Perivascular interleukin-8 messenger ribonucleic acid expression in human endometrium varies across the menstrual cycle and in early pregnancy decidua

Biomarkers in abnormal uterine bleeding†

Abnormal uterine bleeding (AUB) is an extremely common problem and represents a clinical area of unmet need. It has clinical implications and a high cost for the healthcare system. The PALM-COEIN acronym proposed by FIGO may be used as a foundation of care; it improves the understanding of the causes of AUB, and in doing so facilitates effective history taking, examination, investigations, and management. Heavy menstrual bleeding, a subset of AUB, is a subjective diagnosis and should be managed in the context of improving the woman's quality of life. Available evidence suggests that there is poor satisfaction with standard treatment options often resulting in women opting for major surgery such as hysterectomy. Such women would benefit from a tailored approach, both for diagnosis and treatment, highlighting the deficiency of biomarkers in this area. This article focuses on the causes of AUB as per the PALM-COEIN acronym, the researched biomarkers in this area, and the potential pathogenetic mechanisms. In the future, these approaches may improve our understanding of AUB, thereby enabling us to direct women to most suitable current treatments and tailor investigative and treatment strategies to ensure best outcomes, in keeping with the principles of personalized or precision medicine.

Endometrial apoptosis and neutrophil infiltration during menstruation exhibits spatial and temporal dynamics that are recapitulated in a mouse model

Menstruation is characterised by synchronous shedding and restoration of tissue integrity. An in vivo model of menstruation is required to investigate mechanisms responsible for regulation of menstrual physiology and to investigate common pathologies such as heavy menstrual bleeding (HMB). We hypothesised that our mouse model of simulated menstruation would recapitulate the spatial and temporal changes in the inflammatory microenvironment of human menses. Three regulatory events were investigated: cell death (apoptosis), neutrophil influx and cytokine/chemokine expression. Well-characterised endometrial tissues from women were compared with uteri from a mouse model (tissue recovered 0, 4, 8, 24 and 48 h after removal of a progesterone-secreting pellet). Immunohistochemistry for cleaved caspase-3 (CC3) revealed significantly increased staining in human endometrium from late secretory and menstrual phases. In mice, CC3 was significantly increased at 8 and 24 h post-progesterone-withdrawal. Elastase+ human neutrophils were maximal during menstruation; Ly6G+ mouse neutrophils were maximal at 24 h. Human endometrial and mouse uterine cytokine/chemokine mRNA concentrations were significantly increased during menstrual phase and 24 h post-progesterone-withdrawal respectively. Data from dated human samples revealed time-dependent changes in endometrial apoptosis preceding neutrophil influx and cytokine/chemokine induction during active menstruation. These dynamic changes were recapitulated in the mouse model of menstruation, validating its use in menstrual research.

Inflammation, leukocytes and menstruation

Menstruation has many of the features of an inflammatory process. The complexity and sequence of inflammatory-type events leading to the final tissue breakdown and bleeding are slowly being unravelled. Progesterone has anti-inflammatory properties, and its rapidly declining levels (along with those of estrogen) in the late secretory phase of each non-conception cycle, initiates a sequence of interdependent events of an inflammatory nature involving local inter-cellular interactions within the endometrium. Intracellular responses to loss of progesterone (in decidualized stromal, vascular and epithelial cells) lead to decreased prostaglandin metabolism and loss of protection from reactive oxygen species (ROS). Increased ROS results in release of NFκB from suppression with activation of target gene transcription and increased synthesis of pro-inflammatory prostaglandins, cytokines, chemokines and matrix metalloproteinases (MMP). The resultant leukocyte recruitment, with changing phenotypes and activation, provide further degradative enzymes and MMP activators, which together with a hypoxic environment induced by prostaglandin actions, lead to the tissue breakdown and bleeding characteristic of menstruation. In parallel, at sites where shedding is complete, microenvironmentally-induced changes in phenotypes of neutrophils and macrophages from pro- to anti-inflammatory, in addition to induction of growth factors, contribute to the very rapid re-epithelialization and restoration of tissue integrity.

