Proof of concept : analysis of spermtozoa motility

Introduction

Antimicrobial peptides (AMPs) have a great affinity for spermatozoa membranes. They are composed of anionic phospholipids such as phosphatidylglycerol and phosphatidylserine in the plasma membrane. Therefore AMP have to ability to inhibit motility of spermatozoa and prevent the fertilization. [1]
Antisperm antibodies are antibodies that can fix on specific parts of spermatozoa (YLP12 antigen) and inhibit their motility. The exact mechanism for this motility inhibition is not known yet.[2] We quantified the action of the AMPs and antibodies on the motility of spermatozoa. This is our proof of concept to test the anticonceptional efficiency of the molecules produced by our bacteria.

Use of mice sperm

The animals that we are using are males Mus musculus, 8 weeks old. They are used by the team of Thomas Robert, at the IGF of Montpellier, that is working on the genetic factors that control the integrity of the meiotic cell division. For our study, the epididymis was taken to collect the sperm of the animal. This tissue is not used by the team of Thomas Robert. The epididymis is squeezed to take the sperm out of it. Following extraction, the sperm is stored in BWW buffer for the experiments.

We are using the spermatozoa from the mice’s epididymis cauda (figure 1) because the maturation of spermatozoa is more advanced in this region of the epididymis and thus represent in the best way fully mature spermatozoa while still being easy to extract. Figure 1 : Mouse Epididymis
For our experiments there were two cases. Experiments could be done right after the dissection and extraction of the sperm, else we did the experiment one or two days after the dissection. In the first case we put the sperm in Biggers-Whitten-Whittingham medium (BWW). Otherwise we used a conservation method, which allows to conserve spermatozoa and their motility during 72 hours. (preservation protocol)

The use of mice sperm is discussed in our ethics page : Ethics

Measurements

We carried out different types of measurements, including their controls. Negative controls allow us to quantify the motility of spermatozoa alone, while positive controls measure the efficiency and the concentration needed to completely stop the motility of spermatozoa of a commercial molecule. (figure 1)

Negative control :

Negative controls were done for each experiment. This was done because the motility can vary depending on the mouse so it is not possible to have only one negative control for all experiments. The negative control consisted of spermatozoa in the BWW buffer. This control permitted to know the normal motility of sperm.

Positive control :

Our positive control was the use of a peptide whose activity against sperm motility was demonstrated [] : nisin. According to our bibliography 400µg/mL of nisin was enough to inhibit motility of 100% of spermatozoa. Our first negative control was to put sperm in BWW containing different concentrations of nisin. Nisin was prepared with commercial Sigma nisin peptide and according to nisin elution protocol (Nisin preparation). The standard effect dose curve of nisin was done with 400µg/mL being the highest concentration to verify the results from the publication.

The control for this experiments was to analyze the motility of sperm in BWW alone. As our experiment for the nisin took one hour to be completed we decided to have as a negative control the motility of sperm during an our.

Results :

This results show that nisin has an effect on the sperm motility that is significantly higher than the one of time alone. Moreover this experiment confirms that 400µg/mL of nisin is the concentration that inhibit 100% of sperm motility.

Supernatant :

The goal of this experiment is to show the effect of molecules present in the supernatant (secreted and from dead cells) on the mice sperm motility. The control for this experiment is to put the sperm in contact with only the culture media and no bacteria. This permits to have information about the effect of the media on sperm motility. The other control needed is the presence of wild non transformed bacteria culture media After doing both controls we can measure and quantify the activity of bacteria supernatant on mice sperm.

For the medium control we put a half of BWW buffer with sperm diluted to 1/100 and half of media (LB and MRS) [4].

We concluded that it was not possible to have supernatant of bacteria as an experiment as the media themselves completely inhibited sperm motility with the concentrations used. The use of different concentrations or of a different protocol could prove the usefulness of such an experiment.

Lysed bacteria :

Our LL-37 part was not designed so that the peptide is secreted. Our analysis was based on the effect of lysed bacteria on the sperm. (Cell lysis protocol)

Tracking

Our script for tracking spermatozoa is based on Trackpy v0.3.2 Package. Trackpy is able to track any biological samples because it performs a band pass and threshold to locate any particle. Different parameters for the characterization of the tracked object like its size and its intensity (mass) are to take into account to allow good tracking [5]. All of those are specified in the protocol for the tracking (Tracking). We also use tolls for filtering out spurious features, and also to filter the data by their appearance to eliminate undesirable data that has been tracked. Our script track the spermatozoa over time and then give us the X and Y positions for each frame. This allows us to determine each spermatozoa trajectory and velocity. Therefore, we can calculate the mean velocity to analyze the motility of sperm samples depending on different conditions. We are sharing the fully commented script so everyone can freely understand it and use it as they want : *insert script*