Circular RNAs: Novel potential regulators in embryogenesis, female infertility, and pregnancy-related diseases

Identification of circRNA Expression Profile and Potential Systemic Immune Imbalance Modulation in Premature Rupture of Membranes

Premature rupture of membrane (PROM) refers to the rupture of membranes before the onset of labor which increases the risk of perinatal morbidity and mortality. Recently, circular RNAs (circRNAs) have emerged as promising regulators of diverse diseases. However, the circRNA expression profiles and potential circRNA-miRNA-mRNA regulatory mechanisms in PROM remain enigmatic. In this study, we displayed the expression profiles of circRNAs and mRNAs in plasma and fetal membranes of PROM and normal control (NC) groups based on circRNA microarray, the Gene Expression Omnibus database, and NCBI's Sequence Read Archive. A total of 1,459 differentially expressed circRNAs (DECs) in PROM were identified, with 406 upregulated and 1,053 downregulated. Then, we constructed the circRNA-miRNA-mRNA network in PROM, encompassing 22 circRNA-miRNA pairs and 128 miRNA-mRNA pairs. Based on the analysis of gene ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway and gene set enrichment analysis (GSEA), DECs were implicated in immune-related pathways, with certain alterations persisting even postpartum. Notably, 11 host genes shared by DECs of fetal membrane tissue and prenatal plasma in PROM were significantly implicated in inflammatory processes and extracellular matrix regulation. Our results suggest that structurally stable circRNAs may predispose to PROM by mediating systemic immune imbalances, including peripheral leukocyte disorganization, local immune imbalance at the maternal-fetal interface, and local collagen disruption. This is the first time to decipher a landscape on circRNAs of PROM, reveals the pathogenic cause of PROM from the perspective of circRNA, and opens up a new direction for the diagnosis and treatment of PROM.

Involvement of circular RNAs in the control of porcine ovarian cell functions: Upregulation by ciR-00596 and downregulation by ciR-00646

The current understanding of the role of circular RNAs (circRNAs) in regulating ovarian functions is inadequate. To assess the impact of ciR-00596 and ciR-00646 on the regulation of basic porcine ovarian granulosa cell functions, we conducted upregulation (utilizing overexpressing vectors) and downregulation (utilizing shRNA vectors) of these circRNAs. The relative expression of both circRNAs, cell viability and proliferation (accumulation of PCNA, cyclin B1, and XTT-positive cells), cytoplasmic (accumulation of bax and caspase-3) and nuclear (DNA fragmentation) apoptosis, and the release of progesterone, testosterone, estradiol, IGF-I, and oxytocin were evaluated. Transfection of cells with the ciR-00596 overexpression vector resulted in increases in cell viability and proliferation and the release of progesterone and IGF-I, while it decreased the cytoplasmic and nuclear apoptosis, testosterone, estradiol, and oxytocin output. CiR-00596 inhibition had the opposite effects. The overexpression of ciR-00646 decreased cell viability and proliferation, and the release of progesterone, IGF-I, and oxytocin, while increasing cytoplasmic and nuclear apoptosis and the output of testosterone and estradiol. Our findings are the first to show the stimulatory action of ciR-00596 and the inhibitory effect of ciR-00646 on ovarian cell functions, including the cell cycle, apoptosis, and secretory activity.

CircTHBS1 promotes trophoblast cell migration and invasion and inhibits trophoblast apoptosis by regulating miR-136-3p/IGF2R axis

The precise molecular mechanism behind fetal growth restriction (FGR) is still unclear, although there is a strong connection between placental dysfunction, inadequate trophoblast invasion, and its etiology and pathogenesis. As a new type of non-coding RNA, circRNA has been shown to play a crucial role in the development of FGR. This investigation identified the downregulation of hsa_circ_0034533 (circTHBS1) in FGR placentas through high-sequencing analysis and confirmed this finding in 25 clinical placenta samples using qRT-PCR. Subsequent in vitro functional assays demonstrated that silencing circTHBS1 inhibited trophoblast proliferation, migration, invasion, and epithelial mesenchymal transition (EMT) progression and promoted apoptosis. Furthermore, when circTHBS1 was overexpressed, cell function experiments showed the opposite result. Analysis using fluorescence in situ hybridization revealed that circTHBS1 was primarily found in the cytoplasmic region. Through bioinformatics analysis, we anticipated the involvement of miR-136-3p and IGF2R in downstream processes, which was subsequently validated through qRT-PCR and dual-luciferase assays. Moreover, the inhibition of miR-136-3p or the overexpression of IGF2R partially reinstated proliferation, migration, and invasion abilities following the silencing of circTHBS1. In summary, the circTHBS1/miR-136-3p/IGF2R axis plays a crucial role in the progression and development of FGR, offering potential avenues for the exploration of biological indicators and treatment targets.

