Myosin Heavy Chain IIx Research Articles

Adaptation of Alpha-Actinin Isoforms to Endurance Exercise Training in Adult and Old Rat Plantaris Muscle

We recently reported that that the increase in α-actinin-3 expression was associated with a type I to type II myosin heavy chain (MyHC) shift, and a chronic increase in muscular activity imposed by sprint training enhanced α-actinin-2 expression in rat skeletal muscles (Ogura et al. 2008, 2009). PURPOSE: To clarify the effects of 1) ageing-induced type II to type I MyHC shift and 2) endurance training on the expressions of α-actinin isoforms in rat plantaris muscle. METHODS: Adult (18 mo, n = 12) and old (28 mo, n = 12) male Fischer 344 rats were assigned to either a sedentary or an endurance training group (4 groups, n = 6/each). Animals in the training groups ran on a treadmill for 8 wk. The training intensity was adjusted to be relatively equal for adult and old training groups. After the training program was completed, the plantaris muscles were taken for analyses of α-actinin-2 and α-actinin-3 (western blot), MyHC composition (SDS-PAGE), and citrate synthase (CS) activity (spectrophotometory). Data were analyzed by two-way ANOVA (age × endurance training). RESULTS: Because no interaction was found, data were interpreted with main effect. The proportion of type IIb MyHC was lower (P < 0.05), and that of type I MyHC was higher (P < 0.05) in old animals than in adult animals, suggesting ageing-induced type II to type I MyHC shift. α-Actinin-3 was lower in old animals than in adult animals (adult: 0.97±0.02 vs. old: 0.84 ± 0.04 OD unit, P < 0.05). No significant difference was found in α-actinin-2 and CS activity between adult and old animals. CS activity was higher (+25%, P < 0.05) in trained animals than in sedentary animals. The proportion of type IIb and IIx MyHC were lower (P < 0.05), and that of type IIa MyHC was higher (P < 0.05) in trained animals than in sedentary animals, indicating a fast to slow shift within type II MyHC isoforms by endurance training. α-Actinin-2 was higher in trained animals than in sedentary animals (sedentary: 0.99±0.07 vs. training: 1.40±0.10 OD unit, P < 0.05). No significant difference was found in α-actinin-3 between trained and sedentary animals. CONCLUSIONS: These results support the α-actinin adaptation at the isoform level and show that the α-actinin-3 expression depends on the amount of type II MyHC, whereas α-actinin-2 expression is associated with improvement of muscular aerobic capacity.

Selectively reshaping a muscle phenotype: Functional overload of cat plantaris

Functional overload (FO) of the fast plantaris muscle was studied in treadmill-exercised (FO-Ex) or sedentary (FO-Sed) adult cats. Mechanical, phenotype, and kinematics analyses were performed. Plantigrade vs. normal digitigrade posture was observed early post-FO. Relative plantaris mass was greater in FO-Sed (10%) and FO-Ex (60%) cats than in controls 12 weeks post-FO. Specific tension was similar across groups, indicating functional hypertrophy. Fiber size was greater, percent slow fibers higher, percent IIa myosin heavy chain (MHC) higher, and IIx MHC lower in FO-Ex than controls. Twitch and half-relaxation times were longer, and the frequency-tension curve shifted toward that observed in slow muscles. Electromyography (EMG) and tendon force amplitudes during stepping were larger, and the yield (lengthening) phase occurred at a longer muscle length before compared with after FO. Reshaping the plantaris phenotype was highly dependent on the overload stimulus, indicating that electrical stimulation paradigms used during rehabilitation should be performed with the muscles under "loaded" conditions.

Myosin heavy chain pattern in the Akhal-Teke horses

This study investigates the myosin heavy chain (MyHC) isoform composition in the gluteus medius muscle of the Akhal-Teke horses using SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis). Fifteen horses aged between 1.5 and 23.5 years were used in this study and divided into three age groups: 1.5 to 4 (n = 6), 9 to 13 (n = 5) and 18.5 to 23.5 years (n = 4). The average content of the MyHC I isoform was 11.72 ± 1.07% (variation between individuals: 7.09% to 20.14%). The relative content of the MyHC IIa and IIx isoforms was subsequently 38.20 ± 1.46% (30.73% to 48.78%) and 50.07 ± 1.10% (43.8% to 56.78%) from the total MyHC. The MyHC pattern in the skeletal muscles of the Akhal-Teke horses shows that the muscles of these horses have a high capacity both for endurance and speed.

