The fate of normal senescent human megakaryocytes was investigated by seeding normal CD34+ hematopoietic progenitor cells in serum-free chemically-defined suspension cultures. In the presence of optimal [ 100 ng/ml) concentrations of thrombopoietin (TPO), CD 34-derived cells showed an 8-fold numerical expansion accompanied by a progressive maturation along the megakaryocytic lineage. Mature polyploid megakaryocytes were characterized ultrastructurally by the presence of dense core granules, u demarcation membrane system and cytoplasm ic fragmentation into platelets, and phenotypically by the progressive surface expression of cqib33. The peak of mature megakaryocytes was reached at days 12-15 of culture. After day 15, however, the number of viable cells progressively dropped in spite of the continuous readditon of TPO. and an increasing number of megakaryocytes showed the characteristic features of apoptosis, as evaluated by transmission electron microscopy, TdT-mediated d-UTP-biotin nick end labeling technique and uplake of propidium iodide. In other experiments, mature ct[ib3 + megakaryocytes were directly purified from the B M aspirates of normal donors and seeded in serum-free suspension cultures. A progressive increase of apoptosis was observed also in mature megakaryocytes. The addition of 100 ng/ml of TPO showed some protection from apoptosis of mature megakaryocyies a1 early culture times, but it was unable to prevent it at huer time points. Taken together, our findings suggest that Ihe terminal phase of the megakaryocyte life span under physiological conditions is characterized by the onset of upoptotic ceil ft path.
|Number of pages||1|
|Publication status||Published - 1997|
ASJC Scopus subject areas
- Cancer Research
- Cell Biology