Role of Myokines in Regulating Skeletal Muscle Mass and Function

Effects of exercise interventions on brain-derived neurotrophic factor levels in overweight and obesity: A systematic review and meta-analysis

Background

/Objective. An explosion in global obesity epidemic poses threats to the healthcare system by provoking risks of many debilitating diseases, including cognitive dysfunction. Physical activity has been shown to alleviate the deleterious effects of obesity-associated cognitive deficits across the lifespan. Given the strong neuroprotective role of brain-derived neurotrophic factor (BDNF) and exercise training as a known modulator for its elevation, this systematic review sought to examine the strength of the association between exercise and BDNF levels in healthy people with overweight and obesity.

Methods

Six electronic databases (PubMed, MEDLINE, EMBASE, Web of Science, Ovid Nursing Database, and SPORTDiscus) were searched from their inceptions through December 2022. The primary outcome of interest was BDNF levels. Interventional studies (randomized and quasi-experimental) with English full text available were included. Risk of bias of the included studies was assessed using the Physiotherapy Evidence Database Scale. Data were extracted for meta-analyses by random-effects models.

Results

Thirteen studies (n = 750), of which 69.2% (9/13) had low risk of bias, were included. In the meta-analysis, exercise interventions had no significant effect on resting BDNF levels (standardized mean difference: -0.30, 95% CI -0.80 to 0.21, P = 0.25). Subgroup analyses also indicated no effects of age and types of control groups being compared on moderating the association.

Conclusion

To further inform the role of BDNF in obesity-related cognitive functioning, rigorous studies with larger samples of participants and raw data available were imperatively deserved.

Roles of natural products on myokine expression and secretion in skeletal muscle atrophy

Skeletal muscles serve both in movement and as endocrine organs. Myokines secreted by skeletal muscles activate biological functions within muscles and throughout the body via autocrine, paracrine, and/or endocrine pathways. Skeletal muscle atrophy can influence myokine expression and secretion, while myokines can impact the structure and function of skeletal muscles. Regulating the expression and secretion of myokines through the pharmacological approach is a strategy for alleviating skeletal muscle atrophy. Natural products possess complex structures and chemical properties. Previous studies have demonstrated that various natural products exert beneficial effects on skeletal muscle atrophy. This article reviewed the regulatory effects of natural products on myokines and summarized the research progress on skeletal muscle atrophy associated with myokine regulation. The focus is on how small-molecule natural products affect the regulation of interleukin 6 (IL-6), irisin, myostatin, IGF-1, and FGF-21 expression. We contend that the development of small-molecule natural products targeting the regulation of myokines holds promise in combating skeletal muscle atrophy.

Exercise improves load bearing bone structural properties in female secreted protein acidic and rich in cysteine (SPARC) null mice but not in males

Secreted protein acidic and rich in cysteine (SPARC) is the most abundant glycoprotein in bone and is thought to play a critical role in bone remodeling and homeostasis. However, the effect of SPARC in relation to gender and exercise on bone quality is not well understood. The purpose of this study was to quantify differences in the structural and biomechanical properties between calvarial and femoral bone from male and female wild-type (WT) and SPARC null (SPARC(-/-)) mice as well as the ability of exercise to rescue bone health. Male and female WT and transgenic SPARC(-/-) mice were given either a fixed or rotating running wheel for exercise. Bone structural, biomechanical, and morphological parameters were quantified using micro computed tomography, push out testing for the calvaria, three-point flexural testing for the femurs, histological and immunofluorescent staining. Similar reductions in structural and biomechanical strength were observed in both male and female SPARC(-/-) calvaria, most of which were not significantly affected by exercise. In femurs, SPARC(-/-) had a significant effect on structural parameters in both sexes, but was more pronounced in females with some properties being rescued with running. Interestingly, the effect of SPARC(-/-) on bone mineral density was only detected in female SPARC(-/-) mice, not males, and was subsequently rescued with exercise. This study emphasizes the differences between sexes in WT and SPARC(-/-) mice in regard to structural parameters and biomechanical properties. Research into gender differences can help inform and personalize treatment options to more accurately meet patient needs.

Selenium supplementation via modulation of selenoproteins ameliorates binge drinking-induced oxidative, energetic, metabolic, and endocrine imbalance in adolescent rats' skeletal muscle

Adolescence is characterized by increased vulnerability to addiction and ethanol (EtOH) toxicity, particularly through binge drinking (BD), a favored acute EtOH-ingestion pattern among teenagers. BD, highly pro-oxidant, induces oxidative stress (OS), affecting skeletal muscle (SKM), where selenium (Se), an antioxidant element and catalytic center of selenoproteins, is stored, among other tissues. Investigating the effects of Se supplementation on SKM after BD exposure holds therapeutic promise. For this, we randomised 32 adolescent Wistar rats into 4 groups, exposed or not to intermittent i.p. BD [BD and control (C)] (3 g EtOH per kg per day), and supplemented with selenite [BDSe and CSe] (0.4 ppm). In SKM, we examined the oxidative balance, energy status (AMPK, SIRT-1), protein turnover (IRS-1, Akt1, mTOR, IGF-1, NF-κB p65, MAFbx, ULK1, pelF2α), serum myokines (myostatin, IL-6, FGF21, irisin, BDNF, IL-15, fractalkine, FSTL-1, FABP-3), and selenoproteins (GPx1, GPx4, SelM, SelP). In the pancreas, we studied the oxidative balance and SIRT-1 expression. Selenite supplementation mitigated BD-induced OS by enhancing the expression of selenoproteins, which restored oxidative balance, notably stimulating protein synthesis and normalizing the myokine profile, leading to improved SKM mass growth and metabolism, and reduced inflammation and apoptosis (caspase-3). Selenite restoration of SelP's receptor LRP1 expression, reduced by BD, outlines the crucial role of SKM in the SelP cycle, linking Se levels to SKM development. Furthermore, Se attenuated pancreatic OS, preserving insulin secretion. Se supplementation shows potential for alleviating SKM damage from BD, with additional beneficial endocrine effects on the pancreas, adipose tissue, liver, heart and brain that position it as a broad-spectrum treatment for adolescent alcohol consumption, preventing metabolic diseases in adulthood.

Bone-muscle crosstalk under physiological and pathological conditions

Anatomically connected bones and muscles determine movement of the body. Forces exerted on muscles are then turned to bones to promote osteogenesis. The crosstalk between muscle and bone has been identified as mechanotransduction previously. In addition to the mechanical features, bones and muscles are also secretory organs which interact closely with one another through producing myokines and osteokines. Moreover, besides the mechanical features, other factors, such as nutrition metabolism, physiological rhythm, age, etc., also affect bone-muscle crosstalk. What's more, osteogenesis and myogenesis within motor system occur almost in parallel. Pathologically, defective muscles are always detected in bone associated diseases and induce the osteopenia, inflammation and abnormal bone metabolism, etc., through biomechanical or biochemical coupling. Hence, we summarize the study findings of bone-muscle crosstalk and propose potential strategies to improve the skeletal or muscular symptoms of certain diseases. Altogether, functional improvement of bones or muscles is beneficial to each other within motor system.

Diet Based on Pereskia aculeata Miller Flour Increases Muscle Volume and Modulates the Expression of Myokines in Mice Subjected to Resistance Training

The study aimed to evaluate the effects of Pereskia aculeata Miller (ora-pro-nobis [OPN]) flour on body and biochemical parameters, thermogenic activity, and molecular expression of markers in the muscle tissue of mice subjected to resistance training (RT). Twelve mice were randomly assigned to two groups (n=6 animals/group): G1: control (Control) fed a standard diet + RT and G2: experimental (OPN) fed a diet based on OPN flour + RT. The RT consisted of a 6-week program using a vertical ladder combined with a fixed weight attached to the animal. Several parameters were measured, including assessment of body composition, biochemical markers, thermogenic activity, and molecular (mRNA expression of interleukin (IL)-6, fibronectin type III domain-containing protein 5 (FNDC5), peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), nuclear respiratory factor 1 (NRF1), and mitochondrial transcription factor A (TFAM). The OPN group exhibited a decrease in body weight and visceral adiposity, higher energy expenditure, and lipid oxidation rate. In addition, it was observed an increase in muscle volume and in mRNA expression levels of IL-6, FNDC5, PGC-1α, and TFAM. These findings suggest that OPN flour could be a nutritional option to enhance performance in RT.

Skeletal muscle: molecular structure, myogenesis, biological functions, and diseases

Skeletal muscle is an important motor organ with multinucleated myofibers as its smallest cellular units. Myofibers are formed after undergoing cell differentiation, cell-cell fusion, myonuclei migration, and myofibril crosslinking among other processes and undergo morphological and functional changes or lesions after being stimulated by internal or external factors. The above processes are collectively referred to as myogenesis. After myofibers mature, the function and behavior of skeletal muscle are closely related to the voluntary movement of the body. In this review, we systematically and comprehensively discuss the physiological and pathological processes associated with skeletal muscles from five perspectives: molecule basis, myogenesis, biological function, adaptive changes, and myopathy. In the molecular structure and myogenesis sections, we gave a brief overview, focusing on skeletal muscle-specific fusogens and nuclei-related behaviors including cell-cell fusion and myonuclei localization. Subsequently, we discussed the three biological functions of skeletal muscle (muscle contraction, thermogenesis, and myokines secretion) and its response to stimulation (atrophy, hypertrophy, and regeneration), and finally settled on myopathy. In general, the integration of these contents provides a holistic perspective, which helps to further elucidate the structure, characteristics, and functions of skeletal muscle.

