Promotion of oxidative stress is associated with mitochondrial dysfunction and muscle atrophy in aging mice

Better maintenance of enzymatic capacity and higher levels of substrate transporter proteins in skeletal muscle of aging female mice

This study investigated sex-specific differences in high-energy phosphate, glycolytic, and mitochondrial enzyme activities and also metabolite transporter protein levels in the skeletal muscles of adult (5 months old), middle-aged (12 months old), and advanced-aged (24 months old) mice. While gastrocnemius glycogen content increased with age regardless of sex, gastrocnemius triglyceride levels increased only in advanced-aged female mice. Aging decreased creatine kinase and adenylate kinase activities in the plantaris muscle of both sexes and in the soleus muscle of male mice but not in female mice. Irrespective of sex, phosphofructokinase and lactate dehydrogenase (LDH) activities decreased in the plantaris and soleus muscles. Additionally, hexokinase activity in the plantaris muscle and LDH activity in the soleus muscle decreased to a greater extent in aged male mice compared with those in aged female mice. Mitochondrial enzyme activities increased in the plantaris muscle of aged female mice but did not change in male mice. The protein content of the glucose transporter 4 in the aged plantaris muscle and fatty acid translocase/cluster of differentiation 36 increased in the aged plantaris and soleus muscles of both sexes, with a significantly higher content in female mice. These findings suggest that females possess a better ability to maintain metabolic enzyme activity and higher levels of metabolite transport proteins in skeletal muscle during aging, despite alterations in lipid metabolism. Our data provide a basis for studying muscle metabolism in the context of age-dependent metabolic perturbations and diseases that affect females and males differently.

Physical Activity and Oxidative Stress in Aging

Biological aging, characterized by changes in metabolism and physicochemical properties of cells, has an impact on public health. Environment and lifestyle, including factors like diet and physical activity, seem to play a key role in healthy aging. Several studies have shown that regular physical activity can enhance antioxidant defense mechanisms, including the activity of enzymes such as superoxide dismutase (SOD), catalase, and glutathione peroxidase. However, intense or prolonged exercise can also lead to an increase in reactive oxygen species (ROS) production temporarily, resulting in oxidative stress. This phenomenon is referred to as "exercise-induced oxidative stress". The relationship between physical activity and oxidative stress in aging is complex and depends on various factors such as the type, intensity, duration, and frequency of exercise, as well as individual differences in antioxidant capacity and adaptation to exercise. In this review, we analyzed what is reported by several authors regarding the role of physical activity on oxidative stress in the aging process as well as the role of hormesis and physical exercise as tools for the prevention and treatment of sarcopenia, an aging-related disease. Finally, we reported what has recently been studied in relation to the effect of physical activity and sport on aging in women.

Early onset age increases the risk of musculoskeletal damage in patients with type 2 diabetes

Introduction

It's not clear whether there are differences in musculoskeletal damage and body composition among different age groups of type 2 diabetes. Therefore, the purpose of this study is to analyze the difference between early-onset type 2 diabetes (EOT2D) and non-early-onset type 2 diabetes (NOT2D) in musculoskeletal damage.

Methods

A total of 964 patients with type 2 diabetes mellitus were selected by 1:1 propensity score matching, including 534 males and 430 females, with an average age of 52 ± 7 years and an average course of 10 ± 8.5 years. Bone mineral density and body composition were measured, and combined with biochemical tests, linear regression and binary logic regression were used to analyze the relationship between EOT2D, NOT2D and musculoskeletal damage. In addition, 414 patients with T2DM were selected according to whether they were hospitalized twice or not, and the median follow-up period was 44 months. COX survival analysis further elucidates the relationship between EOT2D, NOT2D and musculoskeletal damage.

Results

Compared with patients with non-early-onset type 2 diabetes, A/G was negatively correlated with the age of onset, and had statistical significance. EOT2D has a higher risk of sarcopenia, osteoporosis and even musculoskeletal damage. With the prolongation of the course of the disease, the risk of muscle mass and/or bone mineral density decrease in EOT2D increases.

Conclusion

EOT2D brings a greater risk of sarcopenia and/or osteoporosis, as well as a higher risk of reduced ASM and BMD. In addition, fat distribution may be more central.

Zebrafish as an Emerging Model for Sarcopenia: Considerations, Current Insights, and Future Directions

Sarcopenia poses a significant challenge to public health and can severely impact the quality of life of aging populations. Despite extensive efforts to study muscle degeneration using traditional animal models, there is still a lack of effective diagnostic tools, precise biomarkers, and treatments for sarcopenia. Zebrafish models have emerged as powerful tools in biomedical research, providing unique insights into age-related muscle disorders like sarcopenia. The advantages of using zebrafish models include their rapid growth outside of the embryo, optical transparency during early developmental stages, high reproductive potential, ease of husbandry, compact size, and genetic tractability. By deepening our understanding of the molecular processes underlying sarcopenia, we may develop novel diagnostic tools and effective treatments that can improve the lives of aging individuals affected by this condition. This review aims to explore the unique advantages of zebrafish as a model for sarcopenia research, highlight recent breakthroughs, outline potential avenues for future investigations, and emphasize the distinctive contributions that zebrafish models offer. Our research endeavors to contribute significantly to address the urgent need for practical solutions to reduce the impact of sarcopenia on aging populations, ultimately striving to enhance the quality of life for individuals affected by this condition.

