Up-regulation of avian uncoupling protein in cold-acclimated and hyperthyroid ducklings prevents reactive oxygen species production by skeletal muscle mitochondria

<p>Abstract</p> <p>Background</p> <p>Although identified in several bird species, the biological role of the avian homolog of mammalian uncoupling proteins (avUCP) remains extensively debated. In the present study, the functional properties of isolated mitochondria were examined in physiological or pharmacological situations that induce large changes in avUCP expression in duckling skeletal muscle.</p> <p>Results</p> <p>The abundance of avUCP mRNA, as detected by RT-PCR in gastrocnemius muscle but not in the liver, was markedly increased by cold acclimation (CA) or pharmacological hyperthyroidism but was down-regulated by hypothyroidism. Activators of UCPs, such as superoxide with low doses of fatty acids, stimulated a GDP-sensitive proton conductance across the inner membrane of muscle mitochondria from CA or hyperthyroid ducklings. The stimulation was much weaker in controls and not observed in hypothyroid ducklings or in any liver mitochondrial preparations. The production of endogenous mitochondrial reactive oxygen species (ROS) was much lower in muscle mitochondria from CA and hyperthyroid ducklings than in the control or hypothyroid groups. The addition of GDP markedly increased the mitochondrial ROS production of CA or hyperthyroid birds up to, or above, the level of control or hypothyroid ducklings. Differences in ROS production among groups could not be attributed to changes in antioxidant enzyme activities (superoxide dismutase or glutathione peroxidase).</p> <p>Conclusion</p> <p>This work provides the first functional <it>in vitro </it>evidence that avian UCP regulates mitochondrial ROS production in situations of enhanced metabolic activity.</p

Hypoxia refines plasticity of mitochondrial respiration to repeated muscle work

Purpose: We explored whether altered expression of factors tuning mitochondrial metabolism contributes to muscular adaptations with endurance training in the condition of lowered ambient oxygen concentration (hypoxia) and whether these adaptations relate to oxygen transfer as reflected by subsarcolemmal mitochondria and oxygen metabolism in muscle. Methods: Male volunteers completed 30 bicycle exercise sessions in normoxia or normobaric hypoxia (4,000m above sea level) at 65% of the respective peak aerobic power output. Myoglobin content, basal oxygen consumption, and re-oxygenation rates upon reperfusion after 8min of arterial occlusion were measured in vastus muscles by magnetic resonance spectroscopy. Biopsies from vastus lateralis muscle, collected pre and post a single exercise bout, and training, were assessed for levels of transcripts and proteins being associated with mitochondrial metabolism. Results: Hypoxia specifically lowered the training-induced expression of markers of respiratory complex II and IV (i.e. SDHA and isoform 1 of COX-4; COX4I1) and preserved fibre cross-sectional area. Concomitantly, trends (p<0.10) were found for a hypoxia-specific reduction in the basal oxygen consumption rate, and improvements in oxygen repletion, and aerobic performance in hypoxia. Repeated exercise in hypoxia promoted the biogenesis of subsarcolemmal mitochondria and this was co-related to expression of isoform 2 of COX-4 with higher oxygen affinity after single exercise, de-oxygenation time and myoglobin content (r≥0.75). Conversely, expression in COX4I1 with training correlated negatively with changes of subsarcolemmal mitochondria (r<−0.82). Conclusion: Hypoxia-modulated adjustments of aerobic performance with repeated muscle work are reflected by expressional adaptations within the respiratory chain and modified muscle oxygen metabolism

Prevention of unloading-induced atrophy by vitamin E supplementation: Links between oxidative stress and soleus muscle proteolysis?

