Anti-phospholipid antibodies increase non-apoptotic trophoblast shedding: a contribution to the pathogenesis of pre-eclampsia in affected women?

Antiphospholipid-exposed trophoblast-derived extracellular vesicles express elevated levels of TLR7/8-activating microRNAs and induce endometrial endothelial activation, in part, through TLR7

Women with antiphospholipid syndrome (APS) are at high risk for miscarriage and preeclampsia. Unlike pro-thrombotic systemic APS, obstetric APS is associated with insufficient placentation, as well as inflammation and vascular dysfunction at the maternal-fetal interface. Antiphospholipid antibodies (aPL) can target the placental trophoblast and induce inflammation. We reported that aPL trigger trophoblast cells to produce elevated levels of IL-8 through activation of Toll-like receptor 4 (TLR4). Downstream of TLR4, we found this IL-8 response is mediated by a TLR8-activating microRNA (miR), miR-146a-3p, which is also released by the trophoblast via extracellular vesicles (EVs). Since endothelial dysfunction is a feature of obstetric APS, we sought to determine if other miRs that can activate the RNA sensors, TLR7 and/or TLR8, are released by the trophoblast via EVs after exposure to aPL, and if these EVs can activate human endometrial endothelial cells (HEECs). Using a human first trimester extravillous trophoblast cell line we found that aPL elevated their release of small EVs (<150 nm). These extracellular vesicles released from trophoblast cells exposed to aPL expressed elevated levels of TLR7/8-activating miR-21a and miR-29a, in addition to the previously reported miR-146a-3p. Extracellular vesicles from aPL-exposed human trophoblast cells triggered human endometrial endothelial cells to generate an inflammatory IL-8 response, in part through TLR7. This study highlights EVs as a mode of communication between the placenta and the maternal vasculature, as well as a potential role for TLR7/8-activating miRs in contributing to inflammation at the maternal-fetal interface in obstetric APS.

The pathogenesis of obstetric APS: a 2023 update

The antiphospholipid syndrome (APS) is an autoimmune disease characterized by the persistent presence of antibodies directed against phospholipids and phospholipid-binding proteins that are associated with thrombosis and pregnancy-related morbidity. The latter includes fetal deaths, premature birth and maternal complications. In the early 1990s, a distinct set of autoantibodies, termed collectively antiphospholipid antibodies (aPL), were identified as the causative agents of this disorder. Subsequently histological analyses of the placenta from APS pregnancies revealed various abnormalities, including inflammation at maternal-fetal interface and poor placentation manifested by reduced trophoblast invasion and limited uterine spiral artery remodeling. Further preclinical investigations identified the molecular targets of aPL and the downstream intracellular pathways of key placental cell types. While these discoveries suggest potential therapeutics for this disorder, definitive clinical trials have not been completed. This concise review focuses on the recent developments in the field of basic and translational research pursuing novel mechanisms underlying obstetric APS.

Trophoblast Cell Function in the Antiphospholipid Syndrome

Antiphospholipid syndrome (APS) is a complex thrombo-inflammatory autoimmune disease characterized by the presence of antiphospholipid antibodies (aPL). Women with APS are at high risk of recurrent early pregnancy loss as well as late obstetrical complications-premature birth due to placental insufficiency or severe preeclampsia. Accumulating evidence implies that vascular thrombosis is not the only pathogenic mechanism in obstetric APS, and that the direct negative effect of aPL on the placental cells, trophoblast, plays a major role. In this review, we summarize the current findings regarding the potential mechanisms involved in aPL-induced trophoblast dysfunction. Introduction on the APS and aPL is followed by an overview of the effects of aPL on trophoblast-survival, cell function and aPL internalization. Finally, the implication of several non-coding RNAs in pathogenesis of obstetric APS is discussed, with special emphasis of their possible role in trophoblast dysfunction and the associated mechanisms.

Treatment of Refractory/High-Risk Pregnancies With Antiphospholipid Syndrome: A Systematic Review of the Literature

Different treatment protocols have been employed to manage heparin/low-dose aspirin refractory or high-risk pregnancies in antiphospholipid antibody syndrome (APS) pregnancies. A systematic review of the literature on additional treatments used in refractory and/or high-risk APS pregnancies was conducted. Records from February 2006 to October 2021 were retrieved from PubMed, Web of Science, Cochrane, and the www.clinicaltrials.gov platform. Twenty-one studies met our eligibility criteria. Live birth rate is this study’s primary endpoint, while pregnancy complications and adverse events are secondary endpoints. A total of 434 pregnancies, 162 (37.3%) refractory and 272 (62.7%) high-risk/refractory pregnancies, were included. Both IVIG &lt;2 gr/kg/monthly/HCQ/LDS and PEX/IA ± LDS led to 100% viable infants in refractory APS. Furthermore, HCQ 200–400 mg showed a higher live birth rate than HCQ + LDS (88.6% vs. 82.7%). Following treatment protocol with HCQ 200–400 mg and IVIG &lt;2 gr/kg/monthly/HCQ/LDS, pregnancy complications rates of 16.7 and 83.3% were registered, respectively. Pravastatin 20 mg, IA weekly + IVIG 2 gr/monthly, and PEX weekly + IVIg 2 gr/kg/monthly showed higher live birth rates in high-risk APS pregnancies of 100, 100 and 92%, respectively, whereas the lower severe pregnancy complications were reported in pregnancies treated with PEX weekly + IVIg 2 gr/kg/monthly (11.1%). One (0.6%) case of dermatitis during treatment with HCQ was observed. The results of this study showed that HCQ 200–400 mg and PEX weekly + IVIG 2 gr/kg/monthly achieved a higher live birth rate in refractory APS and high-risk/refractory APS, respectively. The results presented provide clinicians with up-to-date knowledge in the management of APS pregnancies according to risk stratification.

