Muscle Growth Capacity Research Articles

Nonsense-mediated mRNA decay promote C2C12 cell proliferation by targeting PIK3R5.

Nonsense mediated mRNA decay (NMD) is a highly conserved RNA quality control system, which can specifically clear abnormal mRNA and play an important role in tumorigenesis. Myoblast proliferation plays an important role in the repair of skeletal muscle injury and the development of myosarcoma, and is controlled by a variety of transcription factors and signals. The molecular mechanism by which NMD regulates the proliferation of myoblast cells is not completely clear. In this study, we found that the NMD activity of skeletal muscle is high in 1-week-old mice but decreases gradually with age, corresponding to a weakening capacity for muscle growth and regeneration. Here, we provide evidence that NMD plays an important role in myoblast proliferation and apoptosis. In addition, we found that PIK3R5 is an NMD substrate gene which can inhibit AKT activity and C2C12 cell proliferation. Therefore, NMD can target PIK3R5 to enhance AKT activity, which in turn promotes C2C12 cell proliferation. This study provides new insights into NMD regulatory mechanisms in muscular development and into potential novel therapeutic strategies for muscle atrophy.

211 Overcoming the Growth Deficits Programmed by Maternofetal Stress

Abstract Prolonged maternofetal stress stunts placental development and causes fetal programming that reduces fetal growth and birthweight. Low birthweight due to intrauterine growth restriction (IUGR) of the fetus increases perinatal mortality. More commonly, however, it results in lifelong impairment of muscle growth capacity and metabolic function. In humans, low birthweight increases risk for obesity, diabetes, and other metabolic disorders by an estimated 18-fold. Similarly, low birthweight livestock exhibit greater early death loss, poor growth efficiency, and lower-quality carcasses at harvest. These animals manifest poor feed-to-gain ratios, less lean mass, and greater fat deposition. Together, these outcomes increase production costs, decrease value, and reduce the amount of meat produced per animal. The fetal programming mechanisms linking stress induced IUGR to impaired postnatal growth and metabolic efficiency are largely unknown. However, recent findings in IUGR fetal and neonatal lambs produced experimentally by maternal heat stress and maternofetal inflammation (and pair-fed controls) indicated skeletal muscle-centric programming of adrenergic and inflammatory pathways. Specifically, studies found reduced β2 adrenergic tone and enriched inflammatory signaling pathways. These changes coincided with intrinsic myoblast dysfunction, reduced muscle fiber hypertrophy, and impaired skeletal muscle glucose metabolism. Additionally, IUGR fetal and neonatal lambs exhibited impaired β cell function that may also be associated with adrenergic and inflammatory programming. Subsequent studies have investigated these mechanisms as potential therapeutic targets for interventions and treatments, which is a fundamental step in developing strategies to improve outcomes in low birthweight humans and livestock.

Neither myonuclear accretion nor a myonuclear domain size ceiling is a feature of the attenuated hypertrophic potential of aged human skeletal muscle

Ageing limits growth capacity of skeletal muscle (e.g. in response to resistance exercise), but the role of satellite cell (SC) function in driving this phenomenon is poorly defined. Younger (Y) (~ 23 years) and older (O) men (~ 69 years) (normal-weight BMI) underwent 6 weeks of unilateral resistance exercise training (RET). Muscle biopsies were taken at baseline and after 3-/6-week training. We determined muscle size by fibre CSA (and type), SC number, myonuclei counts and DNA synthesis (via D2O ingestion). At baseline, there were no significant differences in fibre areas between Y and O. RET increased type I fibre area in Y from baseline at both 3 weeks and 6 weeks (baseline: 4509 ± 534 µm2, 3 weeks; 5497 ± 510 µm2P < 0.05, 6 weeks; 5402 ± 352 µm2P < 0.05), whilst O increased from baseline at 6 weeks only (baseline 5120 ± 403 µm2, 3 weeks; 5606 ± 620 µm2, 6 weeks; 6017 ± 482 µm2P < 0.05). However, type II fibre area increased from baseline in Y at both 3 weeks and 6 weeks (baseline: 4949 ± 459 µm2, 3 weeks; 6145 ± 484 µm2 (P < 0.01), 6 weeks; 5992 ± 491 µm2 (P < 0.01), whilst O showed no change (baseline 5210 ± 410 µm2, 3 weeks; 5356 ± 535 µm2 (P = 0.9), 6 weeks; 5857 ± 478 µm2 (P = 0.1). At baseline, there were no differences in fibre myonuclei number between Y and O. RET increased type I fibre myonuclei number from baseline in both Y and O at 3 weeks and 6 weeks with RET (younger: baseline 2.47 ± 0.16, 3 weeks; 3.19 ± 0.16 (P < 0.001), 6 weeks; 3.70 ± 0.29 (P < 0.0001); older: baseline 2.29 ± 0.09, 3 weeks; 3.01 ± 0.09 (P < 0.001), 6 weeks; 3.65 ± 0.18 (P < 0.0001)). Similarly, type II fibre myonuclei number increased from baseline in both Y and O at 3 weeks and 6 weeks (younger: baseline 2.49 ± 0.14, 3 weeks; 3.31 ± 0.21 (P < 0.001), 6 weeks; 3.86 ± 0.29 (P < 0.0001); older: baseline 2.43 ± 0.12, 3 weeks; 3.37 ± 0.12 (P < 0.001), 6 weeks; 3.81 ± 0.15 (P < 0.0001)). DNA synthesis rates %.d−1 exhibited a main effect of training but no age discrimination. Declines in myonuclei addition do not underlie impaired muscle growth capacity in older humans, supporting ribosomal and proteostasis impairments as we have previously reported.

