Dynamics of extracellular vesicle-coupled microRNAs in equine follicular fluid associated with follicle selection and ovulation.

Innumerable similarities in reproductive cyclicity and hormonal alterations highlight the considerable utility of the mare to study aspects of follicular dynamics and reproductive function in view of the largely constricted, human research subjects. The bi-directional communication between the growing oocyte and the surrounding somatic cells embodies the hallmark of mammalian follicular development, partially mediated by extracellular vesicles (EVs) encapsulated with microRNAs (miRNAs) and present in the follicular fluid (FF). Here, we aimed to decipher the dynamics of the miRNAs in EVs from equine FF aspirated in vivo during different stages of follicular development, namely, predeviation (PreDev; 18-20 mm), deviation (Dev; 22-25 mm), postdeviation (PostDev; 26-29 mm), preovulatory (PreOV; 30-35 mm), and impending ovulation (IMP; ∼40 mm). Approximately 176 known miRNAs were found in all groups with 144 mutually detected among all groups. Cluster analysis exhibited 15 different expression patterns during follicular development. Among these patterns, a group of 22 miRNAs (including miR-146b-5p, miR-140, and miR-143) exhibited a sharp reduction in expression from the PreDev until the PreOV stage. Another cluster of 23 miRNAs (including miR-106b, miR-199a-5p, and miR-125a-5p) exhibited a stable expression pattern at the PreDev stage until the PostDev stage, with a significant increase at the PreOV stage followed by a significant decrease at the IMP stage. In conclusion, this study provides greater insights into the stage-specific expression dynamics of FF EV-miRNAs during equine follicular development, which may propose novel approaches to improve ART and provide new biomarkers to facilitate the assessment of ovarian pathophysiological conditions.