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PubMed1993

Modulation of IGF mRNA abundance during muscle denervation atrophy.

Changes in skeletal muscle activity cause dramatic alterations in muscle mass. Increased load on a muscle (synergistic overload) results in muscle hypertrophy. During hypertrophy, skeletal muscle concentrations of insulin-like growth factors (IGF-I and IGF-II) mRNAs increase. To clarify the role of IGFs in regulating muscle mass, this study examined whether IGF-I and -II mRNA levels were altered during decreased muscle activity (denervation). Gastrocnemius weights decreased 4.2%, 7.7%, 18.1%, 27.7%, 35.1%, 45.0%, and 60.3% at 2, 3, 5, 7, 10, 12, and 17 d following denervation, respectively. Muscle DNA content remained constant throughout the first 12 d after surgery, but increased above control levels at day 17. During the first week after surgery, gastrocnemius IGF-II mRNA remained constant. However, IGF-II mRNA abundance was 2.5-fold greater than controls by 10 d of denervation, 3-fold by 12 d, and 6.8-fold by 17 d. On the other hand, IGF-I mRNA levels were not affected by denervation. In conclusion, although increased muscle activity results in a change of IGF-I mRNA expression, decreased muscle activity has no effect on IGF-I mRNA expression. In contrast, IGF-II mRNA levels increase with long-term denervation as well as with increased muscle activity. This study suggests that muscle activity may not be the only factor affecting IGF-I and -II expression.

Animals↗
PubMed1987

Effects of low and high frequency patterns of stimulation on contractile properties, enzyme activities and myosin light chain accumulation in slow and fast denervated muscles of the chicken.

The effects of denervation and direct stimulation in fast and slow latissimus dorsii muscles were investigated in chicken. In slow ALD muscle, denervation resulted in an incompleteness of the relaxation, a decrease in MDH and CPK activities and an increase in fast myosin light chains (MLC) accumulation. Direct stimulation at either fast or slow rhythm prevented the effects of denervation on relaxation and CPK activity but was ineffective on MDH activity and fast MLC accumulation. Moreover, direct stimulation of denervated ALD caused rhythm-dependent change in tetanic contraction. In fast PLD muscle, the main changes in muscle properties following denervation were a slowing down of the time course of the twitch and an incompleteness of the relaxation, a decrease in LDH and CPK activities and in LC3F accumulation. Stimulation at a high frequency partly prevented the effects of denervation and resulted in a large accumulation of LC3F, while a low frequency stimulation did not restore the twitch time to peak, increased MDH activity and induced synthesis of slow MLC. This study emphasizes the role of muscle activity and its pattern in some properties of slow and fast chicken muscles following denervation.

Animals↗
PubMed2005

Differentiation of activated satellite cells in denervated muscle following single fusions in situ and in cell culture.

Satellite cells represent a cellular source of regeneration in adult skeletal muscle. It remains unclear why a large pool of stem myoblasts in denervated muscle does not compensate for the loss of muscle mass during post-denervation atrophy. In this study, we present evidence that satellite cells in long-term denervated rat muscle are able to activate synthesis of contractile proteins after single fusions in situ. This process of early differentiation leads to formation of abnormally diminutive myotubes. The localization of such dwarf myotubes beneath the intact basal lamina on the surface of differentiated muscle fibers shows that they form by fusion of neighboring satellites or by the progeny of a single satellite cell following one or two mitotic divisions. We demonstrated single fusions of myoblasts using electron microscopy, immunocytochemical labeling and high resolution confocal digital imaging. Sequestration of nascent myotubes by the rapidly forming basal laminae creates a barrier that limits further fusions. The recruitment of satellite cells in the formation of new muscle fibers results in a progressive decrease in their local densities, spatial separation and ultimate exhaustion of the myogenic cell pool. To determine whether the accumulation of aberrant dwarf myotubes is explained by the intrinsic decline of myogenic properties of satellite cells, or depends on their spatial separation and the environment in the tissue, we studied the fusion of myoblasts isolated from normal and denervated muscle in cell culture. The experiments with a culture system demonstrated that the capacity of myoblasts to synthesize contractile proteins without serial fusions depended on cell density and the availability of partners for fusion. Satellite cells isolated from denervated muscle and plated at fusion-permissive densities progressed through the myogenic program and actively formed myotubes, which shows that their myogenic potential is not considerably impaired. The results of this study suggest that under conditions of denervation, progressive spatial separation and confinement of many satellite cells within the endomysial tubes of atrophic muscle fibers and progressive interstitial fibrosis are the important factors that prevent their normal differentiation. Our findings also provide an explanation of why denervated muscle partially and temporarily is able to restore its functional capacity following injury and regeneration: the release of satellite cells from their sublaminal location provides the necessary space for a more active regenerative process.

