Thromboxane A2 Limits Differentiation and Enhances Apoptosis of Cultured Human Trophoblasts

Abstract

Prostanoids influence differentiation in diverse cell types. Altered expression of cyclooxygenase and prostaglandins has been implicated in the pathophysiology of placental dysfunction, which results in preeclampsia and fetal growth restriction. We hypothesized that prostanoids modulate differentiation and apoptosis in cultured human trophoblasts. Villous cytotrophoblasts were isolated from term human placentas and cultured in serumfree medium. The level of human chorionic gonadotropin was used as a marker of biochemical differentiation of primary trophoblasts, and syncytia formation was used as a marker of morphologic differentiation. Of the prostanoids tested, we found exposure to thromboxane A 2 hindered both biochemical and morphologic differentiation of cultured trophoblasts. As expected, human chorionic gonadotropin levels in the media were elevated in a concentration-dependent manner in the presence of the thromboxane synthase inhibitor, sodium furegrelate, or the thromboxane A 2 receptor blocker SQ 29,548. Furthermore, thromboxane A 2 enhanced trophoblast apoptosis, determined using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining, cell morphology, and a concentrationdependent increase in p53 expression. We conclude that thromboxane A 2 hinders differentiation and enhances apoptosis in cultured trophoblasts from term human placenta. We speculate that thromboxane may contribute to placental dysfunction by restricting differentiation and enhancing apoptosis in human trophoblasts. The function of the human placenta depends on multinucleated, terminally differentiated syncytiotrophoblasts. This epithelium is in direct contact with maternal blood and regulates maternal-fetal exchange of micronutrients and gases. The syncytiotrophoblast arises from fusion of relatively undifferentiated, mitotically active cytotrophoblasts. This process involves morphologic and biochemical differentiation. Morphologic differentiation is defined by fusion of mononucleated cytotrophoblasts with adjacent syncytium (1). Biochemical differentiation is characterized by production of hormones such as hCG and human placental lactogen (2-4). Preeclampsia and FGR are associated with trophoblast hypoxia and placental dysfunction (5). Villi from women with these conditions typically exhibit diminished villus formation, prominent cytotrophoblasts, enhanced syncytial knot formation, and apoptosis (6, 7). An increase in TX synthesis has been demonstrated in villi (8, 9) and trophoblasts (10, 11) from preeclamptic women compared with healthy control subjects. Importantly, FGR (12) and preeclampsia (13) are associated with elevated TXA 2 levels in the circulation of pregnant women. Although the effect of prostanoids on vascular reactivity is well known (14), recent studies indicate that prostanoids also regulate proliferation, differentiation, and apoptosis in many cell types (15-18). We tested the hypothesis that prostanoids influence the differentiation of cultured trophoblasts from term human placenta. We found ...

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

“…Importantly, undifferentiated cytotrophoblasts are most susceptible to the apoptosis induced by apoptotic stimuli while the syncytiotrophoblast is relatively resistant (8,27). Our caspase studies point to one mechanism that explains this differential susceptibility.…”

“…Hypoxia and thromboxane treatment hinder differentiation (7,26,27), and enhance apoptosis in cultured trophoblast (8,27). Importantly, undifferentiated cytotrophoblasts are most susceptible to the apoptosis induced by apoptotic stimuli while the syncytiotrophoblast is relatively resistant (8,27).…”

Intra-uterine growth restriction is associated with increased apoptosis and altered expression of proteins in the p53 pathway in villous trophoblast

“…Increased expression of p53 in trophoblast has also been reported in other placental pathologies, including HELLP syndrome and gestational trophoblastic disease [19,42]. p53 may be upregulated by noxious environments and has been investigated by exposing trophoblast to severe hypoxia and treatment with thromboxane-A 2 , potential factors in the development of placental dysfunction in IUGR; both culture conditions lead to increased apoptosis and expression of p53 [36,43,44]. Interestingly, p53 expression is reportedly high in first trimester villous tissue [45], when apoptosis is infrequent suggesting that the role of p53 may change over the duration of pregnancy.…”

Molecular Mechanisms Regulating the Vascular Prostacyclin Pathways and Their Adaptation during Pregnancy and in the Newborn

“…Some studies suggest that placental insufficiency in IUGR may be related to increased TXA 2 production secondary to tissue hypoxia. TXA 2 limits biochemical and morphologic differentiation and promotes apoptosis in cultured human villous trophoblasts exposed to hypoxia (Yusuf et al, 2001). In addition, in chorionic vessels isolated from IUGR placentas and examined at low oxygen levels, the TXA 2 agonist U46619 causes greater venous contraction and no change in arterial contraction compared with vessels from normal placentas exposed to the same oxygen concentration.…”