Human platelets express and are activated by galectin-8.

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.

Glanzmann thrombasthenia in children from Argentina.

PURPOSE: Glanzmann thrombasthenia is a well-defined inherited disorder of platelet function characterized by a decrease or absence of functional platelet glycoprotein (GP) GPIIbIIIa. The diagnosis must be considered in patients presenting with mucocutaneous bleeding, purpura, a normal platelet count, abnormal platelet aggregation, and a prolonged bleeding time. In most of the patients, the presence of small amounts of either GPIIb or GPIIIa was detected in their platelets. These observations could provide a basis for determining the clinical and laboratory heterogeneity of the disease. PATIENTS AND METHODS: We studied 10 patients of seven unrelated families with the usual methods and an immunoalkaline phosphatase technique (APAAP) to analyze the biosynthesis of GP in megakaryocytes. RESULTS: The results allowed us to classify six patients as GT type I, three as type II, and one as a variant. CONCLUSION: The nature and severity of the bleeding manifestations, in our patients, were not predictible by the laboratory findings. These confirm the clinical and laboratory heterogeneity of the disease.