Soleus Muscle Mass Research Articles

Time Course Analysis of Skeletal Muscle Pathology of GDE5 Transgenic Mouse.

Glycerophosphodiesterase 5 (GDE5) selectively hydrolyses glycerophosphocholine to choline and is highly expressed in type II fiber-rich skeletal muscles. We have previously generated that a truncated mutant of GDE5 (GDE5dC471) that lacks phosphodiesterase activity and shown that transgenic mice overexpressing GDE5dC471 in skeletal muscles show less skeletal muscle mass than control mice. However, the molecular mechanism and pathophysiological features underlying decreased skeletal muscle mass in GDE5dC471 mice remain unclear. In this study, we characterized the skeletal muscle disorder throughout development and investigated the primary cause of muscle atrophy. While type I fiber-rich soleus muscle mass was not altered in GDE5dC471 mice, type II fiber-rich muscle mass was reduced in 8-week-old GDE5dC471 mice. Type II fiber-rich muscle mass continued to decrease irreversibly in 1-year-old transgenic mice with an increase in apoptotic cell. Adipose tissue weight and blood triglyceride levels in 8-week-old and 1-year-old transgenic mice were higher than those in control mice. This study also demonstrated compensatory mRNA expression of neuromuscular junction (NMJ) components, including nicotinic acetylcholine receptors (α1, γ, and ε subunits) and acetylcholinesterase in type II fiber-rich quadriceps muscles in GDE5dC471 mice. However, we did not observe morphological changes in NMJs associated with skeletal muscle atrophy in GDE5dC471 mice. We also found that HSP70 protein levels are significantly increased in the skeletal muscles of 2-week-old GDE5dC471 mice and in mouse myoblastic C2C12 cells overexpressing GDE5dC471. These findings suggest that GDE5dC471 mouse is a novel model of early-onset irreversible type II fiber-rich myopathy associated with cellular stress.

Heat stress-induced protection against skeletal muscle atrophy via suppression of the apoptotic and proteolytic systems

Heat stress has been shown to attenuate reduction in soleus muscle mass and fiber size in various animal models, and it appears likely that heat shock protein 72 (HSP72) plays a key role in heat stress-induced suppression of muscle atrophy. However, there is no evidence that repeated heat stress attenuates the acceleration of apoptotic and proteolytic systems in atrophied rat skeletal muscle. We recently examined the effects of repeated heat stress on muscle atrophy and in terms of apoptosis and proteolysis in unloaded rat skeletal muscle induced by hindlimb unloading. Our results revealed that repeated bouts of heat stress elicited protective effects against disuse atrophy in both soleus and plantaris muscles. Interestingly, this heat stress-induced protection against muscular atrophy may be partially attributed to the suppression of apoptotic activation in slow- and fast-twitch muscles, and decreased ubiquitination in only the soleus muscle. Thus, we have established that repeated heat stress attenuates skeletal muscle atrophy via both upregulation of HSP72 and suppression of apoptotic and proteolytic systems.

Vitamin D deficiency impairs skeletal muscle function in a smoking mouse model.

Chronic obstructive pulmonary disease (COPD) is associated with skeletal muscle dysfunction. Vitamin D plays an important role in muscle strength and performance in healthy individuals. Vitamin D deficiency is highly prevalent in COPD, but its role in skeletal muscle dysfunction remains unclear. We examined the time-course effect of vitamin D deficiency on limb muscle function in mice with normal or deficient vitamin D serum levels exposed to air or cigarette smoke for 6, 12 or 18 weeks. The synergy of smoking and vitamin D deficiency increased lung inflammation and lung compliance from 6 weeks on with highest emphysema scores observed at 18 weeks. Smoking reduced body and muscle mass of the soleus and extensor digitorum longus (EDL), but did not affect contractility, despite type II atrophy. Vitamin D deficiency did not alter muscle mass but reduced muscle force over time, downregulated vitamin D receptor expression, and increased muscle lipid peroxidation but did not alter actin and myosin expression, fiber dimensions or twitch relaxation time. The combined effect of smoking and vitamin D deficiency did not further deteriorate muscle function but worsened soleus mass loss and EDL fiber atrophy at 18 weeks. We conclude that the synergy of smoking and vitamin D deficiency in contrast to its effect on lung disease, had different, independent but important noxious effects on skeletal muscles in a mouse model of mild COPD.