Antiphospholipid antibodies do not cause retargeting of placental extracellular vesicles in the maternal body

Antiphospholipid antibodies (aPL) are autoantibodies that cause pregnancy disorders by a poorly defined mechanism that involves the placenta. The human placenta is covered by a single multinucleated cell, the syncytiotrophoblast, which extrudes vast numbers of extracellular vesicles (EVs) into the maternal blood. Extracellular vesicles are tiny packages of cellular material used by cells for remote signalling. In normal pregnancy, placental EVs assist maternal adaptations to pregnancy. We have previously shown that aPL alter the cargo of placental EVs, increasing the load of danger signals. These changes in EV cargo may explain how aPL contribute to the increased risk of recurrent miscarriage, preeclampsia and stillbirths observed in aPL-affected pregnancies. An additional possibility, that aPL alters the targeting of placental EVs to maternal organs to cause maternal maladaptation to pregnancy was investigated in this study.

Effects of anti-beta 2-glycoprotein 1 antibodies and its association with pregnancy-related morbidity in antiphospholipid syndrome

Antiphospholipid syndrome (APS) is an autoimmune disease characterized by venous, arterial, or small-vessel thrombosis and/or pregnancy-related morbidity, associated with persistent positivity of antiphospholipid antibodies (aPL). Pregnancy-related morbidity in APS patients is characterized by unexplained fetal deaths, premature birth of morphologically normal newborns, and/or consecutive pregnancy losses before the 10^th week of gestation. Beta 2-glycoprotein 1 (ß2GP1) is the main antigen recognized by aPL and plays an essential role in the pathogenesis of APS. Antibodies against ß2GP1 (aß2GP1) are involved in damage-generating mechanisms in APS due to their interaction with trophoblasts, decidua, and endothelial cells. aß2GP1 might be used as a prognostic tool for obstetric risk stratification and ß2GP1 could be a target for molecular-targeted treatment to prevent pregnancy morbidity in APS. This review describes these aspects of aß2GP1, including effects on different cellular targets, its association with the severity of obstetric manifestations and the potential of ß2GP1-targeted therapies for APS.

Obstetric anti-phospholipid syndrome: from pathogenesis to treatment

Antiphospholipid syndrome (APS) is an autoimmune disease characterized by clinical manifestations such as thrombosis and obstetric complications with documented persistence of antiphospholipid antibodies (aPLs). Recent studies have revealed that the cause of aPL-related obstetric complications is dysfunction of placental trophoblasts and inflammation of the maternal-fetal interface induced by aPLs, not thrombosis. Although aPLs are associated with recurrence of serious complications during pregnancy, appropriate combination therapy with heparin and low-dose aspirin can improve the course of 70-80% of subsequent pregnancies. Preconception counseling and patient-tailored treatment are fundamental to improving maternal and fetal outcomes. Non-anticoagulant treatments such as hydroxychloroquine and statins are being developed for cases refractory to conventional treatment. Risk factors for thrombosis after pregnancy complications were identified based on the analysis of large databases of obstetric APS.

Comparison of treatments for the prevention of fetal growth restriction in obstetric antiphospholipid syndrome: a systematic review and network meta-analysis

Women with criteria and non-criteria obstetric antiphospholipid syndrome (APS) carry an increased risk of pregnancy complications, including fetal growth restriction (FGR). The management of obstetric APS traditionally involves clinicians, obstetricians and gynaecologists; however, the most appropriate prophylactic treatment strategy for FGR prevention in APS is still debated. We performed a systematic review and network meta-analysis (NetMA) to summarize current evidence on pharmacological treatments for the prevention of FGR in APS. We searched PubMed and Embase from inception until July 2020, for randomized controlled trials and prospective studies on pregnant women with criteria or non-criteria obstetric APS. NetMA using a frequentist framework were conducted for the primary outcome (FGR) and for secondary outcomes (fetal or neonatal death and preterm birth). Adverse events were narratively summarised. Out of 1124 citations, we included eight studies on 395 pregnant patients with obstetric APS treated with low-dose aspirin (LDA) + unfractionated heparin (UFH) (n = 132 patients), LDA (n = 115), LDA + low molecular weight heparin (n = 100), LDA + corticosteroids (n = 29), LDA + UFH + intravenous immunoglobulin (n = 7), or untreated (n = 12). No difference among treatments emerged in terms of FGR prevention, but estimates were largely imprecise, and most studies were at high/unclear risk of bias. An increased risk of fetal or neonatal death was found for LDA monotherapy as compared to LDA + heparin, and for no treatment as compared to LDA + corticosteroids. The risk of preterm birth was higher for LDA + UFH + IVIg as compared to LDA or LDA + heparin, and for LDA + corticosteroids as compared to LDA or LDA + LMWH. No treatment was associated with an increased risk of bleeding, thrombocytopenia or osteopenia.

Melatonin, a Potential Therapeutic Agent for Preeclampsia, Reduces the Extrusion of Toxic Extracellular Vesicles from Preeclamptic Placentae

Preeclampsia, characterised by maternal endothelial cell activation, is triggered by toxic factors, such as placental extracellular vesicles (EVs) from a dysfunctional placenta. The increased oxidative stress seen in the preeclamptic placenta links to endoplasmic reticulum (ER) stress. The ER regulates protein folding and trafficking. When the ER is stressed, proteins are misfolded, and misfolded proteins are toxic. Misfolded proteins can be exported from cells, via EVs which target to other cells where the misfolded proteins may also be toxic. Melatonin is a hormone and antioxidant produced by the pineal gland and placenta. Levels of melatonin are reduced in preeclampsia. In this study we investigated whether melatonin treatment can change the nature of placental EVs that are released from a preeclamptic placenta. EVs were collected from preeclamptic (n = 6) and normotensive (n = 6) placental explants cultured in the presence or absence of melatonin for 18 h. Misfolded proteins were measured using a fluorescent compound, Thioflavin-T (ThT). Endothelial cells were exposed to placental EVs overnight. Endothelial cell activation was measured by the quantification of cell-surface ICAM-1 using a cell-based ELISA. EVs from preeclamptic placentae carried significantly (p < 0.001) more misfolded proteins than normotensive controls. Incubating preeclamptic placental explants in the presence of melatonin (1 µM and 10 µM) significantly (p < 0.001) reduced the misfolded proteins carried by EVs. Culturing endothelial cells in the presence of preeclamptic EVs significantly increased the expression of ICAM-1. This increased ICAM-1 expression was significantly reduced when the endothelial cells were exposed to preeclamptic EVs cultured in the presence of melatonin. This study demonstrates that melatonin reduces the amount of misfolded proteins carried by EVs from preeclamptic placentae and reduces the ability of these EVs to activate endothelial cells. Our study provides further preclinical support for the use of melatonin as a treatment for preeclampsia.