Muscle characteristics and meat quality traits are affected by divergent selection on residual feed intake in pigs1

Residual feed intake (RFI) is defined as the difference between the observed feed intake and that expected based on requirements for maintenance and production. A divergent selection was conducted during 4 generations in Large White male pigs to produce low and high RFI lines. The present study aims at determining the influence of this selection on biochemical and histological traits of skeletal muscle, and relating these changes to correlated effects on growth, carcass composition, and meat quality traits. At 8 d preslaughter, biopsies from the LM were taken in the fed state on 14 females from each RFI line fed ad libitum. Animals were slaughtered at 107.8 ± 8.0 kg of BW without any previous fasting. Samples of LM, semimembranosus (SM), biceps femoris (BFM), and rhomboideus muscles were taken at both 30 min and 24 h postmortem. Myofiber typing was only assessed in LM. Low RFI pigs ("efficient") had leaner carcasses with greater muscle content (P < 0.001), less backfat thickness (P < 0.001), and less intramuscular fat content in all 4 muscles (P < 0.01 to P = 0.04). Their greater muscle content was associated with hypertrophy of all fast-twitch fibers. Glycogen content in all glycolytic muscles (i.e., LM, SM and BFM), was greater in low than high RFI pigs. The greater accumulation of glycogen in LM of low RFI pigs was specifically located in the fast-twitch glycolytic IIBW fibers, which correspond to fibers containing IIb, IIb + IIx, or IIx myosin heavy chains. The difference in muscle glycogen content between RFI line pigs was more significant in the living animals (P = 0.0003) than at 30 min postmortem (P = 0.08). This was associated with a decreased ultimate pH (P = 0.001), and greater lightness of color (P = 0.002) and drip loss (P = 0.04) in LM of low than high RFI line pigs, suggesting that selection for reduced RFI may impair some meat quality traits, such as water-holding capacity. Pigs from the low RFI line exhibited a greater (P = 0.02) percentage of IIBW fibers in LM and tended (P < 0.10) to have less lipid β-oxidative capacity in LM, SM, and BFM. In contrast, no difference (P > 0.10) between lines was found for citrate synthase and lactate dehydrogenase activities, mitochondrial activity, and expression of genes coding for uncoupling proteins 2 and 3. Differences between RFI pigs in plasma leptin, cortisol, and thyroid hormone concentrations are presented and discussed. In conclusion, selection for low RFI influenced muscle properties in a way favoring muscle mass, but likely impairing meat quality.

What causesin vivomuscle specific tension to increase following resistance training?

It is not known why in vivo muscle specific tension increases following resistance training in humans but changes in muscle fibre-type composition, increased single-fibre specific tension or lateral force transmission might provide explanations. Lateral force transmission would increase specific tension but decrease contraction velocity, thus not affecting maximal power per unit muscle volume. In vivo muscle specific tension, power output and muscle volume were determined in the quadriceps femoris of 42 young men, while myosin heavy chain (MyHC) isoform composition, single-fibre (SF) specific tension, SF maximal shortening velocity (V(max)) and SF peak power (W(max)) of the vastus lateralis were established in a subsample (n = 17) before and after high-intensity leg-extension resistance training (3 sessions week(-1) for 9 weeks). Following training, in vivo muscle specific tension increased by 17% but the power output/muscle volume ratio remained unaltered. Furthermore, there was no relationship between the training-induced decrease in MyHC IIX and the change in specific tension in vivo. In addition, SF specific tension, V(max) and W(max) were unchanged following training. In conclusion, a change in fibre-type composition does not explain the increased in vivo specific tension, nor does it seem likely that increased myofilament packing occurred with resistance training. However, an unchanged in vivo power per unit muscle volume is in accordance with the notion of enhanced lateral force transmission after strength training.

