Upregulation of METTL3 expression and m6A RNA methylation in placental trophoblasts in preeclampsia

METTL3 shapes m6A epitranscriptomic landscape for successful human placentation

Methyltransferase-like 3 (METTL3), the catalytic enzyme of methyltransferase complex for m6A methylation of RNA, is essential for mammalian development. However, the importance of METTL3 in human placentation remains largely unexplored. Here, we show that a fine balance of METTL3 function in trophoblast cells is essential for successful human placentation. Both loss-of and gain-in METTL3 functions are associated with adverse human pregnancies. A subset of recurrent pregnancy losses and preterm pregnancies are often associated with loss of METTL3 expression in trophoblast progenitors. In contrast, METTL3 is induced in pregnancies associated with fetal growth restriction (FGR). Our loss of function analyses showed that METTL3 is essential for the maintenance of human TSC self-renewal and their differentiation to extravillous trophoblast cells (EVTs). In contrast, loss of METTL3 in human TSCs promotes syncytiotrophoblast (STB) development. Global analyses of RNA m6A modification and METTL3-RNA interaction in human TSCs showed that METTL3 regulates m6A modifications on the mRNA molecules of critical trophoblast regulators, including GATA2, GATA3, TEAD1, TEAD4, WWTR1, YAP1, TFAP2C and ASCL2, and loss of METTL3 leads to depletion of mRNA molecules of these critical regulators. Importantly, conditional deletion of Mettl3 in trophoblast progenitors of an early post-implantation mouse embryo also leads to arrested self-renewal. Hence, our findings indicate that METLL3 is a conserved epitranscriptomic governor in trophoblast progenitors and ensures successful placentation by regulating their self-renewal and dictating their differentiation fate.

Demethylase FTO-mediated m6A modification of SIK1 modulates placental cytotrophoblast syncytialization in type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) represents a common complication during pregnancy that affects fetoplacental development. We demonstrated the existence of impaired trophoblast syncytialization under hyperglycemic conditions. However, the exact mechanism remains unknown. RNA N6-methyladenosine (m6A) is an emerging regulatory mechanism of mRNA and participates in various biological processes. We described the global m6A modification pattern in T2DM placenta by the combined analysis of methylated RNA immunoprecipitation sequencing (MeRIP-Seq) and RNA sequencing (RNA-Seq). Both the m6A modification and expression of SIK1, which is critical for syncytialization, were significantly decreased in trophoblast exposed to hyperglycemic conditions. In addition, the m6A demethylase fat mass and obesity-associated protein (FTO) affects the expression and mRNA stability of SIK1 by binding to its 3'-untranslated region (UTR) m6A site. This work reveals that the FTO-m6A-SIK1 axis plays critical roles in regulating syncytialization in the placenta.

N6-methyladenosine dynamics in placental development and trophoblast functions, and its potential role in placental diseases

N6-methyladenosine (m6A) is the most abundant modification controlling RNA metabolism and cellular functions, but its roles in placental development are still poorly understood. Here, we characterized the synchronization of m6A modifications and placental functions by mapping the m6A methylome in human placentas (n = 3, each trimester), revealing that the dynamic patterns of m6A were associated with gene expression homeostasis and different biological pathways in placental development. Then, we generated trophoblast-specific knockout mice of Wtap, a critical component of methyltransferase complex, and demonstrated that Wtap was essential for trophoblast proliferation, placentation and perinatal growth. Further in vitro experiments which includes cell viability assays and series molecular binding assays demonstrated that WTAP-m6A-IGF2BP3 axis regulated the RNA stability and translation of Anillin (ANLN) and VEGFA, promoting trophoblast proliferation and secretion. Dysregulation of this regulatory axis was observed in placentas from pregnancies with fetal growth restriction (FGR) or preeclampsia, revealing the pathogenic effects of imbalanced m6A modifications. Therefore, our findings provide novel insights into the functions and regulatory mechanisms of m6A modifications in placental development and placental-related gestational diseases.

Overexpression of RBM15 modulated the effect of trophoblast cells by promoting the binding ability between YTHDF2 and the CD82 3'UTR to decrease the expression of CD82

Background

Pre-eclampsia (PE) is a syndrome with no specific pathological mechanism and is specific to pregnancy. The combined analysis of proteomics and transcriptomics possesses many benefits for treating this disease. m6A modification plays a major role in PE; however, mechanism have not been studied clearly. This study investigated the potential mechanism underlying the role of m6A in PE.

Methods

Mass spectrometry-based label-free quantitative proteomics and transcriptomics experiments were conducted on the placenta of patients with pre-eclampsia and normal pregnancies, and the two omics were followed by joint analysis. Total m6A modification in placental tissues, HTR8/SVneo cells, and JEG-3 cells was measured by dot blot. The levels of RBM15 and CD82 in tissues and cells were detected using qPCR. The protein levels of G3BP1, RBM15, MMP-2, YTHDF2, and MMP-9 were measured by western blotting. The function, migration, and invasion characteristics of HTR8/SVneo and JEG-3 cells were measured using Transwell assays. SRAMP predicted the m6A modification site in the CD82 mRNA 3'UTR, and this was confirmed using luciferase activity and YTHDF2-RIP.

Results

m6A modification was promoted in the PE group, and the RBM15 abundance was increased. Overexpression of RBM15 increased m6A modification. However, overexpression of RBM15 suppressed the expression of MMP-2 and MMP-9 and also the migratory and invasive capabilities of HTR8/SVneo and JEG-3 cells. CD82 expression levels were decreased in PE, and CD82 expression was confirmed via qPCR, western blotting and immunofluorescence. Furthermore, RBM15 overexpression reduced CD82 mRNA and protein levels. Luciferase activity and YTHDF2-RIP results verified that overexpression of RBM15 promoted the binding ability between YTHDF2 and the CD82 3'UTR, thereby decreasing CD82 expression. Finally, CD82 overexpression reversed the effect of RBM15 overexpression on the expression of MMP-2 and MMP-9 and on the migratory and invasive capabilities of the cells.

Conclusions

Overexpression of RBM15 hindered the migratory and invasive capabilities of trophoblasts, while concurrently enhancing m6A modification. The potential mechanism was that overexpression of RBM15 promoted the binding capability between YTHDF2 and CD82 3'UTR and decrease the expression of CD82. Thus, this study provides a theoretical basis for the treatment of PE.

Oxidative stress contributes to hypermethylation of Histone H3 lysine 9 in placental trophoblasts from preeclamptic pregnancies

Background and objective

Aberrant epigenetic regulation and increased oxidative stress in the placenta play a significant role in placental pathophysiology and fetal programming in preeclampsia, a hypertensive disorder in human pregnancy. The purpose of the study is to investigate if hypermethylation of histone H3K9 occurs in placental trophoblasts from preeclampsia.

Methods

Trophoblasts were isolated and cultured from 14 placentas, 7 from normotensive pregnant women and 7 from preeclamptic pregnancies. Methylated H3K9 expression and antioxidant superoxide dismutase expression were determined by Western blot. We also examined consequences of oxidative stress and the downstream effects of histone methyltransferase inhibition on H3K9 expression associated with antioxidant CuZn-SOD and Mn-SOD expression in placental trophoblasts.

