microRNAs: a new emerging class of players for disease diagnostics and gene therapy

•  Introduction ‐  Brief history, biogenesis and the regulated mechanism of miRNAs•  Roles of miRNAs in human disease and miRNAs as a novel biomarker for cancer and disease diagnostics ‐  Cancers ‐  Metabolic disease ‐  Virus infection•  miRNAs as new targets for gene therapy ‐  miRNAs as a target for gene therapy ‐  Cancers ‐  Cardiac diseases ‐  Strategies for targeting miRNAs ‐  Designing molecules for targeting miRNAs ‐  Delivering molecules to specific targeted sites•  Concluding remarks and future perspectives ‐  Early detection of cancers ‐  Delivery miRNAs and/or anti‐miRNAs for miRNA gene therapy ‐  Potential toxicity effect of miRNA gene therapy ‐  Potential effect of miRNAs on non‐target genesAbstract microRNAs (miRNAs) are a new class of non‐protein‐coding small RNAs, which regulate the expression of more than 30% protein‐coding genes. The unique expression profiles of different miRNAs in different types of cancers and at different stages in one cancer type suggest that miRNAs can function as novel biomarkers for disease diagnostics and may present a new strategy for miRNA gene therapy. Anti‐miRNAs and antisense oligonucleotides (ASO) have been employed to inhibit specific miRNA expression in vitro and in vivo for investigational and clinical purposes. Although miRNA‐based diagnostics and gene therapy are still in their infancy, their huge potentials will meet our need for future disease diagnostics and gene therapy. High efficient delivery of miRNAs into targeted sites, designing accurate anti‐miRNA/ASOs, and related biosafety issues are three major challenges in this field.