Calcium-activated force of human muscle fibers following a standardized eccentric contraction

Peak Ca(2+)-activated specific force (force/fiber cross-sectional area) of human chemically skinned vastus lateralis muscle fiber segments was determined before and after a fixed-end contraction or an eccentric contraction of standardized magnitude (+0.25 optimal fiber length) and velocity (0.50 unloaded shortening velocity). Fiber myosin heavy chain (MHC) isoform content was assayed by SDS-PAGE. Posteccentric force deficit, a marker of damage, was similar for type I and IIa fibers but threefold greater for type IIa/IIx hybrid fibers. A fixed-end contraction had no significant effect on force. Multiple linear regression revealed that posteccentric force was explained by a model consisting of a fiber type-independent and a fiber type-specific component (r(2) = 0.91). Preeccentric specific force was directly associated with a greater posteccentric force deficit. When preeccentric force was held constant, type I and IIa fibers showed identical susceptibility to damage, while type IIa/IIx fibers showed a significantly greater force loss. This heightened sensitivity to damage was directly related to the amount of type IIx MHC in the hybrid fiber. Our model reveals a fiber-type sensitivity of the myofilament lattice or cytoskeleton to mechanical strain that can be described as follows: type IIa/IIx > type IIa = type I. If these properties extend to fibers in vivo, then alterations in the number of type IIa/IIx fibers may modify a muscle's susceptibility to eccentric damage.

Biochemistry of the Anterior, Medial, and Posterior Genioglossus in the Aged Rat

Age-related tongue weakness may contribute to swallowing deficits in the elderly. One contributing factor may be an alteration in muscle-fiber-type properties with aging. However, it is not clear how muscle fiber types within the aged tongue may vary from those found in young adults, or how fiber types may vary across the anteroposterior axis of the extrinsic tongue muscles. We examined the myosin heavy chain (MHC) composition of anterior, medial, and posterior sections of the genioglossus muscle (GG) in ten old male Fischer 344/Brown Norway rats and compared findings to previously reported data from young adult male rats. Significant differences (p<0.01) between young adult and old rats were found in the distribution of MHC isoforms along the anteroposterior axis of the muscle. In the anterior, medial, and posterior regions, there was a significantly smaller proportion of type IIb MHC in the old rat GG muscles, while the proportion of type IIx MHC was significantly greater. In the medial region, the proportion of type I MHC was found to be significantly greater in the old rats. Thus, we found a shift to more slowly contracting muscle fibers in the aged rat tongue.

Skeletal Muscle Signature of a Champion Sprint Runner

Human skeletal muscle contains three types of the main motor protein myosin heavy chain (MHC) and individual muscle fibers contain only one type of MHC (pure fiber types: I, IIa and IIx) or a mixture of MHC (hybrid fiber types: I/IIa and IIa/IIx). Each of these fiber types has a distinct phenotypic profile that contributes to human locomotion. The mixture of these fiber types within the muscle can have a profound impact on athletic performance. Our laboratory recently had the opportunity to examine the skeletal muscle profile of a World Record holder and World Champion sprint runner. PURPOSE: To examine single muscle fiber MHC composition (i.e. fiber type) and single muscle fiber contractile function (strength, speed and power) from this World Class sprinter. METHODS: A large number of isolated single muscle fibers from the vastus lateralis were analyzed for contractile function (n=53) and fiber type profile (n=329 fibers). RESULTS: Fiber type profile showed that 72% of the muscle contained fast motor proteins (MHC IIa and IIx). The novel finding was that the sprint champion's muscle contained 24% of the pure MHC IIx fiber type. Normal healthy human adult muscle contains less than 2% of the pure MHC IIx fiber type. Power output of the MHC IIx muscle fibers were the highest values recorded to date by a wide margin (35±4 W·l-1). Single fiber power output data from other athletic populations (swimmers and distance runners) and recreational athletes generally fall in the range of 5-10 W·l-1 and do not exceed 20 W·l-1. CONCLUSION: The unusually high abundance and high power output of the rare and powerful pure MHC IIx fiber type represent a unique muscle signature that provides a myocellular basis for the high level of athletic success achieved in sprinting events by this individual.

