Identification of Circular RNAs as a Novel Biomarker for Ovarian Endometriosis

Circ_0001495 influences the development of endometriosis through the miRNA-34c-5p/E2F3 axis

Endometriosis is a chronic gynecological condition characterized by the presence of endometrial glands and stroma outside the uterine cavity., accounting for 7% of all female malignant tumors and 20%- 30% of malignant tumors of the female reproductive system. Multiple studies have shown that circular RNA (circRNA) has the potential to become a targeted target and marker for EM. However, the roles of circ_0001495 in EM are still unclear. Our research aims to reveal the molecular mechanism of circ_0001495 in EM. In this study, RT-PCR or western blot were conducted to determine mRNA and protein expression. cell viability, proliferation, migration, invasion, and apoptosis were assessed by CCK-8, EdU, wound healing, transwell, and flow cytometry analyses, respectively. Additionally, the targeting relationship between miR-34c-5p and circ_0001495 or E2F3 was confirmed through dual-luciferase reporter gene assay. We found significant overexpression of circ_0001495 in EM tissues and cells. Knockdown of circ_0001495 inhibited the proliferation, migration and invasion of ectopic endometrial stromal cells (EESCs) and increased cell apoptosis. Moreover, we found that circ_0001495 regulated E2F3 levels by interacting with miR-34c-5p in EESC. Furthermore, in vitro, miR-34c-5p inhibition or E2F3 overexpression could attenuate the effect of circ_0001495 silencing on EM progression. In addition, the vivo experiment demonstrated that inhibition of circ_0001495 could repress the development of endometriosis by regulating the miR-34c-5p/E2F3 axis. In conclusion, our study suggested that circ_0001495 promoted EM progression in vitro and in vivo through the miR-34c-5p/E2F3 axis, which might be a potential therapeutic target for EM.

Recombinant human granulocyte colony stimulating factor (rhG-CSF) participates in the progression of implantation via the hsa_circ_0001550-miRNA-mRNA interaction network

Inadequate endometrial receptivity is a key factor affecting the successful implantation of embryos. Recombinant human granulocyte colony stimulating factor (rhG-CSF) can increase endometrial thickness and improve the outcomes of assisted reproductive technologies (ARTs). In this preliminary study, the function and possible molecular mechanisms of recombinant human granulocyte colony stimulating factor (rhG-CSF) which affects endometrial receptivity and implantation in human Embryonic Stem Cells (hESCs) were investigated. The cell viability of endometrial stromal cells treated with rhG-CSF 0.5 ng/ml for 24 h was significantly increased. Moreover, the expression of hsa_circ_0001550 was downregulated in endometrial stromal cells treated with rhG-CSF. Furthermore, the hsa_circ_0001550-miRNA-mRNA network was constructed and the downstream target genes (including 4 miRNAs and 117 mRNAs) of hsa_circ_0001550 were mainly involved in the cAMP and calcium signalling pathways, which play important roles in regulating endometrial receptivity and embryo implantation. We conclude that rhG-CSF participates in the regulation of embryo implantation by regulating the hsa_circ_0001550-miRNA-mRNA interaction network.

Circ_0004712 promotes endometriotic epithelial cell proliferation, migration and invasion by regulating miR-488-3p/ROCK1 axis in vitro

Recent evidence indicates that circular RNAs (circRNAs) play crucial regulatory roles in the pathogenesis and development of endometriosis. Circ_0004712 was found to be differentially expressed in endometriosis. However, the detailed function and mechanism of circ_0004712 in endometriosis are still unclear. Quantitative real-time polymerase chain reaction and Western blot were used for the detection of circ_0004712, miR-488-3p and ROCK1 (Rho Associated Coiled-Coil Containing Protein Kinase 1) levels. In vitro experiments in endometrial endothelial cells were performed by cell counting kit-8, EdU, transwell, wound healing assays, and flow cytometry, respectively. The molecular mechanism of circ_0004712 function was investigated using bioinformatics target predication, dual-luciferase reporter, and RNA immunoprecipitation (RIP) assays. The expression of circ_0004712 was higher in endometriotic endometrial tissues and epithelial cells. Knockdown of circ_0004712 suppressed cell proliferation, migration, invasion, EMT process and induced apoptosis in ectopic endometrial epithelial cells in vitro. Mechanistically, circ_0004712 acted as a ceRNA to sponge miR-488-3p, thus elevating the expression of ROCK1, which was confirmed to be a target of miR-488-3p. Rescue experiments suggested that miR-488-3p inhibition reversed the inhibitory effects of circ_0004712 silencing on cell growth and metastasis. Moreover, miR-488-3p restoration restrained the proliferation and metastasis in ectopic endometrial epithelial cells, which were attenuated by ROCK1 overexpression. Circ_0004712 knockdown suppressed the proliferation and metastasis of ectopic endometrial epithelial cells via miR-488-3p/ROCK1 axis in vitro, suggesting a new insight into the pathogenesis of endometriosis.