Role of Fyn and the interleukin-6-STAT-3-autophagy axis in sarcopenia

Sarcopenia is the progressive loss of muscle mass wherein Fyn regulates STAT3 to decrease autophagy. To elucidate the role of inflammation in Fyn-STAT3-dependent autophagy and sarcopenia, here we aimed to investigate the underlying mechanisms using two mouse models of primary and secondary sarcopenia: (1) tail suspension and (2) sciatic denervation. In wild-type mice, the expression of Fyn and IL-6 increased significantly. The expression and phosphorylation levels of STAT3 were also significantly augmented, while autophagic activity was abolished. To investigate Fyn-dependency, we used tail suspension with Fyn-null mice. In tail-suspended wild-type mice, IL-6 expression was increased; however, it was abolished in Fyn-null mice, which maintained autophagy and the expression and ablation of STAT3 phosphorylation. In conclusion, Fyn was found to be associated with the IL-6-STAT3-autophagy axis in sarcopenia. This finding permits a better understanding of sarcopenia-associated metabolic diseases and the possible development of therapeutic interventions.

Accumulation of polyunsaturated fatty acid-derived metabolites in the sarcopenic muscle of aging mice

AIM

Although it is known that advanced age alters skeletal muscle lipid metabolism, the role(s) of polyunsaturated fatty acid-derived metabolites (mostly eicosanoids and docosanoids) in sarcopenia are not clear. We therefore examined the changes in the metabolites of arachidonic acid, eicosapentaenoic acid and docosahexaenoic acid in the sarcopenic muscle of aged mice.

METHODS

We used 6- and 24-month-old male C57BL/6J mice as healthy and sarcopenic muscle models, respectively. Skeletal muscles were removed from the lower limb and subjected to a liquid chromatography-tandem mass spectrometry analysis.

RESULTS

The liquid chromatography-tandem mass spectrometry analysis detected distinct changes of metabolites in the muscles of the aged mice. Of the 63 metabolites identified, nine were significantly higher in the sarcopenic muscle of aged mice compared with the healthy muscle of young mice. In particular, prostaglandin E₂ , prostaglandin F_2a , thromboxane B₂ , 5-hydroxyeicosatetraenoic acid, and 15-oxo-eicosatetraenoic acid (arachidonic acid-derived metabolites), 12-hydroxy-eicosapentaenoic acid and 14,15-epoxy-eicosatetraenoic acid (eicosapentaenoic acid-derived metabolites) and 10-hydroxydocosa-hexaenoic acid and 14-hydroxyoctadeca-pentaenoic acid (docosahexaenoic acid-derived metabolites) were significantly higher in aged tissue compared with young tissue (all P < 0.05).

CONCLUSIONS

We observed the accumulation of metabolites in the sarcopenic muscle of aged mice. Our results may provide new insights into the pathogenesis and progression of aging- or disease-related sarcopenia. Geriatr Gerontol Int ••; ••: ••-•• Geriatr Gerontol Int 2023; ••: ••-••.

Aging, Physical Exercise, Telomeres, and Sarcopenia: A Narrative Review

Human aging is a gradual and adaptive process characterized by a decrease in the homeostatic response, leading to biochemical and molecular changes that are driven by hallmarks of aging, such as oxidative stress (OxS), chronic inflammation, and telomere shortening. One of the diseases associated with the hallmarks of aging, which has a great impact on functionality and quality of life, is sarcopenia. However, the relationship between telomere length, sarcopenia, and age-related mortality has not been extensively studied. Moderate physical exercise has been shown to have a positive effect on sarcopenia, decreasing OxS and inflammation, and inducing protective effects on telomeric DNA. This results in decreased DNA strand breaks, reduced OxS and IA, and activation of repair pathways. Higher levels of physical activity are associated with an apparent increase in telomere length. This review aims to present the current state of the art of knowledge on the effect of physical exercise on telomeric maintenance and activation of repair mechanisms in sarcopenia.

Branched-Chain Amino Acids and Di-Alanine Supplementation in Aged Mice: A Translational Study on Sarcopenia

In age-related sarcopenia, the gradual loss of skeletal muscle mass, function and strength is underpinned by an imbalanced rate of protein synthesis/breakdown. Hence, an adequate protein intake is considered a valuable strategy to mitigate sarcopenia. Here, we investigated the effects of a 12-week oral supplementation with branched-chain amino acids (BCAAs: leucine, isoleucine, and valine) with recognized anabolic properties, in 17-month-old (AGED) C57BL/6J male mice. BCAAs (2:1:1) were formulated in drinking water, alone or plus two L-Alanine equivalents (2ALA) or dipeptide L-Alanyl-L-Alanine (Di-ALA) to boost BCAAs bioavailability. Outcomes were evaluated on in/ex vivo readouts vs. 6-month-old (ADULT) mice. In vivo hind limb plantar flexor torque was improved in AGED mice treated with BCAAs + Di-ALA or 2ALA (recovery score, R.S., towards ADULT: ≥20%), and all mixtures significantly increased hind limb volume. Ex vivo, myofiber cross-sectional areas were higher in gastrocnemius (GC) and soleus (SOL) muscles from treated mice (R.S. ≥ 69%). Contractile indices of isolated muscles were improved by the mixtures, especially in SOL muscle (R.S. ≥ 20%). The latter displayed higher mTOR protein levels in mice supplemented with 2ALA/Di-ALA-enriched mixtures (R.S. ≥ 65%). Overall, these findings support the usefulness of BCAAs-based supplements in sarcopenia, particularly as innovative formulations potentiating BCAAs bioavailability and effects.

