Exercise-induced muscle growth is muscle-specific and age-dependent

PCDH7 as the key gene related to the co-occurrence of sarcopenia and osteoporosis

Sarcopenia and osteoporosis, two degenerative diseases in older patients, have become severe health problems in aging societies. Muscles and bones, the most important components of the motor system, are derived from mesodermal and ectodermal mesenchymal stem cells. The adjacent anatomical relationship between them provides the basic conditions for mechanical and chemical signals, which may contribute to the co-occurrence of sarcopenia and osteoporosis. Identifying the potential common crosstalk genes between them may provide new insights for preventing and treating their development. In this study, DEG analysis, WGCNA, and machine learning algorithms were used to identify the key crosstalk genes of sarcopenia and osteoporosis; this was then validated using independent datasets and clinical samples. Finally, four crosstalk genes (ARHGEF10, PCDH7, CST6, and ROBO3) were identified, and mRNA expression and protein levels of PCDH7 in clinical samples from patients with sarcopenia, with osteoporosis, and with both sarcopenia and osteoporosis were found to be significantly higher than those from patients without sarcopenia or osteoporosis. PCDH7 seems to be a key gene related to the development of both sarcopenia and osteoporosis.

Sarcopenia: Molecular Pathways and Potential Targets for Intervention

Aging is associated with sarcopenia. The loss of strength results in decreased muscle mass and motor function. This process accelerates the progressive muscle deterioration observed in older adults, favoring the presence of debilitating pathologies. In addition, sarcopenia leads to a decrease in quality of life, significantly affecting self-sufficiency. Altogether, these results in an increase in economic resources from the National Health Systems devoted to mitigating this problem in the elderly, particularly in developed countries. Different etiological determinants are involved in the progression of the disease, including: neurological factors, endocrine alterations, as well as nutritional and lifestyle changes related to the adoption of more sedentary habits. Molecular and cellular mechanisms have not been clearly characterized, resulting in the absence of an effective treatment for sarcopenia. Nevertheless, physical activity seems to be the sole strategy to delay sarcopenia and its symptoms. The present review intends to bring together the data explaining how physical activity modulates at a molecular and cellular level all factors that predispose or favor the progression of this deteriorating pathology.

Antioxidants Reduce Muscular Dystrophy in the dy2J/dy2J Mouse Model of Laminin α2 Chain-Deficient Muscular Dystrophy

Congenital muscular dystrophy with laminin α2 chain-deficiency (LAMA2-CMD) is a severe neuromuscular disorder without a cure. Using transcriptome and proteome profiling as well as functional assays, we previously demonstrated significant metabolic impairment in skeletal muscle from LAMA2-CMD patients and mouse models. Reactive oxygen species (ROS) increase when oxygen homeostasis is not maintained and, here, we investigate whether oxidative stress indeed is involved in the pathogenesis of LAMA2-CMD. We also analyze the effects of two antioxidant molecules, N-acetyl-L-cysteine (NAC) and vitamin E, on disease progression in the dy^2J/dy^2J mouse model of LAMA2-CMD. We demonstrate increased ROS levels in LAMA2-CMD mouse and patient skeletal muscle. Furthermore, NAC treatment (150 mg/kg IP for 6 days/week for 3 weeks) led to muscle force loss prevention, reduced central nucleation and decreased the occurrence of apoptosis, inflammation, fibrosis and oxidative stress in LAMA2-CMD muscle. In addition, vitamin E (40 mg/kg oral gavage for 6 days/week for 2 weeks) improved morphological features and reduced inflammation and ROS levels in dy^2J/dy^2J skeletal muscle. We suggest that NAC and to some extent vitamin E might be potential future supportive treatments for LAMA2-CMD as they improve numerous pathological hallmarks of LAMA2-CMD.

A focused review of myokines as a potential contributor to muscle hypertrophy from resistance-based exercise

PURPOSE

Resistance exercise induces muscle growth and is an important treatment for age-related losses in muscle mass and strength. Myokines are hypothesized as a signal conveying physiological information to skeletal muscle, possibly to "fine-tune" other regulatory pathways. While myokines are released from skeletal muscle following contraction, their role in increasing muscle mass and strength in response to resistance exercise or training is not established. Recent research identified both local and systemic release of myokines after an acute bout of resistance exercise. However, it is not known whether myokines with putative anabolic function are mechanistically involved in producing muscle hypertrophy after resistance exercise. Further, nitric oxide (NO), an important mediator of muscle stem cell activation, upregulates the expression of certain myokine genes in skeletal muscle.

METHOD

In the systemic context of complex hypertrophic signaling, this review: (1) summarizes literature on several well-recognized, representative myokines with anabolic potential; (2) explores the potential mechanistic role of myokines in skeletal muscle hypertrophy; and (3) identifies future research required to advance our understanding of myokine anabolism specifically in skeletal muscle.

RESULT

This review establishes a link between myokines and NO production, and emphasizes the importance of considering systemic release of potential anabolic myokines during resistance exercise as complementary to other signals that promote hypertrophy.

CONCLUSION

Investigating adaptations to resistance exercise in aging opens a novel avenue of interdisciplinary research into myokines and NO metabolites during resistance exercise, with the longer-term goal to improve muscle health in daily living, aging, and rehabilitation.

