Regulation of birthweight by placenta-derived miRNAs: evidence from an arsenic-exposed birth cohort in Bangladesh

Arsenic and the placenta: A review with emphasis on the immune system

Chronic arsenic exposure affects over 140 million people globally. While arsenic easily crosses the placenta, the specific mechanisms impacting placental immune cell populations and fetal health are unclear. Maternal arsenic exposure is epidemiologically linked to increased infection risk, mortality, and cancer susceptibility in offspring, emphasizing the importance of understanding placentally-mediated immune effects. This review explores the potential role of the placenta, a key organ for immune transfer to the developing fetus, in mediating chronic low-dose arsenic exposure effects. Examining three potential pathways-direct contaminant transfer, altered immune transfer from the mother, and indirect impact on fetal immune programming via maternal and placental signaling-the review highlights studies associating maternal arsenic levels with immune-related outcomes, including changes in cord blood T cell populations and increased placental inflammation. Placental gene expression analysis reveals alterations in pathways related to oxidative stress, proteasome activity, and aquaglyceroporin transporter expression. Impact on placental DNA methylation and microRNA regulation as well as on trophoblast dysfunction is discussed, with evidence suggesting inhibited trophoblast migration and placental growth factor expression. The complexity of mixtures, nutrition, and environmental interactions add challenges to investigating the placenta's role in immune programming. Despite inconsistent findings on placental morphology alterations, evidence suggests a potential link between arsenic exposure, placental anomalies, and adverse birth outcomes. Further research is crucial to comprehend the effects of prenatal arsenic exposure on trophoblasts, placental immune cells, and subsequent long-term consequences for fetal immune development and birth outcomes.

MicroRNA expression profile in the basal plate of human placenta associates with spontaneous preterm birth

INTRODUCTION

MicroRNAs regulate post-transcriptional gene expression. Their expression has been linked to many pregnancy complications, including preterm birth. Placental microRNA levels differ between preterm and term pregnancies. Not much is known about the targets that are affected by these differences in microRNA expression. We investigated associations between microRNA expression levels in the basal plate of the placenta and their targets and the onset of preterm birth.

METHODS

MiRNAomes of spontaneous preterm (n = 6) and term (n = 6) placentas were characterized using RNA sequencing. MicroRNA target and enrichment analyses were performed to explore potential gene targets and pathways. Selected findings were validated using qPCR (n = 41). MicroRNA mimic transfection and luciferase reporter assays were performed to test if certain microRNAs regulate their predicted target, SLIT2, the expression of which has been shown to associate with preterm birth.

RESULTS

We identified 39 differentially expressed microRNAs from the preterm placentas compared to term. Many downregulated microRNAs were from the placenta-specific C14MC microRNA cluster. Target gene and pathway analyses showed that microRNAs that associate with preterm birth target transcription related factors and genes linked with protein binding and invasive pathways. Eight of the identified microRNAs putatively target SLIT2, including miR-766-3p and miR-489-3p. Luciferase reporter assay suggested that these microRNAs regulate SLIT2 expression.

DISCUSSION

MicroRNA expression changes are associated with spontaneous preterm birth. A group of microRNAs targeting the same gene or genes belonging to the same pathway can have a significant effect on the critical processes maintaining pregnancy and placental functions.

Whole transcriptome landscape in HAPE under the stress of environment at high altitudes: new insights into the mechanisms of hypobaric hypoxia tolerance

Background

High altitude pulmonary edema (HAPE) is an idiopathic, noncardiogenic form of pulmonary edema that occurs at high altitudes. It is characterized by a severe clinical course and carries a significant mortality risk. Despite its clinical relevance, the molecular mechanisms underlying HAPE are not well understood.

Methods

We conducted whole-transcriptome RNA sequencing on blood samples from 6 pairs of HAPE patients and healthy controls to identify differentially expressed (DE) mRNAs, miRNAs, circRNAs, lncRNAs, along with alternative splicing (AS) events, gene fusions, and novel transcripts. To explore the regulatory dynamics, we constructed ceRNA networks and analyzed immune cell infiltration patterns, further annotating the biological functions of these transcripts. For empirical validation, we selected five circRNAs from the ceRNA network and conducted RT-qPCR on 50 paired samples. Additionally, we assessed the correlations between circRNA expression levels and clinical data to evaluate their diagnostic potential.