48 MUSCLE CHARACTERISTICS OF BOVINE CLONE OFFSPRING F1 COMPARED WITH CLONES

Information on clone offspring F1 is limited, especially in species with a long inter-generation interval such as cattle. As cloned cattle exhibit a slight delay in muscle maturation until puberty (Jurie et al. 2009 Animal 3, 244-250), the present study aimed to investigate the contractile and metabolic muscle characteristics of F1 at 8, 12, and 18 months of age. Repeated biopsies of the semitendinosus muscle were collected on 10 F1 heifers born after AI of cloned cows at the experimental farm of INRA. Muscle characteristics of these offspring were compared with those of 9 female clones and 8 AI control heifers previously biopsied at the same ages. All animals (clones, F1, and controls) were female Holstein, born and raised under the same conditions in the same farm. Biopsy samples were stored frozen at -80°C until analysis for contractile and metabolic characteristics. The type of contractile fibers was determined from the proportion of the different myosin heavy chain (MyHC) isoforms separated by electrophoresis. Oxidative metabolism was assessed by isocitrate dehydrogenase (ICDH) and cytochrome-c oxidase (COX) activities (μmol min-1 per gram of muscle). Data were analyzed separately for each time of biopsy using the GLM procedure of SAS (SAS Institute, Cary, NC, USA). The statistical model contained the group as fixed effect. When a significant effect was detected, differences between least squares means were further separated by the PDIFF option of SAS. Comparison of contractile characteristics from the 3 groups of animals is presented in Table 1. The proportion of MyHC I (slow oxidative isoform) and MyHC IIx (fast glycolytic isoform) in the muscles of F1 was not significantly different from those of controls at 8 and 12 months of age. F1 had different muscle contractile properties compared with clones at 12 months of age. At 8 months of age, F1 had greater ICDH activity than controls (1.39 ± 0.22 v. 0.54 ± 0.007; P ≤ 0.002) and greater COX activities (11.4 ± 1.6 v. 4.2 ± 0.9; P ≤ 0.003), but this was not observed later on. Altogether, these data indicate that the muscles of F1 were more oxidative than those of controls. This was not related to a higher percentage of type I fibers but rather to a higher percentage of type IIA fibers. A delay in muscle maturation was only partially found in F1. Table 1.Contractile characteristics (mean ± SE) of the semitendinosus muscle from controls (n = 8), clones (n = 9) and clone offspring (F1, n = 10) heifers

Effects of strength training with eccentric overload on muscle adaptation in male athletes

In classic concentric/eccentric exercise, the same absolute load is applied in concentric and eccentric actions, which infers a smaller relative eccentric load. We compared the effects of 6 weeks of classic concentric/eccentric quadriceps strength training (CON/ECC, 11 subjects) to eccentric overload training (CON/ECC+, 14 subjects) in athletes accustomed to regular strength training. The parameters determined included functional tests, quadriceps and fibre cross-sectional area (CSA), fibre type distribution by ATPase staining, localisation of myosin heavy chain (MHC) isoform mRNAs by situ hybridization and the steady-state levels of 48 marker mRNAs (RT-PCR) in vastus lateralis biopsies taken before and after training. Both training forms had anabolic effects with significant increases in quadriceps CSA, maximal strength, ribosomal RNA content and the levels of mRNAs involved in growth and regeneration. Only the CON/ECC+ training led to significantly increased height in a squat jump test. This was accompanied by significant increases in IIX fibre CSA, in the percentage of type IIA fibres expressing MHC IIx mRNA, in the level of mRNAs preferentially expressed in fast, glycolytic fibres, and in post-exercise capillary lactate. The enhanced eccentric load apparently led to a subtly faster gene expression pattern and induced a shift towards a faster muscle phenotype plus associated adaptations that make a muscle better suited for fast, explosive movements.