Physical exercise as a modulator of the purinergic system in the control of sarcopenia in individuals with chronic kidney disease on hemodialysis

The word sarcopenia derives from the Greek terms "sarx" for meat and "penia" for loss, thus being used to define reductions in muscle mass, muscle strength, and lower physical performance that compromise, mainly, the elderly population. Its high negative impact on patients' quality of life encourages the production and publication of new studies that seek to find methods to prevent and reverse cases of loss of muscle mass and strength. Furthermore, the high prevalence of sarcopenia in patients with chronic kidney disease (CKD) is closely related to its pathophysiology, which consists of a state of increased protein catabolism and decreased muscle tissue synthesis. Also considering the inflammatory nature of CKD and sarcopenia, the purinergic system has been an important target of studies, which seek to relate it to the two previous conditions. This system achieves anti-inflammatory action by inhibiting, through adenosine, pro-inflammatory factors such as interleukin-12 (IL-12), tumor necrosis factor alpha (TNF-α), and nitric oxide (NO), as well as by releasing anti-inflammatory substances such as interleukin-10 (IL-10). Simultaneously, the purinergic system presents pro-inflammatory activity, signaled by adenosine triphosphate (ATP), which occurs through the activation of T cells and the release of pro-inflammatory factors such as those mentioned above. Therefore, the ability of this system to act on inflammatory processes can promote positive and negative changes in the clinical aspect of patients with CKD and/or sarcopenia. Furthermore, it appears that there is a correlation between the practice of repeated physical exercise with the clinical improvement and in the quality of life of these patients, presenting a decrease in the levels of C-reactive protein (CRP), NTPDase, and the pro-inflammatory cytokine IL-6, such as increases in IL-10 resulting from modulation of the purinergic system. In this way, the present article seeks to evaluate the effect of physical exercise as a modulator of the purinergic system in the control of sarcopenia in patients with CKD on hemodialysis, in order to trace a relationship that can bring benefits both for biological markers and for quality of life of these patients.

Post-natal muscle growth and protein turnover: a narrative review of current understanding

A model explaining the dietary-protein-driven post-natal skeletal muscle growth and protein turnover in the rat is updated, and the mechanisms involved are described, in this narrative review. Dietary protein controls both bone length and muscle growth, which are interrelated through mechanotransduction mechanisms with muscle growth induced both from stretching subsequent to bone length growth and from internal work against gravity. This induces satellite cell activation, myogenesis and remodelling of the extracellular matrix, establishing a growth capacity for myofibre length and cross-sectional area. Protein deposition within this capacity is enabled by adequate dietary protein and other key nutrients. After briefly reviewing the experimental animal origins of the growth model, key concepts and processes important for growth are reviewed. These include the growth in number and size of the myonuclear domain, satellite cell activity during post-natal development and the autocrine/paracrine action of IGF-1. Regulatory and signalling pathways reviewed include developmental mechanotransduction, signalling through the insulin/IGF-1-PI3K-Akt and the Ras-MAPK pathways in the myofibre and during mechanotransduction of satellite cells. Likely pathways activated by maximal-intensity muscle contractions are highlighted and the regulation of the capacity for protein synthesis in terms of ribosome assembly and the translational regulation of 5-TOPmRNA classes by mTORC1 and LARP1 are discussed. Evidence for and potential mechanisms by which volume limitation of muscle growth can occur which would limit protein deposition within the myofibre are reviewed. An understanding of how muscle growth is achieved allows better nutritional management of its growth in health and disease.

Association of endothelial dysfunction and peripheral arterial disease with sarcopenia in chronic kidney disease

BACKGROUND

Endothelial dysfunction and peripheral arterial disease (PAD), which disturb skeletal muscle microperfusion, are highly prevalent in patients with chronic kidney disease (CKD). We evaluated the association of endothelial dysfunction and PAD with sarcopenia in patients with non-dialysis CKD.

METHODS

This cross-sectional study included 420 patients with stages 3-5 non-dialysis CKD aged 69.0 ± 11.8 years. Skeletal muscle index (skeletal muscle mass/height2), handgrip strength, 6-m gait speed and strength of hip flexion and knee extension were measured. Sarcopenia was defined according to the Asian Working Group for Sarcopenia 2019. Endothelial dysfunction and PAD were assessed using the vascular reactivity index (VRI) and ankle-brachial index (ABI), respectively. A VRI < 1.0 was classified as poor endothelial function, and an ABI < 0.9 was defined as PAD. Additionally, endothelial and inflammatory biomarkers, including intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), asymmetric dimethylarginine, endothelin-1 (ET-1) and interleukin-6, were measured in a subgroup of 262 patients.

RESULTS

Among the participants, 103 (24.5%) were classified as having sarcopenia. Compared with patients without sarcopenia, those with sarcopenia had significantly lower ABI (1.04 ± 0.16 vs. 1.08 ± 0.15, P = 0.028 for the right ABI; 1.01 ± 0.16 vs. 1.06 ± 0.16, P = 0.002 for the left ABI) and VRI (0.83 ± 0.57 vs. 1.08 ± 0.56, P < 0.001) and had higher serum levels of ICAM-1 (P < 0.001), VCAM-1 (P = 0.003) and ET-1 (P = 0.037). Multivariate logistic regression revealed that, beyond age and body mass index, the average ABI (odds ratio [OR]: 0.81/0.1 increase; 95% confidence interval [CI]: 0.67-0.98; P = 0.032) and VRI (OR: 0.93/0.1 increase; 95% CI: 0.88-0.98; P = 0.010) were independently associated with sarcopenia. Among the endothelial biomarkers measured, ICAM-1 (OR: 2.47/1-SD increase; 95% CI: 1.62-3.75) and VCAM-1 (OR: 1.91/1-SD increase; 95% CI: 1.27-2.87) were independent predictors of sarcopenia. Group stratification based on the cut-offs of VRI and ABI showed that those with both poor VRI and ABI had the greatest risk for sarcopenia (OR: 4.22; 95% CI: 1.69-10.49), compared with those with normal VRI and ABI.

CONCLUSIONS

Endothelial dysfunction and PAD are independently associated with sarcopenia in patients with stages 3-5 CKD, suggesting the dominant role of vascular dysfunction in sarcopenia.

Effects of Resistance Exercise and Essential Amino Acid Intake on Muscle Quality, Myokine, and Inflammation Factors in Young Adult Males

BACKGROUND

Recently, many studies have been devoted to discovering nutrients for exercise-like effects. Resistance exercise and the intake of essential amino acids (EAAs) are known to be factors that can affect muscle mass and strength improvement. The purpose of this study was to investigate changes in muscle quality, myokines, and inflammation in response to resistance exercise and EAA supplementation.

METHODS

Thirty-four males volunteered to participate in this study. They were assigned to four groups: (1) placebo (CO), (2) resistance exercise (RE), (3) EAA supplementation, and (4) RE + EAA supplementation. Body composition, muscle quality, myokines, and inflammation were measured at baseline and four weeks after treatment.

RESULTS

Lean body fat had decreased in both RE and RE + EAA groups. Lean body mass had increased in only the RE + EAA group. In all groups except for CO, irisin, myostatin A, and TNF-α levels had decreased. The grip strength of the right hand and trunk flexion peak torque increased in the RE group. The grip strength of the left hand, trunk flexion peak torque, and knee flexion peak torque of the left leg were increased in RE + EAA.

CONCLUSIONS

RE, EAA, and RE + EAA could effectively improve the muscle quality, myokine, and inflammation factors of young adult males. This finding highlights the importance of resistance exercise and amino acid intake.

Role of Myostatin in Rheumatoid Arthritis: A Review of the Clinical Impact

Rheumatoid arthritis (RA) is a chronic inflammatory disease that affects synovial joints and that frequently involves extra-articular organs. A multiplicity of interleukins (IL) participates in the pathogenesis of RA, including IL-6, IL-1β, transforming growth factor-beta (TGF-β), and tumor necrosis factor (TNF)-α; immune cells such as monocytes, T and B lymphocytes, and macrophages; and auto-antibodies, mainly rheumatoid factor and anti-citrullinated protein antibodies (ACPAs). Skeletal muscle is also involved in RA, with many patients developing muscle wasting and sarcopenia. Several mechanisms are involved in the myopenia observed in RA, and one of them includes the effects of some interleukins and myokines on myocytes. Myostatin is a myokine member of the TGF-β superfamily; the overproduction of myostatin acts as a negative regulator of growth and differentiates the muscle fibers, limiting their number and size. Recent studies have identified abnormalities in the serum myostatin levels of RA patients, and these have been found to be associated with muscle wasting and other manifestations of severe RA. This review analyzes recent information regarding the relationship between myostatin levels and clinical manifestations of RA and the relevance of myostatin as a therapeutic target for future research.

Exercise training mode effects on myokine expression in healthy adults: A systematic review with meta-analysis

BACKGROUND

The benefits of exercise are well known; however, many of the underlying molecular mechanisms are not fully understood. Skeletal muscle secretes myokines, which mediate muscle-organ crosstalk. Myokines regulate satellite-cell proliferation and migration, inflammatory cascade, insulin secretion, angiogenesis, fatty oxidation, and cancer suppression. To date, the effects of different exercise modes (namely, aerobic and resistance exercise) on myokine response remain to be elucidated. This is crucial considering the clinical implementation of exercise to enhance general health and wellbeing and as a medical treatment.

METHODS

A systematic search was undertaken in PubMed, Medline, CINAHL, Embase, SPORTDiscus, and Web of Science in April 2023. Eligible studies examining the effects of a single bout of exercise on interleukin15 (IL-15), irisin, secreted protein acidic and rich in cysteine (SPARC), oncostatin M (OSM), and decorin were included. A random-effects meta-analysis was also undertaken to quantify the magnitude of change.

