PB0736 - Platelets show functional specialization over their lifespan gaining proinflammatory function as they age in vitro and in circulation

Background: Platelets are crucial players in hemostasis and thrombosis, but also contribute to immune regulation and host defense, using distinct receptors, signaling pathways and effector functions, respectively. If there are subsets of platelets that specialize in these diverse tasks is insufficiently understood.

Aims: We aimed to assess platelet function and phenotype over their life time in circulation under steady state and under thrombotic and inflammatory conditions.

Methods: Here, we employed an in vivo pulse labelling method in Mus musculus models for tracking different age cohorts of platelets over time. Using in vitro and in vivo assays, we assessed platelet function in separate age cohorts using single cell analyses. We combined this with murine models of thrombosis and inflammation, and employed state-of-the art platelet proteomics.

Results: We confirm that young, reticulated platelets show heightened responses in the setting of clot formation, with corresponding, increased responses to agonists, adhesion, and retractile function. Unexpectedly, aged platelets lose their thrombotic proficiency, but are more prone to react to inflammatory challenge: compared to reticulated platelets, this cohort was more likely to form platelet leukocyte aggregates and showed increased adhesion to neutrophils in vitro. In vivo, this was reflected in increased pulmonary recruitment of aged platelets in an acute lung injury model. Proteomic analyses confirmed increased immune pathways in this cohort, including upregulated procoagulant propensity. In mouse models of prolonged platelet half-life, this resulted in increased pulmonic leukocyte infiltration and inflammation upon acute lung injury. Similarly, human platelet concentrates decreased their hemostatic and elevated their immunomodulatory potential in vitro over time, and in a mouse model of platelet transfusion, aged platelet concentrates resulted in augmented inflammation.

Conclusion(s): In summary, we functionally show that platelets divide labor and exhibit age-dependent specialization to fulfill their diverse tasks in the vasculature. As this extends to platelet concentrates, this holds important implications for transfusion medicine.