Progress in Understanding the Relationship Between Circular RNAs and Neurological Disorders

Circ-AGTPBP1 promotes white matter injury through miR-140-3p/Pcdh17 axis role of Circ-AGTPBP1 in white matter injury

White matter injury (WMI) resulting from intracerebral hemorrhage (ICH) is closely associated with adverse prognoses in ICH patients. Although Circ-AGTPBP1 has been reported to exhibit high expression in the serum of premature infants with WMI, its effects and mechanisms in ICH-induced WMI remain unclear. This study aimed to investigate the role of circ-AGTPBP1 in white matter injury after intracerebral hemorrhage. An intracerebral hemorrhage rat model was established by injecting autologous blood into rat left ventricles and circ-AGTPBP1 was knocked down at the ICH site using recombinant adeno-associated virus, AAV2/9. Magnetic resonance imaging (MRI) and gait analysis were conducted to assess long-term neurobehavioral effects. Primary oligodendrocyte progenitor cells (OPCs) were isolated from rats and overexpressed with circ-AGTPBP1. Downstream targets of circ-AGTPBP1 in OPCs were investigated using CircInteractome, qPCR, FISH analysis, and miRDB network. Luciferase gene assay was utilized to explore the relationship between miR-140-3p and Pcdh17 in OPCs and HEK-293T cells. Finally, CCK-8 assay, EdU staining, and flow cytometry were employed to evaluate the effects of mi-RNA-140-3p inhibitor or silencing of sh-pcd17 on the viability, proliferation, and apoptosis of OPCs. Low expression of circ-AGTPBP1 alleviates white matter injury and improves neurological functions in rats after intracerebral hemorrhage. Conversely, overexpression of circ-AGTPBP1 reduces the proliferative and migrative potential of oligodendrocyte progenitor cells and promotes apoptosis. CircInteractome web tool and qPCR confirmed that circ-AGTPBP1 binds with miR-140-3p in OPCs. Additionally, miRDB network predicted Pcdh17 as a downstream target of miR-140-3p. Moreover, pcdh17 expression was increased in the brain tissue of rats with intracerebral-induced white matter injury. Furthermore, inhibiting miR-140-3p suppressed the proliferation and migration of OPCs and facilitated apoptosis through Pcdh17. Circ-AGTPBP1 promotes white matter injury through modulating the miR-140-3p/Pcdh17 axis. The study provides a new direction for developing therapeutic strategies for white matter injury.

Screening of Human Circular RNAs as Biomarkers for Early Onset Detection of Alzheimer’s Disease

Circular RNAs (circRNAs) are a distinctive type of endogenous non-coding RNAs, and their regulatory roles in neurological disorders have received immense attention. CircRNAs significantly contribute to the regulation of gene expression and progression of neurodegenerative disorders including Alzheimer’s disease (AD). The current study aimed to identify circRNAs as prognostic and potential biomarkers in AD. The differentially expressed circRNAs among subjective cognitive decline, amnestic mild cognitive impairment, and age-matched normal donors were determined through Arraystar Human circRNA Array V2 analysis. The annotations of circRNAs-microRNA interactions were predicted by employing Arraystar’s homemade microRNAs (miRNA) target prediction tool. Bioinformatics analyses comprising gene ontology enrichment, KEGG pathway, and network analysis were conducted. Microarray analysis revealed the 33 upregulated and 11 downregulated differentially expressed circRNAs (FC ≥ 1.5 and p-values ≤ 0.05). The top 10 differentially expressed upregulated and downregulated circRNAs have been chosen for further expression validation through quantitative real-time PCR and subsequently, hsa-circRNA_001481 and hsa_circRNA_000479 were confirmed experimentally. Bioinformatics analyses determined the circRNA-miRNA-mRNA interactions and microRNA response elements to inhibit the expression of miRNAs and mRNA targets. Gene ontology enrichment and KEGG pathways analysis revealed the functional clustering of target mRNAs suggesting the functional verification of these two promising circRNAs. It is concluded that human circRNA_001481 and circRNA_000479 could be utilized as potential biomarkers for the early onset detection of AD and the development of effective therapeutics.

