Supplemental nitric oxide augments satellite cell activity on cultured myofibers from aged mice

Metformin ablates high fat diet-induced skeletal muscle hypertrophy and elevation of sarcolemmal GLUT4 when feeding is initiated in young adult male mice

A high-fat diet (HFD) and metabolic disease can impair insulin signaling in skeletal muscle, including a reduction in IRS-1 and GLUT-4 at the cell membrane. Other sarcolemmal proteins (e.g. caveolin-3, nNOS) within the dystrophin-glycoprotein complex (DGC) are partially lost with Type II diabetes. Thus, we hypothesized that a HFD would cause a significant loss of sarcolemmal DGC proteins and GLUT4, and the anti-diabetic drug metformin would mitigate the disruption of the DGC and preserve sarcolemmal GLUT4 on the soleus muscle. Eight-week-old mice were fed a high-fat diet for 12 weeks. After 8 weeks, one-half of the HFD mice received metformin for the remaining 4 weeks. HFD caused a marked increase in soleus muscle mass and fiber cross-sectional area and elevated sarcolemmal GLUT4, even though systemic insulin resistance was greater. HFD-induced muscle hypertrophy and elevated membrane GLUT4 were unexpectedly attenuated by metformin. In addition, IRS-1 positive staining was not reduced by HFD but rather enhanced in the metformin mice fed a high-fat diet. Sarcolemmal staining of dystrophin and caveolin-3 was reduced by HFD but not in the metformin group, while nNOS intensity was unaffected by HFD and metformin. These findings suggest that skeletal muscles in young adult mice can compensate for a high-fat diet and insulin resistance, with a minor disruption of the DGC, by maintaining cell membrane nNOS and IRS-1 and elevating GLUT4. We postulate that a window of compensatory GLUT4 and nNOS signaling allows calorically dense food to enhance skeletal muscle fiber size when introduced in adolescence.

Nitric oxide and hormesis

This present paper provides an assessment of the occurrence of nitric oxide (NO)-induced hormetic-biphasic dose/concentration relationships in biomedical research. A substantial reporting of such NO-induced hormetic effects was identified with particular focus on wound healing, tumor promotion, and sperm biology, including mechanistic assessment and potential for translational applications. Numerous other NO-induced hormetic effects have been reported, but require more development prior to translational applications. The extensive documentation of NO-induced biphasic responses, across numerous organs (e.g., bone, cardiovascular, immune, intestine, and neuronal) and cell types, suggests that NO-induced biological activities are substantially mediated via hormetic processes. These observations are particularly important because broad areas of NO biology are constrained by the quantitative features of the hormetic response. This determines the amplitude and width of the low dose stimulation, affecting numerous biomedical implications, study design features (e.g., number of doses, dose spacing, sample sizes, statistical power), and the potential success of clinical trials.

Positional Context of Myonuclear Transcription During Injury-Induced Muscle Regeneration

Fundamental aspects underlying downstream processes of skeletal muscle regeneration, such as myonuclear positioning and transcription are poorly understood. This investigation begins to address deficiencies in knowledge by examining the kinetics of myonuclear accretion, positioning, and global transcription during injury-induced muscle regeneration in mice. We demonstrate that myonuclear accretion plateaus within 7 days of an injury and that the majority (∼70%) of myonuclei are centrally aligned in linear arrays (nuclear chains) throughout the course of regeneration. Relatively few myonuclei were found in a peripheral position (∼20%) or clustered (∼10%) together during regeneration. Importantly, transcriptional activity of individual myonuclei in nuclear chains was high, and greater than that of peripheral or clustered myonuclei. Transcription occurring primarily in nuclear chains elevated the collective transcriptional activity of regenerating myofibers during the later stage of regeneration. Importantly, the number of myonuclei in chains and their transcriptional activity were statistically correlated with an increase in myofiber size during regeneration. Our findings demonstrate the positional context of transcription during regeneration and highlight the importance of centralized nuclear chains in facilitating hypertrophy of regenerating myofibers after injury.

Enhancing health span: muscle stem cells and hormesis

Sarcopenia is a significant public health and medical concern confronting the elderly. Considerable research is being directed to identify ways in which the onset and severity of sarcopenia may be delayed/minimized. This paper provides a detailed identification and assessment of hormetic dose responses in animal model muscle stem cells, with particular emphasis on cell proliferation, differentiation, and enhancing resilience to inflammatory stresses and how this information may be useful in preventing sarcopenia. Hormetic dose responses were observed following administration of a broad range of agents, including dietary supplements (e.g., resveratrol), pharmaceuticals (e.g., dexamethasone), endogenous ligands (e.g., tumor necrosis factor α), environmental contaminants (e.g., cadmium) and physical agents (e.g., low level laser). The paper assesses both putative mechanisms of hormetic responses in muscle stem cells, and potential therapeutic implications and application(s) of hormetic frameworks for slowing muscle loss and reduced functionality during the aging process.

