microRNA

MicroRNAs (miRNAs) are short, non-coding RNA molecules, typically about 22 nucleotides long, that regulate gene expression at the post-transcriptional level. They are transcribed as longer primary hairpin transcripts, processed in the nucleus and cytoplasm into mature duplexes, and loaded into the RNA-induced silencing complex. There, the guide strand directs the complex to partially complementary sequences in the 3′ untranslated regions of target messenger RNAs, causing translational repression or transcript destabilization. Because base pairing is imperfect, a single miRNA can suppress many transcripts and a single transcript can be tuned by many miRNAs, placing miRNAs at the center of regulatory networks governing differentiation, proliferation, apoptosis, metabolism, cellular senescence, and immune signaling. Individual family members such as MIR21 act on defined pathway components, and miRNA activity intersects with signaling axes including Transforming growth factor beta (TGF-β) and Wnt/β-catenin.

In biomedical research, miRNAs are studied both as disease biomarkers and as therapeutic targets. Altered miRNA expression accompanies cancer, cardiovascular disease, inflammatory and fibrotic conditions, and neurodegeneration, and miRNAs are also carried by extracellular vesicles and extracellular exosomes, which shield them from plasma nucleases and allow them to act in intercellular communication. This stability makes circulating miRNAs attractive analytes for minimally invasive liquid biopsy in blood, plasma, serum, cerebrospinal fluid, and other biofluids, alongside markers such as cell-free tumour DNA, and for applications ranging from cancer screening and treatment monitoring to studies of aging. Because miRNAs are present at low abundance and are closely related in sequence, detection typically relies on quantitative PCR, sequencing, or amplified biosensing strategies — including CRISPR-Cas methods built on CRISPR-Cas12a combined with isothermal amplification schemes such as catalytic hairpin assembly and hybridization chain reaction. On the therapeutic side, synthetic mimics and antisense inhibitors delivered by lipid nanoparticle are being explored to restore or block specific miRNA activities.