Embryo quality assessment by the small noncoding RNA expression profile in an embryo culture medium in assisted reproductive technology programs

Objective. To investigate of the small noncoding RNA (sncRNA) (microRNA and piwiRNA) prof ile in an embryo culture medium on day 4 of cultivation to identify the potential biomarkers for embryo quality. Materials and methods. The deep sequencing method was used to identify the spectrum of sncRNA present in the blastocyst cavity and embryo culture medium, which were quantified using a real-time reverse-transcription polymerase chain reaction assay in 48 samples of the culture medium of embryos transferred into the uterine cavity. Results. Partial least squares-discriminant analysis (PLS-DA) was used to analyze the contribution of six sncRNAs to determining the embryo quality, which was characterized by the variable importance in projection (VIP) values. The analysis showed that the greatest contribution was made by four sncRNAs: piR020401 (VIP = 1.46027), let-7c-5p (VIP = 1.17416), let-7b-5p (VIP = 0.994657), and let-7i-5p (VIP = 0.942665), and the smallest contribution was by miR-143-5p (VIP = 0.623108) and miR-92a-3p (VIP = 0.471951). The Spearman rank correlation method was used to reveal a statistically significant correlation between the expression level of sncRNA (hsa-let-7b-5p, hsa-let-7c-5p, and hsa-piR020401) in the culture medium and the quality of the embryo transferred to the uterine cavity. The Mann- Whitney non-parametric test revealed statistically signif icant differences in the expression level of piR020401 and miR-92a-3p in the culture medium of embryos forming groups according to morphofunctional parameters. Conclusion. The sncRNAs (let-7c-5p, let- 7b-5p,piR020401) found in the culture medium statistically significantly correlate with embryo morphofunctional characteristics on day 4 after fertilization, among which piR020401 makes the greatest contribution to determining the embryo quality. The expression level of miR-92a-3p and piR020401 in the culture medium depends on the stage of embryonic development, differentiating the morula and blastocyst stage. Considering that the lag in the embryonic development rate by day 5 of cultivation did not always predetermine the absence of embryo implantation into the uterus, it is not advisable to focus exclusively on embryo morphological parameters when choosing a candidate for transfer to the uterus, and it is recommended that the expression profile of let-7c-5p, let-7b-5p, miR-92a-3p, andpiR020401 should be additionally estimated on day 4 of embryo cultivation. Thus, the findings make it possible to optimize the choice of an embryo and to implement an assisted reproductive technology program.

piwiRNA, microRNA, sncRNA, piwiRNA, microRNA, culture medium, embryos, ART, pregnancy, implantation, embryo quality, IVF