Serum Concentrations of Losartan Metabolites Correlate With Improved Physical Function in a Pilot Study of Prefrail Older Adults

Losartan is an oral antihypertensive agent that is rapidly metabolized to EXP3174 (angiotensin-subtype-1-receptor blocker) and EXP3179 (peroxisome proliferator-activated receptor gamma [PPARγ] agonist), which was shown in animal studies to reduce inflammation, enhance mitochondrial energetics, and improve muscle repair and physical performance. We conducted an exploratory pilot study evaluating losartan treatment in prefrail older adults (age 70-90 years, N = 25). Participants were randomized to control (placebo) or treatment (daily oral losartan beginning at 25 mg per day and increasing every 8 weeks) for a total of 6 months. Fatigue, hyperkalemia, and hypotension were the most observed side effects of losartan treatment. Participants in the losartan group had an estimated 89% lower odds of frailty (95% confidence interval [CI]: 18% to 99% lower odds, p = .03), with a 0.3-point lower frailty score than the placebo group (95% CI: 0.01-0.5 lower odds, p = .04). Frailty score was also negatively associated with serum losartan and EXP3179 concentrations. For every one standard deviation increase in EXP3179 (ie, 0.0011 ng/μL, based on sample values above detection limit) and EXP3174 (ie, 0.27 ng/μL, based on sample values above detection limit), there was a 0.0035 N (95% CI: 0.0019-0.0051, p < .001) and a 0.0027 N (95% CI: 0.00054-0.0043, p = .007) increase in average knee strength, respectively.

Exercise and mitochondrial mechanisms in patients with sarcopenia

Sarcopenia is a severe loss of muscle mass and functional decline during aging that can lead to reduced quality of life, limited patient independence, and increased risk of falls. The causes of sarcopenia include inactivity, oxidant production, reduction of antioxidant defense, disruption of mitochondrial activity, disruption of mitophagy, and change in mitochondrial biogenesis. There is evidence that mitochondrial dysfunction is an important cause of sarcopenia. Oxidative stress and reduction of antioxidant defenses in mitochondria form a vicious cycle that leads to the intensification of mitochondrial separation, suppression of mitochondrial fusion/fission, inhibition of electron transport chain, reduction of ATP production, an increase of mitochondrial DNA damage, and mitochondrial biogenesis disorder. On the other hand, exercise adds to the healthy mitochondrial network by increasing markers of mitochondrial fusion and fission, and transforms defective mitochondria into efficient mitochondria. Sarcopenia also leads to a decrease in mitochondrial dynamics, mitophagy markers, and mitochondrial network efficiency by increasing the level of ROS and apoptosis. In contrast, exercise increases mitochondrial biogenesis by activating genes affected by PGC1-ɑ (such as CaMK, AMPK, MAPKs) and altering cellular calcium, ATP-AMP ratio, and cellular stress. Activation of PGC1-ɑ also regulates transcription factors (such as TFAM, MEFs, and NRFs) and leads to the formation of new mitochondrial networks. Hence, moderate-intensity exercise can be used as a non-invasive treatment for sarcopenia by activating pathways that regulate the mitochondrial network in skeletal muscle.

Lipid metabolism in sarcopenia

Sarcopenia is an age-related disease associated with loss of muscle mass and strength. This geriatric syndrome predisposes elderly individuals to a disability, falls, fractures, and death. Fat infiltration in muscle is one of the hallmarks of sarcopenia and aging. Alterations in fatty acid (FA) metabolism are evident in aging, type 2 diabetes, and obesity, with the accumulation of lipids inside muscle cells contributing to muscle insulin resistance and ceramide accumulation. These lipids include diacylglycerol, lipid droplets, intramyocellular lipids, intramuscular triglycerides, and polyunsaturated fatty acids (PUFAs). In this review, we examine the regulation of lipid metabolism in skeletal muscle, including lipid metabolization and storage, intervention, and the types of lipases expressed in skeletal muscle responsible for the breakdown of adipose triglyceride fats. In addition, we address the role of FAs in sarcopenia and the potential benefits of PUFAs.

The non-modifiable factors age, gender, and genetics influence resistance exercise

Muscle mass and force are key for movement, life quality, and health. It is well established that resistance exercise is a potent anabolic stimulus increasing muscle mass and force. The response of a physiological system to resistance exercise is composed of non-modifiable (i.e., age, gender, genetics) and modifiable factors (i.e., exercise, nutrition, training status, etc.). Both factors are integrated by systemic responses (i.e., molecular signaling, genetic responses, protein metabolism, etc.), consequently resulting in functional and physiological adaptations. Herein, we discuss the influence of non-modifiable factors on resistance exercise: age, gender, and genetics. A solid understanding of the role of non-modifiable factors might help to adjust training regimes towards optimal muscle mass maintenance and health.

Effect of Physical Activity/Exercise on Oxidative Stress and Inflammation in Muscle and Vascular Aging

Functional status is considered the main determinant of healthy aging. Impairment in skeletal muscle and the cardiovascular system, two interrelated systems, results in compromised functional status in aging. Increased oxidative stress and inflammation in older subjects constitute the background for skeletal muscle and cardiovascular system alterations. Aged skeletal muscle mass and strength impairment is related to anabolic resistance, mitochondrial dysfunction, increased oxidative stress and inflammation as well as a reduced antioxidant response and myokine profile. Arterial stiffness and endothelial function stand out as the main cardiovascular alterations related to aging, where increased systemic and vascular oxidative stress and inflammation play a key role. Physical activity and exercise training arise as modifiable determinants of functional outcomes in older persons. Exercise enhances antioxidant response, decreases age-related oxidative stress and pro-inflammatory signals, and promotes the activation of anabolic and mitochondrial biogenesis pathways in skeletal muscle. Additionally, exercise improves endothelial function and arterial stiffness by reducing inflammatory and oxidative damage signaling in vascular tissue together with an increase in antioxidant enzymes and nitric oxide availability, globally promoting functional performance and healthy aging. This review focuses on the role of oxidative stress and inflammation in aged musculoskeletal and vascular systems and how physical activity/exercise influences functional status in the elderly.

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.

