Circular RNAs in Cardiovascular Diseases: Regulation and Therapeutic Applications

Abstract

Cardiovascular disease is one of the leading causes of mortality worldwide. Recent studies have shown that circular RNAs (circRNAs) have emerged as important players in the prevention and treatment of cardiovascular diseases. circRNAs are a class of endogenous noncoding RNAs that are generated by back-splicing and are involved in many pathophysiological processes. In this review, we outline the current research progress on the regulatory roles of circRNAs in cardiovascular diseases. Further, new technologies and methods available for identifying, validating, synthesizing, and analyzing circRNAs, as well as their applications in therapeutics, are highlighted here. Moreover, we summarize the increasing insights into the potential use of circRNAs as circulating diagnostic and prognostic biomarkers. Finally, we discuss the prospects and challenges of circRNA therapeutic applications for cardiovascular disease therapy, with a particular focus on developing circRNA synthesis and engineering delivery systems.

Fig. 1.

Overview of circRNA biogenesis and regulation. (A) Three main biogenesis mechanisms of circRNAs: exon cyclization, intron cyclization, and RBP-dependent cyclization. (B) circRNA exerts its regulatory functions by miRNA sponging protein sponging, gene transcription regulation, or peptide (or protein) encodings. SNP, small nuclear ribonucleoproteins; nt, nucleotide; Pol II, polymerase II.

Fig. 2.

Workflow of circRNA study in cardiovascular research. Samples were collected from human or animal tissues/body fluids, and circRNAs are identified. Next, functional studies are conducted to confirm the mechanism of action of candidate circRNAs. Finally, drugs or biomarkers are developed for medical research and clinical applications.

Fig. 3.

General overview of the process of circRNA functional characterization in cardiovascular system. Methodologies that are usually implemented in circRNA characterization (validation, stability, and localization), functional determination (loss of functional assay, translation, synthesis, and circRNA interaction protein identification), FISH (fluorescence in situ hybridization), and RNA FISH. shRNA, short hairpin RNA; RNAi, RNA interference.

Fig. 4.

Strategies of engineered circRNA design. Four synthetic strategies (chemical synthesis, IVT/enzymatic ligation, group I intron PIE-mediated in vitro cyclization, and group II intron PIE-mediated in vitro cyclization) used for circRNA synthesis in vitro. Engineered circRNAs can be categorized into engineer-designed synthetic circRNAs (native RNA synthesis) and engineer-designed artificial circRNA. Engineered artificial circRNAs are designed to act as miRNA sponges or encode proteins. BrCN, cyanogen bromide; EDC, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide.

Fig. 5.

Summary of circRNAs in CVDs. The regulation of circRNAs involved in cardiac fibrosis, MI, atherosclerosis, cardiomyopathy, and cardiac hypertrophy. Green, downregulated; red, upregulated.

Fig. 6.

Flowchart of circRNA therapeutic strategies based on different delivery systems. Lentivirus, adenovirus, and AAVs are the most frequently used virus systems for RNA delivery, while exosomes (and other cell-derived membrane vesicles) and LNPs are the common nonvirus carriers for RNA delivery.