Results

We found that expression of mono-, di-, and tri-methylation of histone H3 lysine 9 (H3K9me1, H3K9me2 and H3K9me3) was significantly increased, p<0.01, which correlated with downregulation of antioxidant superoxide dismutase CuZn-SOD and Mn-SOD expression, in trophoblasts from preeclamptic placentas compared to those from uncomplicated control placentas. We further demonstrated hypoxia could promote histone H3K9 methylation in placental trophoblasts, and hypoxia-induced upregulation of H3K9me1, H3K9me2 and H3K9me3 expression was reversible when hypoxic condition was removed. In addition, we also uncovered that inhibition of methyltransferase not only prevented hypoxia-induced upregulation of H3K9me1, H3K9me2 and H3K9me3 expression, but also abolished hypoxia-induced downregulation of CuZn-SOD and Mn-SOD expression in placental trophoblasts.

Conclusions

These findings are noteworthy and provide further evidence that increased oxidative stress in the intrauterine environment is likely a mechanism to induce aberrant histone modification in placental trophoblasts in preeclampsia. Moreover, CuZn-SOD and Mn-SOD expression/activity are possibly H3K9 methylation-dependent in placental trophoblasts, which further suggest that oxidative stress and aberrant histone modification have significant impact on placental trophoblasts/fetal programming in preeclampsia.

METTL3 promotes trophoblast ferroptosis in preeclampsia by stabilizing the ACSL4 m6A modification

This study aims to explore the role of methyltransferase-like 3 (METTL3) modulation of ferroptosis in the pathogenesis of trophoblast-mediated preeclampsia. The expression of METTL3 and acyl-CoA synthetase long chain family member 4 (ACSL4) was measured in clinical placental tissues and trophoblasts using qPCR and Western blot techniques. The effects of METTL3 on the symptoms of preeclampsia were also validated in rat models. METTL3 and ACSL4 were upregulated in placental tissues from patients with preeclampsia and in hypoxia-induced trophoblasts. METTL3 silencing increased the migration and invasion of trophoblasts cultured under hypoxic conditions. Knockdown of METTL3 increased cell viability and suppressed ferroptosis in hypoxia-stimulated trophoblasts. Hypoxia increased the level of m6A in cells, whereas silencing METTL3 partially reversed this change. Silencing METTL3 resulted in a decrease in m6A modification of ACSL4 mRNA, which led to a reduction in ACSL4 mRNA stability. ACSL4 upregulation partially reversed the effects of METTL3 silencing on cell viability, migration, invasion, and ferroptosis in hypoxia-stimulated trophoblasts. Inhibition of METTL3 in preeclampsia rats decreased blood pressure, urine protein levels, fetal survival rate, and ACSL4-mediated ferroptosis. METTL3 elevates ferroptosis to inhibit the migration and invasion of trophoblasts and in vivo preeclampsia symptoms by catalyzing the m6A modification of ACSL4 mRNA.

LAT1-dependent placental methionine uptake is a key player in fetal programming of metabolic disease

The Developmental Origins of Health and Disease hypothesis sustains that exposure to different stressors during prenatal development prepares the offspring for the challenges to be encountered after birth. We studied the gestational period as a particularly vulnerable window where different stressors can have strong implications for fetal programming of the offspring's life-long metabolic status via alterations of specific placentally expressed nutrient transporters. To study this mechanism, we used a murine prenatal stress model, human preeclampsia, early miscarriage, and healthy placental tissue samples, in addition to in vitro models of placental cells. In stressed mice, placental overexpression of L-type amino acid transporter 1 (Lat1) and subsequent global placental DNA hypermethylation was accompanied by fetal and adult hypothalamic dysregulation in global DNA methylation and gene expression as well as long-term metabolic abnormalities exclusively in female offspring. In human preeclampsia, early miscarriage, and under hypoxic conditions, placental LAT1 was significantly upregulated, leading to increased methionine uptake and global DNA hypermethylation. Remarkably, subgroups of healthy term placentas with high expression of stress-related genes presented increased levels of placental LAT1 mRNA and protein, DNA and RNA hypermethylation, increased methionine uptake capacity, one-carbon metabolic pathway disruption, higher methionine concentration in the placenta and transport to the fetus specifically in females. Since LAT1 mediates the intracellular accumulation of methionine, global DNA methylation, and one-carbon metabolism in the placenta, our findings hint at a major sex-specific global response to a variety of prenatal stressors affecting placental function, epigenetic programming, and life-long metabolic disease and provide a much-needed insight into early-life factors predisposing females/women to metabolic disorders.

HMOX1 Participates in Pre-Eclampsia by Regulating the Proliferation, Apoptosis, and Angiogenesis Modulation Potential of Mesenchymal Stem Cells via VEGF

Mesenchymal stem cells (MSCs) are involved in the pathogenesis of pre-eclampsia (PE). Heme oxygenase (HMOX) protects against placental cytotoxic injuries associated with PE. Here, we aimed to clarify the roles of HMOX1 in MSC proliferation and apoptosis, trophoblast cell migration, and regulation of angiogenesis, and assess its involvement in the pathogenesis of PE. HMOX1 and vascular endothelial growth factor (VEGF) expression levels in decidual tissues and decidua-derived MSCs (dMSCs) of healthy pregnant women and patients with PE were evaluated via quantitative reverse transcription-polymerase chain reaction and western blotting. Moreover, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, flow cytometry, and transwell assays were used to analyze the cell viability, apoptosis, and migration, respectively. The tube formation ability of human umbilical vein endothelial cells (HUVECs) was also evaluated. Compared to the healthy pregnant women, HMOX1 expression was upregulated in the decidual tissue and downregulated in the dMSCs of patients with PE. HMOX1 overexpression significantly increased dMSC proliferation, decreased cell apoptosis, and increased VEGF expression. Moreover, HMOX1-plasmid transfected dMSC culture supernatant promoted the migration of HTR-8/SVneo cells and improved angiogenesis by HUVECs. The opposite effects were observed in HMOX1-small interfering RNA-treated dMSCs cells. However, VEGF-siRNA reversed the effects of HMOX1-plasmid. HMOX1 is involved in the pathogenesis of PE by regulating the proliferation, apoptosis, and angiogenesis modulation potential of MSCs via VEGF, acting as a potential therapeutic target for PE.

Propofol Promoted the Cell Growth and Epithelial Mesenchymal Transformation of the HTR-8/SVneo Cells through Targeting the METTL3 Mediated ZEB2

Preeclampsia (PE) belongs to hypertensive disorder complicating pregnancy, which is a serious obstetric complication. Propofol is a new type of fast and short-acting general anesthetic, which has also been demonstrated to promote the cell growth recently. Therefore, this study was carried out to explore the effects of propofol on the cell growth, migration and invasion in the HTR-8/SVneo cells. The cell biological behaviors were analyzed using CCK-8, EdU, transwell assays. The relationship between METTL3 and ZEB2 was confirmed by RIP assay. Western blot and RT-qPCR assays were carried out to detect the protein and mRNA levels. The results showed that propofol enhanced the cell viability, proliferation, migration and invasion of the HTR-8/SVneo cells. Besides, METTL3 overexpression neutralized the propofol role. Furthermore, METTL3 overexpression elevated the m6A levels of ZEB2 and decreased the mRNA levels and stability of ZEB2. ZEB2 overexpression neutralized the role of METTL3 in the propofol treated HTR-8/SVneo cells. In conclusion, this study demonstrated the effects of propofol on promoting the cell growth, migration and invasion of HTR-8/SVneo cells. Mechanistically, propofol indirectly regulated ZEB2 expression by targeting METTL3 mediated m6A methylation modification.

