Background: Platelets shed platelet microparticles (PMP) when activated or stored. Procoagulant PMP may enhance efficacy of components once transfused, and it is important they are cleared efficiently to prevent vaso-occlusion. The majority of PMP are phosphatidylserine (PS)-negative, suggesting other clearance mechanisms. As desialylation is important for platelet clearance, we hypothesised similar mechanisms for PMP.

Aims: To investigate the role of glycans in PMP binding.

Methods: Apheresis platelets were collected, stored in 70% SSP+30% plasma at 22°C with agitation, and tested at day 1, 5 and 7 post-collection. Platelet and PMP were characterised using flow cytometry and annexin V (AnV, PS-exposure), CD41 antibody and/or glycan-binding lectins Ricinus communis Agglutinin-1 (RCA-1; galactose), succinylated Wheat Germ Agglutinin (sWGA, βGlcNAc), Sambucus nigra (SNA, α2-6-linked) and Maackia amurensis (MAA, α2-3-linked sialic acid).
PMP were stained with Deep Red (5 µM) and isolated by centrifugation and binding of PMP was assessed using HepG2 cells. PMP were treated with 20 U/mL galactosidase and neuraminidase to cleave galactose or sialic acid respectively. PS was inhibited with lactadherin (8 µg/mL). p< 0.05 was considered significant using 1-way ANOVA or unpaired t-tests.

Results: Following platelet storage, there was a 2-fold increase in RCA⁺/AnV⁺ PMP (p=0.0323), indicating desialylation, accompanied by an increase in RCA⁺/AnV⁺ platelets (p=0.0584, n=6). RCA⁺/AnV^– PMP numbers were not changed at day 7. MAA⁺/CD41⁺ PMP numbers (n=4) decreased by a 3-fold, whereas SNA⁺/CD41⁺PMP did not change, indicating loss of α2-3-linked sialic acid. sWGA⁺/AnV⁺ PMP numbers remained unchanged, however, there was a 2-fold increase in sWGA⁺/AnV⁺ platelets (n=5, p=0.0115), indicating degalactosylation of procoagulant platelets.
At day 1, in contrast to neuraminidase, galactosidase induced a 30% increase (p=0.0654), while lactadherin reduced HEPG2-binding (p=0.0137), indicating PS was not the main mechanism.

Conclusions: PMP and platelets expose glycans, which are differentially modulated by storage. PMP bind to HepG2 cells in a glycan-mediated mechanism.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/glycans-on-the-surface-of-platelet-microparticles-mediate-binding-by-hepatocytes/