Granulocytes and vascularization regulate uterine bleeding and tissue remodeling in a mouse menstruation model

Menstruation-associated disorders negatively interfere with the quality of life of many women. However, mechanisms underlying pathogenesis of menstrual disorders remain poorly investigated up to date. Among others, this is based on a lack of appropriate pre-clinical animal models. We here employ a mouse menstruation model induced by priming mice with gonadal hormones and application of a physical stimulus into the uterus followed by progesterone removal. As in women, these events are accompanied by menstrual-like bleeding and tissue remodeling processes, i.e. disintegration of decidualized endometrium, as well as subsequent repair. We demonstrate that the onset of bleeding coincides with strong upregulation of inflammatory mediators and massive granulocyte influx into the uterus. Uterine granulocytes play a central role in regulating local tissue remodeling since depletion of these cells results in dysregulated expression of matrix modifying enzymes. As described here for the first time, uterine blood loss can be quantified by help of tampon-like cotton pads. Using this novel technique, we reveal that blood loss is strongly reduced upon inhibition of endometrial vascularization and thus, is a key regulator of menstrual bleeding. Taken together, we here identify angiogenesis and infiltrating granulocytes as critical determinants of uterine bleeding and tissue remodeling in a mouse menstruation model. Importantly, our study provides a technical and scientific basis allowing quantification of uterine blood loss in mice and thus, assessment of therapeutic intervention, proving great potential for future use in basic research and drug discovery.

Global gene expression profiling of proliferative phase endometrium reveals distinct functional subdivisions

The human endometrium follows a predictable pattern of development during the proliferative phase. Endometrial thickness increases after day 3 and then plateaus at days 9 to 10 of the menstrual cycle despite continued high serum levels of estrogen. We hypothesized that proliferative phase endometrium undergoes more than simple estrogen responsive growth, rather it is characterized by complex time-dependent functional activities reflected in differential gene expression. Nine endometrial RNA samples from healthy participants were subjected to microarray analysis and 15 samples were used for quantitative real-time polymerase chain reaction. The samples were divided into early, mid, or late proliferative phase. The early proliferative phase showed higher expression of genes including transforming growth factor β2, chemokine (C-C motif) ligand 18 (CCL18), and metallothionein 2A. The mid-proliferative phase was characterized by higher expression of heat shock proteins and implantation-associated genes including Indian hedgehog, secreted frizzled protein 4, and progesterone receptor. In the late proliferative phase, we identified increased angiotensin II receptor, type 2 and large decrease in expression of genes related to natural killer (NK) cell function. We demonstrate a unique gene expression signature at distinct time points within the proliferative phase. The early proliferative phase is characterized by tissue remodeling, angiogenesis, and modulation of inflammation; the mid-proliferative phase is characterized not only by proliferation in response to estrogens but also marks the onset of expression of genes required for endometrial receptivity and a dampening of estrogen responsiveness. In the late proliferative phase, changes in immune function and NK cells predominate. The proliferative phase is not simply a uniform period of estrogen responsive endometrial growth that can be considered as a single experimental time point when evaluating endometrial development; rather the proliferative phase is complex with differing functions and patterns of gene expression.

Global alteration in gene expression profiles of deciduas from women with idiopathic recurrent pregnancy loss

Recurrent pregnancy loss (RPL) occurs in ∼5% of women. However, the etiology is still poorly understood. Defects in decidualization of the endometrium during early pregnancy contribute to several pregnancy complications, such as pre-eclampsia and intrauterine growth restriction (IUGR), and are believed to be important in the pathogenesis of idiopathic RPL. We performed microarray analysis to identify gene expression alterations in the deciduas of idiopathic RPL patients. Control patients had one antecedent term delivery, but were undergoing dilation and curettage for current aneuploid miscarriage. Gene expression differences were evaluated using both pathway and gene ontology (GO) analysis. Selected genes were validated using quantitative reverse transcription-polymerase chain reaction (qRT-PCR). A total of 155 genes were found to be significantly dysregulated in the deciduas of RPL patients (>2-fold change, P < 0.05), with 22 genes up-regulated and 133 genes down-regulated. GO analysis linked a large percentage of genes to discrete biological functions, including immune response (23%), cell signaling (18%) and cell invasion (17.1%), and pathway analysis revealed consistent changes in both the interleukin 1 (IL-1) and IL-8 pathways. All genes in the IL-8 pathway were up-regulated while genes in the IL-1 pathway were down-regulated. Although both pathways can promote inflammation, IL-1 pathway activity is important for normal implantation. Additionally, genes known to be critical for degradation of the extracellular matrix, including matrix metalloproteinase 26 and serine peptidase inhibitor Kazal-type 1, were also highly up-regulated. In this first microarray approach to decidual gene expression in RPL patients, our data suggest that dysregulation of genes associated with cell invasion and immunity may contribute significantly to idiopathic recurrent miscarriage.

