microRNAs (miRNAs) 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 illnesses, including cardiovascular and muscle disease. These RNAs are transcribed from genes; however, unlike messenger RNA (mRNA) they do not encode proteins.

miRNAs function by preventing the translation of mRNAs into proteins and/or by triggering degradation of these mRNAs. Studies have shown that miRNA 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 situations. miRNAs have been found in nearly every biological system examined to date. According to the Sanger Institute, over 850 miRNAs have been found in humans.

miRNAs can be modulated with chemically synthesized oligonucleotides by either decreasing the levels (anti-miRs or inhibitors) or increasing the levels (pro-miRs or mimics) of expressed miRNAs. These modulators can then directly affect the protein expression of the specific miRNA’s targets. Typically, in laboratory settings, miRNA mimics are introduced as double stranded oligonucleotides and inhibitors are introduced as single strand oligonucleotides.