Phloretin attenuates behavior deficits and neuroinflammatory response in MPTP induced Parkinson's disease in mice

Neuroinflammation is one of the significant neuropathological conditions in Parkinson's disease (PD) which is due to microglial and astrocytes activation leads to progressive dopaminergic neuronal loss. To date, Current PD drugs offers only symptomatic relief with adverse effects and lack of ability to prevent the progression of neurodegeneration. Therefore, a better approach to develop a multi potent drug of natural origin would be beneficial in managing the disease. Therefore, the present study aimed to investigate the neuroprotective and anti-inflammatory effects of PHL by exploring its neuroprotective mechanism in 1-methyl-4-phenyl-1,2,3,6-tetrahydro pyridine (MPTP) induced PD in mice. MPTP intoxication in mice cause motor abnormalities, decreased dopamine (DA) levels, reduced tyrosine hydroxylase (TH) enzyme protein expression and inflammation which were effectively restored by PHL. Moreover gliotic specific inflammatory markers like glial fibrillary acidic protein (GFAP), ionized calcium-binding adaptor protein-1 (Iba-1), iNOS and COX-2 were found to be expressed more in MPTP intoxicated mice, Further the levels of proinflammatory cytokines like IL-β, IL-6, and TNF-α were significantly upregulated in MPTP intoxicated mice, these deleterious responses were diminished to extend neuroprotection by PHL treatment. Our findings strongly suggest PHL as a potent therapeutic agent in treating PD.

Effects of Moderate- and High-Intensity Chronic Exercise on the Adiponectin Levels in Slow-Twitch and Fast-Twitch Muscles in Rats

Background and objectives: Adipose tissue and skeletal muscle secrete adiponectin, a hormone abundantly secreted by adipocytes, that through the adiponectin receptor, regulate glucose and lipid metabolism. Adiponectin appears to protect skeletal muscles from inflammatory damage induced by oxidative stress. It has been suggested that decreased adiponectin levels could be associated with pathologic conditions, including obesity and diabetes. Furthermore, some studies suggest that exercise could have a beneficial effect by increasing adiponectin levels, but this observation remains controversial. It is also unknown if physical exercise modifies adiponectin expression in skeletal muscles. The aim of this study was to investigate the effect of chronic exercise on serum adiponectin and adiponectin expression in slow-twitch (soleus) and fast-twitch (plantaris) muscles in healthy rats. Materials and methods: Two-month-old male Wistar rats were randomly divided into three groups with n = 6 in each group: control (C), moderate-intensity training (MIT), and high-intensity training (HIT). The rats were conditioned to run on a treadmill for the 8-week period. Forty-eight hours after the last session, blood samples were collected for adiponectin measurements and total RNA was isolated from plantaris and soleus muscles to measure by RT-qPCR adiponectin receptor 1 and adiponectin mRNA expression level. Results: MIT and HIT groups had reduced adiponectin protein levels in serum and the plantaris muscle, but not changes in adiponectin protein were observed in the soleus muscle. No significant differences in Adiponectin receptor 1 (AdipoR1) gene expression were observed following intense or moderate exercise in either muscle group studied. Conclusions: Our study shows that decreasing levels of circulating adiponectin is a result of physical exercise and should not be generalized as a predictive marker of disease.

Skeletal Muscle Hypertrophy, Insulin-like Growth Factor 1, Myostatin and Follistatin in Healthy and Sarcopenic Elderly Men: The Effect of Whole-body Resistance Training

Background:

Sarcopenia describes the inevitable deterioration in muscle mass and strength that accompanies biological aging. The purpose of this study was to investigate the effects of resistance training (RT) on quadriceps hypertrophy and related biochemistry in sarcopenic and healthy elderly men.

Methods:

A total of 31 elderly men (55–70 years old) were classified as sarcopenic and nonsarcopenic and were divided into two groups. Both groups participated in a progressive RT program for 8 weeks.

Results:

Data indicated that the strength in the sarcopenic group increased more than the healthy group (P < 0.05). Quadriceps cross-sectional area also increased more in the healthy group (P < 0.05). Myostatin concentration decreased in both groups after training (P < 0.05). Follistatin and testosterone increased in the healthy group; in contrast, only testosterone increased in the sarcopenic group after training (P < 0.05).

Conclusions:

The findings from this study suggest that RT improves muscle cross-sectional area and biomarker-related muscle loss in both healthy and sarcopenic elderly men. The findings also demonstrate that growth factor profiles at baseline and changes in testosterone levels play an important role in muscle hypertrophy observed in both groups.

Effects of metformin on congenital muscular dystrophy type 1A disease progression in mice: a gender impact study

Congenital muscular dystrophy with laminin α2 chain-deficiency (LAMA2-CMD) is a severe muscle disorder with complex underlying pathogenesis. We have previously employed profiling techniques to elucidate molecular patterns and demonstrated significant metabolic impairment in skeletal muscle from LAMA2-CMD patients and mouse models. Thus, we hypothesize that skeletal muscle metabolism may be a promising pharmacological target to improve muscle function in LAMA2-CMD. Here, we have investigated whether the multifunctional medication metformin could be used to reduce disease in the dy^2J/dy^2J mouse model of LAMA2-CMD. First, we show gender disparity for several pathological hallmarks of LAMA2-CMD. Second, we demonstrate that metformin treatment significantly increases weight gain and energy efficiency, enhances muscle function and improves skeletal muscle histology in female dy^2J/dy^2J mice (and to a lesser extent in dy^2J/dy^2J males). Thus, our current data suggest that metformin may be a potential future supportive treatment that improves many of the pathological characteristics of LAMA2-CMD.

