Regular endurance training reduces the exercise induced HIF-1α and HIF-2α mRNA expression in human skeletal muscle in normoxic conditions

Regular exercise induces a variety of adaptive responses that enhance the oxidative and metabolic capacity of human skeletal muscle. Although the physiological adjustments of regular exercise have been known for decades, the underlying mechanisms are still unclear. The hypoxia inducible factors 1 and 2 (HIFs) are clearly related heterodimeric transcription factors that consist of an oxygen-depended α-subunit and a constitutive β-subunit. With hypoxic exposure, HIF-1α and HIF-2α protein are stabilized. Upon heterodimerization, HIFs induce the transcription of a variety of genes including erythropoietin (EPO), transferrin and its receptor, as well as vascular endothelial growth factor (VEGF) and its receptor. Considering that several of these genes are also induced with exercise, we tested the hypothesis that the mRNA level of HIF-1α and HIF-2α subunits increases with a single exercise bout, and that this response is blunted with training. We obtained muscle biopsies from a trained (5days/week during 4weeks) and untrained leg from the same human subject before, immediately after, and during the recovery from a 3h two-legged knee extensor exercise bout, where the two legs exercised at the same absolute workload. In the untrained leg, the exercise bout induced an increase (P<0.05) in HIF-1α fold and HIF-2α fold mRNA at 6h of recovery. In contrast, HIF-1α and HIF-2α mRNA levels were not altered at any time point in the trained leg. Obviously, HIF-1α and HIF-2α mRNA levels are transiently increased in untrained human skeletal muscle in response to an acute exercise bout, but this response is blunted after exercise training. We propose that HIFs expression is upregulated with exercise and that it may be an important transcription factor that regulates adaptive gene responses to exercis

Kidney-synthesized erythropoietin is the main source for the hypoxia-induced increase in plasma erythropoietin in adult humans

Purpose: Erythropoietin (EPO) is mainly synthesized within renal peritubular fibroblasts, and also other tissues such as the liver possess the ability. However, to what extent non-kidney produced EPO contributes to the hypoxia-induced increase in circulating EPO in adult humans remains unclear. Methods: We aimed to quantify this by assessing the distribution of EPO glycoforms which are characterized by posttranslational glycosylation patterns specific to the synthesizing cell. The analysis was performed on samples obtained in seven healthy volunteers before, during and after 1month of sojourn at 3,454m altitude. Results: Umbilical cord (UC) plasma served as control. As expected a peak (p<0.05) in urine (2.3±0.5-fold) and plasma (3.3±0.5-fold) EPO was observed on day 1 of high-altitude exposure, and thereafter the concentration decreased for the urine sample obtained after 26days at altitude, but remained elevated (p<0.05) by 1.5±0.2-fold above the initial sea level value for the plasma sample. The EPO glycoform heterogeneity, in the urine samples collected at altitude, did not differ from values at sea level, but were markedly lower (p<0.05) than the mean percent migrated isoform (PMI) for the umbilical cord samples. Conclusion: Our studies demonstrate (1) UC samples express a different glycoform distribution as compared to adult humans and hence illustrates the ability to synthesis EPO in non-kidney cells during fetal development (2) as expected hypoxia augments circulating EPO in adults and the predominant source here for remains being kidney derived

Resistance exercise training increases skeletal muscle mitochondrial respiration in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is associated with skeletal muscle mitochondrial dysfunction. Resistance exercise training (RT) is a training modality with a relatively small pulmonary demand that has been suggested to increase skeletal muscle oxidative enzyme activity in COPD. Whether a shift into a more oxidative profile following RT also translates into increased mitochondrial respiratory capacity in COPD is yet to be established. This study investigated the effects of 13 weeks of RT on m. vastus lateralis mitochondrial capacity in 11 per sons with moderate COPD [45% females, age: 69 ± 4 years (mean ± SD), predicted forced expiratory volume in 1 s (FEV1): 56 ± 7%] and 12 healthy controls (75% females, age: 66 ± 5 years, predicted FEV1: 110 ± 16%). RT was supervised and carried out two times per week. Leg exercises included leg press, knee extension, and knee flexion and were performed unilaterally with one leg conducting high-load training (10 repetitions maximum, 10RM) and the other leg conducting low-load training (30 repetitions maximum, 30RM). One-legged muscle mass, maximal muscle strength, and endurance performance were determined prior to and after the RT period, together with mitochondrial respiratory capacity using high-resolution respirometry and citrate synthase (CS) activity (a marker for mitochondrial volume density). Transcriptome analysis of genes associated with mitochondrial function was performed. Resistance exercise training led to similar improvements in one-legged muscle mass, muscle strength, and endurance performance in COPD and healthy individuals. In COPD, mitochondrial fatty acid oxidation capacity and oxidative phosphorylation increased following RT (+13 ± 22%, P = 0.033 and +9 ± 23%, P = 0.035, respectively). Marked increases were also seen in COPD for mitochondrial volume density (CS activity, +39 ± 35%, P = 0.001), which increased more than mitochondrial respiration, leading to lowered intrinsic mitochondrial function (respiration/CS activity) for complex-1- supported respiration ( 12 ± 43%, P = 0.033), oxidative phosphorylation ( 10 ± 42%, P = 0.037), and electron transfer system capacity ( 6 ± 52%, P = 0.027). No differences were observed between 10RM and 30RM RT, nor were there any adaptations in mitochondrial function following RT in healthy controls. RT led to differential expression of numerous genes related to mitochondrial function in both COPD and healthy controls, with no difference being observed between groups. Thirteen weeks of RT resulted in augmented skeletal muscle mitochondrial respiratory capacity in COPD, accompanied by alterations in the transcriptome and driven by an increase in mitochondrial quantity rather than improved mitochondrial quality.publishedVersio

