenal aorta and inferior vena cava diameters (P > 0.18) or velocities (P > 0.38). Hindlimb perfusion recovery and muscle capillary densities were also unaffected by AAV-HSA-mCAT treatment. In contrast to muscle mass and myofiber size which were not different between groups, both absolute and specific muscle contractile forces measured via a nerve-mediated in-situ preparation were significantly greater in AAV-HSA-mCAT treated mice (P = 0.0012 and P = 0.0002). Morphological analysis of the post-synaptic neuromuscular junction uncovered greater acetylcholine receptor cluster areas (P = 0.0094) and lower fragmentation (P = 0.0010) in AAV-HSA-mCAT treated mice. Muscle mitochondrial oxidative phosphorylation was not different between groups, but AAV-HSA-mCAT treated mice had lower succinate-fueled mitochondrial hydrogen peroxide emission compared to AAV-HSA-GFP mice (P < 0.001). In summary, muscle-specific scavenging of mitochondrial hydrogen peroxide significantly improves neuromotor function in mice with CKD following AVF creation.

Sarcopenia in a type 2 diabetic state: Reviewing literature on the pathological consequences of oxidative stress and inflammation beyond the neutralizing effect of intracellular antioxidants

Sarcopenia remains one of the major pathological features of type 2 diabetes (T2D), especially in older individuals. This condition describes gradual loss of muscle mass, strength, and function that reduces the overall vitality and fitness, leading to increased hospitalizations and even fatalities to those affected. Preclinical evidence indicates that dysregulated mitochondrial dynamics, together with impaired activity of the NADPH oxidase system, are the major sources of oxidative stress that drive skeletal muscle damage in T2D. While patients with T2D also display relatively higher levels of circulating inflammatory markers in the serum, including high sensitivity-C-reactive protein, interleukin-6, and tumor necrosis factor-α that are independently linked with the deterioration of muscle function and sarcopenia in T2D. In fact, beyond reporting on the pathological consequences of both oxidative stress and inflammation, the current review highlights the importance of strengthening intracellular antioxidant systems to preserve muscle mass, strength, and function in individuals with T2D.

ROCK1 activates mitochondrial fission leading to oxidative stress and muscle atrophy

Chronic kidney disease (CKD) is often associated with protein-energy wasting (PEW), which is characterized by a reduction in muscle mass and strength. Although mitochondrial dysfunction and oxidative stress have been implicated to play a role in the pathogenesis of muscle wasting, the underlying mechanisms remain unclear. In this study, we used transcriptomics, metabolomics analyses and mouse gene manipulating approaches to investigate the effects of mitochondrial plasticity and oxidative stress on muscle wasting in mouse CKD models. Our results showed that the expression of oxidative stress response genes was increased, and that of oxidative phosphorylation genes was decreased in the muscles of mice with CKD. This was accompanied by reduced oxygen consumption rates, decreased levels of mitochondrial electron transport chain proteins, and increased cellular oxidative damage. Excessive mitochondrial fission was also observed, and we found that the activation of ROCK1 was responsible for this process. Inducible expression of muscle-specific constitutively active ROCK1(mROCK1ca)exacerbated mitochondrial fragmentation and muscle wasting in CKD mice. Conversely, ROCK1 depletion (ROCK1-/-) alleviated these phenomena. Mechanistically, ROCK1 activation promoted the recruitment of Drp1 to mitochondria, thereby facilitating fragmentation. Notably, the pharmacological inhibition of ROCK1 mitigated muscle wasting by suppressing mitochondrial fission and oxidative stress. Our findings demonstrate that ROCK1 participates in CKD-induced muscle wasting by promoting mitochondrial fission and oxidative stress, and pharmacological suppression of ROCK1 could be a therapeutic strategy for combating muscle wasting in CKD conditions.

Metabolic Priming as a Tool in Redox and Mitochondrial Theragnostics

Theragnostics is a promising approach that integrates diagnostics and therapeutics into a single personalized strategy. To conduct effective theragnostic studies, it is essential to create an in vitro environment that accurately reflects the in vivo conditions. In this review, we discuss the importance of redox homeostasis and mitochondrial function in the context of personalized theragnostic approaches. Cells have several ways to respond to metabolic stress, including changes in protein localization, density, and degradation, which can promote cell survival. However, disruption of redox homeostasis can lead to oxidative stress and cellular damage, which are implicated in various diseases. Models of oxidative stress and mitochondrial dysfunction should be developed in metabolically conditioned cells to explore the underlying mechanisms of diseases and develop new therapies. By choosing an appropriate cellular model, adjusting cell culture conditions and validating the cellular model, it is possible to identify the most promising therapeutic options and tailor treatments to individual patients. Overall, we highlight the importance of precise and individualized approaches in theragnostics and the need to develop accurate in vitro models that reflect the in vivo conditions.