Additive Effects of Levodopa and a Neurorestorative Diet in a Mouse Model of Parkinson's Disease

Though Parkinson’s disease (PD) clinical picture is generally dominated by motor impairment, non-motor symptoms, such as cognitive decline and gastrointestinal dysfunctions, may develop before motor symptoms and have major effects on quality of life. L-3,4-di-hydroxy-phenylalanine (Levodopa) is the most commonly used treatment of motor symptoms but has serious side-effects with prolonged use and does not stop the degenerative process. Moreover, gastrointestinal dysfunctions interfere with the absorption of levodopa and modify its effectiveness. Since most patients are on levodopa treatment, there is a need for combinational therapies that allow for an effective reduction of both motor and non-motor symptoms. We have recently shown that a diet containing precursors and cofactors required for membrane phospholipid synthesis, as well as prebiotic fibers, had therapeutic effects in a PD mouse model. We now investigate the effects of combined administration of the same diet together with levodopa in the rotenone model of PD. Mice were injected with rotenone or vehicle in the striatum. The dietary intervention started after full induction of motor symptoms. The effects of dietary intervention and oral treatment with different doses of levodopa were assessed weekly. Motor and cognitive functions were tested, intestinal transit was analyzed and histological examination of the brain and the colon was assessed. Our results confirm our previous findings that rotenone-induced motor and non-motor problems were alleviated by the Active diet (AD). Levodopa showed an additive beneficial effect on rotarod performance in rotenone-treated animals fed with the AD. No negative interaction effects were found between the AD and levodopa. Our findings suggest that the dietary intervention might confer additional clinical benefits on patients receiving levodopa treatment.

Reduced dietary intake of micronutrients with antioxidant properties negatively impacts muscle health in aged mice

BACKGROUND

Inadequate intake of micronutrients with antioxidant properties is common among older adults and has been associated with higher risk of frailty, adverse functional outcome, and impaired muscle health. However, a causal relationship is less well known. The aim was to determine in old mice the impact of reduced dietary intake of vitamins A/E/B6/B12/folate, selenium, and zinc on muscle mass, oxidative capacity, strength, and physical activity (PA) over time.

METHODS

Twenty-one-month-old male mice were fed either AIN-93-M (control) or a diet low in micronutrients with antioxidant properties (=LOWOX-B: 50% of mouse recommended daily intake of vitamins A, E, B6, and B12, folate, selenium, and zinc) for 4 months. Muscle mass, grip strength, physical activity (PA), and general oxidative status were assessed. Moreover, muscle fatigue was measured of m. extensor digitorum longus (EDL) during an ex vivo moderate exercise protocol. Effects on oxidative capacity [succinate dehydrogenase (SDH) activity], muscle fibre type, number, and fibre cross-sectional area (fCSA) were assessed on m. plantaris (PL) using histochemistry.

RESULTS

After 2 months on the diet, bodyweight of LOWOX-B mice was lower compared with control (P < 0.0001), mainly due to lower fat mass (P < 0.0001), without significant differences in food intake. After 4 months, oxidative status of LOWOX-B mice was lower, demonstrated by decreased vitamin E plasma levels (P < 0.05) and increased liver malondialdehyde levels (P = 0.018). PA was lower in LOWOX-B mice (P < 0.001 vs. control). Muscle mass was not affected, although PL-fCSA was decreased (~16%; P = 0.028 vs. control). SDH activity and muscle fibre type distribution remained unaffected. In LOWOX-B mice, EDL force production was decreased by 49.7% at lower stimulation frequencies (P = 0.038), and fatigue resistance was diminished (P = 0.023) compared with control.

CONCLUSIONS

Reduced dietary intake of vitamins A, E, B6, and B12, folate, selenium, and zinc resulted in a lower oxidative capacity and has major impact on muscle health as shown by decreased force production and PA, without effects on muscle mass. The reduced fCSA in combination with similar SDH activity per fibre might explain the reduced oxidative capacity resulting in the increased fatigue after exercise in LOWOX-B mice.

Exercise-Induced Hypertrophic and Oxidative Signaling Pathways and Myokine Expression in Fast Muscle of Adult Zebrafish

Skeletal muscle is a plastic tissue that undergoes cellular and metabolic adaptations under conditions of increased contractile activity such as exercise. Using adult zebrafish as an exercise model, we previously demonstrated that swimming training stimulates hypertrophy and vascularization of fast muscle fibers, consistent with the known muscle growth-promoting effects of exercise and with the resulting increased aerobic capacity of this tissue. Here we investigated the potential involvement of factors and signaling mechanisms that could be responsible for exercise-induced fast muscle remodeling in adult zebrafish. By subjecting zebrafish to swimming-induced exercise, we observed an increase in the activity of mammalian target of rapamycin (mTOR) and Mef2 protein levels in fast muscle. We also observed an increase in the protein levels of the mitotic marker phosphorylated histone H3 that correlated with an increase in the protein expression levels of Pax7, a satellite-like cell marker. Furthermore, the activity of AMP-activated protein kinase (AMPK) was also increased by exercise, in parallel with an increase in the mRNA expression levels of pgc1α and also of pparda, a β-oxidation marker. Changes in the mRNA expression levels of slow and fast myosin markers further supported the notion of an exercise-induced aerobic phenotype in zebrafish fast muscle. The mRNA expression levels of il6, il6r, apln, aplnra and aplnrb, sparc, decorin and igf1, myokines known in mammals to be produced in response to exercise and to signal through mTOR/AMPK pathways, among others, were increased in fast muscle of exercised zebrafish. These results support the notion that exercise increases skeletal muscle growth and myogenesis in adult zebrafish through the coordinated activation of the mTOR-MEF2 and AMPK-PGC1α signaling pathways. These results, coupled with altered expression of markers for oxidative metabolism and fast-to-slow fiber-type switch, also suggest improved aerobic capacity as a result of swimming-induced exercise. Finally, the induction of myokine expression by swimming-induced exercise support the hypothesis that these myokines may have been produced and secreted by the exercised zebrafish muscle and acted on fast muscle cells to promote metabolic remodeling. These results support the use of zebrafish as a suitable model for studies on muscle remodeling in vertebrates, including humans.

