MicroRNAs as messengers of liver diseases: has the message finally been decrypted?

MicroRNAs (miRNAs), which are regarded as crucial regulators of gene expression and diverse aspects of cell biology, can be present in various body fluids as highly stable molecules. It is also known that miRNAs exert tissue-specific regulation of gene transcription. Large amount of clinical and experimental evidence provided the rationale for raising the intriguing question of whether miRNAs can mediate cell-cell communication. For those reasons, miRNAs have been considered as the 'Holy Grail' of biomarkers allowing non-invasive diagnostic screening and early detection of a variety of diseases, including solid and non-solid cancers. In a study published in Clin. Sci. (Lond.) (2011) 120(5):183-193 (https://doi.org/10.1042/CS20100297), Gui et al. investigated the hypothesis that circulating miRNAs could be used to identify patients with liver pathologies. Specifically, the authors profiled circulating miRNAs in patients with hepatocellular carcinoma (HCC), liver cirrhosis (LC), and healthy controls and found that serum miR-885-5p levels were significantly higher in samples of patients with HCC (6.5-fold increase) and LC (8.8-fold increase). In this commentary, we highlight biological aspects associated with mir-122-the 'liver-specific' miRNA, which has been associated with a diverse range of liver pathologies. In addition, we discuss the relevance of mir-885-5p as potential biomarker for detecting human cancers. Finally, we provide some clues about how presumably unrelated miRNAs such as miR-122 and miR-885-5p may act in similar biological processes (BPs), making the miRNA regulatory networks more complex than anticipated.