Lipotoxicity-related sarcopenia: a review

A body of literature supports the postulation that a persistent lipid metabolic imbalance causes lipotoxicity, "an abnormal fat storage in the peripheral organs". Hence, lipotoxicity could somewhat explain the process of sarcopenia, an aging-related, gradual, and involuntary decline in skeletal muscle strength and mass associated with several health complications. This review focuses on the recent mechanisms underlying lipotoxicity-related sarcopenia. A vicious cycle occurs between sarcopenia and ectopic fat storage via a complex interplay of mitochondrial dysfunction, pro-inflammatory cytokine production, oxidative stress, collagen deposition, extracellular matrix remodeling, and life habits. The repercussions of lipotoxicity exacerbation of sarcopenia can include increased disability, morbidity, and mortality. This suggests that appropriate lipotoxicity management should be considered the primary target for the prevention and/or treatment of chronic musculoskeletal and other aging-related disorders. Further advanced research is needed to understand the molecular details of lipotoxicity and its consequences for sarcopenia and sarcopenia-related comorbidities.

Skeletal muscle oxidative stress and inflammation in aging: Focus on antioxidant and anti-inflammatory therapy

With aging, the progressive loss of skeletal muscle will have negative effect on multiple physiological parameters, such as exercise, respiration, thermoregulation, and metabolic homeostasis. Accumulating evidence reveals that oxidative stress and inflammation are the main pathological characteristics of skeletal muscle during aging. Here, we focus on aging-related sarcopenia, summarize the relationship between aging and sarcopenia, and elaborate on aging-mediated oxidative stress and oxidative damage in skeletal muscle and its critical role in the occurrence and development of sarcopenia. In addition, we discuss the production of excessive reactive oxygen species in aging skeletal muscle, which reduces the ability of skeletal muscle satellite cells to participate in muscle regeneration, and analyze the potential molecular mechanism of ROS-mediated mitochondrial dysfunction in aging skeletal muscle. Furthermore, we have also paid extensive attention to the possibility and potential regulatory pathways of skeletal muscle aging and oxidative stress mediate inflammation. Finally, in response to the abnormal activity of oxidative stress and inflammation during aging, we summarize several potential antioxidant and anti-inflammatory strategies for the treatment of sarcopenia, which may provide beneficial help for improving sarcopenia during aging.

The Whole-transcriptome Landscape of Diabetes-related Sarcopenia Reveals the Specific Function of Novel lncRNA Gm20743

While the exact mechanism remains unclear, type 2 diabetes mellitus increases the risk of sarcopenia which is characterized by decreased muscle mass, strength, and function. Whole-transcriptome RNA sequencing and informatics were performed on the diabetes-induced sarcopenia model of db/db mice. To determine the specific function of lncRNA Gm20743, the detection of Mito-Sox, reactive oxygen species, Ethynyl-2′-deoxyuridine, and myosin heavy chain was performed in overexpressed and knockdown-Gm20743 C2C12 cells. RNA-seq data and informatics revealed the key lncRNA-mRNA interactions and indicated a potential regulatory role of lncRNAs. We characterized three core candidate lncRNAs Gm20743, Gm35438, 1700047G03Rik, and their potential function. Furthermore, the results suggested lncRNA Gm20743 may be involved in regulating mitochondrial function, oxidative stress, cell proliferation, and myotube differentiation in skeletal muscle cells. These findings significantly improve our understanding of lncRNAs that may mediate muscle mass, strength, and function in diabetes and represent potential therapeutic targets for diabetes-induced sarcopenia.

The role of lncRNA Gm20743 in the development of diabetic sarcopenia is explored using a mouse model.

Frailty in rodents: Models, underlying mechanisms, and management

Frailty is a clinical geriatric syndrome characterized by decreased multisystem function and increased vulnerability to adverse outcomes. Although numerous studies have been conducted on frailty, the underlying mechanisms and management strategies remain unclear. As rodents share homology with humans, they are used extensively as animal models to study human diseases. Rodent frailty models can be classified broadly into the genetic modification and non-genetic modification models, the latter of which include frailty assessment models (based on the Fried frailty phenotype and frailty index methods) and induced frailty models. Such models were developed for use in investigating frailty-related physiological changes at the gene, cellular, molecular, and system levels, including the organ system level. Furthermore, exercise, diet, and medication interventions, in addition to their combinations, could improve frailty status in rodents. Rodent frailty models provide novel and effective tools for frailty research. In the present paper, we review research progress in rodent frailty models, mechanisms, and management, which could facilitate and guide further clinical research on frailty in older adults.

miR-24 and its target gene Prdx6 regulate viability and senescence of myogenic progenitors during aging

Satellite cell-dependent skeletal muscle regeneration declines during aging. Disruptions within the satellite cells and their niche, together with alterations in the myofibrillar environment, contribute to age-related dysfunction and defective muscle regeneration. In this study, we demonstrated an age-related decline in satellite cell viability and myogenic potential and an increase in ROS and cellular senescence. We detected a transient upregulation of miR-24 in regenerating muscle from adult mice and downregulation of miR-24 during muscle regeneration in old mice. FACS-sorted satellite cells were characterized by decreased levels of miR-24 and a concomitant increase in expression of its target: Prdx6. Using GFP reporter constructs, we demonstrated that miR-24 directly binds to its predicted site within Prdx6 mRNA. Subtle changes in Prdx6 levels following changes in miR-24 expression indicate miR-24 plays a role in fine-tuning Prdx6 expression. Changes in miR-24 and Prdx6 levels were associated with altered mitochondrial ROS generation, increase in the DNA damage marker: phosphorylated-H2Ax and changes in viability, senescence, and myogenic potential of myogenic progenitors from mice and humans. The effects of miR-24 were more pronounced in myogenic progenitors from old mice, suggesting a context-dependent role of miR-24 in these cells, with miR-24 downregulation likely a part of a compensatory response to declining satellite cell function during aging. We propose that downregulation of miR-24 and subsequent upregulation of Prdx6 in muscle of old mice following injury are an adaptive response to aging, to maintain satellite cell viability and myogenic potential through regulation of mitochondrial ROS and DNA damage pathways.

