Regulation of cytosolic phospholipase A2 expression by cytokines in human amnion cells

cPLA(2)α gene activation by IL-1β is dependent on an upstream kinase pathway, enzymatic activation and downstream 15-lipoxygenase activity: a positive feedback loop

Cytosolic phospholipase A(2)α (cPLA(2)α) is the most widely studied member of the Group IV PLA(2) family. The enzyme is Ca(2+)-dependent with specificity for phospholipid substrates containing arachidonic acid. As the pinnacle of the arachidonic acid pathway, cPLA(2)α has a primary role in the biosynthesis of a diverse family of eicosanoid metabolites, with potent physiological, inflammatory and pathological consequences. cPLA(2)α activity is regulated by pro-inflammatory stimuli through pathways involving increased intracellular Ca(2+) levels, phosphorylation coupled to increased enzymatic activity and de novo gene transcription. This study addresses the signal transduction pathways for protein phosphorylation and gene induction following IL-1β stimulation in human fetal lung fibroblasts. Our results utilizing both inhibitors and kinase-deficient cells demonstrate that cPLA(2)α is phosphorylated within 10min of IL-1β treatment, an event requiring p38 MAPK as well as the upstream kinase, MKK3/MKK6. Inhibition of p38 MAPK also blocks the phosphorylation of a downstream, nuclear kinase, MSK-1. Our results further demonstrate that the activities of both cPLA(2)α and a downstream lipoxygenase (15-LOX2) are required for IL-1β-dependent induction of cPLA(2)α mRNA expression. Overall, these data support an MKK3/MKK6→p38 MAPK→MSK-1→cPLA(2)α→15-LOX2-dependent, positive feedback loop where a protein's enzymatic activity is required to regulate its own gene induction by a pro-inflammatory stimulus.

The association between maternal cervicovaginal proinflammatory cytokines concentrations during pregnancy and subsequent early-onset neonatal infection

OBJECTIVE

The aim of this study was to investigate the relationship between the concentration of selected proinflammatory cytokines (IL-1alpha, IL-1beta, IL-6 and IL-8) in cervicovaginal fluid, as measured in midgestation, and the risk of early-onset neonatal infection (EONI).

METHOD

Cervicovaginal fluids were obtained from a cohort of 114 pregnant women at 22 to 34 weeks' gestation. The samples were analyzed for the concentrations of selected proinflammatory cytokines using standard enzyme-linked immunosorbent assay technique (ELISA). Lower genital tract microbiology was diagnosed using Gram stain method according to Spiegel's criteria and by culture.

RESULTS

Mean gestational age at the time of sampling was 29.0 weeks. Mean time between sampling and delivery was 9.3 (SD 4.7) weeks. Bacterial vaginosis (BV) was diagnosed in 27.2% of subjects and M. hominis and U. urealyticum in 22.8% and 26.3%, respectively. Out of 114 women examined, 20 (17.5%) delivered newborns with EONI. Median cervicovaginal concentrations of IL-1alpha, IL-1beta, IL-6 and IL-8 did not differ between women who delivered newborns with EONI as compared to women who delivered newborns without EONI. Women with pathological lower genital tract microflora and low IL-8 concentration (below 25(th) percentile) during pregnancy presented a significant risk of delivering newborns with EONI (OR=4.9; 95% CI, 1.1-22.8). Subjects with pathological lower genital tract microflora and a low concentration of more than one cytokine had the highest risk of delivering a newborn with EONI, OR=16.2, 95% CI, 1.1-234.0.

CONCLUSIONS

Cytokine measurement in cervicovaginal fluid in early gestation could be useful for predicting subsequent EONI only among pregnant women with lower genital tract infection. Maternal genital tract immune hyporesponsiveness as represented by low concentrations of proinflammatory cytokines may create a permissive environment for ascending infection and may lead to subsequent EONI.

Decreased Proinflammatory Cytokines in Cervicovaginal Fluid, as Measured in Midgestation, are Associated with Preterm Delivery

PROBLEM

The main aim of this study was to investigate the relationship between selected proinflammatory cytokines [interleukin IL-1 alpha (IL-1alpha), IL-1 beta (IL-1beta), IL-6 and IL-8] concentrations in cervicovaginal fluid, as measured in midgestation, and the risk of subsequent preterm delivery.

METHOD OF STUDY

Cervicovaginal fluids were obtained from a cohort of 114 pregnant women at 22-34 weeks' gestation and analyzed for the concentrations of IL-1alpha, IL-1beta, IL-6 and IL-8 using enzyme-linked immunosorbent assay technique. Lower genital tract microbiology was diagnosed using Gram stain method and by culture.