RESULTS

Sixty-two studies were included (n = 1193). Overall, exercise appeared to induce small to large increases in myokine expression, with effects observed immediately after to 60 min post-exercise, although these were mostly not statistically significant. Both aerobic and resistance exercise resulted in changes in myokine levels, without any significant difference between training modes, and with the magnitude of change differing across myokines. Myokine levels returned to baseline levels within 180 min to 24 h post-exercise. However, owing to potential sources of heterogeneity, most changes were not statistically significant, indicating that precise conclusions cannot be drawn.

CONCLUSION

Knowledge is limited but expanding with respect to the impact of overall and specific effects of exercise on myokine expression at different time points in the systemic circulation. Further research is required to investigate the effects of different exercise modes at multiple time points on myokine response.

Investigating the Effects of Diet-Induced Prediabetes on Skeletal Muscle Strength in Male Sprague Dawley Rats

Type 2 diabetes mellitus, a condition preceded by prediabetes, is documented to compromise skeletal muscle health, consequently affecting skeletal muscle structure, strength, and glucose homeostasis. A disturbance in skeletal muscle functional capacity has been demonstrated to induce insulin resistance and hyperglycemia. However, the modifications in skeletal muscle function in the prediabetic state are not well elucidated. Hence, this study investigated the effects of diet-induced prediabetes on skeletal muscle strength in a prediabetic model. Male Sprague Dawley rats were randomly assigned to one of the two groups (n = 6 per group; six prediabetic (PD) and six non-pre-diabetic (NPD)). The PD group (n = 6) was induced with prediabetes for 20 weeks. The diet that was used to induce prediabetes consisted of fats (30% Kcal/g), proteins (15% Kcal/g), and carbohydrates (55% Kcal/g). In addition to the diet, the experimental animals (n = 6) were supplied with drinking water that was supplemented with 15% fructose. The control group (n = 6) was allowed access to normal rat chow, consisting of 35% carbohydrates, 30% protein, 15% fats, and 20% other components, as well as ordinary tap water. At the end of week 20, the experimental animals were diagnosed with prediabetes using the American Diabetes Association (ADA) prediabetes impaired fasting blood glucose criteria (5.6-6.9 mmol/L). Upon prediabetes diagnosis, the animals were subjected to a four-limb grip strength test to assess skeletal muscle strength at week 20. After the grip strength test was conducted, the animals were euthanized for blood and tissue collection to analyze glycated hemoglobin (HbA1c), plasma insulin, and insulin resistance using the homeostatic model of insulin resistance (HOMA-IR) index and malondialdehyde (MDA) concentration. Correlation analysis was performed to examine the associations of skeletal muscle strength with HOMA-IR, plasma glucose, HbA1c, and MDA concentration. The results demonstrated increased HbA1c, FBG, insulin, HOMA-IR, and MDA concentrations in the PD group compared to the NPD group. Grip strength was reduced in the PD group compared to the NPD group. Grip strength was negatively correlated with HbA1c, plasma glucose, HOMA-IR, and MDA concentration in the PD group. These observations suggest that diet-induced prediabetes compromises muscle function, which may contribute to increased levels of sedentary behavior during prediabetes progression, and this may contribute to the development of hyperglycemia in T2DM.

Myokines: A central point in managing redox homeostasis and quality of life

Redox homeostasis is a crucial phenomenon that is obligatory for maintaining the healthy status of cells. However, the loss of redox homeostasis may lead to numerous diseases that ultimately result in a compromised quality of life. Skeletal muscle is an endocrine organ that secretes hundreds of myokines. Myokines are peptides and cytokines produced and released by muscle fibers. Skeletal muscle secreted myokines act as a robust modulator for regulating cellular metabolism and redox homeostasis which play a prime role in managing and improving metabolic function in multiple organs. Further, the secretory myokines maintain redox homeostasis not only in muscles but also in other organs of the body via stabilizing oxidants and antioxidant levels. Myokines are also engaged in maintaining mitochondrial dynamics as mitochondria is a central point for the generation of reactive oxygen species (ROS). Ergo, myokines also act as a central player in communicating signals to other organs, including the pancreas, gut, liver, bone, adipose tissue, brain, and skin via their autocrine, paracrine, or endocrine effects. The present review provides a comprehensive overview of skeletal muscle-secreted myokines in managing redox homeostasis and quality of life. Additionally, probable strategies will be discussed that provide a solution for a better quality of life.

Cardiac commitment driven by MyoD expression in pericardial stem cells

Cellular therapy holds immense promise to remuscularize the damaged myocardium but is practically hindered by limited allogeneic sources of cardiac-committed cells that engraft stably in the recipient heart after transplantation. Here, we demonstrate that the pericardial tissue harbors myogenic stem cells (pSCs) that are activated in response to inflammatory signaling after myocardial infarction (MI). The pSCs derived from the MI rats (MI-pSCs) show in vivo and in vitro cardiac commitment characterized by cardiac-specific Tnnt2 expression and formation of rhythmic contraction in culture. Bulk RNA-seq analysis reveals significant upregulation of a panel of genes related to cardiac/myogenic differentiation, paracrine factors, and extracellular matrix in the activated pSCs compared to the control pSCs (Sham-pSCs). Notably, we define MyoD as a key factor that governs the process of cardiac commitment, as siRNA-mediated MyoD gene silencing results in a significant reduction of myogenic potential. Injection of the cardiac-committed cells into the infarcted rat heart leads to long-term survival and stable engraftment in the recipient myocardium. Therefore, these findings point to pericardial myogenic progenitors as an attractive candidate for cardiac cell-based therapy to remuscularize the damaged myocardium.

Equine Asthma Does Not Affect Circulating Myostatin Concentrations in Horses

(1) Background: The number of horses suffering from chronic respiratory diseases, resembling human asthma, is increasing but there is still a lack of reliable and accurate methods to detect these disorders. Numerous studies have found elevated plasma concentrations of one of the myokines, namely, myostatin (MSTN), in people suffering from severe asthma. MSTN normally inhibits myoblast proliferation and differentiation through autocrine or paracrine signals. Therefore, given the pathogenesis of asthma, we hypothesize that MSTN could be a useful biomarker of equine asthma. Thus, this study aimed to compare the concentration of MSTN in the blood plasma of fully healthy and asthmatic horses. (2) Methods: A total of 61 horses were clinically examined to confirm or exclude the occurrence of equine asthma, including bronchoalveolar lavage (BAL) fluid cytology performed on 49 horses. This study included three groups of horses, two of which were clinically healthy, and one of which was asthmatic. (3) Results: The mean circulatory MSTN concentration determined using the ELISA method in asthmatic horses was significantly higher than that in clinically healthy young Thoroughbred racehorses (p < 0.05), but it did not differ as compared to the group of healthy, adult leisure horses. (4) Conclusions: The obtained results did not unambiguously support our original hypothesis that MSTM may be a reliable marker for the early diagnosis of equine asthma. To the best of the authors' knowledge, this is the first study to analyze the plasma MSTN concentration in equine asthma patients, and therefore further studies are needed to confirm our novel findings.

Serum myostatin as a candidate disease severity and progression biomarker of spinal muscular atrophy

The identification of biomarkers for spinal muscular atrophy is crucial for predicting disease progression, severity, and response to new disease-modifying therapies. This study aimed to investigate the role of serum levels of myostatin and follistatin as biomarkers for spinal muscular atrophy, considering muscle atrophy secondary to denervation as the main clinical manifestation of the disease. The study evaluated the differential gene expression of myostatin and follistatin in a lesional model of gastrocnemius denervation in mice, as well as in a meta-analysis of three datasets in transgenic mice models of spinal muscular atrophy, and in two studies involving humans with spinal muscular atrophy. Subsequently, a case-control study involving 27 spinal muscular atrophy patients and 27 controls was conducted, followed by a 12-month cohort study with 25 spinal muscular atrophy cases. Serum levels of myostatin and follistatin were analysed using enzyme-linked immunosorbent assay at a single centre in southern Brazil. Skeletal muscle gene expression of myostatin decreased and of follistatin increased following lesional muscle denervation in mice, consistent with findings in the spinal muscular atrophy transgenic mice meta-analysis and in the iliopsoas muscle of five patients with spinal muscular atrophy type 1. Median serum myostatin levels were significantly lower in spinal muscular atrophy patients (98 pg/mL; 5-157) compared to controls (412 pg/mL; 299-730) (P < 0.001). Lower myostatin levels were associated with greater disease severity based on clinician-rated outcomes (Rho = 0.493-0.812; P < 0.05). After 12 months, there was a further reduction in myostatin levels among spinal muscular atrophy cases (P = 0.021). Follistatin levels did not differ between cases and controls, and no significant changes were observed over time. The follistatin:myostatin ratio was significantly increased in spinal muscular atrophy subjects and inversely correlated with motor severity. Serum myostatin levels show promise as a novel biomarker for evaluating the severity and progression of spinal muscular atrophy. The decrease in myostatin levels and the subsequent favourable environment for muscle growth may be attributed to denervation caused by motor neuron dysfunction.