Site specific bone loss induced by spaceflight in mice: a multiscale evaluation of trabecular and cortical structure and quality

Intrinsic quality, micro and nano structure of bone after 1 month of spaceflight and during 1 week of recovery had never been investigated. The aim was to explore these properties in appendicular and axial skeleton of mature mice.Ten C57/Bl6 male mice flew on the 30-day space Russian BION-M1 high-orbit satellite mission (Biomedical Ethics Commission of IBMP, n°319). Five were euthanized 12 h after landing, the others 8 days later. A ground control group was kept in the same conditions as in flight (housing, food and climate).Body weight, soleus muscle mass, and femur length were not significantly different between groups.In the femur, microgravity significantly decreased trabecular BV/TV (−65% vs Ctr) (micro-CT), increased trabecular and periosteal TRAP+ osteoclast surfaces and marrow adiposity (X22 vs Ctr), and decreased Ct.Th (−5.4% vs Ctr). Nano-indentation analysis indicated that cortical modulus, hardness and working energy were significantly decreased whereas the degree of mineralization (micro radiography) was not affected by microgravity. Microgravity did not affect cortical osteocyte lacuna density but decreased their mean 3D volume (Synchrotron Radiation nanotomography, n>8000 lacunae per sample). Eight days after landing, osteoclast cell surface were restored but trabecular BV/TV and Ct.Th remained lower than Ctr group.In vertebrae, microgravity significantly decreased BV/TV (−36% vs Ctr) and the modulus in the younger mineralized matrix which tended to increase after recovery. Degree of mineralization, mineral and collagen intrinsic quality (infra-red spectroscopy) were not changed by microgravity.To summarize, microgravity severely decreased bone mass, altered bone structure and intrinsic mechanical properties in both sites and increased femoral marrow adiposity. One week after landing, these properties tended to be rescued in vertebrae but remained altered in the femur despite normalized osteoclastic cell surfaces. The decrease of osteocyte lacunar volume suggests the existence of an intra-cortical bone preservation mechanism in absence of mechanical loading.

Sarcolipin is Upregulated in Response to Soleus Unloading Caused by Tenotomy and Opposes Muscle Atrophy

Previous studies have shown that sarcolipin (SLN), a small inhibitor of the sarco(endo)plasmic reticulum Ca2+‐ATPase (SERCA) pump, is upregulated in conditions of muscle atrophy. To date, however, the role of SLN in muscle atrophy remains unknown. In another unpublished study from our laboratory, we mechanically overloaded plantaris muscles by performing soleus and gastrocnemius tenotomy (surgical transection of the tendon), and found that SLN is critical in mediating muscle growth and fiber type remodeling. In this study we questioned the role of SLN in the tenotomized soleus, which is a model of muscle unloading known to cause muscle degeneration, atrophy, and a fast‐glycolytic muscle phenotype. We hypothesized that in the absence of Sln, soleus muscles would exhibit greater muscle atrophy and an accelerated slow‐to‐fast fiber type shift. Our results show that 2 weeks after tenotomy, SLN protein was upregulated 14‐fold (P ≤ 0.05) in WT muscle compared with sham. Furthermore, removing this 14‐fold upregulation led to a greater percent reduction in soleus muscle mass relative to body weight in SlnKO mice compared with WT (WT, −51.0 ± 3.5% vs. SlnKO, −59.0 ± 1.8%, P ≤ 0.05). In addition, significant reductions in myofiber cross‐sectional area were found in WT mice (−29% to −38%, P ≤ 0.05, two‐way repeated ANOVA), and also in SlnKO mice, but perhaps to a greater extent (−33% to −42%, P ≤ 0.05, two‐way repeated ANOVA). With respect to the slow‐to‐fast fiber type shift, the WT mice exhibited a partial shift in response to tenotomy with a significant decrease and trending increase in type IIA (P ≤ 0.05) and type IIX (P = 0.10) fiber percent, respectively. In contrast, in response to tenotomy, SlnKO mice exhibited an accelerated slow‐to‐fast fibre type shift with a significant decrease in type I (P ≤ 0.05) and increase in type IIX (P ≤ 0.05) fiber percent, respectively. Since calcineurin stabilizes the deleterious effects of reduced mechanical loading, we examined the phosphorylation status of its well‐known substrate nuclear factor of activated T‐cell (pNFAT). Our results show that, in response to tenotomy, WT soleus muscles had significantly lower pNFAT compared with sham (−57%, P ≤ 0.05); however pNFAT was not different between SlnKO sham and tenotomized soleus muscles. Thus, our results show that SLN upregulation in tenotomized soleus muscles is required to counteract muscle atrophy and the transition to the fast, glycolytic fiber phenotype, and may do so through its stimulatory effect on calcineurin.Support or Funding InformationThis work was supported by the Canadian Institutes of Health Research (CIHR; MOP 86618 and MOP 47296 to A.R.T).

