Mucor circinelloides induces platelet aggregation through integrin αIIbβ3 and FcγRIIA

Thrombosis is a hallmark of the fatal fungal infection mucormycosis. Yet, the platelet activation pathway in response to mucormycetes is unknown. In this study we determined the platelet aggregation potential of Mucor circinelloides (M. circinelloides) NRRL3631, characterized the signaling pathway facilitating aggregation in response to fungal spores, and identified the influence of the spore developmental stage upon platelet aggregation potential. Using impedance and light-transmission aggregometry, we showed that M. circinelloides induced platelet aggregation in whole blood and in platelet-rich plasma, respectively. The formation of large spore-platelet aggregates was confirmed by light-sheet microscopy, which showed spores dispersed throughout the aggregate. Aggregation potential was dependent on the spore's developmental stage, with the strongest platelet aggregation by spores in mid-germination. Inhibitor studies revealed platelet aggregation was mediated by the low affinity IgG receptor Fc gamma RIIA and integrin alpha IIb beta 3; Src and Syk tyrosine kinase signaling; and the secondary mediators TxA(2) and ADP. Flow cytometry of antibody stained platelets showed that interaction with spores increased expression of platelet surface integrin alpha IIb beta 3 and the platelet activation marker CD62P. Together, this is the first elucidation of the signaling pathways underlying thrombosis formation during a fungal infection, highlighting targets for therapeutic intervention.