Plasma-derived exosomal circular RNA hsa_circ_0005540 as a novel diagnostic biomarker for coronary artery disease
Aims: Exosomes exist in almost all body fluid and contain diverse biological contents which may be reflective of disease state. Circular RNAs (CircRNAs) are stable in structure and have a long half-life in exosomes without degradation, thus making them reliable biomarkers. However, the potential of exosomal circRNAs as biomarkers of coronary artery disease (CAD) remains to be established. Here we aimed to investigate the expression levels and the potential use of exosomal circRNAs as diagnostic biomarkers of CAD. Main methods: CircRNAs expression levels in exosomes obtained from three plasma samples from CAD patients and three paired controls were analyzed using RNA sequencing. Exosomal circRNAs obtained in the profiling phase were then verified in two-center validation cohorts. Finally, the ability of exosomal circRNAs, adjusting for Framingham Heart Study (FHS) risk factors, was determined to discriminate between CAD patients and non-CAD controls. Key findings: 355 circRNAs were differentially expressed between these two groups: 164 were upregulated, and 191 were downregulated. Here we selected potential circRNAs (fold change > 4, P < 0.05) as candidate biomarkers for further validation. Our data showed that only hsa_circ_0005540 was significantly associated with CAD (P < 0.0001). After adjustment for risk factors, hsa_circ_0005540 showed a high discriminatory power for CAD in ROC analyses (AUC = 0.853; 95% confidence interval [CI] = 0.799 - 0.906, P < 0.001). Significance: Our results suggest that plasma exosomal hsa_circ_0005540 can be used as a promising diagnostic biomarker of CAD. Overall design: circRNA sequencing on ribosomal RNA-depleted total RNA from  CAD patients and non-CAD controls