exRNA

exRNA refers to extracellular RNA, non‑coding or coding ribonucleic acids that are found outside cells in biological fluids such as blood, urine, saliva, cerebrospinal fluid, and breast milk. These molecules are released actively via vesicles (exosomes, microvesicles, and apoptotic bodies) or passively through cell lysis and can also be transported bound to proteins like Argonaute 2. exRNA species include microRNAs, small interfering RNAs, long non‑coding RNAs, tRNA fragments, piRNAs, and messenger RNA fragments. Their extreme stability in extracellular space, largely due to encapsulation or protein binding, makes them attractive candidates for non‑invasive biomarkers in diseases such as cancer, cardiovascular disease, and neurological disorders. Clinical studies have identified characteristic exRNA signatures that can aid in early detection, prognosis, and monitoring of therapeutic response.

Research into the functional roles of exRNA has revealed that it can modulate recipient cell gene expression by shuttling RNA‑silencing machinery or by acting as ligands for pattern‑recognition receptors. However, the mechanisms governing selective loading of RNA into vesicles, the efficiency of intercellular transfer, and the eventual biological impact remain incompletely understood. Technical challenges such as standardization of isolation methods, contamination control, and quantification sensitivity also limit the translation of exRNA research into routine diagnostics. Continued advances in high‑throughput sequencing, sensitive detection platforms, and clear guidelines for sample handling are expected to accelerate the development of exRNA‑based clinical tools.