Epo activates the vessel wall. Schematic representation of effects of Epo on the vessel wall. Epo induces phosphorylation of Stat5 in endothelial cells (Figure 5C). Endothelial cells that were activated by TNFα and Epo express enhanced levels of PDGF-BB (Figure 6B). PDGF-BB expressed by endothelial cells subsequently stimulates phosphorylation of Stat5 in SMCs (Figure 6C) and induces SMC proliferation.¹⁵  See “Discussion” for further details. Epo-R indicates erythropoietin receptor; and PDGF-R, PDGF receptor.