Presence of sperm cells triggers a protective cascade of proteins
Female pigs can detect when a boar’s sperm arrives in their oviducts after mating - triggering the release of proteins that protect sperm cells and help fertilisation and implantation of the embryo. If corresponding proteins can be found in humans, they could be used during in vitro fertilisation to boost the chances of successful conception.
Alireza Fazeli’s team at the University of Sheffield, UK, with colleagues at the University of Murcia, Spain, analysed fluid from the oviducts before and after artificial insemination. They identified a total of 32 different proteins in the fluid of which 19 more than doubled in concentration in response to the presence of sperm cells.
Mating is a dangerous time for the female because harmful bacteria can enter the reproductive tract along with seminal fluid. However, Fazeli’s study shows that oviduct cells can differentiate between alien proteins arriving with bacteria and those of her mate and prevent the immune system attacking the latter.
The female response not only protects sperm cells from attack it also helps them survive the wait until the egg or oocyte arrives. ’Sperm cells are very sensitive to heat and in vitro they would be completely destroyed within four or five hours at the temperature found within the reproductive tract. But by nourishing and protecting them in the oviduct they can be kept alive for several days,’ Fazeli explains.
For example, one of the proteins - the fibrinogen A-alpha chain - prevents the sperm cell being destroyed by immune cells, while another - hyaluronidase - digests the protective layer of hyaluronic acid around the egg to aid fertilisation.
Fazeli says adding appropriate proteins may also help to improve the results of in vitro fertilization methods, which succeed in less than 30 per cent of treatments. But he is also concerned that the absence of these protective proteins from IVF media may cause babies conceived through the method to suffer more illness in later life. ’Are we creating a deficient environment at conception that will influence these babies throughout their lives?’
The mechanism may also help to explain post-copulatory sexual selection, in which females that have mated with several partners play a role in determining which sperm fertilizes their egg. But the team’s next task is to identify the chemical signal produced by the sperm cells that triggers the response, Fazeli adds.
Joanna Ellington, an expert in oviduct physiology at Washington State University, told Chemistry World the study demonstrates the importance of Fallopian tube chemistry. ’It provides further evidence that the Fallopian tube is not merely a conduit, but is a finely tuned micro environment.’
But Barry Shur from the school of medicine at Emory University, Atlanta, US, points out that male hormones are already known to trigger changes in the chemical environment of the reproductive tract. ’I would want to know that the authors were careful to avoid carrying over any male factors that are known to induce oestrus, as opposed to being induced by sperm per se.’
et al, J. Proteome Res., 2007 (DOI: 10.1021/pr070349m)