Circular RNA in Exosomes

Circular RNAs (circRNAs) are a novel family of non-coding endogenous RNAs discovered in all eukaryotic cells and generated through a particular mechanism of alternative splicing called “back-splicing”. These molecules show multiple functions, by acting as modulators of gene and miRNA expression, and may have a role in several biological processes, such as cell proliferation and invasion with, tumour development and progression, and in several mechanisms underlying other diseases. Their presence has been shown to be abundant in several body fluids such as blood and saliva. Based on their biogenesis mechanism, cir- cRNAs may be categorized into five classes: exonic circRNAs, intronic circRNAs, anti- sense circRNAs, sense overlapping circRNAs and intergenic circRNAs. Recently, the pres- ence of circRNAs, in addition to that of miR- NAs and long non-coding RNAs, has been detected also in small extracellular vesicles called exosomes. Investigating the presence and expression levels of serum exosomal cir- cRNAs could allow us, in future, to discrimi- nate cancer patients from healthy individuals,identifying new potential exosome-based can- cer biomarkers. In this chapter, we briefly will describe the major features and functions of exosomal cir- cRNAs, discussing their potential role as molecular biomarkers for diagnosis, progno- sis and monitoring of complex diseases, including cancer.