Akt/mTOR pathway contributes to skeletal muscle anti-atrophic effect of aerobic exercise training in heart failure mice

BackgroundExercise intolerance is one of the main clinical symptoms of heart failure (HF) and is associated with skeletal muscle wasting due to an imbalance between proteolysis and protein synthesis. In this study, we tested whether aerobic exercise training (AET) would counteract skeletal muscle atrophy by activating IGF-I/Akt/mTOR pathway in HF mice. MethodsSympathetic hyperactivity induced HF mice were assigned into 8-week moderate intensity AET. Untrained wild type and HF mice were used as control. Soleus cross sectional area was evaluated by histochemistry and motor performance by rotarod. 26S proteasome activity was assessed by fluorimetric assay, and components of IGF-I/Akt/mTOR pathway or myostatin pathway by qRT-PCR or immunoblotting. A different subset of mice was used to evaluate the relative contribution of mTOR inhibition (rapamycin) or activation (leucine) on AET-induced changes in muscle mass regulation. ResultsAET prevented exercise intolerance and impaired motor performance in HF mice. These effects were associated with attenuation of soleus atrophy. Rapamycin treatment precluded AET effects on soleus mass in HF mice suggesting the involvement of IGF signaling pathway in this response. In fact, AET increased IGF-I Ea and IGF-I Pan mRNA levels, while it reduced myostatin and Smad2 mRNA levels in HF mice. At protein levels, AET prevented reduced expression levels of IGF-I, pAkt (at basal state), as well as, p4E-BP1 and pP70S6K (leucine-stimulated state) in HF mice. Additionally, AET prevented 26S proteasome hyperactivity in HF mice. ConclusionsTaken together, our data provide evidence for AET-induced activation of IGF-I/Akt/mTOR signaling pathway counteracting HF-induced muscle wasting.

Icaritin requires Phosphatidylinositol 3 kinase (PI3K)/Akt signaling to counteract skeletal muscle atrophy following mechanical unloading.

Counteracting muscle atrophy induced by mechanical unloading/inactivity is of great clinical need and challenge. A therapeutic agent that could counteract muscle atrophy following mechanical unloading in safety is desired. This study showed that natural product Icaritin (ICT) could increase the phosphorylation level of Phosphatidylinositol 3 kinase (PI3K) at p110 catalytic subunit and promote PI3K/Akt signaling markers in C2C12 cells. This study further showed that the high dose ICT treatment could significantly attenuate the decreases in the phosphorylation level of PI3K at p110 catalytic subunit and its downstream markers related to protein synthesis, and inhibit the increases in protein degradation markers at mRNA and protein levels in rat soleus muscle following 28-day hindlimb unloading. In addition, the decreases in soleus muscle mass, muscle fiber cross-sectional area, twitch force, specific force, contraction time and half relaxation time could be significantly attenuated by the high dose ICT treatment. The low dose ICT treatment could moderately attenuate the above changes induced by unloading. Wortmannin, a specific inhibitor of PI3K at p110 catalytic subunit, could abolish the above effects of ICT in vitro and in vivo, indicating that PI3K/Akt signaling could be required by ICT to counteract skeletal muscle atrophy following mechanical unloading.

