Glucose Metabolism and Erythropoietin Stimulation of Erythroid Progenitor Cells

Abstract 4232

Erythropoietin (EPO) is known for its activity in stimulating erythroid progenitor cell survival, proliferation and differentiation. EPO is produced in the interstitial cells of the kidney in a hypoxic responsive manner and is used in treatment of anemia in patients with chronic kidney disease. Suggestions that EPO may affect metabolic parameters led to a recent report that high dose erythropoietin treatment in mice resulted in reduced blood glucose level in addition to increased hematocrit (Hojman et al., Plos One 2009). To examine the link between EPO and metabolic processes further, we treated wild type C57Bl/6 mice fed normal diet (11 kcal% fat) and high fat diet (45 kcal% fat) with EPO (3,000 U/kg three times a week for 3 weeks). As expected from the stimulation of erythropoiesis by exogenous EPO, both groups showed the expected increase in hematocrit up to 80%. We also found that EPO decreased fasting blood glucose level in both normal diet fed mice and high fat diet fed mice, compared with mice treated with saline. An improvement in glucose tolerance was also observed. Since hematopoietic tissue is the major target of EPO, we speculate that EPO may stimulate glucose uptake in hematopoietic tissue, especially during erythropoiesis. To examine EPO stimulation and glucose uptake in vitro, we used cultures of primary human adult erythroid progenitor cells isolated from peripheral blood. We found that with EPO stimulation, glucose uptake per cell increased with erythroid differentiation and peaked in late erythroid progenitor cells at day 8 to 10, then decreased during terminal differentiation. This pattern was observed at both 21% O₂ and 5% O₂. EPO increased glucose uptake in a dose dependent manner up to 10 U/ml. Cellular glucose uptake appeared to follow EpoR expression and was maximal when EpoR levels, and therefore EPO response, were highest. Glucose uptake decreased as EpoR levels decreased with the progression of erythroid maturation. These data suggest that EPO stimulation regulates glucose uptake in erythroid progenitor/precursor cells depending on the stage of erythroid differentiation and that glucose uptake is reduced in late erythroid precursor cells with the down regulation of EpoR and loss of EPO dependence as the cells differentiate into mature erythrocytes. We also examined the effect of high glucose concentration on EPO response in primary human adult erythroid progenitor cell cultures. We found that high glucose concentration in erythroid progenitor cell cultures inhibited EPO stimulated differentiating erythroid progenitor cell proliferation. The combination of EPO with high dose glucose increased hemoglobinization as determined by the increase in benzidine positive cells, suggesting premature hemoglobin accumulation and differentiation. This activity of elevated glucose level suggests that elevated blood glucose concentration contributes to the blunted EPO response, giving rise to EPO resistance. The findings from this study provide us with new insight on EPO stimulation of erythropoiesis and the potential interplay between erythropoiesis and glucose metabolism.