Hindlimb suspension induces the expression of multiple myosin heavy chain isoforms in single fibres of the rat soleus muscle

The aim of our experiment was to test the hypothesis that the performance of maximal isometric exercise every 20 s would reduce the intermediate frequency force, i.e. the force that appears while stimulating the muscle at 15 and 20 Hz, and would produce less decrease the force at 10 and 50 Hz, while Pt would increase. Such changes in stimulated force should demonstrate the coexistence of potentiation, low frequency fatigue (LFF) and `post-contractile depression' (PCD). The quadriceps muscle of 14 healthy men (aged 19–37 years) was studied. The results have shown, that during isometric exercise of maximal intensity there was significant (P < 0.05) decrease in P15 and P20, increase in Pt, however, MVC and P10 and P50 was unchanged (P > 0.05). LFF manifested itself most significantly which is evident from decrease in P20/P50. During recovery after work there was significant increase in LFF and decrease in P50 which is indicative of the manifestation of PCD. Besides, there was significant (P < 0.05) decrease immediately after exercise in RTP20 and RTP50, while no changes in T50 and RT. There were no significant changes (P > 0.05) however, either in RTP20 and RTP50 or in T50 and RT 20 min after exercise if compared to the initial and immediately post-exercise values.     

Nandrolone decanoate reduces changes induced by hindlimb suspension in voltage-dependent tension of rat soleus muscle

The effect of 8 weeks of nandrolone decanoate treatment (15 mg kg(-1)/week, 5 weeks under normal conditions followed by 3 weeks of unloading) was tested for the voltage-dependence of activation and steady-state inactivation of contraction in isolated small bundles (2-4 cells) of intact slow-twitch skeletal muscle in rats. Twenty-four male rats were divided into three groups (8 rats/group, weight matched) for 8 weeks: (1) control, (2) unloaded, and (3) unloaded-treated. Compared with age-matched control values (unloaded vs. control), suspension induced a shift in the isometric tension characteristics toward fast-twitch types in the soleus muscle. In contrast, nandrolone decanoate treatment of suspended animals reduced unweighting-induced atrophy in the muscle and maintained: (1) the relative amplitude of twitch tension to the maximal Ca(2+) activated in saponin-treated fibers (control: 3.6 +/- 0.4%, unloaded: 6.9 +/- 1.1% and unloaded-treated: 4.6 +/- 0.2%), (2) the time to peak tension (control: 130 +/- 18 ms, unloaded: 85 +/- 12 ms and unloaded-treated: 110 +/- 11 ms), (3) the time constant of relaxation (control: 320 +/- 12 ms, unloaded: 120 +/- 13 ms and unloaded-treated: 349 +/- 20 ms), (4) the relative amplitude of K(+) contracture tension to the maximal Ca(2+) activated in saponin-treated fibers (control: 82.9 +/- 3.1%, unloaded: 65.1 +/- 2.8%, and unloaded-treated: 91.7 +/- 1.9%), (5) the potential at 50% of the activation curve (control: -40.4 +/- 1.2 mV, unloaded: -35.5 +/- 1.6 mV, and unloaded-treated: -48.4 +/- 1.2 mV), and (6) the potential at 50% of the inactivation curve (control: 42.2 +/- 1.9 mV, unloaded: -34.5 +/- 1.1 mV, and unloaded-treated: -37.9 +/- 1.1 mV). This study clearly shows that treatment with anabolic-androgenic steroids can prevent atrophy and functional changes induced by 3 weeks of unweighting in rat skeletal muscles.     

Hindlimb suspension inhibits air-righting due to altered recruitment of neck and back muscles in rats

Effects of 9-week hindlimb suspension and 8-week recovery on air-righting reaction in response to drop from a supine position were studied in adult rats. The righting time in rats at the end of suspension (approximately 220 ms) was longer than the age-matched controls (approximately 120 ms, p <0.05). The unloading-related change in righting time was accompanied by lowered activities of electromyogram (EMG) and altered recruitment of both neck and back muscles at a specific stage of drop. After 8 weeks of reambulation, righting time recovered toward the control level (approximately 153 ms, p <0.05), but the EMG activity of back muscle was still less than controls. In contrast, the EMG of neck muscle during fall was even increased. The differences in the characteristics of the muscle fibers between two groups were minor. It is suggested that inhibition of recruitment, rather than the changes in the fiber characteristics, of neck and back muscles is one of the major causes of the slow air-righting.     