Effects of icing or heat stress on the induction of fibrosis and/or regeneration of injured rat soleus muscle.

The effects of icing or heat stress on the regeneration of injured soleus muscle were investigated in male Wistar rats. Bupivacaine was injected into soleus muscles bilaterally to induce muscle injury. Icing (0°C, 20min) was carried out immediately after the injury. Heat stress (42°C, 30min) was applied every other day during 2-14days after the bupivacaine injection. Injury-related increase in collagen deposition was promoted by icing. However, the level of collagen deposition in heat-stressed animals was maintained at control levels throughout the experimental period and was significantly lower than that in icing-treated animals at 15 and 28days after bupivacaine injection. Furthermore, the recovery of muscle mass, protein content, and muscle fiber size of injured soleus toward control levels was partially facilitated by heat stress. These results suggest that, compared with icing, heat stress may be a beneficial treatment for successful muscle regeneration at least by reducing fibrosis.

Effectiveness of daily eccentric contractions induced via kilohertz frequency transcutaneous electrical stimulation on muscle atrophy

The effects of daily repeated bouts of concentric, isometric, or eccentric contractions induced by high frequency (kilohertz) transcutaneous electrical stimulation in ameliorating atrophy of the soleus muscle in hindlimb unloaded rats were determined. Five groups of male rats were studied: control, hindlimb unloaded for 2 weeks (HU), or HU plus two daily bouts of concentric, isometric, or eccentric high-frequency electrical stimulation-induced contractions of the calf musculature. Soleus mass and fiber size were smaller, the levels of phosphorylated Akt1 and FoxO3a lower, and atrogin-1 and ubiquitinated proteins higher in the HU, and the HU plus concentric or isometric contraction groups than in the control group. In contrast, daily bouts of eccentric contractions maintained these values at near control levels and all measures were significantly different from all other HU groups. These results indicate that daily bouts of eccentric contractions induced by high-frequency stimulation inhibited the ubiquitin–proteasome catabolic pathway and enhanced the Akt1/FoxO3a anabolic pathway that resulted in a prevention of the atrophic response of the soleus muscle to chronic unloading.

Slow recovery of the impaired fatigue resistance in postunloading mouse soleus muscle corresponding to decreased mitochondrial function and a compensatory increase in type I slow fibers

Unloading or disuse rapidly results in skeletal muscle atrophy, switching to fast-type fibers, and decreased resistance to fatigue. The recovery process is of major importance in rehabilitation for various clinical conditions. Here we studied mouse soleus muscle during 60 days of reloading after 4 wk of hindlimb suspension. Unloading produced significant atrophy of soleus muscle with decreased contractile force and fatigue resistance, accompanied by switches of myosin isoforms from IIa to IIx and IIb and fast troponin T to more low-molecular-weight splice forms. The total mass, fiber size, and contractile force of soleus muscle recovered to control levels after 15 days of reloading. However, the fatigue resistance showed a trend of worsening during this period with significant infiltration of inflammatory cells at days 3 and 7, indicating reloading injuries that were accompanied by active regeneration with upregulations of filamin-C, αB-crystallin, and desmin. The fatigue resistance partially recovered after 30-60 days of reloading. The expression of peroxisome proliferator-activated receptor γ coactivator 1α and mitofusin-2 showed changes parallel to that of fatigue resistance after unloading and during reloading, suggesting a causal role of decreased mitochondrial function. Slow fiber contents in the soleus muscle were increased after 30-60 days of reloading to become significantly higher than the normal level, indicating a secondary adaption to compensate for the slow recovery of fatigue resistance.

