IL-1beta stimulates IL-6 production in cultured skeletal muscle cells through activation of MAP kinase signaling pathway and NF-kappa B

Skeletal muscle atrophy after sciatic nerve damage: Mechanistic insights

Sciatic nerve injury leads to molecular events that cause muscular dysfunction advancement in atrophic conditions. Nerve damage renders muscles permanently relaxed which elevates intracellular resting Ca2+ levels. Increased Ca2+ levels are associated with several cellular signaling pathways including AMPK, cGMP, PLC-β, CERB, and calcineurin. Also, multiple enzymes involved in the tricarboxylic acid cycle and oxidative phosphorylation are activated by Ca2+ influx into mitochondria during muscle contraction, to meet increased ATP demand. Nerve damage induces mitophagy and skeletal muscle atrophy through increased sensitivity to Ca2+-induced opening of the permeability transition pore (PTP) in mitochondria attributed to Ca2+, ROS, and AMPK overload in muscle. Activated AMPK interacts negatively with Akt/mTOR is a highly prevalent and well-described central pathway for anabolic processes. Over the decade several reports indicate abnormal behavior of signaling machinery involved in denervation-induced muscle loss but end up with some controversial outcomes. Therefore, understanding how the synthesis and inhibitory stimuli interact with cellular signaling to control muscle mass and morphology may lead to new pharmacological insights toward understanding the underlying mechanism of muscle loss after sciatic nerve damage. Hence, the present review summarizes the existing literature on denervation-induced muscle atrophy to evaluate the regulation and expression of differential regulators during sciatic damage.

Photobiomodulation mitigates Bothrops jararacussu venom-induced damage in myoblast cells by enhancing myogenic factors and reducing cytokine production

BACKGROUND

Photobiomodulation has exhibited promise in mitigating the local effects induced by Bothrops snakebite envenoming; however, the mechanisms underlying this protection are not yet fully understood. Herein, the effectiveness of photobiomodulation effects on regenerative response of C2C12 myoblast cells following exposure to Bothrops jararacussu venom (BjsuV), as well as the mechanisms involved was investigated.

METHODOLOGY/PRINCIPAL FINDINGS

C2C12 myoblast cells were exposed to BjsuV (12.5 μg/mL) and irradiated once for 10 seconds with laser light of 660 nm (14.08 mW; 0.04 cm2; 352 mW/cm2) or 780 nm (17.6 mW; 0.04 cm2; 440 mW/ cm2) to provide energy densities of 3.52 and 4.4 J/cm2, and total energies of 0.1408 and 0.176 J, respectively. Cell migration was assessed through a wound-healing assay. The expression of MAPK p38-α, NF-Кβ, Myf5, Pax-7, MyoD, and myogenin proteins were assessed by western blotting analysis. In addition, interleukin IL1-β, IL-6, TNF-alfa and IL-10 levels were measured in the supernatant by ELISA. The PBM applied to C2C12 cells exposed to BjsuV promoted cell migration, increase the expression of myogenic factors (Pax7, MyF5, MyoD and myogenin), reduced the levels of proinflammatory cytokines, IL1-β, IL-6, TNF-alfa, and increased the levels of anti-inflammatory cytokine IL-10. In addition, PBM downregulates the expression of NF-kB, and had no effect on p38 MAKP.

CONCLUSION/SIGNIFICANCE

These data demonstrated that protection of the muscle cell by PBM seems to be related to the increase of myogenic factors as well as the modulation of inflammatory mediators. PBM therapy may offer a new therapeutic strategy to address the local effects of snakebite envenoming by promoting muscle regeneration and reducing the inflammatory process.

Postnatal skeletal muscle myogenesis governed by signal transduction networks: MAPKs and PI3K-Akt control multiple steps

Skeletal muscle myogenesis represents one of the most intensively and extensively examined systems of cell differentiation, tissue formation, and regeneration. Muscle regeneration provides an in vivo model system of postnatal myogenesis. It comprises multiple steps including muscle stem cell (or satellite cell) quiescence, activation, migration, myogenic determination, myoblast proliferation, myocyte differentiation, myofiber maturation, and hypertrophy. A variety of extracellular signaling and subsequent intracellular signal transduction pathways or networks govern the individual steps of postnatal myogenesis. Among them, MAPK pathways (the ERK, JNK, p38 MAPK, and ERK5 pathways) and PI3K-Akt signaling regulate multiple steps of myogenesis. Ca2+, cytokine, and Wnt signaling also participate in several myogenesis steps. These signaling pathways often control cell cycle regulatory proteins or the muscle-specific MyoD family and the MEF2 family of transcription factors. This article comprehensively reviews molecular mechanisms of the individual steps of postnatal skeletal muscle myogenesis by focusing on signal transduction pathways or networks. Nevertheless, no or only a partial signaling molecules or pathways have been identified in some responses during myogenesis. The elucidation of these unidentified signaling molecules and pathways leads to an extensive understanding of the molecular mechanisms of myogenesis.

IFN-γ blockade after genetic inhibition of PD-1 aggravates skeletal muscle damage and impairs skeletal muscle regeneration

BACKGROUND

Innate immune responses play essential roles in skeletal muscle recovery after injury. Programmed cell death protein 1 (PD-1) contributes to skeletal muscle regeneration by promoting macrophage proinflammatory to anti-inflammatory phenotype transition. Interferon (IFN)-γ induces proinflammatory macrophages that appear to hinder myogenesis in vitro. Therefore, we tested the hypothesis that blocking IFN-γ in PD-1 knockout mice may dampen inflammation and promote skeletal muscle regeneration via regulating the macrophage phenotype and neutrophils.

METHODS

Anti-IFN-γ antibody was administered in PD-1 knockout mice, and cardiotoxin (CTX) injection was performed to induce acute skeletal muscle injury. Hematoxylin and eosin (HE) staining was used to view morphological changes of injured and regenerated skeletal muscle. Masson's trichrome staining was used to assess the degree of fibrosis. Gene expressions of proinflammatory and anti-inflammatory factors, fibrosis-related factors, and myogenic regulator factors were determined by real-time polymerase chain reaction (PCR). Changes in macrophage phenotype were examined by western blot and real-time PCR. Immunofluorescence was used to detect the accumulation of proinflammatory macrophages, anti-inflammatory macrophages, and neutrophils.

RESULTS

IFN-γ blockade in PD-1 knockout mice did not alleviate skeletal muscle damage or improve regeneration following acute cardiotoxin-induced injury. Instead, it exacerbated skeletal muscle inflammation and fibrosis, and impaired regeneration via inhibiting macrophage accumulation, blocking macrophage proinflammatory to anti-inflammatory transition, and enhancing infiltration of neutrophils.

CONCLUSION

IFN-γ is crucial for efficient skeletal muscle regeneration in the absence of PD-1.

Impaired muscle stem cell function and abnormal myogenesis in acquired myopathies

Skeletal muscle possesses a high plasticity and a remarkable regenerative capacity that relies mainly on muscle stem cells (MuSCs). Molecular and cellular components of the MuSC niche, such as immune cells, play key roles to coordinate MuSC function and to orchestrate muscle regeneration. An abnormal infiltration of immune cells and/or imbalance of pro- and anti-inflammatory cytokines could lead to MuSC dysfunctions that could have long lasting effects on muscle function. Different genetic variants were shown to cause muscular dystrophies that intrinsically compromise MuSC function and/or disturb their microenvironment leading to impaired muscle regeneration that contributes to disease progression. Alternatively, many acquired myopathies caused by comorbidities (e.g., cardiopulmonary or kidney diseases), chronic inflammation/infection, or side effects of different drugs can also perturb MuSC function and their microenvironment. The goal of this review is to comprehensively summarize the current knowledge on acquired myopathies and their impact on MuSC function. We further describe potential therapeutic strategies to restore MuSC regenerative capacity.

