Effect of betaine supplementation on cycling sprint performance

<p>Abstract</p> <p>Purpose</p> <p>To examine the effect of betaine supplementation on cycling sprint performance.</p> <p>Methods</p> <p>Sixteen recreationally active subjects (7 females and 9 males) completed three sprint tests, each consisting of four 12 sec efforts against a resistance equal to 5.5% of body weight; efforts were separated by 2.5 min of cycling at zero resistance. Test one established baseline; test two and three were preceded by seven days of daily consumption of 591 ml of a carbohydrate-electrolyte beverage as a placebo or a carbohydrate-electrolyte beverage containing 0.42% betaine (approximately 2.5 grams of betaine a day); half the beverage was consumed in the morning and the other half in the afternoon. We used a double blind random order cross-over design; there was a 3 wk washout between trials two and three. Average and maximum peak and mean power were analyzed with one-way repeated measures ANOVA and, where indicated, a Student Newman-Keuls.</p> <p>Results</p> <p>Compared to baseline, betaine ingestion increased average peak power (6.4%; p < 0.001), maximum peak power (5.7%; p < 0.001), average mean power (5.4%; p = 0.004), and maximum mean power (4.4%; p = 0.004) for all subjects combined. Compared to placebo, betaine ingestion significantly increased average peak power (3.4%; p = 0.026), maximum peak power max (3.8%; p = 0.007), average mean power (3.3%; p = 0.034), and maximum mean power (3.5%; p = 0.011) for all subjects combined. There were no differences between the placebo and baseline trials.</p> <p>Conclusions</p> <p>One week of betaine ingestion improved cycling sprint power in recreationally active males and females.</p

Stress granules regulate stress-induced paraspeckle assembly

Eukaryotic cells contain a variety of RNA-protein macrocomplexes termed RNP granules. Different types of granules share multiple protein components; however, the crosstalk between spatially separated granules remains unaddressed. Paraspeckles and stress granules (SGs) are prototypical RNP granules localized exclusively in the nucleus and cytoplasm, respectively. Both granules are implicated in human diseases, such as amyotrophic lateral sclerosis. We characterized the composition of affinity-purified paraspeckle-like structures and found a significant overlap between the proteomes of paraspeckles and SGs. We further show that paraspeckle hyperassembly is typical for cells subjected to SG-inducing stresses. Using chemical and genetic disruption of SGs, we demonstrate that formation of microscopically visible SGs is required to trigger and maintain stress-induced paraspeckle assembly. Mechanistically, SGs may sequester negative regulators of paraspeckle formation, such as UBAP2L, alleviating their inhibitory effect on paraspeckles. Our study reveals a novel function for SGs as positive regulators of nuclear RNP granule assembly and suggests a role for disturbed SG-paraspeckle crosstalk in human disease

Mechanisms of stress granules assembly under oxidative and osmotic stresses

Les granules de stress (GSs) sont des entités cytoplasmiques très dynamiques et dépourvues de membranes, ils apparaissent suite à des conditions de stress. En raison du fait que les GSs sont instables et dépourvus de membranes, leur isolement biochimique n'a pas été accompli. En effet, toutes les fonctions qui sont attribuées aux GSs se basent principalement sur l'observation par microscopie optique de quelques protéines régulatrices des ARNm. A travers cette étude, nous avons déterminé la composition des GSs à l'échelle nanométrique dans deux conditions de stress différentes (stress osmotique et stress oxydatif). Nous avons d'abord cartographié les GSs par microscopie électronique puis ces mêmes granule sont été analysés par microscopie ionique. Grâce au marquage isotopique de l'ARN, nous avons montré que ces structures sont très riche sen ARN, par rapport au reste du cytoplasme et ceci dans les deux conditions de stress. Le deuxième volet de notre étude nous a permis de mettre en évidence un rôle fonctionnel des GSs dans la réponse au stress osmotique. En effet, l'augmentation de la force ionique et de l'encombrement macromoléculaire (deux paramètres qui sont accentués dans les conditions de stress osmotique) permet la dissociation des polysomes et l'assemblage des GSs. Néanmoins, quelques heures après, l'accumulation des osmolytes compatibles dans le cytoplasme par les transporteurs spécifiques réduit la force ionique et l'encombrement macromoléculaire permettant ainsi la dissociation des GSs et le retour progressif de la traduction. Nous avons démontré également que le préconditionnement des cellules avec des osmolytes compatibles avant leur exposition à un stress osmotique sévère bloque la formation des GSs et augmente le taux de survie des cellules. L'ensemble de ces résultats prouve que les osmolytes compatibles favorisent la survie cellulaire et l'adaptation des cellules aux conditions de stress osmotique partiellement via la dissociation des GSs et la reprise de la traduction.Stress granules (SGs) are highly dynamical cytoplasmic bodies laking encapsuling membarnes which appear in reponse to a wide variety of stresses. Due to their lack of membranes and their instability, their biochemical isolation from cells has not yet been accomplished. All functions attributed to SGs are mostly based on optical microscopy observations of key proteins involved in mRNA processing. In the first part of our study, we explored the RNA composition SGs at a nanometric scale and their biophysical properties in two different conditions (osmotic and oxydative stresses). To do so, we imaged and identified the SGs by electron microscopy and analyzed the distribution of N15-uridine labeled-RNA via ionic microscopy. We show that the SGs are enriched in RNA compared to rest of cytoplasm in the two stress conditions. The second part of our study, we tackled the functional role of the SGs in response to osmotic stress. The increase of ionic strength and macromolecular crowding which are the hallmark of osmotic stress lead to SGs assembly in cells after polysome disassembly. However, several hours after the onset of stress, the compatible osmolyte accumulation in the cell by specific transporters reduces the ionic strength and macromolecular crowding thus allowing the diassembly of SGs and the progressive return of translation. In line with this, celle preconditioning with compatible osmolytes before their exposition to severe osmotoc stress prevents the assembly of SGs and increases the rate of cell survival. Together, these results show that compatible osmolytes favors cell survival and adaptation to osmotoc stress via the disassembly of SGs ans recovery of translation

