Endocrine Abstracts

Introduction: Mitochondrial uncoupling proteins (UCPs) are mitochondrial transmembrane channels belonging to the anion carrier family. Six UCP homologues (UCP1-6) had been identified with a ubiquitous distribution throughout the body and many different physiological functions. UCPs are important regulators of several biological processes, including thermogenesis, oxidative phosphorylation, ROS production, as well as cellular metabolism. However, the knowledge concerning the molecular action mechanisms is limited. UCPs’ (dys)function is pivotal to the onset of metabolic diseases and consequent increased oxidative stress. Although the molecular mechanisms are poorly understood, there is an interconnection between oxidative stress, male infertility, and metabolic disorders, such as obesity and diabetes mellitus. In addition, the expression and function of UCPs in the human spermatozoa remains to be explored.

Aim of the study: This study aimed to evaluate the expression of UCPs homologues (UCP1-6) in human spermatozoa. In addition, the influence of UCPs in spermatozoa viability, total and progressive motility, mitochondrial activity, and ROS production was evaluated through its inhibition by genipin, a selective UCP inhibitor.

Matherials and methods: Highly motile and viable spermatozoa were isolated from seminal samples of normozoospermic men (n=10) by density gradient centrifugation. The mRNA expression of UCPs homologues (UCP1-6) was evaluated by RT-PCR and the protein expression (UCP1-3) by immunofluorescence. Samples were incubated in BWW media supplemented with genipin (0, 0.5, 5, and 50 μM) at 37°C. After 3 h, total motility and viability were analyzed. The mitochondrial activity and total ROS production were accessed by JC-1 dye and CM-H2DCFDA probe, respectively. The culture media were collected and evaluated by 1H-NMR. To further study the observed loss of motility and its reversibility, total and progressive motility were evaluated each 15 min up to a total of 105 min.

Results: We were able to identify the mRNA expression of all UCPs homologues (UCP1-6) in human spermatozoa. Inhibition of UCPs by the highest concentration of genipin (50 μM) led to the irreversible loss of motility. Mitochondrial membrane potential was also found diminished, although no alterations in human spermatozoa viability, metabolic profile, or ROS production were observed.

Conclusion: UCPs are major regulators of human spermatozoa’s mitochondrial activity and motility. Our data suggests that the dysfunction of human spermatozoa UCPs is not only potentially interconnected to metabolic diseases, oxidative stress, and male infertility but also a potential novel target for the development of male contraceptives.