Nrf2 Activation Inhibits Effects of Thrombin in Human Amnion Cells and Thrombin-Induced Preterm Birth in Mice

Role of Transcription Factors in the Management of Preterm Birth: Impact on Future Treatment Strategies

Preterm birth is defined as the birth of a neonate before 37 weeks of gestation and is considered as a leading cause of the under five deaths of neonates. Neonates born preterm are known to have higher perinatal mortality and morbidity with associated risks of low birth weight, respiratory distress syndrome, gastrointestinal, immunologic, central nervous system, hearing, and vision problems, cerebral palsy, and delayed development. India leads the list of countries with the greatest number of preterm births. The studies focusing on the molecular mechanisms related to the etiology of preterm birth have described the role of different transcription factors. With respect to this, transcription factors like peroxisome proliferator activated receptors (PPAR), nuclear factor kappa β (NF-kβ), nuclear erythroid 2-related factor 2 (Nrf2), and progesterone receptor (PR) are known to be associated with preterm labor. All these transcription factors are linked together with a common cascade involving inflammatory processes. Thus, the current review describes the possible cross-talk between these transcription factors and their therapeutic potential to prevent or manage preterm labor.

Stretch Causes Cell Stress and the Downregulation of Nrf2 in Primary Amnion Cells

Nuclear-factor-E2-related factor 2 (Nrf2) is a key transcription factor for the regulation of cellular responses to cellular stress and inflammation, and its expression is significantly lower after spontaneous term labor in human fetal membranes. Pathological induction of inflammation can lead to adverse pregnancy outcomes such as pre-eclampsia, preterm labor, and fetal death. As stretch forces are known to act upon the fetal membranes in utero, we aimed to ascertain the effect of stretch on Nrf2 to increase our understanding of the role of this stimulus on cells of the amnion at term. Our results indicated a significant reduction in Nrf2 expression in stretched isolated human amnion epithelial cells (hAECs) that could be rescued with sulforaphane treatment. Downregulation of Nrf2 as a result of stretch was accompanied with activation of proinflammatory nuclear factor-kB (NF-kB) and increases in LDH activity, ROS, and HMGB1. This work supports stretch as a key modulator of cellular stress and inflammation in the fetal membranes. Our results showed that the modulation of the antioxidant response pathway in the fetal membranes through Nrf2 activation may be a viable approach to improve outcomes in pregnancy.

Molecular and endocrine mechanisms involved in preterm birth

Preterm birth is a worldwide social problem. Incidence rates may vary from 5 to 18% of all deliveries, with important differences observed between developed and developing countries. Preterm birth has a negative impact on newborns and neonatal mortality and morbidity are high. Despite improvements in modern neonatal care, we know little of the mechanisms that determine the onset and development of preterm birth. Infections seem to be one the most important triggers, determining the activation of protective mechanisms aimed at ending the pregnancy and safeguarding the health of the woman. However, threatened preterm birth often occurs even in women who do not have any ongoing infectious process. Of these, which are the majority, the causes and the activation mechanisms remain unknown or unclear; however, there are several molecular and endocrine mechanisms that finally lead to preterm birth. In this review, we seek to shed light and summarize the molecular and endocrine mechanisms underlying the development of preterm birth. Their understanding could help us to understand the dynamics of premature birth but, above all, to allow an early diagnosis and primary prevention of the problem.

The role of nuclear factor erythroid 2-related factor 2 (NRF2) in normal and pathological pregnancy: A systematic review

OBJECTIVE

A homeostatic balance between reactive oxygen species production and the antioxidant redox system is an important component of normal pregnancy. Nuclear Factor Erythroid 2-Related Factor 2 (Nrf2) preserves cellular homeostasis by enhancing the cell's innate antioxidant status to reduce oxidative stress and inflammatory damage to the cell during pregnancy. Active Nrf2, in the nucleus of the cell, transactivates various antioxidant genes. The objective of this systematic review was to synthesize evidence on the role of Nrf2 in various adverse pregnancy outcomes (APOs).

METHODS

We conducted a systematic review of the role of Nrf2 in pregnancy. Articles written in English, Portuguese, and Spanish were obtained from three different databases from inception until January 2021. The titles, abstracts and full text were reviewed independently by six reviewers. The quality of the included studies was assessed using a quality assessment tool developed to assess basic science and clinical studies. Nrf2 expression (gene and protein), functional contributions, and association with APOs were assessed.

