Effect of acute altitude exposure on ventilatory thresholds in recreational athletes.

PURPOSE: High altitude (HA) training is frequently used in endurance sports and recreational athletes increasingly participate in cross mountain competitions. At high altitude aerobic physiology changes profoundly. Ventilatory thresholds (VTs) are measures for endurance performance but the impact of exposure to acute altitude (AA) on VTs in recreational athletes has been insufficiently explored to date and most studies investigated effects under normobaric hypoxia. METHODS: In this cross-sectional study we investigated the effects of AA exposure at 2650 m/715 mbar on anerobic threshold (VT1) and respiratory compensation point (VT2) in a graded cycling test in 14 recreational athletes (4 female, 10 male) compared to baseline levels (521 m, 949 mbar). RESULTS: At VT1, a decline in power output (PO) from median 115.5 W to 105.0 W (median -12.3 %, p = 0.032; Wilcoxon test) during exposure to HA was observed. VO2/body weight and VO2/heart rate decreased markedly (- 9.5 %, p = 0.016; -10.5 %, p = 0.012). At VT2 we found a significant decline of PO from 184.5-170.5 W (-13.1 %, p = 0.0014), of VO2/body weight and of VO2/heart rate (-10.1 %, p = 0.0015; -8.7 %, p = 0.002) compared to baseline values. Absolute VO2 decreased (-9.5 %, p = 0.0014 and -10.1 %, p = 0.0002) while minute ventilation and heart rates remained unchanged at both thresholds. CONCLUSION: Our data allows a quantification of performance loss at HA in recreational athletes and demonstrates that VT-guided training intensities and workloads need to be adapted for training at HA.

Deceleration Capacity and Periodic Repolarization Dynamics As Predictors of Acute Mountain Sickness.

Hamm, Wolfgang, Sari Kassem, Lukas von Stülpnagel, Florian Maier, Mathias Klemm, Dominik Schüttler, Felix Grabher, Ludwig T. Weckbach, Bruno C. Huber, Axel Bauer, Konstantinos D. Rizas, and Stefan Brunner. Deceleration capacity and periodic repolarization dynamics as predictors of acute mountain sickness. High Alt Med Biol. 21:417-422, 2020. Background: The autonomic nervous system plays an important role in adaptive changes after acute altitude exposure. Periodic repolarization dynamics (PRD) and deceleration capacity (DC) of heart rate are advanced electrocardiogram (ECG)-based parameters reflecting sympathetic (PRD) and parasympathetic (DC) tone. These parameters have not been investigated in the context of acute mountain sickness (AMS) yet. Methods: In 23 healthy individuals (13 women), a high-resolution digital 30-minute ECG in Frank leads configuration was performed in a resting supine position at baseline (521 m altitude) and after a sojourn of 24 hours at the Environmental Research Station Schneefernerhaus (UFS) at Zugspitze (2,650 m altitude). PRD and DC were assessed using validated software. Symptoms of AMS were assessed with the Lake Louise Acute Mountain Sickness Score (LLS). Results: During altitude exposure, PRD significantly increased from 1.50 ± 1.01 (mean ± standard deviation) deg2 to 3.51 ± 4.46 deg2 (p = 0.03). DC significantly decreased from 11.48 ± 2.91 ms to 9.94 ± 2.78 ms (p = 0.001). An increase of PRD and/or a decrease of DC correlated significantly with the level of LLS. The combined finding of an increase of PRD and a decrease of DC had a sensitivity of 100% and a specificity of 76.5% to diagnose AMS (LLS ≥3). Receiver operating characteristic (ROC) analysis showed an AUC (area under the ROC curve) of 0.77. Linear regression analysis revealed a significant association between LLS and an increase in PRD during high-altitude exposure. Conclusions: Our findings show an increase of PRD and a decrease of DC during altitude exposure. Combined PRD and DC analysis may have potential for the diagnosis of AMS.

Histone exchange is associated with activator function at transcribed promoters and with repression at histone loci.

Transcription in eukaryotes correlates with major chromatin changes, including the replacement of old nucleosomal histones by new histones at the promoters of genes. The role of these histone exchange events in transcription remains unclear. In particular, the causal relationship between histone exchange and activator binding, preinitiation complex (PIC) assembly, and/or subsequent transcription remains unclear. Here, we provide evidence that histone exchange at gene promoters is not simply a consequence of PIC assembly or transcription but instead is mediated by activators. We further show that not all activators up-regulate gene expression by inducing histone turnover. Thus, histone exchange does not simply correlate with transcriptional activity, but instead reflects the mode of action of the activator. Last, we show that histone turnover is not only associated with activator function but also plays a role in transcriptional repression at the histone loci.