Additive effects of a steroidal implant and zilpaterol hydrochloride on feedlot performance, carcass characteristics, and skeletal muscle messenger ribonucleic acid abundance in finishing steers1

This experiment investigated the effects of zilpaterol hydrochloride (ZH) and the steroidal implant Revalor-S (RS; 120 mg of trenbolone acetate and 24 mg of estradiol-17beta) on finishing steer performance and the mRNA concentration of beta-adrenergic receptors (beta-AR) types I and II, and types I, IIA, and IIX myosin heavy chain (MHC) isoforms. A total of 2,279 feedlot steers weighing 426 +/- 6.4 kg were administered no implant or RS on d 0, and fed 0 or 8.3 mg of ZH/kg of diet DM during the last 30 d with a 3-d withdrawal. Treatments were randomly assigned to 24 pens (n = 6 pens/treatment). At slaughter, semimembranosus muscle tissue was excised for RNA isolation from 4 carcasses per pen. No interactions were detected for any of the variables measured in the experiment. Administration of ZH during the last 30 d of the feeding period increased (P < 0.01) ADG, G:F, HCW, and LM area; decreased (P < 0.01) 12th-rib fat depth and marbling; and improved (P < 0.01) yield grade. Treatment had no effect on beta1-AR mRNA levels, but there was an increase (P = 0.01) in beta(2)-AR mRNA levels due to ZH inclusion. Myosin heavy chain-I (MHC-I) mRNA levels were unaffected by treatment. For MHC-IIA mRNA concentrations, administration of RS tended (P = 0.08) to increase mRNA levels, whereas ZH feeding the last 30 d tended (P = 0.08) to decrease mRNA levels for this isoform of myosin. Feeding ZH the last 30 d before slaughter increased (P < 0.01) mRNA concentrations of MHC-IIX in semimembranosus muscle of steers. These data indicate the combined use of ZH and RS additively contributes to BW and carcass gain in finishing feedlot steers and decreases marbling scores and USDA quality grades. The LM area increased and fat thickness decreased. In addition, ZH feeding changes the mRNA levels of MHC isoforms to a faster, more glycolytic fiber type in bovine skeletal muscle. These changes in mRNA concentrations of MHC isoforms, due to ZH feeding, could be affecting skeletal muscle hypertrophy.

Calcineurin plays a modulatory role in loading-induced regulation of type I myosin heavy chain gene expression in slow skeletal muscle

The role of calcineurin (Cn) in skeletal muscle fiber-type expression has been a subject of great interest because of reports indicating that it controls the slow muscle phenotype. To delineate the role of Cn in phenotype remodeling, particularly its role in driving expression of the type I myosin heavy chain (MHC) gene, we used a novel strategy whereby a profound transition from fast to slow fiber type is induced and examined in the absence and presence of cyclosporin A (CsA), a Cn inhibitor. To induce the fast-to-slow transition, we first subjected rats to 7 days of hindlimb suspension (HS) + thyroid hormone [triiodothyronine (T(3))] to suppress nearly all expression of type I MHC mRNA in the soleus muscle. HS + T(3) was then withdrawn, and rats resumed normal ambulation and thyroid state, during which vehicle or CsA (30 mg x kg(-1) x day(-1)) was administered for 7 or 14 days. The findings demonstrate that, despite significant inhibition of Cn, pre-mRNA, mRNA, and protein abundance of type I MHC increased markedly during reloading relative to HS + T(3) (P < 0.05). Type I MHC expression was, however, attenuated by CsA compared with vehicle treatment. In addition, type IIa and IIx MHC pre-mRNA, mRNA, and relative protein levels were increased in Cn-treated compared with vehicle-treated rats. These findings indicate that Cn has a modulatory role in MHC transcription, rather than a role as a primary regulator of slow MHC gene expression.

Rapid muscle atrophy response to unloading: pretranslational processes involving MHC and actin

