Key Points• Adsorption of VWF type 2B mutants to platelets induces thrombocytopenia in VWD type 2B mice.• VWF/platelet complexes are phagocytosed by macrophages in liver and spleen.Von Willebrand disease (VWD) type 2B is characterized by mutations causing enhanced binding of von Willebrand factor (VWF) to platelets. Bleeding tendency is associated with heterogeneous clinical manifestations, including moderate to severe thrombocytopenia. The underlying mechanism of the thrombocytopenia has remained unclear. Here, a mouse model of VWD type 2B was used to investigate pathways contributing to thrombocytopenia. Immunohistochemical analysis of blood smears revealed that mutant VWF was exclusively detected on platelets of thrombocytopenic VWD type 2B mice, suggesting that thrombocytopenic VWD type 2B mice were elevated two-to threefold upon chemical macrophage depletion. Colocalization of platelets with CD68-positive Kupffer cells and CD168-positive marginal macrophages in liver and spleen, respectively, confirmed the involvement of macrophages in the removal of VWF/platelet complexes. Significantly more platelets were found in liver and spleen of VWD type 2B mice compared with control mice. Finally, platelet survival was significantly shorter in VWD type 2B mice compared with control mice, providing a rationale for lower platelet counts in VWD type 2B mice. In conclusion, our data indicate that VWF type 2B binds to platelets and that this is a signal for clearance by macrophages, which could contribute to the thrombocytopenia in patients with VWD type 2B. (Blood. 2013;122(16):2893-2902

To cite this article: van der Wal DE, Du VX, Lo KSL, Rasmussen JT, Verhoef S, Akkerman JWN. Platelet apoptosis by cold-induced glycoprotein Iba clustering. J Thromb Haemost 2010; 8: 2554-62.Summary. Background: Cold-storage of platelets followed by rewarming induces changes in Glycoprotein (GP) Iba-distribution indicative of receptor clustering and initiates thromboxane A 2 -formation. GPIba is associated with 14-3-3 proteins, which contribute to GPIba-signaling and in nucleated cells take part in apoptosis regulation. Objectives and methods: We investigated whether GPIba-clustering induces platelet apoptosis through 14-3-3 proteins during cold (4 h 0°C)-rewarming (1 h 37°C). Results: During cold-rewarming, 14-3-3 proteins associate with GPIba and dissociate from Bad inducing Baddephosphorylation and activation. This initiates pro-apoptosis changes in Bax/Bcl-x L and Bax-translocation to the mitochondria, inducing cytochrome c release. The result is activation of caspase-9, which triggers phosphatidylserine exposure and platelet phagocytosis by macrophages. Responses are prevented by N-acetyl-D-glucosamine (GN), which blocks GPIba-clustering, and by O-sialoglycoprotein endopeptidase, which removes extracellular GPIba. Conclusions: Cold-rewarming triggers apoptosis through a GN-sensitive GPIba-change indicative of receptor clustering. Attempts to improve platelet transfusion by cold-storage should focus on prevention of the GPIba-change.

No abstract

No abstract