Erythropoietin Expression and Regulation: <scp> <i>Piecing Together Known Mechanisms and Emerging Insights</i> </scp>

Erythropoietin (EPO) is a circulating glycoprotein hormone essential for red blood cell production. The history of EPO stretches from early observations of hypoxia in the mid-19th century to its gene cloning and the clinical use of recombinant forms. Structurally, EPO's extensive glycosylation shapes stability, receptor binding, and therapeutic potential, inspiring engineered analogs with distinct pharmacokinetics. Developmentally, EPO expression shifts from embryonic neural crest and fetal hepatocytes to renal interstitial fibroblasts after birth. EPO gene regulation integrates hypoxia-inducible factors, transcriptional repressors, enhancers, with HIF-2α as the principal activator, and post-translational mechanisms. Recent findings reveal genetic variants within the EPO gene in patients with erythrocytosis. Isoelectric focusing profiles of EPO in these patients was similar to the hepatic-derived EPO profiles in premature newborns, highlighting a dynamic and context-dependent regulation. These findings suggest that reactivation of EPO expression in the liver could be therapeutically valuable, given that hepatic-derived EPO exhibits enhanced activity. Clinically, erythropoiesis-stimulating agents transformed anemia management but raised safety concerns, leading to refined guidelines. The recent introduction of hypoxia-inducible factor prolyl hydroxylase inhibitors represents a new strategy that restores endogenous EPO production and coordinates iron metabolism through transient HIF stabilization. Outstanding challenges include the absence of faithful human EPO-producing cell models and incomplete understanding of the full molecular mechanisms controlling EPO expression and production. Combining insights from developmental biology, genetics, and epigenomics may open new avenues for therapies targeting disorders of erythropoiesis and oxygen homeostasis.