Synthesis of glycosaminoglycans by human cervical fibroblasts in culture: effects of prostaglandin E2 and cyclic AMP

Signaling Pathways Regulating Human Cervical Ripening in Preterm and Term Delivery

At the end of gestation, the cervical tissue changes profoundly. As a result of these changes, the uterine cervix becomes soft and vulnerable to dilation. The process occurring in the cervical tissue can be described as cervical ripening. The ripening is a process derivative of enzymatic breakdown and inflammatory response. Therefore, it is apparent that cervical remodeling is a derivative of the reactions mediated by multiple factors such as hormones, prostaglandins, nitric oxide, and inflammatory cytokines. However, despite the research carried out over the years, the cellular pathways responsible for regulating this process are still poorly understood. A comprehensive understanding of the entire process of cervical ripening seems crucial in the context of labor induction. Greater knowledge could provide us with the means to help women who suffer from dysfunctional labor. The overall objective of this review is to present the current understanding of cervical ripening in terms of molecular regulation and cell signaling.

Molecular mechanisms of parturition

The initial signal for triggering human parturition might be fetal but of trophoblastic origin. Concomitantly, this placental signal would have as its target not only the uterus but also the fetus by activating its hypothalamo-pituitary-adrenocortical axis. The latter would represent a second fetal signal which, at the fetomaternal interface, would amplify and define in time the mechanisms responsible for the onset of labor, implying changes in the myometrial and cervical extracellular matrix associated with the accession of the contractile phenotype for myometrial cells. At each phase of these processes in the utero-feto-placental system, the nature of these signals remains to be identified. Is there a single substance, or rather, and more likely, a combination of several?

We appear to be in the presence of dynamic systems of a neuro-immuno-hormonal type which are difficult to describe. Nevertheless, steroid hormones appear to coordinate their successive equilibriums until they become irreversible. Such irreversibility constitutes the essential sign of parturition.

Prostaglandin E2 differentially modulates proinflammatory/prodestructive effects of TNF-alpha on synovial fibroblasts via specific E prostanoid receptors/cAMP

The present study investigated the influence of PGE(2), E prostanoid (EP) receptors, and their signaling pathways on matrix metalloproteinase (MMP)-1 and IL-6 expression in synovial fibroblasts (SFs) from rheumatoid arthritis (RA) patients. RASFs expressed all four EP receptors, with selective induction of EP2 by TNF-alpha. TNF-alpha time-dependently increased intracellular cAMP/protein kinase A signaling (maximum, 6-12 h) and PGE(2) secretion (maximum, 24 h). PGE(2) and the EP2 agonists butaprost or ONO-AE1-259 ((16)-9-deoxy-9beta-chloro-15-deoxy-16-hydroxy-17,17-trimethylene-19,20-didehydro PGE(1)), in turn, induced a rapid, time-dependent (maximum, 15-30 min) increase of cAMP. Additionally, cyclooxygenase-2 inhibition by NS-398 (N-(2-cyclohexyloxy-4-nitrophenyl)-methanesulfonamide) reduced the TNF-alpha-induced increase in IL-6 mRNA/protein, which was restored by stimulation with PGE(2) or EP2, EP3, and EP4 agonists. In contrast, TNF-alpha-induced MMP-1 secretion was not influenced by NS-398 and diminished by PGE(2) via EP2. Finally, 3-isobutyl-1-methylxanthine enhanced the effects of PGE(2) on MMP-1, but not on IL-6 mRNA. In conclusion, PGE(2) differentially affects TNF-alpha-induced mRNA expression of proinflammatory IL-6 and prodestructive MMP-1 regarding the usage of EP receptors and the dependency on cAMP. Although specific blockade of EP2 receptors is considered a promising therapeutic strategy in RA, opposite regulation of proinflammatory IL-6 and prodestructive MMP-1 by PGE(2) via EP2 may require more complex approaches to successfully inhibit the cyclooxygenase-1/2 cAMP axis.

Prostaglandin E2-regulated cervical ripening: analysis of proteoglycan expression in the rat cervix

OBJECTIVE

Prostaglandins reduce cervical resistance by reorganizing collagen fibrils. Proteoglycans are involved in collagen fibril organization and structure. We evaluated the changes in proteoglycan composition induced by prostaglandin E(2) (PGE(2)).

STUDY DESIGN

Prostaglandins were administered intravaginally to induce cervical ripening in timed pregnant Sprague-Dawley rats. Changes in proteoglycan messenger ribonucleic acid (mRNA) expression were measured using reverse transcription (RT-PCR) for core protein. Fluorophore assisted carbohydrate gel electrophoresis (FACE) was used to evaluate proteoglycan glycosaminoglycan composition along with size exclusion high-performance liquid chromatography (HPLC).

