Muscle satellite cells:one of the important factors in the occurrence and development of sarcopenia

Sarcopenia,or muscle loss,has been one of the hot topics in the medical field in recent years.Due to limited attention and effective treatments for sarcopenia in the past,many patients,especially the elderly,suffered irreversible damage to their motor function caused by sarcopenia.However,recent scientific studies have found that the occurrence and development of sarcopenia are closely related to the function and quantity of muscle satellite cells.This article briefly discusses the relationship between muscle satellite cells and sarcopenia.

Protective Effect of ATP on Skeletal Muscle Satellite Cells Damaged by H_2O_2

This study investigated the protective effect of ATP on skeletal muscle satellite cells damaged by H2O2 in neonatal rats and the possible mechanism. The skeletal muscle satellite cells were randomly divided into four groups： normal group, model group（cells treated with 0.1 mmol/L H2O2 for 50 s）, protection group（cells treated with 16, 8, 4, 2, 1, 0.5, or 0.25 mmol/L ATP for 24 h, and then with 0.1 mmol/L H2O2 for 50 s）, proliferation group（cells treated with 16, 8, 4, 2, 1, 0.5, or 0.25 mmol/L ATP for 24 h）. MTT assay, FITC＋PI＋DAPI fluorescent staining, Giemsa staining and immunofluorescence were performed to examine cell viability and apoptosis, and apoptosis-related proteins. The results showed that the survival rate of skeletal muscle satellite cells was decreased and the apoptosis rate was increased after H2O2 treatment（P〈0.01）. Different doses of ATP had different effects on skeletal muscle satellite cells damaged by H2O2： the survival rate of muscle satellite cells treated with ATP at 4, 2, or 1 mmol/L was increased. The protective effect was most profound on cells treated with 2 mmol/L ATP. Immunofluorescence showed that ATP could increase the number of Bcl-2-positive cells（P〈0.01） and decrease the number of the Bax-positive cells（P〈0.01）. It was concluded that ATP could protect skeletal muscle satellite cells against H2O2 damage in neonatal rats, which may be attributed to the up-regulation of the expression of Bcl-2 and down-regulation of Bax, resulting in the suppression of apoptosis.

Effects of Soybean Isoflavones on In vitro Antioxidative Capacity of Satellite Cells of Porcine Skeletal Muscles

A synthetic isoflavone （ISO-S） or genistein was added in culture medium at different concentrations （0, 10, 20, 30, 40, and 80 p.mol L^-1） to investigate the effects of soybean isoflavones on antioxidative capacity of porcine skeletal muscle satellite cells. After 48 h incubation, the suspension was cryopreserved for the determination of superoxide dismutase （SOD）, catalase （CAT）, glutathione peroxidase （GSH-Px） activities, and malondialdehyde （MDA） content. The mRNA levels of SOD, CAT, and GSH-Px gene in cells were detected with Taqman fluorescent probe method. The results showed that the content of MDA and the activities and the mRNA levels of SOD of porcine skeletal muscle satellite cells were influenced by supplemented soybean isoflavone （P〈0.05） when adding 10-80 μmol L^-1 ISO-S or genistein in the medium. The MDA contents, SOD and CAT activities and their mRNA expression levels of porcine skeletal muscle cells responded quadratically （P〈 0.05） as the level of ISO-S or genistein increased. Pre-incubation of porcine skeletal muscle satellite cells with ISO-S or genistein at 10-40 pmol L-1 elevated the activities and the mRNA expression levels of SOD and CAT in cells concurrently and decreased the cellular content of MDA （P〈 0.05）. The results indicated that pre-incubation of ISO-S or genistein at 10- 40μmol L^-1 could improve the antioxidative capacity of porcine skeletal muscle satellite cells.

Impact of Bovine Skeletal Muscle Satellite Cell Differentiation by Small Interfering RNA Targeting Myogenin Gene

To examine the effect of myogenin gene on the differentiation of bovine skeletal muscle satellite cell, we constructed small interfering RNA plasmid vector to obtain myogenin knockdown bovine skeletal muscle cells, then used cell transfection, real time RCR and Western Blot to detect the influence of myogenin to cell differentiation. Results showed that the knockdown of myogenin significantly decreased its expression and other muscle-specific genes. Compared to the control, it could differentiate into few myotubes when challenged by low serum in the medium. These findings provided an important theoretical basis for further explore of the genetic mechanism in adult skeletal muscle, the remedy of muscle injuries and the cultivation of high-yield transgenic cattle.

