B-293 Non-renal Sources of Erythropoietin: Complications for Interpreting Erythropoietin Assays

Abstract

Abstract Background Erythropoietin (EPO) is a glycoprotein that stimulates the production of red blood cells, in response to systemic hypoxia. Generally, the kidney is thought to be the sole producer of EPO. Emerging data shows Epo mRNA expression can occur in non-renal tissues, yet the significance of this remains uninvestigated. Clinically, EPO assays are primarily used to identify the underlying cause of anemia and polycythemia. Interestingly, EPO serum levels are elevated following a myocardial infarct (MI); the source is always assumed to be kidney with no further investigations into non-renal sources of EPO. Here we investigate the heart as a novel source of serum EPO following a MI. We hypothesize that the heart, not the kidney, produces EPO in response to organ-specific hypoxia (i.e., MI). Methods To assess which organs are producing EPO following a MI, we examined EPO mRNA expression. mRNA levels correlate strongly with EPO protein synthesis, as EPO is exclusively regulated at the transcription level. To induce a MI, CD1 mice were subjected to ligation of the lateral anterior descending artery. Left ventricle and kidney tissues were collected at 24 h, 4 weeks and 18 weeks following MI or sham surgery; tissue was snap frozen and stored at −80°C for qPCR analysis. Hematocrit was measured at 2-, 4-, and 18-weeks following MI or sham surgery. Results 24 h following a MI, the left ventricle showed a ∼100-fold increase in EPO mRNA expression in comparison to sham group (P = 0.0012); the kidney showed no significant differences in EPO mRNA between MI and sham group. Hematocrit was measured from the carotid artery. At 2- and 4- weeks following surgery, hematocrit in MI group was significantly elevated in comparison to baseline hematocrit levels (Baseline: 40.8% ± 4, 2-week: 47.8% ± 3.1, and 4-week: 46% ± 2.6 (P = 0.0003, P = 0.0103, respectively). Whereas there were no significant differences in hematocrit between baseline and the sham group. Conclusion Here we show that following a MI, the heart, not the kidney, produces EPO. Subsequently, there is an increase in hematocrit as a result of cardiac-specific EPO production. Further, perturbations in EPO serum levels are not disease specific. In cases where EPO assays are conducted on MI patients, interpretation of EPO levels should be cautioned as it may not be exclusively diagnostic of the underlying cause of anemia or other bone marrow disorders. Therefore, an alternative diagnosis may be warranted for elevated EPO levels in this specific patient population.