RESULTS

A total of 747 citations were identified; 80 were retained for full review. Most studies on Nrf2 have been carried out using placental tissues and placenta-derived cells. Limited studies have been conducted using fetal membranes, uterus, and cervix. Nuclear translocation of Nrf2 results in transactivation of antioxidant enzymes, including glutathione peroxidase, hemeoxygenase-1, and superoxide dismutase in gestational cells during pregnancy. This antioxidant response maintains cellular homeostasis during pregnancy. This promotes trophoblast cell survival and prevents cell death and abnormal angiogenesis in the placenta. Excessive and insufficient Nrf2 response may promote oxidative and reductive stress, respectively. This Nrf2 dysregulation has been associated with APOs including gestational diabetes mellitus, intrauterine growth restriction, reproductive toxicity, preeclampsia, and preterm birth.

CONCLUSION

Several studies have localized and reported an association between Nrf2's differential expression in reproductive tissues and the pathogenesis of APOs. However, a comprehensive functional understanding of Nrf2 in reproductive tissues is still lacking. Nrf2's activation and functions are complex, and therefore, current in vitro and in vivo studies are limited in their experimental approaches. We have identified key areas for future Nrf2 research that is needed to fill knowledge gaps.

Chronic abruption-oligohydramnios sequence (CAOS) revisited: possible implication of premature rupture of membranes

AIM

The pathogenic mechanism of chronic abruption-oligohydramnios sequence (CAOS) remains unknown, and there are no objective standards for diagnosis on imaging or using pathological evidence. We aimed to reconsider and clarify the true pathology of CAOS by integrating clinical, magnetic resonance imaging (MRI) and histopathological findings of the placenta.

MATERIAL AND METHODS

This is a case series of patients with CAOS managed at our hospital between 2010 and 2020. The clinical data of the patients, including MRI findings and placental pathology, were reviewed retrospectively.

RESULTS

A total of 18 patients were eligible. Preterm birth occurred in 17 (94%) cases; the median gestational age at delivery was 25. Three neonates (17%) died within two years, and 10 neonates (56%) developed chronic lung disease. MRI was performed in 13 cases and clearly showed intrauterine hematoma and hemorrhagic amniotic fluid. Pathologically, in all cases, retroplacental hematoma was not detected, and fetal membranes were extremely fragile and ragged. Shedding and necrosis of the amniotic epithelium was a characteristic finding, which was confirmed in 17 cases (94%). Diffuse chorionic hemosiderosis (DCH) was detected in all cases.

CONCLUSIONS

The fundamental cause of CAOS is repeated intrauterine hemorrhage and subsequent subchorionic hematoma, which induces hemorrhagic amniotic fluid and DCH. Consequently, these factors result in the necrosis and weakening of the amnion. Therefore, the true pathology of CAOS is believed to be premature rupture of membranes rather than chronic abruption.

Novel Insights into the Regulatory Role of Nuclear Factor (Erythroid-Derived 2)-Like 2 in Oxidative Stress and Inflammation of Human Fetal Membranes

Fetal membrane dysfunction in response to oxidative stress (OS) is associated with adverse pregnancy outcomes. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is one of the regulators of innate OS response. This study evaluated changes in Nrf2 expression and its downstream targets heme oxygenase (HO-1) and peroxisome proliferator-activated receptor gamma (PPARγ) in fetal membranes during OS and infection in vitro. Furthermore, we tested the roles of sulforaphane (SFN; an extract from cruciferous vegetables) and trigonelline (TRN; an aromatic compound in coffee) in regulating Nrf2 and its targets. Fetal membranes (n = 6) collected at term were placed in an organ explant system were treated with water-soluble cigarette smoke extract (CSE), an OS inducer (1:10), and lipopolysaccharide (LPS; 100 ng/mL). Nrf2 expression, expression, its enhancement by sulforaphane (SFN, 10 µM/mL) and down regulation by TRN (10uM/mL) was determined by western blots. Expression of Nrf2 response elements PPARγ (western) heme oxygenase (HO-1), and IL-6 were quantified by ELISA. CSE and LPS treatment of fetal membranes increased nrf2, but reduced HO-1 and PPARγ and increased IL-6. Co-treatment of SFN, but not with TRN, with CSE and LPS increased Nrf2 substantially, as well as increased HO-1 and PPARγ and reduced IL-6 expression. Risk factor-induced Nrf2 increase is insufficient to generate an antioxidant response in fetal membranes. Sulforaphane may enhance innate antioxidant and anti-inflammatory capacity by increasing NRF-2 expression.

