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- Chaillou, Thomas, 1985-, et al.
(författare)
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Effect of hypoxia exposure on the phenotypic adaptation in remodelling skeletal muscle submitted to functional overload
- 2013
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Ingår i: Acta Physiologica. - Hoboken, USA : Blackwell Publishing. - 1748-1708 .- 1748-1716. ; 209:4, s. 272-282
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Tidskriftsartikel (refereegranskat)abstract
- Aim: To determine whether hypoxia influences the phenotypic adaptation of skeletal muscle induced by mechanical overload.Methods: Plantaris muscles of female rats were submitted to mechanical overload following synergist ablation. After 3 days of overload, rats were exposed to either hypobaric hypoxia (equivalent to 5500 m) or normoxia. Muscles were collected after 5, 12 and 56 days of overload (i.e. after 3, 9 and 53 days of hypoxia). We determined the myosin heavy chain (MHC) distribution, mRNA levels of myocyte-enriched calcineurin-integrating protein 1 (MCIP1) to indirectly assess calcineurin activity, the changes in oxidative capacity from the activities of citrate synthase (CS) and cytochrome c oxidase (COX), and the expression of regulators involved in mitochondrial biogenesis (Pgc-1α, NRF1 and Tfam) and degradation (BNIP-3).Results: Hypoxia did not alter the fast-to-slow MHC shift and the increase in calcineurin activity induced by overload; it only transiently slowed down the overload-induced transition in MHC isoforms. Hypoxia similarly decreased CS and COX activities in overloaded and control muscles. Nuclear respiratory factor 1 (NRF1) and transcription factor A (Tfam) mRNA and BNIP-3 protein were not influenced by hypoxia in overloaded muscles, whereas Pgc-1α mRNA and protein contents did not correlate with changes in oxidative capacity.Conclusion: Hypoxia is not a critical stimulus to modulate the fast-to-slow MHC transition associated with overload. Thus, the impairment of the fast-to-slow fibre shift often observed during post-natal development in hypoxia could be explained by the lower voluntary locomotor activity associated with hypoxia. Hypoxia alters mitochondrial oxidative capacity, but this adaptive response is similar in overloaded and control muscles.
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| 2. |
- Chaillou, Thomas, 1985-, et al.
(författare)
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Pitfalls in target mRNA quantification for real-time quantitative RT-PCR in overload-induced skeletal muscle hypertrophy
- 2011
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Ingår i: Physiological Genomics. - Bethesda, USA : American Physiological Society. - 1094-8341 .- 1531-2267. ; 43:4, s. 228-235
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Tidskriftsartikel (refereegranskat)abstract
- Quantifying target mRNA using real-time quantitative reverse transcription-polymerase chain reaction requires an accurate normalization method. Determination of normalization factors (NFs) based on validated reference genes according to their relative stability is currently the best standard method in most usual situations. This method controls for technical errors, but its physiological relevance requires constant NF values for a fixed weight of tissue. In the functional overload model, the increase in the total RNA concentration must be considered in determining the NF values. Here, we pointed out a limitation of the classical geNorm-derived normalization. geNorm software selected reference genes despite that the NF values extensively varied under experiment. Only the NF values calculated from four intentionally selected genes were constant between groups. However, a normalization based on these genes is questionable. Indeed, three out of four genes belong to the same functional class (negative regulator of muscle mass), and their use is physiological nonsense in a hypertrophic model. Thus, we proposed guidelines for optimizing target mRNA normalization and quantification, useful in models of muscle mass modulation. In our study, the normalization method by multiple reference genes was not appropriate to compare target mRNA levels between overloaded and control muscles. A solution should be to use an absolute quantification of target mRNAs per unit weight of tissue, without any internal normalization. Even if the technical variations will stay present as a part of the intergroup variations, leading to less statistical power, we consider this method acceptable because it will not generate misleading results.
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| 3. |
- Malgoyre, A, et al.
(författare)
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Aerobic performance improvment and mitochondrial adaptations after endurance training in hypoxia
- 2011
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Ingår i: Acta Physiologica. - : John Wiley & Sons. - 1748-1708 .- 1748-1716. ; 202:Suppl. 685
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Tidskriftsartikel (refereegranskat)abstract
- Aim: The aim of the present study was to examine the effects of hypoxic endurance training on both aerobic performance and mitochondrial changes within plantaris muscle, independently of hematopoietic modifications.Methods: Four groups of female rats were constituted either sedentary (S) or trained (T), in either hypoxia (H) or normoxia (N). H conditions corresponded to 14% O2 and the training program to 5 running sessions/week for 5 weeks. Duration and intensity reached progressively 75Õ up to 80% of individual maximal aerobic running velocity (MAV) in either H or N. Performances of each rat were analysed through MAV values and time to exhaustion at 65% MAV (T65). Mitochondrial oxidative capacities (Vmax) for pyruvate (pyr), palmitoyl-carnitine (PC) and palmitoyl-CoA (PCoA) were measured in plantaris skinned fibers. Citrate synthase (CS) and HAD activities were also measured.Results: MAV increased in both TN and TH rats (respectively +52%, +39%, P<0.001) without difference between H and N, whereas hypoxia specifically increased T65 (+ 39%, P<0.05) independently of training effect. The training-induced increase in CS activity (P<0.001) was more marked in TN than in TH group (+39% vs +26%, P<0.001) whereas HAD activity rose similarly in TN and TH (respectively +83%, +64%, P<0.05). Physical training increased Vmaxpyr only in N rats (+30%, P<0.001), while VmaxPCoA decreased in hypoxia (P<0.05) without change in VmaxPC. This suggests that LCFA transport by CPT-1 was limiting in hypoxia. As expected, training improved creatine kinase efficiency in N rats (+80%, P<0.005), but no change was shown in H rats.Conclusion: Regarding the modest changes in mitochondrial function, it is likely that other factors contribute to explain the improvement of physical performance after an endurance training in hypoxia.
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