ROLE OF GALECTIN-8 AS A MODULATOR OF PLATELET ACTIVATION

M. A. ROMANIUK, M. V. TRIBULATTI, V. CATTANEO, J. ETULAIN, O. CAMPETELLA, M. SCHATTNER

Boston, USA

Congreso; XXII Congress of the International Society on Thrombosis and Haemostasis; 2009

International Society on Thrombosis and Haemostasis

Galectin-8 (Gal-8) is a 35 kDa protein formed by two carbohydrate recognition domains linked by a peptide. It is expressed in a wide variety of tissues and tumors and participates in cellular interactions that involve integrins as adhesion molecules. We determined by MALDI-MS that Gal-8 binds the integrin alpha IIb in mouse splenocytes. Considering that this integrin is part of the glycoproteic complex IIbIIIa which is the most relevant molecule in platelet function and the fact that in previous studies we have demonstrated the capability of Galectin-1 to promote platelet activation, we now evaluated the effect of Gal-8 in platelet physiology. The results obtained demonstrate that human platelets express Gal-8 and that recombinant Gal-8 is able to induce platelet activation through outside-in signaling. It also promotes aggregation in washed platelets as well as in plasma (EC 50= 0.6 ± 0.052 M, 3.45 ± 0.220 M, n=4) and potentiates the response induced by other platelet agonists. The aggregation response induced by Gal-8 was inhibited by the preincubation of platelets with Lactose (30 mM) and Thiodigalactoside (30 mM) but not with Sucrose (30 mM) indicating Gal-8 binding specificity to surface glycans. The absence of activation in platelets preincubated with EDTA (2 mM) and the absence of inhibition by Aspirin (0.5 mM) reveal that the observed response is not an agglutination phenomenon and that it does not involve thromboxane generation. Flow cytometry studies demonstrated that Gal-8 promotes intracellular calcium mobilization (C: 3 ± 1%, Gal-8 1 M: 49 ± 2% positive cells) and expression of neoepitopes in the glycoproteic complex IIbIIIa (C: 2 ± 1%, Gal-8 1 M: 75 ± 3%) as well as fibrinogen binding (C: 3 ± 2%, Gal-8 1 M: 80 ± 2%) and P-selectin exposure (C: 3 ± 1%, Gal-8 1 M: 45 ± 2%). These data reveal galectins as important regulators of platelet function.