Smith, Leslie A

The present study is aimed at investigating the contribution of endothelial nitric oxide synthase (eNOS) to erythropoietin (EPO)‐induced mobilization of stem (c‐kit + ,sca‐1 + ,lin‐1 − ; KSL) cells and hematopoietic progenitor (CD34 + ) cells. Wild type (WT) and eNOS −/− mice were injected biweekly with recombinant erythropoietin (1000 U/kg, s.c.) for 14 days. The percentage of KSL cells in spleen, bone marrow and peripheral blood were quantitated by flow cytometry (Becton Dickinson) and analyzed by Cell Quest software. The effect of EPO on number of CD34 + cells in peripheral blood was quantitated by ProCount Progenitor Cell Enumeration Kit (BD Biosciences). Treatment of eNOS −/− mice with EPO increased the percentage of KSL cells by two folds only in bone marrow and spleen, while the percentage of KSL cells in peripheral blood remained unchanged. Treatment with EPO significantly increased the number of CD34 + cells in blood of WT mice (2.75 ± 0.30 cells in WT, 38.39 ± 10.35 in WT+EPO, n=5, P<0.01). However, the number of CD34 + cells remained unchanged in blood of eNOS −/− mice (2.51 ± 1.31 in eNOS −/− , 4.65 ± 1.40 in eNOS −/− + EPO, n=5, P=ns). Results of the present study suggest that eNOS plays an important role in the mobilization of hematopoietic stem/progenitor cells by erythropoietin.