circNBPF10/miR-224 Axis Regulates PBX3 to Promote the Malignant Progression of Lung Cancer

This study aims to reveal the potential effect of circNBPF10 on the malignant progression of lung cancer. The expression levels of circNBPF10 in lung cancer tissues and cell lines were detected via real-time quantitative PCR (RT-qPCR). The relationship between circNBPF10 expression and lung cancer metastasis was further analyzed. Effects on lung cancer cells after the knockout or overexpression of circNBPF10 were detected. Subsequently, the regulatory relationship of circNBPF10 with miR-224 was detected by using the dual-luciferase reporter gene. In addition, the role of pre-B-cell homeo box 3 (PBX3) in the progression of lung cancer affected by circNBPF10 was evaluated through a rescue experiment. circNBPF10 was highly expressed in lung cancer tissues and lung cancer cell lines. The expression level of circNBPF10 was significantly higher in patients with lung cancer and lymphatic metastasis or distant metastasis than in patients with nonmetastatic lung cancer. The downregulation of circNBPF10 reduced the proliferation, migration, and invasion of lung cancer cells. In lung cancer cells, circNBPF10 negatively regulated the expression of miR-224, whereas miR-224 directly targeted the expression of PBX3. The results of the rescue experiment confirmed that PBX3 was the key gene for the promoting effect of circNBPF10 on the malignant progression of lung cancer. circNBPF10 was highly expressed in lung cancer tissues and was associated with distant metastasis and poor prognosis in patients with lung cancer. circNBPF10 upregulated PBX3 by targeting miR-224 and promoted the malignant progression of lung cancer.

Downregulationof circ_0001578 promotes gestational diabetes mellitus by inducing placental inflammation via the NF-κB and JNKs pathways

Gestational diabetes mellitus (GDM) is one of the most common diseases during pregnancy. Some patients with GDM have adverse pregnancy outcomes. However, the pathogenesis of GDM is very complex and not well understood. In this study, we characterized the expression and functions of a circular RNA, circ_0001578, in GDM. In particular, using qRT-PCR, we verified previous RNA-seq results showing that circ_0001578 is significantly downregulated in the placental villous tissues of pregnant women with GMD. We demonstrated that plasma exosome circ_0001578 expression in the second trimester effectively predicts GDM at 28 weeks. Furthermore, in HTR-8/SVneo trophoblasts, the downregulation of circ_0001578 inhibited proliferation and migration and induced apoptosis. These changes may induce chronic inflammation in the placenta. These effects of circ_0001578 downregulation may be mediated by the upregulation of the NF-κB and JNK pathways, combined with increased expression levels of IL-1, IL-6, IL-8, TNF-α, and CRP. Collectively, the downregulation of circ_0001578 may promote GDM by inducing chronic inflammation in the placenta via the NF-κB and JNK pathways. Furthermore, our findings support that circ_0001578 has potential to serve as an early marker of GDM.

Research Progress on Circular RNA in Glioma

The discovery of circular RNA (circRNA) greatly complements the traditional gene expression theory. CircRNA is a class of non-coding RNA with a stable cyclic structure. They are highly expressed, spatiotemporal-specific and conservative across species. Importantly, circRNA participates in the occurrence of many kinds of tumors and regulates the tumor development. Glioma is featured by limited therapy and grim prognosis. Cancer-associated circRNA compromises original function or creates new effects in glioma, thus contributing to oncogenesis. Therefore, this article reviews the biogenesis, metabolism, functions and properties of circRNA as a novel potential biomarker for gliomas. We elaborate the expression characteristics, interaction between circRNA and other molecules, aiming to identify new targets for early diagnosis and treatment of gliomas.

