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Find video protocols related to scientific articles indexed in Pubmed.
The growth-promoting activity of egg white proteins in the C2C12 myoblast cell line.
Anim. Sci. J.
PUBLISHED: 09-03-2014
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In this study, we examined the effects of several egg white proteins (ovalbumin, ovomucoid, ovotransferrin and lysozyme) on proliferation and myotube growth in C2C12 murine myoblast cells. Cell proliferation was measured using a water-soluble tetrazolium salt (WST-8)-based assay and then validated using Giemsa staining. Significant proliferative activities of C2C12 cells were observed in response to the addition of 10(-5) -10(-4) ?mol/L ovalbumin or ovomucoid. Ovotransferrin decreased C2C12 cell proliferation and lysozyme showed no significant effects on the proliferation of C2C12 cells. In contrast, the proliferative effects of ovalbumin and ovomucoid were not observed in 3T3-L1 murine preadipocyte cells. We also measured the effects of ovalbumin and ovomucoid on C2C12 myotube diameters by using histological analysis. In comparison to control cells, myotube diameters were significantly increased in cells cultured in 10(-6) -10(-4) ?mol/L ovalbumin or ovomucoid, suggesting that ovalbumin and ovomucoid stimulate the growth of myotubes. Thus, our results clearly demonstrated that ovalbumin or ovomucoid stimulated the proliferation of myoblasts and growth of myotubes.
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Supplementary immunocytochemistry of hepatocyte growth factor production in activated macrophages early in muscle regeneration.
Anim. Sci. J.
PUBLISHED: 09-03-2014
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Regenerative intramuscular motor-innervation is thought to reside in the spatiotemporal expression of axon-guidance molecules. Our previous studies showed that resident myogenic stem cells, satellite cells, up-regulate a secreted neural-chemorepellent semaphorin 3A (Sema3A) during the early-differentiation period, in response to hepatocyte growth factor (HGF) elevated in injured muscle. However, a paracrine source of the HGF release is still unknown. Very recently, we proposed a possible contribution of anti-inflammatory macrophages (CD206-positive M2) by showing that M2 cells infiltrate predominantly at the early-differentiation phase (3-5 days post-injury) and produce/secrete large amounts of HGF. However, in understanding this concept there still remains a critical need to examine if phagocytotic pro-inflammatory macrophages (CD86-positive M1), another activated-phenotype still present at the early-differentiation phase concerned, produce HGF upon muscle injury. The current immunocytochemical study demonstrated that the HGF expression is negative for M1 prepared from cardiotoxin-injured Tibialis anterior muscle at day 5, in contrast to the intense fluorescent-signal of M2 served as a positive control. This supplementary result advances our understanding of a spatiotemporal burst of HGF secretion from M2 populations (not M1) to impact Sema3A expression, which ensures a coordinated delay in attachment of motoneuron terminals onto damaged and generating fibers during the early phase of muscle regeneration.
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Implication of anti-inflammatory macrophages in regenerative moto-neuritogenesis: promotion of myoblast migration and neural chemorepellent semaphorin 3A expression in injured muscle.
Int. J. Biochem. Cell Biol.
PUBLISHED: 01-15-2014
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Regenerative mechanisms that regulate intramuscular motor innervation are thought to reside in the spatiotemporal expression of axon-guidance molecules. Our previous studies proposed a heretofore unexplored role of resident myogenic stem cell (satellite cell)-derived myoblasts as a key presenter of a secreted neural chemorepellent semaphorin 3A (Sema3A); hepatocyte growth factor (HGF) triggered its expression exclusively at the early-differentiation phase. In order to verify this concept, the present study was designed to clarify a paracrine source of HGF release. In vitro experiments demonstrated that activated anti-inflammatory macrophages (CD206-positive M2) produce HGF and thereby promote myoblast chemoattraction and Sema3A expression. Media from pro-inflammatory macrophage cultures (M1) did not show any significant effect. M2 also enhanced the expression of myoblast-differentiation markers in culture, and infiltrated predominantly at the early-differentiation phase (3-5 days post-injury); M2 were confirmed to produce HGF as monitored by in vivo/ex vivo immunocytochemistry of CD11b/CD206/HGF-positive cells and by HGF in situ hybridization of cardiotoxin- or crush-injured tibialis anterior muscle, respectively. These studies advance our understanding of the stage-specific activation of Sema3A expression signaling. Findings, therefore, encourage the idea that M2 contribute to spatiotemporal up-regulation of extracellular Sema3A concentrations by producing HGF that, in turn, stimulates a burst of Sema3A secretion by myoblasts that are recruited to site of injury. This model may ensure a coordinated delay in re-attachment of motoneuron terminals onto damaged fibers early in muscle regeneration, and thus synchronize the recovery of muscle-fiber integrity and the early resolution of inflammation after injury.
