Sperm parameters and epididymis function in transgenic rats overexpressing the Ca2+-binding protein regucalcin: a hidden role for Ca2+ in sperm maturation?

S Correia,P F Oliveira,J E Cavaco,A V M Canario,M G Alves,G Lopes,P M Guerreiro,S Socorro

doi:10.1093/molehr/gat030

S Correia, P F Oliveira + Show 6 more

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https://doi.org/10.1093/molehr/gat030

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Abstract

Sperm undergo maturation acquiring progressive motility and the ability to fertilize oocytes through exposure to the components of the epididymal fluid (EF). Although the establishment of a calcium (Ca(2+)) gradient along the epididymis has been described, its direct effects on epididymal function remain poorly explored. Regucalcin (RGN) is a Ca(2+)-binding protein, regulating the activity of Ca(2+)-channels and Ca(2+)-ATPase, for which a role in male reproductive function has been suggested. This study aimed at comparing the morphology, assessed by histological analysis, and function of epididymis, by analysis of sperm parameters, antioxidant potential and Ca(2+) fluxes, between transgenic rats overexpressing RGN (Tg-RGN) and their wild-type littermates. Tg-RGN animals displayed an altered morphology of epididymis and lower sperm counts and motility. Tissue incubation with (45)Ca(2+) showed also that epididymis of Tg-RGN displayed a diminished rate of Ca(2+)-influx, indicating unbalanced Ca(2+) concentrations in the epididymal lumen. Sperm viability and the frequency of normal sperm, determined by the one-step eosin-nigrosin staining technique and the Diff-Quik staining method, respectively, were higher in Tg-RGN. Moreover, sperm of Tg-RGN rats showed a diminished incidence of tail defects. Western blot analysis demonstrated the presence of RGN in EF as well as its higher expression in the corpus region. The results presented herein demonstrated the importance of maintaining Ca(2+)-levels in the epididymal lumen and suggest a role for RGN in sperm maturation. Overall, a new insight into the molecular mechanisms driving epididymal sperm maturation was obtained, which could be relevant to development of better approaches in male infertility treatment and contraception.

Highlights

Sperm leave the testis as non-functional gametes and it is only during passage through the epididymis that they acquire the ability to move progressively, and to capacitate, eventually gaining the ability to fertilize (reviewed by Cornwall (2009))
Our results demonstrate the importance of RGN and Ca2+ on epididymis function contributing to detail the molecular mechanisms associated with sperm maturation, which could be a fundamental step to treat male infertility and develop new targets for male contraception
The effect of increased Ca2+ levels on sperm motility was tested in vitro by incubating sperm isolated from epididymis cauda in physiological (0.2 mM, Weissgerber et al, 2012) and supra-physiological (2 mM) Ca2+ concentrations (Fig. 1D)

Summary

Introduction

Sperm leave the testis as non-functional gametes and it is only during passage through the epididymis that they acquire the ability to move progressively, and to capacitate, eventually gaining the ability to fertilize (reviewed by Cornwall (2009)). This occurs in the unique microenvironment of the epididymal lumen, which is created by the specific secretory and absorptive activities of the epididymis epithelial cells (reviewed by Guyonnet et al (2011)). Very little is known about the role of calcium ions (Ca2+) in epididymal function, a decrease of concentrations along the epididymal duct generating a luminal Ca2+ gradient has been described (Jenkins et al, 1980)

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