Extracellular Vesicles and Antiphospholipid Syndrome: State-of-the-Art and Future Challenges

Antiphospholipid syndrome (APS) is a systemic autoimmune disorder characterized by thromboembolism, obstetric complications, and the presence of antiphospholipid antibodies (aPL). Extracellular vesicles (EVs) play a key role in intercellular communication and connectivity and are known to be involved in endothelial and vascular pathologies. Despite well-characterized in vitro and in vivo models of APS pathology, the field of EVs remains largely unexplored. This review recapitulates recent findings on the role of EVs in APS, focusing on their contribution to endothelial dysfunction. Several studies have found that APS patients with a history of thrombotic events have increased levels of EVs, particularly of endothelial origin. In obstetric APS, research on plasma levels of EVs is limited, but it appears that levels of EVs are increased. In general, there is evidence that EVs activate endothelial cells, exhibit proinflammatory and procoagulant effects, interact directly with cell receptors, and transfer biological material. Future studies on EVs in APS may provide new insights into APS pathology and reveal their potential as biomarkers to identify patients at increased risk.

Antiphospholipid antibodies and extracellular vesicles in pregnancy

Antiphospholipid antibodies (aPL) are autoantibodies that target phospholipid-binding proteins, such as β2 glycoprotein I (β2GPI), and can induce thrombosis systemically, as well as increase the risk of obstetric complications such as recurrent miscarriage and preeclampsia. Due to the expression of β2GPI by placental trophoblasts, aPL readily target the maternal-fetal interface during pregnancy and many studies have investigated the deleterious effects of aPL on placental trophoblast function. This review will focus on studies that have examined the effects of aPL on the production and modification of extracellular vesicles (EVs) from trophoblasts, as EVs are a key mode of feto-maternal communication in both normal and pathological pregnancy. A more comprehensive understanding of the effects of aPL on the quantity and cargo of EVs extruded by the human placenta may contribute to our current knowledge of how aPL induce both systemic and obstetric disease.

Antiphospholipid antibodies can specifically target placental mitochondria and induce ROS production

Women with antiphospholipid antibodies (aPL) have increased risks of pregnancy complications, including a ten-fold increased risk of preeclampsia, which is potentially triggered by the release of placental toxins. Previously, aPL were shown to enter the outer layer of the placenta, the syncytiotrophoblast, associate with mitochondria, and alter mitochondrial function. We hypothesised that aPL may also increase mitochondrial reactive oxygen species (ROS) production, leading to cellular dysfunction and release of toxins. First trimester placental explants were incubated with monoclonal aPL, ID2 and IIC5 (25, 50, and 100 μg/mL), for 3 h at 37 °C and ROS production followed using CellROX Deep Red. In addition, the candidate treatment compounds chloroquine, melatonin, and Mito-Q were tested at therapeutic concentrations for their ability to prevent ROS production. Mitochondria isolated from term placentae were incubated with fluorescently-labelled ID2, IIC5, or control IgG antibodies (2.5, 5, 10, or 20 μg/mL) for 30 min, and mitochondria with bound antibodies were quantified using flow cytometry. In addition, respirometry coupled with fluorimetry was used to interrogate explant mitochondrial respiration and ROS production following incubation with 25, 50, or 100 μg/mL ID2, IIC5, or control IgG for 3 h at 37 °C. ID2 increased explant ROS production in a manner that was completely prevented by the endocytosis inhibitor chloroquine, and partially prevented by the antioxidants melatonin and Mito-Q. Both ID2 and IIC5 displayed a greater ability to bind isolated mitochondria than control antibodies, and increased ROS production attributable to the mitochondrial enzyme glycerol 3-phosphate dehydrogenase (mGPDH). Our evidence supports the hypothesis that aPL interact with syncytiotrophoblast mitochondria, likely via the binding of cardiolipin and β₂ glycoprotein I in mitochondrial membranes, and induce ROS production which contributes to overall oxidative stress and placental dysfunction.

MicroRNAs in Preeclampsia

Preeclampsia (PE) continues to represent a worldwide problem and challenge for both clinicians and laboratory-based doctors. Despite many efforts, the knowledge acquired regarding its pathogenesis and pathophysiology does not allow us to treat it efficiently. It is not possible to arrest its progressive nature, and the available therapies are limited to symptomatic treatment. Furthermore, both the diagnosis and prognosis are frequently uncertain, whilst the ability to predict its occurrence is very limited. MicroRNAs are small non-coding RNAs discovered two decades ago, and present great interest given their ability to regulate almost every aspect of the cell function. A lot of evidence regarding the role of miRNAs in pre-eclampsia has been accumulated in the last 10 years. Differentially expressed miRNAs are characteristic of both mild and severe PE. In many cases they target signaling pathway-related genes that result in altered processes which are directly involved in PE. Immune system, angiogenesis and trophoblast proliferation and invasion, all fundamental aspects of placentation, are controlled in various degrees by miRNAs which are up- or downregulated. Finally, miRNAs represent a potential therapeutic target and a diagnostic tool.

Harvesting and Characterization of Syncytial Nuclear Aggregates Following Culture of First Trimester Human Placental Explants

There is currently no effective method to study multinucleated trophoblast debris extruded from the syncytiotrophoblast into the maternal circulation. In Chapter 9 , an in vitro placental explant culture model to generate trophoblast debris was described. Here, we detail the method utilized to isolate individual large multinucleated syncytial nuclear aggregates (SNAs) that are extruded from the syncytiotrophoblast following the culture of first trimester human placental explants. Syncytial nuclear aggregates have been observed in the peripheral maternal circulation as early as 6 weeks' gestation and may play a role in tolerating the maternal immune system during pregnancy. Conversely, aberrant cell death processes in the syncytiotrophoblast due to various maternal factors leading to the extrusion of SNAs that are altered in nature have been implicated in the development of preeclampsia. The methods described herein allow for the isolation and harvest of SNAs without other types of extruded trophoblast debris and can be used to investigate the effect of various maternal factors on the nature of SNAs extruded from the placenta in vitro.