Mechanism of skeletal muscle atrophy after spinal cord injury: A narrative review

Spinal cord injury leads to loss of innervation of skeletal muscle, decreased motor function, and significantly reduced load on skeletal muscle, resulting in atrophy. Factors such as braking, hormone level fluctuation, inflammation, and oxidative stress damage accelerate skeletal muscle atrophy. The atrophy process can result in skeletal muscle cell apoptosis, protein degradation, fat deposition, and other pathophysiological changes. Skeletal muscle atrophy not only hinders the recovery of motor function but is also closely related to many systemic dysfunctions, affecting the prognosis of patients with spinal cord injury. Extensive research on the mechanism of skeletal muscle atrophy and intervention at the molecular level has shown that inflammation and oxidative stress injury are the main mechanisms of skeletal muscle atrophy after spinal cord injury and that multiple pathways are involved. These may become targets of future clinical intervention. However, most of the experimental studies are still at the basic research stage and still have some limitations in clinical application, and most of the clinical treatments are focused on rehabilitation training, so how to develop more efficient interventions in clinical treatment still needs to be further explored. Therefore, this review focuses mainly on the mechanisms of skeletal muscle atrophy after spinal cord injury and summarizes the cytokines and signaling pathways associated with skeletal muscle atrophy in recent studies, hoping to provide new therapeutic ideas for future clinical work.

LP07 and LLC preclinical models of lung cancer induce divergent anabolic deficits and expression of pro-inflammatory effectors of muscle wasting

Preclinical models have been instrumental to elucidate the mechanisms underlying muscle wasting in lung cancer (LC). We investigated anabolic deficits and the expression of proinflammatory effectors of muscle wasting in the LP07 and Lewis lung carcinoma (LLC) tumor models. Tumor growth resulted in significant weakness in LP07 but not in LLC mice despite similar reductions in gastrocnemius muscle mass in both models. The LP07 tumors caused a reduction in ribosomal (r)RNA and a decrease in rRNA gene (rDNA) transcription elongation, whereas no changes in ribosomal capacity were evident in LLC tumor-bearing mice. Expression of RNA Polymerase I (Pol I) elongation-associated subunits Polr2f, PAF53, and Znrd1 mRNAs was significantly elevated in the LP07 model, whereas Pol I elongation-related factors FACT and Spt4/5 mRNAs were elevated in the LLC mice. Reductions in RPS6 and 4E-BP1 phosphorylation were similar in both models but were independent of mTOR phosphorylation in LP07 mice. Muscle inflammation was also tumor-specific, IL-6 and TNF-α mRNA increased with LLC tumors, and upregulation of NLRP3 mRNA was independent of tumor type. In summary, although both models caused muscle wasting, only the LP07 model displayed muscle weakness with reductions in ribosomal capacity. Intracellular signaling diverged at the mTOR level with similar reductions in RPS6 and 4E-BP1 phosphorylation regardless of tumor type. The increase in proinflammatory factors was more pronounced in the LLC model. Our results demonstrate novel divergent anabolic deficits and expression of proinflammatory effectors of muscle wasting in the LP07 and LLC preclinical models of lung cancer.NEW & NOTEWORTHY We provide novel data demonstrating significant divergence in anabolic deficits and the expression of proinflammatory effectors of muscle wasting consequent to different lung-derived tumors.

Lipopolysaccharide Promotes the Proliferation and Differentiation of Goose Embryonic Myoblasts by Promoting Cytokine Expression and Appropriate Apoptosis Processes

Lipopolysaccharide (LPS) can trigger a series of immune reactions, leading to the occurrence of disease and a decrease in the growth performance of geese. However, the mechanisms of LPS in geese muscle development have not been reported. This study aimed to investigate the effects and mechanisms of LPS on proliferation and differentiation of goose embryonic myoblasts. Embelin and belnacasan combined with LPS were used to explore these effects. Our results demonstrated that LPS significantly induced inflammatory cytokine production in both proliferation and differentiation stages. LPS and embelin treatment significantly improved the proliferation ability (p < 0.05), while LPS reduced the differentiation ability of goose embryonic myoblasts. By adding embelin, the differentiation ability of myoblasts was enhanced, while by adding belnacasan, LPS treatment led to a lower differentiation ability. Combined with the correlation of the expression levels of myogenic, cell cycle, and inflammatory-related genes and proteins, it is speculated that one of the reason for the decrease of differentiation ability of goose embryo myoblasts induced by LPS is the increase of the expression levels of pro-inflammatory factors. Moreover, LPS, embelin and belnacasan, and LPS treatments could significantly increase the apoptosis rate of goose embryonic myoblasts. Taken together, these findings suggest that LPS promotes the proliferation and differentiation of goose embryonic myoblasts by promoting cytokine expression and appropriate apoptosis processes. These findings lay a foundation for the study of the mechanisms of LPS in goose muscle development.

Brassica oleracea L. var. botrytis Leaf Extract Alleviates Gentamicin-Induced Hepatorenal Injury in Rats—Possible Modulation of IL-1β and NF-κB Activity Assisted with Computational Approach

Background: Recently, crop byproducts are considered a hot topic and can be converted into beneficial products. Cauliflower is well-known for its protective effects against oxidative stress-induced damage. The current study aimed to investigate the chemical profile and the ameliorative effects of cauliflower leaf extract (CL) on gentamicin-induced renal and hepatic injuries in rats. Methods: Cauliflower leaf was extracted with methanol to give the total methanol extract (TME) followed by the determination of total phenolic contents (TPC). Rats were divided into five groups; Group I was assigned as the control group, while the other groups were injected with gentamicin for ten days. Group II was given distilled water. Rats in groups III and IV were treated with oral CL (200 mg/kg and 400 mg/kg, respectively). Group V received L-cysteine (as a positive control). The functions of the kidneys and liver; oxidative stress and morphological and apoptotic changes of renal and hepatic tissues were assessed. Results: The TME was subjected to chromatographic techniques to yield ferulic acid, vanillic acid, p-coumaric acid and quercetin. TPC was 72.31 mg GAE/g of dried extract. CL treatment dose-dependently ameliorated gentamicin-induced impaired kidney and liver functions and improved the histopathological appearance of both organs. It also reduced gentamicin-induced oxidative stress. CL demonstrated downregulation of mRNA and protein expressions of IL-1β and NF-κB compared to nontreated rats. In silico interaction of the isolated compounds with amino acid residues of IL-1β and NF-κB might explain the current findings. Conclusion: Taken together, this study raises the waste-to-wealth potential of cauliflower to mitigate gentamicin-induced hepatorenal injury and convert the waste agromaterials into valuable products.

Betaine Alleviates LPS-Induced Chicken Skeletal Muscle Inflammation with the Epigenetic Modulation of the TLR4 Gene

Simple Summary

The poultry meat we eat is the skeletal muscle which comprises approximately three-quarters of the body weight of a chicken. In the modern poultry industry, the intensively raised broilers face the risk of exposure to environmental factors which can cause acute or chronic systemic inflammation. Inflammation, in return, contributes to the pathology of skeletal muscle diseases which are characterized by the loss of skeletal muscle mass. By adding betaine, a natural component, into the water of the newly hatched broilers for two weeks, we found that inflammation-related gene expression in the leg muscle was remarkably reduced. Specifically, we found that betaine inhibited the LPS-induced abnormal expression of IL-6 and TLR4. Further study indicated that the methylation modulation of the gene may be involved in betaine’s action. We suggest that betaine could be considered a safe and cheap preventive reagent candidate for chicken skeletal muscle inflammatory diseases.

Abstract

Betaine was found to alleviate inflammation in different studies. Here, newly hatched broilers were randomly divided into control and betaine consumptive groups, who had access to normal drinking water and water with betaine at a dose of 1000 mg/L, respectively. At the age of two weeks, the boilers were intraperitoneally treated with LPS. The protective effects of betaine against LPS-induced skeletal muscle inflammation were studied. Betaine attenuated the LPS-induced overexpression of IL-6 significantly in the leg muscle. Furthermore, LPS lowered the expression of TLR4 and TLR2 but increased the expression of MyD88. Betaine eliminated the effect of LPS on the expression of TLR4 but not TLR2 and MyD88. LPS also increased the expression of Tet methylcytosine dioxygenase 2 (Tet2), and this effect was also eliminated by betaine consumption. MeDIP-qPCR analysis showed that the methylation level in the promoter region of IL-6 was decreased by LPS treatment, whilst betaine cannot prevent this effect. On the contrary, LPS significantly increase the methylation level in the promoter region of TLR4, which was decreased by the consumption of betaine. Our findings suggest that betaine can alleviate LPS-induced muscle inflammation in chicken, and the regulation of aberrant DNA methylation might be a possible mechanism.