Exploring the role of m6A modification in the great obstetrical syndromes

BACKGROUND

N6-methyladenosine (m6A) is one of the predominant RNA epigenetic modifications that modify RNAs reversibly and dynamically by "writers" (methyltransferase), "erasers" (demethylase), and "readers."

OBJECTIVE

This review aimed to provide a comprehensive understanding of the complexity of m6A regulation in the great obstetrical syndromes to understand its pathogenesis and potential therapeutic targets.

METHODS

The terms "placenta or trophoblast" and "m6A or N6-methyladenosine" were searched in PubMed databases (June 2023).

RESULTS

In this review, we discuss the regulatory role of m6A in the great obstetrical syndromes such as preeclampsia (PE), spontaneous abortion (SA), hyperglycemia in pregnancy (HIP) and fetal growth to emphasize the clinical relevance of m6A dysregulation in pregnancy. We also describe mechanisms that potentially involve the participation of m6A methylation, such as proliferation, invasion, migration, apoptosis, autophagy, endoplasmic reticulum stress, macrophage polarization, and inflammation.

CONCLUSION

We summarize the recent research progress on the role of m6A modification in the great obstetrical syndromes and placental function and provide a brief perspective on its prospective applications.

N6-methyladenosine (m6A) Modification in Preeclampsia

Recently, epitranscriptional modification of N6-methyladenosine (m6A) has received growing attention in the research on the pathogenesis of preeclampsia. Advances in m6A sequencing have revealed the molecular mechanism and importance of m6A modification. In addition, epitranscriptional modification of m6A is closely related to the metabolic processes of placental tissues and cells in preeclampsia. This article reviews the composition, mode of action, and bioinformatics analysis of m6A modification-related proteins, and their biological function in the progression of preeclampsia. The relationship between m6A modification and preeclampsia risk factors, such as diabetes, cardiovascular disease, obesity, and psychological stress, is summarized to provide new ideas for studying PE-targeting molecules.

Low m6A modification-mediated upregulation of PLAC8 promotes trophoblast cell invasion and migration in preeclampsia

BACKGROUND

The main symptoms of preeclampsia (PE), a specific ailment that develops during pregnancy, are proteinuria and hypertension. The pathological root of the onset and progression of PE is widely regarded as abnormal placental trophoblast cell function. This study aimed to look into the character and mechanism of Placenta-specific 8 (PLAC8) in trophoblast cell invasion and migration.

METHODS

Expressions of PLAC8 and AlkB homologue 5 (ALKBH5) were examined by western blot and quantitative real-time PCR. The m6A level of PLAC8 mRNA was detected by methylated RNA Immunoprecipitation. Using Transwell experiments, cell invasion and migration were examined. The enzyme-linked immunosorbent assay was utilized to analyze the MMP-2 and MMP-9 secretion levels. RNA pull-down and RNA immunoprecipitation were conducted to detect the binding between ALKBH5 and PLAC8.

RESULTS

In PE tissue and hypoxia-treated HTR-8/SVneo cells, levels of ALKBH5 and PLAC8 were increased, and PLAC8 m6A methylation levels were decreased. There was a positive correlation between PLAC8 and ALKBH5 expression in clinical tissues. In addition, overexpressing PLAC8 promoted HTR-8/SVneo cell migration and invasion, and so as the levels of MMP-2 and MMP-9; while interference with PLAC8 reduced the migration and invasion of hypoxia-treated HTR-8/SVneo cells, and so as the levels of MMP-2 and MMP-9. Moreover, the PLAC8 mRNA's m6A modification site was GAACU (Position 1449, Site 2). Increased levels of MMP-2 and MMP-9, as well as migration and invasion of HTR-8/SVneo cells exposed to hypoxia, were all facilitated by the m6A Site2 mutation. Furthermore, ALKBH5 could bind to PLAC8, reduce its m6A modification, and promote its expression.

CONCLUSION

High-expressed ALKBH5 inhibits the m6A level of PLAC8 mRNA and promotes PLAC8 expression, while PLAC8 overexpression can promote hypoxia-induced invasion and migration of HTR-8/Svneo cells, indicating its potential protective function in PE.

The role of m6A methylation in prenatal maternal psychological distress and birth outcome

BACKGROUND

Prenatal maternal psychological distress (PMPD) is a known risk factor for adverse birth outcomes. N6-methyladenosine RNA (m6A) methylation is crucial in moderating RNA biology. This study aimed to evaluate the relationships between PMPD, birth outcomes, and placental m6A methylation.

METHODS

This was a prospective cohort study. PMPD exposure was assessed by questionnaires about prenatal stress, depression, and anxiety. Placental m6A methylation was measured using a colorimetric assay. The relationships between PMPD, m6A methylation, gestational age (GA), and birth weight (BW) were analyzed using structural equation models (SEMs). Maternal weight gain during pregnancy and infant sex were included as covariables.

RESULTS

The study included 209 mother-infant dyads. In an adjusted SEM, PMPD was associated with BW (B = -26.034; 95 % CI: -47.123, -4.868) and GA (B = -0.603; 95 % CI: -1.102, -0.154). M6A methylation was associated with PMPD (B = 0.055; 95 % CI: 0.040,0.073) and BW (B = -305.799; 95 % CI: -520.164, -86.460) but not GA. The effect of PMPD on BW was partially mediated by m6A methylation (B = -16.817; 95 % CI: -31.348, -4.638) and GA (B = -12.280; 95 % CI: -23.612, -3.079). Maternal weight gain was associated with BW (B = 5.113; 95 % CI: 0.229,10.438).

LIMITATIONS

The study sample size was small, and the specific mechanism of m6A methylation on birth outcomes needs to be further explored.

CONCLUSIONS

In this study, PMPD exposure negatively affected BW and GA. Placental m6A methylation was associated with PMPD and BW and partially mediated the effect of PMPD on BW. Our findings highlight the importance of perinatal psychological evaluation and intervention.

The landscape of implantation and placentation: deciphering the function of dynamic RNA methylation at the maternal-fetal interface

The maternal-fetal interface is defined as the interface between maternal tissue and sections of the fetus in close contact. RNA methylation modifications are the most frequent kind of RNA alterations. It is effective throughout both normal and pathological implantation and placentation during pregnancy. By influencing early embryo development, embryo implantation, endometrium receptivity, immune microenvironment, as well as some implantation and placentation-related disorders like miscarriage and preeclampsia, it is essential for the establishment of the maternal-fetal interface. Our review focuses on the role of dynamic RNA methylation at the maternal-fetal interface, which has received little attention thus far. It has given the mechanistic underpinnings for both normal and abnormal implantation and placentation and could eventually provide an entirely novel approach to treating related complications.