Animals↗
PubMed1984

Effect of nerve extract on number of acetylcholine receptors in denervated muscles of rats.

We have shown elsewhere that injection of an extract of peripheral nerves reduces the atrophy of denervated muscle fibers in vivo. Denervated muscle fibers exhibit supersensitivity to acetylcholine owing to the production of extrajunctional acetylcholine receptors. We sought to determine whether or not injection of nerve extract can influence the numbers of acetylcholine receptors in normal, immobilized, or denervated extensor digitorum longus muscles of rats. The receptors were assayed by measuring the binding of 125I-alpha-bungarotoxin. Normally innervated muscles injected with nerve extract exhibited slightly increased binding of the toxin, but this was due to the injections per se. Immobilization caused a small, transient increase in binding of alpha-bungarotoxin, whereas denervated muscles bound considerably more toxin than innervated controls. The nerve extract did not reduce or prevent the increase in acetylcholine receptors caused by denervation but instead caused an even greater increase. We concluded that the neurotrophic factor extracted from peripheral nerve that is responsible for the maintenance of the sizes of the fibers probably does not down-regulate extrajunctional acetylcholine receptors. The limitation of acetylcholine receptors to the end-plate regions is probably effected by a different mechanism which has yet to be elucidated.

Acetylcholine↗
PubMed1992

Effect of electrostimulation on denervated muscle.

The influence of electrostimulation on denervated and reinnervated muscle was investigated. First, the left peroneal nerve was severed in rats. Wet weight and muscle fiber diameter of denervated anterior tibial muscle was compared as a percentage of contralateral muscle in stimulated and non-stimulated rats. In a second experiment, four weeks after the peroneal nerve was severed, the tibial nerve was cross-sutured to the distal stump of the peroneal nerve. Electrostimulation was continued in rats that had electrostimulation before nerve-crossing. Recovery of wet weight was assessed at eight weeks and at one year after nerve-crossing. The mean decrease in weight and fiber diameter of the denervated muscle was significantly less in the group that was electrostimulated for eight weeks. Recovery of weight of reinnervated muscle was significantly better in the electrostimulated group. Electrostimulation of denervated muscle retarded denervation atrophy and improved recovery after reinnervation.

Animals↗
PubMed1998

Electrophysiologic evaluation of denervated muscles in incomplete paraplegia using macro electromyography.

