Impact of ageing on muscle cell regeneration

Satellite glial cell manipulation prior to axotomy enhances developing dorsal root ganglion central branch regrowth into the spinal cord

The central and peripheral nervous systems (CNS and PNS, respectively) exhibit remarkable diversity in the capacity to regenerate following neuronal injury with PNS injuries being much more likely to regenerate than those that occur in the CNS. Glial responses to damage greatly influence the likelihood of regeneration by either promoting or inhibiting axonal regrowth over time. However, despite our understanding of how some glial lineages participate in nerve degeneration and regeneration, less is known about the contributions of peripheral satellite glial cells (SGC) to regeneration failure following central axon branch injury of dorsal root ganglia (DRG) sensory neurons. Here, using in vivo, time-lapse imaging in larval zebrafish coupled with laser axotomy, we investigate the role of SGCs in axonal regeneration. In our studies we show that SGCs respond to injury by relocating their nuclei to the injury site during the same period that DRG neurons produce new central branch neurites. Laser ablation of SGCs prior to axon injury results in more neurite growth attempts and ultimately a higher rate of successful central axon regrowth, implicating SGCs as inhibitors of regeneration. We also demonstrate that this SGC response is mediated in part by ErbB signaling, as chemical inhibition of this receptor results in reduced SGC motility and enhanced central axon regrowth. These findings provide new insights into SGC-neuron interactions under injury conditions and how these interactions influence nervous system repair.

Effects and Mechanisms of Polyunsaturated Fatty Acids on Age-Related Musculoskeletal Diseases: Sarcopenia, Osteoporosis, and Osteoarthritis-A Narrative Review

Background: The process of the globally aging population has been accelerating, leading to an increasing social burden. As people age, the musculoskeletal system will gradually go through a series of degenerative and loss of function and eventually develop age-related musculoskeletal diseases, like sarcopenia, osteoporosis, and osteoarthritis. On the other hand, several studies have shown that polyunsaturated fatty acids (PUFAs) possess various important physiological functions on the health of muscles, bones, and joints. Objective: This narrative review paper provides a summary of the literature about the effects and mechanisms of PUFAs on age-related musculoskeletal diseases for the prevention and management of these diseases. Methods: Web of Science, PubMed, Science Direct, and Scopus databases have been searched to select the relevant literature on epidemiological, cellular, and animal experiments and clinical evidence in recent decades with keywords "polyunsaturated fatty acids", "PUFAs", "omega-3", "omega-6", "musculoskeletal diseases", "sarcopenia", "osteoporosis", "osteoarthritis", and so on. Results: PUFAs could prevent and treat age-related musculoskeletal diseases (sarcopenia, osteoporosis, and osteoarthritis) by reducing oxidative stress and inflammation and controlling the growth, differentiation, apoptosis, and autophagy of cells. This review paper provides comprehensive evidence of PUFAs on age-related musculoskeletal diseases, which will be helpful for exploitation into functional foods and drugs for their prevention and treatment. Conclusions: PUFAs could play an important role in the prevention and treatment of sarcopenia, osteoporosis, and osteoarthritis.

Inhibitor of FTO, Rhein, Restrains the Differentiation of Myoblasts and Delays Skeletal Muscle Regeneration

N6-methyladenosine (m6A) is a crucial RNA modification affecting skeletal muscle development. Rhein, an anti-inflammatory extract, inhibits FTO, a key demethylase in m6A metabolism. Our study showed that during muscle fiber formation, FTO and ALKBH5 expression increased while m6A levels decreased. After muscle injury, FTO and ALKBH5 expression initially rose but later fell, while m6A levels initially dropped and then recovered. Inhibition of FTO by Rhein reduced MyHC and MyoG expression, indicating myoblast differentiation suppression. In a mouse model, Rhein decreased MyHC expression and muscle fiber cross-sectional area, delaying muscle regeneration. Rhein's ability to increase RNA m6A modification delays skeletal muscle remodeling post-injury, suggesting a new medicinal application for this plant extract.

The increasing prevalence of cancer in the elderly: An investigation of epidemiological trends

Cancer poses a significant health threat to the elderly, accounting for a substantial proportion of cancer patients aged 65 and above. As life expectancy continues to rise and the population ages, the incidence of cancer in the elderly is expected to increase further. Age is a major risk factor for the majority of common cancers, with the incidence and prevalence rising as individuals grow older. Factors such as chemoprevention and environmental carcinogen elimination may influence the process of carcinogenesis. Studies reveal that the incidence and mortality rates of various cancers in the elderly and extremely old individuals are on the rise worldwide, with most types peaking around the age of 75 to 90, followed by a sharp decline. Birth cohort and period effects also play a complex role in the connection between aging and cancer risk. Clinical trials often exclude older individuals, limiting our understanding of cancer treatments' effects on this particular age group. More research is needed to focus on the unique requirements of older adults with cancer.

Characterization of Proteome Changes in Aged and Collagen VI-Deficient Human Pericyte Cultures

Pericytes are a distinct type of cells interacting with endothelial cells in blood vessels and contributing to endothelial barrier integrity. Furthermore, pericytes show mesenchymal stem cell properties. Muscle-derived pericytes can demonstrate both angiogenic and myogenic capabilities. It is well known that regenerative abilities and muscle stem cell potential decline during aging, leading to sarcopenia. Therefore, this study aimed to investigate the potential of pericytes in supporting muscle differentiation and angiogenesis in elderly individuals and in patients affected by Ullrich congenital muscular dystrophy or by Bethlem myopathy, two inherited conditions caused by mutations in collagen VI genes and sharing similarities with the progressive skeletal muscle changes observed during aging. The study characterized pericytes from different age groups and from individuals with collagen VI deficiency by mass spectrometry-based proteomic and bioinformatic analyses. The findings revealed that aged pericytes display metabolic changes comparable to those seen in aging skeletal muscle, as well as a decline in their stem potential, reduced protein synthesis, and alterations in focal adhesion and contractility, pointing to a decrease in their ability to form blood vessels. Strikingly, pericytes from young patients with collagen VI deficiency showed similar characteristics to aged pericytes, but were found to still handle oxidative stress effectively together with an enhanced angiogenic capacity.

Sex-dependent regulation of vertebrate somatic growth and aging by germ cells

The function of germ cells in somatic growth and aging has been demonstrated in invertebrate models but remains unclear in vertebrates. We demonstrated sex-dependent somatic regulation by germ cells in the short-lived vertebrate model Nothobranchius furzeri. In females, germ cell removal shortened life span, decreased estrogen, and increased insulin-like growth factor 1 (IGF-1) signaling. In contrast, germ cell removal in males improved their health with increased vitamin D signaling. Body size increased in both sexes but was caused by different signaling pathways, i.e., IGF-1 and vitamin D in females and males, respectively. Thus, vertebrate germ cells regulate somatic growth and aging through different pathways of the endocrine system, depending on the sex, which may underlie the sexual difference in reproductive strategies.

Exploring the Role of Extracellular Vesicles in Skeletal Muscle Regeneration

Skeletal muscle regeneration entails a multifaceted process marked by distinct phases, encompassing inflammation, regeneration, and remodeling. The coordination of these phases hinges upon precise intercellular communication orchestrated by diverse cell types and signaling molecules. Recent focus has turned towards extracellular vesicles (EVs), particularly small EVs, as pivotal mediators facilitating intercellular communication throughout muscle regeneration. Notably, injured muscle provokes the release of EVs originating from myofibers and various cell types, including mesenchymal stem cells, satellite cells, and immune cells such as M2 macrophages, which exhibit anti-inflammatory and promyogenic properties. EVs harbor a specific cargo comprising functional proteins, lipids, and nucleic acids, including microRNAs (miRNAs), which intricately regulate gene expression in target cells and activate downstream pathways crucial for skeletal muscle homeostasis and repair. Furthermore, EVs foster angiogenesis, muscle reinnervation, and extracellular matrix remodeling, thereby modulating the tissue microenvironment and promoting effective tissue regeneration. This review consolidates the current understanding on EVs released by cells and damaged tissues throughout various phases of muscle regeneration with a focus on EV cargo, providing new insights on potential therapeutic interventions to mitigate muscle-related pathologies.