Deficiency of heat shock transcription factor 1 suppresses heat stress‐associated increase in slow soleus muscle mass of mice

Effects of heat shock transcription factor 1 (HSF1) deficiency on heat stress-associated increase in slow soleus muscle mass of mice were investigated. Both HSF1-null and wild-type mice were randomly assigned to control and heat-stressed groups. Mice in heat-stressed group were exposed to heat stress (41 °C for 60 min) in an incubator without anaesthesia. Significant increase in wet and dry weights, and protein content of soleus muscle in wild-type mice was observed seven days after the application of the heat stress. However, heat stress had no impact on soleus muscle mass in HSF1-null mice. Neither type of mice exhibited much effect of heat stress on HSF mRNA expression (HSF1, HSF2 and HSF4). On the other hand, heat stress upregulated heat shock proteins (HSPs) at the mRNA (HSP72) and protein (HSP72 and HSP110) levels in wild-type mice, but not in HSF1-null mice. The population of Pax7-positive nuclei relative to total myonuclei of soleus muscle in wild-type mice was significantly increased by heat stress, but not in HSF1-null mice. Furthermore, the absence of HSF1 gene suppressed heat stress-associated phosphorylation of Akt and p70 S6 kinase (p-p70S6K) in soleus muscle. Heat stress-associated increase in skeletal muscle mass may be induced by HSF1 and/or HSF1-mediated stress response that activates muscle satellite cells and Akt/p70S6K signalling pathway.

Myostatin dysfunction is associated with reduction in overload induced hypertrophy of soleus muscle in mice.

The aim of the study was to investigate if myostatin dysfunction would promote the gain in muscle mass and peak isometric force (P0 ) of soleus muscle (SOL) in response to functional overloading (FO) after ablation of the gastrocnemius muscle. Fifteen male Berlin high (BEH) mice homozygous for the compact mutation causing dysfunction of myostatin and 17 mice with the corresponding wild-type allele (BEH+/+) were subjected to FO of SOL for 28 days at the age of 14 weeks. Compared with BEH+/+ mice, SOL of BEH was heavier (mean ± SD, 13.5 ± 1.5 vs 21.4 ± 1.8 mg, respectively, P < 0.001). After FO, SOL mass increased relatively more in BEH+/+ than BEH strain (34.9 ± 11.5 vs 17.7 ± 11.9%, respectively, P < 0.01). P0 fell (P < 0.01) only in BEH strain, which also showed an increase (P < 0.01) in optimal muscle length. Specific P0 became even more depressed in BEH compared with BEH+/+ strain (8.4 ± 1.4 vs 10.8 ± 1.3 N/g, respectively, P < 0.001). Phosphorylation p70 S6 kinase did not differ between the strains. In summary, myostatin dysfunction impairs adaptation of SOL muscle to high functional demands.

Effects of exercise on soleus in severe burn and muscle disuse atrophy

BackgroundMuscle loss is a sequela of severe burn and critical illness with bed rest contributing significantly to atrophy. We hypothesize that exercise will mitigate muscle loss after burn with bed rest. Materials and methodsMale rats were assigned to sham ambulatory (S/A), burn ambulatory (B/A), sham hindlimb unloading (S/H), or burn hindlimb unloading (B/H). Rats received a 40% scald burn or sham and were ambulatory or placed in hindlimb unloading, a model of bed rest. Half from each group performed twice daily resistance climbing. Hindlimb isometric forces were measured on day 14. ResultsSoleus mass and muscle function were not affected by burn alone. Mass was significantly lower in hindlimb unloading (79 versus 139 mg, P < 0.001) and no exercise (103 versus 115 mg, P < 0.01). Exercise significantly increased soleus mass in B/H (86 versus 77 mg, P < 0.01). Hindlimb unloading significantly decreased muscle force in the twitch (12 versus 31 g, P < 0.001), tetanic (55 versus 148 g, P < 0.001), and specific tetanic measurements (12 versus 22 N/cm2, P < 0.001). Effects of exercise on force depended on other factors. In B/H, exercise significantly increased twitch (14 versus 8 g, P < 0.05) and specific tetanic force (14 versus 7 N/cm2, P < 0.01). Fatigue index was lower in ambulatory (55%) and exercise (52%) versus hindlimb (69%, P = 0.03) and no exercise (73%, P = 0.002). ConclusionsHindlimb unloading is a significant factor in muscle atrophy. Exercise increased the soleus muscle mass, twitch, and specific force in this model. However, the fatigue index decreased with exercise in all groups. This suggests exercise contributes to functional muscle change in this model of disuse and critical illness.

