GPVI expression is linked to platelet size, age, and reactivity

Platelets within one individual display heterogeneity in reactivity, size, age, and expression of surface receptors. To investigate the combined intra-individual contribution of platelet size, platelet age, and receptor expression levels on the reactivity of platelets, we studied fractions of large and small platelets from healthy donors separated by differential centrifugation. Size-separated platelet fractions were perfused over a collagen-coated surface to assess thrombus formation. Multicolour flow cytometry was used to characterise resting and stimulated platelet subpopulations. Platelet age was determined based on RNA and HLA-I labelling. Signal transduction was analysed by measuring consecutive phosphorylation of serine/threonine-protein kinase Akt. Large platelets adhered faster to collagen under flow and formed larger thrombi, compared to small platelets. Among the large platelets a highly reactive juvenile platelet subpopulation was identified with high GPVI expression. Elevated GPVI expression correlated with high HLA-I expression, RNA content and increased platelet reactivity. Akt phosphorylation and activation upon collagen stimulation differed stronger between juvenile and older platelets than between large and small platelets. GPVI expression and platelet reactivity decreased throughout platelet storage at 22°C and was better maintained throughout cold storage at 4°C. We further detected a higher GPVI expression in platelets of patients with immune thrombocytopenia. Our findings show that high GPVI expression is a feature of highly reactive juvenile platelets, which are predominantly found among the large platelet population explaining the better performance of large platelets during thrombus formation. These data are important for studies of thrombus formation, platelet storage and ITP.