Cyclooxygenase-2 expression is induced during human megakaryopoiesis and characterizes newly formed platelets

Publisher Website
Google Scholar
Abstract
Cyclooxygenase (COX)-1 or -2 and prostaglandin (PG) synthases catalyze the formation of various PGs and thromboxane (TX) A 2 . We have investigated the expression and activity of COX-1 and -2 during human megakaryocytopoiesis. We analyzed megakaryocytes from bone marrow biopsies and derived from thrombopoietin-treated CD34 + hemopoietic progenitor cells in culture. Platelets were obtained from healthy donors and patients with high platelet regeneration because of immune thrombocytopenia or peripheral blood stem cell transplantation. By immunocytochemistry, COX-1 was observed in CD34 + cells and in megakaryocytes at each stage of maturation, whereas COX-2 was induced after 6 days of culture, and remained detectable in mature megakaryocytes. CD34 + cells synthesized more PGE 2 than TXB 2 (214 ± 50 vs. 30 ± 10 pg/10 6 cells), whereas the reverse was true in mature megakaryocytes (TXB 2 8,440 ± 2,500 vs. PGE 2 906 ± 161 pg/10 6 cells). By immunostaining, COX-2 was observed in 2 and TXB 2 to a significantly greater extent in patients than in healthy subjects. Finally, we found that COX-2 and the inducible PGE-synthase were coexpressed in mature megakaryocytes and in platelets. We conclude that both COX-isoforms contribute to prostanoid formation during human megakaryocytopoiesis and that COX-2-derived PGE 2 and TXA 2 may play an unrecognized role in inflammatory and hemostatic responses in clinical syndromes associated with high platelet turnover.