Changes In Myosin Heavy Chain Research Articles

Ractopamine-induced fiber type-specific gene expression in porcine skeletal muscles is independent of growth.

Feeding ractopamine (RAC), a β-adrenergic agonist (BAA), to pigs increases type IIB muscle fiber type-specific protein and mRNA expression. However, increases in the abundance of these fast-twitch fiber types occur with other forms of muscle hypertrophy and thus BAA-induced changes in myosin heavy chain (MyHC) composition may simply be associated with increased muscle growth known to occur in response to BAA feeding. The objective of this study was to determine whether RAC feeding could change the MyHC gene expression in the absence of maximal muscle growth. Pigs were fed either an adequate diet that supported maximal muscle hypertrophy or a low nutrient diet that limited muscle growth. RAC was included in diets at 0 or 20 mg/kg for 1, 2, or 4 wk. Backfat depth was less (P < 0.05) in pigs fed the low nutrient diet compared with the adequate diet but was not affected by RAC. Loin eye area was greater (P < 0.05) in pigs fed an adequate diet plus RAC at 1 wk but did not differ among remaining pigs. At 2 and 4 wk, however, pigs fed the adequate diet had greater loin eye areas (P < 0.05) than pigs fed the low nutrient diet regardless of RAC feeding. Gene expression of the MyHC isoforms, I, IIA, IIX, and IIB, as well as glycogen synthase, citrate synthase, β 1-adrenergic receptor (AR), and β 2-AR were determined in longissimus dorsi (LD) and red (RST) and white (WST) portions of the semitendinosus muscles. MyHC type I gene expression was not altered by RAC or diet. Feeding RAC decreased (P < 0.01) MyHC type IIA gene expression in all muscles, but to a greater extent in WST and LD. MyHC type IIX gene expression was lower (P < 0.05) in WST and LD muscles in response to RAC but was not altered in RST muscles. RAC increased (P < 0.05) MyHC type IIB gene expression in all muscles, but to a greater extent in RST. β 1-AR gene expression was unaffected by RAC or diet, whereas the expression of the β 2-AR gene was decreased (P < 0.001) by RAC. No significant RAC * diet interactions were observed in gene expression in this study, indicating that RAC altered MyHC and β 2-AR gene expression in porcine skeletal muscles independent of growth.

Immunohistochemical analysis of laryngeal muscle of horses clinically affected with recurrent laryngeal neuropathy.

As myosin heavy chain (MyHC) profile of muscle fibres is heavily influenced by neural input, changes in MyHC expression are expected in horses clinically affected with recurrent laryngeal neuropathy (RLN) yet, this has not been thoroughly investigated. To describe the changes in MyHC and fibre diameter in left cricoarytenoideus dorsalis (L-CAD) muscle of horses with clinical signs of RLN. Observational cohort study. Immunohistochemistry was used to assess the MyHC-based fibre-type proportion, size and grouping in the L-CAD of 10 Thoroughbred horses, five clinically affected with RLN and five unaffected controls based on resting endoscopic examination. The Mann-Whitney U test was used to compare the two groups. Compared to controls (of mean age 3.0±1.7years) which only expressed type I, IIA and IIX MyHC, the L-CAD of affected horses (of mean age 2.8±0.8years) had obvious fibre-type grouping, and despite apparent compensatory hypertrophy of a small number of fibres, a decrease in overall fibre diameter (median difference -35.2µm, 95% CI -47.4 to -7.9, P=.02) and diameter of type IIA fibres (median difference -46.8µm, 95% CI -52.1 to -5.0, P=.03) was observed. Anti-fast MyHC (MY32) cross-immunoreacted with embryonic-MyHC. Whereas MY32-positive fibres were identified as type IIX in controls, in affected horses these fibres were less than 50µm diameter with internal nuclei and were MYH3-positive for embryonic myosin indicating depletion of type IIX fibres, yet active regeneration and fibre renewal. Small sample size that did not include subclinical cases. Fibre size and appearance rather than staining colour were relied upon to differentiate embryonic from type IIX MyHC. Horses clinically affected with RLN have overall atrophy of fibres, loss of IIX fibres and expression of embryonic myosin indicating regenerative capacity. Despite hypertrophy of some remaining fibres, the overall decline in the bulk of fibres, including those most fatigue-resistant, may be the critical change that results in failure to maintain arytenoid abduction during exercise although direct comparison to subclinical cases is needed to confirm this.