"Known Unknowns": Current Questions in Muscle Satellite Cell Biology

Our understanding of satellite cells, now known to be the obligate stem cells of skeletal muscle, has increased dramatically in recent years due to the introduction of new molecular, genetic, and technical resources. In addition to their role in acute repair of damaged muscle, satellite cells are of interest in the fields of aging, exercise, neuromuscular disease, and stem cell therapy, and all of these applications have driven a dramatic increase in our understanding of the activity and potential of satellite cells. However, many fundamental questions of satellite cell biology remain to be answered, including their emergence as a specific lineage, the degree and significance of heterogeneity within the satellite cell population, the roles of their interactions with other resident and infiltrating cell types during homeostasis and regeneration, and the relative roles of intrinsic vs extrinsic factors that may contribute to satellite cell dysfunction in the context of aging or disease. This review will address the current state of these open questions in satellite cell biology.

Biochemical Pathways of Sarcopenia and Their Modulation by Physical Exercise: A Narrative Review

Aging is a complex process characterized by progressive multisystem derangement predisposing individuals to increased risk of developing negative health outcomes. Sarcopenia is the age-related decline of muscle mass and function/strength and represents a highly prevalent correlate of aging. Several factors have been indicated to play a role in the onset and progression of sarcopenia; however, its pathophysiology is still unclear. Physical exercise is to date one of the few strategies able to improve muscle health in old age through multiple metabolic and transcriptional adaptations. Although the benefits of different exercise modalities on the function and structure of aged myocytes is acknowledged, the cellular and molecular mechanisms underlying such effects are not yet fully identified. Here, we briefly overview the current knowledge on the biochemical pathways associated with the onset and progression of sarcopenia. We subsequently describe the effects of exercise on relevant signaling pathways involved in sarcopenia pathophysiology.

Promising Effects of Neurorestorative Diets on Motor, Cognitive, and Gastrointestinal Dysfunction after Symptom Development in a Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is characterized by the progressive degeneration of dopaminergic nigrostriatal neurons, with reductions in the function and amount of dopaminergic synapses. Therefore, synapse loss and membrane-related pathology provide relevant targets for interventions in PD. We previously showed the beneficial preventive effects of a dietary intervention containing uridine and DHA, two precursors for membrane synthesis, in the intrastriatal rotenone model for PD. Here, we examined the therapeutic potential of the same dietary intervention on motor, cognitive, and gastrointestinal symptoms. In addition, we tested the effects of an extended nutritional formula based on the same precursors plus other nutrients that increase membrane phospholipid synthesis as well as prebiotic fibers. C57BL/6J mice received a unilateral rotenone injection in the striatum. Dietary interventions started 28 days after surgery, when motor-symptoms had developed. Readout parameters included behavioral tasks measuring motor function and spatial memory as well as intestinal function and histological examination of brain and gut to assess PD-like pathology. Our results show that rotenone-induced motor and non-motor problems were partially alleviated by the therapeutic dietary interventions providing uridine and DHA. The extended nutritional intervention containing both precursors and other nutrients that increase phospholipid synthesis as well as prebiotic fibers was more effective in normalizing rotenone-induced motor and non-motor abnormalities. The latter diet also restored striatal DAT levels, indicating its neurorestorative properties. This is the first study demonstrating beneficial effects of specific dietary interventions, given after full development of symptoms, on a broad spectrum of motor and non-motor symptoms in a mouse model for PD.

Using pre-operative MRI to predict intraoperative hamstring graft size for anterior cruciate ligament reconstruction

PURPOSE

Large variation in tendon size between individuals makes hamstring graft diameter for anterior cruciate ligament (ACL) reconstruction unpredictable. Inadequate graft diameter may necessitate an alternative source of tissue requiring pre-operative planning. The purpose of this study was to determine whether magnetic resonance image (MRI) measurements and clinical anthropometric data are predictive of hamstring tendon graft diameter.

METHODS

Data from 109 patients having ACL reconstruction with semitendinosus-gracilis (STGT) autograft were retrospectively evaluated. Cross-sectional area (CSA) of the gracilis tendon (GT) and semitendinosus tendon (ST) were determined from pre-operative MRI scans. Variables included pre-operative height, weight, body mass index (BMI), age and gender; and intra-operative graft diameter.

RESULTS

Correlations between anthropometric variables, hamstring tendons CSA and intra-operative graft diameter were calculated. Multiple stepwise regression was performed to assess the predictive value of these variables to graft diameter. Sensitivity and specificity were calculated to evaluate the utility of MRI CSA measurements in accurately identifying inadequate graft diameter (<8 mm). All anthropometric variables were positively correlated with intraoperative graft diameter (p < 0.01). Semitendinosus-gracilis tendon CSA (p < 0.001) and STGT CSA and weight (p < 0.001) were significantly predictive models of graft diameter. Sensitivity and specificity were 79 and 74 %, respectively.

