Activated THP-1 Macrophage-Derived Factors Increase the Cytokine, Fractalkine, and EGF Secretions, the Invasion-Related MMP Production, and Antioxidant Activity of HEC-1A Endometrium Cells

Endometrium receptivity is a multifactor-regulated process involving progesterone receptor-regulated signaling, cytokines and chemokines, and additional growth regulatory factors. In the female reproductive system, macrophages have distinct roles in the regulation of receptivity, embryo implantation, immune tolerance, and angiogenesis or oxidative stress. In the present study, we investigated the effects of PMA-activated THP-1 macrophages on the receptivity-related genes, cytokines and chemokines, growth regulators, and oxidative stress-related molecules of HEC-1A endometrium cells. We established a non-contact co-culture in which the culture medium of the PMA-activated macrophages exhibiting the pro-inflammatory phenotype was used for the treatment of the endometrial cells. In the endometrium cells, the expression of the growth-related factors activin and bone morphogenetic protein 2, the growth hormone EGF, and the activation of the downstream signaling molecules pERK1/2 and pAkt were analyzed by ELISA and Western blot. The secretions of cytokines and chemokines, which are involved in the establishment of endometrial receptivity, and the expression of matrix metalloproteinases implicated in invasion were also determined. Based on the results, the PMA-activated THP-1 macrophages exhibiting a pro-inflammatory phenotype may play a role in the regulation of HEC-1A endometrium cells. They alter the secretion of cytokines and chemokines, as well as the protein level of MMPs of HEC-1A cells. Moreover, activated THP-1 macrophages may elevate oxidative stress protection of HEC-1A endometrium cells. All these suggest that pro-inflammatory macrophages have a special role in the regulation of receptivity-related and implantation-related factors of HEC-1A cells.

Menstrual blood-derived endometrial stem cell, a unique and promising alternative in the stem cell-based therapy for chemotherapy-induced premature ovarian insufficiency

Chemotherapy can cause ovarian dysfunction and infertility since the ovary is extremely sensitive to chemotherapeutic drugs. Apart from the indispensable role of the ovary in the overall hormonal milieu, ovarian dysfunction also affects many other organ systems and functions including sexuality, bones, the cardiovascular system, and neurocognitive function. Although conventional hormone replacement therapy can partly relieve the adverse symptoms of premature ovarian insufficiency (POI), the treatment cannot fundamentally prevent deterioration of POI. Therefore, effective treatments to improve chemotherapy-induced POI are urgently needed, especially for patients desiring fertility preservation. Recently, mesenchymal stem cell (MSC)-based therapies have resulted in promising improvements in chemotherapy-induced ovary dysfunction by enhancing the anti-apoptotic capacity of ovarian cells, preventing ovarian follicular atresia, promoting angiogenesis and improving injured ovarian structure and the pregnancy rate. These improvements are mainly attributed to MSC-derived biological factors, functional RNAs, and even mitochondria, which are directly secreted or indirectly translocated with extracellular vesicles (microvesicles and exosomes) to repair ovarian dysfunction. Additionally, as a novel source of MSCs, menstrual blood-derived endometrial stem cells (MenSCs) have exhibited promising therapeutic effects in various diseases due to their comprehensive advantages, such as periodic and non-invasive sample collection, abundant sources, regular donation and autologous transplantation. Therefore, this review summarizes the efficacy of MSCs transplantation in improving chemotherapy-induced POI and analyzes the underlying mechanism, and further discusses the benefit and existing challenges in promoting the clinical application of MenSCs in chemotherapy-induced POI.

Fractalkine Improves the Expression of Endometrium Receptivity-Related Genes and Proteins at Desferrioxamine-Induced Iron Deficiency in HEC-1A Cells

