Thrombopoietin (TPO), is a key regulator of megakaryocytopoiesis and thrombopoiesis. It is principally produced in the liver and is bound and internalized by the receptor Tpo R/c-mpl. Defects in the Tpo-Tpo R signaling pathway are associated with a variety of platelet disorders. The activity of recombinant mouse TPO was measured in a cell proliferation assay using MO7e human megakaryocytic leukemic cells. MO7e cells were seeded into triplicate wells of 96-well plates at a density of 30,000 cells/well in RPMI-1640 with the addition of various concentrations of rmTPO. After incubated for 72h, cells were observed by inverted microscope and cell proliferation was measured by Cell Counting Kit-8 (CCK-8). Briefly, 10 µl of CCK-8 solution was added to each well of the plate, then the absorbance at 450 nm was measured using a microplate reader after incubating the plate for 1-4 hours at 37 °C. Cell proliferation of MO7e cells after incubation with rmTPO for 72h observed by inverted microscope was shown in Figure 1. The dose-effect curve of rmTPO was shown in Figure 2. It was obvious that rmTPO significantly promoted cell proliferation of MO7e cells .The EC50 for this effect is typically 0.26 ug/ml.

Figure 2. The dose-effect curve of rmTPO on MO7e cells