Losac and Lopap Recombinant Proteins from Lonomia obliqua Bristles Positively Modulate the Myoblast Proliferation Process

The pursuit of better therapies for disorders creating deficiencies in skeletal muscle regeneration is in progress, and several biotoxins are used in skeletal muscle research. Since recombinant proteins derived from Lonomia obliqua bristles, recombinant Lonomia obliqua Stuart-factor activator (rLosac) and recombinant Lonomia obliqua prothrombin activator protease (rLopap) act as cytoprotective agents and promote cell survival, we hypothesize that both rLosac and rLopap favour the skeletal muscle regeneration process. In the present work, we investigate the ability of these recombinant proteins rLosac and rLopap to modulate the production of key mediators of the myogenic process. The expression of myogenic regulatory factors (MRFs), cell proliferation, the production of prostaglandin E2 (PGE₂) and the protein expression of cyclooxygenases COX-1 and COX-2 were evaluated in C2C12 mouse myoblasts pre-treated with rLosac and rLopap. We found an increased proliferation of myoblasts, stimulated by both recombinant proteins. Moreover, these proteins modulated PGE₂ release and MRFs activities. We also found an increased expression of the EP4 receptor in the proliferative phase of C2C12 cells, suggesting the involvement of this receptor in the effects of PGE₂ in these cells. Moreover, the recombinant proteins inhibited the release of IL-6 and PGE₂, which is induced by an inflammatory stimulus by IL-1β. This work reveals rLopap and rLosac as promising proteins to modulate processes involving tissue regeneration as occurs during skeletal muscle injury.

Acid Sphingomyelinase Controls Early Phases of Skeletal Muscle Regeneration by Shaping the Macrophage Phenotype

Skeletal muscle regeneration is a complex process involving crosstalk between immune cells and myogenic precursor cells, i.e., satellite cells. In this scenario, macrophage recruitment in damaged muscles is a mandatory step for tissue repair since pro-inflammatory M1 macrophages promote the activation of satellite cells, stimulating their proliferation and then, after switching into anti-inflammatory M2 macrophages, they prompt satellite cells' differentiation into myotubes and resolve inflammation. Here, we show that acid sphingomyelinase (ASMase), a key enzyme in sphingolipid metabolism, is activated after skeletal muscle injury induced in vivo by the injection of cardiotoxin. ASMase ablation shortens the early phases of skeletal muscle regeneration without affecting satellite cell behavior. Of interest, ASMase regulates the balance between M1 and M2 macrophages in the injured muscles so that the absence of the enzyme reduces inflammation. The analysis of macrophage populations indicates that these events depend on the altered polarization of M1 macrophages towards an M2 phenotype. Our results unravel a novel role of ASMase in regulating immune response during muscle regeneration/repair and suggest ASMase as a supplemental therapeutic target in conditions of redundant inflammation that impairs muscle recovery.

The Effect of Acute and Chronic Thermotherapy on Type 2 Diabetic Skeletal Muscle Gene Expression and Inflammatory Markers

BACKGROUND

Type 2 diabetes (T2D) is a chronic illness associated with resistance to or defective insulin secretion. This study investigates the effects of thermotherapy on cell viability, gene expression and inflammation in skeletal muscle cell lines.

METHODS

Healthy and T2D human skeletal muscle cell lines (HSMM and D-HSMM, respectively) were subjected to acute or chronic thermo-therapy (AT or CT, respectively). CT consisted of a 30 min exposure to 40 °C, three times a week for three weeks; AT was a one-time exposure.

RESULTS

A significant decrease in D-HSMM cell viability percentage followed AT; however, no significant change occurred in CT. HSMM yielded the highest elevations of genes following CT. In D-HSMM, both treatments yielded gene upregulation. Both treatments significantly down-regulated IL-1β, IL-6, IL-10 and TNF-α in HSMM. AT significantly decreased IL-1β, IL-6 and upregulated IL-10 and TNF-α levels in D-HSMM, while CT yielded a reduction in IL-4, TNF-α and an upregulation of IL-6 and IL-10.

CONCLUSIONS

An increase in gene expression indicates actin activity and cellular responses, suggesting an increase in transcriptional regulation. The upregulation of IL-6 and IL-10 in D-HSMM negatively correlated with a decrease in TNF-α and IL-1β, indicating improved adverse inflammatory effects associated with the disease.

γ-Oryzanol Improves Exercise Endurance and Muscle Strength by Upregulating PPARδ and ERRγ Activity in Aged Mice

SCOPE

γ-Oryzanol, a well-known antioxidant, has been used by body builders and athletes to boost strength and increase muscle gain, without major side effects. However, the effect of γ-Oryzanol on sarcopenia and the underlying molecular mechanism is poorly understood.

RESULTS

Aged mice fed with the γ-Oryzanol diet do not show significant changes in muscle weight, but show increased running endurance as well as improved grip strength. The expression and activity of PPARδ and ERRγ are increased in skeletal muscle of γ-Oryzanol supplemented mice. γ-Oryzanol upregulates oxidative muscle fibers by MEF2 transcription factor, and PGC-1α and ERRα expressions. Fatty acid oxidation related genes and mitochondria biogenesis are upregulated by γ-Oryzanol. In addition, γ-Oryzanol inhibits TGF-β-Smad-NADPH oxidase 4 pathway and inflammatory cytokines such as TNF-α, IL-1β, IL-6, and p65 NF-κB subunit, which cause skeletal muscle weakness. Collectively, γ-Oryzanol attenuates muscle weakness pathway and increases oxidative capacity by increasing PPARδ and ERRγ activity, which contributes to enhance strength and improve oxidative capacity in muscles, consequently enhancing exercise capacity in aged mice. Particularly, γ-Oryzanol directly binds to PPARδ.

CONCLUSIONS

These are the first findings showing that γ-Oryzanol enhances skeletal muscle function in aged mice by regulating PPARδ and ERRγ activity without muscle gain.

Redox Homeostasis in Muscular Dystrophies

In recent years, growing evidence has suggested a prominent role of oxidative stress in the pathophysiology of several early- and adult-onset muscle disorders, although effective antioxidant treatments are still lacking. Oxidative stress causes cell damage by affecting protein function, membrane structure, lipid metabolism, and DNA integrity, thus interfering with skeletal muscle homeostasis and functionality. Some features related to oxidative stress, such as chronic inflammation, defective regeneration, and mitochondrial damage are shared among most muscular dystrophies, and Nrf2 has been shown to be a central player in antagonizing redox imbalance in several of these disorders. However, the exact mechanisms leading to overproduction of reactive oxygen species and deregulation in the cellular antioxidants system seem to be, to a large extent, disease-specific, and the clarification of these mechanisms in vivo in humans is the cornerstone for the development of targeted antioxidant therapies, which will require testing in appropriately designed clinical trials.

Evaluation of triclosan exposures on secretion of pro-inflammatory cytokines from human immune cells

Triclosan (TCS) is widely used in personal hygiene products, such as mouthwash and toothpaste, and is found in human tissues. Interleukin (IL)-1 beta (IL-1β), IL-6, tumor necrosis factor alpha (TNFα), and interferon gamma (IFNγ) are pro-inflammatory cytokines and inappropriately elevated levels of each have been associated with pathologies including rheumatoid arthritis and certain cancers. Here we examine effects of TCS on the secretion of the pro-inflammatory cytokines from human immune cell preparations. TCS at concentrations between 0.05-5 μM consistently increased the secretion of IL-1β, IL-6, and TNFα within 24 h of exposure and the increases often maintained out to 6 days of exposure. TCS also induced increases in IFNγ secretion, however the increases were most consistent after 48 h of exposure rather than within 24 h. Additionally, a role for both p44/42 and p38 MAPK in TCS-stimulated increases in IL-1β was seen in cells from some donors.

Skeletal muscle redox signaling in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by synovitis and the presence of serum autoantibodies. In addition, skeletal muscle weakness is a common comorbidity that contributes to inability to work and reduced quality of life. Loss in muscle mass cannot alone account for the muscle weakness induced by RA, but instead intramuscular dysfunction appears as a critical factor underlying the decreased force generating capacity for patients afflicted by arthritis. Oxidative stress and associated oxidative post-translational modifications have been shown to contribute to RA-induced muscle weakness in animal models of arthritis and patients with RA. However, it is still unclear how and which sources of reactive oxygen and nitrogen species (ROS/RNS) that are involved in the oxidative stress that drives the progression toward decreased muscle function in RA. Nevertheless, mitochondria, NADPH oxidases (NOX), nitric oxide synthases (NOS) and phospholipases (PLA) have all been associated with increased ROS/RNS production in RA-induced muscle weakness. In this review, we aim to cover potential ROS sources and underlying mechanisms of oxidative stress and loss of force production in RA. We also addressed the use of antioxidants and exercise as potential tools to counteract oxidative stress and skeletal muscle weakness.