NO-Dependent Mechanisms of Myosin Heavy Chain Transcription Regulation in Rat Soleus Muscle After 7-Days Hindlimb Unloading.

It is known that nitric oxide (NO) may affect myosin heavy chain (MyHC) isoform mRNA transcription in skeletal muscles. The content of NO in soleus muscles decreases during rat hindlimb unloading as well as slow MyHC mRNA transcription. We aimed to detect which signaling pathways are involved in NO-dependent prevention of hindlimb-suspension (HS)-induced changes in MyHCs’ expression pattern. Male Wistar rats were divided into four groups: cage control group (C), hindlimb suspended for 7 days (7HS), hindlimb suspended for 7 days with L-arginine administration (7HS+A) (500 mg/kg body mass), and hindlimb suspended for 7 days with both L-arginine (500 mg/kg) and NO-synthase inhibitor L-NAME administration (50 mg/kg) (7HS+A+N). L-arginine treatment during 7 days of rat HS prevented HS-induced NO content decrease and slow MyHC mRNA transcription decrease and attenuated fast MyHC IIb mRNA transcription increase; it also prevented NFATc1 nuclear content decrease, calsarcin-2 expression increase, and GSK-3β Ser 9 phosphorylation decrease. Moreover, L-arginine administration prevented the HS-induced myh7b and PGC1α mRNAs content decreases and slow-type genes repressor SOX6 mRNA transcription increase. All these slow fiber-type protective effects of L-arginine were blocked in HS+A+N group, indicating that these effects were NO-dependent. Thus, NO decrease prevention during HS restores calcineurin/NFATc1 and myh7b/SOX6 signaling.

Comparison ofPost‐mortemMass Changes in Myosin Heavy Chain and Textural Characteristics amongOncorhynchus mykiss(Walbaum, 1972),Salmo trutta fario(Linnaeus, 1758) andSalvelinus fontinalis(Mitchill, 1814)

In this study, post‐mortem myofibril proteins change in myosin heavy chain (MHC) mass using sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE), texture properties such as hardness, stickiness, cohesiveness, elasticity, chewiness, gumminess and stress relaxation test parameters (Fmax, Fmin and Fmax‐Fmin) were determined and compared on the days 0, 3, 6 and 9 in three different trout species (Oncorhynchus mykiss, Salmo trutta fario and Salvelinus fontinalis). In terms of texture properties, post‐mortem hardness, cohesiveness, elasticity, chewiness and gumminess were decreased day by day, whereas stickiness, Fmax, Fmin and Fmax‐Fmin were significantly increased (p < .05). According to SDS‐PAGE results, a decreased value on MHC was determined (p < .05). Texture properties and SDS‐PAGE results were found different among groups (p < .05). Correlation between chewiness, gumminess, MHC and hardness; between chewiness and gumminess; between Fmin, Fmax‐Fmin and Fmax; between Fmin and Fmax‐Fmin were significant. As a result of the study, S. fontinalis exhibited least deterioration in comparison with other species and it was determined that SDS‐PAGE results and texture properties support each other.

Estrogen‐related Receptor α Overexpression Drives a Metabolic and Gene Expression Program Mimicking Aerobic Exercise in Skeletal Muscle

