Human Erythropoietin (EPO) is also known as EP, erythropoetin or erthropoyetin, and is a glycoprotein hormone that controls erythropoiesis, or red blood cell production. EPO is a cytokine for erythrocyte (red blood cell) precursors in the bone marrow. is synthesized by renal peritubular cells in adults, with a small amount being produced in the liver. Regulation is believed to rely on a feed-back mechanism measuring blood oxygenation. Constitutively synthesized transcription factors for EPO, known as hypoxia-inducible factors (HIFs), are hydroxylated and proteosomally digested in the presence of oxygen. It binds to the erythropoietin receptor (EpoR) on the red cell surface and activates a JAK2 cascade. Erythropoietin has its primary effect on red blood cells by promoting red blood cell survival through protecting these cells from apoptosis. It also cooperates with various growth factors involved in the development of precursor red cells. EPO has a range of actions including vasoconstriction-dependent hypertension, stimulating angiogenesis, and inducing proliferation of smooth muscle fibers. It has also been shown that erythropoietin can increase iron absorption by suppressing the hormone hepcidin. Erythropoietin has been shown to interact with the Erythropoietin receptor as its mechanism of action within the body. erythropoietin plays an important role in the brain's response to neuronal injury. EPO is also involved in the wound healing process.