Analysis of the Impact of Selected Vitamins Deficiencies on the Risk of Disability in Older People

Vitamin deficiencies have a serious impact on healthy aging in older people. Many age-related disorders have a direct or indirect impact on nutrition, both in terms of nutrient assimilation and food access, which may result in vitamin deficiencies and may lead to or worsen disabilities. Frailty is characterized by reduced functional abilities, with a key role of malnutrition in its pathogenesis. Aging is associated with various changes in body composition that lead to sarcopenia. Frailty, aging, and sarcopenia all favor malnutrition, and poor nutritional status is a major cause of geriatric morbidity and mortality. In the present narrative review, we focused on vitamins with a significant risk of deficiency in high-income countries: D, C, and B (B6/B9/B12). We also focused on vitamin E as the main lipophilic antioxidant, synergistic to vitamin C. We first discuss the role and needs of these vitamins, the prevalence of deficiencies, and their causes and consequences. We then look at how these vitamins are involved in the biological pathways associated with sarcopenia and frailty. Lastly, we discuss the critical early diagnosis and management of these deficiencies and summarize potential ways of screening malnutrition. A focused nutritional approach might improve the diagnosis of nutritional deficiencies and the initiation of appropriate clinical interventions for reducing the risk of frailty. Further comprehensive research programs on nutritional interventions are needed, with a view to lowering deficiencies in older people and thus decreasing the risk of frailty and sarcopenia.

Aging under Pressure: The Roles of Reactive Oxygen and Nitrogen Species (RONS) Production and Aging Skeletal Muscle in Endothelial Function and Hypertension-From Biological Processes to Potential Interventions

The proportion of adults living with hypertension increases significantly with advancing age. It is therefore important to consider how health and vitality can be maintained by the aging population until end of life. A primary risk factor for the progression of cardiovascular diseases (CVD) is hypertension, so exploring the factors and processes central to this burden of disease is essential for healthy aging. A loss of skeletal muscle quantity and quality is characteristic in normal aging, with a reduction of vasodilatory capacity caused by endothelial dysfunction, and subsequent increase in peripheral resistance and risk for hypertension. Reactive Oxygen and Nitrogen Species (RONS) encompass the reactive derivatives of NO and superoxide, which are continuously generated in contracting skeletal muscle and are essential mediators for cellular metabolism. They act together as intra and intercellular messengers, gene expression regulators, and induce programmed cell death. In excessive amounts RONS can inflict damage to endothelial and skeletal muscle cells, alter signaling pathways or prematurely promote stress responses and potentially speed up the aging process. The age-related increase in RONS by skeletal muscle and endothelial mitochondria leads to impaired production of NO, resulting in vascular changes and endothelial dysfunction. Changes in vascular morphology is an early occurrence in the etiology of CVDs and, while this is also a normal characteristic of aging, whether it is a cause or a consequence of aging in hypertension remains unclear. This review serves to focus on the roles and mechanisms of biological processes central to hypertension and CVD, with a specific focus on the effects of aging muscle and RONS production, as well as the influence of established and more novel interventions to mediate the increasing risk for hypertension and CVD and improve health outcomes as we age.

The emerging role of the sympathetic nervous system in skeletal muscle motor innervation and sarcopenia

Examining neural etiologic factors'role in the decline of neuromuscular function with aging is essential to our understanding of the mechanisms underlying sarcopenia, the age-dependent decline in muscle mass, force and power. Innervation of the skeletal muscle by both motor and sympathetic axons has been established, igniting interest in determining how the sympathetic nervous system (SNS) affect skeletal muscle composition and function throughout the lifetime. Selective expression of the heart and neural crest derivative 2 gene in peripheral SNs increases muscle mass and force regulating skeletal muscle sympathetic and motor innervation; improving acetylcholine receptor stability and NMJ transmission; preventing inflammation and myofibrillar protein degradation; increasing autophagy; and probably enhancing protein synthesis. Elucidating the role of central SNs will help to define the coordinated response of the visceral and neuromuscular system to physiological and pathological challenges across ages. This review discusses the following questions: (1) Does the SNS regulate skeletal muscle motor innervation? (2) Does the SNS regulate presynaptic and postsynaptic neuromuscular junction (NMJ) structure and function? (3) Does sympathetic neuron (SN) regulation of NMJ transmission decline with aging? (4) Does maintenance of SNs attenuate aging sarcopenia? and (5) Do central SN group relays influence sympathetic and motor muscle innervation?