RESULTS

No change in core protein mRNA expression was detected after PGE(2) treatment. Total glycosaminoglycan (GAG) decreased more than 20% after PGE(2) (P = .02). FACE demonstrated a shift in disaccharide subunit composition after PGE(2), with a decrease in 4-sulfated disaccharides (P = .02). HPLC confirmed a decrease in total GAG (P = .04).

CONCLUSION

Although there was no change in core protein mRNA expression, alterations in GAG composition was detected after PGE(2). The decrease in sulfated GAG could decrease electrostatic interactions that would weaken interfibrillar interactions. These findings would be consistent with a decline in cervical resistance.

Prostaglandins and the myometrium and cervix

Prostaglandins have long been thought to play important roles in the mechanism of parturition. Here we review the involvement of prostaglandins in myometrial and cervical functions with emphasis on human labor and birth. In addition, the cellular sources of prostaglandins as well as their interactions with various other endocrine, paracrine and physical factors, such as oxytocin, corticotropin releasing hormone, nitric oxide, platelet activating factor, cytokines, endothelin and stretch are also addressed together with their potential role in the molecular reorganization of cervical structure associated with labor and delivery. Finally, the premier role of progesterone in pregnancy maintenance and parturition is juxtaposed with the proposed "fine-tuning", modulatory role of prostaglandins and the above listed factors in the regulation of parturition.

Interleukin-1beta induces glycosaminoglycan synthesis via the prostaglandin E2 pathway in cultured human cervical fibroblasts

The aim of this study was to identify, in cultured human cervical fibroblasts, the mechanisms by which interleukin (IL)-1beta induces the synthesis of glycosaminoglycans (GAG) and to explore the putative role of prostaglandin E(2) (PGE(2)) in this process. Exposure of the cells for 24 h to IL-1beta induced a significant (P < 0.05) dose-dependent increase in GAG synthesis. IL-1beta (1 ng/ml) induced the expression of cyclooxygenase-2 (COX-2) protein 6 h after treatment, accompanied by a 7.5-fold increase in PGE(2) production. We confirmed that NS398, a selective COX-2 inhibitor, dose-dependently blocked PGE(2) augmentation following IL-1beta treatment. AH23848, the selective EP(4) receptor antagonist, completely abolished IL-1beta-induced GAG synthesis, whereas AH6809, an EP(2) receptor antagonist, had no effect on the stimulatory effects of IL-1beta. Furthermore, we demonstrated that 6 h exposure to IL-1beta induced a notable increase in EP(4) receptor mRNA expression and a decrease in EP(1) receptor mRNA but had no effect on the expression of EP(2) and EP(3) receptor transcripts. In conclusion, these findings indicate that IL-1beta not only induced GAG synthesis by increasing COX-2 protein expression and the subsequent PGE(2) production but also enhanced the responsiveness of cervical fibroblasts to PGE(2) by selectively up-regulating EP(4) receptor mRNA expression. These results suggest that PGE(2) may regulate human cervical ripening in an autocrine/paracrine manner via EP(4) receptors.

Induction of the hyaluronic acid-binding protein, tumor necrosis factor-stimulated gene-6, in cervical smooth muscle cells by tumor necrosis factor-alpha and prostaglandin E(2)

