Summary

Connective tissue growth factor (CTGF) is overexpressed inwound healing, fibrosis and advanced atherosclerotic lesions.Platelets adhere to CTGF, suggesting that this protein may beinvolved in the formation of platelet-rich thrombi at the sites oftissue injury or atherosclerotic plaque rupture. Since plateletscontain a wide array of biologically active proteins, we investigatedthe presence, localization and release of CTGF fromthese cells. For this purpose, human platelets from healthydonors were washed and stimulated with thrombin or ADP.Following incubation, proteins from unstimulated and stimulatedcell lysates and the supernatants were analysed by Westernblotting. The experiments showed that unstimulated plateletscontain considerable amounts of CTGF, whereas no CTGF wasdetectable in platelet-poor plasma. To elucidate the origin of CTGF in platelets, we performed immunohistochemical analy-sisof human bone marrow sections. The analysis showed thatalthough CTGF protein is widely expressed in bone marrowcells, it is not expressed by platelet-producing megakaryocytes,suggesting that CTGF presence in platelets is a result of endocytosisfrom extracellular environment in bone marrow.Agonist-stimulation of platelets resulted in a significant releaseof CTGF from the storage granules, with thrombin at 0.1 U/mLbeing a more potent activator than ADP at 20 µmol/L.The agonist-dependent CTGF secretion was significantly inhibited byaspirin. In conclusion, CTGF is stored in normal human platelets,and can be released upon platelet activation. Aspirin treat-mentprevents CTGF release, suggesting that clinical benefits ofthis drug may involve the inhibition of CTGF secretion.