Endothelin-1 stimulates phospholipid hydrolysis and prostaglandin F2 alpha production in primary human decidua cell cultures

Initiation of human parturition: signaling from senescent fetal tissues via extracellular vesicle mediated paracrine mechanism

A better understanding of the underlying mechanisms by which signals from the fetus initiate human parturition is required. Our recent findings support the core hypothesis that oxidative stress (OS) and cellular senescence of the fetal membranes (amnion and chorion) trigger human parturition. Fetal membrane cell senescence at term is a natural physiological response to OS that occurs as a result of increased metabolic demands by the maturing fetus. Fetal membrane senescence is affected by the activation of the p38 mitogen activated kinase-mediated pathway. Similarly, various risk factors of preterm labor and premature rupture of the membranes also cause OS-induced senescence. Data suggest that fetal cell senescence causes inflammatory senescence-associated secretory phenotype (SASP) release. Besides SASP, high mobility group box 1 and cell-free fetal telomere fragments translocate from the nucleus to the cytosol in senescent cells, where they represent damage-associated molecular pattern markers (DAMPs). In fetal membranes, both SASPs and DAMPs augment fetal cell senescence and an associated ‘sterile’ inflammatory reaction. In senescent cells, DAMPs are encapsulated in extracellular vesicles, specifically exosomes, which are 30–150 nm particles, and propagated to distant sites. Exosomes traffic from the fetus to the maternal side and cause labor-associated inflammatory changes in maternal uterine tissues. Thus, fetal membrane senescence and the inflammation generated from this process functions as a paracrine signaling system during parturition. A better understanding of the premature activation of these signals can provide insights into the mechanisms by which fetal signals initiate preterm parturition.

Physiological involvement of placental endothelin-1 and prostaglandin F2alpha in uteroplacental circulatory disturbance in pregnant rats exposed to heat stress

Several studies suggest that heat stress affects placental functions including uteroplacental circulation, subsequently leading to pregnancy failure and birth weight reduction. To clarify the involvement of endothelin and placental prostaglandin (PG) systems in the uteroplacental circulation during heat stress, we examined the effects of i.v. administration of the endothelin receptor antagonist bosentan and the cyclooxygenase inhibitor indomethacin on uteroplacental blood flow and on placental PGE2 and PGF2alpha levels and their 13,14-dyhydro-15-keto-metabolites (PGEM and PGFM, respectively) in heat-exposed or non-heat-exposed pregnant rats. The administration of bosentan or indomethacin did not change uteroplacental blood flow in non-heat-exposed pregnant rats. In contrast, heat reduced uteroplacental blood flow in pregnant rats, but the reduction was reversed by the administration of bosentan or indomethacin before heat exposure. Heat did not change placental PGE2 or PGEM levels, but in pregnant rats it increased placental PGF2alpha and PGFM levels, which were reversed by bosentan or indomethacin. Our results suggest that the activation of placental endothelin receptor and PGF2alpha systems are involved in the uteroplacental circulatory disturbances produced by heat. PGF2alpha systems activated by heat may be involved in the vasoconstricting effects of endothelin-A and -B receptors during heat exposure.

Stimulation or endothelin-1 secretion by human breast cancer cells through protein kinase A activation: a possible novel paracrine loop involving breast fibroblast-derived prostaglandin E2