Role of circular RNA/miRNA axes in the pathophysiology of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a disorder resulted from interactions between genetic and environmental factors. Based on the importance of epigenetic factors in the pathoetiology of PCOS, the current review focused on identification of circular RNAs (circRNAs) that are involved in PCOS through acting as molecular sponges for microRNAs (miRNAs). The literature search led to identification of circ_0043533/miR-1179, circ_0030018/miR-136, circ_FURIN/miR-423-5p, circ-FURIN/miR-195-5p, circ_0043532/miR-182, circ_RANBP9/miR-136-5p, circRHBG/miR-515-5p, circMTO1/miR-320b, circASPH/miR-375, circPSMC3/miR-296-3p, circLDLR/miR-1294, circPUM1/miR-760, and hsa_circ_0118530/miR-136 as molecular axes contributing to the pathogenesis of PCOS. To set the stage for future research on the role of the ceRNA network in PCOS, in-silico analyses were performed using miRWalk, miRNet, and miRDIP databases. miRWalk identified 80 genes regulated by 5 miRNAs, miRNet revealed 6449 circRNAs potentially controlling 11 miRNAs, and miRDIP identified 11 miRNAs associated with 35 human pathways. These targets can be used in the treatment options, design of personalized medicine and prediction of prognosis of PCOS.

Role of CircCHD2 in the pathogenesis of gestational diabetes mellitus by regulating autophagy via miR-33b-3p/ULK1 axis

Gestational diabetes mellitus (GDM) is a common pregnancy complication with a high incidence in women; however, its pathophysiology remains unknown. Our previous study suggested that the circCHD2/miR-33b-3p/ULK1 axis may be involved in GDM pathogenesis. However, the mechanism through which circCHD2 regulates GDM development requires further investigation. We found that high-glucose (HG, 25 mmol/L) significantly induced the expression of circCHD2, increased autophagy and apoptosis, and decreased cell viability in human placental trophoblast HTR-8/SVneo cells. In contrast, the downregulation of circCHD2 significantly attenuated the effects of HG on HTR-8/SVneo cells. MiR-33b-3p downregulated in the placenta of GDM patients was reduced by HG and detected as a target of circCHD2 using bioinformatics analysis, a dual-luciferase reporter assay, and qRT-PCR assay. Further studies showed that the inhibition of miR-33b-3p significantly blocked the effects of circCHD2 downregulation on cell viability, apoptosis, and autophagy in HG-treated HTR-8/SVneo cells. ULK1 is a target of miR-33b-3p, based on bioinformatics analysis, a dual-luciferase reporter assay, qRT-PCR assay, and Western blot analysis. Compared to miR-33b-3p, ULK1 is upregulated in the placenta of GDM patients. ULK1 overexpression notably blocked the effects of miR-33b-3p mimics on cell viability, apoptosis, and autophagy in HG-treated HTR-8/SVneo cells. These findings suggested that circCHD2 acts as an autophagy promoter via the miR-33b-3p/ULK1 axis to induce apoptosis in HTR-8/SVneo cells, suggesting that circCHD2 is a potential diagnostic and therapeutic target for GDM.

