Alterations in the pro-resolving lipid mediator machinery within first trimester maternal tissue: Implications in decidualization and miscarriage risk

A pivotal event in uterine receptivity and human reproduction is the differentiation of endometrial stromal cells into decidual cells, known as decidualization. Decidualization is interlinked with its inflammatory environment. Our study aimed to investigate the presence and role of pro-resolving lipid mediators in first trimester maternal tissue. We assessed the levels of LXA4 and RvD1, along with their metabolic LOX enzymes, in elective (control) and sporadic miscarriage samples. We investigated the effects of LXA4 and RvD1 on decidualization using primary endometrial stromal cells and the immortalized endometrial stromal St-T1b cell line. The upregulation of 12- and 15-LOX expression was observed in pregnancy tissue after sporadic miscarriage, suggesting an inflammatory imbalance. Furthermore, incubation with these lipid mediators led to a decrease in decidualization biomarkers PRL and IGFBP-1, accompanied by morphological changes indicative of aberrant differentiation. The expression of LOX enzymes in decidual natural killer cells suggests their involvement in regulating the inflammatory surroundings and the extent of decidualization.

Lipoxin A4 interferes with embryo implantation via suppression of epithelial-mesenchymal transition

PROBLEM

To test whether lipoxin A4 (LXA4) interferes with embryo implantation via suppression of epithelial-mesenchymal transition (EMT).

METHOD OF STUDY

We developed a mouse model of LXA4 blocking embryo implantation and detected the indicators of EMT to confirm that LXA4 inhibits EMT might be a mechanism of interfering with the embryo implantation. We detected integrin-linked kinase (ILK), N-formylpeptide receptor 2 (FPR2), vascular endothelial growth factor, matrix metalloproteinases (MMPs), Akt, GSK3β, NF-ĸB, twist, vimentin, fibronectin, and β-catenin mRNA expression using reverse transcriptase-polymerase chain reaction (RT-PCR) and real-time RT-PCR; localized protein expression using immunohistochemistry and Western blotting assay; MMPs activity assay by gelatin zymography; and the status of implantation in pregnant animals assessed by pontamine blue reaction test.

RESULTS

Preimplantation administration of LXA4 resulted in implantation failure. LXA4 has a time- and dose-dependent effect on embryo implantation. Day 0.5 after fertilization is the most effective time to use LXA4 to block embryo implantation. (a) LXA4 reduced endometrial stroma edema; (b) LXA4 inhibited the activity of MMP9 and significantly upregulated the expression of β-catenin, and downregulated the expression of vimentin, fibronectin, twist, NF-κB, Akt, and Gsk-3β in the endometrium and TEV-1 cells; (c) LXA4 upregulated the expression of FPR2, and downregulated the expression of ILK; FPR2-overexpressing had an inhibitory effect on ILK in TEV-1 cells.

CONCLUSION

LXA4 inhibits EMT which attenuates ILK action by enhancing FPR2; therefore, this might be a mechanism of interfering with embryo implantation.

MRP4 regulates ENaC-dependent CREB/COX-2/PGE2 signaling during embryo implantation

Multi-drug resistance protein 4 (MRP4), a potential chemotherapeutic target as well as a transporter for endogenous signaling molecules (e.g. prostaglandins), is known to be expressed in the endometrium, although its possible role(s) in the physiology of the endometrium remains unknown. Here, we show that MRP4 is upregulated at implantation window and localized to the basolateral membrane of the endometrial epithelium, the interface between the epithelium and stroma in mice. In human endometrial epithelial cells, MRP4 expression is upregulated by ENaC activation and the inhibition of MRP4 blocks ENaC-dependent PGE₂ release as well as phosphorylation of CREB. Intrauterine injection of MRP4 inhibitor in mice prior to implantation significantly downregulated implantation markers COX-2, Claudin4 and Lif, and reduced implantation rate. These results in together have revealed a previously undefined role of MRP4 in mediating ENaC-dependent CREB/COX-2/PGE₂ signaling essential to embryo implantation with implication in cancer progression as well.

Protein Inhibitor of Activated STAT3 (PIAS3) Is Down-Regulated in Eutopic Endometrium of Women with Endometriosis

Endometriosis is a major cause of chronic pelvic pain and infertility. Activation of STAT3 appears central to the inflammatory phenotype of eutopic endometrium in women with endometriosis. However, the molecular mechanism by which this occurs remains unknown. Our objective is to determine how STAT3 activity is regulated in endometriosis. Protein inhibitor of activated STAT3 (PIAS3) is a negative regulator of STAT3 activity. We examined the levels of PIAS3 in endometrium from women with and without endometriosis using Western blot analysis and immunohistochemistry. Levels of PIAS3 are significantly lower, in contrast with phosphorylation of STAT3, in women with endometriosis compared to women without endometriosis. Furthermore, induction of endometriosis in the baboon showed a significant reduction of PIAS3 expression during the progression of the disease. Interferon-γ (INFγ) reduces PIAS3 protein levels and increases phospho-STAT3 levels through CXCL10 in endometrial cells, Ishikawa, and 12Z cells. These results suggest that attenuation of PIAS3 causes aberrant activation of STAT3 in endometriosis, leading to inflammatory changes that may impair fertility or cause pain.