Fractalkine (CX3CL1/FKN) is a unique chemokine belonging to the CX3C chemokine subclass. FKN exists in two forms: a membrane-bound form expressed by both endometrium cells and trophoblasts thought to be implicated in maternal-fetal interaction and a soluble form expressed by endometrium cells. Endometrium receptivity is crucial in embryo implantation and a complex process regulated by large numbers of proteins, e.g., cytokines, progesterone receptor (PR), SOX-17, prostaglandin receptors (PTGER2), and tissue inhibitors of metalloproteinases (TIMPs). It has also been reported that iron is important in fertility and affects the iron status of the mother. Therefore, iron availability in the embryo contributes to fertilization and pregnancy. In this study, we focused on the effect of iron deficiency on the secreted cytokines (IL-6, IL-1β, leukocyte inhibitory factor, TGF-β), chemokines (IL-8, FKN), and other regulatory proteins (bone morphogenic protein 2, activin, follistatin, PR, SOX-17, prostaglandin E2 receptor, TIMP2), and the modifying effect of FKN on the expression of these proteins, which may improve endometrium receptivity. Endometrial iron deficiency was mediated by desferrioxamine (DFO) treatment of HEC-1A cells. FKN was added to the cells 24 h and 48 h after DFO with or without serum for modelling the possible iron dependence of the alterations. Our findings support the hypothesis that FKN ameliorates the effects of anemia on the receptivity-related genes and proteins in HEC-1A cells by increasing the secretion of the receptivity-related cytokines via the fractalkine receptor (CX3CR1). FKN may contribute to cell proliferation and differentiation by regulating activin, follistatin, and BMP2 expressions, and to implantation by altering the protein levels of PR, SOX-17, PTGER2, and TIMP2. FKN mitigates the negative effect of iron deficiency on the receptivity-related genes and proteins of HEC-1A endometrium cells, suggesting its important role in the regulation of endometrium receptivity.

Losartan impairs HTR-8/SVneo trophoblast migration through inhibition of angiotensin II-induced pro-inflammatory profile in human endometrial stromal cells

A deep interaction between the endometrium and the invading trophoblast occurs during implantation in humans, with the acquisition of uterine receptivity to the invading embryo promoted by an elevation of pro-inflammatory cytokines in the endometrium, and the invasiveness of decidualizing endometrial stromal cells, augmented by trophoblast-derived signals. Considering that usage of angiotensin II type 1 (AT1) receptor blockers, among other renin-angiotensin system (RAS) antagonists, is associated with adverse pregnancy outcomes, here we aim to analyse the involvement of AT1 receptor in the reciprocal dialogue occurring between endometrial stroma and trophoblast cells. In human endometrial stromal cells (T-HESC) pre-incubated with a decidualization cocktail, angiotensin (Ang) II increased protein expression of prolactin and FOXO1, markers of endometrial decidualization, while promoting nuclear translocation of FOXO1. In addition, Ang II treatment increased CXCL8, and matrix metalloprotease (MMP)-2 levels in T-HESC. Incubation with the AT1 receptor blocker losartan or with an NFAT signalling inhibitor, decreased Ang II-induced secretion of prolactin, CXCL8, and MMP-2 in T-HESC. In a wound healing assay, conditioned medium (CM) obtained from Ang II-treated T-HESC, but not CM from losartan-pre-incubated T-HESC, increased migration of HTR-8/SVneo trophoblasts, effect that was inhibited in the presence of a CXCL8-neutralizing antibody. An increased secretion of CXCL8 and MMP-2 was observed after treatment of T-HESC with CM obtained from HTR-8/SVneo cells, which was not observed in T-HESC pre-incubated with losartan or with the NFAT inhibitor. This study evidenced a reciprocal RAS-coded messaging between trophoblast and ESC which is affected by the AT1 receptor blocker losartan.

Modulation of Nod-like Receptor Expression in the Thymus during Early Pregnancy in Ewes

Nucleotide-binding oligomerization domain receptors (NOD-like receptors, NLRs) are involved in modulating the innate immune responses of the trophoblast and the placenta in normal pregnancy. The thymus participates in regulation of innate and adaptive immune responses. However, it is unclear whether expression of NLR is modulated in the maternal thymus during early pregnancy. In this study, thymuses were sampled at day 16 of the estrous cycle, and at days 13, 16 and 25 of gestation (n = 6 for each group) from ewes after slaughter. Different stages were chosen because the maternal thymus was under the different effects of interferon-tau and/or progesterone or not. RT-qPCR, Western blot and immunohistochemistry analysis were used to analyze the expression of the NLR family, including NOD1; NOD2; major histocompatibility complex class II transactivator (CIITA); NLR family apoptosis inhibitory protein (NAIP); nucleotide-binding oligomerization domain and Leucine-rich repeat and Pyrin domain containing protein 1 (NLRP1), NLRP3 and NLRP7. The results showed that expression level of NOD1 was changed with the pregnancy stages, and expression levels of NOD2, CIITA, NAIP, NLRP1, NLRP3 and NLRP7 mRNA and proteins were peaked at day 13 of pregnancy. The levels of NOD2 and CIITA were increased during early pregnancy. The stainings for NOD2 and NLRP7 proteins were located in epithelial reticular cells, capillaries and thymic corpuscles. In summary, pregnancy stages changed expression of NLR family in the maternal thymus, which may be related to the modulation of maternal thymic immune responses, and beneficial for normal pregnancy in sheep.