Mutations in the NOT Genes or in the Translation Machinery Similarly Display Increased Resistance to Histidine Starvation.

The NOT genes encode subunits of the conserved Ccr4-Not complex, a global regulator of gene expression, and in particular of mRNA metabolism. They were originally identified in a selection for increased resistance to histidine starvation in the yeast S. cerevisiae. Recent work indicated that the Not5 subunit, ortholog of mammalian CNOT3, determines global translation levels by defining binding of the Ccr4-Not scaffold protein Not1 to ribosomal mRNAs during transcription. This is needed for optimal translation of ribosomal proteins. In this work we searched for mutations in budding yeast that were resistant to histidine starvation using the same selection that originally led to the isolation of the NOT genes. We thereby isolated mutations in ribosome-related genes. This common phenotype of ribosome mutants and not mutants is in good agreement with the positive role of the Not proteins for translation. In this regard, it is interesting that frequent mutations in RPL5 and RPL10 or in CNOT3 have been observed to accumulate in adult T-cell acute lymphoblastic leukemia (T-ALL). This suggests that in metazoans a common function implicating ribosome subunits and CNOT3 plays a role in the development of cancer. In this perspective we suggest that the Ccr4-Not complex, according to translation levels and fidelity, could itself be involved in the regulation of amino acid biosynthesis levels. We discuss how this could explain why mutations have been identified in many cancers.

Not5-dependent co-translational assembly of Ada2 and Spt20 is essential for functional integrity of SAGA.

Acetylation of histones regulates gene expression in eukaryotes. In the yeast Saccharomyces cerevisiae it depends mainly upon the ADA and SAGA histone acetyltransferase complexes for which Gcn5 is the catalytic subunit. Previous screens have determined that global acetylation is reduced in cells lacking subunits of the Ccr4­Not complex, a global regulator of eukaryotic gene expression. In this study we have characterized the functional connection between the Ccr4­Not complex and SAGA. We show that SAGA mRNAs encoding a core set of SAGA subunits are tethered together for co-translational assembly of the encoded proteins. Ccr4­Not subunits bind SAGA mRNAs and promote the co-translational assembly of these subunits. This is needed for integrity of SAGA. In addition, we determine that a glycolytic enzyme, the glyceraldehyde-3-phosphate dehydrogenase Tdh3, a prototypical moonlighting protein, is tethered at this site of Ccr4­Not-dependent co-translational SAGA assembly and functions as a chaperone.

Translational Capacity of a Cell Is Determined during Transcription Elongation via the Ccr4-Not Complex.

The current understanding of gene expression considers transcription and translation to be independent processes. Challenging this notion, we found that translation efficiency is determined during transcription elongation through the imprinting of mRNAs with Not1, the central scaffold of the Ccr4-Not complex. We determined that another subunit of the complex, Not5, defines Not1 binding to specific mRNAs, particularly those produced from ribosomal protein genes. This imprinting mechanism specifically regulates ribosomal protein gene expression, which in turn determines the translational capacity of cells. We validate our model by SILAC and polysome profiling experiments. As a proof of concept, we demonstrate that enhanced translation compensates for transcriptional elongation stress. Taken together, our data indicate that in addition to defining mRNA stability, components of the Ccr4-Not imprinting complex regulate RNA translatability, thus ensuring global gene expression homeostasis.

The Not5 subunit of the ccr4-not complex connects transcription and translation.

Recent studies have suggested that a sub-complex of RNA polymerase II composed of Rpb4 and Rpb7 couples the nuclear and cytoplasmic stages of gene expression by associating with newly made mRNAs in the nucleus, and contributing to their translation and degradation in the cytoplasm. Here we show by yeast two hybrid and co-immunoprecipitation experiments, followed by ribosome fractionation and fluorescent microscopy, that a subunit of the Ccr4-Not complex, Not5, is essential in the nucleus for the cytoplasmic functions of Rpb4. Not5 interacts with Rpb4; it is required for the presence of Rpb4 in polysomes, for interaction of Rpb4 with the translation initiation factor eIF3 and for association of Rpb4 with mRNAs. We find that Rpb7 presence in the cytoplasm and polysomes is much less significant than that of Rpb4, and that it does not depend upon Not5. Hence Not5-dependence unlinks the cytoplasmic functions of Rpb4 and Rpb7. We additionally determine with RNA immunoprecipitation and native gel analysis that Not5 is needed in the cytoplasm for the co-translational assembly of RNA polymerase II. This stems from the importance of Not5 for the association of the R2TP Hsp90 co-chaperone with polysomes translating RPB1 mRNA to protect newly synthesized Rpb1 from aggregation. Hence taken together our results show that Not5 interconnects translation and transcription.