肌卫星细胞在失重肌萎缩中的可塑性变化及机制

肌卫星细胞在骨骼肌生长发育和出生后骨骼肌损伤修复中起着重要的作用,但是有关肌萎缩中肌卫星细胞的可塑性变化、作用及其机制尚不清楚.本研究采用小鼠尾悬吊模拟失重效应诱导失重肌萎缩,动态分析了失重肌萎缩发生过程中不同类型肌纤维的肌卫星细胞数量和增殖、分化潜能可塑性的改变,发现在失重肌萎缩过程中,处于安静状态的肌卫星细胞显著增多、激活增殖的肌卫星细胞显著减少,而具有成肌分化潜能的肌卫星细胞有持续减少趋势.此外,在失重肌萎缩比目鱼肌单根肌纤维移出的体外培养中,证明了失重肌萎缩肌纤维肌卫星细胞可塑性降低的特征性变化.进一步,通过对比分析Smad3基因敲除及其同窝野生型小鼠,在失重肌萎缩中肌卫星细胞可塑性的差异性变化,揭示了Smad3在调控失重肌萎缩肌卫星细胞可塑性变化中的关键作用.     

肥胖诱导的骨骼肌萎缩机制研究进展

骨骼肌是人体氨基酸和蛋白质的主要贮存、代谢库,其正常功能和代谢过程受到多种病理因素的影响。骨骼肌萎缩发生于骨骼肌稳态严重失衡状态下,对患者生活和社会医疗造成了沉重负担。近年来,由于世界肥胖人群数量激增,肥胖诱导的骨骼肌萎缩正日益成为公共卫生的严峻挑战之一。肥胖诱导的骨骼肌萎缩过程涉及多种信号分子或通路的改变,如泛素蛋白酶系统、自噬溶酶体系统、胰岛素/IGF1-PI3K-Akt、肌肉生长抑制素、白细胞介素-6、肿瘤坏死因子等;这些信号分子或通路在肥胖状态下被激活或抑制后,可共同影响蛋白质合成/分解平衡进而造成骨骼肌萎缩。基于上述信号分子或通路,系统总结并讨论了肥胖诱导的骨骼肌萎缩机制,以期为寻找缓解/治疗肥胖诱导的肌萎缩靶点和进一步开发利用天然植物化学物提供理论依据。     

加压运动对去负荷肌萎缩的影响及机制研究进展

骨骼肌加压运动(KAATSU training)是神经肌肉训练的新方法,通过对肢体近端的适度压迫,可有效闭塞血管、限制血流量,致使肢体远端相对缺血,达到以小强度的骨骼肌加压运动刺激肌肉生长,得到普通大强度抗阻训练的效果。本文主要介绍加压运动的特点、效果和作用,分析加压运动在不同因素下引起的骨骼肌应激性和适应性变化,并对其防治去负荷肌萎缩的前景进行展望。为进一步深入研究提供参考。     

失重/模拟失重对内皮细胞的影响实验研究进展

血管内皮作为血管壁的衬里,参与调节组织器官的局部血流和机体其它生理进程,在维持血管完整性和内环境稳定中发挥关键作用。内皮细胞对包括重力在内的机械应力刺激极为敏感,重力变化可对其形态和功能构成不同程度的影响。研究发现,失重/模拟失重通过诱导内皮细胞细胞骨架重塑、质膜caveolae重布,使其合成分泌血管活性物质、炎性介质的能力以及细胞表面粘附分子表达发生改变,这些分子变化又对内皮细胞的生长、增殖、凋亡、迁移和血管生成等具有精细调控作用。本文综合评述了失重/模拟失重对内皮细胞功能的影响,同时围绕文献报道中一些尚存争议的观点进行了适当讨论。     

失重效应模拟实验方法及对机体功能影响的研究进展

我国载人航天已经进入中长期飞行阶段,失重是航天员在长期的航天飞行和空间驻留时面临的一种极端的航天特因环境,除了会对航天员的身体健康产生严重的影响,还极易诱发神经精神功能紊乱,包括反应、判断、决策等认知功能减退。由于航天飞行的特殊性,在地面采用实验模拟航天失重,探究失重对机体的影响,并找到防护措施是至关重要的。因此,本文从失重效应模拟实验方法出发,综述模拟失重对机体功能的影响。     