Treadmill Exercise Increases NGF and Skeletal Muscle Mass of Experimental Autoimmune Encephalomyelitis Rodents

Experimental autoimmune encephalomyelitis (EAE) is a T-cell mediated animal model of multiple sclerosis. Brain derived neurotrophic factor (BDNF) and nerve growth factor (NGF) produced in muscle have the potential for retrograde transport into the central nervous system to protect against neurodegeneration. The extent to which exercise can modulate skeletal muscle concentrations of BDNF and NGF is unknown. PURPOSE: To determine whether 10 days of forced treadmill running can increase skeletal muscle BDNF and NGF concentrations in EAE rats. METHODS: Forty female Lewis rats were randomly assigned to either EAE sedentary (EAE-Sed), EAE exercise (EAE-Ex), Control sedentary (Con-Sed) and Control exercise (Con-Ex) groups. EAE was induced with 100 μl solution of myelin oligodendrocyte glycoprotein mixed with Freund’s complete adjuvant injected intradermally at the tail base. Control rats were injected with 100 μl saline. Exercising animals ran on motorized treadmills for 10 days (60 min on days 1 and 2; 90 min on days 3-10). First 30 min of running was at 15 m/min then 30 m/min for the remainder of time. Hind limb skeletal muscles were excised and weighed. BDNF and NGF was measured in soleus lysate using commercially available ELISA kits. Data were analyzed using one-way ANOVA. RESULTS: All exercising animals tolerated the training protocol. No significant difference in body mass or disability was observed between the EAE groups. Exercising animals (EAE-Ex and Con-Ex) had significantly greater bilateral soleus, plantaris, gastrocnemius and EDL muscle mass compared to the sedentary groups (p=0.01). The EAE-Ex group had significantly higher soleus NGF concentration (1.98 ± 0.3 pg/mg) compared to Con-Ex (0.96 ± 0.07, p=0.003) and Con-Sed (1.2 ± 0.2; p=0.04) groups and tended to have higher NGF compared to EAE-Sed (1.48 ± 0.1, p=0.09). BDNF was significantly lower in the Con-Ex group (7.9 ± 0.2) compared to EAE-Sed (10.6± 0.8, p=0.04). No differences were observed in BDNF concentrations between EAE groups. CONCLUSIONS: Our study provides preliminary evidence that exercise increases skeletal muscle concentrations of NGF in EAE rats. Future work is necessary to determine if this effect may be neuroprotective. Results also indicate that EAE rats engaged in daily exercise can increase muscle mass compared to their sedentary counterparts.

Chronic hindlimb suspension unloading markedly decreases turnover rates of skeletal and cardiac muscle proteins and adipose tissue triglycerides.

We previously showed that a single bolus of "doubly-labeled" water ((2)H2 (18)O) can be used to simultaneously determine energy expenditure and turnover rates (synthesis and degradation) of tissue-specific lipids and proteins by modeling labeling patterns of protein-bound alanine and triglyceride-bound glycerol (Bederman IR, Dufner DA, Alexander JC, Previs SF. Am J Physiol Endocrinol Metab 290: E1048-E1056, 2006). Using this novel method, we quantified changes in the whole body and tissue-specific energy balance in a rat model of simulated "microgravity" induced by hindlimb suspension unloading (HSU). After chronic HSU (3 wk), rats exhibited marked atrophy of skeletal and cardiac muscles and significant decrease in adipose tissue mass. For example, soleus muscle mass progressively decreased 11, 43, and 52%. We found similar energy expenditure between control (90 ± 3 kcal · kg(-1)· day(-1)) and hindlimb suspended (81 ± 6 kcal/kg day) animals. By comparing food intake (∼ 112 kcal · kg(-1) · day(-1)) and expenditure, we found that animals maintained positive calorie balance proportional to their body weight. From multicompartmental fitting of (2)H-labeling patterns, we found significantly (P < 0.005) decreased rates of synthesis (percent decrease from control: cardiac, 25.5%; soleus, 70.3%; extensor digitorum longus, 44.9%; gastrocnemius, 52.5%; and adipose tissue, 39.5%) and rates of degradation (muscles: cardiac, 9.7%; soleus, 52.0%; extensor digitorum longus, 27.8%; gastrocnemius, 37.4%; and adipose tissue, 50.2%). Overall, HSU affected growth of young rats by decreasing the turnover rates of proteins in skeletal and cardiac muscles and adipose tissue triglycerides. Specifically, we found that synthesis rates of skeletal and cardiac muscle proteins were affected to a much greater degree compared with the decrease in degradation rates, resulting in large negative balance and significant tissue loss. In contrast, we found a small decrease in adipose tissue triglyceride synthesis paired with a large decrease in degradation, resulting in smaller negative energy balance and loss of fat mass. We conclude that HSU in rats differentially affects turnover of muscle proteins vs. adipose tissue triglycerides.

