Abstract
MicroRNAs (miRNAs) are smáll non-coding single-strand- ed RNAs of about 22 nucleotides in length that act as post-transcriptional regulators of gene expression. Depending on the complementarity between miRNA and target mRNA, cleavage or destabilization or translational suppression of mRNA occurs within RISC complex (RNA induced silencing complex).
More than 50% of the genes are controlled by at least one miRNA. Moreover, one miRNA can regulate the expression of several genes, and one gene can be regulated by multiple miRNAs.
As gene expression regulators, miRNAs are involved in a variety of biological functions. Dysregulation of miRNAs and their target genes contribute to pathophysiology of many diseases including rheumatological disorders.
MiRNAs are also present extracellulariy in their stable form in body fluids. Their incorporation into membrane vezicles or protein complexes with Ago2, HDL or nucleophosmin 1 protéct them against RNases.
Cell-free miRNAs can be delivered to another cell in vitro and maintain their func- tional potential. Therefore, miRNAs can be considered mediators of intercellular communication.
Remarkable stability of cell-free miRNAs and their accessibility in body fluid makes them potential diagnostic or prognostic biomarkers and potential therapeutic targets.