The Price of Surviving on Adrenaline: Developmental Programming Responses to Chronic Fetal Hypercatecholaminemia Contribute to Poor Muscle Growth Capacity and Metabolic Dysfunction in IUGR-Born Offspring.

Maternofetal stress induces fetal programming that restricts skeletal muscle growth capacity and metabolic function, resulting in intrauterine growth restriction (IUGR) of the fetus. This thrifty phenotype aids fetal survival but also yields reduced muscle mass and metabolic dysfunction after birth. Consequently, IUGR-born individuals are at greater lifelong risk for metabolic disorders that reduce quality of life. In livestock, IUGR-born animals exhibit poor growth efficiency and body composition, making these animals more costly and less valuable. Specifically, IUGR-associated programming causes a greater propensity for fat deposition and a reduced capacity for muscle accretion. This, combined with metabolic inefficiency, means that these animals produce less lean meat from greater feed input, require more time on feed to reach market weight, and produce carcasses that are of less quality. Despite the health and economic implications of IUGR pathologies in humans and food animals, knowledge regarding their specific underlying mechanisms is lacking. However, recent data indicate that adaptive programing of adrenergic sensitivity in multiple tissues is a contributing factor in a number of IUGR pathologies including reduced muscle mass, peripheral insulin resistance, and impaired glucose metabolism. This review highlights the findings that support the role for adrenergic programming and how it relates to the lifelong consequences of IUGR, as well as how dysfunctional adrenergic signaling pathways might be effective targets for improving outcomes in IUGR-born offspring.

Neuromuscular Impairment Following Chronic Moderate-Severe Contusion in Spinal Cord Injured Rats

Muscle atrophy and neuromuscular impairment are consequences of spinal cord injury (SCI) that impede quality of life and functional recovery. PURPOSE: To examine time course changes in muscle fiber type distribution, fiber cross-sectional area (fCSA), and other histologic characteristics of muscle pathology occurring in rats in response to moderate-severe contusion SCI. METHODS: Twenty-four 4-month old male Sprague-Dawley rats received SHAM surgery or T9 laminectomy plus moderate-severe (250 kilodyne) contusion SCI by a computer-guided impactor. Body weight and Basso-Beattie-Bresnahan (BBB) hindlimb locomotor rating scores were measured weekly. Animals were euthanized and soleus were harvested at 2-weeks, 1-month, 2-months, or 3-months post-surgery. Soleus fiber-type distribution, fCSA, and muscle-nerve bundle morphology were assessed by immunofluorescent staining, imaged using an epifluorescent microscope, and quantified with semi-automatic muscle analysis using segmentation of histology (SMASH). RESULTS: At 1-week post-surgery, SCI animals exhibited near-complete hindlimb paralysis (indicated by BBB scores <3), with minimal improvement in voluntary hindlimb locomotor function thereafter. Body weight, soleus mass, and median fCSA were significantly lower in SCI vs SHAM animals (p<0.01 at all timepoints). A slow-to-fast fiber-type shift was observed in SCI animals, with a progressive ~20% decrease in the number of type I fibers, ~8% increase in type IIa fibers, and ~5% increase in hybrid type I/IIa fibers at each consecutive timepoint, along with the emergence of unstained type IIx/b muscle fibers (~30% of total) at 3-months. In addition, muscle fiber splitting was present in SCI animals at 2-months, as well as reduced neurofilament staining in SCI muscle-nerve bundles. Furthermore, evidence of growth related remodeling occurred in SHAM muscles from increased centrally nucleated fibers across timepoints but not in SCI. CONCLUSION: Deterioration in motor ability accompanying SCI produced muscle atrophy and progressive impairments in muscle oxidative capacity that may have resulted from repetitive denervation-reinnervation cycles. These factors may have contributed to muscle pathology resulting in limited capacity for muscle growth and remodeling.

