SMAD7 regulates proinflammatory and prolabor mediators in amnion and myometrium

Pathophysiological Implication of Pattern Recognition Receptors in Fetal Membranes Rupture: RAGE and NLRP Inflammasome

Preterm prelabor ruptures of fetal membranes (pPROM) are a pregnancy complication responsible for 30% of all preterm births. This pathology currently appears more as a consequence of early and uncontrolled process runaway activation, which is usually implicated in the physiologic rupture at term: inflammation. This phenomenon can be septic but also sterile. In this latter case, the inflammation depends on some specific molecules called “alarmins” or “damage-associated molecular patterns” (DAMPs) that are recognized by pattern recognition receptors (PRRs), leading to a microbial-free inflammatory response. Recent data clarify how this activation works and which receptor translates this inflammatory signaling into fetal membranes (FM) to manage a successful rupture after 37 weeks of gestation. In this context, this review focused on two PRRs: the receptor for advanced glycation end-products (RAGE) and the NLRP7 inflammasome.

Transcriptional control of parturition: insights from gene regulation studies in the myometrium

The onset of labour is a culmination of a series of highly coordinated and preparatory physiological events that take place throughout the gestational period. In order to produce the associated contractions needed for foetal delivery, smooth muscle cells in the muscular layer of the uterus (i.e. myometrium) undergo a transition from quiescent to contractile phenotypes. Here, we present the current understanding of the roles transcription factors play in critical labour-associated gene expression changes as part of the molecular mechanistic basis for this transition. Consideration is given to both transcription factors that have been well-studied in a myometrial context, i.e. activator protein 1, progesterone receptors, oestrogen receptors, and nuclear factor kappa B, as well as additional transcription factors whose gestational event-driving contributions have been demonstrated more recently. These transcription factors may form pregnancy- and labour-associated transcriptional regulatory networks in the myometrium to modulate the timing of labour onset. A more thorough understanding of the transcription factor-mediated, labour-promoting regulatory pathways holds promise for the development of new therapeutic treatments that can be used for the prevention of preterm labour in at-risk women.

GIT2 deficiency attenuates inflammation-induced expression of pro-labor mediators in human amnion and myometrial cells†

Untimely activation of the inflammatory response by sterile or infective insults in uterine tissues can result in preterm birth. Pro-inflammatory cytokines and pathogenic activation of toll-like receptors (TLRs) initiate a biochemical cascade of events leading to myometrial activation and contractility, cervical dilatation, and rupture of the chorioamniotic membranes. GIT2 is a signaling protein known to play a role in innate and adaptive immunity; however, its role in the inflammatory pathways of human labor is not known. In this article, we report that GIT2 expression is lower in human myometrium and fetal membranes with term labor, and in preterm amnion with histological chorioamnionitis. GIT2 knockdown by siRNA in primary myometrial and amnion cells exhibited reduced expression of pro-inflammatory cytokines and chemokines in response to inflammatory challenge by cytokines or TLR ligands. In addition, the pro-inflammatory cytokines IL1B and TNF could not induce the expression of extracellular matrix degrading enzymes in GIT2-deficient amnion cells. Myometrial activation in response to pro-inflammatory cytokines was also significantly suppressed in GIT2-deficient cells as evidenced by decreased prostaglandin release and expression of contraction-associated proteins. Further to this, collagen gel assays demonstrated that TNF had a reduced ability to induce myometrial contractility in situ in GIT2-deficient myometrial cells compared to control-transfected cells. In summary, the loss of GIT2 diminishes the effects inflammatory mediators have in promoting myometrial contraction and fetal membrane rupture in vitro, suggesting that GIT2 could be a possible target for preterm birth therapies.

Identification of SMAD3 as a Novel Mediator of Inflammation in Human Myometrium In Vitro

Preterm birth remains the primary cause of early neonatal death and is a major determinant for long-term health consequences. Aberrant intrauterine inflammation and infection are known to augment the synthesis of proinflammatory cytokines and induce uterine contractions, which can subsequently lead to preterm birth. The transforming growth factor-β (TGF-β) superfamily members regulate numerous cellular processes through the activation of intracellular mediators known as mothers against decapentaplegic homolog (SMADs). Studies in nongestational tissues have shown that SMAD3 plays a role in immune regulation and inflammation; however, its role in human labour remains unknown. Thus, the present study aimed at (i) characterising the expression of SMAD3 in the human myometrium; (ii) determining the effect of bacterial and viral products and proinflammatory cytokines on SMAD3 transcriptional activity in primary human myometrial cells; and (iii) investigating the effect of SMAD3 siRNA knockdown on the production of prolabour mediators in primary human myometrial cells. Phosphorylated (i.e., active) SMAD3 protein expression was lower in the myometrium after spontaneous term labour compared to the myometrium from nonlabouring women. Using a luciferase assay, the proinflammatory cytokines IL-1β and TNF, and viral analogue polyinosinic : polycytidylic acid (poly(I : C)) significantly reduced SMAD3 transcriptional activity in human primary myometrial cells. Loss-of-function studies found that SMAD3 knockdown in myometrial cells significantly increased IL-1β- and poly(I : C)-induced proinflammatory cytokines (IL-1A, IL-6), chemokines (IL-8, MCP-1), the adhesion molecule ICAM-1, COX-2 mRNA expression, and subsequent PGF2α release. In conclusion, SMAD3 deficiency is associated with increased production of proinflammatory and prolabour mediators in the human myometrium.

DREAM Is Involved in the Genesis of Inflammation-Induced Prolabour Mediators in Human Myometrial and Amnion Cells

Preterm birth is the primary cause of perinatal morbidity and mortality worldwide. Inflammation induces a cascade of events leading to preterm birth by activating nuclear factor-κB (NF-κB). In nongestational tissues, downstream regulatory element antagonist modulator (DREAM) regulates NF-κB activity. Our aims were to analyse DREAM expression in myometrium and fetal membranes obtained at term and preterm and to determine the effect of DREAM inhibition on prolabour mediators in primary myometrial and amnion cells. DREAM mRNA expression was significantly higher in fetal membranes obtained after spontaneous labour compared to nonlabour and in amnion from women with histological preterm chorioamnionitis when compared to amnion from women without chorioamnionitis. In primary myometrial and amnion cells, the effect of DREAM silencing by siRNA was a significant decrease in the expression of proinflammatory cytokine IL-6, the chemokines IL-8 and MCP-1, the adhesion molecule ICAM-1, MMP-9 mRNA expression and activity, and NF-κB transcriptional activity when stimulated with the proinflammatory cytokine IL-1β, the bacterial products fsl-1 or flagellin, or the viral dsRNA analogue poly(I:C). These data suggest that, in states of heightened inflammation, DREAM mRNA expression is increased and that, in myometrial and amnion cells, DREAM regulates proinflammatory and prolabour mediators which may be mediated via NF-κB.