结合模拟失重, 改进大学生理学骨骼肌收缩实验

骨骼肌收缩实验作为大学生理学课程中一个传统的教学实验,在国内各高校的生理学教学中多有开设。本教研室一直致力于模拟失重致骨骼肌废用性萎缩方面的研究,结合科研课题对该教学实验进行了改进：以模拟失重小鼠作为实验动物,代替原用的蛙或蟾蜍;在保留原有实验内容的基础上,加入正常小鼠与模拟失重小鼠骨骼肌收缩能力的测定等新内容。通过在教学中的实际应用,发现改进后的实验不但能够完成传统的实验内容,还可通过模拟失重小鼠与正常小鼠收缩能力的测定和对比,体现模拟失重对骨骼肌收缩功能的影响,进而加深学生对骨骼肌收缩过程的理解,提高学生对失重影响人体生理功能的认识。改进后的骨骼肌收缩实验丰富了传统实验的内容,拓宽了该实验的理论和应用,有助于激发学生对生理学的学习兴趣,明显提升教学效果。     

肌管细化是失重性肌萎缩结构和功能变化的基础

本文通过新生大鼠原代培养获取骨骼肌肌管,利用水平回转器模拟失重效应,通过F-actin/G-actin以及F-actin/pERK免疫细胞化学染色,观察研究了模拟失重对肌管形态、微丝及磷酸化ERK表达的影响。通过建立的航天飞行失重性肌萎缩的细胞学模型研究发现:回转后肌管变细,F-actin染色减弱伴有G-actin染色增强,同时pERK染色减弱。表明回转模拟失重条件下肌管发生萎缩、微丝解聚并伴随信号转导活性分子磷酸化ERK表达下降。提示肌管细化是失重性肌萎缩结构和功能变化的结构基础     

一种复方制剂对尾部悬吊大鼠比目鱼肌mATP酶活性升高及肌萎缩的对抗效应观察

目的:探讨一种中药复方制剂RC对模拟失重条件下大鼠比目鱼肌(SOL)的mATP酶活性及肌萎缩的影响.方法:尾部悬吊法建立大鼠模拟失重模型,测量比目鱼肌的湿重体重比(mg/g),以Ca2 -ATPase法测定比目鱼肌中mATP酶活性,计算Ⅰ型和Ⅱ型肌纤维的比例,测定比目鱼肌中Ⅰ型和Ⅱ型肌纤维的横截面积(CSA).结果:与吊尾 溶媒灌胃组相比,吊尾14天后,吊尾 RC灌胃组的湿重体重比增加了33.33%(P<0.01);比目鱼肌中Ⅰ型和Ⅱ型肌纤维CSA均显著增加(143.03%, P<0.01; 83.25%, P<0.01);比目鱼肌中Ⅰ型肌纤维比例明显升高,Ⅱ型肌纤维比例明显降低(P<0.01).结论:复方制剂RC对模拟失重条件下大鼠比目鱼肌mATP酶活性的升高与模拟失重引起的肌萎缩有显著的对抗作用.     

废用性肌萎缩的信号机制研究进展

长时间废用会导致骨骼肌明显萎缩,主要表现为肌纤维横截面积的减少及慢肌纤维向快肌纤维类型的转换等。新近的研究表明,NF-κB是废用性肌萎缩过程中重要的信号转录因子I,GF-1/PI3K/Akt通路的抑制也参与了废用性肌萎缩的发生,其它诸如TGF-β/Smad、p38通路的参与和氧化应激等机制在废用时均导致蛋白质功能的改变。本文主要对上述参与废用性肌萎缩中的信号通路进行综述。     

Acupuncture ameliorated skeletal muscle atrophy induced by hindlimb suspension in mice

Preventing skeletal muscle atrophy is critical for maintaining quality of life, but it is often a challenging goal for the elderly and patients with severe conditions. We hypothesized that acupuncture in place of exercise training is an alternative non-pharmacological intervention that can help to prevent muscle atrophy. To elucidate the effects of acupuncture on skeletal muscle atrophy caused by hindlimb suspension (HS), we performed acupuncture on mice according to two different methods: acupuncture with electrical stimulation (EA: electroacupuncture) and without electrical stimulation (MA: manual acupuncture). A needle was retained in the gastrocnemius muscle for 30 min every day for 2 weeks in the EA and MA groups. In the EA group, 30 min of repetitive electrical stimulation (1 Hz, 1 ms pulse width, 6.5 mA intensity) was also applied. HS significantly reduced muscle mass and the cross-sectional area of the soleus muscles. This HS-induced reduction was significantly improved in the EA group, although the level of improvement remained insufficient when compared with the control group. We found that the mRNA expression levels of atrogin-1 and MuRF1, which play a principal role in muscle-specific degradation as E3 ubiquitin ligases, were significantly increased in the HS group compared to the control group. EA and MA reduced the HS-induced upregulation of atrogin-1 (p < 0.01 in EA and MA) and MuRF1 (p < 0.01 in EA) mRNAs. We also found that the expression levels of PI3K, Akt1, TRPV4, adenosine A1 receptor, myostatin, and SIRT1 mRNAs tended to be increased by HS. EA and MA further increased the HS-induced upregulation of Akt1 (p < 0.05 in MA) and TRPV4 (p < 0.05 in MA) mRNAs. We concluded that acupuncture partially prevented skeletal muscle atrophy. This effect might be due to an increase in protein synthesis and a decrease in protein degradation.     