METTL3 silenced inhibited the ferroptosis development via regulating the TFRC levels in the Intracerebral hemorrhage progression

Intracerebral hemorrhage (ICH) refers to the hemorrhage caused by the increase and rupture of vascular brittleness in non traumatic brain parenchyma, which has been demonstrated to be closely related to ferroptosis. This study aimed to examine the effects of methyltransferase like 3 (METTL3) on the ferroptosis in the ICH progression. The PC12 cells was stimulated by hemin to establish a ICH model. The cell viability was tested by CCK8 assay. The Fe²⁺, reactive oxygen species (ROS), and malondialdehyde (MDA) levels were determined by the corresponding commercial kits. The cell death was analyzed by propidium Iodide (PI) staining. The lactylation levels were detected by western blot. M6A dot blot assay was performed to detected the total m6A levels and MeRIP assay was conducted to determine the m6A levels of transferrin receptor (TFRC). We found that the METTL3 and m6A levels were increased in the hemin treated PC12 cells. METTL3 knockdown increased the cell viability and decreased Fe²⁺, ROS and MDA levels in the hemin treated PC12 cells. The role of METTL3 knockdown in the hemin treated PC12 cells was reversed after TFRC overexpression. Mechanistically, the METTL3 lactylation was increased in the hemin treated PC12 cells, which further enhanced the protein stability and expression of METTL3. The up-regulated METTL3 increased the m6A levels and mRNA expressions of TFRC, which further induced the ferroptosis of the PC12 cells. In conclusion, the up-regulation of METTL3 lactylation enhanced the METTL3 protein stability and expression levels in hemin treated PC12 cells. METTL3 silenced suppressed the ferroptosis development through regulating the m6A levels of TFRC mRNA.

N6-methyladenosine modifications in maternal-fetal crosstalk and gestational diseases

As a medium among pregnant women, environment and fetus, placenta owns powerful and delicate epigenetic processes to regulate gene expression and maintain cellular homeostasis. N6-methyladenosine (m6A) is the most prevalent modification that determines the fate of RNA, and its dynamic reversibility indicates that m6A may serve as a sensitive responder to environmental stimuli. Emerging evidence suggests that m6A modifications play an essential role in placental development and maternal-fetal crosstalk, and are closely related to gestational diseases. Herein, we summarized the latest techniques for m6A sequencing and highlighted current advances of m6A modifications in maternal-fetal crosstalk and the underlying mechanisms in gestational diseases. Therefore, proper m6A modifications are important in placental development, but its disturbance mainly caused by various environmental factors can lead to abnormal placentation and function with possible consequences of gestational diseases, fetal growth and disease susceptibility in adulthood.

RNA N6-methyladenosine modification in female reproductive biology and pathophysiology

Gene expression and posttranscriptional regulation can be strongly influenced by epigenetic modifications. N⁶-methyladenosine, the most extensive RNA modification, has been revealed to participate in many human diseases. Recently, the role of RNA epigenetic modifications in the pathophysiological mechanism of female reproductive diseases has been intensively studied. RNA m⁶A modification is involved in oogenesis, embryonic growth, and foetal development, as well as preeclampsia, miscarriage, endometriosis and adenomyosis, polycystic ovary syndrome, premature ovarian failure, and common gynaecological tumours such as cervical cancer, endometrial cancer, and ovarian cancer. In this review, we provide a summary of the research results of m⁶A on the female reproductive biology and pathophysiology in recent years and aim to discuss future research directions and clinical applications of m⁶A-related targets. Hopefully, this review will add to our understanding of the cellular mechanisms, diagnostic biomarkers, and underlying therapeutic strategies of female reproductive system diseases. Video Abstract.

RBM15 suppresses hepatic insulin sensitivity of offspring of gestational diabetes mellitus mice via m6A-mediated regulation of CLDN4

BACKGROUND

Gestational diabetes Mellitus (GDM) is a common pregnancy-specific disease with high morbidity, which is linked to a high risk of obesity and diabetes in offspring. N6-methyladenosine modification of RNA is emerging as an important epigenetic mechanism that is widely manifested in many diseases. This study aimed to investigate the mechanism of m6A methylation in metabolic syndrome in offspring result from intrauterine hyperglycemia.

METHODS

GDM mice were established by feeding a high-fat diet 1 weeks before pregnancy. The m6A RNA methylation quantification kit was used to detect liver tissue methylation levels. PCR array was used to determine the expression of the m6A methylation modification enzyme. Immunohistochemistry, qRT-PCR, and western blot were used to examine the expression of RBM15, METTL13, IGF2BP1, and IGF2BP2. Subsequently, methylated RNA immunoprecipitation sequencing combined with mRNA sequencing, followed by dot blot and glucose uptake tests, were performed.

RESULTS

In this study, we found that offspring from a GDM mother were more vulnerable to glucose intolerance and insulin resistance. GC-MS revealed significant metabolic changes including saturated fatty acids and unsaturated fatty acids in liver of GDM offspring. We also demonstrated that global mRNA m6A methylation level was significantly increased in the fetal liver of GDM mice, indicating epigenetic change may have a strong relationship with the mechanism of metabolism syndrome. Concordantly, RBM15, the RNA binding methyltransferase, was upregulated in the liver. In vitro, RBM15 suppressed insulin sensitivity and increased insulin resistance through m6A-regulated epigenetic inhabitation of CLDN4. Moreover, MeRIP-sequencing and mRNA-sequencing revealed that differently regulated genes with differential m6A peaks were enriched in metabolic pathways.

CONCLUSION

Our study revealed the essential role of RBM15 in insulin resistance and the effect of RBM15-regulated m6A modification in the metabolic syndrome of offspring of GDM mice.

Methyltransferase-like 3 aggravates endoplasmic reticulum stress in preeclampsia by targeting TMBIM6 in YTHDF2-dependent manner

BACKGROUND

With the increasing morbidity and mortality of preeclampsia (PE), it has posed a huge challenge to public health. Previous studies have reported endoplasmic reticulum (ER) stress could contribute to trophoblastic dysfunction which was associated with the N⁶-methyladenosine (m⁶A) modification by methyltransferase-like 3 (METTL3), resulting in PE. However, little was known about the relationship between METTL3 and ER stress in PE. Thus, in vitro and in vivo studies were performed to clarify the mechanism about how METTL3 affects the trophoblasts under ER stress in PE and to explore a therapeutic approach for PE.

METHODS

An ER stress model in HTR-8/SVneo cells and a preeclamptic rat model were used to study the mechanism and explore a therapeutic approach for PE. Western blot, immunohistochemistry, quantitative reverse transcription-polymerase chain reaction (qRT-PCR), and methylated RNA immunoprecipitation (MeRIP)-qPCR were performed to detect the protein, RNA, and methylated transmembrane BAX inhibitor motif containing 6 (TMBIM6) expression levels. The m⁶A colorimetric and mRNA stability assays were used to measure the m⁶A levels and TMBIM6 stability, respectively. Short hairpin RNAs (shRNAs) were used to knockdown METTL3 and YTH N6-methyladenosine RNA binding protein 2 (YTHDF2). Flow cytometry and Transwell assays were performed to evaluate the apoptosis and invasion abilities of trophoblasts.

