title: Cyclooxygenase-2 expression is induced during human megakaryopoiesis and characterizes newly formed platelets.
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 <10% of circulating platelets from healthy controls, whereas up to 60% of COX-2-positive platelets were found in patients. A selective COX-2 inhibitor reduced platelet production of both PGE(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.
authors.affiliation: Research Center on Physiopathology of Hemostasis, Catholic University of Rome, 00168 Rome, Italy. b.rocca@tiscali.it
authors.forename: Bianca
authors.initials: B
authors.lastname: Rocca
authors.forename: Paola
authors.initials: P
authors.lastname: Secchiero
authors.forename: Giovanni
authors.initials: G
authors.lastname: Ciabattoni
authors.forename: Franco O
authors.initials: FO
authors.lastname: Ranelletti
authors.forename: Lucia
authors.initials: L
authors.lastname: Catani
authors.forename: Lia
authors.initials: L
authors.lastname: Guidotti
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Melloni
authors.forename: Nicola
authors.initials: N
authors.lastname: Maggiano
authors.forename: Giorgio
authors.initials: G
authors.lastname: Zauli
authors.forename: Carlo
authors.initials: C
authors.lastname: Patrono
mesh_terms: D015703:Antigens, CD / Q000032:analysis; D018952:Antigens, CD34 / Q000032:analysis; D016718:Arachidonic Acid / Q000494:pharmacology; D001792:Blood Platelets / Q000201:enzymology*; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D006410:Hematopoiesis; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000187:drug effects; D006801:Humans; D007213:Indomethacin / Q000494:pharmacology; D007527:Isoenzymes / Q000097:blood* / Q000235:genetics; D008533:Megakaryocytes / Q000201:enzymology*; D008565:Membrane Proteins; D010641:Phenotype; D011451:Prostaglandin-Endoperoxide Synthases / Q000097:blood* / Q000235:genetics; D013926:Thrombopoietin / Q000494:pharmacology
chemical_list: D015703:Antigens, CD; D018952:Antigens, CD34; D007527:Isoenzymes; D008565:Membrane Proteins; D016718:Arachidonic Acid; D013926:Thrombopoietin; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; C496511:PTGS1 protein, human; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases; D007213:Indomethacin