OBJECTIVE: To evaluate denervated muscles in persons with incomplete paraplegia due to thoracolumbar spinal injury (TLSI) using macro electromyography in determining indications for functional electrical stimulation (FES). DESIGN: A randomized clinical trial and a criterion standard. SETTING: A department of orthopedic surgery in a university hospital. PATIENTS AND OTHER PARTICIPANTS: Eighteen patients with incomplete paraplegia, including 11 with TSLI, and 50 healthy adults. INTERVENTION: Area and amplitude of macro motor unit potential (macro MUP) were measured at the tibialis anterior, the vastus lateralis, and the vastus medialis. The normal limits of macro MUP parameters were defined based on values from healthy subjects. Abnormal denervated muscles were detected by macro EMG and conventional EMG in paralytic patients. The correlation between macro MUP parameter values and muscle forces of the tibialis anterior and quadriceps femoris induced by electrical stimulation was analyzed. MAIN OUTCOME MEASURES: The number of abnormal muscles, parameter values, and muscle force induced by electrical stimulation. RESULTS: Abnormal muscles were found only in the TLSI patients and 13 abnormal muscles were detected by macro EMG only. The abnormal muscles defined by macro EMG showed insufficient contraction induced by electrical stimulation. The increase of parameter value negatively correlated with the muscle force (tibialis anterior area r=-.797, amplitude r=-.866; quadriceps area r=-.866, amplitude r=-.893; p < .001). CONCLUSIONS: These results suggest that macro EMG is useful in detecting denervated muscles, in determining indications for FES, and in predicting FES effects before implantation of electrodes.

Adolescent↗
PubMed1975

Macromolecular characterization of muscle membranes. Endogenous membrane kinase and phosphorylated protein substrate from normal and denervated muscle.

Light density membranes derived from the "microsomal" fraction of rat skeletal muscle contained an endogenous protein kinase which catalyzed the phosphorylation of an endogenous membrane substrate. No other membrane fraction contained any significant protein kinase activity. The optimal specific activity of the enzyme in these membranes was 350 pmol/mg/min. The endogenous muscle membrane protein kinase required magnesium, was stimulated by micromolar concentrations of calcium, had a pH optimum between 7.0 and 7.5, and demonstrated a K-m for ATP of 2.6 times 10 minus 5 M. The enzyme was markedly heat labile and demonstrated a linear Arrhenius plot with an apparent energy of activation of 12,100 cal/mol. There was no stimulation by cyclic nucleotides; and neither monovalent cations nor various neurotransmitters exerted any effect. It is presently unclear where the membranes exhibiting protein phosphorylation are localized within the muscle fiber. Enzyme markers suggest that these membranes are not derived from sarcolemma or sarcoplasmic reticulum but may originate in transverse tubules. The membrane phosphorylation was largely confined to a polypeptide with an apparent molecular weight of 28,000. Phosphorylation could also be detected in a lower molecular weight substrate as well as two polypeptides with apparent molecular weights of 95,000 and 56,000. The M-r-28,000 endogenous protein kinase substrate was isolated by preparative gel electrophoresis in sodium dodecyl sulfate. High voltage electrophoresis of a partial acid hydrolysate of the phosphorylated M-r-28,000 substrate identified the phosphate bond to be that of phosphoserine. The amino acid composition of the substrate was neither strongly acidic nor basic. It had a high content of glycine, glutamic acid, serine, and lysine. Hydrophobic residues constituted only 45% of the total composition. Following muscle denervation for 10 days, there was a significant decrease in the amount of the M-r-28,000 polypeptide as well as the extent of phosphorylation.

Animals↗
PubMed1988

Resistance of protein and glucose metabolism to insulin in denervated rat muscle.

Denervated (1-10 days) rat epitrochlearis muscles were isolated, and basal and insulin-stimulated protein and glucose metabolism were studied. Although basal rates of glycolysis and glucose transport were increased in 1-10-day-denervated muscles, basal glycogen-synthesis rates were unaltered and glycogen concentrations were decreased. Basal rates of protein degradation and synthesis were increased in 1-10-day-denervated muscles. The increase in degradation was greater than that in synthesis, resulting in muscle atrophy. Increased rates of proteolysis and glycolysis were accompanied by elevated release rates of leucine, alanine, glutamate, pyruvate and lactate from 3-10-day-denervated muscles. ATP and phosphocreatine were decreased in 3-10-day-denervated muscles. Insulin resistance of glycogen synthesis occurred in 1-10-day denervated muscles. Insulin-stimulated glycolysis and glucose transport were inhibited by day 3 of denervation, and recovered by day 10. Inhibition of insulin-stimulated protein synthesis was observed only in 3-day-denervated muscles, whereas regulation by insulin of net proteolysis was unaffected in 1-10-day-denervated muscles. Thus the results demonstrate enhanced glycolysis, proteolysis and protein synthesis, and decreased energy stores, in denervated muscle. They further suggest a defect in insulin's action on protein synthesis in denervated muscles as well as on glucose metabolism. However, the lack of concurrent changes in all insulin-sensitive pathways and the absence of insulin-resistance for proteolysis suggest multiple and specific cellular defects in insulin's action in denervated muscle.