Cancer-Associated Muscle Wasting-Candidate Mechanisms and Molecular Pathways

Excessive muscle loss is commonly observed in cancer patients and its association with poor prognosis has been well-established. Cancer-associated sarcopenia differs from age-related wasting in that it is not responsive to nutritional intervention and exercise. This is related to its unique pathogenesis, a result of diverse and interconnected mechanisms including inflammation, disordered metabolism, proteolysis and autophagy. There is a growing body of evidence that suggests that the tumor is the driver of muscle wasting by its elaboration of mediators that influence each of these pro-sarcopenic pathways. In this review, evidence for these tumor-derived factors and putative mechanisms for inducing muscle wasting will be reviewed. Potential targets for future research and therapeutic interventions will also be reviewed.

Effect of intraperitoneally administered propentofylline in a rat model of postoperative pain

Background

In this study, we sought to evaluate whether systemic propentofylline (PPF) has antiallodynic effects in a rat model of postoperative pain, and to assess the mechanism involved.

Methods

After plantar incision, rats were intraperitoneally injected with various doses of PPF to evaluate its antiallodynic effect. To investigate the involved mechanism, rats were intraperitoneally injected with yohimbine, dexmedetomidine, prazosin, naloxone, atropine or mecamylamine, following the incision of the rat hind paws, and then PPF was administered intraperitoneally. The mechanical withdrawal threshold (MWT) was evaluated using von Frey filaments at various time points and serum levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 were measured to determine the inflammatory response level.

Results

MWT was significantly increased after intraperitoneal injection of 30 mg/kg of PPF when compared with the control group. Injection of PPF and yohimbine, atropine or mecamylamine showed significant decreases in the MWT, while injection of PPF and dexmedetomidine showed a significant increase. Systemic administration of PPF inhibited the post-incisional increase in serum level of TNF-α and IL-1β.

Conclusions

Systemic administration of PPF following surgery presented antiallodynic effects in a rat model of postoperative pain. The antiallodynic effects against mechanical allodynia could be mediated by α-adrenergic and cholinergic receptors.

IL-1β and TNF-α Modulation of Proliferated and Committed Myoblasts: IL-6 and COX-2-Derived Prostaglandins as Key Actors in the Mechanisms Involved

In this study, we investigated the effects and mechanisms of the pro-inflammatory cytokines IL-1β and TNF-α on the proliferation and commitment phases of myoblast differentiation. C2C12 mouse myoblast cells were cultured to reach a proliferated or committed status and were incubated with these cytokines for the evaluation of cell proliferation, cyclooxygenase 2 (COX-2) expression, release of prostaglandins (PGs) and myokines, and activation of myogenic regulatory factors (MRFs). We found that inhibition of the IL-6 receptor reduced IL-1β- and TNF-α-induced cell proliferation, and that the IL-1β effect also involved COX-2-derived PGs. Both cytokines modulated the release of the myokines myostatin, irisin, osteonectin, and IL-15. TNF-α and IL-6 reduced the activity of Pax7 in proliferated cells and reduced MyoD and myogenin activity at both proliferative and commitment stages. Otherwise, IL-1β increased myogenin activity only in committed cells. Our data reveal a key role of IL-6 and COX-2-derived PGs in IL-1β and TNF-α-induced myoblast proliferation and support the link between TNF-α and IL-6 and the activation of MRFs. We concluded that IL-1β and TNF-α induce similar effects at the initial stages of muscle regeneration but found critical differences between their effects with the progression of the process, bringing new insights into inflammatory signalling in skeletal muscle regeneration.

The role of mitochondria in redox signaling of muscle homeostasis

In the past, contraction-induced production of reactive oxygen species (ROS) has been implicated in oxidative stress to skeletal muscle. As research advances, clear evidence has revealed a more complete role of ROS under both physiologic and pathologic conditions. Central to the role of ROS is the redox signaling pathways that control exercise-induced major physiologic and cellular responses and adaptations, such as mitochondrial biogenesis, mitophagy, mitochondrial morphologic dynamics, antioxidant defense, and inflammation. The current review focuses on how muscle contraction and immobilization may activate or inhibit redox signalings and their impact on muscle mitochondrial homeostasis and physiologic implications.

IMPACTS OF COVID-19 ON THE IMMUNE, NEUROMUSCULAR, AND MUSCULOSKELETAL SYSTEMS AND REHABILITATION

ABSTRACT The new coronavirus, which causes the infectious disease named COVID-19 by the World Health Organization (WHO), was notified in 2020 in China. The main clinical manifestations in infected patients are fever, cough and dyspnoea. These patients are prone to developing cardiac changes, diffuse myopathy, decreased pulmonary function, decreased inspiratory muscle strength, and a deterioration in functional capacity. Thus, it is expected that patients affected by COVID-19 will suffer musculoskeletal consequences as a result of the inflammatory process and loss of muscle mass caused by immobility, generating motor incapacities that are not yet quantifiable. It is important to understand the clinical implications caused by COVID-19, in order to have better rehabilitation strategies for these patients. The aim of this study was to conduct a reflective analysis of the impact of COVID-19 on the immune, neuromuscular and musculoskeletal systems, and its rehabilitation process. This is a reflexive analysis, developed in the Laboratory for the Study of Movement of the Institute of Orthopaedics’ and Traumatology, at the Universidade de São Paulo School of Medicine, SP, Brazil. In this analysis, we reflect on the following topics related to COVID-19: immunological mechanisms, impact on the neuromuscular and musculoskeletal systems, and the rehabilitation of patients. Level of evidence V; Opinion of the specialist.

Regenerative Repair of Volumetric Muscle Loss Injury is Sensitive to Age

In this study, the influence of age on effectiveness of regenerative repair for the treatment of volumetric muscle loss (VML) injury was explored. Tibialis anterior (TA) VML injuries were repaired in both 3- and 18-month-old animal models (Fischer 344 rat) using allogeneic decellularized skeletal muscle (DSM) scaffolds supplemented with autologous minced muscle (MM) paste. Within the 3-month animal group, TA peak contractile force was significantly improved (79% of normal) in response to DSM+MM repair. However, within the 18-month animal group, muscle force following repair (57% of normal) was not significantly different from unrepaired VML controls (59% of normal). Within the 3-month animal group, repair with DSM+MM generally reduced scarring at the site of VML repair, whereas scarring and a loss of contractile tissue was notable at the site of repair within the 18-month group. Within 3-month animals, expression of myogenic genes (MyoD, MyoG), extracellular matrix genes (Col I, Col III, TGF-β), and key wound healing genes (TNF-α and IL-1β) were increased. Alternatively, expression was unchanged across all genes examined within the 18-month animal group. The findings suggest that a decline in regenerative capacity and increased fibrosis with age may present an obstacle to regenerative medicine strategies targeting VML injury. Impact Statement This study compared the recovery following volumetric muscle loss (VML) injury repair using a combination of minced muscle paste and decellularized muscle extracellular matrix carrier in both a younger (3 months) and older (18 months) rat population. Currently, VML repair research is being conducted with the young patient population in mind, but our group is the first to look at the effects of age on the efficacy of VML repair. Our findings highlight the importance of considering age-related changes in response to VML when developing repair strategies targeting an elderly patient population.

The Emerging Roles of Nicotinamide Adenine Dinucleotide Phosphate Oxidase 2 in Skeletal Muscle Redox Signaling and Metabolism

Significance: Skeletal muscle is a crucial tissue to whole-body locomotion and metabolic health. Reactive oxygen species (ROS) have emerged as intracellular messengers participating in both physiological and pathological adaptations in skeletal muscle. A complex interplay between ROS-producing enzymes and antioxidant networks exists in different subcellular compartments of mature skeletal muscle. Recent evidence suggests that nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) are a major source of contraction- and insulin-stimulated oxidants production, but they may paradoxically also contribute to muscle insulin resistance and atrophy. Recent Advances: Pharmacological and molecular biological tools, including redox-sensitive probes and transgenic mouse models, have generated novel insights into compartmentalized redox signaling and suggested that NOX2 contributes to redox control of skeletal muscle metabolism. Critical Issues: Major outstanding questions in skeletal muscle include where NOX2 activation occurs under different conditions in health and disease, how NOX2 activation is regulated, how superoxide/hydrogen peroxide generated by NOX2 reaches the cytosol, what the signaling mediators are downstream of NOX2, and the role of NOX2 for different physiological and pathophysiological processes. Future Directions: Future research should utilize and expand the current redox-signaling toolbox to clarify the NOX2-dependent mechanisms in skeletal muscle and determine whether the proposed functions of NOX2 in cells and animal models are conserved into humans.