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Effect of dietary fat type on anxiety-like and depression-like behavior in mice.
Springerplus
PUBLISHED: 12-01-2013
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Dietary fat plays an important role in higher brain functions. We aimed to assess the short and long term intake of three different types of dietary fat (soybean oil, lard, and fish oil) on anxiety-like and depression-like behavior in mice. For the short term intake assessment, a behavioral test battery for anxiety and depression was carried out for a 3-day feeding period. For the long term intake assessment, a behavioral test battery began after the 4-week feeding period. During the short term intake, the time spent in the open arms of the elevated plus-maze was the longest in the fish oil fed group, followed by the soybean oil and lard-fed groups. The elevated plus-maze is a common animal model to assess anxiety, in which an increased time spent in the open arms indicates an anxiolytic effect. The difference between the fish oil-fed group and lard-fed group was statistically significant (p < 0.01), but there was no significant difference between the soybean oil-fed group and the other two groups. Similar results were observed after a 4-week feeding period. On the other hand, there was no significant difference among the three groups in behavior tests to evaluate depression. Thus, the dietary fat types appeared to influence anxiety but not depression in mice, both in short term (3 days) and long term (4 weeks) feeding.
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Effect of 48-h food deprivation on the expressions of myosin heavy-chain isoforms and fiber type-related factors in rats.
J. Nutr. Sci. Vitaminol.
PUBLISHED: 09-26-2013
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The primary aim of this study was to examine the effects of 48-h food deprivation on rat skeletal muscle fiber type, according to myosin heavy-chain (MyHC) isoform composition and some metabolism-related factors in both slow-type dominant and fast-type dominant muscle tissues. Male Wistar rats (7 wk old) were treated with 48-h food deprivation or ad libitum feeding as control. After the treatment, the soleus muscle (slow-type dominant) and the extensor digitorum longus (EDL, fast-type dominant) were excised. We found that 48-h food deprivation did not affect MyHC composition in either the soleus or EDL, compared with fed rats by electrophoretic separation of MyHC isoforms. However, 48-h food deprivation significantly increased the mRNA expression of fast-type MyHC2B in the EDL muscle. Moreover, food deprivation increased fatty acid metabolism, as shown by elevated levels of related serum energy substrates and mRNA expression of mitochondrial uncoupling protein (UCP) 3 and lipoprotein lipase (LPL) in both the soleus and EDL. UCP3 and LPL are generally expressed at higher levels in slow-type fibers. Furthermore, we found that food deprivation significantly decreased the protein amounts of PGC1? and phosphorylated FOXO1, which are known as skeletal muscle fiber type regulators. In conclusion, 48-h food deprivation increased mRNA expression of fast-type MyHC isoform and oxidative metabolism-related factors in EDL, whereas MyHC composition at the protein level did not change in either the soleus or EDL.
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Cold exposure increases slow-type myosin heavy chain 1 (MyHC1) composition of soleus muscle in rats.
Anim. Sci. J.