Aerobic exercise is considered one of the most effective interventions to prevent obesity and type 2 diabetes (T2D). Exercise increases skeletal muscle insulin sensitivity by stimulating mitochondrial respiration and fatty acid oxidation through coordinated regulation of metabolic genes. Transcriptional pathways that regulate exercise‐induced metabolic gene programs present an attractive class of therapeutic targets to combat obesity and related metabolic diseases. We and others have shown that the Estrogen‐related Receptor α (ERRα) nuclear receptor regulates mitochondrial biogenesis, respiration and fatty acid oxidation and is required for metabolic reprogramming in response to exercise training. The objective of these studies is to determine whether ERRα over‐expression is sufficient to mediate exercise‐induced adaptations in muscle. We generated a conditional ERRα transgenic mouse line that expresses the Flag‐tagged human ERRα in skeletal muscle‐specific manner when crossed with Mck‐Cre recombinase mice (ERRαMOE). We examined gene expression (trancript and protein) and characterized the metabolic phentoype of the ERRαMOE mice. ERRαMOE mice exhibited a reddening of the superficial gastrocnemius and quadriceps, characteristic of oxidative muscles, accompanied by a reciprocal change in myosin heavy chain (MHC) IIb (−35%) and IIa (+80%) expression. Mitochondrial content was higher in skeletal muscle and heart, but not in non‐muscle tissues, based on mtDNA quantitation and citrate synthase protein expression. Consistently, basal (+32%) and maximal (+70%) O2 consumption rates were increased in FDB fibers isolated from ERRα‐MOE compared to WT. Signaling through the AMP‐activated kinase (AMPK) pathway, which mediates exercise‐dependent metabolic reprogramming, was unchanged in the basal state; however, maximal activation by AICAR was enhanced in ERRα‐overexpressing myotubes. We assessed systemic glucose homeostasis in adult chow fed mice. Although fasting glucose (6 hr) was slightly lower in ERRαMOE, no significant difference in glucose tolerance was observed. However, the results of insulin tolerance tests showed that ERRαMOE mice were more insulin sensitive than WT. In future studies we will investigate whether ERRα activation in skeletal muscle protects against high fat diet‐induced insulin resistance. Based on the results from these studies, ERRα over‐expression mimics the effects of exercise on skeletal muscle mitochondrial respiratory capacity and improves whole body insulin sensitivity.Support or Funding InformationSupported by Diabetes and Metabolic Research Institute (DMRI) and Shared Resource Pilot Awards from the City of Hope and NIH U24DK097748This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Ontogeny of myosin isoform expression and prehensile function in the tail of the gray short-tailed opossum (Monodelphis domestica).

Terrestrial opossums use their semiprehensile tail for grasping nesting materials as opposed to arboreal maneuvering. We relate the development of this adaptive behavior with ontogenetic changes in myosin heavy chain (MHC) isoform expression from 21 days to adulthood. Monodelphis domestica is expected to demonstrate a progressive ability to flex the distal tail up to age 7 mo, when it should exhibit routine nest construction. We hypothesize that juvenile stages (3-7 mo) will be characterized by retention of the neonatal isoform (MHC-Neo), along with predominant expression of fast MHC-2X and -2B, which will transition into greater MHC-1β and -2A isoform content as development progresses. This hypothesis was tested using Q-PCR to quantify and compare gene expression of each isoform with its protein content determined by gel electrophoresis and densitometry. These data were correlated with nesting activity in an age-matched sample of each age group studied. Shifts in regulation of MHC gene transcripts matched well with isoform expression. Notably, mRNA for MHC-Neo and -2B decrease, resulting in little-to-no isoform translation after age 7 mo, whereas mRNA for MHC-1β and -2A increase, and this corresponds with subtle increases in content for these isoforms into late adulthood. Despite the tail remaining intrinsically fast-contracting, a critical growth period for isoform transition is observed between 7 and 13 mo, correlating primarily with use of the tail during nesting activities. Functional transitions in MHC isoforms and fiber type properties may be associated with muscle "tuning" repetitive nest remodeling tasks requiring sustained contractions of the caudal flexors.NEW & NOTEWORTHY Little is understood about skeletal muscle development as it pertains to tail prehensility in mammals. This study uses an integrative approach of relating both MHC gene and protein expression with behavioral and morphometric changes to reveal a predominant fast MHC expression with subtle isoform transitions in caudal muscle across ontogeny. The functional shifts observed are most notably correlated with increased tail grasping for nesting activities.

