A Validation Study to Detect Markers of Proliferation Adequacy in the Endometrium

Abstract

Throughout the human female menstrual cycle, the endometrial lining of the uterus transitions from a non-receptive proliferative state to a receptive secretory state. This transition is required to prepare the endometrium for an embryo to successfully implant. Transitioning of the endometrium is governed by various genes, but the cellular processes are poorly understood. Unfortunately, for some women this process is compromised, resulting in the endometrium being inadequately primed for implantation and conception repeatedly fails. This is known as recurrent implantation failure (RIF). The aim of this study was to identify different markers within the functionalis layer of the endometrium that are important for implantation success. Qualitative and quantitative protein analysis was used to compare endometrial tissue biopsies between women with different fertility phenotypes. Biopsies were collected from women attending a single fertility clinic, with collection completed during the early-secretory (pre-receptive LH+2) phase of the menstrual cycle. Cryo-sectioning was used to cut tissue sections, revealing glandular epithelium, luminal epithelium, and stromal cells. Immunofluorescence and SDS-PAGE combined with Western blots were used to assess protein expression. Expression levels of 25 different proteins previously reported to be involved in endometrial proliferation that feature in endometrial focal adhesion or cell cycle pathways were compared between four cohorts; Fertile (n=5), RIF(n=6), Research (n=6), and Other (n=4). Quantitative PCR was also used to detect relative mRNA expression levels in the endometrium between the internal references (ACTB and CYC1) and the target genes (EGFR, PCNA, PGR, and MCM2). It was found that endometrial protein profiles differ during the early-secretory, LH+2, phase of the menstrual cycle, between women who are fertile and women with clinically defined RIF. Immunofluorescence results showed a statistically significant increase of CCNA, PCNA, MKI67, and SMAD3, and decrease of IL1R1, in the fertile cohort in comparison to the RIF cohort. Western blot also showed statistically significant up-regulation of PCNA in the fertile group, as well as PGR and YWHAZ. Gene expression profiles did not differ between fertile women and women with RIF, however there was a significant reduction of PGR and PCNA in the Research and Other groups in comparison to the Fertile and RIF groups. In this pilot study, protein and gene analysis was able to detect alterations of expression in groups of women with different fertility phenotypes. Further exploration of these markers could help determine their possible role in endometrial dysfunction in RIF women and establish a clinical panel to indicate endometrial preparation adequacy.