Twitch Fibers Research Articles

Reply from Daniel C. Andersson, Matthew J. Betzenhauser, Steven Reiken, Alisa Umanskaya, Takayuki Shiomi and Andrew R. Marks

We appreciate the comments from Roatta and Farina concerning our paper (Andersson et al. 2012) on the molecular mechanism of adrenergic-induced force potentiation in fast twitch skeletal muscle. Our study explores how modulation of the ryanodine receptor (RyR1), which regulates sarcoplasmic reticulum (SR) Ca2+ release, can affect skeletal muscle force production. The hypothesis we tested was that protein kinase A (PKA)-mediated phosphorylation of the RyR1 enhances twitch force in the fast twitch skeletal muscle in mice. Inotropic effects in skeletal muscle following adrenergic receptor stimulation have been reported in many studies (Cairns & Dulhunty, 1993a; Cairns et al. 1993; Liu et al. 1997). The potentiating effect on isometric twitch force is evident in many different animal species (Bowman, 1980). We and others observe a small, but robust, increase in twitch force (∼10–20%) after adrenergic stimulation (Tashiro, 1973; Cairns & Dulhunty, 1993a; Cairns et al. 1993; Liu et al. 1997; Andersson et al. 2012). More recently, changes in Ca2+ handling have been linked to force potentiation (Cairns & Dulhunty, 1993a,b; Cairns et al. 1993; Liu et al. 1997). Cairns et al. (Cairns & Dulhunty, 1993a,b; Cairns et al. 1993) demonstrated enhanced SR Ca2+ release as the underlying mechanism for increased inotropy. In our paper we show that RyR1 PKA phosphorylation results in increased SR Ca2+ release and is a molecular mechanism underlying fast twitch skeletal muscle inotropy in mice. Indeed, mice harbouring RyR1 that cannot be PKA phosphorylated due to a substitution of an alanine for the serine phosphorylated by PKA in RyR1 fail to respond to catecholamines in terms of increasing the calcium transient or muscle force production (Andersson et al. 2012). Roatta and Farina challenge the view that adrenergic activation increases muscle force development in humans (Roatta & Farina, 2011). They correctly point out that the effect of adrenergic potentiation of skeletal muscle force has been difficult to detect in humans. Moreover, Roatta and Farina note that adrenergic stimulation of slow twitch (type 1) muscle can reduce twitch tension (Tashiro, 1973; Bowman, 1980). With the exception of some postural muscles (e.g. soleus), the mice have predominantly fast twitch fibres (Mathewson et al. 2012). In contrast, human muscles exhibit a substantial mix in fibre type and have considerably more slow twitch fibres, ∼40–70% are type 1 fibres in most human muscles (Johnson et al. 1973). Interestingly, the ability to maintain isometric force production in humans correlates with blood catecholamine levels (French et al. 2007). Therefore, the effect of adrenergic stimulation in human in vivo muscle experiments probably reflects the balance between the force potentiation and reduction depending on the fibre type. The net result of adrenergic stimulation in humans may well depend on the intensity and duration of the stimulation. Proving this in humans may be difficult. Nevertheless, the high degree of evolutionary conservation of the key molecules regulating excitation– contraction coupling strongly argues that the fundamental mechanisms are common in mammalian skeletal muscle.

The physiological basis of rehabilitation in chronic heart and lung disease

Cardiopulmonary rehabilitation is recognized as a core component of management of individuals with congestive heart failure (CHF) or chronic obstructive pulmonary disease (COPD) that is designed to improve their physical and psychosocial condition without impacting on the primary organ impairment. This has lead the scientific community increasingly to believe that the main effects of cardiopulmonary rehabilitative exercise training are focused on skeletal muscles that are regarded as dysfunctional in both CHF and COPD. Accordingly, following completion of a cardiopulmonary rehabilitative exercise training program there are important peripheral muscular adaptations in both disease entities, namely increased capillary density, blood flow, mitochondrial volume density, fiber size, distribution of slow twitch fibers, and decreased lactic acidosis and vascular resistance. Decreased lactic acidosis at a given level of submaximal exercise not only offsets the occurrence of peripheral muscle fatigue, leading to muscle task failure and muscle discomfort, but also concurrently mitigates the additional burden on the respiratory muscles caused by the increased respiratory drive, thereby reducing dyspnea sensations. Furthermore in patients with COPD, exercise training reduces the degree of dynamic lung hyperinflation leading to improved arterial oxygen content and central hemodynamic responses, thus increasing systemic muscle oxygen availability. In patients with CHF, exercise training has beneficial direct and reflex sympathoinhibitory effects and favorable effects on normalization of neurohumoral excitation. These physiological benefits apply to all COPD and CHF patients independently of the degree of disease severity and are associated with improved exercise tolerance, functional capacity, and quality of life.