Ca2+ sensitivity of skinned ventricular cardiac muscle and expression of cardiac myosin heavy chain isoforms in hibernating versus active frogs

Hibernation is a biological phenomenon enabling animals to endure hypothermia. This study was designed to find the changes in myosin heavy chain (MHC) isoforms and their relationship to calcium sensitivity in frog ventricular muscle during hibernation. MHC profile was determined by SDS-4% polyacrylamide gel electrophoresis in active and hibernating frogs for different intervals of time (10, 20, 30, and 60 days). Calcium sensitivity of Triton-skinned ventricular muscle fiber bundles was determined. Compared with active and hibernated frogs for 10 and 20 days, hibernated frogs for 30 and 60 days expressed significant amount (p < 0.05) of MHC type β (15. 3 ± 3.8%, 35.6 ± 1.5%, respectively). This change in myosin heavy chain profile seen in long period of hibernation was associated with significant decrease (p < 0.05) in sensitivity of skinned myofilaments to Ca2+ where skinned ventricular muscle taken from hibernating frogs for 30 and 60 days p Ca value were 5.52 and 5.50, respectively, while active frog showed p Ca = 5.67. In conclusion, expression of increased amount of β-MHC in hibernated frog for 30 days and more was associated with a decrease in contractile responses of skinned ventricular myocardium to calcium.

Moderate-intensity resistance exercise alters skeletal muscle molecular and cellular structure and function in inactive older adults with knee osteoarthritis.

High-intensity resistance exercise (REX) training increases physical capacity, in part, by improving muscle cell size and function. Moderate-intensity REX, which is more feasible for many older adults with disease and/or disability, also increases physical function, but the mechanisms underlying such improvements are not understood. Therefore, we measured skeletal muscle structure and function from the molecular to the tissue level in response to 14 wk of moderate-intensity REX in physically inactive older adults with knee osteoarthritis (n = 17; 70 ± 1 yr). Although REX training increased quadriceps muscle cross-sectional area (CSA), average single-fiber CSA was unchanged because of reciprocal changes in myosin heavy chain (MHC) I and IIA fibers. Intermyofibrillar mitochondrial content increased with training because of increases in mitochondrial size in men, but not women, with no changes in subsarcolemmal mitochondria in either sex. REX increased whole muscle contractile performance similarly in men and women. In contrast, adaptations in single-muscle fiber force production per CSA (i.e., tension) and contractile velocity varied between men and women in a fiber type-dependent manner, with adaptations being explained at the molecular level by differential changes in myosin-actin cross-bridge kinetics and mechanics and single-fiber MHC protein expression. Our results are notable compared with studies of high-intensity REX because they show that the effects of moderate-intensity REX in older adults on muscle fiber size/structure and myofilament function are absent or modest. Moreover, our data highlight unique sex-specific adaptations due to differential cellular and subcellular structural and functional changes.NEW & NOTEWORTHY Moderate-intensity resistance training causes sex-specific adaptations in skeletal muscle structure and function at the cellular and molecular levels in inactive older adult men and women with knee osteoarthritis. However, these responses were minimal compared with high-intensity resistance training. Thus adjuncts to moderate-intensity training need to be developed to correct underlying cellular and molecular structural and functional deficits that are at the root of impaired physical function in this mobility-limited population.

Modulation of Muscle Fiber Compositions in Response to Hypoxia via Pyruvate Dehydrogenase Kinase-1.

Muscle fiber-type changes in hypoxic conditions in accordance with pyruvate dehydrogenase kinase (Pdk)-1 and hypoxia inducible factor (Hif)-1α were investigated in rats. Hif-1α and its down-stream molecule Pdk-1 are well known for readily response to hypoxia. We questioned their roles in relation to changes in myosin heavy chain (MyHC) composition in skeletal muscles. We hypothesize that the level of Pdk-1 with respect to the level of Hif-1α determines MyHC composition of the muscle in rats in hypoxia. Young male rats were housed in a chamber maintained at 11.5% (for sustained hypoxia) or fluctuating between 11.5 and 20.8% (for intermittent hypoxia or IH) oxygen levels. Then, muscle tissues from the geniohyoid (GH), soleus, and anterior tibialis (TA) were obtained at the end of hypoxic conditionings. After both hypoxic conditionings, protein levels of Pdk-1 and Hif-1 increased in GH muscles. GH muscles in acute sustained hypoxia favor an anaerobic glycolytic pathway, resulting in an increase in glycolytic MyHC IIb protein-rich fibers while maintain original fatigue-resistant MyHC IIa protein in the fibers; thus, the numbers of IIa- and IIb MyHC co-expressing fibers increased. Exogenous Pdk-1 over-expression using plasmid vectors elevated not only the glycolytic MyHC IIb, but also IIx as well as IIa expressions in C2C12 myotubes in ambient air significantly. The increase of dual expression of IIa- and IIb MyHC proteins in fibers harvested from the geniohyoid muscle has a potential to improve endurance as shown in our fatigability tests. By increasing the Pdk-1/Hif-1 ratio, a mixed-type muscle could alter endurance within the innate characteristics of the muscle toward more fatigue resistant. We conclude that an increased Pdk-1 level in skeletal muscle helps maintain MyHC compositions to be a fatigue resistant mixed-type muscle.