Skeletal muscles, especially weight-bearing muscles, are very sensitive to changes in loading state. The aim of this paper was to characterize the dynamic changes in the unloaded soleus muscle in vivo following a short bout of hindlimb suspension (HS), testing the hypothesis that transcriptional events respond early to the atrophic stimulus. In fact, we observed that after only 1 day of HS, primary transcript levels of skeletal alpha-actin and type I myosin heavy chain (MHC) genes were significantly reduced by more than 50% compared with ground control levels. The degree of the decline for the mRNA expression of actin and type I MHC lagged behind that of the pre-mRNA levels after 1 day of HS, but by 2 and 7 days of HS, large decreases were observed. Although the faster MHC isoforms, IIx and IIb, began to be expressed in soleus after 1 day of HS, a relatively significant shift in mRNA expression from the slow MHC isoform type I toward these fast MHC isoforms did not emerge until 7 days of HS. One day of HS was sufficient to show significant decreases in mRNA levels of putative signaling factors serum response factor (SRF), suppressor of cytokine signaling-3 (SOCS3), and striated muscle activator of Rho signaling (STARS), although transcription factors yin-yang-1 (YY1) and transcriptional enhancing factor-1 (TEF-1) were not significantly affected by HS. The protein levels of actin and type I MHC were significantly decreased after 2 days of HS, and SRF protein was significantly decreased after 7 days HS. Our results show that after only 1 day of unloading, pre-mRNA and mRNA expression of muscle proteins and muscle-specific signaling factors are significantly reduced, suggesting that the downregulation of the synthesis side of the protein balance equation that occurs in atrophying muscle is initiated rapidly.

Chronic activation of 5'-AMP-activated protein kinase changes myosin heavy chain expression in growing pigs

The purpose of this study was to determine the effect of 5'-AMP-activated protein kinase (AMPK) on energy metabolism and myosin heavy chain (MyHC) isoform expression in growing pigs using chronic treatment with 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR) as a model. Four-week-old pigs were given daily injections of AICAR or 0.9% saline for 10 d. Treatment with AICAR increased (P < 0.05) AMPK activity in semitendinosus muscles (STM). Expression of skeletal muscle specific glucose transporter 4 (GLUT4) was also enhanced (P < 0.05) by AICAR treatment. Using real-time PCR, electrophoresis, and Western blot analyses, we confirmed that AICAR treatment caused a decrease (P < 0.05) in type IIa MyHC isoform mRNA and protein levels and a concomitant increase (P < 0.05) in type IIx MyHC containing fibers. Consistent with a MyHC isoform shift from IIa to IIx, muscles from pigs treated with AICAR had greater (P < 0.05) lactate dehydrogenase (LDH) activity. Moreover, muscle of treated pigs expressed greater (P < 0.05) message for LDH. Administration of AICAR, however, did not alter expression of PPAR-gamma coactivator-1alpha, fatty acid translocase, citrate synthase, or the activity of cytochrome c oxidase. Overall, these results indicate that activation of AMPK by AICAR causes muscle to assume a faster-contracting, more glycolytic nature. These data are in direct contrast to documented effects in rodent models, but these effects may be dependent on the time of administration and the overall growth status of the animal.

Continuous mild heat stress induces differentiation of mammalian myoblasts, shifting fiber type from fast to slow

Local hyperthermia has been widely used as physical therapy for a number of diseases such as inflammatory osteoarticular disorders, tendinitis, and muscle injury. Local hyperthermia is clinically applied to improve blood and lymphatic flow to decrease swelling of tissues (e.g., skeletal muscle). As for muscle repair following injury, the mechanisms underlying the beneficial effects of hyperthermia-induced muscle repair are unknown. In this study, we investigated the direct effects of continuous heat stress on the differentiation of cultured mammalian myoblasts. Compared with control cultures grown at 37 degrees C, incubation at 39 degrees C (continuous mild heat stress; CMHS) enhanced myotube diameter, whereas myotubes were poorly formed at 41 degrees C by primary human skeletal muscle culture cells, human skeletal muscle myoblasts (HSMMs), and C2C12 mouse myoblasts. In HSMMs and C2C12 cells exposed to CMHS, mRNA and protein levels of myosin heavy chain (MyHC) type I were increased compared with the control cultures. The mRNA level of MyHC IIx was unaltered in HSMMs and decreased in C2C12 cells, compared with cells that were not exposed to heat stress. These results indicated a fast-to-slow fiber-type shift in myoblasts. We also examined upstream signals that might be responsible for the fast-to-slow shift of fiber types. CMHS enhanced the mRNA and protein levels of peroxisome proliferator-activated receptor-gamma coactivator (PGC)-1alpha in HSMMS and C2C12 cells but not the activities of MAPKs (ERK1/2 and p38 MAPK) in HSMMs and C2C12 cells. These data suggest that CMHS induces a fast-to-slow fiber-type shift of mammalian myoblasts through PGC-1alpha.