Pathogenesis of sarcopenia and the relationship with fat mass: descriptive review

Age-associated obesity and muscle atrophy (sarcopenia) are intimately connected and are reciprocally regulated by adipose tissue and skeletal muscle dysfunction. During ageing, adipose inflammation leads to the redistribution of fat to the intra-abdominal area (visceral fat) and fatty infiltrations in skeletal muscles, resulting in decreased overall strength and functionality. Lipids and their derivatives accumulate both within and between muscle cells, inducing mitochondrial dysfunction, disturbing β-oxidation of fatty acids, and enhancing reactive oxygen species (ROS) production, leading to lipotoxicity and insulin resistance, as well as enhanced secretion of some pro-inflammatory cytokines. In turn, these muscle-secreted cytokines may exacerbate adipose tissue atrophy, support chronic low-grade inflammation, and establish a vicious cycle of local hyperlipidaemia, insulin resistance, and inflammation that spreads systemically, thus promoting the development of sarcopenic obesity (SO). We call this the metabaging cycle. Patients with SO show an increased risk of systemic insulin resistance, systemic inflammation, associated chronic diseases, and the subsequent progression to full-blown sarcopenia and even cachexia. Meanwhile in many cardiometabolic diseases, the ostensibly protective effect of obesity in extremely elderly subjects, also known as the 'obesity paradox', could possibly be explained by our theory that many elderly subjects with normal body mass index might actually harbour SO to various degrees, before it progresses to full-blown severe sarcopenia. Our review outlines current knowledge concerning the possible chain of causation between sarcopenia and obesity, proposes a solution to the obesity paradox, and the role of fat mass in ageing.

The neuroprotective effects of intermittent fasting on brain aging and neurodegenerative diseases via regulating mitochondrial function

Intermittent fasting (IF) has been studied for its effects on lifespan and the prevention or delay of age-related diseases upon the regulation of metabolic pathways. Mitochondria participate in key metabolic pathways and play important roles in maintaining intracellular signaling networks that modulate various cellular functions. Mitochondrial dysfunction has been described as an early feature of brain aging and neurodegeneration. Although IF has been shown to prevent brain aging and neurodegeneration, the mechanism is still unclear. This review focuses on the mechanisms by which IF improves mitochondrial function, which plays a central role in brain aging and neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and Huntington's disease. The cellular and molecular mechanisms of IF in brain aging and neurodegeneration involve activation of adaptive cellular stress responses and signaling- and transcriptional pathways, thereby enhancing mitochondrial function, by promoting energy metabolism and reducing oxidant production.

Modeling Functional Limitations, Gait Impairments, and Muscle Pathology in Alzheimer's Disease: Studies in the 3xTg-AD Mice

Gait impairments in Alzheimer's disease (AD) result from structural and functional deficiencies that generate limitations in the performance of activities and restrictions in individual's biopsychosocial participation. In a translational way, we have used the conceptual framework proposed by the International Classification of Disability and Health Functioning (ICF) to classify and describe the functioning and disability on gait and exploratory activity in the 3xTg-AD animal model. We developed a behavioral observation method that allows us to differentiate qualitative parameters of psychomotor performance in animals' gait, similar to the behavioral patterns observed in humans. The functional psychomotor evaluation allows measuring various dimensions of gait and exploratory activity at different stages of disease progression in dichotomy with aging. We included male 3xTg-AD mice and their non-transgenic counterpart (NTg) of 6, 12, and 16 months of age (n = 45). Here, we present the preliminary results. The 3xTg-AD mice show more significant functional impairment in gait and exploratory activity quantitative variables. The presence of movement limitations and muscle weakness mark the functional decline related to the disease severity stages that intensify with increasing age. Motor performance in 3xTg-AD is accompanied by a series of bizarre behaviors that interfere with the trajectory, which allows us to infer poor neurological control. Additionally, signs of physical frailty accompany the functional deterioration of these animals. The use of the ICF as a conceptual framework allows the functional status to be described, facilitating its interpretation and application in the rehabilitation of people with AD.

AUF1 gene transfer increases exercise performance and improves skeletal muscle deficit in adult mice

Muscle function and mass begin declining in adults long before evidence of sarcopenia and include reduced mitochondrial function, although much remains to be characterized. We found that mRNA decay factor AU-rich mRNA binding factor 1 (AUF1), which stimulates myogenesis, is strongly reduced in skeletal muscle of adult and older mice in the absence of evidence of sarcopenia. Muscle-specific adeno-associated virus (AAV)8-AUF1 gene therapy increased expression of AUF1, muscle function, and mass. AAV8 AUF1 muscle gene transfer in 12-month-old mice increased the levels of activated muscle stem (satellite) cells, increased muscle mass, reduced markers of muscle atrophy, increased markers of mitochondrial content and muscle fiber oxidative capacity, and enhanced exercise performance to levels of 3-month-old mice. With wild-type and AUF1 knockout mice and cultured myoblasts, AUF1 supplementation of muscle fibers was found to increase expression of Peroxisome Proliferator-activated Receptor Gamma Co-activator 1-alpha (PGC1α), a major effector of skeletal muscle mitochondrial oxidative metabolism. AUF1 stabilized and increased translation of the pgc1α mRNA, which is strongly reduced in adult muscle in the absence of AUF1 supplementation. Skeletal muscle-specific gene transfer of AUF1 therefore restores muscle mass, increases exercise endurance, and may provide a therapeutic strategy for age-related muscle loss.

