Isolation of serum-derived placental/amniochorionic extracellular vesicles across pregnancy by immunoaffinity using PLAP and HLA-G.

Extracellular vesicles (EVs) are membrane-bound nanovesicles secreted from the cells into extracellular space and body fluids. They are considered "fingerprints of parent cells" which can reflect their physiological and functional states. During pregnancy, extracellular vesicles (EVs) are produced by the syncytiotrophoblasts and extravillous trophoblasts and are released into the maternal bloodstream. In the present study, placental alkaline phosphatase (PLAP)-specific extracellular vesicles were isolated from maternal serum-derived EVs (SDE) across pregnancy. Transmission electron microscopy and dynamic light scattering analysis showed that the isolated EVs exhibited spherical morphology with ~30-150 nm size range. Nanoparticle tracking analysis indicated that the concentration of PLAP+ serum-derived EVs (PLAP+-SDE) increased across the gestation. PLAP+-SDE contained DNA with LINE1 promoter methylation pattern. C19 miRNA cluster miRNAs (miR 515-5p, 519e, and 520f) were present in PLAP+ -SDE along with other miRNAs (miR-133-3p, miR210-3p, and miR-223-3p). PLAP+ -SDE confirmed presence of EVs markers (CD63 and CD9), along with placental protein (PLAP and Cullin-7). A modified novel strategy to extract enriched population of circulating placental/amniochorionic EVs was devised employing an additional marker of extravillous trophoblasts, Human Leukocyte Antigen-G (HLA-G) along with PLAP. The isolated pooled placental/amniochorionic (PLAP+ HLA-G+) serum-derived EVs (PP-SDE) showed ~2-fold increased protein levels of HLA-G in the 3rd trimester pregnant women compared to the non-pregnant controls. Future studies will be focused on validation of this novel strategy to isolate an enriched population of placental/amniochorionic EVs to facilitate better understanding of placental physiology and pathophysiology.