Heparanase regulation of sFLT-1 release in trophoblasts in vitro

Introduction: Preeclampsia is a common pregnancy disorder which is characterized by new onset hypertension and endothelial dysfunction. Despite efforts to determine the causal factors of this disease, little progress has been made in discerning the etiology. The hypoxic and ischemic placenta, however, is generally accepted as the source for secreted factors in the maternal circulation, such as sFLT-1, which drive the maternal syndrome. Methods: Using BeWo placental trophoblast cells, we measured the role of hypoxia on sFLT-1 mRNA as well as protein production. We also exposed the cells to treatment with heparin and heparanase inhibitor OGT-2115. Results: We found that under hypoxic conditions mRNA levels of sFLT-1 were unchanged compared to normoxic controls. Although the message level did not differ under hypoxic conditions, the sFLT-1 release into the media was significantly greater in hypoxia. Additionally, we found that sFLT-1 is able to bind heparan strands in the extracellular matrix with its heparin binding site. These heparan strands can be cleaved by the extracellular enzyme heparanase. We found that heparanase expression was significantly increased in hypoxia, and inhibiting the actions of heparanase attenuated the release of sFLT-1 into the media. Discussion: While the placenta remains a source of sFLT-1, the mechanism of increased circulating sFLT-1 may differ than simple upregulation of the protein. These data demonstrate the potential importance of the role heparanase may play in releasing previously made sFLT-1 into the maternal circulation.