Inflammation-Related Molecules at the Maternal-Fetal Interface during Pregnancy and in Pathologically Altered Endometrium

The blastocyst expresses paternally derived alloantigens and induces inflammation during implantation. However, it is necessary for the onset of pregnancy. An abnormal response might result in a pathological course of pregnancy or pregnancy failure. On the other hand, a state of maternal immune tolerance is necessary to ensure the normal development of pregnancy by suppressing inflammatory processes. This article discusses recognized mechanisms and the significance of inflammatory processes for embryo implantation and pregnancy establishment. We would also like to present disorders involving excessive inflammatory response and their influence on events occurring during embryo implantation. The chain of correlation between the processes responsible for embryo implantation and the subsequent physiological course of pregnancy is complicated. Many of those interrelationships are still yet to be discovered. Undoubtedly, their recognition will give hope to infertile couples for the emergence of new treatments that will increase the chance of giving birth to a healthy child.

Benzo[a]pyrene exposure promotes RIP1-mediated necroptotic death of osteocytes and the JNK/IL-18 pathway activation via generation of reactive oxygen species

Benzo[a]pyrene (BaP) is a polycyclic aromatic hydrocarbon (PAH) of environmental pollutants, readily produced during the processing of petroleum and fatty foods. BaP exposure can cause skeletal deformities. However, whether BaP affects osteocytes, making up over 95% of all the bone cells, remains unknown. This study aimed to investigate the effect of BaP on osteocytes in vivo and in vitro, as well as explore the underlying mechanisms. The in vivo data showed that BaP (50mg/kg) exposure for 12 weeks could cause bone destruction, and increase osteocytes death in mouse cortical femur. Our in vitro results revealed that BaP (25-100 μmol/L) exposure inhibited cell viability of MLO-Y4 cells, and resulted in cell death in a dose-dependent manner. Furthermore, BaP exposure significantly triggered necroptosis of MLO-Y4 cells, as indicated by increased propidium iodide (PI)-positive cells and up-regulation of necroptosis-related protein expressions of receptor-interacting protein kinase 1 (RIP1), RIP3, and mixed lineage kinase domain-like protein (MLKL). This necrotic effect was reversed by the RIP1 inhibitor necrostatin-1 (Nec-1). Simultaneously, BaP activated the downstream c-Jun N-terminal kinase (JNK)/ interleukin (IL)-18 signaling pathway, which was suppressed after the JNK inhibitor SP600125 or Nec-1 treatment. In addition, BaP exposure promoted the production of intracellular reactive oxygen species (ROS), mitochondrial ROS (mtROS), and elevated malondialdehyde (MDA) levels; while BaP decreased superoxide dismutase (SOD) activity and antioxidant enzymes including nuclear factor E₂-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) levels, leading to oxidative damage. The ROS scavenger N-acetylcysteine (NAC) inhibited this necroptotic death and the JNK/IL-18 pathway activation. Collectively, BaP exposure may cause RIP1-mediated necroptotic death of osteocytes and activate the JNK/IL-18 pathway via ROS generation.

A review of key cytokines based on gene polymorphism in the pathogenesis of pre-eclampsia

Although a number of theories have been suggested, including roles for oxidative stress, an abnormal maternal-fetal interface, and genetic and environmental factors, the etiopathology of pre-eclampsia (PE) remains unclear. Maternal immune tolerance is important for maintaining pregnancy, and researchers have increasingly focused on the critical roles of cytokines in the pathogenesis of PE in recent years. The assessment of candidate genetic polymorphisms in PE could partially elucidate the mechanisms of susceptibility to disease, and contribute to seeking for new diagnosis and treatment methods of PE. PE can lead to severe complications, and even the death of both mother and fetus. Although the complex pathology is not yet clear, some evidence suggested that the occurrence of PE is related to inflammatory factors. We reviewed the current understandings of roles of cytokines in PE, and provided an extensive overview of the role of single nucleotide chain polymorphisms (SNPs) in the genes potentially underlying the pathophysiology of PE.