Antiphospholipid antibodies increase the levels of mitochondrial DNA in placental extracellular vesicles: Alarmin-g for preeclampsia

The pathogenesis of preeclampsia remains unclear but placental factors are known to play a crucial role causing maternal endothelial cell dysfunction. One potential factor is placental micro- and nano- vesicles. Antiphospholipid antibodies (aPL) increase the risk of preeclampsia ten-fold, in part by damaging the mitochondria in the syncytiotrophoblast. Since mitochondrial DNA (mtDNA) is a danger- associated molecular pattern (DAMP/alarmin) that may activate endothelial cells, the aims of the current study were to investigate whether aPL affect the number of placental vesicles extruded, their mtDNA content and their ability to activate endothelial cells. Exposure of first trimester human placental explants to aPL affected neither the number nor size of extruded micro- and nano- vesicles (n = 5), however their levels of mtDNA were increased (n = 6). These vesicles significantly activated endothelial cells (n = 5), which was prevented by blocking toll-like receptor 9 (TLR-9), a receptor for extracellular DNA. Thus, aPL may increase the risk of preeclampsia in part by increasing the amount of mtDNA associated with placental vesicles. That mitochondrial DNA is recognised as a DAMP by TLR-9 to cause endothelial cell activation, raises the possibility that placental vesicles or TLR-9 might be a target for pharmaceutical intervention to reduce the consequences of aPL in pregnancy.

Melatonin prevents preeclamptic sera and antiphospholipid antibodies inducing the production of reactive nitrogen species and extrusion of toxic trophoblastic debris from first trimester placentae

BACKGROUND

The exact cause of preeclampsia is unknown. However a "toxin" from the placenta triggers the condition via activation of the maternal endothelium. Extracellular vesicles (EVs) from the syncytiotrophoblast, may be an endothelial-activating toxin. Antiphospholipid antibodies (aPL) and preeclamptic sera both induce the production of endothelial cell-activating EVs by mechanisms which may produce excess free-radicals in the placenta. Melatonin is produced by the human placenta and has both direct and indirect anti-free-radical properties and may therefore counter the effects of aPL and preeclamptic sera.

METHODS

First trimester placental explants were exposed to preeclamptic sera or aPL in the presence or absence of melatonin. Nitrosylative damage was assessed in the explants by immunohistochemistry and the effect of EVs from these explants on endothelial cell activation determined by ICAM-1. Release of nitrosylated proteins from the explants was also measured.

RESULTS

Placental explants showed reduced secretion of melatonin after treatment with preeclamptic sera. Nitrosylated proteins were more abundant in placentae that had been treated with aPL or preeclamptic sera and EVs from such placentae induced endothelial cell activation. Adding melatonin to the aPL or preeclamptic sera reversed the protein nitrosylation and production of endothelial-activating EVs.

DISCUSSION

Our data are consistent with reports that the levels of circulating melatonin are reduced in preeclampsia and suggest that aPL and factors in preeclamptic sera induce free-radical-mediated damage in the placenta leading to the production of endothelial-activating EVs. Melatonin reversing production of endothelial-activating EVs indicates that melatonin may have therapeutic benefits in women with preeclampsia and/or aPL.

Do adverse pregnancy outcomes contribute to accelerated cardiovascular events seen in young women with systemic lupus erythematosus?

Cardiovascular events (CVEs) are prevalent in patients with systemic lupus erythematosus (SLE), and it is the young women who are disproportionately at risk. The risk factors for accelerated cardiovascular disease remain unclear, with multiple studies producing conflicting results. In this paper, we aim to address both traditional and SLE-specific risk factors postulated to drive the accelerated vascular disease in this cohort. We also discuss the more recent hypothesis that adverse pregnancy outcomes in the form of maternal-placental syndrome and resultant preterm delivery could potentially contribute to the CVEs seen in young women with SLE who have fewer traditional cardiovascular risk factors. The pathophysiology of how placental-mediated vascular insufficiency and hypoxia (with the secretion of placenta-like growth factor (PlGF) and soluble fms-tyrosine-like kinase-1 (sFlt-1), soluble endoglin (sEng) and other placental factors) work synergistically to damage the vascular endothelium is discussed. Adverse pregnancy outcomes ultimately are a small contributing factor to the complex pathophysiological process of cardiovascular disease in patients with SLE. Future collaborative studies between cardiologists, obstetricians, obstetric physicians and rheumatologists may pave the way for a better understanding of a likely multifactorial aetiological process.

Increased levels of HMGB1 in trophoblastic debris may contribute to preeclampsia

Preeclampsia is triggered by an as yet unknown toxin from the placenta. Antiphospholipid antibodies (aPL), a strong risk factor for preeclampsia, have been shown to induce the production of toxic trophoblastic debris from the placenta. High mobility group box 1 (HMGB1) is a proinflammatory danger signal, and the expression of it has been reported to be increased in preeclampsia. This study examined whether aPL or preeclamptic sera increase the expression of HMGB1 in the syncytiotrophoblast or trophoblastic debris. Trophoblastic debris from normal placental explants that had been cultured with aPL or preeclamptic sera was exposed to endothelial cells. Endothelial cell activation was quantified by cell-surface ICAM-1 expression and U937 monocyte adhesion. The expression of HMGB1 in placental explants and trophoblastic debris that had been treated with aPL or preeclamptic sera was measured by immunohistochemistry and western blotting. The expression of the receptor for advanced glycation end products (RAGE) in endothelial cells was quantified by western blotting. Compared with controls, the expression of HMGB1 in the cytoplasm of the syncytiotrophoblast and trophoblastic debris was increased by treating placental explants with aPL or preeclamptic sera. The increased levels of HMGB1 contributed to endothelial cell activation, mediated in part by the RAGE. Preeclamptic sera and aPL both induced an increase in the cytoplasmic levels of the danger signal HMGB1 in trophoblastic debris. This increased HMGB1 in trophoblastic debris may be one of the toxic factors released from the placenta in preeclampsia.