Dynamic subcellular localization of estrogen receptor alpha during the first two cleavages of mouse preimplantation embryos

Zygotic gene activation (ZGA) is one of the most important events after mouse fertilization, but the mechanisms underpinning it are still unclear. Estrogen receptor alpha (ERα) is a versatile player in animal development. Our preliminary studies showed that ERα-specific antagonists blocked mouse 2-cell development and inhibited ZGA related gene expression, indicating an indispensable role of maternal ERα in early mouse preimplantation embryo development (PED). Here, we performed immunostaining detection to investigate the cell cycle specific subcellular localization of ERα, and serine 118 phosphorylated ERα (pERα-S118), during the first two cleavages of mouse PED. Our results showed that ERα nuclear localization appeared at 1-cell S-phase, disappeared at metaphase, and reappeared since the G1 phase of 2-cell embryos. Nuclear expression of pERα-S118 started at the 1-cell S-phase, but was absent at the G1 phase of 2-cell embryos, and reappeared since the 2-cell S-phase. Interestingly, pERα-S118 showed a dynamic expression pattern among nuclear, nuclear surface, cytoplasm and cell membrane. These results indicate that maternal derived ERα might still function in the first two cleavages of mouse PED, during which ZGA occurs.

The resolution code of acute inflammation: Novel pro-resolving lipid mediators in resolution

Studies into the mechanisms in resolution of self-limited inflammation and acute reperfusion injury have uncovered a new genus of pro-resolving lipid mediators coined specialized pro-resolving mediators (SPM) including lipoxins, resolvins, protectins and maresins that are each temporally produced by resolving-exudates with distinct actions for return to homeostasis. SPM evoke potent anti-inflammatory and novel pro-resolving mechanisms as well as enhance microbial clearance. While born in inflammation-resolution, SPM are conserved structures with functions discovered in microbial defense, pain, organ protection and tissue regeneration, wound healing, cancer, reproduction, and neurobiology-cognition. This review covers these SPM mechanisms and other new omega-3 PUFA pathways that open their path for functions in resolution physiology.

Aberrant activation of signal transducer and activator of transcription-3 (STAT3) signaling in endometriosis

STUDY QUESTION

Are STAT3 signaling molecules differentially expressed in endometriosis?

SUMMARY ANSWER

Levels of phospho-STAT3 and HIF1A, its downstream signaling molecule, are significantly higher in eutopic endometrium from women with endometriosis when compared with women without the disease.

WHAT IS KNOWN ALREADY

Endometriosis is an estrogen-dependent inflammatory condition. Interleukin 6 (IL-6) is an inflammatory survival cytokine known to induce prolonged activation of STAT3 via association with the IL-6 receptor.

STUDY DESIGN, SIZE, DURATION

Cross-sectional measurements of STAT3 and HIF1A protein levels in eutopic endometrium from women with endometriosis versus those without.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Levels of phospho-STAT3 (pSTAT3) and HIF1A were examined in the endometrium of patients with and without endometriosis as well as in a non-human primate animal model using western blot and immunohistochemical analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

Levels of pSTAT3 were significantly higher in the eutopic endometrium from women with endometriosis when compared with women without the disease in both the proliferative and secretory phases. HIF1A is known to be stabilized by STAT3 and IL-6. Our immunohistochemistry results show abundant HIF1A expression within the eutopic endometrial epithelial cells of women with endometriosis. Furthermore, pSTAT3 and HIF1A proteins are co-localized in endometriosis. This aberrant activation of pSTAT3 and HIF1A is confirmed by sequential analysis of eutopic endometrium using a baboon animal model of induced endometriosis. Lastly, we confirmed this IL-6 induction of both STAT3 phosphorylation and HIF1A mRNA expression in Ishikawa human endometrial adenocarcinoma cell line.

LIMITATIONS, REASONS FOR CAUTION

Ishikawa cancer cell line was used to study a benign disease. The peritoneal fluid contains various inflammatory cytokines in addition to IL-6 and so it is possible that other cytokines may affect the activity and expression of STAT3 signaling molecules.