Chemical profiling of Houttuynia cordata Thunb. by UPLC-Q-TOF-MS and analysis of its antioxidant activity in C2C12 cells

Houttuynia cordata Thunb. ("Yu-Xing-Cao"), a traditional Chinese medicinal herb, has long been used to treat various diseases. However, detailed information regarding the chemical constituents of H. cordata aqueous extract is lacking, and the molecular basis of its beneficial effects on muscle is unknown. To investigate these points, in this study, we used ultra-performance liquid chromatography coupled with quadrupole-time-of-flight-mass spectrometry (UPLC-Q-TOF-MS) in positive and negative ion modes to profile and identify the major constituents of H. cordata water extract. A total of 63 peaks were identified based on mass and fragmentation characteristics, including 29 organic acids and their glycosides, 17 flavonoids, 7 volatiles, 4 pyrimidine and purine derivatives, 2 alkaloids, 2 amino acids, 1 isovanillin, and 1 coumarin. The total flavonoid and polyphenol contents of the extract were 4.77 and 139.15 mg/mL, respectively, by ultraviolet spectrophotometry. The cytoprotective activity of H. cordata aqueous extract was evaluated using C2C12 cells treated with tumor necrosis factor (TNF)-α to induce oxidative challenge. The TNF-α induced decrease in cell viability was reversed by treatment for 48 h with the extract; moreover, superoxide dismutase activity was increased while reactive oxygen species level was decreased. These results provide molecular-level evidence for the antioxidant effect of H. cordata extract and highlight its therapeutic potential for the treatment of muscle injury or diseases caused by oxidative stress.

Effects of Rehmannia glutinosa polysaccharides on bone tissue structure and skeletal muscle atrophy in rats with disuse

PURPOSE

To study effects of Rehmannia glutinosa polysaccharides (RGP) on bone tissue structure and skeletal muscle atrophy in rats with disuse.

METHODS

A rat model of disuse osteoporosis combined with muscle atrophy was established by removing the bilateral ovaries of rats and fixing their hind limbs for a long time. Forty SD rats were administered intragastrically for 12 weeks. The bone histomorphometry parameters and the level of oxidative stress were measured. In addition, the changes of muscle atrophy F-box (MAFbx), muscle RING-finger protein-1 (MuRF1), forkhead box O1 (FOXO1) mRNA expression in skeletal muscle of rats were observed.

RESULTS

RGP significantly increased the percentage of fluorescence perimeter and bone mineralization deposition rate of the second lumbar vertebrae of rats. It also significantly increased the wet weight ratio and muscle fiber cross-sectional area of the gastrocnemius muscle of rats. At the same time, RGP significantly increased the levels of super oxide dismutase (SOD) and catalase (CAT) in the skeletal muscle of rats, and reduced the content of malondialdehyde (MDA). Rehmannia glutinosa polysaccharides also significantly reduced the expression levels of FOXO1, MAFbx and MuRF1 mRNA in rat skeletal muscle.

CONCLUSIONS

RGP could improve the bone structure of osteoporotic rats. It could also improve muscle that atrophy may be related to the inhibition of FOXO1-mediated ubiquitin-proteasome pathway.

Beta 2 microglobulin correlates with oxidative stress in elderly

Beta 2 microglobulin (Β2M) is expressed in all nucleated cells, it interplays with mediators to regulate and modulate cellular functions. Its role in aging associated disorders has been documented recently. Oxidative stress has been known to play a direct implication on these disorders. Therefore, there is a rationality to explore the function of Β2M in oxidative stress in elderly people. The aim of the study was to assess the Β2M levels in different group of age, and to study the correlation between Β2M and oxidative stress. Actually, the serum levels of Β2M increased significantly in old people comparing to youngers. In addition, there was a positive correlation between Β2M levels and the age of participants (p < 0.001). In addition, there was a positive correlation between Β2M levels and Malondialdehyde (MDA) (p < 0.001), which underscored the possible role of Β2M in oxidative stress. To confirm the previous result, the correlation between total antioxidant capacity (TAC) and Β2M was assessed. There was a negative correlation between them (p < 0.001). These results suggested a possible role of Β2M in oxidative stress status in elderly people; in addition, it suggested the ability of using Β2M as a novel biomarker for oxidative stress. However, further work should be conducted to explore the exact role of Β2M in oxidative stress, and to include large sample size to confirm the results before translating the findings to clinic.

Mechanism of thyroid hormone signaling in skeletal muscle of aging mice

BACKGROUND AND AIM

Skeletal muscle (SM) has been shown as a target of thyroid hormones (THs). However, the status of TH signaling in aged SM remains unclear. This study aimed to explore the mechanism of TH signaling in SM of aging mice.

METHODS

Thirty C57BL/6J male mice were divided into 6-, 15- and 22-month (6, 15 and 22M) groups according to different age. Physical parameters were evaluated by analytical balance, grip strength test and histological analysis. Thyroid function was detected by enzyme-linked immunosorbent assay. TH signaling was compared among the three groups by real-time PCR and western blotting analysis.

RESULTS

p16, p21, and p53 mRNA levels in SM increased in age-dependent manner. The muscle weight and strength decreased in 22M group compared to 6 and 15M groups. Concentrations of thyroid hormones, including free triiodothyronine (FT3), free thyroxine (FT4) and thyroid-stimulating hormone (TSH) in 22 M mice were not shown significant difference compared to 6M or 15M mice, although FT3 showed slightly decrease and TSH appeared a mild increase accompanying with age. mRNA levels of TH transporters, including MCT8 and MCT10, as well as iodothyronine deiodinase type 2 (DIO2) and type 3 (DIO3), were higher in 22M, while TH receptor α (TRα) mRNA and protein expression was lower in 22M, compared to the other groups. Type-I myosin heavy chain (MyHC I), MyHC IIx, and MyHC IIa were upregulated and Type-IIb MyHC (MyHC IIb) was downregulated in SM with advancing age.

CONCLUSIONS

TH signaling in SM changes with aging.