CONCLUSION

The strongest indicators of a four-stranded STGT graft for primary ACL reconstruction were STGT CSA on MRI plus weight. Measurement of graft diameter can be performed pre-operatively via MRI to identify tendons that may be of inadequate size for ACL reconstruction. This can assist with surgical planning to determine the most appropriate graft choice.

LEVEL OF EVIDENCE

III.

Sarcopenia in older mice is characterized by a decreased anabolic response to a protein meal

Ageing is associated with sarcopenia, a progressive decline of skeletal muscle mass, muscle quality and muscle function. Reduced sensitivity of older muscles to respond to anabolic stimuli, i.e. anabolic resistance, is part of the underlying mechanisms. Although, muscle parameters have been studied in mice of various ages/strains; the aim was to study if mice display similar deteriorating processes as human ageing. Therefore, 10,16,21 and 25 months-old C57BL6/6J male mice were studied to measure parameters of sarcopenia and factors contributing to its pathophysiology, with the aim of characterizing sarcopenia in old mice. Muscle mass of the hind limb was lower in 25 as compared to 10 month-old mice. A significant decrease in physical daily activity, muscle grip strength and ex vivo muscle maximal force production was observed in 25 compared to 10 month-old mice. The muscle anabolic response to a single protein meal showed increased muscle protein synthesis in young, but not in old mice, indicative to anabolic resistance. However, by increasing the protein content in meals, anabolic resistance could be overcome, similar as in human elderly. Additionally, aged mice showed higher fasted insulin and hepatic malondialdehyde (MDA) levels (=marker oxidative stress). This study shows clear characteristics of sarcopenia that coincide with anabolic resistance, insulin resistance and oxidative stress in 25 month-old C57/BL6 male mice, similar to human ageing. Furthermore, similar decline in muscle mass, strength and function was observed in this aged-mice-model. These observations offer potential for the future to explore in old mice the effects of interventions targeting sarcopenia.

Altered Satellite Cell Responsiveness and Denervation Implicated in Progression of Rotator-Cuff Injury

Background

Rotator-cuff injury (RCI) is common and painful; even after surgery, joint stability and function may not recover. Relative contributions to atrophy from disuse, fibrosis, denervation, and satellite-cell responsiveness to activating stimuli are not known.

Methods and Findings

Potential contributions of denervation and disrupted satellite cell responses to growth signals were examined in supraspinatus (SS) and control (ipsilateral deltoid) muscles biopsied from participants with RCI (N = 27). Biopsies were prepared for explant culture (to study satellite cell activity), immunostained to localize Pax7, BrdU, and Semaphorin 3A in satellite cells, sectioning to study blood vessel density, and western blotting to measure the fetal (γ) subunit of acetylcholine receptor (γ-AchR). Principal component analysis (PCA) for 35 parameters extracted components identified variables that contributed most to variability in the dataset. γ-AchR was higher in SS than control, indicating denervation. Satellite cells in SS had a low baseline level of activity (Pax7+ cells labelled in S-phase) versus control; only satellite cells in SS showed increased proliferative activity after nitric oxide-donor treatment. Interestingly, satellite cell localization of Semaphorin 3A, a neuro-chemorepellent, was greater in SS (consistent with fiber denervation) than control muscle at baseline. PCAs extracted components including fiber atrophy, satellite cell activity, fibrosis, atrogin-1, smoking status, vascular density, γAchR, and the time between symptoms and surgery. Use of deltoid as a control for SS was supported by PCA findings since “muscle” was not extracted as a variable in the first two principal components. SS muscle in RCI is therefore atrophic, denervated, and fibrotic, and has satellite cells that respond to activating stimuli.

Conclusions

Since SS satellite cells can be activated in culture, a NO-donor drug combined with stretching could promote muscle growth and improve functional outcome after RCI. PCAs suggest indices including satellite cell responsiveness, atrogin-1, atrophy, and innervation may predict surgical outcome.

Resistance exercise reduced the expression of fibroblast growth factor-2 in skeletal muscle of aged mice

BACKGROUND

Fibroblast growth factor-2 (FGF-2) protein level has been shown to be elevated in aged mice muscle compared to adult mice. It activates the satellite cell quiescence, which leads to satellite cell depletion and may accelerate aging process. The purpose of this study was to see the effect of resistance exercise on skeletal muscle FGF-2 protein level in aged mice.

METHODS

This study included eight young adult control C57BL/6 male mice (age 12 weeks, YCON group) and 14 aged C57BL/6 male mice (age 19 months), randomly divided into two groups (old control, OCON, n = 7; old resistance exercise, ORT, n = 7). Resistance ladder climbing exercise was conducted 3 d/wk for 12 weeks. Soleus and tibialis anterior muscles were collected for body composition, relative grip strength, and muscle wet weight and for enzyme-linked immunosorbent assay protein analysis.

RESULTS

Relative soleus muscle wet weight and hindlimb lean mass showed a significant increase in ORT group compared to OCON group (p = 0.013 and p = 0.015, respectively). In relative grip strength, both OCON and ORT showed a significant decrease compared to YCON (p < 0.001 and p = 0.011, respectively). However, ORT showed a significant increase compared to OCON (p = 0.02). OCON showed a significant increase in skeletal muscle FGF-2 protein level compared to YCON in soleus (p = 0.035), and ORT showed a significant decrease compared to OCON in soleus muscle (p = 0.045). FGF-2 protein level was significantly decreased in tibialis anterior muscle in the ORT group compared to OCON (p = 0.022). Correlation analysis showed a negative correlation between FGF-2 protein level and soleus and tibialis anterior muscle weight (r2 = 0.514, p = 0.0035; r2 = 0.312, p = 0.025, respectively).

