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Maternal-paternal communication in cattle: understanding how male-induced environmental changes in the female reproductive tract influence reproductive success

Periodic Reporting for period 1 - M-P Communication (Maternal-paternal communication in cattle: understanding how male-induced environmental changes in the female reproductive tract influence reproductive success )

Reporting period: 2018-09-01 to 2020-08-31

Infertility is a worldwide problem affecting the cattle industry. Despite most inseminations resulting in successful fertilisation, embryonic and foetal mortality occurs in about 50% of the cases, with an estimated 70–80% of losses sustained before implantation. Due to beef and dairy constituting 20.8% of the EU agricultural output, reproductive inefficiency translates into a tremendous social and bioeconomic impact. Although many factors can be involved in preimplantation loss, there is increasing evidence for the role of the maternal immune system and its regulation by seminal plasma (SP). Studies in rodents, humans and pigs have described beneficial effects of SP in improving embryo development and implantation. However, evidence for a role of SP in fertility in cattle, where removal of SP before artificial insemination is routine, is relatively weak. Thus, this project will use a model of heifers mated to vasectomised (a bull in which the vas deferens has been sectioned, so that the only contribution to the ejaculate comes from the accessory glands, i.e the ejaculate is made of SP with no sperm) or intact bulls (the ejaculate will be comprised of SP and sperm), to study the role of SP in paternal-maternal communication as it pertains to embryo development and immune modulation. If the beneficial effects of SP on fertility is recapitulated in cattle, the associated increased production and efficiency could have a tremendous impact in the beef and dairy industries.

The specific objectives are:
1) To interrogate the global transcriptome profiles of endometrium from heifers mated to vasectomised or intact bulls, and compare it to a cyclic control. Sperm have the potential to transport SP components to distal areas of the reproductive tract, in addition to having a direct effect on these tissues.

2) To characterise the protein composition of uterine fluid after exposure to SP and sperm so that we can evaluate the biological effect of the transcriptomic changes studied in the previous objective. As this is the environment in which the early embryo resides, it will give a notion of paternally-derived changes that drive embryo development.

3) To histologically characterise the immune cell population in the oviduct and uterine horn after exposure to SP and sperm. This will provide information about the recruitment of immune cells to the female reproductive tract by SP or sperm. Together with the results obtained from accomplishing the previous two objectives, it will provide evidence on whether paternal factors play a role in the modulation of the female immune response toward the semi-allogeneic embryo.

4) To assess size and developmental markers in conceptuses recovered from females exposed to SP, and compare them to those collected from control animals. This will determine whether the possible changes that we observe in the female environment translate into an enhanced developmental potential of the early embryo.
To test our specific hypothesis, two animal trials have been carried out:

1) Cross breed heifers (n=23) were oestrus synchronised and either mated to a vasectomised bull (n=9; 3 bulls used), an intact bull (n=7; 2 bulls used) or left unmated as cyclic controls (n=7). Approximately 24 h after mating, heifers were slaughtered at a commercial abattoir and their reproductive tracts were collected. Samples were obtained from the vagina, cervix, uterus, and oviduct to carry out gene expression analysis and histology. Uterine luminal fluid was also collected to look at protein content. These samples are currently being analysed.

2) Cross breed heifers were estrous synchronised and either mated to a vasectomised bull (n=12 heifers, 3 bulls), or left unmated (control, n=13). Seven days later, the corpus luteum (CL) was measured by ultrasound scanning, and in vitro-produced blastocysts were transferred (n=12-15 blastocysts/heifer). All heifers were slaughtered on Day 14, to recover their CLs and conceptuses. The conceptuses were measured and then frozen for future analysis of developmental markers.
This project constitutes an innovative challenge in cattle reproductive physiology as it will constitute the first in depth characterisation of the regulatory function of SP in the immune system of the female reproductive tract, after mating. The literature in this topic in limited for this species, and mainly evaluates changes in the uterine environment after direct exposure with SP. However, bulls, as men, deposit the ejaculate in the vagina, not the uterus. Thus, we hypothesise that the inflammatory response that is initiated in the vagina due to SP, propagates to more distal regions of the reproductive tract. Therefore, as opposed to other species like rodents or swine, where SP comes into direct contact with the uterus. SP in cattle probably has an indirect effect that we aim to elucidate through our model based of natural mating.

The results of the present study will provide novel data on the gene expression profile of reproductive tract exposed to SP (or not) in cattle. Together with the analysis of the proteins in the tract fluids, the study has the potential to identify factors that enhance embryo development, be it by a direct interaction with the embryo, or by modulating the immune response of the female towards the embryo. Thus, in the short-term the scientific community will benefit from the exhaustive gene and protein expression data, which can be exploited to open new lines of investigation. In the longer-term the cattle industry can benefit from potential improvements in reproductive efficiency.