Prostaglandins in muscle regeneration

Muscle regeneration is a tightly orchestrated process where activated satellite cells (myoblasts) respond to external stimuli in order to proliferate, differentiate and fuse to damaged myofibers. Simultaneously, the injured tissue undergoes an inflammatory response and communication between leukocytes and the spectrum of differentiated and undifferentiated muscle cells is essential for proper healing. This communication is mediated by cytokines, growth factors and prostaglandins and dissecting the role of these signaling molecules might be the key to positively manipulate muscle regeneration in the future. This review will focus on the roles of prostaglandins and will consider the potential cost of using non-steroidal inflammatory drugs as popular treatment of muscle injury.     

Adaptive control for backward quadrupedal walking. II. Hindlimb muscle synergies

1. To compare the basic hindlimb synergies for backward (BWD) and forward (FWD) walking, electromyograms (EMG) were recorded from selected flexor and extensor muscles of the hip, knee, and ankle joints from four cats trained to perform both forms of walking at a moderate walking speed (0.6 m/s). For each muscle, EMG measurements included burst duration, burst latencies referenced to the time of paw contact or paw off, and integrated burst amplitudes. To relate patterns of muscle activity to various phases of the step cycle, EMG records were synchronized with kinematic data obtained by digitizing high-speed ciné film. 2. Hindlimb EMG data indicate that BWD walking in the cat was characterized by reciprocal flexor and extensor synergies similar to those for FWD walking, with flexors active during swing and extensors active during stance. Although the underlying synergies were similar, temporal parameters (burst latencies and durations) and amplitude levels for specific muscles were different for BWD and FWD walking. 3. For both directions, iliopsoas (IP) and semitendinosus (ST) were active as the hip and knee joints flexed at the onset of swing. For BWD walking, IP activity decreased early, and ST activity continued as the hip extended and the knee flexed. For FWD walking, in contrast, ST activity ceased early, and IP activity continued as the hip flexed and the knee extended. For both directions, tibialis anterior (TA) was active throughout swing as the ankle flexed and then extended. A second ST burst occurred at the end of swing for FWD walking as hip flexion and knee extension slowed for paw contact. 4. For both directions, knee extensor (vastus lateralis, VL) activity began at paw contact. Ankle extensor (lateral gastrocnemius, LG) activity began during midswing for BWD walking but just before paw contact for FWD walking. At the ankle joint, flexion during the E2 phase (yield) of stance was minimal or absent for BWD walking, and ankle extension during BWD stance was accompanied by a ramp increase in LG-EMG activity. At the knee joint, the yield was also small (or absent) for BWD walking, and increased VL-EMG amplitudes were associated with the increased range of knee extension for BWD stance. 5. Although the uniarticular hip extensor (anterior biceps femoris, ABF) was active during stance for both directions, the hip flexed during BWD stance and extended during FWD stance.(ABSTRACT TRUNCATED AT 400 WORDS)     

Skeletal muscle development and regeneration

In the late stages of muscle development, a unique cell population emerges that is a key player in postnatal muscle growth and muscle regeneration. The location of these cells next to the muscle fibers triggers their designation as satellite cells. During the healing of injured muscle tissue, satellite cells are capable of forming completely new muscle fibers or restoring damaged muscle fibers. A major problem in muscle healing is the formation of dysfunctional scar tissue, which leads to incomplete functional recovery. Therefore, the identification of factors that improve the process of muscle healing and reduce the formation of scar tissue is of great interest. Because satellite cells possess the capability of self-renewal, a unique feature of stem cells, they play a central role in the search for therapies to improve muscle healing. Growth factor-based and (satellite) cell-based therapies are being investigated to treat minor muscle injuries and intrinsic muscle defects. Major muscle injury that involves the loss of muscle tissue requires the use of scaffolds with or without (satellite) cells. Scaffolds are also being developed to generate muscle tissue in vitro. These approaches aim to restore the structure and function of the injured muscle without dysfunctional scarring.     