Differences in serum IL-6 response after 1 °C rise in core body temperature in individuals with spinal cord injury and cervical spinal cord injury during local heat stress

OBJECTIVES

Passive rise in core body temperature achieved by head-out hot water immersion (HHWI) results in acute increases in serum interleukin (IL)-6 but no change in plasma adrenaline in patients with cervical spinal cord injury (CSCI). The purpose of the present study was to determine the mechanism of heat stress-induced increase in serum IL-6.

SETTING

A cross-sectional study.

METHODS

The study subjects were nine with CSCI, ten with thoracic and lumbar spinal cord injury (TLSCI) and eight able-bodied (AB) subjects. Time since injury was 16.1 ± 3.4 years in TLSCI and 16.4 ± 4.1 years in CSCI. Subjects were subjected to lower-body heat stress (LBH) by wearing a hot water-perfused suit until 1 °C increase in core temperature. The levels of serum IL-6, plasma adrenaline, tumour necrosis factor (TNF)-α, C-reactive protein (CRP), and counts of blood cells were measured at normothermia and after LBH.

RESULTS

Serum IL-6 concentrations increased significantly immediately after LBH in all the three groups. ΔIL-6% was lower in CSCI subjects compared with AB subjects. Plasma adrenaline concentrations significantly increased after LBH in AB and TLSCI subjects, but did not change throughout the study in CSCI subjects. Cardiac output and heart rate increased at the end of LBH in all three groups.

CONCLUSIONS

Under a similar increase in core temperature, ΔIL-6% was lower in the CSCI group compared with the AB group. These findings suggest that the observed rise in IL-6 during hyperthermia is mediated, at least in part, by plasma adrenaline.

Synthesis of interleukin 1 beta and interleukin 6 in human lymphocytes is stimulated by tributyltin

Tributyltin (TBT) is a widespread environmental contaminant that is present in human blood and other tissues. It has been shown to disrupt the immune function of human natural killer (NK) cells and to alter the secretion of a number of pro-inflammatory cytokines from immune cells. Secretion of both interleukin 1β (IL-1β) and interleukin 6 (IL-6) from human lymphocytes can be increased dependent upon the level of TBT exposure. This study shows that the TBT-induced increases in secretion of both cytokines are due to TBT-induced increases in the synthesis of these proteins and not simply because of the release of pre-existing cytokine. Furthermore, the data indicate that these TBT-induced increases in IL-1β and IL-6 synthesis require MAP kinase signaling pathways. Additionally, elevated synthesis of IL-1β and IL-6 seen at the highest exposures to TBT (200, 200, 50 nM) were accompanied by increases in the mRNA for these cytokines. TBT-induced increases in IL-1β and IL-6 mRNAs were also shown to be dependent on MAP kinase signaling. The study suggests that TBT has the capacity to increase immune cell production of these 2 important pro-inflammatory cytokines and that this increase is in part explained by increased mRNA for the cytokines.

Rapamycin regulates macrophage activation by inhibiting NLRP3 inflammasome-p38 MAPK-NFκB pathways in autophagy- and p62-dependent manners

Excessive and prolonged activation of macrophages underlies many inflammatory and autoimmune diseases. To regulate activation and maintain homeostasis, macrophages have multiple intrinsic mechanisms, one of which is modulation through autophagy. Here we demonstrate that autophagy induction by rapamycin suppressed the production of IL-1β and IL-18 in lipopolysaccharide- and adenosine triphosphate-activated macrophages at the post-transcriptional level by eliminating mitochondrial ROS (mtROS) and pro-IL1β in a p62/SQSTM1-dependent manner. In addition, rapamycin activated Nrf2 through up-regulation of p62/SQSTM1, which further contributed to the reduction of mtROS. Reduced IL-1β subsequently diminished the activation of p38 MAPK-NFκB pathways, leading to transcriptional down-regulation of IL-6, IL-8, MCP-1, and IκBα in rapamycin-treated macrophages. Therefore, our results suggest that rapamycin negatively regulates macrophage activation by restricting a feedback loop of NLRP3 inflammasome-p38 MAPK-NFκB pathways in autophagy- and p62/SQSTM1-dependent manners.

Skeletal muscle regeneration is modulated by inflammation

Skeletal muscle regeneration is a complex process orchestrated by multiple steps. Recent findings indicate that inflammatory responses could play central roles in bridging initial muscle injury responses and timely muscle injury reparation. The various types of immune cells and cytokines have crucial roles in muscle regeneration process. In this review, we briefly summarise the functions of acute inflammation in muscle regeneration.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

Immune system is closely relevant to the muscle regeneration. Understanding the mechanisms of inflammation in muscle regeneration is therefore critical for the development of effective regenerative, and therapeutic strategies in muscular disorders. This review provides information for muscle regeneration research regarding the effects of inflammation on muscle regeneration.

Butyltin compounds alter secretion of interleukin 6 from human immune cells

Butyltins (BTs), tributyltin (TBT) and dibutyltin (DBT) are organotin compounds that have been used in a variety of industrial applications; as a result, these compounds have been found in human blood. Interleukin (IL)-6 is a proinflammatory mediator that is produced by T lymphocytes and monocytes. It is responsible for immune response regulation as well as tissue repair and cellular growth. Both BTs decrease the ability of human natural killer cells to destroy tumor cells and alter the secretion of proinflammatory cytokines tumor necrosis factor alpha, interferon gamma and IL-1 beta (β) from human lymphocytes ex vivo. Here, we show that BTs alter the secretion of IL-6 from increasingly reconstituted preparations of human immune cells. IL-6 secretion was examined after 24 hour, 48 hour or 6 day exposures to TBT and DBT in highly enriched human natural killer cells, monocyte-depleted peripheral blood mononuclear cells (PBMCs), PBMCs, granulocytes and a preparation combining both PBMCs and granulocytes (PBMCs + granulocytes). The results indicated that both BTs altered IL-6 secretion from all cell preparations. Significant decreases of IL-6 secretion were seen at the highest concentration of TBT (200 nm) and DBT (5-2.5 μm) while the lower concentrations of DBT (0.05 and 0.1 μm) caused elevation of IL-6 secretion. The data indicate that BT-induced alterations of IL-6 secretion from immune cells may be a significant consequence of BT exposures that may potentially affect immune competence.

Compensatory anabolic signaling in the sarcopenia of experimental chronic arthritis

Inflammatory activity in rheumatoid arthritis may alter the regulation of muscle mass leading to a secondary sarcopenia, commonly termed rheumatoid cachexia (RC). We characterized alterations to muscle structure and various pro-inflammatory, catabolic and regenerative markers in an animal model of RC. Antigen induced arthritis (AiA) was performed in 20 male adult rabbits. AiA animals exhibited significantly less weight gain, a markedly elevated serum C-reactive protein (CRP), lighter muscles with shorter cross-sectional diameter and increased myonuclei when compared to controls. Atrogin-1 and MuRF-1 were up-regulated alongside an increase in IL-1β, active NF-κB and a higher ratio of phosphorylated to inactive p38 MAPK. CCL-2 and TNF levels were reduced and IL-6 was unchanged between groups. We observed decreased pSTAT3, unchanged pSTAT1 and Myf5, but increased Pax7, MyoD and myogenin. AiA rabbits had a reduction in myostatin from gastrocnemii and synovium with a congruent decrease in serum myostatin compared to controls. Chronic arthritis induced an RC-like secondary sarcopenia with increased muscle protein breakdown. Elevated IL-1β may trigger proteolysis via elevated NF-κB and p38 MAPK signaling with a compensatory anabolic response suggested by myonuclear expansion, increased Pax7, MyoD and myogenin, reduced pSTAT3 as well as reduced serum, synovial and muscular myostatin.

The role of myokines in muscle health and disease

PURPOSE OF REVIEW

This article updates on the concept that muscle-derived cytokines (myokines) play important roles in muscle health and disease.