Reduced Expression of Septin7 Hinders Skeletal Muscle Regeneration

Septins are considered the fourth component of the cytoskeleton with the septin7 isoform playing a critical role in the formation of diffusion barriers in phospholipid bilayers and intra- and extracellular scaffolds. While its importance has already been confirmed in different intracellular processes, very little is known about its role in skeletal muscle. Muscle regeneration was studied in a Sept7 conditional knock-down mouse model to prove the possible role of septin7 in this process. Sterile inflammation in skeletal muscle was induced which was followed by regeneration resulting in the upregulation of septin7 expression. Partial knock-down of Sept7 resulted in an increased number of inflammatory cells and myofibers containing central nuclei. Taken together, our data suggest that partial knock-down of Sept7 hinders the kinetics of muscle regeneration, indicating its crucial role in skeletal muscle functions.

Interplay of skeletal muscle and adipose tissue: sarcopenic obesity

Sarcopenic obesity is becoming a global health concern, owing to the rising older population, causing cardiometabolic morbidity and mortality. Loss of muscle exceeding normal age-related changes has been revealed to be associated with obesity, aggravating each other through complex interactions. Physiological regeneration and proliferation of muscle tissue are achieved through harmonious processes of regulated inflammation, autophagy, muscle satellite cell proliferation, and signaling molecule function. Adipokines and myokines are signaling molecules from adipose tissue and muscle, respectively, that exert autocrine, paracrine, and endocrine effects on fat and muscle tissues. These signaling molecules interact with each other to regulate metabolic homeostasis. However, excessive adiposity creates pro-inflammatory conditions, leading to metabolic disorders and the disorganization of systemic homeostasis. Therefore, obesity impedes muscle tissue regeneration and induces the loss of muscle mass and function. Numerous studies have attempted to demonstrate the pathophysiological interaction between sarcopenia and obesity, but the interwoven matrix of the relationship between myokines and adipokines has made it difficult for researchers to understand them. This review briefly describes updated information about the crosstalk between muscle and adipose tissue.

Spatial compartmentalization of signaling imparts source-specific functions on secreted factors

Efficient regeneration requires multiple cell types acting in coordination. To better understand the intercellular networks involved and how they change when regeneration fails, we profile the transcriptome of hematopoietic, stromal, myogenic, and endothelial cells over 14 days following acute muscle damage. We generate a time-resolved computational model of interactions and identify VEGFA-driven endothelial engagement as a key differentiating feature in models of successful and failed regeneration. In addition, the analysis highlights that the majority of secreted signals, including VEGFA, are simultaneously produced by multiple cell types. To test whether the cellular source of a factor determines its function, we delete VEGFA from two cell types residing in close proximity: stromal and myogenic progenitors. By comparing responses to different types of damage, we find that myogenic and stromal VEGFA have distinct functions in regeneration. This suggests that spatial compartmentalization of signaling plays a key role in intercellular communication networks.

Secreted Protein Acidic and Rich in Cysteine (SPARC)-Mediated Exercise Effects: Illustrative Molecular Pathways against Various Diseases

The strong benefits of exercise, in addition to the development of both the therapeutic applications of physical activity and molecular biology tools, means that it has become very important to explore the underlying molecular patterns linking exercise and its induced phenotypic changes. Within this context, secreted protein acidic and rich in cysteine (SPARC) has been characterized as an exercise-induced protein that would mediate and induce some important effects of exercise. Herein, we suggest some underlying pathways to explain such SPARC-induced exercise-like effects. Such mechanistic mapping would not only allow us to understand the molecular processes of exercise and SPARC effects but would also highlight the potential to develop novel molecular therapies. These therapies would be based on mimicking the exercise benefits via either introducing SPARC or pharmacologically targeting the SPARC-related pathways to produce exercise-like effects. This is of a particular importance for those who do not have the ability to perform the required physical activity due to disabilities or diseases. The main objective of this work is to highlight selected potential therapeutic applications deriving from SPARC properties that have been reported in various publications.

Dietary Leucine Supplementation Improves Muscle Fiber Growth and Development by Activating AMPK/Sirt1 Pathway in Blunt Snout Bream (Megalobrama amblycephala)

This research is aimed at evaluating the effects of leucine supplementation on muscle fibers growth and development of blunt snout bream through a feeding trial and a primary muscle cells treatment. An 8-week trial with diets containing 1.61% leucine (LL) or 2.15% leucine (HL) was conducted in blunt snout bream (mean initial weight = 56.56 ± 0.83 g). Results demonstrated that the specific gain rate and the condition factor of fish in the HL group were the highest. The essential amino acids content of fish fed HL diets was significantly higher than that fed LL diets. The texture (hardness, springiness, resilience, and chewiness), the small-sized fiber ratio, fibers density, and sarcomere lengths in fish all obtained the highest in the HL group. Additionally, the proteins expression related with the activation of the AMPK pathway (p-Ampk, Ampk, p-Ampk/Ampk, and Sirt1) and the expression of genes (myogenin (myog), myogenic regulatory factor 4 (mrf4) and myoblast determination protein (myod), and protein (Pax7) related to muscle fiber formation were significantly upregulated with increasing level of dietary leucine. In vitro, the muscle cells were treated with 0, 40 and 160 mg/L leucine for 24 h. The results showed that treated with 40 mg/L leucine significantly raised the protein expressions of BCKDHA, Ampk, p-Ampk, p-Ampk/Ampk, Sirt1, and Pax7 and the gene expressions of myog, mrf4, and myogenic factor 5 (myf5) in muscle cells. In summary, leucine supplementation promoted muscle fibers growth and development, which may be related to the activation of BCKDH and AMPK.

Mechanical strain drives exosome production, function, and miRNA cargo in C2C12 muscle progenitor cells

Mesenchymal stem cells (MSCs) have been proven to promote tissue repair. However, concerns related to their clinical application and regulatory hurdles remain. Recent data has demonstrated the proregenerative secretome of MSCs can result in similar effects in the absence of the cells themselves. Within the secretome, exosomes have emerged as a promising regenerative component. Exosomes, which are nanosized lipid vesicles secreted by cells, encapsulate micro-RNA (miRNA), RNA, and proteins that drive MSCs regenerative potential with cell specific content. As such, there is an opportunity to optimize the regenerative potential of MSCs, and thus their secreted exosome fraction, to improve clinical efficacy. Exercise is one factor that has been shown to improve muscle progenitor cell function and regenerative potential. However, the effect of exercise on MSC exosome content and function is still unclear. To address this, we used an in vitro culture system to evaluate the effects of mechanical strain, an exercise mimetic, on C2C12 (muscle progenitor cell) exosome production and proregenerative function. Our results indicate that the total exosome production is increased by mechanical strain and can be regulated with different tensile loading regimens. Furthermore, we found that exosomes from mechanically stimulated cells increase proliferation and myogenic differentiation of naïve C2C12 cells. Lastly, we show that exosomal miRNA cargo is differentially expressed following strain. Gene ontology mapping suggests positive regulation of bone morphogenetic protein signaling, regulation of actin-filament-based processes, and muscle cell apoptosis may be at least partially responsible for the proregenerative effects of exosomes from mechanically stimulated C2C12 muscle progenitor cells.

Electroacupuncture of Weizhong (BL-40) Acupoint Inspires Muscular Satellite Cell Regeneration and Promotes Muscle Repair Capacity after Back Muscle Injury in Sprague-Dawley Rat Model

Background

Back muscle injury is the most common illness involved in aged people. Muscular satellite cells, playing a key role in the muscle repairing process, are gradually losing their regenerative ability with aging, which attenuates the injured muscle repairing process. Electroacupuncture at Weizhong acupoint has been widely used in the treatment of young and aged patients with back muscle damage. Its efficacy has been proven by a randomized double-blind placebo clinical trial. However, the rehabilitation mechanisms are largely unknown. This study will explore the possible mechanisms associated with electroacupuncture at the Weizhong acupoint (BL 40) promoting muscle repairing ability.