Results

We observed 2,023 differentially expressed mRNAs (DEmRNAs), 84 DEmiRNAs, 200 DEcircRNAs, and 3,573 DElncRNAs. A total of 139 'A3SS' events, 103 'A5SS' events, 545 'MXE' events, 14 'RI' events, and 1,482 'SE' events were identified in the AS events analysis between the two groups. Two ceRNA networks were constructed. T cells, follicular helper, and Macrophages M1 cells exhibited the strongest positive correlation (R=0.82), while naive B cells and memory B cells demonstrated the strongest negative correlation (R=-0.62). In total, the expression of three circRNAs was significantly different in a larger cohort. Hsa_circ_0058497, hsa_circ_0081006, and hsa_circ_0083220 demonstrated consistent with the RNA sequencing results. These three circRNAs strongly correlate with clinical indicators and exhibit potential as diagnostic biomarkers. Finally, we verified five genes (CXCR4, HSD17B2, ANGPTL4, TIMP3, N4BP3) that were differentially expressed in endothelial cells under normoxia and hypoxia through bioinformatics and RT-qPCR analyses.

Conclusion

This study elucidates the differential expression of coding and non-coding RNAs (ncRNAs) in HAPE, identifies new transcripts and genes, and enhances our understanding of the transcriptional characteristics of HAPE. Moreover, it highlights the potential role of circRNAs in advancing the diagnosis and treatment of HAPE.

Arsenic toxicity: sources, pathophysiology and mechanism

Background

Arsenic is a naturally occurring element that poses a significant threat to human health due to its widespread presence in the environment, affecting millions worldwide. Sources of arsenic exposure are diverse, stemming from mining activities, manufacturing processes, and natural geological formations. Arsenic manifests in both organic and inorganic forms, with trivalent meta-arsenite (As3+) and pentavalent arsenate (As5+) being the most common inorganic forms. The trivalent state, in particular, holds toxicological significance due to its potent interactions with sulfur-containing proteins.

Objective

The primary objective of this review is to consolidate current knowledge on arsenic toxicity, addressing its sources, chemical forms, and the diverse pathways through which it affects human health. It also focuses on the impact of arsenic toxicity on various organs and systems, as well as potential molecular and cellular mechanisms involved in arsenic-induced pathogenesis.

Methods

A systematic literature review was conducted, encompassing studies from diverse fields such as environmental science, toxicology, and epidemiology. Key databases like PubMed, Scopus, Google Scholar, and Science Direct were searched using predetermined criteria to select relevant articles, with a focus on recent research and comprehensive reviews to unravel the toxicological manifestations of arsenic, employing various animal models to discern the underlying mechanisms of arsenic toxicity.

Results

The review outlines the multifaceted aspects of arsenic toxicity, including its association with chronic diseases such as cancer, cardiovascular disorders, and neurotoxicity. The emphasis is placed on elucidating the role of oxidative stress, genotoxicity, and epigenetic modifications in arsenic-induced cellular damage. Additionally, the impact of arsenic on vulnerable populations and potential interventions are discussed.

Conclusions

Arsenic toxicity represents a complex and pervasive public health issue with far-reaching implications. Understanding the diverse pathways through which arsenic exerts its toxic effects is crucial to developing effective mitigation strategies and interventions. Further research is needed to fill gaps in our understanding of arsenic toxicity and to inform public health policies aimed at minimising exposure.Arsenic toxicity is a crucial public health problem influencing millions of people around the world. The possible sources of arsenic toxicity includes mining, manufacturing processes and natural geological sources. Arsenic exists in organic as well as in inorganic forms. Trivalent meta-arsenite (As3+) and pentavalent arsenate (As5+) are two most common inorganic forms of arsenic. Trivalent oxidation state is toxicologically more potent due to its potential to interact with sulfur containing proteins. Humans are exposed to arsenic in many ways such as environment and consumption of arsenic containing foods. Drinking of arsenic-contaminated groundwater is an unavoidable source of poisoning, especially in India, Bangladesh, China, and some Central and South American countries. Plenty of research has been carried out on toxicological manifestation of arsenic in different animal models to identify the actual mechanism of aresenic toxicity. Therefore, we have made an effort to summarize the toxicology of arsenic, its pathophysiological impacts on various organs and its molecular mechanism of action.