RESULTS

Mean gestational age at the time of sampling was 29.0 weeks. Mean time between sampling and delivery was 9.3 weeks (S.D. 4.7). Median cervicovaginal concentrations of IL-1alpha, IL-1beta, IL-6 and IL-8 did not differ between preterm and term delivery group. Women with lower genital tract pathological flora and IL-1alpha concentration below 25th percentile presented significant risk of subsequent preterm delivery as compared with women with no low cytokines (OR = 10.7; 95% CI, 2.0-58.1). Women with more than one cytokine' low concentration (below 25th percentile) presented an increased risk of preterm delivery--OR = 11.8 (95% CI, 1.8-78.0).

CONCLUSIONS

The midgestation cytokines' measurement in cervicovaginal fluid of pregnant women could be useful for prediction of preterm delivery only among women with lower genital tract pathological flora.

Modulation of cytokine-induced cyclooxygenase 2 expression by PPARG ligands through NFkappaB signal disruption in human WISH and amnion cells

Cyclooxygenase (COX) activity increases in the human amnion in the settings of term and idiopathic preterm labor, contributing to the generation of uterotonic prostaglandins (PGs) known to participate in mammalian parturition. Augmented COX activity is highly correlated with increased COX2 (also known as prostaglandin-endoperoxide synthase 2, PTGS2) gene expression. We and others have demonstrated an essential role for nuclear factor kappaB (NFkappaB) in cytokine-driven COX2 expression. Peroxisome proliferator-activated receptor gamma (PPARG), a member of the nuclear hormone receptor superfamily, has been shown to antagonize NFkappaB activation and inflammatory gene expression, including COX2. We hypothesized that PPARG activation might suppress COX2 expression during pregnancy. Using primary amnion and WISH cells, we evaluated the effects of pharmacological (thiazolidinediones) and putative endogenous (15-deoxy-Delta(12,14)-prostaglandin J2, 15d-PGJ2) PPARG ligands on cytokine-induced NFkappaB activation, COX2 expression, and PGE2 production. We observed that COX2 expression and PGE2 production induced by tumor necrosis factor alpha (TNF) were significantly abrogated by 15d-PGJ2. The thiazolidinediones rosiglitazone (ROSI) and troglitazone (TRO) had relatively little effect on cytokine-induced COX2 expression except at high concentrations, at which these agents tended to increase COX2 abundance relative to cells treated with TNF alone. Interestingly, treatment with ROSI, but not TRO, led to augmentation of TNF-stimulated PGE2 production. Mechanistically, we observed that 15d-PGJ2 markedly diminished cytokine-induced activity of the NFkappaB transcription factor, whereas thiazolidinediones had no discernable effect on this system. Our data suggest that pharmacological and endogenous PPARG ligands use both receptor-dependent and -independent mechanisms to influence COX2 expression.

Transcriptional regulation of genes for enzymes of the prostaglandin biosynthetic pathway

Numerous studies over the years have demonstrated changes in prostaglandin (PG) levels in intrauterine tissues in association with labour, and PG administration has long been used to induce delivery. While it is now widely accepted that PGs play a major role in human parturition, the complex regulation of their levels is still being elucidated, with the focus on the transcriptional control of the enzymes responsible for the various steps in PG biosynthesis and catabolism.

Glucocorticoids induce cytosolic phospholipase A2 and prostaglandin H synthase type 2 but not microsomal prostaglandin E synthase (PGES) and cytosolic PGES expression in cultured primary human amnion cells

This study examines the regulation of major enzymes in prostaglandin E(2) (PGE(2)) synthesis by glucocorticoids in separate cultures of human amnion epithelial and fibroblast cells at term. Cytosolic phospholipase A(2) (cPLA(2)), cytosolic PGES (cPGES), and microsomal PGES (mPGES) mRNA were expressed at similar levels in both cell types, whereas a greater prostaglandin H synthase type 2 (PGHS-2) mRNA expression was observed in amnion fibroblasts than in epithelial cells. Amnion fibroblasts produced 50-fold more PGE(2) per cell than epithelial cells. Dexamethasone (0.01-1 microM) increased PGE(2) production in amnion fibroblasts in a concentration-dependent manner but did not affect PGE(2) production in amnion epithelial cells. Both mRNA and protein expression of cPLA(2) and PGHS-2 but not cPGES and mPGES were increased in a dose-dependent manner by dexamethasone (0.01-1 microM) in amnion fibroblasts. Induction of cPLA(2) and PGHS-2 mRNA by dexamethasone was blocked by RU486. Dexamethasone did not affect PGHS-2, cPGES, and mPGES mRNA expression in amnion epithelial cells. In conclusion, amnion fibroblasts express a higher level of PGHS-2 mRNA and produced more PGE(2) per cell than amnion epithelial cells at term of human pregnancy. Glucocorticoids increase PGE(2) production only in the amnion fibroblasts mainly through induction of cPLA(2) and PGHS-2 expression.