Pharmacological inhibition of GSK-3 in a guinea pig model of LPS-induced pulmonary inflammation: II. Effects on skeletal muscle atrophy

Background

Chronic obstructive pulmonary disease (COPD) is accompanied by pulmonary inflammation and associated with extra-pulmonary manifestations, including skeletal muscle atrophy. Glycogen synthase kinase-3 (GSK-3) has been implicated in the regulation of muscle protein- and myonuclear turnover; two crucial processes that determine muscle mass. In the present study we investigated the effect of the selective GSK-3 inhibitor SB216763 on muscle mass in a guinea pig model of lipopolysaccharide (LPS)-induced pulmonary inflammation-associated muscle atrophy.

Methods

Guinea pigs were pretreated with either intranasally instilled SB216763 or corresponding vehicle prior to each LPS/saline challenge twice weekly. Pulmonary inflammation was confirmed and indices of muscle mass were determined after 12 weeks. Additionally, cultured skeletal muscle cells were incubated with tumor necrosis factor α (TNF-α) or glucocorticoids (GCs) to model the systemic effects of pulmonary inflammation on myogenesis, in the presence or absence of GSK-3 inhibitors.

Results

Repeated LPS instillation induced muscle atrophy based on muscle weight and muscle fiber cross sectional area. Intriguingly, GSK-3 inhibition using SB216763 prevented the LPS-induced muscle mass decreases and myofiber atrophy. Indices of protein turnover signaling were unaltered in guinea pig muscle. Interestingly, inhibition of myogenesis of cultured muscle cells by TNF-α or synthetic GCs was prevented by GSK-3 inhibitors.

Conclusions

In a guinea pig model of LPS-induced pulmonary inflammation, GSK-3 inhibition prevents skeletal muscle atrophy without affecting pulmonary inflammation. Resistance to inflammation- or GC-induced impairment of myogenic differentiation, imposed by GSK-3 inhibition, suggests that sustained myogenesis may contribute to muscle mass maintenance despite persistent pulmonary inflammation. Collectively, these results warrant further exploration of GSK-3 as a potential novel drug target to prevent or reverse muscle wasting in COPD.     

The contractile apparatus of striated muscle in the course of atrophy and regeneration

Summary The ultrastructure of the contractile apparatus of the rat soleus muscle during the course of denervation atrophy was investigated. It was found that the ratio of thin to thick filaments increased in myofibrils of atrophying muscle fibers. Elevation of the ratio was observed as early as the second day after denervation, and became more pronounced with the progress of atrophy. Parallel measurements of the amounts of actin and myosin in the myofibrils and in the muscle protein extracts revealed a lower proportion of myosin heavy chains to actin in the fractions from denervated muscles, compared with the control values. Both the electron-microscopic observations and the biochemical evaluation of the actin content of the muscle, suggests that the elevated ratio of thin to thick filaments seen in the course of the muscle atrophy appears as the result of an earlier and more intensive disappearance of thick filaments. Thin filaments disappeared more slowly, in parallel to the decrease in muscle weight.On the basis of the results presented a mechanism of progress of simple atrophy of muscle in suggested.     

Proteomic analysis of rat laryngeal muscle following denervation

Laryngeal muscle atrophy induced by nerve injury is a major factor contributing to the disabling symptoms associated with laryngeal paralysis. Alterations of global proteins in rat laryngeal muscle following denervation were, therefore, studied using proteomic techniques. Twenty-eight adult Sprague-Dawley rats were divided into normal control and denervated groups. The thyroarytenoid (TA) muscle was excised 60 days after right recurrent laryngeal nerve was resected. Protein separation and identification were preformed using 2-DE and MALDI-MS with database search. Forty-four proteins were found to have significant alteration in expression level after denervation. The majority of these proteins (57%), most of them associated with energy metabolism, cellular proliferation and differentiation, signal transduction and stress reaction, were decreased levels of expression in denervated TA muscle. The remaining 43% of the proteins, most of them involved with protein degradation, immunoreactivity, injury repair, contraction, and microtubular formation, were found to have increased levels of expression. The protein modification sites by phosphorylation were detected in 22% of the identified proteins that presented multiple-spot patterns on 2-D gel. Significant changes in protein expression in denervated laryngeal muscle may provide potential therapeutic strategies for the treatment of laryngeal paralysis.     