The effect of caffeine on skeletal muscle anabolic signaling and hypertrophy.

Caffeine is a widely consumed stimulant with the potential to enhance physical performance through multiple mechanisms. However, recent in vitro findings have suggested that caffeine may block skeletal muscle anabolic signaling through AMP-activated protein kinase (AMPK)-mediated inhibition of mechanistic target of rapamycin (mTOR) signaling pathway. This could negatively affect protein synthesis and the capacity for muscle growth. The primary purpose of this study was to assess the effect of caffeine on in vivo AMPK and mTOR pathway signaling, protein synthesis, and muscle growth. In cultured C2C12 muscle cells, physiological levels of caffeine failed to impact mTOR activation or myoblast proliferation or differentiation. We found that caffeine administration to mice did not significantly enhance the phosphorylation of AMPK or inhibit signaling proteins downstream of mTOR (p70S6k, S6, or 4EBP1) or protein synthesis after a bout of electrically stimulated contractions. Skeletal muscle-specific knockout of LKB1, the primary AMPK activator in skeletal muscle, on the other hand, eliminated AMPK activation by contractions and enhanced S6k, S6, and 4EBP1 activation before and after contractions. In rats, the addition of caffeine did not affect plantaris hypertrophy induced by the tenotomy of the gastrocnemius and soleus muscles. In conclusion, caffeine administration does not impair skeletal muscle load-induced mTOR signaling, protein synthesis, or muscle hypertrophy.

Effects of steroid treatment on growth, nutrient partitioning, and expression of genes related to growth and nutrient metabolism in adult triploid rainbow trout (Oncorhynchus mykiss)

The contribution of sex steroids to nutrient partitioning and energy balance during gonad development was studied in rainbow trout. Specifically, 19-mo old triploid (3N) female rainbow trout were fed treatment diets supplemented with estradiol-17β (E2), testosterone (T), or dihydrotestosterone at 30-mg steroid/kg diet for a 1-mo period. Growth performance, nutrient partitioning, and expression of genes central to growth and nutrient metabolism were compared with 3N and age-matched diploid (2N) female fish consuming a control diet not supplemented with steroids. Only 2 N fish exhibited active gonad development, with gonad weights increasing from 3.7% to 5.5% of body weight throughout the study, whereas gonad weights in 3N fish remained at 0.03%. Triploid fish consuming dihydrotestosterone exhibited faster specific growth rates than 3N-controls (P < 0.05). Consumption of E2 in 3N fish reduced fillet growth and caused lower fillet yield compared with all other treatment groups (P < 0.05). In contrast, viscera fat gain was not affected by steroid consumption (P > 0.05). Gene transcripts associated with physiological pathways were identified in maturing 2N and E2-treated 3N fish that differed in abundance from 3N-control fish (P < 0.05). In liver these mechanisms included the growth hormone/insulin-like growth factor (IGF) axis (igf1, igf2), IGF binding proteins (igfbp1b1, igfbp2b1, igfbp5b1, igfbp6b1), and genes associated with lipid binding and transport (fabp3, fabp4, lpl, cd36), fatty acid oxidation (cpt1a), and the pparg transcription factor. In muscle, these mechanisms included reductions in myogenic gene expression (fst, myog) and the proteolysis-related gene, cathepsin-L, suggesting an E2-induced reduction in the capacity for muscle growth. These findings suggest that increased E2 signaling in the sexually maturing female rainbow trout alters physiological pathways in liver, particularly those related to IGF signaling and lipid metabolism, to partition nutrients away from muscle growth toward support of maturation-related processes. In contrast, the mobilization of viscera lipid stores appear to be mediated less by E2 and more by energy demands associated with gonad development. These findings improve the understanding of how steroids regulate nutrient metabolism to meet the high energy demands associated with gonad development during sexual maturation.

