Spatiotemporal glycoproteome remodelling in neutrophils

Neutrophils are short-lived yet vital innate immune cells equipped with bioactive glycoproteins packed in cytosolic granules that can readily be mobilised to elicit an effective and timely response against invading pathogens. Since the dynamic glycosylation processes underpinning the dramatic metamorphosis associated with myeloid progenitor-to-neutrophil differentiation remain unmapped, we here perform a comprehensive spatiotemporal profiling of the complex N-glycoproteome of isolated granule populations from blood-derived neutrophils and during maturation of bone marrow-derived progenitors using glycomics-assisted glycoproteomics. Firstly, glycomics indicated that the granule populations of mature (resting) neutrophils exhibit distinctive glycophenotypes including, most strikingly, unusual paucimannosidic- and monoantennary complex-type N-glycans in azurophilic granules. The granule-specific N-glycosylation features were recapitulated by glycoproteomics, which also uncovered extensive site- and protein-specific N-glycosylation decorating 4,772 N-glycopeptides from 352 N-glycoproteins across the neutrophil granules. Excitingly, comprehensive mining of proteomics and transcriptomics data collected from discrete myeloid progenitor stages for glycopeptide and glyco-enzyme expression revealed that dramatic glycoproteome remodelling underpins the promyelocytic-to-metamyelocyte transition and that remodelling is driven predominantly by proteome expression changes rather than modulation of the glycosylation machinery. Notable exceptions were the oligosaccharyltransferase subunits responsible for initiation of N-glycoprotein biosynthesis that were strongly reduced with myeloid differentiation leading to reduced N-glycosylation efficiency in late-stage neutrophil maturation and in corresponding granules. Our study provides new spatiotemporal insights into the dynamic neutrophil N-glycoproteome, which exhibits intriguingly complex site-, protein- and granule-specific N-glycosylation features and which undergoes strong remodelling during myeloid progenitor-to-neutrophil metamorphosis.