Erythropoietin contributes to slow oxidative muscle fiber specification via PGC-1α and AMPK activation

Erythropoietin activity, required for erythropoiesis, is not restricted to the erythroid lineage. In light of reports on the metabolic effects of erythropoietin, we examined the effect of erythropoietin signaling on skeletal muscle fiber type development. Skeletal muscles that are rich in slow twitch fibers are associated with increased mitochondrial oxidative activity and corresponding expression of related genes compared to muscle rich in fast twitch fibers. Although erythropoietin receptor is expressed on muscle progenitor/precursor cells and is down regulated in mature muscle fibers, we found that skeletal muscles from mice with high erythropoietin production in vivo exhibit an increase in the proportion of slow twitch myofibers and increased mitochondrial activity. In comparison, skeletal muscle from wild type mice and mice with erythropoietin activity restricted to erythroid tissue have fewer slow twitch myofibers and reduced mitochondrial activity. PGC-1α activates mitochondrial oxidative metabolism and converts the fast myofibers to slow myofibers when overexpressed in skeletal muscle and PGC-1α was elevated by 2-fold in mice with high erythropoietin. In vitro erythropoietin treatment of primary skeletal myoblasts increased mitochondrial biogenesis gene expression including PGC-1α by 2.6-fold, CytC by 2-fold, oxygen consumption rate by 2-fold, and citrate synthase activity by 58%. Erythropoietin also increases AMPK, which induces PGC-1α and stimulates slow oxidative fiber formation. These data suggest that erythropoietin contributes to skeletal muscle fiber programming and metabolism, and increases PGC-1α and AMPK activity during muscle development directly to affect the proportion of slow/fast twitch myofibers in mature skeletal muscle

Efeito de diferentes doses de nandrolona associado ao treinamento de força sobre o perfil fenotípico e área de secção transversa do músculo de ratos

O presente estudo avaliou a influência de diferentes doses de decanoato de nandrolona (DN) associado ao Treinamento de Força (TF) sobre o fenótipo de fibras e área de secção transversa (AST) do músculo extensor longo dos dedos (EDL) em ratos "Wistar". Os animais foram divididos em sete grupos: controle (GC) e grupos de acordo com a concentração de DN (0,1, 1, 2, 5, 10 e 20 mg/kg) administrada intramuscular 3 vezes/semana. O TF consistiu de saltos em meio líquido (carga 50-70% do peso corporal) 3x/semana, durante cinco semanas. A associação do TF e DN promoveu ação modulatória sobre os tipos de fibras. Houve hipertrofia das fibras de contração rápida (tipo II) em comparação com as fibras de contração lenta (tipo I). Em conclusão, apesar da associação do TF com DN aumentar a AST muscular e alterar o fenótipo das fibras, não houve efeito gradual das doses mais altas.

지능형 비삽입식 요실금 치료기의 구현

In this paper, we have developed the intellectual kegel trainer with the biofeedback. The pelvic muscles of female are composed of a slow twitch fiber and a fast twitch fiber. If two twitch fiber be not well done, then the urine be frequently called by nature. In order to recover the function of pelvic muscles, we use the kegel trainer with biofeedback training. Such a trainer make strengthen the weakness pelvic muscles by biofeedback training and get exercise the pelvic muscles in physical suppress of 10 kg. The biofeedback training against the physical suppress can have strengthen the pelvic muscles and can display the operation graph of strengthen movement in monitor.

