ROLE OF VASCULAR ENDOTHELIAL GROWTH-FACTOR ON ERYTHROPOIETIN-RELATED ENDOTHELIAL-CELL PROLIFERATION

The vascular actions of recombinant human erythropoietin (rhEPO) are o f particular relevance for fully understanding rhEPO effects. This stu dy examines the mechanisms of action of rhEPO on endothelial cells fro m bovine aorta (BAEC), First, the studies demonstrated that rhEPO acts on BAEC proliferation as a comitogenic growth factor in the presence of fetal calf serum (FCS). The main experimental findings disclosed th at an interaction between rhEPO and vascular endothelial growth factor (VEGF) is instrumental fur the growth-promoting action of rhEPO, as s hown by the blockade (92.8 +/- 2.2% inhibition, P < 0.01) of the rhEPO -induced BAEC proliferation by a specific anti-VEGF antibody and by th e capability of VEGF for substituting FCS in the induction of rhEPO-re lated BAEC proliferation (increase in BAEC number in the absence of FC S: 20 U/ml rhEPO alone, 0.3 +/- 2.8%; 5 x 10(-11) M VEGF alone, 52.9 /- 3.1%; 20 U/ml rhEPO +/- 5 x 10(-11) M VEGF, 117.8 +/- 6.9%, P < 0.0 1 between the two agents combined with respect to each agent alone). T he existence of a positive interaction between rhEPO and VEGF was furt her demonstrated by observing an increased cytosolic Ca2+ ([Ca2+](i)) mobilization response to VEGF(10(-11) M) in BAEC pretreated or not wit h 20 U/ml rhEPO (Delta[Ca2+](i) = 704 +/- 111 versus 246 +/- 36 nM, re spectively, P < 0.01). To further examine the mechanism of the potenti ation of VEGF effect by rhEPO, we analyzed the mRNA expression of the VEGF receptors KDR/flk-1 and flt-1. The results disclosed that BAEC pr etreatment with rhEPO upregulated the expression of both KDR/flk-1 and flt-1, therefore providing a structural basis For the aforementioned positive interactions between VEGF and rhEPO. Furthermore, inhibition by genistein suggests that tyrosine phosphorylation was involved in th e VEGF receptor upregulation. The mechanisms identified in the present study disclose an interaction at the level of mRNA expression and fun ctional effects between a hormone with predominantly hemopoietic effec ts, namely, erythropoietin, and an angiogenic factor, namely, VEGF. Th is relationship between rhEPO and VEGF might be of particular importan ce in neovascularization processes and in patients receiving rhEPO as a treatment.