Myokines Produced by Cultured Bovine Satellite Cells Harvested from 3- and 11-Month-Old Angus Steers

The myokines interleukin 6 (IL-6), interleukin 15 (IL-15), myonectin (CTRP15), fibronectin type III domain containing protein 5/irisin (FNDC5), and brain-derived neurotrophic factor (BDNF) are associated with skeletal muscle cell proliferation, differentiation, and muscle hypertrophy in biomedical model species. This study evaluated whether these myokines are produced by cultured bovine satellite cells (BSCs) harvested from 3- and 11-month-old commercial black Angus steers and if the expression and secretion of these targets change across 0, 12, 24, and 48 h in vitro. IL-6, IL-15, FNDC5, and BDNF expression were greater (p ≤ 0.05) in the differentiated vs. undifferentiated BSCs at 0, 12, 24, and 48 h. CTRP15 expression was greater (p ≤ 0.03) in the undifferentiated vs. differentiated BSCs at 24 and 48 h. IL-6 and CTRP15 protein from culture media were greater (p ≤ 0.04) in undifferentiated vs. differentiated BSCs at 0, 12, 24, and 48 h. BDNF protein was greater in the media of differentiated vs. undifferentiated BSCs at 0, 12, 24, and 48 h. IL-6, 1L-15, FNDC5, and BDNF are expressed in association with BSC differentiation, and CTRP15 appears to be expressed in association with BSC proliferation. This study also confirms IL-6, IL-15, CTRP15, and BDNF proteins present in media collected from primary cultures of BSCs.

Physical performance and negative events in very old adults: a longitudinal study examining the ilSIRENTE cohort

BACKGROUND

Declining physical performance in old age is associated with a wide range of negative health-related outcomes. However, it is unclear which physical capabilities should be prioritized to obtain prognostic information in older adults.

AIMS

To examine the associations between the performance on several physical function tests and falls, disability, and death in a well-characterized sample of very old Italian adults.

METHODS

This was a prospective cohort study of older adults who lived in the mountain community of the Sirente geographic area in Central Italy. Physical performance was assessed using isometric handgrip strength (IHG), walking speed (WS) at a usual and fast pace, 5-time sit-to-stand test (5STS), and sit-to-stand power measures. Appendicular skeletal muscle mass was estimated from calf circumference using a validated equation. History of falls, incident falls, and disability status according to basic Activities of Daily Living (ADLs) were recorded over two years. Survival status was obtained from the participants' general practitioners and was confirmed by the National Death Registry over 10 years from enrolment. Linear, binary, and Cox regressions were performed to evaluate the association between physical performance measures and health outcomes.

RESULTS

The mean age of the 255 participants was 84.2 ± 5.1 years, and 161 (63.1%) were women. Logistic regression indicated that IHG was significantly associated with incident ADL disability, whereas specific sit-to-stand muscle power was an independent predictor of death. No significant associations were observed between physical function and falls.

CONCLUSIONS

Our findings indicate selective associations between physical function tests and the occurrence of negative events in very old adults, with poor IHG predicting disability and specific sit-to-stand muscle power being longitudinally associated with death.

Probiotics as Potential Therapeutic Agents: Safeguarding Skeletal Muscle against Alcohol-Induced Damage through the Gut-Liver-Muscle Axis

Probiotics have shown the potential to counteract the loss of muscle mass, reduce physical fatigue, and mitigate inflammatory response following intense exercise, although the mechanisms by which they work are not very clear. The objective of this review is to describe the main harmful effects of alcohol on skeletal muscle and to provide important strategies based on the use of probiotics. The excessive consumption of alcohol is a worldwide problem and has been shown to be crucial in the progression of alcoholic liver disease (ALD), for which, to date, the only therapy available is lifestyle modification, including cessation of drinking. In ALD, alcohol contributes significantly to the loss of skeletal muscle, and also to changes in the intestinal microbiota, which are the basis for a series of problems related to the onset of sarcopenia. Some of the main effects of alcohol on the skeletal muscle are described in this review, with particular emphasis on the "gut-liver-muscle axis", which seems to be the primary cause of a series of muscle dysfunctions related to the onset of ALD. The modulation of the intestinal microbiota through probiotics utilization has appeared to be crucial in mitigating the muscle damage induced by the high amounts of alcohol consumed.

Secondary Sarcopenia and Spinal Cord Injury: Clinical Associations and Health Outcomes

Background: Sarcopenia and spinal cord injury (SCI) often coexist, but little is known about the associations. This study aimed to assess the impact of SCI on muscle and bone mass and the correlations between the clinical characteristics of SCI patients and sarcopenia. Methods: A total of 136 patients with SCI admitted to rehabilitation hospital were included in this study. The type and severity of injury (AIS), level of spasticity (MAS), bone mineral density and Appendicular Lean Muscle Mass (ALM) were assessed. Sarcopenia was diagnosed according to EWGSOP2 cut-off points for ALM. Results: Subjects were divided into two groups: Group S-SCI (N = 66, sarcopenia group) and Group NS-SCI (N = 70, without sarcopenia). Mean ALM values in the two groups were 0.49 and 0.65, respectively. A total of 75% of women and 42.9% of men developed sarcopenia. The mean age was 35.8 years in the sarcopenic patients and 41.5 in the non-sarcopenia group. Over 55% of AIS Grades A and B cases, 69.7% of MAS level 0 cases and 51.6% of the patients with osteoporosis had sarcopenia. The mean number of comorbidities was 2.7 in the sarcopenia group. Conclusions: Gender, type of injury, presence of multiple comorbidities and age were directly associated with sarcopenia; meanwhile, surprisingly, spasticity level and the presence of immobilization osteoporosis were not.

Cloning, characterization, and spatio-temporal expression patterns of HdhSPARC and its responses to multiple stressors

SPARC is an extracellular Ca2+-binding, secreted glycoprotein that plays a dynamic role in the growth and development of organisms. This study aimed to describe the isolation, characterization, and expression analysis of HdhSPARC in Pacific abalone (Haliotis discus hannai) to infer its potential functional role. The isolated HdhSPARC was 1633 bp long, encoding a polypeptide of 284 amino acid residues. Structurally, the SPARC protein in abalone is comprised of three biological domains. However, the structure of this protein varied between vertebrates and invertebrates, as suggested by their distinct clustering patterns in phylogenetic analysis. In early development, HdhSPARC was variably expressed, and higher expression was found in veliger larvae. Moreover, HdhSPARC was highly expressed in juvenile abalone with rapid growth compared to their slower-growing counterparts. Among the testicular development stages, the growth stage exhibited higher HdhSPARC expression. HdhSPARC was also upregulated during muscle remodeling and shell biomineralization, as well as in response to different stressors such as heat shock, LPS, and H2O2 exposure. However, this gene was downregulated in Cd-exposed abalone. The present study first comprehensively characterized the HdhSPARC gene, and its spatio-temporal expressions were analyzed along with its responses to various stressors.

Differences in Functional Capacity between Oncologic and Non-Oncologic Populations: Reference Values

This study is focused on the fact that in the context of increasing global aging and cancer diagnoses, additional challenges arise in clinical care. Adequate functionality and body composition are key to coping with antineoplastic treatment, which can lead to better treatment tolerance, survival, and quality of life. This is a cross-sectional comparative study focused on the assessment and comparison of body composition and functionality between cancer patients and a reference population, with the aim of establishing meaningful baseline values. Techniques such as manual dynamometry, the Five-Times Sit-to-Stand test, and bioimpedance were used to collect data from 374 oncologic patients and 1244 reference individuals. The results reveal significant disparities in functionality and body composition among participants, and provide age group-specific adjusted baseline values for those diagnosed with cancer. These findings may have crucial clinical implications for applying particular cut-off points designed for this population group, which makes the assessment process faster and more accurate, enhances the capacity of medical personnel to act quickly, and improves the management of frailty in cancer patients.

Muscle Strength and Male Sexual Function

Sexual dysfunction, in particular erectile dysfunction, is a common complaint among aging men. Obesity, diabetes, hypertension, and smoking are shown to be independent risk factors for erectile dysfunction, while cardiorespiratory fitness is shown to be protective. Less is known about the role of muscle strength in male sexual function. Our objective was to study the association between male sexual function and typical cardiovascular risk factors, together with exercise and muscle strength. We included data from the fourth wave of the RHINE study. Data on anthropometrics, exercise habits, diseases, muscle strength, and sexual function were collected using questionnaires, including the Aging Males' Symptoms (AMS) scale. We used multivariable logistic regression analysis to measure the association between sexual function and body mass index (BMI), age, smoking, diabetes, hypertension, exercise and muscle strength status. We included 2116 men aged 48-75 from four Nordic-Baltic countries. BMI, age, smoking, diabetes, and hypertension were found to be associated with higher odds of reporting decreased sexual function, while reporting intact muscle strength was associated with lower odds. In a large Nordic-Baltic male study population, we show that known cardiovascular risk factors are associated with decreased sexual function, while reporting intact muscle strength is associated with lower odds of reporting decreased sexual function.

High-intensity combination exercise has the highest effect on increasing serum irisin and interleukin 6 levels in women with obesity

OBJECTIVES

Lifestyle, overnutrition, socioeconomic status, environmental conditions, and genetics are factors that cause obesity. Lifestyle modification with a nonpharmacological approach based on physical exercise is the starting point in overcoming obesity. However, physical exercise with the appropriate and effective intensity for obese subjects is still debated. Therefore, this study aims to prove the effect of intensity differences with aerobic-resistance combination exercise on increasing irisin and IL-6 levels in obese women.

METHODS

A total of 32 obese women were selected as subjects and administered the interventions of low-intensity combination exercise (Q2), moderate-intensity combination exercise (Q3), and high-intensity combination exercise (Q4). ELISA was used to measure irisin and IL-6 levels in all samples. Statistical analysis used one-way ANOVA and Turkey's-Honest Significant Difference (HSD) post hoc test.