CONCLUSION

Twelve weeks of resistance exercise reduced soleus and tibialis anterior muscle FGF-2 protein level in aged mice with improvement in appendicular lean mass and muscle strength. Thus, resistance exercise could be an efficient intervention for preventing age-related increase of FGF-2 in skeletal muscle.

Muscle wasting and aging: Experimental models, fatty infiltrations, and prevention

Identification of cost-effective interventions to maintain muscle mass, muscle strength, and physical performance during muscle wasting and aging is an important public health challenge. It requires understanding of the cellular and molecular mechanisms involved. Muscle-deconditioning processes have been deciphered by means of several experimental models, bringing together the opportunities to devise comprehensive analysis of muscle wasting. Studies have increasingly recognized the importance of fatty infiltrations or intermuscular adipose tissue for the age-mediated loss of skeletal-muscle function and emphasized that this new important factor is closely linked to inactivity. The present review aims to address three main points. We first mainly focus on available experimental models involving cell, animal, or human experiments on muscle wasting. We next point out the role of intermuscular adipose tissue in muscle wasting and aging and try to highlight new findings concerning aging and muscle-resident mesenchymal stem cells called fibro/adipogenic progenitors by linking some cellular players implicated in both FAP fate modulation and advancing age. In the last part, we review the main data on the efficiency and molecular and cellular mechanisms by which exercise, replacement hormone therapies, and β-hydroxy-β-methylbutyrate prevent muscle wasting and sarcopenia. Finally, we will discuss a potential therapeutic target of sarcopenia: glucose 6-phosphate dehydrogenase.

Hepatocyte Growth Factor and Satellite Cell Activation

Satellite cells are the "currency" for the muscle growth that is critical to meat production in many species, as well as to phenotypic distinctions in development at the level of species or taxa, and for human muscle growth, function and regeneration. Careful research on the activation and behaviour of satellite cells, the stem cells in skeletal muscle, including cross-species comparisons, has potential to reveal the mechanisms underlying pathological conditions in animals and humans, and to anticipate implications of development, evolution and environmental change on muscle function and animal performance.

Double-row repair of the distal attachment of the superficial medial collateral ligament: a basic science pilot study

PURPOSE

To describe a novel repair for tibial-sided superficial medial collateral ligament (sMCL) lesions and determine whether it restores medial joint opening to uninjured state. Agreement among experienced knee surgeons when evaluating medial joint laxity was also explored.

METHODS

On a series of eight human cadaveric knees, surgical elevation of the distal insertion of the sMCL was performed to replicate injury. The cut ligament was repaired using a novel double-row 'suture-bridge' technique. Valgus stress fluoroscopic images were taken with the ligament in three states: (I)ntact, (C)ut and (R)epaired, in two positions: 0 and 20° flexion. Joint opening was measured on calibrated fluoroscopic images (in mm) based on methods described by LaPrade. Joint space opening was also estimated by three experienced knee surgeons without fluoroscopy.

RESULTS

On fluoroscopy, no significant differences in mean joint opening were observed between an intact versus repaired ligament in 0 and 20° flexion [0.5 mm (95 % CI -1.6, 0.73; n.s.) and 0.3 mm (95 % CI -1.17, 1.71; n.s.)], respectively. Agreement among surgeons was substantial (ICC = 0.622, 95 % CI 0.52, 0.73).

CONCLUSION

The surgical technique adequately restored joint opening to an intact state with response to valgus stress. Agreement among surgeons when quantifying joint opening in mm was substantial. This paper addresses a technically difficult problem and provides pragmatic and practical information for surgeons who manage complicated multi-ligament knee injuries.

Atrophy, inducible satellite cell activation, and possible denervation of supraspinatus muscle in injured human rotator-cuff muscle

The high frequency of poor outcome and chronic pain after surgical repair of shoulder rotator-cuff injury (RCI) prompted this study to explore the potential to amplify muscle regeneration using nitric oxide (NO)-based treatment. After preoperative magnetic resonance imaging (MRI), biopsies of supraspinatus and ipsilateral deltoid (as a control) were collected during reparative surgery for RCI. Muscle fiber diameter, the pattern of neuromuscular junctions observed with alpha-bungarotoxin staining, and the γ:ε subunit ratio of acetylcholine receptors in Western blots were examined in tandem with experiments to determine the in vitro responsiveness of muscle satellite cells to activation (indicated by uptake of bromodeoxyuridine, BrdU) by the NO-donor drug, isosorbide dinitrate (ISDN). Consistent with MRI findings of supraspinatus atrophy (reduced occupation ratio and tangent sign), fiber diameter was lower in supraspinatus than in deltoid. ISDN induced a significant increase over baseline (up to 1.8-fold), in the proportion of BrdU+ (activated) Pax7+ satellite cells in supraspinatus, but not in deltoid, after 40 h in culture. The novel application of denervation indices revealed a trend for supraspinatus muscle to have a higher γ:ε subunit ratio than deltoid (P = 0.13); this ratio inversely with both occupancy ratio (P < 0.05) and the proportion of clusters at neuromuscular junctions (P = 0.05). Results implicate possible supraspinatus denervation in RCI and suggest NO-donor treatment has potential to promote growth in atrophic supraspinatus muscle after RCI and improve functional outcome.