Prenatal arsenite exposure alters maternal cardiac remodeling during late pregnancy

Exposure to inorganic arsenic through drinking water is widespread and has been linked to many chronic diseases, including cardiovascular disease. Arsenic exposure has been shown to alter hypertrophic signaling in the adult heart, as well as in utero offspring development. However, the effect of arsenic on maternal cardiac remodeling during pregnancy has not been studied. As such, there is a need to understand how environmental exposure contributes to adverse pregnancy-related cardiovascular events. This study seeks to understand the impact of trivalent inorganic arsenic exposure during gestation on maternal cardiac remodeling in late pregnancy, as well as offspring outcomes. C57BL/6 J mice were exposed to 0 (control), 100 or 1000 μg/L sodium arsenite (NaAsO2) beginning at embryonic day (E) 2.5 and continuing through E17.5. Maternal heart function and size were assessed via transthoracic echocardiography, gravimetric measurement, and histology. Transcript levels of hypertrophic markers were probed via qRT-PCR and confirmed by western blot. Offspring outcomes were assessed through echocardiography and gravimetric measurement. We found that maternal heart size was smaller and transcript levels of Esr1 (estrogen receptor alpha), Pgrmc1 (progesterone receptor membrane component 1) and Pgrmc2 (progesterone receptor membrane component 2) reduced during late pregnancy with exposure to 1000 μg/L iAs vs. non-exposed pregnant controls. Both 100 and 1000 μg/L iAs also reduced transcription of Nppa (atrial natriuretic peptide). Akt protein expression was also significantly reduced after 1000 μg/L iAs exposure in the maternal heart with no change in activating phosphorylation. This significant abrogation of maternal cardiac hypertrophy suggests that arsenic exposure during pregnancy can potentially contribute to cardiovascular disease. Taken together, our findings further underscore the importance of reducing arsenic exposure during pregnancy and indicate that more research is needed to assess the impact of arsenic and other environmental exposures on the maternal heart and adverse pregnancy events.

Periconceptional and Prenatal Exposure to Metals and Extracellular Vesicle and Particle miRNAs in Human Milk: A Pilot Study

Human milk is a rich source of microRNAs (miRNAs), which can be transported by extracellular vesicles and particles (EVPs) and are hypothesized to contribute to maternal-offspring communication and child development. Environmental contaminant impacts on EVP miRNAs in human milk are largely unknown. In a pilot study of 54 mother-child pairs from the New Hampshire Birth Cohort Study, we examined relationships between five metals (arsenic, lead, manganese, mercury, and selenium) measured in maternal toenail clippings, reflecting exposures during the periconceptional and prenatal periods, and EVP miRNA levels in human milk. 798 miRNAs were profiled using the NanoString nCounter platform; 200 miRNAs were widely detectable and retained for downstream analyses. Metal-miRNA associations were evaluated using covariate-adjusted robust linear regression models. Arsenic exposure during the periconceptional and prenatal periods was associated with lower total miRNA content in human milk EVPs (PBonferroni < 0.05). When evaluating miRNAs individually, 13 miRNAs were inversely associated with arsenic exposure, two in the periconceptional period and 11 in the prenatal period (PBonferroni < 0.05). Other metal-miRNA associations were not statistically significant after multiple testing correction (PBonferroni ≥ 0.05). Many of the arsenic-associated miRNAs are involved in lactation and have anti-inflammatory properties in the intestine and tumor suppressive functions in breast cells. Our findings raise the possibility that periconceptional and prenatal arsenic exposure may reduce levels of multiple miRNAs in human milk EVPs. However, larger confirmatory studies, which can apply environmental mixture approaches, evaluate potential effect modifiers of these relationships, and examine possible downstream consequences for maternal and child health and breastfeeding outcomes, are needed.

Prenatal Arsenite Exposure Alters Maternal Cardiac Remodeling During Late Pregnancy

Exposure to inorganic arsenic through drinking water is widespread and has been linked to many chronic diseases, including cardiovascular disease. Arsenic exposure has been shown to alter hypertrophic signaling in the adult heart, as well as in-utero offspring development. However, the effect of arsenic on maternal cardiac remodeling during pregnancy has not been studied. As such, there is a need to understand how environmental exposure contributes to adverse pregnancy-related cardiovascular events. This study seeks to understand the impact of trivalent inorganic arsenic exposure during gestation on maternal cardiac remodeling in late pregnancy, as well as offspring outcomes. C57BL/6J mice were exposed to 0 (control), 100 or 1000 µg/L sodium arsenite (NaAsO 2 ) beginning at embryonic day (E) 2.5 and continuing through E17.5. Maternal heart function and size were assessed via transthoracic echocardiography, gravimetric measurement, and histology. Transcript levels of hypertrophic markers were probed via qRT-PCR and confirmed by western blot. Offspring outcomes were assessed through echocardiography and gravimetric measurement. We found that exposure to 1000 µg/L iAs abrogated normal physiologic growth of the maternal heart during late pregnancy and reduced transcript levels of estrogen receptor alpha (ERα), progesterone receptor membrane component 1 (Pgrmc1) and progesterone receptor membrane component 2 (Pgrmc2). Both 100 and 1000 µg/L iAs also reduced transcription of protein kinase B (Akt) and atrial natriuretic peptide (ANP). Akt protein expression was also significantly reduced after 1000 µg/L iAs exposure in the maternal heart with no change in activating phosphorylation. This significant abrogation of maternal cardiac hypertrophy suggests that arsenic exposure during pregnancy can potentially contribute to cardiovascular disease. Taken together, our findings further underscore the importance of reducing arsenic exposure during pregnancy and indicate that more research is needed to assess the impact of arsenic and other environmental exposures on the maternal heart and adverse pregnancy events.