HDAC2-mediated proliferation of trophoblast cells requires the miR-183/FOXA1/IL-8 signaling pathway

Pre-eclampsia (PE) is a major cause of maternal and perinatal death. Previous research has indicated the role of histone deacetylase 2 (HDAC2) in the pathogenesis of PE but the relevant molecular mechanisms are unknown. However, there is hitherto little information concerning the molecular mechanism behind HDAC2 in PE. Herein, we hypothesized that HDAC2 promotes trophoblast cell proliferation and this requires the involvement of microRNA-183 (miR-183), forkhead box protein A1 (FOXA1), and interleukin 8 (IL-8). We collected placental specimens from 30 PE affected and 30 normal pregnant women. HDAC2 and FOXA1 were poorly expressed while miR-183 and IL-8 were highly expressed in placental tissues in PE. In vitro, HDAC2 overexpression enhanced the proliferation, migration, and invasion of human trophoblast cells HTR-8/SVNEO. HDAC2 inhibited the expression of miR-183 by diminishing H4 acetylation in the miR-183 promoter region. miR-183 inhibition by its specific inhibitor increased the expression of FOXA1 and thus enhanced HTR-8/SVNEO cell proliferation, migration, and invasion. FOXA1, a transcriptional factor, enhanced HTR-8/SVNEO cell proliferation, migration, and invasion by inhibiting the transcription of IL-8. We also observed HDAC2 knockdown was lost upon FOXA1 overexpression, suggesting that HDAC2 could promote HTR-8/SVNEO proliferation, migration, and invasion through the miR-183/FOXA1/IL-8 pathway. In summary, the results highlighted the role of the HDAC2/miR-183/FOXA1/IL-8 pathway in PE pathogenesis and thus suggest a novel molecular target for PE.

Receptor-interacting protein kinase 2 contributes to host innate immune responses against Fusobacterium nucleatum in macrophages and decidual stromal cells

PROBLEM

Chorioamnionitis is caused by a bacterial infection that ascends from the vagina and can cause adverse pregnancy outcomes (APOs). Fusobacterium nucleatum (F. nucleatum) is a periodontal pathogen associated with the occurrence of APOs. In this study, we evaluated whether receptor-interacting protein kinase 2 (Ripk2), an adaptor protein of the cytosolic receptors nucleotide-binding oligomerization domain (NOD)1 and NOD2, in macrophages and human decidual stromal cells (hDSCs) contributes to immune responses against F. nucleatum.

METHOD OF STUDY

Bone marrow-derived macrophages (BMDMs) isolated from wild-type (WT) and Ripk2-deficient mice and hDSCs were cultured with F. nucleatum (MOI 1, 10, 100). BMDMs and hDSCs were assessed using enzyme-linked immunosorbent assay, Western blot analysis, real-time PCR, and nitrite assay.

RESULTS

Fusobacterium nucleatum-induced production of IL-6, but not of TNF-α and IL-10, was lower in Ripk2-deficient BMDMs than in WT cells. Western blotting revealed a decrease in F. nucleatum-induced p65 phosphorylation in Ripk2-deficient macrophages, whereas mitogen-activated protein kinases activation was comparable between WT and Ripk2-deficient cells. The production of nitric oxide (NO) in response to F. nucleatum and the gene and protein expression of inducible NO synthase was impaired in Ripk2-deficient BMDMs. In hDSCs, F. nucleatum upregulated the gene and protein expression of NOD1, NOD2, and Ripk2 in a time-dependent manner. F. nucleatum also increased the production of IL-6, CXCL8, and CCL2, whereas this production was decreased by the Ripk2 inhibitors SB203580 and PP2.

CONCLUSIONS

In conclusion, Ripk2 signaling appears to contribute to the F. nucleatum-induced immune response and can be a preventive and therapeutic target against APOs.

