**1. Introduction**

MicroRNAs (miRNAs) belong to a family of small non-protein-coding RNAs with a single strand of 18–25 nucleotides that regulate multiple target genes at the post-transcriptional level. Functionally, miRNAs bind to 6–8 bp seed sequences in the 3' Untranslated Region (3' UTR) of targets mRNA and induce mRNA degradation or repression of protein translation. The term "non-coding RNA" is commonly defined a group of RNA that does not encode a protein. With a rapid advancement of molecular technology, many new classes of noncoding RNA have been founded. Among those noncoding RNAs, miRNA has attracted considerable attention because its endogenous origin and its role in the regulation of gene makes it more likely target for drug discovery and potential biomarker for specific disease.

miRNA research is a relatively new topic, with research ranging back for the past 25 years; it has its beginnings in its detection in *C. elegans* in 1993 and its detection in humans in 2000 [1]. Their use in transgenic mice in 2005 to

#### *Antisense Therapy*

eventually efficacy studies of modified inhibitors of miRNAs in primates in 2010 illustrates the explosion of research surrounding miRNAs in just 5 years. There are now over 2000 miRNAs that have been discovered in humans and it is believed that they collectively regulate one third of the genes in the genome [2]. miRNAs have been linked to many human diseases and are being pursued as clinical diagnostics and as therapeutic targets, showing promise in many fields, ranging from cancer therapy to cardiac disease, to even suggestions as a potential biomarker for numerous diseases and treatment responses. This chapter will briefly discuss the miRNAs biogenesis, their function, regulation, and implication in disease, then discuss the miRNA-based therapeutic strategies, their therapeutic implication in diseases, and some of the current clinical trials involving miRNAs.
