Interaction of preimplantation factor with the bovine global endometrial transcriptome.

Application This is the first study to show that preimplantation factor (PIF) interacts with the bovine endometrial transcriptome, paving the way for future research to investigate the importance of PIF in bovine pregnancy. Introduction Preimplantation factor (PIF) is a novel peptide secreted from viable embryos as early as the 2 cell stage. Synthetic PIF (sPIF) has been shown to interact with human endometrial stromal cells in culture through three distinct pathways relating to the implantation and acceptance of the embryo by the maternal immune system (Paidas et al., 2010). There is limited knowledge related to bovine PIF, although it has been determined that the peptide is secreted by viable embryos and detectable in maternal serum (Ramu et al., 2013; Stamatkin et al., 2011). The present preliminary study aimed to improve the current knowledge on the interaction of sPIF with the bovine endometrium through RNA-sequencing. Material and methods Endometrium from bovine heifer uteri (n=4), in the follicular stage of the oestrous cycle, were sampled and intercaruncular tissue explants from each replicate were cultured with or without sPIF (100 nM) for 24 hours. Medium was replaced with fresh medium containing sPIF (100 nM) for a further 6 hours. At the end of the incubation, tissue was stored in RNA later and total RNA subsequently extracted and quality assessed. Extracted RNA that was of a suitable quality was subjected to library preparation for RNA sequencing on the Illumina HiSeq 2500 platform. Following sequencing, a previously described data analysis workflow was adapted for the sample set to determine differentially expressed genes (DEG) and biological pathways modulated by sPIF treatment (McCabe et al., 2012). A p-adjusted value of less than 0.1 was used to determine statistically significant differential expression in the transcript data set. Results A total of 60 DEG were identified, with 16 down-regulated and 44 up-regulated following treatment with sPIF; however, none showed greater than 2 fold change in expression. There was a strong influence of animal replicates on the data variance, with the native gene expression differing between animals. sPIF treatment up-regulated several genes shown to be important in the endometrium, such as OXTR (oxytocin receptor); PTGER2 (prostaglandin E receptor 2) and IL6R (IL-6 receptor). Furthermore, LEF1 (lymphoid enhancer-binding factor 1) and ITGA2 (integrin alpha-2), shown to be up-regulated in human endometrium following sPIF treatment were also upregulated in the bovine samples. Six biological pathways were over represented in the set of DEG following sPIF treatment (P<0.01) such as the ‘Immunoregulatory interactions between a lymphoid and a non-lymphoid cell’. The KEGG pathway ‘Biosynthesis of unsaturated fatty acids’ was also over represented following sPIF treatment, through upregulation of genes coding for the enzymes fatty acid desaturase 1 and 2. Conclusion This preliminary study showed that sPIF interacts with the bovine endometrial transcriptome, although the response appears to be relatively weak compared to that identified in humans. Bovine homologs of genes altered by sPIF in the human endometrium were upregulated, however only 2 genes of the 60 DEGs were in that set. The tissue used in the present study was non decidualized endometrial tissue, sPIF may have a greater effect on the pregnancy primed bovine endometrium and future work will reveal if it may show a more similar response to that observed in human studies. Acknowledgements The authors gratefully acknowledge Aberystwyth University for DCDS studentship funding and Randall Parker Foods for sample collection. References McCabe, M., Waters, S., Morris, D., Kenny, D., Lynn, D. and Creevey, C. (2012). BMC Genomics, 13:193. Paidas, M. J., Krikun, G., Huang, S. J., Jones, R., Romano, M., Annunziato, J. and Barnea, E. R. 2010. American Journal of Obstetrics and Gynecology, 202: 459 e1-8. Ramu, S., Stamatkin, C., Timms, L., Ruble, M., Roussev, R.G. and Barnea, E.R. (2013). Reproductive Biology and Endocrinology, 11: 105. Stamatkin, C. W., Roussev, R. G., Stout, M., Absalon-Medina, V., Ramu, S., Goodman, C., Coulam, C. B., Gilbert, R. O., Godke, R. A. and Barnea, E. R. 2011. Reproductive Biology and Endocrinology, 9: 63.