Uterine fluid EV miR-223-3p as endometrial receptivity biomarker and regulator in implantation

Endometrial receptivity (ER) is a pivotal determinant of successful embryo implantation, yet its regulation by uterine fluid (UF) extracellular vesicles (EVs) remains poorly understood. This study aimed to identify key UF EV miRNAs during the endometrial receptive period and observe the role in implantation. .UF EVs were isolated from the same in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) patients at two time points: the pre-receptive (LH + 3/p + 1) and receptive (LH + 7/p + 5). miRNA sequencing and validation identified miR-223-3p as the key miRNA. Bioinformatic analysis predicted FOXO1 as a primary target, forming a hub genes complex with H3-3B and SIRT1. To investigate the functional role of UF EVs miR_223-3p, EVs with reduced miR-223-3p were isolated from the culture medium of sh-miR-223-3p ishikawa cells. Functional studies demonstrated that after EVs internalization by trophoblast cells, led to a significant reduction in miR-223-3p levels. This knockdown resulted in markedly impaired trophoblast proliferation, migration, invasion, and adhesion. Concurrently, FOXO1 were significantly downregulated. We propose a novel model whereby receptive endometrium selectively packages miR-223-3p into UF EVs, which are then internalized by the embryo to modulate trophoblast function through the FOXO1/H3-3B/SIRT1 complex. UF EV miR-223-3p emerges as a critical regulator of ER and a promising non-invasive biomarker for assessing implantation competence.