RESULTS

The mean Δ IL-6 levels in the control groups (Q1), Q2, Q3, and Q4 were 0.27 ± 2.54, 2.07 ± 2.55, 5.99 ± 6.25, and 7.98 ± 2.82 pg/mL with (p=0.015). The mean Δ irisin levels were 0.06 ± 0.81 ng/mL in Q1, 0.59 ± 0.67 ng/mL in Q2, 1.99 ± 1.65 ng/mL in Q3, 4.63 ± 3.57 ng/mL in Q4 with (p=0.001).

CONCLUSIONS

This study proved that all three types of combined exercise intensity increased myokine levels, such as irisin and IL-6. However, high-intensity combination exercise provided the most optimal improvement in myokine levels in obese women. Future studies are needed to design long-term exercise programs specifically for obese adolescent women using the findings from this study.

Soluble Factors Associated with Denervation-induced Skeletal Muscle Atrophy

Skeletal muscle tissue has the critical function of mechanical support protecting the body. In addition, its functions are strongly influenced by the balanced synthesis and degradation processes of structural and regulatory proteins. The inhibition of protein synthesis and/or the activation of catabolism generally determines a pathological state or condition called muscle atrophy, a reduction in muscle mass that results in partial or total loss of function. It has been established that many pathophysiological conditions can cause a decrease in muscle mass. Skeletal muscle innervation involves stable and functional neural interactions with muscles via neuromuscular junctions and is essential for maintaining normal muscle structure and function. Loss of motor innervation induces rapid skeletal muscle fiber degeneration with activation of atrophy-related signaling and subsequent disassembly of sarcomeres, altering normal muscle function. After denervation, an inflammation stage is characterized by the increased expression of pro-inflammatory cytokines that determine muscle atrophy. In this review, we highlighted the impact of some soluble factors on the development of muscle atrophy by denervation.

Crohn's disease and clinical management today: How it does?

Crohn's Disease (CD) is an Inflammatory Bowel Disease and is characterized by an immune-mediated nature. Its etiology results from the interaction between genetic, enviromental and microbial factors. Regarding pathophysiology, it involves high levels of interleukin (IL)-12, IL-17, and Th1 profile, along with loss of tolerance mechanisms, an increase in pro-inflammatory interleukins, beyond the possibility to affect any part of the gastrointestinal tract. Its symptoms include abdominal pain, chronic diarrhea, weight loss, anorexia, and fatigue, as well as blood in the stool or rectum. Additionally, conditions comprising musculoskeletal, cutaneous, ocular, hepatic, and hematological alterations may be associated with this scenario and extra-intestinal presentation, such as erythema nodosum, anterior uveitis, osteoporosis, and arthritis can also occur. Today, clinical history, exams as fecal calprotectin, ileocolonocopy, and capsule endoscopy can be performed in the diagnosis investigation, along with treatments to induce and maintain remission. In this sense, anti-inflammatory drugs, such as corticosteroids, immunomodulators, and biological agents, as well as surgery and non-pharmacological interventions plays a role in its therapy. The aim of this review is to bring more current evidence to clinical management of CD, as well as to briefly discuss aspects of its pathophysiology, surveillance, and associated disorders.

Current and investigational medications for the treatment of sarcopenia

Sarcopenia, defined as the loss of muscle mass and function, is a widely prevalent and severe condition in older adults. Since 2016, it is recognized as a disease. Strength exercise training and nutritional support are the frontline treatment of sarcopenia, with no drug currently approved for this indication. However, new therapeutic options are emerging. In this review, we evidenced that only very few trials have focused on sarcopenia/sarcopenic patients. Most drug trials were performed in different clinical older populations (e.g., men with hypogonadism, post-menopausal women at risk for osteoporosis), and their efficacy were tested separately on the components of sarcopenia (muscle mass, muscle strength and physical performances). Results from trials testing the effects of Testosterone, Selective Androgen Receptor Modulators (SARMs), Estrogen, Dehydroepiandrosterone (DHEA), Insulin-like Growth Factor-1 (IGF-1), Growth Hormone (GH), GH Secretagogue (GHS), drug targeting Myostatin and Activin receptor pathway, Vitamin D, Angiotensin Converting Enzyme inhibitors (ACEi) and Angiotensin Receptor Blockers (ARBs), or β-blockers, were compiled. Although some drugs have been effective in improving muscle mass and/or strength, this was not translated into clinically relevant improvements on physical performance. Finally, some promising molecules investigated in on-going clinical trials and in pre-clinical phase were summarized, including apelin and irisin.

Biomechanical Stimulation of Muscle Constructs Influences Phenotype of Bone Constructs by Modulating Myokine Secretion

Diabetes is a chronic metabolic disorder that can lead to diabetic myopathy and bone diseases. The etiology of musculoskeletal complications in such metabolic disorders and the interplay between the muscular and osseous systems are not well understood. Exercise training promises to prevent diabetic myopathy and bone disease and offer protection. Although the muscle-bone interaction is largely biomechanical, the muscle secretome has significant implications for bone biology. Uncoupling effects of biophysical and biochemical stimuli on the adaptive response of bone during exercise training may offer therapeutic targets for diabetic bone disease. Here, we have developed an in vitro model to elucidate the effects of mechanical strain on myokine secretion and its impact on bone metabolism decoupled from physical stimuli. We developed bone constructs using cross-linked gelatin, which facilitated osteogenic differentiation of osteoprogenitor cells. Then muscle constructs were made from fibrin, which enabled myoblast differentiation and myotube formation. We investigated the myokine expression by muscle constructs under strain regimens replicating endurance (END) and high-intensity interval training (HIIT) in hyperglycemic conditions. In monocultures, both regimens induced higher expression of Il15 and Igf1, whereas END supported more myoblast differentiation and myotube maturation than HIIT. When co-cultured with bone constructs, HIIT regimen increased Glut4 expression in muscle constructs more than END, supporting higher glucose uptake. Likewise, the muscle constructs under the HIIT regimen promoted a healthier and more matured bone phenotype than END. Under static conditions, myostatin (Mstn) expression was significantly downregulated in muscle constructs co-cultured with bone constructs compared with monocultures. Together, our in vitro co-culture system allowed orthogonal manipulation of mechanical strain on muscle constructs while facilitating bone-muscle biochemical cross-talk. Such systems can provide an individualized microenvironment that allows decoupled biomechanical manipulation, help identify molecular targets, and develop engineered therapies for metabolic bone disease. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

The impact of resistance training on brain-derived neurotrophic factor and depression among older adults aged 60 years or older: A systematic review and meta-analysis of randomized controlled trials

OBJECTIVE

This systematic review and meta-analysis aimed to investigate the impact of resistance training on brain-derived neurotrophic factor (BDNF) and depression among older adults aged 60 years or older.

METHOD

Four electronic databases were systematically searched.

RESULTS

A total of 11 randomized controlled trials, with a pooled sample of 868 participants, met our inclusion criteria. Meta-analysis demonstrated that resistance training significantly improved circulating BDNF levels (mean difference; MD: 0.73 ng/ml; 95% CI [0.04, 1.42]; p = 0.04). Additionally, resistance training was associated with significant improvements in depression (standardized mean difference; SMD: -0.38; 95% CI [- 0.62, -0.14]; p = 0.002).

DISCUSSION

These findings suggest that resistance training may be an effective intervention for improving BDNF levels and reducing depression symptoms in older adults. Further research is needed to confirm these findings and to investigate the underlying mechanisms.

Binge drinking leads to an oxidative and metabolic imbalance in skeletal muscle during adolescence in rats: endocrine repercussion

Binge drinking (BD) is an especially pro-oxidant model of alcohol consumption, mainly used by adolescents. It has recently been related to the hepatic IR-process. Skeletal muscle is known to be involved in insulin action and modulation through myokine secretion. However, there is no information on muscle metabolism and myokine secretion after BD exposure in adolescents. Two experimental groups of adolescent rats have been used: control and BD-exposed one. Oxidative balance, energy status and lipid, and protein metabolism have been analyzed in muscle, together with myokine serum levels (IL-6, myostatin, LIF, IL-5, fractalkine, FGF21, irisin, BDNF, FSTL1, apelin, FABP3, osteocrin, osteonectin (SPARC), and oncostatin). In muscle, BD affects the antioxidant enzyme balance leading to lipid and protein oxidation. Besides, it also increases the activation of AMPK and thus contributes to decrease SREBP1 and pmTOR and to increase FOXO3a expressions, promoting lipid and protein degradation. These alterations deeply affect the myokine secretion pattern. This is the first study to examine a general myokine response after exposure to BD. BD not only caused a detrimental imbalance in myokines related to muscle turnover, decreased those contributing to increase IR-process, decreased FST-1 and apelin and their cardioprotective function but also reduced the neuroprotective BDNF. Consequently, BD leads to an important metabolic and energetic disequilibrium in skeletal muscle, which contributes to exacerbate a general IR-process.

Personalized accelerated physiologic pacing

Heart failure with preserved ejection fraction (HFpEF) is increasingly prevalent with a high socioeconomic burden. Pharmacological heart rate lowering was recommended to improve ventricular filling in HFpEF. This article discusses the misperceptions that have resulted in an overprescription of beta-blockers, which in all likelihood have untoward effects on patients with HFpEF, even if they have atrial fibrillation or coronary artery disease as a comorbidity. Directly contradicting the lower heart rate paradigm, faster heart rates provide haemodynamic and structural benefits, amongst which lower cardiac filling pressures and improved ventricular capacitance may be most important. Safe delivery of this therapeutic approach is feasible with atrial and ventricular conduction system pacing that aims to emulate or enhance cardiac excitation to maximize the haemodynamic benefits of accelerated pacing. This conceptual framework was first tested in the myPACE randomized controlled trial of patients with pre-existing pacemakers and preclinical or overt HFpEF. This article provides the background and path towards this treatment approach.

