History and Biology of Erythropoietin in Hematopoietic and Non-Neural Tissues

Erythropoietin (EPO) is a glycoprotein hormone, which is produced in kidney and liver, and is mainly involved in regulating proliferation and maturation of red blood cells. EPO gene expression is induced by hypoxia through the transcription factor hypoxia inducible factor-1, which has been found to be the main regulator of oxygen homeostasis in the body. Suppression of apoptosis is the principle mechanism of action of EPO in maintaining erythropoiesis. It has been recently recognized that EPO is a member of the cytokine type I superfamily and it has multiple effects in organs and tissues different from the hematopoietic system. Recent evidence of EPO as a protective factor in various injury models in the nervous system and heart has raised the possibility that EPO can exert protective effects in many organs in the body. However, whether the mechanism of protective action involves inhibition of apoptosis remains to be seen.