microRNAs are short (approximately 20-25 nucleotides long), single-stranded RNA molecules that regulate gene expression and play a vital role in influencing the pathways responsible for many disease processes, including cardiovascular disease and fibrosis. These RNAs are transcribed from genes; however, unlike messenger RNA they do not encode proteins.
microRNAs function by preventing the translation of microRNAs into proteins and/or by triggering degradation of these microRNAs. Studies have shown that microRNA gene regulation is often not a decisive on and off switch but a subtle function that fine-tunes cellular phenotypes that becomes more pronounced during stress or disease conditions. microRNAs were first discovered in 1993 and have since been found in nearly every biological system examined to date. They are highly conserved, demonstrating their importance to biological functions and cellular processes. According to the Sanger Institute, over 1000 microRNAs have been identified in humans.
microRNAs can be modulated with chemically synthesized oligonucleotides by either decreasing the activity (anti-miRs or inhibitors) or increasing the levels (pro-miRs or mimics) of expressed microRNAs. These modulators can then directly affect the protein expression of the specific microRNA’s targets. Typically, in laboratory settings, microRNA mimics are introduced as double stranded oligonucleotides and inhibitors are introduced as single strand oligonucleotides.