Emerging important roles of circRNAs in human cancer and other diseases

CircRNAs are a large class of endogenous single-stranded RNA that is different from other linear RNA, which are produced by back-splicing and fusion of either exons, introns, or both exon-intron into covalently closed loops. CircRNAs are found in almost all living organisms and have emerged as potentially important players effecting on all life activities. It was characterized by stable structure, resistant to RNA degradation, highly abundance and conservation and tissue-specific expression. Early circRNAs were ignored as a by-product of meaningless abnormally cut RNA and had little biological function. Currently, circRNAs have become a research hotspot due to its special characteristics. CircRNAs could function as miRNA sponges, interfere with splicing and bind to protein to regulate the expression of parental genes and so on. In recent years, an increasing number of studies have revealed that circRNAs are closely related to a series of physiological and pathological processes. Additionally, circRNAs play an important role in the occurrence and development of a variety of diseases, suggesting circRNAs may be as novel indicators or biomarkers for cancer and other diseases with which they are associated. In this article, we review the biogenesis, biological functions of circRNAs and recent advances in circRNAs research in human diseases. Results will provide new insights on the roles and new ideas of circRNAs for the diagnosis and treatment of diseases and possible directions and approach for future circRNA applications.

CircMRE11A_013 binds to UBXN1 and integrates ATM activation enhancing lens epithelial cells senescence in age-related cataract

Ultraviolet B (UVB) irradiation could trigger DNA double-strand breaks (DDSBs) and senescence in lens epithelial cells (LECs), thus inducing age-related cortical cataract (ARCC) formation. Cell-cycle irreversible arrest induced by DDSBs depended on excessive activation of ataxia-telangiectasia mutated kinase (ATM). We studied the up-regulated circular RNA circMRE11A_013 (circMRE11A) in LECs of ARCC and SRA01/04 cell lines under UVB exposure. In vitro, knockdown of circMRE11A in SRA01/04 cell lines enhanced cell viability and cell cycle, while over-expression of circMRE11A exhibited an opposite trend. Additionally, circMRE11A could bind to UBX domain-containing protein 1 (UBXN1), which might enhance excessive activation of ATM and initiate ATM/p53/p21 signaling pathway causing LECs cell-cycle arrest and senescence. In vivo, recombinant adeno-associated virus vectors (rAAV-2) virions of circMRE11A (circMRE11A-AAV2) was injected to Institute of Cancer Research mouse vitreous cavity. The circMRE11A-AAV2 could express in mouse lens at 4 weeks. The LECs aging and opacity lens were observed at 8 weeks after the injection. Together, our findings reveal a previously unidentified role of circMRE11A interacting with UBXN1 in enhancing ATM activity and inhibiting LECs cell-cycle in ARCC formation. The findings might give us a better understanding of ARC pathology and provide a novel and more effective therapeutic approaches for ARC treatment.

Circulating expression of Hsa_circRNA_102893 contributes to early gestational diabetes mellitus detection

Due to a poor availability of reliable biomarkers, detecting gestational diabetes mellitus (GDM) in early pregnancy remains a challenge. Novel biomarkers like Circular RNAs (circRNAs) may be a promising diagnostic tool. The aim of this study was (a) to identify circRNAs deregulated in GDM and (b) evaluate the potential of circRNAs in detecting GDM. The circRNAs expression profiling in 6 paired women (with and without GDM) was measured by microarray. The levels of five most relevant circRNAs were validated in 12 paired participants by qRT-PCR. To verify the reproducibility of qRT-PCR, significantly differential expressed circRNA levels were confirmed in 18 paired participants. A receiver operating characteristic (ROC) curve was used to evaluate the diagnostic value. The areas under ROC curves of hsa_circRNA_102893 were 0.806 (95% CI 0.594–0.937) and 0.741 (0.568–0.872) in training set and test set, respectively. Circulating circRNAs reflect the presence of GDM. Hsa_circRNA_102893 may be a potential novel and stable noninvasive biomarker for detecting GDM in early pregnancy.

Circular RNAs in gastrointestinal cancer: Current knowledge, biomarkers and targeted therapy (Review)

Circular RNAs (circRNAs) are a type of endogenous non‑coding RNAs that are connected at the 3' and 5' ends by exon or intron cyclization, which forms a covalently closed loop. They are stable, well conserved, exhibit specific expression in mammalian cells and can function as microRNA (miRNA or miR) sponges to regulate the target genes of miRNAs, which influences biological processes. Such as tumor proliferation, invasion, metastasis, apoptosis and tumor stage. circRNAs represent promising candidates for clinical diagnosis and treatment. In the present review, the biogenesis, classification and functions of circRNAs in tumors are briefly summarized and discussed. In addition, the participation of circRNAs in signal transduction pathways regulating gastrointestinal cancer cellular functions is highlighted.

