Characterization and profiling analysis of bovine oviduct and uterine extracellular vesicles and their miRNA cargo through the estrous cycle.

Extracellular vesicles (EVs) found in various biological fluids and particularly in reproductive fluids, have gained considerable attention for their possible role in cell- to- cell communication. Among, the different bioactive molecules cargos of EVs, MicroRNAs (miRNAs) are emerging as promising diagnostic biomarkers with high clinical potential. Aiming to understand the roles of EVs in bovine reproductive tract, we intended to characterize and profile the EVs of oviduct and uterine fluids (OF-EVs, UF-EVs) and their miRNA across the estrous cycle. Nanoparticle tracking analysis and transmission electron microscopy confirmed the existence of small EV population in OF and UF at all stages, (size between 30 and 200 nm; concentration: 3.4 × 10 10  EVs/ml and 6.0 × 10 10  EVs/ml for OF and UF, respectively, regardless of stage). The identification of EV markers (CD9, HSP70, and ALIX proteins) was confirmed by western blot. The miRNA analysis revealed the abundance of 310 and 351 miRNAs in OF-EVs and UF-EVs, respectively. Nine miRNAs were differentially abundant in OF-EVs between stages of the cycle, eight of them displayed a progressive increase from S1 to S4 (p < .05). In UF-EVs, a total of 14 miRNAs were differentially abundant between stages. Greater differences were observed between stage 1 (S1) and stage 3 (S3), with 11 miRNAs enriched in S3 compared to S1. Functional enrichment analysis revealed the involvement of these miRNAs in relevant pathways such as cell signaling, intercellular junctions, and reproductive functions that may be implicated in oviduct and uterus modulation across the cycle, but also in their preparation for embryo/conceptus presence and development.