LAUSR

In cattle, most pregnancy losses are sustained before implantation. Many factors are involved in implantation failure, but in mice, pigs and humans there is increased evidence of a role for the maternal immune system and its regulation by seminal plasma (SP). However, there is little evidence for a role of SP in bovine fertility, where dilution or removal of SP before AI is routine. Therefore, the aim of this work was to determine the effect of bull SP or sperm on endometrial gene expression. To this end, 6 heifers were oestrous synchronised and slaughtered 12h after the onset of oestrus. Five endometrial explants from the horn ipsilateral to the preovulatory follicle were obtained from each animal. Explants were incubated with (1) RPMI medium (control); (2) epididymal sperm (106 epididymal sperm mL−1); (3) complete ejaculate (106 ejaculated sperm mL−1+25% SP); (4) ejaculated sperm alone (106 ejaculated sperm mL−1); and (5) SP alone (25% SP). Epididymal sperm were collected and pooled from the cauda epididymis of 3 bulls slaughtered in a commercial abattoir. In addition, complete ejaculates were obtained from 3 other bulls using an artificial vagina. After pooling the samples, a small volume was washed through a density gradient to obtain the ejaculated sperm, and the rest of the ejaculate was filtered to obtain sperm-free SP. The RPMI media was used to dilute sperm and SP to the working concentrations. After 6h of incubation, explants were snap frozen. The RNA quality was assessed with an Agilent 2100 bioanalyzer (Agilent, Santa Clara, CA, USA) before RT-qPCR analysis. Interestingly, SP had a dramatic effect on endometrium RNA integrity, as evidenced by a lower RNA integrity number in explants exposed to a complete ejaculate (2.4±0.14) or SP (2.4±0.06), in comparison with the control, epididymal sperm, or ejaculated sperm treatments (6.7±0.43, 6.9±0.32, 6.7±0.30, respectively; P<0.05). Due to the low RNA quality, those treatments were excluded from further analysis. However, this finding is currently being explored, along with the possibility of this effect being inherent to species that ejaculate intravaginally. We then compared the ability of ejaculated sperm (which have been exposed to SP) and epididymal sperm (which have never had contact with SP) to regulate the endometrial expression of IL1A, IL1B, IL8, IL6, PTGES2, TNFA, and LIF. Although IL6, IL1A and LIF increased in all animals when exposed to either ejaculated or epididymal sperm, there was no effect of treatment. In conclusion, these data did not support the notion that exposure of sperm to SP is important for the immune regulation of the bovine uterus. In addition, the negative effect of SP on the endometrium, together with the fact that bulls are intravaginal ejaculators, suggests that any putative immunoregulatory role of this fluid in the cattle uterus is indirect. Further analysis of the effect of SP on the vagina and cervix will help elucidate whether this response is present in this species and whether it can propagate to more distal regions of the reproductive tract. This work was supported by Science Foundation Ireland (13/IA/1983, 16/IA/4474).