Novel roles for hypoxia and prostaglandin E2 in the regulation of IL-8 during endometrial repair

The endometrium has a remarkable capacity for efficient repair; however, factors involved remain undefined. Premenstrual progesterone withdrawal leads to increased prostaglandin (PG) production and local hypoxia. Here we determined human endometrial expression of interleukin-8 (IL-8) and the roles of PGE(2) and hypoxia in its regulation. Endometrial biopsy specimens (n = 51) were collected. Endometrial cells and explants were exposed to 100 nmol/L of PGE(2) or 0.5% O(2). The endometrial IL-8 concentration peaked during menstruation (P < 0.001) and had a significant proangiogenic effect. IL-8 was increased by PGE(2) and hypoxia in secretory but not proliferative explants, which suggests that exposure to progesterone is essential. In vitro progesterone withdrawal induced significant IL-8 up-regulation in proliferative explants primed with progestins, but only in the presence of hypoxia. Epithelial cells treated simultaneously with PGE(2) and hypoxia demonstrated synergistic increases in IL-8. Inhibition of HIF-1 by short hairpin RNA abolished hypoxic IL-8 induction, and inhibition of NF-κB by an adenoviral dominant negative inhibitor decreased PGE(2)-induced IL-8 expression (P > 0.05). Increased menstrual IL-8 is consistent with a role in repair. Progesterone withdrawal, hypoxia, and PGE(2) regulate endometrial IL-8 by acting via HIF-1 and NF-κB. Hence, progesterone withdrawal may activate two distinct pathways to initiate endometrial repair.

TGFβ1 attenuates expression of prolactin and IGFBP-1 in decidualized endometrial stromal cells by both SMAD-dependent and SMAD-independent pathways

BACKGROUND

Decidualization (differentiation) of the endometrial stromal cells during the secretory phase of the menstrual cycle is essential for successful implantation. Transforming Growth Factor β1 (TGFβ1) canonically propagates its actions via SMAD signalling. A role for TGFβ1 in decidualization remains to be established and published data concerning effects of TGFβ1 on markers of endometrial decidualization are inconsistent.

METHODOLOGY/PRINCIPAL FINDINGS

Non-pregnant endometrial stromal cells (ESC) and first trimester decidual stromal cells (DSC) were cultured in the presence or absence of a decidualizing stimulus. Incubation of ESCs with TGFβ1 (10 ng/ml) down-regulated the expression of transcripts encoding the decidual marker proteins prolactin (PRL), insulin-like growth factor binding protein-1 (IGFBP-1) and tissue factor (TF). TGFβ1 also inhibited secretion of PRL and IGFBP-1 proteins by ESCs and surprisingly this response preceded down-regulation of their mRNAs. In contrast, DSCs were more refractory to the actions of TGFβ1, characterized by blunted and delayed down-regulation of PRL, IGFBP-1, and TF transcripts, which was not associated with a significant reduction in secretion of PRL or IGFBP-1 proteins. Addition of an antibody directed against TGFβ1 increased expression of IGFBP-1 mRNA in decidualised cells. Knockdown of SMAD 4 using siRNAs abrogated the effect of TGFβ1 on expression of PRL in ESCs but did not fully restore expression of IGFBP-1 mRNA and protein.

CONCLUSIONS/SIGNIFICANCE

TGFβ1 inhibits the expression and secretion of decidual marker proteins. The impact of TGFβ1 on PRL is SMAD-dependent but the impact on IGFBP1 is via an alternative mechanism. In early pregnancy, resistance of DSC to the impact of TGFβ1 may be important to ensure tissue homeostasis.