The role of anti-phospholipid antibodies in autoimmune reproductive failure

Anti-phospholipid antibodies (aPL) are autoantibodies that are associated with thrombosis and a range of pregnancy complications including recurrent pregnancy loss and pre-eclampsia. The three clinically relevant, well-characterized aPL are anti-cardiolipin antibodies, lupus anticoagulant and anti-beta-2-glycoprotein I (β2GPI) antibodies. aPL do not bind directly to phospholipids but instead bind to a plasma-binding ‘cofactor’. The most extensively studied cofactor is β2GPI, whose role in pregnancy is not fully elucidated. Although the pathogenicity of aPL in recurrent pregnancy loss is well established in humans and animal models, the association of aPL with infertility does not appear to be causative. aPL may exert their detrimental effects during pregnancy by directly binding trophoblast cells of the placenta, altering trophoblast signalling, proliferation, invasion and secretion of hormones and cytokines, and by increasing apoptosis. Heparin is commonly used to treat pregnant women with aPL; however, as thrombotic events do not occur in the placentae of all women with aPL, it may exert a protective effect by preventing the binding of aPL to β2GPI or by acting through non-thrombotic pathways. The aim of this review is to present evidence summarizing the current understanding of this field.

Antiphospholipid antibody-induced miR-146a-3p drives trophoblast interleukin-8 secretion through activation of Toll-like receptor 8

STUDY QUESTION

What is the role of microRNAs (miRs) in antiphospholipid antibody (aPL)-induced trophoblast inflammation?

SUMMARY ANSWER

aPL-induced up-regulation of trophoblast miR-146a-3p is mediated by Toll-like receptor 4 (TLR4), and miR-146a-3p in turn drives the cells to secrete interleukin (IL)-8 by activating the RNA sensor, TLR8.

WHAT IS KNOWN ALREADY

Obstetric antiphospholipid syndrome (APS) is an autoimmune disorder characterized by circulating aPL and an increased risk of pregnancy complications. We previously showed that aPL recognizing beta2 glycoprotein I (β2GPI) elicit human first trimester trophoblast secretion of IL-8 by activating TLR4. Since some miRs control TLR responses, their regulation in trophoblast cells by aPL and functional role in the aPL-mediated inflammatory response was investigated. miRs can be released from cells via exosomes, and therefore, miR exosome expression was also examined. A panel of miRs was selected based on their involvement with TLR signaling: miR-9; miR-146a-5p and its isomiR, miR-146a-3p; miR-155, miR-210; and Let-7c. Since certain miRs can activate the RNA sensor, TLR8, this was also investigated.

STUDY DESIGN, SIZE, DURATION

For in vitro studies, the human first trimester extravillous trophoblast cell line, HTR8 was studied. HTR8 cells transfected to express a TLR8 dominant negative (DN) were also used. Plasma was evaluated from pregnant women who have aPL, either with or without systemic lupus erythematous (SLE) (n = 39); SLE patients without aPL (n = 30); and healthy pregnant controls (n = 20).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Trophoblast HTR8 wildtype and TLR8-DN cells were incubated with or without aPL (mouse anti-human β2GPI mAb) for 48-72 h. HTR8 cells were also treated with or without aPL in the presence and the absence of a TLR4 antagonist (lipopolysaccharide from Rhodobacter sphaeroides; LPS-RS), specific miR inhibitors or specific miR mimics. miR expression levels in trophoblast cells, trophoblast-derived exosomes and exosomes isolated from patient plasma were measured by qPCR. Trophoblast IL-8 secretion was measured by ELISA.

MAIN RESULTS AND THE ROLE OF CHANCE

aPL significantly increased trophoblast cellular and exosome expression of miR-146a-5p, miR-146a-3p, miR-155 and miR-210. aPL-induced up-regulation of trophoblast miR-146a-5p, miR-146a-3p and miR-210, but not miR-155, was inhibited by the TLR4 antagonist, LPS-RS. While inhibition or overexpression of miR-146a-5p had no effect on aPL-induced trophoblast IL-8 secretion, miR-146a-3p inhibition significantly reduced this response. aPL-induced trophoblast IL-8 secretion was inhibited by the presence of the TLR8-DN. In the absence of aPL, transfection of trophoblast cells with a miR-146a-3p mimic significantly increased IL-8 secretion and this was inhibited by the presence of the TLR8-DN. Patients with aPL and adverse pregnancy outcomes (APOs) expressed significantly higher levels of circulating miR-146a-3p compared with healthy pregnant controls with no pregnancy complications (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

While the enrichment of miR-146a-3p in trophoblast-derived exosomes support the role of this miR acting in a paracrine or endocrine manner through exosome delivery, this has not been demonstrated. However, miR-146a-3p may also exert its pro-inflammatory effect intracellularly within the same trophoblast cell targeted by aPL.

WIDER IMPLICATIONS OF THE FINDINGS

These findings provide a novel mechanism of trophoblast inflammation through miRs activating RNA-sensing receptors. Furthermore, circulating exosomal-associated miR-146a-3p in APS patients may serve clinically as a biomarker for related APOs.

STUDY FUNDING/COMPETING INTERESTS

This study was supported in part by grants from the American Heart Association (#10GRNT3640032 to V.M.A.), the March of Dimes Foundation (Gene Discovery and Translational Research Grant #6-FY12-255 to V.M.A.), NICHD, NIH (R01HD049446 to V.M.A.), the Gina M. Finzi Memorial Student Summer Fellowship from the Lupus Foundation of America (to S.M.G.), and the Yale University School of Medicine Medical Student Fellowship (to S.M.G.). The authors declare no competing financial interests.

TRIAL REGISTRATION NUMBER

N/A.