RECENT FINDINGS

Interleukin-6 (IL-6) is released from normal skeletal muscle in response to exercise, mediating both anti-inflammatory responses and metabolic adaptations, actions contradictory to the prevailing view that IL-6 is a proinflammatory cytokine that is inducing and propagating disease. The anti-inflammatory effects of IL-6 result from its trans-membrane signalling capability, via membrane-bound receptors, whereas its proinflammatory effects result instead from signalling via the soluble IL-6 receptor and gp130. IL-15 is elevated following exercise, promoting muscle fibre hypertrophy in some circumstances, while inducing fibre apoptosis in others. This functional divergence appears because of variations in expression of IL-15 receptor isoforms. Decorin, a recently described myokine, is also elevated following exercise in normal muscle, and promotes muscle fibre hypertrophy by competitively binding to, and thus inhibiting, myostatin, a negative regulator of muscle protein synthesis. Exercise-induced myostatin downregulation thus promotes muscle fibre growth, prompting recent trials of a biological myostatin inhibitor in inclusion body myositis.

SUMMARY

Myokines appear to exert diverse beneficial effects, though their mechanistic roles in myositis and other myopathologies remain poorly understood.

Inflammation and age-associated skeletal muscle deterioration (sarcopaenia)

Ageing is accompanied by chronic inflammatory responses due to elevated circulatory inflammatory cytokine production. Several inflammatory cytokines have been shown to be responsible for a decrease in muscle mass. However, little is known about the possible relationship between inflammation and sarcopaenia. This review aims to summarise the existing evidence about inflammation and sarcopaenia. Sarcopaenia is defined as an age-related decrease of muscle mass and/or muscle strength; it is caused by multiple factors, such as skeletal muscle atrophy, neuromuscular junction degeneration, hormone imbalance, cytokine imbalance, protein synthesis and proteolysis. Several inflammatory cytokines have been considered to promote muscle loss; C-reactive protein levels are significantly upregulated in sarcopaenia and sarcopenic obesity, and high levels of interleukin-6 are associated with reduced muscle mass and muscle strength (the administration of interleukin-6 could lead to a reduction in muscle mass). Up-regulation of tumour necrosis factor-α expression is also related to the development of sarcopaenia. Signalling pathways, such as protein kinase B/mammalian target of rapamycin, Janus kinase/signal transducer and activator of transcription-5 and signal transducer and activator of transcription 3 signalling, involved in muscle metabolism are regulated by insulin-like growth factor-1, tumour necrosis factor-α and interleukin-6 respectively. In conclusion, the inflammatory cytokines produced during chronic inflammation due to ageing, may influence their respective related pathways, thus leading to age-related muscle deterioration.

The translational potential of this article

This review can provide more information for sarcopaenia medicine research in terms of anti-inflammation therapy.

A Phosphoproteomic Screen Identifies a Guanine Nucleotide Exchange Factor for Rab3A Protein as a Mitogen-activated Protein (MAP) Kinase Phosphatase-5-regulated MAP Kinase Target in Interleukin 6 (IL-6) Secretion and Myogenesis

The mitogen-activated protein kinases (MAPKs) have been shown to regulate skeletal muscle function. Previously, we showed that MAPK phosphatase-5 (MKP-5) negatively regulates myogenesis and regeneration of skeletal muscle through inhibition of p38 MAPK and c-Jun N-terminal kinase (JNK). However, the identity and contribution of MKP-5-regulated MAPK targets in the control of skeletal muscle function and regenerative myogenesis have not been established. To identify MKP-5-regulated MAPK substrates in skeletal muscle, we performed a global differential phospho-MAPK substrate screen in regenerating skeletal muscles of wild type and MKP-5-deficient mice. We discovered a novel MKP-5-regulated MAPK substrate called guanine nucleotide exchange factor for Rab3A (GRAB) that was hyperphosphorylated on a phospho-MAPK motif in skeletal muscle of MKP-5-deficient mice. GRAB was found to be phosphorylated by JNK on serine 169. Myoblasts overexpressing a phosphorylation-defective mutant of GRAB containing a mutation at Ser-169 to Ala-169 (GRAB-S169A) inhibited the ability of C2C12 myoblasts to differentiate. We found that GRAB phosphorylation at Ser-169 was required for the secretion of the promyogenic cytokine interleukin 6 (IL-6). Consistent with this observation, MKP-5-deficient mice exhibited increased circulating IL-6 expression as compared with wild type mice. Collectively, these data demonstrate a novel mechanism whereby MKP-5-mediated regulation of JNK negatively regulates phosphorylation of GRAB, which subsequently controls secretion of IL-6. These data support the notion that MKP-5 serves as a negative regulator of MAPK-dependent signaling of critical skeletal muscle signaling pathways.

Heat induces interleukin-6 in skeletal muscle cells via TRPV1/PKC/CREB pathways

Interleukin-6 (IL-6) is released from skeletal muscle cells and induced by exercise, heat, catecholamine, glucose, lipopolysaccharide, reactive oxygen species, and inflammation. However, the mechanism that induces release of IL-6 from skeletal muscle cells remains unknown. Thermosensitive transient receptor potential (TRP) proteins such as TRPV1-4 play vital roles in cellular functions. In this study we hypothesized that TRPV1 senses heat, transmits a signal into the nucleus, and produces IL-6. The purpose of the present study is to investigate the underlying mechanisms whereby skeletal muscle cells sense and respond to heat. When mouse myoblast cells were exposed to 37-42°C for 2 h, mRNA expression of IL-6 increased in a temperature-dependent manner. Heat also increased IL-6 secretion in myoblast cells. A fura 2 fluorescence dual-wavelength excitation method showed that heat increased intracellular calcium flux in a temperature-dependent manner. Intracellular calcium flux and IL-6 mRNA expression were increased by the TRPV1 agonists capsaicin and N-arachidonoyldopamine and decreased by the TRPV1 antagonists AMG9810 and SB366791 and siRNA-mediated knockdown of TRPV1. TRPV2, 3, and 4 agonists did not change intracellular calcium flux. Western blotting with inhibitors demonstrated that heat increased phosphorylation levels of TRPV1, followed by PKC and cAMP response element-binding protein (CREB). PKC inhibitors, Gö6983 and staurosporine, CREB inhibitors, curcumin and naphthol AS-E, and knockdown of CREB suppressed the heat-induced increases in IL-6. These results indicate that heat increases IL-6 in skeletal muscle cells through the TRPV1, PKC, and CREB signal transduction pathway.NEW & NOTEWORTHY Heat increases the release of interleukin-6 (IL-6) from skeletal muscle cells. IL-6 has been shown to serve immune responses and metabolic functions in muscle. It can be anti-inflammatory as well as proinflammatory. However, the mechanism that induces release of IL-6 from skeletal muscle cells remains unknown. Here we show that heat increases IL-6 in skeletal muscle cells through the transient receptor potential vannilloid 1, PKC, and cAMP response element-binding protein signal transduction pathway.

AMPK activation by prolonged stimulation with interleukin-1β contributes to the promotion of GLUT4 translocation in skeletal muscle cells

Impaired insulin signaling in skeletal muscle cells causes insulin resistance associated with the onset of type 2 diabetes. Although interleukin (IL)-1β has been considered to be implicated in the pathogenesis of type 2 diabetes, the action of prolonged stimulation with IL-1β on the insulin signaling pathway in skeletal muscle cells remains poorly understood. In the current study, we investigated the effect of IL-1β stimulation on insulin signal transduction from the insulin receptor (IR), resulting in glucose transporter 4 (GLUT4) translocation in skeletal muscle cells. In L6-GLUT4myc cells, stimulation with IL-1β for 24 h promoted GLUT4 translocation to the plasma membrane and increased glucose uptake in a concentration-dependent manner, whereas short-term stimulation with IL-1 for up to 6 h did not affect that. In addition, stimulation with IL-1β for 24 h further increased insulin-stimulated GLUT4 translocation. Interestingly, stimulation with IL-1β for 24 h did not cause any change in the phosphorylation of insulin signal molecules IR, insulin receptor substrate (IRS)-1, Akt, and p21-activated kinase (PAK1). Stimulation with IL-1β for 24 h significantly increased AMP-activated protein kinase (AMPK) phosphorylation and GLUT4 protein expression. Small interfering RNA (siRNA) targeting AMPK1/2 significantly inhibited IL-1β-stimulated GLUT4 translocation. These results suggest that prolonged stimulation with IL-1β positively regulates GLUT4 translocation in skeletal muscle cells. IL-1β may have a beneficial effect on maintaining glucose homeostasis in skeletal muscle cells in patients with type 2 diabetes. .

