Proteases and sFlt-1 release in the human placenta

Increased placental release of soluble VEGF receptor-1 (sFlt-1) is believed to play an important role in the pathogenesis of preeclampsia (PE). Although the reason for increased placental sFlt-1 release in PE is unknown, proteolytic effect has been proposed as one of the mechanisms that mediate sFlt-1 release in the placenta. In this study, using various protease inhibitors, we tested the possible role of proteases in sFlt-1 release by human placenta. Villous explants from normal term placentas were incubated with various protease inhibitors including serine protease inhibitors (PMSF, aprotini, and specific chymotrypsin inhibitor (CI)), cysteine protease inhibitor E-64, metalloendopeptidase inhibitor PAD, and universal metalloprotease (ADAM) inhibitor PTM. Culture medium was collected and measured for sFlt-1 by ELISA. Our results showed that villous tissue treated with CI and PTM produced significantly less sFlt-1 than those of controls. PMSF, aprotini, E-64, and PAD had no effect on sFlt-1 release. We further examined chymotrypsin-like protease/chymase and ADAM10 expressions in tissue sections from normal and PE placentas by immunohistochemistry. We found that immunostaining for chymase and ADAM10 was significantly increased in the layer of syncytiotrophoblasts in PE placentas compared to normal placentas. These results suggest chymotrypsin-like serine protease and ADAM10, but not cysteine protease and metalloendopeptidase, may play a role in inducing sFlt-1 release in PE placentas.