PUBLISHED: 05-16-2013
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The aim of this study was to examine the effects of cold exposure on rat skeletal muscle fiber type, according to myosin heavy chain (MyHC) isoform and metabolism-related factors. Male Wistar rats (7 weeks old) were housed individually at 4?±?2°C as a cold-exposed group or at room temperature (22?±?2°C) as a control group for 4 weeks. We found that cold exposure significantly increased the slow-type MyHC1 content in the soleus muscle (a typical slow-type fiber), while the intermediate-type MyHC2A content was significantly decreased. In contrast to soleus, MyHC composition of extensor digitorum longus (EDL, a typical fast-type fiber) and gastrocnemius (a mix of slow-type and fast-type fibers) muscle did not change from cold exposure. Cold exposure increased mRNA expression of mitochondrial uncoupling protein 3 (UCP3) in both the soleus and EDL. Cold exposure also increased mRNA expression of myoglobin, peroxisome proliferator-activated receptor gamma coactivator 1? (PGC1?) and forkhead box O1 (FOXO1) in the soleus. Upregulation of UCP3 and PGC1? proteins were observed with Western blotting in the gastrocnemius. Thus, cold exposure increased metabolism-related factors in all muscle types that were tested, but MyHC isoforms changed only in the soleus.
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Preliminary time-course study of antiinflammatory macrophage infiltration in crush-injured skeletal muscle.
Anim. Sci. J.
PUBLISHED: 05-16-2013
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Muscle damage induces massive macrophage infiltration of the injury site, in which activated pro-inflammatory and anti-inflammatory phenotypes (currently classified as M1 and M2, respectively) have been documented as distinct functional populations predominant at different times after the conventional acute injury by intramuscular injection of snake venoms (cardiotoxin, notexin) or chemicals (bupivacaine hydrochloride, barium chloride). The present study employed a muscle-crush injury model that may better reflect the physiologic damage and repair processes initiated by contusing a gastrocnemius muscle in the lower hind-limb of adult mice with hemostat forceps, and examined the time-course invasion of M1 and M2 macrophages during muscle regeneration by immunocytochemistry of CD197 and CD206 marker proteins. CD197-positive M1 macrophages were observed exclusively at 1-4 days after crush followed by the alternative prevalence of CD206-positive M2 at 7 days of myogenic differentiation, characterized by increasing levels of myogenin messenger RNA expression. Preliminary PCR analysis showed that M2 may produce hepatocyte growth factor (HGF) in culture, providing additional benefit to understanding that M2 populations actively promote regenerative myogenesis (muscle fiber repair) and moto-neuritogenesis (re-attachment of motoneuron terminals onto damaged fibers) through their time-specific infiltration and release of growth factor at the injury site early in muscle regeneration.
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Dietary fat influences the expression of contractile and metabolic genes in rat skeletal muscle.
PLoS ONE
PUBLISHED: 01-01-2013
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Dietary fat plays a major role in obesity, lipid metabolism, and cardiovascular diseases. To determine whether the intake of different types of dietary fats affect the muscle fiber types that govern the metabolic and contractile properties of the skeletal muscle, we fed male Wistar rats with a 15% fat diet derived from different fat sources. Diets composed of soybean oil (n-6 polyunsaturated fatty acids (PUFA)-rich), fish oil (n-3 PUFA-rich), or lard (low in PUFAs) were administered to the rats for 4 weeks. Myosin heavy chain (MyHC) isoforms were used as biomarkers to delineate the skeletal muscle fiber types. Compared with soybean oil intake, fish oil intake showed significantly lower levels of the fast-type MyHC2B and higher levels of the intermediate-type MyHC2X composition in the extensor digitorum longus (EDL) muscle, which is a fast-type dominant muscle. Concomitantly, MyHC2X mRNA levels in fish oil-fed rats were significantly higher than those observed in the soybean oil-fed rats. The MyHC isoform composition in the lard-fed rats was an intermediate between that of the fish oil and soybean oil-fed rats. Mitochondrial uncoupling protein 3, pyruvate dehydrogenase kinase 4, and porin mRNA showed significantly upregulated levels in the EDL of fish oil-fed rats compared to those observed in soybean oil-fed and lard-fed rats, implying an activation of oxidative metabolism. In contrast, no changes in the composition of MyHC isoforms was observed in the soleus muscle, which is a slow-type dominant muscle. Fatty acid composition in the serum and the muscle was significantly influenced by the type of dietary fat consumed. In conclusion, dietary fat affects the expression of genes related to the contractile and metabolic properties in the fast-type dominant skeletal muscle, where the activation of oxidative metabolism is more pronounced after fish oil intake than that after soybean oil intake.