Female-specific regulation of skeletal muscle mass by USP19 in young mice.

17β-Estradiol (E₂) is thought to be responsible for sex-specific differences in skeletal muscle mass. The biological function of E₂ is exerted through its binding to estrogen receptor α (ERα). The expression of ubiquitin-specific peptidase 19 (USP19) is upregulated during muscle atrophy and by E₂-activated ERα. Here, we investigated the involvement of USP19 in sex difference in muscle mass in young mice. Knockdown of USP19 in hindlimb muscles increased the mass and fiber size in soleus muscle in females but not males. Using Usp19 promoter reporter constructs, a functional half-estrogen response element (hERE) was identified in intron 1 of Usp19. ERα bound to hERE in an E₂-dependent manner in C2C12 myoblasts and in soleus muscle in ovariectomized (OVX) female mice. Furthermore, under normal physiological conditions, ERα bound to hERE in soleus muscle only in females. In contrast, administration of E₂ resulted in increased Usp19 mRNA expression, decreased muscle mass, and recruitment of ERα to hERE in soleus muscle in males. Knockdown of ERα in hindlimb muscles decreased Usp19 mRNA expression and increased the mass of soleus muscle only in females. Knockdown of USP19 resulted in increased levels of ubiquitin conjugates in soleus muscle in females. OVX increased the levels of ubiquitin conjugates and administration of E₂ decreased OVX-induced levels of ubiquitin conjugates. These results demonstrate that in soleus muscle in young female mice under physiological conditions, E₂ upregulates USP19 expression through ERα and consequently leads to decreases in ubiquitin conjugates and muscle mass.

Intermittent stretch training of rabbit plantarflexor muscles increases soleus mass and serial sarcomere number.

In humans, enhanced joint range of motion is observed after static stretch training and results either from an increased stretch tolerance or from a change in the biomechanical properties of the muscle-tendon unit. We investigated the effects of an intermittent stretch training on muscle biomechanical and structural variables. The left plantarflexors muscles of seven anesthetized New Zealand (NZ) White rabbits were passively and statically stretched three times a week for 4 wk, while the corresponding right muscles were used as nonstretched contralateral controls. Before and after the stretching protocol, passive torque produced by the left plantarflexor muscles as a function of the ankle angle was measured. The left and right plantarflexor muscles were harvested from dead rabbits and used to quantify possible changes in muscle structure. Significant mass and serial sarcomere number increases were observed in the stretched soleus but not in the plantaris or medial gastrocnemius. This difference in adaptation between the plantarflexors is thought to be the result of their different fiber type composition and pennation angles. Neither titin isoform nor collagen amount was modified in the stretched compared with the control soleus muscle. Passive torque developed during ankle dorsiflexion was not modified after the stretch training on average, but was decreased in five of the seven experimental rabbits. Thus, an intermittent stretching program similar to those used in humans can produce a change in the muscle structure of NZ White rabbits, which was associated in some rabbits with a change in the biomechanical properties of the muscle-tendon unit.