Immediately before parturition the cervix undergoes striking changes in structure (ripening) that facilitate dilatation and effacement. Cervical ripening shares many features in common with inflammation-associated tissue remodeling, making it a valuable process to explore with respect to the biochemical events in extracellular matrix restructuring. Cervical ripening can be pharmacologically induced with prostaglandin E(2) (PGE(2)). Among the biochemical changes in the cervix at parturition is a marked increase in the hyaluronic acid (HA) content. HA and HA-binding proteins have been implicated in tissue hydration, release of collagenase, and leukocyte migration, but their roles in cervical ripening have not been explored. In the present study we examined the ability of PGE(2) to induce expression of the HA-binding protein, tumor necrosis factor-stimulated gene (TSG)-6, in human cervical smooth muscle cells (hCSMCs) and compared the PGE(2) response to that of tumor necrosis factor-alpha (TNF-alpha), an established inducer of TSG-6. TNF-alpha stimulated TSG-6 mRNA accumulation in a dose- and time-dependent manner, with the maximal response observed at 10 ng/ml after 6 hours of incubation. PGE(2) stimulated TSG-6 mRNA expression, but the magnitude of response was substantially less than that produced by TNF-alpha, and it was maximal only after 24 hours of incubation. Quantitative real-time polymerase chain reaction was performed to assess the induction of TSG-6 mRNA and nascent transcripts at 24 hours of treatment. Induction of TSG-6 mRNA and nascent transcripts in response to 10 micromol/L of PGE(2) was 5.7-fold and 6.3-fold greater than control values, respectively, whereas TNF-alpha (10 ng/ml) induced TSG-6 mRNA and nascent transcripts by 80-fold and 134-fold, respectively. TNF-alpha and PGE(2) stimulated secretion of TSG-6 into the culture medium as detected by Western blotting. The effects of PGE(2) on secretion of TSG-6 were delayed compared to TNF-alpha. A 1.3-kb fragment of the human TSG-6 proximal promoter drove luciferase expression in transfected hCSMCs. PGE(2) increased TSG-6 promoter activity 1.75-fold. Paradoxically, TNF-alpha reduced TSG-6 promoter activity by 50%. We conclude that hCSMCs express the hyaladherin TSG-6; that TSG-6 expression in these cells is regulated by PGE(2) as well as proinflammatory cytokines; responses of hCSMCs to TNF-alpha and PGE(2) are distinct in terms of magnitude and the time course; and PGE(2) and TNF-alpha exert different effects on the TSG-6 proximal promoter.

Identification and expression of Go1 and Go2 alpha-subunit transcripts in human myometrium in relation to pregnancy

The 39-kDa Goalpha protein, the alpha subunit of a major heterotrimeric G protein of brain and neuroendocrine cells, was found to be present in human myometrium. Using three different antisera, we showed its strong expression in myometrium from pregnant patients as compared to nonpregnant ones. This is in agreement with the high expression level of its two isoforms (alphao1 and alphao2), previously described in late pregnancy. To better ascertain the nature of these immunoreactive isoforms, we investigated transcripts of the Goalpha gene in myometrium from pregnant and nonpregnant patients by reverse transcription-polymerase chain reaction (RT-PCR). In this tissue, the amplified cDNA product of a region common to both Go1alpha and Go2alpha mRNA variants was recognized as the Goalpha nucleotide sequence. Transcripts of Go1alpha and Go2alpha were identified by sequencing. A partial cDNA Go2alpha sequence was described, which differed from the Goalpha gene by two nucleotides in exon 8B. Levels of Go1alpha and Go2alpha transcripts analyzed by semi-quantitative RT-PCR were significantly higher in myometrium from pregnant than from nonpregnant patients. It is suggested that Goalpha gene expression in this tissue may contribute to modifications seen in the signaling pathways observed at the end of pregnancy.

Regional variations in contractile responses to prostaglandins and prostanoid receptor messenger ribonucleic acid in pregnant baboon uterus

OBJECTIVES

The aims of this study were to compare (1) the contractile responses of the lower uterine segment and fundus to prostaglandins, (2) expression of genes encoding prostanoid receptors in myo-metrium from different regions of the uterus, and (3) the distribution of expression of genes encoding prostanoid receptors (P receptors) in key intrauterine tissues.

STUDY DESIGN

Cesarean hysterectomy was performed in 8 pregnant baboons, not in labor, in the last third of pregnancy. Contractile responses of fresh tissue were quantified in a superfusion system. Polyadenylated ribonucleic acid was extracted from frozen tissue and gene expression was quantified by Northern blot analysis with complementary deoxyribonucleic acid probes.

RESULTS

Prostaglandin E2 contracted strips of myometrium from the fundus but had no significant effect on strips from lower uterine segment. Prostaglandin F2 alpha contracted myometrium from both regions equally. Compared with fundus tissue, lower uterine segment tissue had greater expression of EP2 receptor messenger ribonucleic acid, less expression of EP3 receptor messenger ribonucleic acid, but similar levels of EP4 receptor and FP receptor messenger ribonucleic acid. EP2 receptor, EP3 receptor, and EP4 receptor messenger ribonucleic acids were also detected in cervix, decidua, and chorion. EP2 receptor messenger ribonucleic acid was most abundant in the cervix, EP3 receptor messenger ribonucleic acid was most abundant in the myometrium, and EP4 receptor messenger ribonucleic acid was most abundant in the decidua.

CONCLUSIONS

The reduced contractile response of lower uterine segment tissue to prostaglandin E2 is paralleled by greater inhibitory EP2 receptor expression and less contractile EP3 receptor expression, a pattern similar to that seen in the cervix. Drugs with selective activity at prostanoid receptor types and subtypes are likely to allow safer and more effective control of the uterus and cervix than native prostaglandins.