Satellite cell activity in muscle regeneration after contusion in rats

1. The role of satellite cells in muscle growth during development is well documented, but the involvement of these cells in muscle repair after contusion is less well known. In the present study, we investigated the time‐course of satellite cell activity (from 3 h to 7 days) after contusion of rat gastrocnemius muscle using specific molecular markers for immunofluorescence and real‐time polymerase chain reaction (PCR). 2. Inflammation of the injured muscle occurred within 6 h, followed by disintegration of the damaged myofibres within 12 h. Newly formed myofibres appeared by Day 7. 3. The number of MyoD‐positive nuclei (activated satellite cells) in the injured muscle was significantly increased by 6 h, reaching a maximum by 12 h after contusion. However, the number of MyoD‐positive nuclei decreased towards control levels by Day 7. Changes in the number of bromodeoxyuridine‐labelled nuclei (proliferating satellite cells) paralleled the changes seen in the number of MyoD‐positive nuclei. Conversely, expression of myogenin protein was not apparent until Day 3 and increased further by Day 7. Colabelling of MyoD and myogenin was seen in only a few cells. 4. The time‐course of MyoD mRNA expression corresponded with MyoD protein expression. However, there were two peaks in myogenin mRNA expression: 6 h and Day 7 after contusion. The second peak coincided with upregulation of myostatin mRNA levels. 5. The results of the present study suggest that contusion activates a homogeneous population of satellite cells to proliferate within 3 days, followed by differentiation to form new myofibres. The latter may be regulated, in part, by myostatin.     

Suppression of Myostatin Stimulates Regenerative Potential of Injured Antigravitational Soleus Muscle in Mice under Unloading Condition

Effects of myostatin (MSTN)-suppression on the regeneration of injured skeletal muscle under unloading condition were investigated by using transgenic mice expressing a dominant-negative form of MSTN (MSTN-DN). Both MSTN-DN and wild-type (WT) mice were subjected to continuous hindlimb suspension (HS) for 6 weeks. Cardiotoxin (CTX) was injected into left soleus muscle under anesthesia 2 weeks after the initiation of HS. Then, the soleus muscles were excised following 6-week HS (4 weeks after CTX-injection). CTX-injection caused to reduce the soleus fiber cross-sectional area (CSA) in WT mice under both unloading and weight-bearing conditions, but not in MSTN-DN mice. Under unloading condition, CTX-injected muscle weight and fiber CSA in MSTN-DN mice were significantly higher than those in WT mice. CTX-injected muscle had many damaged and regenerating fibers having central nuclei in both WT and MSTN-DN mice. Significant increase in the population of Pax7-positive nuclei in CTX-injected muscle was observed in MSTN-DN mice, but not in WT mice. Evidences indicate that the suppression of MSTN cause to increase the regenerative potential of injured soleus muscle via the increase in the population of muscle satellite cells regardless of unloading conditions.     

Effects of maternal immunisation against myostatin on post-natal growth and skeletal muscle mass of offspring in mice

The objective of this study was to examine the effect of maternal immunisation against myostatin, a potent negative regulator of skeletal muscle growth, on the skeletal muscle growth of offspring in mice. Twenty female mice were divided into four groups and immunised against keyhole limpet haemocyanin (control) or recombinant mature myostatin (rMyo), or two different myostatin synthetic peptides conjugated to keyhole limpet haemocyanin (Myo1 and Myo2). Offspring were sacrificed at 8 weeks of age to measure carcass, muscle and fat masses. Sera collected from 3-day-old neonates of the rMyo, Myo1 and Myo2 groups showed titres against myostatin, confirming the maternal transfer of anti-myostatin antibodies to offspring. No significant effects of immunisation on offspring weight were observed. The offspring of the Myo2 group, but not the rMyo and Myo1 groups, had significantly heavier gastrocnemius and triceps muscle mass than those of the control (p<0.01). All IgGs of the three treatment groups showed affinity to mature myostatin monomer in Western blot analysis, but none of the IgGs showed affinity to myostatin dimer. The IgGs of all the treatment groups failed to suppress the biological activity of myostatin in an A204 cell-based pGL3 (CAGA)₁₂-luciferase reporter system, demonstrating that the increase in skeletal muscle mass observed in the offspring of the Myo2 group might not result from the inhibition of myostatin's biological activity by the anti-Myo2 antibodies. In conclusion, the results of this study suggest that antigen preparation may affect the responsiveness of skeletal muscle growth of offspring when maternal immunisation against myostatin is used as a potential tool to improve skeletal muscle growth of offspring.     