Progestins Inhibit Interleukin-1β-Induced Matrix Metalloproteinase 1 and Interleukin 8 Expression via the Glucocorticoid Receptor in Primary Human Amnion Mesenchymal Cells

Preterm premature rupture of membranes is a leading cause of preterm births. Cytokine induced matrix metalloproteinase1 and interleukin 8 production from amnion mesenchymal cells may contribute to fetal membrane weakening and rupture. Progestins inhibit inflammation induced fetal membrane weakening but their effect on the inflammatory response of amnion mesenchymal cells is unknown. This study was designed to determine the role of progesterone receptor membrane component 1 and the glucocorticoid receptor in mediating the effects of progestins on interleukin-1β induced matrix metalloproteinase 1 and interleukin-8 expression in human amnion mesenchymal cells. Primary amnion mesenchymal cells harvested from human fetal membranes were passaged once and treated with vehicle, progesterone or medroxyprogesterone acetate at 10-6 M for 1 h followed by stimulation with interleukin-1β at 1 ng/ml for 24 h. Medroxyprogesterone acetate but not progesterone inhibited interleukin-1β-induced interlukin-8 and matrix metalloproteinase 1 mRNA expression. In subsequent dose response studies, medroxyprogesterone acetate, but not progesterone, at doses of 10-6-10-8 M inhibited interleukin-1β induced interleukin-8 and matrix metalloproteinase 1 mRNA expression. We further demonstrated that inhibition of glucocorticoid receptor expression, but not progesterone receptor membrane component 1 knockdown with small interfering RNA transfection, resulted in a reversal in medroxyprogesterone acetate's (10-7 M) inhibition of interleukin-1β- induced matrix metalloproteinase 1 mRNA expression and interleukin-8 mRNA expression and protein expression. Our findings demonstrate that medroxyprogesterone acetate exerts its anti-inflammatory effect primarily through the glucocorticoid receptor in human amnion mesenchymal cells. Modulation of glucocorticoid receptor signaling pathways maybe a useful therapeutic strategy for preventing inflammation induced fetal membrane weakening leading to preterm premature rupture of membranes.

Porphyromonas gingivalis, a cause of preterm birth in mice, induces an inflammatory response in human amnion mesenchymal cells but not epithelial cells

INTRODUCTION

Inflammation and infection, including dental infectious diseases, are factors that can induce preterm birth. We previously reported that mice with dental Porphyromonas gingivalis infection could be used as a model of preterm birth. In this model, cyclooxygenase (COX)-2 and interleukin (IL)-1β levels are increased, and P. gingivalis colonies are observed in the fetal membrane. However, the mechanism underlying fetal membrane inflammation remains unknown. Therefore, we investigated the immune responses of human amnion to P. gingivalis in vitro.

METHODS

Epithelial and mesenchymal cells were isolated from human amnion using trypsin and collagenase, and primary cell cultures were obtained. Confluent cells were stimulated with P. gingivalis lipopolysaccharide (P.g-LPS) or P. gingivalis. mRNA expressions of IL-1β, IL-8, IL-6 and COX-2, protein expressions of nuclear factor (NF)-κB pathway components and culture medium levels of prostaglandin E₂ were evaluated.

RESULTS

Following stimulation with 1 μg/mL P.g-LPS, the mRNA expression levels of IL-1β, IL-8, IL-6 and COX-2 in mesenchymal cells were increased 5.9-, 3.3-, 4.2- and 3.1-fold, respectively. Similarly, the expression levels of IL-1β, IL-8, IL-6 and COX-2 in mesenchymal cells were increased by 7.6-, 8.2-, 13.4- and 9.3-fold, respectively, after coculture with P. gingivalis. Additionally, stimulation with P.g-LPS or P. gingivalis resulted in the activation of NF-κB signaling and increased production of IL-1β and prostaglandin E₂. In contrast, no significant changes were observed in epithelial cells.

DISCUSSION

Our findings suggest that mesenchymal cells might mediate the inflammatory responses to P. gingivalis and P.g-LPS, thereby producing inflammation that contributes to the induction of preterm birth.

Mouse models of preterm birth: suggested assessment and reporting guidelines

Preterm birth affects approximately 1 out of every 10 births in the United States, leading to high rates of mortality and long-term negative health consequences. To investigate the mechanisms leading to preterm birth so as to develop prevention strategies, researchers have developed numerous mouse models of preterm birth. However, the lack of standard definitions for preterm birth in mice limits our field's ability to compare models and make inferences about preterm birth in humans. In this review, we discuss numerous mouse preterm birth models, propose guidelines for experiments and reporting, and suggest markers that can be used to assess whether pups are premature or mature. We argue that adoption of these recommendations will enhance the utility of mice as models for preterm birth.