Method

A total of 58 male and female Sprague-Dawley rats were divided into a younger group (4-month-old) and an aged group (16-month-old), younger and aged rats were further divided as a sham, injured, injured rats treated with electroacupuncture at Weizhong point or treated with Non-Weizhong point groups. The back muscle injury model was produced in rats as a previously described method with modification. Furthermore, Weizhong acupoints underwent electroacupuncture treatment with 15 V magnitude, 2 Hz/10 Hz frequency density, 1.0 mA current intensity, and 10 min each day for 10 consecutive days using HANS's electroacupuncture apparatus. After the last treatment, the paravertebral muscles and serum of all animals were undergone histological, immunohistochemistry, and flow cytometry analysis. Serum levels of Creatine Kinase (CK) and proinflammatory cytokine, interleukin 6 (IL-6), were measured separately by using ELISA kit.

Results

Electroacupuncture of Weizhong (BL 40) acupoints significantly attenuated back muscle damage in both young and aged rats, increasing PAX7 (a marker of muscle satellite cells) and MYOD (major marker of myoblasts) cells, simultaneously, reducing serum proinflammatory cytokines, IL-6, and downregulation of p38 MAPK signaling in aged muscular satellite cells.

Conclusion

Our studies suggest that electroacupuncture of Weizhong (BL 40) acupoints can restore aged back muscular satellite cells and their regeneration capacity. These suggested electroacupuncture may be a potential means of promoting rehabilitation for muscular injury in aged patients.

The Effect of Voluntary Physical Activity in an Enriched Environment and Combined Exercise Training on the Satellite Cell Pool in Developing Rats

Aim: Postnatal skeletal muscle growth is strongly associated with a satellite cell pool. Early adolescence might be a crucial period when different exercise training interventions have specific consequence on satellite cells. Pax7 and MyoD have been suggested as the leading indicators of satellite cell activation.

Methods: In this study, pre-adolescent male rats (n = 18) were either subjected to an enriched environment that facilitated physical activities or combined training or control for three weeks. The flexor hallucis longus muscle was removed for biochemical and histochemical analysis.

Results: Findings demonstrated that exercise trained rats displayed high levels of serum IGF-1 (p <0.05). There was an increase in Pax7 (p <0.05) and MyoD (p <0.001) mRNA expression. A significant increase in the mean fiber area (p <0.01), satellite cell (p <0.001), and myonuclear numbers (p <0.01) were also observed in both intervention groups. Importantly, enriched rats showed lower corticosterone levels (p <0.05) compared to training ones. Regarding performance, trained and enriched rats had significant improvement in forelimb grip strength (p <0.01) and load-carrying capacity (p <0.05).

Conclusion: Type of physical exercise is an essential part in changing satellite cells pool. Different and frequent physical activities in an enriched environment can be effective for muscle development.

Development of a histopathological index for skeletal muscle analysis in Rattus norvegicus (Rodentia: Muridae)

Skeletal muscle histopathological changes induced or caused by pathologies in animal models, can impair functionality, being the main focus of therapeutic studies. This study aimed to propose a histopathological index to assess, in a quantitative manner, skeletal muscle changes induced by experimental protocols for Rodentia's models. For the development, evaluation of fit and parsimony, replicability, and sensitivity index, Wistar rats from experiments with the same experimental design, but with different variation factors, were used to achieve different levels of damage. The anterior tibial muscle of these animals was collected, processed histologically, and stained with hematoxylin and eosin. The adjustment and parsimony of the index were availed through Confirmatory Factor Analysis, reproducibility for evaluation of three people trained through the Intra-Class Correlation, and the discrimination capacity through a one-way ANOVA Test. We pointed out the adjustment for the proposed index while the ICC showed high reproducibility (n = 56; k = 3; ICC = 0.9790) and differences in the extent of damage between groups, following the hierarchical association promoted by experimental model stresses. The results show that the proposed index has a good fit and parsimony (χ² = 426.34; p < 0.0001), in addition to being easily replicable by other researchers who know the morphology of muscle tissue and its morphological changes. It is worth mentioning that the development of tools that facilitate histopathological analysis, and that can quantitatively express the findings, are of great importance for the studies of regenerative science, reinforcing the relevance of this study.

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.

Secreted Protein Acidic and Rich in Cysteine (Sparc) KO Leads to an Accelerated Ageing Phenotype Which Is Improved by Exercise Whereas SPARC Overexpression Mimics Exercise Effects in Mice

Secreted protein acidic and rich in cysteine (SPARC) is a matricellular glycoprotein implicated in various functions, including metabolism, tissue regeneration, and functional homeostasis. SPARC/Sparc declines with ageing but increases with exercise. We aim to verify two hypotheses: (1) SPARC deficiency leads to an ageing-like phenotype (metabolic decline, muscle loss, etc.), and (2) SPARC overexpression would mimic exercise, counteract ageing, and improve age-related changes. Our mice experiments are divided into two parts. First, we explore the consequences of Sparc knockout (KO) and compare them to the ageing effects. We also observe the effects of exercise. In the second part, we study the effects of SPARC overexpression and compare them to the exercise benefits. At the end, we make an analysis of the results to point out the analogies between Sparc KO and the ageing-like phenotype on the one hand and make comparisons between SPARC overexpression and exercise in the context of exercise counteracting ageing. The measurements were mainly related to tissue weights, adiposity, metabolism, and muscle strength. The main findings are that Sparc KO reduced glucose tolerance, muscle glucose transporter expression, and abdominal adipose tissue weight but increased glycogen content in the muscle. SPARC overexpression increased muscle strength, muscle mass, and expressions of the muscle glucose transporter and mitochondrial oxidative phosphorylation but lowered the glycemia and the adiposity, especially in males. Collectively, these findings, and the data we have previously reported, show that Sparc KO mice manifest an ageing-like phenotype, whereas SPARC overexpression and exercise generate similar benefits. The benefits are towards counteracting both the SPARC deficiency-induced ageing-like phenotype as well as reversing the age-related changes. The potential applications of these findings are to build/optimize Sparc KO-based animal models of various health conditions and, on the other hand, to develop therapies based on introducing SPARC or targeting SPARC-related pathways to mimic exercise against age-related and metabolic disorders.

Multifactorial Mechanism of Sarcopenia and Sarcopenic Obesity. Role of Physical Exercise, Microbiota and Myokines

Obesity and ageing place a tremendous strain on the global healthcare system. Age-related sarcopenia is characterized by decreased muscular strength, decreased muscle quantity, quality, and decreased functional performance. Sarcopenic obesity (SO) is a condition that combines sarcopenia and obesity and has a substantial influence on the older adults’ health. Because of the complicated pathophysiology, there are disagreements and challenges in identifying and diagnosing SO. Recently, it has become clear that dysbiosis may play a role in the onset and progression of sarcopenia and SO. Skeletal muscle secretes myokines during contraction, which play an important role in controlling muscle growth, function, and metabolic balance. Myokine dysfunction can cause and aggravate obesity, sarcopenia, and SO. The only ways to prevent and slow the progression of sarcopenia, particularly sarcopenic obesity, are physical activity and correct nutritional support. While exercise cannot completely prevent sarcopenia and age-related loss in muscular function, it can certainly delay development and slow down the rate of sarcopenia. The purpose of this review was to discuss potential pathways to muscle deterioration in obese individuals. We also want to present the current understanding of the role of various factors, including microbiota and myokines, in the process of sarcopenia and SO.

