Abnormal megakaryopoiesis and platelet function in cyclooxygenase-2-deficient mice.
Previous studies suggest that cyclooxygenase-2 (COX-2) might influence megakaryocyte (MK) maturation and platelet production in vitro. Using a gene deletion model, we analysed the effect of COX-2 deficiency on megakaryopoiesis and platelet function. COX-2-/- mice (10-12 weeks old) have hyper-responsive platelets as suggested by their enhanced aggregation, TXA2 biosynthesis, CD62P and CD41/CD61 expression, platelet-fibrinogen binding, and increased thromboembolic death after collagen/epinephrine injection compared to wild-type (WT). Moreover, increased platelet COX-1 expression and reticulated platelet fraction were observed in COX-2-/- mice while platelet count was similar to WT. MKs were significantly reduced in COX-2-/- bone marrows (BMs), with high nuclear/cytoplasmic ratios, low ploidy and poor expression of lineage markers of maturation (CD42d, CD49b). However, MKs were significantly increased in COX-2-/- spleens, with features of MK maturation markers which were not observed in MKs of WT spleens. Interestingly, the expression of COX-1, prostacyclin and PGE2 synthases and prostanoid pattern were modified in BMs and spleens of COX-2-/- mice. Moreover, COX-2 ablation reduced the percentage of CD49b+ cells, the platelet formation and the haematopoietic stem cells in bone marrow and increased their accumulation in the spleen. Splenectomy decreased peripheral platelet number, reverted their hyper-responsive phenotype and protected COX-2-/- mice from thromboembolism. Interestingly, fibrosis was observed in spleens of old COX-2-/- mice (28 weeks old). In conclusion, COX-2 deletion delays BM megakaryopoiesis promoting a compensatory splenic MK hyperplasia, with a release of hyper-responsive platelets and increased thrombogenicity in vivo. COX-2 seems to contribute to physiological MK maturation and pro-platelet formation.
Silvia S. Barbieri, PhD, Centro Cardiologico Monzino, IRCCS, Via Parea 4, 20138 Milano, Italy, Tel.: +39 02 50318357, Fax: +39 02 50318250, E-mail: silvia.barbieri@ccfm.it.
Silvia S
SS
Barbieri
Giovanna
G
Petrucci
Eva
E
Tarantino
Patrizia
P
Amadio
Bianca
B
Rocca
Maurizio
M
Pesce
Kellie R
KR
Machlus
Franco O
FO
Ranelletti
Sara
S
Gianellini
Babette
B
Weksler
Joseph E
JE
Italiano
Elena
E
Tremoli
D000818:Animals; D015703:Antigens, CD / Q000096:biosynthesis / Q000235:genetics; D000943:Antigens, Differentiation / Q000096:biosynthesis / Q000235:genetics; D001792:Blood Platelets / Q000502:physiology*; D001853:Bone Marrow / Q000378:metabolism / Q000473:pathology; D003433:Crosses, Genetic; D051545:Cyclooxygenase 1 / Q000096:biosynthesis / Q000235:genetics; D051546:Cyclooxygenase 2 / Q000172:deficiency* / Q000235:genetics / Q000502:physiology; D006412:Hematopoietic Stem Cells / Q000378:metabolism / Q000473:pathology; D006965:Hyperplasia; D008533:Megakaryocytes / Q000378:metabolism / Q000648:ultrastructure; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010976:Platelet Count; D011003:Ploidies; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000503:physiopathology / Q000601:surgery; D044244:Receptors, Thromboxane A2, Prostaglandin H2 / Q000096:biosynthesis / Q000235:genetics; D013154:Spleen / Q000378:metabolism / Q000473:pathology; D013156:Splenectomy; D013923:Thromboembolism / Q000139:chemically induced / Q000209:etiology / Q000517:prevention & control; D019851:Thrombophilia / Q000201:enzymology / Q000235:genetics; D034061:Thrombopoiesis / Q000502:physiology*; D013929:Thromboxane B2 / Q000097:blood
D015703:Antigens, CD; D000943:Antigens, Differentiation; D008565:Membrane Proteins; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D013929:Thromboxane B2; C077623:Ptgs2 protein, mouse; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; C496512:Ptgs1 protein, mouse
COX-2; megakaryocytes; platelets; thrombosis