Effect of allopurinol on phosphocreatine recovery and muscle function in older people with impaired physical function: a randomised controlled trial

Background

Allopurinol has vascular antioxidant effects and participates in purinergic signalling within muscle. We tested whether allopurinol could improve skeletal muscle energetics and physical function in older people with impaired physical performance.

Methods

We conducted a randomised, double blind, parallel group, placebo-controlled trial, comparing 20 weeks of allopurinol 600 mg once daily versus placebo. We recruited community-dwelling participants aged 65 and over with baseline 6-min walk distance of <400 m and no contraindications to magnetic resonance imaging scanning. Outcomes were measured at baseline and 20 weeks. The primary outcome was post-exercise phosphocreatine (PCr) recovery rate measured using ³¹P magnetic resonance spectroscopy of the calf. Secondary outcomes included 6-min walk distance, short physical performance battery (SPPB), lean body mass measured by bioimpedance, endothelial function and quality of life.

Results

In total, 124 participants were randomised, mean age 80 (SD 6) years. A total of 59 (48%) were female, baseline 6-min walk distance was 293 m (SD 80 m) and baseline SPPB was 8.5 (SD 2.0). Allopurinol did not significantly improve PCr recovery rate (treatment effect 0.10 units [95% CI, −0.07 to 0.27], P = 0.25). No significant changes were seen in endothelial function, quality of life, lean body mass or SPPB. Allopurinol improved 6-min walk distance (treatment effect 25 m [95% 4–46, P = 0.02]). This was more pronounced in those with high baseline oxidative stress and urate.

Conclusion

Allopurinol improved 6-min walk distance but not PCr recovery rate in older people with impaired physical function. Antioxidant strategies to improve muscle function for older people may need to be targeted at subgroups with high baseline oxidative stress.

Exercise-induced oxidative stress: Friend or foe?

The first report demonstrating that prolonged endurance exercise promotes oxidative stress in humans was published more than 4 decades ago. Since this discovery, many ensuing investigations have corroborated the fact that muscular exercise increases the production of reactive oxygen species (ROS) and results in oxidative stress in numerous tissues including blood and skeletal muscles. Although several tissues may contribute to exercise-induced ROS production, it is predicted that muscular contractions stimulate ROS production in active muscle fibers and that skeletal muscle is a primary source of ROS production during exercise. This contraction-induced ROS generation is associated with (1) oxidant damage in several tissues (e.g., increased protein oxidation and lipid peroxidation), (2) accelerated muscle fatigue, and (3) activation of biochemical signaling pathways that contribute to exercise-induced adaptation in the contracting muscle fibers. While our understanding of exercise and oxidative stress has advanced rapidly during the last decades, questions remain about whether exercise-induced increases in ROS production are beneficial or harmful to health. This review addresses this issue by discussing the site(s) of oxidant production during exercise and detailing the health consequences of exercise-induced ROS production.

Targeting reactive oxygen species (ROS) to combat the age-related loss of muscle mass and function

The loss of muscle mass and function with age, termed sarcopenia, is an inevitable process, which has a significant impact on quality of life. During ageing we observe a progressive loss of total muscle fibres and a reduction in cross-sectional area of the remaining fibres, resulting in a significant reduction in force output. The mechanisms which underpin sarcopenia are complex and poorly understood, ranging from inflammation, dysregulation of protein metabolism and denervation. However, there is significant evidence to demonstrate that modified ROS generation, redox dis-homeostasis and mitochondrial dysfunction may have an important role to play. Based on this, significant interest and research has interrogated potential ROS-targeted therapies, ranging from nutritional-based interventions such as vitamin E/C, polyphenols (resveratrol) and targeted pharmacological compounds, using molecules such as SS-31 and MitoQ. In this review we evaluate these approaches to target aberrant age-related ROS generation and the impact on muscle mass and function.

Cherry intake as a dietary strategy in sport and diseases: a review of clinical applicability and mechanisms of action

Cherries are fruits rich in phytochemical compounds, particularly anthocyanins. Thus, consumption of cherries has gained attention in both clinical and sport-related fields for their antioxidant and anti-inflammatory properties. Mechanistically, anthocyanins from the intake of cherries may help to attenuate pain and decrease blood concentrations of biomarkers linked to skeletal muscle degradation, which in turn may provide ergogenic effects. In addition, the ability of anthocyanins to balance the redox state represents a conceivable target for rheumatic disorders (e.g. gout and arthritis). Moreover, cherry anthocyanins are emerging as a potential non-pharmacological remedy for cardiometabolic diseases (hypertension and dyslipidemia). Herein, we summarize the effects of cherry intake in sport and diseases, and discuss their purported mechanisms of action to provide insights into practical application.

Compartmentalized muscle redox signals controlling exercise metabolism - Current state, future challenges

Exercise imposes cellular stress on contracting skeletal muscle fibers, forcing them to complete molecular adaptations to maintain homeostasis. There is mounting evidence that redox signaling by reactive oxygen species (ROS) is vital for skeletal muscle exercise adaptations across many different exercise modalities. The study of redox signaling is moving towards a growing appreciation that these ROS do not signal in a global unspecific way, but rather elicit their effects in distinct subcellular compartments. This short review will first outline the sources of ROS in exercising skeletal muscle and then discuss some examples of exercise adaptations, which are evidenced to be regulated by compartmentalized redox signaling. We speculate that knowledge of these redox pathways might one day allow targeted manipulation to increase redox-signaling in specific compartments to augment the exercise-hormetic response in health and disease.