A burst of genomic innovation at the origin of placental mammals mediated embryo implantation

The origin of embryo implantation in mammals ~148 million years ago was a dramatic shift in reproductive strategy, yet the molecular changes that established mammal implantation are largely unknown. Although progesterone receptor signalling predates the origin of mammals and is highly conserved in, and critical for, successful mammal pregnancy, it alone cannot explain the origin and subsequent diversity of implantation strategies throughout the placental mammal radiation. MiRNAs are known to be flexible and dynamic regulators with a well-established role in the pathophysiology of mammal placenta. We propose that a dynamic core microRNA (miRNA) network originated early in placental mammal evolution, responds to conserved mammal pregnancy cues (e.g. progesterone), and facilitates species-specific responses. Here we identify 13 miRNA gene families that arose at the origin of placental mammals and were subsequently retained in all descendent lineages. The expression of these miRNAs in response to early pregnancy molecules is regulated in a species-specific manner in endometrial epithelia of species with extreme implantation strategies (i.e. bovine and human). Furthermore, this set of miRNAs preferentially target proteins under positive selective pressure on the ancestral eutherian lineage. Discovery of this core embryo implantation toolkit and specifically adapted proteins helps explain the origin and evolution of implantation in mammals.

MiR-1290: a potential therapeutic target for regenerative medicine or diagnosis and treatment of non-malignant diseases

MicroRNAs are a set of small non-coding RNAs that could change gene expression with post-transcriptional regulation. MiRNAs have a significant role in regulating molecular signaling pathways and innate and adaptive immune system activity. Moreover, miRNAs can be utilized as a powerful instrument for tissue engineers and regenerative medicine by altering the expression of genes and growth factors. MiR-1290, which was first discovered in human embryonic stem cells, is one of those miRNAs that play an essential role in developing the fetal nervous system. This review aims to discuss current findings on miR-1290 in different human pathologies and determine whether manipulation of miR-1290 could be considered a possible therapeutic strategy to treat different non-malignant diseases. The results of these studies suggest that the regulation of miR-1290 may be helpful in the treatment of some bacterial (leprosy) and viral infections (HIV, influenza A, and Borna disease virus). Also, adjusting the expression of miR-1290 in non-infectious diseases such as celiac disease, necrotizing enterocolitis, polycystic ovary syndrome, pulmonary fibrosis, ankylosing spondylitis, muscle atrophy, sarcopenia, and ischemic heart disease can help to treat these diseases better. In addition to acting as a biomarker for the diagnosis of non-malignant diseases (such as NAFLD, fetal growth, preeclampsia, down syndrome, chronic rhinosinusitis, and oral lichen planus), the miR-1290 can also be used as a valuable instrument in tissue engineering and reconstructive medicine. Consequently, it is suggested that the regulation of miR-1290 could be considered a possible therapeutic target in the treatment of non-malignant diseases in the future.

Fetal Growth and Intrauterine Epigenetic Programming of Obesity and Cardiometabolic Disease

Epidemiologic studies have shown an association between an adverse intrauterine environment (eg, exposure to malnutrition) and an increased risk of developing cardiometabolic disease in adulthood. These studies laid the foundation for the developmental origins of health and disease hypothesis, which states that limited nutrient supply to the fetus results in physiologic and metabolic adaptations that favor survival but result in unfavorable consequences in the offspring if there is excess nutrition after birth. This discrepancy in the pre- and postnatal milieus, perceived as stress by the offspring, may confer an increased risk of developing cardiometabolic disease later in life. Thus, early life exposures result in programming or changes in cellular memory that have effects on health throughout the life course. One of the mechanisms by which programming occurs is via epigenetic modifications of genes, processes that result in functionally relevant changes in genes (ie, gene expression) without an alteration in the genotype. In this review, we will describe how fetal exposures, including under- and overnutrition, affect neonatal and childhood growth and the future risk for cardiometabolic disease.

