Circular RNAs: the Emerging Class of Non-coding RNAs and Their Potential Role in Human Neurodegenerative Diseases.

The exciting world of research with RNAs has to its credit some breakthrough findings that led to newer insights on multiple problems including that of human diseases. After the advent of siRNA, microRNA, and lncRNA, exciting novel molecules called circular RNAs (circRNAs) have been recently described. circRNAs are a class of non-coding RNAs, which are produced by scrambling of exons at the time of splicing. They are primarily produced in the brain region and are naturally present inside the cell. The best known ones so far include a particular type of circRNA namely "circular RNA sponge for miR-7" (ciRS-7 and CDR1as) which is the inhibitor of miR-7 microRNA-known to regulate various diseases like, cancer, neurodegenerative diseases, diabetes, and atherosclerosis. Similarly, another circRNA molecule called circmbl modulates the ratio of linear mRNA by competing with linear muscleblind gene through which it is synthesized. Considering the complex association of these molecules with critical microRNAs and gene families, circRNAs might have important roles in the cause and progression of human diseases. In particular, the multi-factorial nature of neurodegenerative diseases does warrant studies employing novel approaches towards identifying underlying root causes of these ailments. The non-coding RNAs, like circRNAs and microRNAs, could well present a common genetic trigger to multiple factors associated with neurodegenerative diseases. A specific fingerprint of a combination of various marker circRNAs could be explored for early diagnostic purpose as well. Herein, we review the possibility of exploring the role of circRNAs in the context of the central nervous system (CNS) and age-associated neurodegenerative diseases.