Chronic sleep deprivation alters the myosin heavy chain isoforms in the masseter muscle in rats

To investigate the changes in myosin heavy chain (MyHC) isoforms of rat masseter muscle fibres caused by chronic sleep deprivation and a possible link with the pathogenesis of disorders of the temporomandibular joint (TMJ). A total of 180 male rats were randomly divided into three groups (n=60 in each): cage controls, large platform controls, and chronic sleep deprivation group. Each group was further divided into three subgroups with different observation periods (7, 14, and 21 days). We investigated he expression of MyHC isoforms in masseter muscle fibres by real-time quantitative polymerase chain reaction (PCR), Western blotting, and immunohistochemical staining. In rats with chronic sleep deprivation there was increased MyHC-I expression in layers of both shallow and deep muscles at 7 and 21 days compared with the control groups, whereas sleep deprivation was associated with significantly decreased MyHC-II expression. At 21 days, there were no differences in MyHC-I or MyHC-II expression between the groups and there were no differences between the two control groups at any time point. These findings suggest that chronic sleep deprivation alters the expression of MyHC isoforms, which may contribute to the pathogenesis of disorders of the TMJ.

Protein Degradation and Instrumental Textural Changes in Fresh Nile Tilapia (Oreochromis niloticus) during Frozen Storage

Textural changes as well as protein degradation during frozen storage of Nile tilapia (Oreochromis niloticus) at −18C for 150 days were studied. Salt-soluble protein and protein solubility decreased significantly during the frozen storage period. Sodium dodecyl sulfate polyacrylamide gel electrophoresis was performed, and no visible changes in myosin heavy chain were observed up to 90th day of frozen storage period; however, the thickness of band was found to decrease thereafter. A new lighter band with molecular weight of 29 kDa was found on 120th and 150th day of sampling period. Actin was found more resistant to proteolysis. Texture profile analysis revealed that hardness 1, hardness 2, gumminess and chewiness gradually decreased up to 120th day, but showed an increase thereafter. Although sensory attributes decreased with the progress of frozen storage period, the fish was in acceptable condition on 150th day. Gradual toughening of muscle was recorded by the sensory panelists. Practical Application The popularity of tilapia is gaining importance for the development of different value-added fish products as well as for canning purposes. Therefore, it is important from the part of fish processor to know the changes of protein and texture profile during frozen storage. Although there was protein degradation and changes in texture profile during the study period of 150 days, the fish was in acceptable condition.

α-Actinin-3 deficiency alters muscle adaptation in response to denervation and immobilization