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Growth factor regulation of neural chemorepellent Sema3A expression in satellite cell cultures.
Am. J. Physiol., Cell Physiol.
PUBLISHED: 08-24-2011
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Successful regeneration and remodeling of the intramuscular motoneuron network and neuromuscular connections are critical for restoring skeletal muscle function and physiological properties. The regulatory signals of such coordination remain unclear, although axon-guidance molecules may be involved. Recently, satellite cells, resident myogenic stem cells positioned beneath the basal lamina and at high density at the myoneural junction regions of mature fibers, were shown to upregulate a secreted neural chemorepellent semaphorin 3A (Sema3A) in response to in vivo muscle-crush injury. The initial report on that expression centered on the observation that hepatocyte growth factor (HGF), an essential cue in muscle fiber growth and regeneration, remarkably upregulates Sema3A expression in early differentiated satellite cells in vitro [Tatsumi et al., Am J Physiol Cell Physiol 297: C238-C252, 2009]. Here, we address regulatory effects of basic fibroblast growth factor (FGF2) and transforming growth factor (TGF)-?s on Sema3A expression in satellite cell cultures. When treated with FGF2, Sema3A message and protein were upregulated as revealed by reverse transcription-polymerase chain reaction and immunochemical studies. Sema3A upregulation by FGF2 was dose dependent with a maximum (8- to 1-fold relative to the control) at 2.5 ng/ml (150 pM) and occurred exclusively at the early differentiation stage. The response was highly comparable in dose response and timing to effects of HGF treatment, without any additive or synergistic effect from treatment with a combination of both potent upregulators. In contrast, TGF-?2 and -?3 potently decreased basal Sema3A expression; the maximum effect was at very low concentrations (40 and 8 pM, respectively) and completely cancelled the activities of FGF2 and HGF to upregulate Sema3A. These results therefore encourage the prospect that a time-coordinated increase in HGF, FGF2, and TGF-? ligands and their receptors promotes a programmed strategy for Sema3A expression that guarantees successful intramuscular motor reinnervation by delaying sprouting and reattachment of motoneuron terminals onto damaged muscle fibers early in regeneration pending restoration of muscle fiber contractile integrity.
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In vitro measurement of post-natal changes in proliferating satellite cell frequency during rat muscle growth.
Anim. Sci. J.
PUBLISHED: 05-05-2010
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Satellite cells, resident myogenic stem cells found in postnatal skeletal muscle, are most abundant during early postnatal development and sharply decline in frequency thereafter to adult levels in mice and rats. Therefore, postnatal changes in satellite cell mitotic activities are important aspects for further understanding a muscle growth strategy. In large meat-production animals, however, the traditional in vivo proliferation assay may be less realistic because it requires intra-peritoneal (ip) injection of huge dosage of mutagenic nucleosides, (3)H-labeled thymidine or bromodeoxyuridine (BrdU), at each age-time of sacrifice. We report in the present pilot study using rats that in vivo proliferation activity of satellite cells can be evaluated by an in vitro BrdU-incorporation assay in early cultures. Briefly, satellite cells were prepared from upper hind-limb and back muscles and maintained for 24 h with imposing by BrdU addition for the last 2 h, followed by the regular immunocytochemistry for determining BrdU-incorporated cell percentage. This in vitro assay demonstrated a rapid decrease in proliferating satellite cell frequency to the adult level during about 3-month period after birth, and yielded a high correlation to the measurements by the in vivo BrdU ip-injection method during the postnatal period examined from day-2 to month-11. The in vitro proliferation assay may be further adaptable for large domestic animals by the combination with a muscle biopsy technique that enables age-interval sampling from the same growing animals.
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Deficiency in APOBEC2 leads to a shift in muscle fiber type, diminished body mass, and myopathy.