IGF-1, bFGF EXPRESSION AND VASCULAR REGENERATION IN ACUTE INFARCTED CANINE MYOCARDIUM AFTER AUTOLOGUS SKELETAL MUSCLE SATELLITE CELL IMPLANTATION

Objective To study the cell growth factor secretion and vascular regeneration in acute in-farcted myocardium after autologous skeletal muscle satellite cell implantation. Methods Autologous skeletal muscle satellite cells from adult mongrel canine were implanted into the acute myocardial infarct site via the ligated left anterior descending (LAD) artery. Specimens were harvested at 2, 4 , 8 weeks after implantation for the expression of insulin-like growth factor-1 (IGF-1), basic fibroblast growth factor ( bFGF) and the vascular density. Results The expression of IGF-1, bFGF and the vascular density in skeletal muscle satellite cell implant group were higher than that in the control group. Conclusion The skeletal muscle satellite cells, after being implanted into the acute myocardial infarction, not only showed myocardial regeneration, but also showed the ability to secrete the cell factors, hence representing a positive effect on the regeneration of the infarcted myocardium.

THE IMPROVEMENT OF INFARCTED MYOCARDIAL CONTRACTILE FORCE AFTER AUTOLOGOUS SKELETAL MUSCLE SATELLITE CELL IMPLANTATION

Objective To study the improvement of infarcted myocardial contractile force after autologous skeletal muscle satellite cell implantation via intracoronary arterial perfusion. Methods Skeletal muscle cells were harvested from gluteus max of adult mongrel dogs and the cells were cultured and expanded before being labeled with DAPI (4’, 6-diamidino-2-phenylindone). The labeled cells were then implanted into the acute myocardial infarct site via the ligated left anterior descending (LAD) coronary artery. Specimens were taken at 2nd, 4th, 8th week after myoblast implantation for histologic and contractile force evaluation, respectively. Results The satellite cells with fluorescence had been observed in the infarct site and also in papi- llary muscle with consistent oriented direction of host myocardium. A portion of the implanted cells had differen- tiated into muscle fibers. Two weeks after implantation, the myocardial contractile force showed no significant difference between the cell implant group and control group. At 4 and 8 week, the contractile force in the cell implant group was better than that in control group. Conclusion The skeletal muscle satellite cells, implanted into infarct myocardium by intracoronary arterial perfusion, could disseminate through the entire infarcted zone with myocardial regeneration and improve the contractile function of the infarcted myocardium.

Time-dependent gene expression analysis after mouse skeletal muscle contusion

Background:Though the mechanisms of skeletal muscle regeneration are deeply understood,those involved in muscle contusion,one of the most common muscle injuries in sports medicine clinics,are not.The objective of this study is to explore the mechanisms involved in muscle regeneration after contusion injury.Methods:In this study,a total of 72 mice were used.Eight of them were randomly chosen for the control group,while the rest were subjected to muscle contusion.Subsequently,their gastrocnemius muscles were harvested at different time points.The changes in muscle morphology were assessed by hematoxylin and eosin(HE) stain.In addition,the gene expression was analyzed by real-time polymerase chain reaction.Results:The data showed that the expression of many genes,i.e.,specific markers of immune cells and satellite cells,regulatory factors for muscle regeneration,cytokines,and chemokines,increased in the early stages of recovery,especially in the first 3 days.Furthermore,there were strict rules in the expression of these genes.However,almost all the genes returned to normal at 14 days post-injury.Conclusion:The sequence of immune cells invaded after muscle contusion was neutrophils,M1 macrophages and M2 macrophages.Some CC(CCL2,CCL3,and CCL4) and CXC(CXCL10) chemokines may be involved in the chemotaxis of these immune cells.HGF may be the primary factor to activate the satellite cells after muscle contusion.Moreover,2 weeks are needed to recover when acute contusion happens as used in this study.

Research Progress of Vitamins on Muscle Regeneration

Muscle satellite cells,as muscle stem cells,play a critical role in the process of muscle regeneration,and effective muscle regeneration helps to restore muscle function and maintain the homeostasis of muscle tissues.In damaged muscle,muscle satellite cells are activated to form new myofibers through the process of cell proliferation,migration,differentiation and fusion to complete muscle tissue regeneration.Meanwhile,this process is mainly affected by endogenous gene expression and many exogenous factors.Researches in recent years have shown that vitamins,as important nutrients,play an extremely important role in the process of muscle regeneration.Therefore,this article reviewed the roles of vitamins in the regeneration of muscle satellite cells,according to the latest research progress.It would provide more theoretical and data support for the regeneration and repair of muscle damage,muscle atrophy and other muscle diseases,so that it could be better applied in the field of muscle regeneration researches and serve human health.