A Dormant Microbial Component in the Development of Preeclampsia

Preeclampsia (PE) is a complex, multisystem disorder that remains a leading cause of morbidity and mortality in pregnancy. Four main classes of dysregulation accompany PE and are widely considered to contribute to its severity. These are abnormal trophoblast invasion of the placenta, anti-angiogenic responses, oxidative stress, and inflammation. What is lacking, however, is an explanation of how these themselves are caused. We here develop the unifying idea, and the considerable evidence for it, that the originating cause of PE (and of the four classes of dysregulation) is, in fact, microbial infection, that most such microbes are dormant and hence resist detection by conventional (replication-dependent) microbiology, and that by occasional resuscitation and growth it is they that are responsible for all the observable sequelae, including the continuing, chronic inflammation. In particular, bacterial products such as lipopolysaccharide (LPS), also known as endotoxin, are well known as highly inflammagenic and stimulate an innate (and possibly trained) immune response that exacerbates the inflammation further. The known need of microbes for free iron can explain the iron dysregulation that accompanies PE. We describe the main routes of infection (gut, oral, and urinary tract infection) and the regularly observed presence of microbes in placental and other tissues in PE. Every known proteomic biomarker of "preeclampsia" that we assessed has, in fact, also been shown to be raised in response to infection. An infectious component to PE fulfills the Bradford Hill criteria for ascribing a disease to an environmental cause and suggests a number of treatments, some of which have, in fact, been shown to be successful. PE was classically referred to as endotoxemia or toxemia of pregnancy, and it is ironic that it seems that LPS and other microbial endotoxins really are involved. Overall, the recognition of an infectious component in the etiology of PE mirrors that for ulcers and other diseases that were previously considered to lack one.

Antiphospholipid antibodies bind syncytiotrophoblast mitochondria and alter the proteome of extruded syncytial nuclear aggregates

INTRODUCTION

Antiphospholipid antibodies (aPL) are autoantibodies that increase the risk of women developing the hypertensive disorder pre-eclampsia. aPL are internalised by the syncytiotrophoblast and increase extrusion of necrotic multinucleated syncytial nuclear aggregates (SNAs), which may trigger endothelial dysfunction in pre-eclampsia. The mechanisms by which aPL alter death processes in the syncytiotrophoblast leading to extrusion of SNAs are unknown.

METHODS

First trimester human placentae (n = 10) were dissected into explants and cultured either with aPL (50 μg/mL), isotype-matched control antibody (50 μg/mL), or media for 24 h. Harvested SNAs underwent iTRAQ proteomic analysis. Mitochondria in syncytiotrophoblast treated with aPL labelled with FluoroNanogold were visualised using transmission electron microscopy (TEM).

RESULTS

aPL altered the expression of 72 proteins in SNAs. Thirteen proteins were involved in mitochondrial function. TEM demonstrated that aPL bind to mitochondria in the syncytiotrophoblast and may cause mitochondrial swelling.

DISCUSSION

aPL disrupt mitochondria increasing the extrusion of SNAs with an altered proteome from the syncytiotrophoblast. These altered SNAs may trigger endothelial dysfunction and pre-eclampsia in these pregnancies.

Histopathology in the placentae of women with antiphospholipid antibodies: A systematic review of the literature

BACKGROUND

Antiphospholipid antibodies (aPLs) are a heterogenous group of autoantibodies associated with recurrent miscarriage, stillbirth, foetal growth restriction and premature birth. The cause of obstetric morbidity in women with aPLs is not completely understood. Workers have attempted to understand the role of aPLs in obstetric morbidity by investigating the histopathology of placentae from aPL-positive women. However, it is unclear from these diverse, and at times contradictory reports what histopathological lesions are common in the placentae of women with aPLs. This systematic review was undertaken to generate a complete picture of the placental features associated with aPLs in an attempt to understand the pathological processes that occur in pregnancies affected by aPLs.

METHODS

Pubmed, Scopus, Web of Science and Embase were searched on the 27th November 2014 using the keywords "placenta" OR "trophoblast" AND "antiphospholipid antibody" OR "antiphospholipid antibody syndrome". Records that were relevant and eligible were qualitatively assessed and given a score out of 24.

RESULTS

Of the 1112 records that were retrieved from the systematic search, 34 records were eligible for review, and were qualitatively scored. Of the 44 histopathological features that were reported in 580 placentae from aPL-positive women, six features appeared to be more common in the placentae of aPL-positive women compared to control women, including: placental infarction, impaired spiral artery remodelling, decidual inflammation, increased syncytial knots, decreased vasculosyncytial membranes and the deposition of complement split product C4d.

CONCLUSION

Based on the evidence in this systematic review, a human placental aPL fingerprint has been proposed. The diversity of the human placental aPL fingerprint suggests that multiple pathological processes may occur in pregnancies affected by aPL.

Antiphospholipid antibodies and the placenta: a systematic review of their in vitro effects and modulation by treatment

BACKGROUND

Antiphospholipid antibodies (aPL) are a family of auto-antibodies that are associated with an increased risk of recurrent miscarriage, intrauterine growth restriction and preterm birth. The placenta is a major target of aPL and it is likely that these antibodies promote pregnancy morbidity by affecting trophoblast function. Numerous studies have investigated the effect of aPL on trophoblast function in vitro. However, different trophoblast models and a variety of culture conditions have been employed, resulting in a myriad of different reported findings. This review systematically summarized those published studies that have investigated the effect of aPL on trophoblast function in vitro. In addition, the reported effects of pharmacological treatment on trophoblast function in the presence of aPL were also systematically reviewed.

METHODS

PubMed, Scopus, Embase and Web of Science databases were searched using the keywords 'placenta OR trophoblast' AND 'antiphospholipid antibody OR antiphospholipid syndrome' up to 25 April 2014. Studies were excluded based on the absence of appropriate controls. The effects of aPL on trophoblast proliferation, death, syncytialization, invasion, hormone production, cytokine production, coagulation and complement activation were recorded. The effects of different treatments on the function of trophoblasts in the presence of aPL were also recorded.

RESULTS

A total of 1071 records were retrieved from the four databases. After removing duplicates, the titles and abstracts of 529 articles were reviewed. Of those, 48 articles were read and relevant experimental results were extracted from 47 articles.

CONCLUSIONS

This systematic review provides an overview of all the studies performed to date on the effects of aPL on trophoblast function in vitro. There is considerable support for aPL decreasing trophoblast viability, syncytialization and invasion in vitro. Some work has also suggested that aPL may affect the production of hormones and signalling molecules by trophoblasts, and may stimulate coagulation and complement activation in vitro. Current reports of the in vitro effects of therapeutic treatments on trophoblast function in the presence of aPL are inconclusive. This systematic review has highlighted many gaps in our knowledge of how aPL work and may direct future research in this area.