The Emerging Roles of Nicotinamide Adenine Dinucleotide Phosphate Oxidase 2 in Skeletal Muscle Redox Signaling and Metabolism

Significance: Skeletal muscle is a crucial tissue to whole-body locomotion and metabolic health. Reactive oxygen species (ROS) have emerged as intracellular messengers participating in both physiological and pathological adaptations in skeletal muscle. A complex interplay between ROS-producing enzymes and antioxidant networks exists in different subcellular compartments of mature skeletal muscle. Recent evidence suggests that nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) are a major source of contraction- and insulin-stimulated oxidants production, but they may paradoxically also contribute to muscle insulin resistance and atrophy. Recent Advances: Pharmacological and molecular biological tools, including redox-sensitive probes and transgenic mouse models, have generated novel insights into compartmentalized redox signaling and suggested that NOX2 contributes to redox control of skeletal muscle metabolism. Critical Issues: Major outstanding questions in skeletal muscle include where NOX2 activation occurs under different conditions in health and disease, how NOX2 activation is regulated, how superoxide/hydrogen peroxide generated by NOX2 reaches the cytosol, what the signaling mediators are downstream of NOX2, and the role of NOX2 for different physiological and pathophysiological processes. Future Directions: Future research should utilize and expand the current redox-signaling toolbox to clarify the NOX2-dependent mechanisms in skeletal muscle and determine whether the proposed functions of NOX2 in cells and animal models are conserved into humans.

Associations of fat-soluble micronutrients and redox biomarkers with frailty status in the FRAILOMIC initiative

BACKGROUND

A poor fat-soluble micronutrient (FMN) and a high oxidative stress status are associated with frailty. Our aim was to determine the cross-sectional association of FMNs and oxidative stress biomarkers [protein carbonyls (PrCarb) and 3-nitrotyrosine] with the frailty status in participants older than 65 years.

METHODS

Plasma levels of vitamins A (retinol), D3 , E (α-tocopherol and γ-tocopherol) and carotenoids (α-carotene and β-carotene, lycopene, lutein/zeaxanthin, and β-cryptoxanthin), PrCarb, and 3-nitrotyrosine were measured in 1450 individuals of the FRAILOMIC initiative. Participants were classified into robust, pre-frail, and frail using Fried's frailty criteria. Associations between biomarkers and frailty status were assessed by general linear and logistic regression models, both adjusted for cohort, season of blood sampling, gender, age, height, weight, and smoking.

RESULTS

Robust participants had significantly higher vitamin D3 and lutein/zeaxanthin concentrations than pre-frail and frail subjects; had significantly higher γ-tocopherol, α-carotene, β-carotene, lycopene, and β-cryptoxanthin concentrations than frail subjects, and had significantly lower PrCarb concentrations than frail participants in multivariate linear models. Frail subjects were more likely to be in the lowest than in the highest tertile for vitamin D3 (adjusted odds ratio: 2.15; 95% confidence interval: 1.42-3.26), α-tocopherol (2.12; 1.39-3.24), α-carotene (1.69; 1.00-2.88), β-carotene (1.84; 1.13-2.99), lycopene (1.94; 1.24-3.05), lutein/zeaxanthin (3.60; 2.34-5.53), and β-cryptoxanthin (3.02; 1.95-4.69) and were more likely to be in the highest than in the lowest tertile for PrCarb (2.86; 1.82-4.49) than robust subjects in multivariate regression models.

CONCLUSIONS

Our study indicates that both low FMN and high PrCarb concentrations are associated with pre-frailty and frailty.

Endurance training improves plasma superoxide dismutase activity in healthy elderly

We aimed to characterize the plasma redox homeostasis as underlying physiological mechanisms of specific training on healthy elderly. 51 healthy volunteers were trained to endurance, resistance, Neuro-Muscular Electrical Stimulation for 12 weeks, 3 sessions/w, all applied to lower limbs. We assessed ex-post quadriceps' maximal voluntary contraction, handgrip strength, five-times-sit to stand and timed up-and-go tests, oxidative damage (lipid peroxidation, protein carbonyl groups), antioxidant enzyme activities (superoxide dismutase, Catalase, Glutathione peroxidase, Glutathione homeostasis), free thiols and total antioxidant status. We found significant difference in ex-post × protocol and in post-hoc analysis specifically for plasma superoxide dismutase activity in endurance training.

Lipotoxicity, aging, and muscle contractility: does fiber type matter?

