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- Chaillou, Thomas, 1985-, et al.
(author)
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Effect of hypoxia exposure on the recovery of skeletal muscle phenotype during regeneration
- 2014
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In: Molecular and Cellular Biochemistry. - : Kluwer Academic Publishers. - 0300-8177 .- 1573-4919. ; 390:1-2, s. 31-40
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Journal article (peer-reviewed)abstract
- Hypoxia impairs the muscle fibre-type shift from fast-to-slow during post-natal development; however, this adaptation could be a consequence of the reduced voluntary physical activity associated with hypoxia exposure rather than the result of hypoxia per se. Moreover, muscle oxidative capacity could be reduced in hypoxia, particularly when hypoxia is combined with additional stress. Here, we used a model of muscle regeneration to mimic the fast-to-slow fibre-type conversion observed during post-natal development. We hypothesised that hypoxia would impair the recovery of the myosin heavy chain (MHC) profile and oxidative capacity during muscle regeneration. To test this hypothesis, the soleus muscle of female rats was injured by notexin and allowed to recover for 3, 7, 14 and 28 days under normoxia or hypobaric hypoxia (5,500 m altitude) conditions. Ambient hypoxia did not impair the recovery of the slow MHC profile during muscle regeneration. However, hypoxia moderately decreased the oxidative capacity (assessed from the activity of citrate synthase) of intact muscle and delayed its recovery in regenerated muscle. Hypoxia transiently increased in both regenerated and intact muscles the content of phosphorylated AMPK and Pgc-1α mRNA, two regulators involved in mitochondrial biogenesis, while it transiently increased in intact muscle the mRNA level of the mitophagic factor BNIP3. In conclusion, hypoxia does not act to impair the fast-to-slow MHC isoform transition during regeneration. Hypoxia alters the oxidative capacity of intact muscle and delays its recovery in regenerated muscle; however, this adaptation to hypoxia was independent of the studied regulators of mitochondrial turn-over.
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- Chaillou, Thomas, 1985-, et al.
(author)
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Hypoxia transiently affects skeletal muscle hypertrophy in a functional overload model
- 2012
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In: American Journal of Physiology. Regulatory Integrative and Comparative Physiology. - : HighWire Press. - 0363-6119 .- 1522-1490. ; 302, s. R643-R654
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Journal article (peer-reviewed)abstract
- Hypoxia induces a loss of skeletal muscle mass, but the signaling pathways and molecular mechanisms involved remain poorly understood. We hypothesized that hypoxia could impair skeletal muscle hypertrophy induced by functional overload (Ov). To test this hypothesis, plantaris muscles were overloaded during 5, 12, and 56 days in female rats exposed to hypobaric hypoxia (5,500 m), and then, we examined the responses of specific signaling pathways involved in protein synthesis (Akt/mTOR) and breakdown (atrogenes). Hypoxia minimized the Ov-induced hypertrophy at days 5 and 12 but did not affect the hypertrophic response measured at day 56. Hypoxia early reduced the phosphorylation levels of mTOR and its downstream targets P70(S6K) and rpS6, but it did not affect the phosphorylation levels of Akt and 4E-BP1, in Ov muscles. The role played by specific inhibitors of mTOR, such as AMPK and hypoxia-induced factors (i.e., REDD1 and BNIP-3) was studied. REDD1 protein levels were reduced by overload and were not affected by hypoxia in Ov muscles, whereas AMPK was not activated by hypoxia. Although hypoxia significantly increased BNIP-3 mRNA levels at day 5, protein levels remained unaffected. The mRNA levels of the two atrogenes MURF1 and MAFbx were early increased by hypoxia in Ov muscles. In conclusion, hypoxia induced a transient alteration of muscle growth in this hypertrophic model, at least partly due to a specific impairment of the mTOR/P70(S6K) pathway, independently of Akt, by an undefined mechanism, and increased transcript levels for MURF1 and MAFbx that could contribute to stimulate the proteasomal proteolysis.
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- Chaillou, Thomas, 1985-, et al.
(author)
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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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In: Physiological Genomics. - Bethesda, USA : American Physiological Society. - 1094-8341 .- 1531-2267. ; 43:4, s. 228-235
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Journal article (peer-reviewed)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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- Magnusson, Yvonne, 1957, et al.
(author)
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Antigenic analysis of the second extra-cellular loop of the human beta-adrenergic receptors.
- 1989
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In: Clinical and experimental immunology. - 0009-9104. ; 78:1, s. 42-8
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Journal article (peer-reviewed)abstract
- Polyclonal antibodies were raised in rabbits by immunization with free peptides corresponding to positions 197-222 of the human beta 1-adrenergic receptor (beta 1 peptide) and the corresponding sequence (172-197) of the human beta 2-adrenergic receptor (beta 2 peptide). While the beta 2 peptide yielded antibodies that cross-reacted with the beta 1 peptide, the antibodies against the beta 1 peptide did not cross-react with the beta 2 sequence. Cross-reactivity of the anti-beta 2 peptide antibodies and the selectivity of the anti-beta 1 peptide antibodies were also revealed in the recognition by immunoblots of the beta 1- and beta 2-adrenergic receptors of different species or of the receptor gene products expressed in a bacterial vector. These antibodies could be used immunohistochemically to visualize the beta-adrenergic receptors on rabbit heart. The anti-beta 2 peptide antibodies did not show any functional effect on the beta-adrenergic receptors; the anti-beta 1 peptide antibodies were able to displace agonist affinity to higher values. Recognition of truncated peptides by the anti-beta 1 and anti-beta 2 peptide antibodies suggested that the cross-reaction of the anti-beta 2 peptide antibodies was due to the recognition of a common epitope on the C-terminal part of the peptides. The anti-beta 1 peptide antibodies recognized the N-terminal part of the peptide better than the C-terminal part. These results suggest that the second extracellular loop postulated in the structure of the human beta-adrenergic receptor contains the T and B cell epitopes necessary for induction of an immune response. The selectivity and the functional properties of the antibodies raised against that loop in the beta 1 adrenergic receptor could have relevance in induction of auto antibodies in certain cardiomyopathic conditions.
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