Matchmaking: SK channels, C‐boutons and motor units

Matchmaking: SK channels, C‐boutons and motor units

Erratum to: Impact of nutrition on muscle mass, strength, and performance in older adults

Muscle strength plays an important role in determining risk for falls, which result in fractures and other The online version of the original article can be found at http:// dx.doi.org/10.1007/s00198-012-2236-y. A. Mithal (*) Medanta Medicity, Sector 38, Gurgaon, India e-mail: ambrishmithal@hotmail.com J.-P. Bonjour : R. Rizzoli Division of Bone Diseases, University Hospitals and Faculty of Medicine, Geneva, Switzerland S. Boonen Centre for Metabolic Bone Diseases and Division of Geriatric Medicine, University of Leuven, Leuven, Belgium P. Burckhardt Clinique Bois Cerf/Hirslanden, Lausanne, Switzerland H. Degens Institute for Biomedical Research into Human Movement and Health, Manchester Metropolitan University, Manchester, UK H. Degens Division Space Physiology, Institute of Aerospace Medicine, German Aerospace Center, Cologne, Germany G. El Hajj Fuleihan Calcium Metabolism & Osteoporosis Program, American University of Beirut Medical Center, Beirut, Lebanon R. Josse Division of Endocrinology and Metabolism, University of Toronto, St. Michael’s Hospital Health Centre, Toronto, Canada P. Lips Division of Internal Medicine, Endocrine Section, VU University Medical Center, Amsterdam, Netherlands J. M. Torres Hospital Aranda de la Parra, Hidalgo, Leon, Mexico N. Yoshimura Department of Joint Disease Research, 22nd Century Medical and Research Center, The University of Tokyo, Tokyo, Japan D. A. Wahl International Osteoporosis Foundation, Nyon, Switzerland C. Cooper MRC Lifecourse Epidemiology Unit, University of Southampton, Southampton General Hospital, Southampton, UK C. Cooper NIHR Musculoskeletal Biomedical Research Unit, Institute of Musculoskeletal Sciences, University of Oxford, Oxford, UK B. Dawson-Hughes Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA, USA Osteoporos Int (2013) 24:1527–1528 DOI 10.1007/s00198-013-2278-9 injuries. While bone loss has long been recognized as an inevitable consequence of aging, sarcopenia—the gradual loss of skeletal muscle mass and strength that occurs with advancing age—has recently received increased attention. A review of the literature was undertaken to identify nutritional factors that contribute to loss of muscle mass. The role of protein, acid–base balance, vitamin D/calcium, and other minor nutrients like B vitamins was reviewed. Muscle wasting is a multifactorial process involving intrinsic and extrinsic alterations. A loss of fast twitch fibers, glycation of proteins, and insulin resistance may play an important role in the loss of muscle strength and development of sarcopenia. Protein intake plays an integral part in muscle health and an intake of 1.0–1.2 g/kg of body weight per day is probably optimal for older adults. There is a moderate relationship between vitamin D status and muscle strength. Chronic ingestion of acid-producing diets appears to have a negative impact on muscle performance, and decreases in vitamin B12 and folic acid intake may also impair muscle function through their action on homocysteine. An adequate nutritional intake and an optimal dietary acid–base balance are important elements of any strategy to preserve muscle mass and strength during aging. 1528 Osteoporos Int (2013) 24:1527–1528

Upregulation of RGK Protein Expression in Aging Mouse Fast Twitch Skeletal Muscle

A component of muscle weakness in older individuals is directly attributable to compromised excitation-contraction (EC) coupling. In skeletal muscle, the L-type Ca2+ channel (CaV1.1) serves as the voltage sensor for EC coupling by triggering Ca2+ release from the sarcoplasmic reticulum (SR) in response to plasma membrane depolarization.Although it has been established that impaired EC coupling (termed “EC uncoupling” by O. Delbono and colleagues) in aged individuals is caused by a reduction in the number of L-type channels present in the plasma membrane, the molecular mechanisms responsible for transducing age-dependent cellular signals (e.g., oxidative stress) to decreased CaV1.1 membrane expression remain enigmatic. In this study, we have investigated a role for RGK (Rad, Rem, Rem2, Gem/Kir) family small G proteins in EC uncoupling because: 1) expression of endogenous Rad is enhanced in response to oxidative stress in skeletal muscle, and 2) overexpression of Rem in muscle cells mimics EC uncoupling. We have found that exogenous overexpression of Rad in cultured myotubes also mimics EC uncoupling. Moreover, immunoblotting of fast-twitch tibialis anterior and mixed gastrocnemius muscle lysates revealed progressive age-dependent enhancement of Rad protein levels while Rad expression was largely absent in slow-twitch soleus muscle in all age groups (ranging from 2-36 months). Taken together, our observations raise the possibility that Rad acts as one molecular link between elevated oxidative stress and EC uncoupling in aging fast-twitch muscle. Conversely, the lack of Rad expression in slow twitch muscle suggests that Rad may play a role in the disproportionate retention of slow twitch fibers in aged individuals.

