Deciphering the role of reticulated platelets in myocardial ischemia/reperfusion injury

Platelets have traditionally been viewed as anucleate blood cells with primarily hemostatic functions. Growing evidence demonstrates that platelets, including specialized subpopulations such as reticulated platelets (RP), play roles extending well beyond hemostasis, particularly in the context of cardiovascular disease. RP are young, RNA-rich platelets derived from megakaryocytes, historically considered markers of platelet turnover but increasingly implicated as active participants in thromboinflammation. Despite clinical associations linking elevated RP levels with worse outcomes after myocardial infarction, their molecular characteristics and functional roles remain incompletely defined. This thesis sought to address these gaps by combining conceptual syntheses (Chapters 2 and 3) with experimental investigations (Chapters 4 and 5). The reviews outlined RP biology, detection methods, and clinical implications, while underscoring methodological limitations that constrain mechanistic insight. To overcome these, 2 complementary tools were established: (1) an optimized SYTO 13–based flow cytometric assay enabling minimally manipulative and reproducible RP quantification in mice; and (2) a RiboTag transgenic mouse model providing a genetic platform for ribosome-specific detection of platelet subpopulations (RP and non-RP). Applying these methods to a murine model of myocardial ischemia/reperfusion (I/R) injury revealed several important findings. RP displayed distinct surface phenotypes, including heightened activation responses and altered glycan patterns, compared to non-RP. RNA sequencing of SYTO 13–sorted RP identified unique transcriptional programs enriched in cytoskeletal remodeling, receptor trafficking, and inflammatory signaling. Ligand–receptor analyses further suggested enhanced interactions between RP and cardiac cells following myocardial I/R injury, implicating them in endothelial dysfunction, leukocyte recruitment, and fibroblast activation. Notably, RP abundance increased after reperfusion, accompanied by prothrombotic and pro-inflammatory phenotypic and transcriptomic shifts. Collectively, this thesis reframes RP as functionally distinct effectors in cardiovascular pathology.