The emerging roles of circular RNAs in ovarian cancer

Circular RNA (circRNA) is a novel class of regulatory noncoding RNA (ncRNA) molecules with a unique covalently closed loop structure. Next-generation sequencing shows that thousands of circRNAs are widely and stably expressed in multiple eukaryotes. As novel regulatory ncRNAs, circRNAs possess several specific molecular functions, including regulating gene transcription and translation, acting as miRNA sponges, and interacting with functional proteins. Ovarian cancer (OvCa) is one of the most aggressive malignant diseases affecting the lives of thousands of women worldwide, and the majority of OvCa cases are diagnosed at advanced stages. Accumulating evidence has revealed the significant roles of circRNAs in the occurrence and progression of OvCa, indicating the function of circRNAs as promising biomarkers and their therapeutic relevance in this disease. This review aims to summarize the mechanisms by which circRNAs mediate OvCa progression as well as their diagnostic and prognostic values in OvCa.

Advances in circular RNAs and their role in glioma (Review)

Glioma is the most common primary tumour of the central nervous system, and is associated with a high postoperative recurrence rate and resistance to chemotherapy. High‑grade glioblastoma in particular has a very poor prognosis and poses a serious threat to human health. Related studies have confirmed that the occurrence and development of gliomas are closely associated with the abnormal expression and regulation of genes. Moreover, the number of studies on the association of the expression of non‑coding RNAs [linear RNAs, microRNAs and circular RNAs (circRNAs)] in human cells with glioma has been gradually increasing in recent years. Among those, circRNAs, previously considered to be 'splicing errors', have been shown to be highly expressed in eukaryotic cells and regulate the biological behaviour of gliomas. circRNAs are highly abundant and stable, and have become a research hotspot in the field of glioma molecular biology. The aim of the present review was to focus on the research progress regarding the association between circRNA expression and gliomas, and to provide a theoretical basis according to the currently available literature for further exploring this association. The present study may be of value for the early diagnosis, pathological grading, targeted therapy and prognostic evaluation of gliomas.

Genome-wide, integrative analysis of circular RNA dysregulation and the corresponding circular RNA-microRNA-mRNA regulatory axes in autism

Circular RNAs (circRNAs), a class of long noncoding RNAs, are known to be enriched in mammalian neural tissues. Although a wide range of dysregulation of gene expression in autism spectrum disorder (ASD) have been reported, the role of circRNAs in ASD remains largely unknown. Here, we performed genome-wide circRNA expression profiling in postmortem brains from individuals with ASD and controls and identified 60 circRNAs and three coregulated modules that were perturbed in ASD. By integrating circRNA, microRNA, and mRNA dysregulation data derived from the same cortex samples, we identified 8170 ASD-associated circRNA-microRNA-mRNA interactions. Putative targets of the axes were enriched for ASD risk genes and genes encoding inhibitory postsynaptic density (PSD) proteins, but not for genes implicated in monogenetic forms of other brain disorders or genes encoding excitatory PSD proteins. This reflects the previous observation that ASD-derived organoids show overproduction of inhibitory neurons. We further confirmed that some ASD risk genes (NLGN1, STAG1, HSD11B1, VIP, and UBA6) were regulated by an up-regulated circRNA (circARID1A) via sponging a down-regulated microRNA (miR-204-3p) in human neuronal cells. Particularly, alteration of NLGN1 expression is known to affect the dynamic processes of memory consolidation and strengthening. To the best of our knowledge, this is the first systems-level view of circRNA regulatory networks in ASD cortex samples. We provided a rich set of ASD-associated circRNA candidates and the corresponding circRNA-microRNA-mRNA axes, particularly those involving ASD risk genes. Our findings thus support a role for circRNA dysregulation and the corresponding circRNA-microRNA-mRNA axes in ASD pathophysiology.

