Human Erythropoietin (EPO) Recombinant Protein, eBioscience?. Erythropoietin (EPO) protein is a growth factor essential for the survival, proliferation, and differentiation of erythroid precursors. EPO is not responsible for early commitment to the lineage, and instead induces the final maturation of partially differentiated erythroid cells and the production of red cell-specific proteins, such as hemoglobin. The EPO receptor (EPOR) is present in higher levels on precursor cells, and expression diminishes with cell maturation.Hepatocytes are the main source of EPO in the fetus, followed by interstitial cells of the kidney after birth and through adulthood. EPO expression is upregulated during hypoxia, and low levels of transcription h