Skeletal muscle damage and impaired regeneration due to LPL-mediated lipotoxicity

According to the concept of lipotoxicity, ectopic accumulation of lipids in non-adipose tissue induces pathological changes. The most prominent effects are seen in fatty liver disease, lipid cardiomyopathy, non-insulin-dependent diabetes mellitus, insulin resistance and skeletal muscle myopathy. We used the MCK(m)-hLPL mouse distinguished by skeletal and cardiac muscle-specific human lipoprotein lipase (hLPL) overexpression to investigate effects of lipid overload in skeletal muscle. We were intrigued to find that ectopic lipid accumulation induced proteasomal activity, apoptosis and skeletal muscle damage. In line with these findings we observed reduced Musculus gastrocnemius and Musculus quadriceps mass in transgenic animals, accompanied by severely impaired physical endurance. We suggest that muscle loss was aggravated by impaired muscle regeneration as evidenced by reduced cross-sectional area of regenerating myofibers after cardiotoxin-induced injury in MCK(m)-hLPL mice. Similarly, an almost complete loss of myogenic potential was observed in C2C12 murine myoblasts upon overexpression of LPL. Our findings directly link lipid overload to muscle damage, impaired regeneration and loss of performance. These findings support the concept of lipotoxicity and are a further step to explain pathological effects seen in muscle of obese patients, patients with the metabolic syndrome and patients with cancer-associated cachexia.     

Delphinidin prevents disuse muscle atrophy and reduces stress-related gene expression

Delphinidin is a member of the anthocyanidin class of plant pigments. We examined the effects of delphinidin on muscle atrophy. Oral administration of delphinidin suppressed the muscle weight loss induced by mechanical unloading. Microarray analysis showed that delphinidin suppresses the upregulation of oxidative stress-related gene expression, including the expression of Cbl-b. Thus, delphinidin may prevent unloading-mediated muscle atrophy.     

Mitochondrial fission and remodelling contributes to muscle atrophy

Mitochondria are crucial organelles in the production of energy and in the control of signalling cascades. A machinery of pro‐fusion and fission proteins regulates their morphology and subcellular localization. In muscle this results in an orderly pattern of intermyofibrillar and subsarcolemmal mitochondria. Muscular atrophy is a genetically controlled process involving the activation of the autophagy‐lysosome and the ubiquitin–proteasome systems. Whether and how the mitochondria are involved in muscular atrophy is unknown. Here, we show that the mitochondria are removed through autophagy system and that changes in mitochondrial network occur in atrophying muscles. Expression of the fission machinery is per se sufficient to cause muscle wasting in adult animals, by triggering organelle dysfunction and AMPK activation. Conversely, inhibition of the mitochondrial fission inhibits muscle loss during fasting and after FoxO3 overexpression. Mitochondrial‐dependent muscle atrophy requires AMPK activation as inhibition of AMPK restores muscle size in myofibres with altered mitochondria. Thus, disruption of the mitochondrial network is an essential amplificatory loop of the muscular atrophy programme.     

Models in which many cross-bridges attach simultaneously can explain the filament movement per ATP split during muscle contraction

Contractile filaments in skeletal muscle are moved by less than 2 nm for each ATP used. If just one cross-bridge is attached to each thin filament at any instant then this distance represents the fundamental myosin cross-bridge step size (i.e. the distance one cross-bridge moves a thin filament in one ATP-splitting cycle). However, most contraction models assume many cross-bridges are attached at any instant along each thin filament. The purpose of this study was to establish whether the net filament sliding per ATP used could be explained quantitatively in terms of a cross-bridge model in which multiple cross-bridges are attached along each thin filament. It was found that the relationship between net filament sliding per ATP split and the load against which the muscle shortens is compatible with such a model and furthermore predicts that the cross-bridge step size is between 7.5 and 12.5 nm over most of the range of loads. These values were similar for different muscle fibre types.     

Proteomics of skeletal muscle glycolysis

Glycolysis represents one of the best-understood and most ancient metabolic pathways. In skeletal muscle fibres, energy for contraction is supplied by adenosine triphosphate via anaerobic glycolysis, the phosphocreatine shuttle and oxidative phosphorylation. In this respect, the anaerobic glycolytic pathway supports short duration performances of contractile tissues of high intensity. The catalytic elements associated with glycolysis are altered during development, muscle differentiation, physiological adaptations and many pathological mechanisms, such as muscular dystrophy, diabetes mellitus and age-related muscle weakness. Although gel electrophoresis-based proteomics is afflicted with various biological and technical problems, it is an ideal analytical tool for studying the abundant and mostly soluble enzymes that constitute the glycolytic system. This review critically examines the proteomic findings of recent large-scale studies of glycolytic enzymes and associated components in normal, transforming and degenerating muscle tissues. In the long term, proteins belonging to the glycolytic pathway may be useful as biomarkers of muscle adaptations and pathophysiological mechanisms and can be employed to improve diagnostics and in the identification of novel therapeutic targets in neuromuscular disorders.