The Role of Non-Coding RNAs in the Human Placenta

Non-coding RNAs (ncRNAs) play a central and regulatory role in almost all cells, organs, and species, which has been broadly recognized since the human ENCODE project and several other genome projects. Nevertheless, a small fraction of ncRNAs have been identified, and in the placenta they have been investigated very marginally. To date, most examples of ncRNAs which have been identified to be specific for fetal tissues, including placenta, are members of the group of microRNAs (miRNAs). Due to their quantity, it can be expected that the fairly larger group of other ncRNAs exerts far stronger effects than miRNAs. The syncytiotrophoblast of fetal origin forms the interface between fetus and mother, and releases permanently extracellular vesicles (EVs) into the maternal circulation which contain fetal proteins and RNA, including ncRNA, for communication with neighboring and distant maternal cells. Disorders of ncRNA in placental tissue, especially in trophoblast cells, and in EVs seem to be involved in pregnancy disorders, potentially as a cause or consequence. This review summarizes the current knowledge on placental ncRNA, their transport in EVs, and their involvement and pregnancy pathologies, as well as their potential for novel diagnostic tools.

Epigenetic modifications from arsenic exposure: A comprehensive review

Arsenic is a notorious element with the potential to harm exposed individuals in ways that include cancerous and non-cancerous health complications. Millions of people across the globe (especially in South and Southeast Asian countries including China, Vietnam, India and Bangladesh) are currently being unknowingly exposed to precarious levels of arsenic. Among the diverse effects associated with such arsenic levels of exposure is the propensity to alter the epigenome. Although a large volume of literature exists on arsenic-induced genotoxicity, cytotoxicity, and inter-individual susceptibility due to active research on these subject areas from the last millennial, it is only recently that attention has turned on the ramifications and mechanisms of arsenic-induced epigenetic changes. The present review summarizes the possible mechanisms involved in arsenic induced epigenetic alterations. It focuses on the mechanisms underlying epigenome reprogramming from arsenic exposure that result in improper cell signaling and dysfunction of various epigenetic components. The mechanistic information articulated from the review is used to propose a number of novel therapeutic strategies with a potential for ameliorating the burden of worldwide arsenic poisoning.

An Insight into miR-1290: An Oncogenic miRNA with Diagnostic Potential

For more than two decades, the view of the roles of non-coding RNAs (ncRNAs) has been radically changing. These RNA molecules that are transcribed from our genome do not have the capacity to encode proteins, but are critical regulators of gene expression at different levels. Our knowledge is constantly enriched by new reports revealing the role of these new molecular players in the development of many pathological conditions, including cancer. One of the ncRNA classes includes short RNA molecules called microRNAs (miRNAs), which are involved in the post-transcriptional control of gene expression affecting various cellular processes. The aberrant expression of miRNAs with oncogenic and tumor-suppressive function is associated with cancer initiation, promotion, malignant transformation, progression and metastasis. Oncogenic miRNAs, also known as oncomirs, mediate the downregulation of tumor-suppressor genes and their expression is upregulated in cancer. Nowadays, miRNAs show promising application in diagnosis, prediction, disease monitoring and therapy response. Our review presents a current view of the oncogenic role of miR-1290 with emphasis on its properties as a cancer biomarker in clinical medicine.

Urinary metals and maternal circulating extracellular vesicle microRNA in the MADRES pregnancy cohort

Exposure to metals increases risk for pregnancy complications. Extracellular vesicle (EV) miRNA contribute to maternal-foetal communication and are dysregulated in pregnancy complications. However, metal impacts on maternal circulating EV miRNA during pregnancy are unknown. Our objective was to investigate the impact of multiple metal exposures on EV miRNA in maternal circulation during pregnancy in the MADRES Study. Associations between urinary concentrations of nine metals and 106 EV miRNA in maternal plasma during pregnancy were investigated using robust linear regression (N = 231). Primary analyses focused on metal-miRNA associations in early pregnancy (median: 12.3 weeks gestation). In secondary analyses, we investigated associations with late pregnancy miRNA counts (median: 31.8 weeks gestation) in a subset of participants (N = 184) with paired measures. MiRNA associated with three or more metals (P_FDR<0.05) were further investigated using Bayesian Kernel Machine Regression (BKMR), an environmental mixture method. Thirty-five miRNA were associated (P_FDR<0.05) with at least one metal in early pregnancy. One association (an inverse association between cobalt and miR-150-5p) remained statistically significant when evaluating late pregnancy miRNA counts. Eight miRNA (miR-302b-3p, miR-199a-5p, miR-188-5p, miR-138-5p, miR-212-3p, miR-608, miR-1272, miR-19b-3p) were associated with three metals (barium, mercury, and thallium) in early pregnancy, and their predicted target genes were enriched in pathways important for placental development. Results were consistent when using BKMR. Early pregnancy exposure to barium, mercury, and thallium may have short-term impacts on a common set of EV miRNA which target pathways important for placental development.