A critical appraisal of the circulating levels of differentially expressed microRNA in endometriosis†

Endometriosis is a common gynecological condition characterized by estrogen dependence, chronic pelvic pain, infertility, and diagnostic delay of between 5.4 and 12 years. Despite extensive study, no biomarker, either alone or in combination with other markers, has proven superior to laparoscopy for the diagnosis of endometriosis. Recent studies report that circulating levels of differentially expressed microRNA (miRNA) in women with endometriosis compared with controls are potential diagnostic tools. However, the lack of replication and absence of validated differential expression in novel study populations have led some to question the diagnostic value of miRNA. To elucidate potential reasons for the lack of replication of study results and explore future directions to enhance replicability of circulating miRNA results, we carried out an electronic search of the miRNA literature published between 2000 and 2020. Eighteen studies were identified in which 63 different miRNAs were differentially expressed in the circulation of women with endometriosis compared with controls. However, the differential expressions of only 14 miRNAs were duplicated in one or more studies. While individual miRNAs lacked diagnostic value, miRNA panels yielded sensitivity and specificity equal to or better than laparoscopy in five studies. Important differences in study design, sample processing, and analytical methods were identified rendering direct comparisons across studies problematic and could account for the lack of reproducibility of study results. We conclude that while the results of miRNA studies to date are encouraging, refinements to study design and analytical methods should enhance the reliability of circulating miRNA for the diagnosis of endometriosis.

Translational Applications of Linear and Circular Long Noncoding RNAs in Endometriosis

Endometriosis is a chronic gynecologic disease that negatively affects the quality of life of many women. Unfortunately, endometriosis does not have a cure. The current medical treatments involve hormonal manipulation with unwanted side effects and high recurrence rates after stopping the medication. Sadly, a definitive diagnosis for endometriosis requires invasive surgical procedures, with the risk of complications, additional surgeries in the future, and a high rate of recurrence. Both improved therapies and noninvasive diagnostic tests are needed. The unique molecular features of endometriosis have been studied at the coding gene level. While the molecular components of endometriosis at the small RNA level have been studied extensively, other noncoding RNAs, such as long intergenic noncoding RNAs and the more recently discovered subset of long noncoding RNAs called circular RNAs, have been studied more limitedly. This review describes the molecular formation of long noncoding and the unique circumstances of the formation of circular long noncoding RNAs, their expression and function in endometriosis, and promising preclinical studies. Continued translational research on long noncoding RNAs, including the more stable circular long noncoding RNAs, may lead to improved therapeutic and diagnostic opportunities.

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.

Estrogen-decreased hsa_circ_0001649 promotes stromal cell invasion in endometriosis

Endometriosis (EMs) is an estrogen (E2)-dependent inflammatory disorder. Although EMs is considered a benign disease, it presents with malignant characteristics, such as migration and invasion. An increasing number of studies have shown that aberrantly expressed circular RNAs (circRNAs) play an essential role in disease development and progression. However, the mechanisms by which circRNAs exert their pathological effects in EMs remain unclear. Hsa_circ_0001649, a novel cancer-associated circRNA, has been previously reported to be downregulated in several cancer types and related to cell migration and invasion. In the present study, real-time PCR (qRT-PCR) was carried out to measure hsa_circ_0001649 levels in human tissues, human primary endometrial stromal cells (ESCs) and a human endometrial stromal cell line (ThESCs). Matrix metalloproteinase 9 (MMP9) levels in ESCs and ThESCs were assessed by qRT-PCR and Western blotting, and the migration and invasion capacities of ThESCs were evaluated by transwell assay. As a result, hsa_circ_0001649 expression was significantly decreased in ectopic and eutopic endometrial samples compared with that in normal endometrial samples. E2 decreased hsa_circ_0001649 expression but increased MMP9 expression in ESCs and ThESCs. Furthermore, ThESCs were more invasive under E2 stimulation. However, these effects disappeared when ICI or hsa_circ_0001649 transfection was used. Collectively, our findings reveal that decreased hsa_circ_0001649 expression plays a role in E2-increased MMP9 expression through E2 receptors (ERs), which have critical functions in EMs.