Simultaneous time course analysis of multiple markers based on DNA microarray in incised wound in skeletal muscle for wound aging

Assessment of incised wound age in skeletal muscles is important because fatal injuries are often complicated with muscle involvement. Transcriptome of injured skeletal muscle along with histopathological and immunohistochemistry staining, were analyzed to explore the biological effect of incised injuries using a mouse incised injury model. An incisional wound was made at the biceps femoris muscle of anesthetized mice, and the muscles were sampled at 6, 12, 24, 36 and 48h post-injury. DNA microarray analysis using RNA extracted from the muscle samples of 12h post-injury identified 3,655 upregulated and 3,583 downregulated genes. Referring to the results of the gene ontology and gene expression pathway analysis, time course expression of five cytokines, namely chemokine (C-C motif) ligand 4 (CCL4), chemokine (C-X-C motif) ligand 5 (CXCL5), interleukin-1 beta (IL-1β), interleukin- 6 (IL-6) and interleukin-7 (IL-7), were analyzed by quantative reverse transcription PCR (qRT-PCR). CXCL5 was the most upregulated gene throughout the post-injury period with higher expression from 6 through 36h post injury. Upregulation of CCL4 and IL-1β was also persisted until 36h post injury. IL-6 mRNA was highly and rapidly expressed at 6h post-injury followed by significant decrease at 12h. Unlike other four cytokines, IL-7 showed slow and steady increasing over time until 48h post-injury. Immunohistochemical staining of post-injury samples showed gradual mild increase of staining intensity proportional to increasing time points especially around the wound edges. The present study highlights the unique dynamics of each cytokine and reflects their roles in the process of muscle wound healing, and suggests the potential of them as a tool for forensic wound age estimation.

MicroRNA-Regulated Proinflammatory Cytokines in Sarcopenia

Sarcopenia has been defined as the aging-related disease with the declined mass, strength, and function of skeletal muscle, which is the major cause of frailty and falls in elders. The activation of inflammatory signal pathways due to diseases and aging is suggested to reveal the critical impact on sarcopenia. Several proinflammatory cytokines, especially interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α), play crucial roles in modulation of inflammatory signaling pathway during the aging-related loss of skeletal muscle. MicroRNAs (miRNAs) have emerged as the important regulators for the mass and functional maintenance of skeletal muscle through regulating gene expression of proinflammatory cytokines. In this paper, we have systematically discussed regulatory mechanisms of miRNAs for the expression and secretion of inflammatory cytokines during sarcopenia, which will provide some novel targets and therapeutic strategies for controlling aging-related atrophy of skeletal muscle and corresponding chronic inflammatory diseases.

Structure and function of chicken interleukin-1 beta mutants: uncoupling of receptor binding and in vivo biological activity

Receptor-binding and subsequent signal-activation of interleukin-1 beta (IL-1β) are essential to immune and proinflammatory responses. We mutated 12 residues to identify sites important for biological activity and/or receptor binding. Four of these mutants with mutations in loop 9 (T117A, E118K, E118A, E118R) displayed significantly reduced biological activity. Neither T117A nor E118K mutants substantially affected receptor binding, whereas both mutants lack the IL-1β signaling in vitro but can antagonize wild-type (WT) IL-1β. Crystal structures of T117A, E118A, and E118K revealed that the secondary structure or surface charge of loop 9 is dramatically altered compared with that of wild-type chicken IL-1β. Molecular dynamics simulations of IL-1β bound to its receptor (IL-1RI) and receptor accessory protein (IL-1RAcP) revealed that loop 9 lies in a pocket that is formed at the IL-1RI/IL-1RAcP interface. This pocket is also observed in the human ternary structure. The conformations of above mutants in loop 9 may disrupt structural packing and therefore the stability in a chicken IL-1β/IL-1RI/IL-1RAcP signaling complex. We identify the hot spots in IL-1β that are essential to immune responses and elucidate a mechanism by which IL-1β activity can be inhibited. These findings should aid in the development of new therapeutics that neutralize IL-1 activity.

Tissue communication in a systemic immune response of Drosophila

Several signaling pathways, including the JAK/STAT and Toll pathways, are known to activate blood cells (hemocytes) in Drosophila melanogaster larvae. They are believed to regulate the immune response against infections by parasitoid wasps, such as Leptopilina boulardi, but how these pathways control the hemocytes is not well understood. Here, we discuss the recent discovery that both muscles and fat body take an active part in this response. Parasitoid wasp infection induces Upd2 and Upd3 secretion from hemocytes, leading to JAK/STAT activation mainly in hemocytes and in skeletal muscles. JAK/STAT activation in muscles, but not in hemocytes, is required for an efficient encapsulation of wasp eggs. This suggests that Upd2 and Upd3 are important cytokines, coordinating different tissues for the cellular immune response in Drosophila. In the fat body, Toll signaling initiates a systemic response in which hemocytes are mobilized and activated hemocytes (lamellocytes) are generated. However, the contribution of Toll signaling to the defense against wasps is limited, probably because the wasps inject inhibitors that prevent the activation of the Toll pathway. In conclusion, parasite infection induces a systemic response in Drosophila larvae involving major organ systems and probably the physiology of the entire organism.

Satellite Cells and Skeletal Muscle Regeneration

Skeletal muscles are essential for vital functions such as movement, postural support, breathing, and thermogenesis. Muscle tissue is largely composed of long, postmitotic multinucleated fibers. The life-long maintenance of muscle tissue is mediated by satellite cells, lying in close proximity to the muscle fibers. Muscle satellite cells are a heterogeneous population with a small subset of muscle stem cells, termed satellite stem cells. Under homeostatic conditions all satellite cells are poised for activation by stimuli such as physical trauma or growth signals. After activation, satellite stem cells undergo symmetric divisions to expand their number or asymmetric divisions to give rise to cohorts of committed satellite cells and thus progenitors. Myogenic progenitors proliferate, and eventually differentiate through fusion with each other or to damaged fibers to reconstitute fiber integrity and function. In the recent years, research has begun to unravel the intrinsic and extrinsic mechanisms controlling satellite cell behavior. Nonetheless, an understanding of the complex cellular and molecular interactions of satellite cells with their dynamic microenvironment remains a major challenge, especially in pathological conditions. The goal of this review is to comprehensively summarize the current knowledge on satellite cell characteristics, functions, and behavior in muscle regeneration and in pathological conditions.

Liver kinase B1 inhibits the expression of inflammation-related genes postcontraction in skeletal muscle

Skeletal muscle-specific liver kinase B1 (LKB1) knockout mice (skmLKB1-KO) exhibit elevated mitogen-activated protein kinase (MAPK) signaling after treadmill running. MAPK activation is also associated with inflammation-related signaling in skeletal muscle. Since exercise can induce muscle damage, and inflammation is a response triggered by damaged tissue, we therefore hypothesized that LKB1 plays an important role in dampening the inflammatory response to muscle contraction, and that this may be due in part to increased susceptibility to muscle damage with contractions in LKB1-deficient muscle. Here we studied the inflammatory response and muscle damage with in situ muscle contraction or downhill running. After in situ muscle contractions, the phosphorylation of both NF-κB and STAT3 was increased more in skmLKB1-KO vs. wild-type (WT) muscles. Analysis of gene expression via microarray and RT-PCR shows that expression of many inflammation-related genes increased after contraction only in skmLKB1-KO muscles. This was associated with mild skeletal muscle fiber membrane damage in skmLKB1-KO muscles. Gene markers of oxidative stress were also elevated in skmLKB1-KO muscles after contraction. Using the downhill running model, we observed significantly more muscle damage after running in skmLKB1-KO mice, and this was associated with greater phosphorylation of both Jnk and STAT3 and increased expression of SOCS3 and Fos. In conclusion, we have shown that the lack of LKB1 in skeletal muscle leads to an increased inflammatory state in skeletal muscle that is exacerbated by muscle contraction. Increased susceptibility of the muscle to damage may underlie part of this response.

