FIG 1.

In the absence of oxygen, HIF-1α increases transcription of the erythropoeitin (EPO) gene, creating more EPO. EPO binds to its receptor on colony-forming unit-erythron (CFU-E) cells in the bone marrow and prevents apoptosis, enhancing proliferation and maturation to RBCs, which increase oxygen-carrying capacity. When oxygen is present, prolyl hydroxylase is stabilized and increases degradation of HIF-1α, preventing EPO production. HIF-1 = hypoxia-inducible factor 1, EPO R = erythropoeitin receptor