title: Heparin promotes soluble VEGF receptor expression in human placental villi to impair endothelial VEGF signaling.
abstract: BACKGROUND
  Severe preeclampsia is characterized by hypertension, renal injury and placental dysfunction. Prothrombotic disorders are discovered in 10-20% of women with preeclampsia, providing the rationale for prescribing low-molecular-weight heparin (LMWH) in future pregnancies. Heparin has diverse molecular actions and appears to reduce the recurrence risk of preeclampsia in women without prothrombotic disorders. The placenta-derived anti-angiogenic splice-variant protein soluble vascular endothelial growth factor (VEGF) receptor-1 (sFLT1) is strongly implicated in the pathogenesis of the underlying endothelial dysfunction. As the placental syncytiotrophoblast is the principal source of sFLT1, we tested the hypothesis that heparin suppresses placental sFLT1 secretion.
  
  
  RESULTS
  First trimester placental villi exposed to LMWH (0.25-25 IU mL(-1)) in an in vitro explant model significantly increased the expression and release of sFLT1 by the syncytiotrophoblast into culture media, reducing phosphorylation of FLT1 and KDR receptors in cultured human umbilical vein endothelial cells. This response was significantly diminished in placental villi from healthy term pregnancies. Placental villi from severely preeclamptic pregnancies had a higher baseline sFLT1 release, compared with first trimester placental villi and did not respond to LMWH treatment. LMWH promoted villous cytotrophoblast proliferation (BrdU incorporation) and impaired syncytial fusion-differentiation, causing syncytiotrophoblast apoptosis (by caspase 3&7 activity and TUNEL staining) and necrosis (ADP/ATP ratio).
  
  
  CONCLUSIONS
  LMWH promotes sFLT1 synthesis and release from first trimester placental villi in a manner similar to that of severely preeclamptic placental villi, which antagonizes VEGF signaling in endothelial cells. These effects in part are mediated by an interaction between heparin and the cytotrophoblasts that regenerates the overlying syncytiotrophoblast responsible for sFLT1 secretion into the maternal blood.
authors: Program in Development and Fetal Health, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Canada. Drewlo@lunenfeld.ca
authors: S
authors: S
authors: Drewlo
authors: K
authors: K
authors: Levytska
authors: M
authors: M
authors: Sobel
authors: D
authors: D
authors: Baczyk
authors: S J
authors: SJ
authors: Lye
authors: J C P
authors: JC
authors: Kingdom
mesh_terms: D000328:Adult; D001483:Base Sequence; D002824:Chorionic Villi / Q000187:drug effects* / Q000378:metabolism; D017931:DNA Primers; D004730:Endothelium, Vascular / Q000378:metabolism*; D005260:Female; D006495:Heparin, Low-Molecular-Weight / Q000494:pharmacology*; D006801:Humans; D010766:Phosphorylation; D011247:Pregnancy; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects*; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*; D040281:Vascular Endothelial Growth Factor Receptor-1 / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D006495:Heparin, Low-Molecular-Weight; D042461:Vascular Endothelial Growth Factor A; C501162:FLT1 protein, human; D040281:Vascular Endothelial Growth Factor Receptor-1