Analysis of differentially expressed circular RNAs in endothelial cells under impinging flow

BACKGROUND

Circular RNAs (circRNAs) are a special type of non-coding RNA. To elucidate the relationship between hemodynamics and the function of circRNAs in endothelial cells (ECs), a modified T chamber system was designed and produced for the present experiment. This T chamber system can be used to simulate the hemodynamic environment at the bifurcation of the arteries.

METHODS

Normal ECs cultured on glass slides were placed in the T chamber, the cell layer was impacted at a flow rate of 500 mL/min, and high-throughput microarrays were used to analyze the expression profiles of circRNAs in ECs. The differential expressions of circRNAs in the ECs treated with impinging flow were compared to those in ECs in conventional culture conditions. The characteristics of the differentially expressed circRNAs were analyzed with bioinformatics and quantitative reverse transcription polymerase chain reaction analyses were conducted to verify results.

RESULTS

Compared to normal samples, there were changes in the expressions of many circRNAs. A total of 974 circRNAs were differentially expressed, and of these, 378 were upregulated and 596 were downregulated (fold change [FC] ≥ 2 and P < 0.05), which suggests that these circRNAs were altered under hemodynamic conditions.

CONCLUSIONS

We present the differential expression profiles of circRNAs in ECs after the application of impinging flow; our results indicate that these differentially expressed circRNAs may be involved in inflammatory responses and damage in ECs. The present findings provide valuable information on cRNA profiles as well as clues for future studies that will investigate the roles that circRNAs play in ECs after inflammatory injury.

Role of Circular RNAs in Preeclampsia

Circular RNAs (circRNAs) are noncoding RNAs characterized by circular covalently closed structures, which are generated by back-splicing. circRNA is more stable and conserved than linear RNA and exists in various organisms. Preeclampsia (PE), a common hypertensive disorder of pregnancy, has a profound impact on maternal and neonatal mortality and morbidity. Recent studies demonstrated that circRNAs were differentially expressed in PE maternal-fetal interface compared with those in the control and might mediate pathological processes in pregnancy complications. However, the mechanisms of action of circRNAs in PE are still unclear. Here, we provide a comprehensive review on the current state of knowledge on circRNAs associated with PE. We summarize the known expression profiles of circRNAs and discuss their potential application as biomarkers of PE. The possible mechanisms underlying circRNA dysregulation in the etiology of PE are also explored.

Roles of CircRNAs in Autoimmune Diseases

Circular RNAs (circRNAs) are covalently linked single-stranded RNAs, compared to linear counterparts that are relatively abundant, conserved, stable, and specific. Previously, most studies have revealed that circRNAs function in gene expression processes and participate in the pathogenesis of cancers, cardiovascular diseases, and neurological diseases. With advances in biotechnology, more biological functions of circRNAs have been found in several signaling pathways that are related to tumorigenesis, immunity, and metabolism. Recently, many circRNAs have been reported to be expressed abnormally and play important roles in the progression of autoimmune diseases. Thus, circRNAs may not only serve as potential biomarkers but also act as immune regulators and offer potential opportunities for therapy. This review briefly introduces the properties as well as the functions of circRNAs in different stages of gene expression. In addition, this article summarizes the available knowledge about abnormally expressed circRNAs in different autoimmune diseases and discusses their potential roles in these diseases, which helps us understand their regulatory mechanisms and provides future research perspectives.

Circular RNAs: Functions and Prospects in Glioma

Improving the survival rate of patients with glioma, a malignant tumor of the human brain has become increasingly important. In recent years, the function of circular RNAs (circRNAs) in different diseases and the pathophysiological mechanisms involved have been elucidated. In the pathophysiological mechanism, the primary function of circRNAs is to act as microRNA sponges. An increasing number of studies have found that circRNAs are differentially expressed in gliomas and regulate the occurrence, proliferation, and invasion of glioma and thus may be potential markers for the diagnosis of gliomas. Additionally, some circRNAs have been associated with glioma staging and may be useful in determining prognosis. Based on the stability and high conservation of circRNAs, we believe that circRNAs may have molecular targets that are useful for the treatment of glioma. In this review, we summarize the current research regarding the role of circRNAs in gliomas, discuss the potential value and role of circRNAs in gliomas, and provide new perspectives for future research.