RESULTS

Upregulated METTL3 and m⁶A levels and downregulated TMBIM6 levels were observed in preeclamptic placentas under ER stress. The ER stress model was successfully constructed, and knockdown of METTL3 had a beneficial effect on HTR-8/SVneo cells under ER stress as it decreased the levels of methylated TMBIM6 mRNA. Moreover, overexpression of TMBIM6 was beneficial to HTR-8/SVneo cells under ER stress as it could neutralize the harmful effects of METTL3 overexpression. Similar to the knockdown of METTL3, downregulation of YTHDF2 expression resulted in the increased expression and mRNA stability of TMBIM6. Finally, improved systemic symptoms as well as protected placentas and fetuses were demonstrated in vivo.

CONCLUSIONS

METTL3/YTHDF2/TMBIM6 axis exerts a significant role in trophoblast dysfunction resulting in PE while inhibiting METTL3 may provide a novel therapeutic approach for PE.

Oxidative Stress Mediated by N6-Methyladenosine Methylation Contributes to High-Fat Diet Induced Male Reproductive Dysfunction

OBJECTIVE

To determine the mechanism of oxidative stress mediated by N6-methyladenosine (m6A) methylation contributing to high fat diet-induced reproductive dysfunction.

RESULTS

In vivo, compared with those in the Control group, the sperm count and sperm motility decrease significantly; the testosterone, luteinizing hormone levels, hyaluronidase, acrosomal enzyme levels, and total antioxidant capacity decrease significantly; malondialdehyde increases significantly in the DIO and DIO-R groups. The expression of nuclear factor erythroid 2-related factor 2 (Nrf2), superoxide dismutase 1 (SOD1), and NAD(P)H quinone dehydrogenase 1 (NQO1) decreases significantly in the DIO and DIO-R groups; m6A levels in testis tissue in the DIO and DIO-R groups increase; the enrichment of m6A-modified Nrf2 mRNA in testis in the DIO group and DIO-R group increases significantly. Also the m6A regulatory proteins increase significantly in the DIO group and DIO-R group. In vitro, compared to palmitic acid treated cells, the reactive oxygen species (ROS) level significantly decreases in STM2457, S-Adenosylhomocysteine treated cells and YTHDC2, YTHDF2 gene silence cells; however, Nrf2 expression increases in all treated cells. In addition, m6A expression decreases.

CONCLUSIONS

Oxidative stress mediates by methylation of m6A may contribute to high fat diet-induced male reproductive dysfunction.

Comprehensive analysis of transcriptomic profiling of 5-methylcytosin modification in placentas from preeclampsia and normotensive pregnancies

Increasing evidence suggests that RNA m5C modification and its regulators have been confirmed to be associated with the pathogenesis of many diseases. However, the distribution and biological functions of m5C in mRNAs of placental tissues remain unknown. we collected placentae from normotensive pregnancies (CTR) and preeclampsia patients (PE) to analyze the transcriptomic profiling of m5C RNA methylation through m5C RNA immunoprecipitation (UMI-MeRIP-Seq). we discovered that overall m5C methylation peaks were decreased in placental tissues from PE patients. And, 2844 aberrant m5C peaks were identified, of which respectively 1304 m5C peaks were upregulated and 1540 peaks were downregulated. The distribution of m5C peaks were mainly located in CDS (coding sequences) regions in placental tissues of both groups, but compared with the CTR group, the m5C peak in PE group before the stop code of CDS was significantly increased and even higher than the peak value after start code in CDS. Differentially methylated genes were mainly enriched in MAPK/cAMP signaling pathway. Moreover, the up-regulated genes with hypermethylated modification were enriched in the processes of hypoxia, inflammation/immune response. Finally, through analyzing the mRNA expression levels of m5C RNA methylation regulators, we found only DNMT3B and TET3 were significantly upregulated in PE samples than in control group. And they are not only negatively correlated with each other, but also closely related to those differentially expressed genes modified by differential methylation.Our findings provide new insights regarding alterations of m5C RNA modification into the pathogenic mechanisms of PE.

IGF2BP2 enhances LincRNA01116 stability via m6 A: A potential biomarker and therapeutic target for patients with pre-eclampsia

Pre-eclampsia (PE) is a serious complication in pregnant women characterized by failure of placental remodeling and is one of the primary causes of changes in the placental structure and function. The aberrant expression of long noncoding RNA is associated with the occurrence and progression of PE. This study found that linc01116 expression was significantly downregulated in PE patients and was related to poor uterine spiral artery remodeling. Knockdown of linc01116 remarkably decreased the angiogenesis of trophoblast cells in vitro and in vivo. Mechanistically, IGF2BP2 regulated linc01116 RNA stability via m⁶ A methylation. Bioinformatics and other experiments further revealed that linc01116 upregulates AAMP expression by adsorbing miR-210-3p in trophoblast cells. In conclusion, this study revealed the critical role of linc01116 in regulating trophoblast angiogenesis. Furthermore, the study provides new clues for detecting placental pathology in PE.

N6-methyladenosine modification in trophoblasts promotes circSETD2 expression, inhibits miR-181a-5p, and elevates MCL1 transcription to reduce apoptosis of trophoblasts

Preeclampsia (PE) is an obstetric disorder. N6-methyladenosine (m6A) modification is related to PE trophoblast biological behaviors. This study explored the mechanism of m6A-modified circSETD2 in trophoblast biological behaviors. Chorionic trophoblast apoptosis and circSETD2 expression in PE rat models were detected. HTR8/SVneo cells were induced by CoCl2 to establish PE trophoblast models. circSETD2 was silenced or overexpressed to evaluate its effect on cell proliferation, invasion, and apoptosis. m6A level of circSETD2 in trophoblasts was changed by pcDNA3.1-METTL3 and pcDNA3.1-FTO. The targeting relations among miR-181a-5p, circSETD2, and MCL1 were verified by dual-luciferase assay. miR-181a-5p and MCL1 expressions were interfered with to confirm the effect of m6A-modified circSETD2. m6A methylation level was changed in PE rats for in vivo validation. PE rats showed diminished circSETD2 expression and increased apoptosis index. circSETD2 overexpression promoted trophoblast proliferation and invasion, and reduced apoptosis. METTL3 overexpression increased total m6A, circSETD2 m6A, and circSETD2 levels. m6A modification mediated circSETD2 upregulation. circSETD2 was a sponge of miR-181a-5p to elevate MCL1 transcription. miR-181a-5p overexpression or MCL1 silencing annulled the role of m6A-modified circSETD2. circSETD2 inhibition negated suppression of METTL3 overexpression on chorionic trophoblast apoptosis in vivo. Collectively, m6A modification of circSETD2 suppressed miR-181a-5p and increased MCL1 transcription, thus regulating trophoblasts.