Sarcopenia is a universal characteristic of the aging process and is often accompanied by increases in whole-body adiposity. These changes in body composition have important clinical implications, given that loss of muscle and gain of fat mass are both significantly and independently associated with declining physical performance as well as an increased risk for disability, hospitalizations, and mortality in older individuals. This increased fat mass is not exclusively stored in adipose depots but may become deposited in non-adipose tissues, such as skeletal muscle, when the oxidative capacity of the adipose tissue itself is exceeded. The redistributed adipose tissue is thought to exert detrimental local effects on the muscle environment given the close proximity. Thus, sarcopenia observed with aging may be better defined in the context of loss of muscle quality rather than loss of muscle quantity per se. In this perspective, we briefly review the age-related physiological changes in cellularity, secretory profiles, and inflammatory status of adipose tissue which drive lipotoxicity (spillover) of skeletal muscle and then provide evidence of how this may affect specific fiber type contractility. We focus on biological contributors (cellular machinery) to contractility for which there is some evidence of vulnerability to lipid stress distinguishing between fiber types.

Micro(RNA)-managing muscle wasting

Progressive skeletal muscle wasting is a natural consequence of aging and is common in chronic and acute diseases. Loss of skeletal muscle mass and function (strength) often leads to frailty, decreased independence, and increased risk of hospitalization. Despite progress made in our understanding of the mechanisms underlying muscle wasting, there is still no treatment available, with exercise training and dietary supplementation improving, but not restoring, muscle mass and/or function. There has been slow progress in developing novel therapies for muscle wasting, either during aging or disease, partially due to the complex nature of processes underlying muscle loss. The mechanisms of muscle wasting are multifactorial, with a combination of factors underlying age- and disease-related functional muscle decline. These factors include well-characterized changes in muscle such as changes in protein turnover and more recently described mechanisms such as autophagy or satellite cell senescence. Advances in transcriptomics and other high-throughput approaches have highlighted significant deregulation of skeletal muscle gene and protein levels during aging and disease. These changes are regulated at different levels, including posttranscriptional gene expression regulation by microRNAs. microRNAs, potent regulators of gene expression, modulate many processes in muscle, and microRNA-based interventions have been recently suggested as a promising new therapeutic strategy against alterations in muscle homeostasis. Here, we review recent developments in understanding the aging-associated mechanisms of muscle wasting and explore potential microRNA-based therapeutic avenues.

Mitochondrial oxidative stress impairs contractile function but paradoxically increases muscle mass via fibre branching

BACKGROUND

Excess reactive oxygen species (ROS) and muscle weakness occur in parallel in multiple pathological conditions. However, the causative role of skeletal muscle mitochondrial ROS (mtROS) on neuromuscular junction (NMJ) morphology and function and muscle weakness has not been directly investigated.

METHODS

We generated mice lacking skeletal muscle-specific manganese-superoxide dismutase (mSod2KO) to increase mtROS using a cre-Lox approach driven by human skeletal actin. We determined primary functional parameters of skeletal muscle mitochondrial function (respiration, ROS, and calcium retention capacity) using permeabilized muscle fibres and isolated muscle mitochondria. We assessed contractile properties of isolated skeletal muscle using in situ and in vitro preparations and whole lumbrical muscles to elucidate the mechanisms of contractile dysfunction.

RESULTS

The mSod2KO mice, contrary to our prediction, exhibit a 10-15% increase in muscle mass associated with an ~50% increase in central nuclei and ~35% increase in branched fibres (P < 0.05). Despite the increase in muscle mass of gastrocnemius and quadriceps, in situ sciatic nerve-stimulated isometric maximum-specific force (N/cm² ), force per cross-sectional area, is impaired by ~60% and associated with increased NMJ fragmentation and size by ~40% (P < 0.05). Intrinsic alterations of components of the contractile machinery show elevated markers of oxidative stress, for example, lipid peroxidation is increased by ~100%, oxidized glutathione is elevated by ~50%, and oxidative modifications of myofibrillar proteins are increased by ~30% (P < 0.05). We also find an approximate 20% decrease in the intracellular calcium transient that is associated with specific force deficit. Excess superoxide generation from the mitochondrial complexes causes a deficiency of succinate dehydrogenase and reduced complex-II-mediated respiration and adenosine triphosphate generation rates leading to severe exercise intolerance (~10 min vs. ~2 h in wild type, P < 0.05).

CONCLUSIONS

Increased skeletal muscle mtROS is sufficient to elicit NMJ disruption and contractile abnormalities, but not muscle atrophy, suggesting new roles for mitochondrial oxidative stress in maintenance of muscle mass through increased fibre branching.

Dietary Patterns, Skeletal Muscle Health, and Sarcopenia in Older Adults

In recent decades, the significance of diet and dietary patterns (DPs) for skeletal muscle health has been gaining attention in ageing and nutritional research. Sarcopenia, a muscle disease characterised by low muscle strength, mass, and function is associated with an increased risk of functional decline, frailty, hospitalization, and death. The prevalence of sarcopenia increases with age and leads to high personal, social, and economic costs. Finding adequate nutritional measures to maintain muscle health, preserve function, and independence for the growing population of older adults would have important scientific and societal implications. Two main approaches have been employed to study the role of diet/DPs as a modifiable lifestyle factor in sarcopenia. An a priori or hypothesis-driven approach examines the adherence to pre-defined dietary indices such as the Mediterranean diet (MED) and Healthy Eating Index (HEI)—measures of diet quality—in relation to muscle health outcomes. A posteriori or data-driven approaches have used statistical tools—dimension reduction methods or clustering—to study DP-muscle health relationships. Both approaches recognise the importance of the whole diet and potential cumulative, synergistic, and antagonistic effects of foods and nutrients on ageing muscle. In this review, we have aimed to (i) summarise nutritional epidemiology evidence from four recent systematic reviews with updates from new primary studies about the role of DPs in muscle health, sarcopenia, and its components; (ii) hypothesise about the potential mechanisms of ‘myoprotective’ diets, with the MED as an example, and (iii) discuss the challenges facing nutritional epidemiology to produce the higher level evidence needed to understand the relationships between whole diets and healthy muscle ageing.