Muscular dystrophy and muscle regeneration

An animal model of muscular dystrophy, the dystrophic (129ReJ dy/dy) mutant mouse, was used to evaluate the regenerative phenomenon in dystrophic muscle. The effect of age on "spontaneous" regeneration (i.e., regeneration in the absence of secondary trauma) was assessed by quantitative morphometric analysis and evaluation of myosatellite cell dynamics (i.e., myosatellite cell frequency, proliferative activity, and fusion capability). Spontaneous regeneration ceased by the time the mice were 8 weeks old. The findings suggested that the small "regenerating" myofibers found in older dystrophic muscle had been formed earlier in the time course of the disease and were growth-inhibited. To determine the cause of the cessation of regeneration, dystrophic muscle was subjected to the severe trauma of whole-muscle transplantation, a trauma that results in total myofiber necrosis followed by de novo myotube formation. When young dystrophic muscle (from 4- to 6-week-old dystrophic mice) was orthotopically transplanted, the time course of degeneration-regeneration was similar to that seen in age-matched normal muscle. Moreover, the regenerated dystrophic myofibers were capable of long-term survival (200 days or longer after transplantation), and they failed to show evidence of histologic changes consistent with murine dystrophy. When older dystrophic muscle (from 17-week-old dystrophic mice), muscle that failed to display spontaneous regeneration, was transplanted, it displayed remarkable regenerative capacity. It was suggested that the cessation of spontaneous regeneration in older dystrophic murine muscle is due not to exhaustion of myosatellite cell proliferative capacity, but rather to age-related loss of the mitogenic effect of dystrophy on the myosatellite cells of dystrophic muscle.     

Towards understanding skeletal muscle regeneration

Factors which effect proliferation and fusion of muscle precursor cells have been studied extensively in tissue culture, although little is known about these events in vivo. This review assesses the tissue culture derived data with a view to understanding factors which may control the regeneration of mature skeletal muscle in vivo. The following topics are discussed in the light of recent developments in cell and molecular biology: 1) Injury and necrosis of mature skeletal muscle fibres 2) Phagocytosis of myofibre debris 3) Revascularisation of injured muscle 4) Activation and proliferation of muscle precursor cells (mpc) in vivo Identification of mpcs; Satellite cell relationships; Extracellular matrix; Growth factors; Hormones; Replication. 5) Differentiation and fusion of muscle precursor cells in vivo Differentiation; Fusion; Extracellular matrix; Cell surface molecules: Growth factors and prostaglandins 6) Myotubes and innervation.     

尾吊影响大鼠比目鱼肌Dystrophin表达分布以及血清乳酸脱氢酶活性***◆

背景：抗肌萎缩蛋白Dystrophin在肌肉运动性损伤时易发生改变。 目的：观察模拟失重效应对大鼠比目鱼肌抗肌萎缩蛋白Dystrophin表达、分布及血清乳酸脱氢酶活性的影响。 方法：采用大鼠后肢尾吊模拟失重效应模型,分别在尾吊1,4,7,10,14 d分离SD大鼠比目鱼肌并提取血清进行检测。 结果与结论：随着尾吊时间的延长,大鼠肌纤维横截面积减小;肌膜上Dystrophin呈现弥散性分布的趋势,甚至出现Dystrophin断裂现象;Dystrophin mRNA表达下降。同时尾吊7 d,大鼠血清乳酸脱氢酶活性升高。提示失重引起的肌萎缩,伴随着Dystrophin mRNA的表达下降和蛋白分布弥散性变化,而乳酸脱氢酶活性变化提示失重性肌萎缩可能与肌损伤的发生有关。关键词：肌萎缩;失重;比目鱼肌;Dystrophin;乳酸脱氢酶 doi:10.3969/j.issn.1673-8225.2012.15.036     

Skeletal muscle regeneration in young rats

The source of myotube nuclei in regeneration of skeletal muscle in young rats was studied by comparing frequencies of labeled nuclei in two experiments. In a single injury experiment, multiple injections of thymidine-H³ were given during a three day period, skeletal muscle was injured 12 days later and the rats were killed four days after injury. There were almost no labeled myotube nuclei in this experiment. In a double injury experiment, thymidine-H³ was injected two days after injury, the muscle was reinjured 12 days later, and the rats were killed four days after the second injury. Half of the myotube nuclei were radioactive and most of the centrally placed nuclei in maturing muscle fibers from the initial injury were radioactive. Since nuclei at the periphery of muscle fibers, including satellite cell nuclei, would have been labeled in both experiments, whereas myonuclei were extensively labeled only in the double injury experiment, it was concluded that the myotube nuclei were derived mainly from myonuclei.     

Bioengineered nerve regeneration and muscle reinnervation

The peripheral nervous system has the intrinsic capacity to regenerate but the reinnervation of muscles is often suboptimal and results in limited recovery of function. Injuries to nerves that innervate complex organs such as the larynx are particularly difficult to treat. The many functions of the larynx have evolved through the intricate neural regulation of highly specialized laryngeal muscles. In this review, we examine the responses of nerves and muscles to injury, focusing on changes in the expression of neurotrophic factors, and highlight differences between the skeletal limb and laryngeal muscle systems. We also describe how artificial nerve conduits have become a useful tool for delivery of neurotrophic factors as therapeutic agents to promote peripheral nerve repair and might eventually be useful in the treatment of laryngeal nerve injury.     