Bioinformatics analysis combined with clinical sample screening reveals that leptin may be a biomarker of preeclampsia

Introduction: Preeclampsia (PE) is a gestational hypertensive disease with unclear pathogenesis. This study aimed to identify the genes that play an important role in determining the pathogenesis of PE using bioinformatics analysis and fundamental researches. Materials and methods: Datasets from the Gene Expression Omnibus (GEO) database were used to screen for differentially expressed genes (DEGs). The NCBI, SangerBox, and other databases were used to analyze the functions of the DEGs. Targetscan7, miRWalk, ENCORI, DIANA TOOLS, CircBank databases, and the Cytoscape tool were used to construct the lncRNA/circRNA-miRNA- LEP network. SRAMP, RPISeq, RBPsuite, and catRPAID were used to analyze the RNA modifications of LEP. Immune cell infiltration was analyzed using the dataset GSE75010. Placental tissues from normal pregnant women and PE patients were collected, screened for gene expression using reverse transcription quantitative polymerase chain reaction (RT-qPCR) and western blotting. The results were further verified in HTR-8/SVneo cell line hypoxia model and PE mouse model. Results: Our analyses revealed that LEP was significantly upregulated in eight datasets. Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analyses indicated that LEP was involved in the JAK/STAT signaling pathway, angiogenesis, and placental development. Immune cell infiltration analysis showed that M1 and M2 macrophages differed between normal pregnancies and those in PE patients. A competing endogenous RNA (ceRNA) network was constructed, and proteins interacting with LEP were identified. RNA modification sites of LEP were also identified. Finally, the overexpression of LEP in PE was confirmed in clinical samples, HTR-8/SVneo cell line and PE mouse model. Conclusion: Our results indicate that LEP overexpression is associated with PE and may be a potential diagnostic marker and therapeutic target.

The m6A methyltransferase METTL3 promotes trophoblast cell invasion by regulating MYLK expression

INTRODUCTION

The progression of placental diseases such as preeclampsia is closely related to trophoblast dysfunction. Recent studies indicated the dysregulation of N6-methyladenosine (m⁶A) RNA modification in trophoblast disorders, while the function of METTL3, a methyltransferase of m⁶A, in trophoblasts remains to be studied.

METHODS

The expression of METTL3 was determined by real-time PCR and immunoblotting. METTL3 expression in trophoblast cell lines HTR-8/SVneo and JEG-3 was knocked down using shRNA. The invasion of trophoblast cells in Matrigel was determined using xCELLigence. The m⁶A-containing transcripts was determined by m⁶A-sequencing in HTR-8/SVneo cells. The myosin light chain kinase (MYLK) gene was transfected into HTR-8/SVneo cells.

RESULTS

The expression of METTL3 was downregulated in preeclamptic placentae compared to normal placentae. Knockdown of METTL3 repressed the invasion of extravillous trophoblast cells. Mechanistically, METTL3 promoted the stability of MYLK mRNA through m⁶A modification. Overexpression of MYLK rescued retarded cell invasion by METTL3 depletion.

DISCUSSION

Collectively, our results highlight an essential role of METTL3-MYLK axis in trophoblast invasion.

Research progress on N6-methyladenosine in the human placenta

OBJECTIVES

N6-methyladenosine (m6A) is one of the most common epigenetic modifications of eukaryotic RNA. Under the jointly reversible regulation of related enzymes, m6A regulates many aspects of RNA, such as translation, stability and degradation. The aim of this study is to investigate the role of m6A in placenta-related diseases.

METHODS

Data were compiled from 2018 to 2021 citations in PubMed and Google Scholar using the keywords: placenta AND N6-methyladenosine. Seven studies were included.

RESULTS

In this study, we introduced some conventional methods to detect m6A modification at the whole RNA, region (peak) and single base levels. We also summarized the current studies of m6A modification in the placenta and briefly describe m6A in placental-related diseases, including recurrent miscarriage (RM), preeclampsia (PE) and gestational diabetes mellitus (GDM).

CONCLUSIONS

Although the relevant reports are still in the preliminary stage and some results are inconsistent, studies on methylation m6A modification have contributed new ideas for the research of reproductive diseases, providing a new basis for the diagnosis, treatment, prognosis and monitoring of related diseases.

The regulation and potential roles of m6A modifications in early embryonic development and immune tolerance at the maternal-fetal interface

The immune microenvironment at the maternal-fetal interface was determined by the crosstalk between the trophoblast and maternal-derived cells, which dynamically changed during the whole gestation. Trophoblasts act as innate immune cells and dialogue with maternal-derived cells to ensure early embryonic development, depending on the local immune microenvironment. Therefore, dysfunctions in trophoblasts and maternal decidual cells contribute to pregnancy complications, especially recurrent pregnancy loss in early pregnancy. Since many unknown regulatory factors still affect the complex immune status, exploring new potential aspects that could influence early pregnancy is essential. RNA methylation plays an important role in contributing to the transcriptional regulation of various cells. Sufficient studies have shown the crucial roles of N6-methyladenosine (m6A)- and m6A-associated- regulators in embryogenesis during implantation. They are also essential in regulating innate and adaptive immune cells and the immune response and shaping the local and systemic immune microenvironment. However, the function of m6A modifications at the maternal-fetal interface still lacks wide research. This review highlights the critical functions of m6A in early embryonic development, summarizes the reported research on m6A in regulating immune cells and tumor immune microenvironment, and identifies the potential value of m6A modifications in shaping trophoblasts, decidual immune cells, and the microenvironment at the maternal-fetal interface. The m6A modifications are more likely to contribute to embryogenesis, placentation and shape the immune microenvironment at the maternal-fetal interface. Uncovering these crucial regulatory mechanisms could provide novel therapeutic targets for RNA methylation in early pregnancy.

Aberrant endothelial expression of hnRNPC1/C2 and VDR and reduced maternal vitamin D levels in women with preeclampsia

Vitamin D deficiency is a widespread health problem globally and vitamin D deficiency/ insufficiency in pregnancy is a risk factor for preeclampsia, a hypertensive disorder in human pregnancy. Vitamin D elicits its biological effects through binding to its receptor VDR. In the present study, we determined maternal vascular expression of VDR and hnRNPC1/C2, a native repressor of VDR, in subcutaneous adipose tissue from women with normal pregnancy and preeclampsia. Maternal antenatal and postnatal vitamin D levels were measured. We found that hnRNPC1/C2 expression was markedly increased, while VDR expression was markedly reduced, in maternal vessel endothelium and smooth muscle cells from women with preeclampsia compared to that from normal pregnant controls. Reduced VDR expression was relevant to low maternal antenatal and postnatal vitamin D levels in women with preeclampsia. Using human umbilical vein endothelial cells (HUVECs) as an endothelial model, we further investigated the role of hnRNPC1/C2-mediated VDR expression in endothelial cells, and tested effect of hnRNPC1/C2 inhibition on endothelial response to bioactive vitamin D, 1,25(OH)₂D₃. Our results showed that inhibition of hnRNPC1/C2 by hnRNPC1/C2 siRNA resulted in not only an increase in endothelial VDR expression, but further improved endothelial response to 1,25(OH)₂D₃. These findings indicate that aberrant hnRNPC1/C2 expression may contribute to reduced vascular expression of VDR in women with preeclampsia and suggest that hnRNPC1/C2 could be a target for improving vascular endothelial cell response to vitamin D.