Exposure to reduced activity induces skeletal muscle atrophy. Oxidative stress might contribute to muscle wasting via proteolysis activation. This study aimed to test two hypotheses in rats. First, supplementation of the antioxidant vitamin E, prior and during the phase of unloading, would partly counteract unloading-induced soleus muscle atrophy. Secondly, vitamin E supplementation would decrease the rate of muscle proteolysis by reducing expression of calpains, caspases-3, -9, and -12, and E3 ubiquitin ligases (MuRF1 and MAFbx). Soleus muscle atrophy (-49%) induced by 14 days of hindlimb unloading was reduced to only 32% under vitamin E. Vitamin E partly prevented the decrease in type I and IIa fiber size. Supplementation increased HSP72 content and suppressed the rise in muscle level of thiobarbituric acid-reactive substance caused by unloading but failed to modify the lower ratio of reduced vs oxidized glutathione, the higher uncoupling proteins mRNA, and the antioxidant enzyme activities (superoxide dismutase, catalase, and glutathione peroxidase) observed after unloading. Vitamin E treatment abolished the large upregulation of caspases-9 and -12 and MuRF1 transcripts in unloaded muscle and greatly decreased the upregulation of mu-calpain, caspase-3, and MAFbx mRNA. In conclusion, the protective effect of vitamin E might be due to modulation of muscle proteolysis-related genes rather than to its antioxidant function

Spaceflight Effects on Single Skeletal Muscle Fiber Function in the Rhesus Monkey

The purpose of this investigation was to understand how 14 days of weightlessness alters the cellular properties of individual slow- and fast-twitch muscle fibers in the rhesus monkey. The diameter of the soleus (Sol) type I, medial gastrocnemius (MG) type I, and MG type II fibers from the vivarium controls averaged 60 ± 1, 46 ± 2, and 59 ± 2 µm, respectively. Both a control 1-G capsule sit (CS) and spaceflight (SF) significantly reduced the Sol type I fiber diameter (20 and 13%, respectively) and peak force, with the latter declining from 0.48 ± 0.01 to 0.31 ± 0.02 (CS group) and 0.32 ± 0.01 mN (SF group). When the peak force was expressed as kiloNewtons per square meter (kN/m2), only the SF group showed a significant decline. This group also showed a significant 15% drop in peak fiber stiffness that suggests that fewer cross bridges were contracting in parallel. In the MG, SF but not CS depressed the type I fiber diameter and force. Additionally, SF significantly depressed absolute (mN) and relative (kN/m2) force in the fast-twitch MG fibers by 30% and 28%, respectively. The Ca2+ sensitivity of the type I fiber (Sol and MG) was significantly reduced by growth but unaltered by SF. Flight had no significant effect on the mean maximal fiber shortening velocity in any fiber type or muscle. The post-SF Sol type I fibers showed a reduced peak power and, at peak power, an elevated velocity and decreased force. In conclusion, CS and SF caused atrophy and a reduced force and power in the Sol type I fiber. However, only SF elicited atrophy and reduced force (mN) in the MG type I fiber and a decline in relative force (kN/m2) in the Sol type I and MG type II fibers

Trichostatin A, a histone deacetylase inhibitor, modulates unloaded-induced skeletal muscle atrophy

International audienc

Transcriptional reprogramming during reloading of atrophied rat soleus muscle

The hypothesis was tested that differential, coregulated transcriptional adaptations of various cellular pathways would occur early with increased mechanical loading of atrophied skeletal muscle and relate to concurrent damage of muscle fibers. Atrophy and slow-to-fast fiber transformation of rat soleus muscle was provoked by 14 days of hindlimb suspension (HS). Subsequent reloading of hindlimbs caused a fourfold increase in the percentage of muscle fibers, demonstrating endomysial tenascin-C staining. Five days after reloading, when 10% of the fibers were damaged, the normal muscle weight and slow-type fiber percentage were reestablished. Microarray analysis revealed major, biphasic patterns of gene expressional alterations with reloading that distinguish between treatments and gene ontologies. Transcript levels of factors involved in protein synthesis and certain proteasomal mRNAs were increased after 1 day of reloading and correlated to the percentage of fibers surrounded by tenascin-C. By contrast, levels of gene messages for fatty acid transporters, respiratory chain constituents, and voltage-gated cation channels were transiently reduced after 1 day of muscle loading and associated with the number of damaged fibers and the regain in muscle weight. This coregulation points toward important retooling of oxidative metabolism and the T- and SR-tubular systems with rebuilding of slow fibers. The observations demonstrate that early nuclear reprogramming with reloading of atrophic soleus muscle is coordinated and links to the processes involved in mechanical damage and regeneration of muscle fibers