Summary
Connective tissue growth factor (CTGF) is overexpressed in wound healing, fibrosis
and advanced atherosclerotic lesions. Platelets adhere to CTGF, suggesting that this
protein may be involved in the formation of platelet-rich thrombi at the sites of
tissue injury or atherosclerotic plaque rupture. Since platelets contain a wide array
of biologically active proteins, we investigated the presence, localization and release
of CTGF from these cells. For this purpose, human platelets from healthy donors were
washed and stimulated with thrombin or ADP. Following incubation, proteins from unstimulated
and stimulated cell lysates and the supernatants were analysed by Western blotting.
The experiments showed that unstimulated platelets contain considerable amounts of
CTGF, whereas no CTGF was detectable in platelet-poor plasma. To elucidate the origin
of CTGF in platelets, we performed immunohistochemical analysis of human bone marrow
sections. The analysis showed that although CTGF protein is widely expressed in bone
marrow cells, it is not expressed by platelet-producing megakaryocytes, suggesting
that CTGF presence in platelets is a result of endocytosis from extracellular environment
in bone marrow. Agonist-stimulation of platelets resulted in a significant release
of CTGF from the storage granules, with thrombin at 0.1 U/mL being a more potent activator
than ADP at 20 µmol/L. The agonist-dependent CTGF secretion was significantly inhibited
by aspirin. In conclusion, CTGF is stored in normal human platelets, and can be released
upon platelet activation. Aspirin treatment prevents CTGF release, suggesting that
clinical benefits of this drug may involve the inhibition of CTGF secretion.
Keywords
Platelets - connective tissue growth factor - atherosclerosis