Key concepts in muscle regeneration: muscle "cellular ecology" integrates a gestalt of cellular cross-talk, motility, and activity to remodel structure and restore function

This review identifies some key concepts of muscle regeneration, viewed from perspectives of classical and modern research. Early insights noted the pattern and sequence of regeneration across species was similar, regardless of the type of injury, and differed from epimorphic limb regeneration. While potential benefits of exercise for tissue repair was debated, regeneration was not presumed to deliver functional restoration, especially after ischemia-reperfusion injury; muscle could develop fibrosis and ectopic bone and fat. Standard protocols and tools were identified as necessary for tracking injury and outcomes. Current concepts vastly extend early insights. Myogenic regeneration occurs within the environment of muscle tissue. Intercellular cross-talk generates an interactive system of cellular networks that with the extracellular matrix and local, regional, and systemic influences, forms the larger gestalt of the satellite cell niche. Regenerative potential and adaptive plasticity are overlain by epigenetically regionalized responsiveness and contributions by myogenic, endothelial, and fibroadipogenic progenitors and inflammatory and metabolic processes. Muscle architecture is a living portrait of functional regulatory hierarchies, while cellular dynamics, physical activity, and muscle-tendon-bone biomechanics arbitrate regeneration. The scope of ongoing research-from molecules and exosomes to morphology and physiology-reveals compelling new concepts in muscle regeneration that will guide future discoveries for use in application to fitness, rehabilitation, and disease prevention and treatment.

NO-HDAC dual inhibitors

HDAC inhibitors and NO donors have both demonstrated independently broad therapeutic potential in a variety of diseases. Borretto et al. presented the topic of NO-HDAC dual inhibitors for the first time in 2013 as an attractive new topic. Here we collected the general structure of all synthesized NO-HDAC dual inhibitors, lead compounds, synthesis methods and biological features of the most potent dual NO-HDAC inhibitor in each category with the intention of assisting in the synthesis and optimization of new drug-like compounds for diverse diseases. Based on studies done so far, NO-HDAC dual inhibitors have displayed satisfactory results against wound healing (3), heart hypertrophy (3), inflammatory, cardiovascular, neuromuscular illnesses (11a-11e) and cancer (6a-6o, 9a-9d, 10a-10d, 16 and 17). NO-HDAC dual inhibitors can have high therapeutic potential for various diseases due to their new properties, NO properties, HDAC inhibitor properties and also due to the effects of NO on HDAC enzymes.

Targeting angiogenesis in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) represents one of the most devastating types of muscular dystrophies which affect boys already at early childhood. Despite the fact that the primary cause of the disease, namely the lack of functional dystrophin is known already for more than 30 years, DMD still remains an incurable disease. Thus, an enormous effort has been made during recent years to reveal novel mechanisms that could provide therapeutic targets for DMD, especially because glucocorticoids treatment acts mostly symptomatic and exerts many side effects, whereas the effectiveness of genetic approaches aiming at the restoration of functional dystrophin is under the constant debate. Taking into account that dystrophin expression is not restricted to muscle cells, but is present also in, e.g., endothelial cells, alterations in angiogenesis process have been proposed to have a significant impact on DMD progression. Indeed, already before the discovery of dystrophin, several abnormalities in blood vessels structure and function have been revealed, suggesting that targeting angiogenesis could be beneficial in DMD. In this review, we will summarize current knowledge about the angiogenesis status both in animal models of DMD as well as in DMD patients, focusing on different organs as well as age- and sex-dependent effects. Moreover, we will critically discuss some approaches such as modulation of vascular endothelial growth factor or nitric oxide related pathways, to enhance angiogenesis and attenuate the dystrophic phenotype. Additionally, we will suggest the potential role of other mediators, such as heme oxygenase-1 or statins in those processes.