Regulatory roles of non-coding RNAs and m6A modification in trophoblast functions and the occurrence of its related adverse pregnancy outcomes

Adverse pregnancy outcomes, such as preeclampsia, gestational diabetes mellitus, fetal growth restriction, and recurrent miscarriage, occur frequently in pregnant women and might further induce morbidity and mortality for both mother and fetus. Increasing studies have shown that dysfunctions of human trophoblast are related to these adverse pregnancy outcomes. Recent studies also showed that environmental toxicants could induce trophoblast dysfunctions. Moreover, non-coding RNAs (ncRNAs) have been reported to play important regulatory roles in various cellular processes. However, the roles of ncRNAs in the regulation of trophoblast dysfunctions and the occurrence of adverse pregnancy outcomes still need to be further investigated, especially with exposure to environmental toxicants. In this review, we analyzed the regulatory mechanisms of ncRNAs and m6A methylation modification in the dysfunctions of trophoblast cells and the occurrence of adverse pregnancy outcomes and also summarized the harmful effects of environmental toxicants. In addition to DNA replication, mRNA transcription, and protein translation, ncRNAs and m6A modification might be considered as the fourth and fifth elements that regulate the genetic central dogma, respectively. Environmental toxicants might also affect these processes. In this review, we expect to provide a deeper scientific understanding of the occurrence of adverse pregnancy outcomes and to discover potential biomarkers for the diagnosis and treatment of these outcomes.

Methyltransferase-like 3 facilitates lung cancer progression by accelerating m6A methylation-mediated primary miR-663 processing and impeding SOCS6 expression

OBJECTIVE

Lung cancer (LC) remains a threatening health issue worldwide. Methyltransferase-like protein 3 (METTL3) is imperative in carcinogenesis via m6A modification of microRNAs (miRNAs). This study estimated the effect of METTL3 in LC by regulating m6A methylation-mediated pri-miR-663 processing.

METHODS

miR-663 expression in 4 LC cell lines and normal HBE cells was determined using RT-qPCR. A549 and PC9 LC cells selected for in vitro studies were transfected with miR-663 mimics or inhibitor. Cell viability, migration, invasion, proliferation, and apoptosis were detected by CCK-8, Transwell, EdU, and flow cytometry assays. The downstream target genes and binding sites of miR-663 were predicted via Starbase database and validated by dual-luciferase assay. LC cells were delivered with oe-METTL3/sh-METTL3. Crosslinking between METTL3 and DGCR8 was verified by co-immunoprecipitation. Levels of m6A, miR-663, and pri-miR-663 were measured by m6A dot blot assay and RT-qPCR. m6A modification of pri-miR-663 was verified by Me-RIP assay. Finally, the effects of METTL3 in vivo were ascertained by tumor xenograft in nude mice.

RESULTS

miR-663 was upregulated in LC cells, and miR-663 overexpression promoted cell proliferation, migration, invasion, and inhibited apoptosis, but miR-663 knockdown exerted the opposite effects. miR-663 repressed SOCS6 expression. SOCS6 overexpression annulled the promotion of miR-663 on LC cell growth. METTL3 bound to DGCR8, and METTL3 silencing elevated the levels of pri-miR-663 and m6A methylation-modified pri-miR-663, and suppressed miR-663 maturation and miR-663 expression. METTL3 facilitated tumor growth in mice through the miR-663/SOCS6 axis.

CONCLUSION

METTL3 promotes LC progression by accelerating m6A methylation-mediated pri-miR-663 processing and repressing SOCS6.

Gene model-related m6A expression levels predict the risk of preeclampsia

Background

This is the first study to explore the potential functions and expression patterns of RNA N6-methyladenosine (m6A) and potential related genes in preeclampsia.

Methods

We identified two m6A modification patterns through unsupervised cluster analysis and validated them by principal component analysis. We quantified the relative abundance of specific infiltrating immunocytes using single-sample gene set enrichment analysis (ssGSEA) and the Wilcoxon test. To screen hub genes related to m6A regulators, we performed weighted gene coexpression network analysis. Functional enrichment analysis was conducted for differential signalling pathways and cellular processes. Preeclampsia patients were grouped by consensus clustering based on differentially expressed hub genes and the relationship between different gene-mediated classifications and clinical features.

Results

Two m6A clusters in preeclampsia, cluster A and cluster B, were determined based on the expression of 17 m6A modification regulators; ssGSEA revealed seven significantly different immune cell subtypes between the two clusters. A total of 1393 DEGs and nine potential m6A-modified hub genes were screened. We divided the patients into two groups based on the expression of these nine genes. We found that almost all the patients in m6A cluster A were classified into hub gene cluster 1 and that a lower gestational age may be associated with more m6A-associated events.

Conclusions

This study revealed that hub gene-mediated classification is consistent with m6A modification clusters for predicting the clinical characteristics of patients with preeclampsia. Our results provide new insights into the molecular mechanisms of preeclampsia.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01254-4.

N6-Methyladenosine Modifications in the Female Reproductive System: Roles in Gonad Development and Diseases

N6-methyladenosine (m⁶A) is the most prevalent chemical modification in eukaryotic messenger RNAs. By participating in various RNA-related bioprocesses including RNA decay, splicing, transport and translation, m⁶A serves as a pivotal regulator of RNA fate and plays an irreplaceable role in cellular activities. The m⁶A modifications of transcripts are coordinately regulated by methyltransferase “writers” and demethylase “erasers”, and produce variable effects via different m⁶A reading protein “readers”. There is emerging evidence that m⁶A modifications play a critical role in a variety of physiological and pathological processes in the female reproductive system, subsequently affecting female fertility. Here, we introduce recent advances in research on m⁶A regulators and their functions, then highlight the role of m⁶A in gonad development and female reproductive diseases, as well as the underlying mechanisms driving these processes.

circRNA N6-methyladenosine methylation in preeclampsia and the potential role of N6-methyladenosine-modified circPAPPA2 in trophoblast invasion

Here, we performed N6-methyladenosine (m6A) RNA sequencing to determine the circRNA m6A methylation changes in the placentas during the pathogenesis of preeclampsia (PE). We verified the expression of the circRNA circPAPPA2 using quantitative reverse transcription-PCR. An invasion assay was carried out to identify the role of circPAPPA2 in the development of PE. Mechanistically, we investigated the cause of the altered m6A modification of circPAPPA2 through overexpression and knockdown cell experiments, RNA immunoprecipitation, fluorescence in situ hybridization and RNA stability experiments. We found that increases in m6A-modified circRNAs are prevalent in PE placentas and that the main changes in methylation occur in the 3’UTR and near the start codon, implicating the involvement of these changes in PE development. We also found that the levels of circPAPPA2 are decreased but that m6A modification is augmented. Furthermore, we discovered that methyltransferase‑like 14 (METTL14) increases the level of circPAPPA2 m6A methylation and that insulin-like growth factor 2 mRNA-binding protein 3 (IGF2BP3) maintains circPAPPA2 stability. Decreases in IGF2BP3 levels lead to declines in circPAPPA2 levels. In summary, we provide a new vision and strategy for the study of PE pathology and report that placental circRNA m6A modification appears to be an important regulatory mechanism.