Knockdown of circ_0075503 suppresses cell migration and invasion by regulating miR-15a-5p and KLF12 in endometriosis

Endometriosis is an estrogen-dependent disease. Several researches have reported the dysregulated circular RNAs (circRNAs) in endometriosis, whereas the functions of circRNAs are largely unknown. This study aims to explore the role and mechanism of circ_0075503 in migration and invasion of eutopic endometrial stromal cells. 30 paired ectopic and eutopic endometrium tissues were collected from patients with endometriosis. And primary endometrial stromal cells (ESCs) were stimulated with estradiol (E2) to establish the in vitro cellular model of endometriosis. The levels of circ_0075503, miR-15a-5p and Krüppel-like factor 12 (KLF12) were measured by quantitative reverse transcription polymerase chain reaction or western blot assays. Cell viability, migration and invasion were examined via 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide, transwell assay or western blot assays. The target relationship between miR-15a-5p and circ_0075503 or KLF12 was analyzed by dual-luciferase reporter assay and RNA Immunoprecipitation (RIP) assay. Circ_0075503 expression was elevated in ectopic endometrium and ectopic ESCs. Down-regulation of circ_0075503 suppressed E2-induced promotion of cell viability, migration and invasion in eutopic ESCs. Circ_0075503 could act as a sponge for miR-15a-5p, and KLF12 was targeted by miR-15a-5p. Inhibition of miR-15a-5p reversed the effects of circ_0075503 knockdown on E2-treated ESCs migration and invasion. Besides, miR-15a-5p repressed E2-induced promotion effects on cell migration and invasion via targeting KLF12. Circ_0075503 could regulate KLF12 expression by sponging miR-15a-5p. Knockdown of circ_0075503 inhibited E2-induced enhancement of cell migration and invasion in eutopic ESCs by regulating miR-15a-5p/KLF12 axis, indicating a novel target for the treatment of endometriosis.

Current biomarkers for the detection of endometriosis

A clinically reliable non-invasive test for endometriosis is expected to reduce the diagnostic delay. Although varieties of biomarkers have been investigated for decades, and cancer antigen-125, cancer antigen-199, interleukin-6, and urocortin were the most studied ones among hundreds of biomarkers, no clinically reliable biomarkers have been confirmed so far. Some emerging technologies including “omics” technologies, molecular imaging techniques, and microRNAs are promising in solving these challenges, but their utility to detect endometriosis has yet to be verified. New combinations of researched indicators or other non-invasive methods and further exploration of the emerging technologies may be new targets and future research hotspots for non-invasive diagnosis of endometriosis. In conclusion, researches of biomarkers for the detection of endometriosis are still ongoing and may benefit from novel molecular biology, bioinformatics methods and a combination of more diverse monitoring methods. Though it will be a daunting task, the identification of a specific set of diagnostic biomarkers will undoubtedly improve the status of endometriosis.

Downregulation of circ_0000673 Promotes Cell Proliferation and Migration in Endometriosis via the Mir-616-3p/PTEN Axis

Endometriosis is a common gynecological disease, affecting up to 10% of women of reproductive age and approximately 50% of women with infertility. Circular RNAs (circRNAs) have been shown to be involved in a number of diseases. Dysregulated expression of circRNAs in endometriosis has been reported, and circ_0000673 was significantly downregulated. However, the details of its role in the pathogenesis of endometriosis are still poorly understood. We investigated the location and effects of the downregulation of circ_0000673 in endometriosis. We demonstrated that knockdown of circ_0000673 significantly increased the proliferation and migration of eutopic and normal endometrial cells. Bioinformatics analysis predicted that circ_0000673 might act as a sponge for miR-616-3p. We found that the effect of circ_0000673 knockdown could be recovered by miR-616-3p inhibitor and enhanced by miR-616-3p mimics. qPCR and western blot assays showed that circ_0000673 knockdown could decrease the expression of PTEN and increase the expression of PI3K and p-AKT. PTEN was confirmed to be a target of miR-616-3p. These results demonstrated that the downregulation of circ_0000673 could promote the progression of endometriosis by inactivating PTEN via the deregulation of miR-616-3p.

