Circulating MicroRNAs: What Is Their Relevance?

nucleotide) RNA molecules that posttranscriptionally regulate protein-coding gene expression by binding to either fully or partially complimentary sequences within target messenger RNA (mRNA). Over 2000 unique miRNAs have been identified in humans (1) and these miRNAs can act to either fine tune or mark-edly alter protein expression of numerous mRNA tar-gets simultaneously, allowing for an enormously com-plex layer of regulation of cellular pathways. Much interest has focused on the clinical and therapeutic po-tential of miRNAs, and pharmacological treatments targeting miRNAs are being developed and tested in research trials (2). miRNAs have recently been identi-fied extracellularly in bodily fluids, and differences in peripheral miRNA profiles have been observed in sev