Matrisome, innervation and oxidative metabolism affected in older compared with younger males with similar physical activity

BACKGROUND

Due to the interaction between skeletal muscle ageing and lifestyle factors, it is often challenging to attribute the decline in muscle mass and quality to either changes in lifestyle or to advancing age itself. Because many of the physiological factors affecting muscle mass and quality are modulated by physical activity and physical activity declines with age, the aim of this study is to better understand the effects of early ageing on muscle function by comparing a population of healthy older and young males with similar physical activity patterns.

METHODS

Eighteen older (69 ± 2.0 years) and 20 young (22 ± 2.0 years) males were recruited based on similar self-reported physical activity, which was verified using accelerometry measurements. Gene expression profiles of vastus lateralis biopsies obtained by RNA sequencing were compared, and key results were validated using quantitative polymerase chain reaction and western blot.

RESULTS

Total physical activity energy expenditure was similar between the young and old group (404 ± 215 vs. 411 ± 189 kcal/day, P = 0.11). Three thousand seven hundred ninety-seven differentially expressed coding genes (DEGs) were identified (adjusted P-value cut-off of <0.05), of which 1891 were higher and 1906 were lower expressed in the older muscle. The matrisome, innervation and inflammation were the main upregulated processes, and oxidative metabolism was the main downregulated process in old compared with young muscle. Lower protein levels of mitochondrial transcription factor A (TFAM, P = 0.030) and mitochondrial respiratory Complexes IV and II (P = 0.011 and P = 0.0009, respectively) were observed, whereas a trend was observed for Complex I (P = 0.062), in older compared with young muscle. Protein expression of Complexes I and IV was significantly correlated to mitochondrial capacity in the vastus lateralis as measured in vivo (P = 0.017, R2  = 0.42 and P = 0.030, R2  = 0.36). A trend for higher muscle-specific receptor kinase (MUSK) protein levels in the older group was observed (P = 0.08).

CONCLUSIONS

There are clear differences in the transcriptome signatures of the vastus lateralis muscle of healthy older and young males with similar physical activity levels, including significant differences at the protein level. By disentangling physical activity and ageing, we appoint early skeletal muscle ageing processes that occur despite similar physical activity. Improved understanding of these processes will be key to design targeted anti-ageing therapies.

Sarcopenia versus cancer cachexia: the muscle wasting continuum in healthy and diseased aging

Muscle wasting is one of the major health problems in older adults and is traditionally associated to sarcopenia. Nonetheless, muscle loss may also occur in older adults in the presence of cancer, and in this case, it is associated to cancer cachexia. The clinical management of these conditions is a challenge due to, at least in part, the difficulties in their differential diagnosis. Thus, efforts have been made to better comprehend the pathogenesis of sarcopenia and cancer cachexia, envisioning the improvement of their clinical discrimination and treatment. To add insights on this topic, this review discusses the current knowledge on key molecular players underlying sarcopenia and cancer cachexia in a comparative perspective. Data retrieved from this analysis highlight that while sarcopenia is characterized by the atrophy of fast-twitch muscle fibers, in cancer cachexia an increase in the proportion of fast-twitch fibers appears to happen. The molecular drivers for these specificmuscle remodeling patterns are still unknown; however, among the predominant contributors to sarcopenia is the age-induced neuromuscular denervation, and in cancer cachexia, the muscle disuse experienced by cancer patients seems to play an important role. Moreover, inflammation appears to be more severe in cancer cachexia. Impairment of nutrition-related mediators may also contribute to sarcopenia and cancer cachexia, being distinctly modulated in each condition.

Skeletal muscle wasting after a severe burn is a consequence of cachexia and sarcopenia

Muscle wasting is common and persistent in severely burned patients, worsened by immobilization during treatment. In this review, we posit two major phenotypes of muscle wasting after severe burn, cachexia and sarcopenia, each with distinguishing characteristics to result in muscle atrophy; these characteristics are also likely present in other critically ill populations. An online search was conducted from the PubMed database and other available online resources and we manually extracted published articles in a systematic mini review. We describe the current definitions and characteristics of cachexia and sarcopenia and relate these to muscle wasting after severe burn. We then discuss these putative mechanisms of muscle atrophy in this condition. Severe burn and immobilization have distinctive patterns in mediating muscle wasting and muscle atrophy. In considering these two pathological phenotypes (cachexia and sarcopenia), we propose two independent principal causes and mechanisms of muscle mass loss after burns: (1) inflammation-induced cachexia, leading to proteolysis and protein degradation, and (2) sarcopenia/immobility that signals inhibition of expected increases in protein synthesis in response to protein loss. Because both are present following severe burn, these should be considered independently in devising treatments. Discussing cachexia and sarcopenia as independent mechanisms of severe burn-initiated muscle wasting is explored. Recognition of these associated mechanisms will likely improve outcomes.

3D in vitro models of skeletal muscle: myopshere, myobundle and bioprinted muscle construct

Typical two-dimensional (2D) culture models of skeletal muscle-derived cells cannot fully recapitulate the organization and function of living muscle tissues, restricting their usefulness in in-depth physiological studies. The development of functional 3D culture models offers a major opportunity to mimic the living tissues and to model muscle diseases. In this respect, this new type of in vitro model significantly increases our understanding of the involvement of the different cell types present in the formation of skeletal muscle and their interactions, as well as the modalities of response of a pathological muscle to new therapies. This second point could lead to the identification of effective treatments. Here, we report the significant progresses that have been made the last years to engineer muscle tissue-like structures, providing useful tools to investigate the behavior of resident cells. Specifically, we interest in the development of myopshere- and myobundle-based systems as well as the bioprinting constructs. The electrical/mechanical stimulation protocols and the co-culture systems developed to improve tissue maturation process and functionalities are presented. The formation of these biomimetic engineered muscle tissues represents a new platform to study skeletal muscle function and spatial organization in large number of physiological and pathological contexts.

Small heat-shock protein HSPB3 promotes myogenesis by regulating the lamin B receptor

One of the critical events that regulates muscle cell differentiation is the replacement of the lamin B receptor (LBR)-tether with the lamin A/C (LMNA)-tether to remodel transcription and induce differentiation-specific genes. Here, we report that localization and activity of the LBR-tether are crucially dependent on the muscle-specific chaperone HSPB3 and that depletion of HSPB3 prevents muscle cell differentiation. We further show that HSPB3 binds to LBR in the nucleoplasm and maintains it in a dynamic state, thus promoting the transcription of myogenic genes, including the genes to remodel the extracellular matrix. Remarkably, HSPB3 overexpression alone is sufficient to induce the differentiation of two human muscle cell lines, LHCNM2 cells, and rhabdomyosarcoma cells. We also show that mutant R116P-HSPB3 from a myopathy patient with chromatin alterations and muscle fiber disorganization, forms nuclear aggregates that immobilize LBR. We find that R116P-HSPB3 is unable to induce myoblast differentiation and instead activates the unfolded protein response. We propose that HSPB3 is a specialized chaperone engaged in muscle cell differentiation and that dysfunctional HSPB3 causes neuromuscular disease by deregulating LBR.

Recent advances and future avenues in understanding the role of adipose tissue cross talk in mediating skeletal muscle mass and function with ageing

Sarcopenia, broadly defined as the age-related decline in skeletal muscle mass, quality, and function, is associated with chronic low-grade inflammation and an increased likelihood of adverse health outcomes. The regulation of skeletal muscle mass with ageing is complex and necessitates a delicate balance between muscle protein synthesis and degradation. The secretion and transfer of cytokines, long non-coding RNAs (lncRNAs) and microRNAs (miRNAs), both discretely and within extracellular vesicles, have emerged as important communication channels between tissues. Some of these factors have been implicated in regulating skeletal muscle mass, function, and pathologies and may be perturbed by excessive adiposity. Indeed, adipose tissue participates in a broad spectrum of inter-organ communication and obesity promotes the accumulation of macrophages, cellular senescence, and the production and secretion of pro-inflammatory factors. Pertinently, age-related sarcopenia has been reported to be more prevalent in obesity; however, such effects are confounded by comorbidities and physical activity level. In this review, we provide evidence that adiposity may exacerbate age-related sarcopenia and outline some emerging concepts of adipose-skeletal muscle communication including the secretion and processing of novel myokines and adipokines and the role of extracellular vesicles in mediating inter-tissue cross talk via lncRNAs and miRNAs in the context of sarcopenia, ageing, and obesity. Further research using advances in proteomics, transcriptomics, and techniques to investigate extracellular vesicles, with an emphasis on translational, longitudinal human studies, is required to better understand the physiological significance of these factors, the impact of obesity upon them, and their potential as therapeutic targets in combating muscle wasting.