卵泡抑素对肿瘤恶病质小鼠骨骼肌消耗的影响及其作用机制

目的：观察卵泡抑素（FST）对肿瘤恶病质小鼠骨骼肌消耗及肌肉生长抑制素（Mstn）、长链非编码RNA（LncRNA）-肺癌转移相关转录本1（MALAT1）和Caspase-3表达的影响,阐明其缓解肿瘤恶病质小鼠骨骼肌消耗的可能机制。方法：32只BALB/c小鼠随机分为健康对照组（HC组）、FST预防组（FP组）、FST治疗组（FT组）和肿瘤恶病质组（CC组）,每组8只,后3组小鼠皮下接种小鼠结肠癌CT26细胞诱导肿瘤恶病质。监测各组小鼠体质量、自发性活动量和肿瘤生长情况。于接种后第6、12天FP和FT组小鼠分别给予FST（5 μg· kg^-1·d^-1）腹腔注射。第20天采集标本,称肿瘤及腓肠肌质量,检测小鼠血清生化代谢指标及腓肠肌纤维横切面积,Real-time PCR法检测小鼠腓肠肌和肿瘤组织中Mstn、Caspase-3及LncRNA-MALAT1 mRNA表达水平,Western blotting法检测小鼠腓肠肌组织中Mstn和Caspase-3蛋白表达水平。结果：与CC组比较,FP和FT组小鼠体质量、自发性活动量、腓肠肌质量及其肌纤维横切面积均增加（P < 0.05）,生化代谢指标改善（P < 0.05）。与HC组比较,CC组小鼠腓肠肌组织中Mstn和Caspase-3 mRNA及蛋白表达水平均升高（P < 0.05）,LncRNA-MALAT1 mRNA表达水平降低（P < 0.05）;与CC组比较,FP和FT组小鼠腓肠肌组织中Mstn和Caspase-3 mRNA及蛋白表达水平均降低（P < 0.05）,LncRNA-MALAT1mRNA表达水平升高（P < 0.05）,且FP组预防效果优于FT组（P < 0.05）。结论：FST可缓解肿瘤恶病质小鼠骨骼肌消耗,其机制可能与抑制Mstn表达、上调LncRNA-MALAT1表达从而降低Caspase-3表达有关。     

Myostatin inhibition: a potential performance enhancement strategy?

A decade has passed since myostatin was first identified as a negative regulator of muscle growth. Since then, studies in both humans and animals have demonstrated that decreasing the levels of this growth factor or inhibiting its function can dramatically increase muscle size, and a number of therapeutic applications of myostatin inhibition to the treatment of myopathies and muscle atrophy have been proposed. As such treatments would be likely to also stimulate muscle growth in healthy individuals, there is a growing concern among anti-doping authorities that myostatin inhibitors may be among the next generation of ergogenic pharmaceuticals or even in the vanguard of "gene doping" technology. While the ability to stimulate muscle growth through myostatin inhibition is well documented, a growing body of evidence suggests such increases may not translate into an improvement in athletic performance. This article briefly reviews the function of this potent regulator of muscle development and explores the potential therapeutic uses, and potential ergogenic abuses, of myostatin manipulation.     

血清肌肉生长抑制素和肌肉环指蛋白-1对慢性阻塞性肺疾病急性加重期并发肺动脉高压的预测价值

目的 观察慢性阻塞性肺疾病(chronic obstructive pulmonary disease,COPD)急性加重期并发肺动脉高压(pulmonary hypertension,PH)患者血清肌肉生长抑制素(myostatin,MSTN)和肌肉环指蛋白-1(muscle ring finger protein-...     

