A bovine 3D endometrium-on-a-chip revelas the role fo conceptus-derived factors CAPG and PDI in conceptus-endometrium communication

Early embryo loss affects all mammalian species, including humans and agriculturally important food-producing mammals such as cattle. The developing conceptus (embryo and extra-embryonic membranes) secretes factors which modify the endometrium and can be critical for early pregnancy processes such maternal recognition of pregnancy (MRP) and enhancing uterine receptivity to implantation. For example, a competent bovine conceptus secretes IFNT to initiate MRP. The bovine conceptus also secretes other proteins at the time of MRP, including CAPG and PDI, which are highly conserved among placental mammals. We have previously shown that these proteins act upon the endometrium to modulate receptivity, embryo development, and implantation in species with different implantation strategies (humans and cattle). We hypothesise that developing a novel 3D bovine endometrium on a chip system will enhance our understanding of the role of conceptus-derived factors in altering the endometrium and/or ULF secretion. Here we have developed a 3D bovine endometrium on a chip system, comprising both stromal and epithelial cell culture combined with culture medium flow better mimics the in vivo endometrium and exposure to conceptus-derived factors than conventional 2D endometrial cell culture. We have demonstrated that the conceptus-derived proteins CAPG and PDI modulate the endometrial transcriptome and secretory response to promote pathways associated with early pregnancy and alter ULF composition. This work highlights the critical need for more robust and in vivo-like culture systems to study endometrial-conceptus interactions in vitro to further investigate the role of conceptus derived factors for pregnancy success. Primary bovine endometrial epithelial and stromal cells were co-cultured in a 3D endometrial organ on a chip. They were exposed on the epithelial-side to the conceptus-derived factors CAPG and PDI for 24 hours under microfluidic flow, alongside controls (N=3). Conditioned medium was collected and analysed for proteomics alongside unconditioned controls. Cells were removed, RNA extracted, and RNA sequenced.