Quadriceps muscle strength in scoliosis

Quadriceps muscle weakness is an important component of chronic obstructive pulmonary disease (COPD). We hypothesised that quadriceps weakness would also be a feature of restrictive lung disease due to scoliosis. We studied 10 patients with severe scoliosis (median (interquartile range (IQR)) forced expiratory volume in 1 s (FEV(1))() 35.3 (11)% predicted), 10 patients with severe COPD (FEV(1) 26.5 (9.0)% pred) and 10 healthy age-matched adults. We measured quadriceps strength, exercise capacity and analysed quadriceps muscle biopsies for myosin heavy-chain (MyHC) isoform expression and the presence of oxidative stress. Both groups exhibited quadriceps weakness with median (IQR) maximal voluntary contraction force being 46.0 (17.0) kg, 21.5 (21.0) kg and 31.5 (11.0) kg, respectively (p = 0.02 and 0.04, respectively, for each patient group against controls). Oxidative stress was significantly greater in the quadriceps of both restrictive and COPD patients. The scoliosis patients exhibited a decrease in the proportion of MyHC type I compared with controls; median (IQR) 35.3 (18.5)% compared with 47.7 (9.3)%, p = 0.028. The scoliosis patients also showed an increase in MyHC IIx (26.3 (15.5)% compared with 11.3 (13.0)%, p = 0.01. Quadriceps weakness is a feature of severe scoliosis; the similarities between patients with scoliosis and patients with COPD suggest a common aetiology to quadriceps weakness in both conditions.

Potential Application of Essential Amino Acid Supplementation to Treat Sarcopenia in Elderly People

Aging is universally associated with a progressive decline in both physical and metabolic function across a diverse rangeofspeciesfromnematodestohumans.Moreover,progressive reductions in skeletal muscle mass, strength, and quality (referred to as sarcopenia) are often observed with aging. An associated problem is decline in maximal aerobic capacity, and all of these factors together contribute to the physical frailty of older people. In light of the rapidly expanding aging population, sarcopenia and related disorders are emerging as a major public health problem of the 21st century. This is particularly pertinent considering the loss of independence that is associated with frailty and falls that increase the risk of fractures. Another consequence of the sarcopenia of aging is a deleterious change in body composition resulting in many metabolic alterations leading on to metabolic syndrome and increased cardiovascular disease risk. Indeed, sarcopenia has received considerable attention by both researchers and clinicians over the last two decades. Muscle changes with age include reduction in fiber numbers, motor units, and a relative loss of type II fibers with a preservation of type I fibers (1) that may result from reductions in transcript levels of myosin heavy chain isoforms IIa and IIx without any decline of isoform I as reported in older people (2). Thus, a relative increase of type I fibers occurs with age, but these fibers are lower in abundance of mitochondria (3) than those in longdistance runners who also have a relatively high proportion of type I fibers but with high abundance of mitochondria. Reductionsinskeletalmuscleproteinabundances(thebalancebetween protein synthesis and degradation) are a key contributing factor to the development of sarcopenia. Mechanistically, it has been extensively reported that skeletal muscle protein synthesis is reduced in aging adults (2, 4, 5). The reduction in skeletal muscle mitochondrial protein synthesis (6) occurs in conjunction with reducedmitochondrialcapacityforATPproduction(3).Thank

Decreased muscle ACE activity enhances functional response to endurance training in rats, without change in muscle oxidative capacity or contractile phenotype