Expression and regulation of c-Jun N-terminal kinase (JNK) in endometrial cells in vivo and in vitro

JNK(c-Jun N-terminal kinase) is one of the main types of mitogen-activated protein kinases. JNK modulates inflammation and apoptosis in response to stress. Our hypothesis is that temporal and spatial changes in JNK activity regulate inflammation in human endometrium and that fluctuation in estrogen and progesterone levels may play a role in JNK activation. Therefore, we aimed to determine total-(t-) and active-(phosphorylated, p-) JNK expression in endometrial tissues in vivo by immunohistochemistry, and in vitro by immunocytochemistry and Western blot analysis. Immunohistochemistry revealed moderate cytoplasmic and nuclear t-JNK immunoreactivity, and mostly nuclear p-JNK immunoreactivity throughout the menstrual cycle and early pregnancy. The highest p- and t-JNK immunoreactivity was detected in late secretory phase (P < 0.05). We observed that endometrial stromal cell (ESC)s showed a significant increase in p-JNK expression following 48 h of estrogen combined with progesterone (E(2) + P(4)) withdrawal from the culture conditions, compared to control and non-withdrawal groups (P < 0.05). Upon treatment with JNK inhibitor SP600125, we observed a significantly decreased interleukin (IL)-8 level (P < 0.05) in the presence and absence of E(2). These results demonstrate that JNK expression increases during the late secretory phase when the inflammatory response is highest. Inhibition of IL-8 expression by SP600125 suggests that JNK is involved in regulation of proinflammatory mediators of endometrium.

A critical period of progesterone withdrawal precedes menstruation in macaques

Macaques are menstruating nonhuman primates that provide important animal models for studies of hormonal regulation in the uterus. In women and macaques the decline of progesterone (P) at the end of the cycle triggers endometrial expression of a variety of matrix metalloproteinase (MMP) enzymes that participate in tissue breakdown and menstrual sloughing. To determine the minimal duration of P withdrawal required to induce menses, we assessed the effects of adding P back at various time points after P withdrawal on both frank bleeding patterns and endometrial MMP expression. Artificial menstrual cycles were induced by treating the animals sequentially with implants releasing estradiol (E2) and progesterone (P). To assess bleeding patterns, P implants were removed at the end of a cycle and then added back at 12, 24, 30, 36, 40, 48, 60, or 72 hours (h) after the initial P withdrawal. Observational analysis of frank bleeding patterns showed that P replacement at 12 and 24 h blocked menses, replacement at 36 h reduced menses but replacement after 36 h failed to block menses. These data indicate that in macaques, a critical period of P withdrawal exists and lasts approximately 36 h. In other similarly cycled animals, we withdrew P and then added P back either during (12-24 h) or after (48 h) the critical period, removed the uterus 24 h after P add back and evaluated endometrial MMP expression. Immunocytochemistry showed that replacement of P during the critical period suppressed MMP-1, -2 and -3 expression along with menses, but replacement of P at 48 h, which failed to suppress mense, suppressed MMP-1 and MMP-3 but did not block MMP-2. We concluded that upregulation of MMPs is essential to menses induction, but that after the critical period, menses will occur even if some MMPs are experimentally blocked.

Interleukin-8 can stimulate progesterone secretion from a human trophoblast cell line, BeWo

Precise paracrine cross-talk between the embryo and the endometrium is essential for the establishment of a successful pregnancy. Previous studies have demonstrated that the expression of interleukin-8 (IL-8) in the endometrium is enhanced during the late-secretory phase and early pregnancy. Furthermore, IL-8 receptor (IL-8R) expression has been detected in trophoblast cells of the developing embryo. To clarify the roles of IL-8 in the endometrium-embryo interactions, the effects of IL-8 on hormone secretion by trophoblast cells were studied using the BeWo trophoblast cell line that retains hormone-secreting properties of normal trophoblast cells. Using reverse transcription-polymerase chain reaction, we found that IL-8R messenger ribonucleic acid (mRNA) was expressed in BeWo cells. The levels of IL-8R mRNA and protein expression in BeWo cells were similar to those in primary first-trimester trophoblast cells. Progesterone (P4) secretion of BeWo cells was comparable with that of first-trimester trophoblast cells but higher than that of third-trimester trophoblast cells. Treatment of BeWo cells with recombinant human IL-8 (rhIL-8) had no effect on cell proliferation, as determined by the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay. Interestingly, secretion of P4, but not human chorionic gonadotropin, from cultured BeWo cells was significantly enhanced when the cells were incubated with rhIL-8. Our results demonstrate that IL-8 may play an important role in the endometrium-embryo interactions by stimulating trophoblast secretion of P4 for maintenance of a successful pregnancy.