Neuropilin-1 is uniquely expressed on small syncytiotrophoblast extracellular vesicles but not on medium/large vesicles from preeclampsia and normal placentae

Preeclampsia (PE) is a multisystem progressive hypertensive disorder unique to human pregnancy. The placenta is fundamental to its pathogenesis and releases placental factors as well as extracellular vesicles (small and medium/large syncytiotrophoblast extracellular vesicles (STB-EVs)) as a response to syncytiotrophoblast stress such as tissue factor and plasminogen activator inhibitors 1. Neuropilin 1 (NRP-1) is an anti-angiogenic factor involved in development, angiogenesis, arteriogenesis, and vascular permeability. NRP-1 acts as a co-receptor for growth factors such as vascular endothelial growth factor (VEGF), placenta growth factor (PLGF), and epidermal growth factor (EGF). Given the documented pro and anti-angiogenic roles of STB-EVs, we hypothesized that 1) STB-EVs might express NRP-1; and 2) the expression of NRP-1 might differ between normal and preeclampsia STB-EVs.

Methods: We isolated STB-EVs (both small and medium/large) from PE and NP placentae using the physiologic ex vivo dual lobe perfusion model. The enriched STB-EVs were characterized by Western blot, transmission electron microscopy (TEM), and nanoparticle tracking analysis (NTA) according to the international society of extracellular vesicles (ISEV) guidelines. We assessed for NRP-1 expression with Western blot (placenta and STB-EVs) and immunohistochemistry (placenta). We performed co-expression analysis for placenta alkaline phosphatase (PLAP - a known STB-EV marker) and NRP-1 with immunoprecipitation followed by Western blot.

Results: We confirmed NRP-1 expression in NP and PE placenta. We showed that NRP-1 Expression was limited to small syncytiotrophoblast membrane extracellular vesicles (S STB-EVs) but not medium/large STB-EVs and that NRP-1 is co-expressed with PLAP.

Conclusion: Neuropilin-1 is uniquely expressed on small syncytiotrophoblast extracellular vesicles but not on medium/large vesicles from preeclampsia and normal placentae.