Adenosine Triphosphate↗
PubMed1989

Continuous electromyographic recordings of pharyngeal muscle activity in normal and previously denervated muscles in dogs.

Continuous electromyographic recordings of pharyngeal muscle activity were made in 5 clinically normal control dogs and in 7 dogs 3 years after partial denervation of the pharyngeal muscles. Electromyographic recordings were made of the sequence of actions of each muscle and of the combined muscle activity, at rest and during swallowing of food. During 30-second periods, the recordings were digitalized and stored on diskette for further analysis. All control dogs had a distinct pattern of muscle activity during swallowing, the onset being in a constant order (hyopharyngeal, thyropharyngeal, and cricopharyngeal) and bilaterally synchronous. While eating, each dog had about 5 to 12 short periods of synchronous activity in each muscle, between the swallowing actions. During the resting period, there were longer periods of activity, which were synchronous with respiration. In each denervated dog, there were normal and irregular swallowing actions. Swallowing activity was recognized, but the sequence of hyopharyngeal, thyropharyngeal, and cricopharyngeal muscle activity was irregular and different from that in control dogs. Partial denervation of the pharyngeal muscles does not seriously impair motor activity of the muscles, but does alter the sequence of activity in the pharyngeal muscles during swallowing.

Animals↗
PubMed1997

Muscle apoptosis in humans occurs in normal and denervated muscle, but not in myotonic dystrophy, dystrophinopathies or inflammatory disease.

Recent data suggest that death of muscle cells during development and in selected pathological conditions occurs via apoptosis. We investigated the occurrence of apoptosis in normal and pathological human skeletal muscle, using in situ end-labeling (ISEL) to detect DNA fragmentation, and immunohistochemistry for the expression of tissue transglutaminase and interleukin-1beta-converting enzyme (ICE)-like proteases. In normal subjects, apoptotic myonuclei were occasionally observed as evidence of normal tissue turnover. Myonuclear apoptosis due to a deficit of trophic support from nerve cells also occurred in spinal muscular atrophies. No apoptosis of muscle cells was found in dystrophinopathies, myotonic dystrophy and inflammatory myopathies, suggesting that death of myofibers in those conditions is not due to activation of a gene-directed program of death. In dystrophinopathies and inflammatory myopathies, apoptosis was found in interstitial mononuclear cells, as a likely mechanism of clearance of the inflammatory infiltrates.

Adolescent↗
PubMed1996

Electrical stimulation of denervated muscle: is it worthwhile?

Research conducted over the past 25 years has demonstrated that muscle activity, not neurotrophic substances, is the most important factor in the regulation of specific physiological and biochemical properties of muscle fibers. Application of this knowledge has led to considerable experimentation with chronic electrical stimulation as a possible clinical tool for the treatment of denervated muscles. Evidence accumulated from animal studies has indicated that direct electrical stimulation of denervated muscles can to a large extent substitute for innervation and preserve or restore the normal properties of the muscles. Appropriate stimulation parameters were critical for a successful intervention, and the best results were obtained when the stimulation pattern resembled the firing pattern of the normal motoneuron. Thus, fast muscles required intermittent, brief, high frequency stimulation and slow muscles needed continuous, low frequency stimulation. For human denervated muscles, critical questions still remain to be resolved before electrical stimulation will yield the optimum benefit. Research must be performed in human subjects to define the appropriate stimulation parameters the stimulation current, and the type and placement of electrodes.