Influence of selection for muscle growth capacity on meat quality traits and properties of the rectus abdominis muscle of Charolais steers

Twenty-three Charolais steers, slaughtered at 31 months of age and an average live weight of either 674kg (light group; n=13) or 751kg (heavy group; n=10) were used to determine the effect of increasing weight at slaughter by genetic selection on meat quality traits. Steers were born to pure-bred Charolais cows from an INRA experimental herd, reared and finished under the same breeding practices. The quality of meat from the M. rectus abdominis excised 24h postmortem was scored after 14 days ageing between 0 and 10 by sensory analysis using four descriptors: global assessment, initial tenderness, overall tenderness, juiciness and flavor intensity. Shear force measurements were evaluated on raw and broiled meat after 14 days of ageing. The pH, collagen and lipid contents, the collagen solubility, isocitrate dehydrogenase (ICDH), lactate dehydrogenase and cytochrome-c oxidase activities and the proportion of myosin heavy chain isoforms were measured 24h post-slaughter.The heavy group was characterized by a significantly higher empty live weight (683 vs 614kg) and carcass weight (before removing external fat: 469 vs 408kg; after removing external fat: 463 vs 403kg) at slaughter than the light one but an equivalent fatness score (2.74 on 5).Scores of heavy steer M. rectus abdominis were significantly higher for descriptors of initial tenderness (6.95 vs 6.31) and overall tenderness (6.79 vs 6.22) although the intramuscular fat content was equivalent for light and heavy group samples (16.6% of dry matter on average). Global assessment and flavor intensity were also slightly in favor of heavy group samples (6.49 vs 5.85 and 6.48 vs 6.07), but no differences were found between the two groups in meat juiciness (6.10 on average). Shear force on raw and broiled meat was not significantly different between groups (5.13 and 6.98 daN on average).No significant differences were found between groups on total and soluble collagen contents (p=0.32 and p=0.49 respectively). The heavy group was associated with a more glycolytic metabolism (LDH enzyme: 620 vs 528μmol/min/g; p=0.03) and a higher myosin heavy chain IIx proportion (39.1% vs 32.3%; p=0.07) without any modification in oxidative enzyme activities (ICDH and COX; p=0.49 and 0.84).

Delayed Satellite Cell Activation in Relation to Myostatin Expression Following Acute Resistance Exercise in Older and Younger Adults

Muscle growth is regulated by a unique population of muscle stem cells (satellite cells: SC). Depletion or dysfunction of SC leads to a loss in muscle mass and capacity for muscle growth. It remains unknown if this cell population is adversely affected by the aging process. PURPOSE: To quantify the SC pool size and SC cell-cycle response to acute resistance exercise in healthy young (Y) and Old (O) humans in relation to muscle myostatin. METHODS: Subjects (young (Y) 21.3±3.1y; N=9; Older adults (O) 69.6±3.9y; N=9) preformed 4 sets of 10 rep of unilateral leg extensions and leg press at 75% of 1RM. Blood and muscle biopsies (vastus lateralis) were obtained pre-exercise (PRE) and 3, 24 and 48h post exercise. SC number and cell-cycle kinetics were analyzed via flow cytometry. Gene analysis was analyzed via qRT-PCR and muscle cross-sections were analyzed for Pax7, myostatin, and activin IIb (ActRIIb) via IHC. RESULTS: PRE SC numbers were 53.9% lower in O vs. Y (8665 vs 13 345 Pax7+ cells/mg p<0.05). At 24h, SC remained 48.6% lower in O vs Y. SC increased significantly in both Y and O at 48h (32 342.7 vs 32 0161.1 Pax7+ cells/mg, Y vs O respectively). There were more SC in G0/ G1 at PRE and 24h in Y vs O (p<0.05), with no age effect at 48h. SC in S-phase and G2/M were not significantly elevated until 48h (no age effect) with a trend for more SC in S-phase in Y at 24h and 48h (p=0.08). PRE myostatin mRNA was 47% higher in O vs Y (p=0.06). Myostatin was similar across time in Y and O, significantly decreasing at 3, 24 and 48h post exercise (p<0.05). However, myostatin expression was 141% and 148% higher in O vs Y at 24h and 48h (p<0.001). Both follistatin and follistatin-like-1mRNA expression did not change post exercise. However basal follistatin expression was 59% higher in O vs Y (p=0.04). Myf5 expression in O was unchanged while Myf5 mRNA in Y increased 1.5-fold at 48h (p=0.04). IHC confirmed Pax7+ cells were positive for myostatin and co-localized with ActRIIb. CONCLUSION: These data illustrate an effect of age on the SC pool. The SC pool remained lower at 24h, with fewer cells in G1 suggesting a blunted SC activation in O. This deficit in the SC response is supported by the expression pattern of Myf5. Localization of myostatin and ActRIIb with Pax7 and higher expression of myostatin in O vs Y suggest a potential mechanism for the blunted SC response.