Current and Future Roles of Circular RNAs in Normal and Pathological Endometrium

The uterine endometrium, which lines the mammalian uterus, is essential for embryo implantation. This lining undergoes significant changes during sexual and menstrual cycles. The endometrium is also associated with hormone-related diseases such as endometriosis and endometrial cancer. Circular RNAs (circRNAs) play a role in various biological processes. Recent studies have determined that circRNAs function in both normal and pathological endometrial environments. Here, we review high-throughput studies pertaining to circRNAs as well as individual circRNAs active in the endometrium, in order to explore the myriad functions of circRNAs in the endometrium and mechanisms underlying these functions, from panoramic and individual perspectives. Owing to their abundant expression, stability, and small size, circRNAs have displayed potential usefulness as diagnostic markers and treatment targets for endometrial-related diseases. Therefore, the specific role of circRNAs in the endometrium warrants systematic investigation in the future.

Circ_0007331 knock-down suppresses the progression of endometriosis via miR-200c-3p/HiF-1α axis

Endometriosis is considered a benign gynaecological disease with cancer-like characterizations, which has a high incidence among women of reproductive age. However, this disease has so far lacked timely diagnosis and effective treatment owing to its unclear aetiology. In this study, we identified aberrant high expression of circ_0007331 in ectopic endometrial cells by comparing the endometrial samples from patients with and without endometriosis. Further functional experiments revealed that circ_0007331 knock-down effectively suppressed the viability, proliferation and invasive capacity of ectopic endometrial cells. Additionally, we attempted to define the molecular mechanism of circ_0007331 in the initiation and progression of endometriosis. Circ_0007331 acted as a miRNA sponge for miR-200c-3p to indirectly regulate the function of HIF-1α, which plays a key role in the local angiogenesis and hypoxic mechanisms of ectopic endometrium. A final in vivo experiment confirmed that circ_0007331 knock-down could suppress the development of endometriosis through down-regulating the expression of HIF-1α. Collectively, we preliminarily characterized the role and possible insights of circ_0007331/miR-200c-3p/HIF-1α axis in the proliferation and invasion of ectopic endometrial cells. We hope that by exploring the potential function and molecular mechanism of circ_0007331, we can increase our biological insight into the pathogenesis of endometriosis, which will bring the new ways for the diagnosis and therapy of this disease.

Circular RNA as a potential diagnostic and/or therapeutic target for endometriosis

Endometriosis is a pathology form of endometrium that behaves in a similar way to malignancies, such as invasion and resistance to apoptosis. Circular RNAs (CircRNAs) are a class of noncoding RNAs that have several biological functions including, miRNA sponging, sequestering of proteins, enhancing parental gene expression and translation resulting in polypeptides. In this review, we highlighted the roles of circRNAs as potential diagnostic and therapeutic biomarkers in endometriosis. Moreover, we summarized the roles of circRNAs in the pathogenesis of endometriosis via different signaling pathways, such as the miRNA network and apoptosis.

An integration analysis of mRNAs and miRNAs microarray data to identify key regulators for ovarian endometriosis based on competing endogenous RNAs

This study aimed to uncover effects of non-coding RNA transcripts on ovarian endometriosis (OEM) development. Two transcription datasets (GSE105764 and GSE105765) about OME were downloaded from Gene Expression Omnibus (GEO) database and the differentially expressed mRNAs, lncRNAs and miRNAs (DEmRNAs, DElncRNAs and DEmiRNAs) between OEM cases and controls were identified followed by protein-protein interaction analysis. Then, co-expression analysis was conducted and DEmiRNAs-DEmRNAs as well as DElncRNAs-DEmiRNAs pairs were predicted to construct the ceRNA network followed by sub-ceRNA network associated with OEM extraction. Functional analyses of DEmRNAs in ceRNA and sub-module network and the survival analysis were also performed to evaluate the correlation of key regulators and OV outcomes. Totally, 1910 DEmRNAs, 158 DElncRNAs and 118 DEmiRNAs were screened between OEM cases and controls and the functional analyses of DEmRNAs showed that they were significantly enriched in cell adhesion. Furthermore, there were 505 nodes in PPI network and ceRNA network included 762 interaction pairs among 357 DEmRNAs, 28 DElncRNAs and 24 DEmiRNAs. The KEGG analysis suggested several genes including FOXO1, STAT5A and RUNX1 were predominately associated with pathways in cancer while IL15 was primarily enriched in cytokine-cytokine receptor interaction pathway. Importantly, these two pathways were also found to be implicated with OEM development. Finally, survival analysis implied that overexpression of ZFPM2-AS1 had a good clinical outcome while the under-expression levels of FOXO1, JUP, STAT5A, RUNX1 and PRKG1-AS1 exhibited a better prognosis for OV. FOXO1, STAT5A, RUNX1 and IL15, PRKG1-AS1 and ZFPM2-AS1 were promising diagnostic makers for OME.