Imaging of muscle activity-induced morphometric changes in fibril network of myofascia by two-photon microscopy

Myofascia, deep fascia enveloping skeletal muscles, consists of abundant collagen and elastin fibres that play a key role in the transmission of muscular forces. However, understanding of biomechanical dynamics in myofascia remains very limited due to less quantitative and relevant approaches for in vivo examination. The purpose of this study was to evaluate the myofascial fibril structure by means of a quantitative approach using two-photon microscopy (TPM) imaging in combination with intravital staining of Evans blue dye (EBD), a far-red fluorescence dye, which potentially labels elastin. With focus on myofascia of the tibial anterior (TA) muscle, the fibril structure intravitally stained with EBD was observed at the depth level of collagen fibrous membrane above the muscle belly. The EBD-labelled fibril structure and orientation in myofascia indicated biomechanical responses to muscle activity and ageing. The orientation histograms of EBD-labelled fibrils were significantly modified depending upon the intensity of muscle activity and ageing. Moreover, the density of EBD-labelled fibrils in myofascia decreased with habitual exercise but increased with muscle immobilization or ageing. In particular, the diameter of EBD-labelled fibrils in aged mice was significantly higher. The orientation histograms of EBD-labelled fibrils after habitual exercise, muscle immobilization and ageing showed significant differences compared to control. Indeed, the histograms in bilateral TA myofascia of exercise mice made simple waveforms without multiple sharp peaks, whilst muscular immobilization or ageing significantly shifted a histogram with sustaining multiple sharp peaks. Therefore, the dynamics of fibre network with EBD fluorescence in response to the biomechanical environment possibly indicate functional tissue adaptation in myofascia. Furthermore, on the basis of the knowledge that neutrophil recruitment occurs locally in working muscles, we suggested the unique reconstruction mechanism involving neutrophilic elastase in the myofascial fibril structure. In addition to the elastolytic susceptibility of EBD-labelled fibrils, distinct immunoreactivities and activities of neutrophil elastase in the myofascia were observed after electric pulse stimulation-induced muscle contraction for 15 min. Our findings of EBD-labelled fibril dynamics in myofascia through quantitative approach using TPM imaging and intravital fluorescence labelling potentially brings new insights to examine muscle physiology and pathology.

Antioxidant Apigenin Relieves Age-Related Muscle Atrophy by Inhibiting Oxidative Stress and Hyperactive Mitophagy and Apoptosis in Skeletal Muscle of Mice

Skeletal muscle atrophy in the aged causes loss in muscle mass and functions. Naturally occurring antioxidant flavonoid apigenin is able to ameliorate obesity- and denervation-induced muscle atrophies, but its effects on age-related muscle atrophy remain unknown. We hypothesized that apigenin can relieve muscle atrophy in aged mice, probably through special effects on reactive oxygen species and enzymes with antioxidant functions. For the male mice of the study, apigenin showed significant dose-dependent effects in relieving aging-related muscle atrophy according to results of frailty index as indicator of frailty associated with aging, grip strength, and running distance. Apigenin also improved myofiber size and morphological features and increased mitochondria number and volume, as manifested by succinate dehydrogenase staining and transmission electron microscopy. Our tests also suggested that apigenin promoted activities of enzymes such as superoxide dismutase and glutathione peroxidase for antioxidation and those for aerobic respiration such as mitochondrial respiratory enzyme complexes I, II, and IV, increased ATP, and enhanced expression of genes such as peroxisome proliferator-activated receptor-γ coactivator 1α, mitochondrial transcription factor A, nuclear respiratory factor-1, and ATP5B involved in mitochondrial biogenesis. The data also suggested that apigenin inhibited Bcl-2/adenovirus E1B 19kD-interacting protein 3 and DNA fragmentation as indicators of mitophagy and apoptosis in aged mice with skeletal muscle atrophy. Together, the results suggest that apigenin relieves age-related skeletal muscle atrophy through reducing oxidative stress and inhibiting hyperactive autophagy and apoptosis.

Effect of endurance exercise duration on muscle hypertrophy induced by functional overload

For many ball games, both resistance and endurance training are necessary to improve muscle strength and endurance capacity. Endurance training has been reported to inhibit muscle strength and hypertrophy, but some studies have reported that endurance exercise (EE) does not inhibit the effects of resistance exercise. Here, we examined the effect of short‐ or long‐duration EE on mouse skeletal muscle hypertrophy induced by functional overload (OL) at the molecular level. Plantaris muscle hypertrophy was induced by OL with synergist ablation in mice. Body mass was reduced with endurance training, but EE duration (30 or 90 min) had no effect. The ratio of plantaris muscle weight to body weight was higher in the OL and EE for 30 min (OL+EE30) and OL and EE for 90 min (OL+EE90) groups compared with the OL group. Expression of mechanistic target of rapamycin signaling proteins, which is related to protein synthesis and hypertrophy, was increased in the OL+EE30 group. Expression of Forkhead box‐containing protein O1, which is related to protein breakdown and atrophy, remained unchanged. However, microtubule‐associated protein 1 light chain 3, a known marker of autophagy, and MAFbx, which is related to protein breakdown, were significantly increased in the OL+EE90 group. Furthermore, markers of oxidative stress, ubiquitin and 4‐hydroxynonenal were also significantly increased in the OL+EE90 group compared with other groups. In conclusion, EE duration did not affect body mass and plantaris mass and did not interfere with mechanistic target of rapamycin signaling, but it did increase ubiquitinated proteins and oxidative stress. It is therefore necessary to consider training durations for EE when combining endurance and resistance training.