Human Aging and Expression of Proteins Interacting with the Ryanodine Receptor in Skeletal Muscle

Sarcopenia is characterised by reduced muscle mass and reduced force that is only partially attributable to muscle atrophy. Fiber type distribution changes with aging (fast twitch decreases, slow twitch increases). Excitation-contraction coupling (ECC) may be impaired by an uncoupling of the dihydropyridine receptor (DHPR) and the ryanodine receptor (RyR1), possibly due to decreased expression of the DHPR α1s subunit (Delbono et al., J Membr Biol. 1995;148:211-22). The DHPR β1a subunit, which may contribute to ECC (Rebbeck et al., Biophys J. 2011;100:922-30), increases (Taylor et al., Aging cell 2009;8:584-94). The 12KDa FK506 binding protein (FKBP12) stabilizes RyR1 and its dissociation may contribute to decreased ECC (Andersson et al., Cell Metab.2011; 14:196-207). Previous studies have used animal models; here we investigate the expression of these proteins in aging human muscle.Human muscle samples were obtained from 42 male and female donors (age 40-90) undergoing knee (vastus medialis) and hip (gluteus minimus or gluteus medius) replacements. Results of fiber type distribution in muscle homogenates from female subjects shows fast twitch fibers decreasing and slow twitch increasing with age. Preliminary data shows that levels of FKBP12 relative to RyR1, determined in microsomal vesicles using western blot and densitometry decrease with age. Expression levels of the DHPR α1s and β1a subunits relative to that of actin determined in muscle homogenates using western blot and densitometry are being analysed. We find that β1a subunit is mostly in the homogenate and not associated with membrane fractions. The preliminary data indicates that the levels of several of the proteins that associate with RyR1 and modulate its activity change with age and could affect the release of Ca2+ during ECC and muscle function in human sarcopenia.

Impact of nutrition on muscle mass, strength, and performance in older adults

Muscle strength plays an important role in determining risk for falls, which result in fractures and other injuries. While bone loss has long been recognized as an inevitable consequence of aging, sarcopenia-the gradual loss of skeletal muscle mass and strength that occurs with advancing age-has recently received increased attention. A review of the literature was undertaken to identify nutritional factors that contribute to loss of muscle mass. The role of protein, acid-base balance, vitamin D/calcium, and other minor nutrients like B vitamins was reviewed. Muscle wasting is a multifactorial process involving intrinsic and extrinsic alterations. A loss of fast twitch fibers, glycation of proteins, and insulin resistance may play an important role in the loss of muscle strength and development of sarcopenia. Protein intake plays an integral part in muscle health and an intake of 1.0-1.2 g/kg of body weight per day is probably optimal for older adults. There is a moderate [corrected] relationship between vitamin D status and muscle strength. Chronic ingestion of acid-producing diets appears to have a negative impact on muscle performance, and decreases in vitamin B12 and folic acid intake may also impair muscle function through their action on homocysteine. An adequate nutritional intake and an optimal dietary acid-base balance are important elements of any strategy to preserve muscle mass and strength during aging.

Comparative analysis of physical development and functional capacity of different sports athletes during competition period

The aim of this study was to compare physical fitness of high performance canoeists, rowers, Greek-Roman style wrestlers, basketball players and skiers during their competition period. Indices of physical development, muscle and fat mass and their ratios were obtained. Single muscular contraction power (SMCP) and anaerobic alactic muscular power (AAMP) were also measured. The anaerobic glycolytic power (AGP) was estimated by ergometer. The Bosco methodology was used to estimate the activity of fast twitch fibres (FTF). The psychomotor response time (PRT) and movement frequency (MF) per 10 s were estimated and Roufier index (RI) was applied to measure functional capacity of circulatory and respiratory systems. The examination of athletes specialising in five different sports allowed for identification of the peculiarities of sports specialisation. The distinctive height, highest body weight and static hand power values characterised rowers and basketball players; while canoeists had the highest muscle mass. Only canoeists achieved high SMCP during the competition period. The SMCP of rowers and skiers was optimal, whereas the basketball players and wrestlers demonstrated an insufficient single muscular contraction power. The highest anaerobic alactic muscle power was observed in basketball players and canoeists, whereas in the muscles the basketball players and wrestlers the activity of FTF was insufficient. Though its parameters were approximate to endurance-trained rowers, they considerably fell behind those of canoeists. The functional capacity of circulatory and respiratory system of skiers was highest. The research revealed that the majority of indices of skiers and wrestlers’ physical fitness were lowest among the other studied athletes. Such results reflect their limited potential to achieve high results in international competitions.