Modulation of Ki67 and myogenic regulatory factor expression by tocotrienol-rich fraction ameliorates myogenic program of senescent human myoblasts

INTRODUCTION

Replicative senescence results in dysregulation of cell proliferation and differentiation, which plays a role in the regenerative defects observed during age-related muscle atrophy. Vitamin E is a well-known antioxidant, which potentially ameliorates a wide range of age-related manifestations. The aim of this study was to determine the effects of tocotrienol-rich fraction (TRF) in modulating the expression of proliferation- and differentiation-associated proteins in senescent human myoblasts during the differentiation phase.

MATERIAL AND METHODS

Human skeletal muscle myoblasts were cultured until senescence. Young and senescent cells were treated with TRF for 24 h before and after differentiation induction, followed by evaluation of cellular morphology and efficiency of differentiation. Expression of cell proliferation marker Ki67 protein and myogenic regulatory factors MyoD and myogenin were determined.

RESULTS

Our findings showed that treatment with TRF significantly improved the morphology of senescent myoblasts. Promotion of differentiation was observed in young and senescent myoblasts with TRF treatment as shown by the increased fusion index and larger size of myotubes. Increased Ki67 and myogenin expression with TRF treatment was also observed in senescent myoblasts, suggesting amelioration of the myogenic program by TRF during replicative senescence.

CONCLUSIONS

TRF modulates the expression of regulatory factors related to proliferation and differentiation in senescent human myoblasts and could be beneficial for ameliorating the regenerative defects during aging.

Redox-dependent regulation of satellite cells following aseptic muscle trauma: Implications for sports performance and nutrition

Skeletal muscle satellite cells (SCs) are indispensable for tissue regeneration, remodeling and growth. Following myotrauma, SCs are activated, and assist in tissue repair. Exercise-induced muscle damage (EIMD) is characterized by a pronounced inflammatory response and the production of reactive oxygen species (ROS). Experimental evidence suggests that SCs kinetics (the propagation from a quiescent to an activated/proliferative state) following EIMD is redox-dependent and interconnected with changes in the SCs microenvironment (niche). Animal studies have shown that following aseptic myotrauma, antioxidant and/or anti-inflammatory supplementation leads to an improved recovery and skeletal muscle regeneration through enhanced SCs kinetics, suggesting a redox-dependent molecular mechanism. Although evidence suggests that antioxidant/anti-inflammatory compounds may prevent performance deterioration and enhance recovery, there is lack of information regarding the redox-dependent regulation of SCs responses following EIMD in humans. In this review, SCs kinetics following aseptic myotrauma, as well as the intrinsic redox-sensitive molecular mechanisms responsible for SCs responses are discussed. The role of redox status on SCs function should be further investigated in the future with human clinical trials in an attempt to elucidate the molecular pathways responsible for muscle recovery and provide information for potential nutritional strategies aiming at performance recovery.

The application of bone marrow mesenchymal stem cells and biomaterials in skeletal muscle regeneration

Skeletal muscle injuries have bothered doctors and caused great burdens to the public medical insurance system for a long time. Once injured, skeletal muscles usually go through the processes of inflammation, repairing and remodeling. If repairing and remodeling stages are out of balance, scars will be formed to replace injured skeletal muscles. At present, clinicians usually use conventional methods to restore the injured skeletal muscles, such as flap transplantation. However, flap transplantation sometimes needs to sacrifice healthy autologous tissues and will bring extra harm to patients. In recent years, stem cells-based tissue engineering provides us new treatment ideas for skeletal muscle injuries. Stem cells are cells with multiple differentiation potential and have ability to differentiate into adult cells under special condition. Skeletal muscle tissues also have stem cells, called satellite cells, but they are in small amount and new muscle fibers that derived from them may not be enough to replace injured fibers. Bone marrow mesenchymal stem cells (BM-MSCs) could promote musculoskeletal tissue regeneration and activate the myogenic differentiation of satellite cells. Biomaterial is another important factor to promote tissue regeneration and greatly enhance physiological activities of stem cells in vivo. The combined use of stem cells and biomaterials will gradually become a mainstream to restore injured skeletal muscles in the future. This review article mainly focuses on the review of research about the application of BM-MSCs and several major biomaterials in skeletal muscle regeneration over the past decades.

Caloric restriction: implications for sarcopenia and potential mechanisms

Sarcopenia is a potential risk factor for weakness, disability and death in elderly individuals. Therefore, seeking effective methods to delay and treat sarcopenia and to improve the quality of life of elderly individuals is a trending topic in geriatrics. Caloric restriction (CR) is currently recognized as an effective means to extend the lifespan and delay the decline in organ function caused by aging. In this review, we describe the effects of CR on improving muscle protein synthesis, delaying muscle atrophy, regulating muscle mitochondrial function, maintaining muscle strength, promoting muscle stem cell (MuSC) regeneration and differentiation, and thus protecting against sarcopenia. We also summarize the possible cellular mechanisms by which CR delays sarcopenia. CR can delay sarcopenia by reducing the generation of oxygen free radicals, reducing oxidative stress damage, enhancing mitochondrial function, improving protein homeostasis, reducing iron overload, increasing autophagy and apoptosis, and reducing inflammation. However, the relationships between CR and genetics, sex, animal strain, regimen duration and energy intake level are complex. Therefore, further study of the proper timing and application method of CR to prevent sarcopenia is highly important for the aging population.

Remodeling of the soleus muscle of ovariectomized old female rats submitted to resistance training and different diet intake

Sarcopenia is a common condition that is associated mainly with hormonal factors, nutritional status, physical activity, leading to a lower quality of life. Thus, this study aimed to evaluate the effects of diets with vegetable or animal proteins (AP) associated with resistance training on the structure of the soleus muscle in aged Wistar rats. The histochemical technique was used for the typing of muscle fibers, the cross-sectional area of myocytes, and volume densities of myocytes and interstitium. Picrosirius stain was used to quantify the collagen density. Diet intake, mainly animal protein, associated with resistance training leaded to muscle remodeling, and increased deposit of collagen fibers. We observed hypertrophy in animal groups that consumed animal protein diet, even the sedentary group, although more evident in those trained.

Bioengineered Skeletal Muscle as a Model of Muscle Aging and Regeneration

With age, adult skeletal muscle (SkM) is known to decrease in muscle mass, strength, and functional capacity, a state known as sarcopenia. Here we developed an in vitro three-dimensional (3D) bioengineered senescent SkM tissue using primary human myoblasts. These tissues exhibited the characteristics of atrophied muscle, including expression of senescent genes, decreased number of satellite cells, reduced number and size of myofibers, and compromised metabolism and calcium flux. As a result, senescent SkM tissues showed impaired ability to generate force in response to electrical stimulation compared with young tissues. Furthermore, in contrast to young SkM tissues, senescent tissues failed to regenerate in response to injury, possibly as a result of persistent apoptosis and failure to initiate a proliferation program. Our findings suggest that 3D senescent SkM may provide a powerful model for studying aging and a platform for drug testing and discovery of therapeutic compounds to improve the function of sarcopenic muscle. Impact statement Skeletal muscle (SkM) plays important physiological roles and has significant regenerative capacity. However, aged SkM lose their functionality and regeneration ability. In this article, we present a senescent human bioengineering SkM tissue model that can be used to investigate senescence, metabolic or genetic diseases that inflict SkM, and to test various strategies including novel small molecules that restore muscle function and promote regeneration. One key limitation of two-dimensional cell culture system is the detachment of contractile myotubes from the surface over time, thereby limiting the evaluation of myogenic function. Here we use primary human myoblasts, which exhibit all major hallmarks of aging to mimic the organization and function of native muscle. Using this system, we were able to measure the contractile function, calcium transients, and regeneration capacity of SkM tissues. We also evaluated the response of senescent SkM tissues to injury and their ability to regenerate and recover, compared with "young" tissues. Our results suggest that three-dimensional constructs enable organization of contractile units including myosin and actin filaments, thereby providing a powerful platform for the quantitative assessment of muscle myotubes in response to injury, genetic or metabolic disorders, or pharmacological testing.