Long‐term Dietary Quercetin Enrichment Improves Muscle Function in Dystrophic Skeletal Muscle

Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease characterized by progressive muscle injury culminating in loss of ambulation and death. It is now clear that increased muscle PGC‐1α pathway activity improves many aspects of disease pathology. Translating this work to human patients necessitates identification of a safe PGC‐1α activator. The purpose of this investigation was to determine the extent to which dietary enrichment of quercetin, a known PGC‐1α activator, improved skeletal muscle function in mdx mice, a model of DMD. mdx mice were maintained on a control or 0.2% quercetin‐enriched diet from two to 14 months of age before sacrifice and tissue collection. Healthy, C57 mice were maintained on a control diet. At 14 months of age body weight was decreased by 12% (p&lt;0.05) in mdx and by 20% in mdxQ (p&lt;0.05 v C57 and mdx) compared to C57. Soleus muscle mass was increased by 35 and 30% (p&lt;0.05) in mdx and mdxQ, respectively, compared to C57. Tetanic force was similar between all groups. Importantly, dietary quercetin enrichment decreased the 42% reduction in specific tension in the mdx soleus compared to C57 by half (p&lt;0.05). In soleus muscle from mdx mice the force produced during the final contraction of a 10 minute fatigue protocol was 8% of the initial force while that of C57 was 16% (p&lt;0.05). Force produced by mdxQ was 12% of initial force though was similar to both groups. In total, these data clearly indicate that long‐term dietary quercetin enrichment provides a benefit to soleus muscle function and should be considered as part of a therapeutic regimen for DMD patients. Supported by the Duchenne Alliance.

Morfologia dos músculos sóleo e tibial anterior de ratos Wistar imobilizados e remobilizados em meio aquático

Introdução: O músculo esquelético se adapta continuamente a estímulos. Objetivo: Analisar os efeitos da imobilização e remobilização sobre parâmetros morfológicos dos músculos sóleo e tibial anterior de ratos Wistar. Métodos: Dezoito animais foram imobilizados por 15 dias, divididos em três grupos de seis componentes cada: G1 – somente imobilizados; G2 – remobilizados livremente; G3 – remobilizados em meio aquático. Foram coletados os músculos sóleo e tibial anterior, direitos (imobilizados ou tratados) e esquerdos (controle). Resultados: A imobilização reduziu massa, diâmetro da fibra e comprimento do músculo sóleo, e massa muscular do tibial anterior. Em G2 e G3, houve aumento da massa e comprimento muscular do tibial anterior; e aumento do menor diâmetro da fibra do sóleo em G3. Conclusão: A imobilização afeta a morfologia dos músculos estudados, a remobilização livre e em meio aquático foram eficientes na recuperação do tibial anterior, enquanto para o sóleo apenas os exercícios aquáticos foram eficazes.

Effects of chronic high-fat feeding on skeletal muscle mass and function in middle-aged mice.

Increased adipose tissue may promote catabolic events in skeletal muscle. The aim of this study was to test whether high-fat diet (HFD)-induced obesity would accelerate the onset of muscle wasting in middle-aged mice. Muscle was collected from C57BL/6 mice at 9months of age (baseline) and 14months of age after consuming a control (C) or HFD. Mice in C and HFD were also subjected to evaluations of body composition and function before and after their respective diets. HFD demonstrated significant (p<0.05) losses of grip strength (-15%) and sensorimotor coordination (-11%), whereas C did not. Lean mass decreased to a greater degree in HFD although not significantly (C: -20.69±7.94 vs. HFD: -31.14±5.49%, p>0.05). Gastrocnemius, quadriceps, and hamstrings mass in C and HFD were significantly reduced from baseline (-27 to 43 and -39 to 47%, respectively, p<0.05) with no differences between the two; however, soleus mass was lower only in HFD (-24%, p=0.03). Myofiber area, satellite cells, and myonuclei of the gastrocnemius were lower only in HFD (-23, -19, and -16%, respectively, p<0.05) compared to baseline. HFD-induced obesity adversely affected function in middle-aged mice. Atrophy of the soleus in HFD but not C suggests sensitivity of oxidative muscle to HFD-dependent catabolism more so than aging. In the muscles containing fast/mixed fibers, aging effects may have concealed the catabolic nature of HFD; however, morphological changes in the gastrocnemius including decreased fiber area, satellite cells, and myonuclei are consistent with an atrophic phenotype related to HFD.