Breast cancer cells secrete endothelin-1 (ET-1), which may act as a paracrine mitogen in breast tumours. The paracrine factors and signal transduction pathways responsible for regulating ET-1 production in breast cancer are unknown. In this study we have examined the involvement of the protein kinase A (PKA) signalling pathway in the control of ET-1 secretion in the human breast cancer cell line MCF-7. Treatment of MCF-7 cells with various agents that activate protein kinase A (PKA) through increases in intracellular cAMP levels including forskolin, cholera toxin (ChT), the cAMP analogue 8-Br-cAMP, or the cAMP phosphodiesterase inhibitor, 3-isobutyl-1-methyl-xanthine (IBMX) all markedly increased ET-1 release. Prostaglandin E2 (PGE2) while stimulating cAMP production, but not inositol lipid hydrolysis also significantly stimulated ET-1 release. Activation of PKC by 2-O-tetradecanoyl phorbol 13-acetate (TPA) also stimulated ET-1 secretion in MCF-7 cells. The PKA inhibitor H-89 attenuated the ET-1 response to PGE2, forskolin and ChT, but not that due to the PKC agonist TPA. The possibility that human breast fibroblasts (HBFs) are a target for ET-1 action with regard to PGE2 production was also investigated, and revealed that while HBFs were unresponsive to ET-1 alone, pretreatment with the cytokine IL-beta greatly potentiated PGE2 release in response to ET-1. In conclusion our results show that activation of either the PKA or PKC signalling pathways in human breast cancer cells increases ET-1 secretion. We also found that HBFs release PGE2 after treatment with ET-1 and that PGE2 itself stimulates ET-1 production in MCF-7 cells. The implication of this potential novel paracrine loop may be significant in view of the high levels of PGE2 and ET-1 found in malignant breast tissues.

Prostaglandin E2 production and metabolism in human breast cancer cells and breast fibroblasts. Regulation by inflammatory mediators

Malignant human breast tumours contain high levels of prostaglandin E2 (PGE2). However, the mechanisms controlling PGE2 production in breast cancer are unknown. This in vitro study investigates the capacity for PGE2 synthesis and metabolism in several human breast cancer cell lines and early passage human breast fibroblasts and seeks to identify potential regulatory factors which may control these pathways. Basal PGE2 production rose up to 30-fold in breast fibroblast lines on addition of exogenous arachidonic acid (10 microM), whereas no such changes were observed in six out of seven cancer cell lines, with the exception of modest increases in MDA-MB-231 cells. Interleukin 1 beta (IL-1 beta) also induced PGE2 production in breast fibroblasts in the presence of excess substrate, consistent with cyclo-oxygenase induction by the cytokine. Under these conditions only Hs578T cells and MDA-MB-231 cells demonstrated large increases in PGE2 in response to IL-1 beta or phorbol ester; no such responses were seen in MCF-7, T47-D, ZR-75-1, BT-20 or CLF-90-1 cells. In the absence of added arachidonate, bradykinin (BK) and endothelin-1 (ET-1), potentiated PGE2 production in IL-1 beta-treated fibroblasts, possibly by mobilising endogenous substrate. PGE2 also stimulated ET-1 production by breast cancer cells. In co-cultures with T47-D cells both basal and stimulated PGE2 production by breast fibroblasts was greatly reduced. This appeared to be due to metabolic inactivation by the cancer cell since T47-D cells readily converted PGE2 to 15-keto-PGE2. This apparent 15-hydroxy-PG dehydrogenase activity was stimulated by TPA and inhibited by cycloheximide. In conclusion, breast fibroblasts, particularly under the influence of inflammatory mediators, provide a potentially rich source for PGE2 production in breast tumours, whereas significant contributions from the epithelial tumour component may be restricted to cancer cells exhibiting an invasive phenotype. Metabolic inactivation by the cancer cells may also play an important role in the regulation of breast tumour PGE2 levels.

Evidence for decidual modulation of contractile function in the pregnant rat uterus

This study tested the hypothesis that the decidua of pregnant uterus modulates contractile behavior of the underlying myometrium. Isometric contractile function was measured in transverse rings of pregnant rat uterus with or without the decidua. Observations were made of spontaneous contractions after in vitro isolation, and also of contractile responses to oxytocin and prostaglandin F2 alpha (PGF2 alpha) after the tissues had ceased spontaneous mechanical activity. The amplitude and frequency of spontaneous uterine contractions progressively declined after in vitro isolation; during this period, amplitude of spontaneous contractions was greater in the presence of the decidua, whereas contraction frequency was similar in the decidua-intact and decidua-removed tissues. Reinsertion of donor decidua reproduced contractile characteristics of intact tissue. PGF2 alpha and oxytocin stimulated myometrial contractions, but contraction frequency was greater in the absence than in the presence of the decidua. Depending upon the stimulus, the decidua seems able to express both excitatory and inhibitory factors which can selectively modulate either strength or frequency of uterine contractions.