Identification of m6A Modification Regulated by Dysregulated circRNAs in Decidua of Recurrent Pregnancy Loss

N6-methyladenosine (m6A) modification is a prevalent modification of messenger ribonucleic acid (mRNA) in eukaryote cells and is closely associated with recurrent pregnancy loss (RPL). Circular RNAs (circRNAs) play critical roles in embryo implantation, trophoblast invasion and immune balance, which are important events during pregnancy. However, how m6A modification is regulated by circRNAs and the potential regulatory mechanism of circRNAs on RPL occurrence remain largely unclassified. We displayed the expression profiles of circRNAs and mRNAs in the decidua of normal pregnancies and RPL patients based on circRNA sequencing and the Gene Expression Omnibus database. A total of 936 differentially expressed circRNAs were identified, including 509 upregulated and 427 downregulated circRNAs. Differentially expressed circRNAs were enriched in immune, metabolism, signaling and other related pathways via the analysis of Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway. The competitive endogenous RNA (ceRNA) network was predicted to supply the possible role of circRNAs in RPL occurrence, and we further analyzed the profiles of nine m6A regulators (seven readers, one writer and one eraser) managed by circRNAs in this network. We also showed the expression profiles of circRNAs in the serum, trying to seek a potential biomarker to help in the diagnosis of RPL. These data imply that circRNAs are involved in pathogenesis of RPL by changing immune activities, metabolism and m6A modification in the ceRNA network. Our study might provide assistance in exploring the pathogenesis and diagnosis of RPL.

LH/hCG Regulation of Circular RNA in Mural Granulosa Cells during the Periovulatory Period in Mice

Ovarian follicles undergo a series of dynamic changes following the ovulatory surge of luteinizing hormone including cumulus expansion, oocyte maturation, ovulation, and luteinization. Post-transcriptional gene regulatory events are critical for mediating LH follicular responses, and among all RNA isoforms, circular RNA (circRNA) is one of the most abundant forms present in cells, yet they remain the least studied. Functionally, circRNA can act as miRNA sponges, protein sponges/decoys, and regulators of transcription and translation. In the context of ovarian follicular development, the identity and roles of circRNA are relatively unknown. In the present study, high throughput RNA sequencing of granulosa cells immediately prior to and 4-h after the LH/hCG surge identified 42,381 circRNA originating from 7712 genes. A total of 54 circRNA were identified as differentially expressed between 0-h and 4-h time points (Fold Change ± 1.5, FDR ≤ 0.1), among them 42 circRNA were upregulated and 12 circRNA were downregulated. All differentially expressed circRNA between the 0-h and 4-h groups were subjected to circinteractome analysis and identified networks of circRNA-protein and circRNA-miRNA were further subjected to "micro-RNA target filter analysis" in Ingenuity Pathway Analyses, which resulted in the identification of miRNA targeted mRNAs. A comparison of these circRNA target mRNAs with LH-induced mRNAs identified Runx2, Egfr, Areg, Sult1el, Cyp19a1, Cyp11a1, and Hsd17b1 as targets of circKif2, circVcan, circMast4, and circMIIt10. These newly identified LH/hCG-induced circRNA, their target miRNA and protein networks provide new insights into the complex interactions associated with periovulatory follicular development.

Circular RNA as a Novel Regulator and Promising Biomarker in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a prevalent metabolic and reproductive disorder that causes low fertility in females. Despite its detrimental effects on women's health, care for PCOS has been impeded by its undefined pathogenesis. Thus, there is an urgent need to explore novel biomarkers and therapeutic targets for the diagnosis and treatment of PCOS. Circular RNAs (circRNAs) are a class of noncoding RNAs with covalently closed cyclic structures, present in high abundance, and show development-stage specific expression patterns. Recent studies have demonstrated that circRNAs participate in PCOS progression by modulating various biological functions, including cell proliferation, apoptosis, and steroidogenesis. In addition, circRNAs are widely present in the follicular fluid of women with PCOS, indicating their potential as diagnostic biomarkers and therapeutic targets for PCOS. This review provides the current knowledge of circRNAs in PCOS, including their regulatory functions and molecular mechanisms, and explores their potential as diagnostic biomarkers and therapeutic targets.

The Circ-CYP24A1-miR-224-PRLR Axis Impairs Cell Proliferation and Apoptosis in Recurrent Miscarriage

Aim

Recurrent miscarriage (RM) is associated with numerous clinical factors. However, some RM occurred without specific factors. It has been revealed that some molecules such as hormones, miRNAs, and transcription factors are involved in RM by regulating proliferation, apoptosis, etc. However, the mechanism of RM has yet to be identified clearly. Circular RNAs (circRNAs) are a class of endogenous non-coding RNAs that often act as sponges for miRNAs or binds to proteins involved in biological processes. However, the functional role of circRNAs in the uterine decidua of patients with early RM is still unclear. In this study, we aimed to investigate the mechanisms of circ-CYP24A1 in RM.