Mouse skeletal muscle adaptations to different durations of treadmill exercise after the cessation of FOLFOX chemotherapy

FOLFOX (5-fluorouracil, leucovorin, oxaliplatin) chemotherapy is a treatment for colorectal cancer that can induce persistent fatigue and metabolic dysfunction. Regular exercise after chemotherapy cessation is widely recommended for cancer patients and has been shown to improve fatigue resistance in mice. However, gaps remain in understanding whether the early systemic and skeletal muscle adaptations to regular exercise are altered by prior FOLFOX chemotherapy treatment. Furthermore, the effects of exercise duration on early metabolic and skeletal muscle transcriptional adaptations are not fully established. Purpose: Investigate the effects of prior FOLFOX chemotherapy treatment on the early adaptations to repeated short- or long-duration treadmill exercise, including the fasting regulation of circulating metabolic regulators, skeletal muscle COXIV activity and myokine/exerkine gene expression in male mice. Methods: Male C57BL6/J mice completed 4 cycles of FOLFOX or PBS and were allowed to recover for 4-weeks. Subsets of mice performed 14 sessions (6 d/wk, 18 m/min, 5% grade) of short- (10 min/d) or long-duration (55 min/d) treadmill exercise. Blood plasma and muscle tissues were collected 48-72 h after the last exercise bout for biochemical analyses. Results: Long-duration exercise increased fasting plasma osteocalcin, LIF, and IL-6 in healthy PBS mice, and these changes were ablated by prior FOLFOX treatment. Slow-oxidative soleus muscle COXIV activity increased in response to long-duration exercise in PBS mice, which was blocked by prior FOLFOX treatment. Fast-glycolytic plantaris muscle COXIV activity increased with short-duration exercise independent of FOLFOX administration. There was a main effect for long-duration exercise to increase fasting muscle IL-6 and COXIV mRNA expression independent of FOLFOX. FOLFOX administration reduced muscle IL-6, LIF, and BDNF mRNA expression irrespective of long-duration exercise. Interestingly, short-duration exercise suppressed the FOLXOX induction of muscle myostatin mRNA expression. Conclusion: FOLFOX attenuated early exercise adaptations related to fasting circulating osteocalcin, LIF, and IL-6. However, prior FOLFOX treatment did not alter the exercise adaptations of plantaris muscle COXIV activity and plasma adiponectin. An improved understanding of mechanisms underlying exercise adaptations after chemotherapy will provide the basis for successfully treating fatigue and metabolic dysfunction in cancer survivors.

Effect of exercise interventions on brain-derived neurotrophic factor expression in people with overweight and obesity: protocol for a systematic review and meta-analysis

INTRODUCTION

Epidemic obesity ('globobesity') has led to a considerable rise in the prevalence and incidence of many disabling conditions, including cognitive dysfunction. Recent evidence has suggested that habitual exercise can alleviate the deleterious effects of obesity on cognitive functioning across the lifespan. Given that there is a potential link among obesity, exercise, cognitive health and brain-derived neurotrophic factor (BDNF), this systematic review aims to critically appraise interventional trials on exercise and BDNF and to estimate the pooled effect of exercise training on BDNF levels among healthy individuals with overweight and obesity.

METHODS AND ANALYSIS

Six electronic databases-PubMed, MEDLINE, EMBASE, Web of Science, Ovid Nursing Database and SPORTDiscus-will be searched from their inception through December 2022. Only interventional studies, including randomised controlled trials and quasi-experimental studies, with full text available and reported in English will be included. The primary outcomes will be changes in BDNF levels among healthy subjects with overweight and obesity following either acute or chronic bouts of exercise interventions. Two reviewers will independently conduct data extraction and risk of bias assessment for included trials using the Physiotherapy Evidence Database Scale. We will produce a narrative synthesis, with findings categorised by sex, age groups and types of exercise training. Data will be extracted and pooled for meta-analyses using random-effects models.

ETHICS AND DISSEMINATION

No formal ethical approval is required for this systematic review. The findings of this review will be disseminated through peer-reviewed publications.

PROSPERO REGISTRATION NUMBER

CRD42023414868.

Androgen action on myogenesis throughout the lifespan; comparison with neurogenesis

Androgens' pleiotropic actions in promoting sex differences present not only a challenge to providing a comprehensive account of their function, but also an opportunity to gain insights by comparing androgenic actions across organ systems. Although often overlooked by neuroscientists, skeletal muscle is another androgen-responsive organ system which shares with the nervous system properties of electrochemical excitability, behavioral relevance, and remarkable capacity for adaptive plasticity. Here we review androgenic regulation of mitogenic plasticity in skeletal muscle with the goal of identifying areas of interest to those researching androgenic mechanisms mediating sexual differentiation of neurogenesis. We use an organizational-activational framework to relate broad areas of similarity and difference between androgen effects on mitogenesis in muscle and brain throughout the lifespan, from early organogenesis, through pubertal organization, adult activation, and aging. The focus of the review is androgenic regulation of muscle-specific stem cells (satellite cells), which share with neural stem cells essential functions in development, plasticity, and repair, albeit with distinct, muscle-specific features. Also considered are areas of paracrine and endocrine interaction between androgen action on muscle and nervous system, including mediation of neural plasticity of innervating and distal neural populations by muscle-produced trophic factors.

Highlighting the idea of exerkines in the management of cancer patients with cachexia: novel insights and a critical review

BACKGROUND

Exerkines are all peptides, metabolites, and nucleic acids released into the bloodstream during and after physical exercise. Exerkines liberated from skeletal muscle (myokines), the heart (cardiokines), liver (hepatokines), white adipose tissue (adipokines), brown adipose tissue (batokines), and neurons (neurokines) may benefit health and wellbeing. Cancer-related cachexia is a highly prevalent disorder characterized by weight loss with specific skeletal muscle and adipose tissue loss. Many studies have sought to provide exercise strategies for managing cachexia, focusing on musculoskeletal tissue changes. Therefore, understanding the responses of musculoskeletal and other tissue exerkines to acute and chronic exercise may provide novel insight and recommendations for physical training to counteract cancer-related cachexia.

METHODS

For the purpose of conducting this study review, we made efforts to gather relevant studies and thoroughly discuss them to create a comprehensive overview. To achieve this, we conducted searches using appropriate keywords in various databases. Studies that were deemed irrelevant to the current research, not available in English, or lacking full-text access were excluded. Nevertheless, it is important to acknowledge the limited amount of research conducted in this specific field.

RESULTS

In order to obtain a comprehensive understanding of the findings, we prioritized human studies in order to obtain results that closely align with the scope of the present study. However, in instances where human studies were limited or additional analysis was required to draw more robust conclusions, we also incorporated animal studies. Finally, 295 studies, discussed in this review.

CONCLUSION

Our understanding of the underlying physiological mechanisms related to the significance of investigating exerkines in cancer cachexia is currently quite basic. Nonetheless, this demonstrated that resistance and aerobic exercise can contribute to the reduction and control of the disease in individuals with cancer cachexia, as well as in survivors, by inducing changes in exerkines.

Cancer Cachexia: Underlying Mechanisms and Potential Therapeutic Interventions

Cancer cachexia, a multifactorial metabolic syndrome developed during malignant tumor growth, is characterized by an accelerated loss of body weight accompanied by the depletion of skeletal muscle mass. This debilitating condition is associated with muscle degradation, impaired immune function, reduced functional capacity, compromised quality of life, and diminished survival in cancer patients. Despite the lack of the known capability of fully reversing or ameliorating this condition, ongoing research is shedding light on promising preclinical approaches that target the disrupted mechanisms in the pathophysiology of cancer cachexia. This comprehensive review delves into critical aspects of cancer cachexia, including its underlying pathophysiological mechanisms, preclinical models for studying the progression of cancer cachexia, methods for clinical assessment, relevant biomarkers, and potential therapeutic strategies. These discussions collectively aim to contribute to the evolving foundation for effective, multifaceted counteractive strategies against this challenging condition.

Nordic Walking training in BungyPump form improves cognitive functions and physical performance and induces changes in amino acids and kynurenine profiles in older adults

Introduction

Although impacts of physical activity on cognitive functions have been intensively investigated, they are still far from being completely understood. The aim of this study was to evaluate the effect of 12 weeks of the Nordic Walking training with BungyPump resistance poles (NW-RSA) on the amino acid and kynurenine profiles as well as selected myokine/exerkine concentrations, which may modify the interface between physical and cognitive functions.

Methods

A group of 32 older adults participated in the study. Before and after the intervention, body composition, cognitive functions, and physical performance were assessed. Blood samples were taken before and 1 h after the first and last sessions of the NW-RSA training, to determine circulating levels of exercise-induced proteins, i.e., brain-derived neurotrophic factor (BDNF), irisin, kynurenine (KYN), metabolites, and amino acids.

Results

The NW-RSA training induced a significant improvement in cognitive functions and physical performance as well as a reduction in fat mass (p = 0.05). Changes were accompanied by a decline in resting serum BDNF (p = 0.02) and a slight reduction in irisin concentration (p = 0.08). Still, changes in irisin concentration immediately after the NW-RSA intervention depended on shifts in kynurenine-irisin dropped as kynurenine increased. The kynurenine-to-tryptophan and phenylalanine-to-tyrosine ratios decreased significantly, suggesting their possible involvement in the amelioration of cognitive functions. No changes of glucose homeostasis or lipid profile were found. Shifts in the concentrations of selected amino acids might have covered the increased energy demand in response to the NW-RSA training and contributed to an improvement of physical performance.

