Functional Identification of miR-21-5p from Fallopian Tubal Extracellular Vesicles as a Promoter of Preimplantation Embryo Viability

Extracellular vesicles (EVs) released by the maternal reproductive tract provide essential biochemical support for early embryo development, yet the identity of their functional molecular cargo remains largely unclear. In this study, we isolated and characterized human Fallopian tube-derived EVs (oviductal EVs, oEVs) and demonstrated that they are efficiently internalized by preimplantation embryos. Supplementation with oEVs enhanced blastocyst formation and reduced apoptosis without impairing implantation or post-implantation development, suggesting a physiological role for oEV signals in sustaining embryo viability. To identify candidate effector molecules, we performed cross-dataset analysis of reproductive EV miRNA profiles and highlighted miR-21-5p as a conserved and abundant candidate. In vivo vs. in vitro expression comparison revealed that miR-21-5p is markedly depleted in in vitro-cultured embryos from the four-cell stage onward. Supplementation with miR-21-5p recapitulated the developmental benefits of oEVs, including improved blastocyst progression and reduced apoptosis. Transcriptomic profiling further revealed suppression of PTEN/p53-mediated stress-response and apoptotic pathways, supporting a mechanistic link between maternal EV-derived miRNAs and enhanced embryonic resilience under culture conditions. Together, these findings identify miR-21-5p as a functional mediator of oEV-driven embryo support, reveal a nanoscale maternal-embryo communication mechanism, and suggest potential translational strategies using miRNA-based supplements or EV-mimetic nanocarriers to improve assisted reproductive technologies.