Endoplasmic reticulum stress occurs in association with the extrusion of toxic extracellular vesicles from human placentae treated with antiphospholipid antibodies

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.

MicroRNA analysis of medium/large placenta extracellular vesicles in normal and preeclampsia pregnancies

Background

Preeclampsia (PE) is a hypertensive disorder of pregnancy, affecting 2%-8% of pregnancies worldwide, and is the leading cause of adverse maternal and fetal outcomes. The disease is characterized by oxidative and cellular stress and widespread endothelial dysfunction. While the precise mechanisms are not entirely understood, the pathogenesis of PE is closely linked to placental dysfunction and, to some extent, syncytiotrophoblast extracellular vesicle release (STB-EVs). These vesicles can be divided into the less well-studied medium/large EVs (220-1,000 nm) released in response to stress and small EVs (<220 nm) released as a component of intercellular communication. The previously described production of m/lSTB-EVs in response to cellular stress combined with the overwhelming occurrence of cellular and oxidative stress in PE prompted us to evaluate the microRNAome of PE m/lSTB-EVs. We hypothesized that the microRNAome profile of m/lSTB-EVs is different in PE compared to normal pregnancy (NP), which might permit the identification of potential circulating biomarkers not previously described in PE.

Methods/study design

We performed small RNA sequencing on medium/large STB-EVs isolated from PE and NP placentae using dual-lobe ex vivo perfusion. The sequencing data was bioinformatically analyzed to identify differentially regulated microRNAs. Identified microRNAs were validated with quantitative PCR analysis. We completed our analysis by performing an in-silico prediction of STB-EV mechanistic pathways.

Results

We identified significant differences between PE and NP in the STB-EVs micro ribonucleic acid (microRNA) profiles. We verified the differential expression of hsa-miR-193b-5p, hsa-miR-324-5p, hsa-miR-652-3p, hsa-miR-3196, hsa-miR-9-5p, hsa-miR-421, and hsa-miR-210-3p in the medium/large STB-EVs. We also confirmed the differential abundance of hsa-miR-9-5p in maternal serum extracellular vesicles (S EVs). In addition, we integrated the results of these microRNAs into the previously published messenger RNA (mRNA) data to better understand the relationship between these biomolecules.

Conclusions

We identified a differentially regulated micro-RNA, hsa-miR-9-5p, that may have biomarker potential and uncovered mechanistic pathways that may be important in the pathophysiology of PE.

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.

Necroptosis in the pathophysiology of preeclampsia

Necroptosis is a newly-identified form of gene-regulated cell necrosis that is increasingly considered to be a pathway associated with human pathophysiological conditions. Cells undergoing necroptosis exhibit necrotic phenotypes, including disruption of the plasma membrane integrity, organelle swelling, and cytolysis. Accumulating evidence suggests that trophoblast necroptosis plays a complex role in preeclampsia (PE). However, the exact pathogenesis remains unclear. Its unique mechanisms of action in various diseases are expected to provide prospects for the treatment of PE. Therefore, it is necessary to further explore its molecular mechanism in PE in order to identify potential therapeutic options. This review examines the current knowledge regarding the role and mechanisms of necroptosis in PE and provides a theoretical basis for new therapeutic targets for PE.

The Many Faces of MLKL, the Executor of Necroptosis

Necroptosis is a recently discovered form of regulated cell death characterized by the disruption of plasma membrane integrity and the release of intracellular content. Mixed lineage kinase domain-like (MLKL) protein is the main player of this cell death pathway as it mediates the final step of plasma membrane permeabilization. Despite the significant progress in our knowledge of the necroptotic pathway and MLKL biology, the precise mechanism of how MLKL functions remain unclear. To understand in what way MLKL executes necroptosis, it is crucial to decipher how the molecular machinery of regulated cell death is activated in response to different stimuli or stressors. It is also indispensable to unveiling the structural elements of MLKL and the cellular players that are required for its regulation. In this review, we discuss the key steps that lead to MLKL activation, possible models that explain how it becomes the death executor in necroptosis, and its emerging alternative functions. We also summarize the current knowledge about the role of MLKL in human disease and provide an overview of existing strategies aimed at developing new inhibitors that target MLKL for necroptosis intervention.

Exporting Proteins Associated with Senescence Repair via Extracellular Vesicles May Be Associated with Early Pregnancy Loss

Introduction: Dysfunction of placental development is involved in early pregnancy loss. Senescent changes have been seen in missed miscarriage, one type of pregnancy loss. Extracellular vesicles (EVs) have been widely implicated in the pathogenesis of diseases. In this study, we investigated the protein profiles in placental EVs derived from missed miscarriage in comparison with healthy pregnancy. We also investigated whether cargos packed into EVs are involved in the dysfunctional development of the placenta seen in missed miscarriage. Methods: Proteomic analysis of placental EVs derived from healthy and missed-miscarriage placentae was performed. Three senescence-repair-associated proteins, replication protein A-70 (RPA-70), proteasome activator subunit-4 (PMSE-4), and protein activated kinase-2, (PAK-2) were examined in placental EVs and placentae, and in placental explants that had been treated with or without GW4869, by western blotting and immunohistochemistry. Results: The total number of proteins associated with placental EVs was not different between the two groups. However, there were 106 and 151 abundantly expressed proteins associated with placental micro- or nano-EVs from missed miscarriage in comparison with EVs from controls. Of these abundant proteins, 59 and 81 proteins in placental micro- or nano-EVs, respectively, are associated with DNA damage/repair and cell death/survival. We further found higher levels of three senescence-repair-associated proteins (RPA-70, PMSE-4, and PAK-2) associated with placental EVs, but lower levels of these proteins in missed-miscarriage placentae. Regarding inhibition of EV formation or release by GW4869, we found that the expression of these three proteins was higher in GW4869-treated placental explants from missed miscarriage. Discussion: Our data may suggest that “inadvertently” sorting of cargos and exporting proteins associated with senescence-repair by placental EVs may be associated with the dysfunction of placental development seen in missed miscarriage.