Redox Control of Skeletal Muscle Regeneration

Skeletal muscle shows high plasticity in response to external demand. Moreover, adult skeletal muscle is capable of complete regeneration after injury, due to the properties of muscle stem cells (MuSCs), the satellite cells, which follow a tightly regulated myogenic program to generate both new myofibers and new MuSCs for further needs. Although reactive oxygen species (ROS) and reactive nitrogen species (RNS) have long been associated with skeletal muscle physiology, their implication in the cell and molecular processes at work during muscle regeneration is more recent. This review focuses on redox regulation during skeletal muscle regeneration. An overview of the basics of ROS/RNS and antioxidant chemistry and biology occurring in skeletal muscle is first provided. Then, the comprehensive knowledge on redox regulation of MuSCs and their surrounding cell partners (macrophages, endothelial cells) during skeletal muscle regeneration is presented in normal muscle and in specific physiological (exercise-induced muscle damage, aging) and pathological (muscular dystrophies) contexts. Recent advances in the comprehension of these processes has led to the development of therapeutic assays using antioxidant supplementation, which result in inconsistent efficiency, underlying the need for new tools that are aimed at precisely deciphering and targeting ROS networks. This review should provide an overall insight of the redox regulation of skeletal muscle regeneration while highlighting the limits of the use of nonspecific antioxidants to improve muscle function. Antioxid. Redox Signal. 27, 276-310.

Nitric oxide controls fat deposition in dystrophic skeletal muscle by regulating fibro-adipogenic precursor differentiation

Duchenne muscular dystrophy (DMD) is an hereditary disease characterized by loss of muscle fibers and their progressive substitution by fat and fibrous tissue. Mesenchymal fibro-adipogenic progenitors (FAPs) expressing the platelet-derived growth factor receptor alpha (PDGFRα) are an important source of fibrosis and adipogenesis in dystrophic skeletal muscle. Among the therapies suggested for dystrophy are those based on nitric oxide (NO) donating drugs, the administration of which slows disease progression. NO has been shown to act by enhancing the regenerative potential of the diseased muscle. Whether it acts also by inhibiting fibrosis and adipogenesis was not known. Here, we show in vitro that NO regulates FAP fate through inhibition of their differentiation into adipocytes. In mdx mice, an animal model of DMD, treatment with the NO donating drug molsidomine reduced the number of PDGFRα(+) cells as well as the deposition of both skeletal muscle fat and connective tissues. Inhibition of adipogenesis was due to NO-induced increased expression of miR-27b leading to downregulation of peroxisome proliferator-activated receptors gamma (Pparγ1) expression in a pathway independent of cGMP generation. These findings reveal an additional effect of NO in dystrophic muscle that conceivably synergizes with its known effects on regeneration improvement and explain why NO-based therapies appear effective in the treatment of muscular dystrophy.

The effects of age upon the expression of three miRNAs in muscle stem cells isolated from two different porcine skeletal muscles

Aging is associated with a gradual loss of skeletal muscle mass and an impaired ability of this tissue to compensate for trauma. Studies in rodents and humans have also shown that resident stem cells within muscle have a reduced ability to proliferate and differentiate. In this study muscle stem cells have been isolated from two muscles, the diaphragm (DIA) and the semimembranosus (SM), from young and old pigs. The levels of three micro-RNAs (miRNAs) were measured when cells were in a proliferative phase and after 24 and 72h in differentiation medium. All three miRNAs are abundant in skeletal muscle with miR-1 and miR-206 known to regulate myogenic differentiation and miR-24 is involved in cell cycle regulation. The levels of expression of Pax7 and the myogenic regulatory factors MyoD and myogenin were also measured. There were marked differences in expression of all three miRNAs between the two age groups. Both miR-1 and miR-206 were reduced in the cells from the older animals. In contrast miR-24 expression was significantly higher in cells from older animals under differentiation conditions. There were also significant differences in the relative expression of all three miRNAs between cells from the SM and DIA in both young and old animals. The changes in miRNA expression described in this study that relate to age, may play a role in the impaired differentiation capacity of older muscle stem cells.

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.

Nitric oxide prevents atorvastatin-induced skeletal muscle dysfunction and alterations in mice

INTRODUCTION

Myopathy is the most common side effect of statins. Because nitric oxide (NO) has a key role in regulating skeletal muscle function, we studied whether the NO-donating atorvastatin NCX 6560 could show a better profile on skeletal muscle function and structure compared with atorvastatin.

METHODS

C57BL/6 mice received atorvastatin 40 mg/kg/day or an equivalent dose of NCX 6560 for 2 months. Muscle function assessed by treadmill test, serum creatine kinase (CK) activity, citrate synthase (CS) activity, and muscle histology were evaluated.