The Ubiquitin Ligase Nedd4-1 Participates in Denervation-Induced Skeletal Muscle Atrophy in Mice

Skeletal muscle atrophy is a consequence of muscle inactivity resulting from denervation, unloading and immobility. It accompanies many chronic disease states and also occurs as a pathophysiologic consequence of normal aging. In all these conditions, ubiquitin-dependent proteolysis is a key regulator of the loss of muscle mass, and ubiquitin ligases confer specificity to this process by interacting with, and linking ubiquitin moieties to target substrates through protein∶protein interaction domains. Our previous work suggested that the ubiquitin-protein ligase Nedd4-1 is a potential mediator of skeletal muscle atrophy associated with inactivity (denervation, unloading and immobility). Here we generated a novel tool, the Nedd4-1 skeletal muscle-specific knockout mouse (myoCre;Nedd4-1flox/flox) and subjected it to a well validated model of denervation induced skeletal muscle atrophy. The absence of Nedd4-1 resulted in increased weights and cross-sectional area of type II fast twitch fibres of denervated gastrocnemius muscle compared with wild type littermates controls, at seven and fourteen days following tibial nerve transection. These effects are not mediated by the Nedd4-1 substrates MTMR4, FGFR1 and Notch-1. These results demonstrate that Nedd4-1 plays an important role in mediating denervation-induced skeletal muscle atrophy in vivo.

Calcium buffering properties of sarcoplasmic reticulum and calcium-induced Ca2+ release during the quasi-steady level of release in twitch fibers from frog skeletal muscle

Experiments were performed to characterize the properties of the intrinsic Ca2+ buffers in the sarcoplasmic reticulum (SR) of cut fibers from frog twitch muscle. The concentrations of total and free calcium ions within the SR ([CaT]SR and [Ca2+]SR) were measured, respectively, with the EGTA/phenol red method and tetramethylmurexide (a low affinity Ca2+ indicator). Results indicate SR Ca2+ buffering was consistent with a single cooperative-binding component or a combination of a cooperative-binding component and a linear binding component accounting for 20% or less of the bound Ca2+. Under the assumption of a single cooperative-binding component, the most likely resting values of [Ca2+]SR and [CaT]SR are 0.67 and 17.1 mM, respectively, and the dissociation constant, Hill coefficient, and concentration of the Ca-binding sites are 0.78 mM, 3.0, and 44 mM, respectively. This information can be used to calculate a variable proportional to the Ca2+ permeability of the SR, namely d[CaT]SR/dt ÷ [Ca2+]SR (denoted release permeability), in experiments in which only [CaT]SR or [Ca2+]SR is measured. In response to a voltage-clamp step to −20 mV at 15°C, the release permeability reaches an early peak followed by a rapid decline to a quasi-steady level that lasts ∼50 ms, followed by a slower decline during which the release permeability decreases by at least threefold. During the quasi-steady level of release, the release amplitude is 3.3-fold greater than expected from voltage activation alone, a result consistent with the recruitment by Ca-induced Ca2+ release of 2.3 SR Ca2+ release channels neighboring each channel activated by its associated voltage sensor. Release permeability at −60 mV increases as [CaT]SR decreases from its resting physiological level to ∼0.1 of this level. This result argues against a release termination mechanism proposed in mammalian muscle fibers in which a luminal sensor of [Ca2+]SR inhibits release when [CaT]SR declines to a low level.

Exercise for Better ALS Management?

Exercise for Better ALS Management?

RARE MYOPATHIES AND EXPERIMENTAL APPROACHES - POSTER PRESENTATIONS G.P.125 ACTN3 genotype influences skeletal muscle performance through alterations in calcineurin signaling