Potential Role of Tocotrienols on Non-Communicable Diseases: A Review of Current Evidence

Tocotrienol (T3) is a subfamily of vitamin E known for its wide array of medicinal properties. This review aimed to summarize the health benefits of T3, particularly in prevention or treatment of non-communicable diseases (NCDs), including cardiovascular, musculoskeletal, metabolic, gastric, and skin disorders, as well as cancers. Studies showed that T3 could prevent various NCDs, by suppressing 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) in the mevalonate pathway, inflammatory response, oxidative stress, and alternating hormones. The efficacy of T3 in preventing/treating these NCDs is similar or greater compared to tocopherol (TF). TF may lower the efficacy of T3 because the efficacy of the combination of TF and T3 was lower than T3 alone in some studies. Data investigating the effects of T3 on osteoporosis, arthritis, and peptic ulcers in human are limited. The positive outcomes of T3 treatment obtained from the preclinical studies warrant further validation from clinical trials.

Barium chloride injures myofibers through calcium-induced proteolysis with fragmentation of motor nerves and microvessels

Background

Local injection of BaCl₂ is an established model of acute injury to study the regeneration of skeletal muscle. However, the mechanism by which BaCl₂ causes muscle injury is unresolved. Because Ba²⁺ inhibits K⁺ channels, we hypothesized that BaCl₂ induces myofiber depolarization leading to Ca²⁺ overload, proteolysis, and membrane disruption. While BaCl₂ spares resident satellite cells, its effect on other tissue components integral to contractile function has not been defined. We therefore asked whether motor nerves and microvessels, which control and supply myofibers, are injured by BaCl₂ treatment.

Methods

The intact extensor digitorum longus (EDL) muscle was isolated from male mice (aged 3–4 months) and irrigated with physiological salt solution (PSS) at 37 °C. Myofiber membrane potential (V_m) was recorded using sharp microelectrodes while intracellular calcium concentration ([Ca²⁺]_i) was evaluated with Fura 2 dye. Isometric force production of EDL was measured in situ, proteolytic activity was quantified by calpain degradation of αII-spectrin, and membrane disruption was marked by nuclear staining with propidium iodide (PI). To test for effects on motor nerves and microvessels, tibialis anterior or gluteus maximus muscles were injected with 1.2% BaCl₂ (50–75 μL) in vivo followed by immunostaining to evaluate the integrity of respective tissue elements post injury. Data were analyzed using Students t test and analysis of variance with P ≤ 0.05 considered statistically significant.

Results

Addition of 1.2% BaCl₂ to PSS depolarized myofibers from − 79 ± 3 mV to − 17 ± 7 mV with a corresponding rise in [Ca²⁺]_i; isometric force transiently increased from 7.4 ± 0.1 g to 11.1 ± 0.4 g. Following 1 h of BaCl₂ exposure, 92 ± 3% of myonuclei stained with PI (vs. 8 ± 3% in controls) with enhanced cleavage of αII-spectrin. Eliminating Ca²⁺ from PSS prevented the rise in [Ca²⁺]_i and ameliorated myonuclear staining with PI during BaCl₂ exposure. Motor axons and capillary networks appeared fragmented within 24 h following injection of 1.2% BaCl₂ and morphological integrity deteriorated through 72 h.

Conclusions

BaCl₂ injures myofibers through depolarization of the sarcolemma, causing Ca²⁺ overload with transient contraction, leading to proteolysis and membrane rupture. Motor innervation and capillarity appear disrupted concomitant with myofiber damage, further compromising muscle integrity.

Deficient Skeletal Muscle Regeneration after Injury Induced by a Clostridium perfringens Strain Associated with Gas Gangrene

Gas gangrene, or clostridial myonecrosis, is usually caused by Clostridium perfringens and may occur spontaneously in association with diabetes mellitus, peripheral vascular disease, or some malignancies but more often after contamination of a deep surgical or traumatic lesion. If not controlled, clostridial myonecrosis results in multiorgan failure, shock, and death, but very little is known about the muscle regeneration process that follows myonecrosis when the infection is controlled. In this study, we characterized the muscle regeneration process after myonecrosis caused in a murine experimental infection with a sublethal inoculum of C. perfringens vegetative cells. The results show that myonecrosis occurs concomitantly with significant vascular injury, which limits the migration of inflammatory cells. A significant increase in cytokines that promote inflammation explains the presence of an inflammatory infiltrate; however, impaired interferon gamma (IFN-γ) expression, a reduced number of M1 macrophages, deficient phagocytic activity, and a prolongation of the permanence of inflammatory cells lead to deficient muscle regeneration. The expression of transforming growth factor β1 (TGF-β1) agrees with the consequent accumulation of collagen in the muscle, i.e., fibrosis observed 30 days after infection. These results provide new information on the pathogenesis of gas gangrene caused by C. perfringens, shed light on the basis of the deficient muscle regenerative activity, and may open new perspectives for the development of novel therapies for patients suffering from this disease.

Systemic and Local Phenotypes of Barium Chloride Induced Skeletal Muscle Injury in Mice

Skeletal muscle regeneration in mice has traditionally been studied using local freeze burn or snake venom injection models. More recently, a barium chloride (BaCl2)-induced muscle injury model has been established and is gaining popularity due to the relatively simple procedure and accessibility to required reagents. Here we sought to characterize the local and systemic effects of BaCl2-induced muscle injury. For this study, a 1.2% BaCl2 solution was locally administered to the tibialis anterior (TA) muscle and local and systemic phenotypes were analyzed at different timepoints. When 50 μL of the solution was injected unilaterally in the TA muscle, no mortality was observed. However, when 100 μL of the solution was injected, 50% of the mice died within 24 h. Serum analysis of the mice injected with 50 μL of BaCl2 solution at days 1 and 7 revealed changes resembling rhabdomyolysis. At day 1 post-injection of 50 μL of the BaCl2 solution, acute suppurative inflammation was observed in gross examination of the TA muscle, while extensive hemorrhagic necrosis was revealed on histological examination. At day 7, regenerated myofibers with centralized nuclei appeared with the resolution of acute inflammatory infiltration and the muscle tissue displayed molecular signatures consistent with myofiber differentiation. The overall muscle injury and regeneration phenotypes in the BaCl2-induced muscle injury model were similar to those of the well-established freeze burn or snake venom injection models. Taken together, the BaCl2-induced muscle injury model is comparable to conventional muscle injury and regeneration models, with considerations for possible systemic effects.