Methods

The Dual-Luciferase Activity Assay was designed to analyze the bonding between circ-CYP24A1 and miR-224, and miR-224 and prolactin receptor (PRLR) mRNA 3′UTR. In situ hybridization (ISH) and immunohistochemistry (IHC) were used to observe the expression of circ-CYP24A1 and PRLR in the decidua. Rescue experiments were performed to investigate the regulating effects of circ-CYP24A1, miR-224, and PRLR. Western blotting was conducted to test the expression level of PRLR. The proliferation and apoptosis-related markers in Ishikawa cells were analyzed using CCK8, immunofluorescence staining, and the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay.

Results

In this study, based on the microarray analysis data, we identified a high level of circ-CYP24A1 and PRLR in the decidua of patients with early RM. Based on the bioinformatics prediction, the binding relationship between circ-CYP24A1 and miR-224, as well as miR-224 and PRLR, were verified. Functional experiments demonstrated that circ-CYP24A1 regulated proliferation and apoptosis by binding to and inhibiting miR-224, resulting in increased PRLR expression. Taken together, this study provides new insights into the mechanism of RM.

Conclusion

In this study, we found that circ-CYP24A1 plays a role in RM by impairing the balance of cell proliferation and apoptosis by sponging miR-224, thereby regulating PRLR.

Circular RNA in disease: Basic properties and biomedical relevance

Circular RNAs (circRNAs) represent a class of covalently closed RNA molecules with great diversity in molecular features, functions, and regulatory mechanisms. Emerging advances in our understanding of circRNA biogenesis, nuclear export, and stability control have been made very recently. In particular, novel roles of circRNAs in diverse human diseases are increasingly recognized. Various circRNAs have been found to affect many disease-relevant pathways through a diverse array of mechanisms, including forming R-loops, sponging miRNAs or proteins, and translating functional proteins, resulting in different pathological phenotypes. This recent progress calls for a revised view of circRNAs in diseases threatening the lives and health of humans. In this review, we focus on the recently described functional relevance of disease-associated circRNAs as well as the potential of circRNAs in diverse clinical applications. This article is categorized under: RNA in Disease and Development > RNA in Disease Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs.

Circular RNA circZFPM2 promotes epithelial-mesenchymal transition in endometriosis by regulating miR-205-5p/ZEB1 signalling pathway

Endometriosis is a debilitating gynecological disease affecting millions of women worldwide, but its exact pathogenesis remains unclear. Circular RNAs (circRNAs) have been demonstrated to be important regulators in multiple diseases. Nonetheless, the potential regulatory mechanism of aberrant circRNA expression in endometriosis has been elusive. The up-regulated circZFPM2 in ectopic endometrial tissues was previously screened by circRNA high-throughput sequencing and was furtherly validated by quantitative real time reverse transcriptase polymerase chain reaction (RT-qPCR). Overexpression of circZFPM2 promoted the proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT) in Ishikawa and End1/E6E7 cells, whereas silencing circZFPM2 produced the opposite effect. Luciferase reporter assays validated that circZFPM2 could directly target miR-205-5p and miR-205-5p target ZEB1. RT-qPCR results showed that miR-205-5p was underexpressed while ZEB1 was overexpressed in ectopic endometrial tissues compared with their expression in eutopic endometria and non-endometriosis control endometria. The expression level of miR-205-5p was inversely proportional and that of ZEB1 was directly proportional with the proliferative, migrative, and invasive ability of endometrial cells. Further in vitro investigation indicated that miR-205-5p could inhibit EMT by targeting ZEB1. Subsequent rescue experiments confirmed that circZFPM2 could induce EMT and promote cell proliferation, migration, and invasion cascades through the miR-205-5p /ZEB1 signaling pathway. Conclusively, circZFPM2 may present a promising biomarker in the diagnosis and treatment of endometriosis.