Down-regulation of circ_0061140 attenuates ectopic endometrial cell proliferation, migration and invasion in endometriosis via inactivating Notch2

Endometriosis is a frequent gynecologic disease in the world. CircRNAs can exert a crucial role in various diseases. Nevertheless, little is known about its roles in endometriosis. We investigated the involvement of circ_0061140 in endometriosis. Tissues from endometriosis women displayed an increased expression of circ_0061140. Then, we found loss of circ_0061140 significantly repressed ectopic endometrial cell proliferation, migration and invasion. Meanwhile,miR-140-3pcan demonstrate an important role in several cancers.Here, we reported miR-140-3p was reduced in ectopic endometrial cells and it acted as a target of circ_0061140. Moreover, miR-140-3p was able to reverse the effect of circ_0061140 on ectopic endometrial cells. Furthermore, Notch2 was predicted as a putative target of miR-140-3p. A positive correlation between circ_0061140 and Notch2 was indicated. miR-140-3p and Notch2 were operated as downstream effectors in the circ_0061140 mediated signaling in endometriosis. Decrease of circ_0061140 could depress endometriosis progression through modulating miR-140-3p and Notch2.

Diagnostic value of circular RNAs in female reproductive system diseases: A PRISMA-compliant meta-analysis

Circular RNAs (circRNAs) are novel non-coding RNAs that have been reported to be involved in the progression of numerous diseases. However, the clinical diagnostic value of circRNAs in female reproductive system diseases remains unknown. The present study is a systemic review and meta-analysis of the available literature on circRNAs as novel biomarkers for female reproductive system diseases. Relevant studies were systematically searched using the PubMed, Embase, Web of Science and Cochrane Library databases. The data obtained from the included studies were analyzed by RevMan5.3 and STATA 14.2. A total of six studies involving 613 individuals across three types of disease examined the diagnostic capabilities of circRNAs. Within these publications, the pooled sensitivity of circRNAs was 0.70 (95% CI, 0.64-0.76), and the pooled specificity was 0.70 (95% CI, 0.64-0.75). The pooled positive likelihood ratio and negative likelihood ratio were 2.33 and 0.42, respectively. The diagnostic score was 1.70 and the pooled diagnostic odds ratio was 5.48. The area under the summary receiver operator characteristic curve was 0.76 (95% CI, 0.72-0.79), indicating that circRNAs exhibited a moderate diagnostic value for female reproductive system diseases and may function as potential diagnostic biomarkers. However, further studies are required to verify the clinical applications of circRNAs.

Diagnostic performance of circular RNAs in human cancers: A systematic review and meta-analysis

BACKGROUND

Recently, accumulating evidence have revealed that circular RNA (circRNA) was deregulated in multiple types of cancer, suggesting that circRNA might serve as a novel candidate biomarker of cancer diagnosis. However, inconsistent results have become an obstacle in applying circRNAs to clinical practice. The aim of this study is to evaluate diagnostic value of circRNAs among cancers.

METHODS

A literature search was systematically performed among PubMed, Sciencedirect, Cochrane Library, Web of Science, Wanfang, and Chinese National Knowledge Infrastructure databases up to February 15, 2019. The pooled sensitivity (SEN), specificity (SPE), positive likelihood ratios, negative likelihood ratios, diagnostic odds ratio, and area under the SROC curve (AUC) were applied to evaluate diagnostic performance of circRNAs.

RESULTS

In total, the study included 64 studies with single circRNA and 13 studies with combined circRNAs. Overall, the study presented that a single circRNA had moderate diagnostic value, with a SEN of 0.75, a SPE of 0.76, and an AUC of 0.82. The plasma circRNAs had higher diagnostic accuracy than tissue (AUC: 0.87, 95% confidence interval [CI]: 0.83-0.89 for plasma/serum subgroup; AUC: 0.79, 95% CI: 0.75-0.82 for tissue subgroup). Furthermore, the combined circRNAs had good diagnostic efficacy for GC, with a SEN of 0.89, a SPE of 0.94, and an AUC of 0.97, respectively.