Myokines in Home-Based Functional Electrical Stimulation-Induced Recovery of Skeletal Muscle in Elderly and Permanent Denervation

Neuromuscular disorders, disuse, inadequate nutrition, metabolic diseases, cancer and aging produce muscle atrophy and this implies that there are different types of molecular triggers and signaling pathways for muscle wasting. Exercise and muscle contractions may counteract muscle atrophy by releasing a group of peptides, termed myokines, to protect the functionality and to enhance the exercise capacity of skeletal muscle. In this review, we are looking at the role of myokines in the recovery of permanent denervated and elderly skeletal muscle tissue. Since sub-clinical denervation events contribute to both atrophy and the decreased contractile speed of aged muscle, we saw a parallel to spinal cord injury and decided to look at both groups together. The muscle from lifelong active seniors has more muscle bulk and more slow fiber-type groupings than those of sedentary seniors, demonstrating that physical activity maintains slow motoneurons that reinnervate the transiently denervated muscle fibers. Furthermore, we summarized the evidence that muscle degeneration occur with irreversible Conus and Cauda Equina syndrome, a spinal cord injury in which the human leg muscles may be permanently disconnected from the peripheral nervous system. In these patients, suffering with an estreme case of muscle disuse, a complete loss of muscle fibers occurs within five to ten years after injury. Their recovered tetanic contractility, induced by home-based Functional Electrical Stimulation, can restore the muscle size and function in compliant Spinal Cord Injury patients, allowing them to perform electrical stimulation-supported stand-up training. Myokines are produced and released by muscle fibers under contraction and exert both local and systemic effects. Changes in patterns of myokine secretion, particularly of IGF-1 isoforms, occur in long-term Spinal Cord Injury persons and also in very aged people. Their modulation in Spinal Cord Injury and late aging are also key factors of home-based Functional Electrical Stimulation - mediated muscle recovery. Thus, Functional Electrical Stimulation should be prescribed in critical care units and nursing facilities, if persons are unable or reluctant to exercise. This will result in less frequent hospitalizations and a reduced burden on patients' families and public health services.

Resistance training does not induce uniform adaptations to quadriceps

Resistance training may differentially affect morphological adaptations along the length of uni-articular and bi-articular muscles. The purpose of this study was to compare changes in muscle morphology along the length of the rectus femoris (RF) and vastus lateralis (VL) in response to resistance training. Following a 2-wk preparatory phase, 15 resistance-trained men (24.0 ± 3.0 y, 90.0 ± 13.8 kg, 174.9 ± 20.7 cm) completed pre-training (PRE) assessments of muscle thickness (MT), pennation angle (PA), cross-sectional area (CSA), and echo-intensity in the RF and VL at 30, 50, and 70% of each muscle’s length; fascicle length (FL) was estimated from respective measurements of MT and PA within each muscle and region. Participants then began a high intensity, low volume (4 x 3–5 repetitions, 3min rest) lower-body resistance training program, and repeated all PRE-assessments after 8 weeks (2 d ∙ wk^-1) of training (POST). Although three-way (muscle [RF, VL] x region [30, 50, 70%] x time [PRE, POST]) repeated measures analysis of variance did not reveal significant interactions for any assessment of morphology, significant simple (muscle x time) effects were observed for CSA (p = 0.002) and FL (p = 0.016). Specifically, average CSA changes favored the VL (2.96 ± 0.69 cm², p < 0.001) over the RF (0.59 ± 0.20 cm², p = 0.011), while significant decreases in average FL were noted for the RF (–1.03 ± 0.30 cm, p = 0.004) but not the VL (–0.05 ± 0.36 cm, p = 0.901). No other significant differences were observed. The findings of this study demonstrate the occurrence of non-homogenous adaptations in RF and VL muscle size and architecture following 8 weeks of high-intensity resistance training in resistance-trained men. However, training does not appear to influence region-specific adaptations in either muscle.

The Importance of Biophysical and Biochemical Stimuli in Dynamic Skeletal Muscle Models

Classical approaches to engineer skeletal muscle tissue based on current regenerative and surgical procedures still do not meet the desired outcome for patient applications. Besides the evident need to create functional skeletal muscle tissue for the repair of volumetric muscle defects, there is also growing demand for platforms to study muscle-related diseases, such as muscular dystrophies or sarcopenia. Currently, numerous studies exist that have employed a variety of biomaterials, cell types and strategies for maturation of skeletal muscle tissue in 2D and 3D environments. However, researchers are just at the beginning of understanding the impact of different culture settings and their biochemical (growth factors and chemical changes) and biophysical cues (mechanical properties) on myogenesis. With this review we intend to emphasize the need for new in vitro skeletal muscle (disease) models to better recapitulate important structural and functional aspects of muscle development. We highlight the importance of choosing appropriate system components, e.g., cell and biomaterial type, structural and mechanical matrix properties or culture format, and how understanding their interplay will enable researchers to create optimized platforms to investigate myogenesis in healthy and diseased tissue. Thus, we aim to deliver guidelines for experimental designs to allow estimation of the potential influence of the selected skeletal muscle tissue engineering setup on the myogenic outcome prior to their implementation. Moreover, we offer a workflow to facilitate identifying and selecting different analytical tools to demonstrate the successful creation of functional skeletal muscle tissue. Ultimately, a refinement of existing strategies will lead to further progression in understanding important aspects of muscle diseases, muscle aging and muscle regeneration to improve quality of life of patients and enable the establishment of new treatment options.

Differential gene expression analysis in ageing muscle and drug discovery perspectives

Identifying therapeutic target genes represents the key step in functional genomics-based therapies. Within this context, the disease heterogeneity, the exogenous factors and the complexity of genomic structure and function represent important challenges. The functional genomics aims to overcome such obstacles via identifying the gene functions and therefore highlight disease-causing genes as therapeutic targets. Genomic technologies promise to reshape the research on ageing muscle, exercise response and drug discovery. Herein, we describe the functional genomics strategies, mainly differential gene expression methods microarray, serial analysis of gene expression (SAGE), massively parallel signature sequence (MPSS), RNA sequencing (RNA seq), representational difference analysis (RDA), and suppression subtractive hybridization (SSH). Furthermore, we review these illustrative approaches that have been used to discover new therapeutic targets for some complex diseases along with the application of these tools to study the modulation of the skeletal muscle transcriptome.

Modulating the metabolism by trimetazidine enhances myoblast differentiation and promotes myogenesis in cachectic tumor-bearing c26 mice

Trimetazidine (TMZ) is a metabolic reprogramming agent able to partially inhibit mitochondrial free fatty acid β-oxidation while enhancing glucose oxidation. Here we have found that the metabolic shift driven by TMZ enhances the myogenic potential of skeletal muscle progenitor cells leading to MyoD, Myogenin, Desmin and the slow isoforms of troponin C and I over-expression. Moreover, similarly to exercise, TMZ stimulates the phosphorylation of the AMP-activated protein kinase (AMPK) and up-regulates the peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC1α), both of which are known to enhance the mitochondrial biogenesis necessary for myoblast differentiation. TMZ also induces autophagy which is required during myoblast differentiation and promotes myoblast alignment which allows cell fusion and myofiber formation. Finally, we found that intraperitoneally administered TMZ (5mg/kg) is able to stimulate myogenesis in vivo both in a mice model of cancer cachexia (C26 mice) and upon cardiotoxin damage. Collectively, our work demonstrates that TMZ enhances myoblast differentiation and promotes myogenesis, which might contribute recovering stem cell blunted regenerative capacity and counteracting muscle wasting, thanks to the formation of new myofibers; TMZ is already in use in humans as an anti-anginal drug and its repositioning might impact significantly on aging and regeneration-impaired disorders, including cancer cachexia, as well as have implications in regenerative medicine.

