LAUSR

Extracellular vesicles (EVs) in utero play a role in cellular interactions between endometrium-conceptuses (embryo plus extraembryonic membranes) during peri-implantation periods. However, how intrauterine EVs function on endometrium have not been well characterized. In our previous study, bta-miR-98 found in intrauterine EVs from uterine flushing fluids (UFs) on pregnant day 20 (a half day after initial conceptus attachment, P20) could regulate the maternal immune system and collaborate with other miRNAs and/or components of EVs for conceptus implantation. We, therefore, hypothesized that in addition to bta-miR-98, other miRNAs present in bovine intrauterine EVs may regulate the maternal immune system in the endometrial epithelium. A global analysis of differentially expressed proteins between EVs from P17 and P20 UFs revealed that components of intrauterine P20 EVs had the effect on the down-regulation of "neutrophil activation involved in immune response" and "neutrophil mediated immunity". In silico analyses predicted bta-miR-26b as one of potential miRNA to regulate maternal immune system. In our cell culture experiments, bta-miR-26b negatively regulated several immune system-related genes PSMC6, CD40, and IER3 in bovine endometrial epithelial cells. Our findings revealed that intrauterine EV-derived bta-miR-26b contributes to the down-regulation of the maternal immune system, allowing conceptus implantation to the uterine endometrium. Furthermore, our results suggest that intrauterine EVs extracted from P20 UFs could regulate neutrophils, the first line of immunological defense, to modulate endometrial immune and inflammatory responses for implanting conceptuses.