Angiopoietin 2 stimulates trophoblast invasion via a mechanism associated with JNK signaling

Extravillous trophoblast cell (EVT) invasion is tightly controlled, and its dysregulation can lead to altered spiral artery remodeling and contribute to a number of different pregnancy complications. Angiopoietin-2 (Ang-2) is expressed by trophoblast cells and various cells in the decidua, and trophoblast cells express its receptor, Tie2. Ang-2 has been shown to play roles in tumor progression and metastasis but it is not known if it also regulates EVT invasion. Here, we show that both the HTR-8/SVneo cell line and primary isolates of human EVT expressed various integrins and the Tie2 receptor, and Ang-2 stimulated their migration and/or invasion. Ang-2 increased expression of matrix metalloproteinase (MMP)2 and MMP9, altered the cytoskeleton of HTR-8/SVneo cells and also induced phosphorylation of Tie2, JNK and c-Jun. Inhibition of p-JNK (using SP600125) blocked the Ang-2 induced invasion of HTR-8/SVneo cells. In addition, inhibition of Tie2 (pexmetinib) and integrin signaling (RGDS and ATN-161) also blocked Ang-2-induced invasion. In conclusion, we demonstrate that Ang-2 can stimulate EVT invasion via a mechanism associated with activation of both the Tie2 receptor and integrins, which appear to work through different pathways; Tie2 through the JNK/c-JUN pathway and integrins through an as yet unidentified pathway(s). We therefore propose that any alterations in Ang-2 expression in the decidua would lead to an imbalance in pro- and anti-invasive factors, disrupting regulation of EVT invasion and spiral artery remodeling and thereby contribute to the etiology of several complications of pregnancy.

Necroptosis regulates tumor repopulation after radiotherapy via RIP1/RIP3/MLKL/JNK/IL8 pathway

Background

Tumor cell repopulation after radiotherapy is a major cause for the tumor radioresistance and recurrence. This study aims to investigate the underlying mechanism of tumor repopulation after radiotherapy, with focus on whether and how necroptosis takes part in this process.

Methods

Necroptosis after irradiation were examined in vitro and in vivo. And the growth-promoting effect of necroptotic cells was investigated by chemical inhibitors or shRNA against necroptosis associated proteins and genes in in vitro and in vivo tumor repopulation models. Downstream relevance factors of necroptosis were identified by western blot and chemiluminescent immunoassays. Finally, the immunohistochemistry staining of identified necroptosis association growth stimulation factor was conducted in human colorectal tumor specimens to verify the relationship with clinical outcome.

Results

Radiation-induced necroptosis depended on activation of RIP1/RIP3/MLKL pathway, and the evidence in vitro and in vivo demonstrated that the inhibition of necroptosis attenuated growth-stimulating effects of irradiated tumor cells on living tumor reporter cells. The JNK/IL-8 were identified as downstream molecules of pMLKL during necroptosis, and inhibition of JNK, IL-8 or IL-8 receptor significantly reduced tumor repopulation after radiotherapy. Moreover, the high expression of IL-8 was associated with poor clinical prognosis in colorectal cancer patients.

Conclusions

Necroptosis associated tumor repopulation after radiotherapy depended on activation of RIP1/RIP3/MLKL/JNK/IL-8 pathway. This novel pathway provided new insight into understanding the mechanism of tumor radioresistance and repopulation, and MLKL/JNK/IL-8 could be developed as promising targets for blocking tumor repopulation to enhance the efficacy of colorectal cancer radiotherapy.

SIRT1 negatively regulates invasive and angiogenic activities of the extravillous trophoblast

PROBLEM

Dysregulation of extravillous trophoblast (EVT) invasion leads to pregnancy complications, such as pre-eclampsia, fetal growth restriction, and placenta accreta. The aim of this study was to explore the role of SIRT1 in EVT invasion and its underlying mechanism.

METHOD OF STUDY

SIRT1-specific siRNA was transfected into Swan 71 cells, an immortalized first trimester trophoblast cell line. The Boyden chamber invasion assay, the scratch wound healing assay, and cell proliferation assay were performed. The expression levels of epithelial-to-mesenchymal transition (EMT) markers, matrix metalloproteinase-2 (MMP-2), MMP-9, p-Akt, Akt, p-p38MAPK, p38MAPK, p-ERK, ERK, p-JNK, JNK, Fas, and Fas ligand (FasL) were examined by western blot. Tube formation assay was conducted by using Matrigel.