Homozygosity for a common null polymorphism (R577X) in the ACTN3 gene results in the absence of the fast fibre-specific protein, α-actinin-3 in ∼16% of humans worldwide. α-Actinin-3 deficiency is detrimental to optimal sprint performance and benefits endurance performance in elite athletes. In the general population, α-actinin-3 deficiency is associated with reduced muscle mass, strength and fast muscle fibre area, and poorer muscle function with age. The Actn3 knock-out (KO) mouse model mimics the human phenotype, with fast fibres showing a shift towards slow/oxidative metabolism without a change in myosin heavy chain (MyHC) isoform. We have recently shown that these changes are attributable to increased activity of the calcineurin-dependent signalling pathway in α-actinin-3 deficient muscle, resulting in enhanced response to exercise training. This led us to hypothesize that the Actn3 genotype influences muscle adaptation to disuse, irrespective of neural innervation. Separate cohorts of KO and wild-type mice underwent 2 weeks immobilization and 2 and 8 weeks of denervation. Absence of α-actinin-3 resulted in reduced atrophic response and altered adaptation to disuse, as measured by a change in MyHC isoform. KO mice had a lower threshold to switch from the predominantly fast to a slower muscle phenotype (in response to immobilization) and a higher threshold to switch to a faster muscle phenotype (in response to denervation). We propose that this change is mediated through baseline alterations in the calcineurin signalling pathway of Actn3 KO muscle. Our findings have important implications for understanding individual responses to muscle disuse/disease and training in the general population.

Heart failure-induced skeletal myopathy in spontaneously hypertensive rats

BackgroundAlthough skeletal muscle atrophy and changes in myosin heavy chain (MyHC) isoforms have often been observed during heart failure, their pathophysiological mechanisms are not completely defined. In this study we tested the hypothesis that skeletal muscle phenotype changes are related to myogenic regulatory factors and myostatin/follistatin expression in spontaneously hypertensive rats (SHR) with heart failure. MethodsAfter developing tachypnea, SHR were subjected to transthoracic echocardiogram. Pathological evidence of heart failure was assessed during euthanasia. Age-matched Wistar–Kyoto (WKY) rats were used as controls. Soleus muscle morphometry was analyzed in histological sections, and MyHC isoforms evaluated by electrophoresis. Protein levels were assessed by Western blotting. Statistical analysis: Student'st test and Pearson correlation. ResultsAll SHR presented right ventricular hypertrophy and seven had pleuropericardial effusion. Echocardiographic evaluation showed dilation in the left chambers and left ventricular hypertrophy with systolic and diastolic dysfunction in SHR. Soleus weight and fiber cross sectional areas were lower (WKY 3615±412; SHR 2035±224μm2; P<0.001), and collagen fractional volume was higher in SHR. The relative amount of type I MyHC isoform was increased in SHR. Myogenin, myostatin, and follistatin expression was lower and MRF4 levels higher in SHR. Myogenin and follistatin expression positively correlated with fiber cross sectional areas and MRF4 levels positively correlated with I MyHC isoform. ConclusionReduced myogenin and follistatin expression seems to participate in muscle atrophy while increased MRF4 protein levels can modulate myosin heavy chain isoform shift in skeletal muscle of spontaneously hypertensive rats with heart failure.

Myosin heavy chain changes in heart failure‐rat diaphragm muscle are not related to myogenic regulatory factors expression

ObjectiveIn this study we tested the hypothesis that diaphragm myosin heavy chain (MyHC) isoform changes are related to alterations of myogenic regulatory factors (MRF) expression in chronic heart failure.MethodsWe studied Sham (n=10) and infarcted rats with heart failure (MI/HF, n=10). Cardiac structures and ventricular function were assessed by echocardiogram. MyHC isoforms were analyzed by electrophoresis. MRF myogenin, MyoD, and MRF4 gene expression was evaluated by real time RT‐PCR and protein expression was analyzed by Western‐blot. Statistical analysis was performed by Student's t test and Pearson correlation.ResultsAll MI/HF rats had pulmonary congestion and right ventricular hypertrophy. In echocardiographic evaluation, MI/HF presented left cardiac chambers dilation and left ventricular systolic and diastolic dysfunction. The percentage of MyHC I isoform was higher and IIb isoform was lower in MI/HF. Left atrial diameter‐to‐body weight ratio positively correlated with MyHC I and negatively correlated with MyHC IIb isoform percentage. No differences were observed in MRF gene and protein expressions between groups.ConclusionMRF expression does not modulate diaphragm MyHC isoforms changes in rats with chronic heart failure. Diaphragm MyHC changes are related to ventricular dysfunction severity. Financial support: Fapesp.

