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.