Effect of active recovery on acute strength deficits induced by passive stretching

We herein examined whether immediate muscular activity (active recovery) after stretching decreased stretch-induced strength deficits in human muscles. Our within-subject study included 8 subjects who were used as their own controls. For each subject, both legs were subjected to the same warm-up and stretching treatments, and then one leg was exposed to active recovery (experimental treatment) while the other was allowed to recover passively (control). Unilateral maximal voluntary contraction (MVC) of knee extensors was measured at baseline, poststretching, and postrecovery to monitor strength evolution. Our results revealed that the MVC strength at the baseline time point for control (590.8 +/- 104.2) and treated (602.2 +/- 112.7) legs decreased poststretching by 8.0 and 8.9%, respectively, and further decreased postrecovery by 1.3 and 1.2%, respectively. Maximal voluntary contraction strength tests demonstrated very good reliability, having intraclass coefficients of correlation ranging from 0.92-0.98. Mixed analysis of variance showed that the stretching program yielded significantly increased flexibility (p < 0.01) and significantly decreased MVC (p < 0.001) in both legs. The over-time variability between legs was marginal (1%), and no significant between-leg differences were observed. Indeed, the improvement in strength restoration due to active vs. passive recovery was -0.5 +/- 15 N, which was significantly lower (p < 0.01; 1-tailed t-test) than the amount of strength inhibition (32.6 N), estimated as 60% of the overall strength deficit (54.3 +/- 29.7 N). These results confirm that significant strength is lost poststretching but fail to show greater improvement in strength following active vs. passive recovery. Collectively, the present findings indicate that, contrary to the belief of many coaches, muscular exercises during the poststretching period are unlikely to minimize stretch-induced strength deficits.     

Change in lipid composition in eastern oyster (Crassostrea virginica Gmelin) exposed to constant or fluctuating temperature regimes

A temperature decrease usually induces an ordering effect in membrane phospholipids that can lead to membrane dysfunction. Ectotherms typically counteract this temperature effect by remodeling membrane lipids as stipulated in the homeoviscous adaptation theory (HVA). Previous studies mostly focused on the remodeling of membrane lipids during long-term acclimatization or acclimation at constant temperature regimes, whereas in nature, many organisms experience variations in temperature on a daily basis and must react to this changing thermal environment. The objective of this study was to examine the composition of membrane lipids in oysters subjected to long-term acclimation at constant temperatures (12 or 25 degrees C) or to environmentally realistic daily fluctuations in temperature between 12 and 25 degrees C for 7 d. The lipid composition of gill in oysters subjected to long-term acclimation at a constant temperature or to daily temperature fluctuations varied in a way consistent with HVA: oysters adjusted their phospholipid to sterol ratio in response to long-term acclimation to a constant temperature but not to daily temperature fluctuations. In contrast, the unsaturation index of polar lipids in oysters varied in response to both long-term acclimation to a constant temperature and to daily temperature fluctuations, mainly due to changes in 22:6n-3 and 20:5n-3. The 20:4n-6 levels in oyster gills increased as temperature rose, suggesting an increasing availability of this fatty acid for eicosanoid biosynthesis during stress responses.     

Structural and functional characterization of the interaction between cyclophilin B and a heparin-derived oligosaccharide

The chemotaxis and integrin-mediated adhesion of T lymphocytes triggered by secreted cyclophilin B (CypB) depend on interactions with both cell surface heparan sulfate proteoglycans (HSPG) and the extracellular domain of the CD147 membrane receptor. Here, we use NMR spectroscopy to characterize the interaction of CypB with heparin-derived oligosaccharides. Chemical shift perturbation experiments allowed the precise definition of the heparan sulfate (HS) binding site of CypB. The N-terminal extremity of CypB, which contains a consensus sequence for heparin-binding proteins was modeled on the basis of our experimental NMR data. Because the HS binding site extends toward the CypB catalytic pocket, we measured its peptidyl-prolyl cis-trans isomerase (PPIase) activity in the absence or presence of a HS oligosaccharide toward a CD147-derived peptide. We report the first direct evidence that CypB is enzymatically active on CD147, as it is able to accelerate the cis/trans isomerization of the Asp(179)-Pro(180) bond in a CD147-derived peptide. However, HS binding has no significant influence on this PPIase activity. We thus conclude that the glycanic moiety of HSPG serves as anchor for CypB at the cell surface, and that the signal could be transduced by CypB via its PPIase activity toward CD147.     