Modelling the role of redox-related mechanisms in musculoskeletal ageing

The decline in the musculoskeletal system with age is driven at the cellular level by random molecular damage. Cells possess mechanisms to repair or remove damage and many of the pathways involved in this response are regulated by redox signals. However, with ageing there is an increase in oxidative stress which can lead to chronic inflammation and disruption of redox signalling pathways. The complexity of the processes involved has led to the use of computational modelling to help increase our understanding of the system, test hypotheses and make testable predictions. This paper will give a brief background of the biological systems that have been modelled, an introduction to computational modelling, a review of models that involve redox-related mechanisms that are applicable to musculoskeletal ageing, and finally a discussion of the future potential for modelling in this field.

Comparison between the effect of human Wharton's jelly-derived mesenchymal stem cells and levetiracetam on brain infarcts in rats

BACKGROUND

Stroke represents one of the major causes of death worldwide. Neuroprotection remains an important goal of stroke therapy. Stem cell therapeutic effect is attributed to the neuroprotective effect and the regulation of the oxidant stress. Levetiracetam (LEV), a second-generation antiepileptic drug, was reported to confer neuronal protection after cerebral ischemia reperfusion.

AIM

To investigate the effect of human Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) and LEV on the size of brain infarcts, the histological structure, the neurotrophic, and the antioxidant gene expression in middle cerebral artery occlusion in rats.

METHOD

The rats were divided into five equal groups of 12 rats each as follows. Sham control group: received phosphate-buffered saline (PBS); ischemia/reperfusion (I/R) group: received PBS before ligation; stem cell-treated group: the animal received MSCs before ligation; LEV-treated group: the animal received LEV before occlusion; combined group: the animals received both MSCs and LEV before occlusion. Hematoxylin and eosin staining was performed to study the histological structure of the brain. Real-time polymerase chain reaction (RT-PCR) was performed to assess gene expression.

RESULTS

Both MSCs and LEV improved memory and learning in the treated groups compared with I/R group. Significant reduction of the infarct size in WJ-MSC- or LEV-treated groups when compared with untreated ones was found. By RT-PCR, a significant decrease of the expression values of glial-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), phosphatidylethanolamine binding protein 1 (PEBP1), and copper-zinc SOD (Cu/ZnSOD) genes and a significant increase of pro-oxidant iNOS gene in the I/R rats compared with the sham group was detected. There was a significant increase in the expression values of GDNF, BDNF, PEBP1, and Cu/ZnSOD genes in both treated groups when compared with the I/R group. Rats treated with WJ-MSCs showed better results than rats treated with LEV. Finally, the combined use of LEV and WJ-MSCs was the most effective regimen as regard infarction volume and functional learning and memory tests.

CONCLUSION

In the brain ischemia model, combined WJ-MSCs and LEV have demonstrated striking protective effects in brain infarction by the modulation of the oxidant status and neuroprotective effect.

Effects of dietary supplementation with milk fat globule membrane on the physical performance of community-dwelling Japanese adults: a randomised, double-blind, placebo-controlled trial

We conducted a randomised, double-blind, placebo-controlled trial to elucidate the effects of dietary milk fat globule membrane (MFGM) on the physical performance of community-dwelling Japanese adults. For this 24-week study, 115 middle-aged subjects (range 50–70 years old) were invited, of whom 113 (seventy-two women, forty-one men) completed the trial. Participants were then divided into either the placebo control or MFGM group. Measurements of physical performance (without undertaking any mandatory exercise) examining muscle strength, agility and balance were tested every 6 weeks until 24 weeks. Analyses were performed using the intention-to-treat method for all participants. Although the effects of MFGM on muscle strength and agility were not significant, we noted that the parameter for balance (such as the ability to stand on one leg with eyes closed for longer durations) increased in the MFGM group (mean 10·1 (95 % CI 8·25, 12·4) s) compared with the placebo (mean 7·53 (95 % CI 6·11, 9·30) s) (P = 0·046). Similarly, application of the mixed-effect model for repeated measures under unstructured covariance also revealed that the effect of MFGM was significant when compared with the placebo (10·2 (95 % CI 8·33, 12·4) v. 7·61 (95 % CI 6·17, 9·30) s) (P = 0·045). In conclusion, we demonstrated that MFGM had an effect on the physical performance of community-dwelling Japanese adults despite mandatory exercise. However, studies using larger cohorts of individuals from different demographic backgrounds are required to further elucidate the mechanisms underlying these effects and to extend the application of MFGM.