J. Biol. Chem.
PUBLISHED: 12-17-2009
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The apoB RNA-editing enzyme, catalytic polypeptide-like (APOBEC) family of proteins includes APOBEC1, APOBEC3, and activation-induced deaminase, all of which are zinc-dependent cytidine deaminases active on polynucleotides and involved in RNA editing or DNA mutation. In contrast, the biochemical and physiological functions of APOBEC2, a muscle-specific member of the family, are unknown, although it has been speculated, like APOBEC1, to be an RNA-editing enzyme. Here, we show that, although expressed widely in striated muscle (with levels peaking late during myoblast differentiation), APOBEC2 is preferentially associated with slow-twitch muscle, with its abundance being considerably greater in soleus compared with gastrocnemius muscle and, within soleus muscle, in slow as opposed to fast muscle fibers. Its abundance also decreases following muscle denervation. We further show that APOBEC2-deficient mice harbor a markedly increased ratio of slow to fast fibers in soleus muscle and exhibit an approximately 15-20% reduction in body mass from birth onwards, with elderly mutant animals revealing clear histological evidence of a mild myopathy. Thus, APOBEC2 is essential for normal muscle development and maintenance of fiber-type ratios; although its molecular function remains to be identified, biochemical analyses do not especially argue for any role in RNA editing.
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High concentrations of HGF inhibit skeletal muscle satellite cell proliferation in vitro by inducing expression of myostatin: a possible mechanism for reestablishing satellite cell quiescence in vivo.
Am. J. Physiol., Cell Physiol.
PUBLISHED: 12-09-2009
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Skeletal muscle regeneration and work-induced hypertrophy rely on molecular events responsible for activation and quiescence of resident myogenic stem cells, satellite cells. Recent studies demonstrated that hepatocyte growth factor (HGF) triggers activation and entry into the cell cycle in response to mechanical perturbation, and that subsequent expression of myostatin may signal a return to cell quiescence. However, mechanisms responsible for coordinating expression of myostatin after an appropriate time lag following activation and proliferation are not clear. Here we address the possible role of HGF in quiescence through its concentration-dependent negative-feedback mechanism following satellite cell activation and proliferation. When activated/proliferating satellite cell cultures were treated for 24 h beginning 48-h postplating with 10-500 ng/ml HGF, the percentage of bromodeoxyuridine-incorporating cells decreased down to a baseline level comparable to 24-h control cultures in a HGF dose-dependent manner. The high level HGF treatment did not impair the cell viability and differentiation levels, and cells could be reactivated by lowering HGF concentrations to 2.5 ng/ml, a concentration that has been shown to optimally stimulate activation of satellite cells in culture. Coaddition of antimyostatin neutralizing antibody could prevent deactivation and abolish upregulation of cyclin-dependent kinase (Cdk) inhibitor p21. Myostatin mRNA expression was upregulated with high concentrations of HGF, as demonstrated by RT-PCR, and enhanced myostatin protein expression and secretion were revealed by Western blots of the cell lysates and conditioned media. These results indicate that HGF could induce satellite cell quiescence by stimulating myostatin expression. The HGF concentration required (over 10-50 ng/ml), however, is much higher than that for activation, which is initiated by rapid release of HGF from its extracellular association. Considering that HGF is produced by satellite cells and spleen and liver cells in response to muscle damage, local concentrations of HGF bathing satellite cells may reach a threshold sufficient to induce myostatin expression. This time lag may delay action of the quiescence signaling program in proliferating satellite cells during initial phases of muscle regeneration followed by induction of quiescence in a subset of cells during later phases.
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Differential expression of sarcoplasmic and myofibrillar proteins of rat soleus muscle during denervation atrophy.
Biosci. Biotechnol. Biochem.