Conclusion

Regular Nordic Walking training with additional resistance (BungyPump) improved cognitive functions and physical performance. These positive effects were associated with a reduced BDNF concentration and kynurenine-to-tryptophan ratio as well as changes in the amino acid profile.

Effects of high-intensity interval training (HIIT) on skeletal muscle atrophy, function, and myokine profile in diabetic myopathy

PURPOSE

Diabetes is a metabolic disorder characterized by chronic hyperglycemia due to insulin deficiency and/or loss of its action. Diabetic myopathy causes functional limitations in diabetic patients. The beneficial effects of high-intensity interval training (HIIT) are widely reported. We have hypothesized that HIIT application would prevent the development of diabetic myopathy.

METHODS

Male, Wistar albino rats (10 W) were randomly divided into four groups (1)Control(C), (2)Diabetes(DM), (3)Training(HIIT), and (4)Diabetes + Training(DM + HIIT). Streptozotocin(60 mg/kg) was injected for the induction of diabetes. The maximum exercise capacity(MEC) of animals was determined by an incremental load test. HIIT protocol (4 min 85-95 % MEC, 2 min 40-50 % MEC, 6 cycles, 5 days/week) was applied for 8 weeks. In the end, functional parameters, atrophy, and resistance to fatigue in soleus and EDL muscles were evaluated. IL-6, FNDC5, and myonectin levels were measured in EDL, soleus, and serum.

RESULTS

We observed atrophy, fatigue sensitivity, and proinflammatory alterations (IL-6 increase) in the EDL samples due to diabetic myopathy which were not observed in the soleus samples. HIIT application prevented the aforementioned detrimental alterations. Both force-frequency response and parallelly the twitch amplitude increased significantly in the DM + HIIT group. Half relaxation time (DT50) increased in both exercising and sedentary diabetics. FNDC5 was significantly higher in the exercising animals in soleus samples. Myonectin was significantly higher in the soleus muscle only in the DM + HIIT group.

CONCLUSION

Current findings show that diabetic myopathy develops earlier in glycolytic-fast-twitch fibers(EDL) than in oxidative-slow-twitch fibers(soleus). Furthermore, HIIT application prevents atrophy in skeletal muscle, increases resistance to fatigue, and has an anti-inflammatory effect.

NEW FINDINGS

The current study analyzes the myokine profile and skeletal muscle function under the effect of diabetes HIIT-type exercise. We also measured maximal exercise capacity and tailored the exercise program individually according to the result. Diabetic myopathy is an important complication of diabetes yet still, it is not understood completely. Our results show that HIIT-type training would be beneficial in diabetic myopathy but further investigation is needed to understand the whole molecular mechanism.

Mitochondrial dysfunction and skeletal muscle atrophy: Causes, mechanisms, and treatment strategies

Skeletal muscle, which accounts for approximately 40% of total body weight, is one of the most dynamic and plastic tissues in the human body and plays a vital role in movement, posture and force production. More than just a component of the locomotor system, skeletal muscle functions as an endocrine organ capable of producing and secreting hundreds of bioactive molecules. Therefore, maintaining healthy skeletal muscles is crucial for supporting overall body health. Various pathological conditions, such as prolonged immobilization, cachexia, aging, drug-induced toxicity, and cardiovascular diseases (CVDs), can disrupt the balance between muscle protein synthesis and degradation, leading to skeletal muscle atrophy. Mitochondrial dysfunction is a major contributing mechanism to skeletal muscle atrophy, as it plays crucial roles in various biological processes, including energy production, metabolic flexibility, maintenance of redox homeostasis, and regulation of apoptosis. In this review, we critically examine recent knowledge regarding the causes of muscle atrophy (disuse, cachexia, aging, etc.) and its contribution to CVDs. Additionally, we highlight the mitochondrial signaling pathways involvement to skeletal muscle atrophy, such as the ubiquitin-proteasome system, autophagy and mitophagy, mitochondrial fission-fusion, and mitochondrial biogenesis. Furthermore, we discuss current strategies, including exercise, mitochondria-targeted antioxidants, in vivo transfection of PGC-1α, and the potential use of mitochondrial transplantation as a possible therapeutic approach.

Plasma Myokine Profiles in Patients With AChR- and MuSK-Ab-Positive Myasthenia Gravis

BACKGROUND AND PURPOSE

Myokines include cytokines secreted by muscle fibers, which are the final targets of myasthenia gravis (MG). This pilot study investigated whether myokine plasma concentrations are altered in patients with MG and assessed the association between the concentration of each myokine and disease severity.

METHODS

We compared the plasma concentrations of 15 myokines in 63 patients with acetylcholine receptor antibody (Ab)-positive MG and 14 with muscle-specific tyrosine kinase Ab-positive MG (MuSK MG) with those in 15 healthy controls. Plasma myokine concentrations were measured using a Luminex multiplex assay kit with magnetic beads that contained Abs for 15 myokines. Correlations between myokine concentration and clinical scale results were analyzed.

RESULTS

The concentration of fractalkine in plasma was higher in MG (median [interquartile range]=419.6 [38.7-732.5] pg/mL) than in controls (158.5 [0.0-313.2] pg/mL, p=0.034). The leukemia inhibitory factor concentration was also found to be higher in MuSK MG (29.9 [8.7-40.1] pg/mL) than in healthy controls (7.6 [0.0-15.6] pg/mL, p=0.013). Fatty-acid-binding protein 3 (FABP3) concentrations in plasma were positively associated with clinical parameters for MG severity, including scores on the Quantitative Myasthenia Gravis score (p=0.008), Myasthenia Gravis Activities of Daily Living (p=0.003), and Myasthenia Gravis Composite (p=0.024) scales. FABP3 concentration in plasma tended to decrease after treatment in patients without additional relapse but increased in those with further relapse.

CONCLUSIONS

The plasma myokine profile was significantly altered in patients with MG. FABP3 concentration may be useful in assessing disease severity and predicting the treatment response.

Exercise training induces depot-specific remodeling of protein secretion in skeletal muscle and adipose tissue of obese male mice

Acute exercise induces changes in circulating proteins, which are known to alter metabolism and systemic energy balance. Skeletal muscle is a primary contributor to changes in the plasma proteome with acute exercise. An important consideration when assessing the endocrine function of muscle is the presence of different fiber types, which show distinct functional and metabolic properties and likely secrete different proteins. Similarly, adipokines are important regulators of systemic metabolism and have been shown to differ between depots. Given the health-promoting effects of exercise, we proposed that understanding depot-specific remodeling of protein secretion in muscle and adipose tissue would provide new insights into intertissue communication and uncover novel regulators of energy homeostasis. Here, we examined the effect of endurance exercise training on protein secretion from fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus muscle and visceral and subcutaneous adipose tissue. High-fat diet-fed mice were exercise trained for 6 wk, whereas a Control group remained sedentary. Secreted proteins from excised EDL and soleus muscle, inguinal, and epididymal adipose tissues were detected using mass spectrometry. We detected 575 and 784 secreted proteins from EDL and soleus muscle and 738 and 920 proteins from inguinal and epididymal adipose tissue, respectively. Of these, 331 proteins were secreted from all tissues, whereas secretion of many other proteins was tissue and depot specific. Exercise training led to substantial remodeling of protein secretion from EDL, whereas soleus showed only minor changes. Myokines released exclusively from EDL or soleus were associated with glycogen metabolism and cellular stress response, respectively. Adipokine secretion was completely refractory to exercise regulation in both adipose depots. This study provides an in-depth resource of protein secretion from muscle and adipose tissue, and its regulation following exercise training, and identifies distinct depot-specific secretion patterns that are related to the metabolic properties of the tissue of origin.NEW & NOTEWORTHY The present study examines the effects of exercise training on protein secretion from fast-twitch and slow-twitch muscle as well as visceral and subcutaneous adipose tissue of obese mice. Although exercise training leads to substantial remodeling of protein secretion from fast-twitch muscle, adipose tissue is completely refractory to exercise regulation.

Sex-Specific Associations between Serum IL-16 Levels and Sarcopenia in Older Adults

Epidemiological studies of older adults have suggested a differential sex-specific prevalence of sarcopenia, which is a condition characterized by a progressive loss of skeletal muscle mass and function. Recently, we collected serum samples from 80 fully evaluated older adults and identified CXCL12α as a sex-independent serum marker of sarcopenia. Here, we used this serum collection to find potential sex-specific serum markers via the simultaneous quantification of 34 inflammatory cytokines/chemokines. The appendicular skeletal muscle index (ASMI) was used as a decisive criterion for diagnosing sarcopenia. A Pearson correlation analysis revealed a negative correlation between ASMI and serum IL-16 in females only (p = 0.021). Moreover, women with sarcopenia exhibited significantly higher IL-16 (p = 0.025) serum levels than women in a control group. In contrast, males with sarcopenia had lower IL-16 (p = 0.013) levels than males in a control group. The further use of Fisher's exact test identified obesity (p = 0.027) and high serum levels of IL-16 (p = 0.029) as significant risk factors for sarcopenia in females. In male older adults, however, malnutrition (p = 0.028) and low serum levels of IL-16 (p = 0.031) were the most significant risk factors for sarcopenia. The differential sex-specific associations of IL-16 in older adults may contribute to the development of more precise regression models for future research and elucidate the role of IL-16 in the progression of sarcopenic obesity.

