Microarray expression profile of circular RNAs in chronic thromboembolic pulmonary hypertension

Circular RNA and its mechanisms in disease: From the bench to the clinic

The emerging recognition of the functional roles of circular RNAs (circRNAs) has given rise to a new perspective regarding our understanding of cellular physiology and disease pathogenesis. Unlike linear RNAs, circRNAs are covalently closed continuous loops that act as gene regulators in mammals, and their sequence composition determines the mode of circRNA biogenesis. The availability and integrated use of advanced genome analysis platforms have allowed the identification of a large number of these molecules. Their high abundance, stability and evolutionary conservation among species endow circRNAs with numerous potential functions, such as acting as microRNA (miRNA) sponges or binding to RNA-associated proteins to form RNA-protein complexes that regulate gene transcription. Moreover, circRNAs have been shown to be expressed in a tissue-specific manner and in pathological conditions, which has stimulated significant interest in their role in human disease and cancer. In this concise review, we outline the characteristics, functions and mechanisms of action of circRNAs as well as their involvement in different diseases. Although their exact roles and mechanisms of gene regulation remain to be clarified, circRNAs have potential applications as disease biomarkers and novel therapeutic targets.

Circular RNAs: A novel type of non-coding RNA and their potential implications in antiviral immunity

Circular RNAs (circRNAs), a novel type of non-coding RNAs (ncRNAs), are ubiquitously expressed in eukaryotic cells during post-transcriptional processes. Unlike linear RNAs, circRNAs form covalent-closed continuous loops without 5' to 3' polarities and poly (A) tails. With advances in high-throughput sequencing technology, numerous circRNAs have been identified in plants, animals and humans. Notably, circRNAs display cell-type, tissue-type and developmental-stage specific expression patterns in eukaryotic transcriptome, which reveals their significant regulatory functions in gene expression. More importantly, circRNAs serve as microRNA (miRNA) sponges and crucial regulators of gene expression. Additionally, circRNAs modulate pre-mRNA alternative splicing and possess protein-coding capacity. CircRNAs exhibit altered expression under pathological conditions and are strongly associated with the development of various human diseases. Interestingly, circRNAs can also induce antiviral immune responses. A recent study found that the delivery of circRNAs generated in vitro activates RIG-I-mediated innate immune responses and provides protection against viral infection. The antiviral dsRNA-binding proteins, NF90/NF110, act as key regulators in circRNA biogenesis. NF90/NF110 are also functional in inhibiting viral replication through binding to viral mRNAs. In this review, we provide a comprehensive overview on the classification, biogenesis and functions of circRNAs. We also discuss the critical role of circRNAs in eliciting antiviral immunity, providing evidence for the potential implications of circRNAs in antiviral therapies.

Circular RNAs in rat models of cardiovascular and renal diseases

Circular RNAs (circRNAs) have emerged as an important new class of genomic regulatory molecules contributing to the development of various diseases, but their relevance to the development and progression of hypertension remains largely unknown. A major impediment to begin studying circRNAs in rat models of inherited hypertension is that the rat as a valuable model of human diseases lags far behind the mouse and human in providing knowledge on circRNAs. In this study, a genome-wide circRNA profiling was performed from four rat strains that are widely used in hypertension research: the Dahl salt-sensitive rat (S), the Dahl salt-resistant rat (R), the spontaneously hypertensive rat (SHR), and the Wistar Kyoto rat (WKY). Combined hybridization data obtained from these four strains allowed for the identification of 12,846 circRNAs as being expressed in the rat kidneys. Out of these, 318 and 110 circRNAs were differentially expressed with a fold change > 1.5 (P < 0.05) in S vs. R and SHR vs. WKY, respectively. Among these circRNAs, circRNA/microRNA interaction was predicted since circRNAs are known as microRNA sponges to sequester microRNAs. Several circRNAs were further validated by quantitative real-time PCR. To our knowledge, our study is the primary report of profiling circRNAs in renal tissue and illustrates that circRNAs could be candidate genetic factors controlling blood pressure.