PUBLISHED: 08-07-2009
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Denervation is known to induce skeletal muscle atrophy and fiber-type transitions, the molecular mechanisms of which are poorly understood. To investigate the effect of denervation on skeletal muscle, proteomic analysis was performed to compare denervated soleus muscle with normal soleus muscle. The muscles were fractionated to myofibrillar and sarcoplasmic fractions, which were analysed using two-dimensional gel electrophoresis (2-DE), followed by MALDI-TOF-MS. At least 30 differentially regulated proteins were identified in the sarcoplasmic fractions of normal and denervated soleus muscles. This group included metabolic enzymes, signaling molecules, chaperones, and contractile proteins. We also found two proteins, APOBEC-2 (RNA-editing enzyme) and Gamma-synuclein (breast cancer related protein), which have not been recognized as denervation-induced proteins to date. Our results might prove to be beneficial in elucidating the molecular mechanisms of denervation-induced muscle atrophy.
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A role for calcium-calmodulin in regulating nitric oxide production during skeletal muscle satellite cell activation.
Am. J. Physiol., Cell Physiol.
PUBLISHED: 01-21-2009
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When skeletal muscle is stretched or injured, myogenic satellite cells are activated to enter the cell cycle. This process depends on nitric oxide (NO) production by NO synthase (NOS), matrix metalloproteinase activation, release of hepatocyte growth factor (HGF) from the extracellular matrix, and presentation of HGF to the c-met receptor as demonstrated by a primary culture and in vivo assays. We now add evidence that calcium-calmodulin is involved in the satellite cell activation cascade in vitro. Conditioned medium from cultures that were treated with a calcium ionophore (A23187, ionomycin) for 2 h activated cultured satellite cells and contained active HGF, similar to the effect of mechanical stretch or NO donor treatments. The response was abolished by addition of calmodulin inhibitors (calmidazolium, W-13, W-12) or a NOS inhibitor N(G)-nitro-l-arginine methyl ester hydrochloride but not by its less inactive enantiomer N(G)-nitro-d-arginine methyl ester hydrochloride. Satellite cells were also shown to express functional calmodulin protein having a calcium-binding activity at 12 h postplating, which is the time at which the calcium ionophore was added in this study and the stretch treatment was applied in our previous experiments. Therefore, results from these experiments provide an additional insight that calcium-calmodulin mediates HGF release from the matrix and that this step in the activation pathway is upstream from NO synthesis.
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Satellite cells produce neural chemorepellent semaphorin 3A upon muscle injury.
Anim. Sci. J.
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Regenerative mechanisms that regulate intramuscular motor innervation. including configuration of the neuromuscular connections are thought to reside in the spatiotemporal expression of axon-guidance molecules. Our previous studies proposed a heretofore unexplored role of satellite cells as a key source of a secreted neural chemorepellent semaphorin 3A (Sema3A) expression. In order to verify this concept, there is still a critical need to provide direct evidence to show the up-regulation of Sema3A protein in satellite cells in vivo upon muscle injury. The present study employed a Sema3A/MyoD double-immunohistochemical staining for cryo-sections prepared from cardiotoxin injected gastrocnemius muscle of adult mouse lower hind-limb. Results clearly demonstrated that Sema3A expression was up-regulated in myogenic differentiation-positive satellite cells at 4-12 days post-injury period, the time that corresponds to the cell differentiation phase characterized by increasing myogenin messenger RNA expression. This direct proof encourages a possible implication of satellite cells in the spatiotemporal regulation of extracellular Sema3A concentrations, which potentially ensures coordinating a delay in neurite sprouting and re-attachment of motoneuron terminals onto damaged muscle fibers early in muscle regeneration in synchrony with recovery of muscle-fiber integrity.
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Comparative analysis of semaphorin 3A in soleus and EDL muscle satellite cells in vitro toward understanding its role in modulating myogenin expression.
Int. J. Biochem. Cell Biol.
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Resident myogenic stem cells, satellite cells, up-regulate a secreted multi-functional modulator, semaphorin 3A (Sema3A), exclusively at the early-differentiation phase in response to muscle-crush injury and treatment with hepatocyte growth factor (HGF) or basic fibroblast growth factor (FGF2). Here, we add evidence that the Sema3A expression and secretion induced by the growth factors is significantly higher in primary cultures from adult rat soleus than from the fast-twitch extensor digitorum longus (EDL) muscle. The higher Sema3A response, revealed by quantitative PCR and Western blotting of cell lysates and conditioned media, may account for the higher myogenin expression of soleus muscle satellite cells early in differentiation since addition of recombinant Sema3A stimulates myogenin expression in cultures. These experiments also showed that mRNA expression of plexin A2, which together with neuropilins, constitutes Sema3A composite-receptors, was higher in satellite cells from soleus than EDL with no difference in plexin A1 and A3 and neuropilin-1 and 2 levels. These comparative studies, therefore, highlight a possible Sema3A-plexin A2-myogenin signaling axis that may ensure promoting early differentiation by soleus muscle satellite cells.