CD4 interacts constitutively with multiple CCR5 at the plasma membrane of living cells. A fluorescence recovery after photobleaching at variable radii approach

The entry of human immunodeficiency virus into target cells requires successive interactions of the viral envelope glycoprotein gp120 with CD4 and the chemokine receptors CCR5 or CXCR4. We previously demonstrated, by F?rster resonance energy transfer experiments, the constitutive association of CD4 and CCR5 at the surface of living cells. We therefore speculated that this interaction may correlate with compartmentalization of CD4 and CCR5 within the plasma membrane. Here, we characterize the lateral distribution, the dynamics, and the stoichiometry of these receptors in living cells stably expressing CD4 and/or CCR5 by means of fluorescence recovery after photobleaching at variable radii experiments. We found that (i) these receptors expressed alone are confined into 1-microm-sized domains, (ii) CD4-CCR5 associations occur outside and inside smaller domains, and (iii) these interactions involve multiple CCR5 molecules per CD4.     

The heparin/heparan sulfate sequence that interacts with cyclophilin B contains a 3-O-sulfated N-unsubstituted glucosamine residue

Many of the biological functions of heparan sulfate (HS) proteoglycans can be attributed to specialized structures within HS moieties, which are thought to modulate binding and function of various effector proteins. Cyclophilin B (CyPB), which was initially identified as a cyclosporin A-binding protein, triggers migration and integrin-mediated adhesion of peripheral blood T lymphocytes by a mechanism dependent on interaction with cell surface HS. Here we determined the structural features of HS that are responsible for the specific binding of CyPB. In addition to the involvement of 2-O,6-O, and N-sulfate groups, we also demonstrated that binding of CyPB was dependent on the presence of N-unsubstituted glucosamine residues (GlcNH2), which have been reported to be precursors for sulfation by 3-O-sulfotransferases-3 (3-OST-3). Interestingly, 3-OST-3B isoform was found to be the main 3-OST isoenzyme expressed in peripheral blood T lymphocytes and Jurkat T cells. Moreover, down-regulation of the expression of 3-OST-3 by RNA interference potently reduced CyPB binding and consequent activation of p44/42 mitogen-activated protein kinases. Altogether, our results strongly support the hypothesis that 3-O-sulfation of GlcNH2 residues could be a key modification that provides specialized HS structures for CyPB binding to responsive cells. Given that 3-O-sulfation of GlcNH2-containing HS by 3-OST-3 also provides binding sites for glycoprotein gD of herpes simplex virus type I, these findings suggest an intriguing structural linkage between the HS sequences involved in CyPB binding and viral infection.     

Inhibition of nonsense-mediated mRNA decay (NMD) by a new chemical molecule reveals the dynamic of NMD factors in P-bodies

In mammals, nonsense-mediated mRNA decay (NMD) is a quality-control mechanism that degrades mRNA harboring a premature termination codon to prevent the synthesis of truncated proteins. To gain insight into the NMD mechanism, we identified NMD inhibitor 1 (NMDI 1) as a small molecule inhibitor of the NMD pathway. We characterized the mode of action of this compound and demonstrated that it acts upstream of hUPF1. NMDI 1 induced the loss of interactions between hSMG5 and hUPF1 and the stabilization of hyperphosphorylated isoforms of hUPF1. Incubation of cells with NMDI 1 allowed us to demonstrate that NMD factors and mRNAs subject to NMD transit through processing bodies (P-bodies), as is the case in yeast. The results suggest a model in which mRNA and NMD factors are sequentially recruited to P-bodies.     

Two members of the Arabidopsis CLC (chloride channel) family, AtCLCe and AtCLCf, are associated with thylakoid and Golgi membranes, respectively

Though numerous pieces of evidence point to major physiological roles for anion channels in plants, progress in the understanding of their biological functions is limited by the small number of genes identified so far. Seven chloride channel (CLC) members could be identified in the Arabidopsis genome, amongst which AtCLCe and AtCLCf are both more closely related to bacterial CLCs than the other plant CLCs. It is shown here that AtCLCe is targeted to the thylakoid membranes in chloroplasts and, in agreement with this subcellular localization, that the clce mutants display a phenotype related to photosynthesis activity. The AtCLCf protein is localized in Golgi membranes and functionally complements the yeast gef1 mutant disrupted in the single CLC gene encoding a Golgi-associated protein.     