Axonal regeneration through acellular muscle grafts

The management of peripheral nerve injury remains a major clinical problem. Progress in this field will almost certainly depend upon manipulating the pathophysiological processes which are triggered by traumatic injuries. One of the most important determinants of functional outcome after the reconstruction of a transected peripheral nerve is the length of the gap between proximal and distal nerve stumps. Long defects (> 2 cm) must be bridged by a suitable conduit in order to support axonal regrowth. This review examines the cellular and acellular elements which facilitate axonal regrowth and the use of acellular muscle grafts in the repair of injuries in the peripheral nervous system.     

Skeletal muscle regeneration induced by chorio-allantoic grafting

To examine whether the expression pattern of fast-muscle type troponin-T (TnT) isoforms was fixed in cell lineage, breast muscle pieces (pectoralis major) from chick embryos and young and adult chickens were grafted on to chorio-allantoic membrane of 9-day-old chick embryos and cultured until the host embryos hatched out. Muscle fibre formation of the grafts was investigated by histological and immunohistochemical methods with anti-fast-muscle type and anti-slow-muscle type TnT sera, and the expression of fast-muscle type TnT in the grafts from chick embryos and young chickens was studied by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), two-dimensional SDS-PAGE, and immunoblotting. In the chorio-allantoic grafting, the breast muscle initially degenerated forming pyknotic nuclei and hyaline cytoplasm. The surviving cells, which were supposed to be satellite cells, regenerated new muscle fibres of the same type as those of the grafted muscle in respect of TnT isoform expression. Therefore, we considered that the ability to express specific isoforms of TnT was fixed in the satellite cells, and that chorio-allantoic grafting was a useful technique for studying muscle differentiation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cellular and molecular regulation of muscle regeneration

Under normal circumstances, mammalian adult skeletal muscle is a stable tissue with very little turnover of nuclei. However, upon injury, skeletal muscle has the remarkable ability to initiate a rapid and extensive repair process preventing the loss of muscle mass. Skeletal muscle repair is a highly synchronized process involving the activation of various cellular responses. The initial phase of muscle repair is characterized by necrosis of the damaged tissue and activation of an inflammatory response. This phase is rapidly followed by activation of myogenic cells to proliferate, differentiate, and fuse leading to new myofiber formation and reconstitution of a functional contractile apparatus. Activation of adult muscle satellite cells is a key element in this process. Muscle satellite cell activation resembles embryonic myogenesis in several ways including the de novo induction of the myogenic regulatory factors. Signaling factors released during the regenerating process have been identified, but their functions remain to be fully defined. In addition, recent evidence supports the possible contribution of adult stem cells in the muscle regeneration process. In particular, bone marrow-derived and muscle-derived stem cells contribute to new myofiber formation and to the satellite cell pool after injury.     

P-selectin inhibition suppresses muscle regeneration following injury

This investigation sought to determine if P-selectin-mediated mechanisms contributed to macrophage localization in damaged muscle, an essential process for muscle regeneration. Mice were injected intravenously (i.v.) with soluble P-selectin glycoprotein ligand-1 (sPSGL-1) at 5, 50, or 200 microg/mouse or with 100 microl vehicle alone, and then, lengthening contractions were induced in hindlimb plantar-flexor muscles. The contractions caused fiber damage in soleus muscles, with maximal invasion by CD11b+ mononuclear cells at 24 h post-injury and substantial accumulation of CD11b+ mononuclear cells in the extracellular matrix up to 7 days post-injury. sPSGL-1 treatment caused a dose-dependent decrease in the number of regenerating fibers (P=0.021), as determined by developmental myosin heavy chain (dMHC) expression. This expression was reduced 93% at 7 days post-injury by the highest dose of sPSGL-1, which had no significant influence on intrafiber or extracellular accumulation of cells expressing CD11b, a general marker for phagocytic cells. Additional mice were injected i.v. with 20 microg anti-P-selectin or isotype-control immunoglobulin G and were then subjected to lengthening contractions as before. At 7 days post-injury, soleus muscles from anti-P-selectin-treated mice contained 48% fewer mononuclear cells that bound ER-BMDM1 (P=0.019), a marker for mature macrophages and dendritic cells, and 84% fewer fibers expressing dMHC (P = 0.006), compared with muscles from isotype-injected, control mice. The number of CD11b+ cells was not significantly different between groups. The results are consistent with the concept that P-selectin is involved in the recruitment, maturation, and/or activation of cells that are critical for muscle fiber regeneration.     