Redox responses are preserved across muscle fibres with differential susceptibility to aging

Age-related loss of muscle mass and function is associated with increased frailty and loss of independence. The mechanisms underlying the susceptibility of different muscle types to age-related atrophy are not fully understood. Reactive oxygen species (ROS) are recognised as important signalling molecules in healthy muscle and redox sensitive proteins can respond to intracellular changes in ROS concentrations modifying reactive thiol groups on Cysteine (Cys) residues. Conserved Cys residues tend to occur in functionally important locations and can have a direct impact on protein function through modifications at the active site or determining protein conformation. The aim of this work was to determine age-related changes in the redox proteome of two metabolically distinct murine skeletal muscles, the quadriceps a predominantly glycolytic muscle and the soleus which contains a higher proportion of mitochondria. To examine the effects of aging on the global proteome and the oxidation state of individual redox sensitive Cys residues, we employed a label free proteomics approach including a differential labelling of reduced and reversibly oxidised Cys residues. Our results indicate the proteomic response to aging is dependent on muscle type but redox changes that occur primarily in metabolic and cytoskeletal proteins are generally preserved between metabolically distinct tissues.

BIOLOGICAL SIGNIFICANCE

Skeletal muscle containing fast twitch glycolytic fibres are more susceptible to age related atrophy compared to muscles with higher proportions of oxidative slow twitch fibres. Contracting skeletal muscle generates reactive oxygen species that are required for correct signalling and adaptation to exercise and it is also known that the intracellular redox environment changes with age. To identify potential mechanisms for the distinct response to age, this article combines a global proteomic approach and a differential labelling of reduced and reversibly oxidised Cysteine residues in two metabolically distinct skeletal muscles, quadriceps and soleus, from adult and old mice. Our results indicate that the global proteomic changes with age in skeletal muscles are dependent on fibre type. However, redox specific changes are preserved across muscle types and accompanied with a reduction in the number of redox sensitive Cysteine residues.

Redox Homeostasis in Age-Related Muscle Atrophy

Muscle atrophy and weakness, characterized by loss of lean muscle mass and function, has a significant effect on the independence and quality of life of older people. The cellular mechanisms that drive the age-related decline in neuromuscular integrity and function are multifactorial. Quiescent and contracting skeletal muscle can endogenously generate reactive oxygen and nitrogen species (RONS) from various cellular sites. Excessive RONS can potentially cause oxidative damage and disruption of cellular signaling pathways contributing to the initiation and progression of age-related muscle atrophy. Altered redox homeostasis and modulation of intracellular signal transduction processes have been proposed as an underlying mechanism of sarcopenia. This chapter summarizes the current evidence that has associated disrupted redox homeostasis and muscle atrophy as a result of skeletal muscle inactivity and aging.

Role of Oxidative Stress as Key Regulator of Muscle Wasting during Cachexia

Skeletal muscle atrophy is a pathological condition mainly characterized by a loss of muscular mass and the contractile capacity of the skeletal muscle as a consequence of muscular weakness and decreased force generation. Cachexia is defined as a pathological condition secondary to illness characterized by the progressive loss of muscle mass with or without loss of fat mass and with concomitant diminution of muscle strength. The molecular mechanisms involved in cachexia include oxidative stress, protein synthesis/degradation imbalance, autophagy deregulation, increased myonuclear apoptosis, and mitochondrial dysfunction. Oxidative stress is one of the most common mechanisms of cachexia caused by different factors. It results in increased ROS levels, increased oxidation-dependent protein modification, and decreased antioxidant system functions. In this review, we will describe the importance of oxidative stress in skeletal muscles, its sources, and how it can regulate protein synthesis/degradation imbalance, autophagy deregulation, increased myonuclear apoptosis, and mitochondrial dysfunction involved in cachexia.

Redox homeostasis and age-related deficits in neuromuscular integrity and function

Skeletal muscle is a major site of metabolic activity and is the most abundant tissue in the human body. Age-related muscle atrophy (sarcopenia) and weakness, characterized by progressive loss of lean muscle mass and function, is a major contributor to morbidity and has a profound effect on the quality of life of older people. With a continuously growing older population (estimated 2 billion of people aged >60 by 2050), demand for medical and social care due to functional deficits, associated with neuromuscular ageing, will inevitably increase. Despite the importance of this 'epidemic' problem, the primary biochemical and molecular mechanisms underlying age-related deficits in neuromuscular integrity and function have not been fully determined. Skeletal muscle generates reactive oxygen and nitrogen species (RONS) from a variety of subcellular sources, and age-associated oxidative damage has been suggested to be a major factor contributing to the initiation and progression of muscle atrophy inherent with ageing. RONS can modulate a variety of intracellular signal transduction processes, and disruption of these events over time due to altered redox control has been proposed as an underlying mechanism of ageing. The role of oxidants in ageing has been extensively examined in different model organisms that have undergone genetic manipulations with inconsistent findings. Transgenic and knockout rodent studies have provided insight into the function of RONS regulatory systems in neuromuscular ageing. This review summarizes almost 30 years of research in the field of redox homeostasis and muscle ageing, providing a detailed discussion of the experimental approaches that have been undertaken in murine models to examine the role of redox regulation in age-related muscle atrophy and weakness.