Transcriptomics and Other Omics Approaches to Investigate Effects of Xenobiotics on the Placenta

The conceptus is most vulnerable to developmental perturbation during its early stages when the events that create functional organ systems are being launched. As the placenta is in direct contact with maternal tissues, it readily encounters any xenobiotics in her bloodstream. Besides serving as a conduit for solutes and waste, the placenta possesses a tightly regulated endocrine system that is, of itself, vulnerable to pharmaceutical agents, endocrine disrupting chemicals (EDCs), and other environmental toxicants. To determine whether extrinsic factors affect placental function, transcriptomics and other omics approaches have become more widely used. In casting a wide net with such approaches, they have provided mechanistic insights into placental physiological and pathological responses and how placental responses may impact the fetus, especially the developing brain through the placenta-brain axis. This review will discuss how such omics technologies have been utilized to understand effects of EDCs, including the widely prevalent plasticizers bisphenol A (BPA), bisphenol S (BPS), and phthalates, other environmental toxicants, pharmaceutical agents, maternal smoking, and air pollution on placental gene expression, DNA methylation, and metabolomic profiles. It is also increasingly becoming clear that miRNA (miR) are important epigenetic regulators of placental function. Thus, the evidence to date that xenobiotics affect placental miR expression patterns will also be explored. Such omics approaches with mouse and human placenta will assuredly provide key biomarkers that may be used as barometers of exposure and can be targeted by early mitigation approaches to prevent later diseases, in particular neurobehavioral disorders, originating due to placental dysfunction.

Health Effects Associated With Pre- and Perinatal Exposure to Arsenic

Inorganic arsenic is a well-established human carcinogen, able to induce genetic and epigenetic alterations. More than 200 million people worldwide are exposed to arsenic concentrations in drinking water exceeding the recommended WHO threshold (10μg/l). Additionally, chronic exposure to levels below this threshold is known to result in long-term health effects in humans. The arsenic-related health effects in humans are associated with its biotransformation process, whereby the resulting metabolites can induce molecular damage that accumulates over time. The effects derived from these alterations include genomic instability associated with oxidative damage, alteration of gene expression (including coding and non-coding RNAs), global and localized epigenetic reprogramming, and histone posttranslational modifications. These alterations directly affect molecular pathways involved in the onset and progression of many conditions that can arise even decades after the exposure occurs. Importantly, arsenic metabolites generated during its biotransformation can also pass through the placental barrier, resulting in fetal exposure to this carcinogen at similar levels to those of the mother. As such, more immediate effects of the arsenic-induced molecular damage can be observed as detrimental effects on fetal development, pregnancy, and birth outcomes. In this review, we focus on the genetic and epigenetic damage associated with exposure to low levels of arsenic, particularly those affecting early developmental stages. We also present how these alterations occurring during early life can impact the development of certain diseases in adult life.

High-throughput miRNA sequencing of the human placenta: expression throughout gestation

Aim: To understand miRNA changes across gestation in healthy human placentae. This is essential before miRNAs can be used as biomarkers or prognostic indicators during pregnancy. Materials & methods: Using next-generation sequencing, we characterize the normative human placenta miRNome in first (n = 113) and third trimester (n = 47). Results & conclusion: There are 801 miRNAs expressed in both first and third trimester, including 182 with similar expression across gestation (p ≥ 0.05, fold change ≤2) and 180 significantly different (false discovery rate <0.05, fold change >2). Of placenta-specific miRNA clusters, chromosome 14 miRNA cluster decreases across gestation and chromosome 19 miRNA cluster is overall highly expressed. Chromosome 13 clusters are upregulated in first trimester. This work provides a rich atlas of healthy pregnancies to direct functional studies investigating the epigenetic differences in first and third trimester placentae.

