Successful implantation relies upon the firm adhesion of a good quality blastocyst to a receptive endometrium. Cross-talk between the blastocyst and the endometrium during the peri-implantation period is poorly understood. Microarray studies have identified microRNAs (miRs) to be differentially altered across the human menstrual cycle and dysregulated with infertility. The aim of this study was to identify miRs dysregulated in the pre-receptive phase infertile endometrium and define the effects on endometrial epithelial adhesion.
miR expression levels in endometrial tissue was determined by microarray and confirmed by qRT-PCR. In situ hybridisation was used to localise miRs in endometrium. Primary human endometrial epithelial cells (HEEC) were transfected with miR mimic (synthetic miR) and control and used in a functional trophoblast cell line (HTR8/SVneo) spheroid-HEEC co-culture adhesion assay to model blastocyst adhesion to the endometrium. miR predicted and confirmed targets were identified using bioinformatics and their expression levels determined in HEEC transfected with miR mimic via qRT-PCR. Protein production was assessed by immunohistochemistry.
miR-29c expression was elevated in pre-receptive phase infertile endometrium, compared to fertile endometrium (p<0.05). miR-29c localised to endometrial luminal and glandular epithelium. Transfection of HEEC with miR-29c mimic reduced HTR8/SVneo spheroid adhesion compared to HEEC compared to control (p<0.05). Collagen type IV alpha 1 (COL4A1) is an abundant basement membrane component and a predicted target of miR-29c. miR-29c overexpression in HEEC significantly reduced COL4A1 mRNA expression (p<0.05). COL4A1 is localised to the luminal epithelium basement membrane and vascular endothelial cells in human endometrium. Protein expression remained unchanged between fertile and infertile pre-receptive phase endometrium.
This is the first study to reveal miR-29c dysregulation in the infertile endometrium and a functional effect. Collectively, this data demonstrates that miR-29c overexpression significantly impaired HEEC adhesive capacity, suggesting that miR-29c dysregulation in the infertile endometrium may impair blastocyst adhesion and implantation, contributing to infertility.