Voice perturbations under the stress overload in young individuals: phenotyping and suboptimal health as predictors for cascading pathologies

Verbal communication is one of the most sophisticated human motor skills reflecting both-the mental and physical health of an individual. Voice parameters and quality changes are usually secondary towards functional and/or structural laryngological alterations under specific systemic processes, syndrome and pathologies. These include but are not restricted to dry mouth and Sicca syndromes, body dehydration, hormonal alterations linked to pubertal, menopausal, and andropausal status, respiratory disorders, gastrointestinal reflux, autoimmune diseases, endocrinologic disorders, underweight versus overweight and obesity, and diabetes mellitus. On the other hand, it is well-established that stress overload is a significant risk factor of cascading pathologies, including but not restricted to neurodegenerative and psychiatric disorders, diabetes mellitus, cardiovascular disease, stroke, and cancers. Our current study revealed voice perturbations under the stress overload as a potentially useful biomarker to identify individuals in suboptimal health conditions who might be strongly predisposed to associated pathologies. Contextually, extended surveys applied in the population might be useful to identify, for example, persons at high risk for respiratory complications under pandemic conditions such as COVID-19. Symptoms of dry mouth syndrome, disturbed microcirculation, altered sense regulation, shifted circadian rhythm, and low BMI were positively associated with voice perturbations under the stress overload. Their functional interrelationships and relevance for cascading associated pathologies are presented in the article. Automated analysis of voice recordings via artificial intelligence (AI) has a potential to derive digital biomarkers. Further, predictive machine learning models should be developed that allows for detecting a suboptimal health condition based on voice recordings, ideally in an automated manner using derived digital biomarkers. Follow-up stratification and monitoring of individuals in suboptimal health conditions are recommended using disease-specific cell-free nucleic acids (ccfDNA, ctDNA, mtDNA, miRNA) combined with metabolic patterns detected in body fluids. Application of the cost-effective targeted prevention within the phase of reversible health damage is recommended based on the individualised patient profiling.

A novel PAI-1 inhibitor prevents ageing-related muscle fiber atrophy

Sarcopenia is among the most common medical problems of the aging population worldwide and a major social concern. Here, we explored the therapeutic potential of TM5484, a novel orally available PAI-1 inhibitor, to prevent sarcopenia. The sarcopenic phenotypes of the calf muscle of 12- and 6-month-old middle-aged mice were compared. Although significant decline of isometric gastrocnemius muscle force was detected in the older untreated mice, those administered TM5484 had significantly greater calf muscle force, as determined using isometric measurements by electrical stimulation. Histological analysis indicated that cross-sectional gastrocnemius muscle fibers in untreated older mice were thinner than those in younger mice; however, TM5484-treated group showed thicker fibers than younger mice. Treatment with TM5484 for 6 months enhanced Igf1, Atrogin-1, Mt-Co1, and Chrna1 mRNA expression in the mice gastrocnemius muscle, with increased serum IGF-1 concentration. TM5484 induced dose-dependent Igf1, Atrogin-1, and Chrna1 expression in C2C12 myoblastic cells, confirming cell autonomous effect. Further, the presence of plasmin for 72 h caused significantly increased Igf1 expression in C2C12 cells. These findings suggest that oral PAI-1 inhibitors represent a promising therapeutic candidate for preventing sarcopenia progression in humans.

Association of advanced glycation end products with sarcopenia and frailty in chronic kidney disease

Prevalence of sarcopenia is high in patients with chronic kidney disease (CKD), especially in those with dialysis. Various pathological conditions related to CKD, such as chronic inflammation, insulin resistance, and endothelial dysfunction, are thought to be associated with the development and progression of sarcopenia. Advanced glycation end products (AGE), one of the representative uremic toxins, have been shown to contribute to various CKD-associated complications. This study investigated the role of AGE in frailty and sarcopenia in patients and animals with CKD, respectively. In patients undergoing dialysis, serum AGE levels were significantly increased according to the frailty status and inversely associated with physical performance and activity. AGE accumulated in the gastrocnemius muscle of 5/6 nephrectomy mice in association with morphological abnormalities, capillary rarefaction, and mitochondrial dysfunction, all of which were completely inhibited by DNA-aptamer raised against AGE. Our present findings may suggest the pathological role of AGE in sarcopenia and frailty in CKD.

A subset of microRNAs in the Dlk1-Dio3 cluster regulates age-associated muscle atrophy by targeting Atrogin-1

BACKGROUND

The microRNAs (miRNAs) down-regulated in aged mouse skeletal muscle were mainly clustered within the delta-like homologue 1 and the type III iodothyronine deiodinase (Dlk1-Dio3) genomic region. Although clustered miRNAs are coexpressed and regulate multiple targets in a specific signalling pathway, the function of miRNAs in the Dlk1-Dio3 cluster in muscle aging is largely unknown. We aimed to ascertain whether these miRNAs play a common role to regulate age-related muscle atrophy.

METHODS

To examine anti-atrophic effect of miRNAs, we individually transfected 42 miRNA mimics in fully differentiated myotubes and analysed their diameters. The luciferase reporter assay using target 3' untranslated region (UTR) and RNA pull-down assay were employed to ascertain the target predicted by the TargetScan algorithm. To investigate the therapeutic potential of the miRNAs in vivo, we generated adeno-associated virus (AAV) serotype 9 expressing green fluorescent protein (GFP) (AAV9-GFP) bearing miR-376c-3p and infected it into the tibialis anterior muscle of old mice. We performed morphometric analysis and measured ex vivo isometric force using a force transducer. Human gluteus maximus muscle tissues (ages ranging from 25 to 80 years) were used to investigate expression levels of the conserved miRNAs in the Dlk1-Dio3 cluster.

RESULTS

We found that the majority of miRNAs (33 out of 42 tested) in the cluster induced anti-atrophic phenotypes in fully differentiated myotubes with increasing their diameters. Eighteen of these miRNAs, eight of which are conserved in humans, harboured predicted binding sites in the 3' UTR of muscle atrophy gene-1 (Atrogin-1) encoding a muscle-specific E3 ligase. Direct interactions were identified between these miRNAs and the 3' UTR of Atrogin-1, leading to repression of Atrogin-1 and thereby induction of eIF3f protein content, in both human and mouse skeletal muscle cells. Intramuscular delivery of AAV9 expressing miR-376c-3p, one of the most effective miRNAs in myotube thickening, dramatically ameliorated skeletal muscle atrophy and improved muscle function, including isometric force, twitch force, and fatigue resistance in old mice. Consistent with our findings in mice, the expression of miRNAs in the cluster was significantly down-regulated in human muscle from individuals > 50 years old.

