Bovine endometrium drives and responds to divergence of in vitro produced conceptus biochemistry
In vitro produced (IVP) bovine embryos are used to enhance herd genetics and support advanced reproductive technologies, however, less than 40% survive the first month of gestation after transfer to the surrogate. While the biochemical consequences of in vitro culture on the embryo before transfer have been well documented, less is known after transfer when the embryo interacts with the endometrium and pregnancy failure occurs. To investigate this, we utilized a Day 16 trophectoderm-endometrial mono-culture and co-culture system, integrating transcriptomic and proteomic analyses, to compare crosstalk between the IVP or in vivo derived (IVD) bovine conceptus and endometrium. We found that the IVP conceptus transcriptome (differentially expressed genes; DEG), diverged from the IVD conceptus but only after co-culture with endometrium (377 DEG; FDR < 0.05). Further, of the IVP conceptus DEG, 81 genes (21%) were associated with abnormal embryonic or fetal development. Significant biological processes associated with abundant endometrial DEG induced by IVP conceptuses were related to GTPase activity and the inflammatory response (FDR < 0.01), the latter of which may be associated with increased MHC class II expression, which was specific to IVP conceptuses. Proteomic analysis of the culture media identified 1,031 and 604 differentially abundant proteins (FDR < 0.05) associated with the IVD and IVP conceptus-endometrial co-cultures, respectively, compared to endometrium alone, indicating the proteomic environment surrounding the IVP conceptus may be suboptimal. Collectively, compared to the IVD conceptus, it appears the endometrium drives and responds to divergence of IVP conceptus biochemistry, likely contributing to pregnancy failure. Overall design: All procedures involving animals were approved by the University of Tennessee, Knoxville, Institutional Animal Care and Use Committee (IACUC 2020-67015-31617). Estrus synchronized Angus-Holstein heifers were used to generate cyclic Day 16 endometrial explants or elongated in vivo derived (IVD; artificial insemination) or in vitro produced (IVP) Day 16 bovine conceptuses. Endometrial explants (8 mm) and conceptus sections (5 X 2 mm) were cultured in medium separately (monoculture) or together in a co-culture system. After a 12 h incubation, the endometrial and conceptus tissue RNA was also isolated for RNA sequencing (RNA-Seq). Collectively, 13 cyclic uteri, 9 IVD conceptuses and 7 IVP conceptuses and were used to produce endometrial explants and conceptus sections for mono- and co-cultures. *************************************************************** The table below lists GEO accessions reused/reanalyzed for this study. ***************************************************************