The Sick and the Weak: Neuropathies/Myopathies in the Critically Ill

Critical illness polyneuropathies (CIP) and myopathies (CIM) are common complications of critical illness. Several weakness syndromes are summarized under the term intensive care unit-acquired weakness (ICUAW). We propose a classification of different ICUAW forms (CIM, CIP, sepsis-induced, steroid-denervation myopathy) and pathophysiological mechanisms from clinical and animal model data. Triggers include sepsis, mechanical ventilation, muscle unloading, steroid treatment, or denervation. Some ICUAW forms require stringent diagnostic features; CIM is marked by membrane hypoexcitability, severe atrophy, preferential myosin loss, ultrastructural alterations, and inadequate autophagy activation while myopathies in pure sepsis do not reproduce marked myosin loss. Reduced membrane excitability results from depolarization and ion channel dysfunction. Mitochondrial dysfunction contributes to energy-dependent processes. Ubiquitin proteasome and calpain activation trigger muscle proteolysis and atrophy while protein synthesis is impaired. Myosin loss is more pronounced than actin loss in CIM. Protein quality control is altered by inadequate autophagy. Ca(2+) dysregulation is present through altered Ca(2+) homeostasis. We highlight clinical hallmarks, trigger factors, and potential mechanisms from human studies and animal models that allow separation of risk factors that may trigger distinct mechanisms contributing to weakness. During critical illness, altered inflammatory (cytokines) and metabolic pathways deteriorate muscle function. ICUAW prevention/treatment is limited, e.g., tight glycemic control, delaying nutrition, and early mobilization. Future challenges include identification of primary/secondary events during the time course of critical illness, the interplay between membrane excitability, bioenergetic failure and differential proteolysis, and finding new therapeutic targets by help of tailored animal models.

Interleukin-1 receptor antagonist protects against lipopolysaccharide induced diaphragm weakness in preterm lambs

Chorioamnionitis (inflammation of the fetal membranes) is strongly associated with preterm birth and in utero exposure to inflammation significantly impairs contractile function in the preterm lamb diaphragm. The fetal inflammatory response to intra-amniotic (IA) lipopolysaccharide (LPS) is orchestrated via interleukin 1 (IL-1). We aimed to determine if LPS induced contractile dysfunction in the preterm diaphragm is mediated via the IL-1 pathway. Pregnant ewes received IA injections of recombinant human IL-1 receptor antagonist (rhIL-1ra) (Anakinra; 100 mg) or saline (Sal) 3 h prior to second IA injections of LPS (4 mg) or Sal at 119d gestational age (GA). Preterm lambs were killed after delivery at 121d GA (term = 150 d). Muscle fibres dissected from the right hemi-diaphragm were mounted in an in vitro muscle test system for assessment of contractile function. The left hemi-diaphragm was snap frozen for molecular and biochemical analyses. Maximum specific force in lambs exposed to IA LPS (Sal/LPS group) was 25% lower than in control lambs (Sal/Sal group; p=0.025). LPS-induced diaphragm weakness was associated with higher plasma IL-6 protein, diaphragm IL-1β mRNA and oxidised glutathione levels. Pre-treatment with rhIL-1ra (rhIL-1ra/LPS) ameliorated the LPS-induced diaphragm weakness and blocked systemic and local inflammatory responses, but did not prevent the rise in oxidised glutathione. These findings indicate that LPS induced diaphragm dysfunction is mediated via IL-1 and occurs independently of oxidative stress. Therefore, the IL-1 pathway represents a potential therapeutic target in the management of impaired diaphragm function in preterm infants.

IL-6 and Akt are involved in muscular pathogenesis in myasthenia gravis

Introduction

Anti-acetylcholine receptor (AChR) autoantibodies target muscles in spontaneous human myasthenia gravis (MG) and its induced experimental autoimmune model MG (EAMG). The aim of this study was to identify novel functional mechanisms occurring in the muscle pathology of myasthenia.

Results

A transcriptome analysis performed on muscle tissue from MG patients (compared with healthy controls) and from EAMG rats (compared with control rats) revealed a deregulation of genes associated with the Interleukin-6 (IL-6) and Insulin-Like Growth Factor 1 (IGF-1) pathways in both humans and rats. The expression of IL-6 and its receptor IL-6R transcripts was found to be altered in muscles of EAMG rats and mice compared with control animals. In muscle biopsies from MG patients, IL-6 protein level was higher than in control muscles. Using cultures of human muscle cells, we evaluated the effects of anti-AChR antibodies on IL-6 production and on the phosphorylation of Protein Kinase B (PKB/Akt). Most MG sera and some monoclonal anti-AChR antibodies induced a significant increase in IL-6 production by human muscle cells. Furthermore, Akt phosphorylation in response to insulin was decreased in the presence of monoclonal anti-AChR antibodies.

Conclusions

Anti-AChR antibodies alter IL-6 production by muscle cells, suggesting a putative novel functional mechanism of action for the anti-AChR antibodies. IL-6 is a myokine with known effects on signaling pathways such as Akt/mTOR (mammalian Target of Rapamycin). Since Akt plays a key role in multiple cellular processes, the reduced phosphorylation of Akt by the anti-AChR antibodies may have a significant impact on the muscle fatigability observed in MG patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-014-0179-6) contains supplementary material, which is available to authorized users.

Pro-inflammatory mediation of myoblast proliferation

Skeletal muscle satellite cell function is largely dictated by the surrounding environment following injury. Immune cell infiltration dominates the extracellular space in the injured area, resulting in increased cytokine concentrations. While increased pro-inflammatory cytokine expression has been previously established in the first 3 days following injury, less is known about the time course of cytokine expression and the specific mechanisms of cytokine induced myoblast function. Therefore, the expression of IL-1β and IL-6 at several time points following injury, and their effects on myoblast proliferation, were examined. In order to do this, skeletal muscle was injured using barium chloride in mice and tissue was collected 1, 5, 10, and 28 days following injury. Mechanisms of cytokine induced proliferation were determined in cell culture using both primary and C2C12 myoblasts. It was found that there is a ∼20-fold increase in IL-1β (p≤0.05) and IL-6 (p = 0.06) expression 5 days following injury. IL-1β increased proliferation of both primary and C2C12 cells ∼25%. IL-1β stimulation also resulted in increased NF-κB activity, likely contributing to the increased proliferation. These data demonstrate for the first time that IL-1β alone can increase the mitogenic activity of primary skeletal muscle satellite cells and offer insight into the mechanisms dictating satellite cell function following injury.

Inter-relation between interleukin (IL)-1, IL-6 and body fat regulating circuits of the hypothalamic arcuate nucleus

Interleukin (IL)-1 and IL-6 are immune modulating cytokines that also affect metabolic function because both IL-1 receptor I deficient (IL-1RI⁻/⁻) and IL-6 deficient (IL-6⁻/⁻) mice develop late-onset obesity and leptin resistance. Both IL-1 and IL-6 appear to target the central nervous system (CNS) to increase energy expenditure. The hypothalamic arcuate nucleus (ARC) is a major relay between the periphery and CNS in body fat regulation (e.g. by being a target of leptin). The present study aimed to investigate the possible mechanisms responsible for the effects exerted by endogenous IL-1 and IL-6 on body fat at the level of the ARC, as well as possible interactions between IL-1 and IL-6. Therefore, we measured the gene expression of neuropeptides of the ARC involved in energy balance in IL-1RI⁻/⁻ and IL-6⁻/⁻ mice. We also investigated the interactions between expression of IL-1 and IL-6 in these mice, and mapped IL-6 receptor α (IL-6Rα) in the ARC. The expression of the obesity promoting peptide neuropeptide Y (NPY), found in the ARC, was increased in IL-1RI⁻/⁻ mice. The expression of NPY and agouti-related peptide (AgRP), known to be co-expressed with NPY in ARC neurones, was increased in cold exposed IL-6⁻/⁻ mice. IL-6Rα immunoreactivity was densely localised in the ARC, especially in the medial part, and was partly found in NPY positive cell bodies and also α-melanocyte-stimulating hormone positive cell bodies. The expression of hypothalamic IL-6 was decreased in IL-1RI⁻/⁻ mice, whereas IL-1ß expression was increased in IL-6⁻/⁻ mice. The results of the present study indicate that depletion of the activity of the fat suppressing cytokines IL-1 and IL-6 in knockout mice can increase the expression of the obesity promoting neuropeptide NPY in the ARC. Depletion of IL-1 activity suppresses IL-6 expression, and IL-6Rα-like immunoreactivity is present in neurones in the medial ARC, including neurones containing NPY. Therefore, IL-6, IL-1 and NPY/AgRP could interact at the level of the hypothalamic ARC in the regulation of body fat.