Trophoblast differentiation modulates the activity of caspases in primary cultures of term human trophoblasts

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.