The epididymis is a complex organ where spermatozoa acquire motility and ability to fertilize the egg. Epididymal maturation lasts 1 or 2 weeks and exposes the immature spermatozoa to a sequentially modified milieu, promoting intense interactions with secretions by the epididymal epithelium. Sperm surface modifications in response to interactions with epididymal secretions are key steps to achieve fertility ability. However, the precise molecular mechanisms that convert an immotile and infertile gamete into a highly motile cell capable of fusion with an oocyte are still unknown. Recent data on proteomics and transcriptomics of epididymal fluid and epididymosomes brought new ideas of the physiological roles of proteins and miRNAs in epididymal maturation in spermatozoa. This review focuses on the recent discoveries on epididymal fluid composition and its role on sperm maturation and preservation, linking to their survival and fertility potential.

SUMMARYHypogonadism is defined as the inadequate gonadal production of testosterone. Low serum testosterone leads to infertility by impairing spermatogenesis and reducing sperm count, however, the impact of hypogonadism in epididymal sperm maturation is poorly understood. From the testis, spermatozoa are transported into the epididymis where they find a specific microenvironment composed of a complex mixture of proteins that facilitate sperm storage and maturation. Inside the epididymal ductule, spermatozoa undergo several changes, resulting in their becoming capable of fertilizing eggs. Protein disulfide isomerases (PDIs) are known to participate in the folding and assembly of secreted proteins in the endoplasmic reticulum. However, little is known about the control and function of PDIs in the testis and epididymis, particularly during male development. The aim of this work was to compare the expression and distribution of PDI and PDIA3 (ERp57) in the testis and epididymis of healthy and GnRH-immunized boars. We detected higher amounts of PDIA3 and PDI in sperm preparations and fluid from the proximal regions of the epididymis of healthy boars. However, we observed an increase in PDIA3 expression in the testis and cauda epididymis in the immunocastrated group. GnRH-immunized boars showed a marked increase in PDI content in cauda spermatozoa and fluid, indicating a possible endocrine dysregulation of PDI. The results of our study suggest that PDIs are associated with epididymal sperm maturation and may be attractive candidates for monitoring male fertility.