RESULTS

Atorvastatin significantly (P < 0.001) reduced muscle endurance, increased serum CK by 6-fold, and induced muscle fiber atrophy. Conversely, NCX 6560 preserved muscle function, prevented CK increase and did not modify muscle structure. Interestingly, atorvastatin reduced CS activity, a marker for mitochondrial function, in gastrocnemius, diaphragm, and heart, whereas NCX 6560 prevented such decrease.

CONCLUSIONS

These findings suggest that NO may prevent statin-induced myopathy.

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.

A dual acting compound releasing nitric oxide (NO) and ibuprofen, NCX 320, shows significant therapeutic effects in a mouse model of muscular dystrophy

A resolutive therapy for muscular dystrophies, a heterogeneous group of genetic diseases leading to muscular degeneration and in the severe forms to death, is still lacking. Since inflammation and defects in nitric oxide generation are recognized key pathogenic events in muscular dystrophy, we have analysed the effects of a derivative of ibuprofen, NCX 320, belonging to the class of cyclooxygenase inhibiting nitric oxide donator (CINOD), in the α-sarcoglycan null mice, a severe mouse model of dystrophy. NCX 320 was administered daily in the diet for 8months starting 1month from weaning. Muscle functional recovery was evaluated by free wheel and treadmill tests at 8months. Serum creatine kinase activity, as well as the number of diaphragm inflammatory infiltrates and necrotic fibres, was measured as indexes of skeletal muscle damage. Muscle regeneration was evaluated in diaphragm and tibialis anterior muscles, measuring the numbers of centronucleated fibres and of myogenic precursor cells. NCX 320 mitigated muscle damage, reducing significantly serum creatine kinase activity, the number of necrotic fibres and inflammatory infiltrates. Moreover, NCX 320 stimulated muscle regeneration increasing significantly the number of myogenic precursor cells and regenerating fibres. All these effects concurred in inducing a significant improvement of muscle function, as assessed by both free wheel and treadmill tests. These results describe the properties of a new compound incorporating nitric oxide donation together with anti-inflammatory properties, showing that it is effective in slowing muscle dystrophy progression long term. Of importance, this new compound deserves specific attention for its potential in the therapy of muscular dystrophy given that ibuprofen is well tolerated in paediatric patients and with a profile of safety that makes it suitable for chronic treatment such as the one required in muscular dystrophies.

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

INTRODUCTION

Sarcopenia, and the importance of satellite cells (SCs) in muscle growth led us to examine the effects of exercise and age on SC activation and gene expression.

METHODS

Eight- and 18-month-old mice were either sedentary or underwent 3 weeks of exercise (N = 24). Body mass, distance traveled, and grip strength were recorded at weekly intervals. The extensor digitorum longus (EDL), tibialis anterior (TA), gastrocnemius (GAST), and quadriceps (QUAD) muscles were analyzed along with muscle fiber area, SC activation, neuronal nitric oxide synthase (NOS-I), MyoD, and myostatin protein content.

RESULTS

Older mice demonstrated decreased body mass, grip strength, and fiber area, but these changes were not affected by exercise. The QUAD muscle from young mice demonstrated an exercise-induced increase in SC activation and NOS-I and downregulation of myostatin.

CONCLUSIONS

Exercise-induced activation of SCs and regulation of gene expression are muscle-specific and age-dependent. Perturbed sensitivity to exercise in older mice provides insight into sarcopenia and potential treatments.

Evidence of heterogeneity within bovine satellite cells isolated from young and adult animals

Satellite cells are a heterogeneous population of myogenic precursors responsible for muscle growth and repair in mammals. The objectives of the experiment were to examine the growth rates and degree of heterogeneity within bovine satellite cells (BSC) isolated from young and adult animals. The BSC were harvested from the semimembranosus of young (4.3 ± 0.5 d) and adult (estimated 24 to 27 mo) cattle and cultured en masse. Young animal BSC re-enter the cell cycle sooner and reach maximal 5-ethynyl-2'-deoxyuridine (EdU) incorporation earlier (P < 0.05) than adult contemporaries. Adult BSC contain fewer (P < 0.05) MyoD and myogenin immunopositive nuclei than BSC isolated from young animals after 3, 4, and 5 d in culture. These results indicate that BSC from young animals activate, proliferate, and differentiate sooner than isolates from adult animals. Lineage heterogeneity within BSC was examined using antibodies specific for Pax7 and Myf5, lineage markers of satellite cells, and myoblasts. Immunocytochemistry revealed the majority of Pax7-expressing BSC also express Myf5; a minor population (~5%) fails to exhibit Myf5 immunoreactivity. The percentage of Pax7:Myf5 BSC from young animals decreases sooner (P < 0.05) in culture than adult BSC, indicating a more rapid rate of muscle fiber formation. A subpopulation immunopositive for Myf5 only was identified in both ages of BSC isolates. The growth kinetics and heterogeneity of young BSC was further evaluated by clonal analysis. Single cell clones were established and analyzed after 10 d. Colonies segregated into 2 groups based upon population doubling time. Immunostaining of the slow-growing colonies (population doubling time ≥ 3 d) revealed that a portion exhibited asymmetric distribution of the lineage markers Pax7 and Myf5, similar to self-renewable mouse muscle stem cells. In summary, these results offer insight into the heterogeneity of BSC and provide evidence for subtle differences between rodent and bovine myogenic precursors.

