Leipzig - Glycoconjugates on the fallopian tube epithelium and the sperm plasma membrane play role in the formation of sperm reservoir. Studies from Munich and Dublin show this. The formation of so-called sperm reservoir has already been demonstrated in many species, but not in humans. However, researchers consider the reservoir in the fallopian tube to be essential for successful fertilization. They presented their results in Leipzig.
One cause of unsuccessful fertilization could be malfunction in the sperm reservoir. In study, researchers led by Susanne Bour and (LMU) therefore examined the binding mechanism of human sperm to the fallopian tube epithelium using 15 fallopian tubes and 10 ejaculates.
Their focus was on glycoproteins that are located on the surface of the sperm plasma membrane and the fallopian tube epithelium. Only recently it was shown that different parts of the sperm glycocalyx play an important role in the interaction with the fallopian tube. In their current experiments, the researchers were able to show that molecules of the sperm membrane bind mannose and salinic acid residues.
Five questions for Susanne Bour, biotechnologist and doctoral student in urology for Dr. rer. biol. hum. in the andrological research laboratory of the LMU Munich
DÄ: What is the function of the sperm reservoir? Susanne Bour: The fact is that pregnancy rates are higher in humans are when intercourse took place up to five days before the woman ovulates compared to intercourse on the day of ovulation. The sperm must therefore be stored in the female reproductive tract during this time.
A functioning sperm reservoir is essential for fertilization. Because it has the task of keeping sperm capable of fertilization until the day of ovulation. To do this, the sperm have to save energy reserves and the female immune system protects them from degradation. The acrosomal reaction is delayed by the binding of the sperm to the fallopian tube - the sperm remain in the resting position, so to speak, in the sperm reservoir. Only at the time of ovulation does the bond break through hormonal changes and the sperm swims into the lumen of the fallopian tube. This process has already been demonstrated in many species, but not in humans.
DÄ: What happens if there is malfunction of the sperm reservoir in humans? Susanne Bour: strong > If there is malfunction, we suspect that sperm do not bind to the fallopian tubes and are eliminated too quickly by the female immune system. Without bond, the sperm could use up their energy reserves too quickly. In addition, without reservoir in the fallopian tube, the sperm cannot measure the time of ovulation in order to swim into the fallopian tube lumen.This could reduce the chances of success of fertilization.
DÄ: According to information from the World Health Organization, every sixth couple in Europe is involuntarily childless. For how many could disturbed sperm reservoir be contributory factor? Susanne Bour: In around 15 percent of all couples, unwanted childlessness cannot be justified with medical causes. Since stress and external environmental factors also play very large role here, we cannot say with the current state of research which proportion is due to molecular causes.
The diagnosis of disorder in the formation of sperm reservoir would be novelty and could be decisive for at least some of the previously idiopathic infertile couples. It would allow an earlier decision to use assisted reproductive techniques. However, it is very difficult to postulate dependency of fertility due to molecule. We found out in experiments that sperm can be found in the ampulla region of the fallopian tube up to three days after sexual intercourse.
It is assumed that this bond, as demonstrated in some mammals, is, among other things, caused by Protein-sugar interaction is mediated (lectin-glycoconjugate recognition). In live cell imaging experiments with human fallopian tubes and sperm, researchers were able to show ex vivo that sperm only bind to certain areas of the fallopian tube. There must therefore be structures there that recognize and bind them.
DÄ: Have you already been able to carry out examinations on infertile couples? Susanne Bour: So far, we have only been able to carry out our examinations in isolation in men or women, since the fallopian tubes in women were removed as part of hysterectomy for examinations and experiments. It is often not obvious whether the man or woman is infertile.
DÄ: Which attempts are you planning next? Susanne Bour : We want to find out which sugars are responsible for the human bond. Therefore, further tests for the ability to bind with sugars are planned first, which are already considered potential candidates for sperm reservoir in some mammals. Here - as in the currently presented experiments - ejaculates of men with normozoospermia and pathologically abnormal ejaculates are compared with each other.
At the same time, we want to detect receptors (lectins) on the sperm surface through protein analysis and immunohistochemistry.Furthermore, the fallopian tube preparations are treated with corresponding fluorescent sugars to see whether there are certain areas that have corresponding sugars on their surface. Our goal is to use live cell imaging to identify the sugar (s) that are largely responsible for the formation of sperm store in the fallopian tube.