Phagocytosis of necrotic but not apoptotic trophoblasts induces endothelial cell activation

It is hypothesized that preeclampsia is caused by factors from the placenta that induce endothelial cell activation. Trophoblasts are cells that may be shed from the placenta, then deported in the maternal blood, and finally become trapped in the pulmonary capillaries. The ultimate fate of deported trophoblasts is unknown, but to prevent clogging of the pulmonary circulation they must be cleared from the capillary beds. We examined the hypothesis that endothelial cells phagocytose deported trophoblasts and also examined the consequent effects of the trophoblasts on endothelial cells. Fluorescently labeled trophoblast-derived choriocarcinoma cells were induced to become apoptotic or necrotic and exposed to endothelial cell monolayers. Confocal microscopy demonstrated uptake of both apoptotic and necrotic trophoblasts, and this phagocytosis could be inhibited by cytochalasin B. Phagocytosis of necrotic but not apoptotic trophoblasts induced increased endothelial intercellular adhesion molecule 1 (ICAM-1) expression, as well as increased adhesion of monocytes to endothelial cell monolayers. Inhibiting the phosphatidylinositol 3-kinase and p38 mitogen-activated protein kinase pathways blocked both expression of ICAM-1 and phagocytosis, whereas inhibition of the P42/44 mitogen-activated protein kinase pathway blocked only ICAM-1 expression. This work suggests that endothelial cells can phagocytose deported trophoblasts and that the mechanism of trophoblast death (apoptotic or necrotic) could have major effects on the maternal vascular response to shed trophoblasts.