WIDER IMPLICATIONS OF THE FINDINGS

Our results imply that aberrant activation of STAT3 signaling plays an important role in the pathogenesis of endometriosis. Our findings could progress in our understanding of the etiology and pathophysiology of endometriosis and potential therapeutic interventions by targeted pharmacological.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by NIH R01 HD067721 (to S.L.Y and B.A.L) and NIH R01 HD057873 and American Cancer Society Research Grant RSG-12-084-01-TBG (to J.-W.J.). There are no conflicts of interest.

15-epi-lipoxin A4 reduces the mortality of prematurely born pups in a mouse model of infection-induced preterm birth

Preterm birth remains the leading cause of neonatal mortality and morbidity worldwide. There are currently few effective therapies and therefore an urgent need for novel treatments. Although there is much focus on trying to alter gestation of delivery, the primary aim of preterm birth prevention therapies should be to reduce prematurity related mortality and morbidity. Given the link between intrauterine infection and inflammation and preterm labour (PTL), we hypothesized that administration of lipoxins, key anti-inflammatory and pro-resolution mediators, could be a useful novel treatment for PTL. Using a mouse model of infection-induced PTL, we investigated whether 15-epi-lipoxin A₄ could delay lipopolysaccharide (LPS)-induced PTL and reduce pup mortality. On D17 of gestation mice (n = 9–12) were pretreated with vehicle or 15-epi-lipoxin A₄ prior to intrauterine administration of LPS or PBS. Although pretreatment with 15-epi-lipoxin A₄ did not delay LPS-induced PTL, there was a significant reduction in the mortality amongst prematurely delivered pups (defined as delivery within 36 h of surgery) in mice treated with 15-epi-lipoxin A₄ prior to LPS treatment, compared with those receiving LPS alone (P < 0.05). Quantitative real-time (QRT)-PCR analysis of utero-placental tissues harvested 6 h post-treatment demonstrated that 15-epi-lipoxin A₄ treatment increased Ptgs2 expression in the uterus, placenta and fetal membranes (P < 0.05) and decreased 15-Hpgd expression (P < 0.05) in the placenta and uterus, suggesting that 15-epi-lipoxin A₄ may regulate the local production and activity of prostaglandins. These data suggest that augmenting lipoxin levels could be a useful novel therapeutic option in the treatment of PTL, protecting the fetus from the adverse effects of infection-induced preterm birth.

Glucocorticoids sensitize rat placental inflammatory responses via inhibiting lipoxin A4 biosynthesis

Inflammation dysregulation in placenta is implicated in the pathogenesis of numerous pregnancy complications. Glucocorticoids (GCs), universally considered anti-inflammatory, can also exert proinflammatory actions under some conditions, whereas whether and how GCs promote placental inflammation have not been intensively investigated. In this paper we report the opposing regulation of rat placental inflammation by synthetic GC dexamethasone (Dex). When Dex was subcutaneously injected 1 h after we administered an intraperitoneal lipopolysaccharide (LPS) challenge, neutrophil infiltration and proinflammatory Il1b, Il6, and Tnfa expression in rat placenta were significantly reduced. In contrast, Dex pretreatment for 24 h potentiated rat placental proinflammatory response to LPS and delayed inflammation resolution, which involved MAPKs and NF-kappaB activation. Mechanically, Dex pretreatment promoted 5-lipoxygenase (ALOX5) activation and increased leukotriene B4 production, whereas it inhibited the anti-inflammatory and proresolving lipid mediator lipoxin A4 (LXA4) biosynthesis in rat placenta via downregulating ALOX15 and ALOX15B expression. Moreover, LXA4 supplementation dampened Dex-potentiated placental inflammation and suppressed Dex-mediated ALOX5 activation in vivo and in vitro. Taken together, these findings suggest that GCs exposure could promote placental inflammation initiation and delay resolution via disrupting LXA4 biosynthesis.

Lipoxin A4: The double-edge sword in mice pregnancy

PROBLEM

To evaluate the role for LXA4 in the pregnancy.

METHOD OF STUDY

We detected the changes of LXA4 and LXA4 biosynthetic enzymes in the mice's pregnancy, blocked LXA4 signaling pathway, managed LXA4 level, and treated LPS-induced mouse abortion model to systematically determine how LXA4 impact pregnancy.

RESULTS

The concentrations of LXA4 in serum and uterus were lowest on Days 4.5 of pregnancy and in labor as compared to Day 12.5 of pregnancy (270.2 ± 33.2, 277.5 ± 23.7 versus 457.1 ± 40.9 pg/mL). Inhibition of the LXA4 signaling pathway did not affect pregnancy during the peri-implantation period of pregnancy, but induced abortion when administered after implantation of blastocysts. High levels of LXA4 interfered with implantation, but protected mice from aborting in response to LPS.

CONCLUSION

LXA4 might be involved in the process of pregnancy, and LXA4 might act as the double-edge sword in pregnancy: the anti-implantation effect in the stage of peri-implantation and the anti-abortion affect after blastocyst implantation.