Thrombin Alters Human Endometrial Stromal Cell Differentiation During Decidualization

Vaginal bleeding and subchorionic hematomas are associated with increased risk of both early and late pregnancy loss. Thrombin generation may play a pivotal role in the development of these complications. To determine the effects of thrombin on human endometrial stromal cells (hESCs), cells were treated with thrombin at baseline or during decidualization with cyclic adenosine monophosphate (cAMP)+medroxyprogesterone acetate (MPA). Next-generation RNA sequencing revealed that markers of decidualization (IGF-1, IGFBP-1, and prolactin [PRL]) were induced after the initiation of decidualization, whereas thrombin suppressed insulin-like growth factor ( IGF)-1, Insulin-like growth factor binding protein ( IGFBP)-1, and PRL gene expression at baseline and during decidualization. These effects were mediated through protease activated receptor (PAR)-1- and PAR-1-independent pathways. Thrombin decreased the secretion of a key marker of decidualization (PRL), altered the morphological transformation of decidualizing hESCs, and activated genes involved in matrix degradation and proinflammatory chemokines ( Interleukin-8 and Interleukin-6). Genes encoding factors important for matrix stability ( Col1α1, LOX) were suppressed. We suggest that intrauterine bleeding and generation of thrombin accentuates leukocyte extravasation and endometrial inflammation, impairs decidualization, and endometrial support of early pregnancy.

Rosiglitazone Regulates TLR4 and Rescues HO-1 and NRF2 Expression in Myometrial and Decidual Macrophages in Inflammation-Induced Preterm Birth

INTRODUCTION

Elevated inflammation accounts for approximately 30% of preterm birth (PTB) cases. We previously reported that targeting the peroxisome proliferator-activated receptor gamma (PPARγ) pathway reduced the incidence of PTB in the mouse model of endotoxin-induced PTB. The PPARγ has proven anti-inflammatory functions and its activation via rosiglitazone significantly downregulated the systemic inflammatory response and reduced PTB and stillbirth rate by 30% and 41%, respectively, in our model. Oxidative stress is inseparable from inflammation, and rosiglitazone has a reported antioxidative activity. In the current study, we therefore aimed to evaluate whether rosiglitazone treatment had effects outside of inflammatory pathway, specifically on the antioxidation pathway in our model.

METHODS

Pregnant C57BL/6J mice (E16.5) were treated with phosphate-buffered saline (PBS), rosiglitazone (Rosi), lipopolysaccharide (LPS; 10µg in 200µL 1XPBS), or LPS + Rosi (6 hours after the LPS injection). The myometrial and decidual tissues were collected and processed for macrophage isolation using magnetic cell sorting and F4/80+ antibody. Expression levels of antioxidative factors- Nrf2 and Ho-1-along with the LPS receptor Tlr4 were quantified by quantitative polymerase chain reaction. The protein levels were assessed by immunofluorescence staining.

RESULTS

Both the decidual and myometrial macrophages from the LPS-treated animals showed significantly lowered expression of Ho-1 and Nrf2 and higher expression of Tlr4 when compared to the PBS control group. The macrophages from the animals in the LPS + Rosi group had significantly elevated expression of Ho-1 and Nrf2 and downregulated expression of Tlr4 when compared to the LPS group.

CONCLUSION

Rosiglitazone administration prevents PTB by downregulating inflammation and upregulating antioxidative response.

Nrf2 regulates gene-environment interactions in an animal model of intrauterine inflammation: Implications for preterm birth and prematurity

Preterm birth (PTB) is the leading cause of neonatal mortality, and surviving infants are at increased risk for lifelong disabilities. Intrauterine inflammation is an etiological factor that drives PTB, and oxidative stress is associated with PTB. Nuclear erythroid 2-related factor 2 (Nrf2) is a redox-sensitive transcription factor that is the key regulator of the response to oxidative and inflammatory stress. Here, we used the established mouse model of intrauterine inflammation-induced PTB to determine whether Nrf2 is a modifier of susceptibility to PTB and prematurity-related morbidity and mortality in the offspring. We determined that Nr2-deficient (Nrf2^−/−) mice exhibited a greater sensitivity to intrauterine inflammation, as indicated by decreased time to delivery, reduced birthweight, and 100% mortality. Placentas from preterm Nrf2^−/− mice showed elevated levels of markers of inflammation, oxidative stress, and cell death, and transcriptomic analysis identified numerous key signaling pathways that were differentially expressed between wild-type (WT) and Nrf2^−/− mice in both preterm and control samples. Thus, Nrf2 could be a critical factor for gene-environment interactions that may determine susceptibility to PTB. Further studies are needed to determine if Nrf2 is a viable therapeutic target in women who are at risk for PTB and associated complications in the affected offspring.