Abstract
The transfer of a competent embryo into a uterine cavity during the implantion window is a major objective to ensure success in in vitro fertilization (IVF). My thesis work contributes to (i) the identification of new biomarkers for the evaluation of endometrial receptivity (ii) the understanding of embryo competence in IVF.Concerning the first axis, the team has developed the Win-Test®, an endometrial receptivity evaluation test based on the search for a specific transcriptomic signature in endometrial biopsies taken from patients during their theoretical implantation window. The purpose of this test is to determine the appropriate time to replace the embryo. When the “receptive” period is identify, it allows the embryo transfer date to be adapted to the patient’s effective window of implantation, significantly increasing the pregnancy rate after personalized frozen embryo(s) transfer (Haouzi et al, 2020). To date, this test requires two endometrial biopsies and can only be performed on a frozen/thawed embryo transfer. In order to overcome these two constraints, the objective of my thesis was to participate in the development of a non-invasive approach in the evaluation of endometrial receptivity in IVF. Analysis of microRNA expression profiles from endometrial biopsies allowed us to identify certain endometrial microRNAs associated with endometrial receptivity ("receptive" versus "non-receptive") as well as with the success of the attempt ("implantation failure" versus "sucessfull implantation" and "miscarriage" versus "birth") (Drissennek, Baron, et al, 2020). My preliminary results indicate that some of these microRNAs are detected in the serum of patients, thus opening interesting perspectives for the development of a specific non-invasive test of endometrial receptivity.The second axis of my thesis focused on the improvement of the development and the early implant potential of human embryos. In vivo, the embryo evolves in the fallopian tube until the morula stage and arrives in the uterus at the blastocyst stage around D6 post fertilization, in an endometrium supposed to be receptive which will be able to ensure implantation. Physiologically, it has been shown that the oxygen level is 5% in the fallopian tubes and 2% in the uterus. To date, the majority of IVF laboratories in the world use 5% oxygen from D0 to D6 for the in vitro culture of human embryos. Our results showed that biphasic in vitro culture at 5% oxygen from D0 to D3 and then at 2% oxygen from D3 to D5/D6 (thus mimicking physiological oxygen concentrations) significantly improves human embryo development and live birth rates in IVF. Using a transcriptomic approach, our results highlighted the different expression of 707 genes depending on whether the embryos were cultured at 5% oxygen or at 5% and then 2% oxygen, with an overexpression of the majority (93.8%) of dysregulated transcripts in embryos cultured with biphasic strategy (5-2% oxygen). Functional analysis revealed the involvement of these RNAs in key cellular processes of embryonic growth and implant potential; such as proliferation, DNA repair and maintenance of pluripotency. These results open new perspectives for the improvement of embryonic culture conditions, subject to confirmation in a larger scale study.