Placental microRNA expression associates with birthweight through control of adipokines: results from two independent cohorts

MicroRNAs are non-coding RNAs that regulate gene expression post-transcriptionally. In the placenta, the master regulator of foetal growth and development, microRNAs shape the basic processes of trophoblast biology and specific microRNA have been associated with foetal growth. To comprehensively assess the role of microRNAs in placental function and foetal development, we have performed small RNA sequencing to profile placental microRNAs from two independent mother-infant cohorts: the Rhode Island Child Health Study (n = 225) and the New Hampshire Birth Cohort Study (n = 317). We modelled microRNA counts on infant birthweight percentile (BWP) in each cohort, while accounting for race, sex, parity, and technical factors, using negative binomial generalized linear models. We identified microRNAs that were differentially expressed (DEmiRs) with BWP at false discovery rate (FDR) less than 0.05 in both cohorts. hsa-miR-532-5p (miR-532) was positively associated with BWP in both cohorts. By integrating parallel whole transcriptome and small RNA sequencing in the RICHS cohort, we identified putative targets of miR-532. These targets are enriched for pathways involved in adipogenesis, adipocytokine signalling, energy metabolism, and hypoxia response, and included Leptin, which we further demonstrated to have a decreasing expression with increasing BWP, particularly in male infants. Overall, we have shown a robust and reproducible association of miR-532 with BWP, which could influence BWP through regulation of adipocytokines Leptin and Adiponectin.

Placental genomic and epigenomic signatures associated with infant birth weight highlight mechanisms involved in collagen and growth factor signaling

Birth weight (BW) represents an important clinical and toxicological measure, indicative of the overall health of the newborn as well as potential risk for later-in-life outcomes. BW can be influenced by endogenous and exogenous factors and is known to be heavily impacted in utero by the health and function of the placenta. An aspect that remains understudied is the influence of genomic and epigenomic programming within the placenta on infant BW. To address this gap, we set out to test the hypothesis that genes involved in critical placental cell signaling are associated with infant BW, and are likely regulated, in part, through epigenetic mechanisms based on microRNA (miRNA) mediation. This study leveraged a robust dataset based on 390 infants born at low gestational age (ranged 23-27 weeks) to evaluate genome-wide expression profiles of both mRNAs and miRNAs in placenta tissues and relate these to infant BW. A total of 254 mRNAs and 268 miRNAs were identified as associated with BW, the majority of which showed consistent associations across placentas derived from both males and females. BW-associated mRNAs were found to be enriched for important biological pathways, including glycoprotein VI (the major receptor for collagen), human growth, and hepatocyte growth factor signaling, a portion of which were predicted to be regulated by BW-associated miRNAs. These miRNA-regulated pathways highlight key mechanisms potentially linking endogenous/exogenous factors to changes in birth outcomes that may be deleterious to infant and later-in-life health.

Placental miRNAs in feto-maternal communication mediated by extracellular vesicles

A complex network composed of at least 1900 microRNA (miRNA) species orchestrates the development and function of the human placenta. These molecules regulate genes and pathways operating major functional processes in trophoblast cells such as proliferation, invasion, differentiation, and metabolism. Nevertheless, the cellular localization and role of most placental miRNAs remain to be determined. The existence of eutherian- (C14MC) and primate-specific miRNA clusters (C19MC), together with human placenta-specific miRNAs, indicate the relevance of these molecules in evolution and diversification of the placenta, including the acquisition of its unique features in humans. They may be related also to diseases that are exclusively present in primates, such as preeclampsia. Changes in the miRNA expression profile have been reported in several placental pathologies. Which miRNAs are involved in the pathomechanism of these diseases or act to maintain placental homeostasis is uncertain. Placenta-derived miRNAs are packed into extracellular vesicles (EVs) and distributed through the maternal circulation to distant organs, where they contribute to adaptations required during pregnancy. Similarly, the placenta also receives molecular information from other tissues to adapt fetoplacental metabolic demands to the maternal energetic supply. These processes can be impaired in pathologic conditions. Therefore, the collection of circulating placental miRNAs constitutes potentially a minimally-invasive approach to assess the fetoplacental status and to diagnose pregnancy diseases. Future therapies may include manipulation of miRNA levels for prevention and treatment of placental complications to protect maternal health and fetal development.

Repeated measures of prenatal thallium exposure and placental inflammatory cytokine mRNA expression: The Ma'anshan birth cohort (MABC) study

