Distribution of prostaglandin endoperoxide synthase and prostacyclin synthase in the late pregnant uterus

Spatial and temporal expression of the myometrial mitogen-activated protein kinases p38 and ERK1/2 in the human uterus during pregnancy and labor

OBJECTIVE

We have recently identified a novel putative spliced variant of the activating transcription factor 2 (ATF2) in the human myometrium during pregnancy and labor. This protein, termed ATF2-sm like full-length ATF2, acts as a potent transactivator of cyclic adenosine monophosphate response element (CRE)-containing promoter reporter genes. Similarly, employing microarray gene profiling in myometrial cells, we have shown ATF2-sm to affect the expression of several specific myometrial genes associated with regulating uterine activity during pregnancy and labor. At some point after conception this transcription factor becomes spatially expressed within the body of the uterus, with significantly higher levels detected in the upper (corpus) compared to the lower uterine segment. Because ATF2 species are the primary substrate for phosphorylation by the mitogen-activated protein kinases (MAPKs) p38 and ERK1/2, the purpose of the current investigation was to define the expression levels of these kinases in upper and lower segment myometrium during pregnancy and labor to see if they also correlated with expression of ATF2-sm.

METHODS

Paired myometrial samples were collected from the upper (corpus) and lower uterine segments from term nonlaboring and spontaneously laboring women undergoing elective and emergency cesarean deliveries, respectively. Non-pregnant myometrial samples were collected from premenopausal women having hysterectomies for benign gynecologic disorders. The MAPKs p38 and ERK1/2 present in individual myometrial homogenates were resolved using sodium dodecyl sulfate polacrylamide gel electropheresis (SDS-PAGE) with subsequent Western blotting with specific antibodies and scanning densitometry. Expression of the individual MAPKs in myometrial tissues was confirmed in situ using immunohistochemistry.

RESULTS

In non-pregnant tissues, p38 and ERK1/2 expression was uniform throughout the uterus. In term pregnant nonlaboring and spontaneously laboring samples expression of p38 and ERK1 was significantly elevated in the upper uterine segment compared to the lower segment, respectively. In contrast, there was no difference in ERK2 expression.

CONCLUSION

The data from this study indicate that both p38 and ERK1 are spatially regulated in different uterine regions during pregnancy/labor and suggest that they may be involved in regulating the activity of ATF2 isoforms and their subsequent effects on myometrial function.

17beta-estradiol up-regulates prostacyclin production in cultured human uterine myometrial cells via augmentation of both cyclooxygenase-1 and prostacyclin synthase expression

OBJECTIVE

To investigate whether 17beta-estradiol elevates prostacyclin (PGI(2)) production in human myometrial cells in the middle of gestation.

METHODS

The concentration of 6-keto-PGF(1alpha), a stable metabolite of PGI(2), in the culture medium was assessed using enzyme-linked immunosorbent assay (ELISA). Western blot analysis and quantitative reverse-transcriptase polymerase chain reaction (RT-PCR) using TaqMan (Applied Biosystems, Foster City, CA) technology were performed to evaluate the expression of cytosolic phopholipase A(2) (cPLA(2)), cyclooxygenase-1 (COX-1), COX-2, and prostacyclin synthase (PGIS) in cultured human myometrial cells prepared from second trimester pregnant women (n = 3) after stimulation with 17beta-estradiol.

RESULTS

Treatment with 17beta-estradiol (4-400 nM) dose-dependently elevated PGI(2) secretion from cultured human myometrial cells. Western blot analysis detected cPLA(2) and COX-1 and PGIS protein expression in the cultured human myometrial cells; however, COX-2 protein expression was below the detection sensitivity. Stimulation with 40-nM 17beta-estradiol significantly up-regulated protein and mRNA expression of both COX-1 and PGIS.

CONCLUSION

17beta-Estradiol from placenta may contribute to the augmentation of PGI(2) production in the human myometrium in the middle of gestation via up-regulation of both COX-1 and PGIS expression.

