Human platelets express and are activated by galectin-8

Abstract

Gals (galectins) are proteins with glycan affinity that are emerging as mediators of atherosclerosis. Despite the similarities in structure and sequence, different Gals exert distinct effects on their target cells. We have shown that Gal-1 triggers platelet activation, suggesting a role for Gals in thrombus formation. Since Gal-8 is expressed upon endothelial activation and also contributes to inflammation, to understand further the role of these lectins in haemostasis, we evaluated the effect of Gal-8 on human platelets. Gal-8 bound specific glycans in the platelet membrane and triggered spreading, calcium mobilization and fibrinogen binding. It also promoted aggregation, thromboxane generation, P-selectin expression and granule secretion. GP (glycoprotein) αIIb and Ib-V were identified as putative Gal-8 counter-receptors by MS. Studies performed using platelets from Glanzmann's thromboasthenia and Bernard-Soulier syndrome patients confirmed that GPIb is essential for transducing Gal-8 signalling. Accordingly, Src, PLC2γ (phospholipase C2γ), ERK (extracellular-signal-regulated kinase) and PI3K (phosphoinositide 3-kinase)/Akt downstream molecules were involved in the Gal-8 signalling pathway. Gal-8 fragments containing either the N- or C-terminal carbohydrate-recognition domains showed that activation is exerted through the N-terminus. Western blotting and cytometry showed that platelets not only contain Gal-8, but also expose Gal-8 after thrombin activation. These findings reveal Gal-8 as a potent platelet activator, supporting a role for this lectin in thrombosis and inflammation.

Redundant and Antagonistic Functions of Galectin-1, -3, and -8 in the Elicitation of T Cell Responses

“…We also determined that Gal-8's single N-CRD is sufficient to trigger platelet activation (31). In agreement, in this study we showed that Gal-1 costimulated T cells in the presence of the cognate peptide, but it was unable to trigger proliferation of naive splenocytes, even when tested at a high concentration (20 mM).…”

Galectins: new agonists of platelet activation

“…Platelet activation mediated by galectin-1 or galectin-8 is prevented by lactose but not by sucrose indicating the interaction of these lectins with specific carbohydrate ligands on the platelet surface. MALDI/TOF mass spectrometry analyses determined that both galectins binds the subunit IIb from the IIbβ3 integrin (Pacienza, Pozner et al 2008;Romaniuk, Tribulatti et al 2010). Additionally, while galectin-8 also binds GPIb and V from GPIb-IX-V complex (Romaniuk, Tribulatti et al 2010), galectin-1 interacts with β1.…”

“…Additionally, while galectin-8 also binds GPIb and V from GPIb-IX-V complex (Romaniuk, Tribulatti et al 2010), galectin-1 interacts with β1. However, the use of platelets derived from patients who are deficient in IIbβ3 or in GPIb, revealed that only GPIb and integrin IIbβ3 are essential for galectin-8-and 1 dependent signal transduction respectively, and therefore represent functional counter-receptors (Romaniuk, Tribulatti et al 2010;Romaniuk, Croci et al 2012). …”

“…Through the interaction with the carbohydrate backbone of the major platelet receptors involved in hemostasis, e.g. : GPIbVIX complex and integrin IIbβ3, both galectins are capable to induce all the myriad of platelet responses including adhesion and spreading, aggregation, release of their granule content and the expression of P-selectin on the platelet membrane (Pacienza, Pozner et al 2008;Romaniuk, Tribulatti et al 2010;Romaniuk, Croci et al 2012).…”

“…(Rivera, Lozano et al 2009). It has been recently shown that two structurally different members of the galectin family of proteins, galectin-1 and 8 are potent platelet agonists (Pacienza, Pozner et al 2008;Romaniuk, Tribulatti et al 2010;Romaniuk, Croci et al 2012). Through the interaction with the carbohydrate backbone of the major platelet receptors involved in hemostasis, e.g.…”