microRNAs in rheumatoid arthritis: midget RNAs with a giant impact.

MicroRNAs (miRNAs) are tiny, non-coding molecules that primarily modulate gene expression at the post-transcriptional level by predominantly hybridising to complementary sequences in the 3'-untranslated region of their corresponding mRNAs. Depending on the degree of Watson-Crick base pairing, a miRNA either accelerates the degradation of the corresponding transcript or restricts its translation. There is compelling evidence that miRNAs have crucial roles in controlling and modulating immunity, while dysregulation of miRNAs can lead to autoimmunity and promote tumourigenesis, making miRNA regulation a balancing act between immunity and tumourigenesis. Here, the focus is on the role of miRNAs during the establishment and sustainment of rheumatoid arthritis (RA), a systemic, inflammatory autoimmune disease with irreversible joint destruction. An overview of the known function of miRNAs in RA and what the future might hold for the use of these small RNA molecules in RA diagnosis and treatment is provided.