Erythropoietin, also known as EPO, is a glycoprotein hormone that controlserythropoiesis, or red blood cell production. It is a cytokine (protein signaling molecule) forerythrocyte (red blood cell) precursors in the bone marrow.
It is produced by interstitial fibroblasts in the kidney in close association with peritubular capillary and tubular epithelial tubule. It is also produced in perisinusoidal cells in the liver. Erythropoietin also has other known biological functions.