Abstract
Fucoidan, a sulfated polysaccharide from Fucus vesiculosus, decreases bleeding time and clotting time in hemophilia, possibly through inhibition of tissue factor pathway inhibitor. However, its effect on platelets and the receptor by which fucoidan induces cellular processes has not been elucidated. In this study, we demonstrate that fucoidan induces platelet activation in a concentration-dependent manner. Fucoidan-induced platelet activation was completely abolished by the pan-Src family kinase (SFK) inhibitor, PP2, or when Syk is inhibited. PP2 abolished phosphorylations of Syk and Phospholipase C-γ2. Fucoidan-induced platelet activation had a lag phase, which is reminiscent of platelet activation by collagen and CLEC-2 receptor agonists. Platelet activation by fucoidan was only slightly inhibited in FcRγ-chain null mice, indicating that fucoidan was not acting primarily through GPVI receptor. On the other hand, fucoidan-induced platelet activation was inhibited in platelet-specific CLEC-2 knock-out murine platelets revealing CLEC-2 as a physiological target of fucoidan. Thus, our data show fucoidan as a novel CLEC-2 receptor agonist that activates platelets through a SFK-dependent signaling pathway. Furthermore, the efficacy of fucoidan in hemophilia raises the possibility that decreased bleeding times could be achieved through activation of platelets.
Highlights
Fucoidan was tested as a novel drug for hemophilia, but its effect on platelets has not been studied
Fucoidan Causes Platelet Activation—As fucoidan reduced bleeding times in hemophilia animal models [8, 9], we evaluated whether fucoidan can cause platelet activation
We evaluated the effects of fucoidan on other platelet functional responses, including integrin activation (Fig. 1B), dense granule secretion (Fig. 1C), P-selectin expression (Fig. 1D), and thromboxane generation (Fig. 1E) in human platelets
Summary
Fucoidan was tested as a novel drug for hemophilia, but its effect on platelets has not been studied. Non-anticoagulatory sulfated polysaccharides were originally considered as a novel approach to improve coagulation because of their inhibitory effect on physiological anticoagulation, especially fucoidan, which inhibits tissue factor pathway inhibitor and accelerates clotting in hemophilia A and B patients [8]. We show that fucoidan signals through a tyrosine kinase-dependent signaling pathway downstream of CLEC-2 receptor and propose that this contributes to a decrease in bleeding time in hemophilia animal models. These results support the notion that decreased bleeding times can be achieved in hemophilia patients through activation of platelets
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