Trophoblast Differentiation Modulates the Activity of Caspases in Primary Cultures of Term Human Trophoblasts

Abstract

Cultured human cytotrophoblasts are more susceptible than syncytiotrophoblasts to hypoxia-induced apoptosis. Caspases are cysteine proteases that cleave cellular components to effect the apoptotic cascade. We hypothesized that cultured cytotrophoblasts exhibit a higher activity of caspases when compared with syncytiotrophoblasts. Using western analysis, we demonstrated that the pro-caspases 3, 6, 8, and 9 are expressed in cytotrophoblasts cultured for 24 h, and also, in trophoblasts cultured 72 h when syncytiotrophoblasts have formed. Importantly, we found significantly higher activity of all four caspases in trophoblasts cultured 24 h compared with cells cultured 72 h. Colchicine and DMSO, which hinder trophoblast differentiation, enhanced the activity of all four caspases in cells cultured 72 h. Conversely, caspase activity was reduced in trophoblasts cultured for 24 h in the presence of epidermal growth factor, which enhances differentiation. This effect was most pronounced on caspase 3 and was attenuated by addition of the tyrosine kinase inhibitor AG1478. We conclude that cytotrophoblasts exhibit a higher activity of caspases 3, 6, 8, and 9 when compared with the more differentiated syncytium. This may account for the higher susceptibility of cytotrophoblasts to hypoxia-induced apoptosis. Human placental villi are covered by terminally differentiated, multinucleated syncytiotrophoblasts that are in direct contact with maternal blood. The subjacent mononucleated cytotrophoblasts provide a proliferative, stem cell population that differentiates and fuses to replenish the syncytium. Turnover of the trophoblast bi-layer occurs, in part, through apoptosis (1, 2). The balance of proliferation, differentiation, and apoptosis in the trophoblast layer of villi ultimately determines the mass of functional trophoblast available to regulate nutrient and waste exchange between the maternal and fetal circulations. Preeclampsia and fetal growth restriction (FGR) are associated with placental dysfunction, including villous hypoxia, altered differentiation and enhanced apoptosis in trophoblast (3-6). We previously showed that hypoxia hinders differentiation (7) and enhances apoptosis (8) in cultured trophoblasts from term placentas. Importantly, we found that the cytotrophoblasts were more susceptible than syncytiotrophoblasts to hypoxia-induced apoptosis.The regulation of apoptotic cell death is complex (9). Multiple ligand-receptor interactions and diverse stimuli that modulate mitochondrial function converge to enhance the activity of initiator caspases, cysteine proteases that self-amplify their enzymatic activity when stimulated. These enzymes activate downstream effector caspases that cleave membrane, cytoplasmic, and nuclear components, effectively dismantling the cell. Caspases are well known for their role in cell suicide by apoptosis, but recent studies indicate they also play a role in cell proliferation and differentiation (10 -12). Knowledge of the expression and activity of caspases in placental villi and cult...

Regulation of placental amino acid transporter activity by mammalian target of rapamycin

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Syncytial fusion of human trophoblast depends on caspase 8

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XIAP protein is induced by placenta growth factor (PLGF) and decreased during preeclampsia in trophoblast cells

“…In this pathway, Apaf-1 is responsible for the recruitment and activation of the effector caspase 9 with subsequent activation of caspases 3 and 7, which leads to activation of other caspases and finally cellular destruction [Slee et al 1999]. In the trophoblast, caspase 3, 6, 8, and 9 have been localized with higher activity in cultures of cytotrophoblast than syncytiotrophoblast [Yusuf et al 2002]. Serum deprivation has been associated with the induction of caspase 3 and 9 in other systems but little is known about the activation of caspases by serum deprivation in the trophoblast [Bialik et al 1999].…”