Endometrial extracellular vesicles regulate processes related to embryo development and implantation in human blastocysts.

Extracellular vesicles (EVs) mediate intercellular communication by transporting various molecules, and endometrial EVs have been postulated to be involved in the molecular regulation of embryo implantation. The objective of this study was to investigate the transcriptomic response of human blastocysts following internalization of endometrial EVs in vitro. Primary human endometrial epithelial cells, derived from endometrial biopsies collected from fertile oocyte donors, were cultured in vitro to isolate secreted EVs. Following EV characterization, day 5 human blastocysts were cultured in the presence or absence of the EVs for 24 hours and evaluated by RNA-sequencing. Among the differentially expressed genes (DEGs) in blastocysts co-cultured with EVs, we found 519 were significantly upregulated and 395 were significantly downregulated. These DEGs were significantly enriched in upregulated functions related to embryonic development, cellular invasion and migration, cell cycle, cellular organization and assembly, gene expression and cell viability; and downregulated functions related to cell death and DNA fragmentation. Further, the intracellular signaling pathways regulated by the internalization of endometrial EVs were previously related to early embryo development and implantation potential, for their role in pluripotency, cellular homeostasis, early embryogenesis and implantation-related processes. Finally, integrating data from miRNA cargo of EVs, we found that the miRNAs carried by endometrial EVs targeted nearly 80% of the DEGs in human blastocysts. This study provides novel insights into the functional relevance of EVs secreted by the human endometrium, and particularly the role of EV-miRNA regulation on global transcriptome behavior of human blastocysts during early embryogenesis and embryo implantation. Overall design: To investigate endometrium-embryo crosstalk during implantation, this study uses next-generation sequencing and compares the differential gene expression profiles of day 5 human embryos, cultured with and without extracellular vesicles secreted by primary human endometrial epithelial cells in a secretory-phase hormonal environment.