Strong Heterogeneity in Nucleotidic Composition and Codon Bias in the Pea Aphid (<Emphasis Type="Italic">Acyrthosiphon pisum)</Emphasis> Shown by EST-Based Coding Genome Reconstruction

The aim of this study was to analyze patterns of nucleotidic composition and codon usage in the pea aphid genome (Acyrthosiphon pisum). A collection of 60,000 expressed sequence tags (ESTs) in the pea aphid has been used to automatically reconstruct 5809 coding sequences (CDSs), based on similarity with known proteins and on coding style recognition. Reconstructions were manually checked for ribosomal proteins, leading to tentatively reconstruct the nea-complete set of this category. Pea aphid coding sequences showed a shift toward AT (especially at the third codon position) compared to drosophila homologues. Genes with a putative high level of expression (ribosomal and other genes with high EST support) remained more GC3-rich and had a distinct codon usage from bulk sequences: they exhibited a preference for C-ending codons and CGT (for arginine), which thus appeared optimal for translation. However, the discrimination was not as strong as in drosophila, suggesting a reduced degree of translational selection. The space of variation in codon usage for A. pisum appeared to be larger than in drosophila, with a substantial fraction of genes that remained GC3-rich. Some of those (in particular some structural proteins) also showed high levels of codon bias and a very strong preference for C-ending codons, which could be explained either by strong translational selection or by other mechanisms. Finally, genomic traces were analyzed to build 206 fragments containing a full CDS, which allowed studying the correlations between GC contents of coding and those of noncoding (flanking and introns) sequences.     

In vivo Comet assay on isolated kidney cells to distinguish genotoxic carcinogens from epigenetic carcinogens or cytotoxic compounds

The objective of this study was to determine the ability of the alkaline in vivo Comet assay (pH>13) to distinguish genotoxic carcinogens from epigenetic carcinogens when performed on freshly isolated kidney cells and to determine the possible interference of cytotoxicity by assessing DNA damage induced by renal genotoxic, epigenetic or toxic compounds after enzymatic isolation of kidney cells from OFA Sprague-Dawley male rats. The ability of the Comet assay to distinguish (1) genotoxicity versus cytotoxicity and (2) genotoxic versus non-genotoxic (epigenetic) carcinogens, was thus investigated by studying five known genotoxic renal carcinogens acting through diverse mechanisms of action, i.e. streptozotocin, aristolochic acids, 2-nitroanisole, potassium bromate and cisplatin, two rodent renal epigenetic carcinogens: d-limonene and ciclosporine and two nephrotoxic compounds: streptomycin and indomethacin. Animals were treated once with the test compound by the appropriate route of administration and genotoxic effects were measured at the two sampling times of 3-6 and 22-26h after treatment. Regarding the tissue processing, the limited background level of DNA migration observed in the negative control groups throughout all experiments demonstrated that the enzymatic isolation method implemented in the current study is appropriate. On the other hand, streptozotocin, 20mg/kg, used as positive reference control concurrently to each assay, caused a clear increase in the mean Olive Tail Moment median value, which allows validating the current methodology. Under these experimental conditions, the in vivo rodent Comet assay demonstrated good sensitivity and good specificity: all the five renal genotoxic carcinogens were clearly detected in at least one expression period either directly or indirectly, as in the case of cisplatin: for this cross-linking agent, the significant decrease in DNA migration observed under standard electrophoresis conditions was clearly amplified when the duration of electrophoresis was increased up to 40min. In contrast, epigenetic and nephrotoxic compounds failed to induce any signifcant increase in DNA migration. In conclusion, the in vivo rodent Comet assay performed on isolated kidney cells could be used as a tool to investigate the genotoxic potential of a test compound if neoplasic/preneoplasic changes occur after subchronic or chronic treatments, in order to determine the role of genotoxicity in tumor induction. Moreover, the epigenetic carcinogens and cytotoxic compounds displayed clearly negative responses in this study. These results allow excluding a DNA direct-acting mechanism of action and can thus suggest that a threshold exists. Therefore, the current in vivo rodent Comet assay could contribute to elucidate an epigenetic mechanism and thus, to undertake a risk assessment associated with human use, depending on the exposure level.