Thallium (Tl), a ubiquitous environmental toxicant, can cross the placental barrier during pregnancy. However, the effects of prenatal Tl exposure on placental function are currently unclear. Based on the Ma'anshan Birth Cohort study, we examined whether long-term prenatal Tl exposure was associated with placental inflammation. Tl concentrations were quantified in serum samples (n = 7050) from 2515 pregnancy during each trimester, placental inflammatory cytokine mRNA expression was assessed in 2519 placenta tissues. Geometric mean values of serum Tl concentrations were 63.57, 63.63 and 48.71 ng/L for the first, second and third trimesters, respectively. After adjustment for potential confounders, serum Tl concentration was positively associated with CD68 (β: 0.30; 95% CI: 0.05, 0.56) in the first trimester and TNF-α (β: 0.12; 95% CI: 0.01, 0.23), IL-6 (β: 0.15; 95% CI: 0.05, 0.25) and CD68 (β: 0.25; 95% CI: 0.10, 0.39) in the third trimester, however was negatively associated with IL-4 (β: -0.21; 95% CI: -0.41, -0.01) and CD206 (β: -0.23; 95% CI: -0.45, -0.02) in the first trimester. Repeated measures analysis showed that TNF-α, IL-6 and CD68 increased by 0.11 (95% CI: 0.01, 0.21), 0.12 (0.15, 95% CI: 0.05, 0.25), 0.22 (95% CI: 0.10, 0.39), respectively, with each 1ln-transformed Tl increase in total samples. Gender-specific analyses revealed that these associations were largely driven by male offspring. In addition, immunohistochemistry revealed that nuclear NF-κB p65 expression increased in placenta tissue. The results of this prospective cohort study provide longitudinal evidence that prenatal Tl exposure induces a placental inflammatory response in the Chinese population.

Association between occupational exposure to trichloroethylene and serum levels of microRNAs: a cross-sectional molecular epidemiology study in China

OBJECTIVES

The objective of our study was to evaluate the association between occupational exposure to trichloroethylene (TCE), a suspected lymphomagen, and serum levels of miRNAs in a cross-sectional molecular epidemiology study of TCE-exposed workers and comparable unexposed controls in China.

METHODS

Serum levels of 40 miRNAs were compared in 74 workers exposed to TCE (median: 12 ppm) and 90 unexposed control workers. Linear regression models were used to test for differences in serum miRNA levels between exposed and unexposed workers and to evaluate exposure-response relationships across TCE exposure categories using a three-level ordinal variable [i.e., unexposed, < 12 ppm, the median value among workers exposed to TCE) and ≥ 12 ppm)]. Models were adjusted for sex, age, current smoking, current alcohol use, and recent infection.

RESULTS

Seven miRNAs showed significant differences between exposed and unexposed workers at FDR (false discovery rate) < 0.20. miR-150-5p and let-7b-5p also showed significant inverse exposure-response associations with TCE exposure (Ptrend= 0.002 and 0.03, respectively). The % differences in serum levels of miR-150-5p relative to unexposed controls were - 13% and - 20% among workers exposed to < 12 ppm and ≥ 12 ppm TCE, respectively.

CONCLUSIONS

miR-150-5p is involved in B cell receptor pathways and let-7b-5p plays a role in the innate immune response processes that are potentially important in the etiology of non-Hodgkin lymphoma (NHL). Further studies are needed to replicate these findings and to directly test the association between serum levels of these miRNAs and risk of NHL in prospective studies.

Air pollution-induced placental alterations: an interplay of oxidative stress, epigenetics, and the aging phenotype?

According to the "Developmental Origins of Health and Disease" (DOHaD) concept, the early-life environment is a critical period for fetal programming. Given the epidemiological evidence that air pollution exposure during pregnancy adversely affects newborn outcomes such as birth weight and preterm birth, there is a need to pay attention to underlying modes of action to better understand not only these air pollution-induced early health effects but also its later-life consequences. In this review, we give an overview of air pollution-induced placental molecular alterations observed in the ENVIRONAGE birth cohort and evaluate the existing evidence. In general, we showed that prenatal exposure to air pollution is associated with nitrosative stress and epigenetic alterations in the placenta. Adversely affected CpG targets were involved in cellular processes including DNA repair, circadian rhythm, and energy metabolism. For miRNA expression, specific air pollution exposure windows were associated with altered miR-20a, miR-21, miR-146a, and miR-222 expression. Early-life aging markers including telomere length and mitochondrial DNA content are associated with air pollution exposure during pregnancy. Previously, we proposed the air pollution-induced telomere-mitochondrial aging hypothesis with a direct link between telomeres and mitochondria. Here, we extend this view with a potential co-interaction of different biological mechanisms on the level of placental oxidative stress, epigenetics, aging, and energy metabolism. Investigating the placenta is an opportunity for future research as it may help to understand the fundamental biology underpinning the DOHaD concept through the interactions between the underlying modes of action, prenatal environment, and disease risk in later life. To prevent lasting consequences from early-life exposures of air pollution, policy makers should get a basic understanding of biomolecular consequences and transgenerational risks.