Inhibition of Sialic Acid Loss Greatly Improves Survival of Refrigerated Platelets

Abstract 1133

Platelets have the shortest shelf life of all major blood components and are the most difficult to store, a fact that complicates platelet transfusion practices. Platelet refrigeration could slow bacterial growth and possibly retard the loss of platelet function following storage. However, in contrast to other blood components, platelets do not tolerate refrigeration and are rapidly cleared from the circulation. We demonstrated that two distinct pathways recognizing GPIba remove refrigerated platelets in recipient's livers: 1) α_Mβ₂ integrins (Mac-1) on hepatic resident macrophages (Kupffer cells) selectively recognize irreversibly clustered b-N-acetylglucosamine (β-GlcNAc)–terminated glycans on GPIbα, and 2) hepatic Asialoglycoprotein (Asg) receptors (Ashwell Morell receptors) recognize desialylated GPIba. We here investigated the mechanism of sialic acid loss during refrigeration. We show, that when refrigerated platelets are rewarmed, they secrete active sialidases, including the lysosomal sialidase Neu1 that remove sialic acid from platelet receptors, specifically from GPIbα. Platelets also express Neu3 on their surfaces, however Neu3 expression appears to be unaffected by platelet refrigeration. Importantly, the recovery and circulation of refrigerated platelets is greatly improved by storage in the presence of the competitive sialidase inhibitor N-Acetylneuraminic Acid, 2,3-Dehydro-2-deoxy-Sodium Salt (DANA). Desialylated von Willebrand receptor (vWfR) complex is also a target for metalloproteinases (MMPs), as GPIbα and GPV are cleaved from the surface of refrigerated platelets. Receptor shedding is inhibited by the metalloproteinase inhibitor GM6001 and does not occur in ADAM17^ΔZn/ΔZn platelets expressing inactive ADAM17. Critically, desialylation in the absence of metalloproteinase-mediated receptor shedding is sufficient to induce the rapid clearance of platelets from circulation. Desialylation of platelet vWfR therefore triggers platelet clearance, and primes GPIbα and GPV for metalloproteinase-dependent cleavage. We conclude that desialylation of platelets is caused by increased surface sialidase activity following refrigeration and desialylation of glycoproteins, specifically of GPIbα, promotes receptor cleavage by MMPs.