Trophoblast debris extruded from preeclamptic placentae activates endothelial cells: a mechanism by which the placenta communicates with the maternal endothelium

INTRODUCTION

Preeclampsia is characterized by maternal endothelial dysfunction. While the mechanisms leading to preeclampsia are unclear, a factor(s) from the placenta is responsible for triggering the disease. One placental factor implicated in triggering preeclampsia is trophoblast debris which may transmit pathogenic signals from the placenta to endothelial cells. In this study, we investigated whether trophoblast debris from preeclamptic placentae triggered endothelial cell activation.

METHODS

Trophoblast debris from preeclamptic or normotensive placentae, or trophoblast debris from normal placental explants that had been cultured with preeclamptic (n = 14) or normotensive sera (n = 14) was exposed to endothelial cells. Activation of the endothelial cells was quantified by cell surface ICAM-1 and U937 adhesion to endothelial cells. The levels of IL-1β, pro-caspase-1 and active caspase-1 in the trophoblast debris were measured.

RESULTS

Compared to controls, the levels of ICAM-1 and U937 adhesion to endothelial cells were significantly increased following exposure of the endothelial cells to trophoblast debris from preeclamptic placentae or placentae treated with preeclamptic sera. The levels IL-1β, pro-caspase-1 and active caspase-1 were significantly increased in both trophoblast debris from preeclamptic placentae and placentae treated with preeclamptic sera.

DISCUSSION

These results provide the first direct evidence that trophoblast debris produced from preeclamptic placentae or placentae treated with preeclamptic sera can activate the endothelium.

CONCLUSIONS

Trophoblast debris from preeclamptic but not normotensive placentae can induce endothelial cell activation. This may be one mechanism by which the preeclamptic placenta communicates with the maternal endothelium to induce activation of the endothelium.

Calcium supplementation prevents endothelial cell activation: possible relevance to preeclampsia

OBJECTIVES

Preeclampsia is a leading cause of maternal and fetal mortality and morbidity. A hallmark of preeclampsia is endothelial cell dysfunction/activation in response to 'toxins' from the placenta. Necrotic trophoblastic debris (NTD) is one possible placental toxin and other activators of endothelial cells include inflammatory cytokines. Calcium supplementation appears to protect 'at-risk' women from developing preeclampsia but how is unclear.

METHODS

Placental explants were cultured with interleukin-6 (IL-6) in varied concentrations of calcium. The resultant trophoblastic debris was exposed to endothelial cells. Endothelial cells were exposed to activators including NTD, IL-6, and preeclamptic sera in the presence of varied concentrations of calcium and activation monitored by quantifying cell surface markers by ELISA.

RESULTS

Raising the levels of calcium did not prevent the IL-6-induced shedding of NTD from placental explants but did prevent the activation of endothelial cells in response to IL-6, preeclamptic sera, or NTD. Reducing the level of calcium directly induced the activation of endothelial cells. Inhibiting nitric oxide synthetase ablated the ability of high calcium levels to protect endothelial cell activation. The activity of endothelial cell nitric oxide synthetase was blocked with L-N-nitroarginine methyl ester.

CONCLUSION

Our results demonstrate calcium levels do not affect the shedding of trophoblastic debris but are important to endothelial cell activation and supplemental calcium may reverse the activation of the endothelium in preeclamptic women. These results may in part explain the benefits of calcium supplementation in the reduction of risk for developing preeclampsia and provide in-vitro mechanistic support for the use of calcium supplementation in at-risk women.

NF-κB is activated from endosomal compartments in antiphospholipid antibodies-treated human monocytes

BACKGROUND

The antiphospholipid antibody syndrome (APS) is an autoimmune disease associated with arterial or venous thrombosis and/or recurrent fetal loss and is caused by pathogenic antiphospholipid antibodies (aPLA). We recently demonstrated that Toll-like receptor 2 (TLR2) and CD14 contribute to monocyte activation of aPLA.

OBJECTIVE

To study the mechanisms of cell activation by aPLA, leading to pro-coagulant and pro-inflammatory responses.

METHODS AND RESULTS

For this study, we used purified antibodies from the plasmas of 10 different patients with APS and healthy donors. We demonstrate that aPLA, but not control IgG, co-localizes with TLR2 and TLR1 or TLR6 on human monocytes. Blocking antibodies to TLR2, TLR1 or TLR6, but not to TLR4, decreased TNF and tissue factor (TF) responses to aPLA. Pharmacological and siRNA approaches revealed the importance of the clathrin/dynamin-dependent endocytic pathway in cell activation by aPLA. In addition, soluble aPLA induced NF-κB activation, while bead-immobilized aPLA beads, which cannot be internalized, were unable to activate NF-κB. Internalization of aPLA in monocytes and NF-κB activation were dependent on the presence of CD14.

CONCLUSION

We show that TLR2 and its co-receptors, TLR1 and TLR6, contribute to the pathogenicity of aPLA, that aPLA are internalized via clathrin- and CD14-dependent endocytosis and that endocytosis is required for NF-κB activation. Our results contribute to a better understanding of the APS and provide a possible therapeutic approach.

Antiphospholipid antibodies internalised by human syncytiotrophoblast cause aberrant cell death and the release of necrotic trophoblast debris

Antiphospholipid antibodies (aPL) are the strongest maternal risk factor for pre-eclampsia, a hypertensive disease of human pregnancy. Pre-eclampsia is triggered by a toxic factor released from the placenta that activates the maternal endothelium. Antiphospholipid antibodies cause the release of necrotic trophoblast debris from the placental syncytiotrophoblast and this debris can activate endothelial cells. In this study, we investigated how aPL affects syncytiotrophoblast death and production of necrotic trophoblast debris by examining the interaction between aPL and human first trimester placental explants. Human polyclonal and murine monoclonal aPL, but not control antibodies, were rapidly internalised by the syncytiotrophoblast. Inhibitors of endocytosis or the low-density lipoprotein receptor (LDLR) family, but not toll-like receptors, decreased the internalisation of aPL and prevented the release of necrotic trophoblast debris from the syncytiotrophoblast. Once internalised, aPL increased inner mitochondrial membrane leak and Cytochrome c release while depressing oxidative flux through Complex IV of the electron transport system in syncytiotrophoblast mitochondria. These data suggest that the human syncytiotrophoblast internalises aPL by antigen-dependent endocytosis involving LDLR family members. Once internalised by the syncytiotrophoblast, aPL affects the death-regulating mitochondria, causing extrusion of necrotic trophoblast debris which can activate maternal endothelial cells thereby contributing to the pathogenesis of pre-eclampsia.