Normal hypertrophy accompanied by phosphoryation and activation of AMP‐activated protein kinase α1 following overload in LKB1 knockout mice

The activation of the AMP-activated protein kinase (AMPK) and inhibition of the mammalian target of rapamycin complex 1 (mTORC1) is hypothesized to underlie the fact that muscle growth following resistance exercise is decreased by concurrent endurance exercise. To directly test this hypothesis, the capacity for muscle growth was determined in mice lacking the primary upstream kinase for AMPK in skeletal muscle, LKB1. Following either 1 or 4 weeks of overload, there was no difference in muscle growth between the wild type (wt) and LKB1(-/-) mice (1 week: wt, 38.8 +/- 7.75%; LKB1(-/-), 27.8 +/- 12.98%; 4 week: wt, 75.8 +/- 15.2%; LKB1(-/-), 85.0 +/- 22.6%). In spite of the fact that the LKB1 had been knocked out in skeletal muscle, the phosphorylation and activity of the alpha1 isoform of AMPK were markedly increased in both the wt and the LKB1(-/-) mice. To identify the upstream kinase(s) responsible, we studied potential upstream kinases other than LKB1. The activity of both Ca(2+)-calmodulin-dependent protein kinase kinase alpha (CaMKKalpha) (5.05 +/- 0.86-fold) and CaMKKbeta (10.1 +/- 2.59-fold) increased in the overloaded muscles, and this correlated with their increased expression. Phosphorylation of TAK-1 also increased 10-fold following overload in both the wt and LKB1 mice. Even though the alpha1 isoform of AMPK was activated by overload, there were no increases in expression of mitochondrial proteins or GLUT4, indicating that the alpha1 isoform is not involved in these metabolic adaptations. The phosphorylation of TSC2, an upstream regulator of the TORC1 pathway, at the AMPK site (Ser1345) was increased in response to overload, and this was not affected by LKB1 deficiency. Taken together, these data suggest that the alpha1 isoform of AMPK is preferentially activated in skeletal muscle following overload in the absence of metabolic adaptations, suggesting that this isoform might be important in the regulation of growth but not metabolism.

Prenatal programming of postnatal productivity and health of livestock: a brief review

Human epidemiological evidence has suggested that metabolic perturbations during fetal life may increase predisposition to cardiovascular disease, type 2 diabetes and obesity in later life. A growing number of controlled experiments on sheep and other large animal species are adding to the already large body of experimental evidence from rat studies in supporting the ‘fetal origins’ hypothesis. Of particular practical relevance are findings that maternal undernutrition in late pregnancy can predispose lambs to glucose intolerance and increased adiposity in early adulthood. This effect may be exacerbated by high energy intakes and limited capacity for muscle growth in undernourished or growth-retarded lambs during early postnatal life. Recent Australian studies have demonstrated the effects of prenatal nutrition on postnatal growth and meat production in beef cattle, and on quantity and quality of wool production in sheep.

Age-related changes and location of types I, III, XII and XIV collagen during development of skeletal muscles from genetically different animals.

The ontogenesis of total collagen and of different collagen types was studied in four muscle types from genetically different cattle. Hydroxyproline content was 1.2-fold higher in muscles from cross-bred foetuses with normal muscle growth compared to those of the other genetic types (pure bred with different growth rates, double-muscled breed). A similar tendency was observed for type III collagen content. In all muscles of each animal studied, type XII and XIV collagens were colocated in perimysium. Immunolabelling obtained for type XII collagen was higher during foetal life than after birth, while for type XIV collagen, the opposite result was obtained. Whatever the muscle studied, but especially in semitendinosus muscle, during the foetal and the post-natal period until 15 months of age, immunolabelling with antibody anti-type XIV collagen tended to be more intense in muscles of animals from fathers selected for a low muscle growth capacity compared to those from fathers selected for a high muscle growth capacity. In conclusion, this study shows, that during foetal life, selection according to muscle growth capacity has no significant effect on the contents of total hydroxyproline or type III collagen, but minor effects on collagen localization.