RESULTS

SIRT1 knockdown by siRNA significantly enhanced invasion and migration as well as the expression of MMP-2, MMP-9, and EMT markers in Swan 71 cells, but reduced proliferation. The effects of SIRT1 knockdown on invasion, migration, proliferation, and endothelial-like tube formation in Swan 71 cells were reversely regulated by blockade of Akt and p38MAPK signaling. In addition, SIRT1 knockdown markedly promoted colocalization of Swan 71 cells to human umbilical vein endothelial cell (HUVEC) networks and induced reduction in Fas and enhancement of FasL. Conditioned media of SIRT1 knockdown-Swan 71 cells caused reduction in cell proliferation and augmentation of cytotoxicity along with increased Fas expression in HUVECs.

CONCLUSION

Our results suggest that SIRT1 may be associated with placental development by controlling EVT invasion and spiral artery remodeling via modulation of EMT, MMP-2, MMP-9, Akt/p38MAPK signaling, and Fas/FasL.

Low-Dose Aspirin May Prevent Trophoblast Dysfunction in Women With Chlamydia Pneumoniae Infection

OBJECTIVE

Previously, we demonstrated that live Chlamydia pneumoniae (Cp) impaired extravillous trophoblast (EVT) viability and invasion and that Cp DNA was detected in placentas from cases with preeclampsia. We sought to elucidate whether (1) inactive forms of Cp also affect EVT function; (2) potential therapeutic interventions protect against the effects of Cp; and (3) anti-Cp antibodies are associated with preeclampsia.

METHODS

Human first-trimester EVTs were infected with ultraviolet light-inactivated Cp. Subgroups of EVTs were pretreated with low-dose acetyl-salicylic acid (ASA), dexamethasone, heparin, and indomethacin. We conducted functional assays after infection with inactivated Cp and measured interleukin 8 (IL8), C-reactive protein (CRP), heat shock protein 60 (HSP60), and tumor necrosis factor-α (TNFα) in culture media. We measured anti-Cp IgG serum levels from women who developed preeclampsia (N = 105) and controls (N = 121).

RESULTS

Inactivated Cp reduced EVT invasion when compared to noninfected cells (P < .00001) without adversely affecting cell viability. Increased levels of IL8, CRP, HSP60, and TNFα were detected in EVTs infected with inactivated Cp compared to noninfected cells (P < .0001). Only pretreatment with low-dose ASA prevented reduced EVT invasion and decreased release of inflammatory mediators (P < .01). Elevated anti-Cp IgG antibodies were more prevalent in serum from cases with preeclampsia compared to controls (67/105 vs 53/121; adjusted P = .013); elevated IgG correlated significantly with elevated serum CRP and elevated soluble fms-like tyrosine kinase-1-placental growth factor ratio.

CONCLUSION

Inactivated Cp induces decreased EVT invasion and a proinflammatory response; these effects were abrogated by pretreatment with low-dose ASA. Our results suggest an association between Cp infection, trophoblast dysfunction, and preeclampsia.

Trichlorfon inhibits proliferation and promotes apoptosis of porcine trophectoderm and uterine luminal epithelial cells

Trichlorfon is an organophosphate insecticide widely used in agriculture. Additionally, it is applied to pigs for control of endo- and ectoparasites. Previous studies have shown the effects of trichlorfon in pigs during late stages of gestation; however, little is known about its effects during early pregnancy, including implantation and placentation. We investigated whether trichlorfon affects proliferation and apoptosis of porcine trophectoderm (pTr) and uterine luminal epithelial (pLE) cells. Trichlorfon inhibited the proliferation of pTr and pLE cells, as evidenced by cell cycle arrest, and altered the expression of proliferation-related proteins. In addition, trichlorfon induced cell death and apoptotic features, such as loss of mitochondrial membrane potential and DNA fragmentation, in pTr and pLE cells. Moreover, trichlorfon treatment decreased concentrations of Ca²⁺ in the cytoplasm in both cell lines and increased concentrations of Ca²⁺ in mitochondria of pTr cells. Trichlorfon inhibited the activation of phosphoinositide 3-kinase/AKT and mitogen-activated protein kinase signaling pathways in pTr and pLE cells. Therefore, we suggest that trichlorfon-treated pTr and pLE cells exhibited abnormal cell physiology which might lead to early pregnancy failure.