Increased erythropoiesis in polycythemia vera is associated with increased erythroid progenitor proliferation and increased phosphorylation of Akt/PKB.

OBJECTIVE: The aim of this study was to explore the mechanism by which increased erythropoiesis occurs in polycythemia vera (PV).
METHODS: CD34(+) and erythroid colony-forming cells (ECFC) were purified from normal or PV peripheral blood and then incubated in the presence of erythropoietin (EPO) to generate erythroid progenitor cells. Measurement of proliferation by Ki-67 staining, TUNEL assays to measure apoptosis, and Western blots for detection of Akt/PKB and glycogen synthase kinase 3 (GSK3) phosphorylation were performed in both normal and PV erythroid progenitors.
RESULTS: Polycythemia vera erythroid progenitor cells generated 60% more cells compared to normal cells in liquid medium cell cultures. TUNEL assays revealed no difference between PV and normal erythroid progenitors, but Ki-67 staining for cell proliferation showed many more positive cells in the PV samples. A marked increase of phosphorylation of Akt/PKB occurred in the day-8 erythroid progenitors of 4/5 PV patients, compared to normal cells, after incubation with either stem cell factor (SCF) or EPO. PV cells also had much greater glycogen synthase kinase 3 (GSK3) alpha,beta phosphorylation compared to normal cells after incubation with SCF or EPO. These results are parallel to the cellular hypersensitivity of PV cells to SCF and EPO previously reported.
CONCLUSIONS: Increased erythropoiesis in PV is associated with increased cellular proliferation and increased phosphorylation of Akt/PKB and GSK3. This study provides additional insight into the pathogenesis of PV and the regulation of normal erythropoiesis, even though a specific molecular defect of the disease is still not apparent.