Temporal expression and signalling of prostacyclin receptor in the human endometrium across the menstrual cycle

Prostacyclin (PGI(2)) synthesis and function in the human uterus has been implicated in the regulation of the process of normal and dysfunctional menstruation. PGI(2) synthesis is elevated during normal menstruation and is also associated with blood loss in women who suffer from heavy menses. This study was designed to outline further the role of PGI(2) in menstruation by investigating the temporal pattern and site of expression of prostaglandin I synthase (PGIS) and the prostacyclin receptor (IP receptor) in the non-pregnant human endometrium across the menstrual cycle. Quantitative RT-PCR demonstrated increased expression of PGIS and IP receptor during the menstrual phase of the cycle compared with all other phases (P < 0.05). Furthermore, PGIS and IP receptor were localised to the glandular epithelium, stromal and endothelial cells in the basal and functional layers of the endometrium. Functionality of the IP receptor in the human endometrium was assessed by measuring cAMP generation following treatment with 100 nmol l(-1) of the PGI(2) analogue, iloprost. cAMP generation was significantly higher in endometrial tissue collected during the proliferative compared with the secretory phase of the menstrual cycle (P < 0.05). In conclusion, this study has confirmed increased expression and signalling of PGIS and IP receptor during the menstrual phase and outlines a potential autocrine/paracrine role for PGI(2) on several cellular compartments in the endometrium including the endothelium. This may underscore a pivotal role for PGI(2) receptor signalling in normal and dysfunctional menstruation.

Characterization and functional analysis of cAMP response element modulator protein and activating transcription factor 2 (ATF2) isoforms in the human myometrium during pregnancy and labor: identification of a novel ATF2 species with potent transactivation properties

There is now extensive evidence to indicate that components of the cAMP signaling pathway are up-regulated in the human myometrium during pregnancy so as to potentiate the maintenance of uterine quiescence until term. In many tissue and cell types, increased signaling of the cAMP pathway results in profound changes in gene expression that are catalyzed via stimulation of PKA and activation of cAMP-dependent transcription factors that bind cAMP response elements (CREs) within the promoter regions of affected genes. In the myometrium, these CRE containing genes include beta2-adrenoceptor, cyclo-oxygenase 2, oxytocin receptor, and connexin-43. In preliminary investigations, we reported the differential expression of members of the cAMP bZIP protein family in the myometrium during pregnancy and labor. In this present study, we have now identified and functionally characterized these proteins with respect to myometrial gene expression. We report the identification of a 39,000 mol wt CRE response element modulator protein (CREM)tau2alpha protein having both transactivation and transrepressor properties whose expression is sequentially decreased in the myometrium during gestation and parturition. In contrast, expression of a myometrial 28,000 mol wt CREMalpha protein having only transrepressor actions progressively increased in the myometrium during pregnancy and labor. Similarly, we have isolated two ATF2 proteins of 60,000 and 28,000 mol wts, which represent full-length ATF2 and a novel small isoform of ATF2 that we have termed ATF2-small (ATF2-sm). These proteins are potent transactivators of gene expression and appear to be spatially expressed within the myometrium of the upper and lower uterine regions. The identification and functional characterization of these basic region/leucine zipper proteins in the myometrium may provide further insight into the molecular mechanisms regulating uterine activity during fetal maturation and parturition.

Endothelial vasodilator production by uterine and systemic arteries. V. Effects of ovariectomy, the ovarian cycle, and pregnancy on prostacyclin synthase expression

Prostacyclin (PGI(2)) is a potent vasodilator, the level of which is increased during pregnancy, and is the main eicosanoid of which production is elevated in the endothelium and vascular smooth muscle (VSM) of both uterine and omental (systemic) arteries. We tested the hypothesis that during physiologic states that have high uterine blood flow, such as pregnancy and the follicular phase of the ovarian cycle (versus luteal phase and ovariectomized ewes), there is an increased level of prostacyclin synthase (PGIS) expression in ovine uterine and omental artery endothelium and VSM. To investigate this, the cellular localization and PGIS protein expression level in uterine and systemic arteries was examined by immunohistochemistry as well as by Western immunoblot analysis of endothelial-isolated protein and denuded vessels (VSM). Whole uterine, but not omental (systemic), arteries from the pregnant ewes showed an increase (P < 0.001) in PGIS expression. Further localization of PGIS protein by immunohistochemistry and quantification by Western analysis showed PGIS to be somewhat higher in the uterine artery VSM (69 +/- 7%) than endothelium (31 +/- 7%). PGIS protein levels in uterine and omental artery endothelial isolated protein were not altered by ovariectomy or the ovarian cycle, although they were both significantly elevated by pregnancy. Uterine and omental artery VSM PGIS expression levels also were not altered by ovariectomy or the ovarian cycle, whereas PGIS expression, in uterine but not omental artery VSM showed a significant elevation during pregnancy. Thus, the rise in PGI(2) production by uterine arteries observed in ovine pregnancy is paralleled by an elevation in PGIS expression in both endothelium and VSM, whereas those seen in omental arteries is associated with increases in endothelial PGIS.