Differential expression of myosin heavy chain isoforms in the masticatory muscles of dystrophin-deficient mice

The dystrophin-deficient mouse (mdx) is a homologue animal model of Duchenne muscular dystrophy (DMD) and is characterized by slowly progressive muscle weakness accompanied by changes in myosin heavy chain (MyHC) composition. It is likely that the masticatory muscles undergo similar changes. The aim of this study was to examine the masticatory muscles (masseter, temporal, tongue, and soleus) of 100-day-old mdx and control mice (n = 8-10), and the fibre type distribution (by immunohistochemistry) as well as the expression of the corresponding MyHC messenger RNA (mRNA) (protein and mRNA expression, using Western blot or quantitative real-time polymerase chain reaction (RT-PCR)). Immunohistochemistry and western blot analysis revealed that the masticatory muscles in the control and mdx mice consisted mainly of type 2 fibres, whereas soleus muscle consisted of both type 1 and 2 fibres. In the masseter muscle, the mRNA in mdx mice was not different from that found in the controls. However, the mRNA content of the MyHC-2b isoform in mdx mice was lower in comparison with the controls in the temporal muscle [11.9 versus 36.9 per cent; P < 0.01; mean ± standard error of the mean (SEM), Student's unpaired t-test], as well as in the tongue muscle (65.7 versus 73.8 per cent; P < 0.05). Similarly, the content of MyHC-2x isoforms in mdx tongue muscle was lower than in the controls (25.9 versus 30.8 per cent; P < 0.05). The observed down-regulation of the MyHC-2x and MyHC-2b mRNA in the masticatory muscles of mdx mice may lead to changed fibre type composition. The different MyHC gene expression in mdx mice masticatory muscles may be seen as an adaptive mechanism to muscular dystrophy.

MGF- and myostatin-mRNA regulation in masseter muscle after orthognathic surgery

Patients with prognathism and retrognathism show extensive morphologic changes after orthognathic surgery. The inability of muscles to adapt adequately might be one reason for observed relapses. The aim of this prospective study was to analyze the regulation of functional genes after surgery and changes in myosin heavy chain (MyHC) isoform expression, a potential molecular marker profile for inadequate muscle adaptation. 29 adult patients with prognathic and retrognathic mandibles were involved. A total of 232 muscle biopsies were taken from both masseter muscles presurgically and 6 months later. The mRNA expression of "mechano growth factor" (MGF), myostatin, and 3 MyHC isoforms were quantified by real-time polymerase chain reaction. The MGF mRNA was significantly up-regulated (P < .005), whereas myostatin mRNA showed no significant regulation. There was a shift in MyHC isoform expression. The MyHC-I mRNA was decreased (P < .005), whereas MyHC-IIa mRNA was increased (P < .005). The coherence of increased MGF expression and MyHC isoform shift 6 months after orthognatic surgery indicates an adequate muscle adaptation and higher mastication activity.

Effects of low-intensity training on dihydropyridine and ryanodine receptor content in skeletal muscle of mouse

To evaluate low-intensity exercise training induced changes in the expression of dihydropyridine (DHP) and ryanodine (Ry) receptors both mRNA and protein levels were determined by quantitative RT-PCR and immunoblot analysis from gastrocnemius (GAS) and rectus femoris (RF) muscles of mice subjected to a 15-week aerobic exercise program. The level of muscular work was assayed by changes in myosin heavy chain (MHC) content, myoglobin (Mb) expression and muscle size. The mRNA expression and optical density of DHP receptor increased significantly in GAS by 66.8 and 39.5%, respectively. The expression of Ry receptor, on the other hand, was not up-regulated. In RF, there was a significant increase of 38.4% in the mRNA expression of DHP receptor, although the protein level remained the same. No changes in Ry receptor expression was observed. The training resulted in a 1.58% increase in the amount of MHC IIa and a 2.34% decrease in that of IIb and IId in GAS. A significant 8.3% increase in the Mb content was observed. In RF, no significant changes in MHC or in Mb content were noted. Our results show that an evident increase in the mRNA and protein expression of DHP receptor was induced in GAS even by a relatively low-intensity exercise. Surprisingly, contrast to DHP receptor expression, no changes in Ry receptor mRNA, or protein levels were found, indicating more abundant demand for DHP receptor after increased muscle activity.

