Galectins differentially regulate the release of platelet-derived angiogenic molecules

SCHATTNER M; ETULAIN J; NEGROTTO S; ROMANIUK MA; CROCI DO; CATTANEO V; CAMPETELLA O; RABINOVICH GA

Kioto

Congreso; XXIII Congress of the International Society on Thrombosis and Haemostasis; 2011

We have recently demonstrated that galectin (Gal)-1 and -8 trigger platelet activation. Since these lectins also promote angiogenesis and platelets contribute to the formation of new vessels by releasing angiogenic mediators in a local fashion, here we examined the release of angiogenesis mediators from platelets stimulated with Gal-1 or -8.The levels of angiogenic molecules in the supernatants were determined by ELISA after stimulation of human washed platelets for 5 min. Results are expressed in ng/ml (*p<0.05, ANOVA, n=5). We found that both Gal-1 and -8 triggered the release of vascular endothelial growth factor (VEGF) in a concentration dependent manner (EC50 0.5±0.1 and 0.25±0.05 uM respectively). The amount of VEGF released by saturating concentrations of Gal-1 (3 mM), Gal-8 (0.75uM), and thrombin (1U/ml) were 7.1±0.2*, 7.0±0.2* and 12.5±0.2* respectively (vs. unstimulated controls: 1.0±0.1). However, while Gal-8 (0.75 uM) and thrombin (1U/ml) induced endostatin secretion (1.4±0.6* and 2.5±0.1* vs controls: 0.40±0.01), Gal-1 (5 uM) failed to induce the secretion of this antiangiogenic protein. While VEGF release by Gal-8 was partially prevented (40-50% inhibition, n=3) by inhibitors of PKC, p38 and Src kinases, secretion induced by Gal-1 was only inhibited (32%) by blockade of ERK phosphorylation. Aspirin had no effect on VEGF secretion. Angiogenic arrays showed that G-CSF was the major molecule released upon Gal-1 and -8 platelet stimulation. Gal-8 secreted two times more EGF, ENA-78, VEGF, IL-2 and IL-1 than Gal-1, while the latter triggered two times more MMP-1, MMP-9 and MPC-3 than Gal-8. Our results suggest that secretion of platelet-derived angiogenic molecules represents an alternative mechanism involved in the angiogenic activities of Gal-1 and Gal-8. IWe have demonstrated that galectins, similarly to PAR agonists, selectively regulate angiogenic molecule secretion from platelets.