Antiphospholipid antibodies prolong the activation of endothelial cells induced by necrotic trophoblastic debris: implications for the pathogenesis of preeclampsia

The symptoms of preeclampsia are preceded by endothelial cell activation/dysfunction which is induced by a placental trigger(s) but maternal risk factor(s) also contribute to the pathogenesis of preeclampsia. In this work we have investigated the interactions of a maternal risk factor, antiphospholipid antibodies, and a placental trigger, necrotic trophoblastic debris, on the activation of endothelial cells. Trophoblastic debris, from placental explants, was induced to become necrotic by freeze-thawing then exposed to endothelial cells for 24 h. After washing away residual trophoblastic debris antiphospholipid antibodies or a control antibody were added to the cultures then replaced with fresh medium in the presence or absence of antibodies. Endothelial cell activation was quantified by examining cell-surface ICAM-1 expression and monocyte adhesion. Endothelial cells exposed to necrotic trophoblastic debris for 24 h became activated but the activation was lost 24 h after removal of the debris. Antiphospholipid antibodies alone did not active untreated endothelial cells, but did prolong the activation of endothelial cells which had been activated by pre-treatment with necrotic trophoblastic debris. When exposed to antiphospholipid antibodies the endothelial cells remained activated despite removal of the trophoblastic debris. In contrast, a control antibody did not prolong endothelial cell activation. Our data suggest that in women with antiphospholipid antibodies, activation of endothelial cells induced by necrotic trophoblastic debris could be maintained even if the endothelial cells were only intermittently exposed to necrotic debris. This might in part explain why antiphospholipid antibodies are such a strong maternal risk factor for preeclampsia.

Trophoblast deportation: just a waste disposal system or antigen sharing?

Trophoblast deportation, the removal of trophoblastic debris from the placenta via the maternal blood, was first described over 100 years ago. Deported trophoblastic debris ranges in size from nano-meter scale subcellular particles to large multinucleated syncytial knots. Whether trophoblast deportation has any biological significance remains unclear. However, the (semi) allogeneic fetus must induce maternal tolerance to paternally inherited placental antigens. We propose that the clearance of deported trophoblasts may be a mechanism by which the maternal immune system is maintained in a state of tolerance towards paternal antigens. Using an in vitro model, we have shown that when syncytial knots are shed by an apoptosis-like programmed cell death process, then phagocytosed by macrophages, the macrophages produce a tolerogenic response. However, necrotic syncytial knots, when phagocytosed, appear to be immunostimulatory. We have also shown that endothelial cells are likely to be involved in the clearance of syncytial knots from the pulmonary vessels. Phagocytosis of apoptotic syncytial knots by endothelial cells is silent while phagocytosis of necrotic syncytial knots leads to endothelial cell activation characterised by increased endothelial cell-surface adhesion molecule expression and secretion of IL-6 and TGFβ1. All of these molecules may interact with the maternal immune system to exacerbate any adverse maternal response. We propose that in normal pregnancy clearance of apoptotic syncytial knots is important to maintain maternal immune tolerance to the fetus and that in abnormal pregnancies, especially preeclampsia, clearance of necrotic syncytial knots may contribute to the pathogenesis of that condition.

Pre-eclampsia: fitting together the placental, immune and cardiovascular pieces

The success of pregnancy is a result of countless ongoing interactions between the placenta and the maternal immune and cardiovascular systems. Pre-eclampsia is a serious pregnancy complication that arises from multiple potential aberrations in these systems. The pathophysiology of pre-eclampsia is established in the first trimester of pregnancy, when a range of deficiencies in placentation affect the key process of spiral artery remodelling. As pregnancy progresses to the third trimester, inadequate spiral artery remodelling along with multiple haemodynamic, placental and maternal factors converge to activate the maternal immune and cardiovascular systems, events which may in part result from increased shedding of placental debris. As we understand more about the pathophysiology of pre-eclampsia, it is becoming clear that the development of early- and late-onset pre-eclampsia, as well as intrauterine growth restriction (IUGR), does not necessarily arise from the same underlying pathology.

Antiphospholipid antibodies limit trophoblast migration by reducing IL-6 production and STAT3 activity

PROBLEM

Women with antiphospholipid antibodies (aPL) are at risk of recurrent miscarriage and pre-eclampsia. aPL target the placenta by binding to beta(2)-glycoprotein I (beta(2) GPI) expressed by the trophoblast. The objective of this study was to evaluate if and how aPL affect first trimester trophoblast migration.

METHOD OF STUDY

First trimester trophoblast cells were treated with anti-beta(2) GPI monoclonal antibodies. Migration was determined using a two-chamber assay. Interleukin (IL)-6 production was evaluated by RT-PCR and enzyme-linked immunosorbent assay, and signal transducer and activator of transcription 3 (STAT3) activation was assessed by western blot.

RESULTS

Trophoblast cells constitutively secreted IL-6 in a time-dependent manner and this directly correlated with STAT3 phosphorylation. In the presence of anti-beta(2) GPI Abs, trophoblast IL-6 mRNA levels and secretion was downregulated in a Toll-like receptor 4/MyD88-independent manner and this correlated with a reduction in phosphorylated STAT3 levels. In addition, the anti-beta(2) GPI Abs reduced the migratory potential of trophoblast. Heparin was able to reverse aPL-dependent inhibition of trophoblast IL-6 secretion and migration.

CONCLUSION

This study demonstrates that aPL limit trophoblast cell migration by downregulating trophoblast IL-6 secretion and STAT3 activity. As heparin was unable to prevent these effects, our findings may explain why women with antiphospholipid syndrome, treated with heparin, remain at risk of developing obstetrical syndromes, associated with impaired deep placentation, such as pre-eclampsia.