Screening for recombinant human erythropoietin using [Hb], reticulocytes, the OFFhrscore, OFF z score and Hb z score: status of the Blood Passport

Haemoglobin concentration ([Hb]), reticulocyte percentage (retic%) and OFFhrscore are well-implemented screening tools to determine potential recombinant human erythropoietin (rHuEpo) abuse in athletes. Recently, the International Cycling Union implemented the OFFzscore and the Hbzscore in their anti-doping testing programme. The aim of this study is to evaluate the sensitivity of these indirect screening methods. Twenty-four human subjects divided into three groups with eight subjects each (G1; G2 and G3) were injected with rHuEpo. G1 and G2 received rHuEpo for a 4-week period with 2weeks of "boosting” followed by 2weeks of "maintenance” and a wash-out period of 3weeks. G3 received rHuEpo for a 10-week period (boost=3weeks; maintenance=7weeks; wash out=1week). Three, seven and eight of the 24 volunteers exceeded the cut-off limits for OFFhrscore, [Hb] and retic%, respectively. One subject from G1, nobody from G2, and seven subjects from G3 exceeded the cut-off limit for Hbzscore. In total, ten subjects exceeded the cut-off limit for the OFFzscore; two subjects from G1, two subjects from G2 and six subjects from G3. In total, indirect screening methods were able to indicate rHuEpo injections in 58% of subjects. However, 42% of our rHuEpo-injected subjects were not detected. It should be emphasised that the test frequency in real world anti-doping is far less than the present study, and hence the detection rate will be lowe

Kidney-synthesized erythropoietin is the main source for the hypoxia-induced increase in plasma erythropoietin in adult humans

PURPOSE Erythropoietin (EPO) is mainly synthesized within renal peritubular fibroblasts, and also other tissues such as the liver possess the ability. However, to what extent non-kidney produced EPO contributes to the hypoxia-induced increase in circulating EPO in adult humans remains unclear. METHODS We aimed to quantify this by assessing the distribution of EPO glycoforms which are characterized by posttranslational glycosylation patterns specific to the synthesizing cell. The analysis was performed on samples obtained in seven healthy volunteers before, during and after 1 month of sojourn at 3,454 m altitude. RESULTS Umbilical cord (UC) plasma served as control. As expected a peak (p < 0.05) in urine (2.3 ± 0.5-fold) and plasma (3.3 ± 0.5-fold) EPO was observed on day 1 of high-altitude exposure, and thereafter the concentration decreased for the urine sample obtained after 26 days at altitude, but remained elevated (p < 0.05) by 1.5 ± 0.2-fold above the initial sea level value for the plasma sample. The EPO glycoform heterogeneity, in the urine samples collected at altitude, did not differ from values at sea level, but were markedly lower (p < 0.05) than the mean percent migrated isoform (PMI) for the umbilical cord samples. CONCLUSION Our studies demonstrate (1) UC samples express a different glycoform distribution as compared to adult humans and hence illustrates the ability to synthesis EPO in non-kidney cells during fetal development (2) as expected hypoxia augments circulating EPO in adults and the predominant source here for remains being kidney derived

Hematological adaptations to prolonged heat acclimation in endurance-trained males

