Physiological studies of sperm from normal and sub fertile men

Men produce approximately 1000 sperm in every heartbeat. The main job of the sperm cell is to reach and fertilise the egg. However, we know very little about the journey the sperm makes in the female tract but we do know it must survive for up to 6 days and successfully navigate to the egg and 'drill' its entry path through the tough envelope that surrounds it. Success in this venture requires the deployment of strikingly different movement (motility) patterns which are controlled by the female reproductive tract through a series of finely tuned (but very poorly understood) stop/start signals. One key way the female tract communicates with the sperm is to manipulate the calcium level in a cell which then changes the way the cell moves.

Surprisingly there are a large number of men (1:15) who produce sperm but their cells do not function in an optimal way. Such men have difficulties getting their partner pregnant. A primary cause of the sperm not working well is that they do not swim in the same manner as normal cells and a reason for this is that they have an abnormal calcium response to female reproductive tract signals. We do not know why these sperm have poor calcium responses.

Very recently a specialised technique which allows us to obtain critical information on each sperm has been developed (patch clamping). This technique allows us to examine how calcium is changes in the sperm cell. We will use this specialised technique to study sperm from men with abnormalities and compare them to normal men. We anticipate that this will allow us to determine, for the first time, what are the specific problems in calcium regulation in sperm cells from men with fertility problems.

If we can identify these problems it is possible that in the future we may be able to develop drugs to treat these abnormal cells and, conversely perhaps interrupt the calcium pathways in normal cells to develop a new male contraceptive.

Ion channels in spermatozoa are essential for fertilization since they allow hormones (e.g. progesterone, PGE1) that are found in the female reproductive tract to modulate functional motility. The Cation Channel of Sperm (CatSper), the best characterised such channel, is thought to allow such hormones to evoke Ca influx from the external fluid and the resultant rise in intracellular free Ca seems to trigger motility changes essential for fertilization. In mice, CatSper gene deletion thus abolishes the fertilizing capacity of sperm whilst naturally occurring mutations in CatSper gene family members are associated with infertility in humans. The identification of CatSper has therefore established a new paradigm in reproductive biology and work from this laboratory has shown that progesterone induces abnormally small Ca2+-signals in spermatozoa from men with clinically identified fertility defects. The idea that CatSper is of central importance to the control of intracellular Ca therefore raises the possibility that reduced fertility of these patients might reflect CatSper dysfunction. If this is true then it may be possible to increase the fertilizing capacity of such spermatozoa using drugs that activate CatSper. CatSper blockade, on the other hand, could provide a new contraceptive strategy. Since it is important to understand the physiological role of the ion channels present in spermatozoa and we therefore propose to undertake physiological studies of spermatozoa from sub fertile men and healthy volunteers that will directly characterise the channels expressed by normal sperm and compare their properties with the equivalent channels in men with clinically identified sub fertility. We shall also use fluorimetric techniques to monitor hormone-induced changes in intracellular Ca. It is hoped that the new information provided by these studies will facilitate the development of new ways to treat male factor infertility.

Our projects have a good track record of translation of basic research (see Pathways to Impact Statement). In elucidating the role of CatSper and other key ion channels in normal and dysfunctional cells the proposed work will provide key information for the potential examination of compounds that could modulate sperm function in vitro both negatively and positively. This information will be of direct benefit to industry e.g. companies wanting to develop compounds to enhance the fertilisation capacity of the spermatozoon. This will benefit patients in the potential development of non-ART based treatments. Whilst in vivo treatment of sperm dysfunction is ~10 years from clinical application, the use of in vitro compounds to add to the cell to correct/improve sperm function is a tangible goal. Overcoming functionally debilitating defects in calcium signalling using in vitro compounds could reduce the need of some patients to have more invasive ART treatment e.g. IVF and opt for more cost effective less invasive treatment such as IUI.
Whilst the focus of our work is the understanding of human sperm function, the flip side is the potential to use this knowledge to interrupt the cell as a means to developing new contraceptive approaches. With the world population exceeding 9 billion and the number of pregnancies being terminated in many areas continually increasing, there is an urgent and pressing requirement to develop new contraceptives approaches for the male. The data we generate has obvious potential to be used to investigate pathways for disruption of cell function. Ion channels are a good example and their manipulation represents an ideal initial focus. However, whilst our work provides a strong platform for these studies the end goal would be a more distant prospect.