Comprehensive glycoproteome profiling of resting and thrombin-activated platelets

Platelets play central roles in the vascular and immune systems. Tissue injury promptly activates resting platelets, triggering release of granular proteins (releasate) that mediate injury-related response processes. Despite the documented importance of protein glycosylation in platelet biology, the platelet glycoproteome remains poorly defined. This thesis employs powerful glycomics and glycoproteomics methods to comprehensively and quantitatively map the N-glycoproteome of the lysate and releasate of resting and thrombin-activated platelets from healthy donors. Platelet lysates and releasates displayed profound N-glycome diversity rich in sialylated and core fucosylated complex-type N-glycans across both resting and activated conditions. The N-glycoproteomics data recapitulated and expanded on the glycomics-based findings by uncovering the protein carriers and sites of platelet N-glycans. Interestingly, the data also suggested that platelets exhibit subcellular-specific N-glycosylation featuring sialofucosylated complex-type N-glycans in the α-granules, paucimannosidic N-glycans in lysosomes and, surprisingly, oligomannosylation on the platelet surface. Finally, deep site-specific N-glycoprofiling of the α-granule-resident thrombospondin-1 revealed that this protein undergoes rapid release but only subtle N-glycan remodelling upon platelet activation. Taken together, this thesis has provided the, to date, most comprehensive N-glycoproteome profile of resting and activated platelets, which forms a valuable resource to further explore the fascinating platelet glycobiology in human health and disease.