Erythropoietin: cytoprotection in vascular and neuronal cells.

One of the principal functions of erythropoietin (EPO) is to stimulate the survival, proliferation, and differentiation of immature erythroid cells. Yet, EPO has recently been shown to modulate cellular signal transduction pathways to perform multiple functions other than erythropoiesis. EPO is cytoprotective through the prevention of programmed cell death in both vascular and neuronal systems by modulating two distinct components of programmed cell death that involve the degradation of genomic DNA and the externalization of cellular membrane phosphatidylserine (PS) residues. Cytoprotection by EPO is initiated by the activation of the EPO receptor (EPOR) and subsequent signal transduction pathways that originate with the Janus-tyrosine kinase 2 (Jak2) protein. Further down-stream cellular pathways include the activation of signal transducers and activators of transcription (STATs), Bcl-x(L), phosphoinositide-3-kinase/Akt, mitogen-activated protein kinases, cysteine proteases, protein tyrosine phosphatases, and nuclear factor kappaB. Further understanding of the cellular pathways that modulate EPO cytoprotection in the nervous system will be crucial for the development of therapeutic strategies against neurodegenerative diseases.