P-035 Catecholamine neuroreceptors are differentially located in functional regions of the human sperm
Authors: Girela J  L , De Juan-Perez A , De Juan J 
Published: July 2024

Abstract

Study question
How are the expression and distribution of Adrenergic and Dopamine receptors in human sperm cells?

Summary answer
Using ultra-high-resolution microscopy techniques, we identified that each type of catecholamine receptor is expressed in a different functional region of the human sperm.

What is known already
Human sperm present complex cell signalling complexes with several neuroreceptors in their membrane. The spermatozoa is a terminal differentiated cell showing specialized regions optimized for physiological processes like motility, acrosome reaction and membrane fusion during fertilization. Although indirect methods have determined the presence of catecholamine receptors in human sperm, there is no direct evidence nor description of the exact localisation of these receptors. Catecholamine receptors are the direct target of medications used to treat very frequent health problems like hypertension (beta blockers), asthma (bronchodilators) and mental health disorders (antipsychotics and antidepressants).

Study design, size, duration
We design the study by developing new techniques that allow us to use high-resolution microscopes (i.e. Laser Scanning Confocal Microscopy LSCM and Field Emission Scanning Electron Microscopy or FE-SEM) to identify the localisation and distribution of catecholamine receptors. We determined sperm functional regions and quantified the relative amount of the different receptors on each one of those regions to perform a statistical analysis.

Participants/materials, setting, methods
After informed consent and ethical approval, sperm from young, healthy donors (n = 20) were included in the study. We used the neuroblastoma cell line SH-SY5Y as a positive control. Immunolabelling techniques used specific primary antibodies for each receptor, followed by the gold-conjugated secondary antibodies for FE-SEM. Negative controls were performed by omitting the primary antibody. In FE-SEM images, we quantify the number of gold nanoparticles in the sperm cells and the background.

Main results and the role of chance
We confirm the differential localisation of the different receptors studied. Dopamine D2 receptors are mainly expressed on the equatorial band of the acrosome, while beta-adrenergic receptors are restricted to the terminal piece of the flagellum. In both cases, the mean number of gold particles showed statistical differences (p &lt; 0,001) between the region of expression and the rest of the regions and the background.

Limitations, reasons for caution
The present study only shows the presence of the receptors on the sperm plasma membrane. The activity of those receptors should be investigated by developing bioassays based on the use of agonists and/or antagonists. A more reliable genetic overexpression or knockout approach was impossible in human sperm.

Wider implications of the findings
The presence of receptors on restricted regions of the sperm suggests their participation in critical physiological events, like regulation of sperm motility hyperactivation or acrosome reaction. It may also suggest a possible side effect of beta-blockers or bronchodilators with the male fertility potential that needs to be investigated.

Trial registration number
not applicable