Left Ventricular Gene Expression in Heart Failure With Preserved Ejection Fraction-Profibrotic and Proinflammatory Pathways and Genes

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) is increasingly prevalent and has few treatments. The molecular mechanisms and resultant signaling pathways that underlie the development of HFpEF are poorly defined. It has been proposed that activation of proinflammatory pathways plays a role in the development of cardiac fibrosis. The signature of gene expression (transcriptome) of previously validated left ventricular biopsies obtained from patients with HFpEF and matched referent controls allows for an unbiased assessment of proinflammatory and profibrotic signaling pathways and genes.

METHODS

Epicardial left ventricular biopsies from stringently selected HFpEF patients (HFpEF, n=16) and referent control patients (CTR, n=14) were obtained during aortocoronary bypass surgery. The subepicardial myocardium was flash-frozen to build a repository that was parallel-processed for RNA sequencing to allow for an unsupervised in-depth comparison of the left ventricular transcriptome.

RESULTS

The average patient age was 67±10 years. When compared with controls, patients with HFpEF were hypertensive with a higher body mass index (kg/m2: 30±5 versus 37±6; P<0.01) and elevated NT-proBNP levels (pg/mL: 155 [89-328] versus 1554 [888-2178]; P<0.001). The transcriptome analysis revealed differential expression of 477 genes many of which were involved in profibrotic pathways including extracellular matrix production and posttranslational modification but no proinflammatory signature.

CONCLUSIONS

The transcriptome analysis of left ventricular myocardial samples from patients with HFpEF confirms an overabundant extracellular matrix gene expression, the basis of myocardial fibrosis, without a signature of activated proinflammatory pathways or genes.

Myokines as mediators of exercise-induced cognitive changes in older adults: protocol for a comprehensive living systematic review and meta-analysis

Background

The world's population is aging, but life expectancy has risen more than healthy life expectancy (HALE). With respect to brain and cognition, the prevalence of neurodegenerative disorders increases with age, affecting health and quality of life, and imposing significant healthcare costs. Although the effects of physical exercise on cognition in advanced age have been widely explored, in-depth fundamental knowledge of the underlying mechanisms of the exercise-induced cognitive improvements is lacking. Recent research suggests that myokines, factors released into the blood circulation by contracting skeletal muscle, may play a role in mediating the beneficial effect of exercise on cognition. Our goal in this ongoing (living) review is to continuously map the rapidly accumulating knowledge on pathways between acute or chronic exercise-induced myokines and cognitive domains enhanced by exercise.

Method

Randomized controlled studies will be systematically collected at baseline and every 6 months for at least 5 years. Literature search will be performed online in PubMed, EMBASE, PsycINFO, Web of Science, SportDiscus, LILACS, IBECS, CINAHL, SCOPUS, ICTRP, and ClinicalTrials.gov. Risk of bias will be assessed using the Revised Cochrane Risk of Bias tool (ROB 2). A random effects meta-analysis with mediation analysis using meta-analytic structural equation modeling (MASEM) will be performed. The primary research question is to what extent exercise-induced myokines serve as mediators of cognitive function. Secondarily, the pooled effect size of specific exercise characteristics (e.g., mode of exercise) or specific older adults' populations (e.g., cognitively impaired) on the relationship between exercise, myokines, and cognition will be assessed. The review protocol was registered in PROSPERO (CRD42023416996).

Discussion

Understanding the triad relationship between exercise, myokines and cognition will expand the knowledge on multiple integrated network systems communicating between skeletal muscles and other organs such as the brain, thus mediating the beneficial effects of exercise on health and performance. It may also have practical implications, e.g., if a certain myokine is found to be a mediator between exercise and cognition, the optimal exercise characteristics for inducing this myokine can be prescribed. The living review is expected to improve our state of knowledge and refine exercise regimes for enhancing cognitive functioning in diverse older adults' populations.

Registration

Systematic review and meta-analysis protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO) on the 24th of April 2023 (registration number CRD42023416996).

Association between physical fitness and musculoskeletal health in firefighters

Introduction: Firefighters are often placed in situations that require high levels of physical exertion, leading to significant strain on firefighters' musculoskeletal system, predisposing them to musculoskeletal discomfort (MSD) and/or musculoskeletal injury (MSI). Physical fitness programs are often recommended and justified, in part, to prevent injuries. The aim of this study was to determine the association between physical fitness and musculoskeletal health (MSH) in firefighters. Methods: A total of 308 full-time firefighters took part in the study conducted in Cape Town, South Africa. Physical fitness tests encompassed a non-exercise estimation for cardiorespiratory fitness, grip and leg strength for upper and lower body strength, push-ups and sit-ups for muscular endurance, and sit-and-reach for flexibility. The Nordic Musculoskeletal Questionnaire and Cornell Musculoskeletal Discomfort Questionnaire were used to determine MSIs and MSD, respectively. A p-value <0.05 indicated statistical significance. Results: Every one-unit increase in AbVO2max, push-ups, sit-ups, and sit-and-reach decreased the odds of firefighters reporting MSIs by 5% (p = 0.005), 3% (p = 0.017), 3% (p = 0.006), and 3% (p = 0.034), respectively. Every one repetition increase in push-up capacity increased the odds of firefighters reporting neck, elbow and forearm, wrist and hand, and thigh discomfort by 3% (p = 0.039), 4% (p = 0.031), 5% (p = 0.002), and 5%` (p = 0.007), respectively. Every one repetition increase in sit-up capacity increased the odds of firefighters reporting upper back discomfort and thigh discomfort by 5% (p = 0.045) and 7% (p = 0.013), respectively. Conclusion: Maintenance of physical fitness is likely beneficial in reducing MSIs, which, however, may increase the feeling of MSD in firefighters. In addition, it may be noticed that there is an ideal level of physical fitness that is conducive to the reduction of MSIs and should be studied further.

[Paracrine and endocrine functions of muscles]

BACKGROUND

Myokines discharged from working muscles are intensively researched in view of rising importance of preventive and secondary preventive effects of the autocrine, paracrine and endocrine functions.

OBJECTIVES

Recording of the current state of knowledge on the paracrine and endocrine effects of myokines and evaluation of training measures to optimize myokine concentration.

METHOD

A selective database-driven literature search was carried out on myostatin, interleukin-6 (IL-6), interleukin-15 (IL-15), irisin, cathepsin B, brain-derived neurotrophic factor (BDNF), meteorin-like and kynurenine for the period 2011 until June 2021. The paracrine and endocrine effects of the myokines are analyzed. Their release after acute physical stress and training is described.

RESULTS

IL-6 and IL-15 act in lipid metabolism and carbohydrate metabolism, IL-6 also in the brain and immune system. Irisin produces a conversion of white to brown adipose tissue ("browning"), so does meteorin-like. Cathepsin B has a central effect. Kynurenine acts indirectly via kynurenic acid in the brain. The secretion of myokines depends on the intensity of physical stress and is modified by training. Prevention of vascular and neurologic diseases, cognitive enhancement and increased immunological function can be reached by setting free myokines during physical activity. Therapeutical use by technologically modified myokines is proposed in metabolic and neurological diseases, immobilization and sarcopenia.

CONCLUSIONS

The current research situation on myokines gives reason to recommend regular muscular activity in addition to the previously evidence-based benefits of sport in order to achieve preventive and therapeutic effects.

ProBDNF Upregulation in Murine Hind Limb Ischemia Reperfusion Injury: A Driver of Inflammation

Brain-derived neurotropic factor (BDNF) has been shown to be expressed in many nonneuronal tissues including skeletal muscle. Skeletal muscle BDNF has been studied regarding its function in metabolism and exercise; however, less is known about its role in skeletal muscle injury. The precursor to BDNF, proBDNF, has an unknown role in skeletal muscle. The levels of proBDNF, mature BDNF, and their receptors were compared in the skeletal muscle and brain tissues of C57BL/6J mice. Tourniquet-induced hind limb ischemia-reperfusion injury was used to assess the function of skeletal muscle-derived proBDNF in skeletal muscle injury. Skeletal muscle-specific knockout of BDNF and pharmacological inhibition of p75NTR, the proBDNF receptor, were used to determine the role of proBDNF-p75NTR signaling. We show for the first time that proBDNF is the predominantly expressed form of BDNF in skeletal muscle and that proBDNF is significantly upregulated in skeletal muscle following hind limb ischemia-reperfusion injury. Skeletal muscle-specific knockout of BDNF blunted the inflammatory response in the injured tissue and appears to be mediated by the proBDNF-p75NTR pathway, as shown by the pharmacological inhibition of p75NTR. These findings suggest that skeletal muscle proBDNF plays a critical role in driving the inflammatory response following skeletal muscle injury.

Irisin Is Target of Sphingosine-1-Phosphate/Sphingosine-1-Phosphate Receptor-Mediated Signaling in Skeletal Muscle Cells

Irisin is a hormone-like myokine produced in abundance by skeletal muscle (SkM) in response to exercise. This myokine, identical in humans and mice, is involved in many signaling pathways related to metabolic processes. Despite much evidence on the regulators of irisin and the relevance of sphingolipids for SkM cell biology, the contribution of these latter bioactive lipids to the modulation of the myokine in SkM is missing. In particular, we have examined the potential involvement in irisin formation/release of sphingosine-1-phosphate (S1P), an interesting bioactive molecule able to act as an intracellular lipid mediator as well as a ligand of specific G-protein-coupled receptors (S1PR). We demonstrate the existence of distinct intracellular pools of S1P able to affect the expression of the irisin precursor FNDC. In addition, we establish the crucial role of the S1P/S1PR axis in irisin formation/release as well as the autocrine/paracrine effects of irisin on myoblast proliferation and myogenic differentiation. Altogether, these findings provide the first evidence for a functional crosstalk between the S1P/S1PR axis and irisin signaling, which may open new windows for potential therapeutic treatment of SkM dysfunctions.