Frontiers is fully compliant with open access mandates, by publishing its articles under the Creative Commons Attribution licence (CC-BY). Authors retain copyright of their work and can deposit their publication in any repository. The work can be freely shared and adapted provided that appropriate credit is given and any changes specified.Heat acclimation is associated with plasma volume (PV) expansion that occurs within the first week of exposure. However, prolonged effects on hemoglobin mass (Hbmass) are unclear as intervention periods in previous studies have not allowed sufficient time for erythropoiesis to manifest. Therefore, Hbmass, intravascular volumes, and blood volume (BV)-regulating hormones were assessed with 5½ weeks of exercise-heat acclimation (HEAT) or matched training in cold conditions (CON) in 21 male cyclists [(mean ± SD) age: 38 ± 9 years, body weight: 80.4 ± 7.9 kg, VO2peak: 59.1 ± 5.2 ml/min/kg]. HEAT (n = 12) consisted of 1 h cycling at 60% VO2peak in 40°C for 5 days/week in addition to regular training, whereas CON (n = 9) trained exclusively in cold conditions (<15°C). Before and after the intervention, Hbmass and intravascular volumes were assessed by carbon monoxide rebreathing, while reticulocyte count and BV-regulating hormones were measured before, after 2 weeks and post intervention. Total training volume during the intervention was similar (p = 0.282) between HEAT (509 ± 173 min/week) and CON (576 ± 143 min/week). PV increased (p = 0.004) in both groups, by 303 ± 345 ml in HEAT and 188 ± 286 ml in CON. There was also a main effect of time (p = 0.038) for Hbmass with +34 ± 36 g in HEAT and +2 ± 33 g in CON and a tendency toward a higher increase in Hbmass in HEAT compared to CON (time × group interaction: p = 0.061). The Hbmass changes were weakly correlated to alterations in PV (r = 0.493, p = 0.023). Reticulocyte count and BV-regulating hormones remained unchanged for both groups. In conclusion, Hbmass was slightly increased following prolonged training in the heat and although the mechanistic link remains to be revealed, the increase could represent a compensatory response in erythropoiesis secondary to PV expansion.publishedVersio

Fast-Twitch Glycolytic Skeletal Muscle Is Predisposed to Age-Induced Impairments in Mitochondrial Function

The etiology of mammalian senescence is suggested to involve the progressive impairment of mitochondrial function; however, direct observations of age-induced alterations in actual respiratory chain function are lacking. Accordingly, we assessed mitochondrial function via high-resolution respirometry and mitochondrial protein expression in soleus, quadricep, and lateral gastrocnemius skeletal muscles, which represent type 1 slow-twitch oxidative muscle (soleus) and type 2 fast-twitch glycolytic muscle (quadricep and gastrocnemius), respectively, in young (10-12 weeks) and mature (74-76 weeks) mice. Electron transport through mitochondrial complexes I and III increases with age in quadricep and gastrocnemius, which is not observed in soleus. Mitochondrial coupling efficiency during respiration through complex I also deteriorates with age in gastrocnemius and shows a tendency (p = .085) to worsen in quadricep. These data demonstrate actual alterations in electron transport function that occurs with age and are dependent on skeletal muscle typ

Prolonged heat acclimation and aerobic performance in endurance trained athletes

Frontiers is fully compliant with open access mandates, by publishing its articles under the Creative Commons Attribution licence (CC-BY). Funder mandates such as those by the Wellcome Trust (UK), National Institutes of Health (USA) and the Australian Research Council (Australia) are fully compatible with publishing in Frontiers. Authors retain copyright of their work and can deposit their publication in any repository. The work can be freely shared and adapted provided that appropriate credit is given and any changes specified.Heat acclimation (HA) involves physiological adaptations that directly promote exercise performance in hot environments. However, for endurance-athletes it is unclear if adaptations also improve aerobic capacity and performance in cool conditions, partly because previous randomized controlled trial (RCT) studies have been restricted to short intervention periods. Prolonged HA was therefore deployed in the present RCT study including 21 cyclists [38 ± 2 years, 184 ± 1 cm, 80.4 ± 1.7 kg, and maximal oxygen uptake (VO2max) of 58.1 ± 1.2 mL/min/kg; mean ± SE] allocated to either 5½ weeks of training in the heat [HEAT (n = 12)] or cool control [CON (n = 9)]. Training registration, familiarization to test procedures, determination of VO2max, blood volume and 15 km time trial (TT) performance were assessed in cool conditions (14°C) during a 2-week lead-in period, as well as immediately pre and post the intervention. Participants were instructed to maintain total training volume and complete habitual high intensity intervals in normal settings; but HEAT substituted part of cool training with 28 ± 2 sessions in the heat (1 h at 60% VO2max in 40°C; eliciting core temperatures above 39°C in all sessions), while CON completed all training in cool conditions. Acclimation for HEAT was verified by lower sweat sodium [Na+], reduced steady-state heart rate and improved submaximal exercise endurance in the heat. However, when tested in cool conditions both peak power output and VO2max remained unchanged for HEAT (pre 60.0 ± 1.5 vs. 59.8 ± 1.3 mL O2/min/kg). TT performance tested in 14°C was improved for HEAT and average power output increased from 298 ± 6 to 315 ± 6 W (P < 0.05), but a similar improvement was observed for CON (from 294 ± 11 to 311 ± 10 W). Based on the present findings, we conclude that training in the heat was not superior compared to normal (control) training for improving aerobic power or TT performance in cool conditions.publishedVersio