CONCLUSIONS

Our study suggests that genetic intervention using a muscle-directed miRNA delivery system has therapeutic efficacy in preventing Atrogin-1-mediated muscle atrophy in sarcopenia.

Dietary magnesium supplementation improves lifespan in a mouse model of progeria

Aging is associated with redox imbalance according to the redox theory of aging. Consistently, a mouse model of premature aging (Lmna^G609G/+) showed an increased level of mitochondrial reactive oxygen species (ROS) and a reduced basal antioxidant capacity, including loss of the NADPH‐coupled glutathione redox system. Lmna^G609G/+ mice also exhibited reduced mitochondrial ATP synthesis secondary to ROS‐induced mitochondrial dysfunction. Treatment of Lmna^G609G/+ vascular smooth muscle cells with magnesium‐enriched medium improved the intracellular ATP level, enhanced the antioxidant capacity, and thereby reduced mitochondrial ROS production. Moreover, treatment of Lmna^G609G/+ mice with dietary magnesium improved the proton pumps (complexes I, III, and IV), stimulated extramitochondrial NADH oxidation and enhanced the coupled mitochondrial membrane potential, and thereby increased H⁺‐coupled mitochondrial NADPH and ATP synthesis, which is necessary for cellular energy supply and survival. Consistently, magnesium treatment reduced calcification of vascular smooth muscle cells in vitro and in vivo, and improved the longevity of mice. This antioxidant property of magnesium may be beneficial in children with HGPS.

Voluntary exercise and cardiac remodeling in a myocardial infarction model

We investigated the effects of voluntary exercise after myocardial infarction (MI) on cardiac function, remodeling, and inflammation. Male C57BL/6J mice were divided into the following four groups: sedentary + sham (Sed-Sh), sedentary + MI (Sed-MI), exercise + sham (Ex-Sh), and exercise + MI (Ex-MI). MI induction was performed by ligation of the left coronary artery. Exercise consisting of voluntary wheel running started after the operation and continued for 4 weeks. The Ex-MI mice had significantly increased cardiac function compared with the Sed-MI mice. The Ex-MI mice showed significantly reduced expression levels of tumor necrosis factor-α, interleukin (IL)-1β, IL-6, and IL-10 in the infarcted area of the left ventricle compared with the Sed-MI mice. In the Ex-MI mice, the expression levels of fibrosis-related genes including collagen I and III were decreased compared to the Sed-MI mice, and the expression levels of IL-1β, IL-6, follistatin-like 1, fibroblast growth factor 21, and mitochondrial function-related genes were significantly elevated in skeletal muscle compared with the Sed mice. The plasma levels of IL-6 were also significantly elevated in the Ex-MI group compared with the Sed-MI groups. These findings suggest that voluntary exercise after MI may improve in cardiac remodeling associated with anti-inflammatory effects in the myocardium and myokine production in the skeletal muscles.

Experimental Models of Sarcopenia: Bridging Molecular Mechanism and Therapeutic Strategy

Sarcopenia has been defined as a progressive decline of skeletal muscle mass, strength, and functions in elderly people. It is accompanied by physical frailty, functional disability, falls, hospitalization, and mortality, and is becoming a major geriatric disorder owing to the increasing life expectancy and growing older population worldwide. Experimental models are critical to understand the pathophysiology of sarcopenia and develop therapeutic strategies. Although its etiologies remain to be further elucidated, several mechanisms of sarcopenia have been identified, including cellular senescence, proteostasis imbalance, oxidative stress, and "inflammaging." In this article, we address three main aspects. First, we describe the fundamental aging mechanisms. Next, we discuss both in vitro and in vivo experimental models based on molecular mechanisms that have the potential to elucidate the biochemical processes integral to sarcopenia. The use of appropriate models to reflect sarcopenia and/or its underlying pathways will enable researchers to understand sarcopenia and develop novel therapeutic strategies for sarcopenia. Lastly, we discuss the possible molecular targets and the current status of drug candidates for sarcopenia treatment. In conclusion, the development of experimental models for sarcopenia is essential to discover molecular targets that are valuable as biochemical biomarkers and/or therapeutic targets for sarcopenia.

Effects of Aging on Formalin-Induced Pain Behavior and Analgesic Activity of Gabapentin in C57BL/6 Mice

Improved living conditions have induced an increase of lifespan often accompanied by comorbidities, responsible for pain, and by cognitive impairment and dementia, impairing communication capabilities. In most cases, the elderly do not receive pain relief because of underdiagnosis and of aging-induced changes of systems affecting nociceptive response. Unrelieved pain is involved in the development of behavioral symptoms, as agitation, representing a difficult challenge in this fragile population. Aged C57BL/6 mice and amyloid precursor protein (APP) mice display behavioral disturbances that mimic behavioral and psychological symptoms of dementia (BPSD). Therefore, this original study focuses on the influence of aging on nociception to provide insight into the occurrence of BPSD. We have investigated how aging can affect nociception after formalin administration and gabapentin effect in C57BL/6 mice, since it represents one of the treatments of choice for chronic neuropathic pain. Based on our results, changes of nociceptive behavior in response to an algogen stimulus occur during aging. Formalin-induced behavioral pattern in older C57BL/6 mice presents a temporal shift and an increase in the peak amplitudes. Our data show that the effectiveness of gabapentin is influenced by the age of the animal; though preliminary, the latter provide evidence upon which formalin test induced long-lasting mechanical allodynia might be a reliable as rapid and viable persistent pain model. The disclosed differences in effectiveness of gabapentin according to age can form the rational basis to deepen the study of pain treatment in the elderly.