Animals↗
PubMed2005

Effect of systemic creatine monohydrate supplementation on denervated muscle during reinnervation: experimental study in the rat.

The purpose of this experimental study was to evaluate possible upgrading effects of systemic creatine monohydrate administration on the reinnervation of denervated muscle. At the same time, the protective effect of the agent on denervated muscle until ultimate reinnervation after nerve repair was quantified. The functional outcome of muscle reinnervation after creatine monohydrate application was compared with a control group. Forty adult Wistar rats weighing 180 to 220 g were used. The right sciatic nerve was dissected, exposed, and cut at the level of the midthigh in all rats. The experimental design consisted of two groups: experimental (animals were fed creatine monohydrate) and control (gavage feeding was provided by saline). Both groups were divided into two subgroups: subgroups A and B for the experimental group, and subgroups C and D for the control group. In subgroups A and C, the nerves were repaired with four 10-0 epineurial stitches. In subgroups B and D, both the proximal and distal ends of the nerves were ligated and no neural anastomosis was performed. In the experimental groups (subgroups A and B), the rats were fed by daily supplementation of oral creatine monohydrate, 300 mg/kg body weight. In the controls (subgroups C and D), oral supplementation was provided by saline. Functional recovery was evaluated using walking track analysis, pinching test, and limb circumference and toe contracture measurements at the end of 6 months, after which the rats were sacrificed and nerve specimens from both ends of the repair sites and the whole gastrocnemius muscle were obtained to document the results of the histomorphometric and histochemical studies, including light microscopic examinations and muscle weight measurements. The mean functional recovery values in subgroups A, B, C, and D were 91 percent, 80 percent, 87 percent, and 59 percent, respectively. Functional recovery improved significantly in the experimental groups (in both the surgically repaired and unrepaired subgroups), compared with the control groups (p<0.05). The pinching test revealed a statistically significant difference in nerve conduction between the experimental and control groups (p<0.05). The limb circumference ratio of the surgically treated side to the untouched side in subgroups A, B, C, and D were noted as 0.95, 0.89, 0.91, and 0.87, respectively, and the difference between the experimental and the control groups was statistically significant (p<0.05). The differences between subgroups A and B, C and D, A and C, and B and D were also significant. The surgically repaired and creatine-supplemented subgroups demonstrated the best results in toe contracture index. The muscle weight measurement results were concordant with the results of the limb circumference ratio. In both surgically repaired subgroups (subgroups A and C), there were qualitatively significant amounts of myelinated fibers in the nerve distal to the anastomotic site; there were no myelinated fibers in the distal stumps of subgroups B and D. Histochemical analyses of the contents of the muscle fiber types also revealed no significant difference. Overall, the results showed the useful effect of oral creatine supplementation on both surgically repaired and unrepaired nerve injuries. The best results were obtained from surgically repaired nerve injuries and also from the systemic creatine-supplemented subgroups. This study confirms that systemic administration of creatine monohydrate has a protective and upgrading effect on the functional properties of denervated muscle, especially in surgically reinnervated subjects.

Animals↗
PubMed1988

[Polymorphism of acetylcholinesterase and myosin during development of fast and slow muscles denervated in the newborn rabbit].