CONCLUSION

This study confirmed that circRNAs may be candidate biomarkers for cancer diagnosis. In particular, diagnosis of combined circRNAs will be a new alternative applied to clinical research and practice for cancer.

Progress in understanding the relationship between long noncoding RNA and endometriosis

Endometriosis is a common gynecological disease. However, the etiology of endometriosis is still unclear, and current theories cannot fully elaborate its specific pathogenesis. Recently, some research has suggested that the occurrence and development of endometriosis may be related to genetics. Long-chain non-coding RNA (lncRNAs) is a kind of non-protein-coding RNA molecule with a length of 200-100,000 bp. With complex biological functions, lncRNAs play an important role in the normal development of individuals and the progression of various diseases, and lncRNAs have become an important field of medical research in recent years. This paper mainly illustrates the research progress on lncRNAs as they relate to endometriosis. We also provide some ideas for exploring the pathogenesis of endometriosis.

Circular RNA expression profiles and bioinformatics analysis in ovarian endometriosis

Background

Circular RNAs (circRNAs) with miRNA response elements (MREs) could function as competing endogenous RNA (ceRNA) in regulating gene expression, thus playing vital roles in pathogenesis and progression of many diseases. However, the function of circRNAs in endometriosis remains unknown. This study was carried to profile the expression patterns of circRNAs in ovarian endometriosis.

Methods

High throughput RNA‐Seq was performed in six paired ectopic and eutopic endometrium tissues (ecEM vs. euEM), followed by quantitative real‐time polymerase chain reaction (qRT‐PCR) in 30 paired samples. Through bioinformatics prediction, we constructed a circRNA‐miRNA ‐mRNA network and elucidated circRNAs functions by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses.

Results

A total of 146 upregulated and 148 downregulated circRNAs were identified, binding with 2,495 MREs. The qRT‐PCR validation results of four upregulated circRNAs matched the RNA‐Seq data. The ceRNA network included 48 miRNAs and 296 mRNAs. Functional analysis revealed several important pathways such as MAPK signaling pathway, and PI3K‐AKT signaling pathway, which might be associated with the pathogenesis and development of endometriosis.

Conclusion

Our data suggested that circRNAs are differentially expressed in endometriosis, which might be candidate factors for pathogenesis of this disease and be considered as promising therapeutic targets in the future.

Circular RNAs in gynecological disease: promising biomarkers and diagnostic targets

Circular RNAs (circRNAs) are a category of RNA molecules with covalently closed circles lacking both a 5′ cap and a 3′ tail. In recent years, circRNAs have attracted much attention and become a research hotspot of the RNA field following miRNAs and lncRNAs. CircRNAs exhibit tissue specificity, structural stability, and evolutionary conservation. Although the biological effects of circRNAs are still underestimated, many studies have shown that circRNAs have functions including regulation of transcription, translation into proteins and miRNA sponges. In this review, we briefly described the biogenesis and function of circRNAs and present circular transcripts in gynecological disease.

Analyses of circRNA profiling during the development from pre-receptive to receptive phases in the goat endometrium

BACKGROUND

Recent studies have revealed that noncoding RNAs play important regulatory roles in the formation of endometrial receptivity. Circular RNAs (circRNAs) are a universally expressed noncoding RNA species that have been recently proposed to act as miRNA sponges that directly regulate expression of target genes or parental genes.

RESULTS

We used Illumina Solexa technology to analyze the expression profiles of circRNAs in the endometrium from three goats at gestational day 5 (pre-receptive endometrium, PE) and three goats at gestational day 15 (receptive endometrium, RE). Overall, 21,813 circRNAs were identified, of which 5,925 circRNAs were specific to the RE and 9,078 were specific to the PE, which suggested high stage-specificity. Further analysis found 334 differentially expressed circRNAs in the RE compared with PE (P < 0.05). The analysis of the circRNA-miRNA interaction network further supported the idea that circRNAs act as miRNA sponges to regulate gene expression. Moreover, some circRNAs were regulated by estrogen (E2)/progesterone (P4) in endometrial epithelium cell lines (EECs) and endometrial stromal cell line (ESCs), and each circRNA molecule exhibited unique regulation characteristics with respect to E2 and P4.

CONCLUSIONS

These data provide an endometrium circRNA expression atlas corresponding to the biology of the goat receptive endometrium during embryo implantation.