Extracellular Vesicles Released by Oxidatively Injured or Intact C2C12 Myotubes Promote Distinct Responses Converging toward Myogenesis

Myogenic differentiation is triggered, among other situations, in response to muscle damage for regenerative purposes. It has been shown that during myogenic differentiation, myotubes release extracellular vesicles (EVs) which participate in the signalling pattern of the microenvironment. Here we investigated whether EVs released by myotubes exposed or not to mild oxidative stress modulate the behaviour of targeted differentiating myoblasts and macrophages to promote myogenesis. We found that EVs released by oxidatively challenged myotubes (H₂O₂-EVs) are characterized by an increased loading of nucleic acids, mainly DNA. In addition, incubation of myoblasts with H₂O₂-EVs resulted in a significant decrease of myotube diameter, myogenin mRNA levels and myosin heavy chain expression along with an upregulation of proliferating cell nuclear antigen: these effects collectively lead to an increase of recipient myoblast proliferation. Notably, the EVs from untreated myotubes induced an opposite trend in myoblasts, that is, a slight pro-differentiation effect. Finally, H₂O₂-EVs were capable of eliciting an increased interleukin 6 mRNA expression in RAW264.7 macrophages. Notably, this is the first demonstration that myotubes communicate with surrounding macrophages via EV release. Collectively, the data reported herein suggest that myotubes, depending on their conditions, release EVs carrying differential signals which could contribute to finely and coherently orchestrate the muscle regeneration process.

Recovery from muscle weakness by exercise and FES: lessons from Masters, active or sedentary seniors and SCI patients

Many factors contribute to the decline of skeletal muscle that occurs as we age. This is a reality that we may combat, but not prevent because it is written into our genome. The series of records from World Master Athletes reveals that skeletal muscle power begins to decline at the age of 30 years and continues, almost linearly, to zero at the age of 110 years. Here we discuss evidence that denervation contributes to the atrophy and slowness of aged muscle. We compared muscle from lifelong active seniors to that of sedentary elderly people and found that the sportsmen have more muscle bulk and slow fiber type groupings, providing evidence that physical activity maintains slow motoneurons which reinnervate muscle fibers. Further, accelerated muscle atrophy/degeneration occurs with irreversible Conus and Cauda Equina syndrome, a spinal cord injury in which the human leg muscles may be permanently disconnected from the nervous system with complete loss of muscle fibers within 5-8 years. We used histological morphometry and Muscle Color Computed Tomography to evaluate muscle from these peculiar persons and reveal that contraction produced by home-based Functional Electrical Stimulation (h-bFES) recovers muscle size and function which is reversed if h-bFES is discontinued. FES also reverses muscle atrophy in sedentary seniors and modulates mitochondria in horse muscles. All together these observations indicate that FES modifies muscle fibers by increasing contractions per day. Thus, FES should be considered in critical care units, rehabilitation centers and nursing facilities when patients are unable or reluctant to exercise.

Ablation of S1P3 receptor protects mouse soleus from age-related drop in muscle mass, force, and regenerative capacity

We investigated the effects of S1P3 deficiency on the age-related atrophy, decline in force, and regenerative capacity of soleus muscle from 23-mo-old male (old) mice. Compared with muscle from 5-mo-old (adult) mice, soleus mass and muscle fiber cross-sectional area (CSA) in old wild-type mice were reduced by ~26% and 24%, respectively. By contrast, the mass and fiber CSA of soleus muscle in old S1P3-null mice were comparable to those of adult muscle. Moreover, in soleus muscle of wild-type mice, twitch and tetanic tensions diminished from adulthood to old age. A slowing of contractile properties was also observed in soleus from old wild-type mice. In S1P3-null mice, neither force nor the contractile properties of soleus changed during aging. We also evaluated the regenerative capacity of soleus in old S1P3-null mice by stimulating muscle regeneration through myotoxic injury. After 10 days of regeneration, the mean fiber CSA of soleus in old wild-type mice was significantly smaller (−28%) compared with that of regenerated muscle in adult mice. On the contrary, the mean fiber CSA of regenerated soleus in old S1P3-null mice was similar to that of muscle in adult mice. We conclude that in the absence of S1P3, soleus muscle is protected from the decrease in muscle mass and force, and the attenuation of regenerative capacity, all of which are typical characteristics of aging.

Stem Cells and Tissue Niche: Two Faces of the Same Coin of Muscle Regeneration

Capacity of adult muscle to regenerate in response to injury stimuli represents an important homeostatic process. Regeneration is a highly coordinated program that partially recapitulates the embryonic developmental program. However, muscle regeneration is severely compromised in several pathological conditions. It is likely that the restricted tissue repair program under pathological conditions is due to either progressive loss of stem cell populations or to missing signals that limit the damaged tissues to efficiently activate a regenerative program. It is therefore plausible that loss of control over these cell fates might lead to a pathological cell transdifferentiation, limiting the ability of a pathological muscle to sustain an efficient regenerative process. The critical role of microenvironment on stem cells activity and muscle regeneration is discussed.

Maternal protein restriction during pregnancy and lactation affects the development of muscle fibers and neuromuscular junctions in rats

INTRODUCTION

A balanced maternal diet is a determining factor in normal fetal development. The objective of this study was to evaluate the effects of maternal protein restriction during pregnancy and lactation on muscle fiber and neuromuscular junction (NMJ) morphology of rat offspring at 21 days of age.

METHODS

Wistar rats were divided into a control group (CG), offspring of mothers fed a normal protein diet (17%), and a restricted group (RG), offspring of mothers fed a low-protein diet (6%). After a period of lactation, the animals were euthanized, and soleus muscles were obtained from pups for analysis.

RESULTS

The soleus muscles of the RG exhibited an increase of 133% in the number of fibers and of 79% in the amount of nuclei. Moreover, the number of NMJs was lower in the restricted group than in the CG.

CONCLUSIONS

Maternal protein restriction alters the normal development of the neuromuscular system. Muscle Nerve 55: 109-115, 2017.

Myoprotective effects of bFGF on skeletal muscle injury in pressure-related deep tissue injury in rats

BACKGROUND

Pressure ulcers (PUs) are a major clinical problem that constitutes a tremendous economic burden on healthcare systems. Deep tissue injury (DTI) is a unique serious type of pressure ulcer that arises in skeletal muscle tissue. DTI arises in part because skeletal muscle tissues are more susceptible than skin to external compression. Unfortunately, few effective therapies are currently available for muscle injury. Basic fibroblast growth factor (bFGF), a potent mitogen and survival factor for various cells, plays a crucial role in the regulation of muscle development and homeostasis. The main purpose of this study was to test whether local administration of bFGF could accelerate muscle regeneration in a rat DTI model.

METHODS

Male Sprague Dawley (SD) rats (age 12 weeks) were individually housed in plastic cages and a DTI PU model was induced according to methods described before. Animals were randomly divided into three groups: a normal group, a PU group treated with saline, and a PU group treated with bFGF (10 μg/0.1 ml) subcutaneously near the wound.

RESULTS

We found that application of bFGF accelerated the rate of wound closure and promoted cell proliferation and tissue angiogenesis. In addition, compared to saline administration, bFGF treatment prevented collagen deposition, a measure of fibrosis, and up-regulated the myogenic marker proteins MyHC and myogenin, suggesting bFGF promoted injured muscle regeneration. Moreover, bFGF treatment increased levels of myogenesis-related proteins p-Akt and p-mTOR.

CONCLUSIONS

Our findings show that bFGF accelerated injured skeletal muscle regeneration through activation of the PI3K/Akt/mTOR signaling pathway and suggest that administration of bFGF is a potential therapeutic strategy for the treatment of skeletal muscle injury in PUs.

Engineered matrices for skeletal muscle satellite cell engraftment and function

Regeneration of traumatically injured skeletal muscles is severely limited. Moreover, the regenerative capacity of skeletal muscle declines with aging, further exacerbating the problem. Recent evidence supports that delivery of muscle satellite cells to the injured muscles enhances muscle regeneration and reverses features of aging, including reduction in muscle mass and regenerative capacity. However, direct delivery of satellite cells presents a challenge at a translational level due to inflammation and donor cell death, motivating the need to develop engineered matrices for muscle satellite cell delivery. This review will highlight important aspects of satellite cell and their niche biology in the context of muscle regeneration, and examine recent progresses in the development of engineered cell delivery matrices designed for skeletal muscle regeneration. Understanding the interactions of muscle satellite cells and their niche in both native and engineered systems is crucial to developing muscle pathology-specific cell- and biomaterial-based therapies.