The rabbit Semimembranosus proprius (SMp) and Semimembranosus accessorius (SMa) muscles represent good models for studying the transformations of muscle properties during postnatal differentiation. In the adult, these muscles are homogeneous in slow twitch (SMp) and fast twitch (SMa) fibers, respectively. However, they are heterogeneous at birth and express their adult characteristics from two months onwards. During this period we studied the influence of motor innervation on the development of their properties, particularly at the level of acetylcholinesterase (AChE) molecular forms and myosin slow (LCs) and fast (LCf) light chains. The postnatal alteration of SMa and SMp muscles was characterized by the disappearance of the neonatal heterogeneity and the acquisition of the homogeneous fast or slow fiber type pattern. The fibers of these muscles denervated at birth were altered differently: dramatic atrophy of fast twitch fibers whatever the muscles studied, preservation of SMp slow twitch fiber characteristics and fatty degeneration of SMa. At birth, both muscles presented a similar pattern of myosin fast and slow LC. In control muscles, the alteration of fiber populations to homogeneous types led to the disappearance of supernumerary chains from 15 days onwards. In the slow muscle, neonatal denervation prevented LCf disappearance. In the fast muscle, denervation influenced essentially the installation of LCf which was delayed by 15 days. At birth, the polymorphism of AChE was similar in SMp and SMa muscles. One month after denervation, the specific activity of AChE was twice that of the control. Its polymorphism was not much disturbed, while in the adult denervation induced a large increase in AChE specific activity (x 10) and particularly a great alteration in its polymorphism according to the fast or slow muscle fiber types.

Acetylcholinesterase↗
PubMed1988

[An experimental study on denervated muscle atrophy--effect of electrostimulation and comparison with immobilization muscle atrophy].

The efficacy of causing muscle atrophy was compared among denervation, arthrodesis and tenotomy in rat anterior tibial muscle. Reduction of wet weight was most pronounced in denervated muscle and least in arthrodesed muscle. Histochemical investigation by ATPase stain revealed that atrophy of Type 1 and Type 2 fiber was more severe in denervated muscle group than in the other two groups. Type 2 fiber atrophy was dominant in denervated muscle and in arthrodesed muscle. Type 1 fiber atrophy was dominant in tenotomized muscle. The effect of electrostimulation on denervated muscle was investigated. Electrostimulation significantly reduced the degree of denervation atrophy. Four weeks after severance of peroneal nerve, tibial nerve-crossing was done and electrostimulation was continued for eight weeks. Recovery of wet weight of re-innervated muscle with electrostimulation was significantly better than that without electrostimulation. Electrostimulation applied to denervated muscle reduced the progress of atrophy and improved the recovery after nerve repair.

Animals↗
PubMed2000

The adaptive response of transforming growth factor-beta 2 and -beta RII in the overloaded, regenerating and denervated muscles of rats.

Using a muscle cell line and satellite cell cultures, it has been shown that transforming growth factor-beta (TGF-beta) has a powerful inhibitory effect on myoblast replication and differentiation. However, little work has been done on the possible role of TGF-beta in adult muscle in vivo. Using Western blot and immunohistochemical analyses, we investigated normal distribution of TGF-beta 2 and TGF-beta RII proteins between slow and fast-type muscles, and the adaptive response of these proteins in the mechanically overloaded muscles, in the regenerating muscles following bupivacaine injection and in the denervated muscle after section of sciatic nerve. Slight TGF-beta 2 immunoreactivity was detected both in slow- and fast-type muscles of mature rat. The amount of TGF-beta RII protein was markedly greater in fast-type muscles. In the overloaded muscle, immunohistochemical analysis showed a marked increase in TGF-beta 2 immunoreactivity in the mononuclear cells (probably endothelial and perithelial or smooth muscle cells of endomysial capillaries) of the extracellular space at 3 and 6 days post surgery. Rapid increase of TGF-beta 2 protein and concomitant decrease of the receptor (TGF-beta RII) were observed in the mechanically overloaded and regenerating muscles. On the other hand, denervation of slow- and fast-type muscles showed a rapid increase in TGF-beta 2 protein, but did not elicit a concomitant decrease of TGF-beta RII. These results indicate that TGF-beta RII is preferentially distributed in fast-type muscles. Furthermore, TGF-beta 2 may play an important role in muscle hypertrophy and regeneration by the usage of TGF-beta RII.

Animals↗
PubMed1986

Difference in the ability of neonatal and adult denervated muscle to accumulate acetylcholinesterase at the old sites of innervation.