Effect of age on skeletal muscle myofibrillar mRNA abundance: Relationship to myosin heavy chain protein synthesis rate

Age-related changes in myosin heavy chain (MHC) phenotype impact both the quantity and functional character of skeletal muscle. The present study was undertaken to examine the hypothesis that age-related changes in MHC mRNA abundance underlie alterations in protein synthesis rates and content. We measured the abundance of mRNA for MHC isoforms (MHC I, MHC IIa, IIx) and actin by RT-PCR in 6 young (mean ± SE; 29 ± 3) and 12 elderly (73 ± 1 yr; P < 0.01) volunteers and examined their association to MHC protein synthesis rates and their respective protein products. We found no differences between young and elderly volunteers in MHC isoform or actin transcript levels. Because of the absence of age effects, data were pooled for correlation analyses. Although total MHC mRNA levels were not related to MHC fractional synthesis rates, the relative abundance of MHC I and MHC IIa mRNA were positively ( r = 0.450; P = 0.06) and negatively ( r = −0.493; P < 0.05) associated with MHC protein synthesis rates, respectively. MHC mRNA levels were positively correlated to their respective protein products (range of r-values: 0.551–0.727; P < 0.05 to P < 0.01), but were not related to skeletal muscle IGF-I mRNA abundance, circulating IGF-I or markers of immune activation. Our results argue against the notion that changes in MHC protein synthesis rates with age are related to altered MHC mRNA abundance, although our findings do suggest that possibility that individual variability in MHC protein synthesis rates is related to the relative abundance of MHC I versus MHC IIa transcripts.

Neuromuscular Adaptations to Electrostimulation Resistance Training

A combination of in vivo and in vitro analyses was performed to investigate muscular and neural adaptations of the weaker (nondominant) quadriceps femoris muscle of one healthy individual to short-term electrostimulation resistance training. The increase in maximal voluntary strength (+12%) was accompanied by neural (cross-education effect and increased muscle activation) and muscle adaptations (impairment of whole-muscle contractile properties). Significant changes in myosin heavy chain (MHC) isoforms relative content (+22% for MHC-2A and -28% for MHC-2X), single-fiber cross-sectional area (+27% for type 1 and +6% for type 2A muscle fibers), and specific tension of type 1 (+67%) but not type 2A fibers were also observed after training. Plastic changes in neural control confirm the possible involvement of both spinal and supraspinal structures to electrically evoked contractions. Changes at the single muscle fiber level induced by electrostimulation resistance training were significant and preferentially affected slow, type 1 fibers.

Endurance Training: Volume-Dependent Adaptational Changes in Myosin

The purpose of this study was to find the effect of different endurance training volumes on the composition and turnover of myosin. Sixteen-week-old male rats of the Wistar strain were divided into three different volume-based training groups. Changes in myosin heavy chain (MyHC), myosin light chain (MyLC) isoforms' composition, their synthesis rate, as well as myosin binding C-protein synthesis rate, and muscle protein degradation rate were measured. In slow-twitch (ST) soleus (Sol) muscle MyHC I isoform relative content increased and MyHC IIa isoform decreased during excessive increase in the volume of endurance training (ET). In plantaris (Pla) muscle excessive increase in ET volume decreased MyHC I and IIb isoforms, and increased MyHC IIa and IId relative content. In extensor digitorum longus (EDL) muscle the relative content of MyHC IId isoform increased during ET, but excessive increase in training volume decreased it. In Pla muscle the relative content of MyLC 1 (slow) isoform decreased during ET, but excessive increase in ET volume decreased the relative content of MyLC 3 (fast) isoform in both fast-twitch (FT) muscles. Decrease in MyHC and myosin binding C-protein synthesis rate in Pla muscle had significant correlation with ET volume (r = - 0.537, p < 0.05 and r = - 0.727, p < 0.001 subsequently). MyHC I and IIb isoforms and MyLC 3 (fast) isoform in Pla muscle and MyHC IIb, IId and MyLC 3 (fast) isoforms in EDL muscle are the most sensitive to the increase in ET volume. Excessive increase in ET volume leads to a decrease in physical working capacity. The degradation of muscle protein increased during ET in all groups.