Abstract Approximately 1 billion people worldwide do not express the fast-twitch skeletal muscle fibre protein alpha-actinin-3 (a-act-3) due to homozygosity for a common null polymorphism in the ACTN3 gene. ACTN3 genotype influences skeletal muscle performance in elite athletes and in the general population; a-act-3 deficiency is associated with enhanced endurance capacity. Studies of the Actn3 KO mouse revealed that a-act-3 deficiency leads to a shift in fast muscle fibre contractile and metabolic properties towards those normally associated with slower muscle fibres. To gain mechanistic insights into these changes we performed a microarray and, interestingly, found that downstream targets of the calcineurin signalling pathway are altered in a-act-3 deficient muscle. We have now shown that the activity of calcineurin, which plays a critical role promoting fast-to-slow twitch fibre transition, is increased in KO mouse muscle, which likely accounts for the enhanced endurance performance in KO mice. We hypothesised that, due to the increased calcineurin activity, a-act-3 deficient muscle, may more readily adapt to physical demands that result in a fast-to-slow fibre conversion. KO mice demonstrate greater improvements in endurance performance following forced treadmill endurance training, associated with greater shifts in fast to slow fibre transition, increased fibre size and higher oxidative muscle metabolism compared to WT. We demonstrate that alpha-actinin-2 (a-act-2), which is upregulated in a-act-3 deficient muscle, has increased binding affinity for calsarcin-2, a key inhibitor of calcineurin activity. a-Act-2 competes with calsarcin-2 for binding to calcineurin, resulting in enhanced calcineurin signaling and the activation of the slow myogenic program. Our data provide, for the first time, a mechanistic explanation for the effects of ACTN3 genotype on skeletal muscle performance in elite athletes and adaptation to changing physical demands in the general population.

Changes in serum fast and slow skeletal troponin I concentration following maximal eccentric contractions

ObjectivesWe tested the hypothesis that fast skeletal muscle troponin I (fsTnI) concentration in serum would increase more than those of slow skeletal muscle troponin I (ssTnI) after eccentric exercise of the elbow flexors using a sensitive blood marker to track fibre specific muscle damage. DesignObservational comparison of response in a single experimental group. MethodsEight young men (26.4±6.2 years) performed 210 (35 sets of 6) eccentric contractions of the elbow flexors on an isokinetic dynamometer with one arm. Changes in serum fsTnI and ssTnI concentrations, serum creatine kinase (CK) activity, and maximal voluntary isometric contraction torque (MVIC) before and 1, 2, 3, 4 and 14 days following exercise were analysed by a Student–Newman–Keuls multiple comparison test. The relationship between serum CK activity and fsTnI or ssTnI concentrations was determined using a Pearson's product moment correlation. ResultsSignificant (P<0.05) decreases in MVIC and increases in serum CK activity and fsTnI were evident after exercise, but ssTnI did not change. The time course of changes in fsTnI was similar to that of CK, peaking at 4 days post-exercise, and the two were highly correlated (r=0.8). ConclusionsIncreases in serum fsTnI concentrations reflect muscle damage, and it seems likely that only fast twitch fibres were damaged by eccentric contractions.

Premature expression of a muscle fibrosis axis in chronic HIV infection

BackgroundDespite the success of highly active antiretroviral therapy (HAART), HIV infected individuals remain at increased risk for frailty and declines in physical function that are more often observed in older uninfected individuals. This may reflect premature or accelerated muscle aging.MethodsSkeletal muscle gene expression profiles were evaluated in three uninfected independent microarray datasets including young (19 to 29 years old), middle aged (40 to 45 years old) and older (65 to 85 years old) subjects, and a muscle dataset from HIV infected subjects (36 to 51 years old). Using Bayesian analysis, a ten gene muscle aging signature was identified that distinguished young from old uninfected muscle and included the senescence and cell cycle arrest gene p21/Cip1 (CDKN1A). This ten gene signature was then evaluated in muscle specimens from a cohort of middle aged (30 to 55 years old) HIV infected individuals. Expression of p21/Cip1 and related pathways were validated and further analyzed in a rodent model for HIV infection.ResultsWe identify and replicate the expression of a set of muscle aging genes that were prematurely expressed in HIV infected, but not uninfected, middle aged subjects. We validated select genes in a rodent model of chronic HIV infection. Because the signature included p21/Cip1, a cell cycle arrest gene previously associated with muscle aging and fibrosis, we explored pathways related to senescence and fibrosis. In addition to p21/Cip1, we observed HIV associated upregulation of the senescence factor p16INK4a (CDKN2A) and fibrosis associated TGFβ1, CTGF, COL1A1 and COL1A2. Fibrosis in muscle tissue was quantified based on collagen deposition and confirmed to be elevated in association with infection status. Fiber type composition was also measured and displayed a significant increase in slow twitch fibers associated with infection.ConclusionsThe expression of genes associated with a muscle aging signature is prematurely upregulated in HIV infection, with a prominent role for fibrotic pathways. Based on these data, therapeutic interventions that promote muscle function and attenuate pro-fibrotic gene expression should be considered in future studies.