Identification of transition factors in myotube formation from proteome and transcriptome analyses

Muscle fibers are the main component of skeletal muscle and undergo maturation through the formation of myotubes.During early development,a population of skeletal muscle satellite cells(SSCs)proliferate into myoblasts.The myoblasts then undergo further differentiation and fusion events,leading to the development of myotubes.However,the mechanisms involved in the transition from SSCs to myotube formation remain unclear.In this study,we characterized changes in the proteomic and transcriptomic expression profiles of SSCs,myoblasts(differentiation for 2 d)and myotubes(differentiation for 10 d).Proteomic analysis identified SLMAP and STOM as potentially associated with myotube formation.In addition,some different changes in MyoD,MyoG,Myosin7 and Desmin occurred after silencing SLMAP and STOM,suggesting that they may affect changes in the myogenic marker.GO analysis indicated that the differentiation and migration factors SVIL,ENSCHIG00000026624(AQP1)and SERPINE1 enhanced the transition from SSCs to myoblasts,accompanied by changes in the apoptotic balance.In the myoblast vs.myotube group,candidates related to cell adhesion and signal transduction were highly expressed in the myotubes.Additionally,CCN2,TGFB1,MYL2 and MYL4 were identified as hub-candidates in this group.These data enhance our existing understanding of myotube formation during early development and repair.

TIMP2 promotes intramuscular fat deposition by regulating the extracellular matrix in chicken

The interaction between myocytes and intramuscular adipocytes is a hot scientific topic. Using a co-culture system, this study aims to investigate the regulation of intramuscular fat deposition in chicken muscle tissue through the interaction between myocyte and adipocyte and identify important intermediary regulatory factors. Our proteomics data showed that the protein expression of tissue inhibitor of metalloproteinases 2(TIMP2) increased significantly in the culture medium of the co-culture system, and the content of lipid droplets was more in the co-culture intramuscular adipocytes. In addition, TIMP2 was significantly upregulated(P<0.01) in muscle tissue of individuals with high intramuscular fat content.Weighted gene co-expression network analysis revealed that TIMP2 was mainly involved in the extracellular matrix receptor interaction signaling pathway and its expression was significantly correlated with triglyceride, intramuscular fat,C14:0, C14:1, C16:0, C16:1, and C18:1n9C levels. Additionally, TIMP2 was co-expressed with various representative genes related to lipid metabolism(such as ADIPOQ, SCD, ELOVL5, ELOVL7, and LPL), as well as certain genes involved in extracellular matrix receptor interaction(such as COL1A2, COL4A2, COL5A1, COL6A1, and COL6A3), which are also significantly upregulated(P<0.05 or P<0.01) in muscle tissue of individuals with high intramuscular fat content.Our findings reveal that TIMP2 promotes intramuscular fat deposition in muscle tissue through the extracellular matrix receptor interaction signaling pathway.

Satellite cell proliferation and myofiber cross-section area increase after electrical stimulation following sciatic nerve crush injury in rats

Background:Electrical stimulation has been recommended as an effective therapy to prevent muscle atrophy after nerve injury.However,the effect of electrical stimulation on the proliferation of satellite cells in denervated muscles has not yet been fully elucidated.This study was aimed to evaluate the changes in satellite cell proliferation after electrical stimulation in nerve injury and to determine whether these changes are related to the restoration of myofiber cross-section area(CSA).Methods:Sciatic nerve crush injury was performed in 48 male Sprague-Dawley rats.In half(24/48)of the rats,the gastrocnemius was electrically stimulated transcutaneously on a daily basis after injury,while the other half were not stimulated.Another group of 24 male Sprague-Dawley rats were used as sham operation controls without injury or stimulation.The rats were euthanized 2,4,and 6 weeks later.After 5-bromo-2’-deoxyuridine(BrdU)labeling,the gastrocnemia were harvested for the detection of paired box protein 7(Pax7),BrdU,myofiber CSA,and myonuclei number per fiber.All data were analyzed using two-way analysis of variance and Bonferroni post-hoc test.Results:The percentages of Pax7-positive nuclei(10.81±0.56%)and BrdU-positive nuclei(34.29±3.87%)in stimulated muscles were significantly higher compared to those in non-stimulated muscles(2.58±0.33%and 1.30±0.09%,respectively,Bonferroni t=15.91 and 18.14,P<0.05).The numbers of myonuclei per fiber(2.19±0.24)and myofiber CSA(1906.86±116.51 mm2)were also increased in the stimulated muscles(Bonferroni t=3.57 and 2.73,P<0.05),and both were positively correlated with the Pax7-positive satellite cell content(R2=0.52 and 0.60,P<0.01).There was no significant difference in the ratio of myofiber CSA/myonuclei number per fiber among the three groups.Conclusions:Our results indicate that satellite cell proliferation is promoted by electrical stimulation after nerve injury,which may be correlated with an increase in myonuclei number and myofiber CSA.