LAUSR

The classic view of ribonucleic acids (RNAs) puts emphasis on their central involvement in providing the genetic information for the protein synthesis. However, recent findings have indicated that RNAs can shuttle between various cells of one organism and could be transported also between different organisms (Xiang et al., 2006). Membrane vesicles or protein complexes protect extracellular RNAs (exRNAs) in extracellular space and within biological liquids such as plasma, milk, or cerebrospinal liquid. Since Mandel and Metais first discovered extracellular nucleic acids in human plasma in 1948, exRNA was believed to be a waste material released by damaged cells. Only after discovery of RNA interference, extracellular microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and other regulatory types of RNA in the 2000s, study of regulatory functions of RNAs caught the attention of the field. During the two last decades, it has been shown that exRNAs are not only specific biomarkers for different diseases and conditions but also active players in the regulation of inflammation, cell activation, apoptosis, and migration. This Research Topic has invited original research articles and reviews focused on all aspects of exRNA biology including but not limited to the role of exRNAs in cell-cell communication, their potential as biomarkers, and their therapeutic potential. The topic collected five original research articles and three reviews. In the study by Vulf et al., several microRNAs (miRNAs) such as let-7c-5p, miR-15b-5p, miR-215p, miR-423-5p, and miR-143-3p have been revealed as novel potential biomarkers of non-alcoholic fatty liver disease. The authors demonstrated that these circulating miRNAs are differentially expressed in serum derived from patients with steatosis and steatohepatitis and are involved in the regulation of genes relevant to the insulin resistance and development of non-alcoholic fatty liver disease. In another study within this Research Topic, Cai et al. eloquently demonstrated the advantages of using circulating exRNAs as potential biomarkers and therapeutic targets for Parkinson’s disease (PD). The authors identified novel aberrantly expressed microRNAs in both the plasma and extracellular vesicles (EVs) of PD patients, validated them in clinical samples, as well as in cell and animal models of PD. They also characterized the complicated regulatory network involved in miRNA-mediated modulation of targets genes related to PD pathogenesis. In particular, miR-23b-3p was identified as a novel direct regulator of alpha-synuclein, a crucial pathogenic hallmark of PD. Edited and reviewed by: Ramani Ramchandran, Medical College of Wisconsin, United States