Extrahepatic and Circulating miR-122: Diagnostic Implications and Future Directions

Research on microRNAs is constantly expanding and evolving due to their role in the regulation of gene expression. miR-122, a 22-nucleotide microRNA, was first discovered as a liver-specific miRNA. Subsequently, it was found to be present in a wide range of tissues, such as the breast, testes, ovaries, and heart. The research on miR-122 in the liver has been extensive over the past few decades, leading to several important discoveries. However, its role in extrahepatic tissues is largely incompletely understood. Therefore, in light of the established clinical relevance of miR-122 as a potential biomarker and/or drug target in the liver, available information on miR-122 is compiled as it pertains to health and disease. This review discusses novel information generated in recent years and the corresponding progress in our understanding of the physiology of extrahepatic miR-122.