In the present study, we tested the hypothesis that chronic ANG I-converting enzyme (ACE) inhibition could improve the training-induced improvement in endurance exercise performance and that this could be related to enhanced skeletal muscle metabolic efficiency. Female Wistar rats were assigned to four groups comprising animals either maintained sedentary or endurance trained (Sed and Tr, respectively), and treated or not for 10 wk with an ACE inhibitor, perindopril (2 mg.kg(-1).day(-1)) (Per and Ct, respectively) (n = 8 each). Trained rats underwent an 8-wk treadmill training protocol that consisted of 2 h/day running at 30 m/min on a 8% decline. Before the start of and 1 wk before the end of experimental conditioning, the running time to exhaustion of rats was measured on a treadmill. The training program led to an increase in endurance time, higher in Tr-Per than in Tr-Ct group (125% in Tr-Ct vs. 183% in Tr-Per groups, P < 0.05). Oxidative capacity, measured in saponin-permeabilized fibers of slow soleus and fast plantaris muscles, increased with training, but less in Tr-Per than in Tr-Ct rats. The training-induced increase in citrate synthase activity also was less in soleus from Tr-Per than Tr-Ct rats. The training-induced increase in the percentage of the type IIa isoform of myosin heavy chain (MHC) (45%, P < 0.05) and type IIx MHC (25%, P < 0.05) associated with decreased type IIb MHC (34%, P < 0.05) was minimized by perindopril administration. These findings demonstrate that the enhancement in physical performance observed in perindopril-treated animals cannot be explained by changes in mitochondrial respiration and/or MHC distribution within muscles involved in running exercise.

Novel epigenetic regulation of skeletal muscle myosin heavy chain genes. Focus on “Differential epigenetic modifications of histones at the myosin heavy chain genes in fast and slow skeletal muscle fibers and in response to muscle unloading”

skeletal muscle is a highly plastic tissue, capable of responding and adapting to a variety of physiological stimuli, e.g., muscle loading and unloading. Multiple functional phenotypes of skeletal muscle exist throughout the body at the same time. For example, muscles required for antigravity support of the skeleton or sustained locomotion are generally slow-contracting, low force-generating, and relatively resistant to fatigue, while other muscles required for quick, powerful movements are generally fast-contracting, high force-generating, and easily fatigued. In fact, skeletal muscle phenotypes have been characterized using combinations of muscle properties, including metabolic, fatigability, color, innervation, or predominant contractile protein expression. Myosin heavy chain (MHC) is the most abundant protein in skeletal muscle, comprising ∼25% of the total protein content, and is a major component of the complex responsible for generating contractile force in skeletal muscle. At least nine MHC isoforms, each transcribed from their own gene, exist in mammalian striated muscle; but only slow type I MHC and various isoforms of fast type II (IIa, IIx/d, and IIb MHC isoforms) are present in adult limb skeletal muscle that is not undergoing regeneration (16). It is well established that skeletal muscle phenotype, particularly MHC gene expression, can be altered by different states of muscular activity or inactivity, as well as various hormonal and metabolic factors (1).

Differential epigenetic modifications of histones at the myosin heavy chain genes in fast and slow skeletal muscle fibers and in response to muscle unloading

Recent advances in chromatin biology have enhanced our understanding of gene regulation. It is now widely appreciated that gene regulation is dependent upon post-translational modifications to the histones which package genes in the nucleus of cells. Active genes are known to be associated with acetylation of histones (H3ac) and trimethylation of lysine 4 in histone H3 (H3K4me3). Using chromatin immunoprecipitation (ChIP), we examined histone modifications at the myosin heavy chain (MHC) genes expressed in fast vs. slow fiber-type skeletal muscle, and in a model of muscle unloading, which results in a shift to fast MHC gene expression in slow muscles. Both H3ac and H3K4me3 varied directly with the transcriptional activity of the MHC genes in fast fiber-type plantaris and slow fiber-type soleus. During MHC transitions with muscle unloading, histone H3 at the type I MHC becomes de-acetylated in correspondence with down-regulation of that gene, while upregulation of the fast type IIx and IIb MHCs occurs in conjunction with enhanced H3ac in those MHCs. Enrichment of H3K4me3 is also increased at the type IIx and IIb MHCs when these genes are induced with muscle unloading. Downregulation of IIa MHC, however, was not associated with corresponding loss of H3ac or H3K4me3. These observations demonstrate the feasibility of using the ChIP assay to understand the native chromatin environment in adult skeletal muscle, and also suggest that the transcriptional state of types I, IIx and IIb MHC genes are sensitive to histone modifications both in different muscle fiber-types and in response to altered loading states.