Paracrine up-regulation of monocyte cyclooxygenase-2 by platelets: role of transforming growth factor-beta1.
OBJECTIVE
To examine the role of platelets and platelet-derived products on cyclooxygenase-2 (Cox-2) induction in adherent monocytes and to address the signaling pathways involved.


METHODS
Platelets and monocytes were obtained from peripheral blood of healthy donors. Adherent monocytes were co-cultured with autologous platelets or platelet releasates or exposed to mediators contained in platelet alpha-granules (either from platelet source or recombinant) for 4-24 h. Cox-2 protein and mRNA were determined by Western and RT-PCR analysis, respectively. Thromboxane B2 (TxB2) and prostaglandin E2 (PGE2) synthesis as index of Cox-2 activity, and levels of transforming growth factor-beta1 (TGF-beta1) in platelet releasates were measured by enzyme immunoassay (EIA).


RESULTS
Activated platelets induce rapid and transient Cox-2 de novo synthesis in adherent monocytes. The effect is dependent upon the platelet number but not upon cell-cell contact. Platelet-induced Cox-2 was not affected by prevention of platelet TxA2 synthesis or microparticle formation but was blunted by inhibition of platelet alpha-granule secretion. TGF-beta1, either platelet-derived or recombinant (rTGF-beta1), induced Cox-2 expression and activity in adherent monocytes at concentrations within the range of those detected in releasates from activated platelets; this effect was not shared by recombinant platelet-derived growth factor (rPDGFBB). The time course of Cox-2 induction by TGF-beta1 in monocytes was identical to that observed with platelet releasates. Moreover, TGF-beta1 receptor blockade completely abolished platelet-induced Cox-2 expression. p38 MAPK activation represents a common transduction pathway through which activated platelets and rTGF-beta1 induce Cox-2 in monocytes.


CONCLUSIONS
These findings suggest that TGF-beta1 released by activated platelets has a pivotal role in Cox-2 induction in monocytes and further supports the key role of platelets in the inflammatory and reparative responses.
Eligini
Sonia
S
E. Grossi Paoletti Center, Department of Pharmacological Sciences, University of Milan, Italy.
Barbieri
Silvia S
SS
Arenaz
Izaskun
I
Tremoli
Elena
E
Colli
Susanna
S
D015415:Biomarkers / Q000032:analysis; D001792:Blood Platelets / Q000378:metabolism*; D015153:Blotting, Western / Q000379:methods; D002448:Cell Adhesion; D051546:Cyclooxygenase 2 / Q000096:biosynthesis* / Q000378:metabolism; D015232:Dinoprostone / Q000032:analysis; D006801:Humans; D009000:Monocytes / Q000201:enzymology*; D019899:Paracrine Communication / Q000502:physiology*; D015539:Platelet Activation; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013929:Thromboxane B2 / Q000032:analysis; D053773:Transforming Growth Factor beta1 / Q000032:analysis / Q000378:metabolism*; D015854:Up-Regulation; D014945:Wound Healing / Q000502:physiology
D015415:Biomarkers; D053773:Transforming Growth Factor beta1; D013929:Thromboxane B2; D051546:Cyclooxygenase 2; D015232:Dinoprostone