Titin is not the weak link in the Z‐disk streaming induced by plyometric exercise

The purpose was to analyze the skeletal muscle changes induced by an acute bout of plyometric exercise (PlyEx) before and after a PlyEx training.Healthy untrained individuals (N=13) completed an acute bout of PlyEx (10×10 squat‐jumps, 1 min rest). Thereafter, 8 subjects completed 8 weeks of PlyEx, while 5 subjects were instructed to refrain from doing any jumping activity for 8 weeks. Seven days after the last training session all subjects repeated a second acute bout of PlyEx.The first acute bout of PlyEx induced a rise of creatine kinase activity (CK = 2421 ± 4978 U/l), Z‐line streaming mainly in fast twitch fibers, a stretch of the c‐terminus of titin (observed by immunogold) not limited to fast twitch fibers, and an increase in calpain‐3 autolysis. The second acute bout of PlyEx in the trained group did not induce: a rise of CK (110 ± 58 U/l), Z‐line streaming, or calpain‐3 activation; while in the control group only two subjects exhibited Z‐line streaming, although all subjects presented a stretch of titin.Eccentric explosive exercise induced a stretch of titin, which is not responsible for the weakness of the sarcomere and of the calpain‐3 activation involved in sarcomeric remodelling.Grant Funding Source: Claude Leon Foundation, National Research Foundation (NRF)

IKKα and alternative NF-κB regulate PGC-1β to promote oxidative muscle metabolism

Although the physiological basis of canonical or classical IκB kinase β (IKKβ)-nuclear factor κB (NF-κB) signaling pathway is well established, how alternative NF-κB signaling functions beyond its role in lymphoid development remains unclear. In particular, alternative NF-κB signaling has been linked with cellular metabolism, but this relationship is poorly understood. In this study, we show that mice deleted for the alternative NF-κB components IKKα or RelB have reduced mitochondrial content and function. Conversely, expressing alternative, but not classical, NF-κB pathway components in skeletal muscle stimulates mitochondrial biogenesis and specifies slow twitch fibers, suggesting that oxidative metabolism in muscle is selectively controlled by the alternative pathway. The alternative NF-κB pathway mediates this specificity by direct transcriptional activation of the mitochondrial regulator PPAR-γ coactivator 1β (PGC-1β) but not PGC-1α. Regulation of PGC-1β by IKKα/RelB also is mammalian target of rapamycin (mTOR) dependent, highlighting a cross talk between mTOR and NF-κB in muscle metabolism. Together, these data provide insight on PGC-1β regulation during skeletal myogenesis and reveal a unique function of alternative NF-κB signaling in promoting an oxidative metabolic phenotype.

Novel Approach to Meta-Analysis of Microarray Datasets Reveals Muscle Remodeling-related Drug Targets and Biomarkers in Duchenne Muscular Dystrophy

Elucidation of new biomarkers and potential drug targets from high-throughput profiling data is a challenging task due to a limited number of available biological samples and questionable reproducibility of differential changes in cross-dataset comparisons. In this paper we propose a novel computational approach for drug and biomarkers discovery using comprehensive analysis of multiple expression profiling datasets.The new method relies on aggregation of individual profiling experiments combined with leave-one-dataset-out validation approach. Aggregated datasets were studied using Sub-Network Enrichment Analysis algorithm (SNEA) to find consistent statistically significant key regulators within the global literature-extracted expression regulation network. These regulators were linked to the consistent differentially expressed genes.We have applied our approach to several publicly available human muscle gene expression profiling datasets related to Duchenne muscular dystrophy (DMD). In order to detect both enhanced and repressed processes we considered up- and down-regulated genes separately. Applying the proposed approach to the regulators search we discovered the disturbance in the activity of several muscle-related transcription factors (e.g. MYOG and MYOD1), regulators of inflammation, regeneration, and fibrosis. Almost all SNEA-derived regulators of down-regulated genes (e.g. AMPK, TORC2, PPARGC1A) correspond to a single common pathway important for fast-to-slow twitch fiber type transition. We hypothesize that this process can affect the severity of DMD symptoms, making corresponding regulators and downstream genes valuable candidates for being potential drug targets and exploratory biomarkers.