Peroxisome proliferator-activated receptor-gamma modulates differentiation of human trophoblast in a ligand-specific manner

The ligand-dependent nuclear receptor peroxisome proliferator-activated receptor-gamma (PPARgamma) regulates the differentiation of several tissues and cell types. PPARgamma was recently determined to be essential for murine placental development and differentiation. We therefore assessed the influence of PPARgamma on differentiation of human placental trophoblasts. We initially used immunohistochemistry to examine term human placentas for PPARgamma expression and found that PPARgamma is present in syncytiotrophoblasts and cytotrophoblasts in placental villi. We correlated the expression of PPARgamma with differentiation of primary human trophoblasts and found that 8-bromo-cAMP, a known enhancer of trophoblast differentiation, stimulates PPARgamma activity, but has no effect on PPARgamma expression. We demonstrated that the PPARgamma ligand 15-deoxy-delta12,14-prostaglandin J2 (15deltaPGJ2) and the thiazolidinedione troglitazone stimulate PPARgamma activity in the trophoblast cell line BeWo. Importantly, whereas exposure of cultured primary trophoblasts to troglitazone enhances biochemical and morphological trophoblast differentiation, 15deltaPGJ2 diminishes trophoblast differentiation. Furthermore, 15deltaPGJ2, but not troglitazone, up-regulates p53 expression and promotes trophoblast apoptosis. These data indicate that PPARgamma is expressed in human placental trophoblasts, and that ligand-specific activation of PPARgamma results in opposing effects on trophoblast differentiation. Our results suggest that PPARgamma plays an important role in placental differentiation during human pregnancy.