Hormonal regulation of cytokine release by human fetal membranes at term gestation: effects of oxytocin, hydrocortisone and progesterone on tumour necrosis factor-alpha and transforming growth factor-beta 1 output

Inflammatory cytokines can play an important role in the biomolecular processes leading to labour by regulating prostaglandin production in intrauterine tissues. In the setting of intrauterine infection, an increased production of these cytokines by placenta, decidua and fetal membranes occurs and is responsible for the onset and maintenance of preterm labour. However, the factors involved in the control of cytokine release by these tissues in normal pregnancy at term are still largely unknown. We investigated the possibility that the synthesis and release of tumour necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta1 (TGF-beta1) by human fetal membranes at term gestation is regulated by several hormones potentially involved either in the maintenance of pregnancy or in the parturitional process. In the present study, the effects of hydrocortisone, progesterone and oxytocin on TNF-alpha and TGF-beta1 release by explants of fetal membranes at term gestation were evaluated. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to assess the effect of the above hormones on mRNA expression; TNF-alpha and TGF-beta1 release in culture medium was quantitifed by ELISA assays. Results show that both tissue mRNA expression for TNF-alpha and TNF-alpha release in culture medium were significantly increased by oxytocin, but not by hydrocortisone and progesterone. On the contrary, all the hormones tested increased both tissue TGF-beta1 mRNA expression and release in culture medium. These findings suggest that TNF-alpha and TGF-beta1 production by human fetal membranes in uncomplicated pregnancy at term is selectively modulated by oxytocin, hydrocortisone and progesterone.

Regulation of cyclooxygenase-2 expression by phospholipase D in human amnion-derived WISH cells

Prostaglandins (PGs) are known to play a key role in the initiation of labor, but the mechanisms regulating their synthesis in amnion are largely unknown. In this study, the regulatory mechanisms for PGE(2) production during phospholipase D (PLD) and p38-dependent activation of WISH cells were investigated. We found that the stimulation of WISH cells with interleukin (IL)-1 beta elicited dose-dependent synthesis of cyclooxygenase-2 (COX-2) mRNA, protein, and their products, PGE(2). Moreover, the treatment of [(3)H]myristate-labeled cells in the presence of 1-butanol caused the dose-dependent formation of [(3)H]phosphatidylbutanol (PBt), a product specific to PLD activity. Pretreating the cells with 1-butanol and Ro 31-8220 inhibited the IL-1 beta-induced COX-2 expression, but 3-butanol did not affect this response. In addition, evidence that PLD was involved in the stimulation of COX-2 expression was provided by the observations that COX-2 expression was stimulated by the dioctanoyl phosphatidic acid (PA) and that the prevention of PA dephosphorylation by 1-propranolol potentiated COX-2 expression by IL-1 beta. Moreover, IL-1 beta stimulation of the cells caused the phosphorylation of p38 and extracellular signal-regulated kinase (ERK), and IL-1 beta-induced COX-2 expression was inhibited by the pretreatment of WISH cells with a p38 inhibitor, in contrast ERK upstream inhibitor had no effect. Furthermore, Ro 31-8220 inhibited IL-1 beta-induced p38 phosphorylation but not ERK phosphorylation. The results of this study indicate that in human amnion cells, IL-1 beta might activate PLD through an upstream protein kinase C to elicit p38 and finally induce COX-2 expression.

Cytosolic phospholipase A(2)and 15-hydroxyprostaglandin dehydrogenase mRNA expression in murine uterine and gestational tissues during late pregnancy

We evaluated the changes in mRNA expression of cytosolic phospholipase A(2)(cPLA(2)) and 15-hydroxyprostaglandin dehydrogenase (PGDH) in intrauterine and gestational tissues during mid-late murine pregnancy. Tissues (decidual caps, fetal membranes, and placentae, uterus, and cervix) were collected from pregnant mice at days 12, 14, 16, 18, and 19 (am and pm) of gestation. Total RNA was isolated and evaluated for cPLA(2)and PGDH expression by northern blot analysis normalized to GAPDH expression. Expression of mRNA for cPLA(2)increased in the placentae and decidual caps on day 18 and 19 pm, respectively. There was also increased expression for PGDH mRNA in the placenta and fetal membranes at the later stages of pregnancy. The tissue specific differences in expression of cPLA(2)and PGDH suggest that changes in enzymatic regulation of PG production and degradation may be crucial for the initiation of labour.