Mechanisms governing the health and performance benefits of exercise

Humans are considered among the greatest if not the greatest endurance land animals. Over the last 50 years, as the population has become more sedentary, rates of cardiovascular disease and its associated risk factors such as obesity, type 2 diabetes and hypertension have all increased. Aerobic fitness is considered protective for all-cause mortality, cardiovascular disease, a variety of cancers, joint disease and depression. Here, I will review the emerging mechanisms that underlie the response to exercise, focusing on the major target organ the skeletal muscle system. Understanding the mechanisms of action of exercise will allow us to develop new therapies that mimic the protective actions of exercise.

Aerobic exercise affects myostatin expression in aged rat skeletal muscles: a possibility of antiaging effects of aerobic exercise related with pelvic floor muscle and urethral rhabdosphincter

PURPOSE

Aging-induced loss of muscle mass and subsequent reduction of strength is a fundamental cause of frailty, functional decline, and disability. And this may lead to muscular dysfunction, voiding dysfunction, or urinary incontinence due to pelvic muscle weakness induced by aging. Physical exercise has been recommended for the prevention and the treatment of these age-related frail states. We investigated the effects of treadmill exercise on muscle strength, myostatin mRNA and protein expression, and gastrocnemius myocytes proliferation in aged rats to investigate the possible antiaging effects of aerobic exercise on skeletal muscles such as pelvic floor muscles and urethral rhabdosphincter muscle.

METHODS

In this study, 5-month-old male Sprague-Dawley rats were used as the young-age group (n=20) and 24-month-old rats were used as the old-age group (n=20). Each group was randomly divided into two groups (n=10 in each group): the sedentary and the treadmill exercise group. The rats in the exercise groups were forced to run on a motorized treadmill for 30 minutes, once a day, for 6 weeks. For this study, a weight load test, hematoxylin and eosin staining, real-time and reverse transcription polymerase chain reaction for myostatin mRNA, myostatin western blot, and 5-bromo-2'-deoxyuridine immunohistochemistry were performed in the gastrocnemius muscle.

RESULTS

The age-induced reduction of muscle mass and strength was associated with a decrease in myocyte proliferation and an increase in myostatin mRNA and protein expression in the gastrocnemius. However, treadmill exercise improved muscle mass and strength through suppression of myostatin mRNA and protein expression, and myocyte proliferation increase in the gastrocnemius against the aging process.

CONCLUSIONS

Aerobic exercise is a useful strategy for enhancing muscle function against aging-induced loss of skeletal muscle mass and functions.

Aged skeletal muscle retains the ability to fully regenerate functional architecture

While the general understanding of muscle regenerative capacity is that it declines with increasing age due to impairments in the number of muscle progenitor cells and interaction with their niche, studies vary in their model of choice, indices of myogenic repair, muscle of interest and duration of studies. We focused on the net outcome of regeneration, functional architecture, compared across three models of acute muscle injury to test the hypothesis that satellite cells maintain their capacity for effective myogenic regeneration with age. Muscle regeneration in extensor digitorum longus muscle (EDL) of young (3 mo-old), old (22 mo-old) and senescent female mice (28 mo-old) was evaluated for architectural features, fiber number and central nucleation, weight, collagen and fat deposition. The 3 injury paradigms were: a myotoxin (notexin) which leaves the blood vessels and nerves intact, freezing (FI) that damages local muscle, nerve and blood vessels and denervation-devascularization (DD) which dissociates the nerves and blood vessels from the whole muscle. Histological analyses revealed successful architectural regeneration following notexin injury with negligible fibrosis and fully restored function, regardless of age. In comparison, the regenerative response to injuries that damaged the neurovascular supply (FI and DD) was less effective, but similar across the ages. The focus on net regenerative outcome demonstrated that old and senescent muscle has a robust capacity to regenerate functional architecture.

Physical exercise as an epigenetic modulator: Eustress, the "positive stress" as an effector of gene expression

Physical exercise positively influences epigenetic mechanisms and improves health. Several issues remain unclear concerning the links between physical exercise and epigenetics. There is growing concern about the negative influence of excessive and persistent physical exercise on health. How an individual physically adapts to the prevailing environmental conditions might influence epigenetic mechanisms and modulate gene expression. In this article, we put forward the idea that physical exercise, especially long-term repetitive strenuous exercise, positively affects health, reduces the aging process, and decreases the incidence of cancer through induced stress and epigenetic mechanisms. We propose herein that stress may stimulate genetic adaptations through epigenetics that, in turn, modulate the link between the environment, human lifestyle factors, and genes.

β-hydroxy-β-methylbutyrate did not enhance high intensity resistance training-induced improvements in myofiber dimensions and myogenic capacity in aged female rats

Older women exhibit blunted skeletal muscle hypertrophy following resistance training (RT) compared to other age and gender cohorts that is partially due to an impaired regenerative capacity. In the present study, we examined whether β-hydroxy-β-methylbutyrate (HMB) provision to aged female rodents would enhance regenerative mechanisms and facilitate RT-induced myofiber growth. Nineteen-month old female Sprague-Dawley rats were randomly divided into three groups: HMB (0.48 g/kg/d; n = 6), non-HMB (n = 6), and control (n = 4). HMB and non-HMB groups underwent RT every third day for 10 weeks using a ladder climbing apparatus. Whole body strength, grip strength, and body composition was evaluated before and after RT. The gastrocnemius and soleus muscles were analyzed using magnetic resonance diffusion tensor imaging, RT-PCR, and immunohistochemistry to determine myofiber dimensions, transcript expression, and satellite cells/myonuclei, respectively. ANOVAs were used with significance set at p < 0.05. There were significant time effects (pre vs. post) for whole body strength (+262%), grip strength (+17%), lean mass (+20%), and fat mass (-19%). Both RT groups exhibited significant increases in the mean myofiber cross-sectional area (CSA) in the gastrocnemius and soleus (+8-22%) compared to control. Moreover, both groups demonstrated significant increases in the numbers of satellite cells (+100-108%) and myonuclei (+32%) in the soleus but not the gastrocnemius. A significant IGF-I mRNA elevation was only observed in soleus of the HMB group (+33%) whereas MGF and myogenin increased significantly in both groups (+32-40%). Our findings suggest that HMB did not further enhance intense RT-mediated myogenic mechanisms and myofiber CSA in aged female rats.

