The Mechanism Of EPO Early Decline And Its Predictive Role In Altitude Training

Background and Objectives:It becomes more popular for endurance athletes to improve their sea-level performance by altitude training,but its effect is controversial till now. Inter-individual variations in sea-level performance after altitude training have been attributed,at least in part,to an inter-individual variability in hypoxia induced erythropoiesis.Erythropoietin(EPO)may affect athletic performance by regulating erythropoiesis.The pattern and mechanism of EPO during altitude training is focused on by many researchers,especially the intriguing phenomenon—its early decline at altitude.Until now,about 100 target genes(hypoxia response gene,HRG),including EPO gene,have been shown to be regulated by hypoxia-inducible factor-1(HIF-1). aHIF,a natural antisense transcript of hypoxia-inducible factors 1α,complementary to the 3′-untranslated region of HIF-1αmRNA,is involved in HIF-1αmRNA regulation and therefore in HIF-1αprotein synthesis.So we presume that the early decline of EPO will be related to aHIF and response of EPO,HIF-1α,aHIF to acute altitude exposure migh be the sensitive molecular markers to identify poor and good responders to altitude training.The purpose of the research is:1.reveal the mechanism that EPO is early declined during altitude training;2.examine whether the change of maximal aerobic performance(graded cycle ergometer test)after training at moderate altitude(2366 m)could be predicted by response of serum EPO(s-EPO)and HIF-1α(s-HIF-1α),expression of HIF-1αmRNA and aHIF gene in leukocytes during 12 h exposure to normobaric hypoxia at an ambient PO₂ corresponding to the training altitude.Methods:1.Animal experiment:Six-week-old,sea-level native male Sprague-Dawley rats were randomizedly divided into four groups:Normoxic Control group(NC), Hypoxic Control group(HC),Normoxic Training group(NT)and Hypoxic Training group(HT).The latter three groups fell into three sub-groups:4 h group, 12 h group and 24 h group.Rats of NC and HC were exposed in normoxia and hypoxia(3000 m)environment respectively at rest;rats of NT and HT performed a treadmill exercise for 1 h at 70%MAV(maximal aerobic velocity).Serum EPO, RVPO₂(renal venous PO₂),kidney EPO,HIF-1αand aHIF gene expression were observed at corresponding time-point;2.Human experiment:seven male university athletes were exposed to normobaric hypoxia(12h at 2366 m at rest)and s-EPO,s-HIF-1α,expression of HIF-lαmRNA and aHIF in leukocytes were measured at 0 h,4 h,8 h and 12 h respectively.Maximal aerobic performance was determined(graded cycle ergometer test)before and after 3-week altitude training at 2366 m.Results:1.Animal experiment:in HC and HT,EPO mRNA and EPO protein in kidney were significantly inceased at 4 h and 12 h and decreased at 24 h;RVPO₂ descended at 4 h and still lowered than NC;12 h of hypoxia did not change HIF-1αmRNA in kidney but decreased at 24 h;following the rapid induction of the HIF-1αprotein in kidney observed at 4～12 h,HIF-1αprotein levels diminished and fell to base-line level after 24 h;aHIF in kidney were elevated at 4 h and remained sustained until 12 h,reach peak at 24 h.2.Human experiment:there is considerable inter-individual variation in s-EPO, s-HIF-1α,expression of HIF-1αmRNA and aHIF gene in leukocytes during acute normobaric hypoxia for 12 h(s-EPO:-11.1%～+308.4%,s-HIF-1α:-8.6%～+42.6%,HIF-1αmRNA:-33.3%～+42.6%,aHIF:-51.1%～+437.1%).The change of VO_2maxalso showed a similarly wide variability(-11.7%～+22.3%) after altitude training.Correlation analysis displayed that Spearman's correlation coefficient of the integration change of s-EPO,s-HIF-1α,expression of HIF-1αmRNA,aHIF,aHIF/HIF-lαmRNA in leukocytes and the change of VO_2max were 0.679(P=0.094),-0.071(P=0.879),-0.214(P=0.645),-0.750(P=0.052)and -0.751(P=0.180)respectively.Conclusions:1.Animal experiment:RVPO₂ is a determinative factor of EPO secreting;during sustained hypoxia,s-EPO and EPO gene expression in kidney are both inceased fast and then deceased;hypoxia-induced increases in HIF-1 are likely due to post-translational changes;aHIF in kidney is likely involed in early decline of serum EPO by down-regulation of HIF-1αmRNA during hypoxia and hypoxic training;2.Human experiment:inter-individual variation in response to altitude training is mainly responsible for its controversial effect;iron-deficiency is not the predominant factor related to the inter-individual variation in response to altitude training;integration change of s-EPO and aHIF in leukocytes during 12 h exposure at 2366 m in resting conditions probably allows for prediction of poor and good responders to altitude training at 2366 m.