Nitric oxide donors improve prednisone effects on muscular dystrophy in the mdx mouse diaphragm

In Duchenne muscular dystrophy (DMD), palliative glucocorticoid therapy can produce myopathy or calcification. Since increased nitric oxide synthase activity in dystrophic mice promotes regeneration, the outcome of two nitric oxide (NO) donor drugs, MyoNovin (M) and isosorbide dinitrate (I), on the effectiveness of the anti-inflammatory drug prednisone (P) in alleviating progression of dystrophy was tested. Dystrophic mdx mice were treated (18 days) as controls or with an NO donor ± P. Fiber permeability and DNA synthesis were labeled by Evans blue dye (EBD) and bromodeoxyuridine uptake, respectively. P decreased body weight gain, M increased quadriceps mass, and I increased heart mass. P increased fiber permeability (%EBD+ fibers) and calcification in diaphragm. Treatment with NO donors + P (M+P, I+P) reduced %EBD+ fibers and calcification vs. P alone. %EBD+ fibers in M+P diaphragm did not differ from control. NO donor treatment reduced proliferation and the population of c-met+ cells and accelerated fiber regeneration. Concurrent with P, NO donor treatment suppressed two important detrimental effects of P in mice, possibly by accelerating regeneration, rebalancing satellite cell quiescence and activation in dystrophy, and/or increasing perfusion. Results suggest that NO donors could improve current therapy for DMD.

Are human and mouse satellite cells really the same?

Satellite cells are quiescent cells located under the basal lamina of skeletal muscle fibers that contribute to muscle growth, maintenance, repair, and regeneration. Mouse satellite cells have been shown to be muscle stem cells that are able to regenerate muscle fibers and self-renew. As human skeletal muscle is also able to regenerate following injury, we assume that the human satellite cell is, like its murine equivalent, a muscle stem cell. In this review, we compare human and mouse satellite cells and highlight their similarities and differences. We discuss gaps in our knowledge of human satellite cells, compared with that of mouse satellite cells, and suggest ways in which we may advance studies on human satellite cells, particularly by finding new markers and attempting to re-create the human satellite cell niche in vitro.

Satellite cells are increasingly refractory to activation by nitric oxide and stretch in aged mouse-muscle cultures

Age-related muscle atrophy or sarcopenia results in progressive loss of muscle function and satellite cells in aging muscle are increasingly refractory to activation that could mitigate atrophy. We know that nitric oxide release triggered by mechanical stretch of skeletal muscle, initiates satellite cell activation in vitro in single fiber, single cell and whole-muscle cultures, and in vivo in animals. This study examined muscle cell activation using tritiated-thymidine incorporation into the DNA of muscle cells in cultured muscles from female mice between 6 weeks and 18 months-of-age. Experiments examined age-related changes in activation by mechanical stretch and/or NO treatments (with the substrate of nitric oxide synthase (l-arginine), a nitric oxide donor (isosorbide dinitrate) and/or nitric oxide synthase inhibition). Activation without stretch was highest at 8 months. Stretching muscles by 10% more than doubled activation in muscles at 6 weeks of age and only a 20% stretch similarly activated cells in cultured 6-month-old muscles. Only treatment with ISDN in combination with a 20% stretch activated cell proliferation in muscles from 8-month-old mice. A nitric-oxide donor drug rescued muscle satellite cells in adult, 8-month-old mice from being refractory to mechanical stretch, apparently by overcoming an ineffective release of nitric oxide during stretch. Results suggest that treatment with nitric oxide has the potential to enhance the effectiveness of exercise in preventing the onset of age-related muscle atrophy in adult muscle.