The Critical Roles of Circular RNAs in Basic Research and Clinical Application of Female Reproductive-Related Diseases

CircDDX21 alleviates trophoblast dysfunction and Treg differentiation in recurrent spontaneous abortion via miR-520a-5p/ FOXP3/PD-L1 axis

BACKGROUND

Recurrent spontaneous abortion (RSA) is a common complication during pregnancy, which is a burden to patients both physically and mentally. Circular RNAs (circRNAs) play important roles in RSA. However, the roles of circDDX21 in RSA development remain unknown.

METHODS

Decidual samples were harvested from healthy pregnant women and RSA patients. In HTR-8/SVneo and Bewo trophoblast cells, proliferation and migration were analyzed by cell counting kit-8 (CCK-8)/5-ethynyl-2'-deoxyuridine (EdU) staining and transwell/wound healing assays, respectively. CD4+ T cells from peripheral blood mononuclear cells of patients were incubated with trophoblast-conditioned medium. Regulatory T cells (Treg) proliferation was detected by carboxyfluorescein succinimidyl ester (CFSE) assay. Treg proportion, Treg/T helper 17 cells (Th17) ratio, and cytokines were measured using flow cytometry. The association among genes was validated using dual-luciferase assay, RNA immunoprecipitation (RIP), and chromatin immunoprecipitation (ChIP).

RESULTS

CircDDX21 and Forkhead box P3 (FOXP3) decreased, while miR-520a-5p increased in the decidual tissues of RSA patients. CircDDX21 overexpression promoted trophoblast proliferation and migration, and facilitated CD4+ T cell differentiation into Treg. CircDDX21 targeted miR-520a-5p to elevate FOXP3. MiR-520a-5p overexpression reversed the promoted trophoblast cell function of circDDX21 overexpression in HTR-8/SVneo cells. FOXP3 overexpression reversed the repressed trophoblast cell function elicited by miR-520a-5p overexpression in HTR-8/SVneo cells. FOXP3 promoted Treg differentiation by transcriptionally upregulating programmed cell death ligand 1 (PD-L1).

CONCLUSION

CircDDX21 ameliorated trophoblast dysfunction and Treg differentiation in RSA via miR-520a-5p/FOXP3/PD-L1 axis.

The circRNA Landscape in Recurrent Pregnacy Loss (RPL): A Comparison of Four Reproductive Tissues

Recurrent Pregnancy Loss (RPL), also named Recurrent Spontaneous Abortion (RSA), is a common fertility problem that refers to at least two consecutive pregnancy losses and affects 1-2% of couples all over the world. Despite common causes such as genetic abnormalities, uterine anomalies or hormonal and metabolic disorders, there is still a huge challenge in identifying the causes of about 40-60% of RPL patients. Circular RNAs (circRNAs) are endogenous ncRNAs with a unique closed-loop and single-stranded structure. Accumulated evidence indicates the role of circRNAs in embryonic development and implantation, which may help decipher the mechanisms and causes underlying RSA. Four works were selected in the SRA public repository that used RNAseq analysis in control and RPL samples in four tissues: endometrium, chorionic villus tissue, decidua and decidua immune cells. Two programs were selected for circRNA detection: DCC and CIRI2. A total of 1715 candidate circRNAs were detected after filtering the results. In the differential expression analysis, decidual tissue showed the highest percentage of circRNA with differential expression between cases and controls. CircRNAs originating from genes OGA, FNDC3B, RAB11FIP1, SIPA1L2 and GREB1L showed the highest expression in women suffering from pregnancy losses, in decidual tissue or endometrium. In the GO term enrichment analysis, multiple terms related to embryonic development and immunological response were consistently enriched in villus and decidual tissues. Although some differentially expressed circRNAs were shared between tissues, decidua seems the tissue of choice for analyzing the role of circRNAs in RPL.

Current understanding of circular RNAs in preeclampsia

Preeclampsia (PE) is a multiple organ and system disease that seriously threatens the safety of the mother and infant during pregnancy, and has a profound impact on the morbidity and mortality of the mother and new babies. Presently, there are no remedies for cure of PE as to the mechanisms of PE are still unclear, and the only way to eliminate the symptoms is to deliver the placenta. Thus, new therapeutic targets for PE are urgently needed. Approximately 95% of human transcripts are thought to be non-coding RNAs, and the roles of them are to be increasingly recognized of great importance in various biological processes. Circular RNAs (circRNAs) are a class of non-coding RNAs, with no 5' caps and 3' polyadenylated tails, commonly produced by back-splicing of exons. The structure of circRNAs makes them more stable than their counterparts. Increasing evidence shows that circRNAs are involved in the pathogenesis of PE, but the biogenesis, functions, and mechanisms of circRNAs in PE are poorly understood. In the present review, we mainly summarize the biogenesis, functions, and possible mechanisms of circRNAs in the development and progression of PE, as well as opportunities and challenges in the treatment and prevention of PE.