METTL3 is a key regulator of milk synthesis in mammary epithelial cells

The enzyme m⁶ A methyltransferase-like 3 (METTL3) catalyzes N⁶ -methyladenosine (m⁶ A) modification in eukaryotic messenger RNAs (mRNAs). However, the physiological function and molecular mechanism of METTL3 in mammalian cells have not been fully understood. Here we showed that METTL3 was highly expressed in mouse mammary gland of the lactation period. METTL3 was located in the nucleus of bovine mammary epithelial cells (MECs), and methionine (Met) and β-estrodial (E2) upregulated METTL3 protein level. METTL3 knockdown decreased milk protein and fat synthesis, whereas its overexpression had the opposite effects. METTL3 overexpression stimulated mRNA expression and protein phosphorylation of the mechanistic target of rapamycin (mTOR) and mRNA and protein expression of sterol regulatory element binding protein 1 (SREBP1), whereas METTL3 knockdown blocked the stimulatory effects of Met and E2 on these processes. Furthermore, METTL3 overexpression led to increased mRNA m⁶ A methylation of mTOR and SREBP1, whereas METTL3 knockdown suppressed the stimulatory effects of Met and E2 on these processes. The interaction between METTL3 and glycyl-tRNA synthetase (GlyRS) was confirmed by Co-immunoprecipitation and fluorescence resonance energy transfer approaches, and colocalization observation further showed that Met and E2 treatment increased this interaction. GlyRS knockdown abolished METTL3 protein levels upregulated by Met and E2, and METTL3 knockdown markedly decreased the effects of GlyRS overexpression on mTOR expression and phosphorylation and SREBP1 expression. In summary, we demonstrate that METTL3 is a key positive regulator of Met and E2-stimulated and GlyRS-mediated mTOR and SREBP1 signaling pathways and milk protein and fat synthesis in mammary epithelial cells.

METTL3-mediated mature miR-497-5p/195-5p inhibits trophoblast migration and invasion by targeting WWP1 in preeclampsia

Preeclampsia (PE) is a pregnancy-associated disorder caused by poor placentation. METTL3 as an RNA methyltransferase that plays an essential role in the regulation of the m6A modification. This work investigated the regulation of METTL3-mediated mature miR-497-5p/195-5p cluster in PE progression and identified the downstream mechanisms involved. Differentially expressed miRNAs in PE were obtained from the GSE96983 dataset. The miR-497-5p/195-5p levels in placental samples collected from 20 cases of PE patients and 18 cases of normal controls were measured by RT-qPCR. Effects of miR-497-5p/195-5p and WWP1 on trophoblast proliferation, migration, and invasion were analyzed by CCK8, EdU, wound healing and Transwell assays. Luciferase reporter and RIP experiments were conducted to verify the interaction of WWP1 with miR-497-5p/195-5p. Dot blot assay was performed to determine the m6A levels in PE. The m6A modification of pri-miR-497-5p/195-5p was determined by Me-RIP assay. Immunochemistry (IHC) and western blotting were used to examine the immunoreactivities and protein levels of METTL3 and WWP1 in placental samples from PE patients and normal controls. The miR-497-5p/195-5p levels were high in PE placenta. Functionally, overexpression of miR-497-5p/195-5p prevented trophoblast migration, invasion, and proliferation. WWP1 overexpression enhanced trophoblast migration, invasion, and proliferation. Mechanistically, WWP1 was verified to be targeted by miR-497-5p/195-5p. Moreover, METTL3 promoted the recognition of pri-miR-497-5p/195-5p by DGCR8 and enhanced the formation of mature miR-497-5p/195-5p in an m6A manner. We demonstrated that METTL3-mediated m6A modification promotes the transition of pri-miR-497-5p/195-5p to mature miRNAs, thereby upregulating miR-497-5p/195-5p to aggravate PE progression by targeting WWP1.

Role of epigenetic m6 A RNA methylation in vascular development: mettl3 regulates vascular development through PHLPP2/mTOR-AKT signaling

N⁶ -methyladenosine (m6A) methylation is the most prevalent RNA modification, and it emerges as an important regulatory mechanism of gene expression involved in many cellular and biological processes. However, the role of m⁶ A methylation in vascular development is not clear. The m⁶ A RNA methylation is regulated by dynamic interplay among methyltransferases, binding proteins, and demethylases. Mettl3 is a member of the mettl3-mettl14 methyltransferase complex, referred to as writers that catalyze m6A RNA methylation. Here, we used CRISPR-Cas9 genome editing to develop two lines of knockout (KO) zebrafish for mettl3. Heterozygous mettl3^+/- KO embryos show defective vascular development, which is directly visible in fli-EGFP and flk-EGFP zebrafish. Alkaline phosphatase staining and whole mount in situ hybridization with cdh5, and flk markers demonstrated defective development of intersegmental vessels (ISVs), subintestinal vessels (SIVs), interconnecting vessels (ICVs) and dorsal longitudinal anastomotic vessels (DLAV) in both heterozygous mettl3^+/- and homozygous mettl3^-/- KO zebrafish embryos. Similar phenotypes were observed in zebrafish embryos with morpholino knockdown (KD) of mettl3; however, the vascular defects were rescued fully by overexpression of constitutively active AKT1. KD of METTL3 in human endothelial cells inhibited cell proliferation, migration, and capillary tube formation. Mechanistically, mettl3 KO and KD significantly reduced the levels of m⁶ A RNA methylation, and AKT phosphorylation (S473) by an increase in the expression of phosphatase enzyme PHLPP2 and reduction in the phosphorylation of mTOR (S2481), a member of the phosphatidylinositol 3-kinase-related kinase family of protein kinases. These data suggest that m⁶ A RNA methylation regulates vascular development via PHLPP2/mTOR-AKT signaling.

The Placenta as a Target of Epigenetic Alterations in Women with Gestational Diabetes Mellitus and Potential Implications for the Offspring

Gestational diabetes mellitus (GDM) is a pregnancy complication first detected in the second or third trimester in women that did not show evident glucose intolerance or diabetes before gestation. In 2019, the International Diabetes Federation reported that 15.8% of live births were affected by hyperglycemia during pregnancy, of which 83.6% were due to gestational diabetes mellitus, 8.5% were due to diabetes first detected in pregnancy, and 7.9% were due to diabetes detected before pregnancy. GDM increases the susceptibility to developing chronic diseases for both the mother and the baby later in life. Under GDM conditions, the intrauterine environment becomes hyperglycemic, while also showing high concentrations of fatty acids and proinflammatory cytokines, producing morphological, structural, and molecular modifications in the placenta, affecting its function; these alterations may predispose the baby to disease in adult life. Molecular alterations include epigenetic mechanisms such as DNA and RNA methylation, chromatin remodeling, histone modifications, and expression of noncoding RNAs (ncRNAs). The placenta is a unique organ that originates only in pregnancy, and its main function is communication between the mother and the fetus, ensuring healthy development. Thus, this review provides up-to-date information regarding two of the best-documented (epigenetic) mechanisms (DNA methylation and miRNA expression) altered in the human placenta under GDM conditions, as well as potential implications for the offspring.