Interactions between endoplasmic reticulum stress and extracellular vesicles in multiple diseases

Immune responses can severely perturb endoplasmic reticulum (ER) function. As a protein-folding factory and dynamic calcium storage compartment, the ER plays a pivotal role in resisting pathogens and in the development of autoimmune diseases and various other diseases, including cancer, cardiovascular, neurological, orthopedic, and liver-related diseases, metabolic disorders, etc. In recent years, an increasing number of studies have shown that extracellular vesicles (EVs) play important roles in these conditions, suggesting that cells carry out some physiological functions through EVs. The formation of EVs is dependent on the ER. ER stress, as a state of protein imbalance, is both a cause and consequence of disease. ER stress promotes the transmission of pathological messages to EVs, which are delivered to target cells and lead to disease development. Moreover, EVs can transmit pathological messages to healthy cells, causing ER stress. This paper reviews the biological functions of EVs in disease, as well as the mechanisms underlying interactions between ER stress and EVs in multiple diseases. In addition, the prospects of these interactions for disease treatment are described.

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.

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.

MLKL: Functions beyond serving as the Executioner of Necroptosis

Recently, necroptosis, as a programmed cell death pathway, has drawn much attention as it has been implicated in multiple pathologies, especially in the field of inflammatory diseases. Pseudokinase mixed lineage kinase domain-like protein (MLKL) serves as a terminal-known obligate effector in the process of necroptosis. To date, the majority of research on MLKL has focused on its role in necroptosis, and the prevailing view has been that the sole function of MLKL is to mediate necroptosis. However, increasing evidence indicates that MLKL can serve as a regulator of many diseases via its non-necroptotic functions. These functions of MLKL shed light on its functional complexity and diversity. In this review, we briefly introduce the current state of knowledge regarding the structure of MLKL, necroptosis signaling, as well as cross-linkages among necroptosis and other regulated cell death pathways, and we particularly highlight recent progress related to newly identified functions and inhibitors of MLKL. These discussions promote a better understanding of the role of MLKL in diseases, which will foster efforts to pharmacologically target this molecule in clinical treatments.

Placental mitochondrial function in response to gestational exposures

Poor environmental conditions, including malnutrition, hypoxia and obesity in the mother increase the risk of pregnancy complications, such as pre-eclampsia and gestational diabetes mellitus, which impacts the lifelong health of the mother and her offspring. The placenta plays an important role in determining pregnancy outcome by acting as an exchange interface and endocrine hub to support fetal growth. Mitochondria are energy powerhouses of cells that fuel placental physiology throughout pregnancy, including placental development, substrate exchange and hormone secretion. They are responsive to environmental cues and changes in mitochondrial function may serve to mediate or mitigate the impacts of poor gestational environments on placental physiology and hence, the risks of pregnancy complications. Thus, a more integrated understanding about the role of placental mitochondria in orchestrating changes in relation to environmental conditions and pregnancy outcome is paramount. This review summarises the functions of mitochondria in the placenta and findings from humans and experimental animals that demonstrate how mitochondrial structure and function are altered in different gestational environments (namely complicated pregnancies and adverse environmental conditions). Together the available data suggest that mitochondria in the placenta play a major role in determining placental physiology, fetal growth and pregnancy outcome.

Extracellular Vesicles and Preeclampsia: Current Knowledge and Future Research Directions

Preeclampsia (PE) is associated with long-term morbidity in mothers and lifelong morbidities for their children, ranging from cerebral palsy and cognitive delay in preterm infants, to hypertension, diabetes and obesity in adolescents and young adults. There are several processes that are critical for development of materno-fetal exchange, including establishing adequate perfusion of the placenta by maternal blood, and the formation of the placental villous vascular tree. Recent studies provide persuasive evidence that placenta-derived extracellular vesicles (EVs) represent a significant intercellular communication pathway, and that they may play an important role in placental and endothelial cell (both fetal and maternal) function. These functions are known to be altered in PE. EVs can carry and transport a wide range of bioactive molescules that have potential to be used as biomarkers and therapeutic delivery tools for PE. EV content is often parent cell specific, thus providing an insight or "thumbprint" of the intracellular environment of the originating cell (e.g., human placenta). EV have been identified in plasma under both normal and pathological conditions, including PE. The concentration of EVs and their content in plasma has been reported to increase in association with disease severity and/or progression. Placenta-derived EVs have been identified in maternal plasma during normal pregnancy and PE pregnancies. They contain placenta-specific proteins and miRNAs and, as such, may be differentiated from maternally-derived EVs. The aim of this review, thus, is to describe the potential roles of EVs in preecmpatic pregnancies, focussing on EVs secreted from placental cells. The biogenesis, specificity of placental EVs, and methods used to characterise EVs in the context of PE pregnancies will be also discussed.

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.