Seminal plasma (SP) exposure during breeding alters placental transcriptome and subsequent growth of foals

Abstract

SP proteins are involved in biological functions associated with breeding in horses. Specifically, SP DNAse suppresses neutrophil extracellular traps (NETs), while CRISP-3 and lactoferrin/SOD-3 regulate the protection of viable spermatozoa for safe transport in the presence of an inflammatory uterine environment while allowing for the elimination of dead spermatozoa and bacteria through PMN phagocytosis. While SP is not necessary for establishing pregnancy, it may contribute to a suitable uterine environment and optimal fetal development. We have previously found that SP exposure at the time of breeding is associated with differentially expressed genes (DEG) in the endometrium that are associated with various pathways relating to embryo development and health, immunotolerance, and metabolism. Based on these findings and an association between human in vitro-produced babies and metabolic diseases later in life, we hypothesized that the absence of SP is affecting the uterine environment during pregnancy and subsequently the health of offspring. Therefore, we conducted two experiments to explore the possible role of SP on the transcriptome of placenta in the absence versus exposure to SP during breeding and followed the development of offspring during their first two years of life. Experiment 1: Warmblood mares were bred with exposure to SP (n=9) or recipients of ICSI-produced embryos (n=9; no SP). Samples from the chorioallantois were collected immediately postpartum, and RNA sequencing was performed for transcriptomic analysis. A total of 1580 genes was differentially expressed with an FDR cutoff of p<0.05. KEGG analyses indicated an alteration in pathways associated with hypoxia, metabolism, ribosome biogenesis, innate immunity, chemokines, and altered angiogenesis, including both the EGF pathway and the EGF bypass pathway, all of which may lead to altered translation (eIF-4E and DROSHA). Experiment 2: The growth of foals (n=60) from mares exposed to SP during breeding (n=30) and mares bred in the absence of SP (embryo transfer and ICSI; n=30) was monitored monthly during the first 24 months of age. Overall, offspring produced from embryo transfer and ICSI exhibited greater weight gain during the first two years of age than offspring produced from conventional AI at the same farm, and this was most evident in colts (p<0.05). While advanced growth may be desired in young athletes, it carries an enhanced risk of developmental diseases, such as osteochondrosis dissecans (OCD). In conclusion, the absence of seminal plasma exposure at the time of breeding is associated with placental dysregulation during pregnancy, which may be associated with abnormal growth and possible developmental issues in the offspring.