EPO induction of EPOR in HUVECs. (A) EPO (▪) in combination with reduced oxygen tension (5% and 2% O2) increased EPOR expression in primary HUVECs as measured by quantitative RT-PCR. No change in EPOR was observed with reduced oxygen tension in the absence of EPO (□). Results are normalized to β-actin expression (*P < .05; ***P < .001). (B) Western blot analysis confirmed induction of EPOR protein for HUVECs cultured with EPO at 2% O2. OCIM-1 cell extract was used as a positive control (OCIM1). (C) Expression of eNOS in HUVECs at different oxygen tensions. In the absence of EPO (open bars), expression of eNOS at 2% O2 was less than one-half of the value under normoxia. However, addition of EPO (▪) reversed the decrease in eNOS expression at low oxygen tension, increasing eNOS by 2-fold or more in HUVECs (***P < .001). VEGF (▨) did not induce eNOS expression. Error bars represent SD.
