Effects Of Simulated High Altitude On Erythropoietin Receptor In Rat Bone Marrow Cells

Objective: As an important adaptation mechanism to hypoxia, erythrocytosis resulting from high altitude hypoxia maintains an adequate Oa delivery in blood. Erythropoietin (EPO) is a serum glycoprotein hormone required for survival, proliferation and differentiation of committed erythroid progenitor cells. It has been thought that EPO plays a major role in high altitude hypoxiainduced erythrocytosis. The goal of this study was to investigate the effects of high altitude on the expression of erythropoietin receptor (EPOR) in adult rat bone marrow cells and explore the mechanism of erythrocytosis at high altitude.Methods: Adult Wistar rats were randomly divided into 4 groups: normal control group (normoxia) and the other 3 groups which were exposed to simulated high altitude (5000m) 23 hours per day for 5 days (group H5), 15 days (group HIS) and 30 days (group H30). Total RNA was prepared from rat bone marrow cells, and the expression of EPOR mRNA was examined by RT-PCR with reference to the expression of P -actin gene. The amplifed DNA was fractionated by electrop-horesis and sequenced. Quantitation of relative band densities was performed using densitometry scanning techniques. l 5I-EPO was used to demonstrate expression of saturable, high affinity binding sites for EPO on density-fractionated( P <1.077g/ml) rat bone marrow cells. At last, we observed changes of myelogram by Wrights staining.Results:1. Expression of EPOR mRNA in H5 and HIS groups increased significantly compared with the normoxia group, but in H30 group nostatistically significant difference was found.2. Bone marrow cells expressed high-affinity EPOR. The affinity increased in H5 group, and declined in HI 5 and H30 groups. Binding sites per cell showed an increasing trend along with hypoxia process.3. Through myelogram , we discovered that there was a significant increase of proportion of erythroid progenitor cells at 5 days after hypoxia, and significant increase of proportion of lymphocytic cells at 15 and 30 days after hypoxia, and at 30 days proportion of granulocytic cells decreased.Conclusion:1. Simulated high altitude hypoxia adjusted expression of EPOR mRNA on the surface of rat bone marrow cells. Expression of EPOR mRNA increased at H5 and HI5.2. Myeloid cells expressed high-affinity EPOR (Kd=29-50pM). The affinity increased at H5, and declines at H15,H30. Binding sites per cell showed an increasing trend. The number of EPOR on cellular surface had similar change trend with the expression of EPOR mRNA. EPO-EPOR system was the most important factor that induces erythropoiesis at early altitude hypoxia but at later stage there maybe other factors concerned with erythropoiesis.3. Altitude hypoxia affected not only erythroid progenitors in bone marrow, but also the proportion of granulocytic cells and lymphocytic cells. Morphological changes of myeloid cell were also observed.