Resistance training induced increase in muscle fiber size in young and older men

Muscle strength and mass decline in sedentary individuals with aging. The present study investigated the effects of both age and 21 weeks of progressive hypertrophic resistance training (RT) on skeletal muscle size and strength, and on myostatin and myogenin mRNA expression in 21 previously untrained young men (26.0 ± 4.3 years) and 18 older men (61.2 ± 4.1 years) and age-matched controls. Vastus lateralis muscle biopsies were taken before and after RT. Type I and type II muscle fiber cross-sectional areas increased more in young men than in older men after RT (P < 0.05). Concentric leg extension increased (P < 0.05) more after 10.5 weeks in young men compared to older men, but after 21 weeks no statistical differences existed. The daily energy and protein intake were greater (P < 0.001) in young subjects. Both myostatin and myogenin mRNA expression increased in older when compared with young men after RT (P < 0.05). In conclusion, after RT, muscle fiber size increased less in older compared to young men. This was associated with lower protein and energy intake and increases in myostatin gene expression in older when compared to young men.

Nitric oxide and voluntary exercise together promote quadriceps hypertrophy and increase vascular density in female 18-mo-old mice

Age-related sarcopenia reduces the size, strength, and function of muscle, and the diameter of muscle fibers. It also disrupts the dystrophin-glycoprotein complex, dislocating nitric oxide synthase 1 (NOS-1) and reducing sarcolemmal integrity. This study of quadriceps muscle in 18-mo-old mice showed that NO-donor treatment with isosorbide dinitrate (I) for 6 wk, in combination with voluntary exercise for 3 wk, increased muscle mass by 25% and stimulated cell proliferation. The resulting fiber hypertrophy was accompanied by a lower ratio of protein:DNA, consistent with myogenic-cell hyperplasia. Treatment enhanced the ratio of NOS-1:β-dystroglycan in correlation with fiber diameter, improved sarcolemmal integrity, and increased vascular density after an increase in vascular endothelial growth factor protein at 3 wk. Results demonstrate that age-related muscle refractoriness to exercise can be overcome with NO-donor treatment. Since activation of muscle stem cells and vascular perfusion are limiting factors in the maintenance, regeneration, and growth of aged muscle, results suggest the feasibility of using NO-donor drugs to combat atrophy and muscle ischemia. Improved function and quality of life from the NO-amplified effects of exercise may be useful in aging and other conditions such as disuse, insulin resistance, or microgravity.

The skeletal muscle satellite cell: still young and fascinating at 50

The skeletal muscle satellite cell was first described and named based on its anatomic location between the myofiber plasma and basement membranes. In 1961, two independent studies by Alexander Mauro and Bernard Katz provided the first electron microscopic descriptions of satellite cells in frog and rat muscles. These cells were soon detected in other vertebrates and acquired candidacy as the source of myogenic cells needed for myofiber growth and repair throughout life. Cultures of isolated myofibers and, subsequently, transplantation of single myofibers demonstrated that satellite cells were myogenic progenitors. More recently, satellite cells were redefined as myogenic stem cells given their ability to self-renew in addition to producing differentiated progeny. Identification of distinctively expressed molecular markers, in particular Pax7, has facilitated detection of satellite cells using light microscopy. Notwithstanding the remarkable progress made since the discovery of satellite cells, researchers have looked for alternative cells with myogenic capacity that can potentially be used for whole body cell-based therapy of skeletal muscle. Yet, new studies show that inducible ablation of satellite cells in adult muscle impairs myofiber regeneration. Thus, on the 50th anniversary since its discovery, the satellite cell's indispensable role in muscle repair has been reaffirmed.

Bedrest and sarcopenia

PURPOSE OF REVIEW

The primary focus of this review is to characterize the physiological elements of sarcopenia. In addition, we will also describe the impact of bedrest on sarcopenia and how various countermeasures may be able to offset the deleterious clinical consequences of unanticipated bedrest or hospitalization. It is well known that the aging process presents many challenges to the maintenance of overall health. With the increasing rate of obesity and the potentially simultaneous development of sarcopenia, bedrest presents a difficult clinical challenge to the elderly individual.

RECENT FINDINGS

The etiology of accelerated sarcopenia has been described as a syndrome. The characteristics of this syndrome include combined alterations in neuromuscular control and muscle protein synthesis that increase the risk of morbidity and mortality in the elderly population. Moreover, the acute onset of bedrest-induced insulin resistance may further complicate the nutritionally derived maintenance of muscle mass and physical function.

SUMMARY

Even though many questions remain unresolved concerning the optimal clinical management of elderly individuals who undergo unanticipated bedrest, the supplementation of essential amino acids has shown promise as a therapeutic strategy to minimize the detrimental influence of hospitalization in the elderly. In turn, this nutritional adjunctive therapy may reduce the length of stay and the likelihood of repeated hospitalization.