Extracellular Vesicles: Classification, Biological Functions, Diseases, and Therapeutic Opportunities.

Extracellular vesicles (EVs) are lipid bilayer-enclosed particles released by virtually all cell types and act as mediators of intercellular communication in physiology and disease. By transporting diverse bioactive molecules, including proteins, lipids, and nucleic acids, EVs regulate gene expression, modulate immune responses, and support tissue homeostasis. Rapid advances have revealed their heterogeneity, complex biogenesis, and broad functional relevance, as well as their importance as biomarkers and therapeutic delivery systems. The molecular principles governing selective cargo loading remain incompletely understood, particularly for microRNAs: once viewed as passive carriers, EVs are now known to sort miRNAs through regulated mechanisms that do not simply reflect intracellular abundance. In this review, we provide an integrated overview of EV biology, including classification, biogenesis, and roles in health and disease. We focus on mechanisms underlying selective RNA cargo loading, highlighting RNA-binding proteins such as SYNCRIP and PCBP2, sequence features linked to selective export, and epitranscriptomic regulation, including m6A modifications. We also discuss emerging computational and AI-driven approaches to identify RNA-protein interactions and determinants of cargo selection, alongside developments in EV engineering and clinical translation. By bridging mechanistic insights with translational perspectives, this review positions EVs as platforms for precision medicine, biomarker discovery, and RNA-based therapeutics.