The differential expression of myometrial connexin-43, cyclooxygenase-1 and -2, and Gs alpha proteins in the upper and lower segments of the human uterus during pregnancy and labor

There is evidence from many studies indicating that a number of specific quiescent and contractile associated proteins are temporally regulated in the myometrium during pregnancy. In this present investigation we provide data that strongly suggest that myometrial connexin-43, cyclooxygenase-1 and -2 (COX-1 and -2), and Gs alpha proteins are also spatially expressed within the human uterus during pregnancy and labor. Using paired lower and upper segment myometrial samples taken from individual women at term and during spontaneous labor, we have measured the expression of these proteins by immunoblotting with specific antibodies. We report that the myometrial gap junction connexin-43 protein is expressed at much greater levels in the upper uterine compared to the lower uterine segment and that this difference is even more pronounced during the course of labor. Conversely, myometrial COX-1 and -2 proteins appear to be expressed at much greater levels in the lower compared to the upper uterine segment. Moreover, the level of expression of both proteins is unaffected by the onset of parturition. In contrast, myometrial Gs alpha protein appears to be uniformly expressed in both lower and upper segments and is similarly down-regulated during parturition, as previously reported. The differential expression of COX-1 and -2 and connexin-43 in the uterus may allow cervical ripening before and dilatation during labor and facilitate effective propagation of contractions from fundus to cervix, which may be further facilitated by the down-regulation of Gs alpha at the onset of parturition.

15-Hydroxy-prostaglandin dehydrogenase activity in uterine tissues of late gestational and parturient cows

15-Hydroxy-prostaglandin dehydrogenase activity (PGDH) was measured in endometrium, allanto-chorion, allanto-amnion and the placenta from six cows during late gestation and six parturient cows during caesarean section. Under saturated substrate conditions PGDH activity was lower than 138 pmol g wet tissue-1 min-1 in all uterine tissues in both groups. Human placental reference samples showed a PGDH activity of 16,800 +/- 1200 pmol per g wet weight min-1 (n = 4). Under subsaturational conditions enzyme activity was demonstrated in endometrium and both fetal membranes. These results indicate that PGF2 alpha catabolism in bovine uterine tissue on day 262 and during parturition, contributes little to changing plasma PGFM concentrations.

Changes in plasma levels of PGF2 alpha and PGI2 metabolites at and after delivery at term

Plasma levels of 6-keto-PGF1 alpha and 13,14-dihydro-15-keto-PGF2 alpha (PGFM) were measured by high pressure liquid chromatography and radioimmunoassay during and up to 48 hours after term labor. PGFM levels increased during labor to reach values which at full dilatation, at delivery of the fetal head and at placental separation were each time higher than levels obtained earlier. In all women (n = 10) PGFM levels reached their maximum and started to decline within 10 min. after placental separation. Levels decreased to prelabor values within 2 to 3 hours after delivery and no temporary increases were observed within the first 2 days. Levels of 6-keto-PGF1 alpha on the other hand, showed no consistent trends throughout labor and the early puerperium. The observed changes are believed to be of relevance for ensuring adequate hemostasis after birth.

Prostaglandin production by human myometrium, uterine cervix and leiomyoma

In order to investigate prostacyclin production by human myometrium, uterine cervix and leiomyoma, slices of each tissue were incubated. The 6-keto prostaglandin F1 alpha concentration of the incubation medium was measured by radioimmunoassay. The serosal and endometrial sides of myometrium produce 6-keto prostaglandin F1 alpha, with no significant difference in production between the two sides. The 6-keto PGF1 alpha production of leiomyoma was significantly higher than that of myometrium. Our results suggest that human myometrium and leiomyoma produce prostacyclin regardless of vascularization.