Endocrine Abstracts

Introduction

Metabolic homeostasis in the testis is essential for a healthy spermatogenesis. Insulin is regarded as one of the most important intervenients in the metabolic regulation of spermatogenesis, where it acts directly on the differentiation of spermatogonia into primary spermatocytes or indirectly through the metabolic modulation of Sertoli cells. Additionally, insulin is hypothesized to play a major role on human spermatozoa capacitation, although the mechanisms that regulate its production and secretion remain to be disclosed.

Aim of the study

The main objective of this study was to estimate the capacity of insulin production by human spermatozoa and if they express PC1/3 and PC2, which are enzymes responsible for the cleavage of proinsulin. In addition, we hypothesized that insulin production could respond to glucose stimuli.

Materials and Methods

Seminal samples of normozoospermic men (n = 15) were collected and submitted to a density gradient centrifugation. Two fractions of spermatozoa were then collected according to their motility condition (high vs low motility). The expression of insulin, PC1/3 and PC2 mRNA was evaluated in both spermatozoa fractions by RT-qPCR. The protein expression of insulin, PC1/3 and PC2 in spermatozoa was evaluated by immunofluorescence. The fraction of highly motile spermatozoa was then incubated in a medium conferring capacitating conditions and supplemented with increasing glucose concentrations (in mM: 0, 5.5, 11 and 22). After 6 h, the concentration of insulin in the medium was quantified by ELISA.

Results

Insulin, PC1/3 and PC2 mRNA, as well as the respective proteins, are expressed in human spermatozoa. The mRNA expression was found to be higher in the highly motile spermatozoa. Additionally, human spermatozoa release insulin to the medium in a glucose concentration-dependent manner.

Conclusion

This study shows that human spermatozoa are able to produce and release insulin in a glucose concentration-dependent manner. Future studies are required to further evaluate the role of insulin on human spermatozoa capacitation and fertilization capacity, opening an exciting new line of investigation.