Desialylation of Platelets by Pneumococcal Neuraminidase A Induces ADP-Dependent Platelet Hyperreactivity

Platelets are increasingly recognized to play a role in the complications of Streptococcus pneumoniae infections. S. pneumoniae expresses neuraminidases, which may alter glycans on the platelet surface. In the present study, we investigated the capability of pneumococcal neuraminidase A (NanA) to remove sialic acid (desialylation) from the platelet surface, the consequences for the platelet activation status and reactivity, and the ability of neuraminidase inhibitors to prevent these effects. Our results show that soluble NanA induces platelet desialylation. Whereas desialylation itself did not induce platelet activation (P-selectin expression and platelet fibrinogen binding), platelets became hyperreactive to ex vivo stimulation by ADP and cross-linked collagen-related peptide (CRP-XL). Platelet aggregation with leukocytes also increased. These processes were dependent on the ADP pathway, as inhibitors of the pathway (apyrase and ticagrelor) abrogated platelet hyperreactivity. Inhibition of NanA-induced platelet desialylation by neuraminidase inhibitors (e.g., oseltamivir acid) also prevented the platelet effects of NanA. Collectively, our findings show that soluble NanA can desialylate platelets, leading to platelet hyperreactivity, which can be prevented by neuraminidase inhibitors.