Ontogenetic and in silico models of spatial-packing in the hypermuscular mouse skull

Networks linking single genes to multiple phenotypic outcomes can be founded on local anatomical interactions as well as on systemic factors like biochemical products. Here we explore the effects of such interactions by investigating the competing spatial demands of brain and masticatory muscle growth within the hypermuscular myostatin-deficient mouse model and in computational simulations. Mice that lacked both copies of the myostatin gene (-/-) and display gross hypermuscularity, and control mice that had both copies of the myostatin gene (+/+) were sampled at 1, 7, 14 and 28 postnatal days. A total of 48 mice were imaged with standard as well as contrast-enhanced microCT. Size metrics and landmark configurations were collected from the image data and were analysed alongside in silico models of tissue expansion. Findings revealed that: masseter muscle volume was smaller in -/- mice at day 1 but became, and remained thereafter, larger by 7 days; -/- endocranial volumes begin and remained smaller; -/- enlargement of the masticatory muscles was associated with caudolateral displacement of the calvarium, lateral displacement of the zygomatic arches, and slight dorsal deflection of the face and basicranium. Simulations revealed basicranial retroflexion (flattening) and dorsal deflection of the face associated with muscle expansion and abrogative covariations of basicranial flexion and ventral facial deflection associated with endocranial expansion. Our findings support the spatial-packing theory and highlight the importance of understanding the harmony of competing spatial demands that can shape and maintain mammalian skull architecture during ontogeny.     

Peptide‐2 from mouse myostatin precursor protein alleviates muscle wasting in cancer‐associated cachexia

Cancer cachexia, characterized by continuous muscle wasting, is a key determinant of cancer‐related death; however, there are few medical treatments to combat it. Myostatin (MSTN)/growth differentiation factor 8 (GDF‐8), which is a member of the transforming growth factor‐β family, is secreted in an inactivated form noncovalently bound to the prodomain, negatively regulating the skeletal muscle mass. Therefore, inhibition of MSTN signaling is expected to serve as a therapeutic target for intractable muscle wasting diseases. Here, we evaluated the inhibitory effect of peptide‐2, an inhibitory core of mouse MSTN prodomain, on MSTN signaling. Peptide‐2 selectively suppressed the MSTN signal, although it had no effect on the activin signal. In contrast, peptide‐2 slightly inhibited the GDF‐11 signaling pathway, which is strongly related to the MSTN signaling pathway. Furthermore, we found that the i.m. injection of peptide‐2 to tumor‐implanted C57BL/6 mice alleviated muscle wasting in cancer cachexia. Although peptide‐2 was unable to improve the loss of heart weight and fat mass when cancer cachexia model mice were injected with it, peptide‐2 increased the gastrocnemius muscle weight and muscle cross‐sectional area resulted in the enhanced grip strength in cancer cachexia mice. Consequently, the model mice treated with peptide‐2 could survive longer than those that did not undergo this treatment. Our results suggest that peptide‐2 might be a novel therapeutic candidate to suppress muscle wasting in cancer cachexia.     

肌卫星细胞功能异常在慢性肾脏病骨骼肌消耗中的机制

目的:骨骼肌消耗是慢性肾脏病(CKD)的主要特征,肌卫星细胞(muscle satellite cells,MSC)是具有自我增殖和更新能力的成肌干细胞,MSC功能异常可引起肌肉萎缩.本研究探讨MSC在CKD小鼠骨骼肌消耗中的作用机制. 方法:采用5/6肾切除制作小鼠CKD模型,以假手术组为对照组.以免疫组化标记胫骨前肌层粘连蛋白(laminin),测量肌纤维横截面积,并计算面积百分位图;RT-PCR检测腓肠肌Pax-7、MyoD、Myf-5、Myogenin及myostatin mRNA表达水平;分离并原代培养骨骼肌MSC,原位免疫组化检测Pax-7和MyoD表达,检测分化后新形成的肌纤维胚胎型肌球货白重链(eMyHC). 结果:造模一个月后,CKD小鼠体重和骨骼肌重量明显下降,形态学表现为胫骨前肌明显变细,肌纤维横截面积减少,面积百分位图明显左移;肌肉组织的Pax-7、MyoD、Myf-5和Myogenin mRNA表达水平均有不同程度下降,myostatin mRNA表达则明显上调;原代培养的MSC中,CKD组的Pax-7和MyoD阳性细胞数目明显低于对照组,分化后新形成的eMyHC阳性肌纤维数目也明显降低. 结论:CKD可引起显著的骨骼肌萎缩,使MSC增殖和分化功能下降,myostatin水平升高可能是抑制肌卫星细胞功能的重要原因.