In adult rat sternocleidomastoid muscle, AChE is concentrated in the region rich in motor end-plates (MEP). All major AChE forms, "16 S," "10 S," and "4 S," are accumulated at high levels, and not only "16 S" AChE. After denervation, muscle AChE decreases; 2 weeks after denervation, low levels (20-40% of control) are reached for all forms. During the following weeks, a slow but steady increase in "10 S" and "16 S" AChE occurs in the denervated muscle. At this stage, all forms are again observed to be highly concentrated in the region containing the old sites of innervation. Thus, in adult rat muscle the structures able to accumulate "16 S," "10 S," and "4 S" AChE in the MEP-rich regions remain several months after denervation. In normal young rat sternocleidomastoid muscle at birth, all AChE forms are already accumulated in the MEP-rich region. After denervation at birth, the denervated muscle loses its ability to keep a high concentration of "4 S," "10 S," and "16 S" AChE in the old MEP-rich region. All AChE forms are still present 1 month after denervation, but they are decreased and diffusedly distributed over the whole length of the muscle. In particular, "16 S" AChE is detected in the same proportion (10-15%) all along the denervated muscle. Thus, the diffuse distribution of AChE, and especially "16 S" AChE, after neonatal denervation, contrasts with the maintained accumulation observed in adult denervated muscle. It seems that denervation of young muscle results in a specific loss of the muscle ability to concentrate high levels of all AChE forms at the old sites of innervation.

Acetylcholinesterase↗
PubMed1975

Localization of the acetylcholine receptors in denervated muscles of rats.

ACh contractures of denervated lumbricalis muscles of rats were washed in Tris-methanesulfonate solutions and in sucrose solutions. The peak tension was diminished by about 80% following a 30 min exposure to solutions containing 400-600 mM glycerol when Tris solutions were used in the testing period, and by about 50% when sucrose solutions were used. The amplitude of the membrane potential changes provoked by ACh was decreased by about 36% following the glycerol treatment. The treatment had no effect on the ACh-induced 45Ca uptake of muscles. Electron microscopy of the glycerol-treated muscles showed widespread vacuolization apparently originating from swelling and disruption of the T system. It was concluded that ACh receptors which arise in the muscle membrane following nerve section are distributed in the external surface membrane and in the membranes of the T system.

Acetylcholine↗
PubMed2004

M-cadherin transcription in satellite cells from normal and denervated muscle.

Satellite cells (SC) in adult muscle are quiescent in the G0 phase of the cell cycle. In the present study we determined whether SC after denervation upregulate M-cadherin, an adhesion molecule that is upregulated with differentiation and fusion. We also monitored primary cultures of SC from denervated muscle for expression of the transcription factors of the MyoD family to determine whether SC from denervated muscle can be activated in vitro. Hindlimb muscles of rats were denervated under anesthesia, and rats were killed after 2-28 days. The SC of the denervated limbs were pooled and either assessed for M-cadherin mRNA by using real-time RT-PCR or cultured in vitro. The cultures were processed for RT-PCR or immunofluorescence for expression of the transcription factors of the MyoD family. Hindlimb muscles of M-cadherin knockout mice were denervated under anesthesia, mice were killed after 2-28 days, and cells were stained for beta-galactosidase activity by X-gal histochemistry. In vitro, primary SC cultures from rat muscle denervated for 2-28 days expressed transcripts of myf5, MyoD, myogenin, and MRF4 as SC from normal innervated muscle. In vivo, M-cadherin transcription was not upregulated in SC from denervated rat muscle when compared with normal muscle. Moreover, beta-galactosidase activity was not detected in denervated mouse muscle. The finding that SC do not upregulate M-cadherin after denervation supports the notion that they remain in the G(0) phase of the cell cycle in vivo. However, the cells retain the capacity to pass through the proliferative and differentiative program when robustly stimulated to do so in vitro.

Animals↗