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Time-coordinated prevalence of extracellular HGF, FGF2 and TGF-?3 in crush-injured skeletal muscle.
Anim. Sci. J.
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Successful regeneration and remodeling of neuromuscular junctions are critical for restoring functional capacities and properties of skeletal muscle after damage, and axon-guidance molecules may be involved in the signaling that regulates such restoration. Recently, we found that early-differentiated satellite cells up-regulate a secreted neural chemorepellent Sema3A upon in vivo muscle-crush injury. The study also revealed that Sema3A expression is up-regulated in primary satellite-cell cultures in response to hepatocyte growth factor (HGF) and basic fibroblast growth factor (FGF2) and is prevented by transforming growth factor (TGF)-?2, 3. In order to verify the physiological significance of this regulation in vitro, the present study was designed to estimate the time-course of extracellular HGF, FGF2 and TGF-?3 concentrations after crush-injury of Gastrocnemius muscle in the rat lower hind-limb, using a combination of a non-homogenization/non-spin extraction of extracellular wound fluids and enhanced chemiluminescence-Western blotting analyses. Results clearly demonstrated that active HGF and FGF2 are prevalent in 2-8?days post-crush, whereas active TGF-?3 increases after 12?days, providing a better understanding of the time-coordinated levels of HGF, FGF2 and TGF-?3 that drive regulation of Sema3A expression during regenerative intramuscular moto-neuritogenesis.
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Calcium influx through a possible coupling of cation channels impacts skeletal muscle satellite cell activation in response to mechanical stretch.
Am. J. Physiol., Cell Physiol.
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When skeletal muscle is stretched or injured, satellite cells, resident myogenic stem cells positioned beneath the basal lamina of mature muscle fibers, are activated to enter the cell cycle. This signaling pathway is a cascade of events including calcium-calmodulin formation, nitric oxide (NO) radical production by NO synthase, matrix metalloproteinase activation, release of hepatocyte growth factor (HGF) from the extracellular matrix, and presentation of HGF to the receptor c-met, as demonstrated by assays of primary cultures and in vivo experiments. Here, we add evidence that two ion channels, the mechanosensitive cation channel (MS channel) and the long-lasting-type voltage-gated calcium-ion channel (L-VGC channel), mediate the influx of extracellular calcium ions in response to cyclic stretch in satellite cell cultures. When applied to 1-h stretch cultures with individual inhibitors for MS and L-VGC channels (GsMTx-4 and nifedipine, respectively) or with a less specific inhibitor (gadolinium chloride, Gd), satellite cell activation and upstream HGF release were abolished, as revealed by bromodeoxyuridine-incorporation assays and Western blotting of conditioned media, respectively. The inhibition was dose dependent with a maximum at 0.1 ?M (GsMTx-4), 10 ?M (nifedipine), or 100 ?M (Gd) and canceled by addition of HGF to the culture media; a potent inhibitor for transient-type VGC channels (NNC55-0396, 100 ?M) did not show any significant inhibitory effect. The stretch response was also abolished when calcium-chelator EGTA (1.8 mM) was added to the medium, indicating the significance of extracellular free calcium ions in our present activation model. Finally, cation/calcium channel dependencies were further documented by calcium-imaging analyses on stretched cells; results clearly demonstrated that calcium ion influx was abolished by GsMTx-4, nifedipine, and EGTA. Therefore, these results provide an additional insight that calcium ions may flow in through L-VGC channels by possible coupling with adjacent MS channel gating that promotes the local depolarization of cell membranes to initiate the satellite cell activation cascade.
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