Transcriptional regulation of prostaglandin-H-synthase-1 in the amnion-derived AV3 cell line

Prostaglandin-H-synthase-1 (PGHS-1), while constitutively expressed in most tissues, increases in abundance in human gestational membranes at term. This suggests that PGHS-1 may be up-regulated in preparation for labor, and thus might be a key determinant in timing labor onset. We conducted transient transfection experiments in amnion-derived AV3 cells utilizing pPGHS1CAT to identify substances that might regulate PGHS-1 expression in amnion. Transforming growth factor-beta (1 ng/ml) and 15-deoxy-delta(12,14) prostaglandin J2 (1 microM) significantly (P < 0.05) (33% and 44% respectively) increased PGHS-1 promoter activity. The activity decreased significantly (P < 0.05) in response to interleukin-1 (IL-1)beta (1 ng/ml) (45%), tumor necrosis factor (TNF)-alpha (50 ng/ml) (34%), epidermal growth factor (10 ng/ml) (54%), phorbol myristate acetate (10 nM) (70%), IL-4 (10 ng/ml) (50%), IL-8 (100 ng/ml) (72%) and Activin A (25 ng/ml) (32%). Whether this degree of change in promoter activity leads to physiologically relevant alterations in the amounts of PGHS-1 present in cells remains to be determined.

Tumour necrosis factor-alpha regulation of prostaglandin H synthase-2 transcription is not through nuclear factor-kappaB in amnion-derived AV-3 cells

Tumour necrosis factor (TNF)-alpha-stimulated prostaglandin (PG) E(2)biosynthesis by amnion-derived AV3 cells is accompanied by increased prostaglandin H synthase (PGHS)-2 mRNA expression. PGHS-1 mRNA expression is unchanged. PGHS-2 promoter-reporter constructs (-891/+9 and 5' deletions thereof) were prepared. The regions containing concensus nuclear factor kappaB (NF-kappaB) elements (-447/-438 and -222/-213) did not enhance promoter activity. Elements associated with both basal and TNF-alpha-stimulated expression lie between bases -52 and -203. Site-directed mutagenesis of nuclear factor of interleukin-6 (NF-IL6) and cyclic AMP response elements (CREs) in this region reduced both basal and induced transcriptional activity of the -203/+9 construct by over 95 per cent. Electrophoretic mobility-shift assays using oligonucleotides derived from these sites demonstrated formation of specific DNA-protein complexes. Both NF-IL6 and CRE unlabelled oligonucleotides inhibited complex formation with the NF-IL6 oligonucleotide probe. Unlabelled CRE oligonucleotide also effectively inhibited formation of the complex with the CRE probe, but reduced effectiveness was observed when the NF-IL6 oligonucleotide was the competitor. Finally, unlabelled, consensus NF-kappaB oligonucleotide failed to compete for either probe. TNF-alpha treatment did not increase levels of these complexes. Thus NF-kappaB does not enhance basal or TNF-alpha-responsive PGHS-2 transcription in amnion-derived AV-3 cells. A permissive role for NF-IL6/CRE binding proteins in regulating PGHS-2 expression in these cells is indicated, but requires further clarification.

Expression of cytosolic and secreted forms of phospholipase A(2) and cyclooxygenases in human placenta, fetal membranes, and chorionic cell lines

Lipid mediators play a crucial role in human parturition and phospholipase A(2) (PLA(2)) is a key regulator of the production of these compounds. We have investigated by PCR the expression of different groups of PLA(2) and COX enzymes in human fetal membranes (amnion and chorion), placenta and three chorionic cell lines (JEG-3, Jar, BeWo). Our data show that the cytosolic Group IV PLA(2) and COX-1 are expressed in all of them, whereas the secretory forms of PLA(2), (Groups IIA, and V), have a more restricted expression. Group IIA mRNA is most abundant in placenta and chorion, whereas Group V PLA(2) mRNA is most abundant in placenta and amnion. On the other hand, COX-2 is present in placenta, chorion and amnion, but was not detected in any of the chorionic cell lines. These results suggest that both cytosolic and distinct secreted forms of PLA(2) could be involved in arachidonic acid (AA) release preceding prostaglandin production at the fetal/maternal interface.

Cytokine-induced coordinate expression of enzymes of prostaglandin biosynthesis and metabolism: 15-hydroxyprostaglandin dehydrogenase

The effects of pro-inflammatory cytokines on 15-hydroxyprostaglandin dehydrogenase (PGDH) expression and prostaglandin (PG) metabolizing activity were investigated in placental tissue. Treatment of trophoblast cells in primary culture with interleukin-1beta (IL-1beta) or tumour necrosis factor-alpha (TNF-alpha) resulted in decreased prostaglandin metabolizing activity. This was assessed both by determining the ratio of production of prostaglandins to their metabolites, and by Northern blot analysis of PGDH mRNA abundance. Dexamethasone had similar inhibitory effect. We hypothesize that proinflammatory cytokines act to enhance prostaglandin actions through coordinated effects on activities of enzymes of both prostaglandin biosynthesis and metabolism, perhaps in concert with effects on receptor function.