Macromolecular Crowding Regulates Assembly of mRNA Stress Granules after Osmotic Stress: NEW ROLE FOR COMPATIBLE OSMOLYTES

International audienceThe massive uptake of compatible osmolytes such as betaine, taurine, and myo-inositol is a protective response shared by all eukaryotes exposed to hypertonic stress. Their accumulation results mostly from the expression of specific transporters triggered by the transcriptional factor NFAT5/TonEBP. This allows the recovery of the cell volume without increasing intracellular ionic strength. In this study we consider the assembly and dissociation of mRNA stress granules (SGs) in hypertonic-stressed cells and the role of compatible osmolytes. In agreement with in vitro results obtained on isolated mRNAs, both macromolecular crowding and a high ionic strength favor the assembly of SGs in normal rat kidney epithelial cells. However, after hours of constant hypertonicity, the slow accumulation in the cytoplasm of compatible osmolytes via specific transporters both reduces macromolecular crowding and ionic strength, thus leading to the progressive dissociation of SGs. In line with this, when cells are exposed to hypertonicity to accumulate a large amount of compatible osmolytes, the formation of SGs is severely impaired, and cells increase their chances of survival to another hypertonic episode. Altogether, these results indicate that the impact of compatible osmolytes on the mRNA-associated machineries and especially that associated with SGs may play an important role in cell resistance and adaption to hyperosmolarity in many tissues like kidney and liver

Gap junctions favor normal rat kidney epithelial cell adaptation to chronic hypertonicity

International audienceUpon hypertonic stress most often resulting from high salinity, cells need to balance their osmotic pressure by accumulating neutral osmolytes called compatible osmolytes like betaine, myo-inositol, and taurine. However, the massive uptake of compatible osmolytes is a slow process compared with other defense mechanisms related to oxidative or heat stress. This is especially critical for cycling cells as they have to double their volume while keeping a hospitable intracellular environment for the molecular machineries. Here we propose that clustered cells can accelerate the supply of compatible osmolytes to cycling cells via the transit, mediated by gap junctions, of compatible osmolytes from arrested to cycling cells. Both experimental results in epithelial normal rat kidney cells and theoretical estimations show that gap junctions indeed play a key role in cell adaptation to chronic hypertonicity. These results can provide basis for a better understanding of the functions of gap junctions in osmoregulation not only for the kidney but also for many other epithelia. In addition to this, we suggest that cancer cells that do not communicate via gap junctions poorly cope with hypertonic environments thus explaining the rare occurrence of cancer coming from the kidney medulla

An intercellular polyamine transfer via gap junctions regulates proliferation and response to stress in epithelial cells

International audienceIn the organism, quiescent epithelial cells have the potential to resume cycling as a result of various stimuli, including wound healing or oxidative stress. Because quiescent cells have a low polyamine level, resuming their growth requires an increase of their intracellular polyamine levels via de novo polyamine synthesis or their uptake from plasma. Another alternative, explored here, is an intercellular exchange with polyamine-rich cycling cells via gap junctions. We show that polyamines promote gap junction communication between proliferating cells by promoting dynamical microtubule plus ends at the cell periphery and thus allow polyamine exchange between cells. In this way, cycling cells favor regrowth in adjacent cells deprived of polyamines. In addition, intercellular interactions mediated by polyamines can coordinate the translational response to oxidative stress through the formation of stress granules. Some putative in vivo consequences of polyamine-mediated intercellular interactions are also discussed regarding cancer invasiveness and tissue regeneration

Free mRNA in excess upon polysome dissociation is a scaffold for protein multimerization to form stress granules

International audienceThe sequence of events leading to stress granule assembly in stressed cells remains elusive. We show here, using isotope labeling and ion microprobe, that proportionally more RNA than proteins are present in stress granules than in surrounding cytoplasm. We further demonstrate that the delivery of single strand polynucleotides, mRNA and ssDNA, to the cytoplasm can trigger stress granule assembly. On the other hand, increasing the cytoplasmic level of mRNA-binding proteins like YB-1 can directly prevent the aggregation of mRNA by forming isolated mRNPs, as evidenced by atomic force microscopy. Interestingly, we also discovered that enucleated cells do form stress granules, demonstrating that the translocation to the cytoplasm of nuclear prion-like RNA-binding proteins like TIA-1 is dispensable for stress granule assembly. The results lead to an alternative view on stress granule formation based on the following sequence of events: after the massive dissociation of polysomes during stress, mRNA-stabilizing proteins like YB-1 are outnumbered by the burst of nonpolysomal mRNA. mRNA freed of ribosomes thus becomes accessible to mRNA-binding aggregation-prone proteins or misfolded proteins, which induces stress granule formation. Within the frame of this model, the shuttling of nuclear mRNA-stabilizing proteins to the cytoplasm could dissociate stress granules or prevent their assembly