Activity-induced fiber regeneration in rat soleus muscle

In an attempt to understand why muscle recovery is limited following atrophy due to limb immobilization, satellite cell activity and muscle fiber regeneration were analyzed in rat soleus muscles. Adult rat hindlimbs were immobilized in plaster casts for a period of two to ten weeks. Soleus muscles were examined by electron microscopy for evidence of fiber degeneration or regeneration, and to quantify satellite cell nuclei. Immunocytochemical localization of embryonic myosin was used to identify regenerating myofibers. Soleus muscle wet weight to body weight ratios for the casted muscles significantly decreased over the 10-week immobilization period. The casted muscles displayed ultrastructural evidence of minor fiber damage, including myofibrillar atrophy, Z-disc disruption, and abnormal triadic junctions. No ultrastructural evidence of regeneration was seen in the casted animals. The number of satellite cells in the casted muscles significantly decreased from 6.4% to 3. 3% by eight to 10 weeks of immobilization. Approximately 1.0% of extrafusal fibers in the control soleus muscles appeared to be regenerating since they expressed embryonic myosin and were of a small diameter, while in casted muscles, only 0.1% of the fibers were embryonic myosin-positive. Following release from immobilization, a reappearance of embryonic myosin-positive fibers was noted within four days of renewed activity. In contrast to control muscles, embryonic myosin-positive fibers in the recovery muscles included both small and large diameter fibers. Subtle changes in functional activity influence muscle damage and subsequent myofiber regeneration. Reduced activity reduces muscle fiber regeneration, while increased activity, as seen by increased hindlimb weight bearing and return to normal activity following immobilization, increase regenerating fibers and also the expression of embryonic myosin in adult fibers.     

Cardiac muscle regeneration: lessons from development

The adult human heart is an ideal target for regenerative intervention since it does not functionally restore itself after injury yet has a modest regenerative capacity that could be enhanced by innovative therapies. Adult cardiac cells with regenerative potential share gene expression signatures with early fetal progenitors that give rise to multiple cardiac cell types, suggesting that the evolutionarily conserved regulatory networks that drive embryonic heart development might also control aspects of regeneration. Here we discuss commonalities of development and regeneration, and the application of the rich developmental biology heritage to achieve therapeutic regeneration of the human heart.     

Placental perivascular cells for human muscle regeneration

Perivascular multipotent mesenchymal progenitors exist in a variety of tissues, including the placenta. Here, we suggest that the abundant vasculature present in the human placenta can serve as a source of myogenic cells to regenerate skeletal muscle. Chorionic villi dissected from the mid-gestation human placenta were first transplanted intact into the gastrocnemius muscles of SCID/mdx mice, where they participated in muscle regeneration by producing myofibers expressing human dystrophin and spectrin. In vitro-cultured placental villi released rapidly adhering and migratory CD146+CD34?CD45?CD56? cells of putative perivascular origin that expressed mesenchymal stem cell markers. CD146+CD34?CD45?CD56? perivascular cells isolated and purified from the placental villi by flow cytometry were indeed highly myogenic in culture, and generated dystrophin-positive myofibers, and they promoted angiogenesis after transplantation into SCID/mdx mouse muscles. These observations confirm the existence of mesenchymal progenitor cells within the walls of human blood vessels, and suggest that the richly vascularized human placenta is an abundant source of perivascular myogenic cells able to migrate within dystrophic muscle and regenerate myofibers.     

Wnt7a promotes muscle regeneration in branchiomeric orbicularis oris muscle

Background: The orbicularis oris muscle exhibits a deficiency in cleft lip patients. Compared with the somite-derived limb muscles, the regeneration performance of the branchiomeric orofacial muscle has seldom been investigated. Objective: This study aims to explore the possibility of augmenting the orbicularis oris muscle through the stimulus of Wnt7a. Methods: Adult rat orbicularis oris muscle and tibialis anterior muscle were injected with recombinant human Wnt7a protein. The muscles were harvested at different time points after Wnt7a delivery. Muscle regeneration-related activity, including cell proliferation, stem cell proportion, myofiber plasticity, and total fiber number, was examined. Results: Adult rat orbicularis oris muscle and tibialis anterior muscle exhibit similar regeneration-related activities after Wnt7a administration. Recombinant human Wnt7a administration resulted in enhanced cell proliferation, stem cell expansion, and fiber type remodelling in rat orbicularis oris muscle. In addition, newly formed myofibers were detected, contributing to an increased total fiber number. Conclusion: Wnt7a induces vigorous regeneration in rat orbicularis oris muscle. This study helps lay a foundation for developing biotherapies to combat orofacial muscle deficiency.