Proteomic analysis of N-glycosylation of the human placenta between preeclampsia and normal pregnancies

Protein N-glycosylation plays critical roles in modulating placental function, but little is known about N-glycoproteins in the human placenta and modifications in preeclampsia (PE). Here, we show a large, site-specific Nglycoproteome profiling study of PE and normal placenta using quantitative N-glycoproteomics based on mass spectrometry. The study identified disease signatures of altered N-glycoproteins and N-glycosylation site occupancy in PE and provided a system-level view of human placental N-glycoproteins and in vivo N-glycosylation sites. The study led to the discovery of a roster of glycoproteins with aberrant N-glycosylation levels associated with PE, including CD34, ENPP1 (ectonucleotide pyrophosphatase/phosphodiesterase family member 1), insulin-like growth factor binding protein (IGFBP3), and HYOU1 (hypoxia up-regulated 1). An emerging phenomenon that N-glycosylation is involved in several PE pathways, including cell adhesion molecules, PI3K-Akt signaling, pyrimidine metabolism, and metabolic pathways was revealed by pathway analysis of PE-associated aberrant glycoproteins. After enzymolysis, the proteins in each group were enriched with N-glycosylated peptides by lectin, the glycochain was excised by peptide N-glycosidase F (PNGase F) in H218O, and the glycosylated sites were analyzed by LC-MS/MS to achieve large-scale qualitative and quantitative analysis of N-glycosylated proteins. Our findings highlight the role of N-glycosylation in the pathogenesis of PE and provide new molecular and system-level insights for understanding and treating this disease.