Exosome-derived uterine microRNAs isolated from cows with endometritis impede blastocyst development

As a common disease of cows occurring during their perinatal period, endometritis is known to affect fertility. At present, the studies on endometritis mainly focus on preventing microbial invasion. However, the mechanism that uterine inflammation affects embryo activity and implantation is unclear. Mainly containing lipids, proteins, mRNAs, and microRNAs, exosomes widely exist in various tissues and body fluids. Exosome extractions were used by commercial kits and confirmed through morphological examinations and Western blot. After exosomes' mRNA profiles were generated using RNA sequencing, it was investigated how uterine cavity fluid exosomes affect the developmental competence of in vitro fertilization (IVF) embryos in case of endometritis. In this study, the isolated exosomes were spherical particles with a diameter of 30-150 nm according to the transmission electron microscopy. Identified with Western blotting, positive CD63 and CD9 expressions showed that the isolated exosomes could be used for the subsequent tests. We found 118 differentially expressed miRNAs in the exosomes of the uterine cavity fluid in healthy cows and those with endometritis, among which, 52 miRNAs were down regulated and 66 up regulated. Furthermore, the qRT-PCR results confirmed the up-regulation of three miRNAs and down-regulation of six miRNAs, which were consistent with the deep sequencing results. IVF embryos co-incubated with the endometritis exosomes significantly decreased the blastocyst formation rate in comparison with those co-incubated with the healthy exosomes (21.84+3.17 vs. 32.37+2.69). Therefore, exosome miRNAs may be a cause of infertility in cows with endometritis.