Diurnal normobaric moderate hypoxia raises serum erythropoietin concentration but does not stimulate accelerated erythrocyte production

The circadian clock regulates rhythmic erythropoietin expression in the murine kidney

Generation of circadian rhythms is cell-autonomous and relies on a transcription/translation feedback loop controlled by a family of circadian clock transcription factor activators including CLOCK, BMAL1 and repressors such as CRY1 and CRY2. The aim of the present study was to examine both the molecular mechanism and the hemopoietic implication of circadian erythropoietin expression. Mutant mice with homozygous deletion of the core circadian clock genes cryptochromes 1 and 2 (Cry-null) were used to elucidate circadian erythropoietin regulation. Wild-type control mice exhibited a significant difference in kidney erythropoietin mRNA expression between circadian times 06 and 18. In parallel, a significantly higher number of erythropoietin-producing cells in the kidney (by RNAscope®) and significantly higher levels of circulating erythropoietin protein (by ELISA) were detected at circadian time 18. Such changes were abolished in Cry-null mice and were independent from oxygen tension, oxygen saturation, or expression of hypoxia-inducible factor 2 alpha, indicating that circadian erythropoietin expression is transcriptionally regulated by CRY1 and CRY2. Reporter gene assays showed that the CLOCK/BMAL1 heterodimer activated an E-box element in the 5' erythropoietin promoter. RNAscope® in situ hybridization confirmed the presence of Bmal1 in erythropoietin-producing cells of the kidney. In Cry-null mice, a significantly reduced number of reticulocytes was found while erythrocyte numbers and hematocrit were unchanged. Thus, circadian erythropoietin regulation in the normoxic adult murine kidney is transcriptionally controlled by master circadian activators CLOCK/BMAL1, and repressors CRY1/CRY2. These findings may have implications for kidney physiology and disease, laboratory diagnostics, and anemia therapy.

Application of Altitude/Hypoxic Training by Elite Athletes

At the Olympic level, differences in performance are typically less than 0.5%. This helps explain why many contemporary elite endurance athletes in summer and winter sport incorporate some form of altitude/hypoxic training within their year-round training plan, believing that it will provide the "competitive edge" to succeed at the Olympic level. The purpose of this paper is to describe the practical application of altitude/hypoxic training as used by elite athletes. Within the general framework of the paper, both anecdotal and scientific evidence will be presented relative to the efficacy of several contemporary altitude/hypoxic training models and devices currently used by Olympic-level athletes for the purpose of legally enhancing performance. These include the three primary altitude/hypoxic training models: 1) live high+train high (LH+TH), 2) live high+train low (LH+TL), and 3) live low+train high (LL+TH). The LH+TL model will be examined in detail and will include its various modifications: natural/terrestrial altitude, simulated altitude via nitrogen dilution or oxygen filtration, and hypobaric normoxia via supplemental oxygen. A somewhat opposite approach to LH+TL is the altitude/hypoxic training strategy of LL+TH, and data regarding its efficacy will be presented. Recently, several of these altitude/hypoxic training strategies and devices underwent critical review by the World Anti-Doping Agency (WADA) for the purpose of potentially banning them as illegal performance-enhancing substances/methods. This paper will conclude with an update on the most recent statement from WADA regarding the use of simulated altitude devices.